Experiment Central Understanding Scientific Principles Through Projects
Experiment Central Understanding Scientific Principles Through Projects Second Edition
Experiment Central Understanding Scientific Principles Through Projects Second Edition M. Rae Nelson
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Project Editor: Kristine Krapp Managing Editor: Debra Kirby Rights Acquisition and Management: Margaret Abendroth, Robyn Young Composition: Evi Abou El Seoud, Mary Beth Trimper Manufacturing: Wendy Blurton Product Manager: Julia Furtaw Product Design: Jennifer Wahi # 2010 Gale, Cengage Learning ALL RIGHTS RESERVED. No part of this work covered by the copyright herein may be reproduced, transmitted, stored, or used in any form or by any means graphic, electronic, or mechanical, including but not limited to photocopying, recording, scanning, digitizing, taping, Web distribution, information networks, or information storage and retrieval systems, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without the prior written permission of the publisher. This publication is a creative work fully protected by all applicable copyright laws, as well as by misappropriation, trade secret, unfair competition, and other applicable laws. The authors and editors of this work have added value to the underlying factual material herein through one or more of the following: unique and original selection, coordination, expression, arrangement, and classification of the information.
Cover photographs: Images courtesy of Dreamstime, Photos.com, and iStockPhoto. While every effort has been made to ensure the reliability of the information presented in this publication, Gale, a part of Cengage Learning, does not guarantee the accuracy of the data contained herein. Gale accepts no payment for listing; and inclusion in the publication of any organization, agency, institution, publication, service, or individual does not imply endorsement of the editors or publisher. Errors brought to the attention of the publisher and verified to the satisfaction of the publisher will be corrected in future editions. Library of Congress Cataloging in Publication Data Experiment central : understanding scientific principles through projects. 2nd ed. / M. Rae Nelson, Kristine Krapp, editors. p. cm. Includes bibliographical references and index. ISBN 978 1 4144 7613 1 (set) ISBN 978 1 4144 7614 8 (vol. 1) ISBN 978 1 4144 7615 5 (vol. 2) ISBN 978 1 4144 7616 2 (vol. 3) ISBN 978 1 4144 7617 9 (vol. 4) ISBN 978 1 4144 7618 6 (vol. 5) ISBN 978 1 4144 7619 3 (vol. 6) 1. Science--Experiments--Juvenile literature. I. Nelson, M. Rae. II. Krapp, Kristine M. Q164.E96 2010 507.8--dc22
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Table of Contents
VOLUME 1: A-CH
Reader’s Guide xxi Parent’s and Teacher’s Guide xxv Experiments by Scientific Field xxvii Words to Know xxxix 1. Acid Rain 1
Acid Rain and Animals: How does acid rain affect brine shrimp? 5 Acid Rain and Plants: How does acid rain affect plant growth? 9 Acid Rain: Can acid rain harm structures? 12 2. Adhesives 19
Material Adhesion: How do various glues adhere to different materials? 22 Adhesives in the Environment: Will different environmental conditions affect the properties of different adhesives? 26 3. Air 33
Air Density: Does warm air take up less room than cool air? 36 Convection Currents: How can rising air cause weather changes? 39 4. Air and Water Pollution 45
Pollutant Bioindicators: Can lichens provide clues to an area’s air pollution? 51 Eutrophication: The effect of phosphates on water plants. 55 v
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5. Animal Defenses 61
Camouflage: Does an animal’s living environment relate to the color of the animal life? 63 Ladybug Threats: How do ladybugs defend themselves when they feel threatened? 65 6. Annual Growth 71
Tree Growth: What can be learned from the growth patterns of trees? 74 Lichen Growth: What can be learned from the environment by observing lichens? 79 7. Bacteria 85
Bacterial Growth: How do certain substances inhibit or promote bacterial growth? 90 Bacterial Resistance: Can bacteria gain resistance to a substance after exposure? 95 8. Biomes 103
Building a Temperate Forest Biome 107 Building a Desert Biome 108 9. Bones and Muscles 113
Bone Loss: How does the loss of calcium affect bone strength? 116 Muscles: How does the strength of muscles affect fatigue over time? 120 10. Caves 127
Cave Formation: How does the acidity of a substance affect the formation of a cave? 132 Cave Icicles: How does the mineral content of water affect the formation of stalactites and stalagmites? 135 11. Cells 141
Investigating Cells: What are the differences between a multicellular organism and a unicellular organism? 144 Plant Cells: What are the cell differences between monocot and dicot plants? 145 Yeast Cells: How do they reproduce? 147 12. Chemical Energy 151
Rusting: Is the chemical reaction exothermic, endothermic, or neither? 152 vi
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Exothermic or Endothermic: Determining whether various chemical reactions are exothermic or endothermic 156 13. Chemical Properties 163
Slime: What happens when white glue and borax mix? 167 Chemical Reactions: What happens when mineral oil, water, and iodine mix? 170 Chemical Patination: Producing chemical reactions on metal 173 14. Chemosenses 177
Supertasters: Is there a correlation between the number of taste buds and taste perception? 180 Smell and Taste: How does smell affect the sense of taste? 186 15. Chlorophyll 191
Plant Pigments: Can pigments be separated? 193 Response to Light: Do plants grow differently in different colors of light? 197 Budget Index lxxxv Level of Difficulty Index xcvii Timetable Index cix General Subject Index cxxi VOLUME 2: CO-E
Reader’s Guide xxi Parent’s and Teacher’s Guide xxv Experiments by Scientific Field xxvii Words to Know xxxix 16. Color 203
Color and Flavor: How much does color affect flavor perception? 207 Temperature and Color: What color has the highest temperature? 210 17. Comets and Meteors 215
Comet Nucleus: Linking a Comet’s Composition to its Properties. 218 Experiment Central, 2nd edition
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Meteor Impact: How do the characteristics of a meteorite and its impact affect the shape of the crater? 221 18. Composting/Landfills 229
Living Landfill: What effect do the microorganisms in soil have on the decomposition process? 232 Composting: Using organic material to grow plants 235 19. Crystals 243
Crystal Structure: Will varying shape crystals form from varying substances? 246 Cool Crystals: How does the effect of cooling impact crystal growth? 250 20. Density and Buoyancy 257
Density: Can a scale of relative density predict whether one material floats on another? 260 Buoyancy: Does water pressure affect buoyancy? 264 21. Dissolved Oxygen 271
Decay and Dissolved Oxygen: How does the amount of decaying matter affect the level of dissolved oxygen in water? 274 Goldfish Breath: How does a decrease in the dissolved oxygen level affect the breathing rate of goldfish? 279 22. DNA (Deoxyribonucleic Acid) 285
The Stuff of Life: Isolating DNA 289 Comparing DNA: Does the DNA from different species have the same appearance? 291 23. Dyes 299
Applying Dyes: How does the fiber affect the dye color? 301 Holding the Dye: How do dye fixatives affect the colorfastness of the dye? 304 24. Earthquakes 311
Detecting an Earthquake: How can movement of Earth’s crust be measured? 314 Earthquake Simulation: Is the destruction greater at the epicenter? 317 25. Eclipses 325
Simulating Solar and Lunar Eclipses 327 Phases of the Moon: What does each phase look like? 329 viii
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26. Electricity 333
Electrolytes: Do some solutions conduct electricity better than others? 335 Batteries: Can a series of homemade electric cells form a ‘‘pile’’ strong enough to match the voltage of a D-cell battery? 340 Electroplating: Using electricity to move one metal onto another metal 344 27. Electromagnetism 349
Magnetism: How can a magnetic field be created and detected? 351 Electromagnetism: How can an electromagnet be created? 354 28. Enzymes 359
Finding the Enzyme: Which enzyme breaks down hydrogen peroxide? 362 Tough and Tender: Does papain speed up the aging process? 365 Stopping Enzymes: Does temperature affect enzyme action? 368 29. Erosion 375
Erosion: Does soil type affect the amount of water that runs off a hillside? 377 Plants and Erosion: How do plants affect the rate of soil erosion? 381 30. Ethnobotany 389
Plants and Health: Which plants have anti-bacterial properties? 392 Coiling Reeds: How does the tightness of the coil affect the ability to hold materials? 396 Budget Index lxxxv Level of Difficulty Index xcvii Timetable Index cix General Subject Index cxxi VOLUME 3: F-K
Reader’s Guide xxi Parent’s and Teacher’s Guide xxv Experiments by Scientific Field xxvii Words to Know xxxix Experiment Central, 2nd edition
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31. Fish 401
Fish Breathing: How do different fish take in oxygen? 404 Fish Movement: How do fins and body shape affect the movement of fish? 407 32. Flight 413
Lift-Off: How can a glider be made to fly higher? 415 Helicopters, Propellers, and Centripetal Force: Will it fly high? 418 33. Flowers 423
Self versus Cross: Will there be a difference in reproduction between self-pollinated and cross-pollinated plants of the same type? 427 Sweet Sight: Can changing a flower’s nectar and color affect the pollinators lured to the flower? 431 34. Fluids 439
Viscosity: How can temperature affect the viscosity of liquids? 441 Spinning Fluids: How do different fluids behave when immersed in a spinning rod? 444 35. Food Preservation 451
Sweet Preservatives: How does sugar affect the preservation of fruit? 454 Drying Foods: Does drying fruits help prevent or delay spoilage? 458 36. Food Science 463
Jelly and Pectin: How does acidity affect how fruit gels? 467 Rising Foods: How much carbon dioxide do different leavening agents produce? 470 37. Food Spoilage 477
Preservatives: How do different substances affect the growth of mold? 481 Spoiled Milk: How do different temperatures of liquid affect its rate of spoilage? 485 38. Forces 491
Newton’s Laws in Action: How do water bottle rockets demonstrate Newton’s laws of motion? 493 x
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Centripetal Action: What is the relationship between distance and force in circular motion? 501 39. Forensic Science 507
Fiber Evidence: How can scientific techniques be used to identify fiber? 511 Blood Patterns: How can a blood spatter help recreate the crime? 515 40. Fossils 521
Making an Impression: In which soil environment does a fossil most easily form? 526 Fossil Formation: What are the physical characteristics of an organism that make the best fossils? 530 41. Fungi 537
Decomposers: Food source for a common fungi 541 Living Conditions: What is the ideal temperature for yeast growth? 544 42. Genetics 553
Genetic Traits: Will you share certain genetic traits more with family members than non-family members? 556 Building a Pedigree for Taste 559 43. Germination 565
Effects of Temperature on Germination: What temperatures encourage and discourage germination? 566 Comparing Germination Times: How fast can seeds grow? 570 Seed Scarification: Does breaking the seed shell affect germination time? 573 44. Gravity 579
Gravity: How fast do different objects fall? 581 Measuring Mass: How can a balance be made? 585 45. Greenhouse Effect 589
Creating a Greenhouse: How much will the temperature rise inside a greenhouse? 592 Fossil Fuels: What happens when fossil fuels burn? 596 46. Groundwater Aquifers 601
Aquifers: How do they become polluted? 605 Groundwater: How can it be cleaned? 609 Experiment Central, 2nd edition
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47. Heat 615
Conduction: Which solid materials are the best conductors of heat? 618 Convection: How does heat move through liquids? 622 Heat Capacity: Which liquids have the highest heat capacity? 625 48. Insects 631
Ant Food: What type of foods is one type of ant attracted to? 635 Lightning Bugs: How does the environment affect a firefly’s flash? 638 Budget Index lxxxv Level of Difficulty Index xcvii Timetable Index cix General Subject Index cxxi VOLUME 4: L-PH
Reader’s Guide xxi Parent’s and Teacher’s Guide xxv Experiments by Scientific Field xxvii Words to Know xxxix 49. Life Cycles 645
Tadpoles: Does temperature affect the rate at which tadpoles change into frogs? 647 Insects: How does food supply affect the growth rate of grasshoppers or crickets? 651 50. Light Properties 659
Looking for the Glow: Which objects glow under black light? 661 Refraction and Defraction: Making a rainbow 664 Refraction: How does the material affect how light travels? 666 51. Magnetism 671
Magnets: How do heat, cold, jarring, and rubbing affect the magnetism of a nail? 674 Electromagnets: Does the strength of an electromagnet increase with greater current? 678 xii
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52. Materials Science 685
Testing Tape: Finding the properties that allow tape to support weight. 688 Developing Renewables: Can a renewable packing material have the same qualities as a non-renewable material? 691 53. Memory 697
Memory Mnemonics: What techniques help in memory retention? 701 False Memories: How can memories be influenced? 705 54. Microorganisms 711
Microorganisms: What is the best way to grow penicillin? 713 Growing Microorganisms in a Petri Dish 716 55. Mixtures and Solutions 723
Suspensions and Solutions: Can filtration and evaporation determine whether mixtures are suspensions or solutions? 725 Colloids: Can colloids be distinguished from suspension using the Tyndall effect? 730 56. Mountains 735
Mountain Plates: How does the movement of Earth’s plates determine the formation of a mountain? 738 Mountain Formations: How does the height of the mountain have an affect on desert formation? 741 57. Nanotechnology 747
Nanosize: How can the physical size affect a material’s properties? 750 Nanosize Substances: How can the physical size affect the rate of reaction? 753 58. Nutrition 759
Energizing Foods: Which foods contain carbohydrates and fats? 761 Nutrition: Which foods contain proteins and salts? 764 Daily Nutrition: How nutritious is my diet? 766 59. Oceans 771
Stratification: How does the salinity in ocean water cause it to form layers? 775 Currents: Water behavior in density-driven currents 780 Experiment Central, 2nd edition
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60. Optics and Optical Illusions 787
Optics: What is the focal length of a lens? 788 Optical Illusions: Can the eye be fooled? 791 61. Osmosis and Diffusion 797
Measuring Membranes: Is a plastic bag a semipermeable membrane? 798 Changing Concentrations: Will a bag of salt water draw in fresh water? 803 Changing Sizes: What effect does molecule size have on osmosis 806 62. Oxidation-Reduction 811
Reduction: How will acid affect dirty pennies? 813 Oxidation and Rust: How is rust produced? 817 Oxidation Reaction: Can acid change the color of copper? 820 63. Periodic Table 827
Metals versus Nonmetals: Which areas of the periodic table have elements that conduct electricity? 830 Soluble Families: How does the solubility of an element relate to where it is located on the periodic table? 835 Active Metals: What metals give off electrons more readily than others? 838 64. Pesticides 843
Natural versus Synthetic: How do different types of pesticides compare against a pest? 848 Moving through Water: How can pesticides affect nontarget plant life? 852 65. pH 859
Kitchen Chemistry: What is the pH of household chemicals? 861 Chemical Titration: What is required to change a substance from an acid or a base into a neutral solution? 865 66. Photosynthesis 871
Photosynthesis: How does light affect plant growth? 873 Light Intensity: How does the intensity of light affect plant growth? 877 xiv
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Budget Index lxxxv Level of Difficulty Index xcvii Timetable Index cix General Subject Index cxxi VOLUME 5: PL-SO
Reader’s Guide xxi Parent’s and Teacher’s Guide xxv Experiments by Scientific Field xxvii Words to Know xxxix 67. Plant Anatomy 883
Plant Hormones: What is the affect of hormones on root and stem growth? 886 Water Uptake: How do different plants differ in their water needs? 890 68. Plants and Water 897
Water Flow: How do varying solutions of water affect the amount of water a plant takes in and its turgor pressure? 900 Transpiration: How do different environmental conditions affect plants’ rates of transpiration? 904 69. Polymers 911
Polymer Strength: What are the tensile properties of certain polymers that make them more durable than others? 914 Polymer Slime: How will adding more of a polymer change the properties of a polymer ‘‘slime’’? 919 Polymer Properties: How are the properties of hard plastics different? 923 70. Potential and Kinetic Energy 929
Measuring Energy: How does the height of an object affect its potential energy? 931 Using Energy: Build a roller coaster 934 71. Renewable Energy 941
Capturing Wind Energy: How does the material affect the amount of wind energy harnessed? 944 Hydropower: How does water pressure affect water energy? 948 Experiment Central, 2nd edition
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72. Rivers 955
Weathering Erosion in Glaciers: How does a river make a trench? 957 Stream Flow: Does the stream meander? 960 River Flow: How does the steepness and rate of water flow affect river erosion? 962 73. Rocks and Minerals 969
Mineral Testing: What kind of mineral is it? 971 Rock Classification: Is it igneous, sedimentary, or metamorphic? 975 74. Rotation and Orbits 981
Foucault Pendulum: How can a pendulum demonstrate the rotation of Earth? 985 Spinning Effects: How does the speed of a rotating object affect the way centrifugal force can overcome gravity? 989 75. Salinity 995
Making a Hydrometer: How can salinity be measured? 997 Density Ball: How to make a standard for measuring density 1000 76. Scientific Method 1005
Using the Scientific Method: What are the mystery powders? 1009 Using the Scientific Method: Do fruit flies appear out of thin air? 1013 77. Seashells 1019
Shell Strength: Which shell is stronger: a clam shell or lobster shell? 1022 Classifying Seashells 1025 78. Separation and Identification 1031
Chromatography: Can you identify a pen from the way its colors separate? 1034 Identifying a Mixture: How can determining basic properties of a substance allow you to identify the substances in a mixture? 1039 79. Simple Machines 1047
Wheel and Axle: How can changing the size of the wheel affect the amount of work it takes to lift a load? 1051 Lever Lifting: How does the distance from the fulcrum affect work? 1055 xvi
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The Screw: How does the distance between the threads of a screw affect the work? 1057 80. Soil 1063
Soil Profile: What are the different properties of the soil horizons? 1067 Soil pH: Does the pH of soil affect plant growth? 1074 81. Solar Energy 1081
Capturing Solar Energy: Will seedlings grow bigger in a greenhouse? 1084 Solar Cells: Will sunlight make a motor run? 1087 Retaining the Sun’s heat: What substance best stores heat for a solar system? 1090 82. Sound 1095
Wave Length: How does the length of a vibrating string affect the sound it produces? 1096 Pitch: How does the thickness of a vibrating string affect sound? 1099 Soundproofing: How do different materials affect sound? 1102 Budget Index lxxxv Level of Difficulty Index xcvii Timetable Index cix General Subject Index cxxi VOLUME 6: SP-Z
Reader’s Guide xxi Parent’s and Teacher’s Guide xxv Experiments by Scientific Field xxvii Words to Know xxxix 83. Space Observation 1109
Telescopes: How do different combinations of lenses affect the image? 1113 Doppler Effect: How can waves measure the distance and speed of objects? 1118 Experiment Central, 2nd edition
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84. Stars 1123
Tracking Stars: Where is Polaris? 1125 Tracking the Motion of the Planets: Can a planet be followed? 1128 85. Static Electricity 1133
Building an Electroscope: Which objects are electrically charged? 1135 Measuring a Charge: Does nylon or wool create a stronger static electric charge? 1139 86. Storms 1147
Lightning Sparks: Explore how separating charges causes an attraction between objects 1152 Tornadoes: Making a violent vortex 1155 Forming Hailstones: How do temperature differences affect the formation of hail? 1158 87. Structures and Shapes 1165
Arches and Beams: Which is strongest? 1167 Beams and Rigidity: How does the vertical height of a beam affect its rigidity? 1170 88. Time 1175
Pendulums: How do the length, weight, and swing angle of a pendulum affect its oscillation time? 1180 Water Clock: Does the amount of water in a water clock affect its accuracy? 1185 89. Tropisms 1191
Phototropism: Will plants follow a maze to reach light 1193 Geotropism: Will plant roots turn toward the pull of gravity? 1197 Heliotropism: How does the Sun affect the movement of certain plants? 1201 90. Vegetative Propagation 1207
Auxins: How do auxins affect plant growth? 1209 Potatoes from Pieces: How do potatoes reproduce vegetatively? 1216 91. Vitamins and Minerals 1223
Vitamin C: What juices are the best sources of vitamin C? 1226 Hard Water: Do different water sources have varying mineral content? 1231 xviii
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92. Volcanoes 1237
Model of a Volcano: Will it blow its top? 1240 Looking at a Seismograph: Can a volcanic eruption be detected? 1242 93. Water Cycle 1247
Temperature: How does temperature affect the rate of evaporation? 1248 Surface Area: How does surface area affect the rate of evaporation? 1253 94. Water Properties 1259
Cohesion: Can the cohesive force of surface tension in water support an object denser than water? 1261 Adhesion: How much weight is required to break the adhesive force between an object and water? 1264 95. Weather 1271
Wind: Measuring wind speed with a homemade anemometer 1273 Clouds: Will a drop in air temperature cause a cloud to form? 1277 96. Weather Forecasting 1283
Dewpoint: When will dew form? 1286 Air Pressure: How can air pressure be measured? 1289 97. Wood 1295
Water Absorption: How do different woods absorb water? 1298 Wood Hardness: How does the hardness of wood relate to its building properties? 1302 Budget Index lxxxv Level of Difficulty Index xcvii Timetable Index cix General Subject Index cxxi
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Reader’s Guide
Experiment Central: Understanding Scientific Principles Through Projects provides in one resource a wide variety of science experiments covering nine key science curriculum fields—astronomy, biology, botany, chemistry, ecology, food science, geology, meteorology, and physics—spanning the earth sciences, life sciences, and physical sciences. Experiment Central, 2nd edition combines, expands, and updates the original four-volume and two-volume UXL sets. This new edition includes 20 new chapters, 60 new experiments, and more than 35 enhanced experiments. Each chapter explores a scientific subject and offers experiments or projects that utilize or reinforce the topic studied. Chapters are alphabetically arranged according to scientific concept, including: Air and Water Pollution, Color, Eclipses, Forensic Science, Genetics, Magnetism, Mountains, Periodic Table, Renewable Energy, Storms and Water Cycle. Two to three experiments or projects are included in each chapter.
Entry format Chapters are presented in a standard, easy-to-follow format. All chapters open with an explanatory overview section designed to introduce students to the scientific concept and provide the background behind a concept s discovery or important figures who helped advance the study of the field. Each experiment is divided into eight standard sections to help students follow the experimental process clearly from beginning to end. Sections are: Purpose/Hypothesis
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READER’S GUIDE
Materials Needed
Approximate Budget
Timetable
Step-by-Step Instructions
Summary of Results
Change the Variables
Chapters also include a ‘‘Design Your Own Experiment’’ section that allows students to apply what they have learned about a particular concept and to create their own experiments. This section is divided into:
How to Select a Topic Relating to this Concept
Steps in the Scientific Method
Recording Data and Summarizing the Results
Related Projects
Special Features A ‘‘Words to Know’’ sidebar provides definitions of terms used in each chapter. A cumulative glossary collected from all the ‘‘Words to Know’’ sections is included in the beginning of each volume. The ‘‘Experiments by Scientific Field’’ section categorizes experiments by scientific curriculum area. This section cumulates all experiments across the six-volume series. The Parent’s and Teacher’s Guide recommends that a responsible adult always oversee a student’s experiment and provides several safety guidelines for all students to follow. Standard sidebars accompany experiments and projects.
‘‘What Are the Variables?’’ explains the factors that may have an impact on the outcome of a particular experiment.
‘‘How to Experiment Safely’’ clearly explains any risks involved with the experiment and how to avoid them.
‘‘Troubleshooter’s Guide’’ presents problems that a student might encounter with an experiment, possible causes of the problem, and ways to remedy the problem.
Over 450 photos enhance the text; approximately 450 custom illustrations show the steps in the experiments. xxii
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READER’S GUIDE
Four indexes cumulate information from all the experiments in this six-volume set, including: Budget Index categorizes the experiments by approximate cost.
Level of Difficulty Index lists experiments according to ‘‘easy,’’ ‘‘moderate,’’ or ‘‘difficult,’’ or a combination thereof.
Timetable Index categorizes each experiment by the amount of time needed to complete it, including setup and follow-through time.
General Subject Index provides access to all major terms, people, places, and topics covered in the set.
Acknowledgments The author wishes to acknowledge and thank Laurie Curtis, teacher/ researcher; Cindy O’Neill, science educator; and Joyce Nelson, chemist, for their contributions to this edition as consultants.
Comments and Suggestions We welcome your comments on Experiment Central. Please write: Editors, Experiment Central, U*X*L, 27500 Drake Rd. Farmington Hills, MI 48331-3535; call toll-free: 1-800-347-4253; or visit us at www.gale.cengage.com.
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Pa ren t’s a nd T ea c her ’s Gu i de
The experiments and projects in Experiment Central have been carefully constructed with issues of safety in mind, but your guidance and supervision are still required. Following the safety guidelines that accompany each experiment and project (found in the ‘‘How to Experiment Safely’’ sidebar box), as well as putting to work the safe practices listed below, will help your child or student avoid accidents. Oversee your child or student during experiments, and make sure he or she follows these safety guidelines:
Always wear safety goggle is there is any possiblity of sharp objects, small particles, splashes of liquid, or gas fumes getting in someone’s eyes.
Always wear protective gloves when handling materials that could irritate the skin.
Never leave an open flame, such as a lit candle, unattended. Never wear loose clothing around an open flame.
Follow instructions carefully when using electrical equipment, including batteries, to avoid getting shocked.
Be cautious when handling sharp objects or glass equipment that might break. Point scissors away from you and use them carefully.
Always ask for help in cleaning up spills, broken glass, or other hazardous materials.
Always use protective gloves when handling hot objects. Set them down only on a protected surface that will not be damaged by heat. xxv
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Always wash your hands thoroughly after handling material that might contain harmful microorganisms, such as soil and pond water.
Do not substitute materials in an experiment without asking a knowledgeable adult about possible reactions.
Do not use or mix unidentified liquids or powders. The result might be an explosion or poisonous fumes.
Never taste or eat any substances being used in an experiment.
Always wear old clothing or a protective apron to avoid staining your clothes.
Experiment Central, 2nd edition
Experiments by Scientific Field
Chapter name in brackets, followed by experiment name. The numeral before the colon indicates volume; numbers after the colon indicate page number. ALL SUBJECTS
[Scientific Method] Using the Scientific Method: Do fruit flies appear out of thin air? 5:1013 [Scientific Method] Using the Scientific Method: What are the mystery powders? 5:1009 ASTRONOMY
[Comets and Meteors] Comet Nucleus: Linking a Comet’s Composition to its Properties. 2:218 [Comets and Meteors] Meteor Impact: How do the characteristics of a meteorite and its impact affect the shape of the crater? 2:221 [Eclipses] Phases of the Moon: What does each phase look like? 2:329 [Eclipses] Simulating Solar and Lunar Eclipses 2:327 [Rotation and Orbits] Foucault Pendulum: How can a pendulum demonstrate the rotation of Earth? 5:985 [Rotation and Orbits] Spinning Effects: How does the speed of a rotating object affect the way centrifugal force can overcome gravity? 5:989 [Space Observation] Doppler Effect: How can waves measure the distance and speed of objects? 6:1118 xxvii
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[Space Observation] Telescopes: How do different combinations of lenses affect the image? 6:1113 [Stars] Tracking Stars: Where is Polaris? 6:1125 [Stars] Tracking the Motion of the Planets: Can a planet be followed? 6:1128 BIOLOGY
[Animal Defenses] Camouflage: Does an animal’s living environment relate to the color of the animal life? 1:63 [Animal Defenses] Ladybug Threats: How do ladybugs defend themselves when they feel threatened? 1:65 [Bacteria] Bacterial Growth: How do certain substances inhibit or promote bacterial growth? 1:90 [Bacteria] Bacterial Resistance: Can bacteria gain resistance to a substance after exposure? 1:95 [Bones and Muscles] Bone Loss: How does the loss of calcium affect bone strength? 1:116 [Bones and Muscles] Muscles: How does the strength of muscles affect fatigue over time? 1:120 [Cells] Investigating Cells: What are the differences between a multicellular organism and a unicellular organism? 1:141 [Cells] Plant Cells: What are the cell differences between monocot and dicot plants? 1:145 [Cells] Yeast Cells: How do they reproduce? 1:147 [Chemosenses] Smell and Taste: How does smell affect the sense of taste? 1:186 [Chemosenses] Supertasters: Is there a correlation between the number of taste buds and taste perception? 1:180 [DNA (Deoxyribonucleic Acid)] Comparing DNA: Does the DNA from different species have the same appearance? 2:291 [DNA (Deoxyribonucleic Acid)] The Stuff of Life: Isolating DNA 2:289 [Enzymes] Finding the Enzyme: Which enzyme breaks down hydrogen peroxide? 2:362 [Enzymes] Stopping Enzymes: Does temperature affect enzyme action? 2:368 [Enzymes] Tough and Tender: Does papain speed up the aging process? 2:365 [Fish] Fish Breathing: How do different fish take in oxygen? 3:404 xxviii
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EXPERIMENTS BY SCIENTIFIC FIELD
[Fish] Fish Movement: How do fins and body shape affect the movement of fish? 3:407 [Forensic Science] Blood Patterns: How can a blood spatter help recreate the crime? 3:515 [Forensic Science] Fiber Evidence: How can scientific techniques be used to identify fiber? 3:511 [Fungi] Decomposers: Food source for a common fungi 3:541 [Fungi] Living Conditions: What is the ideal temperature for yeast growth? 3:544 [Genetics] Building a Pedigree for Taste 3:559 [Genetics] Genetic Traits: Will you share certain genetic traits more with family members than non-family members? 3:556 [Insects] Ant Food: What type of foods is one type of ant attracted to? 3:635 [Insects] Lightning Bugs: How does the environment affect a firefly’s flash? 3:638 [Life Cycles] Insects: How does food supply affect the growth rate of grasshoppers or crickets? 4:651 [Life Cycles] Tadpoles: Does temperature affect the rate at which tadpoles change into frogs? 4:647 [Memory] False Memories: How can memories be influenced? 4:705 [Memory] Memory Mnemonics: What techniques help in memory retention? 4:701 [Microorganisms] Growing Microorganisms in a Petri Dish 4:716 [Microorganisms] Microorganisms: What is the best way to grow penicillin? 4:713 [Nutrition] Daily Nutrition: How nutritious is my diet? 4:766 [Nutrition] Energizing Foods: Which foods contain carbohydrates and fats? 4:761 [Nutrition] Nutrition: Which foods contain proteins and salts? 4:764 [Osmosis and Diffusion] Changing Concentrations: Will a bag of salt water draw in fresh water? 4:803 [Osmosis and Diffusion] Changing Sizes: What effect does molecule size have on osmosis 4:806 [Osmosis and Diffusion] Measuring Membranes: Is a plastic bag a semipermeable membrane? 4:798 Experiment Central, 2nd edition
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EXPERIMENTS BY SCIENTIFIC FIELD
[Seashells] Classifying Seashells 5:1025 [Seashells] Shell Strength: Which shell is stronger: a clam shell or lobster shell? 5:1022 BOTANY
[Annual Growth] Lichen Growth: What can be learned from the environment by observing lichens? 1:79 [Annual Growth] Tree Growth: What can be learned from the growth patterns of trees? 1:74 [Chlorophyll] Plant Pigments: Can pigments be separated? 1:193 [Chlorophyll] Response to Light: Do plants grow differently in different colors of light? 1:197 [Ethnobotany] Coiling Reeds: How does the tightness of the coil affect the ability to hold materials? 2:396 [Ethnobotany] Plants and Health: Which plants have antibacterial properties? 2:392 [Flowers] Self versus Cross: Will there be a difference in reproduction between self-pollinated and cross-pollinated plants of the same type? 3:427 [Flowers] Sweet Sight: Can changing a flower’s nectar and color affect the pollinators lured to the flower? 3:431 [Germination] Comparing Germination Times: How fast can seeds grow? 3:570 [Germination] Effects of Temperature on Germination: What temperatures encourage and discourage germination? 3:566 [Germination] Seed Scarification: Does breaking the seed shell affect germination time? 3:573 [Photosynthesis] Light Intensity: How does the intensity of light affect plant growth? 4:877 [Photosynthesis] Photosynthesis: How does light affect plant growth? 4:873 [Plant Anatomy] Plant Hormones: What is the affect of hormones on root and stem growth? 5:886 [Plant Anatomy] Water Uptake: How do different plants differ in their water needs? 5:890 [Plants and Water] Transpiration: How do different environmental conditions affect plants’ rates of transpiration? 5:904 xxx
Experiment Central, 2nd edition
EXPERIMENTS BY SCIENTIFIC FIELD
[Plants and Water] Water Flow: How do varying solutions of water affect the amount of water a plant takes in and its turgor pressure? 5:900 [Tropisms] Geotropism: Will plant roots turn toward the pull of gravity? 6:1197 [Tropisms] Heliotropism: How does the Sun affect the movement of certain plants? 6:1201 [Tropisms] Phototropism: Will plants follow a maze to reach light? 6:1193 [Vegetative Propagation] Auxins: How do auxins affect plant growth? 6:1209 [Vegetative Propagation] Potatoes from Pieces: How do potatoes reproduce vegetatively? 6:1216 CHEMISTRY
[Adhesives] Adhesives in the Environment: Will different environmental conditions affect the properties of different adhesives? 1:26 [Adhesives] Material Adhesion: How do various glues adhere to different materials? 1:22 [Chemical Energy] Exothermic or Endothermic: Determining whether various chemical reactions are exothermic or endothermic 1:156 [Chemical Energy] Rusting: Is the chemical reaction exothermic, endothermic, or neither? 1:152 [Chemical Properties] Chemical Patination: Producing chemical reactions on metal 1:173 [Chemical Properties] Chemical Reactions: What happens when mineral oil, water, and iodine mix? 1:170 [Chemical Properties] Slime: What happens when white glue and borax mix? 1:167 [Crystals] Cool Crystals: How does the effect of cooling impact crystal growth? 2:252 [Crystals] Crystal Structure: Will varying shape crystals form from varying substances? 2:246 [Dyes] Applying Dyes: How does the fiber affect the dye color? 2:301 [Dyes] Holding the Dye: How do dye fixatives affect the colorfastness of the dye? 2:304 Experiment Central, 2nd edition
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[Materials Science] Developing Renewables: Can a renewable packing material have the same qualities as a non-renewable material? 4:691 [Materials Science] Testing Tape: Finding the properties that allow tape to support weight. 4:688 [Mixtures and Solutions] Colloids: Can colloids be distinguished from suspension using the Tyndall effect? 4:730 [Mixtures and Solutions] Suspensions and Solutions: Can filtration and evaporation determine whether mixtures are suspensions or solutions? 4:725 [Oxidation-Reduction] Oxidation and Rust: How is rust produced? 4:817 [Oxidation-Reduction] Oxidation Reaction: Can acid change the color of copper? 4:820 [Oxidation-Reduction] Reduction: How will acid affect dirty pennies? 4:813 [Periodic Table] Active Metals: What metals give off electrons more readily than others? 4:838 [Periodic Table] Metals versus Nonmetals: Which areas of the periodic table have elements that conduct electricity? 4:830 [Periodic Table] Soluble Families: How does the solubility of an element relate to where it is located on the Periodic Table? 4:835 [pH] Chemical Titration: What is required to change a substance from an acid or a base into a neutral solution? 4:865 [pH] Kitchen Chemistry: What is the pH of household chemicals? 4:861 [Polymers] Polymer Properties: How are the properties of hard plastics different? 5:923 [Polymers] Polymer Slime: How will adding more of a polymer change the properties of a polymer ‘‘slime’’? 5:919 [Polymers] Polymer Strength: What are the tensile properties of certain polymers that make them more durable than others? 5:914 [Salinity] Density Ball: How to make a standard for measuring density 5:1000 [Salinity] Making a Hydrometer: How can salinity be measured? 5:997 [Separation and Identification] Chromatography: Can you identify a pen from the way its colors separate? 5:1034 xxxii
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EXPERIMENTS BY SCIENTIFIC FIELD
[Separation and Identification] Identifying a Mixture: How can determining basic properties of a substance allow you to identify the substances in a mixture? 5:1039 [Water Properties] Adhesion: How much weight is required to break the adhesive force between an object and water? 6:1264 [Water Properties] Cohesion: Can the cohesive force of surface tension in water support an object denser than water? 6:1261 ECOLOGY
[Acid Rain] Acid Rain and Animals: How does acid rain affect brine shrimp? 1:5 [Acid Rain] Acid Rain and Plants: How does acid rain affect plant growth? 1:9 [Acid Rain] Acid Rain: Can acid rain harm structures? 1:12 [Air and Water Pollution] Eutrophication: The effect of phosphates on water plants. 1:55 [Air and Water Pollution] Pollutant Bioindicators: Can lichens provide clues to an area’s air pollution? 1:51 [Biomes] Building a Desert Biome 1:108 [Biomes] Building a Temperate Forest Biome 1:107 [Composting/Landfills] Composting: Using organic material to grow plants 2:237 [Composting/Landfills] Living Landfill: What effect do the microorganisms in soil have on the decomposition process? 2:232 [Dissolved Oxygen] Decay and Dissolved Oxygen: How does the amount of decaying matter affect the level of dissolved oxygen in water? 2:274 [Dissolved Oxygen] Goldfish Breath: How does a decrease in the dissolved oxygen level affect the breathing rate of goldfish? 2:279 [Erosion] Erosion: Does soil type affect the amount of water that runs off a hillside? 2:377 [Erosion] Plants and Erosion: How do plants affect the rate of soil erosion? 2:381 [Greenhouse Effect] Creating a Greenhouse: How much will the temperature rise inside a greenhouse? 3:592 [Greenhouse Effect] Fossil Fuels: What happens when fossil fuels burn? 3:596 Experiment Central, 2nd edition
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[Groundwater Aquifers] Aquifers: How do they become polluted? 3:605 [Groundwater Aquifers] Groundwater: How can it be cleaned? 3:609 [Pesticides] Moving through Water: How can pesticides affect nontarget plant life? 4:852 [Pesticides] Natural versus Synthetic: How do different types of pesticides compare against a pest? 4:848 [Renewable Energy] Capturing Wind Energy: How does the material affect the amount of wind energy harnessed? 5:944 [Renewable Energy] Hydropower: How does water pressure affect water energy? 5:948 [Rivers] River Flow: How does the steepness and rate of water flow affect river erosion? 5:962 [Rivers] Stream Flow: Does the stream meander? 5:960 [Rivers] Weathering Erosion in Glaciers: How does a river make a trench? 5:957 [Soil] Soil pH: Does the pH of soil affect plant growth? 5:1074 [Soil] Soil Profile: What are the different properties of the soil horizons? 5:1067 [Solar Energy] Capturing Solar Energy: Will seedlings grow bigger in a greenhouse? 5:1084 [Solar Energy] Retaining the Sun’s heat: What substance best stores heat for a solar system? 5:1090 [Solar Energy] Solar Cells: Will sunlight make a motor run? 5:1087 [Water Cycle] Surface Area: How does surface area affect the rate of evaporation? 6:1253 [Water Cycle] Temperature: How does temperature affect the rate of evaporation? 6:1248 FOOD SCIENCE
[Food Preservation] Drying Foods: Does drying fruits help prevent or delay spoilage? 3:458 [Food Preservation] Sweet Preservatives: How does sugar affect the preservation of fruit? 3:454 [Food Science] Jelly and Pectin: How does acidity affect how fruit gels? 3:467 xxxiv
Experiment Central, 2nd edition
EXPERIMENTS BY SCIENTIFIC FIELD
[Food Science] Rising Foods: How much carbon dioxide do different leavening agents produce? 3:470 [Food Spoilage] Preservatives: How do different substances affect the growth of mold? 3:481 [Food Spoilage] Spoiled Milk: How do different temperatures of liquid affect its rate of spoilage? 3:485 [Vitamins and Minerals] Hard Water: Do different water sources have varying mineral content? 6:1231 [Vitamins and Minerals] Vitamin C: What juices are the best sources of vitamin C? 6:1226 GEOLOGY
[Caves] Cave Formation: How does the acidity of a substance affect the formation of a cave? 1:132 [Caves] Cave Icicles: How does the mineral content of water affect the formation of stalactites and stalagmites? 1:135 [Earthquakes] Detecting an Earthquake: How can movement of Earth’s crust be measured? 2:314 [Earthquakes] Earthquake Simulation: Is the destruction greater at the epicenter? 2:317 [Fossils] Fossil Formation: What are the physical characteristics of an organism that make the best fossils? 3:530 [Fossils] Making an Impression: In which soil environment does a fossil most easily form? 3:526 [Mountains] Mountain Formations: How does the height of the mountain have an affect on desert formation? 4:741 [Mountains] Mountain Plates: How does the movement of Earth’s plates determine the formation of a mountain? 4:738 [Oceans] Currents: Water behavior in density-driven currents 4:780 [Oceans] Stratification: How does the salinity in ocean water cause it to form layers? 4:775 [Rocks and Minerals] Mineral Testing: What kind of mineral is it? 5:971 [Rocks and Minerals] Rock Classification: Is it igneous, sedimentary, or metamorphic? 5:975 [Volcanoes] Looking at a Seismograph: Can a volcanic eruption be detected? 6:1242 [Volcanoes] Model of a Volcano: Will it blow its top? 6:1240 Experiment Central, 2nd edition
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M E T EO RO LO G Y
[Air] Air Density: Does warm air take up less room than cool air? 1:36 [Air] Convection Currents: How can rising air cause weather changes? 1:39 [Storms] Forming Hailstones: How do temperature differences affect the formation of hail? 6:1158 [Storms] Lightning Sparks: Explore how separating charges causes an attraction between objects 6:1152 [Storms] Tornadoes: Making a violent vortex 6:1155 [Weather] Clouds: Will a drop in air temperature cause a cloud to form? 6:1277 [Weather] Wind: Measuring wind speed with a homemade anemometer 6:1273 [Weather Forecasting] Air Pressure: How can air pressure be measured? 6:1289 [Weather Forecasting] Dewpoint: When will dew form? 6:1286 PHYSICS
[Color] Color and Flavor: How much does color affect flavor perception? 2:207 [Color] Temperature and Color: What color has the highest temperature? 2:210 [Density and Buoyancy] Buoyancy: Does water pressure affect buoyancy? 2:264 [Density and Buoyancy] Density: Can a scale of relative density predict whether one material floats on another? 2:260 [Electricity] Batteries: Can a series of homemade electric cells form a ‘‘pile’’ strong enough to match the voltage of a D-cell battery? 2:340 [Electricity] Electrolytes: Do some solutions conduct electricity better than others? 2:335 [Electricity] Electroplating: Using electricity to move one metal onto another metal 2:344 [Electromagnetism] Electromagnetism: How can an electromagnet be created? 2:354 [Electromagnetism] Magnetism:How can a magnetic field be created and detected? 2:351 xxxvi
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EXPERIMENTS BY SCIENTIFIC FIELD
[Flight] Helicopters, Propellers, and Centripetal Force: Will it fly high? 3:418 [Flight] Lift-Off: How can a glider be made to fly higher? 3:415 [Fluids] Spinning Fluids: How do different fluids behave when immersed in a spinning rod? 3:444 [Fluids] Viscosity: How can temperature affect the viscosity of liquids? 3:441 [Forces] Centripetal Action: What is the relationship between distance and force in circular motion? 3:501 [Forces] Newton’s Laws in Action: How do water bottle rockets demonstrate Newton’s laws of motion? 3:493 [Gravity] Gravity: How fast do different objects fall? 3:581 [Gravity] Measuring Mass: How can a balance be made? 3:585 [Heat] Conduction: Which solid materials are the best conductors of heat? 3:618 [Heat] Convection: How does heat move through liquids? 3:622 [Heat] Heat Capacity: Which liquids have the highest heat capacity? 3:625 [Light Properties] Looking for the Glow: Which objects glow under black light? 4:661 [Light Properties] Refraction and Defraction: Making a rainbow 4:664 [Light Properties] Refraction: How does the material affect how light travels? 4:666 [Magnetism] Electromagnets: Does the strength of an electromagnet increase with greater current? 4:678 [Magnetism] Magnets: How do heat, cold, jarring, and rubbing affect the magnetism of a nail? 4:674 [Nanotechnology] Nanosize Substances: How can the physical size affect the rate of reaction? 4:753 [Nanotechnology] Nanosize: How can the physical size affect a material’s properties? 4:750 [Optics and Optical Illusions] Optical Illusions: Can the eye be fooled? 4:791 [Optics and Optical Illusions] Optics: What is the focal length of a lens? 5:788 [Potential and Kinetic Energy] Measuring Energy: How does the height of an object affect its potential energy? 5:931 Experiment Central, 2nd edition
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[Potential and Kinetic Energy] Using Energy: Build a roller coaster 5:934 [Simple Machines] Lever Lifting: How does the distance from the fulcrum affect work? 5:1055 [Simple Machines] The Screw: How does the distance between the threads of a screw affect the work? 5:1057 [Simple Machines] Wheel and Axle: How can changing the size of the wheel affect the amount of work it takes to lift a load? 5:1051 [Sound] Pitch: How does the thickness of a vibrating string affect sound? 5:1099 [Sound] Soundproofing: How do different materials affect sound? 5:1102 [Sound] Wave Length: How does the length of a vibrating string affect the sound it produces? 5:1096 [Static Electricity] Building an Electroscope: Which objects are electrically charged? 6:1135 [Static Electricity] Measuring a Charge: Does nylon or wool create a stronger static electric charge? 6:1139 [Structures and Shapes] Arches and Beams: Which is strongest? 6:1167 [Structures and Shapes] Beams and Rigidity: How does the vertical height of a beam affect its rigidity? 6:1170 [Time] Pendulums: How do the length, weight, and swing angle of a pendulum affect its oscillation time? 6:1180 [Time] Water Clock: Does the amount of water in a water clock affect its accuracy? 6:1185 [Wood] Water Absorption: How do different woods absorb water? 6:1298 [Wood] Wood Hardness: How does the hardness of wood relate to its building properties? 6:1302
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Words to Know
Abdomen: The third segment of an insect body. Abscission: Barrier of special cells created at the base of leaves in
autumn. Absolute dating: The age of an object correlated to a specific fixed time,
as established by some precise dating method. Acceleration: The rate at which the velocity and/or direction of an object
is changing with respect to time. Acid: Substance that when dissolved in water is capable of reacting with a
base to form salts and release hydrogen ions. Acid rain: A form of precipitation that is significantly more acidic than
neutral water, often produced as the result of industrial processes and pollution. Acoustics: The science concerned with the production, properties, and
propagation of sound waves. Acronym: A word or phrase formed from the first letter of other words. Active solar energy system: A solar energy system that uses pumps or
fans to circulate heat captured from the Sun. Additive: A chemical compound that is added to foods to give them
some desirable quality, such as preventing them from spoiling. Adhesion: Attraction between two different substances. Adhesive: A substance that bonds or adheres two substances together. xxxix
WORDS TO KNOW
Aeration: Mixing a gas, like oxygen, with a liquid, like water. Aerobic: A process that requires oxygen. Aerodynamics: The study of the motion of gases (particularly air) and
the motion and control of objects in the air. Agar: A nutrient rich, gelatinous substance that is used to grow bacteria. Air: Gaseous mixture that covers Earth, composed mainly of nitrogen
(about 78%) and oxygen (about 21%) with lesser amounts of argon, carbon dioxide, and other gases. Air density: The ratio of the mass of a substance to the volume it
occupies. Air mass: A large body of air that has similar characteristics. Air pressure: The force exerted by the weight of the atmosphere above a
point on or above Earth’s surface. Alga/Algae: Single-celled or multicellular plants or plant-like organisms
that contain chlorophyll, thus making their own food by photosynthesis. Algae grow mainly in water. Alignment: Adjustment in a certain direction or orientation. Alkali metals: The first group of elements in the periodic table, these
metals have a single electron in the outermost shell. Alkaline: Having a pH of more than 7. Alleles: One version of the same gene. Alloy: A mixture of two or more metals with properties different from
those metals of which it is made. Amine: An organic compound derived from ammonia. Amino acid: One of a group of organic compounds that make up
proteins. Amnesia: Partial or total memory loss. Amperage: A measurement of current. The common unit of measure is
the ampere or amp. Amphibians: Animals that live on land and breathe air but return to the
water to reproduce. Amplitude: The maximum displacement (difference between an original
position and a later position) of the material that is vibrating. Amplitude can be thought of visually as the highest and lowest point of a wave. Anaerobic: A process that does not require oxygen. xl
Experiment Central, 2nd edition
WORDS TO KNOW
Anal fin: Fin on the belly of a fish, used for balance. Anatomy: The study of the structure of living things. Anemometer: A device that measures wind speed. Angiosperm: A flowering plant that has its seeds produced within an
ovary. Animalcules: Life forms that Anton van Leeuwenhoek named when he
first saw them under his microscope; they later became known as protozoa and bacteria. Anther: The male reproductive organs of the plant, located on the tip of
a flower’s stamen. Anthocyanin: Red pigment found in leaves, petals, stems, and other
parts of a plant. Antibiotic: A substance produced by or derived from certain fungi and
other organisms, that can destroy or inhibit the growth of other microorganisms. Antibiotic resistance: The ability of microorganisms to change so that
they are not killed by antibiotics. Antibody: A protein produced by certain cells of the body as an immune
(disease-fighting) response to a specific foreign antigen. Antigen: A substance that causes the production of an antibody when
injected directly into the body. Antioxidants: Used as a food additive, these substances can prevent food
spoilage by reducing the food’s exposure to air. Aquifer: Underground layer of sand, gravel, or spongy rock that collects
water. Arch: A curved structure that spans an opening and supports a weight
above the opening. Artesian well: A well in which water is forced out under pressure. Asexual reproduction: A reproductive process that does not involve the
union of two individuals in the exchange of genetic material. Astronomers: Scientists who study the positions, motions, and compo-
sition of stars and other objects in the sky. Astronomy: The study of the physical properties of objects and matter
outside Earth’s atmosphere. Atmosphere: Layers of air that surround Earth. Experiment Central, 2nd edition
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WORDS TO KNOW
Atmospheric pressure: The pressure exerted by the atmosphere at
Earth’s surface due to the weight of the air. Atom: The smallest unit of an element, made up of protons and neu-
trons in a central nucleus surrounded by moving electrons. Atomic mass: Also known as atomic weight, the average mass of the
atoms in an element; the number that appears under the element symbol in the periodic table. Atomic number: The number of protons (or electrons) in an atom; the
number that appears over the element symbol in the periodic table. Atomic symbol: The one- or two-letter abbreviation for a chemical
element. Autotroph: An organism that can build all the food and produce all the
energy it needs with its own resources. Auxins: A group of plant hormones responsible for patterns of plant
growth. Axis: An imaginary straight line around which an object, like a planet,
spins or turns. Earth’s axis is a line that goes through the North and South Poles.
Bacteria: Single-celled microorganisms that live in soil, water, plants,
and animals that play a key role in the decay of organic matter and the cycling of nutrients. Some are agents of disease. Bacteriology: The scientific study of bacteria, their characteristics, and
their activities as related to medicine, industry, and agriculture. Barometer: An instrument for measuring atmospheric pressure, used
especially in weather forecasting. Base: Substance that when dissolved in water is capable of reacting with
an acid to form salts and release hydrogen ions; has a pH of more than 7. Base pairs: In DNA, the pairing of two nucleotides with each other:
adenine (A) with thymine (T), and guanine (G) with cytosine (C). Beam: A straight, horizontal structure that spans an opening and sup-
ports a weight above the opening. xlii
Experiment Central, 2nd edition
WORDS TO KNOW
Bedrock: Solid layer of rock lying beneath the soil and other loose
material. Beriberi: A disease caused by a deficiency of thiamine and characterized
by nerve and gastrointestinal disorders. Biochemical oxygen demand (BOD5): The amount of oxygen micro-
organisms use over a five-day period in 68º F (20º C) water to decay organic matter. Biodegradable: Capable of being decomposed by biological agents. Biological variables: Living factors such as bacteria, fungi, and animals
that can affect the processes that occur in nature and in an experiment. Bioluminescence: The chemical phenomenon in which an organism can
produce its own light. Biomass: Organic materials that are used to produce usable energy. Biomes: Large geographical areas with specific climates and soils, as well
as distinct plant and animal communities that are interdependent. Biomimetics: The development of materials that are found in nature. Biopesticide: Pesticide produced from substances found in nature. Bivalve: Bivalves are characterized by shells that are divided into two
parts or valves that completely enclose the mollusk like the clam or scallop. Blanching: A cooking technique in which the food, usually vegetables
and fruits, are briefly cooked in boiling water and then plunged into cold water. Blood pattern analysis: The study of the shape, location, and pattern of
blood in order to understand how it got there. Blueshift: The shortening of the frequency of light waves toward the
blue end of the visible light spectrum as they travel towards an observer; most commonly used to describe movement of stars towards Earth. Boiling point: The temperature at which a substance changes from a
liquid to a gas or vapor. Bond: The force that holds two atoms together. Bone joint: A place in the body where two or more bones are connected. Bone marrow: The spongy center of many bones in which blood cells are
manufactured. Experiment Central, 2nd edition
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WORDS TO KNOW
Bone tissue: A group of similar cells in the bone with a common
function. Bony fish: The largest group of fish, whose skeleton is made of bone. Boreal: Northern. Botany: The branch of biology involving the scientific study of plant life. Braided rivers: Wide, shallow rivers with multiple channels and pebbly
islands in the middle. Buoyancy: The tendency of a liquid to exert a lifting effect on a body
immersed in it. By-product: A secondary substance produced as the result of a physical
or chemical process, in addition to the main product.
Calcium carbonate: A substance that is secreted by a mollusk to create
the shell it lives in. Calibration: To standardize or adjust a measuring instrument so its
measurements are correct. Cambium: The tissue below the bark that produces new cells, which
become wood and bark. Camouflage: Markings or coloring that help hide an animal by making
it blend into the surrounding environment. Cancellous bone: Also called spongy bone, the inner layer of a bone that
has cells with large spaces in between them filled with marrow. Canning: A method of preserving food using airtight, vacuum-sealed
containers and heat processing. Capillary action: The tendency of water to rise through a narrow tube by
the force of adhesion between the water and the walls of the tube. Caramelization: The process of heating sugars to the point at which they
break down and lead to the formation of new compounds. Carbohydrate: A compound consisting of carbon, hydrogen, and oxygen
found in plants and used as a food by humans and other animals. Carbonic acid: A weak acid that forms from the mixture of water and
carbon dioxide. Carnivore: A meat-eating organism. xliv
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WORDS TO KNOW
Carotene: Yellow-orange pigment in plants. Cartilage: The connective tissue that covers and protects the bones. Cartilaginous fish: The second largest group of fish whose skeleton is
made of cartilage Cast: In paleontology, the fossil formed when a mold is later filled in by
mud or mineral matter. Catalase: An enzyme found in animal liver tissue that breaks down
hydrogen peroxide into oxygen and water. Catalyst: A compound that starts or speeds up the rate of a chemical
reaction without undergoing any change in its own composition. Caudal fin: Tail fin of a fish used for fast swimming. Cave: Also called cavern, a hollow or natural passage under or into the
ground large enough for a person to enter. Celestial bodies: Describing planets or other objects in space. Cell membrane: The layer that surrounds the cell, but is inside the cell
wall, allowing some molecules to enter and keeping others out of the cell. Cell theory: All living things have one or more similar cells that carry out
the same functions for the living process. Cell wall: A tough outer covering over the cell membrane of bacteria and
plant cells. Cells: The basic unit for living organisms; cells are structured to perform
highly specialized functions. Centrifugal force: The apparent force pushing a rotating body away
from the center of rotation. Centrifuge: A device that rapidly spins a solution so that the heavier
components will separate from the lighter ones. Centripetal force: Rotating force that moves towards the center or axis. Cerebral cortex: The outer layer of the brain. Channel: A shallow trench carved into the ground by the pressure and
movement of a river. Chemical change: The change of one or more substances into other
substances. Chemical energy: Energy stored in chemical bonds. Experiment Central, 2nd edition
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WORDS TO KNOW
Chemical property: A characteristic of a substance that allows it to
undergo a chemical change. Chemical properties include flammability and sensitivity to light. Chemical reaction: Any chemical change in which at least one new
substance is formed. Chemosense: A sense stimulated by specific chemicals that cause the
sensory cell to transmit a signal to the brain. Chitin: Substance that makes up the exoskeleton of crustaceans. Chlorophyll: A green pigment found in plants that absorbs sunlight,
providing the energy used in photosynthesis, or the conversion of carbon dioxide and water to complex carbohydrates. Chloroplasts: Small structures in plant cells that contain chlorophyll and
in which the process of photosynthesis takes place. Chromatography: A method for identifying the components of a sub-
stance based on their characteristic colors. Chromosome: A structure of DNA found in the cell nucleus. Cilia: Hairlike structures on olfactory receptor cells that sense odor
molecules. Circuit: The complete path of an electric current including the source of
electric energy. Circumference: The distance around a circle. Clay: Type of soil comprising the smallest soil particles. Cleavage: The tendency of a mineral to split along certain planes. Climate: The average weather that a region experiences over a long
period. Coagulation: The clumping together of particles in a mixture, often
because the repelling force separating them is disrupted. Cohesion: Attraction between like substances. Cold blooded: When an animals body temperature rises or falls to match
the environment. Collagen: A protein in bone that gives the bone elasticity. Colloid: A mixture containing particles suspended in, but not dissolved
in, a dispersing medium. Colony: A mass of microorganisms that have been bred in a medium. xlvi
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WORDS TO KNOW
Colorfast: The ability of a material to keep its dye and not fade or change
color. Coma: Glowing cloud of gas surrounding the nucleus of a comet. Combustion: Any chemical reaction in which heat, and usually light, is
produced. It is commonly the burning of organic substances during which oxygen from the air is used to form carbon dioxide and water vapor. Comet: An icy body orbiting in the solar system, which partially vapor-
izes when it nears the Sun and develops a diffuse envelope of dust and gas as well as one or more tails. Comet head: The nucleus and the coma of a comet. Comet nucleus: The core or center of a comet. (Plural: Comet nuclei.) Comet tail: The most distinctive feature of comets; comets can display
two basic types of tails: one gaseous and the other largely composed of dust. Compact bone: The outer, hard layer of the bone. Complete metamorphosis: Metamorphosis in which a larva becomes a
pupa before changing into an adult form. Composting: The process in which organic compounds break down and
become dark, fertile soil called humus. Compression: A type of force on an object where the object is pushed or
squeezed from each end. Concave: Hollowed or rounded inward, like the inside of a bowl. Concave lens: A lens that is thinner in the middle than at the edges. Concentration: The amount of a substance present in a given volume,
such as the number of molecules in a liter. Condensation: The process by which a gas changes into a liquid. Conduction: The flow of heat through a solid. Conductivity: The ability of a material to carry an electrical current. Conductor: A substance able to carry an electrical current. Cones: Cells in the retina that can perceive color. Confined aquifer: An aquifer with a layer of impermeable rock above it
where the water is held under pressure. Coniferous: Refers to trees, such as pines and firs, that bear cones and
have needle-like leaves that are not shed all at once. Experiment Central, 2nd edition
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Conservation of energy: The law of physics that states that energy can be
transformed from one form to another, but can be neither created nor destroyed. Constellations: Patterns of stars in the night sky. There are eighty-eight
known constellations. Continental drift: The theory that continents move apart slowly at a
predictable rate. Contract: To shorten, pull together. Control experiment: A set-up that is identical to the experiment but is
not affected by the variable that will be changed during the experiment. Convection: The circulatory motion that occurs in a gas or liquid at a
nonuniform temperature owing to the variation of its density and the action of gravity. Convection current: A circular movement of a fluid in response to
alternating heating and cooling. Convex: Curved or rounded outward, like the outside of a ball. Convex lens: A lens that is thicker in the middle than at the edges. Coprolites: The fossilized droppings of animals. Coriolis force: A force that makes a moving object appear to travel in a
curved path over the surface of a spinning body. Corona: The outermost atmospheric layer of the Sun. Corrosion: An oxidation-reduction reaction in which a metal is oxidized
(reacted with oxygen) and oxygen is reduced, usually in the presence of moisture. Cotyledon: Seed leaves, which contain the stored source of food for the
embryo. Crater: An indentation caused by an object hitting the surface of a planet
or moon. Crest: The highest point reached by a wave. Cross-pollination: The process by which pollen from one plant polli-
nates another plant of the same species. Crust: The hard outer shell of Earth that floats upon the softer, denser
mantle. xlviii
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Crustacean: A type of arthropod characterized by hard and thick skin,
and having shells that are jointed. This group includes the lobster, crab, and crayfish. Crystal: Naturally occurring solid composed of atoms or molecules
arranged in an orderly pattern that repeats at regular intervals. Crystal faces: The flat, smooth surfaces of a crystal. Crystal lattice: The regular and repeating pattern of the atoms in a
crystal. Cultures: Microorganisms growing in prepared nutrients. Cumulonimbus cloud: The parent cloud of a thunderstorm; a tall,
vertically developed cloud capable of producing heavy rain, high winds, and lightning. Current: The flow of electrical charge from one point to another. Currents: The horizontal and vertical circulation of ocean waters. Cyanobacteria: Oxygen-producing, aquatic bacteria capable of manu-
facturing its own food; resembles algae. Cycles: Occurrence of events that take place on a regular, repeating
basis. Cytology: The branch of biology concerned with the study of cells. Cytoplasm: The semifluid substance inside a cell that surrounds the
nucleus and other membrane-enclosed organelles.
Decanting: The process of separating a suspension by waiting for its
heavier components to settle out and then pouring off the lighter ones. Decibel (dB): A unit of measurement for the amplitude of sound. Deciduous: Plants that lose their leaves during some season of the year,
and then grow them back during another season. Decompose: To break down into two or more simpler substances. Decomposition: The breakdown of complex molecules of dead organ-
isms into simple nutrients that can be reutilized by living organisms. Decomposition reaction: A chemical reaction in which one substance is
broken down into two or more substances. Experiment Central, 2nd edition
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WORDS TO KNOW
Deficiency disease: A disease marked by a lack of an essential nutrient in
the diet. Degrade: Break down. Dehydration: The removal of water from a material. Denaturization: Altering an enzyme so it no longer works. Density: The mass of a substance divided by its volume. Density ball: A ball with the fixed standard of 1.0 gram per milliliter,
which is the exact density of pure water. Deoxyribonucleic acid (DNA): Large, complex molecules found in the
nuclei of cells that carry genetic information for an organism’s development; double helix. (Pronounced DEE-ox-see-rye-bo-nooklay-ick acid) Dependent variable: The variable in an experiment whose value depends
on the value of another variable in the experiment. Deposition: Dropping of sediments that occurs when a river loses its
energy of motion. Desert: A biome with a hot-to-cool climate and dry weather. Desertification: Transformation of arid or semiarid productive land into
desert. Dewpoint: The point at which water vapor begins to condense. Dicot: Plants with a pair of embryonic seeds that appear at germination. Diffraction: The bending of light or another form of electromagnetic
radiation as it passes through a tiny hole or around a sharp edge. Diffraction grating: A device consisting of a surface into which are
etched very fine, closely spaced grooves that cause different wavelengths of light to reflect or refract (bend) by different amounts. Diffusion: Random movement of molecules that leads to a net move-
ment of molecules from a region of high concentration to a region of low concentration. Disinfection: Using chemicals to kill harmful organisms. Dissolved oxygen: Oxygen molecules that have dissolved in water. Distillation: The process of separating liquids from solids or from other
liquids with different boiling points by a method of evaporation and condensation, so that each component in a mixture can be collected separately in its pure form. l
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DNA fingerprinting: A technique that uses DNA fragments to identify
the unique DNA sequences of an individual. DNA replication: The process by which one DNA strand unwinds and
duplicates all its information, creating two new DNA strands that are identical to each other and to the original strand. DNA (deoxyribonucleic acid): Large, complex molecules found in nuclei
of cells that carry genetic information for an organism’s development. Domain: Small regions in iron that possess their own magnetic charges. Dominant gene: A gene that passes on a certain characteristic, even when
there is only one copy (allele) of the gene. Doppler effect: The change in wavelength and frequency (number of
vibrations per second) of either light or sound as the source is moving either towards or away from the observer. Dormant: A state of inactivity in an organism. Dorsal fin: The fin located on the back of a fish, used for balance. Double helix: The shape taken by DNA (deoxyribonucleic acid) mole-
cules in a nucleus. Drought: A prolonged period of dry weather that damages crops or
prevents their growth. Dry cell: A source of electricity that uses a non-liquid electrolyte. Dust tail: One of two types of tails a comet may have, it is composed
mainly of dust and it points away from the Sun. Dye: A colored substance that is used to give color to a material. Dynamic equilibrium: A situation in which substances are moving into
and out of cell walls at an equal rate.
Earthquake: An unpredictable event in which masses of rock suddenly
shift or rupture below Earth’s surface, releasing enormous amounts of energy and sending out shockwaves that sometimes cause the ground to shake dramatically. Eclipse: A phenomenon in which the light from a celestial body is
temporarily cut off by the presence of another. Ecologists: Scientists who study the interrelationship of organisms and
their environments. Experiment Central, 2nd edition
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WORDS TO KNOW
Ecosystem: An ecological community, including plants, animals and
microorganisms, considered together with their environment. Efficiency: The amount of power output divided by the amount of
power input. It is a measure of how well a device converts one form of power into another. Effort: The force applied to move a load using a simple machine. Elastomers: Any of various polymers having rubbery properties. Electric charge repulsion: Repulsion of particles caused by a layer of
negative ions surrounding each particle. The repulsion prevents coagulation and promotes the even dispersion of such particles through a mixtures. Electrical energy: Kinetic energy resulting from the motion of electrons
within any object that conducts electricity. Electricity: A form of energy caused by the presence of electrical charges
in matter. Electrode: A material that will conduct an electrical current, usually a
metal; used to carry electrons into or out of a battery. Electrolyte: Any substance that, when dissolved in water, conducts an
electric current. Electromagnetic spectrum: The complete array of electromagnetic radi-
ation, including radio waves (at the longest-wavelength end), microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays (at the shortest-wavelength end). Electromagnetism: A form of magnetic energy produced by the flow of
an electric current through a metal core. Also, the study of electric and magnetic fields and their interaction with charges and currents. Electron: A subatomic particle with a single negative electrical change
that orbits the nucleus of an atom. Electroplating: The process of coating one metal with another metal by
means of an electrical current. Electroscope: A device that determines whether an object is electrically
charged. Element: A pure substance composed of just one type of atom that
cannot be broken down into anything simpler by ordinary chemical means. Elevation: Height above sea level. lii
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Elliptical: An orbital path which is egg-shaped or resembles an elongated
circle. Elongation: The percentage increase in length that occurs before a
material breaks under tension. Embryo: The seed of a plant, which through germination can develop
into a new plant. Embryonic: The earliest stages of development. Endothermic reaction: A chemical reaction that absorbs heat or light
energy, such as photosynthesis, the production of food by plant cells. Energy: The ability to cause an action or to perform work. Entomology: The study of insects. Environmental variables: Nonliving factors such as air temperature,
water, pollution, and pH that can affect processes that occur in nature and in an experiment. Enzyme: Any of numerous complex proteins produced by living cells
that act as catalysts, speeding up the rate of chemical reactions in living organisms. Enzymology: The science of studying enzymes. Ephemerals: Plants that lie dormant in dry soil for years until major
rainstorms occur. Epicenter: The location where the seismic waves of an earthquake first
appear on the surface, usually almost directly above the focus. Equilibrium: A balancing or canceling out of opposing forces, so that an
object will remain at rest. Erosion: The process by which topsoil is carried away by water, wind, or
ice action. Ethnobotany: The study of how cultures use plants in everyday life. Eukaryotic: Multicellular organism whose cells contain distinct nuclei,
which contain the genetic material. (Pronounced yoo-KAR-ee-ah-tic) Euphotic zone: The upper part of the ocean where sunlight penetrates,
supporting plant life, such as phytoplankton. Eutrophication: The process by which high nutrient concentrations in a
body of water eventually cause the natural wildlife to die. Evaporation: The process by which liquid changes into a gas. Experiment Central, 2nd edition
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Exoskeleton: A hard outer covering on animals, which provide protec-
tion and structure. Exothermic reaction: A chemical reaction that releases heat or light
energy, such as the burning of fuel. Experiment: A controlled observation. Extremophiles: Bacteria that thrive in environments too harsh to sup-
port most life forms.
False memory: A memory of an event that never happened or an altered
memory from what happened. Family: A group of elements in the same column of the periodic table or
in closely related columns of the table. A family of chemical compounds share similar structures and properties. Fat: A type of lipid, or chemical compound used as a source of energy, to
provide insulation and to protect organs in an animal body. Fat-soluble vitamins: Vitamins such as A, D, E, and K that can be
dissolved in the fat of plants and animals. Fault: A crack running through rock as the result of tectonic forces. Fault blocks: Pieces of rock from Earth’s crust that press against each
other and cause earthquakes when they suddenly shift or rupture from the pressure. Fault mountain: A mountain that is formed when Earth’s plates come
together and cause rocks to break and move upwards. Fermentation: A chemical reaction in which enzymes break down com-
plex organic compounds (for example, carbohydrates and sugars) into simpler ones (for example, ethyl alcohol). Filament: In a flower, stalk of the stamen that bears the anther. Filtration: The mechanical separation of a liquid from the undissolved
particles floating in it. Fireball: Meteors that create an intense, bright light and, sometimes, an
explosion. First law of motion (Newton’s): An object at rest or moving in a certain
direction and speed will remain at rest or moving in the same motion and speed unless acted upon by a force. liv
Experiment Central, 2nd edition
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Fish: Animals that live in water who have gills, fins, and are cold
blooded. Fixative: A substance that mixes with the dye to hold it to the material. Flagella: Whiplike structures used by some organisms for movement.
(Singular: flagellum.) Flammability: The ability of a material to ignite and burn. Flower: The reproductive part of a flowering plant. Fluid: A substance that flows; a liquid or gas. Fluorescence: The emission of visible light from an object when the
object is bombarded with electromagnetic radiation, such as ultraviolet rays. The emission of visible light stops after the radiation source has been removed. Focal length: The distance from the lens to the point where the light rays
come together to a focus. Focal point: The point at which rays of light converge or from which
they diverge. Focus: The point within Earth where a sudden shift or rupture occurs. Fold mountain: A mountain that is formed when Earth’s plates come
together and push rocks up into folds. Food webs: Interconnected sets of food chains, which are a sequence of
organisms directly dependent on one another for food. Force: A physical interaction (pushing or pulling) tending to change the
state of motion (velocity) of an object. Forensic science: The application of science to the law and justice
system. Fortified: The addition of nutrients, such as vitamins or minerals, to
food. Fossil: The remains, trace, or impressions of a living organism that
inhabited Earth more than ten thousand years ago. Fossil fuel: A fuel such as coal, oil, or natural gas that is formed over
millions of years from the remains of plants and animals. Fossil record: The documentation of fossils placed in relationship to one
another; a key source to understand the evolution of life on Earth. Fracture: A mineral’s tendency to break into curved, rough, or jagged
surfaces. Experiment Central, 2nd edition
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WORDS TO KNOW
Frequency: The rate at which vibrations take place (number of times per
second the motion is repeated), given in cycles per second or in hertz (Hz). Also, the number of waves that pass a given point in a given period of time. Friction: A force that resists the motion of an object, resulting when two
objects rub against one another. Front: The area between air masses of different temperatures or densities. Fuel cell: A device that uses hydrogen as the fuel to produce electricity
and heat with water as a byproduct. Fulcrum: The point at which a lever arm pivots. Fungi: Kingdom of various single-celled or multicellular organisms,
including mushrooms, molds, yeasts, and mildews, that do not contain chlorophyll. Funnel cloud: A fully developed tornado vortex before it has touched the
ground. Fusion: Combining of nuclei of two or more lighter elements into one
nucleus of a heavier element; the process stars use to produce energy to produce light and support themselves against their own gravity.
Galaxy: A large collection of stars and clusters of stars containing any-
where from a few million to a few trillion stars. Gastropod: The largest group of mollusks; characterized by a single shell
that is often coiled in a spiral. Snails are gastropods. Gene: A segment of a DNA (deoxyribonucleic acid) molecule contained
in the nucleus of a cell that acts as a kind of code for the production of some specific protein. Genes carry instructions for the formation, functioning, and transmission of specific traits from one generation to another. Generator: A device that converts mechanical energy into electrical
energy, Genetic engineering: A technique that modifies the DNA of living cells
in order to make them change its characteristics. Also called genetic modification. lvi
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Genetic material: Material that transfers characteristics from a parent to
its offspring. Geology: The study of the origin, history and structure of Earth. Geothermal energy: Energy from deep within Earth. Geotropism: The tendency of roots to bend toward Earth. Germ theory of disease: The theory that disease is caused by micro-
organisms or germs, and not by spontaneous generation. Germination: First stage in development of a plant seed. Gibbous moon: A phase of the Moon when more than half of its surface
is lighted. Gills: Special organ located behind the head of a fish that takes in oxygen
from the water. Glacier: A large mass of ice formed from snow that has packed together
and which moves slowly down a slope under its own weight. Global warming: Warming of Earth’s atmosphere as a result of an
increase in the concentration of gases that store heat, such as carbon dioxide. Glucose: A simple sugar broken down in cells to produce energy. Gnomon: The perpendicular piece of the sundial that casts the shadow. Golgi body: An organelles that sorts, modifies, and packages molecules. Gravity: Force of attraction between objects, the strength of which
depends on the mass of each object and the distance between them. Greenhouse effect: The warming of Earth’s atmosphere due to water
vapor, carbon dioxide, and other gases in the atmosphere that trap heat radiated from Earth’s surface. Greenhouse gases: Gases that absorb infrared radiation and warm the
air before the heat energy escapes into space. Greenwich Mean Time (GMT): The time at an imaginary line that runs
north and south through Greenwich, England, used as the standard for time throughout the world. Groundwater: Water that soaks into the ground and is stored in the
small spaces between the rocks and soil. Group: A vertical column of the periodic table that contains elements
possessing similar chemical characteristics. Experiment Central, 2nd edition
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WORDS TO KNOW
Hardwood: Wood from angiosperm, mostly deciduous, trees. Heartwood: The inner layers of wood that provide structure and have no
living cells. Heat: A form of energy produced by the motion of molecules that make
up a substance. Heat capacity: The measure of how well a substance stores heat. Heat energy: The energy produced when two substances that have
different temperatures are combined. Heliotropism: The tendency of plants to turn towards the Sun through-
out the day. Herbivore: A plant-eating organism. Hertz (Hz): The unit of measurement of frequency; a measure of the
number of waves that pass a given point per second of time. Heterogeneous: Different throughout. Heterotrophs: Organisms that cannot make their own food and that
must, therefore, obtain their food from other organisms. High air pressure: An area where the air is cooler and more dense, and
the air pressure is higher than normal. Hippocampus: A part of the brain associated with learning and memory. Homogenous: The same throughout. Hormones: Chemicals produced in the cells of plants and animals that
control bodily functions. Hue: The color or shade. Humidity: The amount of water vapor (moisture) contained in the air. Humus: Fragrant, spongy, nutrient-rich decayed plant or animal
matter. Hydrologic cycle: Continual movement of water from the atmosphere
to Earth’s surface through precipitation and back to the atmosphere through evaporation and transpiration. Hydrologists: Scientists who study water and its cycle. Hydrology: The study of water and its cycle. lviii
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Hydrometer: An instrument that determines the specific gravity of a
liquid. Hydrophilic: A substance that is attracted to and readily mixes with
water. Hydrophobic: A substance that is repelled by and does not mix with
water. Hydropower: Energy produced from capturing moving water. Hydrotropism: The tendency of roots to grow toward a water source. Hypertonic solution: A solution with a higher concentration of materials
than a cell immersed in the solution. Hypha: Slender, cottony filaments making up the body of multicellular
fungi. (Plural: hyphae) Hypothesis: An idea in the form of a statement that can be tested by
observation and/or experiment. Hypotonic solution: A solution with a lower concentration of materials
than a cell immersed in the solution.
Igneous rock: Rock formed from the cooling and hardening of magma. Immiscible: Incapable of being mixed. Imperfect flower: Flowers that have only the male reproductive organ
(stamen) or the female reproductive organs (pistil). Impermeable: Not allowing substances to pass through. Impurities: Chemicals or other pollutants in water. Inclined plane: A simple machine with no moving parts; a slanted surface. Incomplete metamorphosis: Metamorphosis in which a nymph form
gradually becomes an adult through molting. Independent variable: The variable in an experiment that determines
the final result of the experiment. Indicator: Pigments that change color when they come into contact with
acidic or basic solutions. Inertia: The tendency of an object to continue in its state of motion. Infrared radiation: Electromagnetic radiation of a wavelength shorter than
radio waves but longer than visible light that takes the form of heat. Experiment Central, 2nd edition
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WORDS TO KNOW
Inner core: Very dense, solid center of Earth. Inorganic: Not containing carbon; not derived from a living organism. Insect: A six-legged invertebrate whose body has three segments. Insoluble: A substance that cannot be dissolved in some other substance. Insulated wire: Electrical wire coated with a non-conducting material
such as plastic. Insulation: A material that is a poor conductor of heat or electricity. Insulator: A material through which little or no electrical current or heat
energy will flow. Interference fringes: Bands of color that fan out around an object. Internal skeleton: An animal that has a backbone. Invertebrate: An animal that lacks a backbone or internal skeleton. Ion: An atom or groups of atoms that carry an electrical charge—either
positive or negative—as a result of losing or gaining one or more electrons. Ion tail: One of two types of tails a comet may have, it is composed
mainly of charged particles and it points away from the Sun. Ionic conduction: The flow of an electrical current by the movement of
charged particles, or ions. Isobars: Continuous lines that connect areas with the same air pressure. Isotonic solutions: Two solutions that have the same concentration of
solute particles and therefore the same osmotic pressure.
Jawless fish: The smallest group of fishes, who lacks a jaw.
Kinetic energy: The energy of an object or system due to its motion. Kingdom: One of the five classifications in the widely accepted classi-
fication system that designates all living organisms into animals, plants, fungi, protists, and monerans. lx
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Labyrinth: A lung-like organ located above the gills that allows the fish to
breathe in oxygen from the air. Lactobacilli: A strain of bacteria. Landfill: A method of disposing of waste materials by placing them in a
depression in the ground or piling them in a mound. In a sanitary landfill, the daily deposits of waste materials are covered with a layer of soil. Larva: Immature form (wormlike in insects; fishlike in amphibians) of
an organism capable of surviving on its own. A larva does not resemble the parent and must go through metamorphosis, or change, to reach its adult stage. Lava: Molten rock that occurs at the surface of Earth, usually through
volcanic eruptions. Lava cave: A cave formed from the flow of lava streaming over solid
matter. Leach: The movement of dissolved minerals or chemicals with water as it
percolates, or oozes, downward through the soil. Leaching: The movement of dissolved chemicals with water that is
percolating, or oozing, downward through the soil. Leavening agent: A substance used to make foods like dough and batter
to rise. Leeward: The side away from the wind or flow direction. Lens: A piece of transparent material with two curved surfaces that bend
rays of light passing through it. Lichen: An organism composed of a fungus and a photosynthetic organ-
ism in a symbiotic relationship. Lift: Upward force on the wings of an aircraft created by differences in air
pressure on top of and underneath the wings. Ligaments: Tough, fibrous tissue connecting bones. Light: A form of energy that travels in waves. Light-year: Distance light travels in one year in the vacuum of space,
roughly 5.9 trillion miles (9.5 trillion kilometers). Experiment Central, 2nd edition
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WORDS TO KNOW
The Local Group: A cluster of thirty galaxies, including the Milky Way,
pulled together by gravity. Long-term memory: The last category of memory in which memories
are stored away and can last for years. Low air pressure: An area where the air is warmer and less dense, and the
air pressure is lower than normal. Luminescent: Producing light through a chemical process. Luminol: A compound used to detect blood. Lunar eclipse: An eclipse that occurs when Earth passes between the Sun
and the Moon, casting a shadow on the Moon. Luster: A glow of reflected light; a sheen.
Machine: Any device that makes work easier by providing a mechanical
advantage. Macrominerals: Minerals needed in relatively large quantities. Macroorganisms: Visible organisms that aid in breaking down organic
matter. Magma: Molten rock deep within Earth that consists of liquids, gases,
and particles of rocks and crystals. Magma underlies areas of volcanic activity and at Earth’s surface is called lava. Magma chambers: Pools of bubbling liquid rock that are the source of
energy causing volcanoes to be active. Magma surge: A swell or rising wave of magma caused by the movement
and friction of tectonic plates, which heats and melts rock, adding to the magma and its force. Magnet: A material that attracts other like materials, especially metals. Magnetic circuit: A series of magnetic domains aligned in the same
direction. Magnetic field: The space around an electric current or a magnet in
which a magnetic force can be observed. Magnetism: A fundamental force in nature caused by the motion of
electrons in an atom. Maillard reaction: A reaction caused by heat and sugars and resulting in
foods browning and flavors. lxii
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WORDS TO KNOW
Mammals: Animals that have a backbone, are warm blooded, have
mammary glands to feed their young and have or are born with hair. Mantle: Thick dense layer of rock that underlies Earth’s crust and over-
lies the core; also soft tissue that is located between the shell and an animal’s inner organs. The mantle produces the calcium carbonate substance that create the shell of the animal. Manure: The waste matter of animals. Mass: Measure of the total amount of matter in an object. Also, an
object’s quantity of matter as shown by its gravitational pull on another object. Matter: Anything that has mass and takes up space. Meandering river: A lowland river that twists and turns along its route to
the sea. Medium: A material that contains the nutrients required for a particular
microorganism to grow. Melting point: The temperature at which a substance changes from a
solid to a liquid. Memory: The process of retaining and recalling past events and
experiences. Meniscus: The curved surface of a column of liquid. Metabolism: The process by which living organisms convert food into
energy and waste products. Metamorphic rock: Rock formed by transformation of pre-existing rock
through changes in temperature and pressure. Metamorphosis: Transformation of an immature animal into an adult. Meteor: An object from space that becomes glowing hot when it passes
into Earth’s atmosphere; also called shooting star. Meteor shower: A group of meteors that occurs when Earth’s orbit
intersects the orbit of a meteor stream. Meteorites: A meteor that is large enough to survive its passage through
the atmosphere and hit the ground. Meteoroid: A piece of debris that is traveling in space. Meteorologist: Scientist who studies the weather and the atmosphere. Microbiology: Branch of biology dealing with microscopic forms of life. Microclimate: A unique climate that exists only in a small, localized area. Experiment Central, 2nd edition
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Microorganisms: Living organisms so small that they can be seen only
with the aid of a microscope. Micropyle: Seed opening that enables water to enter easily. Microvilli: The extension of each taste cell that pokes through the taste
pore and first senses the chemicals. Milky Way: The galaxy in which our solar system is located. Mimicry: A characteristic in which an animal is protected against pred-
ators by resembling another, more distasteful animal. Mineral: An inorganic substance found in nature with a definite chem-
ical composition and structure. As a nutrient, it helps build bones and soft tissues and regulates body functions. Mixture: A combination of two or more substances that are not chemi-
cally combined with each other and that can exist in any proportion. Mnemonics: Techniques to improve memory. Mold: In paleontology, the fossil formed when acidic water dissolves a
shell or bone around which sand or mud has already hardened. Molecule: The smallest particle of a substance that retains all the proper-
ties of the substance and is composed of one or more atoms. Mollusk: An invertebrate animal usually enclosed in a shell, the largest
group of shelled animals. Molting: A process by which an animal sheds its skin or shell. Monocot: Plants with a single embryonic leaf at germination. Monomer: A small molecule that can be combined with itself many
times over to make a large molecule, the polymer. Moraine: Mass of boulders, stones, and other rock debris carried along
and deposited by a glacier. Mordant: A substance that fixes the dye to the material. Mountain: A landform that stands well above its surroundings; higher
than a hill. Mucus: A thick, slippery substance that serves as a protective lubricant
coating in passages of the body that communicate with the air. Multicellular: Living things with many cells joined together. Muscle fibers: Stacks of long, thin cells that make up muscle; there are
three types of muscle fiber: skeletal, cardiac, and smooth. Mycelium: In fungi, the mass of threadlike, branching hyphae. lxiv
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Nanobots: A nanoscale robot. Nanometer: A unit of length; this measurement is equal to one-billionth
of a meter. Nanotechnology: Technology that involves working and developing
technologies on the nanometer (atomic and molecular) scale. Nansen bottles: Self-closing containers with thermometers that draw in
water at different depths. Nebula: Bright or dark cloud, often composed of gases and dust, hover-
ing in the space between the stars. Nectar: A sweet liquid, found inside a flower, that attracts pollinators. Neutralization: A chemical reaction in which the mixing of an acidic
solution with a basic (alkaline) solution results in a solution that has the properties of neither an acid nor a base. Neutron: A subatomic particle with a mass of about one atomic mass
unit and no electrical charge that is found in the nucleus of an atom. Newtonian fluid: A fluid that follows certain properties, such as the
viscosity remains constant at a given temperature. Niche: The specific location and place in the food chain that an organ-
ism occupies in its environment. Noble gases: Also known as inert or rare gases; the elements argon,
helium, krypton, neon, radon, and xenon, which are nonreactive gases and form few compounds with other elements. Non-Newtonian fluid: A fluid whose property do not follow Newtonian
properties, such as viscosity can vary based on the stress. Nonpoint source: An unidentified source of pollution, which may
actually be a number of sources. Nucleation: The process by which crystals start growing. Nucleotide: The basic unit of a nucleic acid. It consists of a simple sugar,
a phosphate group, and a nitrogen-containing base. (Pronounced noo-KLEE-uh-tide.) Nucleus: The central part of the cell that contains the DNA; the central
core of an atom, consisting of protons and (usually) neutrons. Experiment Central, 2nd edition
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Nutrient: A substance needed by an organism in order for it to survive,
grow, and develop. Nutrition: The study of the food nutrients an organism needs in order to
maintain well-being. Nymph: An immature form in the life cycle of insects that go through an
incomplete metamorphosis.
Objective lens: In a refracting telescope, the lens farthest away from the
eye that collects the light. Oceanographer: A person who studies the chemistry of the oceans, as
well as their currents, marine life, and the ocean floor. Oceanography: The study of the chemistry of the oceans, as well as their
currents, marine life, and the ocean bed. Olfactory: Relating to the sense of smell. Olfactory bulb: The part of the brain that processes olfactory (smell)
information. Olfactory epithelium: The patch of mucous membrane at the top of the
nasal cavity that contains the olfactory (smell) nerve cells. Olfactory receptor cells: Nerve cells in the olfactory epithelium that
detect odors and transmit the information to the brain. Oort cloud: Region of space beyond our solar system that theoretically
contains about one trillion inactive comets. Optics: The study of the nature of light and its properties. Orbit: The path followed by a body (such as a planet) in its travel around
another body (such as the Sun). Organelle: A membrane-enclosed structure that performs a specific
function within a cell. Organic: Containing carbon; also referring to materials that are derived
from living organisms. Oscillation: A repeated back-and-forth movement. Osmosis: The movement of fluids and substances dissolved in liquids
across a semipermeable membrane from an area of its greater concentration to an area of its lesser concentration until all substances involved reach a balance. lxvi
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Outer core: A liquid core that surrounds Earth’s solid inner core; made
mostly of iron. Ovary: In a plant, the base part of the pistil that bears ovules and
develops into a fruit. Ovule: Structure within the ovary that develops into a seed after
fertilization. Oxidation: A chemical reaction in which oxygen reacts with some other
substance and in which ions, atoms, or molecules lose electrons. Oxidation state: The sum of an atom’s positive and negative charges. Oxidation-reduction reaction: A chemical reaction in which one sub-
stance loses one or more electrons and the other substance gains one or more electrons. Oxidizing agent: A chemical substance that gives up oxygen or takes on
electrons from another substance.
Paleontologist: Scientist who studies the life of past geological periods as
known from fossil remains. Papain: An enzyme obtained from the fruit of the papaya used as a meat
tenderizer, as a drug to clean cuts and wounds, and as a digestive aid for stomach disorders. Papillae: The raised bumps on the tongue that contain the taste buds. Parent material: The underlying rock from which soil forms. Partial solar/lunar eclipse: An eclipse in which our view of the Sun/
Moon is only partially blocked. Particulate matter: Solid matter in the form of tiny particles in the
atmosphere. (Pronounced par-TIK-you-let.) Passive solar energy system: A solar energy system in which the heat of
the Sun is captured, used, and stored by means of the design of a building and the materials from which it is made. Pasteurization: The process of slow heating that kills bacteria and other
microorganisms. Peaks: The points at which the energy in a wave is maximum. Pectin: A natural carbohydrate found in fruits and vegetables. Pectoral fin: Pair of fins located on the side of a fish, used for steering. Experiment Central, 2nd edition
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Pedigree: A diagram that illustrates the pattern of inheritance of a
genetic trait in a family. Pelvic fin: Pair of fins located toward the belly of a fish, used for stability. Pendulum: A free-swinging weight, usually consisting of a heavy object
attached to the end of a long rod or string, suspended from a fixed point. Penicillin: A mold from the fungi group of microorganisms; used as an
antibiotic. Pepsin: Digestive enzyme that breaks down protein. Percolate: To pass through a permeable substance. Perfect flower: Flowers that have both male and female reproductive
organs. Period: A horizontal row in the periodic table. Periodic table: A chart organizing elements by atomic number and
chemical properties into groups and periods. Permeable: Having pores that permit a liquid or a gas to pass through. Permineralization: A form of preservation in which mineral matter has
filled in the inner and outer spaces of the cell. Pest: Any living thing that is unwanted by humans or causes injury and
disease to crops and other growth. Pesticide: Substance used to reduce the abundance of pests. Petal: Leafy structure of a flower just inside the sepals; they are often
brightly colored and have many different shapes. Petrifaction: Process of turning organic material into rock by the
replacement of that material with minerals. pH: A measure of the acidity or alkalinity of a solution referring to the
concentration of hydrogen ions present in a liter of a given fluid. The pH scale ranges from 0 (greatest concentration of hydrogen ions and therefore most acidic) to 14 (least concentration of hydrogen ions and therefore most alkaline), with 7 representing a neutral solution, such as pure water. Pharmacology: The science dealing with the properties, reactions, and
therapeutic values of drugs. Phases: Changes in the portion of the Moon’s surface that is illuminated
by light from the Sun as the Moon revolves around Earth. lxviii
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WORDS TO KNOW
Phloem: The plant tissue that carries dissolved nutrients through the
plant. Phosphorescence: The emission of visible light from an object when the
object is bombarded with electromagnetic radiation, such as ultraviolet rays. The object stores part of the radiation energy and the emission of visible light continues for a period ranging from a fraction of a second to several days after the radiation source has been removed. Photoelectric effect: The phenomenon in which light falling upon
certain metals stimulates the emission of electrons and changes light into electricity. Photosynthesis: Chemical process by which plants containing chloro-
phyll use sunlight to manufacture their own food by converting carbon dioxide and water to carbohydrates, releasing oxygen as a by-product. Phototropism: The tendency of a plant to grow toward a source of light. Photovoltaic cells: A device made of silicon that converts sunlight into
electricity. Physical change: A change in which the substance keeps its molecular
identity, such as a piece of chalk that has been ground up. Physical property: A characteristic that you can detect with your senses,
such as color and shape. Physiologist: A scientist who studies the functions and processes of
living organisms. Phytoplankton: Microscopic aquatic plants that live suspended in the
water. Pigment: A substance that displays a color because of the wavelengths of
light that it reflects. Pili: Short projections that assist bacteria in attaching to tissues. Pistil: Female reproductive organ of flowers that is composed of the
stigma, style, and ovary. Pitch: A property of a sound, determined by its frequency; the highness
or lowness of a sound. Plant extract: The juice or liquid essence obtained from a plant by
squeezing or mashing it. Experiment Central, 2nd edition
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WORDS TO KNOW
Plasmolysis: Occurs in walled cells in which cytoplasm, the semifluid
substance inside a cell, shrivels and the membrane pulls away from the cell wall when the vacuole loses water. Plates: Large regions of Earth’s surface, composed of the crust and
uppermost mantle, which move about, forming many of Earth’s major geologic surface features. Platform: The horizontal surface of a bridge on which traffic travels. Pnematocysts: Stinging cells. Point source: An identified source of pollution. Pollen: Dust-like grains or particles produced by a plant that contain
male sex cells. Pollinate: The transfer of pollen from the male reproductive organs to
the female reproductive organs of plants. Pollination: Transfer of pollen from the male reproductive organs to the
female reproductive organs of plants. Pollinator: Any animal, such as an insect or bird, that transfers the pollen
from one flower to another. Pollution: The contamination of the natural environment, usually
through human activity. Polymer: Chemical compound formed of simple molecules (known as
monomers) linked with themselves many times over. Polymerization: The bonding of two or more monomers to form a
polymer. Polyvinyl acetate: A type of polymer that is the main ingredient of white
glues. Pore: An opening or space. Potential energy: The energy of an object or system due to its position. Precipitation: Any form of water that falls to Earth, such as rain, snow,
or sleet. Predator: An animal that hunts another animal for food. Preservative: An additive used to keep food from spoiling. Primary colors: The three colors red, green, and blue; when combined
evenly they produce white light and by combining varying amounts can produce the range of colors. lxx
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Prism: A piece of transparent material with a triangular cross-section.
When light passes through it, it causes different colors to bend different amounts, thus separating them into a rainbow of colors. Probe: The terminal of a voltmeter, used to connect the voltmeter to a
circuit. Producer: An organism that can manufacture its own food from nonliving
materials and an external energy source, usually by photosynthesis. Product: A compound that is formed as a result of a chemical reaction. Prokaryote: A cell without a true nucleus, such as a bacterium. Prominences: Masses of glowing gas, mainly hydrogen, that rise from
the Sun’s surface like flames. Propeller: Radiating blades mounted on a rapidly rotating shaft, which
moves aircraft forward. Protein: A complex chemical compound consisting of many amino acids
attached to each other that are essential to the structure and functioning of all living cells. Protists: Members of the kingdom Protista, primarily single-celled
organisms that are not plants or animals. Proton: A subatomic particle with a single positive charge that is found
in the nucleus of an atom. Protozoa: Single-celled animal-like microscopic organisms that live by
taking in food rather than making it by photosynthesis. They must live in the presence of water. Pulley: A simple machine made of a cord wrapped around a wheel. Pupa: The insect stage of development between the larva and adult in
insects that go through complete metamorphosis.
Radiation: Energy transmitted in the form of electromagnetic waves or
subatomic particles. Radicule: Seed’s root system. Radio wave: Longest form of electromagnetic radiation, measuring up
to 6 miles (9.6 kilometers) from peak to peak. Radioisotope dating: A technique used to date fossils, based on the
decay rate of known radioactive elements. Experiment Central, 2nd edition
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WORDS TO KNOW
Radiosonde balloons: Instruments for collecting data in the atmosphere
and then transmitting that data back to Earth by means of radio waves. Radon: A radioactive gas located in the ground; invisible and odorless,
radon is a health hazard when it accumulates to high levels inside homes and other structures where it is breathed. Rain shadow: Region on the side of the mountain that receives less
rainfall than the area windward of the mountain. Rancidity: Having the condition when food has a disagreeable odor or
taste from decomposing oils or fats. Reactant: A compound present at the beginning of a chemical reaction. Reaction: Response to an action prompted by stimulus. Recessive gene: A gene that produces a certain characteristic only two
both copies (alleles) of the gene are present. Recycling: The use of waste materials, also known as secondary materials
or recyclables, to produce new products. Redshift: The lengthening of the frequency of light waves toward the red
end of the visible light spectrum as they travel away from an observer; most commonly used to describe movement of stars away from Earth. Reduction: A process in which a chemical substance gives off oxygen or
takes on electrons. Reed: A tall woody perennial grass that has a hollow stem. Reflection: The bouncing of light rays in a regular pattern off the surface
of an object. Reflector telescope: A telescope that directs light from an opening at
one end to a concave mirror at the far end, which reflects the light back to a smaller mirror that directs it to an eyepiece on the side of the tube. Refraction: The bending of light rays as they pass at an angle from
one transparent or clear medium into a second one of different density. Refractor telescope: A telescope that directs light through a glass lens,
which bends the light waves and brings them to a focus at an eyepiece that acts as a magnifying glass. lxxii
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WORDS TO KNOW
Relative age: The age of an object expressed in relation to another like
object, such as earlier or later. Relative density: The density of one material compared to another. Rennin: Enzyme used in making cheese. Resistance: A partial or complete limiting of the flow of electrical
current through a material. The common unit of measure is the ohm. Respiration: The physical process that supplies oxygen to living cells and
the chemical reactions that take place inside the cells. Resultant: A force that results from the combined action of two other
forces. Retina: The light-sensitive part of the eyeball that receives images and
transmits visual impulses through the optic nerve to the brain. Ribosome: A protein composed of two subunits that functions in
protein synthesis (creation). Rigidity: The amount an object will deflect when supporting a weight.
The less it deflects for a given amount of weight, the greater its rigidity. River: A main course of water into which many other smaller bodies of
water flow. Rock: Naturally occurring solid mixture of minerals. Rods: Cells in the retina that are sensitive to degrees of light and
movement. Root hairs: Fine, hair-like extensions from the plant’s root. Rotate: To turn around on an axis or center. Runoff: Water that does not soak into the ground or evaporate, but flows
across the surface of the ground.
Salinity: The amount of salts dissolved in water. Saliva: Watery mixture with chemicals that lubricates chewed food. Sand: Granular portion of soil composed of the largest soil particles. Sapwood: The outer wood in a tree, which is usually a lighter color. Saturated: In referring to solutions, a solution that contains the max-
imum amount of solute for a given amount of solvent at a given temperature. Experiment Central, 2nd edition
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WORDS TO KNOW
Saturation: The intensity of a color. Scanning tunneling microscope: A microscope that can show images of
surfaces at the atomic level by scanning a probe over a surface. Scientific method: Collecting evidence and arriving at a conclusion
under carefully controlled conditions. Screw: A simple machine; an inclined plane wrapped around a cylinder. Scurvy: A disease caused by a deficiency of vitamin C, which causes a
weakening of connective tissue in bone and muscle. Sea cave: A cave in sea cliffs, formed most commonly by waves eroding
the rock. Second law of motion (Newton’s): The force exerted on an object is
proportional to the mass of the object times the acceleration produced by the force. Sediment: Sand, silt, clay, rock, gravel, mud, or other matter that has
been transported by flowing water. Sedimentary rock: Rock formed from compressed and solidified layers
of organic or inorganic matter. Sedimentation: A process during which gravity pulls particles out of a
liquid. Seed crystal: Small form of a crystalline structure that has all the facets of
a complete new crystal contained in it. Seedling: A small plant just starting to grow into its mature form. Seismic belt: Boundaries where Earth’s plates meet. Seismic waves: Vibrations in rock and soil that transfer the force of an
earthquake from the focus into the surrounding area. Seismograph: A device that detects and records vibrations of the ground. Seismology: The study and measurement of earthquakes. Seismometer: A seismograph that measures the movement of the
ground. Self-pollination: The process in which pollen from one part of a plant
fertilizes ovules on another part of the same plant. Semipermeable membrane: A thin barrier between two solutions that
permits only certain components of the solutions, usually the solvent, to pass through. Sensory memory: Memory that the brain retains for a few seconds. lxxiv
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WORDS TO KNOW
Sepal: The outermost part of a flower; typically leaflike and green. Sexual reproduction: A reproductive process that involves the union of
two individuals in the exchange of genetic material. Shear stress: An applied force to a give area. Shell: A region of space around the center of the atom in which electrons
are located; also, a hard outer covering that protects an animal living inside. Short-term memory: Also known as working memory, this memory was
transferred here from sensory memory. Sidereal day: The time it takes for a particular star to travel around and
reach the same position in the sky; about four minutes shorter than the average solar day. Silt: Medium-sized soil particles. Simple machine: Any of the basic structures that provide a mechanical
advantage and have no or few moving parts. Smog: A form of air pollution produced when moisture in the air
combines and reacts with the products of fossil fuel combustion. Smog is characterized by hazy skies and a tendency to cause respiratory problems among humans. Softwood: Wood from coniferous trees, which usually remain green all
year. Soil: The upper layer of Earth that contains nutrients for plants and
organisms; a mixture of mineral matter, organic matter, air, and water. Soil horizon: An identifiable soil layer due to color, structure, and/or
texture. Soil profile: Combined soil horizons or layers. Solar collector: A device that absorbs sunlight and collects solar heat. Solar day: Called a day, the time between each arrival of the Sun at its
highest point. Solar eclipse: An eclipse that occurs when the Moon passes between
Earth and the Sun, casting a shadow on Earth. Solar energy: Any form of electromagnetic radiation that is emitted by
the Sun. Solubility: The tendency of a substance to dissolve in some other
substance. Experiment Central, 2nd edition
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WORDS TO KNOW
Soluble: A substance that can be dissolved in some other substance. Solute: The substance that is dissolved to make a solution and exists
in the least amount in a solution, for example sugar in sugar water. Solution: A mixture of two or more substances that appears to be uni-
form throughout except on a molecular level. Solvent: The major component of a solution or the liquid in which
some other component is dissolved, for example water in sugar water. Specific gravity: The ratio of the density of a substance to the density of
pure water. Specific heat capacity: The energy required to raise the temperature of
1 kilogram of the substance by 1 degree Celsius. Speleologist: One who studies caves. Speleology: Scientific study of caves and their plant and animal life. Spelunkers: Also called cavers, people who explore caves for a hobby. Spiracles: The openings on an insects side where air enters. Spoilage: The condition when food has taken on an undesirable color,
odor, or texture. Spore: A small, usually one-celled, reproductive body that is capable of
growing into a new organism. Stalactite: Cylindrical or icicle-shaped mineral deposit projecting down-
ward from the roof of a cave. (Pronounced sta-LACK-tite.) Stalagmite: Cylindrical or icicle-shaped mineral deposit projecting
upward from the floor of a cave. (Pronounced sta-LAG-mite.) Stamen: Male reproductive organ of flowers that is composed of the
anther and filament. Standard: A base for comparison. Star: A vast clump of hydrogen gas and dust that produces great energy
through fusion reactions at its core. Static electricity: A form of electricity produced by friction in which the
electric charge does not flow in a current but stays in one place. Stigma: Top part of the pistil upon which pollen lands and receives the
male pollen grains during fertilization. Stomata: Pores in the epidermis (surface) of leaves. lxxvi
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WORDS TO KNOW
Storm: An extreme atmospheric disturbance, associated with strong
damaging winds, and often with thunder and lightning. Storm chasers: People who track and seek out storms, often tornadoes. Stratification: Layers according to density; applies to fluids. Streak: The color of the dust left when a mineral is rubbed across a rough
surface. Style: Stalk of the pistil that connects the stigma to the ovary. Subatomic: Smaller than an atom. It usually refers to particles that make
up an atom, such as protons, neutrons, and electrons. Sublime: The process of changing a solid into a vapor without passing
through the liquid phase. Substrate: The substance on which an enzyme operates in a chemical
reaction. Succulent: Plants that live in dry environments and have water storage
tissue. Sundial: A device that uses the position of the Sun to indicate time. Supersaturated: Solution that is more highly concentrated than is nor-
mally possible under given conditions of temperature and pressure. Supertaster: A person who is extremely sensitive to specific tastes due to
a greater number of taste buds. Supplements: A substance intended to enhance the diet. Surface area: The total area of the outside of an object; the area of a body
of water that is exposed to the air. Surface tension: The attractive force of molecules to each other on the
surface of a liquid. Surface water: Water in lakes, rivers, ponds, and streams. Suspension: A temporary mixture of a solid in a gas or liquid from which
the solid will eventually settle out. Swim bladder: Located above the stomach, takes in air when the fish
wants to move upwards and releases air when the fish wants to move downwards. Symbiosis: A pattern in which two or more organisms live in close
connection with each other, often to the benefit of both or all organisms. Experiment Central, 2nd edition
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WORDS TO KNOW
Synthesis reaction: A chemical reaction in which two or more substan-
ces combine to form a new substance. Synthesize: To make something artificially, in a laboratory or chemical
plant, that is generally not found in nature. Synthetic: A substance that is synthesized, or manufactured, in a labo-
ratory; not naturally occurring. Synthetic crystals: Artificial or manmade crystals.
Taiga: A large land biome mostly dominated by coniferous trees. Taste buds: Groups of taste cells located on the papillae that recognize
the different tastes. Taste pore: The opening at the top of the taste bud from which chem-
icals reach the taste cells. Tectonic: Relating to the forces and structures of the outer shell of Earth. Tectonic plates: Huge flat rocks that form Earth’s crust. Telescope: A tube with lenses or mirrors that collect, transmit, and focus
light. Temperate: Mild or moderate weather conditions. Temperature: The measure of the average energy of the molecules in a
substance. Tendon: Tough, fibrous connective tissue that attaches muscle to bone. Tensile strength: The force needed to stretch a material until it breaks. Terminal: A connection in an electric circuit; usually a connection on a
source of electric energy such as a battery. Terracing: A series of horizontal ridges made in a hillside to reduce
erosion. Testa: A tough outer layer that protects the embryo and endosperm of a
seed from damage. Theory of special relativity: Theory put forth by Albert Einstein that
time is not absolute, but it is relative according to the speed of the observer’s frame of reference. Thermal conductivity: A number representing a material’s ability to
conduct heat. lxxviii
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WORDS TO KNOW
Thermal energy: Kinetic energy caused by the movement of molecules
due to temperature. Thermal inversion: A region in which the warmer air lies above the
colder air; can cause smog to worsen. Thermal pollution: The discharge of heated water from industrial proc-
esses that can kill or injure water life. Thiamine: A vitamin of the B complex that is essential to normal
metabolism and nerve function. Thigmotropism: The tendency for a plant to grow toward a surface it
touches. Third law of motion (Newton’s): For every action there is an equal and
opposite reaction. Thorax: The middle segment of an insect body; the legs and wings are
connected to the thorax. Tides: The cyclic rise and fall of seawater. Titration: A procedure in which an acid and a base are slowly mixed to
achieve a neutral substance. Topsoil: The uppermost layers of soil containing an abundant supply of
decomposed organic material to supply plants with nutrients. Tornado: A violently rotating, narrow column of air in contact with the
ground and usually extending from a cumulonimbus cloud. Total solar/lunar eclipse: An eclipse in which our view of the Sun/Moon
is totally blocked. Toxic: Poisonous. Trace element: A chemical element present in minute quantities. Trace minerals: Minerals needed in relatively small quantities. Translucent: Permits the passage of light. Transpiration: Evaporation of water in the form of water vapor from the
stomata on the surfaces of leaves and stems of plants. Troglobite: An animal that lives in a cave and is unable to live outside of
one. Troglophile: An animal that lives the majority of its life cycle in a cave
but is also able to live outside of the cave. Trogloxene: An animal that spends only part of its life cycle in a cave and
returns periodically to the cave. Experiment Central, 2nd edition
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WORDS TO KNOW
Tropism: The growth or movement of a plant toward or away from a
stimulus. Troposphere: The lowest layer of Earth’s atmosphere, ranging to an
altitude of about 9 miles (15 km) above Earth’s surface. Trough: The lowest point of a wave. (Pronounced trawf.) Tsunami: A large wave of water caused by an underwater earthquake. Tuber: An underground, starch-storing stem, such as a potato. Tundra: A treeless, frozen biome with low-lying plants. Turbine: A spinning device used to transform mechanical power from
energy into electrical energy. Turbulence: Air disturbance that affects an aircraft’s flight. Turgor pressure: The force that is exerted on a plant’s cell wall by the
water within the cell. Tyndall effect: The effect achieved when colloidal particles reflect a
beam of light, making it visible when shined through such a mixture.
Ultraviolet: Electromagnetic radiation (energy) of a wavelength just
shorter than the violet (shortest wavelength) end of the visible light spectrum and thus with higher energy than the visible light. Unconfined aquifer: An aquifer under a layer of permeable rock and soil. Unicellular: Living things that have one cell. Protozoans are unicellular,
for example. Unit cell: The basic unit of the crystalline structure. Universal law of gravity: The law of physics that defines the constancy
of the force of gravity between two bodies. Updraft: Warm, moist air that moves away from the ground. Upwelling: The process by which lower-level, nutrient-rich waters rise
upward to the ocean’s surface.
Vacuole: An enclosed, space-filling sac within plant cells containing
mostly water and providing structural support for the cell. lxxx
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WORDS TO KNOW
Van der Waals’ force: An attractive force between two molecules based
on the positive and negative side of the molecule. Variable: Something that can affect the results of an experiment. Vegetative propagation: A form of asexual reproduction in which plants
are produced that are genetically identical to the parent. Velocity: The rate at which the position of an object changes with time,
including both the speed and the direction. Veneer: Thin slices of wood. Viable: The capability of developing or growing under favorable
conditions. Vibration: A regular, back-and-forth motion of molecules in the air. Viscosity: The measure of a fluid’s resistance to flow; its flowability. Visible spectrum: The range of individual wavelengths of radiation
visible to the human eye when white light is broken into its component colors as it passes through a prism or by some other means. Vitamin: A complex organic compound found naturally in plants and
animals that the body needs in small amounts for normal growth and activity. Volatilization: The process by which a liquid changes (volatilizes) to a
gas. Volcano: A conical mountain or dome of lava, ash, and cinders that
forms around a vent leading to molten rock deep within Earth. Voltage: Also called potential difference; a measurement of the amount
of electric energy stored in a mass of electric charges compared to the energy stored in some other mass of charges. The common unit of measure is the volt. Voltmeter: An instrument for measuring the amperage, voltage, or
resistance in an electrical circuit. Volume: The amount of space occupied by a three-dimensional object;
the amplitude or loudness of a sound. Vortex: A rotating column of a fluid such as air or water.
Waste stream: The waste materials generated by the population of an
area, or by a specific industrial process, and removed for disposal. Experiment Central, 2nd edition
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WORDS TO KNOW
Water (hydrologic) cycle: The constant movement of water molecules
on Earth as they rise into the atmosphere as water vapor, condense into droplets and fall to land or bodies of water, evaporate, and rise again. Water clock: A device that uses the flow of water to measure time. Water table: The level of the upper surface of groundwater. Water vapor: Water in its gaseous state. Water-soluble vitamins: Vitamins such as C and the B-complex
vitamins that dissolve in the watery parts of plant and animal tissues. Waterline: The highest point to which water rises on the hull of a ship.
The portion of the hull below the waterline is under water. Wave: A means of transmitting energy in which the peak energy occurs
at a regular interval; the rise and fall of the ocean water. Wavelength: The distance between the peak of a wave of light, heat, or
other form of energy and the next corresponding peak. Weather: The state of the troposphere at a particular time and place. Weather forecasting: The scientific predictions of future weather
patterns. Weathered: Natural process that breaks down rocks and minerals at
Earth’s surface into simpler materials by physical (mechanical) or chemical means. Wedge: A simple machine; a form of inclined plane. Weight: The gravitational attraction of Earth on an object; the measure
of the heaviness of an object. Wet cell: A source of electricity that uses a liquid electrolyte. Wetlands: Areas that are wet or covered with water for at least part of the
year. Wheel and axle: A simple machine; a larger wheel(s) fastened to a
smaller cylinder, an axle, so that they turn together. Work: The result of a force moving a mass a given distance. The greater
the mass or the greater the distance, the greater the work involved.
Xanthophyll: Yellow pigment in plants. lxxxii
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WORDS TO KNOW
Xerophytes: Plants that require little water to survive. Xylem: Plant tissue consisting of elongated, thick-walled cells that trans-
port water and mineral nutrients. (Pronounced ZY-lem.)
Yeast: A single-celled fungi that can be used to as a leavening agent.
Experiment Central, 2nd edition
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1
Acid Rain
D
id you know that acid rain can also be acid snow, acid fog, or even acid dust? Acid rain is a form of precipitation that is significantly more acidic than neutral water. The pH scale offers a way to compare the acidity of substances, including rain. pH (the abbreviation for potential hydrogen) is a measure of the acidity or alkalinity of a solution. The symbol pH refers to the concentration of hydrogen ions present in a liter of fluid. The pH scale ranges from 0 (greatest concentration of hydrogen ions and therefore most acidic) to 14 (least concentration of hydrogen ions and therefore most alkaline). An alkaline solution is also called a base. The number 7 represents a neutral solution, such as pure water. Water with a pH of 4 is 10 times more acidic than water with a pH of 5. A pH of 4 is 100 times more acidic than a pH of 6. So you can see that a small increase or decrease in pH makes a big difference in acid levels.
How does acid get in rain? Normal rainfall is slightly acidic, with a pH of about 5.6. Rain with a pH below 5.6 is considered to be acid rain. Acid rain is created when smoke and fumes from burning fossil fuels— coal, oil, and natural gas—rise into the air. The smoke and fumes come from oil- and coal-fired power plants, factory smokestacks, and automobile exhaust. The main toxic (poisonous) chemicals in this pollution are sulfur dioxide and nitrogen oxides. These chemicals react with sunlight and moisture in the air to produce rain or snow that is a mild solution of sulfuric acid and nitric acid. Some of the pollutant particles fall to the ground as acid dust. When acid rain falls, this dust dissolves in the water, further increasing the rain’s acidity. Why is acid rain a problem? Acid rain can make lakes and streams so toxic that nothing can live there. Amphibians and the young of most 1
Acid Rain
The pH scale shows the acidity and alkalinity of liquids. GAL E GR OU P.
The taller the smokestacks, the longeracidrainstaysintheairand the farther it is likely to travel. P HO TO R ESE AR CH ERS INC .
fish are sensitive to acidity, so they are the first to die. With water at a pH of 5.0, most fish eggs are unable to hatch. If the pH level continues to drop, adult animals begin to die. Experiment 1 will help you determine how sensitive brine shrimp are to acid rain. Acidity kills plants in the water, too, thus upsetting the food chain. Even plant-eating fish that can tolerate low pH levels are soon unable to find enough to eat. With few plant-eating fish able to survive, the fish-eating fish go hungry, too. Acid rain can slowly kill whole forests by dissolving the toxic metals in soil and rock. In their dissolved form, these metals damage tree roots. Acid rain also dissolves nutrients in the soil and washes them away before the trees and plants can use them. In addition, acid rain burns tree leaves and needles and wears away their protective coatings, leaving them unable to produce enough food energy to meet the trees’ needs. Viruses, fungi, and pests can then easily finish off the weakened trees. Experiment 2 will help you determine how acid rain affects plant growth.
2
Experiment Central, 2nd edition
Acid Rain
Along with harming plants and life, acid rain can also damage manmade structures. Many buildings are made of limestone. Limestone is a type of rock that primarily contains calcium carbonate. Statues are often made from marble, a hard substance that is also composed of calcium carbonate. Acids in the rain react with the calcium and slowly dissolve the material. In Experiment 3, you will test how acid rain can affect structures. What can be done? Acid rain was first identified in 1852 by an English chemist named Robert Angus Smith. He suggested that factories that burned coal were sending sulfur dioxide into the air. Since then, the world has gained many more factories—and many more sources of air pollution.
Trees take a long time to recover from damage caused by acid rain. P HO TO RE SE ARC HE RS I NC .
Fortunately, scientists have found ways to wash the sulfur out of coal before it is burned and to wash the sulfur out of smoke before it leaves the smokestacks. In addition, new vehicles must now have a device called a catalytic converter, which uses filters and chemicals to change carbon monoxide and other air pollutants into carbon dioxide
pH levels in the United States. GA LE G RO UP.
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Acid Rain
WORDS TO KNOW Acid rain: A form of precipitation that is significantly more acidic than neutral water, often produced as the result of industrial processes and pollution. Alkaline: Having a pH of more than 7. Amphibians: Animals that live both on land and in water. Base: A water-soluble compound that when dissolved in water makes an alkaline, or basic, solution with a pH of more than 7. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment. Fossil fuel: A fuel such as coal, oil, or natural gas that is formed over millions of years from the remains of plants and animals. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Ion: An atom or groups of atoms that carry an electrical charge—either positive or negative—as a result of losing or gaining one or more electrons. Neutralization: A chemical process in which the mixing of an acidic solution with a basic (alkaline) solution results in a solution that has the properties of neither an acid nor a base. pH: A measure of the acidity or alkalinity of a solution referring to the concentration of hydrogen ions present in a liter of a given fluid. The pH scale ranges from 0 (greatest concentration of hydrogen ions and therefore most acidic) to 14 (least concentration of hydrogen ions and therefore most alkaline), with 7 representing a neutral solution, such as pure water. Toxic: Poisonous. Variable: Something that might affect the results of an experiment.
and water. This device nearly eliminates the nitrogen oxide released by cars’ exhaust systems. Lime, which is a natural base, can be added to streams and lakes to neutralize their acidity. Neutralization is a chemical process in which an acidic solution is mixed with a basic (alkaline) solution, resulting in a solution that is neutral—it has the properties of neither an acid nor a base. However, neutralizing streams and lakes is expensive and must continue as long as acid rain keeps falling. Scientists are also researching more ways to use sources of energy that do not pollute the air, including solar power. We all can help reduce acid rain by reducing our own use of fossil fuels and by learning more about the effects of acid rain. 4
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Acid Rain
EXPERIMENT 1 Acid Rain and Animals: How does acid rain affect brine shrimp? Purpose/Hypothesis In this experiment, you
will use vinegar, which is an acid, to gradually lower the pH level of water containing brine shrimp. (As the pH level drops, acidity increases.) You will measure the changing pH level and observe how the shrimp react. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of acid rain. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the size and health of the brine shrimp • the number of brine shrimp in a given amount of water • the temperature of the water • the kind and amount of food the brine shrimp receive • the pH level of the water In other words, the variables in this experiment are everything that might affect the survival of the brine shrimp. If you change more than one variable, you will not be able to tell which variable had the most effect on the shrimps’ survival.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘All the brine shrimp will be dead by the time the pH level of the water reaches 4.5.’’ In this case, the variable you will change is the pH level of the water, and the variable you will measure is the number of brine shrimp that remain alive. You expect them all to die by the time the pH level reaches 4.5. You will also set up a control experiment. It will be identical to the ‘‘real’’ experiment, except that the pH level will remain the same in the control water and decrease in the experimental water. After each pH decrease in the experimental water, you will estimate the number of brine shrimp that remain alive in the experimental and the control water. If the shrimp in the experimental water are all dead by the time the pH reaches 4.5, while most remain alive in the control water, you will know your hypothesis is correct. Experiment Central, 2nd edition
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Level of Difficulty Moderate, because of the time
How to Experiment Safely Be careful in handling the glass jars. If possible, wear goggles so the vinegar will not splash in your eyes.
• •
• • • • • • • • •
involved. Materials Needed
• 1 tablespoon of live brine shrimp (Brine shrimp are sold as fish food at tropical and saltwater fish shops. The clerk will measure 1 tablespoon of shrimp, which contains several hundred shrimp, and pour it into a container of water.) 2 wide-mouth jars distilled water at room temperature (or tap water that has been in an open container overnight to allow the chlorine in it to evaporate) 2 small, clear containers 2 labels and a marker litmus paper and a color scale white vinegar measuring spoons a stirrer 2 medicine droppers 1 package dry yeast Optional: small aquarium pump with two outlets and plastic tubing
Approximate Budget $5 for the brine shrimp, litmus paper, and yeast.
(The other materials should be available in most households.) Timetable One week. Step-by-Step Instructions
1. Fill both glass jars half-full of water. 2. Use the two small, clear containers to divide the brine shrimp into two equal portions. 3. Pour one portion of shrimp into each of the jars. Rinse the small containers. Label one jar Control and one Experiment. 4. Dip a different strip of litmus paper into each jar, check the color scale, and record the beginning pH level of each jar on a chart like the one illustrated. 6
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5. Use the following steps to take a sample of water from each jar and estimate the number of live shrimp in it: a. Gently stir the water in the experimental jar until the shrimp are distributed evenly. b. Quickly use a medicine dropper to take out a sample of water and shrimp. c. Deposit the sample in one of the clear containers. d. Count or estimate the number of live brine shrimp in it. e. Record the number on your chart. f. Pour the sample back into the same jar. g. Rinse the dropper and container. h. Complete the same process with the control jar. 6. Use the other medicine dropper to slowly add 2 tablespoons (30 ml) of vinegar to the experimental jar. Again measure and record the pH level in that jar. Do not add vinegar to the control jar. 7. Place both jars in a warm, lighted place where they will not receive direct sun. Add a pinch of dry yeast to both jars as food for the brine shrimp. 8. Optional: Attach a length of plastic tubing to each outlet on the aquarium pump. Insert one of the tubes into each jar so it rests on the bottom of the jar. Start the pump, which will keep the water gently moving and increase its oxygen content. 9. Each day for a week:
Step 4: Recording chart for Experiment 1. G AL E GR OUP .
Step 5d: Brine shrimp in a small, clear container. GA LE GRO UP.
a. Add another pinch of dry yeast to both jars. b. Add 2 more tablespoons of vinegar to the experimental jar. Experiment Central, 2nd edition
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Troubleshooters’ Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: All or nearly all the brine shrimp died in both jars.
c. Measure and record the pH levels of both jars. d. Repeat Step 5 to monitor how many live brine shrimp remain in both jars. If no live brine shrimp remain in the experimental jar before the end of the week, end the experiment.
Possible causes: 1. The shrimp were ‘‘old.’’ The fish shop might have kept those shrimp for some time without feeding them. Try again with a fresh batch of shrimp. 2. The water had too much chlorine or other chemicals in it. Try again with water from a different source or let the water sit longer before using it. 3. The yeast polluted the water. Try again, feeding the shrimp much less yeast or not at all. 4. The water became too cold or too hot. Make the necessary adjustments and try again. Problem: Very few of the shrimp died in the experimental jar. Possible cause: The pH did not reach a toxic level. Continue the experiment, further decreasing the pH level of the experimental water.
Summary of Results Use the data on your chart
to create a line or bar graph of your findings. Then study your chart and graph and decide whether your hypothesis was correct. At what pH level did the brine shrimp in the experimental jar start to die in greater numbers? At what level were they all dead? Did most of the shrimp in your control jar survive until the end of the week? Write a paragraph summarizing your findings and explaining whether they supported your hypothesis. Change the Variables To vary this experiment,
consider these possibilities: • Try hatching your own brine shrimp from eggs bought at a pet shop. The hatched shrimp will be very small, but cheap, available, and plentiful. Or use a plankton net to collect small aquatic organisms from pond water. You may need to use a microscope to monitor them during the experiment.
• Change the water temperature. Put two jars of water with a pH of 4.8 (mildly acid rain) under different temperature conditions to see if the shrimp tolerate acid rain better at higher or lower temperatures. • Change the type of acid by using lemon juice. It is more acidic than vinegar and will cause the pH level to drop more quickly. 8
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EXPERIMENT 2 Acid Rain and Plants: How does acid rain affect plant growth? Purpose/Hypothesis In this experiment, you will
use cuttings of plants that are easy to grow, such as ivy, philodendron, begonia, or coleus. You will place two cuttings in water with a pH level of 7.0, which is neutral, and two cuttings in water with a pH of 4.0, which is in the range of acid rain. Your goal is to determine how the acidity affects the growth of roots. Before you begin, make an educated guess or hypothesis about the outcome of this experiment based on your understanding of acid rain. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type, size, and health of the plant cuttings • the air temperature where the jars of cuttings are placed • the amount of sun the cuttings receive • the pH level of the water In other words, the variables in this experiment are everything that might affect the growth of roots. If you change more than one variable, you will not be able to tell which one had the most effect on root growth.
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Cuttings placed in water with a pH level of 4.0 will not grow any roots, while cuttings in water with a pH of 7.0 will begin to grow roots during the experiment.’’ In this case, the variable you will change is the pH level of the water, and the variable you will measure is the amount of roots that grow. You expect no roots to grow in the water with a pH level of 4.0. The cuttings in the water with a pH of 7.0 serve as a control experiment, allowing you to observe root growth when the pH of the water remains neutral. After the two-week period of the experiment, if the cuttings in the neutral water have grown roots, but those in the acid water have not, you will know your hypothesis is correct. Level of Difficulty Moderate, because of the time involved. Experiment Central, 2nd edition
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Materials Needed
How to Experiment Safely Be careful in handling glass jars.
• • • • •
• • • • •
4 small, clear jars 4 labels and a marker 2 large water containers water litmus paper and a color scale
white vinegar baking soda measuring cups and spoons a stirrer 2 cuttings each of two easily grown plants, such as ivy, philodendron, begonia, or coleus (Make sure each cutting has the same number of leaves and same amount of stem.)
Approximate Budget $5 for the plants and litmus paper. (Ask friends,
neighbors, or family members for cuttings so you will not need to buy plants, and the other materials should be available in most households.) Timetable Two weeks to observe plant growth. Step-by-Step Instructions
1. Label the four small jars in this way: (name of plant 1), neutral; (name of plant 1), acid; (name of plant 2), neutral; (name of plant 2), acid. 2. Pour 2 cups of water into each of the large containers. 3. Use the litmus paper and a litmus color scale to measure the pH level of the neutral or control container. It should be 7.0. If it is higher, add a drop or two of vinegar, stir, and check it again. If it is lower than 7.0, sprinkle in a little baking soda, stir, and check again. Repeat until the color scale shows that the pH level is 7.0. 4. Pour 1 tablespoon (15 ml) of vinegar into the acid or experimental container, stir, and check the pH level. It should be 4.0. If it is higher or lower, add vinegar or baking soda, as in Step 3. 5. Nearly fill the two small jars labeled Neutral with the neutral water. Then pour the same amount of acid water into the two 10
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Step 6: Plant cuttings in labeled jars of water. GAL E GR OU P.
6. 7. 8. 9.
small jars labeled Acid. Label and save any leftover water so you can keep the small jars full of water with the correct pH level. Place the four plant cuttings in their labeled jars. Make sure the stem and part of the lowest leaf is under water. Place all four jars in a warm, sunny place. Create a chart like the one illustrated. Draw each cutting to show how it looked at the beginning. For the next two weeks:
Step 8: Recording chart for Experiment 2. GA LE G ROU P.
a. Every day, make sure all cuttings are still in the water. Add more acid or neutral water to replace any that evaporates. (Be careful to add the right kind to each cup.) b. Every other day, check the pH of the water in each cup, and use vinegar or baking soda to adjust it so it is 7.0 or 4.0. c. Every day, record any changes or growth on the chart. Clearly show any roots that grow longer or branch out, leaves that grow larger, and the emergence of new leaves. Summary of Results Study the drawings on your
chart and decide whether your hypothesis was correct. Did both cuttings in acid water not Experiment Central, 2nd edition
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Troubleshooters’ Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: None of the cuttings grew. Possible causes: 1. The cuttings were infected with insects, fungus, or something else. Try the experiment again with fresh cuttings from different plants. Use different jars or wash the old jars well. 2. The cuttings were from old, woody sections of the plant. Try cuttings from the growing tips of the plants. 3. The cuttings did not receive enough sun or became too cold or too hot. Perhaps their stems did not remain in the water. Try again, placing the cups in a warm (not hot) place where they will receive several hours of sun every day. Check to make sure the stems remain underwater. Problem: All of the cuttings grew about the same amount. Possible causes: 1. The pH of the water in the acid jars might not have remained at 4.0. Try the experiment again, carefully checking the pH levels during the observation period.
grow at all? Or did they grow some, but less than those in neutral water? Was the cutting of one plant more tolerant of acid water than the cutting of the other plant? Did both cuttings in neutral water grow as you expected? Write a paragraph summarizing your findings and explaining whether they supported your hypothesis. Change the Variables Here are some ways you
can vary this experiment: • Use different kinds of plants. • Water potted plants with acid and neutral water and compare their leaf and stem growth and appearance, general health, and frequency of blooming, if applicable, over time. • Use water with different pH levels, such as 5.0, 4.0, and 3.0 to determine if growth decreases with each increase in acidity.
EXPERIMENT 3 Acid Rain: Can acid rain harm structures? Purpose/Hypothesis In this experiment, you
will observe how acid rain can harm buildings, statues, and other structures. The acid you will be using is vinegar, which is about 5% acid. Vinegar is slightly more acidic than acid rain, but acid rain works its reaction over a period of years and this experiment will only take about a week. You will test vinegar’s effect on two different forms of structural materials: marble and limestone. For the limestone, you will use chalk, which is a type of limestone. You can determine if some of the materials dissolve by noting the weight and appearance. By weighing the materials both before and
2. Perhaps both kinds of plants are tolerant of acid water. That would mean your hypothesis is incorrect for these kinds of plants.
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Acid Rain
after they are exposed to vinegar, you can measure the effect of acid on structures. What Are the Variables? Before you begin, make an educated guess about the outcome of this experiment based Variables are anything that might affect the results of an experiment. Here are the main on your knowledge of acid rain. This educated variables in this experiment: guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the temperature of the solution • the room temperature • the topic of the experiment • the variable you will change • the size of the materials • the variable you will measure • the shape of the materials • what you expect to happen In other words, the variables in this experiment A hypothesis should be brief, specific, and are everything that might affect the rate at measurable. It must be something you can test which the materials dissolve. If you change more than one variable at the same time, you through further investigation. Your experiment will not be able to tell which variable had the will prove or disprove whether your hypothesis is most effect on the chalk and marble. correct. Here is one possible hypothesis for this experiment: ‘‘Acid will wear away some of the materials, causing the substances to weigh less after they are immersed in acid.’’ In this case, the variable you will change is the acidity. The variable you will measure is the appearance and weight of the material. Conducting a control experiment for each material will help you isolate the variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. In this experiment, you will have two controls: one for the marble and one for the limestone (chalk). For the controls, you will use distilled water. Level of Difficulty Moderate. Materials Needed
• crushed marbles (the size of small pebbles), available from a craft or home garden store • white chalk • gram scale • wax paper • 4 small jars with lids • distilled water • white vinegar • spoons Experiment Central, 2nd edition
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Acid Rain
Approximate Budget $8 (assuming gram scale is
How to Experiment Safely Make sure the experiment is well labeled and stored somewhere safe. Wash your hands after setting up and finishing the experiment.
2. 3.
4. 5. 6.
7. 8. 9.
Step 2: The recording chart for Experiment 3. I LLU STR AT IO N
10.
BY T EM AH NE LS ON.
Starting Ending Weight Weight Marble Marble control Limestone Limestone control
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a household item). Timetable 20 minutes setup; about ten minutes
daily for five to 10 days. Step-by-Step Instructions
1. Label each of the jars: ‘‘Marble,’’ ‘‘Marble Control,’’ ‘‘Limestone,’’ and ‘‘Limestone Control.’’ Make a chart listing the materials, starting weight, ending weight, and appearance. (See chart). Place a sheet of wax paper on the gram scale and weight out 2 grams of the crushed marble. (You can use less but make sure to note the exact weight in your chart.) Carefully pour into the jar labeled ‘‘Marble.’’ Weigh another 2 grams of the marble and pour into the Control jar. Break the chalk into roughly 1-inch (2.5 centimeters) pieces. Using a fresh piece of wax paper, weigh 2 grams of the chalk and place in the jar labeled ‘‘Limestone.’’ Weigh out another 2 grams and place in the Control jar. In both control jars, cover the chalk and marble with distilled water. In both experimental jars, cover the chalk and marble with vinegar. After four days, note the appearance of the materials and solutions in your chart. Does the chalk look smaller? Does the vinegar appear cloudy? After a minimum of a week, when it looks like the acid has affected the material, carefully scoop out the marble and chalk onto separate sheets of wax paper. You may need to rinse them off. Scoop out the control marble and chalk too. Make sure to keep track of the test and control Appearance materials! You can either label the wax papers or keep the material next to the labeled jar. 11. Let the marble and chalk pieces dry overnight. 12. When completely dry, weigh each of the materials and note the results. Experiment Central, 2nd edition
Acid Rain
Summary of Results Examine your results and note the appearance of each of the materials. Calculate the difference between the starting and ending weights. Compare the chalk and marble to the controls. How did the acid from the vinegar affect the materials? Was your hypothesis correct? Change the Variables There are several ways you
can alter the variables in this experiment. You can try different materials, such as metals. Dolomite is a rock that is similar to limestone. You can also vary the strength of the acid. For a weaker acid, more similar to acid rain, add water to the vinegar. For a stronger acid, you can carefully boil away some of the vinegar’s water, leaving more of the acid.
Marble control
Design Your Own Experiment How to Select a Topic Relating to this Concept You can explore many
other aspects of acid rain. Consider what puzzles you about this topic. For example, what would happen if you added vinegar or another acid to a jar of water with limestone (calcium carbonate) gravel in the bottom? Lime is a base that can neutralize acid, so would the pH level of the water still drop with the limestone in there? How does ground lime affect plants that have been damaged by acid rain? Will they begin growing well again if lime neutralizes the soil? What if lime is applied first and then the plants are watered with acid rain? Will the lime protect them? How does acid rain affect the germination of seeds? Which plants are more tolerant of acid rain than others? Check the Further Readings section and talk with your science teacher or school or communLimestone ity media specialist to start gathering informaLimestone tion on acid rain questions that interest you.
Step 3: Carefully pour into the jar labeled ‘‘Marble.&rdquo ILL US TRA TI ON B Y TE MA H NEL SO N.
Step 7: The controlled jars are filled with distilled water. The experimental jars are filled with vinegar. I LL UST RA TI ON BY T EMA H NE LS ON.
Marble Marble control
control
Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think Experiment Central, 2nd edition
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Acid Rain
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The marble weighed the same, even after ten days. Possible cause: Marble is a much harder material than chalk. The pieces may have been too large to dissolve. Try again with marble pieces that are more finely crushed. Problem: There was no notable difference in the weight of the chalk, even though it appears smaller. Possible cause: The chalk may still contain some of the liquid it absorbed, which would add weight. Set the chalk aside in a warm area for another day, then weigh again.
things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In
the two acid rain experiments, your raw data might include not only charts of brine shrimp survival rates and root growth, but also drawings or photographs of these changes. If you display your experiment, limit the amount of information you offer, so viewers will not be overwhelmed by detail. Make clear your beginning question, the variable you changed, the variable you measured, the results, and your conclusions. Viewers—and judges at science fairs— will want to see how your experiment was set up. You might include photographs or drawings of the steps of the experiment. Viewers will want to know what materials you used, how long each step took, and other basic information. Related Projects You can undertake a variety of projects related to
acid rain. For example, you might explore how acid rain affects buildings, statues, and other outdoor structures. Which kinds of stone are most susceptible to damage from acid rain? How do people fare in regions with highly acidic rain? Do they have more respiratory problems? 16
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For More Information Edmonds, Alex. A Closer Look at Acid Rain. Brookfield, CT: Copper Beech Books, 1997. Examines the causes of acid rain; its effects on plants, lakes, and human health; and ways to tackle the problem. Gutnik, Martin. Experiments That Explore Acid Rain. Brookfield, CT: Millbrook Press, 1992. Outlines projects and experiments dealing with acid rain. Parks, Peggy J. Acid Rain. Detroit, MI: KidHaven Press, 2006. Explanation and effects of acid rain. Rainis, Kenneth. Environmental Science Projects for Young Scientists. New York: Franklin Watts, 1994. Outlines detailed projects easily completed by middle school students. U.S. Environmental Protection Agency. ‘‘Acid Rain.’’ http://www.epa.gov/acidrain (accessed on January 17, 2008).
The sulphur in acid rain reacts with the limestone in statues, forming a powder that easily washes away. PHO TO RES EA RC HER S I NC.
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Adhesives
A
n adhesive is any substance that binds or adheres objects together. Adhesives are generally out of sight, but they are all around us. They are holding together the pages of a book, the wood in furniture, and the cardboard in food packages. Adhesives are also a part of modern technologies, such as airplanes, sports equipment, and electronics. And as the development of adhesives continues to improve, they are increasingly becoming a part of products and structures. Nature’s sticky stuff Before the development of synthetic (manmade) adhesives, people used natural adhesives. Many animals and plants have sticky substances. Historians have found evidence that about 3,000 years ago Egyptians made an early form of paper called papyrus (pronounced pa-PI-rus) with a natural starch, like flour. Manuscripts were bound with egg whites. Letters were sealed with beeswax. Humans aren’t the only organisms that use adhesives. The gecko, for example, can produce an adhesive on its feet that it uses to climb vertically. The natural adhesive of this lizard is so strong it can support the gecko’s weight but it can also detach itself from the surface easily. Beetles and other insects also produce natural adhesives. Researchers study the natural adhesives on animals to develop similar synthetic adhesives. Glue it on The manufacturing of modern glues began about the turn of the nineteenth century. The understanding and development of polymers helped advance the manufacturing of glues. Glues are polymers, long chains of molecules made up of smaller, repeating molecules. Both natural and synthetic polymers are all around us. Plastics are a type of synthetic polymer. Natural polymers include silk and rubber, along with other sticky substances in nature. How glues cause materials to bond to one another depends upon the glue polymer. In modern day, there are a variety of glue types. Some examples of commonly used glues include: 19
Adhesives
The gecko can produce an adhesive on its feet that it uses to climb vertically. AP PH OT O/ K EYS TO NE, STE FF EN S CHM ID T.
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• All purpose white glue, which is commonly used in schools and homes, is a substance called polyvinyl acetate (PVA). PVA is a water-based glue that bonds many different types of surfaces together. • Cyanoacrylate glues are also known as superglue. A small amount of this glue will form an extremely strong bond. • Contact cement is a rubber-based glue that can have both a lighter and stronger bond, depending upon how it is applied. • Epoxies come as two parts that must be mixed together. One part causes the other part to link together in crosslinks and harden, resulting in an extremely strong bond. One way that glue bonds surfaces together is through a chemical change. Glue can cause the molecules to become attracted to one another. This attractive force is referred to as a van der Waals’ force. Named after Dutch scientist Johannes Diderik van der Waals (1837–1923), the van der Waals forces relates to the attraction between molecules that have a positive and negative end. The water molecule, for example, is made up of two hydrogen atoms and an oxygen atom. It has a positive hydrogen side and a negative oxygen side. Because opposite charges attract, the hydrogen side of one water molecule is attracted to the negative side of another oxygen molecule. Even though these forces are relatively weak, when millions of separate van der Waals forces occur in millions of water molecules it can form a bond. The PVA glue molecule also has positive charges on one side and negative on the other. If the glue and surface molecules are close to one another a bond can form. Another way glue works is by mechanical bonding. When glue is spread on a surface it seeps into all the tiny pores and cracks of the material. When the glue hardens, a bond is formed. PVA works mainly by evaporation. After spreading it on the surface, the water evaporates and the chemicals bonds to one another. The Experiment Central, 2nd edition
Adhesives
Van der Waals Force
The van der Waals forces relates to the attraction between molecules that have a positive and negative end. I LL US TRA TI ON BY TEM AH N EL SON .
cyanoacrylate glues also depend on water. Cyanoacrylate molecules begin lining up into chains when they come into contact with water. When the molecules can no longer move, the glue is hard. Behind the tape Another form of familiar adhesive is tape. Tapes are relatively new to the adhesive world, with the first tapes developed in the 1800s. Masking tape was invented in the 1920s. Soon after came the first transparent tape. In modern day, there are a wide variety of tapes of all stickiness levels. There are two parts to what makes a tape adhere: the backing material and the adhesive. The adhesive in tapes is also a form of polymer. Unlike glues, which are liquid and harden over time, tape adhesives are solid and remain solid. When pressure is applied to the tape, van der Waals forces are at work and there is stickiness. Tape adhesives are also distinct from glue because a piece of tape can be removed. Some tapes have strong adhesives that can hold a lot of weight and withstand force. These tapes are removable, but they can cause harm the surface of the taped material. Packing tape, for example, can hold a box together, but when it is peeled away it also likely remove some of the cardboard. Experiment Central, 2nd edition
When glue is spread on a surface it seeps into all the tiny pores and cracks of the material. I LL UST RA TIO N BY TEM AH N EL SON .
Glue moves between the fibers, creating a strong bond.
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Adhesives
WORDS TO KNOW Adhesive: A substance that bonds or adheres two substances together. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Polyvinyl acetate: A type of polymer that is the main ingredient of white glues.
Polymer: Chemical compound formed of simple molecules (known as monomers) linked with themselves many times over. Synthetic: Something that is made artificially, in a laboratory or chemical plant, but is generally not found in nature. Variable: Something that can affect the results of an experiment Van der Waals’ force: An attractive force between two molecules based on the positive and negative side of the molecule.
Other tapes were developed with light adhesives so they are easily removed without harming the surface. Sticky notes are an example of this type of adhesive. They stick where they are placed and can be removed without a trace of the stickiness. Adhesives are a wide and fascinating group of materials. What kind of adhesives do you have questions about? You will have an opportunity to explore both glues and tapes in the following two experiments. Sticky notes use a light adhesive so that the item they are attached to is not damaged when the note is removed. A P P HOT O/ JI M MO NE.
EXPERIMENT 1 Material Adhesion: How do various glues adhere to different materials? Purpose/Hypothesis How glues adhere to mate-
rials depend upon both the properties of the glue and the material. Metals, plastics, and wood each have unique properties. Wood, for example, has tiny pores that the glue moves into. In this experiment, you will use three types of glue: rubber cement, a white glue, and a ‘‘super’’ glue. The materials you can glue together are wood, plastic, and metal (aluminum foil). By gluing each material to itself, you can determine what glues adhere to which materials. 22
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Do you think one glue will adhere to all the materials? To begin the experiment, use what you have learned about adhesives and glue to make a guess about what glue will adhere to what materials. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the air temperature • the temperature of the glue • the material being glued • the amount of glue In other words, the variables in this experiment are everything that might affect the bond between the materials. If you change more than one variable at a time, you will not be able to determine which variable had the most effect on whether the materials adhere to one another.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The super glue will adhere all materials to one another; the white glue will only bond wood together; and the rubber cement will not bond to any of the materials.’’ In this case, the variable you will change for each glue is the type of materials being glued together. The variable you will measure is whether there is a bond between the materials.
Step 5: Starting with the white glue, use the cotton swabs to spread the glue on the wood. Press the wood together firmly and note the time. IL LUS TR ATI ON B Y TE MA H NE LSO N.
Level of Difficulty Moderate. (This experiment
requires monitoring over several hours.) Materials Needed
• white glue, such as an all purpose school glue or wood glue • rubber cement, acid-free, craft • cyanoacrylate glue, such as Superglue or Krazy clue, select a glue that says it will not bond to skin instantly • strips of wood, about 0.125 inch (0.32 centimeter) thick and 1 foot (30 centimeter) long (available at craft stores) • aluminum foil Experiment Central, 2nd edition
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How to Experiment Safely Make sure you purchase the cyanoacrylate glue that states it will not bind instantly to skin. Although this type of cyanoacrylate glue will not bind instantly, it can still bond to skin and cause irritation. Have an adult help you wipe the cyanoacrylate glue on the materials. Be careful not to get the glue on your skin. If you do so, immediately follow the instructions on the glue.
2. 3. 4. 5. Step 7: Repeat Steps 5 and 6, using first the rubber cement and then the cyanoacrylate glue. I LL UST RA TI ON BY T EM AH NE LS ON.
White Glue cyanoa
Rubber Cement
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cr yla
e
6.
• • • •
plastic, from a container or bottle scissors cotton swabs wax paper or paper towels
Approximate Budget $10. Timetable 30 minutes to set-up; approximately
45 minutes to monitor results over at least a 12-hour period. Step-by-Step Instructions
1. Break the long wood strip into six pieces, each about 2 inches (5 centimeters) long. Cut the plastic into six pieces, each about 2 inches long and approximately matching the width of the wood strips. Tear six pieces of aluminum foil, each about 2 inches long and approximately matching the width of the wood strips. Set all the materials on wax paper or paper towels to protect the surface. Starting with the white glue, use the cotton swabs to spread the glue on the wood. Press the wood together firmly and note the time. One by one, use the white glue to contine gluing a piece of each material to every other material. You will have three test pieces for each glue: wood to wood; plastic to plastic; and aluminum foil to aluminum foil. 7. Repeat Steps 5 and 6, using first the rubber cement and then the cyanoacrylate glue. See illustration. 8. Wait 15 minutes and test the adhesive bond between the materials. Gently try to move one of the pieces. Does one piece of aluminum foil peel back? If one of the pieces is not bonded, press the pieces back together and set it down. If any of the pieces are bonded, write down the results in a chart and note the approximate time it took. Experiment Central, 2nd edition
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9. Wait 15 minutes and test the adhesive bond between the materials. Gently try to move one of the pieces. Does one piece of aluminum foil peel back? If one of the pieces is not bonded, press the pieces back together and set it down. If any of the pieces are bonded, write down the results in a chart and note the approximate time it took. 10. Continue checking the adhesive bonds between the materials every 30 minutes over the next two to three hours. When the materials are bonded together note the time on a chart and you do not have to test them anymore. 11. Allow the materials that have not bonded to sit overnight or for a 12-hour period before you test adhesion for the final time. Summary of Results Study the results of your
chart. Did one type of glue bond to all of the materials? Was there a glue that only bonded to one type of material? Consider how the properties of plastic, wood, and aluminum foil may have interacted with the glue. Write a paragraph summarizing and explaining your findings.
Troubleshooter’s Guide It’s common for experiments to not work exactly as planned but it can often offer a learning experience. Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The wood pieces did not bond to anything. Possible causes: The pieces may have needed more pressure when forming a bond. Try gluing two wooden pieces together and use a weight to press them together. You can use a heavy book or pot. Place a strip of wax paper between the pieces and the weight so as not to get any glue on the heavy item. Problem: The foil and plastic keep slipping apart when I test them. Possible causes: You may have applied too much glue to the surface and peeling them apart causes them to slip. Try it again, applying less glue. Once you know the general amount of time it takes for the materials to set, wait until that time period before you test the bond.
Change the Variables There are several ways you can change the variables in this experiment. One way is by focusing on one glue type. Rubber cement, for example, is available in several types and can be applied in different ways. Wiping the adhesive to each side of the material and pressing the materials together can give a stronger bond. You can test this bond on all the materials. You can also focus on one type of material. There are many kinds of woods, plastics, and metals. Can the white glue bond certain woods together but not others? Experiment Central, 2nd edition
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EXPERIMENT 2 What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the environmental conditions
Adhesives in the Environment: Will different environmental conditions affect the properties of different adhesives? Purpose/Hypothesis There are adhesives devel-
oped for strength and others that are meant to have a weak adhesive. Sticky notes, for example, was a completely new type of adhesive when it • the type of paper was developed in the 1960s. The removable • the material the adhesive is stuck to paper will adhere where it is placed and is easily • the age of the adhesive removed. Tape made for painting is another • the strength of the fan adhesive that can be removed without a trace. • the type of paper bag All adhesives are designed to work in certain • the type of bottle used to test strength environmental conditions. This experiment explores how temperature In other words, the variables in this experiment are everything that might affect the adhesion. If and the environment affect adhesives. You will you change more than one variable at the same use two types of adhesives: the low-strength time, you will not be able to tell which variable sticky note, and a tape with a strong adhesive. had the most effect on the adhesive properties. You will expose each adhesives to a cold, hot, and humid environment. By comparing how the adhesive ‘‘sticks’’ both before and after each environmental change, you can measure how the environment affects the properties of each adhesive. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of adhesives and the environmental conditions. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the amount of time in each environmental condition
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The cold and heat will change the adhesive properties of the low-adhesive material but not the tape with the strong adhesive.’’ 26
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White Glue
Rubber Cement
cyanoacryla
te Materials needed. IL LU STR AT IO N BY T EM AH NE LS ON.
In this case, the variable you will change is the environmental conditions for each adhesive, one at a time. The variable you will measure is the adhesion properties, as compared to the unchanged adhesive material. Level of Difficulty Moderate (there are a lot of steps to this experiment; to
simplify, you can test adhesive strength for only hot and cold conditions, leaving out the humidity). Materials Needed
• sticky notes • tape with a strong adhesive, such as Duct, packing, or masking tape • paper • fan • 3 blocks of wood, the same type of wood • clamp • 3 small paper bags (lunch bags work well) • 2-liter plastic bottle Experiment Central, 2nd edition
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How to Experiment Safely Be careful when working with the heat lamp after it has been turned on and use caution with the boiling water. Part of this experiment can be messy. If you have a workbench or other movable bench you may want to clamp the block of wood outside.
• • • • • • •
funnel heat lamp, or a warm, sunny day large container or garbage can freezer scissors tall pot, such as a soup pot chest grater, strainer, or other metal item with holes in it that can sit on the top of the pot
Timetable 1 to 2 hours working time; approximately 3 hours total time. Step-by-Step Instructions Testing adhesive strength under ‘‘normal’’ envi-
ronmental conditions.
Steps 2 and 3: Stick one note on a piece of paper and place the paper directly in front of the fan. Turn the fan on to the highest setting and hold the paper for 30 seconds. I LLU ST RAT IO N BY T EM AH NEL SO N.
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1. Sticky note: Stick one note on a piece of paper and place the paper directly in front of the fan. Use the tape measure to measure how far the paper is from the fan. 2. Turn the fan on to the highest setting and hold the paper for 30 seconds and turn off the fan. 3. If the sticky adhesive did not hold the note in place during the 30 seconds, move the paper 1 to 2 inches (2–5 centimeter) farther away from the fan. Sticky on a fresh sticky note, turn the fan on and repeat. Continue moving the paper back until the sticky note does not blow away. If the sticky does not blow away, move the paper 1 to 2 inches closer to the fan. Continue moving the paper forward until the sticky cannot move any more before it blows away. 4. When you have the distance that the sticky adhesive keeps the note on the paper, note distance on a chart. 5. Tape: Tape the paper bag to the bottom half of the piece of wood. Note the size and direction you tape the bag. 6. Clamp the piece of wood to a work bench, chair, or other sturdy item. Make sure the clamp is not touching the bag. 7. Set the empty bottle inside the bag. The bottle should be slightly higher than the bag. You may need to cut the top of the bag with the scissors. Experiment Central, 2nd edition
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8. If you are working inside, set a large container or garbage can underneath the bag/bottle. Place the funnel in the bottle. 9. Carefully add ¼ cup (about 2 ounces) of water to the bottle, being careful not to drip any water on the bag. Continue adding water in ¼ cup increments, remembering to note how much water you are adding. When the tape can no longer support the bottle, write down the amount of weight the tape held. Setup for adhesive strength under warm environmental conditions. 1. Place a new sticky note on a fresh piece of paper. 2. Tape a new paper bag to the wood block in the same direction and using the same length of tape as the normal environmental trial. 3. If it is a hot day outside and the sun is out, place both the paper and wood (with the attached bag) out in the sun. If you are working indoors, place both items under the heat lamp. Setup for adhesive strength under cold environmental conditions. Place a new sticky note on a fresh piece of paper. Tape a new paper bag to a wood block in the same direction and using the same length of tape as the normal environmental trial. Place both items in the freezer.
Steps 5–9: Tape a paper bag to the bottom half of the piece of wood and clamp the piece of wood to a chair. Set the empty bottle inside the bag and insert the funnel. Add ¼ cup (about 2 ounces) of water to the bottle. I LL US TRA TI ON BY TE MAH N EL SON .
Setup for adhesive strength under humid environmental conditions. 1. Place a new sticky note on a fresh piece of paper. 2. Tape a new paper bag to a wood block in the same direction and using the same length of tape as the normal environmental trial. 3. Fill the pot about a quarter way with water and bring to a boil. 4. Remove the pot from the heat and allow it to cool for one to two minutes. Carefully set the cheese grater (or other item) on top of the pot. 5. Place the paper with the sticky and the wood block with the bag on top of the grater with the tape facing upwards. Testing adhesive strength. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The bag keeps breaking when the water is poured in. Possible cause: The funnel might be too narrow and you may be dripping water onto the bag, which would weaken the bag. Have a helper hold the funnel upright while you carefully pour. You may also need a larger funnel. Repeat the tests. Problem: The tape and sticky completely peeled off when it was placed above the hot water. Possible causes: There may have been too much steam. Try it again, allowing the pot to cool another couple minutes before placing the adhesives over the pot.
Wait approximately three hours. Sticky note: Hold the paper with the sticky that was under the hot environmental conditions in front of the fan. Use your chart and tape measure to determine where the paper should be (it should be the same distance as it was in the normal environmental conditions). Again, turn the fan on the highest setting for 30 seconds and note if the sticky adhesive holds. Repeat this step with the sticky note that was undergoing cold conditions and then the humid conditions. Tape: Use your chart to determine how much weight the tape should hold. Repeat the setup in Steps 7 and 8 for each block of wood, carefully pouring in the water. After testing the adhesives that underwent hot, cold, and humid conditions, note the results on a chart.
Summary of Results Examine your data and compare the results of the
tests with your hypothesis. Did your hypothesis prove true? How did the adhesive undergoing each of the different environmental conditions compare to the normal condition? Was there one environment that affected the adhesive the most? Compare each of the two adhesives against one another. Consider why it might be important for different adhesives to withstand certain types of environments. You may want to write a summary of your results. Change the Variables Variables you can change in this experiment
include: • Changing the type of adhesives to determine if there are patterns to environmental conditions and the strength of the tape. • Change the material the adhesive adheres to. • Focus on one environmental condition and measure at what point the environment breaks down the adhesive. 30
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Design Your Own Experiment How to Select a Topic Relating to this Concept You make use of adhesives
every day. Think about what interests you about adhesion and what questions you have. Do you want to know about how the materials play a role in adhesion? Or how synthetic glues differ from natural glues? Make a list of all the types of adhesives and where they are applied. Check the Further Readings section and talk with your science teacher to learn more about adhesives. Because adhesives are so diverse, there are many different types of scientists who work with them. Ask family, teachers, and friends if they know someone who works a lot with adhesives. It could be a carpenter or researcher. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects You can use the materials around you to think of
projects related to adhesives. They are in furniture, school supplies, and many products that you purchase. You could examine how adhesives play Experiment Central, 2nd edition
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a role in everyday products. If you are interested in natural adhesives, you can make your own and test the adhesives against commercial brands. Consider the adhesive properties of tape. Sticky notes and envelopes, for example, make use of adhesives. What makes their adhesive properties unique and why are they important? How does waterproofing play a role in choosing the right adhesive? You could also experiment with what materials can remove adhesives.
For More Information Roach, John. ‘‘Gecko, Mussel Powers Combined in New Sticky Adhesive.’’ National Geographic News. July 18, 2007, http://news.nationalgeographic.com/ news/2007/07/070718 geckel glue.html (accessed on April 1, 2008). This to That. http://www.thistothat.com (accessed on April 1, 2008). Suggestions on what glue to use to adhere one material to another, along with trivia facts and glue news briefs. Fix It Club. ‘‘Glues.’’ HowStuffWorks. http://home.howstuffworks.com/glues.htm (accessed on April 1, 2008). Explanation of how different types of glues adhere. VanCleave, Janice. Janice VanCleave’s 204 Sticky, Gloppy, Wacky and Wonderful Experiments. Hoboken, NJ: J. Wiley, 2002. Weiss, Malcolm E. Why glass breaks, rubber bends, and glue sticks: how everyday materials work. New York: Harcourt Brace Jovanovich, 1977.
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Air
E
ven though you cannot feel it, see it, or smell it, air surrounds you and extends far upward for miles. Air is a mixture of gases, mainly nitrogen and oxygen, with about four times as much nitrogen as oxygen. With few exceptions, all living things on Earth need air to survive. It is what makes all flight possible, from airplanes to birds. It allows fuels to burn and it shields Earth from the sun’s harmful rays. Air is also what gives us our weather patterns. Air’s temperature, pressure, density, and volume all create the weather. Surrounded by air All the air that covers Earth is called the atmosphere. Earth’s gravity holds the atmosphere in place around our planet. The atmosphere is a blanket of air over 600 miles (1,000 kilometers) high. Scientists have divided the atmosphere into five layers, according to differences in the temperature of the air. The layer closest to Earth is called the troposphere. The troposphere extends about 9 miles upward (15 kilometers). It contains almost all of what makes up Earth’s weather, including clouds, rain, and snow. Like any gas, air has pressure, mass, and a temperature. Air is composed of 78% nitrogen, 21% oxygen, 0.9% argon, and the remaining 0.1% a handful of other gases, including carbon dioxide. The molecules in air’s gases are constantly flying around at high speeds. This air can feel completely still because there are billions of individual molecules zipping in all directions. When the molecules travel in one direction, it results in wind.
Oh, the pressure Winds begin with differences in air pressure. Air always moves from areas of high pressure to low pressure. The greater the difference in pressures, the stronger the wind’s force. Air’s pressure is caused by the weight of the air in Earth’s atmosphere pushing down on the air below. Air in the troposphere has the highest pressure of all the layers. The air at the top of the atmosphere has little weight above it to push it down, so its pressure is less. The air at the 33
Air
Air Composition
78% Nitrogen
bottom of the atmosphere is being pushed down by the hundreds of miles of air above it. This results in air low to the ground having more pressure than air high in the atmosphere. The air pressing down on you weighs about 1 ton (0.9 metric ton). You cannot feel this pressure because you are supported by equal air pressure on all sides, and your body is filled with gases and liquid that push back with equal pressure.
21% Oxygen
Meteorologists, or people who study weather, measure air pressure with a barometer. Changes in the air pressure or barometric pressure occur during changes in the weather. The mercury barometer uses the heavy liquid metal .9% Argon mercury, which is about 14 times heavier or .1% other gases denser than water. An empty glass tube with the upper end closed is inserted into a dish of mercury. The height of the column of mercury The air on Earth is composed of in the glass tube is controlled by the air pressing down on the mercury in several different gases. G AL E GRO UP. the dish. Normal air pressure lifts the mercury to a height of about 30 inches (760 millimeters). When air pressure falls, the air does not push on the mercury in the dish as much, and the column of mercury falls. When air pressure increases, the column of mercury will rise. In general, falling air pressure means that clouds and rains or snow are likely. Rising air pressure signals that clear weather is likely. In the mid 1600s Italian mathematician Evangelista Torricelli (1608–47) designed the first barometer to prove that air had weight and pressure. Then in 1648 French philosopher and mathematician Blaise Pascal (1632–62) hypothesized that air pressure decreased with altitude. He sent his brother-in-law up to the peak of a mountain in France with a barometer. The column of mercury dropped lower and lower the higher he went. Today, the international unit of pressure is called the Pascal, in his honor. Changing densities Quick changes in the weather are caused by movements of large bodies of air called air masses. Air masses usually cover very large areas. All the air in an air mass has nearly the same properties. When two air masses that have different densities meet, they mix slowly and form an area between them called a front. 34
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The density of an air mass is related to its pressure and temperature. Air density is the amount of matter or mass in a specific volume. Increasing the temperature of a gas pushes its molecules farther apart. When the sun heats up the air, the space between the molecules increases and the hot air expands. The air becomes less dense and has less pressure. When the temperature of air decreases its molecules move closer together and the air contracts. The air becomes more dense and has greater pressure.
600 miles
increasing air pressure
There are three main types of fronts: cold fronts, warm fronts, and occluded fronts. A cold front forms when a cold air mass meets and pushes under a warm air mass. Violent storms are associated with a cold front. Fair, cool weather usually follows. A warm front forms when a mass of warm air moves into a cold air mass. Rain and showers usually accompany a warm front. Hot, humid weather usually follows. An occluded front happens when a cold front catches up and merges with a warm front. An occluded front often brings heavy rain.
Troposphere
Air presses down from the upper atmosphere, causing more pressure in the layer closest to Earth, the troposphere. GA LE G ROU P.
The closer air lies to the surface of Earth, the denser it is because there are more molecules of air compressed into a smaller volume. The troposphere
Warm Air Mass Cold Air Mass A cold front occurs when a cold air mass meets and pushes under a warm air mass. GA LE GR OU P.
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When mountain climbers trek up high mountains, they often bring tanks of oxygen with them because the air contains less oxygen for them to breathe.
layer is so compressed that it contains about 80% of the air found in the entire atmosphere by mass. The higher up in the atmosphere someone goes, the less dense the air. When mountain climbers trek up high mountains, they often need to bring tanks of oxygen with them because the air is less dense and contains less oxygen for them to breathe. The up-and-down movement of air due to different densities is called convection currents. When the air becomes less dense it rises upward through the denser, cool air above it. As this warm air moves through the cold air it cools off, becomes more dense again, and eventually sinks back to the bottom.
EXPERIMENT 1
AP/ WI DE W OR LD P HOT OS.
The up-and-down movement of air due to different densities is called convection currents.
Air Density: Does warm air take up less room than cool air? Purpose/Hypothesis Density is the mass of anything divided by the
volume it occupies. As the temperature of a given mass of air increases, its volume expands and the air gets less dense as a result—same mass, but larger volume, means o less dense. As the temperature of a given mass o l c s air of air decreases, its volume contracts and the air gets more dense. In this experiment, you will examine the density of air by causing a mass of air in a closed container to become both more warm cool and less dense by changing the temperature. To light air dense see these changes you will place a balloon over rises air sinks the open end of a bottle. When the trapped air expands, the balloon should get bigger; when the air contracts, the balloon should get smaller. Before you begin, make an educated guess air warms up about the outcome of this experiment based on your knowledge of air density. This educated heat source guess, or prediction, is your hypothesis. A hypothesis should explain these things: GAL E GR OU P.
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WORDS TO KNOW Air: Gaseous mixture that covers Earth, composed mainly of nitrogen (about 78%) and oxygen (about 21%) with lesser amounts of argon, carbon dioxide, and other gases. Air density: The ratio of the mass of a substance to the volume it occupies. Air mass: A large body of air that has similar characteristics. Air pressure: The force exerted by the weight of the atmosphere above a point on or above Earth’s surface.
the variable that acts on the experimental group. Convection currents: Circular movement of a gas in response to alternating heating and cooling. Front: The area between air masses of different temperatures or densities. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Atmosphere: Layers of air that surround Earth.
Meteorologists: Professionals who study Earth’s atmosphere and its phenomena, including weather and weather forecasting.
Barometer: An instrument for measuring atmospheric pressure, used especially in weather forecasting.
Troposphere: The lowest layer of Earth’s atmosphere, ranging to an altitude of about 9 miles (15 km) above Earth’s surface.
Control experiment: A setup that is identical to the experiment, but is not affected by
Variable: Something that can affect the results of an experiment.
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘As the air gets warmer and less dense it will cause the the balloon to get larger; as the air gets cooler and less dense it will cause the balloon to get smaller.’’ In this case, the variable you will change is the temperature of the air inside the bottle by warming and cooling the outside of the bottle. The variable you will measure is the balloon’s circumference. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • thickness of the plastic bottles
change between the control and the experimental trials. Your control experiment will not heat or cool the air in the bottles. Level of Difficulty Easy. Materials Needed
• • • •
2 rubber balloons ice hot water 2 plastic bottles, such as plastic soda bottles • 2 containers that go at least midway up the sides of the bottles (one should be heatproof)
• material the balloons are made from In other words, the variables in this experiment are everything that might affect the density of the air. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on air density.
Approximate Budget $2. Steps 3 and 4: Heat causes the air in the bottle to warm; ice causes the air in the bottle to cool. GA LE GRO UP.
Timetable 15 minutes. Step-by-Step Instructions
1. Place a balloon over the mouth of each plastic bottle. Leave one bottle out as your control. 2. Fill up one container with very hot water. Fill up the other container with a little ice and some cold water. 3. Place the experimental bottle in the container of cold water and hold it there for roughly one minute. (Another option is to place the bottle in a freezer for one minute.) Note the size of the balloon compared to the control balloon. 4. Place the experimental bottle in the container of hot water for one minute. (Another option is to carefully hold the bottle under running hot tap water.) Note the size of the balloon compared to the control balloon. 38
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5. Again, place the experimental bottle in the pan of cold water and hold for 30 seconds. Summary of Results Examine how much the
How to Experiment Safely Have an adult present when working with the hot water.
balloon grew or shrunk in your experiment. Was your hypothesis correct? How did the size of the experimental balloon compare to the control balloon? Did the experimental balloon shrink more or at a different rate the second time you placed it in the cold water? Draw a picture of the results of your experiment and write a brief summary.
EXPERIMENT 2 Convection Currents: How can rising air cause weather changes? Purpose/Hypothesis Convection currents occur as rising gas carries heat
upward and the cooler gas is brought downward. In the atmosphere, convection currents rise above warm areas on Earth’s surface. These rising air currents produce differences in air pressure, which cause changes in the weather. Small convection currents can produce winds and rain. Larger convection currents can cause severe thunderstorms and hurricanes. When convection occurs in an enclosed container, the currents help distribute the heat Troubleshooter’s Guide throughout the container. The entire process is Below is a problem that may arise during this driven by the differences in air density. In this experiment, some possible causes, and some experiment, you will create a convection current ways to remedy the problems. in a closed container and look at the air’s actions. Problem: Nothing happened to the balloon. You will cool the air in one glass jar and warm the Possible cause: Your water may not have been air in another. Visible smoke from an incense hot or cold enough. You may also not given stick will go into the warm jar. Then you will enough time to allow the air temperature to observe what occurs to the movements of the change. Try the experiment again, placing smoke. your bottles deeper into the hot and cold Before you begin, make an educated guess water. about the outcome of this experiment based on Possible cause: Your balloon may have a slight your knowledge of air convection. This educated leak. Try the experiment again with a new balloon. guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test • The amount of smoke through further investigation. Your experiment • The temperature of the warm air will prove or disprove whether your hypothesis is • The temperature of the cold air correct. Here is one possible hypothesis for this experiment: ‘‘Air in the warmer container will In other words, the variables in this experiment rise, pushing the cold air above it downward, and are everything that might affect the movement of the smoke. If you change more than one creating movement of the smoke.’’ variable at the same time, you will not be able to In this case, the variable you will change is tell which variable had the most effect on the the temperature of the air in the glass jar. The convection currents. variable you will measure is the visible movement of the smoke. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental trial. Your control experiment will use jars that have not been heated or cooled. Level of Difficulty Easy/Moderate (the experiment is simple, but working
with burning incense increases the difficulty level). Materials Needed
• four glass jars of equal size with equal-sized openings (mayonnaise jars work well; you do not need the lids) • incense stick (do not use smokeless incense) • matches • small piece of thick paper (big enough to cover the opening of the jars) • lamp with at least a 100-watt bulb • black piece of paper or cardstock about the size of the jars • access to freezer or cold-water bath Approximate Budget $5. Timetable 20 minutes. 40
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Step-by-Step Instructions
1. Place one jar in the freezer or cold-water How to Experiment Safely bath for about five minutes. Ask an adult for help with lighting the match. 2. While the first jar is cooling, run hot Make sure an adult is present when you burn water over the outside of the second jar. the incense. Always wet the match and any 3. When about three minutes have passed, leftover incense before you throw them away. turn on the lamp and position the warm jar upside down in front it. Fold the black paper in half and lean it closely against the side of the jar opposite the lamp to help heat the air. 4. After five minutes, take the jar out of the freezer or cold-water bath and have the small piece of thick paper nearby. (You may need to wipe off the outside of the jar so that you can see inside it.) 5. Light the stick of incense, lift up the warm jar (with the opening still facing downward), and hold the burning incense underneath the opening of the warm jar. The incense stick should give off Step 6: Turn the warm jar right black smoke. Blow out the incense stick and capture any remainside up while you hold the thick paper in place. Turn the cold ing black smoke inside the warm jar. jar upside down and set it 6. Quickly place the small piece of thick paper firmly over the directly on top of the warm jar opening in the warm jar to hold the smoke inside. Turn the so their openings line up exactly warm jar right side up while you hold the thick paper in place. and the thick piece of paper is Turn the cold jar upside down and set it directly on top of the between them. GA LE G RO UP. warm jar so their openings line up exactly and the thick piece of paper is between them. 7. Lift the cold jar slightly and pull the paper out from between the jars. Observe what happens to the smoke. 8. For the control experiment, repeat Steps 5 through 7 with two room-temperature glass jars. Note the results. Summary of Results Was your hypothesis correct? Compare the results between the movement in the air of the control jars and the cold and warm jars. Use arrows to draw what was happening to both the cold and warm air in the jars. What do you hypothesize would occur if the Experiment Central, 2nd edition
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
cold jar was placed on the bottom and the warm jar was placed on top of it. Write a brief description of how air of different temperatures causes weather change. Modify the Experiment You can experiment
with convection currents in air without matches in a simple test that illustrates the principles Possible cause: You may have used a smokeless behind hot air balloons. You will need at least incense stick. Try purchasing another type two black balloons, string, and a hot, sunny day. and repeating the experiment. Blow up both balloons about half way. Knot the balloons and tie a piece of string about 4 feet (1.2 meters) long to the knot. Place one balloon in a basement or air conditioned room where the air is cool. Place the second balloon outside in the sun and tie the string to something on the ground. Make a note whether both balloons lie on the ground. Leave the balloons alone for several hours. Look at the balloon outside. Is it still on the ground? It will rise if the air inside the balloon is lighter than the surrounding air. Untie the outside balloon and place it next to the balloon that is sitting in the cool room. What happens? Does the balloon with the warmer air rise? Observe the two balloons for several minutes, as the hot air balloon cools. You can try the experiment again with varying size balloons or at higher outside temperatures. Problem: No black smoke was visible.
Design Your Own Experiment How to Select a Topic Relating to this Concept Whenever you step
outside you are feeling the effects of air’s properties and movement. Consider what types of weather-related topics are of interest to you. Watch the weather forecast carefully and write down what terms and pictures look interesting to you. Check the Further Readings section and talk with your science teacher to learn more about air properties and weather. As you consider possible experiments, make sure to discuss them with your science teacher or another adult before trying them. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be 42
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sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In
any experiment you conduct, you should look for ways to clearly convey your data. You can do this by including charts and graphs for the experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. You might decide to conduct an experiment that lasts several months. In this case, include pictures or drawings of the results taken at regular intervals. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings.
The less-dense hot air in a hot air balloon allows it to rise high above the ground. # DU OM O/ COR BI S.
Related Projects There are many related projects you can undertake
related to air and the weather. Because air is not visible to the naked eye, there are instruments that enable people to ‘‘see’’ how the air reacts. To explore air temperature, you could make a radiometer, an instrument that uses reflection and absorption to measure the sun’s rays. A radiometer will allow you to see how the sun’s energy causes the warm air to move. You could also make a barometer to measure air pressure. By Experiment Central, 2nd edition
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watching changes in the barometer, you can observe how varying air pressures result in changes in the weather. To further explore convection, you can make a convection box as another way to see how air currents with clashing temperatures act. The cyclical process of convection currents also occurs in liquids, which follow the same density rules as gases. Warm water, less dense than cold water, rises to the surface as the cooler water sinks to the bottom. The results cause currents in the water. You can examine convection currents in bodies of water by adding drops of different food colorings to the hot and cold water.
For More Information ‘‘Atmospheric science resources.’’ USA Today. December 19, 2001. http:// www.usatoday.com/weather/wworks0.htm#pressure (accessed February 26, 2008). Graphics and clear text that explains various weather phenomena. Elsom, Derek. Weather Explained. New York: Henry Holt and Company, 1997. From basic weather and air questions to weather extremes, this book answers how weather forms, with lots of colorful pictures. Met Office. Secondary Students. http://www.metoffice.gov.uk/education/ secondary/students/index.html (accessed February 26, 2008). Information on weather topics, including air masses and fronts. Wright, David. ‘‘How Much Does the Sky Weigh?’’ Chain Reaction. http:// chainreaction.asu.edu/weather/digin/wright.htm (accessed February 26, 2008). Article on air and its pressure with ideas for experiments.
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Air and Water Pollution
A
ir or water that is contaminated with impurities is described as polluted. The contamination is the pollution. Directly or indirectly, the overwhelming majority of pollution results from human activity, yet nature can also release pollutants. Pollution usually is in the form of gas, liquid, and solid materials; it results from anything that alters the natural environment, such as a temperature shift and noise. Air and water pollution has become a significant problem since the growth of cities, industry, and travel in the late nineteenth century. All life on Earth depends on air and water to live and grow. Pollution of these substances harms and destroys plants, animals, and microscopic organisms. It causes health problems and death in humans. Pollution upsets the natural cycles on which all life depends, causing a ripple effect that can harm organisms hundreds of miles away from the pollutant. For example, pollutants in a body of water can harm the sea life and poison the plants that depend on the water. In turn, surrounding animals that depend on the plants for food and shelter, such as birds, will need to either move to another location or die. Water and air pollution also destroy Earth’s natural beauty.
What you can’t see . . . Air is essential for life on Earth. It provides oxygen for animals and carbon dioxide for plants. It encircles Earth to form its atmosphere, protecting the planet against harmful rays and causing its weather. Air pollution comes in the form of gases—such as nitrogen dioxide, sulfur dioxide, and carbon monoxide—as well as solid and liquid particles called particulate matter. Measuring about 0.0001 inch (0.0025 millimeters, also called 2.5 microns) in diameter, particulate matter is small enough to be suspended, or float, in the air. There are several major categories of air pollution produced by humans. Pollutants include the gases nitrogen dioxide, sulfur dioxide, and carbon monoxide, along with lead pollution and particulate matter. 45
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Gases: In most industrial nations the majority of air pollution comes from the automobile. The exhaust in cars and trucks releases carbon monoxide, carbon dioxide, nitrogen oxides, and clean water allows sulfur dioxide. Automobiles, especially diesel fish to thrive animals have adequate vehicles, also release smoke particles. The burning food supply of fossil fuels—such as gas, oil, and coal—is also a major source of air pollution. Power plants that burn coal and oil release nitrogen oxides, sulfur oxides, carbon dioxide, and particles. Various industrial processes also produce large amounts Clean air and water support a of these pollutants. healthy life cycle for all Scientists generally agree that the greenhouse effect, also called global organisms. GA LE GRO UP. warming, comes from the buildup of carbon dioxide, methane, and other gases in the atmosphere. The increased levels of carbon dioxide and other greenhouse gases trap heat close to Earth, resulting in an overall increase in temperature. This warmer climate could produce extreme weather events, such as droughts and floods, raise the sea level, and alter the life populations. Another planetwide effect of air pollution is the breakdown of the layer of air in Earth’s upper atmosphere. The upper atmosphere protects people and animals from dangerous ultraviolet rays produced by the Sun. In humans, exposure to ultraviolet rays is linked to skin cancer and harm to the immune system. Chlorofluorocarbon (CFC) gases are one of the main pollutants that bore holes in Earth’s upper atmosphere. Air and water pollutants can Lead: Lead is a toxic or lethal metal that was once a common affect a wide variety of component of gasoline, paints, and various industrial processes. surrounding life. GA LE Unleaded gasoline and paint, along with improvements in industrial GR OU P. processes, have brought about a decrease in the release of lead in the air. Especially harmful to young children, lead can slow down mental air pollutants oil development, and can harm the kidneys, liver, nervous system, and other organs. chemicals, heat, metals Particulates: Particulate matter varies in size. No food supply for animals Larger particles settle near their source after a few Fish can't live in this water minutes in the air; small particles can remain in the air for several days and spread over a wide area. Particles that are especially small can cause health problems in humans and animals. 46
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sunlight enters atmosphere, heating the Earth greenhouse gases cause some of the heat to be trapped
carbon dioxide an d
ot h er
heat is reflected back into the atmosphere Carbon dioxide and other gases trap heat close to Earth, causing a warming in Earth’s climate. GA LE G RO UP.
Particles enter the respiratory system and penetrate deeply into the lungs. Brief exposure can result in symptoms ranging from coughing to a sore throat. Long-term exposure can cause asthma In a thermal inversion, a layer and congestion. of warm air traps the cool air Suspended particles in the atmosphere are seen as dust, smoke, soot, close to Earth. When this and haze. These particles can also cause smog. Smog is a type of large-scale happens the polluted air cannot rise and disperse into the outdoor pollution caused by reactions between strong sunlight and differatmosphere, causing pollution ent pollutants, primarily automobile exhaust and to build up to dangerous levels. industrial emissions. Smog appears as a haze over GAL E GR OU P. wide areas. Smog often worsens in warm temperatures when a thermal inversion can occur. In a thermal inversion, a layer of warm air traps the cool air warm air close to Earth. When this happens the polluted air cannot rise and disperse into the atmosphere. The cooler polluted air pollution can build up to dangerous levels. In 1952, thermal inversion caused a London smog that killed over four thousand people. In the United States, Los Angeles, California, is the city most profoundly affected by smog, according to a 2009 American Lung Association report. Experiment Central, 2nd edition
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Pollutants from nature Air inside homes can also become polluted. Trapped in an enclosed area, indoor pollution can cause people serious health problems because of the large amount of time people spend indoors. Cigarette smoke, cooking and heating appliances, paints, and some cleaning products are all possible sources of indoor pollution. Radon, an odorless natural gas released from the ground, is another possible pollutant. Radon can enter buildings through cracks and can seep into basements of homes. Lung cancer is one health effect of radon. Radon is an example of a natural pollutant. Other types of naturally occurring pollutants include erupting volcanoes, which produce large amounts of sulfur oxides and particulate matter. Some microorganisms that break down plant material also release methane gas, a contributor to the greenhouse effect. Among the places these microorganisms live is in cows’ stomachs to help with their digestion. When the cows belch, methane gas gets released. Smog appears as a haze over large areas. Here, the skyline of New York City is wrapped in a veil of smog. NA TIO NA L AR CH IVE S AN D RE CO RD S ADM IN IS TRA TI ON.
Sickly water About 70% of Earth is covered by the ocean, which makes up almost all the water on the planet. All life on Earth needs water to survive. Oceans, rivers, lakes, and other bodies of water hold a rich diversity of animal, plant, and microscopic life that organisms in both the water and on land depend upon to live. Oil, pesticides, fertilizers, litter, wastes, heat, and toxic chemicals are several major sources of water pollution. Polluted water kills sea life and causes disease in humans. Oils: While oil spills from cargo ships make headline news, these accidents make up only a fraction of the oil released into the oceans. The majority of oil in North American waters comes from industry and road runoff, along with boating. Other sources of oil pollution include drilling, shipping, and improper disposal of oil waste. Oils are also released naturally from eroding rocks at the bottom of the ocean.
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The impact of oil on marine life depends upon the amount of oil, where it is located, and the amount of toxic chemicals in the oil. Oils spills form a visible film on the water called an oil slick. Oil in a slick sticks to birds, fish, and plants, blocking their breathing and possibly causing death. The reduced food supply can have a long-term impact for whole ecosystems. Oils also wash up on beaches and other human recreational areas. Researchers are working to discover how the steady, relatively small release of oil affects ocean and human life. Chemicals: Chemical water pollutants are substances not naturally occurring in the waters. Industrial compounds, such as sulfur and nitrogen oxides, along with herbicides and pesticides are common chemicals released into the waters. Rainwater can carry chemicals from the land into waterways. Heavy metals, such as copper, lead, and mercury, enter the water from industries, automobile exhaust, mines, and even natural soil. Heat: When hot water is poured into a cooler body of water it is called thermal pollution. All life forms have a range of temperature in which they can live. If the water temperature is outside of that range it will upset and kill organisms. Thermal pollution is common near factories and power plants, where water is heated to high temperatures. Although the water is cooled before it is added to natural bodies of water, it often remains hotter than the natural water. Thermal pollution is also caused by the removal of trees and vegetation that shade bodies of waters.
An oil-soaked bird washes up on a beach in northern Spain in November 2002, after a tanker leaked 3,000 tons of oil off the western coast of Spain before eventually sinking. A P/W ID E WOR LD
Natural substances: Upsetting the balance of nutrients can also pollute the waters in a process called eutrophication. Nitrates and phosphates are natural nutrients that plants such as algae use for growth. Fertilizers and untreated sewage can contain many of these nutrients. Rain washes the nutrients into bodies of water where they accumulate and stimulate algae growth. The algae grow more rapidly than fish can eat them, causing two major effects. When the algae die it causes decomposing organisms to thrive, depleting the water of oxygen. The lack of oxygen causes fish and surrounding plants to die. Also, the abundance of algae Experiment Central, 2nd edition
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sunlight passes through water
plants produce oxygen that sea life need to live
sunlight cannot pass through water
overgrowth of algae causes depletion of oxygen
clog the waters and block sunlight for the plants underneath. These plants, which provide food and shelter for sea life, then die. Solid matter: Along with blemishing water’s natural beauty, litter can significantly harm sea life. Litter is often made of plastic, which takes hundreds of years to break down. Birds and fishes can mistake such litter for food. When enough litter is consumed, the animal’s intestines become blocked and it dies. Plastic bags can also suffocate small sea life. Plastic fishing lines and other debris can entangle seabirds and other life. Some estimates put the number of plastic-related deaths at two million seabirds and 100,000 marine mammals each year.
sea life cannot live in water
The process of eutrophication depletes the water of oxygen and blocks needed sunlight, causing fish and plant life to die. GA LE GRO UP.
Pollution prevention In the mid-to-late 1900s, the U.S. government began to enact regulations on pollutants that have helped clear much of the waters and air. In 1970 the Clean Air Act established standards for air quality and emissions. The act required automobile manufacturers to produce cars that use unleaded fuel, which has reduced pollutants, and to install pollution-control devices on the exhaust. Factories, incinerators, and power plants were also required to install pollution-control mechanisms. In the 1970s the Safe Water Drinking Act and the Clean Water Act were enacted. These acts set water standards for public water systems and established regulations for the discharge of pollutants into waters. Other governments also have enacted regulations against releasing pollutants. Companies have developed improved methods to clean up pollution, such as a genetically modified type of bacteria that eats oil from oil spills. As almost all pollutants are the result of human activity, there are multiple ways that individuals can help reduce pollutants. Producing less garbage by recycling, not littering, avoiding disposing of oil or oilrelated products down the drain, and driving less and using a car that conserves fuel are a few ways that one person can reduce air and water pollutants.
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WORDS TO KNOW Control experiment: A setup that is identical to the experiment, but is not affected by the variable that affects the experimental group. Eutrophication: The process by which high nutrient concentrations in a body of water eventually cause the natural wildlife to die. Greenhouse effect: The warming of Earth’s atmosphere due to water vapor, carbon dioxide, and other gases in the atmosphere that trap heat radiated from Earth’s surface.
Radon: A radioactive gas located in the ground; invisible and odorless, radon is a health hazard when it accumulates to high levels inside homes and other structures where it is breathed. Smog: A form of air pollution produced when moisture in the air combines and reacts with the products of fossil fuel combustion. Smog is characterized by hazy skies and a tendency to cause respiratory problems among humans.
Hypothesis: An idea in the form of a statement that can be tested.
Thermal inversion: A region in which the warmer air lies above the colder air; can cause smog to worsen.
Particulate matter: Solid matter in the form of tiny particles in the atmosphere. (Pronounced parTIK-you-let.)
Thermal pollution: The discharge of heated water from industrial processes that can kill or injure water life.
Pollution: The contamination of the natural environment, usually through human activity.
Variable: Something that can affect the results of an experiment.
EXPERIMENT 1 Pollutant Bioindicators: Can lichens provide clues to an area’s air pollution? Purpose/Hypothesis Lichens are organisms that are extremely sensitive to
air pollution. These life forms are actually two types of organisms living in partnership: fungi and either a green algae or a blue-green bacterium. Lichens grow on rocks, buildings, and on trees. These organisms receive virtually all their water and nutrients from the air. Lichens are especially sensitive to certain air pollutants, such as sulfur dioxide. When lichens are exposed to these pollutants they will die. Automobile emissions and some industrial processes can produce these pollutants. Because of this, scientists use lichens as indicators of pollution, or bioindicators. The quantity, diversity, and colors of the lichens all provide evidence of the area’s pollutants. These organisms are colored red, orange, yellow, gray, black, brown, and green. When lichens are affected by pollutants, they turn from their usual color and can peel away from the surface they Experiment Central, 2nd edition
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crustose
foliose
fruticose
There are three main types of lichens. GAL E GR OU P.
live on. There are three main types of lichens: Fruticose lichens look like miniature 1-inch (25-mm) tall shrubs or lettuce leaves and hang from branches; foliose lichens appear like flat leafs; and crustose lichens sit closely to their surface and appear crustlike. The crustose lichens are the most resistant to air pollution, and are often seen in cites. Fruticose lichens are the most sensitive to pollutants. In this experiment you will measure an area’s air pollution by using lichens as the bioindicator. You will choose three different areas and randomly select three trees of similar sizes in each area. You may need to look at pictures of the different types of lichens before you begin. By placing a transparent grid over the tree you can count the amount and type of lichens covering each tree. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of air pollution and lichens. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘There will be fewer and less diversity in the lichens living near high traffic and/or industrial areas than the lichens in more remote areas.’’ 52
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In this case, the variable you will change is the location. The variable you will measure is the quantity and type of lichens. Level of Difficulty Moderate. Materials Needed
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the location
• three locations (sites) of different environments; all should have trees (example: a city street, in a park, near a school parking lot) • trees in each area, of the same or similar species (kinds) • magnifying glass • ball of string or twine • tape measure • transparent piece of grid paper (11 inch squares work well, or slightly larger squares) • marking pen • partner (optional but helpful)
• types of trees • the size of trees In other words, the variables in this experiment are everything that might affect the growth of lichens. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on inhibiting lichen growth.
Approximate Budget $5. Timetable 2.5 hours (including travel time). Step-by-Step Instructions
1. Create a chart for each area, listing ‘‘Tree 1,’’ ‘‘Tree 2,’’ and ‘‘Tree 3’’ across the top columns. Label the rows: ‘‘Fruticose,’’ ‘‘Foliose,’’ ‘‘Crustose,’’ ‘‘Bark,’’ and ‘‘Other.’’ 2. Choose a tree at random in the first area of study. The tree should have lichen growing on it. Circle the string around the trunk at a height that you can comfortably observe, such as 3 feet How to Experiment Safely (0.9 meters). 3. Tie a knot in the string and cut. Mark the If studying trees near the road, be careful of string with a 1 or one mark. traffic. Try to conduct your experiment during a 4. Starting at the marked line, place the low-traffic time of the week and day; and ask an transparency directly below the string. adult to accompany you to a high-traffic area. Count and note the squares covered by Experiment Central, 2nd edition
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: All the lichen looked the same. Possible cause: It is possible that much of the lichen was the same, especially if the sites were close to one another. To categorize lichens it is also helpful to refer to reference material. If possible, take a book out of the library with pictures of the different types of lichen and repeat the experiment, using the photographs as a guide.
each group of lichens, bare bark, and other life forms, such as moss. You may want to use the magnifying glass. Have your partner write down the results for each grid. Continue this along the tree until you have made a complete circle. Repeat the process above the string. 5. Add up the numbers of squares covered by each lichen, bark, and any other growth and then note those numbers on the chart. 6. Also note the color of the lichens on the chart.
7. Repeat this process with two more randomly chosen trees nearby at the same site. For each tree, tie a fresh piece of string at the same height. Mark the second string with a 2 or two marks and the third tree with a 3 or three marks.
Step 4: Count the squares that each type of lichen, plain bark, and other life form(s) takes up on the tree. GA LE GRO UP.
8. At the second site, use the three pieces of string that are marked. Try to measure three trees that have roughly the same circumference as each of the trees at the first site. Again, note the types of lichens and the number of squares each fills. 9. Repeat the process at the third site, choosing three trees randomly that are roughly the same diameter. Summary of Results Calculate the average num-
bers for each site. Use the averages of your data to create a graph of the three sites. How do the numbers of lichens compare between the sites? Is your hypothesis correct? For the same type of lichens, is there a difference in their colors? Determine if there was one dominant type of lichen in each area. How does that dominant type compare to the lichens in the other two areas? Examine the possible pollutants in each area. Write a brief summary of your findings and analysis. 54
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Change the Variables To change the variables in this experiment you can
focus on one location and measure the lichens on different trees. You can focus on specific parts of the trees also, such as a shady or sunny section. You can also concentrate your research on different pollutants, such as automobile exhaust and industrial processes. You can then find areas where you observe each pollutant occurring, and determine its effect on the lichen.
EXPERIMENT 2 Eutrophication: The effect of phosphates on water plants. Purpose/Hypothesis Phosphorus is a vital nutrient that both plants and
people need. Plants use phosphorus for converting sunlight into energy, cell growth, and reproduction. Organisms usually take in phosphorous in the form of phosphate, a phosphorous compound. Because they promote plant growth, phosphates are one of the nutrients in many agricultural and garden fertilizers. Many dishwasher detergents add phosphates to reduce spotting on glasses and dishes. Laundry detergents can contain phosphates to soften the water. In this experiment, you will explore how an excess of phosphates can affect life in lakes, streams, and oceans. When too many nutrients accumulate in a body of water, it can spark eutrophication. This process begins with the growth of algae. Algae are simple water plants that are found near the surface of waters. There are many types of algae, and sea life depends upon them for food. In waters, phosphorous is naturally present in low concentrations, as algae require only small amounts of it to live. In this experiment you will add phosphates to healthy water plants that are living in water with a natural amount of algae. You will add two different concentrations of the phosphate and then observe their effect on the plant. By observing the water plants daily you will be able to determine the effect of the phosphate. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of water pollution and eutrophication. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Experiment Central, 2nd edition
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A hypothesis should be brief, specific, and measurable. It must be something you can test What Are the Variables? through further investigation. Your experiment will prove or disprove whether your hypothesis is Variables are anything that might affect the correct. Here is one possible hypothesis for this results of an experiment. Here are the main variables in this experiment: experiment: ‘‘Water with the highest concentrations of phosphates will cause the algae to clog • the type of plant the waters and cause the plants to die.’’ • the soap In this case, the variable you will change is the • the quantity of soap amount of phosphate added to the water. The • the environmental conditions (sunlight, variable you will measure is the plant’s health. air temperature, water temperature, etc.) To measure the plants health you can observe its In other words, the variables in this experiment height, color, root structure, and leaves. are everything that might affect the growth of Conducting a control experiment will help the plants. If you change more than one variayou isolate each variable and measure the ble at the same time, you will not be able to tell which variable had the most effect on how the changes in the dependent variable. Only one algae affected the plants’ health. variable will change between the control and the experimental setup, and that is the amount of phosphate-soap added to the water. The control in this experiment will be to add no additive to the plant’s water. Note: When making a solid/liquid solution, it is standard to use weight/weight (grams/grams) or weight/volume (grams/milliliters). With water, 1 gram of water equals 1 milliliter. In this experiment, teaspoons and tablespoons are used to measure the solid. Level of Difficulty Easy. Materials Needed
• three small water plants of the same type with roots; elodea work well (available at pet shops) • pond water (preferred) or water that plants were living in: collect enough to fill each of the jars about three-quarters full • three glass jars, large enough to hold plants • detergent with high phosphate content (preferably, a detergent with 7% or higher phosphate content) • masking tape • marking pen • measuring spoons 56
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Approximate Budget $8. Timetable 20 minutes to set up; five minutes
daily for about 10 days.
How to Experiment Safely There are no safety hazards in this experiment.
Step-by-Step Instructions
1. Label the jars ‘‘High Phosphate,’’ ‘‘Low Phosphate,’’ and ‘‘Control.’’ Fill each jar with the pond water. 2. Create a chart with ‘‘Day 1,’’ ‘‘Day 5,’’ and ‘‘Day 10’’ written across the top and the jar labels written down the side. 3. Measure out 1 tablespoon of the detergent and mix into the High Phosphate water. 4. Measure out 1 teaspoon of the detergent and mix into the Low Phosphate water. 5. Place one of the plants in each of the three jars. Do not add detergent to the Control jar. 6. Fill in the physical description of the plant and water for Day 1 on the chart. 7. Place the three jars in the same sunny location. 8. Observe each plant’s health and its water daily for about 10 days (time will vary depending on the amount of algae in the control water and the amount of sun). 9. On Day 5 and Day 10, note in a chart the color of the water for each jar and any physical properties of the plant. Summary of Results Examine the results of your data chart. Hypothesize
Measure the water color and
plant health at Day 1, Day 5, how phosphates would have different effects in shallow and slow-moving and Day 10. GAL E GR OU P. waters compared to that of deep and flowing waters. In which types of water would sea life be the most in danger? Many states now limit the use of phosphates in their detergents. You can research if your state has regulations on phosphate usage and calculate how those amounts compare to the amount used in your experiment. high phosphate low phosphate control
Change the Variables There are several ways that you can alter this experiment. Try using different brands of detergent, either dishwashing or laundry. You can use the same amount of Experiment Central, 2nd edition
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The water in the experiment jars remained the same as the Control.
detergent in the water and place the jars in varying environments, by placing them in a hot- or cold-water bath (you will have to change it daily). Will a cool, sunny environment stimulate algae growth more than a warm, sunny environment? You can also change the type of water plant that you use.
Modify the Experiment This experiment measures how water pollution can harm sea life. You can make this experiment more challenging by experiment with methods of cleaning up water pollution and the affected sea life. Possible cause: Algae grow best in a sunny The water pollution you used in this experienvironment. It also might look like nothing ment dissolved in water. For you to better see and is growing when they will suddenly bloom. test cleaning water pollution, you can pollute the Make sure the jars are in a sunny window and water with oil. Pluck several leaves from the water continue your observations. plants and place them in a container of water. You may want to add other plant life to each container, such as grasses, along with feathers. Pour about a quarter-cup of oil into the container, and gently move it back and forth several times. Collect cotton cloth, string, paper towels, tubing, straws, and liquid soap. Try to remove as much oil as you can with the tools you have collected. Tubing can contain the oil; cloth can absorb it; straws can pull it up, and string can collect it. You may need to conduct several tests before you find a technique that you find effective. When you have cleaned up the pollution as best you can, carefully remove the ‘‘organisms’’ and note how each is affected by the oil. What happens if you gently rub drops of soap on the sea life? Experiment with methods of removing the pollution from the organisms. Could the same techniques be practiced on actual organisms? Consider how soap may affect sea plants, birds, and animals.
Possible cause: You may not have collected enough algae to foster growth. Try to find a pond in your area or use water from another shop. Repeat the experiment with this new water.
Design Your Own Experiment How to Select a Topic Relating to this Concept Air and water pollution is
all around, no matter what your location. To think of a topic, you can first observe the pollution in the waters, cities, and roadways. Think about methods of measuring the air and water pollution. Check the Further Readings section and talk with your science teacher to learn 58
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more about air pollution. You may also want to explore any companies in your area that measure pollutants. Steps in the Scientific Method To conduct an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Projects related to air and water pollution include
examining their effect on organisms. You can visit a lake or stream in your area and collect water samples to determine its pollutants, then compare that to its plant and animal life. You can collect samples of particulate matter in the air by hanging papers smeared with petroleum jelly. After collecting the data, you can compare the test sites to the animal and plant life in the area. For a research project, you could examine how pollutants affect people’s health and determine if those health problems are correlated to locations with high levels of pollution. Other projects include examining methods that scientists have developed to clean up pollutants. Taking a look at pollution around the world and its impact is another area of exploration. Experiment Central, 2nd edition
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For More Information ‘‘Loveable Lichens.’’ Earthlife. http://www.earthlife.net/lichens/intro.html (accessed on March 19, 2008) Photos and information on all types of lichens. Macmillian Encyclopedia of Science: The Environment. New York: Macmillan Publishing USA, 1997. Covers all aspects of our environment and how pollution affects it. Spilsbury, Louise. Environment at Risk: The Effects of Pollution. Chicago: Raintree, 2006. Information and case studies of the effects of pollution. ‘‘Students and Teachers.’’ NOAA’s Office of Response and Restoration. response.restoration.noaa.gov/kids/kids.html (accessed on March 19, 2008) Information and activities on oil spills. U.S. Environmental Protection Agency. ‘‘Air.’’ EPA Student Center. http:// www.epa.gov/students/air.htm (accessed on March 19, 2008) A comprehensive web site with links and information on a wide range of environmental issues including air pollution, air quality standards, and more.
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Animal Defenses
I
f you’ve ever smelled the odor of a skunk or been hissed at by a cat, you’ve experienced an animal defense. Animals have developed a lot of clever defenses to protect them from harm. When attacked by a predator, an animal can run away or fight. Some types of defenses protect the animal from ever being seen by predators (the attacking animal). Other defenses defend the animal when it is attacked.
Playing dead In general, meat-eating animals don’t like to eat animals that they find dead. An animal that is dead could be carrying disease and cause illness. The opossum uses this instinct as a defensive strategy. When threatened or wanting to avoid an attack, the opossum can fall down and play dead. Its tongue rolls out, eyes become glazed and it releases a foul odor. The predator might sniff or poke the opossum but it lies completely still. After the would-be predator leaves, the opossum returns to ‘‘life.’’ Several types of snakes also use the play–dead defense. Blending into the scene One way to avoid danger is to avoid being spotted by a predator. Camouflage is the markings or colors that blend in to the environment. Most animals exhibit some type of camouflage and ‘‘blending in’’ is a common animal defense. The green color of many insects matches leaves; the brown earth tones of deer, squirrels, and other woodland animals matches the woods colors; the patterns and stripes of animals, such as a zebra, break up the animal’s shape so a predator does not identify it. Many insects, mammals, and birds have colors or patterns that match the natural environment so well they are hard to spot, even when you know they are there. At night, the colorful parrot fish covers itself with a dark substance that it makes while breathing. The protective coat shields the parrot fish from its predators. The skin of mossy frogs has the same colors, bumps, and texture as the moss that they live in. A leaf frog features bumps over its eyes and a pointed nose, taking on the color 61
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WORDS TO KNOW Camouflage: A coating that allows an animal to blend in to its surrounding environment.
Mimicry: A characteristic in which an animal is protected against predators by resembling another, more distasteful animal.
Ecosystem: An ecological community, including plants, animals and microorganisms, considered together with their environment.
Predator: An animal that hunts another animal for food.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Variable: Something that can affect the results of an experiment.
and shape of a leaf. The walking stick insect can easily be mistaken for a twig from its appearance and its stillness.
The skunk can omit a strong, foul odor when in danger. AP PH OT O/P HI L CO AL E.
In camouflage, an animal appears as something in its environment. When animals appear as another, more-dangerous or inedible animal, it is called mimicry. Often one type of animal will take on the appearance of a poisonous, similar animal. There are butterflies in the Amazon that take on the appearance of poisonous butterflies. Several species of harmless snakes have the bright red, yellow, and black strips as the venomous (poisonous) coral snake. Some animals simply don’t want to have predators think they taste good. A type of butterfly in Brazil has developed the appearance of another butterfly species that tastes foul. There are also animals that can mimic the appearance of animals that are different species. Several types of jumping spiders mimic ants. One of these spiders is the same size, shape, and color as a weaver ant, which has a sharp bite and painful venom. The mimic octopus gets its nickname from its ability to take on the appearance of several venomous ocean creatures, including a lionfish and sea snake. The smell that scares When an animal is struck with a bad odor, it is usually not going to enjoy eating. After a skunk has tried to scare or move away from a threat, it defends itself with a
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smelly spray. The odor is so strong and foul it can cause nausea. The skunk will often aim for the face of the predator because the spray can also sting. Weasels, bedbugs, and snakes are other animals that use foul odors to ward off predators. Wild and strange defenses There are many other defense strategies animals have evolved. The horned lizards are ant-eating lizards in North America. When attacked or threatened, the lizard shoots blood out of the tear ducts in its eyes. The blood contains substances that make it foul tasting. Having an imposing look is the defense strategy for several animals, including the puffer fish. When the puffer fish is threatened, it can increase up to three times its size by gulping water. The electric eel is one of several animals that defends itself with a jolt of electricity when a predator attacks. Octopi and cuttlefish are just two marine animals that squirt out a black ink for defense.
PROJECT 1 Camouflage: Does an animal’s living environment relate to the color of the animal life?
The electric eel uses a jolt of electricity when a predator attacks. G EOR GE GRA LL . NAT IO NAL GEO GR APH IC , GET TY I MA GES .
Purpose/Hypothesis How an animal defends itself is strongly influenced by its living environment. A wide variety of animals use camouflage as a form of defense. The purpose of this project is to observe the camouflage that small animals use in one isolated outside environment. The area you choose could be the bark of a tree, a grassy patch, leaves, or a stretch of dirt. You will record the animal colors living in that particular environment. You will then compare the percentage of animals living in the first environment to animals living in another type of habitat.
Depending upon the environment, common animals you can look for include butterflies, stick insects, moths, beetles, grasshoppers, frogs, rabbits, squirrels, and crickets. Experiment Central, 2nd edition
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Level of Difficulty Moderate. (This project requires careful observation and patience.) Materials Needed
• • • •
camera (optional) magnifying glass (optional) paper and pencil a nice day
Approximate Budget $0. A wide variety of animals use camouflage as a form of defense. I LL UST RA TI ON BY T EM AH NE LS ON.
Use a similar chart to compare the two environments. I LLU ST RAT IO N BY T EM AH NEL SO N.
Habitat 1 (color) Organi Org n sms
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
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color
Timetable Varies widely, depending upon the
area, animals, and number of animals you want to locate. Step-by-Step Instructions
1. Once you decide on a specific habitat, spend some time looking for insects or other small animals that live in that environment. When you spot an insect or other animal, write down the insect— or describe it if you don’t know it’s name—and note its color. You may want to use a magnifying glass. If you have a camera, take a picture of each organism you find. 2. Continue looking for small animals until you have located at least five to 10 different organisms living in the environment you selected. In some environments, this Habitat 2 may take time and careful attention. (color) Organisms color Remember, some animals might be camouflaged! 3. Determine the percent of organisms that are the color of its surrounding environment. (You can determine the percent by dividing the number of organisms that were a certain color by the total number of organisms located.) 4. Repeat the entire process for another environment, which is a different color. Again, try to located at least five to 10 organisms. Experiment Central, 2nd edition
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Summary of Results Compare the percent of
insects the color of the first environment to the percent in the second environment. If you took pictures, compare the pictures of the animals in each environment. Does the color of the environment predict the color of the organisms that live there? You may want to chart your results. You could also use your notes or pictures to try and identify any unknown animals.
How to Experiment Safely Never touch the insects/animals or disturb their living environment; simply observe them.
EXPERIMENT 2 Ladybug Threats: How do ladybugs defend themselves when they feel threatened? Purpose/Hypothesis In this experiment, you will determine how lady-
bugs defend themselves when they sense a threat. Ladybugs have three methods of defense that help keep them safe. The distinct red color of a ladybug is in itself a defense mechanism. Many animals instinctively know not to eat bright colors organisms because they are often poisonous (many red berries, for example). Ladybugs also can give off a foul odor when threatened and this helps to keep their predator away. Lastly, ladybugs will ‘‘play dead’’ when approached by a potential predator or when unsure of their surroundings. Many insects and animals will not eat dead things and so they move away from the ladybug. In time, the ladybug will resume its activity. You will test different stimuli on the ladybug that it may see as threatening or unknown, and then observe how the ladybugs defend themselves. For the stimuli, you will expose the ladybugs to light, air movement, gentle nudging, vibrations, and sound. You can then observe its reactions for each. Before you begin the experiment, make an educated guess about the outcome based on your knowledge of animal defenses and ladybugs. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
Troubleshooter’s Guide Not locating enough organisms in each environment is the major problem that can occur in this project. Finding organisms can take patience and care. Many animals are more active in the beginning and end of the day, rather than during midday. If you are having trouble locating organisms, look for the organisms another time in the day, such as early morning. You could also try searching in another place, using the same environment.
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • light intensity the ladybug is exposed to • wind movement • movement the ladybug experiences • physical proximity to object • physical proximity to another insect • sound intensity in the background In other words, the variables in this experiment are everything that might effect the reaction of the ladybug to various situations. If you change more than one variable, you will not be able to tell which variable had the most effect on the reaction of the ladybug.
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The ladybug will play dead when it is in a threatening or unknown situation.’’ In this case, the variables you will change are situations that may be perceived as threatening or unknown to the ladybug. The variable you will measure is the reaction of the ladybug to these various new situations. Level of Difficulty Moderate. Materials Needed
Step 8: Approach the ladybug with the pencil and note the reaction. IL LU STR AT ION BY TE MAH NEL SO N.
• 3–5 ladybugs, found or purchased from local nursery or online • plastic container with cover, approximately 5 to 7 inches (13–18 centimeter) long • flashlight • 1–2 ants, caterpillars, inchworms, or spiders (found) • 1 pencil Approximate Budget $10–15 if you have to
purchase ladybugs; $0 if you can find the bugs. Timetable Approximately one hour. Step-by-Step Instructions
1. Place two ladybugs in the plastic container with lid. If one of the ladybugs flies away, replace it with another. 2. Observe and note the ladybugs behavior for several minutes. Wait for them to 66
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3.
4. 5.
6.
7. 8.
9. 10.
11. 12.
become comfortable in their new environment and move around slightly. How to Experiment Safely Shine a flashlight into the plastic container. Note whether the ladybugs react Ladybugs are living animals and should be to the change in light. handled with care so that they are not harmed during the experiment. After the experiment is Wait about two to three minutes until the complete, you can release them into a garden ladybugs resume activity. where they help manage pests. Lift off the lid of the container and blow softly onto one or both of the ladybugs. Note the reaction. Change the intensity of your breath, blowing slightly harder. Note whether the reaction of the ladybug change as well. After waiting for ladybugs to resume activity (two to three minutes) introduce another insect (ant, caterpillar, inchworm, spider) into the box. Note the reaction of the ladybugs. Be careful that the insect does not actually attack the ladybug (if so, remove the insect). Remove the second type of insect and again, wait for the ladybugs to resume normal activity. Without poking the ladybug, approach it with the pencil and note reaction. Gently nudge the ladybug with the pencil and note its reaction. Repeat this on the second ladybug. Wait several minutes until both ladybugs resumes activity. Try clapping your hands at different sound intensities close to the Step 10: Clap your hands at different sound intensities close ladybug. Start with a soft clap and increase to a loud noise. Note to the ladybug. I LLU ST RAT IO N which, if any, sound intensity appears to BY T EMA H NE LS ON. threaten the ladybug and note its reaction. Wait several minutes until the ladybugs resumes normal activity. Try gently shaking the container with the ladybug in it. Does this sudden movement cause the ladybug to react?
Summary of Results Study the observations of
the ladybugs’ reactions to various situations and decide whether your hypothesis was correct. In what situation did the ladybug appear to feel threatened and how did it react? If it played dead, how long did it take for it to start moving Experiment Central, 2nd edition
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Troubleshooter’s Guide Below is the main problem that may occur during this project and ways to remedy the problem. Problem: Ladybug doesn’t play dead. Possible cause: The ladybugs may not feel threatened. Sometimes there is safety in numbers and ladybugs may feel more vulnerable by themselves. Separate ladybugs from one another and try various scenarios with one ladybug. Possible cause: You may have tested possibly very old or sick ladybugs. Try collecting new ladybugs and repeat the tests.
again? Write a summary of your results. You may want to include pictures. Change the Variables Here are some ways you
can vary this experiment: • Test other stimuli that may be potentially threatening to the ladybug, such as strong smells (onion or garlic). • Alter the environment: Conduct the experiment outside in the ladybugs’ natural environment, as opposed to a plastic container. • Change the insect: For example the pill bug, a common insect found in soil, will curl itself into a ball when it senses danger.
Design Your Own Experiment How to Select a Topic Relating to this Concept As you think about
experiments and projects relating to animal defenses, consider animals that are familiar to you. What are some behaviors of cats, dogs, and fish? Consider animals that you have seen in zoos or in the movies. Check the Further Readings section and talk with your science teacher to start gathering information on animal defense questions that interest you. You may want to speak with people who are knowledgeable about different types of animals. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Remember that some animals can be dangerous and you should never provoke any animal. Work with someone familiar with the animal and plan how you will care for or handle any animal that you collect or purchase. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: 68
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• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results The most important part
of the experiment is the information gathered from it. Think of how you can share your results with others. Charts, graphs, and diagrams of the progress and results of the experiments are helpful in informing others about an experiment. You may also want to take photographs. Related Experiments Many experiments or projects with animals can be
made through simple observation. You may want to observe how different animals species interact with one another when they feel threatened or excited. You can observe the interactions between dogs, cats, squirrels, and other familiar animals, or you can observe the behavior of insect interactions. You could also observe the many camouflage adaptations animals have by visiting a local zoo or aquarium. You could conduct a research project on one type of animal that lives in your area or are curious about.
For More Information ‘‘Camouflage.’’ BBC: Walking with Beasts. http://www.abc.net.au/beasts/ fossilfun/camouflage/camouflage.swf (accessed on May 11, 2008). An interactive game on animal camouflage. ‘‘Exploring Mammals.’’ Natural History Museum. http://www.nhm.org/ mammals/home.html (accessed on May 31, 2008). Information on animal behavior and defenses. Kaner, Etta. Animal Defenses: How Animals Protect Themselves. Toronto, ON: Kid’s Can Press, 1999. National Geographic. Animals, http://animals.nationalgeographic.com (accessed on May 11 2008). Information on animal features, with pictures and video.
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6
Annual Growth
D
id you ever measure your height to see how much taller you were than the year before? This change is your annual growth. In humans, annual growth depends on factors such as your age (babies grow at a faster rate than teenagers) and your genes (which make sure your growth pattern is similar to that of your parents and grandparents). How can we determine the annual growth of other organisms, and what factors can we find that affect their growth? Trees are probably the tallest living organisms you will see in your life. Yet most trees around you grew from seeds no larger than the eraser on a pencil. The process by which these tiny seeds become trees is fascinating and easy to observe, when you know what to look for.
How does a tree grow? A tree grows in two ways. The tips of its branches and tips of its roots contain cells that reproduce, making the tree taller and its roots deeper. Another layer of dividing cells increases the width of the tree’s trunk little by little, increasing its support and providing a route for water to reach the upper branches. While a tree is alive, scientists can determine its growth rate by measuring the change in its diameter and also by observing the patterns of new growth on branches and twigs. When a tree has fallen or been cut down, scientists can learn much about the tree’s growth throughout its life and can even learn about changes in climate and soil composition long ago by examining the growth rings inside the main trunk. The growth rings that are visible on a tree stump result from the tree’s cycle of growth and dormancy. The interior of a tree’s trunk contains special tube-like vertical cells called xylem, which function as a vital part of the tree’s water-transport system. Each year, new xylem is produced near the outer layer of bark. In the spring, when conditions are usually wettest, the tree produces large xylem cells. During the drier months of summer, the tree produces smaller xylem cells. In the winter, the tree’s growth cycle 71
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When a tree has fallen or been cut down, its annual growth rings become visible. G AL E GRO UP.
You can learn about a tree’s growth pattern by observing the segments of twigs on the tree. GA LE GRO UP.
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goes into a state of dormancy, a period of inactivity to keep its energy in reserve while water is scarce. This alternating pattern of fast and slow growth causes the dark and light pattern of rings you can see on the tree stump. Each ring represents a growing season. Generally, a larger, more prominent ring marks a longer, wetter growing season. In this way, scientists have been able to pinpoint when climatic changes occurred long ago in a region’s history. A skilled scientist with the right tools can learn even more from a tree’s rings, such as when the tree experienced changes in soil composition, forest fires, and floods. We can also learn about a tree’s growth pattern by observing the segments of twigs on the tree. Each spring, the tree will put out a bud at the end of each twig. That bud forms the beginning of that year’s new growth. Once the twig grows beyond the point where the bud first formed, the remnants of the bud create a scar, or ring. These rings mark off each year of the tree’s growth. The most recent segment is the one closest to the end of the twig (assuming the twig has not been broken). Some twigs exhibit growth rings going back many years. Once a growing season is completed, that season’s segment will not grow any longer. The segments can give you a rough indication of how much growth a tree experienced in one season compared to other seasons. Remember that growth may not be the same from one side of a tree to the other, especially in large trees. The segment indicates most accurately how much growth occurred on that branch of the tree in a given growing season. In the first experiment, you will compare the annual growth pattern of twigs on several trees in your area with the rainfall figures for each year. You will then determine if precipitation in your area has had a measurable effect on the trees’ annual growth. Lichens: Another kind of annual growth Have you ever noticed the patches of colorful plant life that sometimes grow on rocks and buildings? Some resemble greenish-brown stains, while others look like blotches of mold. When examined closely, some appear to be tiny forests of hairy branches. These are actually a unique and Experiment Central, 2nd edition
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On many trees, twigs exhibit evidence of past growing seasons by the distance separating their scars or annual growth rings. GA LE G RO UP.
fascinating life form called lichens. Scientists who study lichens are known as lichenologists. One of the most renowned lichenologists was Beatrix Potter, the author of The Tale of Peter Rabbit. Though better known for her children’s stories, Potter devoted much of her time to the study of lichens and produced detailed watercolor illustrations of different lichen forms. Lichens are far more complex than they appear. Each lichen contains two partners, usually a fungus and an alga, that bond together in a symbiotic relationship. Symbiosis occurs when two organisms form a relationship that benefits both. By combining the advantages of fungus with the advantages of algae, the lichen is able to survive where other organisms would perish. The most visible part of the typical lichen is a fungus. Fungi are plant-like organisms that differ from true plants in that they are heterotrophs, organisms that must get their food from other organisms. Fungi usually get their food from dead and decaying matter. Fungi are composed of thin strands that form Experiment Central, 2nd edition
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Lichens are actually complex partnerships of different organisms working together. P ETE R AR NO LD I NC.
a network that becomes a home for the fungus’s partner. That partner is usually an alga, although some lichens contain cyanobacteria instead. If you examine a cross-section of a lichen, you will usually see the alga as a thin layer of green just under the organism’s top layer. Algae are tiny plants that use photosynthesis to create nutrients, making them autotrophs. Lichens can survive harsh environments The symbiotic relationship between the fungus and the algal cells of the lichen depends on the structure and functioning of each. The fungus is capable of securing itself to inhospitable surfaces, such as bare rock or even plastic. Often, however, a fungus would not find sufficient nutrients in such a habitat. The algal cells, on the other hand, can produce food by photosynthesis, but they could not survive on their own on a bare rock. The two form a symbiotic union. The fungus provides the algae with protection from the harsh environment, while the algae provide the fungus with food. Cyanobacteria are among the most ancient organisms on Earth. They are usually found in water, sometimes joining together in colonies. Cyanobacteria contain chlorophyll and perform photosynthesis, and thus they sometimes are found in lichens in place of algae. Lichen growth patterns can be used to determine the age of rocks and rock formations because the rate of growth is extremely slow and regular. Lichens serve as a good indicator of air pollution levels because of their sensitivity to impurities in the atmosphere. In the second experiment, you will utilize two samples of living lichen to measure differences in air quality in different places.
EXPERIMENT 1 Tree Growth: What can be learned from the growth patterns of trees? Purpose/Hypothesis For this experiment, you will examine and collect
growth data from branches of different trees. Then you will determine 74
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whether these data correspond to the precipitation in your region. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plant growth. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The branches of trees in this area will show similar growth patterns over the past few years because they all received the same amounts of rainfall during each growing season.’’ In this case, the variable you will change is the type of tree, and the variable you will measure is the growth pattern over the past few years. You expect the growth patterns to be similar.
Cyanobacteria are single-celled organisms that perform photosynthesis. PH OTO RES EA RC HER S I NC.
The fungus in a lichen provides a protecting structure for the algal cells, which provide food. GAL E GR OU P.
Level of Difficulty Moderate. Materials Needed
• sketchbook and pencil • ruler (one showing millimeters or sixteenths of an inch) • pruning shears (optional) • camera (optional) Approximate Budget $2. Timetable This experiment should be done in
two periods of at least 15 minutes each: one period to collect and organize data, and the other to interpret the data and present the results. Experiment Central, 2nd edition
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WORDS TO KNOW Alga/Algae: Single-celled or multicellular plants or plant-like organisms that contain chlorophyll, thus making their own food by photosynthesis. Algae grow mainly in water. Autotroph: An organism that can build all the food and produce all the energy it needs with its own resources. Chlorophyll: A green pigment found in plants that absorbs sunlight, providing the energy used in photosynthesis, or the conversion of carbon dioxide and water to complex carbohydrates. Cyanobacteria: Oxygen-producing, aquatic bacteria capable of manufacturing its own food; resembles algae. Dormancy: A state of inactivity in an organism. Fungi: Kingdom of various single-celled or multicellular organisms, including mushrooms, molds, yeasts, and mildews, that do not contain chlorophyll. Gene: A segment of a DNA (deoxyribonucleic acid) molecule contained in the nucleus of a cell that acts as a kind of code for the production of some specific protein. Genes carry instructions for the formation, functioning, and transmission of specific traits from one generation to another.
Heterotrophs: Organisms that cannot make their own food and that must, therefore, obtain their food from other organisms. Hypothesis: An idea in the form of a statement that can be tested by observation and experiment. Lichen: An organism composed of a fungus and a photosynthetic organism in a symbiotic relationship. Niche: The specific location and place in the food chain that an organism occupies in its environment. Photosynthesis: Chemical process by which plants containing chlorophyll use sunlight to manufacture their own food by converting carbon dioxide and water to carbohydrates, releasing oxygen as a by-product. Symbiosis: A pattern in which two or more organisms live in close connection with each other, often to the benefit of both or all organisms. Variable: Something that can affect the results of an experiment. Xylem: Plant tissue consisting of elongated, thickwalled cells that transport water and mineral nutrients.
Step-by-Step Instructions
1. Choose branches or twigs that exhibit the visible signs of annual growth described above. Select different trees in different locations. If you use fallen branches, make sure they are recently fallen. Otherwise, you will not be sure when the most recent growth occurred. Branches that have been split or damaged, especially at the growth tip, may not provide useful results. 76
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2. Ask your teacher or an adult before cutting any branches or twigs. Remember that any change you make to the natural environment will probably have a lasting effect, so avoid damaging trees whenever possible. If you decide to cut a branch to illustrate your project, do not cut the branch too close to the trunk or greater branch, as this could harm the tree. 3. Note the number of segments you can find on the branch you have selected. Determine which is from the most recently completed growing season and then note how many growth seasons are visible on your branch.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the species of tree being examined • the condition of the branches (damaged or not damaged, for example) • variations in rainfall among the areas where the trees are growing • the amount of fertilizer or other nutrients each tree receives • other factors influencing growth, such as the amount of sunlight, level of air pollution, and the presence of disease in the trees
4. Sketch or photograph the branch. Note as If you change more than one variable, you will much information as possible about the tree not be able to tell which variable had the most and its immediate environment. What kind effect on the growth patterns. Try to keep all of tree is it? Is it competing with other trees variables the same except the one you are for water and sunlight? Might there be examining: the amount of annual growth. some other environmental factors affecting its growth, such as air pollution or drainage from parking lots or sidewalks? Check whether the tree is receiving water from an irrigation or sprinkler system. This would have a clear effect on your data, and may make an interesting comparison for your study. 5. Measure each segment and record your data. Use a chart to keep your information consistent. Your chart should look something like the illustration. 6. Once you have found and examined a number of different samples, use your data to test your hypothesis. For each sample, find the year in which the least growth occurred. Then find the year in which the greatest growth occurred. Use the different samples you have for each growing season to find an average growth for that year. Ask your teacher or librarian for help in finding annual rainfall figures for the years for which you have sample. Compare these figures to the results of your branch measurements. Experiment Central, 2nd edition
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How to Experiment Safely If you choose to cut a branch or branches to illustrate your findings, be sure to ask permission before cutting. Use proper protective wear and be careful with the pruning shears.
Summary of Results Examine your results and determine whether your hypothesis is correct. Did the samples show consistently greater or lesser growth for one or more growing seasons? If so, did those years have more or less rainfall than usual? Change the Variables You can vary this experi-
ment by changing the variables. Instead of comparing growth seasons, try simply comparing growth rates from one type of tree to another. See if you can find which tree branches in your area exhibit the most growth in a season. Which tree branches grow the least? Modify the Experiment In this experiment, you learned about how the
growing pattern of trees is affected by the rainfall in an area. For a more in-depth understanding of tree growth, you can use the branches you collected to determine if water absorption differs among trees in the same area. You know that water is an important source of nutrients that trees need to grow. But do all trees in the same area absorb equal amounts of available water? First, make a hypothesis. Select two of the branches you collected from two different types of trees growing in the same area. A twig from a
Step 5: Example of tree growth recording chart. GAL E GR OU P.
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tree with needles and a twig from a tree with large leaves would work well. Snap off two twigs (about Troubleshooter’s Guide the same size) from each of the two branches. You should have four twigs: two from one type of tree Here is a problem that may arise, a possible and two from another, all about the same size. cause, and a way to remedy the problem. Prepare two clear measuring cups. Place the Problem: The amount of growth varies greatly two twigs that are the same in one cup and the from tree to tree. two other twigs in the second cup. Fill each Possible cause: Different types of trees can have of the cups half-full with water, leaving the top drastically different growth rates. Remember of the twigs not immersed. Make sure that the that you are looking for which years had the two cups contain equals amounts of water. For greatest and the least growth for each tree—a example, if the twigs stand slightly past a two-cup factor that may be consistent from tree to tree measuring cup, you may want to fill each cup regardless of each one’s growth rate. with 1.5 cups of water. Write down the amount of water and mark the water line with a piece of masking tape. Cover the tops of the cups with paper. You may need to poke the twigs through the paper so that the paper rests on the cup. Set aside for two days and then note the water level. Was the amount of water absorbed different for each type of tree? What twig absorbed the most water? Place another piece of tape at the water level and wait another day. Continue for several days or until the water is almost gone. Graph your results. What does this tell you about the water usage of different types of trees? What types of trees would fare better in a drought?
EXPERIMENT 2 Lichen Growth: What can be learned from the environment by observing lichens? Purpose/Hypothesis For this experiment, you will need to locate different
lichens in various habitats around your school and/or home. Counting and measuring the number of lichens you find growing in different areas will give you a rough idea of the amounts of air pollution present. Lichens are nearly everywhere. You will need, however, to find samples large enough to examine and measure. In rural environments, this should not be difficult. Lichens can frequently be found on trees, dead wood, and rocks. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of lichens. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
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• • • •
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the species of lichen being examined • the surface on which the lichen is growing • the amount of sunlight and rainfall the lichen receives • the location of the lichen relative to sources of air pollution In other words, the variables in this experiment are everything that might affect the size and numbers of the lichens. If you change more than one variable, you will not be able to tell which variable had the most effect on lichens.
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Fewer and smaller lichens will grow in areas with higher levels of air pollution (near roads and factories) than in areas with cleaner air.’’ In this case, the variable you will change is the location of the lichens, and the variable you will measure is their number and size. You expect fewer and smaller lichens will be found near sources of air pollution. Level of Difficulty Moderate.
Materials Needed
• • • •
sketchbook and pencil magnifying glass ruler (one showing millimeters or sixteenths of an inch) camera (optional)
Approximate Budget $5. Timetable This experiment requires a commitment of several hours
searching and cataloging lichens. Step-by-Step Instructions
1. Your research for this experiment should begin in the library. It will be worthwhile to photocopy photographs and illustrations of different forms of lichen and bring this information with you when you go out looking for lichen. 2. Remember that lichens can be quite fragile. Treat lichens gently while measuring and sketching them. 80
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3. If you are working together with a group, you might find it useful to divide the responsibilities. Have one group member sketch the lichen while others measure or write brief descriptions of the lichen’s habitat. Prepare a chart on which you will record your observations for each lichen you find. Your chart should look something like the illustration.
How to Experiment Safely This project puts you in contact with fungus from the wild. NEVER eat any wild fungus, even one that looks familiar. Fungi that closely resemble edible mushrooms can in fact be highly toxic. Treat lichens the same way. Though some are edible, many are not. You should also wear gloves when handling the fungus.
4. Once you have found a lichen, take note on your chart of the habitat. Is the lichen growing on a tree or rock, or on some other object, such as a rusted barrel? How close is the lichen to the nearest source of air pollution? Note all other environmental factors that might affect the rate of lichen growth, such as shelter from rain and sun. Next examine the lichen itself. Describe it as clearly as possible, identifying its color, form, and texture. 5. Measure the lichen using your ruler. Lichen that grow in patches start with one tiny spore-like structure and then grow outward, like mold on bread. Therefore, try to locate the largest single sample instead of measuring two that have grown together. Measure the lichen’s greatest
Step 3: Example of the lichen recording chart. GA LE G ROU P.
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Troubleshooter’s Guide Here is a problem that may arise, a possible cause, and a way to remedy the problem. Problem: No lichens can be found. Possible cause: Some areas, particularly urban environments with high levels of air pollution, may not have any lichens. If you think this may be possible, check with your teacher before attempting this experiment.
horizontal length and greatest vertical length and record this data on your chart. 6. Select different sites that are more likely to show the effects of air pollution. Try to find lichens at different distances from highways, airports, or factories. Roadway intersections often produce increased pollution levels due to cars and trucks stopping and starting. Summary of Results Examine your results and
determine whether your hypothesis is correct. Did you find a consistent difference in the size (or presence) of lichens on trees closer to roads or parking lots? What other factors did you note that might be affecting lichen growth? Write a summary of your findings.
Change the Variables There are several ways you can vary this experiment.
Try measuring the effect of changes on the lichen, such as treatment of sunlight and moisture, competition with other plants, or exposure to lichen-eating animals.
Design Your Own Experiment How to Select a Topic Relating to this Concept Try growing lichen in a controlled environment. If you find lichen growing on an easily movable object, such as a piece of dead wood or a small rock, try carefully moving that rock into your classroom or laboratory. Remember that the lichen needs light and moisture. If you are able to transport lichen, you can design an experiment that will more accurately test the effects of different air qualities on the lichen. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on annual growth or lichen questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. 82
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• Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the experiments included here and in any experiments you develop, you can try to display your data in more accurate and interesting ways. Collecting samples of the lichen you measure for your experiment will make the results more interesting to viewers. Photographs of the lichen you find can be helpful, but you may discover that careful sketches can reproduce details that are not clear in photographs. Related Projects Projects and experiments in annual growth can reveal much about our environment that usually occurs too slowly for us to notice. Some fascinating experiments can be conducted over longer periods of time if you establish a structure for other students to follow later on. Talk with your teacher and classmates about starting a project to monitor long-term tree or lichen growth in your area. Take measurements of the circumference of the tree trunks near your school and record your data for comparison next year. Look for sources of information on tree growth in the past. Old photographs cannot provide exact measurements, but they can show roughly how much a tree has changed over a period of years or even decades.
For More Information Arbor Day Foundation. Fantastic Arborday.org Tree Guide. http://www. arborday.org/trees/treeguide (accessed on January 19, 2008). Information about classification of trees. Menninger, Edward. Fantastic Trees. Portland, OR: Timber Press, 1995. A fun and fascinating look at strange and little known facts about trees. Oregon State University. Fantastic Lichenland. http://ocid.nacse.org/lichenland (accessed on January 19, 2008). Information about types of lichen. Platt, Rutherford. 1001 Questions Answered About Trees. New York: Dover Publishing, 1992. A question and answer format book covering practically everything about trees. Pollick, Steve. Find Out Everything About Plants. London: BBC Publishing, 1996. Contains a number of interesting and clearly illustrated project ideas on plant and growth related topics.
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Bacteria
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ou cannot see them with the naked eye, but the world is teeming with bacteria. They live around you, inside of you, and are found in environments that would kill most every other life form. Bacteria are microbes, organisms that are so small they can only been seen with a microscope. They are the simplest, most abundant, and oldest life form on Earth, having evolved roughly 3.5 billion years ago. That beats other life forms by a long shot including dinosaurs, which only arrived on the scene 250 million years ago, and humans, who appeared a mere 2 million years ago. Scoop up a teaspoon of soil and, if you could see them, you would count about a billion bacteria. While bacteria often make headline news as the cause of disease, the vast majority are either harmless or helpful to humans. Many bacteria live in the soil and decompose dead plants and animals. This process returns needed nutrients back into the environment, which plants and animals then use to live and grow. Other bacteria change the nitrogen gas from the air into a form of nitrogen that plants needs to survive. For humans, they are used to produce foods, such as yogurt and cheese. Humans and some animals depend on bacteria in their digestive tract to break down the plants they eat so they can process the food. Bacteria are an integral part to all life on Earth. Wretched beasties The discovery that bacteria exist is one of the major breakthroughs in science. It began with the development of the microscope. In the late 1600s Dutch merchant and amateur scientist Antony van Leeuwenhoek (1632–1723) had built microscopes that magnified objects up to 200 times their size. While he was examining water droplets and the white matter on teeth he noted the existence of these ‘‘wretched beasties’’ wriggling about. Although he did not know it, this was the first recorded sighting of bacteria. Two hundred years later researchers connected these tiny microbes to some of the deadly diseases that were sweeping through the world and killing hundreds of millions of people. For thousands of years, people did not 85
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understand the cause of disease; they often blamed a disease on evil spirits or as a punishment to the victim. Then in the 1860s scientists Louis Pasteur found in mouth, causes (1822–1895) and Robert Koch (1843–1910) conplaque bacteroides fragilis ducted a series of experiments that showed microbes could cause disease. They called their evidence the germ theory of disease. Pasteur discovered bacteria could cause food to spoil and he found in large intestine, produces Vitamin K developed a method to destroy these bacteria, now lactobacillus acidophilus called pasteurization. Koch isolated the individual bacteria that caused the deadly diseases anthrax, tuberculosis, and cholera. Understanding that helps digestion, inhibits microbes acted upon other life forms opened the undesirable bacteria and door to an entirely new field of research. Scientists yeasts learned how to destroy and protect against these microbes, saving millions of lives. What they look like There are thousands of species of bacteria, yet all share some basic features. Bacteria are single-celled organisms and fall into a category of life called prokaryotes. Prokaryotes do not have certain specialized structures in their cells and they do not have a cell nucleus, which humans have. A nucleus is a cellular compartment inside cells that surrounds DNA and other organelles. An organelle is an enclosed structure in a cell that performs a specific function, much like the role of an organ in the body. What the typical bacteria does have is a fluid called cytoplasm inside its cell. Cytoplasm is a gooey, gel-like substance that holds everything and helps move materials around inside the cell. All the genetic information is contained in the deoxyribose nucleic acid (DNA) molecule. The DNA in bacteria sits loosely in the cytoplasm. Also located in the cytoplasm are the ribosomes. Ribosomes play a key role in translating the information pili DNA from DNA into proteins. The cytoplasm is surrounded by a simple cell membrane, which has a variety of functions, including bringing nutrients and chemicals into the cells. The cell membrane is enclosed by a rigid cell wall that provides the overall shape. Bacteria come in three basic shapes. There are bacteria ribosome shaped like rods, those that are spherical or round, and those that are helical or spiral. streptococcus mutans
staphylococcus aureus
lives in the nose and prevents harmful microbes from entering lungs
escherichia coli
lives in the gut and plays role in digestive system
The human body houses trillions of bacteria. Bacteria can cause disease if they get out of control, yet many help humans stay healthy. G AL E GRO UP.
Cell structure of the typical bacterium. GA LE GRO UP.
flagellum
cytoplasm
cell wall
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Some bacteria have whiplike structures called flagella that they use to move forward. Some also have small hairlike projections from the cell surface called pili. Pili help the cell stick to surfaces or to each other. The typical bacteria range in size from 1 to 5 micrometers (m). One micrometer equals one millionth of a meter. Scientists use micrometers as the unit of measurement because bacteria are too small to be measured in inches or millimeters. A large clump of bacteria growing together is called a colony. A colony can have millions of individual bacteria and is visible to the naked eye.
Closeup of the Leptospira bacteria. C US TOM MED IC AL STO CK P HO TO
Living and eating Bacteria have survived on Earth for billions of years because they are able to adapt relatively quickly to changing environments. One of the ways they adapt is by having a speedy reproduction rate. Bacteria usually reproduce by simply dividing into two cells. All the genetic information, the DNA, is passed along to each of the cells. Sometimes bacteria reproduce sexually: one bacterium transferring part of its DNA to another Bacteria come in three basic bacterium. This allows bacteria to quickly create or pass along new traits that shapes: rod, spherical or round, help them adapt to different environments. and spiral. GA LE GRO UP. Given ideal conditions, bacteria can reproduce about every twenty minutes. That means one bacterium could multiply to more than five billion in about ten hours. If all bacteria really were to reproduce this quickly, the world would soon be overtaken with these microorganisms. Luckily, in the real world, conditions are never ideal. Once there are too many bacteria in one place their food rod runs out, they crowd each other, and eventually they start dying. Bacteria have a wide range of diets and living spherical conditions. Some bacteria eat other organisms. Many of these feed off dead organisms, the waste of other organisms, or get their food from living in or on other organisms. Many of these bacteria depend on such foods as sugars, proteins, and vitaspiral mins. The bacteria in the human gut, for example, get their food from digested food. Other bacteria make their own food either from sunlight, like Experiment Central, 2nd edition
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Bacteria that live in extreme habitats, such as the boiling hot geysers at Yellowstone National Park, are called extremophiles. # PAT O ’H AR A/C OR BI S.
plants, or from different chemicals in their environment. The chemicals these bacteria use for foods are often unusual, such as iron and sulfur. Scientists have found bacteria in practically every known locale and environment. Until the late 1960s, it was thought that no organism could survive in certain extreme environments, meaning environments that would kill other creatures such as humans. Then a researcher discovered there were bacteria living in the hot springs of Yellowstone National Park, which reached temperatures over 158˚F (70˚C). The bacteria that live in these extreme habitats are called extremophiles. Since that time scientists have discovered an increasing number of extremophiles. There are extremophiles that live in sub-freezing temperatures under sheets of ice; thrive in highly acidic environments; and withstand blasts of radiation thousands of times greater than the level that would kill a human. Extremophiles are of great interest to both industry and basic research. Researchers are interested in how these organisms survive. NASA is conducting experiments on extremophiles to investigate survival in outer space. The biotechnology industry uses extremophiles to manufacture items, such as detergents, diagnostics, and food products. Building up resistance While most bacteria are harmless or helpful to humans, there are a number of bacteria that do cause disease. Lyme 88
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WORDS TO KNOW Antibiotic: A substance derived from certain fungi, bacteria, and other organisms that can destroy or inhibit the growth of other microorganisms; widely used in the prevention and treatment of infectious diseases.
Extremophiles: Bacteria that thrive in environments too harsh to support most life forms.
Antibiotic resistance: The ability of microorganisms to change so that they are not killed by antibiotics.
Germ theory of disease: The theory that disease is caused by microorganisms or germs, and not by spontaneous generation.
Bacteria: Single-celled microorganisms found in soil, water, plants, and animals that play a key role in the decay of organic matter and the cycling of nutrients. Some are agents of disease. (Singular: bacterium.)
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Colony: A visible growth of microorganisms, containing millions of bacterial cells. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Cytoplasm: The semifluid substance inside a cell that surrounds the nucleus and other membrane-enclosed organelles. Deoxyribonucleic acid (DNA): Large, complex molecules found in the nuclei of cells that carry genetic information for an organism’s development.
Flagella: Whiplike structures used by some organisms for movement. (Singular: flagellum.)
Nucleus, cell: Membrane-enclosed structure within a cell that contains the cell’s genetic material and controls its growth and reproduction. (Plural: nuclei.) Organelle: A membrane-enclosed structure that performs a specific function within a cell. Pili: Short projections that assist bacteria in attaching to tissues. Prokaryote: A cell without a true nucleus, such as a bacterium. Ribosome: A protein composed of two subunits that functions in protein synthesis (creation). Variable: Something that can affect the results of an experiment.
disease, anthrax, tuberculosis, and salmonellosis are examples of diseases caused by bacteria. Many bacterial diseases are deadly without treatment and can cause widespread infections. Antibiotics are substances that harm or kill bacteria. Erythromycin and penicillin are examples of commonly used antibiotics. Discovered in the 1920s, these substances are produced naturally by a variety of organisms, such as bacteria themselves and fungi. The production and use of antibiotics has dramatically reduced the number of deaths and illnesses from bacterial disease. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the size of the paper disks • the growth substance • the temperature of the bacteria’s environment • the substance placed on the bacteria • the type of bacteria In other words, the variables in this experiment are everything that might affect the zone of inhibition. If you change more than one variable at a time, you will not be able to tell which variable impacted bacterial growth.
In the modern day, people are facing the growing public-health problem of antibiotic resistance. This is when disease-causing bacteria have become resistant to an antibiotic, thereby lessening the effectiveness of the drug. Resistance can occur when a single bacterium acquires the genetic ability to resist, or block, the antibiotic. This one bacterium will rapidly reproduce and produce an antibiotic-resistant population. An overexposure to an antibiotic is one way bacteria can acquire resistance. The antibiotic will kill the weak bacteria and allow the stronger, resistant ones to survive. Patients who are prescribed antibiotics but do not take the full dosage can also contribute to resistance. If all the bacteria are not killed, the strong, resistant bacteria that live can pass on resistance to the next generation.
EXPERIMENT 1 Bacterial Growth: How do certain substances inhibit or promote bacterial growth? Purpose/Hypothesis There are many kinds of bacteria, but a great many
of the bacteria that you encounter daily share similar growth requirements. In this experiment you will investigate substances that affect the growth of common household bacteria. You will collect a sample of bacteria from one of numerous possible sources. You can use your imagination on where to collect the bacteria. Because bacteria need moisture to live, possible sources include the base of a faucet, on someone’s hands, inside someone’s cheek, or on a bathroom doorknob. You will then streak the bacteria on a growth substance. Bacteria grow well on a substance called agar. Nutrient agar is a jellylike substance that contains food for the bacteria. You can order prepared nutrient agar in a petri dish. You will use paper disks to place the substances on a section of the bacteria. You can use the suggested liquids or select different ones. Saturate each paper disk with the item to be tested, and place the disk on the bacteria. After giving the bacteria time to grow, you will measure the diameter of the clear area around the paper disk where the bacteria did not grow. This area is called the zone of inhibition. If there is a large zone of inhibition, the 90
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substance inhibits bacteria growth. If there is no clear zone of inhibition, the substance does not inhibit bacterial growth. If there is a larger amount of bacteria around and under the disk than when you started, the substance promotes growth. In this experiment, you will be using more than one type of bacteria. Different types of bacteria often live together. When you collect your sample, you will probably gather more than one type. The experiment will still be valid because bacteria that grow together naturally usually do so because they respond the same way to their environment—something that promotes growth for one of them will be good for all of them, and something that inhibits growth for one will be bad for all. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of bacteria. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
How to Experiment Safely When working with bacteria, you should consider the bacteria capable of causing disease and follow the appropriate safety procedures. Handle the cultures carefully. If there is a spill, wipe up the material using a disinfectant-soaked paper towel, then throw the towel away immediately. Throw away or sterilize all items that touch the bacteria. Always wash your hands after using live materials. Thoroughly wipe your working area with a disinfectant cleansing agent after you have finished with the setup. Keep your plate closed and store it in a safe area that will not be disturbed. Keep younger children away from the experiment area. Be careful when working with the hot water.
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The acidic and cleaning substances will inhibit bacterial growth; the protein and sugary substances will promote bacterial growth.’’ In this case, the variable you will change is the substance you place on the bacteria. The variable you will measure is the distance from the disk to the bacterial growth. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental bacterial growth. The control experiment will have no substance on the paper disk. At the end of the experiment, you will compare the growth of the control bacteria with the experimental bacteria. Experiment Central, 2nd edition
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Level of Difficulty Medium to Difficult. Materials Needed
• • • • • • •
rubbing alcohol small cup tweezers paper hole puncher white nonglossy paper cotton swab nutrient agar plates* (available from a biological supply company) • bacteria source • test substances: chicken broth (can be made from bouillon), coffee, lemon juice, syrup, vinegar, liquid soap • distilled water
Step 5: Spread the bacteria over the entire plate. GA LE GRO UP.
Step 11: Lift the petri lid just high enough to place the paper disk into its marked section. GAL E GR OU P.
• • • • • •
5 small cups or plates marking pen filter paper ruler, with millimeters magnifying glass (optional) microscope (optional) Depending on how many bacteria experiments you plan to conduct, you may consider less expensive options than that of purchasing ready-made nutrient agar plates. You can order the nutrient agar and plates separately and pour the agar into the plates yourself. You can also order nutrient agar that needs to be made. This process may take some practice so allow yourself extra time. There are also recipes for agar using common household items. Gelatin is also an alternative for nutrient agar. Look on the Internet for these recipes or ask your science teacher. Allow extra time for this process, as you may have to experiment with what recipe best promotes bacterial growth. Approximate Budget3 $25.
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Timetable One hour setup and followup; two
days waiting. Step-by-Step Instructions
1. Turn the covered petri dish upside down. Use the marker to divide the dish into six even sections, like a pie. On each section write the name of one of the five substances. Write ‘‘Control’’ on the sixth section. 2. Write the date on the side of the dish. 3. Dip a cotton swab in distilled water. 4. Run the swab over the source of bacteria. 0 cm 5. Spread the bacteria over the entire plate. Hold the swab flat or at a slight angle so as not to puncture the agar. 6. Cover the plate and throw the swab away. 7. Use a hole puncher to make at least five paper disks. 8. Sterilize the tweezers: Pour rubbing alcohol into a small cup to cover the bottom. Hold or place the end of the tweezers into the alcohol and wait at least one minute. Rinse in water and shake any excess off the tweezers. 9. Pour several drops of each of the substances you are to test into its own cup or small plate. 10. Pick up a paper disk with the tweezers and dip it into one of the liquids. The disk should be wet but not dripping. 11. Lift the petri lid just high enough to place the paper disk into the middle of its marked section. 12. Hold the tweezers under running water for at least five seconds to clean. 13. Continue wetting each paper disk in the liquid, and placing the disk in its allotted section. Rinse the tweezers in hot water between each paper disk. 14. With clean tweezers, put a plain paper disk in the Control section. 15. Invert or turn the plate upside down. (Condensation may collect on the top lid. Turning the plates upside down prevents the condensation from falling on the bacteria and allows a clear view of growth.) 16. Store the plate in a warm, nonbright area for 24 hours. Experiment Central, 2nd edition
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Step 19: Measure the diameter of the zone of inhibition, in millimeters, from the left edge of the clear area to the right edge. G AL E GR OUP .
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: Bacteria grew in some areas of the plate but not in others. Possible cause: You may not have streaked the entire plate with the bacteria. Repeat the experiment, spreading the bacteria around so that the entire plate is covered with the microorganism. Problem: There was no growth. Possible cause: You may have stored the plate in an environment that harmed the bacteria or caused it not to grow, such as if it was too cold. Repeat the experiment, storing the plate in a warm environment. Possible cause: You may not have picked up enough bacteria on the swab. Make sure the cotton swab is wet and repeat the experiment, using the same or a different source for the bacteria. Problem: My results were not as expected. Possible cause: You may not have rinsed off the tweezers thoroughly after touching each paper disk, mixing together some of the substances on a disk. Repeat the experiment, making sure to rinse the tweezers in the hot water after each disk is complete.
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17. Check the plate for growth. If there is little to no growth, wait another 24 hours. 18. Observe each section for zones of inhibition, the clear area around the disk in which bacteria have not grown. 19. Measure the diameter of the zone of inhibition, in millimeters, from the left edge of the clear area to the right edge. Repeat this step for all 6 substances. 20. Record the measurements in a data chart. Note also if there is no zone of inhibition, or if there is increased growth compared to that of the Control. 21. When you have completed the summary, throw away the agar plate. Summary of Results Create a graph illustrating
the data chart. Make sure you label the graph carefully. Can you tell if the bacteria grew more in certain substances than in others? What substances inhibited bacterial growth the greatest amount? Were there any substances that promoted bacterial growth? Compare each substance to the control experiment. Examine the differences between the growth in the Control section and growth in any substances that were not inhibited by the substance. Analyze the main ingredient in each of your substances that may have inhibited or promoted growth,
Change the Variables You can vary this experiment in several ways: Change the substance on the paper disks Use one substance and change the concentration of that substance Alter the growing temperature of the bacteria Isolate one type of bacteria before you begin the experiment (the easiest way is to purchase a single type of bacteria from a biological supply company; you could also streak a bacteria mix onto an agar Experiment Central, 2nd edition
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plate to thin out the population until a bacteria of one color and shape grow). • Grow the bacteria under different lighting conditions
EXPERIMENT 2 Bacterial Resistance: Can bacteria gain resistance to a substance after exposure? Purpose/Hypothesis Antibiotic resistance is a
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the concentration of soap • the type of bacteria • the type of soap • the environmental conditions of each plate
In other words, the variables in this experiment growing health problem around the world. In are everything that might affect the zone of this experiment, you will explore bacterial resistinhibition. If you change more than one variable ance by experimenting with bacteria and antiat a time, you will not be able to tell which bacterial soap. variable impacted bacterial growth. Ever since the mid 1990s, soap manufacturers have put antibacterial agents in their products, such as body washes, toothpaste, and hand soaps. The number of antibacterial soaps has increased over the years. In modern day, the majority of soaps carry some antibacterial agent. Researchers have theorized that bacteria may develop a resistance to antibacterial agents over time. If the bacteria develop a resistance to the agent, the agent will no longer be effective in slowing down their growth or killing them. In this experiment, you will collect a sample of bacteria and spread it on a growth substance. Bacteria grow well on a substance called agar. Nutrient agar is a jellylike substance that contains food for the bacteria. You can order prepared nutrient agar in a petri dish. On top of the nutrient agar you will spread a low concentration of antibacterial soap. The bacteria that survive this concentration of soap will be introduced to a higher concentration of soap. You will continue this process for five growth cycles. After the last plate of bacteria has grown, you can compare the surviving bacteria with the bacteria that have had no exposure to antibacterial soap. You will measure the bacterial growth by counting the number of colonies. The concentrations of soap provided in this experiments are guidelines. The type of soap you use and the bacteria you collect will influence how bacteria respond to the different concentrations. If you want to determine the concentration that would best suit your materials, read the Troubleshooter’s Guide before you begin. Experiment Central, 2nd edition
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How to Experiment Safely When working with bacteria, you should consider the bacteria capable of causing disease and follow the appropriate safety procedures. Handle the cultures carefully. If there is a spill, wipe up the material using a disinfectant-soaked paper towel, then throw the towel away immediately. Throw away or sterilize all items that touch the bacteria. Always wash your hands after using live materials. Thoroughly wipe your working area with a disinfectant cleansing agent after you have finished with the setup. Keep your plate closed and store it in a safe area that will not be disturbed. Keep younger children away from the experiment area.
In this experiment, you will be using more than one type of bacteria. Different types of bacteria live together. When you gather a swab of bacteria you have gathered a number of different populations. To draw conclusions about a single type of bacteria, you can order one from a biological supply house. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of bacteria and resistance. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Bacteria that are exposed to an increasingly greater concentration of soap will survive a concentration that will kill unexposed bacteria.’’ In this case, the variable you will change is the concentration of the soap. The variable you will measure is the number of bacteria colonies that grow. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental bacterial growth. Each phase of this experiment will have a control. The control bacteria will grow on nutrient agar with no soap. At each phase of the experiment, you should compare the growth of the control bacteria with the experimental bacteria. Level of Difficulty Difficult. Materials Needed
• cotton swabs • 6 (at least) nutrient agar plates* (available from a biological supply company) • antibacterial liquid soap • measuring cups 96
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• • • • • •
measuring spoons 5 containers with covers stirring spoons marking pen magnifying glass (optional) microscope (optional)
*Depending on how many bacteria experiments you plan on conducting, you may consider less expensive options than that of purchasing readymade nutrient agar plates. You can order the nutrient agar and plates separately and pour the agar into the plates yourself. You can also order nutrient agar that needs to be made. This process may take some practice so allow yourself extra time. There are also recipes for agar using common household items. Gelatin is also an alternative for nutrient agar. Look on the Internet for these recipes or ask your science teacher. Allow extra time for this process, as you may have to experiment with what recipe best promotes bacterial growth.
Plate 1 .0001%
control
Plate 2 .001% control
Plate 3 .01% control
Plate 4
.1%
control
Plate 5 1%
Plate 6
control
Approximate Budget $20. Timetable One hour and 30 minutes working time; six days waiting time. Step-by-Step Instructions
1%
control
Experiment 2 setup. Plate progression: Bacteria exposed to soap move to increasingly higher concentrations; the control bacteria are never exposed to soap. GAL E GR OU P.
1. Turn the covered petri dish upside down and use a pen to divide the plate in half. Mark the left half ‘‘.0001%’’ and the right half ‘‘Control.’’ Write the date on the side of the dish. 2. Make up the concentrations by first mixing a 1% concentration of soap water. Stir 1 teaspoon (5 milliliters) of liquid soap with 2 cups and 4 teaspoons (500 milliliters) of water. Mix thoroughly, cover, and label ‘‘1%.’’ 3. To make a .1% concentration: Measure 1 teaspoon of the 1% solution and add to a clean container. Mix in 9 teaspoons of water. Mix thoroughly, cover, and label ‘‘1%.’’ 4. To make a .01percent concentration: Measure 1 teaspoon of the .1% solution and add to another clean container. Mix in 9 teaspoons of water. Mix thoroughly, cover, and label ‘‘.01%.’’ Experiment Central, 2nd edition
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5. To make a .001% concentration: Measure 1 teaspoon of the .01% solution and add to another clean container. Mix in 9 teaspoons of water. Mix thoroughly, cover, and label ‘‘.001%.’’ 6. To make a .0001% concentration: Measure 1 teaspoon of the .001% solution and add to another clean container. Mix in 9 teaspoons of water. Mix thoroughly, cover, and label ‘‘.0001%.’’ 7. Use a fresh cotton swab to spread the .0001% solution over the agar that is marked ‘‘.0001%.’’ Keep the swab flat or at a slight angle so as not to puncture the agar. 8. Dip a cotton swab in distilled water. 9. Run the swab over a source of bacteria and spread the bacteria over the agar in the soap half of the dish. 10. Get a new cotton swab. Use the same source of bacteria and spread the bacteria over the Control half of the dish. 11. Place the lid on Plate 1 and turn it upside down. Store it in a warm temperature for 24 hours. (If there is little to no growth on both the Control and soap sides, let sit another 24 hours.) 12. Repeat Step 1 with Plate 2, marking the left half ‘‘.001%.’’ 13. With a fresh cotton swab, collect bacteria from the soap water side of Plate 1 and spread it on the half of the agar marked ‘‘.001%’’ in Plate 2. 14. Use a fresh cotton swab to collect bacteria from the Control side of Plate 1 and spread it on the half of the agar marked Control in Plate 2. Throw Plate 1 away. Place the lid on Plate 2 and turn it upside down. Store in a warm temperature for 24 hours. 15. Repeat this process for the .01% (Plate 3) and .1% (Plate 4), waiting 24 hours or longer between new plates. 16. Have ready Plate 5 and Plate 6. After dividing the plates, mark the left-hand side of both plates ‘‘1%.’’ 17. Use a cotton swab to collect bacteria from the .1% side of Plate 4 and spread it on the 1% half of Plate 5. 18. With a new swab, collect some of the Control bacteria from Plate 4 and spread it on the Control on Plate 5, the Control for Plate 6, and the 1% on Plate 6. This bacteria has had no exposure to any soap. 19. Place lids on Plates 5 and 6 and turn them upside down. Store in a warm temperature for 24 hours. 20. Count the colonies on the 1% solution on both Plate 5 and Plate 6. 98
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Summary of Results Examine your data. How do
the bacterial growths on Plates 5 and 6 compare with each other? Was your hypothesis correct? Write a description of the bacteria on both plates. If you have a magnifying glass or microscope you could take a closeup look at the bacteria. What was the main difference between the bacteria spread on both plates? Write a summary of the experiment that explains each step in the process and the reason for it. Change the Variables There are several variables
you can change in this experiment to provide new data: • Change the brand or type of soap, to a nonantibacterial soap, for instance, or to an antibacterial soap that has a different main ingredient • Use a cleansing agent instead of soap • Alter the growing temperature of the bacteria • Use one type of bacteria by isolating one type before you begin the experiment (the easiest way is to purchase a single type of bacteria from a biological supply company; you could also streak a bacteria mix onto an agar plate to thin out the population until a bacteria of one color and shape grow) • Use a mixture of different bacteria by collecting it from another source
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: There was no difference in the amount of growth between the bacteria on Plates 5 and 6. Possible cause: The soap that you used may need a higher concentration than 1% to inhibit bacterial growth. Spread varying concentrations of the soap on nutrient agar plates and grow bacteria on each concentration. When you have determined the concentration that kills most of the bacteria, use that figure as the end concentration that will go on Plates 5 and 6. Dilute that concentration one thousand fold and repeat the experiment, increasing the concentration by tenfold each growth period. Problem: At one point there was no growth on a plate. Possible cause: You may have stored the plate in an environment that harmed the bacteria or caused it not to grow, such as if it was too cold. Continue the experiment at the last plate with growth, storing the plate in a warm environment.
Modify the Experiment This experiment requires numerous steps and
careful measuring. For a simpler variation that also explores antibacterial soaps and bacteria you can compare how antibacterial and non-antibacterial soaps affect bacteria. Make a hypothesis on whether antibacterial soap will get rid of the amount of bacteria more, less, or the same as the nonantibacterial counterpart. You will need an antibiotic and non-antibiotic soap that are the same brand and type (such as liquid or a bar), cotton swabs, and three nutrient Experiment Central, 2nd edition
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agar plates (or other growth medium). You can use your fingers for a source of bacteria so find a time right before your hands are ready to be washed. Gently rub a cotton swab down the side of one finger and spread the swab over the agar in a plate labeled ‘‘Control.’’ Wash one of your fingers with bacterial soap, rinse and allow your finger to dry. Make sure you don’t rub your finger against your clothes or other item where bacteria may live. Rub a swab along your finger and spread this swab over the agar in a plate labeled ‘‘Antibacterial.’’ Wash a third finger with non-antibacterial, plain soap. Rinse, dry, swab, and spread the swab to a ‘‘Plain Soap’’ agar plate. Cover and place all three plates in a warm area. After several days examine the three plates for bacteria. How does the control compare to the soap plates? If there is no growth on the control, your fingers may have been too clean! Do the two plates from the different soaps contain about the same amount of bacteria? Was your hypothesis correct? Consider when using antibacterial soap might or might not be a good idea. You may want to allow the plates to sit for several more days to observe bacteria growth.
Design Your Own Experiment How to Select a Topic Relating to this Concept There are thousands of
species of bacteria living and growing around you, in you, and on you. For a project, you could examine the differences among different types of bacteria. You could also examine bacteria’s growth requirements, or how bacteria have impacted life on Earth. Check the Further Readings section and talk with your biology teacher to learn more about bacteria. You could also try to get access to a microscope so that you can look at the bacteria in more detail. Steps in the Scientific Method To conduct an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. 100
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• State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In
any experiment you conduct, you should look for ways to clearly convey your data. You can do this by including charts and graphs for the experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. You might decide to conduct an experiment that lasts several months. In this case, include pictures or drawings of the results taken at regular intervals. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings.
A decomposing house plant is a common example of bacteria at work. Many bacteria live in soil and decompose dead plants, returning needed nutrients back into the environment. # KE LL Y A. QUI N.
Related Projects Bacteria are in and around people every day, opening the
door to many projects that are interesting and inexpensive. You could experiment with different growth mediums, making your own or adding variables to one medium. You could explore bacteria’s role in the life cycle, conducting a project with plants and bacteria. You could look at how different plants use bacteria. Other bacteria roles you could look at are in the soil and natural water sources. People and animals also house thousands of different bacteria. You could try to isolate some types of bacteria and determine their role and growing requirements. You can also examine people’s use of bacteria. Foods make use of these microorganisms’ natural role. You could also examine how bacteria cause foods to spoil. Bacteria are the key to making cheeses. Yogurt and buttermilk are made from the bacteria in milk. You could experiment with using bacteria to grow yogurt. In biotechnology, people use bacteria to produce medicines, improve cleaning products, and make proteins. You could conduct a research project on how extremophiles and other more common types of bacteria are used. Experiment Central, 2nd edition
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For More Information American Museum of Natural History. ‘‘The Microbe Size O Meter.’’ Meet the Microbes! http://www.amnh.org/nationalcenter/infection/01 mic/01d size01. html (accessed on March 2, 2008). A look at the sizes of bacteria relative to familiar objects. American Society of Microbiologists. Meet the Microbes. http://www. microbeworld.org/microbes (accessed on March 2, 2008). Clear information on bacteria and other microorganisms, and the people who study them. ‘‘The Germ Theory of Disease.’’ Timeline Science. http://www. timelinescience.org/resource/students/pencilin/pencilin.htm (accessed on March 2, 2008). A brief history of the many people and events that led to understand microorganisms and disease. ‘‘Microbiology.’’ Cells alive! http://www.cellsalive.com/toc micro.htm (accessed on March 2, 2008). Interactive animations, articles, and real time bacteria growing. U.S. Food and Drug Administration. ‘‘The Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins Handbook.’’ Center for Food Safety & Applied Nutrition. http://vm.cfsan.fda.gov/mow/intro.html (accessed on March 2, 2008). Detailed information on microbes that can contaminate food and cause diseases.
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Biomes
I
f you have ever hiked in a forest or driven through a desert, what you saw was a biome. Biomes are large geographical areas with specific climates and soils, as well as distinct plant and animal communities that are all interdependent. Most biomes are on land. Our oceans make up a single biome. Besides temperate forest and desert, the major land biomes include tundra, taiga (pronounced TIE-gah), temperate deciduous (pronounced deh-SID-youus) forest, tropical rainforest, and grassland. To understand how biomes work, let us look at some of them.
Into the woods Maybe you have hiked in a taiga biome, the biome that receives the most snow. Unlike its neighboring biome, the tundra, which is treeless and characterized by low-lying plants, the taiga is sometimes called the boreal (pronounced BORE-e-al) coniferous (pronounced CONE-if-er-us) forest and is probably the largest of all the land biomes. The taiga biome extends across the northern parts of North America, Asia, and Europe. It is dominated by coniferous, or cone-bearing, trees such as pine, spruce, larch, and fir. These trees resist cold, which is a good thing, because temperatures have been recorded as low as–90˚F (–67˚C) and reach an average of only 59˚F (15˚C). The tree roots do not penetrate deeply and tend to interconnect with other tree roots around them. Each tree is basically held down by its neighbors on all sides. Trees in the taiga biome survive in soil that is frozen for most of the year. Soil moisture comes from melted snow and summer rains, but during the winter, the cold temperatures make water absorption difficult because the ground is frozen. So these trees have built-in adapters to help them survive. For example, spruce and fir trees have long, thin, waxcovered needles. The waxy surface acts as an insulator, helping them retain water and heat. Snow slides off more easily, avoiding branch breakage. These needles conduct photosynthesis so efficiently that they can make food even during winter, when the Sun’s rays are weaker. 103
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Pine, spruce, and fir trees form part of the taiga biome. PH OT O RE SEA RC HE RS I NC.
Trees are not the only inhabitants of this biome. About 50 species of insects, including mites, live here. Moose, snowshoe hares, deer, and elk make their home in the taiga as well as wolves, porcupines, lynxes, and martens, who roam the taiga during the summer. Seeds from the cones of the trees are food for red squirrels and for birds such as crossbills and siskins. Life in the desert—with air conditioning If you drive through a desert, do you see much life from your car window? Do not be fooled. There is more living here than just cactus plants. Desert biomes are on every major continent and cover more than a fifth of Earth’s surface. While these biomes receive less than 10 inches (25 centimeters) of rainfall a year, with temperatures that range from 75˚F (23˚C) to 91˚F (32˚C), desert plants and animals thrive here. Deserts can usually be found in the centers of continents and in the rain shadows of mountains. Lizards, snakes, and other animals pop up at sundown when the soil is cool, then wriggle back into their habitats when the temperature becomes too chilly. They can reappear again at dawn, remaining until the temperature gets too hot. Some of the rodents and other animals that burrow under the soil actually enjoy a kind of underground air-conditioning. They form elaborate tunnels where the Sun’s heat cannot penetrate. And moisture from the animals’ exhaled breath cools the air and makes their burrows a
Low-growing bushes in Monument Valley are part of this biome’s vegetation. PHO TO R ES EAR CH ER S IN C.
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comfortable 85˚F (29˚C). Kangaroo rats in the American Southwest and the gerbils of North African and Asiatic deserts choose foods that reduce the amount of water needed for digestion. These rodents can actually absorb water from their urine before excreting wastes. Many desert plants are xerophytes (pronounced ZERO-fights), plants that require little water to survive. There are also ephemerals (pronounced ehFEM-er-als), plants that can suspend their life processes for years when the soil becomes too dry. When major rainstorms occur, they burst into life. Succulents are another type of plant. They retain water in thick fleshy tissues. Birds use the giant saguaro (pronounced sah-GWA-ro; from the Spanish word for the Pima Native American name of this plant) cactus, a succulent plant that grows 50 feet (15 m) high, as nesting and resting areas in place of trees. The saguaro cactus is a good example of the interdependence that takes place in a biome. Red-tailed hawks use the branches to nest. Hollowed-out trunk and arm spaces are a home for elf owls and gila woodpeckers. The cactus fruits are eaten by rodents, birds, and bats. Why save the rainforests? Many people are concerned about saving rainforests because these biomes contain a large number of unique plants. Several acres of rainforest in Borneo may contain 700 different species of trees. More than 50,000 plant species make their home in the rainforests of the Amazon Basin in South America. Up to 80 different species of plant life might grow on one tree. Tropical rainforests are found only in regions north of the
Heat and humidity helped form this lush Costa Rican rainforest. PH OTO RE SEA RC HER S I NC.
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WORDS TO KNOW Biomes: Large geographical areas with specific climates and soils, as well as distinct plant and animal communities that are interdependent. Boreal: Northern. Coniferous: Refers to trees, such as pines and firs, that bear cones and have needle-like leaves that are not shed all at once. Deciduous: Plants that lose their leaves during some season of the year, and then grow them back during another season. Desert: A biome with a hot-to-cool climate and dry weather. Desertification: Transformation of arid or semiarid productive land into desert.
Fungus (fungi): Various single-celled or multicellular organisms, including mushrooms, molds, yeasts, and mildews, that do not contain chlorophyll. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Succulent: Plants that live in dry environments and have water storage tissue. Taiga: A large land biome mostly dominated by coniferous trees. Temperate: Mild or moderate weather conditions. Tundra: A treeless, frozen biome with low-lying plants.
Ecosystem: An ecological community, including plants, animals and microorganisms, considered together with their enviroment.
Variable: Something that can affect the results of an experiment.
Ephemerals: Plants that lie dormant in dry soil for years until major rainstorms occur.
Xerophytes: Plants that require little water to survive.
Materials for Project 1. GA LE GR OU P.
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equator on the Tropic of Cancer and south of the equator in the Tropic of Capricorn. Destroying the rainforests reduces the diversity of life on Earth. If you have ever been in a steamy greenhouse, then you can imagine what a rainforest is like. Warm temperatures average 75˚F (23˚C) and humidity peaks at a dripping 90% for days at a time. This climate encourages an explosion of plant life that supports many different animals. Some scientists estimate that half the living species on Earth live in the rainforests. Constructing your own mini-biome will help you understand some of the major factors that influence these important areas of life and can cause them to survive or fail. Experiment Central, 2nd edition
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PROJECT 1 Building a Temperate Forest Biome Purpose/Hypothesis Biomes are strongly influ-
How to Experiment Safely Ask for assistance when carrying and lifting the fish tank. Do not leave the light fixture on for more than 10 hours at a time.
enced by the climate and soil type in a particular region. These same factors determine the success of a mini-biome model. In this project, you will attempt to build, grow, and maintain a temperate forest biome. This particular biome is characterized by a temperature range of 32 to 68˚F (0 to 20˚C). It has an annual precipitation of 20 to 95 inches (50 to 240 cm) and a fairly deep soil layer. The purpose of this project is to try to maintain the correct climate, soil, and vegetation in the temperate forest biome.
Level of Difficulty Moderate. (This project requires continuous tending and
attention to maintain a proper climate.) Materials Needed
• • • • • • • •
l0-gallon fish tank (plastic, if possible, for safety) indoor/outdoor thermometer watering container gravel sand topsoil incandescent light fixture with a 40-watt bulb (optional) plants and/or seeds (choose oak, maple, sassafras, hickory, tulip trees, sweet gum, dogwood)
Maple and oak leaves, examples of deciduous trees. GA LE GRO UP .
Note: Choose all deciduous trees. Seeds may be hard to grow unless they have been chilled. If you use trees, they should be very small saplings. Approximate Budget $25. (Try to use an old fish
tank if possible.) Timetable One hour to set up the project and at
least six months to maintain the trees and observe changes. Experiment Central, 2nd edition
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Step-by-Step Instructions
Troubleshooter’s Guide
1. l. Place a 1-inch (2.5-centimeter) layer of gravel on the bottom of the fish tank. When you are building a natural environment, 2. Place a 1-inch (2.5- centimeter) layer of many forces of nature can affect the experisand over the gravel. ment. These include fungus, insects, and too 3. Mix 2 parts of topsoil to 1 part of sand. Place much or too little water. Here are some a 2- to 3-inch (5- to 7.5- centimeter) layer of common problems and a few tips to maintain the sand/topsoil mixture over the sand layer. the best environment. 4. Plant four to six trees. Be sure to cover all the • Mushrooms, a kind of fungus, may grow. roots. If seeds are being used, place them Water less, but never allow the soil to dry 1 inch (2.5 cm) down in the soil and allow completely. one month for them to sprout. • Pests such as insects and spiders may make this biome their home. If they are 5. Place the thermometer inside the terraeating the plants, remove the pests. If rium against the back wall. not, keep them. They are performing 6. Water gently until approximately 0.25 their natural role in the ecosystem. Their inch (0.6 centimeter) of water has accupresence is a sign of a healthy biome. mulated in the gravel layer. • Drastic temperature changes overnight 7. Place the fish tank outside or in a sunny can kill the plants. Do your best to mainplace indoors. You must maintain the temtain an acceptable climate in the fish perature of the fish tank in the range of 32 tank. You may have to move it inside or place it in a shady spot outside, protected to 60˚F (0 to 15˚C). If you need to provide from too much rain. artificial light, place the incandescent fixture above the fish tank and provide five to 10 hours of light per day. 8. Check the project daily, and maintain 0.25 inch (0.6 centimeter) of water in the gravel. Steps 1 to 5: Set-up for fish tank 9. Record the growth of the plants and the temperature range. with plants and overhead light. GA LE GRO UP.
Summary of Results Graph the data you have collected over the six-month period. The overall growth of the plants will demonstrate the health of the biome environment.
PROJECT 2 Building a Desert Biome Purpose/Hypothesis In this project, you will
build, grow, and maintain a desert biome. The desert biome is characterized mainly by its lack of 108
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water, which causes harsh growing conditions. Maintaining the right climate, soil, and vegetation is the goal. This particular biome is characterized by a temperature range of 23 to 60˚F (6 to 30˚C). Level of Difficulty Moderate to difficult because
How to Experiment Safely Ask for assistance when moving the fish tank. Do not leave the light fixture on for more than 10 hours at a time, as it will get too hot.
of the length of time needed for the project. Materials Needed
• • • • • • • •
10-gallon fish tank indoor/outdoor thermometer watering container gravel sand topsoil incandescent light with 60-watt bulb succulent plants, such as jade plant, strawberry cactus, barrel cactus, etc.
Note: Most plants are easily found in local nursery stores selling houseplants. Approximate Budget $25. (Try to get an old fish tank to use.) Timetable One hour to set up the project and at least six months to
maintain the plants and observe changes. Step-by-Step Instructions
1. Place a 1-inch (2.5-centimeter) layer of gravel in the bottom of the fish tank. 2. Mix 1 to 2 cups of topsoil with 6 to 10 cups of sand. Place this mixture over the gravel layer. 3. Place 2 inches (5 centimeter) of sand over the sand/topsoil layer. 4. Plant the cactus and succulents in the fish tank and cover the roots completely. 5. Place the thermometer inside the fish tank, against the back wall. Experiment Central, 2nd edition
Strawberry and barrel cactuses. GA LE G RO UP.
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Troubleshooter’s Guide In this model, climate conditions are designed to be extreme. The plants have special adaptations to adjust. If insects become a problem, remove them.
6. Water sparingly. Pour 2 cups of water on the sand to start. Water the fish tank with 1 cup of water every week after that. 7. Place the light fixture above the fish tank and leave it on for eight to 10 hours a day. 8. Check the fish tank daily. Record any differences in the plants’ growth and in the temperature range. Summary of Results Graph the data you collected
during the project, as illustrated in the Desert Biome Growth Chart. You will notice very little change, as the plants have a very slow growth cycle. Modify the Experiment For a more in depth understanding of desert
biomes, you can further investigate how organisms have adapted to life in the desert. In Project 2 you constructed a desert biome, concentrating on the physical features of a desert. Now you can measure one way in which desert plants have adapted to their environment. Cacti have many adaptations that help them collect and store water. Do you think if cacti were given the same amount of water as a leafy, temperate forest plant it would release the same amount of water? Begin the experiment in the morning. Collect one of the leafy plants you used in the temperate biome project and one cacti from the desert biome. Both should be healthy,
Steps 1 to 5: Set-up for fish tank with cactus, light, thermometer, and sand and gravel layers. GAL E GR OU P.
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Desert Biome Growth Chart. GA LE G RO UP.
growing in a pot. Gently place a small baggie over the top of the cactus and tie with a twisty-tie or string. Tie a small baggie over the leaf of the temperate plant. Pour one-quarter cup of water in each pot. If the plants are large, you may want to use more water. The exact amount does not matter, as long as it is the same for both plants. Place both plants in the sun or under a plant light. At the end of the day, examine the bags. Are there droplets of water in one bag and not the other? Take off the bags and replace them the next morning (the plants need oxygen to live). Did you see the same thing at the end of the second day? Examine the structure of the cactus compared to the temperate plant. Where do you think it is storing water?
Design Your Own Experiment How to Select a Topic Relating to this Concept The fish tank projects are
models of what takes place in a biome. Many plants and animals have specific adaptations that are suited to that biome or region. What happens when you change the climate of a biome? How does the introduction of a plant from a different biome affect the other plants? There are many experiments you could design to investigate the interactions of plants and animals with their biomes. Experiment Central, 2nd edition
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Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on biome questions that interest you. Steps in the Scientific Method To do an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results It is important to docu-
ment as much information as possible about your experiment. Part of your presentation should be visual, using charts and graphs. Remember, whether or not your experiment is successful, your conclusions and experiences can benefit others. Related Projects More specific projects can be performed to get more detailed information about biomes. For instance, scientists are finding that many rainforests are getting drier. Also, a phenomenon called desertification has been occurring, turning naturally dry land into desert. Try an experiment in desertification, reducing water to see what happens.
For More Information Morrison, Marion. The Amazing Rain Forest and Its People. New York: Thompson Learning, 1993. Provides a good summary of this ecological community and how interdependency affects this biome. Rainis, Kenneth. Environmental Science Projects for Young Scientists. New York: Franklin Watts, 1994. Describes biome and related projects for young people. Sayre, April Pulley. Taiga. New York: Twenty First Century Books, 1994. Explores the taiga biome, its animals, plant life, the people who live there, and their impact. University of California Museum of Paleontology. ‘‘The world’s biomes.’’ http://www.ucmp.berkeley.edu/exhibits/biomes/index.php (accessed on January 18, 2008). 112
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Bones and Muscles
W
henever you run, sit, walk, or even stand, your bones and muscles are working together in the activity. Bones are similar to the framework of a building; they provide the shape and protection. Our bones also produce our much-needed supply of daily blood cells—about 200 billion a day! They are the holding places for minerals and other key substances the body needs. Many muscles are attached to bones and they pull the bones for movement. Other muscles provide much-needed functions for daily life. Even when you are just sitting still, your muscles are at work. They are allowing you to breath, swallow, smile, and even move your eyes. And it is a muscle that powers your entire body—the heart muscle. Working nonstop through a person’s life, this vital muscle beats an average of seventy times per minute.
Bones, bones, bones An adult body has about 206 bones. The number varies from person to person because of differences in the number of small bones. Some bones are responsible for movement, including bones in the hands, feet, and limbs. Other bones primarily give protection to the internal structures, such as the skull protecting the brain and the ribs shielding the heart, lungs, and liver. When looking at animal bones or at a skeleton, bones may appear to be static and dead, but in the body they are actually full of activity. Bones grow and change along with the person. They are made of living and nonliving materials: About 70% of an adult’s bones are composed of minerals. The remaining part is bone tissue, a group of similar cells with a common function. Bone tissue is constantly building new bone. In fact, about every seven years your bone tissue makes essentially a whole new skeleton. Wherever two bones meet there is a joint. In some places, such as the bones in the skull, the joints are locked together and do not move. Most joints are movable, though, and are coated with a fluid that acts as a lubricant. Ligaments are a tough connective tissue that links bones together at the joints. Ligaments prevent the bones at the joints from becoming 113
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dislocated. Cartilage is another connective tissue found at the end of the bones and in the joints. This is a smooth and flexible tissue that lets one bone slide smoothly over another. Hard and spongy Almost every bone in the body is made of the same materials: The outside of the bone is the hard layer that is strong. It is made of living cells and is called compact or hard bone. Holes and channels run through the compact bone, carrying blood vessels and nerves to its inner parts. Inside this layer is cancellous bone or spongy bone. Cancellous bone has cells with large spaces in between them like a honeycomb. The spaces in this network are filled with a jellylike red-and-yellow bone marrow. Red bone marrow, found mainly at the ends of bones, makes most of our body’s blood cells. Red bone marrow also produces white blood cells, which help fight infection, and platelets, which help blood clot. Yellow bone marrow stores fat and releases it when it is needed somewhere in the body.
Full frontal view of a human skeleton. PH OT O RE SEA RC HE RS I NC.
Bones contain large amounts of a protein called collagen as well as minerals, including calcium and phosphorous. Collagen gives bones their elasticity. Calcium is what gives bones their strength. Extra minerals are stored in the bone, and the bones release them when they are needed by other parts of the body. The amount of minerals that a person eats affects how many minerals the bones contain and store. As a person gets older, the amount of new bone created slows down and bones break down at a faster rate than they are being made. Women especially may lose the stored calcium in their bodies that helps keep their bones strong and healthy. This causes the bones to become weak, which can lead to breaks. The disease osteoporosis occurs most often among older people. In osteoporosis bone tissue becomes brittle and thin. Bones break easily, and the spine can begin to collapse. Building up adequate stores of calcium in the bones as a young adult is one important way people can prevent or delay the development of this disease.
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Muscular strength Bones are moved by muscles attached to them. These muscles are fastened to bones by a thin, tough tissue called tendons, which also link muscles to other muscles. Muscles come in all shapes and sizes. The human body has about 650 muscles, which make up about 40% of a person’s body weight. Muscles are classified as voluntary or involuntary. Voluntary muscles are those you can control at will, such as moving your arm. Involuntary muscles act automatically, such as your stomach muscles digesting food. Some muscles fit into both categories, such as the muscle used in blinking your eyes. Muscles are made of stacks of long, thin cells called muscle fibers. Each muscle fiber is a single cell and contains at least one nucleus. The nucleus (plural: nuclei) is an enclosed structure that contains the cell’s genetic material and controls its growth and reproduction. There are three types of muscle fibers: skeletal, smooth, and cardiac. Skeletal muscle fibers are attached to bone and are voluntary muscles. They are the most abundant and largest of the three, with some fibers running more than a foot long. Each skeletal muscle fiber has several nuclei. Smooth muscle fibers are involuntary, as in the stomach and intestines. They are smaller than the skeletal muscles and are narrow at the ends, with one nucleus in each cell. Cardiac muscles are found only in the heart. These muscles have fibers that are tightly packed together and have branches. A cardiac muscle cell usually has a single nucleus. When muscles go into action they work in terms of contractions and relaxations. Muscles can only pull bones because they can only contract, or get shorter. They cannot push bones back into their original position. Because of this, muscles work in pairs. When one muscle contracts it can bend a limb; then when that muscle is finished contracting, its partner muscle contracts to extend or straighten the limb. Whenever you bend your arm, for example, the bicep muscle in the front of the upper arm contracts. When the arm Experiment Central, 2nd edition
Cancellous (spongy) Bone Yellow Marrow
Compact (hard) Bone space containing Red Marrow
Parts of the human bone. GA LE GRO UP .
The three types of muscle fibers. GAL E GR OU P.
Skeletal Muscle Fiber Muscle Cell
Smooth Muscle Fiber
Nucleus
Cardiac Muscle Fiber
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straightens, the bicep relaxes and the tricep muscle at the back of the upper arm contracts. All the energy that muscles use is created when muscle cells process the carbohydrates, fats, and proteins in foods. Healthy muscles burn nutrients efficiently. The amount a person exercises and his or her general health will make muscles work better and become less fatigued. Muscle fatigue occurs when the muscle stops contracting. When muscle cells run out of oxygen, they reach a point where the muscles have a reduced ability to contract. When a person builds his or her muscles, the muscle fibers grow. This increases the blood flow in the fibers, increasing their ability to contract.
EXPERIMENT 1 Bone Loss: How does the loss of calcium affect bone strength?
A humped back is a sign of osteoporosis. Elderly women especially are prone to developing this disease.
Purpose/Hypothesis Your bones are lightweight and incredibly strong. Bones get their strength from a hard outer shell that contains the mineral calcium carbonate. The calcium keeps the bone stiff and rigid. A strong acid can chemically react with the bones and remove much of the calcium carbonate.
# LESTER V. BERGMAN/CORBIS.
Muscles work in pairs because they can only contract. Here, one contracts to bend the arm; its partner muscle contracts to straighten it. GAL E GR OU P.
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Biceps contracts
Triceps contracts
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WORDS TO KNOW Bone joint: A place in the body where two or more bones are connected. Bone marrow: The spongy center of many bones in which blood cells are manufactured.
Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Bone tissue: A group of similar cells in the bone with a common function.
Ligaments: Tough, fibrous tissue connecting bones.
Cancellous bone: Also called spongy bone, the inner layer of a bone that has cells with large spaces in between them filled with marrow.
Muscle fibers: Stacks of long, thin cells that make up muscle; there are three types of muscle fiber: skeletal, cardiac, and smooth.
Cartilage: The connective tissue that covers and protects the bones.
Nucleus, cell: Enclosed structure within a cell that contains the cell’s genetic material and controls its growth and reproduction. (Plural: nuclei.)
Collagen: A protein in bone that gives the bone elasticity. Compact bone: The outer, hard layer of the bone. Contract: To shorten, pull together.
Tendon: Tough, fibrous connective tissue that attaches muscle to bone. Variable: Something that can affect the results of an experiment.
In this experiment you will determine how the loss of calcium carbonate affects the strength of bones. You will use vinegar as the acid. The vinegar will react with three bones for varying lengths of time. The longer the vinegar reacts with the bone, the more calcium the vinegar will remove from the bone. How much you can bend the bone will allow you determine the bone’s strength. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of bones and the mineral calcium. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Experiment Central, 2nd edition
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A hypothesis should be brief, specific, and measurable. It must be something you can test What Are the Variables? through further investigation. Your experiment will prove or disprove whether your hypothesis is Variables are anything that might affect the correct. Here is one possible hypothesis for this results of an experiment. Here are the main variables in this experiment: experiment: ‘‘The more calcium a bone loses, the weaker the bone will be and the more it will bend.’’ • the type of bone you use In this case, the variable you will change is the • the thickness of the bone amount of time the bones react with the vinegar • the cleanliness of the bone or acid. The variable you will measure is the • the solution the bone is soaked in bone’s strength or how much the bone bends. • residue in the jars Conducting a control experiment will help • the environment of the bones when they you isolate each variable and measure the are not soaking changes in the dependent variable. Only one In other words, the variables in this experiment variable will change between the control and are everything that might affect the vinegar the experimental bones, and that is the solution reacting with the bone. If you change more that immerses the bones. For the control, you than one variable at the same time, you will not will soak a bone in plain water, which does not be able to tell which variable had the most effect on bone strength. react with the bone. At the end of the experiment you will compare the water-soaked bone with each of the vinegar-soaked bones. For your experiment you will select four bones of the same type that are of equal thickness and general appearance. You will soak three of the bones in vinegar and one of the bones in water. Every four days you will remove each of the vinegar-soaked bones and test its strength. To compare the bones again at the end of the experiment, you will wrap each of the bones after the allotted period of time. If you leave them in the open air, the bone will react with the carbon dioxide in the air and harden again. Level of Difficulty Easy/Moderate. Materials Needed
• 4 similar chicken bones (drumsticks from chicken wings work well) • vinegar, white • 4 glass jars with lids, large enough to hold a bone • marking pen • masking tape • plastic wrap 118
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Approximate Budget $5. Timetable 20 minutes initial setup time; another
30 minutes spread out over the next 12 days. Step-by-Step Instructions
How to Experiment Safely Vinegar is an acid. Be careful about getting any of the vinegar in your eyes. Do not eat any of the vinegar-soaked bones. Throw them out after the experiment is complete.
1. Clean the four bones thoroughly, scrubbing them with water. 2. Place a piece of masking tape on each jar and label the first jar ‘‘Control,’’ the second jar ‘‘4 Days,’’ the third ‘‘8 Days,’’ and the last ‘‘12 Days.’’ 3. In the control jar, cover the bone with water. In the other three jars, cover the bones with vinegar. Set the jars aside. 4. After four days, open the ‘‘4 Day’’ jar and rinse off the bone with water. Test the strength of the bone by trying to bend it. While the bone is still wet, wrap it in plastic wrap thoroughly. Rinse the jar clean and place the wrapped bone back in the jar, screw on the lid and set it aside. 5. Repeat Step 4 after another four days for the bone in the ‘‘8 Day’’ jar. Repeat again four days later for the ‘‘12 Day’’ jar, except do not place the bone in plastic wrap.
Control
4 days
8 days
12 days
Steps 2 and 3: Label each jar. Cover the bone in the control jar with water; cover the bones in the other jars with vinegar. GA LE G RO UP.
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The bones all have the same strength, even after 12 days. Possible cause: The bones you used may be too thick. Try repeating the experiment, increasing the amount of soaking time by doubling the days. You could also repeat the experiment using bones that are thinner.
6. Unwrap the other bones and examine how far each bone bends. Rinse the control bone with water and compare the strength of the three bones to the control. 7. Create a graph of the results, using an estimate of the degree the bones bend for the y-axis, and the number of days of calcium loss on the x-axis. Summary of Results Examine your graph of the
data. How did the control bone compare to the bone with the greatest calcium loss? What do the bones feel like? Do they feel different from each other? Think about how the loss of calcium in bones would affect a person. What can this experiment teach you about osteoporosis in older people? Change the Variables You can vary this experiment by changing the
thickness or type of bone you use. Do you get the same results with a turkey bone as a chicken bone? You could also try leaving the bones out in the air for several days after they have finished soaking in vinegar and compare the results. You could also try comparing the same type bone from a young animal and an old animal. You may have to talk with your local butcher for help in selecting the bones.
EXPERIMENT 2 Muscles: How does the strength of muscles affect fatigue over time? Purpose/Hypothesis Skeleton muscles are the muscles attached to bones
that are at work during physical activity. A muscle contracts when it is flexed or at work. The number of contractions a muscle can make is affected by fatigue. In this experiment you will examine if a muscle can increase the number of contractions with muscle use, thereby reducing muscle fatigue. You will measure your muscle contractions through squats. The quadriceps muscles in the front of the upper legs are one of the main muscles used in a squat. A squat also uses the gluteus, hamstrings, and calf muscles. 120
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A friend or family member will time the length of time you conduct the activity before you are What Are the Variables? fatigued. This partner will also count the number of squats you carry out and note them in a chart Variables are anything that might affect the results of an experiment. Here are the main that you should not look at until you have comvariables in this experiment: pleted the entire experiment. Not allowing you to know the number of muscle contractions you have • the time of day completed will make the experiment more objec• your nutritional level before you conduct tive by not giving you a number to ‘‘beat.’’ Try to the trial think of something else during the experiment so In other words, the variables in this experiment you do not count the squats for yourself. are everything that might affect how many You will repeat the experiment every other times you can complete a squat. If you change more than one variable at the same time, you day, until you have completed 10 trials. will not be able to tell which variable had the Before you begin, make an educated guess most effect on fatigue. about the outcome of this experiment based on your knowledge of muscle strength and fatigue. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The stronger muscles will become less fatigued and will gain strength over time.’’ In this case, the variable you will change is the strength of the muscles. The variable you will measure is the number of times your muscles can contract. To equate all the other variables, conduct the experiment at roughly the same time of day. At the end of the experiment you will examine how your muscles have changed over time. Level of Difficulty Easy Materials Needed
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Approximate Budget $0.
How to Experiment Safely Working a muscle too hard can cause soreness and damage to your muscle. Stop the activity if you feel dizzy or experience physical discomfort. Keep your feet firmly on the floor at all times and breathe regularly. If you have knee problems, do not do this experiment. Check with a parent or physical education teacher for a replacement activity.
2.
3. Step 3: Squat until your knees are above your toes; stop when you get fatigued. G ALE GRO UP.
4. 5.
Timetable Approximately five minutes per trial
for a period of 10 trials. Step-by-Step Instructions
1. Have your partner begin timing when you start your first squat. Your partner will count the number of squats you do at each trial. Try to think of something else during the experiment so you do not count the squats for yourself. To conduct the squat, get into a comfortable upright stance, with your feet shoulder-width apart and your toes pointed straight ahead. Don’t point your toes inward, because this will put a lot of strain on your knees. Extend your arms. Squat down until your knees are over your toes. Pretend you are sitting in a chair. Make sure to keep your heels planted firmly on the floor. Return in an upright position and repeat at a regular pace. 6. When your muscles become fatigued then stop. Have your partner note the number of squats and the amount of time. Do not look at the chart. 7. Repeat this process every other day for a period of 10 trials. Summary of Results Graph the results of your
data from your first trial to the last trial, making the x-axis the number of squats and the y-axis the trial number. Does the number of muscles’ contractions change over time? Construct a second graph that marks the length of time of each trial on the x-axis with the trial number on the y-axis. How does the length of time you were able to contract your muscles change over time? Write a brief summary of the experiment that relates your results to muscle strength and movement. 122
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Modify the Experiment You can alter this experiment by simplifying the activity and focusing on Troubleshooter’s Guide how nutrition contributes to muscle fatigue. The body converts nutrients (carbohydrates, fats, and Below is a problem that may arise during this experiment, a possible cause, and a way to proteins) into energy. Carbohydrates are the remedy the problem. nutrient most quickly turned into energy for muscles. If you match muscle fatigue to nutrient Problem: There is no change in muscle fatigue over the trials. intake, you can gather data about how nutrients Possible cause: You may be squatting further may affect muscles. You will need to test several down over the trials, which uses more people (you can be one of them). First, make a muscle. Repeat the experiment making sure hypothesis about how nutrient intake will affect to stop your squat each time when your muscle fatigue. knees are over your toes. For the physical activity, look for a hard rubber ball that fits in your hand. You will also need a clock with a minute hand. You will measure how many times you can squeeze the ball in a 30 second time period. Make a note of the number in a chart. Conduct the test two to four times throughout the day, both before you have eaten and after. You could conduct the activity in the morning, both before you eat breakfast and 30 minutes after breakfast. Test several people, also before and after they eat. If possible, test people outside of your family. Make sure you always use about the same time period both before and after eating. For example, if you count the number of times you squeeze the ball after you have not eaten for four hours and then 30 minutes after eating, test other people using those same times. You also may want to note what nutrients you and your test subjects ate. Write down the results in a chart. When you finish, look for any patterns in the chart. Was your hypothesis correct? Aside from nutrients, consider what other factors might contribute to muscle fatigue.
Design Your Own Experiment How to Select a Topic Relating to this Concept To select a related project,
you can explore the different ways that you use your bones and muscles throughout the day. An experiment with bones could include comparing bones from different species. An experiment with muscles could work to identify the characteristics of each of the three muscle fibers. Check the Further Readings section and talk with your science, health, or physical education teacher to learn more about bones and muscles. Experiment Central, 2nd edition
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Steps in the Scientific Method To do an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
Regular exercise allows muscles to burn nutrients more efficiently and increases their ability to contract. # KA RL W EAT HE RLY /C OR BI S.
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects You can design your own experiments on bones and
muscles. Think of some other reasons why people might experience bone decalcification. Investigate a method for testing the impact of other minerals in a bone. You could explore how the bones in different species compare to each other. Do species that are physically similar have similar bone structures? For a muscle experiment, you could examine the characteristics of each of the three types of muscle fibers by purchasing the three different muscles from a butcher. Examine muscle fatigue further by investigating if fatigue is greater at certain times of the day. You could investigate if there are 124
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particular activities that women find fatiguing and men do not. Are there different muscles in the bones of women and men?
For More Information KidsHealth. ‘‘The Big Story on Bones.’’ My Body. http://www.kidshealth.org/ kid/body/bones noSW.html (accessed February 25, 2008). Basic information and diagrams about bones and muscles. MyHealthScore.com. Human Anatomy Online. http://www.innerbody.com/ htm/body.html (accessed February 25, 2008). An interactive look at the skeleton and muscular systems, with descriptions and animations. Simon, Seymour. Bones: Your Skeleton System. New York: Morrow Junior Books, 1998. Clear introduction to the skeleton system using photographs. Simon, Seymour. Muscles: Your Muscular System. New York: Morrow Junior Books, 1998. Clear introduction to the muscular system using photographs. White, Katherine. The Muscular System. New York: Rosen Publishing, 2001. Basic information about the muscular system.
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Caves
C
aves, also called caverns, are natural hollow areas inside the ground that are large enough for a person to fit inside. There are millions of caves on Earth. Some caves, are only a few yards (meters) deep. Others stretch hundreds of miles underground, splitting into numerous rooms and passageways. There are caves underwater, on the sides of mountains, and beneath flat land. Interiors of caves often contain unique landscapes and life forms that are spectacular sights.
Along with their awesome beauty, caves have provided people with important clues to ancient life and geology. The scientific study of caves is called speleology (pronounced spee-lee-AH-lu-gy), from the Greek words for cave, spelaion, and knowledge, logos. Scientists who study these caves are known as speleologists and they are only beginning to unearth the treasure of information that caves contain. Speleologists have found unique animals, new plant life, and clues to Earth’s history. Forming the holes Caves take hundreds of thousands of years to form. There are caves in the process of forming right now, and alreadyformed caves that are undergoing continuous change. The majority of caves are made out of the rock limestone. Limestone is a rock formed millions of years ago out of the hardened remains of layers of sea animals. The formation of a limestone cave begins with water. When rain falls it collects a small amount of the gas carbon dioxide from the air. As the water trickles into the soil, it passes through tiny pockets of air in the soil. The soil is where it picks up most of the carbon dioxide. Carbon dioxide that mixes with water causes the water to change into an acid, called carbonic acid. Carbonic acid water slowly eats away at the soft limestone. It seeps into small cracks, causing the cracks to widen and allowing more water to flow through. Gradually, the water causes the rock to dissolve. The dissolved area grows into a hole, then a larger hole, and still larger. Eventually, over a few million years, the water carves an underground room where there was 127
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stream
soil
Cave formation begins: Water mixes with carbon dioxide to form carbonic acid, which seeps into small cracks in the limestone. GAL E GR OU P.
soil
carbonic acid
carbon dioxide
limestone
once only rock. In time, that room increases in size and can become many rooms with passageways between them. A newly formed cave is filled with water. This water can stay in the cave for hundreds or thousands of years. Water drains out of the cave only when some type of geological shift occurs. The cave may be lifted above the water by a
soil
Cave formation continues: The dissolved rock grows in an increasingly larger hole, eventually forming a cave.
limestone
GAL E GR OU P.
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gradual uplifting of the ground. Or a nearby stream of water can flow through the cave, slicing a deep swath through the cave and causing the water level to drop. Caves often contain remnants of the water in streams or ponds. When the cave is lifted above the water, water flows out of the hole and the cave fills with air. There are several other types of caves also. Sea caves form along rocky shores from the constant pounding of ocean waves. The waves wear away the base of the rocky cliff where the rock is soft or has cracks in it. Seawater carries the rock away and, over time, a cave forms. Lava caves are made after a volcano erupts and the molten, hot lava flows down the side of the volcano. The outer layer of the lava cools and hardens; hot lava continues to flow underneath. When this hot lava drains away it can leave a cave behind. More recently, scientists have discovered that caves can also form from a type of bacteria that live deep beneath Earth. These bacteria use oil for food and release the gas hydrogen sulfide. Hydrogen sulfide reacts with oxygen to produce sulfuric acid, which can dissolve limestone. The Carlsbad Caverns in New Mexico is an example of a limestone cave carved out of sulfuric acid. These caverns contain 83 caves and include the nation’s deepest limestone cave at 1,567 feet (478 meters), and one of the world’s largest chambers. Natural extensions The slow drainage of carbonic acid water can cause the formation of dramatic cave features created after the underground chamber is formed. These features come in many shapes and several different colors. Two types of attributes common in limestone caves are icicle-like extensions that sprout up from the floor or hang down from its ceiling. Stalactites are cave features that hang from the ceiling; stalagmites grow upward from the floor. The formation of these two types of features begins with water droplets. After most of the water has drained from a cave, water continues to flow through layers of the limestone rocks. All the water droplets contain a small amount of dissolved limestone, which carries the mineral calcite. A stalactite begins when a drop of this water hangs from the ceiling. The Experiment Central, 2nd edition
Sea caves form along rocky shores from the constant pounding of ocean waves. FIE LD M AR K PU BL ICA TI ONS .
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water evaporates or drips to the ground and the calcite in the water remains. One droplet builds upon another, the calcite deposits increase and a stalactite grows. Stalactites can reach down hundreds of meters, but watching one grow is a lengthy process. On average, a stalactite grows only about half an inch every hundred years. The upward-growing stalagmites form when stalactite water droplets drip from the ceiling or a stalactite above. When the water droplet hits the floor it stalagmite spatters the calcite deposits outward, but close together. The calcite builds up over time to create finger-like shapes with rounded tops. Stalagmites can grow to both amazing widths and heights, some growing more than 45 feet (13 meters) wide and 30 feet (9 meters) tall. Stalactites and stalagmites are often white or nearly white because the most common form of Stalactites and stalagmites, calcite is white. Iron and other minerals or materials mixing with the calcite common in limestone caves, create rich-colored stalactites and stalagmites, including red, yellow, orange, form gradually over time from and black. the buildup of calcite. G AL E Life in the dark lane A cave’s darkness may deter many life forms from GRO UP. making a home inside, but caves are crawling with organisms that like what a cave offers. Scientists have separated cave animals into three distinct types. Animals that can only survive in the deep interior of caves’ pitchblackness are called troglobites, from the Greek word meaning cave life. Types of troglobites include species of shrimp, insects, and spiders. Many of these animals feature small eyes or blindness, no pigment, and a well-developed sense of touch and smell. Other animals are part-time cave dwellers. Called trogloxenes, meaning cave guest, these animals stay in the cave for sleep, warmth, protection, and to raise their young. Bats are an example of this type of animal. The nocturnal bats doze away the sunny hours in the darkness of a cave. Bats live in colonies and feed at night, catching insects such as moths, beetles, and mosquitoes. Bat colonies are among the largest grouping of mammals in the world. The Bracken Cave in Texas houses twenty million Mexican free-tail bats that eat more than 250,000 pounds of insects every night. Bears, crickets, and pack rats are other examples of trogloxenes. The last type, troglophiles, meaning cave lovers, are animals that live most of their lives in caves but also have the ability to live outside. They like the dampness of the cave and may venture outside to forage for food. 130
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Cave life includes three general categories of animals that live in different areas of the cave. GA LE GR OU P.
Troglophiles include species of salamanders, frogs, beetles, millipedes, snails, and mites. Because green plants need light to live, plants only grow near the entrance where light penetrates. Mosses and ferns are the plants commonly found near the cave opening; algae grows on the rocks. Caves are also teeming with fungi and bacteria that keep the chain of cave life flowing. Droppings from animals, such as bats, can provide the major food source for other cave life, yet few animals can feed on these. Bacteria and fungi decompose these materials into simple foods and nutrients. Small animals, such as insects, also munch on fungi and bacteria for their food supply. These insects then become food, in turn, for larger predators.
Fruit bats hang from the walls of a cave in Bali, Indonesia. # R OBE RT GIL L/ COR BI S.
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WORDS TO KNOW Carbonic acid: A weak acid that forms from the mixture of water and carbon dioxide.
Spelunkers: Also called cavers, people who explore caves for a hobby.
Cave: Also called cavern, a hollow or natural passage under or into the ground large enough for a person to enter.
Stalactite: Cylindrical or icicle-shaped mineral deposit projecting downward from the roof of a cave. (Pronounced sta-LACK-tite.)
Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Stalagmite: Cylindrical or icicle-shaped mineral deposit projecting upward from the floor of a cave. (Pronounced sta-LAG-mite.)
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Troglobite: An animal that lives in a cave and is unable to live outside of one.
Lava cave: A cave formed from the flow of lava streaming over solid matter.
Troglophile: An animal that lives the majority of its life cycle in a cave but is also able to live outside of the cave.
Sea cave: A cave in sea cliffs, formed most commonly by waves eroding the rock. Speleologist: One who studies caves.
Trogloxene: An animal that spends only part of its life cycle in a cave and returns periodically to the cave.
Speleology: Scientific study of caves and their plant and animal life.
Variable: Something that can affect the results of an experiment.
Some like it dark Speleologists are not the only people who like to study caves. People who explore caves for a hobby are called cavers or spelunkers. Spelunking can be a somewhat dangerous hobby. There are narrow passages, steep cliffs, and long distances—all in the dark. With caves that stretch steeply downward, spelunkers need to have many of the skills and equipment of mountain climbers. The darkness of a cave and its vastness also take some skill to navigate.
EXPERIMENT 1 Cave Formation: How does the acidity of a substance affect the formation of a cave? Purpose/Hypothesis The majority of caves are formed when limestone is
dissolved by carbonic acid. In this experiment you will determine why acidic substances form caves by comparing how acidic and nonacidic solutions 132
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react with different geologic materials. You will use chalk, seashells, and rocks as the geologic materials. Chalk and seashells are both types of limestone. Carbonic acid, a mixture of carbon dioxide and water, is the same compound found in soda. Carbonic acid is a weak acid. It is carbonic acid that makes soda fizz. A liquid can also be a base or it can be neutral. Pure water is an example of a neutral. A mixture of baking soda in water is an example of a base. After determining the acidity of the liquids, you will place drops of the liquids on each material and note the results. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of limestone and carbonic acid. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the solid material • the liquid • the liquid’s acidity • the amount of liquid poured In other words, the variables in this experiment are everything that might affect the limestone’s reaction with the liquid. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on dissolving the limestone.
• the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Only the limestone materials will have a reaction with the acidic liquids.’’ In this case, the variable you will change is the acidity of the solution. The variable you will measure is the reaction of the liquid on the geologic substance. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental setup, and that is the solution you drop on the solid material. For the control in this experiment you will use plain water. Level of Difficulty Easy to Moderate. Experiment Central, 2nd edition
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Materials Needed
• acid/base indicator strips • baking soda There are no safety hazards in this experiment. • clear soda pop • distilled water • dropper or spoon • six clear or plastic cups • spoon • measuring spoon • dropper • three pieces pure white chalk • three small rocks/pebbles • three seashells or seashell pieces
How to Experiment Safely
Approximate Budget $5. Timetable 30 minutes. Step-by-Step Instructions
Some of the materials needed for Experiment 1. G ALE G RO UP.
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1. Create a data chart, listing the liquids across the top columns and the different substances in the rows. 2. Prepare a basic solution: Mix 1 teaspoon (5 milliliters) of baking soda with one cup of water. Stir thoroughly and label the cup ‘‘Baking soda.’’ 3. Pour water in another cup and label as ‘‘Water’’; pour soda in yet another cup and label as ‘‘Soda.’’ 4. With an acid/base indicator strip, first test the water, then the bakingsoda solution, and, finally, the soda for acidity. Use a new strip for each test and dip the strip briefly in each liquid. An acid will turn the paper red, a base will turn the paper blue, and a neutral substance will not change the color of the strip. Note on your Soda chart whether each liquid is an acid, base, or neutral. 5. Take three new, empty cups: Place one piece of chalk in one; one pebble in a second; and one seashell piece in the third. Experiment Central, 2nd edition
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6. Use a dropper to drip 3 to 4 drops of the soda on the limestone chalk. Note in your chart a description of the sound and appearance. Does the limestone absorb the soda? Does the soda give any indication that it is dissolving the chalk? 7. Drip the same amount of soda over a piece of the seashell and the pebble. Describe the reaction of each on the seashell and the pebble. 8. Repeat Steps 6 and 7, replacing the soda with the baking-soda solution, and then with the water. (You may use the same cups to test all three liquids.) Note the reactions in the chart.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: There was no reaction with any of the substances. Possible cause: You may have used soda that was flat, meaning that all the carbonic dioxide has escaped and there is no carbonic acid. Repeat the experiment, making sure to use a fresh, fizzy can of soda.
Summary of Results Examine the reactions of each liquid on the solid
material. How did the acidity level of the liquid affect the reaction? Was your hypothesis correct? Hypothesize what would occur to each material if you soaked it in the liquids for several weeks. What would happen to each substance if you dropped a stronger acid on it? Write a brief summary of the experiment and your analysis. Change the Variables There are several ways you can modify the experiment
by changing the variables. You can change the type of geologic substance, using different types of rocks or granite, for example. You can vary the acidity level of the liquid, such as by using vinegar (an acid) or soap (a base). There are charts available where you can look up the strengths of the acids and bases. Many cleaning products also contain strong acidic substances: Use these carefully and with adult supervision. You can also alter the experiment by lengthening the amount of time the liquid sits on the substance.
EXPERIMENT 2 Cave Icicles: How does the mineral content of water affect the formation of stalactites and stalagmites? Purpose/Hypothesis The formation of stalactites and stalagmites in a cave
is a slow process that depends on the mineral content of the water and the Experiment Central, 2nd edition
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evaporation rate. In this experiment, you will form your own mini-cave icicles using two differWhat Are the Variables? ent types of minerals. Most caves are formed in limestone. LimeVariables are anything that might affect the results of an experiment. Here are the main stone is a form of the mineral calcite, which is variables in this experiment: made up largely of calcium carbonate. In this experiment, you will use two compounds made • the saturation level of solution from similar minerals: baking soda and Epsom • the environment allowed to grow salt. Baking soda is sodium bicarbonate, a min• the string eral that is a form of carbonate; Epsom salt is • the mineral magnesium sulfate, another type of mineral, but In other words, variables in this experiment are not a carbonate. everything that might affect the formation of In order for the minerals to join together to the stalactites. If you change more than one variable, you will not be able to tell which make a stalactite or stalagmite, you have to variable impacted their formation. make a water solution brimming with the minerals. Hot water can dissolve more minerals than cold water. When as much of a substance as possible is dissolved in hot water and the water is allowed to cool, that solution is called supersaturated. The molecules in a supersaturated solution are so crammed together that they readily stick to each other. When you dip a length of yarn in this solution, the solution will creep up the yarn. As the air evaporates some of the water, the solid material will remain on the string. Just as stalactites and stalagmites form in a cave, the minerals will build up over time. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of the formation of stalactites and stalagmites. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The cave formations will accumulate better when they are made out of baking soda, the same carbonate mineral that is in a cave.’’ 136
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In this case, the variable you will change is the type of mineral in each solution. The variable you will measure is the formation of the stalactites and (perhaps) stalagmites. Level of Difficulty Moderate.
How to Experiment Safely Have an adult present when handling hot water. Be careful when handling the scissors.
Materials Needed
• • • • • • • • • • • •
four clear glasses or small glass jars (same size) hot water baking soda Epsom salt two spoons dark construction paper, 8.5 x 11 inches (22 x 28 centimeters) four small washers (or paper clips) scissors bowl thick woolen yarn, about 2 feet (0.6 meters) masking tape marking pen
Approximate Budget $5. Timetable 45 minutes for setup and followup; 5 to 10 minutes per day for
about 8 to 12 days to observe and record the results. Step-by-Step Instructions
1. Pour 2 cups of very hot water into a bowl and dissolve as much baking soda as you can to make a saturated solution. Stir after every addition. When the solution is saturated, small bits of baking soda will fall to the bottom and will not dissolve no matter how hard you stir. 2. Pour half the water in one cup and half in another cup. 3. Cut the construction paper in half. Place the two glasses close to either end of the dark paper. Experiment Central, 2nd edition
Step 6: The yarn should sag slightly in the center. GA LE GRO UP .
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: No crystals grew in one or more of the solutions. Possible cause: The solution may not have been saturated when the water was hot. You may not have stirred enough to dissolve the solids. Pour the solution back in the saucepan. Reheat the solution, adding more of the substance and stirring well after each addition until you see bits of the substance fall to the bottom. Possible cause: The water may not have been hot enough. It does not need to be at the boiling point, but it does need to be hot. Pour the solution back in the saucepan. Reheat the solution, adding more of the substance and stirring well after each addition until it is saturated.
4. Stretch the yarn between the glasses and cut a piece that is about double that length. The yarn should be long enough to go inside each glass and hang loosely. 5. Tie a washer or paper clip to each end of the yarn. 6. Carefully lower the weighted ends of the yarn into the two glasses. The yarn should sag slightly in the center. 7. Label the two glasses ‘‘sodium bicarbonate.’’ 8. Repeat Steps 1 through 7, replacing the baking soda with Epsom salt. Label the second set of glasses ‘‘magnesium sulfate.’’ 9. Allow the glasses to sit undisturbed for at least 8 to 12 days. (A warm, sunny area works well.) 10. Illustrate what happens each day. Summary of Results Look at your progression of
pictures over the time of the experiment. What has formed on the string? Has anything begun to form on the construction paper? Compare the pictures of the two types of minerals? Write up a summary of the experiment, explaining the process of the mineral formations.
Change the Variables There are several ways you can vary this experiment.
You can use a different type of mineral to form the solution, such as sodium carbonate (washing soda) or sodium chloride (salt). You can also alter the environment that the minerals form in, such as a humid or a dry environment. Modify the Project For an advanced project, you could combine all the concepts you learned about caves to produce a model of a cave. This project will take about two weeks, as you will probably want to grow several stalactites or stalagmites. You can look at the color of different minerals in caves and add dye to the solutions to produce red, yellow or other color cave formations. Once you have grown stalactites or stalagmites, you can form a cave with clay or another hard, moldable material. You can tape the mineral 138
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formations onto the cave floor or ceilings. You can also use the minerals from Experiment 2 to make other cave formation, such as popcorn. Popcorn is a small mineral cluster that often grows on cave walls. Think about where the water will flow in relation to the growth of the cave formations? Consider if you want water at the bottom of your cave. You could also add some plant life at the cave opening. Write down the explanations behind the features and formations of your cave.
Design Your Own Experiment How to Select a Topic Relating to this Concept Cave formations are often
intriguing to view and study. These structures are continuing to provide new information to spelunkers, speleologists, and other explorers. For a related project, you could investigate the history, geology, life, and formation of caves. You could also find out if there are any caves in your area that are open to visitors. Check the Further Readings section and talk with your science teacher to learn more about caves. If you decide to visit a cave, make sure you are accompanied by an adult knowledgeable about caving.
A Native American cave dwelling at Canyonlands National Park, Utah. # PBN J PRO DU CTI ON S/C OR BI S.
Steps in the Scientific Method To conduct an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do • Recognize the variables involved and select one that will help you answer the question at hand • State your hypothesis, an educated guess about the answer to your question • Decide how to change the variable you selected • Decide how to measure your results Recording Data and Summarizing the Results Your data should include
charts and graphs such as the one you did for these experiments. They Experiment Central, 2nd edition
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should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are multiple projects related to caves that you can
undertake. You can study the animal and plant life in a cave through research and visits to museums or other facilities that may house some cave creatures. If there is a cave in your area that is open to the public, you could visit the cave and use a magnifying glass to examine the plant and animal life. Make sure you do not collect or touch any of the plant or animal life so as not to disturb their habitat. This project could also include an examination of how each type of animal and plant has adapted to the cave environment. If you decide to conduct a cave exploration, make sure an adult who is knowledgeable in caving accompanies you. You can also investigate the formation of different types of caves, such as caves that form from volcanoes or out of ice. You could conduct a research project on the information that caves have provided in many fields of study. Another research project could be to examine how cultures throughout history have used caves in their daily life and rituals.
For More Information Good Earth Graphics. ‘‘The Virtual Cave.’’ http://www.goodearth graphics.com/virtcave (accessed on February 3, 2008). Images of different types of caves from around the world. Groleau, Rick ‘‘How Caves Form.’’ NOVA. http://www.pbs.org/wgbh/nova/ caves/form.html# (accessed on February 3, 2008). Animated depiction of the formation of caves with clear explanations. Hadingham, Evan. ‘‘Subterranean Surprises.’’ Smithsonian Magazine, October 2002, pp. 68 74. This article can also be found online at http://www. smithsonianmag.com/science nature/subterranean.html (accessed February 3, 2008). Detailed article on information scientists are learning about caves. Taylor, Michael Ray and Ronal C. Kerbo. Caves: Exploring Hidden Realms.Washington, DC: National Geographic, 2001. The National Speleological Society. http://www.caves.org/ (accessed on February 3, 2008). Homepage for the National Speleological Society describing their purpose and activities.
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Cells
W
hat do slimy earthworms, majestic lions, and giant redwood trees have in common with humans? We all have cells, tiny units of life that grow and duplicate, gather fuel and building materials, and make energy. Cells are present in all living things. Some living things, such as bacteria and some plants, consist of only one cell where all the functions of life take place. They are known as unicellular. The average human has 50 to 100 trillion cells. Living things with a great many cells that are joined together are called multicellular.
Based on his observations from his microscope, Robert Hooke wrote the book Micrographi in 1665, which was the first to describe the structure of plant and animal cells. LI AIS ON AG ENC Y.
Looks like a monk’s cell to me All humans begin life as a single cell. It weighs no more than a millionth of an ounce. The naked eye cannot see anything that tiny. So no one could have known cells existed until the compound microscope was invented in the late sixteenth century. Between 1590 and 1609, Dutchmen Hans Janssen, his son Zacharias, and Hans Lippershey designed several compound microscopes. In a compound microscope, two or more lenses are arranged to produce a greatly enlarged image. In 1660, a Dutch drape maker named Anton van Leeuwenhoek (1632–1723) used a microscope to peer at his textiles. He began studying the invisible worlds of nature. Leeuwenhoek designed 250 different microscopes to further his studies. Around that time, Robert Hooke (1635–1703), an English scientist, slid a piece of cork under a microscope. The mass he saw seemed to be made of chambers, like monks’ cells in a monastery. He called these chambers ‘‘cells.’’ Developing the cell theory Hooke’s cells were from a cork tree’s dead and dry bark. The fact that cells are units of life was not understood until the nineteenth century. Between 1838 and 141
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In this slide of a plant, can you find the nucleus and cytoplasm? PH OT O RE SEA RC HE RS I NC.
Genetic researchers in silhouette against magnified DNA strands. PH OT O R ES EAR CH ER S, I NC.
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1839 Theodor Schwann and Matthias Schleiden, both German zoologists, independently said that all living things have one or more cells, that all cells are similar, and that in order to exist, these cells carry out the same functions. These facts are now called the cell theory. The study of cells is called cytology. Rudolf Virchow, a German pathologist, took the cell theory further in 1855 and suggested that all cells are formed by the division of preexisting cells. Without the cell theory we would never know how organisms grow and develop. We could not treat diseases or pains in our joints, for instance, without knowing what cells do and how they function. What’s in there? Cells are not lifeless blobs. Chemical changes within each cell accomplish many functions, including digestion and breathing. There are two basic types of cells, plant cells and animal cells. Almost all cells share similar features, such as a cell membrane, which surrounds the cell. The cell membrane is a thin wall that lets gases, such as oxygen, and fluids, such as nutrients, pass through. Cytoplasm (pronounced CY-tow-pla-sim) is the gray, jellylike substance inside the cell membrane. It consists mostly of water but also has many other substances important for cells to function. Think of a cell as a factory with each division performing specific jobs. Organelles (pronounced OR-gan-ells) in the cytoplasm represent those divisions. For instance, Golgi bodies are organelles that act as the cleaning crew. Golgi absorb waste, package it up, and send it out for disposal. Vacuoles (pronounced VAC-u-ols) are organelles that act as the storage crew. They store food, waste, and chemicals. While there are similarities in cells, there are differences between plant and animal cells. The cytoplasm of plants, for example, contains chloroplasts, which gives the plant the ability to make its own food. It’s what makes your hair curly The nucleus, another organelle, is the cell’s library. It lies in the center of the cell and contains DNA. DNA, an abbreviation for deoxyribonucleic acid, are molecules that store information. They tell each cell how to develop into a nerve cell, a blood cell, and so on. What makes you unique, as well as what makes you similar to other people, was Experiment Central, 2nd edition
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WORDS TO KNOW Cells: The basic unit for living organisms; cells are structured to perform highly specialized functions. Cell membrane: A thin-layered tissue that surrounds a cell. Cell theory: All living things have one or more similar cells that carry out the same functions for the living process. Chloroplasts: Small structures in plant cells that contain chlorophyll and in which the process of photosynthesis takes place. Cytology: The branch of biology concerned with the study of cells. Cytoplasm: The semifluid substance inside a cell that surrounds the nucleus and the other membrane-enclosed organelles. Dicot: Plants with a pair of embryonic seeds that appear at germination. DNA: Large, complex molecules found in nuclei of cells that carry genetic information for an organism’s development. Embryonic: The earliest stages of development.
Germination: The beginning of growth of a seed. Golgi body: An organelles that sorts, modifies, and packages molecules. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Monocot: Plants with a single embryonic leaf at germination. Multicellular: Living things with many cells joined together. Organelles: Membrane-bounded cellular ‘‘organs’’ performing a specific set of functions within a cell. Pnematocysts: Stinging cells. Protozoan: Minute, one-celled animals. Unicellular: Living things that have one cell. Protozoans are unicellular, for example. Vacuoles: A part of plant cells where food, waste, and chemicals are stored. Variable: Something that can affect the results of an experiment.
programmed into your DNA. Each cell contains many strands of DNA. If you put them all together, they would stretch thousands of miles. Cells are like little companies. They contain tiny workers with functions that help the living organism survive. A company’s main goal is to make a profit. A cell’s main goal is sustaining life. Cells also reproduce themselves by dividing. Cell division is a process where a cell divides into two cells. Yeast cells undergo a process of cell division called budding. The parent cell forms a bud on the outside of the cell wall. This bud continues to grow until it reaches the size of the parent cell and then it separates from the parent cell and Experiment Central, 2nd edition
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How to Experiment Safely Use caution when collecting cells with toothpicks. When carrying the compound microscope, use two hands. After collecting pond water, wash your hands. Be careful not to stain your clothes or furniture when using the iodine.
the process starts again. Conducting projects with a microscope will enable you to see the way in which cells function and reproduce as a life force.
PROJECT 1 Investigating Cells: What are the differences between a multicellular organism and a unicellular organism?
Purpose/Hypothesis In this project, you will collect, prepare, mount, and
compare cells from a multicellular organism and a single-celled protozoan. This will allow you to observe the differences between these two basic forms of organisms. Level of Difficulty Moderate/difficult, because it requires the use of a
compound microscope. (If you are unfamiliar with its use, please ask a teacher or other adult for assistance.) Materials Needed
Step 4: Cell culture slide, with cover slip tipping over the cell culture. GAL E GR OU P.
• compound microscope (try to borrow one from a school or friend) • slides and cover slips, glass or plastic (Note: If your slides are plastic, use plastic cover slips.) • stain (iodine from drugstore is good; avoid any solution with alcohol, as it will kill any organisms) • toothpicks (flat-end toothpicks work best) • eye dropper • small jar filled with pond water, the dirtier the better Approximate Budget $10 for stain, slides, cover
slips, and eye dropper. Timetable About 1 hour. Step-by-Step Instructions
1. Use the flat end of a toothpick to gently scrape the inside of your cheek. Don’t press too hard! Scrape gently five to 10 times. 144
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2. Smear the cells from the end of the toothpick onto a clean slide. Troubleshooter’s Guide 3. Place one drop of stain onto the slide, covering the cells. Here is a problem that may arise, a possible 4. Gently place the cover slip over the cell cause, and a way to remedy the problem. culture. (Hint: Gently rest one side on the Problem: Nothing appears on the slide. slide and slowly lower the cover slip until it Possible cause: You are probably out of focus. rests flat.) Place a small piece of paper on the slide and 5. Examine the slide under the microscope, focus until it is clear. Use the fine focus knob. using low power. 6. Draw what you see and label any parts you recognize. 7. Place two drops of pond water on the center of the slide. 8. Place a drop of stain on the pond water drops. 9. Place the cover slip over the slide using the same technique as with the cheek cells. 10. Examine the slide under the microscope, using low power. 11. Draw what you see and label the parts. Summary of Results Compare your diagrams and data of the cheek cells and protozoans from the pond water. Determine which cells had a more complex structure. Record a list of the differences between cheek cells and protozoan cells. Note differences such as movement, shape, presence of a cell membrane, and the presence of other cell stuctures. Summarize your observations with sketches and in writing.
Step 7: Pond water cheek cells on low power. GAL E GR OU P.
PROJECT 2 Plant Cells: What are the cell differences between monocot and dicot plants? Purpose/Hypothesis In this experiment, you
will collect, prepare, and mount cells from two multicellular plants. The multicellular plants you will be working with are monocot, that is, plants with a single embryonic leaf at germination, and dicot, plants with a pair of embryonic leaves at germination. Experiment Central, 2nd edition
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How to Experiment Safely When carrying the compound microscope, use two hands. Ask an adult to use the razor blade.
• • • •
Level of Difficulty Moderate/difficult, because it requires the use of a compound microscope. (If you are unfamiliar with its use, please ask a teacher or other adult for assistance.) Materials Needed
• compound microscope (try to borrow one from a school or friend) slides and cover slips, glass or plastic (Note: If you are using plastic slides, use plastic cover slips.) single-edge razor blade thread spool plant stems—tulip and daisy preferred (Go to a local florist and ask for a clipping of the stem.)
Approximate Budget $6 for the slides and cover slips. Timetable About 1 hour. Step-by-Step Instructions
1. Push the tulip stem through the hole in the thread spool until it pokes out the opposite end.
Step 1: Tulip stem in the thread spool. GAL E GR OU P.
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2. Have an adult use the razor to trim the tulip stem, flush to the thread spool. Discard the trimmed piece. 3. Push the tulip stem through the thread spool so about .03 inch (1.0 millimeter) of stem is exposed. 4. Carefully using the razor, trim the .03 inch (1 millimeter) of tulip stem flush to the thread spool. Save the trimmed stem. 5. Place the stem slice on the slide and cover with the cover slip. 6. Place the slide on the microscope and examine under low power. Record your observations using drawings and descriptions. 7. Repeat steps 1 through 6 for the daisy stem. 8. Record and compare your observations.
Basic differences between monocot and dicot stems: Dicot stem cells are more orderly; monocot stem cells are more random. G AL E GR OUP .
Summary of Results Compare your diagrams of the tulip and daisy stems.
Which stem had cell patterns that were more orderly? Which stem had more random patterns? A tulip is a monocot, and a daisy is a dicot. Can you tell the difference between monocot and dicot plants by examining their stems?
PROJECT 3 Yeast Cells: How do they reproduce? Purpose/Hypothesis In this experiment, you will prepare a yeast solution
and mount these cells on slides to be viewed under the microscope. Yeast need water, food, and warmth to thrive. The food source you will use is sugar. Once the yeast are in a comfortable environment with food, you can observe the reproduction of the cells.
Step 4: Slice of tulip stem trimmed off spool by razor. GA LE G RO UP.
Level of Difficulty Moderate/Difficult, because it requires the use of a compound microscope. (If you are unfamiliar with its use, please ask a teacher or other adult for assistance.) Materials Needed
• compound microscope (try to use one from your school, local community college, or university) Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise, a possible cause, and a way to remedy the problem. Problem: You cannot see anything. Possible cause: The stem is too thick. Try cutting the plant stem thinner so the light passes through it.
• slides and cover slips, glass or plastic (Note: If you are using plastic slides, use plastic cover slips.) • yeast, available in grocery stores • shallow, glass dish • sugar • warm water • eye dropper Approximate Budget $6 Timetable About 1 hour. Step-by-Step Instructions
How to Experiment Safely
1. Prepare the yeast as recommended on the back of the package, using the warm When lifting or carrying the compound microwater and sugar to activate the yeast. scope, use two hands. If you have not used a 2. Using the eye dropper, place one drop of compound microscope before, you may need water onto the slide. an adult to help you set up. 3. When the yeast mixture begins to froth, place a dab of the frothy yeast onto the drop of water on the slide. Cover with cover slip. 4. Place the slide under the microscope and observe the cells. You will need a magnification of 650 to see the cells. 5. Look for cells that have another smaller cell attached to it. This is Step 1: Warm water and sugar, the beginning of the cell separation known as budding. If you combined with the yeast, look at the cells long enough (about 20 minutes), you should see creates a frothy mixture. the beginning of cell reproduction. ILL US TRA TI ON B Y TE MA H 6. Record your observations using drawings NE LS ON. and descriptions. Summary of Results What did you see? Were
you able to see the yeast cells budding? If possible, continue to observe the yeast every five minutes. Diagram your observations.
Design Your Own Experiment How to Select a Topic Relating to this Concept
If you choose a topic in biology, you can 148
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generally involve the topic of cells. For example, you may be interested in jellyfish and sea anemones. These two creatures share a type of stinging cell called a pnematocyst, which paralyzes and kills their prey. The small differences in cell structure give rise to different behaviors and structure of animals and plants. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on cell questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Step 2: A small amount of yeast is placed on the slide. IL LU STR AT IO N BY T EM AH NE LS ON.
Step 4: Budding can be observed after about 20 minutes. IL LU STR AT ION BY T EMA H NE LS ON.
Recording Data and Summarizing the Results
Your experiment can be useful to others studying the same topic. When designing your experiment, develop a simple method to record your data. This method should be simple and clear enough so that others who want to do the experiment can follow it. Your final results should be summarized and put into simple graphs, tables, and charts to display the outcome of your experiment. Related Projects Creating a project about cells
Yeast Cell Budding
offers endless possibilities. You can create a slide Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise, a possible cause, and a way to remedy the problem. Problem: You cannot see anything. Possible cause: You do not have the correct level of magnification. Make sure the microscope is set with a high enough magnification power in order to observe the cells. Problem: The yeast cells are too close together to observe budding. Possible cause: You may have too much of the yeast mixture on your slide. Take another slide, add a droplet of water and place a smaller amount of the yeast mixture onto the slide. Problem: The yeast cells are not budding. Possible cause: The yeast may not have been alive Purchase a fresh container of yeast. Try again, making sure that the water is not too hot or it may kill the yeast.
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collection of cells from many different plants (stem, seed, leaf, needle, root, etc.). You can create a model of a cell labeling the parts and functions. Making a model from colored plastic clay is inexpensive and informative.
For More Information Andrew Rader Studios. ‘‘Cell Structures.’’ Rader’s Biology4kids.com. http://www.biology4kids.com/ files/cell main.html (accessed on January 19, 2008). Information on cell structures and functions. Bender, Lionel. Atoms and Cells. Glouster, ME: Glouster Press, 1990 Provides background and functions of atoms and cells. Cells Alive! http://cellsalive.com Interactive graphics and pictures of cells in motion. Young, John K. Cells: Amazing Forms and Functions. New York: Franklin Watts, 1990. Good, understandable overview of these units of life for young people.
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Chemical Energy
C
hemical energy is the energy stored within the bonds of atoms. A bond is the force that holds two atoms together. Different substances have bonds held together by different amounts of energy. When those bonds are released, a chemical reaction takes place, and a new substance is created. Chemical reactions that break these bonds and form new ones sometimes release the excess energy as heat and sometimes absorb heat energy from whatever is around them.
Thus, heat energy can be produced or absorbed during a chemical reaction. Reactions that release heat energy are called exothermic. Reactions that take in heat energy from the surrounding environment are called endothermic. Whether heat energy is given off or absorbed during a chemical reaction depends on the bonds that hold the atoms together. In a chemical reaction, the original substances are called reactants. The new substances that are formed are called products. When the bonding structure of the products requires less energy than the bonding structure of the reactants, the excess energy may be released as heat. When the bonding structure of the products requires more energy than the structure of the reactants, it gets that energy by removing heat from its surroundings. For example, when iron rusts, the iron atoms are combining with oxygen molecules in the air to form iron oxide. The chemical reaction of rusting breaks the bonds in the oxygen molecules, releasing heat energy. The bonds between the oxygen atoms and the iron atoms do not require as much heat energy as the bonds within the oxygen molecules, so a small amount of energy is released, making the reaction exothermic. The amount of heat released is quite small, and the reaction is normally quite slow, so rusting iron does not feel hot to us. Yet, the energy released can be measured with a thermometer. In the first experiment, you will observe the change in temperature resulting from rusting. 151
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The chemical reaction that occurs when iron rusts actually gives off small amounts of heat energy. PH OT O RE SEA RC HE RS I NC.
This hot pack releases an exothermic reaction. PH OT O RE SEA RC HE RS I NC.
Some exothermic reactions are quite common. One is combustion, the burning of organic substances during which oxygen is used to form carbon dioxide and water vapor. The substances formed (ashes, for example) hold less heat energy than the substances burned held. The excess energy is released as heat. The reactions between some chemicals, such as aluminum oxide and iron oxide, can produce great amounts of heat. This reaction is used to produce very high temperatures for industrial purposes. Endothermic reactions are more rare in nature, but scientists have found ways to create them. For example, an endothermic reaction occurs when you use a chemical cold pack. These packs contain a chemical in powder form that reacts with water. Squeezing the pack breaks down the wall separating the powder from the water. The reaction that occurs absorbs more energy than it releases, making the pack feel cold to you. In the second experiment, you will compare four chemical reactions and determine whether each one is exothermic or endothermic.
EXPERIMENT 1 Rusting: Is the chemical reaction exothermic, endothermic, or neither? Purpose/Hypothesis In this experiment, you will
measure the heat energy released or absorbed by the chemical reaction of rusting, the transformation of iron and atmospheric oxygen into iron oxide. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of rusting. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen 152
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WORDS TO KNOW Atom: The smallest unit of an element, made up of protons and neutrons in a central nucleus surrounded by moving electrons. Bond: The force that holds two atoms together. Chemical energy: Energy stored in chemical bonds. Chemical reaction: Any chemical change in which at least one new substance is formed. Combustion: Any chemical reaction in which heat, and usually light, is produced. It is commonly the burning of organic substances during which oxygen from the air is used to form carbon dioxide and water vapor. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Endothermic: A chemical reaction that takes in heat energy. Exothermic: A chemical reaction that gives off heat energy. Heat: A form of energy produced by the motion of molecules that make up a substance. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Molecule: The smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms. Product: A compound that is formed as a result of a chemical reaction. Reactant: A compound present at the beginning of a chemical reaction. Variable: Something that can affect the results of an experiment.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A rise in air temperature will show that rusting is an exothermic reaction.’’ In this case, the variable you will change is the number of rusting pads in each cup, and the variable you will measure is any change in air temperature. You expect the temperature to go up in the cups with rusting pads and the temperature to go up the most in the cup with the How to Experiment Safely most pads. As a control experiment, you will leave one cup Wear protective gloves when handling the steel empty and monitor any change in temperature wool and vinegar. there. If the temperature is higher in the cup with Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
more pads and does not change in the empty cup, your hypothesis will be supported. Level of Difficulty Moderate. Materials Needed
• 4 large Styrofoam cups • aluminum foil • 7 steel wool pads (not pads treated with detergent or soap) • vinegar • 4 digital laboratory thermometers • rubber or surgical gloves • paper towels • large bowl
• the type of reactants used (iron in the pads and atmospheric oxygen) • the temperature of the environment in which the samples are tested • the number of rusting pads in each cup In other words, the variables in this experiment are everything that might affect the temperature in the cup. If you change more than one variable, you will not be able to tell which variable had the most effect on the temperature.
Approximate Budget $10. (If four thermometers
are unavailable, the four parts of this experiment can be performed separately with one thermometer.) Timetable About 45 minutes. Step-by-Step Instructions
1. Line the inside of each of the four cups with aluminum foil. 2. Place the seven steel wool pads in the large bowl and soak them thoroughly in vinegar (to remove any coating and encourage rusting). Blot them dry with paper towels. 3. Place one pad in the first cup, two pads in the second cup, and four pads in the third cup. The fourth cup will be empty—your control. 4. Push the bulb of one thermometer gently into the steel wool in the first cup. Do not push the bulb down to or near the bottom of the cup. Cover the opening of the cup with aluminum foil. The stem on the thermometer must be visible. 5. Repeat Step 4 for the second, third, and fourth (control) cups. 6. Place all four cups where no other heat sources will affect their temperature. 7. Prepare a chart similar to the one illustrated so you can record your observations. 154
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Step 4: Illustration of rusting set-up. GAL E GR OU P.
8. Observe and record any change in temperature in any of the four cups every 10 minutes. The rusting process will begin immediately, but the resulting change in temperature will be gradual and
Step 7: Temperature recording chart. GA LE GRO UP. Experiment Central, 2nd edition
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Troubleshooter’s Guide Few problems should arise if the steps in this experiment are followed closely. However, when doing experiments involving the mixing of substances, be aware that a number of variables—such as temperature and impurity of substances—can affect your results. Here is a problem that may arise, a possible cause, and a way to remedy the problem. Problem: You observed little or no temperature change in the cups. Possible cause: The steel wool is not rusting. Try soaking it in vinegar again for several minutes to remove any protective layers and then repeat the experiment.
small. Make sure that external factors are not affecting the temperature, such as sunlight or heat from a lamp. Summary of Results Examine your results and
determine whether your hypothesis is correct. Did the temperature rise higher when more wool pads were in the cup? Did it rise in the empty cup? If the reactions resulted in an increase in temperature, then rusting is indeed exothermic. Make sure that your chart shows clearly the result of the tests on each sample. Change the Variables You can vary this experi-
ment. Here are some possibilities:
• Other metals will oxidize, though at much slower rates. See if you can measure the temperature change resulting from the oxidation of copper (loops of copper wire may be best). • Compare the heat energy released by different kinds of oxidation. What about the oxidation you can see occurring on the cut surface of an apple? Find a way to determine if that reaction is exothermic. Always check first with your teacher before altering the materials used in your experiments.
EXPERIMENT 2 Exothermic or Endothermic: Determining whether various chemical reactions are exothermic or endothermic Purpose/Hypothesis In this experiment, you will measure the heat energy
released or absorbed as four different chemicals (see the materials list) are mixed with water. You expect that the temperature of the solution will go up if the reaction is exothermic and go down if the reaction is endothermic. Before you begin, make an educated guess about the outcome of each reaction based on your knowledge of the chemicals and reactions involved. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: 156
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• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
A hypothesis should be brief, specific, and measurable. It must be something you can test • the type of reactants used through observation. Your experiment will prove • the purity of the reactants or disprove whether your hypothesis is correct. • the temperature of the environment in Here is one possible hypothesis for one of the which the samples are tested reactions in this experiment: ‘‘Mixing water with In other words, the variables in this experiment calcium chloride will produce an exothermic are everything that might affect the temperareaction.’’ ture of the solutions. If you change more than In this case, the variable you will change is one variable, you will not be able to tell which the chemical being reacted with water, and the variable had the most effect on the temperature. variable you will measure is the resulting temperature of the solution. In the case of calcium chloride, you expect the temperature to go up. As a control experiment, you will measure the Wear gloves and safety glasses or goggles at all times while temperature in a beaker of distilled water with no chemical in it. If the performing this experiment. temperature changes in the beakers with chemicals as predicted and GAL E GR OU P. remains steady in the control beaker, you will know your hypothesis is supported. Level of Difficulty Moderate; an adult’s super-
vision is required. Materials Needed
• • • • • • • •
5 glass beakers 1 graduated cylinder 1 glass stirring rod 1 small spoon or spatula 1 digital laboratory thermometer 1 pint (500 milliliters) distilled water 1 tablespoon (14 grams) calcium chloride 1 tablespoon (14 grams) sodium hydrocarbonate • 1 tablespoon (14 grams) ammonium nitrate Experiment Central, 2nd edition
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How to Experiment Safely This experiment involves dangerous and toxic substances. No part of this experiment should be performed without adult supervision. You must be especially careful handling the sulfuric acid, which is highly corrosive. Wear gloves and safety glasses or goggles at all times! When you are finished with the experiment, the chemicals used must be disposed of properly and with supervision. Ask your teacher for help in handling, neutralizing, and disposing of the sulfuric acid.
• 2 teaspoons (10 milliliters) concentrated sulfuric acid • safety glasses or goggles • rubber or surgical gloves Approximate Budget $25. (This experiment
should be performed only with the appropriate lab equipment and materials. Ask your teacher about ordering the chemicals.) Timetable One hour. Step-by-Step Instructions
1. Place the five beakers on a clean, stable surface and use the graduated cylinder to
Step 2: Exothermic vs. endothermic recording chart. GAL E GR OU P.
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2. 3.
4.
5.
6.
7.
measure and pour 3½ tablespoons (about 50 milliliters) of distilled water into each one. Prepare a chart on which you will record your observations. Your chart should look something like the illustration. Place the thermometer in the first beaker and record the temperature on your chart. This sample, which contains only the distilled water, will be your control. Using the spoon or small spatula, add about half the sample of calcium chloride to the second beaker. Stir it gently until it is mixed with the distilled water. Place the thermometer in the beaker and note the temperature once each 30 seconds for five minutes. Record the temperatures on the chart. When you are done, be sure to rinse the thermometer with room-temperature distilled water. Repeat Steps 4 and 5 for the sodium hydrocarbonate and the ammonium nitrate. Remember to rinse the thermometer, stirring rod, spatula, or spoon in distilled water after each test. In the last beaker, slowly and gently add all of the sulfuric acid to the water. Be careful not to spill or splash the acid. Place the thermometer in the beaker and note the temperature once each 30 seconds for five minutes. Record the temperature changes on your chart. When you are done, be sure to rinse the thermometer.
Summary of Results Examine your results and determine whether each
of your hypotheses is correct. If any reactions resulted in an increase in temperature, those reactions are exothermic. If any reactions resulted in
Steps 3 to 7: Exothermic vs. endothermic set-up beakers. GA LE G RO UP.
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Troubleshooter’s Guide When doing experiments involving the mixing of substances, be aware that a number of variables—such as temperature and impurity of substances—can affect your results. When mixing substances, you must keep the mixing containers and utensils clean. Even tiny impurities in a mixture can drastically alter your results.
a decrease in temperature, they are endothermic. Make sure that your chart shows clearly the result of the tests on each set of reactants. It may be helpful to those viewing your results to see a diagram outlining the procedure you followed. Change the Variables You can vary this experi-
Here is a problem that may arise, a possible cause, and a way to remedy the problem.
ment by trying reactions involving different household materials or chemical compounds. Do not mix them with anything other than water. Always check first with your teacher before altering the materials used in your experiments.
Problem: You observed little or no temperature change in the beakers.
Design Your Own Experiment
Possible cause: You are not placing enough of the solid reactants in the water. Try increasing the amount of solid reactant.
How to Select a Topic Relating to this Concept Other kinds of experiments can reveal
interesting facts about endothermic and exothermic reactions. Our bodies produce exothermic reactions when we turn food into energy. Can you measure the amount of food energy available in a sample by burning it and measuring the resulting temperature change in a sample of water? Review the description of how cold packs work. Can you think of a way to design a homemade cold pack? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on chemical reaction questions that interest you.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. 160
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• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the experiments included here and in
any experiments you develop, strive to display your data in accurate and interesting ways. Remember that those who view your results may not have seen the experiment performed, so you must present the information you have gathered as clearly as possible. Including photographs or illustrations of the steps in the experiment is a good way to show a viewer how you got from your hypothesis to your conclusion. Related Projects Chemical energy is a basic and crucial part of life
Some cold packs use a chemical reaction that starts when you squeeze the pack. The pack cools off in an endothermic reaction. PHO TO RE SE AR CHE RS I NC .
processes as well as technological processes. Projects that determine the energy produced by different fuels and compare the by-products of those fuels can help to demonstrate the necessity for developing alternative energy sources. Examining different reactions and determining their endothermic or exothermic rate can help us understand where so much of the energy we use goes.
For More Information BBC. ‘‘Mixtures.’’ Schools. Science: Chemistry. http://www.bbc.co.uk/schools/ ks3bitesize/science/chemistry/index.shtml (accessed on February 18, 2008). Basic information on the chemistry of mixtures. California Energy Commission. ‘‘What is Energy?’’ Energy Story. http:// www.energyquest.ca.gov/story/chapter01.html (accessed on February 28, 2008). Explanation of the different types of energy. Gillett, Kate, ed. The Knowledge Factory. Brookfield, CT: Copper Beech Books, 1996. Provides some fun and enlightening observations on questions relevant to this topic, along with good ideas for projects and demonstrations.
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Chemical Properties
H
ow many ways can you describe a substance? Two common ways are by listing its physical properties and its chemical properties. A physical property is a characteristic of a substance that you can detect with your senses, such as its color, shape, size, smell, taste, texture, temperature, density, or volume. For example, a lemon is yellow, oval-shaped, and smaller than a grapefruit. It has a sharp smell and a rough texture. A physical change changes a physical property but does not change the identity or molecular makeup of the substance. One example of a physical change is salt crystals dissolving in water, which changes their shape. When the water evaporates, you can see the salt crystals again, unchanged by being dissolved in the water. Tearing paper into small pieces is also a physical change. The bits of paper look different, but they are still composed of the same molecules as when they were joined together. A chemical property is the ability of a substance to react with other substances or to decompose. For example, a chemical property of iron is that it reacts with oxygen and rusts. A chemical property of a substance allows it to undergo a chemical change. A chemical change is the change of one or more substances into another substance. A chemical change is also called a chemical reaction. During some chemical reactions, two or more substances are combined to form one new substance. An example is oxygen combining with iron to form rust. This is called a synthesis reaction. During other chemical reactions, one substance is broken down into two or more new substances. An example of this is hydrogen peroxide, which is used to treat small cuts. It breaks down into oxygen and water in the presence of light, which is why hydrogen peroxide is stored in dark bottles. This is called a decomposition reaction. A chemical reaction can be very quick, such as paper burning, or very slow, such as food digesting in your stomach. 163
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Ice melting is an example of a physical change. FI EL DM ARK PUB LI CAT IO NS.
Burning is a chemical change or reaction, producing new substances. Some substances are more flammable than others. A P IM AG ES.
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What are some examples of chemical properties? Chemical properties include flammability (the ability to catch on fire), toxicity (the ability to be poisonous), oxidation (the ability to react with oxygen, which causes apple slices to turn brown and iron to rust), radioactivity (spontaneously emitting energy in the form of particles or waves by the disintegration of their atomic nuclei), and sensitivity to light (which causes newspaper to turn yellow). Being acidic or basic is another kind of chemical property. An acid is a substance that can react with, or corrode, other substances. A base is a substance that feels slippery when dissolved in water. When an acid and a base are combined, they react chemically with each other to produce new substances: a salt and water. Many foods contain acids, including tomatoes, lemons, oranges, and carbonated soft drinks. For most people, eating the small amounts of acid in these foods does not cause a problem. In fact, the hydrochloric acid in our stomachs helps produce the chemical reaction called digestion. However, the acid in tomatoes reacts so strongly with aluminum that foods containing tomato sauce should not be stored in aluminum foil. The acid in tomatoes can actually burn holes in the foil. Acids can also damage the environment. Burning coal produces nitric and sulfuric acids that combine with the water vapor in the air to create acid rain. Acid rain burns trees and plants. It can cause lakes and rivers to become so acidic that fish and plants can no longer survive there. Many cleaning products are bases, including soaps, drain cleaners, and ammonia. Basic substances, too, can damage the skin and eyes. For example, some people who breathe ammonia fumes get nosebleeds as the fumes react with the sensitive tissues in their noses. What happens during a chemical reaction? In a chemical reaction, the substances you begin with are called reactants. The new substances that are formed are called products. Experiment Central, 2nd edition
Chemical Properties
The explosion of fireworks produces heat, light, and sound energy in an exothermic reaction. PHO TO R ES EA RCH ER S I NC.
For example, when the acetic acid in vinegar and baking soda (reactants) are combined, the products are bubbles of carbon dioxide gas, water, and sodium acetate. The chemical properties of the reactants determine what happens during the reaction—and how quickly it happens. For example, one chemical property of magnesium is that it reacts strongly with hydrochloric acid to produce bubbles of hydrogen gas. Not all metals have this property. Dipping a strip of copper into hydrochloric acid produces no hydrogen bubbles. Dipping zinc into the acid results in some bubbles, but fewer than for the magnesium. In the same way, iron reacts strongly with oxygen to produce rust. However, other metals, such as silver and gold, do not react with oxygen (do not have this chemical property) and so do not rust when exposed to the air. Many chemical reactions produce energy. For example, when something burns, it produces heat energy. Thus, smoke is one sign of a chemical reaction. Other signs of chemical reactions include foaming, a smell, a sound, and a change in color. A chemical reaction that releases heat or light energy is called an exothermic reaction. Examples include fireworks explosions, luminescent ‘‘light sticks,’’ and the digestive process in your body. Some chemical reactions absorb heat or light energy and are called endothermic reactions. One example is the way green plants absorb sunlight and change it into the chemical energy in sugar and in oxygen. Experiment Central, 2nd edition
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WORDS TO KNOW Acid: Substance that when dissolved in water is capable of reacting with a base to form salts and release hydrogen ions.
Exothermic reaction: A chemical reaction that releases heat or light energy, such as the burning of fuel.
Base: Substance that when dissolved in water is capable of reacting with an acid to form salts and release hydrogen ions.
Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/or experiment.
Chemical change: The change of one or more substances into other substances. Chemical property: A characteristic of a substance that allows it to undergo a chemical change. Chemical properties include flammability and sensitivity to light. Chemical reaction: Any chemical change in which at least one new substance is formed. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Decompose: To break down into two or more simpler substances. Decomposition reaction: A chemical reaction in which one substance is broken down into two or more substances. Endothermic reaction: A chemical reaction that absorbs heat or light energy, such as photosynthesis, the production of food by plant cells.
Luminescent: Producing light through a chemical process. Physical change: A change in which the substance keeps its molecular identity, such as a piece of chalk that has been ground up. Physical property: A characteristic that you can detect with your senses, such as color and shape. Product: A compound that is formed as a result of a chemical reaction. Reactant: A compound present at the beginning of a chemical reaction. Synthesis reaction: A chemical reaction in which two or more substances combine to form a new substance. Variable: Something that can change the results of an experiment.
In the two experiments that follow, you will have an opportunity to produce chemical reactions by using the chemical properties of certain substances. In one experiment, you will combine white glue and borax (a mineral that acts as a laundry booster) to create an entirely new substance. In the second experiment, you will combine water, iodine, and oil to see what kind of chemical reaction occurs. The more you understand about chemical reactions, the better you will understand the workings of the world around—and inside—you. 166
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EXPERIMENT 1 Slime: What happens when white glue and borax mix? Purpose/Hypothesis In this experiment, you will
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the variables in this experiment:
mix two substances to see if a chemical reaction occurs. The chemical name of one of the substan• the amounts of the substances used in the ces, white glue, is polyvinylacetate. You will mix actual experiment and the control the polyvinylacetate with borax, a laundry booster experiment (sodium borate). Borax is a natural mineral, found • the length of time the mixtures are shaken in the ground. It’s made of boron, sodium, oxyIf you change more than one variable between gen, and water. It is used to strengthen the cleanthe actual experiment and the control experiing power of laundry detergents. ment, you will not be able to determine which To begin the experiment, make an educated variable affected the results. guess about what will happen when you combine these two substances. Will there be a chemical reaction? Will it produce a new substance? If so, what might the substance look like? This guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Mixing polyvinylacetate with borax will create a chemical reaction and produce a new substance.’’ In this experiment, the variable you will change is the mixing of the two substances, and the variable you will measure (or examine) is the product of this mixture. As a control experiment, you will observe a sample of polyvinylacetate that is not mixed with borax to see if a chemical reaction occurs. If only the mixture with the borax in it produces a new substance, your hypothesis will be supported. Level of Difficulty Easy/moderate. Materials Needed
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• • • • • • • •
How to Experiment Safely Wear goggles to protect your eyes from any splashes. Do NOT taste any mixtures or the product that results from the chemical reaction. Avoid getting the product from this experiment on clothing, carpeting, or furniture, as it might leave a stain.
food coloring 3 jars with lids borax labels spoons measuring spoons sealable plastic bag goggles
Approximate Budget Up to $5. Timetable 10 minutes to set up; 1 hour to
observe. Step-by-Step Instructions
Step 7: Use a spoon to scrape the wet borax mixture into the experiment jar. GA LE G RO UP.
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1. Measure 3 tablespoons (44 milliliters) of water and the same amount of white glue into one jar. 2. Add several drops of food coloring to the jar. 3. Close the jar and shake the mixture vigorously until the glue dissolves in the water. Label the jar ‘‘experiment.’’ 4. Repeat Steps 1 to 3, using another jar, and label this jar ‘‘control.’’ 5. In the third jar, put 3 tablespoons (44 milliliters) of water. Slowly pour in 2 tablespoons (30 milliliters) of borax. Allow the mixture to settle for a minute. 6. Carefully pour the excess water from the third jar down a sink drain. 7. Use a spoon to scrape the wet borax mixture into the experiment jar. 8. With the lids closed, shake both the experiment and control jars for at least two minutes. 9. Record your observations of the experiment jar and the control jar in a table similar to the one illustrated. Wait half an hour and record them again. After another half an hour, record your final observations. Experiment Central, 2nd edition
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Step 9: Recording table for Experiment 1. GA LE G ROU P.
10. Open the experimental jar and remove the product you have created. Observe and experiment with its new physical properties. 11. Store your ‘‘slime’’ in the sealable plastic bag to keep it from spoiling. Summary of Results Study your observations and
decide whether your hypothesis was correct. Did the combination of white glue and borax produce a chemical reaction? How do you know? Did the same reaction occur in the control jar without the borax? What happened here? In a liquid form, the molecules in polyvinylacetate are separate, allowing the glue to flow. When you added the borax, a chemical reaction caused the molecules in the white glue to wrap around each other, forming a soft ball. The combination of the two substances produced an entirely new substance that looks and feels like slime. Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Experiment Central, 2nd edition
Step 10: Observe and experiment with the ‘‘slime’’ you have created. G ALE GRO UP .
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of iodine added to the water in the experiment • the temperature of the ingredients (they will remain at room temperature to control this variable) • the kind of oil used (other kinds of oil may react differently) If you change more than one variable, you will not be able to tell which variable had the most effect on the chemical reaction.
Step 3: Add about five drops of iodine to the experiment jar. GA LE G RO UP.
Change the Variables You can vary this experiment by changing the amount of borax you mix with the white glue solution. Your products will range from sticky slime, to a bouncy ball, to a very hard ball. You might also experiment with other types of glue, such as gel glue and washable glue, to see if they form the same kind of product when mixed with borax.
EXPERIMENT 2 Chemical Reactions: What happens when mineral oil, water, and iodine mix? Purpose/Hypothesis In this experiment, you will
mix water with iodine and then add mineral oil to see whether a chemical reaction occurs. Remember the possible signs of a chemical reaction: the production or absorption of heat or light energy, smoke, bubbles of gas, a smell, a sound, and a change in color. You know that water and oil do not mix. Instead, they remain as separate layers. You probably also know that a combination of water and oil does not produce any sign of a chemical reaction. If such a reaction is to occur, it must be caused by the iodine. Make an educated guess about the outcome of this experiment. This guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Iodine will cause a chemical reaction when mixed with mineral oil and water.’’
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In this case, the variable you will change is the presence of iodine. The variable you will measure or observe is evidence of a chemical reaction. As your control experiment, you will combine mineral oil and water, without adding iodine, and watch for signs of a chemical reaction. If a change occurs only in the mixture with the iodine, your hypothesis will be supported.
How to Experiment Safely Wear goggles to protect your eyes from possible splashes of iodine. Avoid getting iodine or mineral oil on your clothing or furniture, as it will stain.
Level of Difficulty Easy/moderate. Materials Needed Note: All ingredients should be at room temperature.
• • • • • • •
2 jars with lids, such as peanut butter jars labels water a container of iodine with a dropper mineral oil measuring cups goggles
Approximate Budget $5 for iodine and mineral oil; other materials
should be available in the average household.
Step 4: Recording table for Experiment 2. GA LE G ROU P. Experiment Central, 2nd edition
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Timetable 30 minutes.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The mixture with iodine did not change color. Possible cause: You did not shake it long enough. Shake it some more and observe what happens.
Step-by-Step Instructions
1. Label one jar ‘‘experiment’’ and one jar ‘‘control.’’ 2. Pour 14 cup (60 milliliters) of water into each jar. 3. Add about five drops of iodine to the experiment jar. 4. Record your observations on a table similar to the one illustrated. 5. Pour 14 cup (60 milliliters) of mineral oil into each jar. Record your observations in the table.
6. Shake both jars, one in each hand, for two minutes. Again, record any changes you observe. Summary of Results Study the observations on your table and decide Step 6: Shake both jars, one in each hand, for two minutes. GA LE GRO UP.
whether your hypothesis was correct. Did a chemical reaction take place in the mixture containing iodine? How can you tell? Did a chemical reaction occur in the mixture without the iodine? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. When you shook the mixture containing iodine, the iodine moved from the water into the oil, causing a color change, which is evidence of a chemical reaction. If you shake the experiment jar long enough, all the iodine will move into the oil, and the water will become clear again. The iodine causes the chemical reaction, so the mixture without iodine did not change. Change the Variables Here are some ways you
can vary this experiment: • Use other kinds of oil, such as safflower or peanut oil, to see if the same color change results. 172
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• Use very hot or icy-cold water to see how a change in temperature affects this chemical reaction.
PROJECT 3 Chemical Patination: Producing chemical reactions on metal
How to Experiment Safely Work in a well-ventilated area because ammonia can have an odor that may cause irritation. Wash your hands after the experiment and dispose of the contents carefully. Never mix ammonia with a substance without first asking a knowledgeable adult.
A patina is a change in an object’s surface layer, which can occur from natural weathering or a controlled reaction. Outdoor copper and bronze are examples of natural greens and browns that are possible. Patinas form from a chemical reaction called oxidation. Chemical patination is often used for decorative effect to produce metals that are black, blues, and greens. The color a chemical patination produces depends upon the type of metal and the chemistry of the solutions applied to the metal. It also depends upon the way the treatment is applied, such as the length of time and temperature. In the project, you will experiment with chemical patination on copper to observe how different solutions react with the metal. In two of the tests, the metal will react with the vapor of the solution while also reacting with oxygen. For the third test, you will wipe the solution onto the metal. Level of Difficulty Moderate, because of the time involved. Materials Needed
• • • • • • •
white vinegar ammonia salt lemon juice measuring cup small bowl 3 sheets of thin copper, several inches long, available from craft or art stores • 3 lidded plastic containers that the copper sheet fits into • sandpaper • washers, brass nuts, or other metal objects that fit inside the plastic containers Experiment Central, 2nd edition
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• aluminum foil • cloth Approximate Budget $12. Timetable 30 minutes to set up; at least eight
hours to three days to observe changes. Step-by-Step Instructions
1. If the copper sheets are not clean, wash with soap and allow them to dry. 2. Lightly sand the copper sheets and wipe well. Test 1 Step 3: Place a metal object, such as a several washers or a brass nut, on the bottom of the container. The copper sheet will sit on the object. ILL US TRA TI ON B Y TE MA H NE LS ON.
Step 4: Pour vinegar slightly below the top of the object. I LLU ST RAT IO N BY T EM AH NEL SO N.
3. Place a metal object, such as a several washers or a brass nut, on the bottom of the container. The copper sheet will sit on the object. You will want the sheet resting slightly above the solution. See illustration. 4. Pour vinegar slightly below the top of the object. 5. Place the copper sheet on the washers (or other object) and loosely cover (do not seal the cover). Leave overnight or for at least eight hours. Test 2 6. Place a metal object, such as a several washers or a brass nut, on the bottom of the container. Again, you will want the sheet resting slightly above the solution. 7. Pour ammonia slightly below the top of the object. 8. Place the copper sheet on the washers (or other object) and loosely cover. Leave overnight or for at least eight hours. Test 3 9. In a small bowl, combine one-quarter cup lemon juice, one-quarter cup table salt, one-quarter cup household ammonia, and one-half cup vinegar.
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10. Set the third copper sheet on a piece of aluminum foil. Use the cloth to wipe the solution onto the sheet. 11. Wait approximately two hours or until the copper is dry. Apply another coat and allow to dry. You will need to apply the solution at least six times. Summary of Results Record how each of the copper sheets appear. Describe the colors and deepness of each chemical patination. Where did the patination occur on the metal? Try scraping the color off with your fingernail. If you want to try and reproduce or produce more of one color, make sure you check with an adult if you are when making up your solutions.
Design Your Own Experiment How to Select a Topic Relating to this Concept
Troubleshooter’s Guide Here is a common problem that you may experience during this project and tips to remedy the problems. Problem: The copper does not change color in the first two trials. Possible causes: 1. The copper may not be getting enough oxygen. Make sure the copper solution is not sealed completely, and the metal is not immersed in the solution. Try the trial again. 2. There may not be enough vapor for the chemical patination to occur. The lid might be too loose. Place the lid so it fits neatly over the container, but do not seal, and try the test again.
The world—and your own life—depend on chemical properties and the chemical reactions that result from them. Consider what you would like to know about these properties and reactions. For example, what chemical reactions occur inside your body? Which ones are essential in manufacturing? What chemical reactions help shape the landscape? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Combining certain materials can be dangerous. Steps in the Scientific Method To do an original
Ammonia
Record how each of the copper sheets appear. IL LUS TR ATI ON BY T EMA H NE LS ON.
Lemon juice Vinegar, etc
Vinegar
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure which question you are answering, Experiment Central, 2nd edition
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what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In your ‘‘slime’’ and iodine
experiments, your raw data might include tables, drawings, and photographs of the changes you observed. If you display your experiment, make clear the question you are trying to answer, the variable you changed, the variable you measured, the results, and your conclusions. Explain what materials you used, how long each step took, and other basic information. Related Projects You can undertake a variety of projects related to chemical
reactions. For example, a number of chemical reactions occur in the kitchen as food cooks on the stove or bakes in the oven. Breads and cakes rise because of a chemical reaction. Some medicines for an upset stomach depend on chemical reactions to cause fizz in a glass of water. You can even make pennies turn green because of a chemical reaction!
For More Information Gardner, Robert. Science Projects about Chemistry. Hillside, NJ: Enslow Publishers, 1994. Focuses on experiments in causing and analyzing chemical reactions. Mebane, Robert, and Thomas Rybolt. Adventures with Atoms and Molecules. Hillside, NJ: Enslow Publishers, 1991. Clearly describes 30 doable experiments in chemistry and chemical reactions. VanCleave, Janice. A+ Projects in Chemistry. New York: Wiley and Sons, 1993. Outlines experiments that show chemical reactions relating to the weather, biochemistry, electricity, and other topics.
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P
eople depend on taste and smell to recognize a delicious meal, but these senses also play a key part in helping keep us alive. Both senses can warn us of trouble and both are linked to what we eat. Pleasant tastes and smells ensure that a person or animal continues to eat and acquire energy from foods. Unpleasant tastes and smells are one way to ensure a person does not eat poisons or other materials that can cause harm. People get information about the world around them through their senses of hearing, touch, sight, taste, and smell. Each of these five senses is tuned to a specific sensation. You are always using at least one of your senses. The senses send messages to the brain, which processes the information. Taste and smell belong to the chemical-sensing system group, known as chemosenses, which means that the sense is stimulated by specific chemicals. These chemicals trigger a nerve signal to the brain that then ‘‘reads’’ the signal. How taste works When people say something tastes good, they are usually referring to the flavor of the food or drink. Flavor is a combination of taste, smell, texture, and other characteristics of the food itself, such as temperature. The sense of taste is complex because it is so intricately linked with flavor and weaves in many of the other senses, especially the sense of smell. There are five basic tastes: sweet, sour, salty, bitter, and umami (pronounced oo-MAM-ee). Umami was described in the early 1900s, but only in the late 1990s did food researchers officially recognize it as a distinct taste. Umami is the taste that occurs when foods with the protein glutamate are eaten. Glutamate is found in meat, fish, and the flavor-enhancing chemical monosodium glutamate, or MSG. Humans get the sensation of taste through their taste cells, which lie within the taste bud. The average person has about 10,000 taste buds. People regenerate new taste buds every three to ten days. As people grow 177
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Tongue
Pore Microvilli
Taste buds are onion-shaped structures located primarily on a person’s tongue. G AL E GRO UP.
older their taste buds regenerate at a slower rate, causing their sense of taste to lessen. An elderly person may have only 5,000 taste buds.
Taste buds are onion-shaped structures located primarily on a person’s tongue. The majority of buds on the tongue are scattered on the papillae Taste cell (pronounced pah-PILL-ee), the small projections that give your tongue its rough appearance. Taste signal travels to brain buds are also located on the throat, roof of the mouth, and pharynx, but the buds on your tongue provide most of your taste experience. Each taste bud is made up of about 50 to 150 taste cells. Every cell has a fingerlike extension called a microvilli that connects with an opening at the top of the taste bud, called the taste pore. For food to have taste, its chemicals need to reach your taste cells. The instant you take a bite of food, saliva or spit in the mouth starts breaking down the food’s chemical components. These components, or molecules, travel through the pores in the papillae to bind to specific taste cells. The chemicals cause a change in the taste cell, sending a signal via nerves to the brain, which processes the signals.
In order for food to have taste, its chemical components need to reach the taste cells in your mouth. COP YR IG HT # K EL LY A. Q UI N.
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The chemical reaction in the taste cells varies depending on the taste group involved. For example, salty foods trigger a change in taste cells when enough sodium (the main component of salt) molecules enter the cells through the microvilli. Odor Molecules Each taste cell has the ability to recognize different taste groups, yet taste cells specialize in processing one particular group. Researchers have found that taste buds with common taste perceptions may be Tongue bunched together on the papillae. Many of the taste buds more sensitive to bitterness, for example, are located on the back of the tongue. This can cause an automatic gagreflex to help prevent poisoning if something too bitter is ingested.
Olfactory Bulb
Olfactory Epithelium
Food
How tastes and smells are recognized. Food and odor molecules attach to olfactory cells that send signals to the brain. GAL E GR OUP .
Smells at work: Lime or lemon? It is the olfactory sense, or sense of smell, that plays a key role in determining your perception of how tasty something is, or its flavor. Flavor is so strongly linked to the olfactory sense that researchers estimate 70–75% of what humans perceive as taste actually comes from the sense of smell. Special olfactory cells, located inside the uppermost part of the nose, recognize specific odors. These odors, or chemical molecules, enter the nose and rise upward until they reach the olfactory epithelium, a postage-stampThe olfactory epithelium. Odor molecules bind to specific size area that contains olfactory receptor cells. Olfactory receptor cells are receptors on the cilia, which nerve cells, and each cell lasts about four to five weeks before it is replaced triggers a chemical signal in the with a new one. These cells have hairlike projections called cilia that are receptor cell. The cell then sends sensitive to odor molecules. A specific odor molecule dissolves in the mucus its signal to the olfactory bulb of of the nose. Mucus is a slippery substance that protects and moistens. The the brain, and then on to other odor molecule binds to specific receptors on the cilia, which trigger a areas of the brain that chemical signal in the receptor cell. The cell then sends its signal to the recognize it as a specific odor. olfactory bulb of the brain, and then on to other areas of the brain that GAL E GR OU P. recognize it as a specific odor. There can be hunReceptor Cell dreds of receptors that take part in recognizing one smell. Olfactory cells can recognize thousands of different odors. The chemical molecules reach the cells through the air you breathe and the food you eat. When you put food in your mouth, Mucus chemicals are released while you are chewing. Molecules from the food travel through the passage between your nose and mouth to the olfactory Odor Molecules Cilia epithelium. Experiment Central, 2nd edition
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If a person’s nose is congested, mucus in the nasal passages can block the odor molecules from reaching the olfactory cells; thus, the brain receives no signal telling it what the object smells like. CO PY RI GHT # K ELL Y A . QU IN.
If a person’s nose is congested, mucus in the nasal passages can block the odor molecules from reaching the olfactory cells. This will block surrounding smells, and food will lose much of its flavor. All senses are not created equal Because the chemosenses are complex mechanisms, there are several reasons why people have varying preferences for smells and tastes. A person’s genetics (physiological makeup), upbringing, and familiarity with specific smells and foods can influence his or her likes and dislikes. Odor molecules transmit their signals to areas of the brain that are involved with emotional behavior and memory. When a person smells something, it often brings back memories associated with the object, and those memories can help shape a person’s perception of that smell. Genetics is also a factor in tasting ability. In the early 1930s researchers discovered an inherited trait that determined people’s sensitivity to a bitter taste. They classified people as ‘‘tasters’’ or ‘‘nontasters’’ based on whether they were able to detect a specific chemical, which tastes bitter to some people and tasteless to others. Later research found that some people are especially sensitive to this bitter taste. These people are born with more than the average number of taste buds and, as a result, perceive tastes more intensely than the average person. For these supertasters bitter tastes more bitter, sweet tastes sweeter, and salt tastes saltier. Researchers theorize that about 25% of the people in the United States are supertasters, 25% are nontasters, and the remaining 50% are regular tasters. In the two experiments that follow, you will use the scientific method to examine if genetics affects the sense of taste and how closely linked these two senses are.
EXPERIMENT 1 Supertasters: Is there a correlation between the number of taste buds and taste perception? Purpose/Hypothesis In this experiment, you will test varying concentra-
tions of three tastes on people to predict whether they fall into the category of nontaster, taster, or supertaster. Then you will test your hypothesis by 180
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WORDS TO KNOW Chemosense: A sense stimulated by specific chemicals that cause the sensory cell to transmit a signal to the brain.
Olfactory epithelium: The patch of mucous membrane at the top of the nasal cavity that contains the olfactory (smell) nerve cells.
Cilia: Hairlike structures on olfactory receptor cells that sense odor molecules.
Olfactory receptor cells: Nerve cells in the olfactory epithelium that detect odors and transmit the information to the brain.
Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Microvilli: The extension of each taste cell that pokes through the taste pore and first senses the chemicals. Mucus: A thick, slippery substance that serves as a protective lubricant coating in passages of the body that communicate with the air.
Papillae: The raised bumps on the tongue that contain the taste buds. Saliva: Watery mixture with chemicals that lubricates chewed food. Supertaster: A person who is extremely sensitive to specific tastes due to a greater number of taste buds. Taste buds: Groups of taste cells located on the papillae that recognize the different tastes.
Olfactory: Relating to the sense of smell.
Taste pore: The opening at the top of the taste bud from which chemicals reach the taste cells.
Olfactory bulb: The part of the brain that processes olfactory (smell) information.
Variable: Something that can affect the results of an experiment.
counting the number of papillae of each person to estimate the number of taste buds each person has. If a person has more than twenty-five in a punch-hole-size area, then he/she is classified as a supertaster, five or less is considered a nontaster, and anywhere in between is an average taster. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of the sense of taste. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Experiment Central, 2nd edition
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A hypothesis should be brief, specific, and measurable. It must be something you can test What Are the Variables? through further investigation. Your experiment will prove or disprove your hypothesis. Here is one Variables are anything that might affect the possible hypothesis for this experiment: ‘‘People results of an experiment. Here are the main variables in this experiment: who are more sensitive to tastes will have a greater number of taste buds.’’ • The participants in the experiment Variables are anything you can change in an • The cleanliness of the person’s palette experiment. In this case, the variable you will change before the experiment will be the concentration of the solutions. The • The size of the paper hole variable you will measure will be the number of • The concentration of the taste taste buds. • The substance people are tasting Setting up a control experiment will help you In other words, the variables in this experiment isolate each variable and measure the changes in are everything that might affect the relationship the dependent variable. Only one variable will between a person’s sensitivity to taste and the change between the control and the experimental number of his or her taste buds. If you change setup, and that is the concentration of the solution. more than one variable at the same time, you will not be able to tell which variable had the For the control in this experiment you will use a most effect on taste. cup of plain water (tasteless). For your experiment, you will determine sensitivity to three tastes: bitter, salty, and sweet. You will first make a 10% solution for each substance, then dilute the solutions. Sugar and salt are solids and you will make a 10% weight/weight (gram/gram) solution. For liquids you will make a 10% volume/volume (milliliter/milliliter) solution. One gram of water equals 1 ml of water. You will rate people’s sensitivity to varying concentrations of grapefruit juice (bitter), sugary water, and salty water. Then you will use blue dye to color each person’s tongue’s papillae. Because you are relying on human subjectivity, the more people you test, the more accurate your results. Level of Difficulty Easy to Moderate. Materials Needed
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grapefruit juice sugar salt water measuring spoons gram scale Experiment Central, 2nd edition
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• • • • • • • • •
3 to 4 helpers 16 small disposable paper cups light-colored pen blue food coloring cotton swabs piece of paper hole punch (standard 1/4-inch size) mirror magnifying glass
Approximate Budget $5.
How to Experiment Safely Check with an adult before you or your helpers taste any of the foods to make sure none of you has any allergies to the foods, or other dietary restrictions. Use each cotton swab only once, one per person. Tasters should also use a fresh cup for their water. You might want to wear an old shirt in case any dye should spill.
Timetable 1 hour. Step-by-Step Instructions
1. Measure out 10 tablespoons (150 milliliters of water) and pour into a cup. Add 4 teaspoons (15 grams) of sugar for a total volume of 150 ml and stir until all the sugar is dissolved. Write on the cup: ‘‘10% sugar.’’ Repeat this process for the salt, labeling the cup: ‘‘10% salt.’’ 2. Measure out 9 tablespoons (135 ml) water and pour into a cup. Add 1 tablespoon (15 ml) grapefruit juice for a total volume of 150 ml and stir thoroughly. Label the cup: ‘‘10% grapefruit.’’ 3. Dilute each solution by 10%. From the sugar solution measure out 1 tablespoon (15 ml) and pour into a clean cup. Add 9 tablespoons (135 ml) of water and stir until all sugar is dissolved. Label the cup: ‘‘1% sugar.’’ 4. To make a 0.1% solution: From the 1% sugar solution measure out 1 tablespoon (15 ml) and pour into a clean cup. Add 9 tablespoons (135 ml) of water and stir until all sugar is dissolved. Label the cup: ‘‘0.1% sugar.’’ 5. To make a 0.01% solution: From the 0.1% sugar solution measure out 1 tablespoon (15 ml) and pour into a clean cup. Add 9 tablespoons (135 ml) of water and stir until all sugar is dissolved. Label the cup: ‘‘0.01% sugar.’’ 6. To make a 0.001% solution: From the 0.01% sugar solution measure out 1 tablespoon (15 ml) and pour into a clean cup. Add 9 tablespoons (135 ml) of water and stir until all sugar is dissolved. Label the cup: ‘‘0.001% sugar.’’ 7. Repeat this process for the salt solution and the grapefruit juice. Experiment Central, 2nd edition
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# of Papillae
SweetBitter Salty 10% 1% .1% .01% .001% Step 9: Data chart for Experiment 1. GAL E GR OU P.
water
8. Place plain water in a cup for the control solution. 9. Create a chart that lists the concentrations and the control on the left, and the three tastes across the top. 10. Have the taster rinse out his or her mouth with water and make sure the mouth is relatively dry before beginning. 11. Start with one taste. Switch the five cups around, including the cup of water, not allowing the taster to see the labels. Have the taster dip a clean cotton swab into the solution, smear it over his/ her tongue, and wait a few moments. Ask the taster if he/she can identify a taste. If the taster can identify a taste, make a checkmark sign in the box; if not, make a ‘‘x’’ in the box.
Step 17: Look at each tongue and count the round structures, the papillae, that are visible in the paper hole. GAL E GR OU P.
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12. Have the taster rinse out his/her mouth with water and repeat the process for all the dilutions, including the control. Once the taster has completed one taste, repeat the process with another taste. 13. When one taster has finished sampling the three sets of tastes, repeat the process with another helper. Have a helper mix the samples so that you can also sample the dilutions yourself. 14. Punch a hole in a piece of paper for each taster. 15. Dip a cotton swab in the blue food coloring and have the tasters wipe the blue swab on the tip of their tongues. 16. Place the paper hole on the blue area of each tongue. 17. Using a magnifying glass, look at each tongue and count the round structures, the papillae, that are visible in the paper hole. Look in the mirror to count your own papillae. Write down the results for each taster. Summary of Results Compare the results of each
Troubleshooter’s Guide Below are some problems that may occur during this experiment, some possible causes, and some ways to remedy the problems. Problem: A person’s responses were inconsistent, sometimes saying he or she could taste the higher concentration and lower concentrated solution, but not the in-between solutions. Possible causes: The person may have been mixing up tastes. Try repeating the test with that person, making sure the taster cleans his/her mouth with water carefully every time. Problem: There was no correlation between number of taste buds and perceived taste. Possible causes: Human error. Examine the taster’s reaction to the control solution to ensure that he/she is not mistakenly identifying tastes where there is none. If the taste of water has a checkmark then try repeating the experiment with that person, or with someone else. The more people you test, the less chance human error will have a statistical impact on your results.
person’s data chart with the number of his or her taste buds. Did your results support your hypothesis? Did the people who were more sensitive to tastes have a greater number of taste buds? Could the people in the nontaster category only taste the higher concentrations, and the supertasters taste the lower concentrations? Share your results and discuss if the tasters with the greater number of taste buds have a higher sensitivity to tastes in general. If there are any supertasters, do they have a strong dislike for broccoli, cabbage, and cauliflower (bitter tastes) and for strong sweet tastes such as frosting? Change the Variables Try repeating the experiment (with new helpers)
using different concentrations of the solutions, both higher and lower, to get an increased number of data points. You can also change the type of bitter solution you use (for example, a beverage with caffeine in it or tonic water). Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • The participants in the experiment • The cleanliness of the person’s palate before the experiment • The substance people are tasting In other words, the variables in this experiment are everything that might affect the relationship between a person’s ability to recognize foods by their smell and taste. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on identifying the foods.
Another variable you can change is to replace one of the tastes with the sour taste (lemon juice). Always check with an adult before you or anyone else tastes any of the solutions to make sure there are no dietary restrictions.
EXPERIMENT 2 Smell and Taste: How does smell affect the sense of taste? Purpose/Hypothesis Humans can perceive only
five tastes, but can recognize thousands of smells. In this experiment you will test how closely the two chemosenses, the sense of smell and taste, are related. Blocking each sense independently, you will test and identify foods to determine which of the two senses sends the clearer message to the brain on what you are eating. You will use foods that have similar textures so that the feel of the food in your mouth is not a factor. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of the sense of taste. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘Humans need both the sense of smell and taste working together to identify foods.’’ Variables are anything you can change in an experiment. In this case, the variable you will change will be which sense or senses you use. The variable you will measure will be the identification of the food. You will test each sense separately, then together. 186
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Level of Difficulty Easy. Materials Needed
• • • • • • • •
onion raw potato roll of flavored candy chocolate ice cream strawberry ice cream knife four spoons helper
How to Experiment Safely Check with an adult before you or your helpers taste any of the foods to make sure none of you has any allergies to the foods, or other dietary restrictions. Use fresh utensils if more than one person conducts this experiment. Always use caution when working with any sharp objects, such as the knife.
Approximate Budget $5. Timetable About 20 minutes. Step-by-Step Instructions
1. Carefully cut off a small piece of the onion and potato and then cut each into even smaller pieces. Place each on a separate spoon. 2. Ready spoonfuls of the chocolate ice cream and strawberry ice cream. 3. Set out two different-flavored hard candies; (e.g., one green and one red). 4. Make a chart listing the foods across the top and writing ‘‘Smell,’’ ‘‘Taste,’’ and ‘‘Both’’ down the page on the left. 5. Close your eyes and hold your nose tightly. Have your helper hand you the spoons one by one, in groups of two: onion and potato, chocolate and strawberry ice creams, and red and green hard candies. Taste each one and say what you think it is—don’t peek. 6. Have your helper write down what you guessed. 7. Keeping your eyes closed, have your partner refill the spoons and again hand you the spoons in the same groups of two as before. This time, only smell what is on the spoon and say what it is. 8. Have your helper write down what you guessed. Experiment Central, 2nd edition
Step 5: Block your sense of smell while tasting the food. G AL E GRO UP .
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Troubleshooter’s Guide Below is a problem that may occur during this experiment, some possible causes, and some ways to remedy the problem. Problem: Results were not as hypothesized. Possible causes: Make sure you do not have a cold or are congested during this experiment. Always make sure the utensils are clean. Make sure you dice the potato and onion into small enough pieces so that they have the same feel on the tongue.
9. Repeat the procedure, keeping your eyes closed, this time using both your sense of taste and smell. Have your helper write down what you guessed. Summary of Results Examine your results and
determine whether your original hypothesis was correct. Which sense identified the correct flavor more often? Did one sense tell your brain the specific food you were eating? Did you need both senses working together to identify the flavors? Summarize the results of your experiment. Change the Variables You can vary this experi-
ment several ways. For example, why is it that you are keeping your eyes covered during this experiment? The sense of vision plays a significant role in identifying foods. People have expectations that certain colors will relate to specific flavors, such as a green jellybean tasting like lime, even when the flavor is different than expected. Try putting different-flavored fruit juices in dark cups and testing how much of an impact your sense of vision has on your taste perception. You can also try holding only half your nose, to see how much of an impact half of your olfactory receptors have on your taste perception. Modify the Experiment This experiment uses single food tastings to
examine how the sense of smell and taste are used to recognize food. You can modify this experiment by conducting multiple food tastings to examine sensory adaptation. Sensory adaptation is when the sensitivity of the receptors decreases after repeated exposure to the same taste, smell, or other experience. For you to explore how sensory adaptation affects your senses, you will need a glass of strong salt water and sugar water, along with plain water. You will also need a helper. Ask your helper to take a small sip of the sugar water and write down the taste. It should taste extremely sweet. Now ask your helper to gargle with the sugar water for at least 30 seconds. After spitting out the water, have your helper take another small sip of the sugar water and ask how it tastes? Repeat the gargling and sip. Again, ask the helper to identify the taste. Is there a difference in how strong it tastes? 188
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Repeat the steps, except have your helper drink several large sips of plain water after gargling. Rinsing the mouth with water should refresh the receptors. When your helper now takes a sip of the sugar water, can he or she better recognize the taste? Does is have the strength as the first sip? Repeat this entire process with the salt water. Compare the taste experiences with and without drinking pure water. Try the experiment on yourself. You can explore whether you need more or less time to sensitize your receptors to the taste.
Design Your Own Experiment How to Select a Topic Relating to this Concept If you are interested in the
senses of taste and smell, there are many other possible experiments and projects. Because taste has a genetic component, you can try repeating Experiment 1 for groups of families. Compare family members’ reactions to different tastes and their number of taste buds to each other. Then compare that data to a different family. Are members of one family more likely to all be either tasters, nontasters, or supertasters? If you are interested in the sense of smell, you can examine the sensitivity of the olfactory sense by collecting and testing different concentrations of scents. Is there a genetic component to the sense of smell? How is the sense of smell different in other species from that of humans? What are some possible explanations for this? Check the Further Readings section and talk with your science teacher or librarian to start gathering information on any questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Experiment Central, 2nd edition
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Recording Data and Summarizing the Results Your data should include charts, such as the ones you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental setup and results. If you have done a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Besides completing your experiments, you could pre-
pare a model that demonstrates a point that you are interested in with regard to the chemosenses. For example, you could construct a model of the brain and illustrate the pathway of the taste and olfactory cells sending signals as they travel to certain parts of the brain. You could also try a similar dilution experiment with smell, observing the effect of varying dilutions of an odor, such as a perfume or a beverage. The effect of temperature also has an effect on smell, and you could chart people’s perception of an odor that is cold, room temperature, and warm.
For More Information Neuroscience for Kids. http://faculty.washington.edu/chudler/chsense.html (accessed March 5, 2008). Clear explanations and activities of the chemosenses. Rouhi, Maureen I. ‘‘Unlocking the Secrets of Taste.’’ Chemical and Engineering News. September 10, 2001. http://pubs.acs.org/cen/coverstory/7937/7937 taste.html (accessed March 5, 2008). Article on recently identified taste receptors and the molecules that stimulate them. ‘‘The Vivid World of Odors.’’ Howard Hughes Medical Institute. http://hhmi. org/senses/d110.html (accessed March 5, 2008). Report from the Howard Hughes Medical Institute on odor and taste receptors. ‘‘Your Sense of Smell.’’ Your Gross and Cool Body. http://yucky.discovery.com/ flash/body/pg000150.html (accessed March 5, 2008). Introductory information on smells and how the sense works.
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Chlorophyll
C
hlorophyll is the green pigment that gives leaves their color. Acting as a solar collector, chlorophyll absorbs light energy from the sun and traps it. This trapped energy is stored, then used to form sugar and oxygen out of carbon dioxide from the air and water from the soil. This extraordinary process is called photosynthesis. It is the way a plant makes its own food. But the key to this process is chlorophyll.
Chlorophyll clusters in the leaves of this healthy rhododendron plant trap solar energy. PH OTO RE SE AR CHE RS I NC .
What’s this green thing? Pierre Joseph Pelletier and Joseph Biernaime Caventou were French chemists who worked together in the early nineteenth century in a new field called pharmacology, the science of preparing medical drugs. These chemists would later discover quinine, caffeine, and other specialized plant products. In 1817, however, they isolated an important plant substance they called chlorophyll, from the Greek words meaning ‘‘green leaf.’’ Scientists first thought that chlorophyll was distributed throughout plant cells. But in 1865 the German botanist Julius von Sachs discovered that this pigment is found within sacs called chloroplasts. Chlorophyll molecules are arranged in clusters within these chloroplasts. One-celled plants, such as algae, contain chlorophyll. They live in water, growing near the surface and the light, or on moist surfaces. Multicelled plants—usually land plants such as mosses, ferns, and seed plants—have chlorophyll-loaded chloroplasts in their stems and leaves. These plants all need light to activate the chlorophyll. Plants such as algae require low light, and certain land plants, such as philodendron, survive well in low levels of sunlight also. Some houseplants thrive in 191
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artificial light, while other plants require high levels of sunlight.
An unhealthy rhododendron plant. If plants do not get enough light to activate their chlorophyll clusters, they cannot make enough food to survive. PH OT O RE SEA RC HE RS I NC.
Why leaves change color Pigments are substances that appear colored to the human eye because of the wavelengths of light they reflect. A pigment absorbs all other wavelengths of light and only reflects the wavelength that we see as a color. For example, a green pigment, like chlorophyll, absorbs all wavelengths except green. Many different pigments are present in sacs within the plant cell. There are two related chlorophyll pigments, chlorophyll A and chlorophyll B. Both appear green, with just a slight color variation from each other. Carotene, a yellowish-orange pigment, and xanthophyll, a yellow pigment, are also present in most leaves. Some plants have a red color in their petals, stems, and leaves called anthocyanin. The different pigments in a plant allow the plant to absorb different light wavelengths. Overall, the greenish chlorophyll pigment is the one that is most plentiful. It is considered a primary pigment, and the secondary pigments act as a support team to help the plant absorb more light energy. Deciduous trees shed their leaves in the autumn. The joining place where the leaf meets the twig is called an abscission. The first step in the process that causes leaves to fall occurs when cork cells develop under the abscission. This cork layer blocks nutrients that travel to and from the leaf. Then the leaf begins to die. Because chlorophyll breaks down faster than the other pigments, the green leaves begin their gradual color change. As the chlorophyll decomposes, the yellow and orange colors from the carotene and xanthophyll stand out. Trees with anthocyanin pigments show bright red leaves in the fall. Anthocyanin pigments need high light intensity and sugar content for their formation, so fiery red leaves usually emerge after bright autumn days. Cool nights act as a refrigerator, preserving the sugar in the leaves. Chlorophyll and other pigments are unique in their function as food makers. Uncovering their presence in plants through experiments will help you ‘‘see’’ them.
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WORDS TO KNOW Abscission: Barrier of special cells created at the base of leaves in autumn.
Germination: First stage in development of a plant seed.
Anthocyanin: Red pigment found in leaves, petals, stems, and other parts of a plant.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Carbohydrate: Any of several compounds composed of carbon, hydrogen, and oxygen, which are used as food for plants and animals.
Pharmacology: The science dealing with the properties, reactions, and therapeutic values of drugs.
Carotene: Yellowish-orange pigment present in most leaves.
Photosynthesis: Chemical process by which plants containing chlorophyll use sunlight to manufacture their own food by converting carbon dioxide and water to carbohydrates, releasing oxygen as a by-product.
Chlorophyll: A green pigment found in plants that absorbs sunlight, providing the energy used in photosynthesis. Chloroplasts: Small structures in plant cells that contain chlorophyll and in which the process of photosynthesis takes place. Chromatography: A method for identifying the components of a substance based on their characteristic colors. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group.
Pigment: A substance that displays a color because of the wavelengths of light that it reflects. Variable: Something that can change the results of an experiment. Wavelength: The peak-to-peak distance between successive waves. Red has the longest wavelength of all visible light, and violet has the shortest wavelength. Xanthophyll: Yellow pigment found in leaves.
EXPERIMENT 1 Plant Pigments: Can pigments be separated? Purpose/Hypothesis In this experiment you will discover what pigments are present in various plants using chromatography, an identification technique based on color. You will cut up various plants and boil them in water, then add a small amount of alcohol to help release the pigments from the plants. To begin the experiment, use what you know about chlorophyll and other pigments found in plants to make an educated guess about what colors you will find. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type and part of the plant being used (Example: carrot roots contain mainly carotene; carrot leaves contain mainly chlorophyll.) • the season in which the plant was harvested (Example: if the plant was harvested in the spring, the leaves contain abundant chlorophyll; in the fall, the leaves have more carotene, xanthophyll, and anthocyanin.) • the maturity of the specimen (Example: leaves from the heart of a celery plant are yellow from xanthophyll; as leaves mature, chlorophyll builds up.) In other words, the variables in this experiment are everything that might affect the colors you find. If you change more than one variable, you will not be able to tell which variable had the most effect on the color. Note: Do not use flowers, fruit, or roots for this experiment. They do not contain the pigments being studied.
How to Experiment Safely This experiment requires the use of a stove or bunsen burner to boil the solutions. Use caution when cooking the solution and ask an adult for assistance. When handling alcohol, wear goggles and be careful not to spill it on your skin or in your eyes. Keep alcohol away from the stove or open flame.
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• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Primary pigments, such as blue-green chlorophyll, and secondary pigments, such as yellow-orange carotene, yellow xanthophyll, and red anthocyanin, are all present in leaves.’’ In this case, the variable you will change is the type and part of the plant being tested, and the variable you will measure is the resulting mix of colors. A bowl filled with various food colorings will serve as a control experiment to allow you measure the effectiveness of the color separation method. If you find many different colors present in your experimental solutions, you will know your hypothesis is correct. Level of Difficulty Moderate. Materials Needed
• 1 cup (236 milliliters) of spinach leaves, cut up • 1 cup (236 milliliters) of parsley leaves, cut up • 1 cup (236 milliliters) of coleus leaves (houseplant with variegated leaves), cut up • food coloring (red, blue, and yellow) • filter paper (strong paper towels also will work) • rubbing alcohol 70% • 4 bowls • 4 glass cups or beakers Experiment Central, 2nd edition
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Step 6: Four cups with pigment solutions (control, spinach, parsley, and coleus). G AL E GR OU P.
• • • • • •
cooking pot labels 4 paper clips measuring spoons and cups water goggles
Approximate Budget $10 for the fresh parsley, spinach, and a coleus
plant. Timetable Approximately 2 hours.
Step 7: Filter paper strip in cup, held in place with a paper clip.
Step-by-Step Instructions
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1. Place one cup of water in a pot and bring it to a boil. Add 20 drops of each color of food coloring and boil for 10 minutes more. Remove the pot from stove and allow to cool. Pour the solution into a bowl and add 4 tablespoons of alcohol. Label the bowl ‘‘#1.’’ This will be your control solution. 2. Wash the pot and add one cup of water and bring it to a boil. Add the cut-up Experiment Central, 2nd edition
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Troubleshooter’s Guide Here are some problems that may occur in this experiment, some possible causes, and ways to remedy the problems. Problem: The pigment does not go up the paper. Possible cause: The paper is wet. Make sure the paper is thoroughly dry before inserting it in the solution. Also make sure the paper is touching the solution. Problem: The control experiment worked well, but the spinach, parsley, and coleus solutions are very light. Possible cause: The solutions are too weak. Place more leaves into the pot and boil the solution longer. Use a low flame, and be cautious when reheating as the mixture contains alcohol.
spinach leaves. Boil for 10 minutes more. Remove the pot from stove and allow to cool. Pour the solution into another bowl and add 4 tablespoons of alcohol. Label the bowl ‘‘#2.’’ 3. Repeat Step 2, substituting parsley for spinach. Label bowl ‘‘#3.’’ 4. Repeat Step 2 again, substituting coleus leaves. Label bowl ‘‘#4.’’ 5. Cut the filter paper into 1-inch-wide (2.5-centimeter) strips. These will be your chromatography papers. 6. Label the cups #1, #2, #3, and #4. Now pour 0.25 inch (0.6 centimeter) of the liquid solution from each bowl into the appropriate numbered cup. 7. Place a filter paper strip into each cup as illustrated. Use a paper clip to hold the paper to the cup. Make sure only the bottom of the filter paper touches the solution.
8. Leave the experiment undisturbed for 30 to 60 minutes. Notice how the solution creeps up the filter paper. 9. Stop the experiment when a pigment reaches the top of the filter paper. Place the pieces of paper on a clean, flat surface to dry.
Sample diagram of chromatography paper from one of the solutions. GA LE GR OU P.
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Summary of Results Make a diagram recording
what colors appeared on your chromatography papers (see sample diagram). The pigments may fade over time, so record the results the same day. Reflect on your original hypothesis. Were you able to detect the primary and secondary pigments present in all the leaves? Were pigments present in your control experiment? Which plant(s) contained the most secondary pigments? Which contained the most primary pigments?
EXPERIMENT 2 Response to Light: Do plants grow differently in different colors of light?
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of seedlings being used • the strength of light (wattage) • the wavelengths (colors) of light being tested • the amount of water given to the seedlings In other words, the variables in this experiment are everything that might affect the growth of the seedlings. If you change more than one variable, you will not be able to tell which variable most affected the seedlings’ growth.
Purpose/Hypothesis In this experiment you will
test the growth of plant seedlings under different colors of light. Within the cells of a plant’s leaves and stems, there are various pigments that react to light to perform photosynthesis. The pigments vary in color and
Step 1: Set-up of boxes with aluminum foil and black plastic. GAL E GR OU P. Experiment Central, 2nd edition
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concentration. Each pigment absorbs all colors of light except the color of the pigment itself, How to Experiment Safely which is reflected. For example, if a plant contains mostly green pigments such as chlorophyll, Incandescent light fixtures and bulbs can get the plant should grow well under all colors of hot. Do not handle or leave the lights on for more than 10 hours at a time. Never leave them light except green because it reflects most of the on overnight. Keep them a safe distance from green light without absorbing it. As a result, the the cellophane filters at all times. plant is ‘‘starved’’ for light and cannot perform the photosynthesis process needed to produce food and grow. To begin this experiment, use what you know about chlorophyll and the pigment colors found in plants to make an educated guess about how plants will grow under various colors of light. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Seedlings will grow best under white light, because they can absorb more energy from the wide range of wavelengths present. They will grow worst under green light, because that is the color of the dominant pigment contained in their leaves and stems, and most of that light will be reflected instead of absorbed.’’ In this case, the variable you will change is the color of the light, and the variable you will measure is the amount of growth of the seedlings over a period of several weeks. If the seedlings grow best under white light and worst under green light, you will know your hypothesis is correct. Level of Difficulty Moderate. (However, great care of the seedlings must
be taken to ensure their growth.) Materials Needed
• 4 boxes, 24 inches (60 centimeters) square in size, open on one side • aluminum foil 198
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• 4 light fixtures with 40-watt white incandescent bulbs, such as small desk lamps • 4 plastic filters about 12 inches (30 centimeters) square, such as cellophane in clear, green, blue, and red • black plastic cut from a garbage bag • 4 shallow trays filled with potting soil • 40 bean seeds, such as lima, kidney, or others (Use all of one type.) • water Note: If you are unable to get light fixtures to use, use natural sunlight and modify the setup described in the following procedure. Approximate Budget $30–$35 for light fixtures, if necessary, and $5 for
seeds and cellophane. Timetable Approximately two months—about 20 days for the seeds to germinate, and two to three weeks before the first true leaves appear. Step-by-Step Instructions
1. Set up four identical boxes. Line the inside of each box with aluminum foil. Cover the front opening with black plastic. Cut a hole in the top, about 10 x 10 inches, (25 x 25 centimeters), to allow light to enter. 2. Tape a different color plastic filter over the hole on each box. 3. Position a light fixture approximately 12 inches (30 centimeters) above the opening on each box and aim the light inside the box. 4. Place a tray of soil into each box and plant 10 seeds slightly below the surface of the soil. Water gently. 5. Turn the lights on for eight to 10 hours a day. Monitor the soil moisture and water gently when needed. 6. Record the seed growth in each box. Record which seedling is the tallest daily for one month after the seeds sprout or until the seedlings reaches the filter. Experiment Central, 2nd edition
Step 3: Light fixture over opening of box. GA LE G RO UP.
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Summary of Results Make a chart to track the
Troubleshooter’s Guide Here is a problem that may arise in this experiment, a possible cause, and a way to remedy it. Problem: The seeds did not grow. Possible Cause: The seeds might be too old. You can try again with new seeds or accept the results if you think it was the lighting. If they died from not getting enough water, then try again.
growth of the seedlings. Reflect on your hypothesis. Were the seedlings more responsive to one color of light? What color stimulated growth the least? Is that color the seedlings’ most dominant pigment? Summarize your results in writing.
Design Your Own Experiment How to Select a Topic Relating to this Concept All the colors in plants and animals
are due to pigments, which have many functions. Chlorophyll’s function is producing energy for photosynthesis. Melanin is a skin pigment that protects people and animals from harmful solar radiation. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on questions that interest you about chlorophyll and other pigments. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some pigments might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure
Step 6: Sample seed growth recording chart. GAL E GR OU P.
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what questions you’re answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Think of how you can
share your results with others. Charts, graphs, and diagrams of the progress and results of the experiments are very helpful in informing others about an experiment.
When cool weather comes in autumn, chlorophyll breaks down more rapidly than carotene and xanthophyll, making leaves such as these look yellow and orange before they fall from the tree. P HOT O RES EA RC HER S I NC.
Related Projects You can create an experiment on pigments by discover-
ing how to extract pigments from their source in nature. Or you could take an extracted pigment and find a use for it. For example, purple grape juice can be used as an acid/base indicator.
For More Information Andrew Rader Studios. ‘‘Photosynthesis.’’ Rader’s Biology4kids.com. http://www. biology4kids.com/files/plants photosynthesis.html (accessed on January 19, 2008). Provides information on plants and photosynthesis. Halpern, Robert. Green Planet Rescue. New York: Franklin Watts, 1993. Discusses the importance of plants and what can be done to protect plants that face extinction. Kalman, Bobbie. How A Plant Grows. New York: Crabtree Publishing, 1997. Examines the stages of a seed plant’s development and includes activities on how to grow plants. Missouri Botanical Garden. Biology of Plants. www.mbgnet.net/bioplants (accessed January 19, 2008). Providing information on the growth and life of plants
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Color
W
hen we look at white light, we are seeing all the colors of the rainbow combined. Our world is filled with color. For humans, colors can add beauty, convey information, and prompt emotions. For many animals and plants, color is an essential part of their survival. What color is and how we perceive it is behind the science of color.
Newton conducted many other experiments with light and color. C OR BI S-B ETT MA NN. RE PR ODU CE D BY PE RM IS SIO N.
What is color? Color is light energy, which is a series of electromagnetic waves. The waves in visible light are a sliver of the electromagnetic spectrum. Microwaves, radio waves, and X rays are other types of waves in the electromagnetic spectrum, but the human eye cannot detect them. White light is a combination of the colors on the electromagnetic spectrum. Each color has its own frequency and wavelength. Frequency is the number of waves that pass a point every second. The wavelength is the distance between similar points on the ‘‘wave.’’ Red light has the longest wavelength and violet light the shortest. All the other colors fall in between. Experiments with bending light It was the English scientist Isaac Newton (1642–1727), who first proved in 1666 that white light could be separated into colors. In one now-famous experiment, Newton darkened his room and made a small slit in the shutters. He placed a glass prism in front of the thin beam of light and saw a rainbow of colors. This band of colors is called a spectrum. Newton conducted many other experiments with light and color. He demonstrated how the colors in sunlight could be separated, then 203
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A rainbow appears because the moisture in the air or raindrops are acting as prisms. AP P HOT O/ WAL LA W AL LA U NIO N-B UL LET IN , JE FF HOR NE R.
joined again to form white light. He found that when light hits a prism, it is bent, or refracted. The wavelength of red light bends the least and the wavelength of violet light bends the most. The wavelengths cause the colors to bend and separate from one another in a certain order: red,
Visible Light
Radio Waves
Microwaves
Infared
Ultra Violet
X-rays
wavelength
length of wavelength Each color has its own frequency and wavelength. I LLU ST RAT IO N BY TEM AH NEL SO N.
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orange, yellow, green, blue, indigo, and violet. Light Refraction The separation of visible light into its different colors is called dispersion. The order of light dispersion is commonly referred to by the more easily remembered name: ROY G. BIV. When we see a rainbow it is because the moisture in the air or raindrops is acting as a prism prism. The white light from the sun hits the drop and bends, dispersing into distinct colors. In the 1800s, scientists learned that white light is actually made up of three colors: red, Isaac Newton first proved in green and blue. These colors are referred to as primary colors. Primary 1666 that white light could be colors cannot be separated into other colors. When red, green, and blue separated into colors. lightwaves are combined evenly they take the appearance of white light. ILL US TRA TI ON B Y TE MA H All the other colors we perceive are mixtures of the three primary colors. NEL SO N. What color we see is the color that is least absorbed. An object appears blue when it absorbs all wavelengths of visible light except blue. When an object absorbs all the light wavelengths, there is no color for us to see and the object appears black. Technically, the black of night is not a color, it is the absence of us seeing any color light at all. (Pigment colors, such as paints, work by different rules than light. Mixing red, green, and blue light will produce white; blending red, green and blue paints will form a muddy black-brown.) Rods and Cones There are two types of cells in the eye that allow us to see light: rods and cones. The rods and cones lie in the retina, a layer in the back of the eye. The cells send nerve impulses to the brain, which the brain interprets as color and images. Rods can detect gradations of light, movements, and shapes. In a room that is dimly lit, rods are what help us see what is in the room. People have about 120 million rods. Overall, it’s the cones that allow us to see color. The eye has only about six million cones. The cones can perRod Cone ceive green, red, or blue but cones do not detect light that well. That’s why when the room is dark we cannot see colors as well as a well-lit room. Iris Retina When a person’s cones do not work properly the person may be color-blind. There are Experiment Central, 2nd edition
Rods and cones allow us to see light. I LL UST RA TI ON BY TEM AH N EL SON .
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WORDS TO KNOW Cones: Cells in the retina that can perceive color. Electromagnetic spectrum: The complete array of electromagnetic radiation, including radio waves (at the longest-wavelength end), microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays (at the shortestwavelength end). Electromagnetic waves: Waves of energy that are part of the electromagnetic spectrum. Hue: The color or shade. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Lens: A piece of transparent material with two curved surfaces that bend rays of light passing through it. Nanometer: A unit of length; this measurement is equal to one-billionth of a meter. Optics: The study of the nature of light and its properties.
Primary colors: The three colors red, green, and blue; when combined evenly they produce white light and by combining varying amounts can produce the range of colors. Prism: A piece of transparent material with a triangular cross-section. When light passes through it, it causes different colors to bend different amounts, thus separating them into a rainbow of colors. Refraction: The bending of light rays as they pass at an angle from one transparent or clear medium into a second one of different density. Retina: The light-sensitive part of the eyeball that receives images and transmits visual impulses through the optic nerve to the brain. Rods: Cells in the retina that are sensitive to degrees of light and movement. Saturation: The intensity of a color.
different degrees and types of color-blindness, but in general, people who are color-blind can still see some color. The most common type of color-blindness is in problems with the red/green cones. When one or more of the cones is not functioning, the brain cannot distinguish certain colors from one another. Color-blindness is an inherited trait, which means it is in the genes. It is far more common in males, affecting an estimated one out of 12 men. How deep and how bright A red rose, apple, and sunset all may appear red, but the color of each is slightly different. A color’s hue, saturation, and brightness are all aspects of color that distinguish them from one another. The hue is the color. Saturation is the intensity of the color. If grey or black is added to a red than it is less saturated and appears 206
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more mauve. A pure red is fully saturated. Brightness is the amount of light in the color. In the following two experiment you will explore two aspects of color: how color affects perception and how heat energy relates to color. As you conduct the following two experiments on color, consider what aspects of color you are curious about and would like to investigate further.
EXPERIMENT 1 Color and Flavor: How much does color affect flavor perception? Purpose/Hypothesis People are used to specific
What Are the Variables? Variables are anything that might affect the results of the experiment. Here are the main variables in this experiment: • the flavor of the juice • the ingredients in the recipe • the temperature of the food • the way the food is served • information the test subjects are told about the experiment In other words, the variables in this experiment are anything that might affect the flavor perception. If you change more than one variable, you will not be able to tell which variable had the most effect on how people perceived the flavor.
colors relating to certain foods or flavors. A lemon is expected to be yellow, a lime green, and a strawberry red. Seeing a certain color sends signals to the brain about what the food will taste like. In this experiment, you will investigate how color relates to the perception of flavor. If the color is different than expected, will test subjects identify the actual flavor? You can manipulate the flavor of a gelatin by using uncolored fruit juice. By adding food coloring, you can turn each gelatin a color that is different than its recognizable color. The next step is to ask at least three people to taste the gelatin. In order to keep the experiment unbiased, do not tell the test subjects what you are testing. You will make up a series of questions, with the taste or flavor being among them. After hearing the results from the test subjects, you can observe how color affects the perception of taste. To begin your experiment, make an educated guess about color and flavor perception. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change Experiment Central, 2nd edition
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• the variable you will measure • what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Test subjects will not identify the actual flavor of the colored gelatin.’’ In this case, the variable you will change is the flavor and the variable you will measure is people’s perception of the flavor.
Use caution when handling the hot juice. You may want to ask an adult to help you heating the juice on the stove.
Level of Difficulty Moderate, due to the time involved in making the
recipe and testing the subjects. Materials Needed
Step 1: Measure out 1 cup of the juice, then pour into the saucepan and bring to a boil. I LLU ST RAT IO N BY T EM AH NEL SO N.
• 6 envelopes of unflavored gelatin • 3 different flavors of clear juice, all the same brand (2 cups of each juice). Apple, grape, pear, lemon, orange, and berry are some options. Clear juice is sold in some supermarkets and health food stores. It is also available from companies online. • food coloring, colors to match the flavors • 3 small rectangle or square pans (bread pans or 8-inch square pans work well) • small saucepan • glass bowl • measuring cup • spoons • knife • stove or microwave Approximate Budget $10 to $20, depending
upon the available juice. Timetable Approximately four to five hours total
time making and chilling the gelatin; 30 minutes testing subjects. 208
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Step-By-Step Instructions
1. For juice 1: Pour 1 cup of the juice in the Troubleshooter’s Guide saucepan and bring to a boil. When conducting experiments with food and 2. While the juice heats, pour 1 cup of cold people, several problems can occur. Here are juice in a bowl and add the gelatin. As two problems you may encounter, possible soon as the cup of juice has boiled pour it cause, and ways to fix the problem. into the bowl and stir until all the gelatin Problem: The gelatin did not taste good. is dissolved. Possible cause: Depending upon the juice you 3. Decide what color you want the gelatin. purchased, you may need to add sugar or Remember to make it a completely differadd more water. Adapt the recipe until you ent color than the traditional juice. For like the way it tastes, and make a new batch. example, if the juice is strawberry (red) Problem: Everyone knew immediately the you could make the color yellow to repgelatins were not ‘‘natural.‘‘ resent lemon. Add the selected food color Possible cause: You may have added too much food coloring to make the gelatin look one drop at a time into the bowl. Stir after unnatural. You might want to purchase and each drop until you have a color that make flavored gelatins and try to match the appears natural. Write down the color color. you selected for the juice. 4. Pour the colored gelatin into the bread pan. 5. Repeat the process for juice 2 and juice 3, making sure to rinse the bowl and saucepan before beginning each recipe. Remember to write down what color you have selected for each flavor juice. Only you will know! Step 7: Cut each of the gelatins 6. Place all three pans in the refrigerator and allow to set for two to into squares and place on a four hours. It should be firm when you jiggle the pan. plate. ILL US TRA TI ON B Y TEM AH N EL SON . 7. Cut each of the gelatins into squares and place on a plate. 8. Write down a series of questions: Is the gelatin too sweet? Is it firm enough? Does the gelatin have enough flavor? What flavor does it taste like? 9. Test each subject one at a time, apart from one another so one does not influence someone else. Tell each test subject you are testing a recipe and want his or her opinion. After the subjects taste each flavor, ask your questions. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the colors along the visible light spectrum • the intensity of the white light being used • the temperature of the room or outside environment • the surface material the color light appears In other words, the variables in this experiment are everything that might affect the temperature of the visible colors visible through the prism. If you change more than one variable, you will not be able to tell which variable had the most effect on the temperature of the colors.
10. Test at least three subjects, or until you run out of gelatin. Summary of Results Was there one flavor more
than the others that the test subjects identified correctly? How sure were the test subjects when they identified the flavor? Was there one color more than the others that the subjects could not identify? Write up a summary of your findings. Change the Variables You can change other variables to investigate color and flavor perception. Try the experiment using different foods, such as colored candies that all actually have the same flavor. You could also change the color of the plate and place setting to measure how that affects food enjoyment or perception.
EXPERIMENT 2 Temperature and Color: What color has the highest temperature? Purpose/Hypothesis Light energy also carries heat energy. The different
colors of light energy all have unique wavelengths, and the energy of light relates to its wavelength. Along the visible spectrum (the range of wavelengths visible to the human eye) the color red has the longest wavelength and violet has the shortest. In this experiment you will determine the temperatures of different colors of light along the visible light spectrum. Using a prism and a white light, you will separate the white light into the colors of the spectrum, much like a rainbow. You then will take temperature readings on both ends of the spectrum: the red and violet ends. The differences in the temperature readings will allow you to determine how a color’s wavelength relates to heat energy. Do you think the color with the longer wavelength will have lower or higher energy than the color with the shorter wavelength? Before you begin the experiment, make an educated guess about the outcome based on your knowledge of the visible light spectrum and the 210
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wavelengths of the different colors. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
How to Experiment Safely There are no safety hazards in this experiment.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The color violet will have the highest temperature reading because it has the shortest wavelength. Wavelength size decreases as the energy of the light increases.’’ In this case, the variable you will change is the color along the spectrum whose temperature you are measuring. The variable you will measure is the temperature of the different colors along the spectrum. Level of Difficulty Moderate. Materials Needed
• large prism or 2 small prisms (approximately 1 inch [2.5 centimeters] thick, available from science stores) • flashlight • digital thermometer • Styrofoam, piece about 5 inches (12.7 centimeters) long, wide enough to cover the glasses (the Styrofoam holding fruit and vegetables in grocery stores or Styrofoam egg cartons work well) • watch or timer • 2 drinking glasses
Steps 1 and 2: Place the flashlight on the table sideways and turn on the flashlight. Position the prism in front of the flashlight so that it catches light. I LL UST RA TI ON BY TEM AH N EL SON .
Approximate Budget $20. Timetable 1 hour. Step-by-Step Instructions
1. Find a table to work on that is steady and place it against a wall. Place the flashlight on the table sideways and turn on the flashlight. Experiment Central, 2nd edition
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2. Position the prism in front of the flashlight so that it catches light and produces a ‘‘rainbow’’ on the wall behind the table. (If using two prisms, place one in front of another at a slight angle.) This can take some time. Keep moving the prisms until you get a strong, clear spectrum of color on the wall. Step 5: The probe senses the temperature. I LLU STR AT IO N BY T EM AH NE LS ON.
3. Set one drinking glass on either side of the rainbow on the table. One glass should be in the middle of the red and the other glass should be in the middle of the violet. 4. Place the Styrofoam on top of the glasses. 5. Note the temperature of the thermometer, which should be at room temperature. Carefully insert the thermometer through the Styrofoam so that it is hanging through the Styrofoam. Place its probe in line with the red color on the spectrum on the wall behind it. (The probe senses the temperature.) 6. Wait 10 minutes and note the temperature. Remove the Styrofoam with the thermometer still in it and wait for it to return to room temperature. This may take about 10 minutes. 7. Move the Styrofoam set up so that thermometer’s probe is in line with the violet color on the spectrum. 8. After 10 minutes check the temperature and record. Summary of Results Study the observations of your temperatures and
decide whether your hypothesis was correct. Did you see a slight difference between the temperature of the red and violet colors? Which one had the higher temperature? What relationship does the temperature have with the wavelength of the colors? Write up a paragraph of your results. You may want to include pictures or drawings of your set-up. Change the Variables You can vary this experiment by measuring the
temperatures of other colors. You can also measure the temperatures of the non-visible spectrum, just to the left and right of the red and violet colors. What are these temperatures and how do they relate to what you know about wavelengths. 212
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Design Your Own Experiment How to Select a Topic Relating to this Concept
There are many aspects of the properties of color you can study. Look at the variety of colors in your home, foods, artwork, and in nature to encourage ideas. Consider if you are interested in exploring color from a physics perspective and/or from a psychological perspective. Check the Further Readings section for this topic, and talk with a science teacher or a knowledgeable adult before finalizing your choice. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
Troubleshooter’s Guide Below are some problems that may occur during this project, possible causes, and ways to remedy the problems. Problem: You could not get the prism to separate the light into a visible spectrum (rainbow). Possible cause: The light may not be focused enough. Try to focus the light from the flashlight by magnifying it with a magnifying lens or shine the light through a small hole cut out of the bottom of a soda can. This will help to concentrate the light for the prism. You can also try using a larger prism. Problem: There is no temperature difference between the red and violet colors. Possible cause: The probe of the thermometer may not be directly over the light. Make sure that probe of thermometer is directly in the path of the red and violet lights as they are shining against the wall.
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Recording Data and Summarizing the Results Your experiment can be
useful to others studying the same topic. When designing your experiment, develop a simple method to record your data. This method should be simple and clear enough so that others who want to do the experiment can follow it. Your final results should be summarized and put into simple graphs, tables, and charts to display the outcome of your experiment. You might also want to have color visual displays. Experiment Central, 2nd edition
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Related Projects Experiment 1 focused on humans and color perception. You may want to explore how animals perceive and react to color. An experiment could focus on what colors different animals can perceive and how color can affect their lives. Plants also may respond to colors in different ways. You may want to focus on saturation or hue. How can you change or measure a color’s saturation, for example. Another aspect you may want to study might be color perception or color blindness. If you choose either of these topics, experiments might be how different colors relate to certain emotions or how color-blindness is inherited. Your project does not have to be an experiment that investigates or answers a question. It can also be a model, such as Newton’s original experiment with window shutters and a prism.
For More Information ‘‘Color and Light.’’ Patterns in Nature. http://acept.asu.edu/PiN/rdg/color/ color.shtml (accessed on April 26, 2008). Detailed information on color and how we see. ‘‘Color Vision and Art.’’ WebExhibits. http://webexhibits.org/colorart (accessed on April 26, 2008). Information and interactives on color. Cobb, Vicki and Josh Cobb. Light Action! Amazing Experiments with Optics. New York: HarperCollins, 1993. Experiments with light and color. Davidson, Michael W. et al. ‘‘Light and Color.’’ Molecular Expressions. http:// micro.magnet.fsu.edu/primer/lightandcolor/index.html (accessed on April 18, 2008). Farndon, John. Color. Tarrytown, NY: Marshall Cavendish, 2001. Experiments in color. Hamilton, Gina L. Light: Prisms, Rainbows, and Colors. Chicago: Raintree, 2004. Seckel, Al. Optical Illusions: The Science of Visual Perception. Buffalo, NY: Firefly Books, 2006. Collection of optical illusions, with information on the science of visual perception.
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Comets and Meteors
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arth is part of a solar system that is filled with celestial objects moving about. Scientists theorize that many of these objects are materials left over from when the solar system formed—about 4.6 billion years ago. Comets and meteors are two such chunks of materials in the solar system. Every so often these objects are visible to the naked eye as brilliant streaks of light across the sky. Meteors appear regularly and are sometimes called ‘‘shooting stars’’; comets show themselves with far less frequency. Astronomers look to these objects to learn more about the universe around Earth and the early history of the solar system. Hot snowballs Comets are often referred to as dirty snowballs because of their makeup: a mixture of ice and dust. They typically move through the solar system in orbits or revolutions around the Sun ranging from a few years to several hundred thousand years. Astronomers theorize there may be more than one trillion comets zipping about the solar system, yet spotting a comet is rare. Most comets are located on the outskirts of the solar system in a giant sphere called the Oort cloud, which surrounds the solar system. The comets in the Oort cloud can take over a million years to make a single revolution around the Sun. Occasionally one of these comets is pulled by a nearby star and gets pushed closer to the Sun. When it approaches the Sun it becomes visible to astronomers. About a dozen of these new comets are discovered every year.
A few comets have a relatively short orbit. For example Halley’s Comet orbits the Sun about every 76 years. This comet is named after English astronomer Edmond Halley (1656–1742), who was the first person to work out the elliptical orbits of comets. After Halley spotted a comet in 1682, he started reading through historical records. He found that two previous comets, in 1531 and 1607, had orbital paths similar to the one he had witnessed. These three comet sightings, he concluded, were actually the same object making three appearances. Halley predicted this comet would 215
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pass through again in 1758 and, although he did not live to see it, the comet appeared as predicted. A tail’s story For a short time during each coma orbit around the Sun, comets can become visible from Earth. When a comet approaches the Sun, it develops three basic parts: a nucleus, a coma, and a tail. nucleus The nucleus is the dirty snowball part of the comet, made of ice and a small amount of dust and other solids. It ranges from about 1 to 10 miles (1.6–16 kilometers) across and is at the Components of a comet. G AL E center of the comet. The nucleus and the coma make up the comet head of GRO UP. the comet. The coma is the blob of gas that roughly encircles the nucleus. It is the brightest part of the comet. This region is formed as the comet approaches the Sun and becomes warmer. The coma is made up of water vapor, carbon dioxide, and other gases that have sublimed from the solid nucleus. Subliming is when a material goes directly from being a solid to being a gas without becoming a liquid. One of the most impressive sights of a comet is its tail, a long extension from the head that always points away from the Sun. Even though it does not have much mass, a comet’s tail can stretch into space several million miles. Comets often have two tails. One type of tail is a dust tail. This is made of dust leaving the nucleus. Gas and heat from the Sun push the tail backward into its long streak. The dust tail is often curved or spread out, and yellowish in appearance. Another type of tail is an ion tail. An ion tail forms when the gas particles become ionized or charged by the Sun. The molecules are pushed away from the nucleus by charged particles streaming Halley’s Comet orbits the Sun out of the Sun. An ion tail is usually very straight and bluish. about every 76 years. AP /W ID E WO RLD PHO TO S A meteor’s story As a comet hurls close to the Sun and its ice melts, pieces of rock sometimes loosen. These tiny solid remnants traveling through space are called meteoroids. While the majority of meteoroids come from comets, some are fragments of planets or other celestial bodies. They are chunks of stone, metal, or a combination of the two. Wherever they originate, all meteoroids are small. Most range in size from a grain of sand to a pebble. They are the smallest known particle to orbit the Sun. They are also fast. Meteoroids are usually dust tail
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traveling at speeds ranging from 25,000 miles per hour (40,000 kilometers per hour) to 160,000 miles per hour (256,000 kilometers per hour).
meteor
When a speedy meteoroid tears into Earth’s atmosphere, the layer of air encircling our planet, it produces a streak of light known as a shooting star, or meteor. The blaze occurs as the meteor’s intense speed heats up the air around it to more than 3,000˚F (1,650˚C). This in turn heats up the meteor and creates a flash of light visible from the ground below. Some large meteors can produce a brilliant flash. These meteors are called fireballs and they can create an explosion that can be heard up to 30 miles (48 kilometers) away. While the intense heat burns up the vast majority of meteors, a small percentage make it through Earth’s atmosphere. These are called meteorites. Because of their high speeds, meteorites can sometimes make huge craters when they hit the ground. A crater is a circular pit created when a celestial object crashes into a planet or other orbiting mass. These craters are found almost everywhere in the solar system and they pocket the surface of the Moon. Scientists have found about 150 craters on Earth. One of the largest and best preserved craters on Earth is the Barringer Meteor Crater in Arizona. The Barringer formed about 50,000 years ago. It stretches nearly 1 mile (1.6 kilometers) wide and is 570 feet (174 meters) deep. The size, speed, and angle of impact of the meteor all determine whether the crater will be simple or complex. Simple craters have a smooth, bowl shape and a raised outer rim. Complex craters have a central peak, or peaks, and a relatively shallower depth. These large craters form this shape when their initial steep wall collapses downward and inward. The explosion of the impact causes the fallen crater floor to rebound. Rock fragments blast outward, creating the central peak or peaks. Experiment Central, 2nd edition
meteoroid crater caused by meteorite
Earth's atmosphere
The progression of particles that break away from a comet: They first become meteoroids, then meteors, and, finally, meteorites. G AL E GR OUP .
A fragment of a meteorite found in 1891 in Arizona, on display at the Monnig Meteor Gallery in Fort Worth, Texas. AP/ WI DE W OR LD
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Showering shooting stars On any clear night, a person can probably spot some meteors. Several times every year, though, storms of meteors will fill the night sky in what is called a meteor shower.
simple crater
Because of their high rates of speed, meteorites can sometimes make huge craters when they hit the ground. GA LE GRO UP.
complex crater
Meteor showers occur when Earth moves through a stream of particles produced by comet leftovers. Since the orbits of comets are known, it is possible to predict many meteor showers. These showers can create a brilliant light show as they enter the atmosphere.
PROJECT 1 Comet Nucleus: Linking a Comet’s Composition to its Properties. Purpose/Hypothesis In this project, you will construct a comet* using
either the same or similar ingredients that make up a real comet. Comets are composed of bits of dirt or dust, held in place by ice. The ice is a combination of water and carbon dioxide ice. Comets contain carbonbased or organic molecules and ammonia. Sodium or salt was found to be
A meteor streaks through the sky over Joshua Tree National Park in California. Stars moving through the sky are seen as a series of short lines across this 30-minute time exposure frame. AP /WI DE W OR LD
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WORDS TO KNOW Coma: Glowing cloud of gas surrounding the nucleus of a comet.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Comet: An icy body orbiting in the solar system, which partially vaporizes when it nears the Sun and develops a diffuse envelope of dust and gas as well as one or more tails.
Ion tail: One of two types of tails a comet may have, it is composed mainly of charged particles and it points away from the Sun.
Comet head: The nucleus and the coma of a comet. Comet nucleus: The core or center of a comet. (Plural: Comet nuclei.) Comet tail: The most distinctive feature of comets; comets can display two basic types of tails: one gaseous and the other largely composed of dust.
Meteor: An object from space that becomes glowing hot when it passes into Earth’s atmosphere; also called shooting star. Meteor shower: A group of meteors that occurs when Earth’s orbit intersects the orbit of a meteor stream. Meteorites: A meteor that is large enough to survive its passage through the atmosphere and hit the ground.
Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Meteoroid: A piece of debris that is traveling in space.
Crater: An indentation caused by an object hitting the surface of a planet or moon.
Oort cloud: Region of space beyond our solar system that theoretically contains about one trillion inactive comets.
Dust tail: One of two types of tails a comet may have, it is composed mainly of dust and it points away from the Sun.
Sublime: The process of changing a solid into a vapor without passing through the liquid phase.
Fireball: Meteors that create an intense, bright light and, sometimes, an explosion.
Variable: Something that can affect the results of an experiment.
in the comet Hale-Bopp. Trapped gas and an uneven surface are other features of a comet. It is these materials in the nucleus that form the brilliant head and tail when they come close to the Sun. Once you have constructed the comet, you can then observe its behavior. *Adapted from ‘‘Making A Comet in the Classroom’’ by Dennis Schatz, Pacific Science Center, 1985. Experiment Central, 2nd edition
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Level of Difficulty Moderate (because of the
number of trials and careful measurements needed).
How to Work Safely Dry ice is carbon dioxide frozen at–110˚F (–79˚C). If you touch a piece of dry ice too long, it will freeze your skin and feel like a burn. Wear gloves when working with dry ice and do not place dry ice in your mouth. Also be careful when you pour the ammonia into the spoon to prevent it from splashing into your eyes.
• • •
Step 7: Wearing gloves, pat the meteor into a snowball shape. Keep the comet in the plastic bag when shaping. GA LE GR OU P.
• • • • • • • •
Approximate Budget $15. Timetable 45 minutes for initial setup; several
hours observation time. Materials Needed
• 2 cups (500 milliliters) of water • 2 cups (500 milliliters) of dry ice, broken into pieces if possible (dry ice is available at ice companies and some butcher shops) 2 to 3 spoonfuls of dirt (a small dinner spoon is fine; the exact size is not important) 1 spoonful of ammonia 1 spoonful of organic material (dark or light corn syrup works, or Worcester sauce works well) thick gloves large plastic bowl 2 heavy-duty garbage bags self-sealing plastic bag hammer or mallet mixing spoon salt paper towels Step-by-Step Instructions
1. Cut open one garbage bag and use it to line your mixing bowl. 2. Add the water and dirt in the mixing bowl. Stir well. 3. Add a dash of ammonia 4. Add a sprinkle of salt and a spoonful of the organic material. Stir well. 5. Put on gloves and place the dry ice in the self-sealing plastic bag. Zip the bag closed and place the bag inside the second 220
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6.
7.
8. 9.
garbage bag. Pound the dry ice with a hammer until it is crushed. Add the dry ice to the ingredients in the mixing bowl and stir rapidly. Continue stirring until the mixture is slushy and almost totally frozen. Lift the garbage bag with the comet out of the bowl and shape it like a snowball. Shape the plastic bag and not the snowball. Wear gloves. Unwrap the comet and place it on the bag. After you have observed the comet for several hours, break it apart and look at the inside.
Troubleshooter’s Guide Below is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: The comet fell apart during the snowball formation. Possible cause: You may not have broken up the dry ice into small enough bits. Try the experiment again, pounding the dry ice thoroughly.
Summary of Results Draw a picture of the comet and note how it appears.
Gently blow on the comet and note your observation. After two hours have passed, note your observations of the comet and compare it to your first description. What has happened to the carbon molecules in the organic substance? Write a brief explanation of how this miniature comet relates to what occurs during a comet’s orbit.
EXPERIMENT 2 Meteor Impact: How do the characteristics of a meteorite and its impact affect the shape of the crater? Purpose/Hypothesis It was in the early 1900s that scientists first concluded a meteorite caused the formation of a crater. (Most astronomers before that time had assumed that craters were formed by volcanoes.) The first crater that scientists proved had come from a meteorite was the Barringer Meteor Crater in the Arizona desert. This gigantic depression is nearly 1 mile (1.6 kilometers) wide and 570 feet (174 meters) deep. Since that time, scientists have studied both the many craters on the Moon and the ones on Earth to study meteorite impact. In this experiment you will investigate the factors that affect the formation of simple meteor craters. You will examine how a meteor’s size, angle of impact, and speed of impact affect the crater shape. Speed in this Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the shape of the object • the weight of the object • the angle of impact • the speed of the object • the substance the object impacts In other words, the variables in this experiment are everything that might affect the shape of the crater. If you change more than one variable at a time, you will not be able to tell which variable changed the crater formation.
experiment is determined by the drop height. The higher the drop height, the faster the simulated meteor hits the surface. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of meteors and craters. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The faster and heavier the simulated meteor, the deeper and wider the crater; a meteor coming in at an angle will form an elongated crater.’’ In this case, the variables you will change, one at a time, are the weight of the meteor, the speed of the meteor, and the angle of impact. The variable you will measure is the depth and diameter of the crater. Conducting a standard experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the standard experiment and each of your trials. To change only one variable at a time, it is important to always use a simulated meteor of standard weight and use a standard drop height. Then you will change one variable at a time. Your control will be a medium-weight meteor, at a vertical, 180-degree drop, and a drop height of 39 inches (1 meter). You will complete three tests in this experiment. You will measure how the weight of a simulated meteor, the speed of the simulated meteor, and the angle of impact of the simulated meteor affect the crater’s physical characteristics. For each variable you will measure the crater’s depth and diameter. The diameter is the measurement across a circle. In this case, it is a point on the peak of the rim to a point on the rim on the opposite side. In actuality there are many factors affecting a meteor’s crater. For increased accuracy, you will conduct three trials of each test, then average the measurements.
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Level of Difficulty Moderate (because of the number of trials and careful measurements needed). Materials Needed
How to Experiment Safely There are no safety hazards in this experiment.
• shallow rectangle pan or plastic container, about 12 to 18 inches (30 to 46 centimeters) long and 2 inches (5 centimeters) deep • fine, dry sand (available at hardware stores or greenhouses) • powder of contrasting color to sand, such as cinnamon, cocoa, or paprika • empty shaker, such as a saltshaker • nine small round objects of similar shape to simulate meteors: three of the same light weight, three of the same medium weight, and three of the same heavy weight (marbles, candies, or pebbles work well) • ruler • protractor • string, about 4 feet (30 centimeters) • tape • newspapers (optional) • cardstock, cut into thin strips about 0.125 (1=8) inches (3 millimeters) wide Approximate Budget $10. Timetable 1 hour. Step-by-Step Instructions
1. Weigh each of the simulated meteors and note on a chart. Create a separate chart for mass, speed, and angle of impact. Each chart should have separate rows for the diameter and depth measurements. Make a note of the standard meteor on the chart. 2. Place newspapers under the pan or conduct the experiment outside to avoid a sandy cleanup. 3. Fill the pan about three-quarters full with sand. Shake until the sand is level. 4. With the shaker, sprinkle a light layer of the contrasting colored powder over the sand. This will help you measure the crater’s shape. Experiment Central, 2nd edition
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Mass
Light
Step 1: Example of the ‘‘Mass’’ data chart; one of the three charts to be created for Experiment 2. GAL E GR OU P.
Step 6: One at a time, drop the three lightest-weight simulated meteors vertically from a height of 39 inches (1 meter) onto the surface. GA LE GRO UP.
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average
(weight)
Medium
Heavy
(weight)
(weight)
diameter
Standard
depth
Standard
5. Make sure the sand is level and the outer layer is even before you continue. 6. To test for the effect of size: One at a time, drop the three lightestweight simulated meteors vertically from a height of 39 inches (1 meter) onto the surface (you may have to stand on a chair). Do not throw the object. Drop the objects so that the craters are several inches apart. 7. Measure the diameter of the resulting craters. Average the three measurements and record on a chart. 8. Measure the depth of the craters by carefully placing one of the narrow strips of paper at the bottom of the crater and marking on the paper where the paper meets the rim of the crater. Average the three measurements and record on chart. 9. Level out the sand and the contrasting-color layer. 10. To test for speed: Increase the drop heights to 79 inches (2 meters) and drop the three medium-weight simulated meteors. Again, drop them so the craters are several inches apart. Record the results. Level the sand and contrasting-color layer. 11. Using the same three medium-weight simulated meteors, decrease the drop height to 20 inches (0.5 meters). Average the measurement results and note in a chart. Level the sand and contrastingcolor layer as before. Experiment Central, 2nd edition
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12. To test for angle impact: Tie the piece of string to the midpoint of the protractor and tape the protractor to the bottom of the container. Use the string as a guide for the angle of impact. 13. Hold the string at a 75-degree angle and drop the three medium-weight meteors into the box at that angle, at the height of 39 inches (1 meter). Measure the diameter and depth of the resulting craters and record the averages on a chart. Level again. 14. Drop the three medium-weight meteors into the box at a 45-degree angle. Record the results.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The crater depth was too shallow to measure in some craters. Possible cause: You may have chosen projectiles that were too light. Set aside the small and medium projectiles, and select two new sets that are heavier than whatever was the heaviest object used before. Repeat the experiment.
Summary of Results Create a graph illustrating the data in each chart. Make sure you use different colors or symbols for each of the variables in the chart and label each chart carefully. Compare each of the variables to the standard projectile. How did the weight of the projectile affect the size of the crater? How did the angle of impact affect crater formation? For years astronomers hypothesized that objects that landed at an angle would produce an elongated-shape crater. Through experimentation scientists discovered that projectiles create round craters, independent of the angle of impact. Do your results match these findings? Change the Variables You can vary this experiment several ways:
• • • •
Try different angles of impact Alter the shape of the projectiles Change the surface the projectile impacts Change the consistency of the surface
Design Your Own Experiment How to Select a Topic Relating to this Concept Meteors and comets are
amazing sights that can provide useful information about the universe. As both celestial bodies are visible to the naked eye, although comet sightings are quite rare, it may be possible to gather data on these objects through Experiment Central, 2nd edition
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observation. Find an amateur astronomer who has observation equipment, and discuss a possible project with him or her. You may also want to investigate whether any science centers in your area have meteorite fragments that you can study. Check the Further Readings section for predicted comet and meteor sightings, along with information gathered from previous sightings. Talk with your science teacher, along with any professional or amateur astronomers, to learn more about comets and meteors. If you do choose to observe meteors or comets during the daylight, remember to never look directly at the Sun, as it can damage your eyes. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In any experiment you conduct, you should look for ways to clearly convey your data. You can do this by including charts and graphs for the experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. You might decide to conduct an experiment that lasts several months. In this case, include pictures or drawings of the results taken at regular intervals. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. 226
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Related Projects There are many related projects you can undertake to learn more about comets and meteors. Meteor showers occur throughout the year. Gathering data from observing meteors is one possible project. Because comet sightings are far more rare, you can create a model of an active comet orbiting the Sun, using household items to represent the objects in the solar system. Research the spatial relationships of celestial bodies in the solar system as you work on your project to ensure you have the model to scale. You could also investigate if any craters are located in your surrounding area and, if so, set out on a field trip to examine the formation. If there are no craters in your area or you cannot visit one, you can use reference materials. You can compare how the sizes and shapes of craters relate to the meteor’s composition. Why would one meteorite form a crater and another simply land on Earth? You can also conduct a research project to examine the data and theoretical information that astronomers have learned about the universe from their studies of comets and meteors.
For More Information The Barringer Meteorite Crater. http://www.barringercrater.com (accessed on January 17, 2008). Story of the famous crater and the persistent scientist who proved a crater was caused by a meteorite, not a volcano. Bonar, Samantha. Comets. New York: Franklin Watts, 1998. The makeup, orbits, and other information on comets, with illustrations. Britt, Robert Roy. ‘‘Meteors and Meteor Showers: The Science.’’ Space.com. http://www.space.com/scienceastronomy/solarsystem/meteors ez.html (accessed on January 18, 2008). Information on meteors and meteor showers, includes animation and meteor composition. Freudenrich, Craig C. ‘‘How Comets Work.’’ How Stuff Works. http://science. howstuffworks.com/comet3.htm (accessed on January 17, 2008). Clear explanation of how comets work. Kronk, Gary W. Comets & Meteor Showers. http://meteorshowersonline.com (accessed on January 18, 2008). Site on comets and meteors includes clear explanations and a calendar of times for future sightings. ‘‘Orbits.’’ Near Earth Object Program. http://neo.jpl.nasa.gov/orbits (accessed on January 18, 2008). Enter any asteroid or comet and see its orbit. World Book’s Young Scientist: Volume 1. Chicago: World Book, Inc., 1995. Well illustrated reference with basics of space and space study.
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omposting is the process in which organic wastes are broken down biologically and become dark, fertile soil called humus. An ancient practice, composting probably began when the original hunter-gatherers began cultivating food and saw that crops grew better in areas where the soil contained manure, the waste matter of animals. Agricultural composting with manure was being used in the Mesopotamia Valley in Asia as early as 13 B . C . E . Not surprisingly, Native American tribes practiced composting long ago, as did the first colonists who arrived in North America. A smelly solution French chemist Jean Baptiste Boussingault (1802–1887) made significant contributions to agricultural chemistry by suggesting that good soil was made by the action of microorganisms, bacteria, and fungi that break down waste. Working on his farm, he applied and studied the results of organic methods of farming from 1834 to 1876. At that time, composting used mostly animal manure or dead fish, as well as nutrient-rich muck from swampy areas. By the twentieth century, large animals such as the buffalo, whose droppings fertilized the prairie soil, were disappearing as were many of the farming communities that contributed barnyard manure to compost piles. In 1934, Sir Albert Howard, an Englishman, developed the modern organic concept of farming. Through several years of research in Indore, India, he formulated the Indore method, a process that used three times more plant waste than manure in sandwich-like layers of green or wet material. Howard also pointed out the importance of microorganisms in the process. In 1942, J.I. Rodale began publishing Organic Farming and Gardening. Rodale used Howard’s techniques and experimented with his own. He is considered the pioneer of organic methods of farming in the United States. 229
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Chomping microbes How does composting work? Let us begin with the basics, the organic waste. That would be vegetable scraps such as carrot tops and peelings, plus leaves, paper bags, grass clippings, tea bags, and coffee grounds. Carbon in these organic waste materials provides food for the microorganisms, starting the composting process. When these microbes chomp away and begin digesting, the carbon is burned off or oxidized, causing the composting pile to heat up. The heat kills any harmful organisms. Macroorganisms— such as earthworms, insects, mites, and grubs— continue the composting process by chewing the organic matter into smaller pieces. Through digestion and excretion, both types of organisms release important chemicals into the compost mass, which then becomes humus, a nutrient-rich soil.
Backyard compost bins are simple to use. PET ER ARN OL D I NC.
The transformation is speeded up by a balanced supply of carbon and nitrogen, the oxygen required by the microorganisms, enough moisture to allow biological activity, and suitable temperatures. But it is really the diverse microorganisms that chomp away and activate the process. Without them, we would be buried in wastes. In the United States, more garbage is generated than in any other country in the world. Materials that could be used in composting make up 20–30% of the waste stream—the waste output of any area or facility. This figure doubles in the autumn when leaves and garden clippings are added. All this waste winds up in landfills. Landfills that raised the roof Landfills are huge depressions in the ground or equally huge mounds above ground where garbage is dumped. Like compost piles, landfills also have centuries-old beginnings. The ancient cities of the Middle East were built up over time on mounds that contained the remains of everyday life. In excavations of the ancient city of Troy, in what is now Greece, building floors were found to have layers of animal bones and artifacts that had been alternated with layers of clay. These layers piled up until it was necessary to raise roofs and rebuild doorways.
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During the Bronze Age (3000–1000 B . C . E .), the city of Troy rose about 4.7 feet (1.4 meters) each century (100 years) because of these accumulations. Landfilling has also been used to extend shorelines. In New York City during the eighteenth century, shorefront roads were extended into the water by landfill that included broken dishes, old shoes, and even the rotted hulls of boats. Sanitary landfills In the 1930s, solid waste materials covered with soil became known as ‘‘sanitary landfill.’’ As with composting, a decomposition process takes place in landfills. The process has an aerobic and an anaerobic phase. Aerobic means requiring oxygen. Anaerobic means functioning without oxygen. In the aerobic phase, biodegradable solid wastes react with the landfill’s oxygen to form carbon dioxide and water. The landfill temperature rises and a weak acid forms within the water, dissolving some of the minerals. Microorganisms that do not need oxygen break down wastes into hydrogen, ammonia, carbon dioxide, and inorganic acids during the anaerobic stage. Gas in the form of carbon monoxide and methane is produced in the third stage of decomposition.
Macroorganisms, such as earthworms, chew organic matter into smaller pieces. PHO TO R ES EAR CH ER S IN C.
In a landfill, many of the materials, such as plastic, glass, and aluminum cans, containers, and bottles, can take up to forty years or more to decompose. As a result, these materials are quickly filling the space available in landfills. That is why recycling is encouraged in most communities. In recycling, waste materials are used to produce new materials. Americans dump slightly over half of our garbage into landfills, according to the U.S. Energy Information Administration. The remaining garbage is either recycled or burned. Landfills are not bottomless pits. Thousands of landfills have become full and closed. For example, one of the largest landfills in the world was the Fresh Kills landfill in New York State. Covering 2,200 acres, the Fresh Kills landfill officially closed in 2001. Understanding how composting and landfills work helps everyone become more aware of what happens to the garbage that is thrown away. Experiment Central, 2nd edition
Dumping garbage in a landfill. COR BI S.
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WORDS TO KNOW Aerobic: A process that requires oxygen. Anaerobic: A process that does not require oxygen. Biodegradable: Materials that can undergo decomposition by biological variables. Biological variables: Living factors such as bacteria, fungi, and animals that can affect the processes that occur in nature and in an experiment.
Landfill: A method of disposing of waste materials by placing them in a depression in the ground or piling them in a mound. In a sanitary landfill, the daily deposits of waste materials are covered with a layer of soil. Macroorganisms: Visible organisms that aid in breaking down organic matter. Manure: The waste matter of animals.
Composting: The process in which organic compounds break down and become dark, fertile soil called humus.
Microorganisms: Living organisms so small that they can be seen only with the aid of a microscope.
Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Organic: Any material containing carbon atoms.
Decomposition: The breakdown of complex molecules of dead organisms into simple nutrients that can be reutilized by living organisms. Environmental variables: Nonliving factors such as air temperature, water, pollution, and pH that can affect processes that occur in nature and in an experiment. Humus: Fragrant, spongy, nutrient-rich decayed plant or animal matter. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
pH scale: Abbreviation for potential hydrogen. The scale ranges from 0 to 14. Neutral pH is 7, such as distilled water. Acids have pH values lower than 7, such as vinegar, which has a pH of 3.3. Alkalines or bases have pH values higher than 7, such as baking soda, which has a pH of 8.2. Recycling: The use of waste materials, also known as secondary materials or recyclables, to produce new products. Variable: Something that can affect the results of an experiment. Waste stream: The waste materials generated by the population of an area, or by a specific industrial process, and removed for disposal.
EXPERIMENT 1 Living Landfill: What effect do the microorganisms in soil have on the decomposition process? Purpose/Hypothesis The purpose of this experiment is to determine what
happens to common household items that are discarded and placed in a landfill. In nature, physical, chemical, and biological factors act upon our 232
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waste and work together in the process of decomposition. This experiment will determine what action organisms in the soil have on garbage. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of composting and decomposition. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Household garbage covered with soil will decay faster than garbage not covered with soil.’’ In this case, the variable you will change is the presence or absence of soil, and the variable you will measure is the differences in condition between the garbage in the two bags after two to three months. If the garbage in the bag with soil has decayed more than the garbage in the bag without soil, you will know your hypothesis is correct. Level of Difficulty Easy/Moderate, because of
the time involved. Materials Needed
What Are the Variables? Variables are anything that might affect the results of an experiment. This experiment involves both environmental variables and biological variables. Here are the main variables in this experiment: • the presence of air—needed for living things, bacteria, fungi, etc. • the presence and amount of water—also needed for living things, bacteria, fungi, etc. • the temperature—warm temperatures promote biological decomposition; cold temperatures (especially freezing temperatures) can cause physical breakdown when water freezes and expands. • the pH—extreme pH levels can stop biological activity and cause chemical breakdown. For example, strong acids and bases are corrosive and can chemically break down debris. • the amount and types of bacteria present—these microscopic organisms in the soil consume organic matter • the amount and types of fungi—these microscopic and macroscopic organisms also consume organic matter In other words, the variables in this experiment are everything that might affect the amount of decomposition of the garbage. If you change more than one variable, you will not be able to tell which variable had the most effect on the decomposition.
• two 1-gallon plastic bags with holes. Each bag should have approximately 20 randomly placed holes. The holes should be about 0.5 inch (1.25 centimeters) in diameter. A hole puncher or pencil can accomplish this task. • 2 twist ties to seal bags • 5 pairs of household garbage items (for example, 2 food containers, 2 glass bottles, 2 pieces of leftover food or bones, 2 small sticks or leaves, and 2 metal cans) Experiment Central, 2nd edition
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How to Experiment Safely Always wear gloves when handling garbage. Use caution when handling sharp objects, glass, or metal.
• permanent marker • 3 to 5 cups of soil • plastic gloves Approximate Budget $5 for the materials that
cannot be found in your household or at school. Timetable Three to four months for decomposi-
tion to take place. Step-by-Step Instructions
Step 4: Completed control and test bags. GA LE GRO UP.
1. Prepare a sketch and written description of the materials being placed into each bag. 2. Prepare the control experiment. The control for this experiment will remove as many variables as possible from the test in order to see the results from a single variable. In one bag place one of each item and sprinkle a little water over them. Do not add soil to the control bag. Seal the bag with a twist tie. 3. Prepare the test bag. In the other bag, place one of each item. Add to the bag 3 to 5 cups of soil to cover the garbage. Sprinkle the mixture with water and seal the bag with a twist tie.
Materials needed for Experiment 1. GAL E GR OU P.
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4. Label each bag (‘‘control’’ or ‘‘test’’) and place both of them outside in a shady spot. 5. Open the bags every two to three weeks, sprinkle more water over the contents, and reseal the bags. 6. After three months, open the bags and pour out the contents of each onto separate pieces of newspaper. Remember to wear gloves. Record what changes have occurred to each item. Compare the differences in breakdown between the control and test bags. Summary of Results When analyzing the contents
Troubleshooter’s Guide Because this experiment requires living organisms to act upon waste, it is essential that the conditions in the landfill be correct. Factors such as extreme weather conditions or excessive temperatures could cause undesirable results in your experiment. If you should have problems, try the following tips: Always keep soil moist, not wet. Make sure the soil does not get too hot or cold. Temperatures between 40˚F and 100˚F (4˚C and 38˚C) are ideal. If you use black garbage bags, keep them out of the sun, because the dark color absorbs light and can overheat the soil easily.
of each bag, sketch the objects and write a brief description of their conditions. Look for any activity of organisms like worms or insects. If anything is smelly, slimy, or has a black stain due to bacterial action, record it in the result chart (see sample chart). Note the difference in decay between the organic waste (food) and the inorganic waste (containers).
Sample landfills results chart for Experiment 1. G ALE GR OU P.
Change the Variables You can vary this experi-
ment by changing the variables. For example, you can place one bag in a chilly basement or the freezer and the other bag in a warm spot outside to determine the effect of temperature. You could also add water to one bag, but not to the other, to determine the effect of water. To determine the effect of pH on decomposition, you could add an acidic material like vinegar to one bag, and add water to the other bag.
EXPERIMENT 2 Composting: Using organic material to grow plants Purpose/Hypothesis This experiment will exam-
ine the principle of composting, the process of converting complex organic matter into the basic nutrients needed by living organisms. This Experiment Central, 2nd edition
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experiment will utilize organic waste (household and yard waste) as nutrients for plants. It will allow you to investigate which waste products can be composted and best utilized by plants. Before you begin, make an educated guess about the outcome of the experiment based on your knowledge of composting and decomposition. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
Step 2: How to fill pot #1. GA LE G RO UP.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Yard waste will break down faster than household waste and will provide more nutrients for plants.’’ In this case, the variable you will change is the type of waste used to make compost, either yard waste or household waste, and the variable you will measure is the amount of decomposition of the waste and the growth of the plants. You expect the yard waste to break down faster and produce taller plants. As a control experiment, you will grow one plant without any waste to judge the growth without compost. If the plant with yard waste compost grows taller than either of the other two plants, and the yard waste has decomposed more than the household waste, your hypothesis will be supported. Level of Difficulty Moderate, because of the time
involved. Materials Needed
• three 2-gallon (7.5-liter) potting containers (terra cotta, ceramic, or plastic) with one or more holes in the bottom for drainage • 3 pounds (1.3 kilograms) topsoil • 3 to 5 pounds (1.3 to 2.3 kilograms) sand • 3 to 5 pounds. (1.3 to 2.3 kilograms) organic waste (use two types: household—table scraps, rotten vegetables, coffee grounds, 236
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etc.—and yard waste—leaves, twigs, grass clippings, weeds, etc.) • 3 small identical living plants (annual flowers or vegetable plants), such as sunflowers, beans, or tomatoes • 3 stakes for markers (Popsicle sticks will work) • plastic or rubber gloves Approximate Budget $5 (use topsoil from your
yard if available). Timetable Two to four months. Step-by-Step Instructions
1. Mix the topsoil and sand together to create the soil base. 2. Prepare the control experiment. Fill pot #1 with the soil base, leaving 2 inches (5 centimeters) at the top of the pot. Place one plant into the soil, covering all the roots. Water generously. 3. Prepare pot #2. Add to the soil base the household waste you collected (scraps, rotten vegetables, etc.). Mix the soil thoroughly. Place a plant into the soil, covering all the roots. Water generously. 4. Prepare pot #3. Follow the directions for pot #2 but substitute the yard waste (grass clippings, leaves, etc.) instead of household waste. 5. Put markers in the pots identifying them as ‘‘control,’’ ‘‘household,’’ or ‘‘yard.’’ Place the pots in a sunny location and monitor the growth of the plants. If possible, take photographs of them at the beginning of the experiment. Water the plants when the soil feels dry. Do not allow them to dry out completely. Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the presence of air—needed for living things, bacteria, fungi, etc. • the presence and amount of water—also needed for living things, bacteria, fungi, etc. • the temperature—warm temperatures promote biological decomposition; cold temperatures (especially freezing temperatures) can cause physical breakdown when water freezes and expands. • the pH—extreme pH levels can stop biological activity and cause chemical breakdown. For example, strong acids and bases are corrosive and can chemically break down debris. • the amount and types of bacteria present—these microscopic organisms in the soil consume organic matter • the amount and types of fungi—these microscopic and macroscopic organisms also consume organic matter • the type of plant—roots of plants aid in the physical breakdown of material by helping to separate materials as the roots grow through the waste In other words, the variables in this experiment are everything that might affect the degree of decomposition and the growth rate of the plants. If you change more than one variable, you will not be able to tell which variable had the most effect on the decomposition and plant growth.
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How to Experiment Safely
6. Graph the weekly growth of the plants, recording the plant height, number of leaves, and root development, if visible.
Wear gloves when handling waste and mixing soil.
7. After two to four months record the final heights and differences in the plant growth between each pot. Empty the pots and evaluate the amount of composting that occurred in the soil. Look for recognizable waste materials, record results.
Summary of Results During the experiment you will be recording the plant growth in the three pots. Ideally, the pot that is composting fastest will provide the most nutrients for its plant. It is essential to measure the height of each plant. You may also want to record which plant flowered first, how often it bloomed, and whether it produced fruit. Change the Variables Try varying the experiment by changing the
Step 3: How to fill pot #2. G AL E
variables. You can make two identical pots with the same soil, garbage, and plants. Give one pot half as much water as the other and compare the differences in growth. You can also experiment with the pH of the waste materials. Most leaves are acidic when composted and have a low pH. Try adding 1 cup (about 0.25 liter) of garden lime (calcium carbonate) to the soil to neutralize the acidic leaves.
GRO UP.
Modify the Experiment You can simplify this
experiment by focusing only on the soil composting and controlling which living organisms are in the soil. Worms break down organic matter. Before you add the topsoil into the pots, make sure it contains worms. If needed, add the worms carefully and divide them evenly among the three pots. Worms need moisture, air, food (organic matter), and warmth (room temperature). First, note the condition of the waste matter before you place it in each pot. Add the topsoil (with worms). After three weeks, pour out the contents of each pot and measure the decomposition of the waste. 238
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You can also use worms to make this experiment more challenging. Add two more pots to the experiment, so that you have five pots in total. In pots #4 and #5, duplicate the waste and process as in pots #2 and #3, except with the addition of worms. Add the same number of worms to pot #4 and pot #4. Make sure to keep all the plants moist. After several months, note the results. After the experiment is complete, carefully release the worms into a yard or other safe environment.
Troubleshooter’s Guide Because of infinite variables, such as the different kinds of organic waste that you can use in this experiment, the result can vary greatly. For instance, if you use oak leaves, which are resistant to decay and highly acidic, your experiment’s results may be different than expected. If one plant dies, the experiment should be restarted from the beginning. If you notice the leaves are being eaten, try to remove the pests, but first ask for help from an adult.
Design Your Own Experiment How to Select a Topic Relating to this Concept To create your own
experiment, consider your available resources. Decide what interests you. You may want to create a compost pile of household waste and create soil for a herb garden, or find ways to reduce your consumption of nonbiodegradable waste such as plastics. Although the choice is yours, you need a clear goal that will keep you motivated and interested.
Step 7: Sample plant height data sheet. GA LE GRO UP. Experiment Central, 2nd edition
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Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on composting questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results It is important that your
experiment’s results are saved for other scientists to examine and compare. You should keep a journal and record notes and measurements in it. Your experiment can then be utilized by others to answer their questions about your topic. Related Projects When thinking about doing a project related to waste
management, you need to limit your focus to one aspect of the field. For example, if you decide that recycling is your interest, choose what type of material you wish to work with. Since organic waste is smelly and metal and glass are dangerous, a good choice may be plastics. You can now begin to research ideas on how to recycle plastics. Recycling, composting, waste reduction, incineration, and conservation are all topics that can be explored and narrowed down to a concept that can lead to an interesting project.
For More Information Appelhof, Mary. Worms Eat My Garbage: How to Set Up & Maintain a Worm Composting System. Kalamazoo, MI: Flower Press, 1997. Franke, Irene, and David Brownstone.The Green Encyclopedia. New York: Prentice Hall, 1992. Good general reference book on environmental practices, including composting. 240
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Leuzzi, Linda. To the Young Environmentalist. Stamford, CT: Franklin Watts, 1997. Interviews with respected environmentalists, including a biologist of a waste management facility. Saunders, Tedd. The Bottom Line of Green is Black: Strategies for Creating Profitable and Environmentally Sound Businesses. New York: Harper and Row, 1992. Profiles of companies, such as Reader’s Digest, that address landfill waste in their business practices. U.S. Environmental Protection Agency. ‘‘Composting.’’ http://www.epa.gov/ compost/ (accessed on January 17, 2008). Explains basic composting information, regional programs, and the environmental benefits.
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Crystals
C
rystals affect your life in countless ways, from what you eat to how your computer works. Any solid matter whose particles are arranged in a regular and repeated pattern is called a crystal. The type of particle and its geometric pattern determine the properties of the crystal. Salt, sugar, and rubies are all crystals, along with many metallic elements, such as iron. Both natural rock and artificial materials are often crystalline. Our bones even contain tiny crystals of a mineral called apatite. All crystals have flat, smooth surfaces, called faces. Some crystals, such as diamonds, are formed over millions of years, while others, such as snowflakes, are formed in a matter of hours. Crystals of the same substance have the same geometric pattern between its particles. This pattern is called a crystal lattice. In crystals the smallest possible repeating structural unit is called a unit cell. The unit cell is repeated in exactly the same neat arrangement over and over throughout the entire material.
Symbols and surgery Crystals have been a part of cultures throughout history, from ancient Egyptians to modern days. Topaz, emeralds, rubies, sapphires, and diamonds are examples of crystals long prized as gems. Their brilliance, durability, and rarity have caused people to attach superstitions and symbolism to them. Emeralds were once thought to blind snakes; amethysts to cure drunkenness; diamonds to make a soldier undefeatable; and rubies were a symbol of power. In the 1900s, researchers began to use crystals to improve many areas of people’s lives, from technology to medicine. The properties of crystals, such as hardness, conductivity, insulation, and durability, make them valuable. In modern day crystals are used in electric fuses, control circuits, industrial tools, and communication equipment. Diamonds are used in drill bits, surgery scalpels, and saw blades. The television, radio, and camera all work because of crystals. Some laser beams used in surgery and welding 243
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are made using crystals. Crystals are also found in watches, flat panels for computer displays, and solar-powered calculators.
Molecule Atoms
Unit Cell
Shapes and structures Crystals are made of either atoms or molecules. An atom is the smallest piece of an element that keeps the element’s chemical properties. A molecule is composed of two or more atoms. It is the smallest particle of a substance that still has the properties of that substance. Inside the core of an atom are positive and negative charges.
The majority of crystals are made of ions, a charged atom or molecule. Inside the core of an atom are both positive and negative electrical charges. Atoms can either lose or gain negative charges. The charge of an atom is neutral when it has equal positive and negative charges. When an atom loses an electron it is called a positive ion and when it gains a negative charge it is called a negative ion. Most minerals and rocks are formed from ions.
Group of Unit Cells
Crystal
From an atom to a crystal: The smallest repeating unit in a crystal is the unit cell. G AL E GRO UP.
From televisions to wristwatches, crystals are a part of everyday life. C OPY RI GH T # K ELL Y A . QU IN.
The inner arrangement of the atoms or molecules, the unit cell, determines the outward shape of the crystal. Because of a crystal’s geometric nature, many have strange and interesting shapes. There are seven basic crystal systems, categorized by their geometric shapes. It is the internal structure of the crystal that determines its properties. Each atom has specific properties, yet crystals made of the same atoms can have unique properties. In graphite, the material in a pencil, carbon atoms are spaced far apart in layers. The layers are held together by weak bonds and can shift over one another. This makes graphite one of the softest minerals. On the other hand, the carbon atoms in diamond are bonded tightly to one another in closer layers. This makes a diamond a rigid and hard substance. How a crystal reacts to electrical forces and light, its shape, hardness, color, and the rate at which it conducts heat all depend on a crystal’s internal structure. Some crystals will split light,
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for example, causing a double image. Other crystals will bend a beam of light. Crystal formation The size and shape of a crystal depends on how it is formed. Impurities, temperature, pressure, and the amount of space will affect what a crystal looks like. In snowflakes, for example, colder temperatures produce crystal snowflakes with sharper tips on the sides. Snowflakes that grow under warmer conditions grow more slowly, resulting in smoother shapes.
Atom
Crystals only grow large and perfect under specific conditions. Most crystals grow irregularly and sometimes it is difficult to distinguish their faces. It is rare to find a flawless crystal, which is why such perfect crystals are worth great amounts of money. While one crystal is growing it may enclose crystals of other minerals. These enclosures will appear as a visible mark in the crystal. A crystal pushed upon by some outside force can develop a twisted or bent shape.
Positive Ion
The majority of crystals are made of ions, a charged atom or molecule. GA LE G RO UP.
While natural crystals can often contain flaws, artificial or synthetic crystals can be made flawless. One reason why crystals are widely used in industry and technology is that scientists learned how to synthesize artificial crystals in the laboratory, making them flawless and relatively inexpensive.
cubic
tetragonal
hexagonal
triclinic
monoclinic
orthombic
trigonal
There are seven basic crystal systems, categorized by their geometric shapes. G ALE GR OU P.
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Crystals start growing by a process called nucleation. Nucleation can start through the molecules themselves or through the help of solid matter already present. The nucleation process begins when the molecules in a solution, the solute molecules, have an attractive force to one another that pulls the molecules together. The more solute molecules in a solution, the greater the chance the molecules will come into contact with each other and form bonds.
Though diamonds and graphite are comprised of carbon atoms, diamonds are rigid and hard, while the graphite used in lead pencils is soft. C OPY RI GH T # K ELL Y A . QU IN.
When a solution contains as much dissolved solute molecules as it can hold at that temperature, it is saturated. The temperature of a solution will affect its saturation. A solution at higher temperatures will be able to dissolve more molecules than a solution at lower temperatures. If a solution is saturated at a high temperature and then cooled, it has a concentration above the saturation point. This solution is called a supersaturated solution. The molecules in a supersaturated solution are so crammed together they readily move together and can form a crystal. The more molecules that are joined together, the stronger their attractive force. They continue to pull other molecules towards them. A small crystal that provides the attractive force to begin forming larger crystals is called a seed crystal.
A solution at higher temperatures can dissolve more molecules than a solution at lower temperatures. G AL E GRO UP.
EXPERIMENT 1 Crystal Structure: Will varying shape crystals form from varying substances?
room temperature
heated
room temperature
Saturated
Saturated
Supersaturated
solute molecules
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Purpose/Hypothesis Crystals come in many shapes and sizes. The substance used to make a crystal and how this substance bonds together dictates the crystal’s unit cell and, thus, its shape.
In this experiment you will compare the unique crystal formations that grow from four different substances. The four crystal substances you will use are alum, Epsom salt, sugar, and salt. You will create supersaturated solutions out of the four substances and examine the crystals that form. Experiment Central, 2nd edition
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WORDS TO KNOW Atom: A unit of matter, the smallest unit of an element, having all the characteristics of that element.
Molecule: The smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms.
Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Nucleation: The process by which crystals start growing.
Crystal: Naturally occurring solid composed of atoms or molecules arranged in an orderly pattern that repeats at regular intervals. Crystal faces: The flat, smooth surfaces of a crystal. Crystal lattice: The regular and repeating pattern of the atoms in a crystal. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Ion: An atom or groups of atoms that carry an electrical charge—either positive or negative— as a result of losing or gaining one or more electrons.
Saturated: In referring to solutions, a solution that contains the maximum amount of solute for a given amount of solvent at a given temperature. Seed crystal: Small form of a crystalline structure that has all the facets of a complete new crystal contained in it. Solute molecules: The substance that is dissolved to make a solution and exists in the least amount in a solution; for example, sugar in sugar water. Supersaturated: Solution that is more highly concentrated than is normally possible under given conditions of temperature and pressure. Synthetic crystals: Artificial or manmade crystals. Unit cell: The basic unit of the crystalline structure. Variable: Something that can affect the results of an experiment.
To begin this experiment, make an educated guess about the outcome of the experiment based on your knowledge of crystals. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the substances that make up the crystal • the temperature of the beginning solution • the temperature of the water
is one possible hypothesis for this experiment: ‘‘Crystals formed from different substances will develop unique shapes.’’ In this experiment the variable you will change will be the substance that will make up the crystal, and the variable you will measure will be the appearance of the crystal. Level of Difficulty Moderate. Materials Needed
• the environment the crystal is grown in In other words, the variables in this experiment are everything that might affect the growth of the crystals. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the crystal’s structure.
• • • • • • • •
• alum (small jar, found in the spice section of the grocery store) • Epsom salt • sugar • salt • water • black saucers (or any color saucers, black construction paper, and scissors) • hot plate or stove
saucepan 4 stirring spoons measuring cup measuring spoons glass cup or jars magnifying glass (optional) masking tape marking pen
Approximate Budget $5 (most materials are common household items). Timetable 45 minutes initial time; 30 minutes over the next week. Step-by-Step Instructions
1. If you do not have black saucers, cut the black construction paper to fit tightly in the bottom of each saucer and place inside. 2. Make a supersaturated solution with the Epsom salt by bringing half a cup of water to the almost-boiling point, then transferring the hot water to a glass. Add 5 tablespoons Epsom salt and stir. Keep adding 248
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3. 4.
5.
6.
Epsom salt until no more salt can be absorbed by the water. You will know this when the salt How to Experiment Safely begins to fall to the bottom no matter how hard you stir. This experiment requires using very hot water to make a supersaturated solution. Ask an Pour the solution into a saucer and label the adult to help you when using the stove or hot saucer accordingly on masking tape. plate. Do not put anything in your mouth, Repeat this process with each of the other such as a sugar crystal, before checking with substances. Make sure to rinse the pot and an adult. use a clean spoon. For the alum, begin with 3 tablespoons; for the salt begin with 1 tablespoon, and for the sugar begin with 4 tablespoons. The sugar solution should be thick. Set the saucers in a quiet place and observe them over the next week until all the liquid evaporates. When all the liquid is gone you should see crystals coating the sides and bottoms of the saucers. Examine the crystals with the magnifying glass.
Summary of Results Draw the results of each of the crystals and write a
written description. Was your hypothesis correct? How does the Epsom salt differ from the salt? How does the salt differ from the sugar? Compare the crystal formations with the physical shape of the substance they were made from. Can you identify to which of the seven basic crystal structures the four crystals belong? Change the Variables You can produce a variety of crystal colors and shapes by altering the substance used to form the crystal. Some substances you may have to order from a lab supply house or ask your science teacher where to get them: Potassium ferricyanide (red crystals); borax; copper acetate monohydrate (blue-green crystals); and calcium copper acetate hexahydrate (blue crystals). You can also vary the temperature of the water when making the saturated solutions and compare crystal growth. Modify the Experiment You can modify this
experiment to see a crystal form under a microscope. You will first need to prepare a supersaturated solution from a crystal, such as salt. Stir several teaspoons of salt into about a half a cup of warm water until the crystals no Experiment Central, 2nd edition
Step 5: Set the four bowls aside in a quiet place until the liquid evaporates. GA LE G RO UP.
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: No crystals grew in one or more of the solutions. Possible cause: The solution may not have been saturated when the water was hot. You may not have stirred enough to dissolve the solids. Pour the solution back in the saucepan. Reheat the solution, adding more of the substance and stirring well after each addition until you see bits of the substance fall to the bottom. Possible cause: The water may not have been hot enough. It should not be at the boiling point but it does need to be very hot. Pour the solution back in the saucepan. Reheat the solution, adding more of the substance and stirring well after each addition until it is saturated.
longer dissolve. Allow the mixture to sit for several hours. Place a drop of the solution onto a microscope slide. Set the slide under a heat lamp or in the hot sun for a few minutes so that much of the water quickly evaporates. Now place the slide under the microscope and focus. Keep observing the crystal shapes under the microscope. Can you see crystals growing? Try to observe different types of crystals and compare the shapes.
EXPERIMENT 2 Cool Crystals: How does the effect of cooling impact crystal growth? Purpose/Hypothesis Temperature is one of the
key environmental factors that affect crystal growth. This experiment examines the outcome of the same crystal-growing solution cooling at three different temperatures. You will place one jar in a cold environment while the crystals grow, the other jar will cool under room temperature conditions, and you will enclose the third jar and store it in a warm area so that it cools the slowest of the three. If the cooling is faster, the particles do not have time to form a large-scale orderly arrangement and a mass of little crystals will form instead. The size of each crystal will demonstrate how temperature impacts the growth of a crystal. To begin this experiment, make an educated guess about the outcome of the experiment based on your knowledge of crystals, temperature, and solutions. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible 250
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hypothesis for this experiment: ‘‘The slower a supersaturated solution cools, the larger the size of the crystal.’’ In this experiment the variable you will change will be the cooling rate of the solution, and the variable you will measure will be the size of the crystal. If the solution that cools the quickest forms the largest crystal, you will know the above hypothesis is incorrect and you will have to reevaluate your hypothesis. Having a control or standard crystal will help you measure the changes in the dependent variable. Only one variable will change between the control and the experimental crystals, and that is the size of the crystal. For the standard crystal, you will soak a seed crystal in plain water, which will not react with the seed crystal. At the end of the experiment you will compare the size and shape of the seed crystal with each of the other crystals.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the solution’s rate of cooling • the crystal-growing substance • the surrounding air temperature • the container the crystals are grown in • the string the crystals are grown on In other words, the variables in this experiment are everything that might affect the growth of the crystals. If you change more than one variable, you will not be able to tell which variable impacted crystal growth.
Level of Difficulty Moderate. Materials Needed
• • • • • • • • • • • • •
Epsom salt dental floss glass saucepan hot plate or stove saucer measuring cup measuring spoons 4 small glass jars small piece of cloth to cover glass container warm towel cold-water bath (pan with ice in cold water) stirring spoon 4 pencils (long enough to lay across the tops of the four small glass containers) • marking pen Experiment Central, 2nd edition
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Approximate Budget $2 (most materials are common household items).
How to Experiment Safely You are using very hot water in this experiment. Ask an adult to help you when using the stove or hot plate.
Timetable 20 minutes initial time; 30 minutes
after several days; 20 minutes over the next two weeks. Step-by-Step Instructions
1. To grow a seed crystal, heat a half a cup of water until it is almost at the boiling point and carefully pour it into a glass. Add 5 tablespoons of Epsom salt and stir mixture until all the salt dissolves. Continue adding Epsom salt, stirring after each addition, until the solution is completely saturated. You will know you are at the saturation point when a small amount of Epsom salt sinks to the bottom no matter how hard you stir. 2. Pour the solution into a saucer and wait at least 24 hours until small crystals have grown in the saucer. This could take two or three days. Pour out any remaining liquid and choose the four largest crystals that are roughly the same size. These are your seed crystals. 3. Cut four pieces of dental floss about 6 inches (10 centimeters) long. Take each piece and tie one end around a pencil. Cut the piece of dental floss so the other end hangs slightly above the bottom of each jar. 4. Carefully tie a seed crystal to the loose end of each piece of dental floss. 5. Heat 2 cups of water in the saucepan until it is almost boiling. Remove from heat and add 3/4 cup of Epsom salt and stir. Continue
Step 6: Hang a seed crystal in each solution by laying the pencil across the jars. GA LE
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to stir while you add as much Epsom salt as you can—until no more will dissolve. When the solution is saturated, set the saucepan aside to cool for two minutes. Pour equal amounts of the solution into three glass jars. 6. In the fourth glass jar pour a roughly equal amount of plain warm water. Hang a seed crystal in each solution by laying the pencil across the jars. 7. Let Jar 1 completely cool and then place it in a cold-water bath. Leave Jar 2 at room temperature. Warm a towel in a clothes dryer, wrap it around Jar 3, and drape the piece of cloth over the top of the jar before placing the jar in a warm area, like a cupboard near the stove. Leave Jar 4 at room temperature. 8. Every day place fresh ice in the cold-water bath for Jar 1, and reheat the towel for Jar 3. After about a week, compare the crystals.
Troubleshooter’s Guide Below are some problems that may arise, some possible causes, and some ways to remedy the problems. Problem: No crystals grew in one or more of the solutions. Possible cause: The solution may not have been saturated when the water was hot. You may not have stirred enough to dissolve the Epsom salt. Take out the seed crystal and pour the solution back into the saucepan. Reheat the solution, adding more of the Epsom salt and stirring well after each addition until you see bits of the Epsom salt fall to the bottom. Possible cause: The water may not have been hot enough to become completely saturated. It should not be at the boiling point, but it does need to be hot. Take out the seed crystal and pour the solution back into the saucepan. Reheat the solution, adding more of the Epsom salt and stirring well after each addition until it is saturated. Problem: The crystals are cloudy.
Summary of Results Compare the rate of crystal
growth, using the control crystal in Jar 4 as your standard. Examine if there are small crystals on the side or the bottom of the jars. Estimate the size of each crystal on the string compared to the standard, or control crystal, that was sitting in the water. Graph your results, using the percentage of growth on the y-axis and the rate of cooling on the x-axis.
Possible cause: There may be impurities in the water or the jar. Examine the jar and, if it is dirty, try the experiment again with a clean jar. If the glass is clean, try repeating the experiment using distilled or purified water.
Change the Variables You can change the variables in the experiment
several ways. You can alter the crystal-growing substance and repeat the experiment. You can also change the temperature of the water to make the saturated solutions. Does anything happen if the crystals are grown on a piece of yarn as opposed to dental floss? Experiment Central, 2nd edition
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Design Your Own Experiment How to Select a Topic Relating to this Concept Crystals have a range of diverse physical
Sugar and salt are examples of crystals that vary in size and shape. COP YR IG HT # K ELL Y A. QU IN.
and mechanical properties that you can explore in experiments. Explore your surroundings and make a list of all the materials made of crystals. An experiment with crystals could include exploring some of the traits crystallographers use to identify them, such as how a crystal reacts to light or its hardness. Check the Further Readings section and talk with your science teacher or librarian to learn more about crystals. As you consider possible experiments, make sure to discuss them with your science teacher or other adult before conducting them. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. 254
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Related Projects Some experiments with crystals will depend on having crystals with different properties. You can examine the crystalline structures of everyday substances around you. Many rocks are crystals. You could identify the unique properties of crystalline rocks and group them according to their common properties. You could also take on a research project. You could examine what crystals are used in appliances, electronic devices, and tools, as well as what properties these crystals supply. Through interviews with professionals or library research, you could examine the work of cystallographers and determine the instruments and properties they use to identify crystals.
For More Information Libbrecht, Kenneth G. SnowCrystals.com. http://www.its.caltech.edu/atomic/ snowcrystals/class/class.htm (accessed February 20, 2008). A guide to the many different crystal shapes of snowflakes. Math Forum. http://mathforum.org/alejandre/workshops/chart.html (accessed February 20, 2008). Descriptions and links to pictures of the basic crystal systems. Shedenhelm, W. R., and Joel E. Arem. Discover Rocks & Minerals. Lincolnwood, IL: Publications International, 1991. Basic facts on rocks and minerals with plenty of photographs. Stangl, Jean. Crystal and Crystal Gardens You Can Grow. New York: Franklin Watts, 1990. Simple explanation of crystals with directions for growing different crystals. Symes, R. F., and R. R. Harding. Crystal & Gem. New York: Alfred A. Knopf, 1991. Clear book with loads of illustrations on identifying and using various types of crystals.
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Density and Buoyancy
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A ship floats in water because of the effects of density and buoyancy. P HOT O RE SE AR CHE RS I NC .
hat does it mean when it is said that one type of matter is more dense than another? What does density tell us about the nature and behavior of a substance? How does density affect the tendency of an object to float or sink in a liquid? The density of matter is determined by the mass of a given volume of that matter. Any object at a given temperature and pressure will have a fixed volume, determined by the quantity of space it occupies and measured in cubic inches (cubic centimeters or milliliters). It also will have a fixed mass, determined by the quantity of matter contained in the substance. Mass is measured in pounds (kilograms). Density equals mass divided by volume. The mass of different substances can vary greatly. The atoms that make up lead are tightly packed (at room temperature and pressure) and possess a large number of subatomic particles—protons, neutrons, and electrons. In contrast, the atoms that make up hydrogen gas are very loosely packed at the same temperature and pressure and possess a very small number of subatomic particles. More atoms with more subatomic particles in a given volume means higher density. Fewer atoms with fewer subatomic particles in a given volume means lower density. Imagine a lifesize sculpture of a goldfish molded in solid clay. Now imagine an identical statue cast in solid lead. Both sculptures occupy the same volume, but the lead has a greater mass and is therefore denser. A third identical sculpture, this time carved from balsa wood, also occupies the same volume but contains less mass than either the clay or the lead. Balsa wood is less dense than both clay and lead. 257
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Density is measured on a relative scale Notice that in comparing the densities of lead, clay, and balsa wood, we have not used any units of measurement. We simply stated that balsa wood is less dense and lead is more dense compared to clay. This is called relative density. To measure density, scientists often use a relative scale. Water is assigned a value of 1.0, and other materials are assigned numerical values greater or less than 1.0 based on their density relative to water. For example, lead has a relative density of 11.3 and balsa wood has a relative density of 0.2. Relative density compared to water is also called specific gravity. Materials placed together in a container will float or sink according to their relative density. PH OT O RE SEA RC HE RS I NC.
Relative density can be observed The relative density of certain materials is easy to determine by observing the behavior of the materials when gravity acts upon them in a liquid. Substances of greater density will sink in liquids of lesser density due to the greater gravitational pull on the mass they contain. Conversely, substances of lesser density will rise. Thus, the lead goldfish will sink through water, while the balsawood goldfish will float. What about the
Three statues of identical shape and size have different densities depending on their mass. GAL E GR OU P.
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clay goldfish? To predict its behavior, we would need to know its relative density. When two immiscible liquids, such as oil and vinegar, are poured into a container, the less-dense liquid will float on top of the moredense liquid. If a third liquid whose density falls between the first and second is poured into the container, it will form a layer between the other two liquids. A solid dropped into the container will sink through the liquids of lesser density than itself, but it will float on the layer of the liquid whose density is greater than the solid’s density. Look! It floats The relationship between density and buoyancy was studied in the third century B . C . E . by Archimedes, a Greek philosopher and inventor. The Archimedes Principle states that the lifting effect of a liquid on an object is equal to the weight of the liquid displaced by the object. Thus, if the object contains less mass than the mass of the displaced liquid, the object will float. The Archimedes Principle is what makes steel ships float. If the mass of the displaced water—that is, the mass of the volume of water pushed aside by the hollow hull of the ship below the waterline—is greater than the mass of the entire ship, then the ship will float, even though steel has a relative density greater than 1.
Archimedes studied the relationship between density and buoyancy. P HOT O RES EA RC HER S, INC .
The behavior of various materials under the effect of gravity can be observed and used to estimate their relative densities. In the first experiment, you will use such observations to create a relative density scale of your own. The experiment should ultimately help you predict the behavior of various materials, like the clay goldfish, according to their assigned density values. The second experiment will examine the effect of increased pressure on a buoyant object containing a gas to see how changing the volume can change the buoyancy. Experiment Central, 2nd edition
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WORDS TO KNOW Buoyancy: The tendency of a fluid to exert a lifting force on a body immersed in it.
Relative density: The density of one material compared to another.
Density: The mass of a substance divided by its volume.
Specific gravity: The density of a material compared to water.
Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/ or experiment.
Subatomic: Smaller than an atom. It usually refers to particles that make up an atom, such as protons, neutrons, and electrons.
Immiscible: Incapable of being mixed.
Variable: Something that can affect the results of an experiment.
Mass: Measure of the total amount of matter in an object. Also, an object’s quantity of matter as shown by its gravitational pull on another object.
Volume: The amount of space occupied by a three-dimensional object.
Matter: Anything that has mass and takes up space.
Waterline: The highest point to which water rises on the hull of a ship. The portion of the hull below the waterline is under water.
EXPERIMENT 1 Density: Can a scale of relative density predict whether one material floats on another? Purpose/Hypothesis In this experiment, you will first create a relative
density scale for eight materials. Then you will use that information to predict whether one material will float on the other when any two of the materials are placed together in a container. To begin the experiment, use what you know about relative density to make an educated guess about whether one material will float on the other. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
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or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A relative density scale based on the behavior of eight materials in one container will accurately predict that a material with a lower relative density will float on one with a higher relative density when the two are placed in another container.’’ In this case, the variables you will change are the two materials, and the variable you will measure is which material floats on the other. If the material with the lower relative density floats on the one with a higher relative density, you will know your hypothesis is correct. Level of Difficulty Moderate. Materials Needed
What Are the Variables? Variables are anything that could affect the results of an experiment. Here are the main variables in this experiment: • the type and purity of the materials • the method by which the materials are added to the container • the order in which materials are added to the container • the temperature at which the materials are kept • the pressure at which the materials are kept In other words, the variables in this experiment are everything that might affect the ability of one material to float on another. If you change more than one variable, you will not be able to tell which variable had the most effect.
• 3 clear, narrow, glass jars with wide mouths (such as beakers or pickle jars) • 1 probe (a knitting needle or drink stirrer will do) • 9 disposable plastic knives • corn oil • motor oil (10W-30) • maple syrup • water, colored blue with food coloring • lemon juice • one 0.5-inch-diameter (1.2 centimeters) ball of clay • one 0.5-inch-diameter (1.2 centimeters) ball of candle wax • 1 small cork
Approximate Budget Less than $10. (Most, if not all, materials may be found in the average household.) Timetable To be performed properly, allowing time for materials to settle
and for careful observing and note taking, this experiment should take 45 to 60 minutes. Experiment Central, 2nd edition
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Step-by-Step Instructions
How to Experiment Safely
1. Divide your materials into liquids and solids. Examine the liquids first and try to predict Before substituting other substances for those which are the most dense. Pour the five on the materials list, check with your science liquids into one container, beginning with teacher to make sure you are not combining the one you predict to be the most dense. chemicals that will create a hazard, such as toxic Pour each liquid slowly, using a plastic knife fumes. Some combinations of household substances mix together easily or are the same color as a guide, as illustrated. Liquids that norand therefore are not useful for this experiment. mally do not mix may accidentally mix if Throw away the knives and glass jars after finthey are shaken or stirred. Use a new knife ishing the experiment because they may be for each liquid. contaminated with motor oil. 2. After all the liquids have been added to the container, wait for one minute to allow them to settle. Make a note of the order in which the liquids have settled, but do not assign relative density values yet. You have not yet added the solid materials, and the behavior of the solids may surprise you! 3. One by one, gently add the three solids to the container. Allow more time for them to settle. If a solid becomes coated with a liquid, its behavior may change temporarily. For example, a solid Step 1: Pouring liquid using a may float higher than normal if it is coated with vegetable oil. If knife as a guide. GA LE G RO UP. you suspect that a solid is not behaving normally, gently poke it with the probe. 4. After you are confident that all the materials have settled to their natural levels, begin assigning relative density values. Start by identifying the layer of blue water and label that ‘‘1.0’’ on your relative density scale (see illustration). Then identify each material above and below the water, record it on your scale, and assign a relative density value for each. Your numerical values do not need to be exact as long as their relative values show which material is denser. For example, you could assign 0.9 to the material just above the water and 0.8 to the material just above that. Likewise you could assign 1.1 to the material just below the water, and so on. 262
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5. Select two different materials and carefully pour or place them in the second glass jar, using a new plastic knife for each liquid. (Do not pair a solid with another solid.) Record the order in which you add each material. Observe the behavior of the materials in the jar. Did your relative density scale accurately predict what would happen? If so, your hypothesis has proven correct so far. 6. Determine whether the behavior of the materials used in the previous step changes when the order of putting the materials into the jar is changed. For example, if you previously added motor oil to a jar already holding water, now reverse the order, pouring the oil in first. Use the third jar and clean knives for this test. Summary of Results Examine your results and
determine whether your hypothesis is correct. Did the observed behavior of the eight materials combined make it possible to create a useful relative scale? If any of the behaviors disagree with the scale’s prediction, try to find a possible
Troubleshooter’s Guide Here are some problems that may arise during the experiment, some possible causes, and ways to remedy the problems. Problem: Two liquids appear to mix. Possible causes: 1. Agitation when pouring the liquid into the container may cause temporary mixing. Wait for the mixture to settle out. 2. Two of your substances are too similar in appearance, such as vegetable oil and motor oil. Replace one substance with something that is similar but provides more contrast. For example, you could use canola oil in place of vegetable oil. Problem: The behavior of a solid in liquids is erratic: sometimes it floats, sometimes it sinks. Possible cause: Surface tension can sometimes cause an object of greater density to float on top of a liquid of lesser density. To counteract this tension, poke the solid with the probe.
Step 4: Sample relative density scale. G AL E GR OUP .
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the rigidity or flexibility of the walls of the object • the gas present inside the objects • the liquid in which the objects are placed • the pressure applied to the objects In other words, the variables in this experiment are everything that might affect the buoyancy of the objects. If you change more than one variable, you will not be able to tell which variable had the most effect on the buoyancy.
explanation for this difference. Did you misread the layers in the first step of your experiment? Go back and double check. Write a summary of your findings. Change the Variables You can vary this experi-
ment in several ways. Try different liquids and solids. Compare the densities of two solids, such as clay and a piece of pencil eraser. Then create and test a combination of solids by wrapping the eraser inside a layer of clay. Be sure to check with your teacher before trying new materials to make sure they are safe when mixed! You can also see if you get the same results when the liquids in your experiment are chilled. (Do not heat your materials.) Freeze a liquid material and see if its relative density is the same whether in liquid or solid form.
EXPERIMENT 2 Buoyancy: Does water pressure affect buoyancy? Purpose/Hypothesis In this experiment, you will observe the effect of
increased water pressure on two buoyant objects floating in a closed bottle of water. The first is a flexible drinking straw filled with air and open at one end. The second is a flexible drinking straw filled with air and sealed at both ends. Because the first straw is open at one end, an increase in pressure allows water to easily force its way into the straw. This decreases the volume of water the straw displaces and it will eventually sink. Because the second straw is sealed at both ends, the water cannot force its way inside and must actually collapse the straw to decrease the displaced volume. To begin the experiment, use what you know about buoyancy to make an educated guess about how the straws will behave when the pressure is increased. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • • 264
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A hypothesis should be brief, specific, and measurable. It must be something you can test How to Experiment Safely through observation. Your experiment will prove or disprove whether your hypothesis is correct. Make sure the bottle’s cap is secured tightly Here is one possible hypothesis for this experibefore applying pressure. ment: ‘‘A flexible drinking straw, filled with air and sealed at one end, will lose its buoyancy and sink at a lower pressure than one sealed at both ends.’’ In this case, the variable you will change is the amount of pressure applied, and the variable you will measure is whether the straws sink. If the straw sealed at one end sinks at a lower pressure than the one sealed at both ends, you will know your hypothesis is correct. Level of Difficulty Moderate. Materials Needed
• one 1-liter transparent plastic bottle filled with water (the bottle must have flexible sides and a cap that seals) • 2 transparent drinking straws • modeling clay • 1 tall drinking glass • water Approximate Budget Less than $5. (Most, if not all, materials may be found in
the average household.) Timetable Approximately 10 to 20 minutes. Step-by-Step Instructions
1. Cut a 4-inch (10-centimeter) length of straw and seal one end with a lump of clay. This will be the top end of the straw. Attach a ring of clay to the straw near the open bottom end to serve as ballast to keep it upright in the water as illustrated. Fill the drinking glass with water and test the buoyancy of the first straw. Add or remove clay from the ballast until the straw floats upright in a stable manner. Experiment Central, 2nd edition
Steps 1 and 2: Set-up of straw 1 and straw 2. GAL E GR OU P.
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2. Repeat this process with the second straw, but seal this one with clay at both ends. Check the seals by submerging the top of the straw in the drinking cup. Look for bubbles coming from the top seal. Then invert the straw and check the bottom seal. 3. Fill the bottle with water to within 1 to 2 inches (2.5 to 5.0 centimeters) of the neck. Carefully lower the two straws into the bottle with the bottom end of the straws down. Close the bottle and make sure it is sealed tightly. 4. Position the bottle on a table or counter so that one person can squeeze the bottle while another takes measurements with the ruler of the change in the bottle’s width where it is squeezed. This measurement will serve as a rough gauge of the pressure applied to the water and objects inside the bottle. 5. Measure and record the approximate diameter of the bottle. Gently squeeze the bottle until its width has decreased by 0.5 inch (1.25 centimeters). Record any change that occurs in the straws (sinking, taking on water, deforming) in the appropriate column on your data chart. Repeat this process for each 0.5-inch (1.25-centimeter) change in the bottle’s width. As increasing pressure is applied, the straw with the open end should sink.
Step 5: Sample recording chart. GAL E GR OU P.
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6. Continue squeezing until the second straw sinks or until no more pressure can safely be applied to the bottle. 7. When pressure is released, the straw or straws should regain their buoyancy and return to the surface. Repeat the experiment, this time noting any changes you observe in the two straws as pressure is applied to the bottle. Watch for water rising in the unsealed straw. This is similar to a submarine flooding its ballast tanks to decrease its buoyancy and dive under water. Watch for deformation of the second straw, which should flatten as the pressure is increased. 8. Examine your results and determine whether your hypothesis is true. Repeat the experiment to double check your results. Write a summary of your findings. Summary of Results Record your data on a chart.
This chart should be as clear as possible. It will contain the information that will show whether your hypothesis is correct. Change the Variables You can vary this experi-
ment. Here are some possibilities. Try different numbers and lengths of straw. Compare the behavior of short straws and long straws. See if you get the same results with different liquids. Try salt water and carbonated water.
Design Your Own Experiment How to Select a Topic Relating to this Concept Demonstrations of the properties of
density and buoyancy exist in our environment in numerous forms. Everyday sights such as helium balloons floating away or a thin slick of oil on a roadside puddle show the principles we Experiment Central, 2nd edition
Troubleshooter’s Guide Here are some problems that may arise during the experiment, some possible causes, and ways to solve the problem. Problem: Neither straw sinks, even when maximum pressure is applied. Possible causes: 1. The bottle may not be properly sealed. Check the seal. If necessary, place a small amount of clay on the threads of the bottle top to help keep a seal. 2. There is too much air in the bottle. Add water. Problem: The first straw sinks, but the second does not. Possible causes: 1. You are not applying enough pressure. Try having two people press on the bottle (carefully!) from either side. 2. The straws are too rigid. Use straws of less rigid plastic. 3. Your hypothesis is incorrect. Problem: Once the straw or straws have sunk, they do not return to the surface when pressure is released. Possible cause: The straw or straws are leaking. Check the clay seals. Problem: The straw or straws are unstable and tend to flip over. Possible cause: The ballast weight is not heavy enough or is not placed properly. Increase the weight or move the ballast weight farther down the straw.
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have investigated in our experiments. Think of ways to vary the conditions you observe that will answer questions you have about buoyancy. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on density and buoyancy questions that may interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some materials or procedures might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure which question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the experiments
included here and in any experiments you develop, you can look for better ways to display your data in more accurate and interesting ways. For example, in the buoyancy experiment, try to find a better way to measure the pressure inside the bottle. Could a pressure gauge be built into the bottle’s cap without altering the results? Remember that those who view your results may not have seen the experiment performed, so you must present the information you have gathered in as clear a way as possible. Including photographs or illustrations of the steps in the experiment is a good way to show a viewer how you got from your hypothesis to your conclusion. Related Projects Although experiments in density and buoyancy can be
challenging and fun, simple demonstrations of the principles involved can also be highly informative and often can reveal surprising facts. Many aspects 268
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of density and buoyancy, such as the effect of salinity, could yield interesting experimental results.
For More Information Gillett, Kate, ed. The Knowledge Factory. Brookfield, CT: Copper Beech Books, 1996. Provides some fun and enlightening observations on questions relevant to this topic, along with good ideas for projects and demonstrations. Ray, C. Claibourne. The New York Times Book of Science Questions and Answers. New York: Doubleday, 1997. Addresses both everyday observations and advanced scientific concepts on a wide variety of subjects. Wolke, Robert L. What Einstein Didn’t Know: Scientific Answers to Everyday Questions. Secaucus, NJ: Birch Lane Press, 1997. Contains a number of interesting entries on the nature of water.
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W
hat turns a body of water into a ‘‘dead zone’’ where nothing can live? One condition that can wipe out most living things in a stream, river, or lake is a low level of dissolved oxygen. The term dissolved oxygen refers to molecules of oxygen that have been dissolved in water. Some of these molecules enter the water from the surrounding air, especially if the water tumbles over falls and rapids. Other dissolved oxygen in the water is a ‘‘byproduct’’ of photosynthesis. During photosynthesis, green plants, including those that live in the water, use the energy in sunlight to combine carbon dioxide and water to produce carbohydrates and oxygen. The oxygen is expelled by the plant and enters the water. The level of dissolved oxygen in water can reach as high as 8 or 9 parts per million. The United States Environmental Protection Agency (EPA) considers water to be healthy if it contains at least 5 parts per million of dissolved oxygen. When the level falls below 4 parts per million, the water quality is considered to be poor. At 2 parts per million, fish become stressed and grow more slowly, and some die.
What affects the level of dissolved oxygen in water? The level of dissolved oxygen in a body of water can vary from hour to hour. The level falls as fish remove oxygen molecules from the water with their gills. The more fish in the water, the more dissolved oxygen they remove. Fish are cold-blooded, so their body systems work more slowly in cold water and speed up in warm water. The warmer the water, the more oxygen their body systems require. Plants in the water, including the tiny floating phytoplankton, also use small amounts of the dissolved oxygen for respiration (breathing). Photosynthesis requires sunlight, so plants do not produce oxygen at night. During these dark hours, plants actually use more oxygen for respiration than they produce. That’s why the level of dissolved oxygen in a body of water is lowest just before dawn, just before the Sun rises and 271
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photosynthesis begins again. If you visit a pond or river at dawn, you might see birds picking fish out of the water. The fish are easy to catch then because they are at the surface, gulping for oxygen because the water does not provide enough for them. Other factors also influence the level of dissolved oxygen, including the water’s temperature, its salinity (salt level), and its elevation above sea level. As the water temperature decreases, the amount of dissolved oxygen increases, because gases, including oxygen, dissolve more easily in cooler water. As the level of salinity increases, the amount of dissolved oxygen decreases. Finally, bodies of water at higher elevations, such as mountain lakes, contain less dissolved oxygen than bodies of water at lower elevations. This makes sense when you remember that much of the dissolved oxygen comes from the air. The amount of oxygen in the air decreases the higher you climb on a mountain. If the air has less dissolved oxygen, the water will, too. As more water surface is exposed to the air, more oxygen molecules enter the water. FI EL DM ARK PUB LI CAT IO NS.
During hot, dry summer months, the water level in streams tends to be low, and the water often becomes stagnant. The heat and the lack of movement combine to lower dissolved oxygen levels. On the other hand, during the early spring, melting snow and cool rain keep the water temperatures low, increasing the dissolved oxygen levels. The rains lead to rushing, tumbling streams that gain more oxygen from the atmosphere. The rains also contribute the oxygen they absorbed from the atmosphere. Another major effect on the level of dissolved oxygen in a body of water is the amount of pollutants in the water. Many pollutants, including the fertilizers that run off farm fields and home lawns, contain nutrients that help plants grow, including plants in the water. This may seem like a benefit of pollution. However, after the plants use up the nutrients in the water, they die and start to decay. The bacteria involved in the decay process use the dissolved oxygen in the water, reducing the amount of
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oxygen available to the fish. This process is called eutrophication. As eutrophication continues to use up the dissolved oxygen, the water can turn into a dead zone. Scientists have measured the biochemical oxygen demand, the amount of oxygen required by bacteria to decay waste material. BOD5 means the amount of oxygen that microorganisms use to decay organic matter over a five-day period in 68˚F (20˚C) water. The more waste in the water, the more decay that occurs, and the higher the BOD5—the need for dissolved oxygen. For example, wastewater that has been treated has a BOD5 of less than 30 parts per million. However, waste from a meat packing plant has a BOD5 of 5,000 parts per million. If this meat packing waste were released into a body of water, the dissolved oxygen level in that water would drop dramatically within a few days. How does a low level of dissolved oxygen affect the ecosystem in the water? If the level of dissolved oxygen drops for any length of time, fish that need large amounts of oxygen, such as trout and bass, go elsewhere if they can. Carp, catfish, worms, and fly larvae (the immature, wormlike stage in a fly’s life cycle) can handle low oxygen levels, so they thrive. The ecosystem begins to include more organisms that can live with little or no oxygen. If the level of dissolved oxygen continues to drop, even the carp and catfish end up gasping for oxygen. The water is on its way to becoming a dead zone.
At high altitudes, cold temperatures raise the level of dissolved oxygen, but the higher elevation lowers it. The level of dissolved oxygen in any body of water is a complex, changing condition. PHO TO RES EA RC HER S I NC.
In the following two experiments, you will use a kit to measure the level of dissolved oxygen in water under several conditions. In one experiment, you will determine how the level changes as the amount of decaying matter in the water changes. In the second experiment, you will measure how the breathing rate of goldfish changes as the amount of dissolved oxygen in the water changes. Both experiments will help you better understand the concept of—and the importance of—dissolved oxygen. Experiment Central, 2nd edition
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A pond overrun with algae is usually not a healthy place. PHO TO R ES EAR CH ER S IN C.
EXPERIMENT 1 Decay and Dissolved Oxygen: How does the amount of decaying matter affect the level of dissolved oxygen in water? Purpose/Hypothesis In this experiment, you will allow different amounts
of food to decay in water and measure any changes that occur in the level of dissolved oxygen. To begin the experiment, use what you have learned about dissolved oxygen to make a guess about what will happen when the food starts to decay in the water. Will the level of dissolved oxygen in the water decrease or increase? Will the amount of change depend on the amount of decaying food? This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The more decaying matter in the water, the lower the level of dissolved oxygen.’’ 274
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WORDS TO KNOW Biochemical oxygen demand (BOD5): The amount of oxygen microorganisms use over a five-day period in 68˚F (20˚C) water to decay organic matter. By-product: A secondary substance produced as the result of a physical or chemical process, in addition to the main product. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment. Dissolved oxygen: Oxygen molecules that have dissolved in water.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Photosynthesis: Chemical process by which plants containing chlorophyll use sunlight to manufacture their own food by converting carbon dioxide and water into carbohydrates, releasing oxygen as a by-product. Phytoplankton: Microscopic aquatic plants that live suspended in the water. Respiration: The physical process that supplies oxygen to living cells and the chemical reactions that take place inside the cells.
Elevation: Height above sea level. Salinity: The amount of salts dissolved in water. Eutrophication: Natural process by which a lake or other body of water becomes enriched in dissolved nutrients, spurring aquatic plant growth.
Variable: Something that can change the results of an experiment.
In this case, the variable you will change is the presence and amount of decaying food, and the variable you will measure is the level of dissolved oxygen. As a control experiment, you will set up one container of water with no decaying food in it. That way, you can determine whether the level of dissolved oxygen changes even with no decaying food in the water. If the level of dissolved oxygen decreases with an increase in decaying food and does not change in the control container, your hypothesis is correct. Level of Difficulty Easy/moderate. Materials Needed
• 3 clear 0.5-gallon (1.9-liter) containers • about 3 ounces (85 grams) of rotting fruit, such as brown apple slices or an overripe banana • scale capable of weighing 2 ounces (57 grams) Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the beginning levels of dissolved oxygen in each container • the amount of decaying food in each container of water • how much the food is decayed • the temperature of the water in all containers
• dissolved oxygen test kit (kits are available from biological supply houses; one popular brand is LaMotte; see the Further Readings section for sources) • 5 gallons (5.6 liters) water (try to obtain water that has not been treated, such as well, stream, or pond water; many water treatment plants try to reduce the level of dissolved oxygen in their water because high levels speed up corrosion in water pipes) • wax paper • goggles • rubber gloves
• the amount of any mixing, pouring, or splashing of the water in the containers (which would raise the dissolved oxygen level)
and $5 for a small food scale; other materials should be available in the average household.
• the length of time the containers are allowed to sit
Timetable 15 minutes to set up; one week to
In other words, the variables in this experiment are everything that might affect the level of dissolved oxygen. If you change more than one variable at a time, you will not be able to determine which variable affected the results.
Approximate Budget $15–$20 for the test kit
observe. Step-by-Step Instructions
1. Label the containers ‘‘1 oz.,’’ ‘‘2 oz.,’’ and ‘‘Control.’’ 2. Mix your water supply thoroughly; stir the water vigorously for 5 minutes or
Step 4: Dissolved Oxygen Levels recording chart. GAL E GR OU P.
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3. 4.
5. 6.
7. 8.
more if you used tap water, which tends to have a low dissolved oxygen level. How to Experiment Safely Nearly fill the three containers with the water. Wear goggles and gloves to protect your eyes and skin while you test the water because you Follow the directions on the water testing will be using chemicals that can be dangerous. kit to measure the beginning level of disYou are strongly urged to have an adult help solved oxygen in each container. Record you complete the tests. the levels in a chart similar to the one illustrated. (The water in all three containers should have the same dissolved oxygen level at this point.) Put wax paper on the scale and measure 1 ounce (28 grams) of rotting fruit; dump the fruit into the container marked ‘‘1 oz.’’ Measure 2 ounces (57 grams) of the same rotting fruit and dump it into the container marked ‘‘2 oz.’’ Put no fruit in the control container. Place all three containers in an area where the air temperature will remain at 70 to 72˚F (21 to 22˚C). Every day at the same time for the next four days, use the kit to test the dissolved oxygen level in each container. Record your findings on your chart. Also note the condition of the water. Are any of the containers becoming cloudy?
Summary of Results Study the data from your observations and decide
whether your hypothesis was correct. How did the dissolved oxygen levels
Steps 5 and 6: Set-up of control, 1 oz., and 2 oz. containers. GA LE G RO UP.
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The level of dissolved oxygen was really low in all three containers in the beginning. Possible cause: Your water came from a source with little dissolved oxygen. Try the experiment again, but increase the beginning level of dissolved oxygen by running a tube from an aquarium pump into the water. Send bubbles of air through the water for at least 8 to 12 hours. Treat all the water so the beginning levels will be identical in all containers. Problem: The level of dissolved oxygen dropped in all containers, including the control. Possible cause: The water already had some decaying matter in it, especially if it was pond water. Focus on the differences in the levels of dissolved oxygen for all three containers. Problem: The level of dissolved oxygen rose in the control container. Possible cause: The room temperature cooled enough so that oxygen from the air entered the water. Make sure the temperature around all three containers stays at 70 to 72˚F (21 to 22˚C).
change in the three containers? Which container had the highest level at the end of the experiment? The lowest level? Did the level change in the control container? If so, why do you think this happened? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables You can vary this experi-
ment in several ways. For example, you might try a different kind of decaying matter, such as another kind of fruit, raw meat, moldy bread, or rotting leaves. You could also increase or decrease the air temperature around all three containers to see how that affects the rate of decay and the levels of dissolved oxygen. At the end of the experiment, use aquarium pumps and tubing to bubble the same amount of air into all three containers to try to raise the level of dissolved oxygen. To change the salinity of the water, you could add different amounts of salt to two containers instead of decaying food and measure any changes in the levels of dissolved oxygen. Modify the Experiment For a moderate to
advanced version of this experiment you could measure the effect of eutrophication on both dissolved oxygen level and water life. To avoid possible harm to fish, you can use aquatic plants, which you can purchase at an aquarium or grow from seed. (Elodea and Cabomba are two popular types of aquatic plants because they are easy to grow and hearty.)
In each of the containers, you will need to first set up the proper environment for the water plants. Add the same number of plants to each container and give them several days to adjust to the new environment. Follow the experiment, adding the decaying foods to the two containers and stirring the water gently after each addition. Every day at the same 278
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time for the next several weeks note the level of dissolved oxygen and the condition of the plants. Instead of rotting fruit, you could also add a small amount of fertilizer to each container. In this case, you can collect or purchase live plankton. Place the same amount of plankton and the same number of plants. in each of the three containers. Add different amounts of the fertilizer to container 2 and container 3. Again, measure the level of dissolved oxygen over the next several weeks and note the condition of the plants.
EXPERIMENT 2 Goldfish Breath: How does a decrease in the dissolved oxygen level affect the breathing rate of goldfish?
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the health and size of all the goldfish • the temperature and cleanliness of all the water • the level of dissolved oxygen in the different containers of water In other words, the variables in this experiment are everything that might affect the breathing rate of the fish. If you change more than one variable at a time, you will not be able to determine which change had more effect on your results.
Purpose/Hypothesis In this experiment, you will observe the breath-
ing rate of goldfish as they swim in water with different levels of dissolved oxygen. [Note: It is recommended that you perform this experiment only if you already have access to an aquarium with four to six goldfish and only with the permission of a responsible adult. This experiment will not harm the fish as long as you limit the duration of the experiment and return the fish to the main aquarium afterwards.] To begin the experiment, use what you know about dissolved oxygen and its effect on fish to make an educated guess about how the fishes’ breathing rate will change as the level of dissolved oxygen drops. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or Experiment Central, 2nd edition
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disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘As How to Experiment Safely the dissolved oxygen level drops, the breathing rate of the goldfish will increase.’’ Treat the goldfish gently; avoid putting them In this experiment the variable you will into water that is warmer or cooler than they are used to. Limit the duration of the test to no change is the level of dissolved oxygen, and the more than 8 to 10 hours. Wear goggles and variable you will measure is the breathing rate of gloves to protect your eyes and skin while you the goldfish. As a control experiment, you will test the water because you will be using observe the breathing rate of goldfish in an aquarchemicals that can be dangerous. You are ium that has been set up for some time and in strongly urged to have an adult help you which the dissolved oxygen remains relatively complete the tests. constant. If the breathing rate of the control goldfish does not change, but the breathing rate of the other goldfish increases as the dissolved oxygen level drops, your hypothesis is correct. Level of Difficulty Easy/moderate. Materials Needed
• one 10-gallon (38-liter) or larger aquarium that has been set up for a month or longer and uses an air pump to constantly bubble air through the water (the aquarium may also include live plants, which add more dissolved oxygen to the water; other fish living in the aquarium will not affect the experiment, as long as they have been there for several weeks) • one half-gallon (1.9-liter) container • 4 to 6 small goldfish • dissolved oxygen test kit (see the Further Readings section for sources) • stopwatch • fish net • red and blue colored pencils • goggles • rubber gloves Approximate Budget $15 to $20 for the test kit. (Ideally, you will be able to use an aquarium that is already set up at school or at home.) 280
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Timetable 15 minutes to set up the small con-
tainer; 20 minutes to check the dissolved oxygen levels and breathing rates every two hours for six hours. Step-by-Step Instructions
1. If you have to purchase additional goldfish to conduct the experiment, place them in the aquarium and allow 24 hours for them to get used to the water. During this period, if the aquarium has a heater, turn it off and allow the water to reach air temperature. Make sure the air pump continues to work. 2. Using water from the aquarium, fill the half-gallon container. 3. Use the kit to test the dissolved oxygen level in the aquarium and in the half-gallon container. They should be the same at this point. On a graph similar to that illustrated, record the level from the aquarium in red and the level from the small container in blue. 4. Use the net to catch half of the goldfish (two or three); put them in the smaller container. 5. Use the stopwatch to measure how many times each goldfish breathes in 30 seconds. Each outward push of the gills is one breath. Average the breathing rates for the goldfish in the aquarium. Use the red
Step 3: Sample graph of dissolved oxygen levels. GA LE GRO UP.
Step 4: Put 2 to 3 goldfish into smaller container. GAL E GR OU P.
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pencil to record the average on a graph similar to that illustrated. Then average the breathing rates for the goldfish in the small container, and use the blue pencil to record that average on the graph. 6. Wait two hours and retest the dissolved oxygen levels in both containers. Then average the breathing rates of the fish in each container. Record your findings. 7. Repeat Step 6 after four hours and after 6 hours. 8. At the end of the experiment, gently put the goldfish from the small container back into the aquarium. If you disconnected the aquarium heater, plug it back in. Step 5: Sample graph of goldfish breathing rates. G AL E GRO UP.
Summary of Results Study the dissolved oxygen levels on the first graph.
What do you notice? Did the levels change in the aquarium? Did they change in the small container? If so, why? Now compare the breathing rates of the two groups of fish, shown on the second graph. Notice whether the breathing rates changed as the levels of dissolved oxygen changed. How did the goldfish respond to any changes in the levels of dissolved oxygen? Was your hypothesis correct? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables You can vary this experiment in several ways.
Measure and compare any change in the breathing rates of goldfish swimming in water with and without live plants. (Disconnect any air pump so the plants are the only source of added dissolved oxygen.) Or you can bubble air through the water in the small container and measure the breathing rate of the goldfish as the level of dissolved oxygen rises.
Design Your Own Experiment How to Select a Topic Relating to this Concept Measuring the amount of
dissolved oxygen in a body of water is one of the best ways to determine the health of that water system and the environment around it. Consider the water sources near your home or school. Which ones might have high 282
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or low levels of dissolved oxygen? What might cause the high or low levels? What approaches might raise a low level? What other factors affect the health of a water system? (Examples include the pH level and the levels of ammonia, nitrates, and nitrites.) Check the Further Readings section and talk with your science teacher or school or community media specialist to gather information on dissolved oxygen questions that interest you. As you consider possible experiments, be sure to discuss them with a knowledgeable adult before trying them. Some of the materials or procedures may be harmful to yourself or to the environment. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure which question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The dissolved oxygen level in the small container remained the same. Possible cause: The fish were too small to affect the level during this time period. Try the experiment again, using bigger or more fish, putting them in a smaller container of water, or extending the time period for the testing to eight or 10 hours. Problem: The breathing rate of the fish in the aquarium and the container dropped. Possible cause: The water temperature might have fallen enough to slow the body processes of the goldfish. If possible, move the aquarium and small container to a warmer spot. Or leave the aquarium heater plugged in and put a heater in the small container to keep the water at the same temperature as the aquarium—a difficult feat to accomplish.
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Recording Data and Summarizing the Results In your decaying food and
goldfish experiments, your raw data might include charts, graphs, drawings, and photographs of the changes you observed. If you display your experiment, make clear the question you are trying to answer, the variable you changed, the variable you measured, the results, and your conclusions. Explain what materials you used, how long each step took, and other basic information. Experiment Central, 2nd edition
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Related Projects You can undertake a variety of projects related to dissolved oxygen and water quality in general. For example, if you have access to salt water from the ocean, you might compare its level of dissolved oxygen with that of fresh water. Or compare the level at the surface of a pond with the level at the bottom. Or compare the level of dissolved oxygen in a body of water during cool weather with the level during a heat wave. Try to determine the factors that influence these levels and whether the levels indicate pollution that is potentially harmful to the health of the organisms living in the water and the people using and drinking it.
For More Information Carolina Biological Supply Company, 2700 York Road, Burlington, NC 27215, 1 800 334 5551. http://www.carolina.com/. Fitzgerald, Karen. The Story of Oxygen. Danbury, CT: Franklin Watts, 1996. Covers the history of oxygen, its chemistry, how it works in our bodies, and its importance in our lives. Frey Scientific, 100 Paragon Parkway, Mansfield, OH 44903, 1 800 225 FREY. http://www.freyscientific.com. LaMotte water test kits. http://www.lamotte.com/. Ward’s Natural Science Establishment, Inc., 5100 West Henrietta Road, PO Box 92912, Rochester, NY 14692, 1 800 962 2660. http://www.wardsci.com/.
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DNA (Deoxyribonucleic Acid)
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our hair color, a leaf’s shape, a bird’s wing: These diverse features all share one key inherited trait known as deoxyribonucleic acid or DNA. DNA is commonly called the building block of life, for it is the inherited substance that all characteristics build from. Passed down from generation to generation, DNA directs how an organism functions, develops, and appears. Every life form on Earth carries DNA. And unless you are an identical twin, your DNA is completely unique to you. The findings of DNA have led to awesome advances in a wide range of fields, from medicine to crime solving. Researchers have used their knowledge of DNA to examine inherited diseases, produce medicines, study the relationships between species, and develop foods with desired characteristics. As the work to understand DNA continues, researchers hope that gaining knowledge about the molecule will help improve people’s lives all over the world.
The transforming factor DNA is a large molecule inside almost every cell in the body. In humans, DNA is found in the nucleus, the brain-center of the cell. Much like a cell, a nucleus is held together by a membrane or nuclear envelope. The DNA molecule coils in the nucleus so tightly that if all of the DNA in your body were unraveled and laid end to end, it would stretch from Earth to the Moon about 6,000 times! In the late 1800s and early 1900s, scientists were working to discover what substance played a role in heredity. From early experiments and observations researchers knew parents passed their characteristics onto their offspring. Then a 1928 experiment showed that there was some substance that transmitted infectiousness to noninfectious bacteria. This was called the ‘‘transforming factor,’’ because it transformed the bacteria. Scientists narrowed the possibilities of the transforming factor down to two substances: proteins or DNA. At this time, researchers knew that an organism’s cells contained DNA. DNA is a simple molecule with 285
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relatively few chemical parts to it. They also knew each cell contained proteins, large molecules made of chemicals called amino acids. There are twenty amino acids that make up the hundreds of thousands of proteins in the human body. Lots of researchers argued that DNA was too simple a molecule to account for the vast diversity of life—from a weed to a human.
American scientist Oswald Avery. L IBR AR Y O F C ONG RE SS.
In 1943, American scientist Oswald Avery (1877–1955) and his colleagues conducted a groundbreaking experiment. First they took DNA from a disease-causing strain of a bacterium. Then they placed this DNA into a strain of the bacterium that did not cause disease, an inactive bacterium. They found the inactive bacterium turned into a disease-causing bacterium. Avery concluded that it was the DNA from the diseasecausing strain that ‘‘transformed’’ the inactive form of the bacterium. Many in the scientific community were skeptical of this conclusion because they still believed DNA was too simple a substance. Then in 1952 biologists Alfred Hershey and Martha Chase conducted an experiment that conclusively proved DNA was the transforming factor, the molecule responsible for heredity. Solving the structure The 1950s were a big decade for DNA. While many researchers were working to prove exactly what DNA did, other scientists were racing to figure out how DNA was structured. In 1953 molecular biologists James D. Watson (1928–) and Francis Crick (1916–2004) solved the puzzle of DNA’s double-helix molecular structure. Their discovery is recognized as one of the most important scientific findings of the twentieth century. Prior to Watson and Crick’s discovery, researchers knew that DNA was made up of units called nucleotides. There are four types of nucleotides found in DNA, differing only in their nitrogen-containing bases: adenine (A), guanine (G), thymine (T), and cytosine (C). Each nucleotide consists of three components: a sugar deoxyribose, a phosphate group, and a nitrogen-containing base.
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Watson and Crick used a type of X-ray image produced by British scientist Rosalind Franklin (1920–58) to develop their model of DNA’s structure. They determined that DNA consists of long chains of repeating nucleotides, joined together and twisted around each other into a spiral shape known as a double helix. It has the appearance of a twisted ladder. The backbone of the ladder is made up of the nucleotides’ sugar and phosphate molecules. The rungs of the two strands are formed by attached bases that are always complementary, A pairs with T (A-T) and G pairs C (G-C). These base pairs are held together with hydrogen bonds.
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Since each nucleotide always pairs with the A same complementary nucleotide, this explains G how DNA replicates itself. During DNA replication, the DNA helix unzips. The exposed bases match up with complementary bases of nucleotides. The nucleotides bind together to form two new strands that are identical to the strand that separated. Sequencing the alphabet Everyone has the same four nucleotides, but it is the order of the nucleotides, the sequence, that determines DNA’s instructions. Reading the sequence of the four bases, A, G, C, and T, is similar to reading the order of letters in words. Different combinations create different meanings. In some cases, just one letter out of place in a sequence can cause a person to have a completely distinct characteristic. In the disease sickle cell anemia, for example, a single base change from an A to a T changes the shape and function of red blood cells, causing blood to clog and anemia (a condition in which the blood cannot carry enough oxygen to body tissues).
A C
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Components of a DNA strand. GA LE G RO UP.
Molecular biologists Francis Crick and James D. Watson were the first to map the structure of DNA. GAL E GR OU P.
Different species have varying amounts and sequences of DNA. Humans have about three billion base pairs in our DNA. Researchers have Experiment Central, 2nd edition
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WORDS TO KNOW Amino acids: The building blocks of proteins. Base: Substance that when dissolved in water is capable of reacting with an acid to form salts and release hydrogen ions; has a pH of more than 7. Base pairs: In DNA, the pairing of two nucleotides with each other: adenine (A) with thymine (T), and guanine (G) with cytosine (C). Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Deoxyribonucleic acid (DNA): Large, complex molecules found in the nuclei of cells that carry genetic information for an organism’s development; double helix. (Pronounced DEE-ox-seerye-bo-noo-klay-ick acid) DNA replication: The process by which one DNA strand unwinds and duplicates all its information, creating two new DNA strands that are identical to each other and to the original strand.
Double helix: The shape taken by DNA (deoxyribonucleic acid) molecules in a nucleus. Enzyme: Any of numerous complex proteins produced by living cells that act as catalysts, speeding up the rate of chemical reactions in living organisms. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Nucleotide: The basic unit of a nucleic acid. It consists of a simple sugar, a phosphate group, and a nitrogen-containing base. (Pronounced noo-KLEE-uh-tide.) Protein: A complex chemical compound consisting of many amino acids attached to each other that are essential to the structure and functioning of all living cells. Variable: Something that can affect the results of an experiment.
found no correlation between DNA length and the complexity of an organism. A species of wheat, for example, has roughly 16 billion base pairs, the fruit fly has an estimated 180 million, and a species of corn checks in at only slightly less than that of humans, at 2.5 billion.
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DNA replication: The DNA strand unwinds and complementary nucleotides bind together. GAL E GR OU P.
As a general rule, the greater the similarity between DNA sequences, the more similar the organisms. In the human species, your DNA sequence is about 99.9% identical to every other person’s. Your DNA sequence is even more similar to your family members. In 2003, researchers completed sequencing the entire human DNA. Experiment Central, 2nd edition
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PROJECT 1
DNA
The Stuff of Life: Isolating DNA Purpose/Hypothesis DNA is present in all life.
In this project, you will extract DNA to see what this molecule looks like. DNA is twisted inside the cell nucleus. A cell’s nucleus also contains proteins and other substances. To see the DNA, you will have to separate out the DNA from all the cell’s other molecules. (Refer to illustration.) You will first liquefy the substance and separate the cells by blending it. Detergent or soap will break apart the cell’s outer and inner membrane, in much the same way that soap loosens dirt and grease. The cell’s membranes are made of a fatty substance that contain proteins. Detergent contains a substance that pulls apart the fats and proteins, freeing the DNA. The DNA in the nucleus is wound up with proteins. To isolate the DNA from these proteins, you will use an enzyme, a protein that quickens a chemical reaction. Meat tenderizer contains enzymes that cut away the proteins. Adding alcohol will then allow you to see the DNA. DNA is not soluble in alcohol. DNA precipitates, or separates out of the solution, in alcohol, moving away from the watery part of the solution and rising towards the alcohol. Proteins and other parts DNA 1 of the cell will remain in the bottom watery layer.
All living organisms carry DNA; its unique sequence determines individual characteristics. G ALE GRO UP .
Figure A. Process of DNA isolation: (1) Detergent breaks up the cell’s membranes; (2) enzymes cut away the protein to (3) isolate the DNA. GA LE GR OU P.
Level of Difficulty Moderate. Materials Needed
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spinach knife salt coldwater blender refrigerator liquid soap with no conditioner chopstick or toothpick
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How to Work Safely Be sure to handle the knife carefully when cutting. If you get any alcohol on your hands, wash your hands immediately and make sure to keep them away from your eyes. Keep the container of alcohol away from open flames. Thoroughly wash the cup, jar, strainer, and chopstick after the experiment. Discard the mixture after you have studied and documented the results.
• • • • •
strainer or cheesecloth cup small glass jar meat tenderizer 91% isopropyl alcohol (available in drug stores) or 95% ethyl alcohol (slightly preferred; available from science supply companies)
Approximate Budget $10. Timetable 1 hour. Step-by-Step Instructions
Step 6: Slowly pour the alcohol down the side of the glass jar (jar should be at a slight tilt) until the jar is almost full.
Alcoh
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GA LE GRO UP.
1. Take ½ cup of the spinach and place it in the blender. Add a large pinch of table salt and about 1=3 cup of cold water. Blend together for 10 seconds and pour the mixture into the cup. 2. Slowly pour the liquid out of the cup and into the glass jar through the cheesecloth or strainer. Fill the jar about one-quarter to onehalf full. 3. Add about 2 teaspoons (10 milliliters) of liquid soap to the jar and stir slowly for five seconds. 4. Let the mixture sit for 10 minutes. 5. Add a pinch of the meat tenderizer and stir the mixture gently. Do not stir too hard. 6. Slowly pour the alcohol down the side of the glass jar (jar should be at a slight tilt) until the jar is almost full. 7. Place the jar in the refrigerator for five minutes, then remove and wait another five minutes. The DNA should have risen to the top of the glass. Use a chopstick or toothpick to extract the spinach DNA. Summary of Results Write down what the DNA
looks like. Your toothpickfull of DNA contains millions of DNA strands clumped together. 290
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Since you were not using chemicals to extract a highly purified DNA, it also contains some proteins and other nucleic acids (ribonucleic acid or RNA) that were not separated. With the right equipment and materials in a laboratory, it is possible to extract pure DNA.
EXPERIMENT 2 Comparing DNA: Does the DNA from different species have the same appearance? Purpose/Hypothesis The DNA molecule produ-
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The DNA is broken into small bits. (DNA should be a long, white strand.) Possible cause: You could have stirred too harshly when you added the enzymes or at different points throughout the experiment and broken the DNA strands. Try repeating the experiment, stirring gently every time. Problem: You do not see any DNA. (DNA looks
ces the unique characteristics for all life forms. white and stringy.) DNA is composed of the same biochemical molPossible cause: The cells may not have broken ecules in all species: four nucleotides and a sugaropen when they were blended. Try repeating phosphate backbone. Nucleotide sequences, the experiment, blending the DNA until is liquidy. which account for the distinctive characteristics, Possible cause: If the soap had conditioner in it, cannot be seen by the naked eye. it would not have broken open the fatty DNA In this experiment you will compare if DNA cell membranes, and the DNA would not appears the same in four different species. You have gotten free. Make sure the soap does will conduct the same DNA extraction process not have any conditioner. on each of the species and then examine its Possible cause: You may not have allowed physical characteristics. enough time for each step. Wait another 45 To extract DNA, you will have to separate minutes for the DNA to rise into the alcohol out the DNA from all the cell’s other molecules. layer. If you still do not see any DNA, try the experiment again, increasing the time slightly You will first liquefy the substance and separate for each step. the cells by blending it. Detergent or soap will Possible cause: You may not have had enough break apart the cell’s outer and inner membrane, DNA from the source. Repeat the experiin much the same way that soap loosens dirt and ment, cutting the amount of water added to grease. The cell’s membranes are made of a fatty the DNA source in half before placing it in the substance that contain proteins. Detergent conblender. tains a substance that pulls apart the fats and proteins, freeing the DNA. The DNA in the nucleus is wound up with proteins. To isolate the DNA from these proteins, you will use an enzyme, a protein that quickens a chemical reaction. Meat tenderizer contains enzymes that cut away the proteins. Adding alcohol will then allow you to see the DNA. DNA is not soluble in alcohol. DNA precipitates or separates out of the solution in Experiment Central, 2nd edition
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alcohol, moving away from the watery part of the solution and rising towards the alcohol. Proteins What Are the Variables? and other parts of the cell will remain in the bottom watery layer. Variables are anything that might affect the To begin this experiment, make an educated results of an experiment. Here are the main variables in this experiment: guess about the outcome of the experiment based on your knowledge of DNA. This educated guess, • the DNA source or prediction, is your hypothesis. A hypothesis • the type of alcohol should explain these things: • the type of detergent • the topic of the experiment • the temperature of the water • the variable you will change In other words, the variables in this experiment • the variable you will measure are everything that might affect the appearance • what you expect to happen of the DNA. If you change more than one varA hypothesis should be brief, specific, and iable at the same time, you will not be able to tell measurable. It must be something you can test which variable had the most effect on the DNA. through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘DNA will have the same physical characteristics in all the species, with each species having a unique quantity of DNA.’’ Variables are anything you can change in an experiment. In this case, the variable you will change will be the DNA source. The variable you will measure will be the DNA itself and the quantity of the DNA. Level of Difficulty Difficult (this experiment is not technically difficult,
but it requires careful attention to timing and each step). Materials Needed
• four DNA sources: possible sources include banana, wheat germ, onion, kiwi, grapes, peas • salt • cold water • knife • blender • refrigerator • liquid soap or detergent with no conditioner • 4 wooden sticks such as chopsticks or toothpicks • strainer • 4 small glass jars 292
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• • • • •
4 cups marking pen masking tape meat tenderizer 91% isopropyl alcohol (available in drug stores) or 95% ethyl alcohol (slightly preferred; available from science supply companies) • filter paper • gram scale (optional)
How to Experiment Safely Be sure to handle the knife carefully when cutting. If you get any alcohol on your hands, wash your hands immediately and make sure to keep them away from your eyes. Keep the container of alcohol away from open flames. Thoroughly wash the cup, jar, strainer, and chopstick after the experiment. Discard the mixtures after you have studied and documented the results.
Approximate Budget $15. Timetable One-and-a-half hours to start; 15 minutes after a three-day waiting period. Step-by-Step Instructions
1. Cut about a ½ cup of one DNA source, such as a banana, and place it in the blender. Add a large pinch of table salt and about twice as much cold water as the source. Blend together for about 10 seconds and pour into a cup. 2. Repeat the procedure with the other DNA sources. 3. Label each glass jar. Pour each mixture from the cup into its marked glass through the cheesecloth or strainer. Make sure to wash the strainer and cup between pours. Fill the jars about onequarter to one-half full. 4. Add 2 teaspoons (10 milliliters) of liquid soap to each jar and stir slowly for five seconds. 5. Let the mixtures sit for 10 minutes. 6. Add a pinch of the meat tenderizer to each glass and stir the mixtures gently. Do not stir too hard. 7. Pour the alcohol down the sides of the glass jars until they are almost full. Experiment Central, 2nd edition
Step 9: Gently extract the DNA from each substance using a toothpick or chopstick. GA LE G RO UP.
kiwi
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The DNA is broken. Possible cause: You could have stirred too harshly when you added the enzymes or at different points throughout the protocol and broken the DNA strands. Try repeating the experiment, stirring gently every time. Problem: There was no DNA. Possible cause: The cells may not have broken open when they were blended. Try repeating the experiment, blending the DNA until is liquidy. Possible cause: If the soap had conditioner in it, it would not have broken open the fatty DNA cell membranes and the DNA would not have gotten free. Make sure the soap did not have any conditioner. Possible cause: You may not have allowed enough time for each step. Wait another 45 minutes for the DNA to precipitate into the alcohol layer. If you still do not see any DNA, try the experiment again, increasing the time slightly for each step. Possible cause: You may not have had enough DNA from the source; some DNA sources contain more water than others. Repeat the experiment, cutting the amount of water added to the DNA source in half before placing it in the blender.
8. Place the jars in the refrigerator for about five minutes and then remove them and wait another five minutes. 9. Use a chopstick or toothpick to gently extract the DNA from each substance and observe its characteristics. 10. Gently place the DNA on filter paper. (If you have a sensitive scale, weigh the filter paper.) 11. Place the filter paper aside and leave for three days or until it is completely dry. Note how much DNA each substance contained by comparing them to one another. On the scale, you can weigh the filter paper with the DNA. Subtract the weight of the filter paper from the total. Note how much the DNA from each source weighs. Summary of Results Examine your results and
determine whether your original hypothesis was correct. Did the DNA react the same way in all the sources? Did the DNA appear the same from all the species? Draw, describe, or take pictures of the DNA, both when it is freshly extracted and when it is dried. (It may be helpful to view the extracted DNA under a microscope.) Write a description of each of the species’ DNA and your conclusions. Change the Variables You can vary this experi-
ment several ways:
• You can alter the DNA sources and observe the DNA from other plant and fruit sources. Whatever you choose, make sure the source is not too watery. Yeast, strawberries, and peas are three other good sources for this experiment. • Using one DNA source, such as wheat germ, you can alter the type of soap or detergent. 294
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• You can also change the amount of the soap used. • You can change the alcohol. What happens to the DNA if you use a lesser concentration of alcohol, such as 70% rubbing alcohol?
Design Your Own Experiment How to Select a Topic Relating to this Concept The study of DNA is a relatively new
topic of study for researchers. There are many intriguing questions and unknowns related to the topic that researchers are beginning to understand. How is the DNA of different species related? What are some ways that DNA sequences are manipulated, and how can this help treat or cure human disease? Check the Further Readings section and talk with your science teacher or librarian to start gathering information on any questions that interest you. You could also consider visiting companies in your local area that conduct DNA research.
Rice, yeast, the pufferfish (pictured), and the rat are among the organisms whose DNA sequences are known. # S TE PHE N F RI NK O F C OR BI S.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. As DNA is difficult to visualize, you may also want to include photographs and drawings of your Experiment Central, 2nd edition
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experimental setup and results. This will help others visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Because the nucleotides or sequences of DNA are
invisible to the naked eye, the majority of experiments with DNA will need special laboratory equipment. With the right equipment, you can compare the bands or fingerprints of DNA from different organisms. Called DNA fingerprinting, this is one technique that forensic scientists use to compare a suspect’s DNA with the DNA found at a crime scene. Check the Resources section for companies that sell kits on DNA fingerprinting. Using a DNA technique that combines bits of DNA from two different organisms is another possible project. Called DNA Transformation, the technique can transfer a desired trait to another organism. To perform transformation, you will need a kit, along with special equipment and adult supervision. Transformation kits are sold at many biological supply companies. The topic of DNA also brings with it many ethical dilemmas. Transformation techniques have allowed researchers to cut-and-paste the DNA of two different species together. Should a person be forced to store his or her DNA in a computer databank if it will help solve crimes? If a DNA sequence predicts that a person may get a certain disease, does that person’s insurance company have the right to know this information? You might focus on one ethical issue from differing viewpoints.
For More Information DNA From the Beginning. http://www.dnaftb.org/dnaftb/ (accessed on March 1, 2008). An animated introduction on the basics of DNA, heredity, and genetics. Genetics Home Reference. ‘‘What is DNA?’’ http://ghr.nlm.nih.gov/handbook/ basics/dna (accessed on March 1, 2008). Illustrated handbook on DNA. Groleau, Rick. ‘‘Journey into DNA.’’ Nova Online. http://www.pbs.org/wgbh/ nova/genome/dna.html (accessed on March 1, 2008). Interactive site on the basics of DNA and related issues. 296
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Howard Hughes Medical Institute. The Genes We Share with Yeast, Flies, Worms, and Mice. http://www.hhmi.org/genesweshare (accessed on March 1, 2008). Clear report from the Howard Hughes Medical Institute. Human Genome Project Information. http://www.ornl.gov/sci/techresources/ Human Genome/education/students.shtml (accessed on March 1, 2008). Information on the background and implications of sequencing human DNA. Ridley, Matt. Genome: The Autobiography of a Species in 23 Chapters. New York: HarperColllins, 2000. Each chapter looks at one gene on a human’s chromosome. The Tech Museum of Innovation. Understanding Genetics. http://www.thetech. org/genetics (accessed on March 1, 2008). Online DNA exhibit includes images of cells and DNA.
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Dyes
I
f you ever stained your clothing from a spilled drink, you have seen a dye at work. A dye is any substance that colors another material. Dyes are in inks, clothing, and furniture. People use them to produce a wide variety of colors in a range of materials.
The British chemist William Henry Perkin is credited with developing the first dye in the 1850s. GE TTY IM AGE S.
A colorful world of nature In the modern day, most dyes are manufactured (synthesized) by a chemical process. But people have been using natural dyes for thousands of years. Records show that dyes were used in ancient China about 2600 B . C . E . There is evidence that ancient Egyptians used dyes for burial cloth. Dyes were used to add color to fibers, skin decorations, and writings. Cultures made dyes from the colors in animals, plants, and minerals. Ancient Romans and Egyptians made a purple dye from a snail. The dye was so rare and expensive to make that purple became a symbol of wealth and royalty. People made a variety of color dyes from leaves, berries, stems, and roots. Indigo plants produced a blue, tree bark a brown, and the turmeric plant a yellow dye. The kermes insect could produce a red dye. Minerals were ground to produce reds and yellows. Lucky dye accident The first synthetic dyes were developed in the 1800s. The person credited with developing the first dye was a British chemist named William Henry Perkin in the 1850s. Perkin was just 18 years old when he was conducting an experiment trying to produce a drug for malaria, a deadly infectious disease. He 299
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In some remote countries, cloth is occasionally still dyed by hand. A P PHO TO /R EBE CC A BL ACK WE LL.
was using a chemical called aniline. The experiment failed but he had produced a deep color, which he pulled out the color purple. He found that it was a deep color that did not fade. Perkins set up a factory in London and began manufacturing the color, which he named mauve. A few years later he synthesized a deep red dye. Holding the dyes How a material dyes depends upon the composition of both the dye and the material. There are dyes for food, fabric, wood, and hair. Leather will accept a dye in a different way than a swatch (piece) of cotton. All dyes attach to the material being dyed. Dyes for fiber, for example, form a strong bond with the fiber. Hair dyes attach to the hair strand. Synthetic dyes have compounds in them that ‘‘fix’’ the dye to the fabric. Natural dyes often need a fixative agent, called a mordant. A mordant reacts with the dye and fiber to bind the dye to the material. Mordants generally contain metal, such as iron and aluminum. There are thousands of unique dye colors manufactured today. Dyes have become a part of everyday life, from the clothes we wear to the paints
dye
mordant material A mordant reacts with the dye and fiber to bind the dye to the material. IL LU STR AT IO N BY TE MA H NEL SO N.
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WORDS TO KNOW Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Colorfast: The ability of a material to keep its dye and not fade or change color.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Mordant: A substance that fixes the dye to the material.
Dye: A colored substance that is used to give color to a material.
Synthetic: Something that is made artificially, in a laboratory or chemical plant, but is generally not found in nature.
Fixative: A substance that mixes with the dye to hold it to the material.
Variable: Something that can affect the results of an experiment.
on the walls. They have also become a part of research and technological developments. In the medical and biological fields, dyes are used to color pills and identify tissues or other biological structures. There are many applications for dyes. In the following two experiment, you will investigate how dyes affect different materials and how a dye stays in the material.
EXPERIMENT 1 Applying Dyes: How does the fiber affect the dye color? Purpose/Hypothesis In this experiment, you will observe the role of the material in dyeing. How a dye colors depends upon the fiber it is coloring. Using a natural dye, you will experiment with both natural and synthetic (man-made) fibers. Natural fibers include cotton, wool, and silk. Natural fibers include fibers from animals, such as wool, and fibers from plants, such as cotton. Synthetic fibers include polyester, nylon and rayon. By making your own natural dye and applying it to different fabrics, you will be able to determine how dyes affect each type of fiber. Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the cleanliness of the fabric • the type of fabric • the color of the fabric • the type of dye • the time dyed In other words, the variables in this experiment are anything that might affect how the fabric dyes. If you change more than one variable, you will not be able to tell which variable had the most effect on the fabric color.
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How to Experiment Safely Be careful and ask an adult for help when working with boiling water. This can be a messy experiment. Make sure an adult knows that the wooden utensil and other materials you work could be dyed slightly, and wear appropriate clothing. Carefully dispose of the dye bath when you are finished.
To begin the experiment, use what you know about fibers and dyes to make an educated guess about how the dyes will affect the different fabrics. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Natural fibers, such as cotton and wool, will accept natural dyes the best.’’ In this case, the variable you will change is the fabric, and the variable you will measure is the color. Level of Difficulty Easy/moderate (due to the time involved). Materials Needed Step 1: Use the scissors to cut each piece in a way that will help you distinguish it from other pieces. I LL UST RA TI ON BY T EM AH NE LS ON.
• 2 to 3 fresh beets for the dye (other dye sources that work well include purple cabbage, coffee grounds, and onion skins) • metal pot • colander • scissors • wooden stirring stick that can pick up dye • plastic plate, which will pick up dye • knife • paper towels • container or pot that can get slightly dyed • 4 to 5 different types of white fabric pieces, about 5 x 5 inches, including cotton, wool, polyester, linen, and silk
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Approximate Budget Less than $5. (The fabric
can be taken from old clothes or fabric stores may give samples away.) Timetable Approximately one hour and 30 minutes to prepare dye, eight hours to three days total time. Step-by-Step Instructions
1. Wash all the fabric pieces by machine or by hand to make sure they are clean. Use the scissors to cut each piece in a way that will help you distinguish it from other pieces. You may want to cut the corner from the polyester, for example, and make the cotton piece a triangle. One can have nothing cut. Write down the identification for each type of fabric. 2. Cut up the beets and place them in the pot. Pour enough water in the pot to cover all the beets and bring to a simmer. Allow the beets to simmer for about an hour. Use the wooden spoon to stir occasionally. 3. Set the container under the colander in a sink or outside, and carefully empty the hot beet-water into the colander. The container holds your dye. 4. Place the fabric swatches into the container. Use the wooden stirrer to move the pieces around. Set aside overnight. 5. Use the wooden utensil to look at the fabric. You may want to leave the fabric in for several more hours or days to absorb more of the dye. When you are ready to take the fabric out of the dye, take the pieces out in a sink or outside. Hold each piece out under clear water and roll it in paper towels. Set the material pieces on the plate and allow to dry.
Step 3: Empty the hot beetwater into the colander. ILL US TRA TI ON B Y TE MA H NEL SO N.
Step 5: Use the wooden utensil to look at the fabric. ILL US TRA TI ON B Y TE MA H NEL SO N.
Summary of Results Match the identification with the type of fabric. How did each fabric dye compared to one another? Was there one type of material that dyed the brightest? Write up a Experiment Central, 2nd edition
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paragraph of your results; you may want to take pictures.
Troubleshooter’s Guide There should not be any significant problems with this experiment. If one of the types of material is clean and does not accept the dye, that may be the material. You could leave all the fabrics in the dye for a longer amount of time to make sure.
Change the Variables You can vary this experi-
ment. Here are some possibilities. Try different dye sources, such as flowers, onion skins, or bark. You could use a synthetic, store-bought dye and compare the color to the natural dye. Try blends of two types of fiber while also dyeing 100% pieces of each blend, to determine which of the types of fibers accepts dye more than the other.
EXPERIMENT 2 Holding the Dye: How do dye fixatives affect the colorfastness of the dye? Purpose/Hypothesis Adding a fixative to the dyeing process helps ensure
that the dye color will stay attached to the material. Dyes can fade over time from washing. Exposure to sunlight and air can also cause a color to fade. Mordants are used to help fix natural dyes. The mordant, a metal-based substance, attaches to the fiber and the dye binds to the mordant. Synthetic dyes can bond directly to the fiber. In this experiment, you can test the colorfastness of a synthetic dye, a natural dye without a mordant, and a natural dye with a mordant. The mordant you will use is alum (aluminum sulfate). After dying the same type of material in each of the three dye baths, you can test for colorfastness by repeatedly washing the materials with soap. By comparing each of the materials against an unwashed piece you can judge how the material held onto the dye relative to the other washed materials. To begin the experiment, use what you know about dyes and colorfastness to make an educated guess about how each material will fix the dye. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove 304
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or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The natural dye with the mordant will retain the dye color more than the synthetic or natural dye alone.’’ In this case, the variable you will change will be the dye fixative. The variable you will measure will be how much each material retains its color relative to one another. If the material with the natural dye and mordant retains its color the best, you will know your hypothesis is correct. Setting up a control will help you isolate one variable. For the control, you will only dye the material. For the experiment, you will compare the experimental material against the control to judge the colorfastness. Level of Difficulty Moderate, because of the time
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of material • the color of the material • the amount of soap • the type of pan used • the amount of times the material is washed In other words, the variables in this experiment are everything that might affect the amount of dye color the material retains. If you change more than one variable, you will not be able to tell which variable had the most effect on the colorfastness.
and care involved. Materials Needed
• purple cabbage or 3 to 4 fresh red beets • synthetic fabric dye, red dye if you are using beets and purple if you are using cabbage (available at drug or fabric stores) • stainless steel pot • 3 plastic container (which may get dyed) • scissors • 6 squares of white wool, about 5 to 6 inches (13–15 cm) square • stove • alum (available in grocery stores) • measuring spoons and cup • liquid soap • strainer • plastic plates • 2 to 3 wooden sticks or spoons • paper towels • glass jar with cover (a mayonnaise jar works well) Approximate Budget $8. Experiment Central, 2nd edition
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How to Experiment Safely Be careful and ask an adult for help when working with boiling water. This can be a messy experiment. You may want to work outside whenever possible. Make sure an adult knows that the wooden utensil and other materials you work may get dyed, and wear appropriate clothing. Carefully dispose of the dye bath when you are finished.
3.
4. 5. 6. Step 2: Use scissors to cut the pieces in three ways to help you identify each pair. I LL UST RA TI ON BY T EM AH NE LS ON.
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Timetable Approximately two hours to prepare dye and carry out experiment, three to four days total time, depending upon how long the material takes to dry. Step-by-Step Instructions
1. Wash the pieces of wool by machine or by hand to make sure they are clean. 2. Use the scissors to cut the pieces in three ways to help you identify which pair will be in each dye bath. You can cut a diagonal off the corner off two pieces; cut a square in the corner of two more pieces, and cut a small triangle in the middle of one side of two more pieces. It does not matter what you cut, as long as there are three sets of two pieces that are identifiable. Assign each identification marking to one of the dye baths and write it down. Bring three cups of water to a boil and reduce to a simmer. Add about a quarter teaspoon alum and stir. Wet the two pieces assigned to the mordant/natural dye bath and place in the hot water. Simmer for about an hour and turn off the stove. Allow the material to sit overnight in the alum water. Before you are about to die, remove the two pieces from the alum water and place on a plate. Wet the remaining four pieces of wool. For the natural dye: Cut up the beets or cabbage and place them in the pot. Pour enough water in the pot to cover the food and simmer for about 30 minutes or until the water is a color you like. Use the wooden spoon to stir occasionally. 7. While the natural dye is simmering, follow the directions on the package. Make sure you use a container that does not matter if it gets dyed. 8. When the cabbage or beets has finished simmering, place a plastic container under the strainer in a sink or outside, and carefully empty the hot beet-water into the colander. The container holds your dye. Experiment Central, 2nd edition
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9. Place the four wet fabric swatches assigned to the natural dye bath into the container. Use the wooden stirrer to move the pieces around. Set aside overnight. 10. Place the two wet fabric swatches assigned to the synthetic dye into the synthetic dye bath. Use a wooden stirrer to move the pieces around. Set aside as directed or until you like the color. 11. When all the squares are dyed, set them on a paper towel and roll the paper towel until the material is damp. Hang them over a plate in the sink or outside and allow to dry. Set one of each pair aside. 12. Fill the glass jar with warm water and add a few drops of soap. Place one of each pair of the dyed wool pieces into the jar. Cover and shake for at least ten seconds. 13. Rinse the wool squares under running water and allow to dry. 14. Repeat the washing and drying process two more times.
Step 3: Wet the two pieces assigned to the mordant/ natural dye bath and place in the hot water. I LLU ST RAT IO N BY T EMA H NE LS ON.
Step 12: Cover and shake with the dyed wool for at least ten seconds. I LL US TRA TI ON BY TEM AH N EL SON .
Summary of Results Compare the control wool
pieces to the washed wool. How does each compare to its non-washed partner? Is there one dye that washed out completely? Did the mordant help fix the dye? Match the identification with the assigned dye bath. Was your hypothesis correct? Write up a paragraph of your results; you may want to take pictures or attach swatches. Change the Variables One variable you can
change to further explore colorfastness is pH. The pH is a measure of how acidic a solution is. Depending upon the material, a low or high pH can affect how the dye bonds and fixes to the material. You can also change the material or type of dye. You can compare different brands of purchased dyes or different types of natural dyes. Experiment Central, 2nd edition
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Design Your Own Experiment How to Select a Topic Relating to this Concept Are you interested in
experimenting with how to make dye, change dye colors, or remove dyes? Perhaps you would like to learn more about the chemistry behind how a dye attaches to a fabric. Have you ever wondered why some dyes dissolve in water and others only dissolve in oil? Check the Further Readings section and talk with your science teacher to gather information about dye questions that interest you. You may also want to explore the museums in your area for special exhibits on color or dyes. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise you may not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts, graphs or some type of visual representation. They should be clearly labeled and easy to read. You may also want to include samples, photos, or colored drawings of your experimental set-up and results. If you are preparing an exhibit, display the materials you dyed or dyes themselves to help explain what you did and what you discovered. Observers could even test them out the dyes for themselves. If you have completed a nonexperimental project, you will want to explain clearly what your research question was and illustrate your findings. Related Projects There are many possible experiments relating to dyes.
You could investigate how dyes are removed or the chemistry behind dye removal. You could further investigate why some clothes retain their dye and others lose their color in the wash. There are many different types of dyes developed for different materials. You could explore how a 308
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wood dye is different from a fabric dye or hair dye. Why does bleach remove some dyes? Look around you for objects or materials that are dyed and consider what questions you can investigate.
For More Information ‘‘Dyeing to Find Out: Extracting Nature’s Colors.’’ Kids Gardening. http://www. kidsgardening.com/growingideas/projects/may03/pg1.html (accessed on April 24, 2008). Information and how techniques how to use plant materials to dye. Gardner, Robert. Science Projects about Chemistry. Hillside, NJ: Enslow Publishers, 1994. Focuses on experiments in causing and analyzing chemical reactions. Van Cleave, Janice. A+ Projects in Chemistry. New York: Wiley, 1993. Outlines many experiments and includes information about the scientific method.
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A
ccording to the ancient Greeks, earthquakes occurred when the god Atlas shifted the weight of the world from one shoulder to the other. Other cultures believed that earthquakes were a sign of punishment. We now know that earthquakes are the shaking or trembling of the earth caused by underground shock waves or vibrations. Believe it or not, over a million earthquakes take place each year. Sometimes the trembling and shaking is gentle and hardly noticeable. Other times the motion is much more violent, causing cracks in the surface of the earth.
There’s a whole lot of shaking going on Huge blocks of rocks called plates make up Earth’s outer shell, or crust. These plates fit together like a cracked egg shell. The plates push and pull on each other constantly. Sometimes this pressure causes a fault, or a break in the rocks. Large pieces of these rocks, called fault blocks, can overlap. Pressure pushes on the rocks for centuries, finally causing them to rupture and snap in one big surge, resulting in a major earthquake. Like a chain reaction, force from the movement of the rocks results in vibrations of the surrounding ground. These vibrations, or seismic waves, (pronounced SIZE-mic; relating to earthquakes) travel away from the break. Strong shaking from these waves lasts from 30 to 60 seconds and can cause buildings and highways to collapse. Earthquakes can actually be beneficial. The constant shifting and upheaval of Earth’s crust builds mountains and highlands. The planet would be flat without them. Developing a theory On November 1, 1755, the port of Lisbon, Portugal, was hit by a terrible earthquake. More than 60,000 people died. The day of the earthquake was a religious holiday, and many of those killed were crushed in churches. Because earthquakes were thought to be a punishment from God, it did not make sense that one would take place on a holy day. People also asked why innocent children would be 311
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punished? Soon after the earthquake, some people started to look for scientific reasons. The Marquez de Pombal, a Portugese nobleman, asked Lisbon’s surviving priests to fill out questionnaires documenting information about the earthquake. The questionnaires included questions about the time and the direction of the earthquake shock. In 1760, John Michell, an English physicist, came up with an interesting theory. He reasoned that if you could record the underground shock waves and the points at which the waves stopped, you could determine the point of origin, or epicenter, of an earthquake. Epicenters existed deep in the rocks beneath the sea, he said. His theories, which were fairly accurate, were the start of seismology, the science of earthquakes and their origins.
Dr. Charles F. Richter developed the Richter Scale, which measures earthquake magnitude. A P/W ID E WO RL D
Measuring an earthquake In the first century, Chang Heng—a Chinese astronomer, mathematician, and writer—invented the earliest earthquake recorder. This device measured the occurrence and direction of an earthquake’s
P HOT OS.
In the famous Lisbon, Portugal, earthquake of 1755, residents were killed by toppling buildings, fires, and high waves. CO RB IS /BE TTM AN N.
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WORDS TO KNOW Earthquake: An unpredictable event in which masses of rock suddenly shift or rupture below Earth’s surface, releasing enormous amounts of energy and sending out shockwaves that sometimes cause the ground to shake dramatically. Epicenter: The location where the seismic waves of an earthquake first appear on the surface, usually almost directly above the focus. Fault: A crack running through rock as the result of tectonic forces.
Plates: Huge blocks of rocks that make up Earth’s outer shell and fit together like a cracked egg. Seismic waves: Vibrations in rock and soil that transfer the force of an earthquake from the focus into the surrounding area. Seismograph: A device that detects and records vibrations of the ground. Seismology: The study and measurement of earthquakes.
Fault blocks: Pieces of rock from Earth’s crust that press against each other and cause earthquakes when they suddenly shift or rupture from the pressure.
Tectonic: Relating to the forces and structures of the outer shell of Earth.
Focus: The point within Earth where a sudden shift or rupture occurs.
Tsunami: A large wave of water caused by an underwater earthquake.
Hypothesis: An idea in the form of a statement that can be tested by observation and experiment.
Variable: Something that can affect the results of an experiment.
motion. Italian physicist Luigi Palmieri has been credited with inventing the first seismograph in 1855. Seismographs detect and record earthquake waves. To pinpoint how dangerous an earthquake was, American seismologist Charles F. Richter (1900–1985) began measuring the peaks and valleys of these waves in the 1930s. He came up with a mathematical formula, known as the Richter (pronounced RIK-ter) Scale, which measures earthquake magnitude on a scale from 1 to 10. The Richter Scale also measures how much energy is released in an earthquake. Increasing one whole number on the Richter Scale, from 5.0 to 6.0 for example, represents an increase of 10 times the magnitude and about 60 times the energy. Earth is a dynamic and changing planet. Conducting experiments will help you understand how earthquakes are part of the changes that are taking place. Experiment Central, 2nd edition
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EXPERIMENT 1 What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of simulated earthquake disturbance
Detecting an Earthquake: How can movement of Earth’s crust be measured? Purpose/Hypothesis In this experiment, you will
construct a simple seismograph and simulate the forces that cause an earthquake. Your seismograph • the distance of the disturbance from the is a simple model, but you will see if it can detect seismograph vibrational activity in your house or building. • the surface on which you place your You probably have an educated guess about seismograph the outcome of this experiment based on what In other words, the variables in this experiment you already know about earthquakes. This eduare everything that might affect the amount of cated guess, or prediction, is your hypothesis. disturbance recorded on your seismograph. If A hypothesis should explain these things: you change more than one variable, you will not • the topic of the experiment be able to tell which variable had the most • the variable you will change effect on the seismograph recordings. • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘By simulating an earthquake with various types of disturbances, you will detect and record various types of vibrational activity on your seismograph.’’ In this case, the variable you will change is the amount of simulated earthquake disturbance, and the variable you will measure is the amount of displacement recorded on your seismograph. If a greater simulated disturbance results in a greater displacement on your seismograph, you will know your hypothesis is correct. Level of Difficulty Moderate. (The design of your seismograph is easy,
but you may need someone to hold some pieces while you attach them. Also, you will need help from friends in creating vibrations.) Materials Needed
• 1 or 2 helpers • cardboard box about 12 inches 12 inches (30 centimeters 30 centimeters) with an opening on top 314
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• • • • • • • • • •
scissors ruler adding machine tape string pencil (or dowel) 5-ounce (about 148-milliliter) paper cup masking tape black marking pen small rocks or marbles modeling clay
How to Experiment Safely Use caution when handling scissors and cutting cardboard. Be careful when simulating an earthquake so you do not damage items in the room or hurt yourself or others.
Approximate Budget $3. Timetable One hour. Step-by-Step Instructions
1. Turn the box on its side so the opening is facing outward. 2. Cut a 2-inch (5-centimeter) circle in the center of the top side of the box. 3. Cut two ½-inch 4-inch (1.25-centimeter 10-centimeter) slots in the box. The first slot should be in the center of the bottom, near the front opening. The second slot should be in the back center near the bottom. See the illustration. 4. Thread the adding machine tape through the slots, so the leading edge comes out the front slot. 5. Cut two 24-inch (61-centimeter) lengths of string. 6. Use the point of a pencil to poke two holes below the rim of the cup opposite each other. 7. Tie one string onto each hole in the cup. 8. Bring the free ends of the string through the 2-inch (5-centimeter) circle in the top side of the box. 9. Tape or tie the ends of the string to the pencil and lay the pencil across the hole. 10. Push the marking pen through the bottom of the cup, tip down. Experiment Central, 2nd edition
Steps 2 to 4: Initial set-up of seismograph box. G ALE GRO UP.
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11. Fill the cup with the rocks or marbles. 12. Adjust the height of the cup/pen/rock device so the marker tip just touches the adding machine tape. (You can adjust the string on the pencil, then fix the pencil in place using the modeling clay and masking tape.) 13. Test the device by pulling the adding machine tape forward with one hand and shaking the box gently with the other and observe the markings left on the paper.
Steps 7 to 12: Completion of seismograph box. G ALE G RO UP.
Steps 14 and 15: Sample recording sheets of seismic results from walking, skipping, jogging, running. GA LE GR OU P.
14. Perform a seismic test indoors. Place your seismograph on the floor in the middle of the room. Have several of your friends walk, skip, jog, and run around in the room in a circle, always keeping the same distance away from the seismograph. While they are moving about, record the seismic waves, or seismic activity, by slowly pulling the adding machine tape through the instrument (see illustration). 15. Label the tape with the location and activities. Summary of Results Compare your tapes. Do they show greater move-
ment when the activity was more vigorous? In other words, does your seismograph accurately detect and record seismic activity? Change the Variables You can change one of the variables and repeat this experiment. For example, you can have your friends move closer or farther away from the seismograph to determine how the recordings vary. You can also place the seismograph on a shaky table, like an old card table, to see if this amplifies the disturbances.
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EXPERIMENT 2 Earthquake Simulation: Is the destruction greater at the epicenter? Purpose/Hypothesis In this experiment, you will
create a simulated city and suburbs with buildings and houses. By locating different types of structures at various distances from the epicenter, you will determine the destructive power of an earthquake. You probably have an educated guess about the outcome of this experiment based on what you already know about earthquakes. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
Troubleshooter’s Guide Experiments do not always work out as planned. Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: Nothing is being recorded on the adding machine tape. Possible cause: The pen is not touching the tape. Adjust the height of the marker pen. Gently shake the box and pull the tape until a mark appears. Problem: The adding machine tape does not move easily through the slots. Possible cause: The slots are too small. Enlarge the slots to allow the tape to move freely. Problem: The model works during the test, but when your friends run or jump, nothing happens.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove Possible cause: The friends are not making strong enough vibrations. Have them jump up or disprove whether your hypothesis is correct. and down. If that doesn’t work, have them Here is one possible hypothesis for this experimove closer to the siesmograph. ment: ‘‘Greater destruction occurs at the epicenter than at the outer limits of an earthquake.’’ In this case, the variable you will change is the distance from the simulated earthquake disturbance, and the variable you will measure is the amount of visible destruction of the structures in your simulated city and suburbs. If there is more destruction near the epicenter, you will know your hypothesis is correct. Level of Difficulty Easy/moderate. Materials Needed
• cardboard sheet, 24 inches 24 inches (60 centimeters 60 centimeters) • 8 sheets of 8-½-inch 11-inch (22 centimeter 28 centimeter) paper Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the size of the balloon, hence the amount of the simulated earthquake disturbance • the positions of the buildings in the simulated city and suburb areas
• • • • • • • •
marking pen 30 sugar cubes 8–10 spherical balloons adhesive tape 4 coffee cans ruler drawing compass safety pin
Approximate Budget $3 for balloons and sugar
cubes.
• the height of the buildings • the type of building construction • the surface on which the buildings are constructed
Timetable 1 hour or less. Step-by-Step Instructions
1. Using tape, connect the edges of four sheets of paper to form a large rectangle—two sheets wide by two sheets long. 2. In the center of the rectangle, where the four corners join together, draw a small bullseye with the compass. Adjust the compass so the first circle has a 1-inch (2.5-centimeter) radius around the center of the bullseye. Continue to draw circles so that each is 1 inch (2.5 centimeters) bigger in radius than the circle inside it. Mark the center of the bullseye X; this will be the epicenter. Label the paper ‘‘City.’’ Using the above illustration as a guide, randomly place ten sugar cubes on your City bullseye pattern. These represent city dwellings of three stories. Outline these cubes on the paper with your marking pen, and write 3, for three stories, in the center of the outlines. Repeat steps 1 and 2 with the remaining pieces of paper, only this time label the paper ‘‘Suburb.’’ Randomly place ten sugar cubes on your Suburb bullseye pattern. Outline these cubes with your marking pen and mark 1 in the center of the outlines. These represent a rural or suburban area that has one-story homes. Place the four coffee cans in a square pattern about 24 inches (61 centimeters) from each other. Place the cardboard sheet on top of the coffee cans.
In other words, the variables in this experiment are everything that might affect the amount of destruction. If you change more than one variable, you will not be able to tell which variable had the most effect on the seismograph recordings.
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8. Blow up two balloons. Make them full, but small enough to fit under the cardboard How to Experiment Safely sheet. Tape one to the center of the underside of the cardboard. Use caution when blowing up and handling 9. Place the City bullseye pattern on the cardballoons. Ask an adult to help. Place the safety pin in fabric or cardboard when it is not being board. Try to position the epicenter mark used. Discard the sugar cubes after you have directly over the spot where the balloon is used them. taped. 10. Stack three sugar cubes on top of each other over each outline. 11. Using your safety pin, carefully pop the balloon. 12. Using a marking pen and ruler, mark and measure the new positions of the cubes with dotted lines. 13. Remove the broken balloon. Tape the second balloon under the center of the cardboard sheet and repeat steps 9 through 12 for the
Step 3: ‘‘City’’ bullseye with ten outlines marked 3 and an X at the epicenter. G ALE GR OUP . Experiment Central, 2nd edition
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Troubleshooter’s Guide Your experiment may not have worked out as planned. Below is a problem that may arise during this experiment, a possible cause, and a way to solve the problem. Problem: My balloon is not creating much damage. Possible cause: The cardboard may be too thick and is absorbing the jolt. Try a thinner piece of cardboard. Also make sure the balloon is firmly attached to the cardboard.
Suburb bullseye pattern. This time, place only one sugar cube over each outline. Summary of Results Compare the destruction
on your two bullseye patterns. How did the simulated city compare to the suburb? Write up your results and describe the differences. Did your hypothesis hold true? Was the destruction near the epicenter greater in both cases? Change the Variables You can change the vari-
ables and repeat the experiment. For example, you can change the thickness of the cardboard to determine if the destruction increases or decreases. You can also change the height of the buildings. One interesting experiment might be to pick one of the threestory building outlines near the epicenter and place four stacks of three sugar cubes centered on the outline and arranged in a tight square so the stacks are touching. You can then compare the amount of damage of this type of building construction with a single three-story stack. Does a wider and broader base increase or decrease the amount of destruction? Remember to change only one variable at a time or you will not be able to determine which variable affected the results.
Steps 6 to 9: Set-up of simulated earthquake using City bullseye pattern. GAL E GR OU P.
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Step 12: Record seismic movement from simulated earthquake. G ALE GRO UP .
Modify the Experiment For a more advanced version of this experiment, you can examine earthquake-resistant structures. As you conduct the experiment, make a note of what structures (sugar cubes) were affected by the earthquake and the properties of each structure. For example, how many stories were the structures that fell as opposed to those that did not move. What shape were the affected and non-affected structures?
In Experiment 2, all the structures were made of the same material (sugar cubes). Some materials are relatively brittle (easily broken). Examples of brittle materials include brick and stone. Building materials that have some elasticity are more likely to move with the quake rather than break. Wood is an example of a relatively elastic material. The foundation of a structure also plays an important role in its stability during an earthquake. In order to determine the properties of an earthquake-resistant structure, experiment with altering the buildings’ foundation and material. For example, how would the quake affect a building made of rubber or clay compared to stone? Make sure to change only one variable at a time and keep track of your data. Experiment Central, 2nd edition
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Design Your Own Experiment How to Select a Topic Relating to this Concept Earth is dynamic and changing. Earth-
quakes, volcanoes, and tidal waves called tsunamis (pronounced SUE-nahm-ease; large waves of water caused by underwater earthquakes) are disastrous forces of nature that demonstrate Earth’s motion. If you are fascinated with the power of these natural disasters, you can explore topics relating to earth science. Major earthquakes are always reported in newspapers. You can look up major earthquakes in your local library. Newspaper accounts cover details such as seismic activity and the severity of the earthquake. One of the more recent ones in the United States took place in 1989 in San Francisco. Another took place in Turkey in 1999. Steps in the Scientific Method To do an original View of the San Andreas Fault in California. U .S . GE OLO GI CA L SU RV EY.
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your experiment can be
useful to others studying the same topic. When designing your experiment, develop a simple method to record your data. This method should 322
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be simple and clear enough so that others who want to do the experiment can follow it. Your final results should be summarized and put into simple graphs, tables, and charts to display the outcome of your experiment. Related Projects Building an actual model of a city, town, or region that
can be affected by a simulated earthquake is another way to understand the dynamics of a real earthquake.
For More Information Bolt, Bruce A. Earthquakes and Geological Discovery. New York: Scientific American Library, 1997. Offers geological facts and photos about earthquakes. Rubin, Ken. Volcano & Earthquakes. New York: Simon & Schuster Books for Young Readers, 2007. Smith, Bruce, and David McKay. Geology Projects For Young Scientists. New York: Franklin Watts, 1992. Describes earthquake experiments and the geological background of why earthquakes occur. U.S. Geological Survey. Earthquakes. http://www.usgs.gov/science/ science.php?term=304 (accessed on January 8, 2008).
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magine living in ancient times. You stroll down a dirt road leading to a favorite temple. It is a nice day, but without warning, the sky starts to get dark. The Sun looks strange and, gradually, something huge blocks it out, although a bright ring can be seen around its edge. We now know that this phenomenon is a solar eclipse. An eclipse occurs when one celestial body passes in front of another, partly or completely cutting off our view of it. Today, we would get advance information through newspapers and magazines or by news reports on television or radio if a major eclipse was expected. To most ancient people, who had no explanations for the darkness, an eclipse was terrifying.
The Moon completely blocks out our view of the Sun during a solar eclipse. P HOT O RE SE AR CHE RS I NC .
Close encounters in the sky In the eighth century B . C . E ., Babylonian scholars began systematically observing and writing down celestial phenonema, as they studied astronomy. These scholars watched the motion of the planets and noticed that sometimes two planets came close together. Sometimes the Moon passed in front of the Sun. Sometimes Earth’s shadow fell on the Moon. After studying these phenomena for many years, they identified certain experiences as occurring in cycles. They also developed mathematical formulas involving time and distances that helped them to predict eclipses. Thales of Miletus (624–546 B . C . E .) was a Greek philosopher who may have learned astronomical methods from the Babylonian scholars. Thales accurately predicted a solar eclipse on May 28, 585 B . C . E .—probably the earliest, most public eclipse prediction. The term eclipse comes from the Greek words meaning ‘‘to leave out,’’ because when one occurred, either the Sun or the Moon was ‘‘left out.’’ In fact, the theory that Earth was a sphere began getting attention 325
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Red light waves from the Sun cause the Moon to turn a reddish color during a lunar eclipse. PH OT O RE SEA RC HE RS I NC.
In 1869, British astronomer Joseph Norman Lockyer became the first person to observe solar prominences in the daytime. PH OT O RE SEA RC HE RS I NC.
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around this time because observers noticed that Earth’s shadow on the Moon during eclipses was always circular. The first eclipse to interest a significant number of astronomers took place on April 22, 1715. The shadow of the eclipse fell across Great Britain and parts of Europe. English astronomer Edmond Halley (1656–1742) plotted its path and prepared maps enabling many to watch its course. Celestial line-up The two most commonly known eclipses are solar and lunar. Earth revolves around the Sun. The Moon revolves around Earth. The Moon takes a month to complete a revolution; Earth takes a year. Sometimes these three bodies end up in a straight line and cause an eclipse. Two conditions have to be met for a total solar eclipse—one in which our view of the Sun is completely blocked. The Sun, Moon, and Earth must lie in a perfectly straight line, and the Moon must be a certain distance from Earth to cover the Sun. When these conditions are met, the Moon totally blocks our view of the Sun for a period of about seven minutes. If the Moon is too far away from Earth, or if it is not exactly aligned between Earth and the Sun, it will only partially block the Sun, causing a partial solar eclipse. For a total lunar eclipse, the Sun, Earth, and Moon must lie in a perfectly straight line. Did you catch the difference? In this case, Earth is in the middle, not the Moon. Earth’s shadow across the Moon is what causes the darkness. Lunar eclipses can happen only during a full Moon, when Earth’s dark side faces the Moon’s bright side. In this position, Earth casts a shadow, causing the Moon to darken. Celestial fireworks The bright ring you might see around the Sun during a solar eclipse is the corona, the Sun’s outermost layer, which appears to be a pearly color. The red plumes that shoot out around this ring are called prominences. Experiment Central, 2nd edition
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WORDS TO KNOW Astronomy: The study of the physical properties of objects and matter outside Earth’s atmosphere.
Lunar eclipse: An eclipse that occurs when Earth passes between the Sun and the Moon, casting a shadow on the Moon.
Celestial bodies: Describing planets or other objects in space.
Partial solar/lunar eclipse: An eclipse in which our view of the Sun/Moon is only partially blocked.
Corona: The outermost atmospheric layer of the Sun.
Phases: Changes in the portion of the Moon’s surface that is illuminated by light from the Sun as the Moon revolves around Earth.
Cycles: Occurrence of events that take place on a regular, repeating basis. Eclipse: A phenomenon in which the light from a celestial body is temporarily cut off by the presence of another. Gibbous moon: A phase of the Moon when more than half of its surface is lighted. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Prominences: Masses of glowing gas, mainly hydrogen, that rise from the Sun’s surface like flames. Solar eclipse: An eclipse that occurs when the Moon passes between Earth and the Sun, casting a shadow on Earth. Total solar/lunar eclipse: An eclipse in which our view of the Sun/Moon is totally blocked. Variable: Something that can affect the results of an experiment.
Like fireworks, these streams of glowing gas shoot out from the Sun and extend many miles into space. No wonder ancient people were terrified. Lunar eclipses have a colorful side also. They can make the Moon turn red. This reddish color is actually an accumulation of light waves from the Sun. By constructing models that simulate eclipses, we can better understand the extraordinary processes that cause them.
PROJECT 1 Simulating Solar and Lunar Eclipses Purpose/Hypothesis This project will create a
How to Experiment Safely Use caution when handling the lamp. Do not touch or move it until it has cooled for at least five minutes.
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eclipse. By adjusting the alignment and distances of the model Sun, Moon, and Earth, you should be able to demonstrate both partial and total eclipses. Level of Difficulty Easy/moderate. (The assem-
bly and principles are not difficult, but it takes patience to adjust the objects to get the desired effect.) Materials Needed
Lamp without shade and measured distance of 12 inches. GAL E GR OU P.
Step 5: Solar eclipse set-up.
• 2 Styrofoam balls, one ball 2 inches (5 centimeters) and one 0.5 inch (1.25 centimeters) in diameter • two 4-inch (10-centimeter) Styrofoam squares • small table lamp (measuring 12 inches in height) with no lamp shade and a 40-watt bulb • 2 wooden dowels (as long as the height of the lamp from its base to the middle of the bulb) • ruler Approximate Budget $3 for the Styrofoam pieces and the dowels.
GA LE G RO UP.
Timetable Less than one hour. Step-by-Step Instructions
1. Poke each dowel into the center of a Styrofoam square. 2. Place the small Styrofoam ball, representing the Moon, onto one dowel. 3. Place the large Styrofoam ball, representing Earth, onto the other dowel. 4. Place the lamp on a sturdy table and plug it in. Turn it on. 5. Here is the challenge! Place the Sun (lamp), Earth (large ball), and Moon (small ball) on a flat surface in perfect alignment to 328
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create a solar and lunar eclipse. Follow the diagrams illustrated. Summary of Results Make a diagram of your
experiment, measuring and marking the distances and height of the experiment parts for others to see and try. Through the shadows you created with the lamp, were you able to create full eclipses or only partial eclipses?
PROJECT 2 Phases of the Moon: What does each phase look like?
Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: You cannot get the shadow to cover the entire object to create the ‘‘eclipse.’’ Possible cause: Your alignment may be off. Make sure you line up the objects on the same level.
Purpose/Hypothesis In this project, you will
create models of the changes in the illuminated Moon surface as the Moon revolves around Earth. These changes are called phases. You will create diagrams called sun prints representing these Moon phases. Step 5: Lunar eclipse set-up.
Level of Difficulty Easy/moderate.
GA LE G RO UP.
Materials Needed
• 8 sheets of dark blue construction paper, 8½ x 11 inches (21.5 x 28 centimeters) • 8 sheets of black construction paper, 8½ x 11 inches (21.5 x 28 centimeters) • adhesive tape • marker • 30 x 30-inch (75 x 75-centimeter) board • sunny day • scissors • drawing compass Approximate Budget $5 for paper supplies. Timetable Approximately 1 hour to set up the
model and a whole day for the sun prints to mature. Experiment Central, 2nd edition
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Step-by-Step Instructions
How to Experiment Safely
1. Use the compass to draw a 7-inch (18centimeter) diameter circle on eight sheets of blue construction paper.
Use caution with the compass and scissors.
2. Draw an 8-inch (20-centimeter) diameter circle on eight sheets of black construction paper. 3. Cut out the circles. 4. Tape eight blue circles onto the board in a circle. 5. Mark the board as shown in the diagram illustrated above. 6. Place the black circles over the blue circles to show: new Moon; crescent Moon; first-quarter Moon; gibbous Moon; full Moon; gibbous Moon; third-quarter Moon; crescent Moon. 7. Leave the board in a sunny location for at least 8 hours. 8. Take the black paper off after 8 hours and examine the results. 9. Highlight the lightened areas or boundaries with the marker. Illustration of the Moon’s revolution around Earth. G AL E GRO UP.
Note: the darker blue areas that were covered are the shaded part of the Moon we cannot see. Summary of Results Label the board and write a
brief description for each Moon phase, that is, how it was caused and what it looks like.
Design Your Own Experiment How to Select a Topic Relating to this Concept
Astronomy is a fascinating field of study, with topics such as meteor/meteorites, telescopes, space travel, and stars. Read your local paper to find out about upcoming events in the sky. Then research who saw the phenomena first and when and how theories developed. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on eclipse questions that interest you. 330
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Step 5: Set-up for recording phases of the moon. GA LE GR OU P.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
Steps 6 to 8: Completed sun prints. GAL E GR OU P.
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results
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Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: The sun prints are not forming. Possible cause: They have not had enough time. Give the sun prints two days, for eight hours each day, in full sunlight.
in a visual manner. Graphs, drawings, or pictures of events are great tools for displaying your data. Related Projects Creating models like these are
always fun and interesting. However, creating a mini-instrument, such as a telescope with lenses and cardboard, might be useful. Ask a teacher or your parents for help.
For More Information
Aronson, Billy. Eclipses: Nature’s Blackouts. New York: Franklin Watts, 1996. Explains what causes eclipses of the Sun and Moon and describes how they have been viewed and studied at different times in history. National Aeronautics and Space Administration. NASA Eclipse Home Page. http://sunearth.gsfc.nasa.gov/eclipse/transit/transit.html (accessed on January 11, 2008).
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W
e know that electricity will flow through certain objects and not others. We are told that it is dangerous to plug in an ungrounded electrical device while standing in water because the electricity may flow through our bodies and the water to the ground, giving us a shock. But how, exactly, does water conduct electricity? Do all liquids conduct electricity equally well? And how have we made this property useful in our everyday lives? How electricity flows through metals Most of the electricity we use every day is conducted from its source through metal wires to the appliances we use. Most metals, such as copper, conduct electricity well because they possess a great number of free electrons. An electron is an extremely small particle with a single electrical charge that orbits the nucleus of an atom. Materials with few or no free electrons do not conduct electricity and are called insulators. They are commonly used to coat the wiring we use, allowing the electric current to flow safely and efficiently through the wire.
The flow of electrons in an electric current was the focus of many experiments done by the French scientist Andre´-Marie Ampere (1775–1836). Ampere developed the system we now use for measuring this electron flow. The common electrical unit of measurement of current, the ampere or amp, is named for him. How electricity flows through liquids Electricity can flow through liquids by the process of ionic conduction, the movement of ions (charged particles) within the liquid. Substances that conduct electricity when they are dissolved in water are called electrolytes. When a positive electrode and a negative electrode (such as wires attached to the terminals of a battery) are placed in an electrolytic solution, ions transport free electrons between the two electrodes, bridging the gap and allowing the flow of electricity. 333
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In the first experiment, you will determine whether certain substances are electrolytes. Using a voltmeter, you will test various solutions and liquids and compare them to find which conducts electricity the best. When the two probes (positive and negative) of the voltmeter are placed in a liquid, the meter will indicate how much current (from the battery inside the meter) is passing between the probes. A strong electrolyte will conduct more current, and a weak electrolyte will conduct less. Acids in water, such as lemon juice, make good electrolytes because they contribute many hydrogen ions. Other solutions, such as organic compounds that contain sugar and starch, contribute few or no hydrogen ions and do not conduct electricity well.
Andre´-Marie Ampere studied electrical current. PH OT O RE SEA RC HE RS I NC.
Electrolytes and ionic conduction make batteries work The batteries used to power watches, flashlights, and cars all rely on electrolytes to function. The first battery was developed by the Italian scientist Alessandro Volta (1745–1827), who also invented and gave his name to the measurement of the force of a current, called voltage. Volta discovered that a weak electric current is created when two different metals (he used copper and zinc) are pressed together, separated only by a thin layer of electrolyte-soaked fabric. The electrolyte between the metals carries free electrons from one to the other, creating an electric current. Combining a number of these ‘‘cells’’ in a series increases the force of the current, forming a useful battery. Today’s common household batteries, called dry cell batteries, use the same principle. One metal serves as a positive electrode, another metal serves as a negative electrode, and a dry electrolyte ‘‘paste’’ allows ionic conduction between the two. The batteries found in most cars are wet cell batteries, which use a liquid electrolyte to allow conduction. In the second experiment, you will construct a single battery cell using two different metals and a lemon as an electrolyte. (Lemons contain citric acid.) After finding the voltage of that single cell, you will estimate how many lemons would be necessary in series to equal the voltage of a single D-cell battery. Finally, you will test your estimate and your
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hypothesis by constructing a multi-cell battery or ‘‘pile’’ and comparing its voltage to that of a D-cell battery. The third project explores one of electricity’s applications: electroplating. Electroplating is a commonly used process of coating (‘‘plating’’) one metal onto another metal. Jewelry and silverware are electroplated to make them look more appealing, car parts are electroplated to protect them from rusting and keep them shiny.
EXPERIMENT 1 Electrolytes: Do some solutions conduct electricity better than others? Purpose/Hypothesis Using a voltmeter, we can determine how well different substances act as electrolytes by measuring their resistance when they are dissolved in water. The lower the resistance, the more conductive the electrolyte. In this experiment, you will predict whether certain substances are electrolytes. Before you begin,
Alessandro Volta studied electrolytes and electrical current. P HOT O RES EA RC HER S I NC.
By combining different metals and a strong electrolyte, Alessandro Volta was able to create an electric current in a ‘‘Volta Pile,’’ illustrated. G ALE GR OU P.
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WORDS TO KNOW Amperage: A measurement of current. The common unit of measure is the ampere or amp.
the result of losing or gaining one or more electrons.
Circuit: The complete path of an electric current including the source of electric energy.
Ionic conduction: The flow of an electrical current by the movement of charged particles, or ions.
Current: The flow of electrical charge from one point to another.
Insulator: A material through which little or no electrical current will flow.
Dry cell: A source of electricity that uses a nonliquid electrolyte.
Probe: The terminal of a voltmeter, used to connect the voltmeter to a circuit.
Electrode: A material that will conduct an electrical current, usually a metal; used to carry electrons into or out of a battery.
Resistance: A partial or complete limiting of the flow of electrical current through a material. The common unit of measure is the ohm.
Electrolyte: Any substance that, when dissolved in water, conducts an electric current.
Variable: Something that can affect the results of an experiment.
Electron: A subatomic particle that orbits the nucleus of an atom. It has a single electrical charge.
Voltage: Also called potential difference; a measurement of the amount of electric energy stored in a mass of electric charges compared to the energy stored in some other mass of charges. The common unit of measure is the volt.
Electroplating: The process of coating one metal with another metal by means of an electrical current. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Voltmeter: An instrument for measuring the amperage, voltage, or resistance in an electrical circuit.
Ion: An atom or groups of atoms that carry an electrical charge—either positive or negative—as
Wet cell: A source of electricity that uses a liquid electrolyte.
make an educated guess about the outcome of this experiment based on your knowledge of electricity and conductivity. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove 336
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or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Acids and other substances that contribute hydrogen ions make better electrolytes than organic compounds such as sugars and starches.’’ In this case, the variable you will change is the material you use as an electrolyte, and the variable you will measure is the resistance of the solution. You expect acids, such as vinegar and lemon juice, will have lower resistance than sugars and starches and are therefore better electrolytes. Level of Difficulty Moderate. Materials Needed
• • • • • • • • •
6 wide-mouth glass jars distilled water salt sugar cornstarch vinegar lemon juice adhesive labels or strips of masking tape voltmeter (most electronics supply stores carry these) • measuring spoons • stirrer
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the substances being tested for conductivity • the concentration of the solutions • the distance between the probes placed in the solutions In other words, the variables in this experiment are everything that might affect conductivity. If you change more than one variable, you will not be able to tell which variable had the most effect on conductivity.
A voltmeter is used to measure the flow of current in a circuit. PHO TO R ES EAR CH ER S IN C.
Approximate Budget $30. (An inexpensive, ana-
log voltmeter will suffice. Try to borrow one from school to reduce costs.) Timetable Less than 1 hour. Step-by-Step Instructions
1. Pour 0.5 cup (0.125 liter) of distilled water in a jar. Add 1 tablespoon of salt and stir. Experiment Central, 2nd edition
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How to Experiment Safely
2. Label the jar with the name of the substance on an adhesive label or strip of masking tape.
3. Rinse your measuring spoon and stirrer thoroughly in distilled water and repeat steps 1 and 2, using the sugar in a second jar, and the cornstarch in a third jar. 4. Pour 0.5 cup (0.125 liter) of lemon juice into the fourth jar and 0.5 cup of vinegar into the fifth jar. The sixth jar will contain only 0.5 cup (0.125 liter) of distilled water. Remember to label each jar, and rinse your measuring spoons and stirrers in distilled water after each mixture is prepared.
The battery in the voltmeter (usually one AA-cell) will provide all the voltage you will need for this experiment. Do not try to add batteries to the experiment, and NEVER experiment with household current or car batteries. Both are dangerous and potentially life-threatening. If you choose to test other substances for conductivity, check with your science teacher to make sure you are not testing materials that will create a hazard (such as flammable liquids).
5. Place the glass jars so that the labels are visible. (Your set-up should look like the illustration.) 6. Set your voltmeter to measure resistance. Resistance is the measure of how much a circuit reduces the flow of electricity. With the probes touching, the voltmeter should read zero because there is no resistance, and all of the current is getting through. When you
Steps 1 to 5: Electrolyte set-up. GAL E GR OU P.
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separate the probes, the meter goes to the other end of the scale and reads ‘‘infinity’’ Troubleshooter’s Guide because none of the current is getting through. To test something for measurable This experiment requires careful attention when setting up your solutions and preparing the resistance, wet your fingertip and place the probes. Failing to wash a measuring spoon or probes on it, just barely separated. The allowing the probes to touch will alter your meter reading should shift slightly away results. Here is a problem that may arise during from infinite resistance because a small the experiment, some possible causes, and current is flowing across your fingertip. If some ways to remedy the problem. you are unsure how to set your voltmeter Problem: The voltmeter is giving inconsistent for resistance or which scale indicates readings or no readings. resistance, check the meter’s instruction Possible causes: manual. 1. The voltmeter is not set properly to 7. When testing the various substances, you measure resistance. Check the instrucmust be sure that the voltmeter probes tion manual. do not touch and that they remain at the 2. Your probe tips are too close to each same distance from each other for each other. Separate them and try again. test. (Otherwise you are adding another 3. You have tape connecting the metal variable to your experiment.) Tape the sections of the meter’s probes. probes together as illustrated. If neces4. The probe connections to the voltmeter sary, place a ball of tape between the are loose. Press the connections firmly probe grips. Do not tape the metal part into the voltmeter. of the probes! The distance between the probe tips should be about 0.5 inch (1.25 centimeter). 8. Dip the electrodes into the first solution and observe the resistance reading on the voltmeter. Record your data, rinse the probes with Step 7: Probe tip set-up. G ALE distilled water, and repeat this step with GRO UP . each jar. Summary of Results Compare your data from
the six different tests. Determine which of the substances are electrolytes and which are not. Rank them from strongest to weakest. Check your findings against the predictions you made in your hypothesis. Which substances did you accurately predict would be electrolytes? Which substances did not behave as you expected? Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of electrolyte used • the metals used as electrodes • the type and gauge (diameter) of wire used • the number of cells placed in series In other words, the variables in this experiment are everything that might affect the output voltage of your multiple-cell battery. If you change more than one variable, you will not be able to tell which variable had the most effect on the voltage.
Change the Variables Think about the other variables you might change to investigate electrolytes. How would combining two electrolytes affect the results? Would lowering or raising the temperature of a solution affect conductivity? Remember to check with your science teacher before heating or mixing substances. Does adding more of an electrolyte to a solution increase the conductivity? A number of interesting follow-up experiments can be performed using the same materials and methods.
EXPERIMENT 2 Batteries: Can a series of homemade electric cells form a ‘‘pile’’ strong enough to match the voltage of a D-cell battery?
Purpose/Hypothesis In this experiment, you will construct a cell from
copper and zinc electrodes and a lemon. The lemon contains citric acid, which is a weak electrolyte. After measuring the voltage of that one cell, you will add more cells to the pile to attempt to match the voltage of a D-cell battery. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of batteries. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A multicell battery constructed of zinc, copper, and lemons can equal the voltage output of a D-cell battery.’’ 340
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In this case, the variable you will change is the number of cells you place in series, and the variable you will measure is the output voltage. You expect that it is possible to equal the output voltage of a D-cell battery. Level of Difficulty Easy/moderate.
How to Experiment Safely Do not change the number or type of battery used in this experiment without first consulting your science teacher. NEVER experiment with household current or car batteries! Both are dangerous and potentially life-threatening.
Materials Needed
• 10 lemons • 10 copper nails (available at most hardware stores) • 10 small zinc or zinc-plated nails or screws (available at most hardware stores) • 10 feet (3 meters) of small diameter insulated copper wire • fresh D-cell battery • small flashlight bulb • voltmeter with alligator-clip probes Approximate Budget $30. (An inexpensive analog voltmeter will suffice. Try to borrow one from school to reduce costs.)
Step 4: A lemon cell. GAL E GR OU P.
Timetable About 20 minutes. Step-by-Step Instructions
1. Cut one 6-inch (15-centimeter) length of wire and strip the insulation off both ends. 2. Wind one end of the wire securely around a copper nail and push the copper nail into a lemon. 3. Cut a second 6-inch (15-centimeter) length of wire, strip the insulation of both ends, and wind one end around a zinc nail. 4. Roll and squeeze the lemons to loosen the juices. Push the zinc nail into the lemon about 1 inch (2.5 centimeters) from the copper nail. Be sure the two nails are not touching, either outside or inside the Experiment Central, 2nd edition
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Step 8: Lemon multicell battery. GAL E GR OU P.
Steps 8 and 9: Sample voltage chart. GAL E GR OU P.
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lemon, and avoid wetting the wire with lemon juice. Your cell should look like the illustration. 5. Set the voltmeter to measure direct current (DC) voltage. Connect the voltmeter to your cell by attaching one of the meter’s alligator clips to each of the two loose wire ends. Observe and make note of the voltage of your cell. 6. Disconnect the voltmeter and use it to test the voltage of your D-cell battery by touching the probes to the positive and negative terminals of the cell. Make note of the voltage. 7. Calculate the minimum number of homemade lemon cells that would be needed to match the voltage of the D-cell battery. Do not be surprised if it is more lemons than you expected. That is one reason we do not power our flashlights with lemons! 8. Build as many lemon cells as needed and connect them in a series, as illustrated. Experiment Central, 2nd edition
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Check the total voltage output of the ‘‘pile’’ after each lemon is added and make a note of the measurement on your data chart (see illustration). Remember the lemons must be connected properly, positive terminal (copper) to negative terminal (zinc). Your multicell battery should look something like the illustration. 9. After your battery is complete, test its voltage by touching the meter’s probes to the loose wire ends. Because some current can be lost due to resistance in the wires and connections, you may need to add another lemon or two to match the D-cell’s voltage. After your battery is powerful enough, connect the loose wire ends to the flashlight bulb—one wire to the bottom of the metal base and one to the side of the base. If your voltage reading is correct, it should light with the same intensity as when connected to the D-cell. 10. Examine your results and determine whether your hypothesis is true. If it is, you might connect both the lemon battery and the D-cell to flashlight bulbs to demonstrate the proof of your findings. Summary of Results Write a summary of your
findings. Your data from Steps 8 and 9 should be recorded on a chart. This chart should contain the information that will show whether your hypothesis is correct. You can increase the clarity of your results by converting the data into graph form. Change the Variables Think about the other
variables you might change to investigate other questions about electrolytes and batteries. Can you increase the output of a lemon cell by using Experiment Central, 2nd edition
Troubleshooter’s Guide This experiment involves a number of electrical connections that may need to be checked and rechecked to ensure that they are not loose. When you are doing experiments in electricity, the results can easily be affected by inexact assembly of your circuit. Many hobby stores carry some simple tools, such as battery holders, that will make experiments easier and more visually impressive. Here are some problems that may arise during your experiment, some possible causes, and some ways to remedy the problems. Problem: The first lemon cell shows no voltage on the voltmeter. Possible causes: 1. The voltmeter may be calibrated incorrectly. Check it by testing the D-cell. (Its voltage is printed on the battery case.) 2. The electrodes are placed too far apart or are touching. Remove and check the electrodes. 3. A connection is loose. Check all your connections and secure them with electrical tape if necessary. Problem: The lemon cells connected together do not increase the total voltage as expected. Possible causes: 1. Resistance in the wires is reducing voltage output. Shorten the length of the wires. Check that the bare wire ends are tightly wrapped around the nails. 2. The electrodes are placed too far apart or are inserted incorrectly. Check your electrodes. 3. Your hypothesis is incorrect. Your materials may not be sufficient to generate the voltage required. Consider what changes you could make to the electrodes and the electrolyte.
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How to Experiment Safely Have an adult helper assist you with connecting the alligator clips to the 6-volt battery. Make sure the negative and positive wires do not touch one another.
different metals? Would lemon juice in a glass jar work more efficiently than an actual lemon? How much current could you produce with a Volta pile instead of a lemon cell? (A simple Volta pile can be constructed using nickels, pennies, and an electrolyte-soaked paper towel.) After you know how to make a cell and measure its output, you can construct a number of interesting experiments comparing their output.
PROJECT 3 Electroplating: Using electricity to move one metal onto another metal Purpose/Hypothesis In this project, you will use electroplating to coat a
Step 3: Attach the strip of copper to the alligator clip that is attached to the positive terminal. I LL UST RA TI ON BY
layer of copper onto a quarter. (A quarter is a mixture of copper and nickel.) Electroplating needs an electric current. You can generate an electric current using a battery, wires, and an electrolyte solution. The metal that will be coated, the quarter, is attached to the negative terminal of the battery. The copper is attached to the positive battery terminal. Both metals are placed in the solution. The electrolyte solution contains vinegar, which helps dissolve the copper. It also contains salt, which contains a positive charge and is attracted to the negatively-charged quarter. The electrical current will move the particles of the copper through the solution and plate them onto the quarter. Level of Difficulty Moderate.
T EM AH NE LS ON.
Materials Needed
• 1 6-volt battery (available from hardware stores) • 2 alligator clips • thin strip of copper, about 1 by 3 inches, such as copper flashing or sheets (available from hardware or craft stores) • tin snips or scissors to cut copper if needed • 1quarter • small plastic container 344
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• dishwashing soap • 1 cup of white vinegar • a pinch of Epsom salt Approximate Budget $15. Timetable 1 hour and 15 minutes. Step-by-Step Instructions
1. In a small plastic container stir together 1 cup of vinegar and a pinch of salt until the salt is dissolved. 2. Attach one alligator clip to the positive battery terminal and one alligator clip to the negative side. Keep the clips separated from one another. 3. Attach the strip of copper to the alligator clip that is attached to the positive terminal. (You may need to use snips to cut the piece of copper into a strip that will fit in the cup.) Only some of the copper needs to be immersed in the solution. 4. Wash the quarter with dishwashing soap, rinse, and dry. Attach the quarter to the alligator clip attached to the negative terminal. 5. Continuing to keep both clips separate, place the copper strip and the quarter into the cup with vinegar solution, making sure that they do not touch one another. The solution does not need to cover all the copper. 6. Observe and record the changes to the quarter, the copper and the vinegar solution over the course of an hour. Disconnect the clips from the battery and remove the metals from the solution.
Step 5: Place the copper strip and the quarter into the cup with vinegar solution. ILL US TRA TI ON B Y TE MA H NEL SO N.
Step 6: Disconnect the clips from the battery and remove the metals from the solution. ILL US TRA TI ON B Y TE MA H NEL SO N.
Summary of Results Take another clean quarter and compare it to the electroplated quarter. How did the quarter and copper change over the course of an hour? Try to scrape the copper plating off of the quarter. Does the copper come off? What color is the electrolyte solution? Write a summary of your findings. You may want to include drawings of the metals. Experiment Central, 2nd edition
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Troubleshooter’s Guide This experiment involves several electrical connections that may need to be checked and rechecked to ensure that they are not loose. When you are doing experiments in electricity, the results can easily be affected by loose connections in a circuit. Here are some problems that may arise during your experiment, some possible causes, and some ways to remedy the problems. Problem: The quarter does not change color Possible causes: 1. The alligator clips may not be properly attached to the battery, check to make sure they are secure and repeat the experiment. 2. The quarter may be attached to the positive terminal on the battery, make sure that it is attached to the negative terminal. Problem: The quarter has a black residue on it. Possible cause: The black residue could be an indicator of too much salt in the solution. Make sure there is just a pinch of salt in the vinegar solution, and try the experiment again.
Design Your Own Experiment How to Select a Topic Relating to this Concept
Our everyday lives rely heavily upon batteries and electricity. Other aspects of this topic you might find valuable for exploration are rechargeable cells, photovoltaic cells, and the relationship between electrolytes and our bodies’ functions. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on electricity questions that interest you. Electricity and electric currents can be dangerous. Before you conduct an electricity experiment or project, always check with an adult. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Recording Data and Summarizing the Results In the experiments
included here and in any experiments you develop, you can look for 346
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ways to make your data displays more accurate and interesting. For example, in the lemon experiment, try displaying the data from your chart in graph form. Remember that those who view your results may not have seen the experiment performed, so you must present the information you have gathered in as clear a way as possible. Including photographs or illustrations of the steps in the experiment is a good way to show a viewer how you got from your hypothesis to your conclusion. Related Projects Simple variations on the experiments and project in this
section can prove valuable and informative. Some solids, for example, will act as electrolytes when melted. Find out which. Will an electrolytic solution work as efficiently when it is chilled in an ice bath? Figure out why or why not.
For More Information Andrew Rader Studios. ‘‘Electricity and Magnetism.’’ Rader’s Physics4kids.com. http://www.physics4kids.com/files/elec intro.html (accessed on February 9, 2008). Basic information on electricity and magnetism. Energy Information Administration. ‘‘Electricity: A Secondary Energy Source.’’ Energy Kid’s Page. http://www.eia.doe.gov/kids/energyfacts/sources/ electricity.html (accessed on February 12, 2008). Explanation of electricity includes information on static electricity. Macaulay, David, and Neil Ardley. The New Way Things Work. Boston: Houghton Mifflin, 1998. Detailed description of how machines work, including those that use electricity and magnetism. McKeever, Susan, ed. The DK Science Encyclopedia. New York: DK Publishing, Inc., 1993. Contains informative entries on current, batteries, and circuits, as well as a number of good ideas for projects and demonstrations. Ray, C. Claibourne. The New York Times Book of Science Questions and Answers. New York: Doubleday, 1997. Addresses both everyday observations and advanced scientific concepts on a wide variety of subjects.
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Electromagnetism
E
lectromagnetism is the energy produced by an electric current moving through a metal core. To understand electromagnetism, you need to understand the basics of electricity.
What is electricity? Electricity is produced by the movement of electrons. Atoms usually have a balanced or neutral electrical charge, with an equal number of electrons (with a negative charge) and protons (with a positive charge). However, some electrons can be removed from atoms, creating an imbalance. The atoms that lost electrons become positively charged, while the atoms that received electrons become negatively charged. When the charge between two objects is unbalanced, the extra electrons on the negatively charged object are drawn toward the positively charged object in order to balance the charges again. This movement of electrons is electricity. How can electricity create a magnet? Objects with like charges (positive-positive or negative-negative) repel or push each other away,
The electromagnetic wavelength is the distance between the wave’s highest points, or peaks. GA LE G RO UP.
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The electromagnetic spectrum. GAL E GR OU P.
A magnetic resonance imaging (MRI) machine uses electricity and magnetism to create clear pictures of internal organs. PH OT O RE SEA RC HE RS I NC.
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while objects with opposite charges (positive-negative) attract each other. A magnetic field can be produced by using electric charges to create attracting or repelling forces. For example, scientists discovered that when a wire is coiled around a piece of iron, and electric current flows through the wire, the iron becomes magnetized—an electromagnet. Electromagnetic waves are everywhere When the force of a magnetic field alternates direction, first attracting and then repelling, it produces an electromagnetic wave that radiates away from the source. A wave of any kind can be described by two numbers: its wavelength and its frequency. The wavelength is the distance between the wave’s highest points, or peaks. The frequency is the number of those peaks that pass any point every second. Like other kinds of waves, electromagnetic waves carry energy at different frequencies, from very low (such as radio waves) to very high (such as gamma rays). X-rays, microwaves, and visible light are all kinds of electromagnetic radiation. The electromagnetic spectrum contains all these frequencies. The study of electromagnetism is the study of the relationship between electricity and magnetism. The principles behind electromagnetism are used in electric motors and generators, televisions, diagnosis of illnesses, and in many other parts of our lives. Experiment Central, 2nd edition
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WORDS TO KNOW Atom: The smallest unit of an element, made up of protons and neutrons in a central nucleus surrounded by moving electrons. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment. Electricity: A form of energy caused by the presence of electrical charges in matter. Electromagnetic spectrum: The complete array of electromagnetic radiation, including radio waves (at the longest-wavelength end), microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays (at the shortest-wavelength end).
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Magnet: A material that attracts other like materials, especially metals. Magnetic field: An area around a magnet where magnetic forces act. Peaks: The points at which the energy in a wave is maximum. Proton: A subatomic particle with a single negative electrical change that is found in the nucleus of an atom. Radiation: Energy transmitted in the form of electromagnetic waves or subatomic particles.
Electron: A subatomic particle with a single negative electrical change that orbits the nucleus of an atom.
Wave: A means of transmitting energy in which the peak energy occurs at a regular interval.
Electromagnetism: A form of magnetic energy produced by the flow of an electric current through a metal core.
Wavelength: The distance between the peak of a wave of light, heat, or other form of energy and the next corresponding peak.
Frequency: The number of times a wave peak passes a given point every second.
Variable: Something that can affect the results of an experiment.
Exploring with magnets and electricity can be fascinating. Do you have questions about electromagnetism? You might be able to answer them by performing the following experiments.
EXPERIMENT 1 Magnetism: How can a magnetic field be created and detected? Purpose/Hypothesis In this experiment, you will demonstrate the relation-
ship between electricity and magnetism and create and detect magnetic fields. Magnetic fields are all around us and are easy to create. Before you begin, make an educated guess about the outcome of this experiment based Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the direction of the wire
on your knowledge of electricity and magnetism. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
• the magnetization of the needle
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove In other words, the variables in this experiment or disprove whether your hypothesis is correct. are everything that might affect the movement of Here is one possible hypothesis for this experithe needle. If you change more than one variable, you will not be able to tell which variable had the ment: ‘‘A magnetized needle will point perpenmost effect on the movement of the needle. dicularly through a charged wire, showing where the magnetic field produced by the wire lies.’’ In this case, the variable you will change will be the magnetism of the needle, and the variable you will measure will be the movement of the needle. You expect the needle to be perpendicular to the wire. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental condition, and that will be the magnetization of the needle. For the control, you will not magnetize the needle. Then you will be able to compare the movement of a magnetized and unmagnetized needle. If only the magnetized needle points perpendicular to the wire, your hypothesis will be supported. • the direction of the current
How to Experiment Safely
Level of Difficulty Moderate. Materials Needed
Any time you are experimenting with electricity, follow the directions exactly. The levels of electricity here are very low and cannot really hurt you, but electricity can always give you a shock if you are not extremely careful. Handle only wires covered with insulation, keep water away from the experiment, and keep your hands dry as you work. Do not use a vehicle battery. It is much too powerful and can cause a serious shock, or may even explode.
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• approximately 8 feet (2.4 meters) of 18-to 24-gauge insulated wire • 2 metal sewing needles • thread • permanent magnet • 6-volt lantern battery • tape • paper • scissors Experiment Central, 2nd edition
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Approximate Budget $20. Timetable 2 hours. Step-by-Step Instructions
1. Magnetize the needle: Rub one side of the permanent magnet against the needle at least 30 times, always in the same direction. 2. Cut the paper into the shape of an arrow and stick the magnetized needle into the arrow lengthwise as illustrated. 3. Tape the thread to the top edge of the arrow. 4. Make a loop of wire about 3 inches (7.5 centimeters) in diameter. Continue to wrap the wire around this original loop, making a coil of five loops. Leave a length of wire free at either end. 5. Use the thread to tie the wire loops together tightly. 6. Then tie your paper arrow to the top of the loop. It should hang freely in the center of the loop. 7. Attach one end of the wire to each terminal of your battery—one to the positive terminal and one to the negative terminal. 8. Carefully observe the paper arrow. 9. Move the wire loop in different directions and watch what happens to the arrow. 10. Repeat the procedure with the other needle, but without magnetizing it. What do you observe?
Step 2: Cut paper into the shape of an arrow and stick the magnetized needle into the arrow lengthwise. GA LE G RO UP.
Steps 4 to 7: Wire loop set-up. GAL E GR OU P.
Summary of Results Record your observations.
Where did the arrow point? What does that tell you about the location of the magnetic field produced by the electric current flowing through your wire loops? Was your hypothesis correct? Change the Variables You can vary this experi-
ment in several ways. Try reversing the direction Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, some possible causes, and ways to remedy the problem. Problem: The arrow is not affected when the wire loop is attached to the battery. Possible causes: 1. The wires are not tightly connected to the battery. Check your connections and try again. 2. Your needle is not magnetized well enough. Pull it out of the arrow and rub your magnet across it a number of times. Be sure to rub it in only one direction with only one pole of the magnet.
of the electric current by attaching the wires to the opposite terminals. Where does the arrow point now? You should find that the direction of the magnetic field depends on the direction of the electric current. You can also use different kinds of batteries with different voltages. See what effects they have on your magnetized needle, if any. Warning! Do not use a vehicle battery.
EXPERIMENT 2 Electromagnetism: How can an electromagnet be created? Purpose/Hypothesis Electric currents create
magnetic fields. When you increase the strength of the current, you increase the strength of the 3. You do not have enough loops of wire. magnetic field. In this experiment, you will demTry looping some more wire around your onstrate this by building an electromagnet and original loop. observing the movement of electric charges. 4. Your battery is dead. Replace it and try Before you begin, make an educated guess about again. the outcome of this experiment based on your knowledge of electricity and magnetism. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Step 1: Loop wire loosely once around the nail. G ALE G RO UP.
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The more wire you wrap around a nail attached to a battery, the stronger the nail’s magnetism and the more objects it can pick up.’’
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In this case, the variable you will change is the amount of wire wrapped around the nail, and the variable you will measure will be the number of objects it will pick up. You expect that by adding turns of wire you will be able to pick up more objects. Level of Difficulty Easy. Materials Needed
• several feet (about 1 meter) of insulated wire • 6-volt lantern battery • large nail or bolt • permanent magnet • supply of metal paper clips Approximate Budget $20. Timetable Two hours to build and test. Step-by-Step Instructions
1. As your control experiment, loop the wire loosely once around the nail. 2. Attach either end of the large wire loop to the battery’s terminals. 3. Place a pile of paper clips on the table. 4. Touch the nail to the paper clips. Record how many it picks up on a data sheet similar to the one illustrated. 5. Remove the nail and wire from the battery. Beginning at one end of the nail, wrap several tight loops around it, all in the same direction. Record the number of loops you wrap. 6. Again attach the end of the wire to the battery terminal. Touch the nail to the paper clips, and record how many stick to it. Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the strength of the magnet • the number of wire coils around nail • the size of the nail • the weight of the objects In other words, the variables in this experiment are everything that might affect the number of objects that the electromagnet can pick up. If you change more than one variable, you will not be able to tell which variable had the most effect on the strength of the magnet. Only one variable will change between the control experiment and the experimental condition, and that is the number of wire coils around the nail. The control will have only one wire coil. You will count how many paper clips your magnet is able to pick up as you add coils. If increasing the number of coils increases the number of objects it can pick up, your hypothesis was supported.
How to Experiment Safely As with any project dealing with electricity, be extremely careful with wires and batteries. Keep everything away from water and keep your hands clean and dry. Do not use a vehicle battery. It is much too powerful and can cause a serious shock or may even explode.
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and ways to remedy the problem. Problem: The electromagnet will not pick up any paper clips. Possible causes: 1. The wire connections are not tight enough on the battery terminals. Check them and tighten. 2. You do not have enough loops around your nail. Try adding more in the same direction. 3. Your paper clips are too big for the strength of the magnet. Try using smaller paper clips or thumbtacks. 4. Your nail or bolt is dirty or not made of iron or steel. Try a different nail or bolt.
7. Wrap more wire loops in the same direction. Attach the wire to the battery again and try picking up clips. 8. Repeat several times with more loops every time. Keep recording how many loops you wrap around the nail and how many clips it picks up. Summary of Results Study the results on your
data sheet. Did more loops create a stronger magnetic field? How could you tell? Was your hypothesis correct? Summarize what you have discovered. Change the Variables You can vary this experi-
ment. For example, try using a different kind of material for your magnet, such as wood or plastic. What happens? What can you conclude? Or try a much larger or smaller metal object as a magnet. What is the effect on the number of objects that the magnet can pick up?
Step 4: Data sheet for Experiment 2. GAL E GR OU P.
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You can also change the wire. Try thinner or thicker wire. What effect does that have on your magnetic field? Try using different kinds of batteries, with smaller and larger voltages. What is your hypothesis about what will happen to the magnetic field? Warning! Do not use a vehicle battery. Finally, you can experiment with different objects to pick up, smaller, larger, or made of different materials. What do you predict will happen?
Design Your Own Experiment How to Select a Topic Relating to this Concept Are you interested in
further exploring kinds of magnets, magnetic fields, and their relation to electric currents? Perhaps you would like to build your own electric motor, investigate static electricity, or explore how electromagnetism is used in generating electricity, computer memory, television images, and many other facets of electrical engineering. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on electromagnetism questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise you may not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
The electromagnet in this electric bell generates a current that activates the bell. PE TER ARN OL D IN C.
Recording Data and Summarizing the Results
Your data should include charts, such as the one you did for these experiments. They should be Experiment Central, 2nd edition
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clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental set-up and results. If you are preparing an exhibit, display the devices you create to help explain what you did and what you discovered. Observers could even test your magnets. If you have done a nonexperimental project, explain clearly what your research question was and illustrate your findings. We depend on electric motors, which depend on electromagnetism. PE TER AR NO LD I NC.
Related Projects In addition to experimental projects, you could build motors and large magnets that produce currents to light up a lamp or run an appliance. Or you could investigate the many uses of electromagnetism, especially the field of medicine. There are many possibilities!
For More Information Andrew Rader Studios. ‘‘Moving Electrons.’’ Rader’s Physics4kids.com. http:// www.physics4kids.com/files/elec intro.html (accessed on January 13, 2008). Steve, Parker. Electricity and Magnetism. Milwaukee, WI: Gareth Stevens Publishing, 2007. Tomecek, Stephen M. Electromagnetism, and How It Works.New York: Chelsea House, 2007. Whalley, Margaret. Electricity and Magnetism. Chicago: World Book, 1997. Introduces basic principles of electricity and magnetism through experiments and activities. Wood, Robert, and Bill Wright. Electricity and Magnetism Fundamentals: Funtastic Science Activities for Kids. Philadelphia: Chelsea House Publishing, 1998. Through several different activities the relationship between electricity and magnetism is demonstrated.
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Enzymes
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ou could not run a race or digest food without enzymes. Actually, you could not grow up without enzymes working in your body. Present in all living things, enzymes are catalysts, that is, little chemical spark plugs that activate some 1,000 to 2,000 reactions in each cell. Enzymes control the way our bodies work. They help other life forms function as well. For example, the silkworm cannot break out of its cocoon without enzymes. A hunk of meat, a hawk, and a discovery Rene Antoine de Reaumur was a French scientist who wanted to know how food was digested. In 1750, he tried a unique experiment. Tying a very tiny metal cage containing a small piece of meat on a long string, he taught his pet hawk to swallow the cage. The string hung out of the bird’s mouth, and de Reaumur very carefully pulled out the cage after 15 minutes without injuring the animal. The meat did not look the same. Its color was gone and it looked puffy and soft. He tried the experiment two more times, leaving the cage inside longer. The meat was totally soft after one hour, and after three it looked like lumpy soup. De Reaumur did not know he had witnessed the work of enzymes, but his experiments gave other scientists the first clue about their existence and function. What’s in a name? The word enzyme comes from two Greek words meaning ‘‘in yeast.’’ German scientist Willy Kuhne came up with the term in 1876. Kuhne noticed that the yeast used to make bread acted as a catalyst, producing a chemical reaction. Once added to the dough in the bread-making process, yeast splits into sugar molecules. They, in turn, produce alcohol and carbon dioxide. Carbon dioxide gas bubbles trapped in the dough cause it to rise. Kuhne reasoned that yeast was a catalyst for this new chemical compound, so he used the word enzyme to describe other catalysts. 359
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Enzymes in yeast help make beer. CO RB IS. Yeast is the catalyst that caused this bread to rise. C OR BI S CO RP ORA TI ON.
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Based on the work of de Reaumur and others, Kuhne understood that digestive juices were also catalysts, because they caused a reaction that broke food down into a simpler form. Catalyst is actually a Swedish word that means ‘‘to break down.’’ Pepsin was the first enzyme prepared from animal tissue. Extracted from the lining of the stomach, it aids digestion. Pepsin is actually a Greek word meaning ‘‘to digest.’’ Later it was discovered that enzymes could work outside the living cell, which made them more useful to scientists. As simple as a lock and key There are thousands of different enzymes in each cell. Each enzyme is responsible for a single reaction within the cell, and the process works like a lock and key. As the key, each enzyme has a specific shape. It targets a specific substrate, the substance on which the enzyme does its work. This substrate, which matches the shape and size of the enzyme, is the lock. Each enzyme can only work with one substrate or, at most, a small number of chemically related substrates. After the substrate and enzyme come together, a new compound is activated and formed. The study of how an enzyme behaves is called enzymology. Enzyme industry By-products of animals slaughtered for meat provide animal enzymes, but no animal is raised just for enzymes. Rennin, an enzyme in the stomach lining of slaughtered calves, is used to make cheese. Plants provide other enzymes. Papain, an enzyme from the fruit of the papaya tree, helps digestion. It also tenderizes meat and is used as an antibacterial cleaner for bad wounds. Enzymes are also chemically produced in factories. Remember the yeast Kuhne observed? Yeast has an enzyme that not only helps to make bread but also activates the process of making beer and wine. The yeast is grown in large tanks. When it Experiment Central, 2nd edition
Enzymes
WORDS TO KNOW Catalase: An enzyme found in animal liver tissue that breaks down hydrogen peroxide into oxygen and water. Catalyst: A compound that starts or speeds up the rate of a chemical reaction without undergoing any change in its own composition.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Papain: An enzyme obtained from the fruit of the papaya used as a meat tenderizer, as a drug to clean cuts and wounds, and as a digestive aid for stomach disorders.
Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group.
Pepsin: Digestive enzyme that breaks down protein.
Decomposition: The breakdown of complex molecules into simple molecules.
Reaction: Response to an action prompted by stimulus.
Denaturization: Altering an enzyme so it no longer works.
Rennin: Enzyme used in making cheese.
Enzymes: Any of numerous complex proteins produced by living cells that act as catalysts. Enzymology: The science of studying enzymes.
Protein: A complex substance consisting of a long chain of molecules linked together. It is produced and used by living cells to perform various functions.
Substrate: The substance on which an enzyme operates in a chemical reaction. Variable: Anything that might affect the results of an experiment.
Chemical formula showing hydrogen peroxide broken down by enzymes into water and oxygen. GAL E GR OU P. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • Tissue freshness—use only fresh, raw materials, nothing cooked or frozen. • Tissue temperature—all materials should be at room temperature. • Tissue quantity—this experiment will tell you how much plant and animal tissue is to be used and how to process it. In other words, the variables in this experiment are everything that might affect the chemical reaction of the materials with the hydrogen peroxide. If you change more than one variable, you will not be able to tell which variable had the most effect on the chemical reaction. Alterations may change the rate of the reaction or result in the denaturization of the enzymes.
starts producing enzymes, they are removed. Other enzymes produced by bacteria are used in some laundry products to help break down stains. Life processes cannot function without enzymes. Conducting experiments will help you become familiar with these important molecules.
EXPERIMENT 1 Finding the Enzyme: Which enzyme breaks down hydrogen peroxide? Purpose/Hypothesis Without enzymes, many
chemical reactions do not take place. In this experiment you will identify the presence of an enzyme in liver tissue, known as catalase, that breaks down highly reactive hydrogen peroxide into harmless water and oxygen. This is an important chemical reaction that takes place inside the body. Catalase prevents the potentially destructive oxidation effects of any hydrogen peroxide that may be generated in the body as the result of various other chemical reactions. To begin this experiment, use what you know about enzymes to make an educated guess about how the enzymes in liver tissue will affect hydrogen peroxide. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Animal liver tissue contains the enzyme that breaks down hydrogen peroxide.’’ 362
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In this case, the variable you will change is the material being tested, liver in one cup and potato in another cup, and the variable you will measure is the presence of oxygen bubbles. Your cup filled with water will serve as a control experiment to allow you to observe any oxygen bubbles that might be produced without the presence of hydrogen peroxide. If the liver sample reacts with hydrogen peroxide and produces oxygen bubbles and the water sample does not, you will know your hypothesis is correct.
How to Experiment Safely Wear goggles when handling hydrogen peroxide. If you accidentally get some on your skin, wash it off quickly. Also be careful not to get it near your eyes, ears, nose, or mouth. You will be handling raw meat, so you must carefully wash all surfaces before and after the experiment. Do not eat the meat after the experiment.
Level of Difficulty Easy/moderate. Materials Needed
• 1 small piece of liver—fresh, never frozen or cooked • 1 potato—fresh, never frozen or cooked • hydrogen peroxide • 4 clear cups—plastic or glass • knife • spoon or lab spatula • water • goggles • labels
Sample recording chart for Experiment 1. GA LE G ROU P. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
Approximate Budget Less than $10 for hydrogen peroxide, potato, and liver. Timetable Approximately 20 minutes. Step-by-Step Instructions
1. Cut a 0.5-inch (1.25-centimeter) cube of liver and smash it into a paste using a Possible cause: The materials may be too old. spoon. Place it in a cup. Check the freshness of the tissue samples as 2. Smash another 0.5-inch (1.25-centiwell as of the hydrogen peroxide. Hydrogen peroxide needs to be stored in a dark bottle and meter) cube of liver into a paste. Place it capped at all times. into a separate cup. (Don’t forget to clean the spoon.) 3. Cut a 0.5-inch (1.25-centimeter) cube of potato and smash it. Place it in a separate cup. 4. Smash another 0.5-inch (1.25-centimeter) cube of potato and place it in the last cup. 5. Label the cups: a. Cup 1: Liver and water b. Cup 2: Liver and hydrogen peroxide c. Cup 3: Potato and water d. Cup 4: Potato and hydrogen peroxide Problem: Nothing happened in any of the cups.
Steps 5 to 7: Set-up of control and test cups. GAL E GR OU P.
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6. Fill cups 1 and 3 halfway with water. These will serve as your control experiment. 7. Fill cups 2 and 4 halfway with hydrogen peroxide. These will test which material has the enzyme. 8. Observe what takes place. If the enzyme for the breakdown of hydrogen peroxide is present, oxygen will form bubbles. When hydrogen peroxide breaks down, it separates into water and oxygen. 9. Record your results.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of meat—only beef from a steak or filet should be used. • the type of tenderizer or enzyme—use the natural tenderizer extracted from the papaya fruit. • the amount of tenderizer used.
Summary of Results Make a chart like the one
illustrated to show what you observed. Determine which tissue has the enzymes that cause the breakdown of the hydrogen peroxide into water and oxygen. Was it the tissue you predicted in your hypothesis? Change the Variables You can change the variables and conduct a similar experiment. For example, place the pieces of liver and potato in the refrigerator to see if temperature affects the action of the enzyme.
• the temperature—the control and experimental meat must both be aged in the refrigerator. • the amount of time the tenderizer is in place on the beef. In other words, the variables in this experiment are everything that might affect the degree of decomposition of the beef. If you change more than one variable, you will not be able to tell which variable had the most effect on the decomposition process.
EXPERIMENT 2 Tough and Tender: Does papain speed up the aging process? Purpose/Hypothesis This experiment deals with the aging process of beef.
The older or more aged meat is, the softer the meat tends to be. This is a natural process of decomposition, the breakdown of organic matter. Beef can take weeks to become tender, but a natural tenderizer called papain can speed up the process. Papain is an enzyme extracted from the papaya fruit. To begin the experiment, use what you know about enzymes to make an educated guess about how papain will affect the aging process of beef. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change Experiment Central, 2nd edition
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• the variable you will measure • what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether you hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Beef will age faster if it is sprinkled with papain.’’ In this case, the variable you will change is whether papain tenderizer is used on the beef, and the variable you will measure is the appearance of the meat after 24 hours. If the meat with the tenderizer is more decomposed, you will know your hypothesis is correct.
In this experiment you will handle raw meat, so you must carefully wash all surfaces before and after the experiment. Do not eat the meat after the experiment. Be careful not to get meat tenderizer in your eyes.
Level of Difficulty Easy/moderate. Materials Needed
• beef from a steak or filet—8 to 10 ounces (230 to 250 grams) is sufficient • Adolph’s All Natural Tenderizer, a natural tenderizer made from papaya • 2 plastic storage containers with lids
Step 2: Sprinkle about ½ teaspoon of meat tenderizer on one steak, leaving the other to age naturally. GAL E GR OU P.
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• • • • •
measuring spoons toothpicks slides microscope stain (optional—congo red or methalene blue)
Note: Do not add any additional solutions to the meat. For example, vinegar may stop the enzyme process. Approximate Budget About $15. (Price of beef
will vary. You can borrow a microscope from a friend or use one in school.)
Step 5: After the storage period, use a clean toothpick to scratch the surface of the meat without the tenderizer. G AL E GR OUP .
Timetable About 24 hours—10 minutes to set up the experiment and
30 minutes to view the results; the rest is storage time in the refrigerator. Step-By-Step Instructions
1. In two plastic containers, place equal amounts of beef steak. 2. Sprinkle about ½ teaspoon of meat tenderizer on one steak. 3. Seal both containers and mark the lid of the container with the tenderized steak ‘‘Tenderizer.’’ 4. Place both containers in the refrigerator and leave for 24 hours. 5. After the storage period, use a clean toothpick to scratch the surface of the meat without the tenderizer.
Step 7: Slide views of naturally aged and tenderized meat cells. GA LE G RO UP.
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: You cannot see a difference in decomposition. Possible cause: Decomposition is not obvious at this point. Stain the cells. Cells that have not experienced decomposition have a nuclei inside. When decomposition takes place, the cell membrane is broken and the nucleus is released.
6. Wipe the toothpick onto a clean slide. (Add one drop of stain if you wish.) 7. View the slide under the microscope at 40 to 70 medium power. Record your results. 8. Repeat Steps 5 to 7 for the piece of meat with the tenderizer. Summary of Results Reflect on your hypothesis.
The goal was to cause an increase in decomposition of meat (speed up the aging process to make the meat tender). Was your hypothesis correct? This should be evident in large amounts of decayed cells. Is it true? Did more cells decay with tenderized meat? Write a summary of your findings.
Change the Variables You can change the variables and conduct similar experiments. For example, you can vary the amount of tenderizer used to see if that changes the degree of decomposition. You can also change the amount of time for the experiment to 36 or 48 hours.
EXPERIMENT 3 Stopping Enzymes: Does temperature affect enzyme action? Purpose/Hypothesis Enzymes are a type of protein. And, like all pro-
teins, enzymes function best at certain temperatures. If the temperature is too low or too high, the enzyme’s structure can change and it will not be able to activate a reaction. In this experiment, you will explore how temperature affects the activity of one particular enzyme. The enzyme you will use is bromelain, which is found in pineapple. Bromelain breaks down proteins. The protein you will use is gelatin. Gelatin is a form of protein called collagen How to Experiment Safely that is found in our bones. As you prepare the gelatin, you will add broThis experiment involves heating pineapple melain-rich pineapple juice, prepared at different juice over a stove or hot plate. Have an adult temperatures. You will heat the bromelain and present when heating the juice. Also, if the freeze the bromelain. Adding small items to the pineapple is purchased whole, have an adult cut gelatin, such as peas, will help you measure the the pineapple into chunks. activity of the enzyme. You can determine if the 368
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bromelain is active by measuring if the gelatin sets. If the gelatin remains in a liquid or partial liquid form, the proteins were broken apart and the food items will not sit firmly in the gelatin. To begin the experiment, use what you know about enzymes to make an educated guess about how temperature will affect the activity of bromelain. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether you hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Heating bromelain will cause it be inactive and allow the gelatin to set.’’ In this case, the variable you will change is the temperature the bromelain is prepared, and the variable you will measure is the appearance of the gelatin and placement of the added items. If the gelatin mixed with the heated bromelain becomes firm, then you will know your hypothesis is correct.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of gelatin • the amount of gelatin used • the bromelain—use the bromelain from the same pineapple • the amount of pineapple juice used • the amount of time the gelatin is allowed to set In other words, the variables in this experiment are everything that might affect the degree to which the gelatin sets. If you change more than one variable, you will not be able to tell which variable had the most effect on the gelling. You will need two controls in this experiment. The first control is the gelatin by itself so that you can observe that it sets firmly. The second control is the gelatin mixed with pineapple juice that is prepared at room temperature. The pineapple juice gelatin will allow you to observe how temperature affects the bromelain in the experimental trials. If the heated pineapple juice sets similar to the gelatin without pineapple juice, than you will know your hypothesis is correct.
Level of Difficulty Moderate. Materials Needed
• pineapple with skin removed and sealed in its juice; or 1 fresh pineapple (do not use canned or frozen pineapple) • 4 glasses (they can be plastic) • 3 small containers for the pineapple juice • gelatin; enough to make 2 cups • measuring cups and spoons • marking tape and pen Experiment Central, 2nd edition
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• hot plate or stove • small pan • 5 tablespoons of small, light food items, such as peas, corn, rice, blueberries or dried cranberries • mixing spoon • tablespoon • freezer or cold water bath (ice cubs and a bowl) Approximate Budget About $8, assuming all
household items are available. Step 2: squeeze 4 tablespoons of pineapple juice into a small container. I LL UST RA TI ON BY T EM AH NE LS ON.
Timetable About two hours—six hours (including waiting time) to prepare and analyze the experiment; the rest is waiting time while the gelatin sets. Step-By-Step Instructions
1. Label the four glasses: ‘‘Gelatin Control,’’ ‘‘Gelatin Bromelain Control,’’ ‘‘Hot Bromelain,’’ ‘‘Cold Bromelain,’’ 2. Pour or squeeze 4 tablespoons of pineapple juice into a small container, label the container ‘‘Cold Bromelain.’’and place in the T EM AH NE LS ON. freezer. You could also place the container in a cold water bath (a container filled with ice cubes and cold water). Allow the juice to freeze for an hour. 3. While the bromelain is freezing, squeeze or pour 5 tablespoons of pineapple juice in a small pan and simmer for at least three minutes. You will need 4 tablespoons of pineapple juice after it has simmered. After three minutes, set the pan aside. hot bromelain 4. After one hour, take the juice out of the freezer and allow to come to room temperature. 5. While you are waiting, prepare 2 cups of the gelatin.
Step 9: In the glass labeled ‘‘Hot Bromelain,’’ add 4 tablespoons of the pineapple juice that was heated. I LL UST RA TI ON BY
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hot bromelain
gelatin control
gelatin bromelain control
cold b romelain
Step 14: When the control gelatin is firm, remove all the glasses from the refrigerator. Gently shake each of the glasses and note the results. IL LU STR AT IO N BY TE MA H NE LSO N.
6. Pour a half cup of gelatin into each of the four glasses. Remove 2 tablespoons of the gelatin from each of the glasses. 7. In the glass labeled ‘‘Gelatin Bromelain Control,’’ mix in 4 tablespoons of room temperature pineapple juice. This is one of your controls. 8. In the glass labeled ‘‘Gelatin Control,’’ mix in 4 tablespoons of water. This is your second control. 9. In the glass labeled ‘‘Hot Bromelain,’’ add 4 tablespoons of the pineapple juice that was heated. Make sure to use a clean spoon. 10. In the glass labeled ‘‘Cold Bromelain,’’ stir in the pineapple juice that was cooled. 11. Set all the containers in the refrigerator and check on them in about 30 minutes. 12. While the gelatin is in the refrigerator, prepare the food item you want to add. Make sure it is clean and dry. If you are adding blueberries, for example, they should be thawed and patted dry with a paper towel. 13. When the control gelatin, labeled ‘‘Gelatin,’’ is thickened, add 1 tablespoon of the blueberries or whatever item you choose to all four of the gelatin glasses. Return them to the refrigerator and wait about another two hours. 14. When the control gelatin is firm, remove all the glasses from the refrigerator. Gently shake each of the glasses and note the results. Summary of Results Shake each of the gelatin glasses gently. Is the gelatin
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: All of the gelatins became firm. Possible cause: The pineapple you used may have been treated at some point, which may have deactivated the bromelain. Try the experiment again, and make sure to use fresh pineapple. Problem: None of the gelatins became firm. Possible cause: The time the gelatin takes to set depends on the temperature in the refrigerator. You may not have allowed enough time for the gelatins to set. Repeat the experiment, doubling the time in the refrigerator. Possible cause: The gelatin you purchased may not be good. Buy another package of gelatin and repeat the experiment.
without bromelain? Was your hypothesis correct? Did freezing the bromelain make any difference? Look at where the blueberries (or whatever item you used) is sitting in the gelatin, compared to the control gelatins. Are they set in the gelatin or did more of them sink towards the bottom of the glass? In the gelatin made without bromelain, the blueberries should be firmly set in the gelatin. Which control do each of the two trials resemble more closely? You can draw your results and write a summary of your findings. Change the Variables There are several ways that
you can change the variables in this experiment. You can try to stop the enzyme activity by altering the acidity (the pH) of the enzyme. You can also change the amount of time the pineapple juice is heated or cooled. What happens if you heat and cool the juice multiple times? You can also try altering the enzyme or source of the enzyme. Bromelain is the main ingredient in many meat tenderizers. Laundry detergents contain different enzymes.
Design Your Own Experiment How to Select A Topic Relating to this Concept Enzymes and the
chemical reactions they produce are all around you. If you can identify one reaction, you have a start. Once you discover a chemical reaction, find out what is taking place. For example, the solid food you eat is turned into other substances by enzymes. What exactly are those enzymes? What do they do? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on enzyme questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of the materials or processes might be dangerous. 372
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Steps in the Scientific Method To do an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Photos, illustrations, and
graphs are great visuals. Make clear the beginning question, the variable you changed, the variable you measured, the results, and your conclusion. Label everything clearly and show how it fits together. Related Projects Try changing the conditions of the enzyme reactions.
For example, add vinegar to the hydrogen peroxide. Or cook the liver and potato before testing.
For More Information Brain, Marshall. ‘‘How Cells Work.’’ HowStuffWorks. http:// science.howstuffworks.com/cell2.htm (accessed on February 16, 2008). Explanation of how enzymes work in cells. The Dorling Kindersley Science Encyclopedia. New York: Dorling Kindersley, Inc., 1993. Contains several well illustrated chapters such as ‘‘Catalysts,’’ ‘‘Digestion,’’ and ‘‘Chemistry of the Body’’ that discuss enzymes. Dr. Saul’s Biology in Motion. Enzyme Characteristics. http:// biologyinmotion.com/minilec/wrench. html (accessed on February 16, 2008). Brief explanation with interactive graphic of enzymes. Lopez, D. A. Enzymes: The Fountain of Life. Neville Press, 1994. Provides examples of how enzymes make our bodies work.
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oil erosion is the process by which topsoil is carried away by water, wind, or ice. Different types of soil have different abilities to absorb water, and so, are affected by erosion in varying degrees. Bare soil and soil on steep slopes are especially vulnerable to erosion.
During the Dust Bowl, winds blew away as much as 3 to 4 inches (8 to 10 centimeters) of topsoil, ruining farmland. PH OTO RE SEA RC HER S I NC.
Is erosion a new problem? Throughout history, people have been affected by soil erosion due to natural conditions, as well as erosion caused by their own actions. As long ago as 4500 B . C . E ,, the Sumerians cleared land to grow food. They irrigated the land by building canals in the fertile valley where the Tigris and Euphrates rivers meet (in present-day Iraq). During the time of the Babylonian culture, which followed the Sumerians in about 1800 B . C . E ., the people continued to dig canals. The rivers became muddy, and deposits of silt, medium-sized soil particles, settled in the irrigation canals and clogged them. The people had to carry silt out of the canals in baskets to keep the water flowing. Over time, the people began to neglect the canals. As silt filled the valley, the land could support fewer and fewer people. About 700 years ago, the Babylonian canals were finally destroyed by the invasion of the Mongols, and the land returned to desert. Is erosion a problem in the United States? Not long ago, in the 1930s, North American prairies suffered from extreme wind erosion. During a period of high rainfall, large expanses of land were plowed to grow wheat. This period was followed by years of drought. The exposed soil of the fields was blown away in hot, dry wind storms. The blowing soil of the Dust Bowl, as it was called, blackened the skies, ruined crops, and left farm fields bare and unproductive. 375
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WORDS TO KNOW Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Results from the control experiment are compared to results from the actual experiment. Drought: A prolonged period of dry weather that damages crops or prevents their growth. Ecosystem: An ecological community, including plants, animals, and microorganisms, considered together with their environment.
Inorganic: Not made of or coming from living things. Organic: Made of or coming from living things. Runoff: Water in excess of what can be absorbed by the ground. Silt: Medium-sized soil particles. Terracing: A series of horizontal ridges made in a hillside to reduce erosion.
Erosion: The process by which topsoil is carried away by water, wind, or ice action.
Topsoil: The uppermost layers of soil containing an abundant supply of decomposed organic material to supply plants with nutrients.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Variable: Something that can affect the results of an experiment.
On hillsides that no longer have tree roots to hold topsoil in place, rain easily carries the soil into the ocean. LI AI SO N AG EN CY.
Today we often hear about erosion. Satellite images show red earth spilling into the ocean off the coast of the island of Madagascar. Here, and in many other places where people clear tropical forests and grow crops on hillsides, extremely high rates of erosion carry away massive quantities of topsoil. It is important to understand why erosion occurs and how humans both cause it and are affected by it. Erosion is something that concerns everyone. Erosion affects the places where we live and our sources of food and water. It also affects our recreation areas—trails, beaches, lakes, and rivers. What kind of questions do you have about erosion? You’ll have an opportunity to explore the erosion process in the following experiments. You will also think about designing your own experiments to learn more about this natural phenomenon and how it can have a huge impact on our lives.
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EXPERIMENT 1 Erosion: Does soil type affect the amount of water that runs off a hillside? Purpose/Hypothesis In this experiment, you
will find out how the type of soil affects how much erosion can occur. Soil is a mixture of inorganic materials (rocks, sand, silt, or clay) and organic materials (decomposing leaves and organisms). The ratio of these components to each other determines the kind of soil and its texture. In turn, the texture of soil determines how well the soil can support plants and withstand erosion. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of soils and erosion. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of soil used • the slope of the soil • the rate at which you pour water on the slope In other words, the variables in this experiment are everything that might affect the amount of water and soil that run off. If you change more than one variable, you will not be able to tell which variable had the most effect on the runoff and erosion.
• the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The looser and coarser the texture of the soil, the less runoff and erosion will occur.’’ In this case, the variable you will change will be the texture of the soil, and the variables you will measure are the amount of water that runs off and the amount of soil it carries with it, judged by the color of the runoff water. You expect the looser and coarser soils to have less water runoff and less soil erosion. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental soil pans, and that variable is the kind of soil used. For the control, you will Experiment Central, 2nd edition
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How to Experiment Safely Wash your hands carefully after you handle soil, especially if you are using soil from outdoors. Be careful when digging to avoid broken glass or other trash in the soil.
use potting soil. For your experimental soil pans, you will use sand, clay, and neighborhood soil. You will measure the amount of water that runs off your soil pans and how much erosion occurs. If the looser- and coarser-textured soils have less runoff, your hypothesis is correct. Level of Difficulty Moderate, because of materi-
als needed. Materials Needed
• • • • • • • • • • • • • Steps 3 to 6: Set-up of soil ‘‘hillside.’’ GA LE GRO UP.
•
2 to 3 pounds (1 to 1.5 kilograms) of purchased potting soil 2 to 3 pounds (1 to 1.5 kilograms) sand 2 to 3 pounds (1 to 1.5 kilograms) clay 2 to 3 pounds (1 to 1.5 kilograms) neighborhood soil 4 shallow pans. Cookie sheets with 0.5 to 1.0 inch (1.25 to 2.5 centimeters) high edges work well. 4 glass jars, approximately 24 fluid ounces (680 milliliters) scrap lumber a sprinkler can or hose nozzle with mist setting water measuring cup labels outdoor area to conduct experiment, since it may be messy a baking dish, approximately 9 13 2 inches (23 33 5 centimeters) magnifying glass (optional) Approximate Budget $10 if soils must be
purchased. Timetable 2 to 3 hours. Step-by-Step Instructions
1. First, examine your soils. You may want to look at their particles with a magnifying glass. On your chart (see illustration) record your soils in the order of their textures, 378
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Steps 8 to 10: Labeled jars containing different types of soil run-off. GAL E GR OU P.
from coarse to fine. If you cannot see separate particles, then the texture is very fine. 2. Place your shallow pans in a row and place a different kind of soil in each one. Fill each pan evenly up to its edges all around.
Recording chart for Experiment 1. GA LE G RO UP.
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Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can definitely be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: Soil is sliding down the pans. Possible cause: The incline of your pans is too steep. Try lowering the support on which you are resting your pans. Problem: No water is running off. Possible cause: You are not using enough water for the amounts and kinds of soil you are using. Use more water, but be sure you use the same amount for all of your trials. Problem: All the runoff water is clear. Possible cause: Your soils are packed very tightly so no soil comes off with the water. Try stirring your soils a bit in their pans. But remember, even if the water is clear, it could still be carrying away nutrients instead of bringing those nutrients to plants that need them.
3. Prop one end of your potting soil pan on a board to simulate a hill. The exact slope is not important, but you must use the same slope for each pan. 4. Place the bottom end of the pan so it is resting in the baking dish. 5. Measure 3 cups of water into your sprinkler can. 6. Sprinkle the water over your ‘‘hillside,’’ mostly from the top edge, and watch what happens. 7. After the can is empty, wait 5 minutes. 8. Pour the water from the baking dish pan into a glass jar. Look at its color and measure how much you have collected. The darker the water, the more soil has run off. 9. Label the jar with the type of soil. 10. Repeat the procedure for sand, clay, and neighborhood soil. Summary of Results Record your results on a
chart like the one illustrated. Compare the amounts and colors of water in each jar. The darker the water, the more soil has run off in it. What have you discovered? Did coarser soils have less runoff? Was your hypothesis correct? Fill in your chart carefully and summarize what you found.
Change the Variables You can vary this experiment by changing the variables. For example, use soils from different areas of your neighborhood (near a stream, a park, a baseball diamond) or buy different kinds of potting soils from a plant-supply store. Or try mixing your soils. Just record how much of each kind you use in each mixture. You can also try propping up your plants at different slopes, such as 30 degrees, 45 degrees, 60 degrees, and so on. Using the same kind of soil and different slopes, run several more trials. What happens? How does slope affect erosion? 380
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EXPERIMENT 2 Plants and Erosion: How do plants affect the rate of soil erosion? Purpose/Hypothesis Soil is an important part of
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
an ecosystem. An ecosystem is a community of • the kind of soil used plants, animals, and microorganisms considered • the slope of the soil together with their environment. Because soil is • the rate at which you pour water on the the foundation for life on Earth, erosion can be a slope serious problem for the living beings that depend In other words, the variables in this experiment upon it—including humans. are everything that might affect the amount of In this experiment, you will explore how the water and soil that run off. If you change more rate of soil erosion is affected by plants growing than one variable, you will not be able to tell on the soil. Plant cover—either growing plants or which variable had the most effect on the runoff fallen leaves and branches—protects soil from and erosion. erosion by slowing down flowing water or absorbing the impact of rain drops. Roots of trees and other plants help to prevent erosion by holding the soil in place. Roots absorb water and provide stability to the soil. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of soils, plants, and erosion. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Less soil will erode from a hillside with plant cover (a layer of leaves or growing grass) than from a hillside with no plant cover.’’ In this case, the variable you will change is the amount of plant cover, and the variables you will measure are the amount of water that runs off and the color of the soil that runs off. You expect the looser and coarser soils to have less water runoff and soil erosion. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental Experiment Central, 2nd edition
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How to Experiment Safely Be careful when collecting fallen leaves or grass clippings, as broken glass or other trash might be in the leaves or grass. Wash your hands thoroughly afterward. If you collect soil from your neighborhood rather than using potting soil, use caution when collecting and handling the soil. Do not dig soil where you do not have permission to do so.
trays, and that variable is the presence or absence of growing plants or plant cover. For the control, you will use potting soil without any vegetation. For your experimental trays, you will use grass and leaf litter (leaves and/or grass clippings). You will measure how much erosion occurs in each of the trays by measuring water that runs off and comparing the color of the water. If the experimental trays show less erosion than the control tray, then your hypothesis was correct. Level of Difficulty Moderate, because of materi-
als and time required. Materials Needed
• • • • •
2 to 3 pounds (1 to 1.5 kilograms) purchased potting soil 1 to 2 pounds (0.5 to 1.0 kilograms) small gravel leaf litter (fallen leaves, twigs, and grass clippings) grass seed 3 shallow pans or trays (plant trays from a garden shop are designed to allow drainage; you may wish to use glass casserole dishes that allow you to observe the roots; otherwise, cookie sheets with edges will work.) • 4 glass jars, approximately 24 fluid ounces (680 milliliters) • a sprinkler can or hose nozzle with mist setting • water
Step 2: Set-up of Tray 1, Tray 2, and Tray 3 and their contents. GAL E GR OU P.
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Steps 5 to 8: Set-up of erosion ‘‘hillside.’’ G AL E GR OUP .
• labels • measuring cup • board or scrap lumber • an area with adequate light for growing grass • an outside area or other place for conducting the experiment, which may be messy • a baking dish, approximately 9 13 2 inches (23 33 5 centimeters) or a dish pan to collect water that runs off Approximate Budget $10 if soil and plant trays are purchased. Timetable Approximately two weeks. Step-by-Step Instructions
1. Prepare three trays by putting an equal amount of potting soil in each tray. If you are using pans or cookie sheets, spread a layer of gravel on the bottom of the pan before adding the soil. This will allow for drainage since you will be watering all three pans while the grass is growing. 2. Set Tray 1 aside. In Tray 2, cover the soil with a layer of leaves and grass clippings. In Tray 3, sprinkle grass seed on the top of the soil. Experiment Central, 2nd edition
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3. Place the three trays in a place where they are level and have similar light and temperature conditions. (The temperature must be above 50˚F (10˚C) for the grass to grow.) 4. Use the sprinkling can to give each tray the same amount of water. Continue watering all three trays approximately every 3 days until the grass in Tray 3 is about 0.5 inches (1.25 centimeters) tall. This may take one week or longer. You may have to adjust your watering schedule depending on how fast the soil dries. Check the soil daily to see if it looks and feels moist. 5. When the grass has grown, you are ready to do the erosion test. Prop the end of Tray 1 (soil only) on a board to simulate a hill. The exact slope is not important, but you must use the same slope for each tray. 6. Place the bottom end of the tray so it is resting in the baking dish or dish pan. 7. Measure 3 cups of water into the sprinkler can. 8. Sprinkle the water over your ‘‘hillside,’’ mostly from the top edge, and watch what happens. 9. When the can is empty, wait five minutes. 10. Pour the water from the baking pan into a glass jar. Look at its color and measure how much you have collected. 11. Label your jar (Tray 1: soil only).
Recording chart for Experiment 2. GAL E GR OU P.
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12. Repeat procedure for Tray 2 (soil with leaf litter) and Tray 3 (soil with grass). Be sure to label each jar so you can compare the quantity and color of the water. Summary of Results Record your results on a
chart like the one illustrated. When you have finished, compare the amounts and colors of water in each jar. The darker the water, the more soil has run off. What have you discovered? Did the trays with leaf litter and grass have less runoff than the control tray? Did the tray with grass have less runoff than the tray with leaf litter? Was your hypothesis correct? Fill in your chart carefully and summarize what you found. Change the Variables You can vary this experi-
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The grass did not grow. Possible cause: Perhaps there was too much or too little light or water, or the temperature was too cold or too hot. Adjust these conditions and plant some more grass seed. If this fails, try another kind of seed. Problem: Soil is sliding down the trays when they are inclined. Possible cause: The incline of your trays is too steep. Try lowering the support on which you are resting your trays.
ment by changing the variables. There are several Problem: No water is running off. possibilities. For example, you could cover the Possible cause: You are not using enough trays of soil with different amounts of leaf litter water for the amounts and kind of soil you are and compare the effect on erosion. When there is using. Use more water, but be sure you use the more leaf litter, is there less erosion? same amount for all of your trials. You could also try growing other types Problem: All the water is the same color. of plants. For instance, what is the difference Possible cause: The grass and leaf cover are not in the amount of runoff from a tray with thick enough to show a difference from the bean plants versus a tray with grass? You might control tray. Add more leaf litter to Tray 2 and try want to combine several types of plants. Some again. Add more grass seed to Tray 3 and conplants have extensive root systems, while other tinue watering all three trays until the grass grows plants have broad leaves. Which characteristic more thickly. Then try the erosion test again. seems to make a greater difference in preventing erosion? Another way to change the variables is to prop a tray at an angle and try terracing the soil (forming ‘‘steps’’ with the soil). If you plant grass on terraced soil, how does the amount of runoff compare with the amount from a tray of grass that was grown on one level? Modify the Experiment The effects of erosion can cause harm both to the soil itself and surrounding areas. Erosion can lead to nutrient loss in the Experiment Central, 2nd edition
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Many organisms live in the soil and are threatened by erosion. PH OT O RE SEA RC HE RS I NC.
soil. It can also lead to the spread of potential pollutants, such as fertilizers in runoff entering lakes. For a more advanced experiment, you can test how erosion may affect substances in the soil and waters. Purchase a soil test kit and fertilizer at a home gardening store. Some of the soil quality measures will most likely be nitrogen, phosphorus, and pH. Make sure the fertilizer you purchase contains phosphates and other substances that the soil test measures. Following the directions, add fertilizer to all the trays. Test each tray’s soil for each measure, including the pH. Follow the steps in the experiment. When you have completed the experiment, check both the runoff and each of the soils again. Note the results. Were there some substances that leached (were removed) more than others? If you want to continue to grow the grass after repeated runoffs, do you think that would alter the growth? Conduct some research and determine what the affect would be if the runoff was to enter lakes, streams, and oceans.
Design Your Own Experiment How to Select a Topic Relating to this Concept If you are interested in
erosion or its effects, you can create many fascinating experiments. For example, you could study the effects on erosion of different kinds of plants growing in the soil. How about the difference between the size or age of plants? Or the number of plants growing in one place? Or perhaps you are interested in the effects of human development (building) on erosion. What are the effects of concrete or pavement? What are the effects of deforestation or drainage of wetlands? Erosion can also be caused by wind or ice. What would happen if you blew a fan over different kinds of soils? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering 386
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information on erosion questions that interest you. You may also want to find out if there is an Agricultural Research Station or Cooperative Extension Office near you. If so, they can tell you about local erosion problems and projects. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts, such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental setup and results. If you are preparing an exhibit, you may want to bring in some of your actual results, such as jars of water or soil clearly labeled with their origins. If you have done a nonexperimental project, you will want to explain clearly what your research question was and provide illustrations of your findings. Related Projects You can design projects that are similar to these experi-
ments, involving trials and charts of data to summarize your results. You could also prepare a model that demonstrates a point you are interested in with regard to erosion or its effects. Or you could do an investigation into agricultural or building considerations that include erosion. You could do a research project on the environmental and ecological effects of erosion and present your findings in a poster or booklet. The possibilities are numerous. Experiment Central, 2nd edition
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For More Information Environmental Defense Fund Worldwide. http://www.environmentaldefense. org/home.cfm Current news relating to many environmental issues, including erosion. Giono, Jean. The Man Who Planted Trees. White River Junction, VT.: Chelsea Green Publishing Company, 1985. Story about a man who single handedly transformed his environment by planting trees over time. Temperate Forests. New York: Habitat Ecology Learning Program, Wildlife Conservation Society, 1995. Provides activities for learning more about trees and forests and humans’ impact on them.
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Ethnobotany
E
thnobotany is the study of how cultures use plants in their everyday lives. ‘‘Ethno’’ refers to cultures and ‘‘botany’’ refers to plants. Since the beginning of civilization, cultures have used plants in numerous ways, including for food, medicine, clothing, dyes, decoration, religious ceremonies, tools, and shelter. An ethnobotanist studies and often lives with cultures to fully understand how and why people incorporate native plants in their lives. An ethnobotanist is usually a botanist or biologist who has had additional training. Ethnobotanists can focus on one or more of the following specialties: archaeology, chemistry, linguistics (study of language), anthropology, ecology (study of how living things interact with one another), or pharmacology (study of medicines).
Plants as medicine Throughout history, cultures have used plants as a
source of medicine. Dating back over 5,000 years, the Sumerians describe using the plants laurel, caraway, and thyme for medicinal uses. The Chinese have long used herbs in healing practices. The first known Chinese herb book dates back from 2700 B . C . E . This book lists 365 plants and their uses. The Egyptians were known to bury their pharaohs with medicinal plants believing the plants would be useful to the deceased in the afterlife. The Egyptians used garlic, mint, coriander, and other herbs for medicinal purposes. Ancient Greeks and Romans also used plants for healing. In the first century, the Greek surgeon Dioscorides published a catalog of 600 plants in the Mediterranean. This illustrated book provided information on the medicinal use of the plant, how and when it was gathered, and whether it was poisonous or edible. This was one of the first books of its kind. During the Middle Ages and into the seventeenth century, plants continued to be widely used as a form of medicine. Herbal medicine books were published and translated into different languages. However, in the nineteenth century, with the rapid advances related to chemistry and 389
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other sciences, plants began to lose their importance in the world of medicine. Chemically synthesized (manufactured) drugs began to replace plants as a source of medicine in industrialized countries. In the late twentieth century there was a shift back to the appreciation of plants and their contributions to medicine. One way that people select plants that may fight human disease is to look at how plants protect themselves against disease and pests. Researchers look at those plants and then isolate and study the disease-fighting compounds plants produce. Many commonly used drugs are derived from plants, such as heart medications and aspirin. Pharmaceutical companies are increasingly interested in the development of new drugs whose origins are from plants. The rainforests and jungles of South America are an area of special interest due to their diverse and abundant plant life. The foxglove plant (Digitalis purpurea) is the source of the cardiac medicine Digoxin. A P PHO TO /DR . S COT T M. LI EBE RM AN.
The World Health Organization (WHO) estimates that 80% of the world’s population uses plant-based medicine for part of their healthcare. In non-industrialized societies the use of plant-based medicines in treating illnesses is universal. It is estimated that 25% of new drugs that are developed in the United States have their origins in plants. Given these statistics, the destruction of the rainforests and the loss of potential medicinal plants is of increasing concern. Plants as a part of life All cultures use plants for tools. A basket is a kind of tool. Think about baskets that you have in your home and consider what they are made of. Ancient cultures, Native American cultures, and people today all used or use baskets to hold items in their home. Native Americans used baskets to hold grain, water, plant materials and even their babies. They also used baskets in ceremonial rituals.
Reeds and grasses are common plant materials used in basket making. The Pomo used shells and bird feathers to decorate their baskets for use during ceremonies. Today, we use baskets to hold foods, magazines, 390
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WORDS TO KNOW Agar: A nutrient rich, gelatinous substance that is used to grow bacteria. Bacteria: Microscopic single celled organisms that reproduce quickly. Botany: The study of plants. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Ethnobotany: The study of how cultures use plants in everyday life.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Plant extract: The juice or liquid essence obtained from a plant by squeezing or mashing it. Reed: A tall woody perennial grass that has a hollow stem. Synthetic: Something that is made artificially, in a laboratory or chemical plant, but is generally not found in nature. Variable: Something that can change the results of an experiment.
and laundry. We also use baskets for decorations in our homes and on our doors. People have used all parts of plants to make weapons for hunting. Spears, blow darts and fishing lines were made from reeds and grasses. Shelters were made from plants: straw, grasses, and large palm leaves are just a few of the materials that were used. Plants were used in religious ceremonies. Dyes derived from plants were used to adorn the bodies of native people during special ceremonies. Often the wrappings used in the basket were dyed in various colors to form unique patterns. The containers used in such ceremonies were often made from plants and leaves. The importance of ethnobotany The relationship between cultures and
plants is complex and diverse. Throughout time people have used plants for food, shelter, clothing, medicine, tools, and religious ceremonies. Ethnobotany helps us understand the nature and importance of our relationship to the plant world. If we want to preserve our natural world from deforestation and development this understanding is vital. In the experiments that follow you will use plants in two different ways. In Experiment 1, you will test the antibacterial properties of three common plants. In Experiment 2, you will make discs out of reeds in the Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the concentration of plant extract • the temperature from the heat lamp • time the bacteria is allowed to grow
same way that Native Americans made baskets and test their ability to hold water.
EXPERIMENT 1 Plants and Health: Which plants have anti-bacterial properties? Purpose/Hypothesis Historically and in the
modern day, people use plants to prevent and fight diseases, such as harmful bacteria. In this • the type of bacteria experiment you will measure the antibacterial In other words, the variables in this experiment are properties of different plants. You will use a everything that might affect the growth of bacnon-harmful type of bacteria, taken from your teria on the agar plates. If you change more than mouth, and place it on agar. Agar is a gel that one variable, you will not be able to tell which supplies bacteria with food and a growth variable had the most affect on bacterial growth. environment. You will then place paper discs saturated with Peoplehaveusedallpartsofplants three different plant extracts: garlic, onion, and thyme. Garlic, onion, and to make weapons for hunting, thyme are all well known for their use in cooking but they have also been used and shelters were also made from for their medicinal properties. People have used garlic to fight off bacterial plants. IL LU STR AT ION BY infections. Onion and thyme have a history of being used to heal skin TE MAH NEL SO N. infections and wounds. By measuring which plant extract has the least amount of bacteria growth around it, you can determine the antibacterial properties of each plant. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plants and ethnobotany. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the amount of bacteria
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here 392
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is one possible hypothesis for this experiment: ‘‘Garlic is known to have antibacterial properties and How to Experiment Safely therefore will inhibit the growth of bacteria on the agar plates.’’ When growing any kind of bacteria, make sure In this case, the variable you will change is to keep all surfaces and materials that come in the type of plant extract placed onto the agar contact with the bacteria clean. When bacteria are disposed of after the experiment, use bleach plate, and the variable you will measure is the to disinfect the Petri dish and place the dish in amount of bacteria growth around the paper disc the trash. Be careful when cutting with the knife soaked in plant extracts. If the garlic has the least and handling the hot water. amount of bacteria growth around the paper disc, you will know your hypothesis is correct. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental discs, and that variable is the solution you use to immerse the disc. For the control, you will use sugar water. For your experimental discs, you are using sugar-water plus a plant extract. Level of Difficulty Moderate (this experiment requires careful attention
to cleanliness). Materials Needed
• • • • • • • • • • • • • • • • • •
agar (obtained at health food store or online science store) 2 sterilized Petri dishes (available online at science stores) cotton swabs 1 teaspoon powdered sugar 1 teaspoon water coffee filter hole punch 1 small yellow onion 1 clove of garlic several leaves of thyme marker spoons (optional) garlic press (optional) mortar and pestle (optional) knife small cup tweezers heat lamp with 125 watt bulb
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Approximate Budget $15 to $20 (try to obtain the Petri dishes from your school). Timetable Approximately one hour working
time; three days total time. Step-by-Step Instructions
Step 1: Use the marker on the outside bottom to divide the Petri dish in quarters. IL LUS TR ATI ON B Y TE MA H
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Step 9: Use the tweezers to place the control disc in the middle of the Control quarter of the agar plate. I LL UST RA TI ON BY T EM AH NE LS ON.
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1. If needed, prepare agar according to directions on the agar bottle or packet. 2. Flip the Petri dish so the bottom is facing up. Use the marker on the outside bottom to divide the Petri dish in quarters. At the edge of the Petri dish, mark each quarter: ‘‘O;’’ (for onion) ‘‘G;’’ (for garlic) ‘‘T;’’ (for thyme) and ‘‘C’’ (for control). Pour the agar into the plate and cover. Let the agar sit until it is hardened (approximately four to five hours). Once hardened, turn the dish upside down to prevent condensation on the agar. Place the dish in the refrigerator until you are ready to use it. You may consider preparing two or more agar dishes at a time in case you want to repeat this experiment. Use the hole punch to punch four circles out of the coffee filter. Do not touch the paper discs with your hands. In a cup, mix 1 teaspoon of powdered sugar into 1 teaspoon of water. Drop the solution onto one of the discs until the disc is completely covered in the sugar-water solution. This is your control. Set aside. Swipe the inside of your cheek with the cotton swab to gather bacteria. Swirl the swab into the sugar solution, stirring it around. 8. Pour the sugar solution with the bacteria onto the agar plate, making sure the solution covers the entire plate. 9. Use the tweezers to place the control disc in the middle of the Control quarter of the agar plate. Clean off the tweezers by placing them in a cup of hot water and shaking them off until dry. 10. To prepare the onion disc: Hold the disc with the tweezers. Slice the onion in half and squeeze a drop of onion juice onto one disc. Make sure the disc is completely Experiment Central, 2nd edition
Ethnobotany
covered in juice. Using the tweezers, place this disc onto the onion quarter of the agar plate. Again, clean off the tweezers in hot water. 11. To prepare the garlic disc: Cut the garlic clove. If you have a garlic press, squeeze a clove until there is enough juice to cover a fresh paper disc. You can also press the garlic with a spoon. Use tweezers to hold and place the disc on the garlic quarter of the agar plate. Clean the tweezers. 12. To prepare the thyme disc: Hold the disc with the tweezers. The thyme leaves can be crushed with a spoon on a cutting board or with a mortar and pestle. You need just enough extract of the plant to wet the paper disc. With the tweezers, place the disc on the thyme quadrant.
Step 13: Cover the agar plate and place it under the heat lamp. I LLU STR AT IO N BY TEM AH N EL SON .
13. Cover the agar plate and place it under the heat lamp. Make observations on bacterial growth every eight hours for two to three days. If possible, count the colonies (groups) of bacteria in each quadrant. Summary of Results Draw or sketch the bacterial growth around each
disc. After observing the bacterial growth over two to three days, what did you observe? Is there less bacteria growth around all the plant extract discs when compared to the control disc? Was your hypothesis correct? Write up a paragraph summarizing your results. Change the Variables You can change the variables and repeat this
experiment. For example, you can use different plant extracts. Research different plants and try ones that have antibacterial properties. You can also grow different bacteria. Our homes are filled with bacteria on doorknobs, toilet seats, and countertops. Take swabs from these places or others and see if they will grow on the agar plates. Temperature is another variable you can change. Will certain extracts prevent bacterial growth only in certain temperatures? When you conduct further experiments, remember to change only one variable at a time or you will not be able to tell which variable affected the results. Experiment Central, 2nd edition
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EXPERIMENT 2 Troubleshooter’s Guide Here are some problems that may arise during this experiment, possible causes, and ways to remedy the problems. Problem: There was no bacteria growth on the agar plate.
Coiling Reeds: How does the tightness of the coil affect the ability to hold materials? Purpose/Hypothesis Baskets are made out of
plant materials such as reeds, grasses, pine needles, and willow branches. Native Americans Possible cause: Bacteria grows well under warm became quite skilled at making baskets from conditions; check the temperature of your heat plant materials that were available to them. The lamp. A 125 watt heat lamp is approximately, 82 Pomo (a Native American tribe from California) degrees Fahrenheit (28 degrees Celsius). If the were known as one of the best basket makers. wattage was not high enough, replace and They used local grasses and wrapped and coiled repeat the experiment. You can also allow the bacteria to grow for several more days. them into baskets. Many reeds and grasses first need to be soaked in water to make them pliable. Possible cause: There may not have been Through a weaving or coiling process, the reeds enough bacteria collected on your cotton swab are then made into baskets to hold a variety of taken from your mouth. Try experiment again objects, such as grains, vegetables, and water. on a new agar plate and make sure you get a generous swab of bacteria from inside your In this experiment you will make two discs out cheek. Repeat the experiment. of reeds using a coiling process. One of the discs will be a looser weave than the second disc. You Problem: The bacteria grew the same around the can then measure how the tightness of the coiling discs with plant extracts as the control. process affects the ability of the reeds to contain Possible cause:The concentration of plant different materials. You will see if the coils will extracts was too weak. Your plants may have hold small objects, such as rice, and water. been too old. Try the experiment again using a Before you begin, make an educated guess fresh garlic, onion, or thyme. about the outcome of this experiment based on your knowledge of baskets and plants. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis 396
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for this experiment: ‘‘The disc that is more tightly coiled will hold small objects such as rice but not water.’’ In this case, the variable you will change is the tightness of the coil, and the variable you will measure is what substances the disc holds. Level of Difficulty Moderate. Materials Needed
• reeds or cane (available at basket making stores or online) • embroidery needle • raffia 1–2 ounces (28–57 grams) (available from craft stores) • dried beans or other similar size item, such as dried fruits • rice • small bowl • teaspoons • damp towel Approximate Budget $15 Timetable 2 hours Step-By-Step Instructions
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of reed • the diameter of the coil • the amount of substance placed on the disc • where the substance is poured on the disc In other words, the variables in this experiment are everything that might affect how the coil holds the materials. If you change more than one variable, you will not be able to tell which variable had the most effect on the ability of the coil to hold materials.
How to Experiment Safely Embroidery needles are sharp. Be careful when sewing through the reeds.
1. Separate the raffia into individual strands. Briefly dip the strands in warm water and keep them in a damp towel. You will use the raffia to wrap around the reeds, and it is easier to work with when it is slightly damp. 2. Gather a bunch of reeds together that are approximately as big as your little finger (1 centimeter). The reeds should be pliable and easily bent without breaking. If this is not the case you may try soaking the reeds in warm water for about two hours or longer until the reed is pliable. 3. Thread a strand of raffia through the embroidery needle. Make sure you use only a single strand of raffia. Experiment Central, 2nd edition
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Step 4: Starting at one end, begin to wrap the raffia around the bundle of reeds until you have covered approximately two inches of the reeds.
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8. Step 5: Bend the 2 inches (5 centimeters) of raffia covered reeds in half so the two lengths meet each other. IL LUS TR ATI ON B Y TE MA H NE LS ON.
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4. Starting at one end, begin to wrap the raffia around the bundle of reeds until you have covered approximately 2 inches (5 centimeters) of the reeds. 5. Bend the 2 inches (5 centimeters) of raffia-covered reeds in half so the two lengths meet each other. With the raffiathreaded needle, thread the raffia through both sides of the raffia-covered reeds to connect the two sides. You have just started your coiling process. Continue wrapping the reeds with raffia while coiling the reeds around themselves. Every inch you will need to sew the reeds together with the raffia. Continue this process until you have a disc approximately 3–4 inches (7.5–10 centimeters) wide. Continue this same process in making a second disc, except this time sew the reeds together every half an inch. Try to coil, wrap and sew this disc as tightly as possible. Stop when the second disc is the same size as the first disc, approximately 3 to 4 inches (7.5–10 centimeters) wide. If possible, bend them both into a bowl shape. Hold the first coiled disc above the bowl and place two tablespoon of rice in the center of the disc. Shake the disc back and forth gently, trying not to have any rice spill off the sides. Measure how much rice fell into the bowl and note the results. 10. Empty the bowl and repeat this same process with the second, tightly-coiled disc. Note how much rice dropped into the bowl. 11. Repeat Steps 8–10 for dried beans (or other small object) and water, making sure to empty the bowl both times. Summary of Results Look at the data for each of the discs. Is the second disc tight enough to hold water or other small objects? For what purposes could you use both discs? If the second disc does not hold water, think about ways you could change the coil to make it hold water.
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Consider other plant parts that may help make the coil contain small objects or a liquid.
Design Your Own Experiment How to Select a Topic Relating to this Concept Many cultures use a wide variety of
plant materials to make containers, baskets, and tools. Research the indigenous plants where you live and make baskets from the materials in your own backyard. Coiling is just one technique used in basket making, weaving is another. Pine needles and willow branches are just some materials that are commonly found in basket making. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on ethnobotany questions that interest you. As you consider possible experiments and projects, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of them might be dangerous.
Step 6: Continue wrapping the reeds with raffia while coiling the reeds around themselves. ILL US TRA TI ON B Y TE MA H NEL SO N.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Experiment Central, 2nd edition
Step 8: Hold the first coiled disc above the bowl and place two tablespoon of rice in the center of the disc. IL LU STR AT ION BY TEM AH N EL SON .
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Recording Data and Summarizing the Results
Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy it. Problem: The reeds did not bend easily, perhaps even broke in half. Possible cause: The reeds should be pliable and easily bent without breaking. If this is not the case you may try soaking the reeds in warm water for a couple of hours or longer until you achieve a pliable reed. Problem: The coils both have large holes and don’t hold anything. Possible cause: Making baskets and coiling reeds takes practice. Initially, your first few discs may be loose and have holes between the stitching. Keep trying. As you gain more skill and are able to tightly coil and sew the reeds together you will begin to form a tighter disc.
Record your data on the bacteria experiment and the disc coiling experiment. You could draw or photograph your results. After the data is collected and analyzed, your final responsibility is to make a conclusion based on your experiment and decide whether your hypothesis was true. Related Projects These
experiments have focused on two ways that people use plants: plants as medicine and plants as containers. Plants are used in many other ways. You could research how cultures use plants in religious ceremonies or as decorations on their clothes or in their homes. When you discover what plants are used for, you can experiment using different types of plants. For example, you could examine which plants make the strongest or deepest dyes. Plants are also used to create musical instruments. You could examine how reeds or other plant materials can make different sounds.
For More Information ‘‘ACT for Kids!’’ Amazon Conservation Team. http://www.ethnobotany.org/ kids/index.html (accessed April 17, 2008). Information and activities related to Amazon rainforest. Bernstein, Bonnie. Native American Crafts Workshop. California: Pittman Learning, 1982. Craft projects for children based on Native American traditions. Buhner, Stephen. Herbal Antibiotics. Vermont: Storey Books, 1999. Examines the natural alternatives for trating drug resistant bacteria.
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Fish
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ish are animals that live in water and have gills. There are more than 25,000 types of fish identified, and new species are discovered every year. There are fish that span 45 feet (13.7 meters) long to species that are the size of your nail. They come in a wide variety of colors and shapes. Fish are an important food source and livelihood to many cultures throughout the world. People also enjoy them for their beauty and recreation. These animals play a vital role in the ecosystem, both in the waters and on land. What makes a fish a fish Fish are a diverse group, but they have certain characteristics that set them apart from land dwellers. Fish have backbones made out of bone or cartilage (a strong and flexible tissue). Most fish have scales on their bodies that cover and protect the skin. Scales come in all sizes and shapes. Fish are also cold blooded, meaning the internal temperature matches the temperature of its environment. There are three main groups of fish: • The jawless fish: The smallest group, jawless fish have a round mouth with small sharp teeth in place of a jaw. The fish use their mouth to suck in food. Lampreys and hagfish are examples of jawless fish. • Cartilaginous fish: This group has skeletons made of cartilage. A skeleton that is light and flexible allows this group of fish to move easily and quickly through the water. Sharks, rays and skates belong to this group. • Bony fish: The bony fish, the largest group of fish, are fish whose skeleton is made of bone. The goldfish and guppy are common bony fish. Where a fish lives shapes its characteristics. There are fish that live the majority of their life in freshwater. Freshwater fish need special gills that help them regulate the salt in their bodies. Most ocean fish live in the top 401
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The lamprey is a type of jawless fish. Fossil records trace the lamprey as far back as any fish, including the prehistoric sturgeon. AP P HO TO/ TH E C OLU MB IAN , DA VE O LS ON.
The goldfish is a type of bony fish. A P PHO TO /TH E AL BU QUE RQ UE J OU RNA L, J AE LY N D EM AR IA.
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layers of the sea where sunlight reaches and plants thrive. The relatively few species of fish that live in the deep sea have adapted to the dark, cold environment. Some deep sea fish produce their own light by a chemical process similar to fireflies. Others have huge mouths to gather food and dagger-like teeth. Breathing underwater Like humans, fish need oxygen to live. Unlike humans, fish do not have lungs to take oxygen out of the air. They have gills that take oxygen out of the water. Gills are specialized organs located behind the mouth. A fish takes in water through its mouth and as it passes over the gills the oxygen from the water moves into the blood in the gills. This process is similar to how your lungs take oxygen from the air and move it into your bloodstream. Just as humans release carbon dioxide into the air as a by-product of the air we breathe, fish also release carbon dioxide through their gills into the water. Some fish have both gills and lungs to breathe in oxygen from the water and air. These fish are called lungfish and are found in Africa, Australia, and South America. This allows the fish to survive in environments when lakes or marshes become dry in the summer or during a drought (an extended period of dry weather). Whales and dolphins are mammals and therefore do not have gills but lungs. They can stay underwater for a long time but eventually they need to return to the surface of to breathe. Moving through water Ever wonder why fish don’t sink in the water? Most bony fish have an organ called a swim bladder that allows them to control their upward and downward movements. The swim bladder, located above the stomach, takes in air when the fish wants to move up and releases air when the fish wants to move down. Not all fish have swim bladders. A shark, for example, does not have a swim bladder but has an oily liver that keeps the shark from sinking because oil is lighter than water. Fins help fish move, turn, stop and control speed. Fins vary in shape, size and location, Experiment Central, 2nd edition
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depending upon the fish and its way of life. Each oxygen filtered into fin has a specific function and name. Fins can be bloodsteam through gills located on the fish’s back (dorsal fin), sides (pectoral fins), belly (anal fin and pelvic fins), and tail (caudal fin). Some fins come in pairs, such as the pectoral and pelvic fins. water in The shape of the body helps determine how speedy a fish moves. A fish with a narrow body is more aerodynamic and is therefore a faster carbon dioxide swimmer compared to a fish that is wider. released into water Fish have powerful body muscles along the sides of their body and in the tail that allow them A fish takes in water through its to move quickly and with force. When a fish wants to move it uses the mouth and as it passes over the gills, the oxygen from the water muscles on the side of its body, bending back and forth in an ‘‘S’’ shape. moves into the blood in the gills. The salmon is an example of a fish that uses its powerful muscles on its ILL US TRA TI ON B Y TE MA H sides and in its tail to propel itself out of the water. NEL SO N. Sensing the surroundings Fish eyes are similar to human eyes, but with a few differences. Fish cannot see as clearly as humans because their lens (the part of the eye that makes an image sharp) is a different shape. For most fish their eyes are located on the sides of their head enabling them to see in every direction except directly behind themselves. The pupil, a part of the eye that expands and contracts in relation to light in the human eye, does not change size in a fish’s eye. Fish need to adjust Most bony fish have an organ their depth in the water to make adjustments for more and less light. called a swim bladder that Fish have ears hidden on both sides of its head. A fish senses allows them to control their sound the same way as humans: through vibrations. Vibrations created upward and downward movements. I LL UST RA TI ON by a sound travel through the water into its ear. In many fish the swim BY T EMA H NE LS ON. bladder and the ears are connected by a series of small bones or tubes. The swim bladder vibrates swim bladder controls when a sound is made and this vibration is up and down movement carried along the bones or tubes to the ear. Many fish have a developed sense of smell and taste. Fish have small holes in their head called nares that act as nostrils. The nares connect to an area lined with sensory pads. When water is pumped over the sensory pads, fish are able to detect chemical signals in the water. The pectoral fin controls signals are transmitted to the brain where it is side to side movement interpreted as food or danger. Taste buds on a Experiment Central, 2nd edition
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WORDS TO KNOW Anal fin: Fin on the belly of a fish, used for balance. Bony fish: The largest group of fish, whose skeleton is made of bone. Cartilaginous fish: The second largest group of fish whose skeleton is made of cartilage Caudal fin: Tail fin of a fish used for fast swimming. Cold blooded: When an animals body temperature rises or falls to match the environment. Dorsal fin: The fin located on the back of a fish, used for balance. Fish: Animals that live in water who have gills, fins, and are cold blooded.
Jawless fish: The smallest group of fish, who lacks a jaw. Labyrinth: A lung-like organ located above the gills that allows the fish to breathe in oxygen from the air. Mammals: Animals that have a backbone, are warm blooded, have mammary glands to feed their young and have or are born with hair. Pectoral fin: Pair of fins located on the side of a fish, used for steering. Pelvic fin: Pair of fins located toward the belly of a fish, used for stability.
Gills: Special organ located behind the head of a fish that takes in oxygen from the water.
Swim bladder: Located above the stomach, takes in air when the fish wants to move upwards and releases air when the fish wants to move downwards.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Variable: Something that can affect the results of an experiment.
fish are found on the lips, head and fins. There are some fish like the cod and catfish that have long feelers around their mouths with taste buds at the ends and are used for detecting food in murky and muddy waters. In the experiments that follow, you will care for your own fish to observe some of their unique characteristics. In Experiment 1 you will measure how two different types of fish breathe. In the second experiment you will observe how body shape and fins affect the way fish move in the water.
EXPERIMENT 1 Fish Breathing: How do different fish take in oxygen? Purpose/Hypothesis In this experiment, you will create an environment to nurture and maintain two different types of fish to observe the way 404
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they breathe. Most fish use their gills to breathe in oxygen from the water. There are some fish How to Experiment Safely who have gills and a lung-like organ called a labyrinth. This lets fish take in oxygen from the Ask for assistance when carrying and lifting air and live in low oxygenated water. The labthe fish tank. Before you begin the experiment, ask an adult if you can care for the yrinth is located in the head of the fish just fish when the experiment is finished. If you above the gills. The fish takes in air through do not want to or cannot care for the fish, its mouth and as it passes over the labyrinth the find a suitable home for the fish before you oxygen flows into the bloodstream and the begin. carbon dioxide is released out of the body through the gills. The Betta has both gills and a labyrinth. The guppy has gills. By creating a comfortable living environment for each of these fish you can measure the differences in how the two fish breathe. Level of Difficulty Moderate. (This project requires continuous care and attention to maintaining a healthy environment for the fish.) Materials Needed
• 2, 2–5 gallon fish tank (plastic tanks work well). Size depends on space available and number of fish in the tank. If you only have one fish tank, you could place the fish in the same tank. However, male Betta fish can be aggressive to other fish, although they usually are not harmful to guppies. If you use one tank and find that your Betta becomes aggressive to the guppy, separate them and make your observations separately. • 2 thermometers for aquarium • gravel • male Betta fish (males have more distinct fins) • guppy (danio or barb fish work well also) • food for both types of fish (usually different) • several aquatic plants • filter (optional)
Steps 7 and 8: Record the number of times you see the Betta rising to the surface of the tank for air and the number of times you see the guppy opening and closing its mouth. IL LU STR AT IO N BY TE MA H NE LSO N.
Approximate Budget $25. (Try to use an old fish
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Troubleshooter’s Guide When you are creating a fish tank, many forces of nature can affect the project. These include the health of the fish and water quality. Here are some common problems and a few tips to maintain the best environment: •
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Timetable 1 hour for set up and 10–15 minutes observation time. Step-by-Step Instructions
1. Place a 1-inch (2.5-centimeter) layer of gravel on the bottom of the fish tanks. 2. Fill the tanks with tap water and let it stand overnight. This will allow the Fish when bought at a pet store are water to reach room temperature and usually healthy and will remain healthy if water additives, such as chlorine, to evapcared for properly. However, a fish could orate. (Some pet stores have special prodhave an illness that is undetectable when purchased and cannot be treated, or ucts that you can add to the water to ready even with treatment may not live. it for the fish.) Clean water without a lot of chemicals is the 3. Place the thermometer in each tank where it best environment for fish. Adding plants to is visible. Bettas and guppies do well in water the tank enhances the water quality. that is 68–75˚Fahrenheit (20–24˚Celsius) Monitor the tank temperature. If the tank (room temperature). Be careful to keep gets too cold or hot it can affect the fish. If the tank out of direct sunlight. you have trouble maintaining an optimal temperature (68–75˚Fahrenheit) you may 4. Plant one or two aquatic plants in the consider adding a heater to the tank. gravel. The plants provide hiding places If you continue your observations, it is for the fish, take in the carbon dioxide important to change the water in the that the fish release into the water, and tank every two weeks, perhaps more can act as a filtration system for the tank. frequently if you do not have a filter or 5. If you have a filter place it in the tank. plants. 6. Gently transfer the Betta and guppy into the fish tank. Feed according to the instructions on their food containers. 7. Over a period of five minutes, record the number of times you see the Betta rising to the surface of the tank for air. 8. For five minutes, record the number of times you see the guppy opening and closing its mouth 9. Wait overnight or 24 hours and repeat Steps 7 and 8. Summary of Results How long can the betta stay underwater before he
rises to the surface? How often does the guppy breathe? Was there a major difference between the two different times you observed the breathing? Consider the benefits and challenges to the two different forms of breathing. Write a paragraph summarizing the results and your conclusions. 406
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EXPERIMENT 2 Fish Movement: How do fins and body shape affect the movement of fish? In this experiment, you will create an environment to nurture and maintain two types of fish to determine how each moves in the water. Fish use their bodies and fins to move in the water. The tetra and angel fish are two common types of fish that have different body and fin shapes. A tetra fish has a sleek body and small fins as compared to an angel fish, who has a triangular body and large, flowing fins. Before you begin, make an educated guess about the outcome of this experiment based upon your knowledge of fish. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • hat you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Due to its shape and fins, the tetra fish will move faster through the water than the betta.’’ What are the variables? Variables are anything that might affect the
results of an experiment. Here are the main variables in this experiment: • the type of fish • the water temperature • the water environment In other words, the variables in this experiment are everything that might affect the movement of the fish. Level of Difficulty Moderate. (This project requires continuous care and attention to maintaining a healthy environment for fish.) Materials Needed
• 2–5 gallon fish tank (plastic tanks work well). Size depends on space available and number of fish in the tank • thermometer for aquarium • gravel Experiment Central, 2nd edition
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How to Experiment Safely Ask for assistance when carrying and lifting the fish tank. Before you begin the experiment, ask an adult if you can care for the fish when the experiment is finished. If you do not want to or cannot care for the fish, find a suitable home for the fish before you begin.
• • • •
heater angel fish (male Betta fish also work well) tetra fish (guppys also work well) food for both types of fish (usually different) • 1 to 3 aquatic plants, depending upon the size of the tank • LED light (small LEDs found on keychains work well) • filter (optional)
Some fish can be aggressive to other fish. Although these fish are usually compatible with each other, if you find that one of your fish becomes aggressive to the other you may want to separate them and make your observations separately. Approximate Budget $25. (Try to find a used fish tank or other
container.) Timetable 60–75 minutes, several hours apart, depending upon the
observation time. Step-by-Step Instructions
1. Place a 1-inch (2.5-centimeter) layer of gravel on the bottom of the fish tank. 2. Fill the tank with tap water and let it stand overnight. This allows the water to reach room temperature and for additives such as chlorine, to evaporate. Some pet stores have special liquids that you can add to the water to ready it for the fish. 3. Place the heater in the tank; this will help regulate the water temperature. 4. Place the thermometer in the tank where it is visible. Angel and tetra fish do well in water that is 75 degrees Fahrenheit (24 degrees Celsius). Be careful to keep the tank out of direct sunlight. 5. Plant one or two aquatic plants into the gravel. The plants provide hiding places for the fish, take in the carbon dioxide from the water, and act as a filtration system for the tank. 6. If you have a filter, place it in tank. 7. Gently place the angel and tetra into the tank. Feed according to the instructions on their food containers. 408
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8. Make a drawing of both fish. Note their different body shapes and coloring. 9. Observe the behavior of both fish for several minutes. 10. Using the LED light, shine the light at a point just ahead and slightly down from the tetra. Be careful not to shine the light directly into its eyes. Move the LED back and forth across the tank two times and watch how it follows the light. Make a note of the fins’ movement they are using to move forward, stop, and turn. 11. Again, move the LED back and forth across the tank two times, having the tetra start at one end of the tank. As you move the light across the tank, have a helper use the stopwatch to time how long it takes for the fish complete its movements. Make a note of the time. Repeat for a second trial. 12. Repeat Step 11 with the angel fish. 13. Wait at least two hours and then repeat Step 11 for both fish, making sure to conduct two trials.
Step 7: Gently place the angel and tetra into the tank. ILL US TRA TI ON B Y TE MA H NEL SO N.
Summary of Results Average the four trials for each fish. Was one fish
faster that the other? How do the fins and body shape relate to the speed of the fish. How do the fins and body shape relate to the way each fish moves in general. Summarize the findings of your results, using drawings or pictures. You may want to label the parts of the fins on your drawings. If you keep the fish, it is important to change the water in the tank every two weeks, or more frequently if you do not have a filter or plants.
Steps 11 and 13: Move the LED back and forth across the tank two times and watch how the fish follow the light. ILL US TRA TI ON B Y TE MA H NEL SO N.
Design Your Own Experiment How to Select a Topic Relating to this Concept In the fish investigations, you observed
two fish that exhibited characteristics common to fish. Many fish have specific adaptations that are suited to the environment in which they live. Consider what types of fish you are curious Experiment Central, 2nd edition
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Troubleshooter’s Guide Experiments do not always work out as planned. When you are conducting an experiment with live animals, many forces of nature can affect the project. Here are some common problems and a few tips to maintain the best environment for the fish. • Problem: The fish was never moving much. • Possible cause: Fish when bought at a pet store are usually healthy and will remain healthy if cared for properly. However, sometimes fish have illnesses that are undetectable when purchased. Try purchasing another fish and repeating. Remember to handle the fish gently and not place stress on it. • Problem: The fish is not following the LED. • Possible cause: There can be many possible reasons your fish is not following the LED. Try again the next day. If the fish still does not follow the LED, simply observe the fish movements. You can also try to purchase another fish and repeat the experiment. • Problem: The fish was not acting well once it went into the tank. • Possible cause: It may be the water quality. It is important for the tap water, if not specifically treated for the fish, to rest overnight so that substances such as chlorine and ammonia evaporate. Make sure the water sat for at least 24 hours, and try adding more water plants to the tank, then repeat. • Possible cause: The temperature of the tank may be too warm or cold. Make sure your thermometer is working and take the tank temperature. Angel fish and tetra fish do well at 75 degrees Fahrenheit (24 degrees Celsius). You may consider adding a heater to the tank.
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about? You may want to research the types of fish common to your area. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on fish questions that interest you. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results It
is important to document as much information as possible about your experiment. Part of your presentation should be visual, using charts and graphs. Remember, whether or not your experiment is successful, your conclusions and experiences can benefit others. Related Projects More specific projects can be
performed to explore detailed information about fish. For instance, scientists are finding that some fish are in danger of becoming extinct due to Experiment Central, 2nd edition
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pollution and from overfishing. Both pollution and over fishing are impacting the shark population along the Great Barrier Reef in Australia. Learn more about pollution and over fishing and what can be done to prevent this. You can also look at fish survival. How do fish defend themselves against predators? What sights and sounds do different types of fish respond to? You can examine why fish travel in schools and how they keep from bumping into one another. There are many experiments you could design to further observe the characteristics of fish.
For More Information ‘‘Animals: Fish.’’ National Geographic. http://animals. nationalgeographic.com/ animals/fish.html (accessed on April 9, 2008). Video and images of fish, along with fish related news and information. ‘‘Fish: Setting Up Your Fish Tank.’’ American Humane Association. http://www. americanhumane.org/kids/aquarium.htm (accessed on April 10, 2008). Provides information on how to set up and maintain a fish tank. Kalman, Bobbie. Animals called Fish. New York: Crabtree publishing, 2005. Describes fish, their breathing, reproduction, and defenses. Sneeden, Robert. What is a fish? Great Britain: Belitha Press Limited, 1993. Describes different types of fish, their breathing, movement senses, food, defenses and birth. Stewart, Melissa. How Do Fish Breathe Underwater? New York: Marshall Cavendish Corporation, 2007. An examination of the phenomena of scientific principles behind the ability of fish to extract oxygen from water. U.S. Fish and Wildlife Service. Kid’s Corner. http://www.fws.gov/endangered/ kids (accessed April 9, 2008). Provides information on the fish and wildlife conservation.
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or birds, flight is moving through the air with wings; but for humans, flight is traveling through the air in an airplane. It is surprising that applying the dynamics of flight did not get off the ground earlier than the twentieth century, because the first human attempts to glide through the sky took place about 3,000 years ago in China using kites. It is recorded that in 196 B . C . E ., General Han Hsin used kites to measure the distance to an enemy stronghold. Kites would later provide the key to wing performance principles used in the twentieth century airplane. It’s a bird, it’s a man, it crashed . . . In the eleventh century, an English inventor named Eilmer fastened wing mechanisms to his hands and feet and launched himself off a tower. Although Eilmer actually glided for a while before crashing, he broke both his legs and regretted forgetting to put a tail device on his back end. In the fifteenth century, Leonardo da Vinci (1452–1519)—an Italian engineer, artist, inventor, theatrical designer, musician, and sculptor—drew one of the first sketches of a flying machine. His detailed drawing of a helicopter featured a wing and a horizontal propeller. Because da Vinci felt his painting should reflect light, space, and other sciences such as anatomy, he drew hundreds of sketches of nature and of inventions such as his flying machine.
The man who discovered lift In the eighteenth century, Daniel Bernoulli (1700–1782)—a Swiss mathematician, botanist, and anatomist—discovered that force arises from differences in pressure as objects move through a gas or liquid. Bernoulli’s discovery later was used to explain what gives birds their lift, or ability to glide without falling. His theory would later be used in the design of the airplane. Making the ‘‘Wright’’ connection By the end of the nineteenth century, several people had made significant headway in developing the airplane. But it was Wilbur and Orville Wright who put all the pieces together to create an airplane that could fly. 413
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Air flows a greater distance over the top of a wing, creating low air pressure there. Higher air pressure under the wing forces the wing upward. GA LE GR OU P.
Three men inspired the Wright brothers, setting the stage for this important invention. One was Otto Lilienthal, a German who made 2,000 unpowered flights with his glider. Another was Samuel Pierpont Langley, a prominent scientist and head of the Smithsonian Institution. Langley launched two model airplanes in 1896 that remained airborne long enough to impress the United States Army, which gave him $50,000 for his experiments. The third was Octave Chanute, an American who also conducted gliding experiments. Both Chanute and Lilienthal felt an aircraft’s wings should be curved on top and concave underneath. This shape reduced air pressure above the wing and increased it below, providing the aircraft’s lift. All three men wrote books about their theories and experiences. Otto Lilienthal made over 2,000 gliding experiments. C OR BI S-B ETT MA NN.
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The Wright brothers were successful because they were able to control their aircraft once it flew, an accomplishment that other inventors had been unable to achieve. The key was twisting the wing tips to maintain balance, just as birds alter their wing shape to change flight direction. Beginning in 1899, these persistent, resourceful men pored over any aviation information they could get their hands on and became flying experts. As businessmen, they ran a small, successful bicycle shop in Dayton, Ohio. During off-hours, they tested airfoil sections in a homemade wind tunnel, designed a lightweight internal combustion gas engine, and experimented with kites and gliders. They spent hundreds of Experiment Central, 2nd edition
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WORDS TO KNOW Aerodynamics: The study of the motion of gases (particularly air) and the motion and control of objects in the air. Centripetal force: Rotating force that moves towards the center or axis. Control experiment: A set-up that is identical to the main experiment but not affected by the variable being tested in the main experiment. Results from the control experiment are compared to results from the actual experiment to determine the effect of the variable.
Hypothesis: An idea in the form of a statement that can be tested by observations and/or experiment. Lift: Upward force on the wings of an aircraft created by differences in air pressure on top of and underneath the wings. Propeller: Radiating blades mounted on a rapidly rotating shaft, which moves aircraft forward. Turbulence: Air disturbance that affects an aircraft’s flight. Variable: Something that can change the results of an experiment.
hours testing their findings in their shop, on empty fields, and in deserted windy areas like the sand dunes at Kitty Hawk, North Carolina. It was there, on December 17, 1903, their airplane soared for 12 seconds, traveling 120 feet (36 meters) before landing. It became the first flying machine to stay aloft on its own power with a passenger. Making objects fly was a challenge to the early inventors. Performing basic experiments in aerodynamics will help you understand some of the basic principles of flight.
EXPERIMENT 1 Lift-Off: How can a glider be made to fly higher?
The Wright brothers’ historic first flight took place in 1903. PH OTO R ES EA RC HER S IN C.
Purpose/Hypothesis In this experiment you will
create an aerodynamic glider capable of moving through the air and modify it so it can soar higher, gaining lift by manipulating the wings. According to Bernoulli’s principle, force arises from differences in pressure. Pilots change the degree of lift by manipulating the flaps on the wings’ edges. To understand the effects of air Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
pressure, examine the diagrams illustrated. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of flight. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
• the type of balsa wood glider used (both gliders should be identical, simple, and lightweight)
• the topic of the experiment
• the type of modifications made to the wing shape of the second glider
• the variable you will measure
• the variable you will change • what you expect to happen
In other words, the variables in this experiment are everything that might affect the flight time of the gliders. If you change more than one variable, you will not be able to tell which variable had the most effect on the gliders’ flight.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Modifying the wing cross-sectional shape will create more lift under the wing that will allow the glider to fly higher.’’ In this case the variable you will change is the wing shape of one of the gliders, and the variable you will measure is the distance the gliders fly.
Steps 3 and 4: Closeup of index card folded over one glider wing and how the glider looks with the index cards on both wings. GAL E GR OU P.
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Level of Difficulty Easy. Materials Needed
• 2 balsa wood gliders (Styrofoam gliders are acceptable substitutes, but the gliders must have no propellers or landing gear.) • 1 high power fan, 16 to 24 inches (41 to 61 cm) in diameter • 2 pieces of string, 18 inches (45 cm) long • 2 index cards, 4 6 inches (10 15 cm) • 1 roll of adhesive tape
How to Experiment Safely Use caution handling fans. Make sure the fan is unplugged when assembling the experimental apparatus and never touch the blades of the fan when it is operating.
Approximate Budget $5 for planes. (Borrow the fan from a family
member or teacher.) Timetable 30 minutes. Step-by-Step Instructions
1. Prepare the control and test gliders. Assemble as shown on the packing bag. 2. Tie one string to the nose of each glider. If there is a metal or plastic clip on the nose, use it to attach the string. 3. Modify the wing of the test glider to create lift. Fold the top and bottom of the index card as shown in the diagram. 4. Tape the cards over the tops of the wings of the test glider. 5. Modify the index card. Push forward from the back of the wing so that the bubble shape is toward the front of the wing. Once you bend the index card, it molds into the shape as illustrated. 6. Attach the two strings from the planes to the bottom of the fan or the fan grating. (Remember, use caution. Make sure fan is unplugged at this stage.) Aim the fan slightly down toward the surface the planes are resting on. 7. Turn the fan on low, then medium. Record your observations. Experiment Central, 2nd edition
Step 5: Index card folded and modified to give lift. G ALE GRO UP .
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Troubleshooter’s Guide Sometimes problems may arise during an experiment. Here is an example of a problem, a possible cause, and a way to remedy the problem. Problem: The gliders will not stay in the air. Possible cause: Gliders fly only for short periods because of invisible disturbances in the air, known as turbulence. For this reason, a glider cannot be expected to fly long distances.
Summary of Results Record your results by describing how each glider moves in response to the air currents. The modified-wing glider, or test glider, should jump up and glide in the air. The other, the control glider, should constantly dive into the table and flip over. You can measure how high the gliders lift off the table with a ruler. Change the Variables To vary this experiment,
use gliders made from different materials, such as Styrofoam or cardboard. Try different fan speeds and change the angle at which the wind hits the glider.
EXPERIMENT 2 Helicopters, Propellers, and Centripetal Force: Will it fly high? Example of a whirly toy, or propeller on a stick. G AL E GRO UP.
Purpose/Hypothesis Centripetal force is force exerted by a spinning
object. When objects such as gyroscopes and tops are set in motion, their spinning creates centripetal force. This centripetal force is directed toward the center point of the spinning object. As centripetal force builds momentum, it creates balance. Helicopters rely on this balance and are designed to create centripetal force with their propellers. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of flight. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will
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prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Centripetal force can be disturbed if the balance is disrupted, thus preventing flight.’’ In this case the variable you will change is the number and position of the dimes on the toy’s propeller, and the variable you will measure is the toy’s flight. Level of Difficulty Easy. Materials Needed
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the number and position of the dimes (weights) on the propellers In other words, the variables in this experiment are everything that might affect the flight of the whirly toy. If you change more than one variable, you will not be able to tell which variable had the most effect on the toy’s flight.
• Whirly toy—a propeller on a stick • 4 dimes • 1 roll of adhesive tape • meterstick Approximate Budget $3 for whirly toy. Timetable 20 minutes.
Step 3: Toy with dimes attached to each end of the propellers. GA LE G RO UP.
Step-by-Step Instructions
1. Spin the whirly toy between the palms of your hands and carefully release it. 2. Use the meterstick to record about how high the toy jumps. 3. Tape two dimes onto the propeller of the toy, repeat step 1, and measure the height of its flight. Record the height of the jumps. 4. Remove one of the dimes and test the toy’s flight again. Use caution. The flight will be erratic. Record the change in balance and flight. 5. Repeat this test with the dimes in different positions, such as those illustrated. Experiment Central, 2nd edition
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How to Experiment Safely Use caution when flying the toys. Avoid contact with eyes.
Summary of Results Reflect on your hypothesis. Did you discover centripetal force and the actions that can disrupt its effect or balance? Record your results in a chart. Describe the behavior or draw what happened so others can learn from your experiment.
Modify the Experiment Helicopters fly by different principles than other
aircraft. In a helicopter, the rotor acts as the wings of an airplane, giving the helicopter lift. The properties of helicopter rotors allows a helicopter to do things a plane cannot, such as hover and move sideways. For a more challenging experiment, you could make your own whirly toy to discover the shape and size of rotor blades that allow the aircraft to carry the most weight (dimes). First, look at pictures or photograph of helicopter rotor. Note how the rotor blades are not flat. You can use
Step 5: Toy with dimes taped in different positions. Test the flight patterns of each position. GAL E GR OU P.
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cardboard, aluminum foil, plastic, or other household materials for your rotors. You can attach the rotors to a dowel, straw, or pencil. Start out making two blades several inches across. When you have completed the design, rub it in your palms and note how far your makeshift helicopter travels without any weights. Add the weights and repeat. Now continue to improve your helicopter design. You may want to slightly alter the angle of the rotor blades, or add two more. You can also change the length or shape. Remember to change one variable at a time, noting how high it moves on its own before you add the dimes.
Troubleshooter’s Guide Here is a problem that may arise, a possible cause, and a way to remedy the problem. Problem: The toy will not fly when the dimes are attached. Possible cause: The dimes are too heavy. Try lightweight buttons that match each other in size and weight.
Design Your Own Experiment How to Select a Topic Relating to this Concept Investigations and experiments in flight are exciting to explore. A toy box or toy store is a great place to discover objects capable of lift. Keep the ideas simple and work with objects familiar to you. Visit an aerospace museum, or try to arrange a personal tour at a local airport. Check the Further Readings section and talk with your science teacher or community media specialist to start gathering information on flight questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Experiment Central, 2nd edition
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Recording Data and Summarizing the Results Ask your mom or dad to videotape
the takeoff in the glider or pinwheel experiments. Or diagram the flight using photos. Keep the results and data charts simple and easy to use. Related Projects Air pressure is an invisible force
that controls many objects and affects our lives. Simple experiments involving balloons or air bags can demonstrate the principles and power of air pressure.
For More Information
Artist and scientist Leonardo da Vinci sketched a flying machine as early as the fifteenth century. PH OT O RE SEA RC HE RS I NC.
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Leuzzi, Linda. Transportation: Life in America 100 Years Ago. New York: Chelsea House, 1995. Chronicles aircraft and people who were instrumental in furthering significant inventions. Nahum, Andrew. Flying Machine. London: Dorling Kindersley, 1990. Covers aviation history, its inventors, and principles of flight. Ohio State University Extension. ‘‘Science Fun with Airplanes.’’ http://www. ag.ohio state.edu/flight/ (accessed on January 17, 2008). Interactive experiments and information on the science of flight. Rinard, Judith E. The Story of Flight. Buffalo, NY: Firefly Books, 2002. Information on the background and different types of flying crafts. Weiss, Harvey. Strange and Wonderful Aircraft. New York: Houghton Mifflin, 1995. Provides good background on aviation.
Experiment Central, 2nd edition
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T
he word flower often brings up images of familiar blooms that enliven homes, such as roses and sunflowers. Yet flowers do far more than beautify the world. A flower is the reproductive structure of flowering plants, which are called angiosperms. Flowering plants include the familiar blooms as well as grasses, shrubs, and trees. The flowers on plants are widely diverse in size, shape, color, and scent. Flower sizes range from the Wolffia, which can fit through the eye of a sewing needle, to the Titan Arum, a cone-shaped flower that can tower 9 feet (2.7 meters). Some flowers resemble insects, and others sport brightly colored petals. Yet all flowers share the same key function: to make seeds to give rise to a new generation of the plant. The evolution of flowers supplied many advantages for plant survival and thus, life on Earth. Flowers provide protection for seeds and a food source for animals. In return for food, the animals supply genetic variation to the flower. Mixing up the genetic material allowed flowers to develop new features that led to plants increasing in types and numbers. First appearing on Earth about 145 million years ago during the era of dinosaurs, today about 90% of plants are flowering plants. The inside story Flowers contain the plant’s male and female parts for reproduction. The male part produces powdery grains called pollen. Each pollen grain contains male reproductive cells, called sperm cells. When pollen joins with the female part of the flower it is called pollination. The result is the development of a seed. There are four basic parts to most flowers: the stamen, pistil, petal, and sepal. The male reproductive organ is called the stamen. The stamens are offshoots that grow in a circle around the blossom. A stamen is made up of the anther located at the top, which holds the pollen, and a filament, which is the thin stalk that supports the anther. The female reproductive organ is called the pistil. The pistil has three major parts: the stigma, a sticky surface at the top that holds the pollen; 423
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the style, the stem that holds the stigma upright; and the ovary, the structure located at the botpetal tom of the stigma that produces ovules, the female reproductive cells or eggs. The most recognizable part of a flower is its petals. Petals enclose the flower’s sex organs. They can bloom in vibrant colors that attract stigma animals to the flower. Sepals are the leaflike anther pistil style structures at the bottom of the petals that protect stamen the flower bud before it opens. When the bud filament opens, the sepals fold back. ovary For pollination to occur the pollen must move from the anther of a stamen to the pistil’s stigma. The sperm cells in the pollen move down a tube that forms from the style to the ovary. There, the sperm cells can fertilize the eggs in the sepal ovule. Not all flowers contain all parts. For examParts of a flower. G AL E ple, grasses do not contain petals in their flowers. Some flowers produce GRO UP. either the male or female part, and others produce both. The flowers with both pistils and stamens are called perfect flowers. Examples of perfect flowers includes the rose, sweet pea, and lily. Flowers that have only the pistil or the stamen are called imperfect flowers. (The same plant, however, can contain both male and female flowers.) An imperfect flower prevents a plant from self-pollinating, meaning when the pollen transfers from the male to female parts of a single flower or plant. This can occur simply by gravity causing the pollen to drop. Closeup of a Zinnia flower. Plants that self-pollinate have the exact same genetic material as the F IEL D M ARK PUB LI CAT IO NS. parent, causing them to have a decreased chance of survival if the environment changes. Even if flowers are capable of self-pollinating it is not the desired method of pollination. Flowers have evolved mechanisms to avoid self-pollination such as developing its stamens and pistils at different times, and having its pistil reach far above the stamen. In cross-pollination pollen is transferred from one flower to another. Cross-pollination combines genetic material and generates greater 424
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diversity in the offspring. Plants are usually A pollen stronger and healthier over the long run than self-pollinators. While cross-pollination has genetic advantages, it also means that plants are more dependent on a way to have their pollen carried about. Pollen on the move In order for pollen to transfer from one flower to another, it must have a way to move. Some flowering plants depend upon the wind to blow its pollen onto another flower. Examples of wind-pollinated plants include pine trees, corn, and grasses. Plants that pollinate by wind— and sometimes splashes of rain—produce large quantities of light pollen, as a large percntage of the pollen will be wasted by not landing on its target spot. These flowers do not need the vibrant features that tempt pollinators and often have plain, small flowers. The large majority of flowering plants depend upon animals to ferry the pollen from one flower to another. These pollen-carriers are called pollinators. Insects, birds, butterflies, and even bats are pollinators. Bees are among the most numerous and important pollinators. Flowers first must attract pollinators by offering food, color, scents, and other temptations. A pollinator that comes into contact with the flower rubs against the anther, causing some pollen to stick to its body. When the pollinator then visits another flower of the same species, its pollen brushes or falls onto that flower’s stigma. Animal-pollinated flowers produce less pollen than the wind-pollinators, as the animal carries the pollen directly to a flower. Allure of the wild In the quest to lure pollinators, flowers have evolved several ingenious features. Many flowers offer food in the form of nectar. Nectar is a sweet liquid that provides nourishment for birds, bees, butterflies, and other animals. Nectar is located deep within the flower at the base of their petals. Petals often sport lines or dots that serve as a guide to the hidden nectar. In some flowers nectar accumulates in long pouches that is available to animals with long beaks or tongues. Some flowers time their production of nectar to coincide with Experiment Central, 2nd edition
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(A) In a self-pollinating flower, pollen falls from the anther to the stigma; (B) a flower can avoid self-pollination if its pistil reaches above the stamen. GAL E GR OU P.
In cross-pollination, genetic material (pollen) is exchanged from one flower to another. GAL E GR OU P.
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the schedule of their desired pollinator. For example, night-blooming flowers increase their production of nectar at night so the scent attracts bats, moths, and other nocturnal pollinators.
Bees are among the most numerous and important pollinators. # GE OR GE D. LE PP/ CO RB IS.
Some plants have many different pollinators, while others are particular to just one type. A plant with many pollinators will have more organisms carrying its pollen, yet there is a greater chance the pollen will not make it to the same type flower. Having a pollinator who only likes one type of flower cuts down the amount of traveling pollen but ensures that the pollen will be delivered to a like flower. For example, the orchid Angraecum sesquipedale ensures that only a specific type of insect pollinates it by having its nectar tucked about 10 to 14 inches within the flower. The hawkmoth, which is an insect but is the size of a small bird, with its 12-inch proboscis is the only insect that can reach the nectar. Animals can get other meals from flowers as well. Some flowers produce a second type of pollen that pollinators can eat. Oils on the flowers are food for some insects.
Flowers have many ways of attracting pollinators. One way is nectar, a sweet liquid located deep within the flower that provides nourishment for birds, bees, butterflies, and other animals. GA LE GRO UP.
Flowers also attract pollinators with their petal colors and shapes. Animals all have unique color perception and are attracted to colors that they can spot. Flowers that appeal to birds are often red (some have evolved a landing area for the bird). Bees are attracted to blues, purples, and yellow pigments. Butterflies prefer to eat sitting down so they prefer flat, wide surfaces and bright colors. Bats need large, sturdy and palecolored flowers to support their weight and show up in the darkness.
anther
ovary ovule
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bee proboscis nectar
Scents—both sweet and foul—are another method of appealing to certain animals. The bee orchid, for example, resembles and smells like a bee. When male bees, tempted by its scent, attempt to mate with the flower they become covered with pollen and spread it to their next flower mate. Another orchid species, the Lady’s Slipper, holds a fragrance in its pouch that has a wild attraction for flies. The flies climb around and inside the pouch, getting pollen stuck to them in the process. Experiment Central, 2nd edition
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Foul odors attract pollinators who feed on decaying matter. The smells are similar to those of the food that these insects and other animals eat. Along with laying claim to the world’s largest flower, the Titan’s flower is also the world’s smelliest. Giving off an odor similar to rotting meat, the stench attracts beetles and flies that feed on or lay eggs in rotting flesh. Some flowers have mechanisms that force a pollinator to stay for a long visit. With flowers up to one foot across, the giant water lily of the Amazon has to work fast as it only blooms for two days. The flower attracts beetles during the day, then traps them inside when it closes for the night. Covered in pollen, the beetles are released when the flower opens at dusk of the following day. The Dutchman’s pipe has a tube-shaped flower with a waxy surface. It emits a putrid smell that appeals to flies. When insects land they slip down the flower and are trapped by its thick hairs. The flies can lap up nectar while they get covered in pollen. The appearance and smell of a flower provides clues as to its pollinator. In the following two experiments you will explore pollination and how a flower’s features shape its pollinators.
EXPERIMENT 1
The pouch on a Lady’s Slipper orchid, which contains the flower’s pollen, has a fragrance that attracts pollinators to it. FIE LD M AR K PU BL ICA TI ONS .
Self versus Cross: Will there be a difference in reproduction between self-pollinated and cross-pollinated plants of the same type? Purpose/Hypothesis Flowering plants can be cross-pollinators or self-
pollinators. Botanists and flower developers cross-pollinate specific plants intentionally to produce a desired trait in the offspring, such as a specific color. The cross between two parent plants produces a hybrid. In this experiment, you will both cross-pollinate and self-pollinate the same type of plant. Because of possible variations, you will use two plants for each trial. You will then wait for the plants to develop and observe any differences in the flowers and outcome. Experiment Central, 2nd edition
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WORDS TO KNOW Angiosperm: A flowering plant that has its seeds produced within an ovary. Anther: The male reproductive organs of the plant, located on the tip of a flower’s stamen. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Petal: Leafy structure of a flower just inside the sepals; they are often brightly colored and have many different shapes. Pistil: Female reproductive organ of flowers that is composed of the stigma, style, and ovary. Pollen: Dust-like grains or particles produced by a plant that contain male sex cells.
Cross-pollination: The process by which pollen from one plant pollinates another plant of the same species.
Pollination: Transfer of pollen from the male reproductive organs to the female reproductive organs of plants.
Filament: In a flower, stalk of the stamen that bears the anther.
Pollinator: Any animal, such as an insect or bird, that transfers the pollen from one flower to another.
Flower: The reproductive part of a flowering plant. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Imperfect flower: Flowers that have only the male reproductive organ (stamen) or the female reproductive organs (pistil). Nectar: A sweet liquid, found inside a flower, that attracts pollinators.
Self-pollination: The process in which pollen from one part of a plant fertilizes ovules on another part of the same plant. Sepal: The outermost part of a flower; typically leaflike and green. Stamen: Male reproductive organ of flowers that is composed of the anther and filament.
Ovary: In a plant, the base part of the pistil that bears ovules and develops into a fruit.
Stigma: Top part of the pistil upon which pollen lands and receives the male pollen grains during fertilization.
Ovule: Structure within the ovary that develops into a seed after fertilization.
Style: Stalk of the pistil that connects the stigma to the ovary.
Perfect flower: Flowers that have both male and female reproductive organs.
Variable: Something that can affect the results of an experiment.
Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of flowers and pollination. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change 428
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• the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The flowers that are cross-pollinated will produce seeds and the self-pollinated plant will not.’’ In this case, the variable you will change is the source of the pollen. The variable you will measure is the development of the flowers and seeds. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental setup, and that is the pollen a plant receives. For the control, you will place a plant in an isolated, indoor area to ensure it receives no pollen from another plant. At the end of the experiment you can compare the results of the control to the experimental plants.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of plant • the source of pollen • the environment (for example, sunlight, wind, air temperature) • the amount of water applied to the plant after pollination In other words, the variables in this experiment are everything that might affect pollination. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on plant reproduction.
Level of Difficulty Moderate. Materials Needed
• eight young flowering, cross-pollinating plants of one type, purchased before any flowers have grown (if not available as young plants, you can grow with seeds, potting soil, and pots. For a faster option, you can order Wisconsin Fast Plant seeds from Carolina Biological; see Further Readings). Talk with an expert at a gardening store or conduct research to make sure that you have selected a plant that cross-pollinates. (In general, geraniums, corn, and cucumbers work well; avoid tomatoes, beans, and peas.) • • • • •
several cotton swabs several toothpicks tweezers marking pen magnifying glass (optional)
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Approximate Budget $20.
How to Experiment Safely There are no safety hazards in this experiment. If you have strong allergies to pollen you may want to check with an adult before conducting this experiment.
Step 4: Gently rub the pollen grains from the stamen against the tip of the stigma. GA LE GR OU P.
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Timetable Varies widely depending on plant;
30 minutes for pollination; about 10 minutes of regular observations for six to 14 weeks. Step-by-Step Instructions
1. Conduct the experiment inside and away from other plants of the same species. There should be two plants in each trial: Label two plants ‘‘A,’’ two plants ‘‘B,’’ two plants ‘‘C,’’ and two plants ‘‘D.’’ The plants labeled ‘‘D’’ will be the Control. Set plants in distant locations from one another, such as in separate parts of a room, or even in separate rooms. Make sure each plant has equal light. 2. After the plants have formed blossoms and before the petals open, gently push aside the petals with a toothpick. On Plants A use the tweezers to remove all the stamens on each flower, leaving the stigma. Label the pot: ‘‘Female/Cross.’’ 3. When all the plants have open flowers, (this should occur at roughly the same time) note whether the stigma stands below, equal, or higher to the anthers. You will need to pollinate, selfpollinate, and not pollinate the same number of flowers on each plant. Count the least number of flowers on one of the plants and use that as the guide. Gently snip off the remaining flower shoots that you will not need. For example, if one of the plants only has three flowers and the rest have over six, snip off the extras on the other plants so all plants have three flowers. 4. Rub a cotton swab against the stamens of Plants B. You should see pollen grains on the swab. You may want to use a magnifying glass. Gently rub those pollen grains against the tip of the stigmas on Plants A. Make sure you see the pollen grains on the stigma. 5. Repeat with a fresh swab for each transfer of pollen flowers. Experiment Central, 2nd edition
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6. Self-pollinate Plants C by taking a fresh swab and moving the pollen from the stamen to the stigma in each flower. Label plants: ‘‘Self-Pollinated.’’ 7. At regular intervals, (depending on plant, could be every three days) note any changes in the pistil in Plants A, C, and D. Note what day the petals fall off and any changes in the sepals. Summary of Results As the flowers continue to develop, construct a chart with the similarities and differences among the plants. Note the pistil development and count the number of seeds in each pistil. Average the seeds for each of the two plants in each group. Compare the control to the self-pollinated plant. How did the groups of plants differ? How were they the same?
Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The plants did not produce seeds. Possible cause: There can be several possible causes: The plant may have been exposed to too much heat, or it may not have had enough water or nutrients. Make sure you use a rich soil that contains nutrients, and follow the directions for the seed carefully. You may want to talk with a professional at a plant store. Possible cause: You may not be able to see the seeds. The pistil should be enlarged, change shape, and become dry. When this happens, carefully look inside the pistil to see if there are seeds, then remove each seed carefully.
Change the Variables To change the variable in
this experiment you can change the type of plant. You can also conduct the same type of pollination on each plant, and alter the environmental conditions. You can also alter the nutrition of the plants by changing the soil content. Use a soil with few nutrients, and then add specific nutrients one by one to determine which nutrients affect seed production.
EXPERIMENT 2 Sweet Sight: Can changing a flower’s nectar and color affect the pollinators lured to the flower? Purpose/Hypothesis Among the many characteristics a flower uses to attract pollinators are its color and nectar. There are some pollinators that respond to certain colors. For example, in general butterflies are attracted to bright reds and oranges; bees to blues and yellows; and beetles to many different colors. Nectar also varies among flowers in the amount of sugar it contains. Some pollinators are attracted to nectar that has about 20 to 25% sugar; other pollinators, such as bees, prefer a richer sugar content of about 50%. In this experiment, you will determine if you can attract a certain type of pollinator based on the color and sugar-concentration of nectar. You can Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the shape of the bowl/cup • the environment the cup is placed • the weather conditions • the time of observations • the concentration of nectar • the color of the flower In other words, the variables in this experiment are everything that might affect the pollinators who approach the cups. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on attracting pollinators.
measure the results by noting the numbers and types of pollinators. Among the animals to look out for are ants, butterflies, bees, birds, and spiders. You will first apply a constant nectar content to three colors: yellow, blue, and white. After finding one color that attracts the most pollinators, you will then vary the nectar by placing an artificial nectar on the color. Nectar is a syrupy-solution made up of several types of sugar, primarily sucrose, which is common table sugar. You will make varying concentrations of artificial nectar: a 20% sugar syrup and a 50% sugar syrup. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of flowers and pollinators. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change
• the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘There will be one combination of color and nectar that will attract the most of one type of pollinator: The yellow, high nectar concentration will lure the most bees.’’ In this case, the variables you will change, one at a time, are the color and then the concentration of the artificial nectar. The variable you will measure is the number and type of pollinators. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. After determining the color that attracts the most of a certain type of pollinator, your control will change the concentration of nectar. For the control in this part of the experiment, you will use plain water instead of nectar. At the end of the experiment you can compare the experimental data to the control data. 432
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Level of Difficulty Moderate to Difficult, because of the attention to detail and time involved.
The artificial nectar should attract bees and other insects. Make sure to stand at least several feet away when making your observations. Do not disturb the insects or other pollinators. Have an adult present when you handle the boiling water.
Materials Needed
• • • • • • • • • • •
How to Experiment Safely
3 cups sugar outside area with a high ledge area 2 nice days 6 cups water six clear plastic cups swatches of blue, yellow, and white felt: enough to fit in the plastic cups colored felt small rocks stirring spoon measuring cup marking pen
Approximate Budget $5. Timetable 1 hour for experiment setup; 1 hour each day for 2 days.
control
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1:4
Steps 3 and 4: After selecting one color, alter the concentration of the sugar in the artificial nectar. GA LE GR OU P. Experiment Central, 2nd edition
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Step-by-Step Instructions
Troubleshooter’s Guide
1. Day 1: Cut a swatch of the colored felts and scrunch each one into a clear cup. Place a Below is a problem that may arise during this small stone in the felt to weigh it down. experiment, some possible causes, and some 2. Set each of the cups in the same general ways to remedy the problem. area outside on a high ledge, at roughly Problem: There were too few pollinators to 2 feet apart from one another. Choose two draw any conclusions. times of day to observe the colored cups Possible cause: Vary the time of day you are for a 30-minute period each time: one making your observations. You may also time in the morning and one in the afterwant to change the location to one with more noon or early evening. You will need to plant growth and surrounding flowers. observe at the same two times the following day. For each color, note the number and type of pollinators that visit the cup. 3. Day 2: Vary the nectar concentration. Use your data from the previous day to select one of the colors that attracted the most pollinators. Place a swatch of the selected color into each of three clear plastic cups. 4. Label the cups according to the ratio of sugar to water: ‘‘1:1,’’ ‘‘1:4,’’ and ‘‘Control.’’ The Control will be plain water. 5. Boil the 6 cups of water. Pour 2 cups of sugar into a glass bowl labeled 1:1. Add 2 cups of boiled water and stir until all sugar has dissolved. Allow the artificial nectar to cool. 6. Pour 12 cup sugar into a glass bowl labeled 1:4. Add 2 cups of boiled water and stir until all sugar has dissolved. Allow to cool. 7. Fill the 1:1 cup and the 1:4 cup with their designated artificial nectar. Fill the Control cup with 2 cups of cooled boiled water without any sugar. Place the cups outside on a ledge. 8. At the same two times of day as the previous day, observe the flowers for 30-minute periods and note the type and number of visitors to each cup. Summary of Results Examine your results for both the color and con-
centration. Graph the major pollinators number of visits by the color. Create another graph of the major pollinators number of visits by the nectar concentration. Could you attract one specific pollinator by altering the nectar and color? Conduct some research and determine what types of flowers this pollinator(s) visits the most frequently. How do the characteristics of these flowers compare to your experimental results? 434
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Change the Variables As it is the combination of many different factors
that influence a flower’s pollinators, you can vary this experiment in many ways to determine the relative effect of each characteristic. • Change the shape of the setup by creating petals of different shapes, then using one concentration of nectar. • Change the colors of the setup, using single colors and multiple colors • Vary the scent of the setup, either by purchasing flower scents or by extracting scents from real flowers • Change the environment to compare pollinators, such as in a wooded area, park, and backyard. Modify the Experiment This experiment involves examining how flower
nectar and color both attract pollinators. You can simplify the setup and focus of this experiment by working with artificial flowers. By comparing artificial flowers to real flowers, which contain nectar, you can determine how flower characteristics affect pollinators. You will need two types of artificial flowers and their matching natural flowers. The flowers should be different colors. Try to chose flowers that have large petals and bright colors, such as roses, sunflowers, or hydrangeas. You will only need one of each. If possible, try to match the artificial flowers to a flower naturally growing outside. If you purchase real flowers, make sure they are freshly cut. To begin the experiment, you should have four flowers: two of one type, one real and one artificial; two of another type, one real and one artificial. On a nice morning, place the artificial flowers several feet away from the natural flowers. Now stand back several feet and observe the insects or other pollinators that visit each flower. It helps to have a friend or adult observe and make notes also. Observe the flowers for at least 15 minutes at least two different times. Does one color flower attract more pollinators than the other? Do the natural flowers attract more pollinators? Do the pollinators stay for a longer period of time at the natural flowers? You can repeat this experiment with several different color and types of flowers? When you have finished, look at all your data and see if you notice a pattern with color or nectar. Chart your results or write a summary of your findings.
Design Your Own Experiment How to Select a Topic Relating to this Concept While flowers all have the
same function, they are widely diverse in appearance. Many flowers, Experiment Central, 2nd edition
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especially the self-pollinators, are so small and nondescript that you may not notice them. To gather ideas for a topic you can look at the many different types of flowers that grow in your area. Visit a greenhouse or a florist to observe species’ shapes, colors, and scents. As flowers are unique to a geographic region, you may want to look up photographs and descriptions of flowers in different locations around the United States and the world. Examine how the flower’s appearance shapes its role, if any, with possible pollinators. Check the Further Readings section and talk with your science teacher to learn more about flowers and pollination. You could also speak with a professional at a local greenhouse or nursery. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. You may also want to display any flowers that you studied. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects With the wide variety of flowers and their pollinators,
there are numerous flower-related projects. You can use a magnifying glass to carefully dissect a flower, separating and labeling each of its parts. 436
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By doing this with several different types of flowers you can compare the flower parts. Flowers have several main attractants to pollinators: color, nectar, shape, and scent. You can examine the relationship between one or all of these with the pollinator. For example, you can examine the effect of flower scents on pollinators. You can look up techniques to capture the scent of a flower and then place the scents outside on the same substance. Different species of flowers release pollen of varying appearance. You can collect and compare the pollen grains from several types of flowers. Look at how the grains from self-pollinators compares to cross-pollinators. You can also examine what types of pollinators are attracted to each of the pollen types. For a research paper, you can examine what the pollen grains offer the pollinator, such as protein, sugar, and shelter. Some flower species have evolved deceptive appearances and smells to entice pollinators that you could also observe and research. You could also look at the biology of pollination and map out the genetics of plant reproduction.
For More Information Attenborough, David. The Private Life of Plants: A Natural History of Plant Behaviour. Princeton, NJ: Princeton University Press, 1995. These stories of plant life and survival feature plants from all over the world with full color photographs. Bailey, Jill. Plants and Plant Life: Flowers & Fruits. Danbury, CT: Grolier Educational, 2001. This volume of the series on plants covers reproduction. Black, David, and Anthony Huxley. Plants: The World of Science. New York: Orbis Publishing, 1985. Contains comprehensive information on plants, with photographs. Ganeri, Anita. Plant Science. New York: Dillon Press, 1993. Answers questions on basic plant characteristics and behavior. Missouri Botanical Garden. ‘‘Pollination.’’ Biology of Plants. http://www. mbgnet.net/bioplants/pollination.html (accessed on February 6, 2008). Information and video about pollination. ‘‘Plants and Animals: Partners in Pollination.’’ Smithsonian Center for Education and Museum Studies. http://www.smithsonianeducation.org/educators/ lesson plans/partners in pollination/index.html (accessed on February 16, 2008) Covers various aspects of how animals help pollinate plants. ‘‘Rice Anatomy.’’ Plant Biology Division of Biological Sciences, University of California, Davis. http://www plb.ucdavis.edu/labs/rost/Rice/reproduction/ flower/flower.html (accessed on February 18, 2008) Shows the various reproductive components of rice flowers and how they interact. Souza, D.M. Freaky Flowers. New York: Franklin Watts, 2002. Filled with photographs that show intriguing flowers from around the world. U.S. Department of Agriculture Forest Service. ‘‘Pollinators.’’ Celebrating Wildflowers. http://www.fs.fed.us/wildflowers/pollinators/index.shtml (accessed on February 16, 2008). A lot of information on pollination, with pictures and examples. Experiment Central, 2nd edition
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Fluids
W
hen people talk about fluids, we are often referring to liquids. In scientific terms, a fluid is both a liquid and a gas. In solids, the particles are packed tightly together and in a regular pattern. Particles in fluids move about freely are in constant motion—they are fluid. What makes a fluid a fluid There are many properties that set fluids and solids apart. A few key properties include:
For a fluid, the pressure at any one point is the same in all directions. ILL US TRA TI ON B Y TE MA H NE LSO N.
• Pressure Direction: Right now, there is pressure all around you from air, a fluid. You cannot feel this pressure because you are supported by equal air pressure on all sides and your body is filled with fluids (gases and liquid) that push back. For solids, the pressure pushes downward. When you stand up the weight of your body is pushing down on the floor. For a fluid, the pressure at any one point is the same in all directions. • Density: One property of all matter is density. Density is a measure of a solid or fluid’s mass in a set amount of space (volume). Any fluid (or solid) at a given temperature and pressure will have a fixed volume. The fluid will also have a certain mass, which is usually measured in pounds or kilograms. Density is a ratio of the mass to its volume. For example, one cup of motor oil weighs far more than one cup of air, making the density of oil higher than the density of air. • Viscosity: Viscosity is a measure of a fluid’s resistance to flow. It is sometimes referred to as the ‘‘flowability’’ of the liquid. This is a common property to measure in science, as it gives information as to how the material will behave. In general, thicker fluids have a greater 439
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WORDS TO KNOW Density: The mass of a substance divided by its volume. Fluid: A substance that flows; a liquid or gas. Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/ or experiment.
Non-Newtonian fluid: A fluid whose property do not follow Newtonian properties, such as viscosity can vary based on the stress. Shear stress: An applied force to a give area. Surface tension: The attractive force of molecules to each other on the surface of a liquid.
Mass: Measure of the total amount of matter in an object. Also, an object’s quantity of matter as shown by its gravitational pull on another object.
Variable: Something that can affect the results of an experiment.
Matter: Anything that has mass and takes up space.
Viscosity: The measure of a fluid’s resistance to flow; its flowability.
Newtonian fluid: A fluid that follows certain properties, such as the viscosity remains constant at a given temperature.
Volume: The amount of space occupied by a three-dimensional object.
resistance to flow, which means a higher viscosity. Motor oil, for example, has a high viscosity when compared to water. In some fluids, viscosity can change. Motor oil thins as it heats and thickens as it cools. A water strider utilizes surface tension of water to float. # VI SU AL S UNL IM IT ED/ CO RB IS.
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Fluid categories Because fluids is such a large category there are many ways to identify and categorize them. One category of fluids is whether it acts as a Newtonian or non-Newtonian fluid. This is named after the English scientist Isaac Newton (1642–1727). Newtonian fluids in general have a constant viscosity given the same temperature and pressure. Water is a Newtonian fluid. When you pour out a large bottle of water the first cup flows at the same rate as the last. If you shake the bottle and pour it again, the water will flow at the same rate. But many fluids fall under the category of non-Newtonian fluids. In non-Newtonian fluids, the viscosity changes depending on the forces acting on the Experiment Central, 2nd edition
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fluid. The force is known as the shear stress, meaning the fluids are sheared or deformed. Applying shear stress to non-Newtonian fluids will change the viscosity. Turn a bottle of ketchup upside down and you’ll usually wait for the ketchup to flow. But if you shake the ketchup bottle and pour again, the ketchup will flow at a much faster rate. Its viscosity has lowered. Some non-Newtonian fluids will become more viscous (thicker) when shear force is applied. A non-Newtonian fluid also may change viscosity with temperature and pressure changes. Yogurt, quicksand, and paints are other examples of non-Newtonian fluids.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of fluid • the temperature of the fluid • the container holding the fluid • the object moving through the fluid • the amount of fluid In other words, the variables in this experiment are everything that might affect the time it takes for the object to sink. If you change more than one variable at a time, you will not be able to determine which variable had the most effect on the viscosity.
Fun with fluids Another important property of fluids is the surface tension, which is a measurement of how much the liquid molecules tend to stick together. Compared to many fluids, water has a relatively high surface tension. This is why water bugs can ‘‘walk’’ along the water’s surface.
Fluids also move at different speeds or velocities. Then there are fluids that form a coil, like a rope, when it streams downwards and others that drop in a straight line. Some fluids spatter more than others. In the experiments that follow, you will examine different properties of fluids. As you conduct the experiments, consider questions about the fluids that you would like to explore further.
EXPERIMENT 1 Viscosity: How can temperature affect the viscosity of liquids? Purpose/Hypothesis Viscosity is an important property of fluids. In
general, liquids that are thick have a relatively high viscosity and thin liquids have a low viscosity. Most fluids have a constant viscosity at a fixed temperature. In this experiment, you will explore how changing the temperature of fluids may affect the viscosity. Experiment Central, 2nd edition
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100 ml
Step 1: Pour honey into the graduated cylinder to the 100 ml mark. I LL UST RA TI ON BY T EM AH NE LS ON.
You will first test the viscosity of the fluid at room temperature by timing how long it takes for an object to move through the fluid. The thicker the fluid, the longer it takes for the object to fall. The fluids in this experiment are honey and cooking oil. By lowering and increasing the temperature of the honey and oil, you can measure how temperature affects the viscosity of the two fluids. To begin the experiment, use what you have learned about fluids and make an educated guess about how temperature will affect the viscosity of a fluid. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The colder the liquid; the higher its viscosity and the warmer the liquid, the lower its viscosity.’’ In this case, the variable you will change for each material is the temperature. The variable you will measure is the time it takes an object to move through the fluid. Level of Difficulty Moderate. Materials Needed
• stopwatch • graduated cylinder, 100 ml (or a narrow see-through container about a foot tall, such as a shampoo bottle) • honey • cooking oil • small paperclips, at least 6 442
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• 2 pots, which the graduated cylinder fits into (stew pots work well); 1 pot will also work • potholders • chopsticks or other long, slender item
How to Experiment Safely Be careful when working with hot water. Always use a potholder and have an adult help you when working with the boiling water.
Approximate Budget $5 (assuming you can find
or borrow a stopwatch). Timetable One hour and 30 minutes. Step-by-Step Instructions
1. Pour honey into the graduated cylinder to the 100 ml mark. If you are using another container, mark a line where you fill the honey. 2. Drop the paperclip into the honey. Use the stopwatch to time how long it takes for the paperclip to hit the bottom. Repeat for two more trials and make a note in a chart. 3. Remove the paperclips (chopsticks work well) and fill the honey again to the 100 ml or to the line. 4. To heat the honey: Fill the pot with water until is slightly below the top of the graduated cylinder. (Be careful not to get any water into the honey) Remove the graduated cylinder and heat the pot of water until it simmers. Turn off the heat. Carefully, place the graduated cylinder in the middle of the pot. Allow it to sit in the hot water for 15 to 20 minutes. 5. Use the potholders to remove the graduated cylinder. Again, drop a paperclip into the honey and time how long it takes for it to hit the bottom. Repeat two more times. 6. Remove the paperclips and fill the honey to the same height. 7. To cool the honey: Fill the second pot with ice. (If you only have one pot, pour Experiment Central, 2nd edition
Step 2: Drop the paperclip into the honey. IL LUS TR ATI ON B Y TEM AH N EL SON .
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Troubleshooter’s Guide It is common for experiments to not work exactly as planned. Learning from what went wrong can also be a learning experience. Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: There was no change in viscosity when the liquids changed temperature. Possible causes: If you were using a container that was insulated, the honey and oil may have been too insulated from the surrounding water temperatures. Make sure the hot water is hot and the cold water is ice-cold, and that the container is not insulated. You can use a thermometer to make sure that the honey and oil are changing temperatures. Repeat the trials. Problem: The paperclip is dropping too quickly to measure. Possible causes: Use a taller container, such as a 100 ml graduated cylinder, and make sure you are using a small paperclip. You may also need to find a more accurate timer or stopwatch. Repeat the experiment.
out the hot water.) The ice should not be higher than the honey in the graduated cylinder. Add cold water and set the graduated cylinder in the middle of the pot. Allow it to set for 20 minutes. 8. Remove the honey and conduct three trials on how long the paperclip takes to fall to the bottom. 9. Clean the graduated cylinder, and repeat the entire process, replacing the honey with cooking oil. Summary of Results Average the three trials for
each of the liquids. How does the viscosity of the liquids compare to one another? How did temperature affect both fluids? You may want to make a bar chart of your results. Write a paragraph summarizing and explaining your findings. Change the Variables If you want to change the
variables in this experiment, you can try changing the fluids. Compare the viscosity of several different liquids. You can focus on different types of oils, for example, or test a variety of liquids. You can also examine how gradations of heat or cold affect viscosity. You can use a thermometer and measure viscosity at specific temperature increments.
EXPERIMENT 2 Spinning Fluids: How do different fluids behave when immersed in a spinning rod? Purpose/Hypothesis One property of some non-Newtonians fluids is the
tendency for the liquid to climb up a spinning rod. This characteristic is known as the Weissenberg effect—named after the scientist Karl Weissenberg, whose experiments demonstrated many properties of non-Newtonian fluids. 444
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In this experiment you will compare the properties of three fluids when the fluids are submerged in a spinning rod. You can compare water, a Newtonian fluid, to two different fluids: egg whites and a viscous fluid made up of glue and borax. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of fluids. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the composition of the liquids • the speed of the spinning rod • the amount of time the rod spins • the temperature of the liquids In other words, the variables in this experiment are everything that might affect the properties of the fluid. If you change more than one variable, you will not be able to tell which variable had the most effect on whether the fluid climbed up the rod or not.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Only the fluid made from glue will climb up a spinning rod.’’ In this case, the variable you will change is the liquid, and the variable you will measure is whether the object moves up the rod or not. Level of Difficulty Easy/moderate (due to the use of a power tool and
cutting). Materials Needed
• • • • • • • • • •
drill white school glue, washable borax thick plastic glass plastic cup plastic spoons drill 3 eggs ruler clock with a minute hand
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• waterproof marker • 1/4-inch diameter aluminum rod (available from hardware stores) • paper towels • hack saw or other tool to cut metal
How to Experiment Safely Have an adult cut the aluminum rod. Be careful when working with the drill and have an adult present.
Approximate Budget $8. (If your household
does not have a drill try to borrow one.) Timetable 20 minutes. Step-by-Step Instructions
Step 6: Place the drill in the glass and turn it on for 1 minute. I LLU ST RAT IO N BY T EM AH NEL SO N.
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1. Have an adult cut the aluminum rod at about the 9-inch (23-centimeter) mark. The exact length does not matter; the rod should be about 2 to 3 inches (5–7 centimeters) longer than the top of the glass. 2. Use the marker and ruler to mark onequarter inch (0.64 centimeters) notches on the rod. Start at the 1-inch (2.54centimeter) mark and continue until you reach about half-way up the rod. 3. Set the rod in the drill and have an adult help you tighten the rod in the drill. 4. Pour approximately three-quarters of a cup of water into the glass. 5. Set the glass on a counter so it is about eye level, or you may need a helper to hold the drill. You should be able to see the marks on the rod. 6. With an adult helping, place the drill in the glass and turn it on for one minute. Observe how the water is behaving as the rod is spinning. 7. Note if the water climbed up the rod at all by looking at the marks. 8. Empty out the glass and wipe off the rod. 9. Carefully, separate the eggs and drop the egg whites into the glass. Experiment Central, 2nd edition
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10. Repeat Steps 5–8, noting how far the egg whites climbs up the rod. 11. Use the plastic spoons to measure out 8 teaspoons (2 tablespoons) of white glue and 8 teaspoons of water into the cleaned glass. 12. In a plastic cup and using a clean spoon, place one-half of a teaspoon of borax and 8 teaspoons of water (one-half cup). Mix well. 13. Pour the borax solution into the glass and briefly stir. 14. Repeat Steps 5–8, noting how far the glue fluid climbs up the rod. Summary of Results Examine how far each fluid climbed up the rod. Was
there a large difference among the fluids? Was your hypothesis correct? Consider the similarities and differences in how the three fluids behaved. You might want to graph your results and write a paragraph on your conclusions.
Step 11: Use the plastic spoons to measure out 8 teaspoons (2 tablespoons) of white glue. ILL US TRA TI ON B Y TE MA H NEL SO N.
Change the Variables To change the variables, you can use one of the
fluids and experiment with changing the temperature. What would happen in a cooler or warmer environment? You could also use many different fluids.
Design Your Own Experiment How to Select a Topic Relating to this Concept The experiments pre-
sented here touch upon only a few aspects of the properties of fluids. With so many fluids, there are many categories and characteristics fluids demonstrate. Consider fluids you use and come across in daily life. Are there questions you have about why they behave in certain ways? Check the Further Readings section and talk with your science teacher for experiment idea that interest you related to fluids. You might also want to read about and investigate polymers. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be Experiment Central, 2nd edition
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Troubleshooter’s Guide When doing experiments, you may not get the results you intended but your findings can still be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problem.
sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Problem: None of the solutions climbed up the rod. Possible cause: Your drill may not have had enough power. If your drill has settings, turn the drill to the most powerful setting and allow the rod to spin for longer. Repeat the experiment. Problem: The glue solution became too puttylike for it to move. You may have used too much borax. If you are using plastic spoons, make sure you are not heaping borax into the teaspoon. You can also try adding a couple teaspoons more water and repeat the experiment.
Recording Data and Summarizing the Results In
the experiments included here and in any experiments you develop, you can look for ways to display your data in more accurate and interesting ways. Problem: The rod keeps moving around. Remember that those who view your results Possible cause: The rod may not be centered in may not have seen the experiment performed, so the drill. Have an adult help loosen and center you must present the information you have gaththe rod, then retighten. Repeat the experiment. ered in as clear a way as possible. Including photographs or illustrations of the steps in the experiment is a good way to show a viewer how you got from your hypothesis to your conclusion. Related Projects To develop other experiments related to fluids, think
about liquids you have used or are familiar with. Why does paint stick to the brush? Investigate the surface tension of water compared to other fluids. Investigate the fluid properties of oobleck, a cornstarch and water mixture. You can also investigate how knowing the properties of fluids can help in food science, crime solving, or materials science.
For More Information Polymer Science Learning Center, University of Southern Mississippi. The MacroGalleria. http://pslc.ws/macrogcss/maindir.html (accessed on 448
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February 26, 2008). Detailed site on all aspects of polymers, from studying them to everyday applications. Ray, C. Claibourne. The New York Times Book of Science Questions and Answers. New York: Doubleday, 1997. Addresses both everyday observations and advanced scientific concepts on a wide variety of subjects. ‘‘The States of Matter.’’ Faces in the Molecular Sciences: Faces in Polymers. http:// www.chemheritage.org/educationalservices/faces/poly/tutorial/states.htm (accessed on April 22, 2008). Information on the states of matter. Van Cleave, Janice. Chemistry For Every Kid. New York: John Wiley and Sons, Inc., 1989. Contains a number of simple and informative demonstrations and investigations, including the properties of water.
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Food Preservation
F
ood preservation is easy to take for granted. It’s become common to open a can of fruit in the winter or keep a bag of frozen vegetables for weeks. We store produce and meats in the refrigerator where we might not grab it for days. If the foods are dried, they can sit on a shelf for months before making their way into a meal. Food preservation certainly makes life more convenient but because we need food to live, it also improves people’s lives. The back story Food preservation is the process of treating foods in order to stop or slow spoilage. The moment after a plant is harvested or an animal is slaughtered, the spoilage process begins. Spoiled food can cause vomiting, nausea, or more severe symptoms. Bugs, microorganisms, and the natural environment can all cause food to spoil. In many cases, spoiled food is noticeable by its odor, sight, or texture. Life before food preservation was challenging. The goal was to eat food before it spoiled. People needed to live near where food was produced or grown so they could eat it soon after it was collected. During seasons when food was scarce, people were hungry. In seasons when there was plenty of food, with no way to preserve it the extra food would spoil. When cultures discovered preservation methods, they could stay in one place instead of constantly traveling to find fresh food. For people who wanted to travel, they now could bring food with them. Oldies but goodies Ancient cultures used some of the same preservation methods we still use today. Many preservation techniques center around removing water and oxygen. Microorganisms need water and oxygen to live, and many chemical reactions that can cause spoilage use these substances. 451
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salt water molecules
Salt pulls water out of the food through the process of osmosis. IL LUS TR ATI ON B Y TE MA H NE LS ON.
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• Salting: Covering a food in salt is one of the oldest forms of food preservation. Salt pulls water out of the food through the process of osmosis. In osmosis, a substance moves across a semipermeable membrane from an area of high concentration to an area of low concentration. A semipermeable membrane lets some substances through but not others. The salt concentration on the outside of the food is higher than the salt concentration inside the cells in the food, and the water moves out of the cells to balance out the concentration. Along with removing water from the food, a high-salt content is not an environment where many microorganisms can grow. • Sugar: Sugar can also cause osmosis, pulling water out of the food. Sugar that is combined with salt and/or other substances is curing. Meats are commonly preserved by curing. • Pickling: Combining the preservation properties of salt with those of an acid is pickling. An acid environment, such as vinegar, is not a desirable living environment for microorganisms. Pickled foods are first soaked in a salt solution and then stored in vinegar, often with spices. • Canning: In the late 1700s, French Emperor Napoleon Bonaparte realized that a lot of the men fighting in his army were starving and sick from poor nutrition. He offered a large amount of money to anyone who could come up with a way of preserving food. Nicholas Appert, a French candy maker, won the prize 14 years later with the first canning method. He placed the food in sealed glass bottles and then heated it. Decades later the French chemist Louis Pasteur (1822–1895), found out why this method worked. (He saw that it was microorganisms causing disease, and that heating the food killed the microorganisms.) Canning kills the microorganisms and then seals up the food from air and microorganisms. Once the can is Experiment Central, 2nd edition
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opened, the food is at risk of becoming spoiled. Fruits, soups, and vegetables are foods commonly canned. • Drying: Also called dehydration, drying is one of the oldest preservation methods that is still widely used today. In drying, heated air evaporates the water in the food. Without water, the microorganisms cannot grow and spoilage chemical reactions cannot take place. Ancient cultures dried food in the sun. The French developed the first artificial dehydrator where it was used in 1795 to dry vegetables. Eggs, milk, pasta, fruits, and vegetables are a few of the foods typically dried. • Freeze drying: A form of drying, freeze drying was first used to preserve blood back in the 1890s. Food that is freeze dried removes water from the food while the food is frozen. The frozen food is placed in a strong vacuum chamber and is heated. Water in the food evaporates, moving from ice straight to gas without ever turning into a liquid. Freeze dried food is light and lasts a relatively long time. Coffee is a food that is typically freeze-dried, along with apples and other fruit. Food for astronauts is freeze-dried. When water is added back to the food, the natural flavor of the food returns. Basic preservations There are several other basic methods of food preservation. Keeping food cold in the refrigerator or freezer slows the growth of microorganisms. When food is vacuum-sealed, the oxygen is removed and microorganisms cannot survive. Chemical additives are also used to preserve food. Some chemicals are natural, such as vitamin C, and others are synthesized (manmade).
Keeping food cold in the refrigerator slows the growth of microorganisms AP P HO TO/ JIM MC NIG HT .
All food preservation techniques can affect the flavor. The type of preservation used depends upon the food and its intended storage time. In the following two experiments, you can experiment with different methods of food preservation. As you conduct these experiments, consider questions you want to find out about food preservation. Experiment Central, 2nd edition
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WORDS TO KNOW Canning: A method of preserving food using airtight, vacuum-sealed containers and heat processing. Concentration: The amount of a substance present in a given volume, such as the number of molecules in a liter. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Osmosis: The movement of fluids and substances dissolved in liquids across a semipermeable membrane from an area of its greater concentration to an area of its lesser concentration until all substances involved reach a balance. Semipermeable membrane: A thin barrier between two solutions that permits only certain components of the solutions, usually the solvent, to pass through.
Dehydration: The removal of water from a material.
Synthesize: Something that is made artificially, in a laboratory or chemical plant, but is generally not found in nature.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Variable: Something that can affect the results of an experiment.
EXPERIMENT 1 Sweet Preservatives: How does sugar affect the preservation of fruit? Purpose/Hypothesis The purpose of this experiment is to measure how
sugar is used in keeping fruit from spoiling. The fruit you will use is strawberries. When strawberries spoil they can become soft and form black or white rot on them, caused by fungus. The experiment will have four strawberry setups. You will use table sugar and water to make two different concentrations of syrup. You can then compare the preservation of strawberries soaked in syrups against a strawberry coated in sugar, and a plain strawberry. The strawberry with nothing added to it will be the control. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of food preservation and fruit. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change 454
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• the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The strawberry with the heaviest syrup— the most sugar—will be preserved the longest.’’ In this case, the variable you will change is the sugar environment surrounding the strawberry. If the strawberry in the heaviest syrup remains unblemished longer than the other test strawberries, you will know your hypothesis is correct. Level of Difficulty Moderate. Materials Needed
• • • • • • • • •
What Are the Variables? Variables are anything that might affect the results of an experiment. This experiment involves both environmental variables and biological variables. Here are the main variables in this experiment: • the presence of air • the type of strawberry • the ripeness of the strawberry • the type of sugar • the temperature of the environment In other words, the variables in this experiment are everything that might affect the spoilage of the strawberry. If you change more than one variable, you will not be able to tell which variable had the most effect on the preservation.
sugar pot measuring cups and tablespoons stirring spoon 2 bowls toothpicks paper and markers, for labeling 4 narrow glasses or small, shallow dishes 4 strawberries, all the same type and purchased at the same time
Step 2: Add 1 cup water and 10 tablespoons sugar (½-cup plus 2 tablespoons). IL LU STR AT IO N BY T EM AH NE LS ON.
Approximate Budget $5. Timetable 1 hour working time; 10 minutes
daily over four to seven days. Step-by-Step Instructions
1. Label each of the glasses: 1) heavy syrup; 2) light syrup; 3) sugar; 4) control. 2. To prepare the heavy syrup: In a pot, add 1 cup water and 10 tablespoons sugar (½-cup plus 2 tablespoons). Experiment Central, 2nd edition
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How to Experiment Safely Ask an adult to help you when working over the hot stove. This experiment will need an environment outside of the refrigerator where food will remain undisturbed for up to a week. Ask an adult for the best place to setup the experiment. After the experiment is complete, throw away all the foods and clean the dishes well. When experimenting with food preservation, do not taste or ingest any of the food items, and make sure to mark the item clearly to keep others away.
3. Heat slowly while stirring until the sugar is dissolved and the water comes to a boil. Pour into a bowl and place in the refrigerator. (If a refrigerator is not available, you can set the bowl in a larger bowl with ice.) Rinse the pot. 4. To prepare the light syrup: In a pot, add 1 cup water and 4 tablespoons sugar. Bring to a boil, stirring occasionally until the sugar is dissolved. Pour into another bowl and place in the refrigerator. 5. Wait approximately 30 minutes. The syrups should be cool to the touch.
6. When the syrups are room temperature or slightly below, place one strawberry in each of the four glasses. Try to find strawberries that are approximately the same size, and make sure each strawberry does not have any blemishes.
control
light syrup
heavy syru
p
sugar
After setting up the experiment, inspect all your strawberries without touching them. I LLU ST RAT IO N BY TEM AH NEL SO N.
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7. Coat the strawberry in the ‘‘sugar’’ glass with sugar and set back in the glass. 8. Pour the heavy syrup over the strawberry in the designated glass and the light syrup in the ‘‘light syrup’’ glass. The syrup should just cover the top of the strawberry. 9. Set the glasses aside in a place where they will be undisturbed (and no one will eat them!).
Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: One of the strawberries that was preserved spoiled faster than the control. Possible cause: You may have selected a strawberry that was already bruised and in the process of spoiling. Repeat the experiment, making sure that all the strawberries are fresh and firm. If you see any blemishes or black indentations in the berry, choose another strawberry.
10. The next day, inspect all your strawberries without touching them. Make a chart and note if there are marks, colors, or any signs of spoilage on each strawberry. Use a toothpick to poke each strawberry and test if it is soft or hard, compared to the control. You may want to sketch a picture of each strawberry.
11. Repeat Step 10 every day, for up to a week or until some of the strawberries are noticeably spoiled. Summary of Results Analyze your results and if you have pictures or
sketches compare them to one another. Look at what day each of the strawberries began to show signs of spoilage. How does the strawberry covered with water compared to those in sugar-water? What does the strawberry coated in sugar illustrate about osmosis? Consider how you would want to preserve strawberries, based on your results. Write up a summary of your experiment. Change the Variables To further explore how sugar affects fruit preser-
vation, you can vary the experiment in the following ways: • Use different types of strawberries, organic versus non-organic, for example, and keep the sugar syrup the same. • Try experimenting with different types of sugar, such as brown sugar or natural cane sugar. • Alter the environment of the strawberries, using a warmer or cooler environment Experiment Central, 2nd edition
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EXPERIMENT 2 What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the time of day • the condition of the fruit • the environment the fruits are kept in • the length of time the fruits sit out • the size of the fruit • the type of fruit In this case, the variable you will change is the moisture content of the fruit. The variable you will measure is mold, blemishes, or an other appearance of spoilage. At the end of the experiment you will compare the dry fruit and moist fruit.
Step 4: Weigh the peach slices on the gram scale. I LLU STR AT IO N BY T EM AH NEL SO N.
Drying Foods: Does drying fruits help prevent or delay spoilage? Drying foods in the sun is one of the oldest preservation techniques people have used. Bacteria and other organisms need water to live, and drying removes the moisture from the food. In this experiment you will dry fruits in the sun and calculate how much moisture the fruit contained. You can then compare spoilage of the dried fruits to the non-dried fruit. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of food preservation and drying. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The dried fruits will delay the appearance of spoilage when compared to the same fruit that is not dried.’’ Level of Difficulty Moderate. Materials Needed
• 2 peaches of about the same size and ripeness • gram scale • wax paper 458
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• netting, about 14 inches (36 centimeters) square (available from fabric stores) • 4 strips of wood or other material, each about 12 inches (30 centimeters) long and an inch (2.5 centimeters) thick, that you can apply tape to • Duct or masking tape • knife • helper • props, such as chairs or books to lift the drying rack off the ground • warm, sunny day
How to Experiment Safely Be careful when handling the knife. Never eat the foods when experiment with food preservation and spoilage. When you have finished the experiment, throw all the foods away and wash your hands. When experimenting with food preservation, do not taste or eat any of the food items, and make sure to mark the item clearly to keep others away. Make sure you tell an adult you are conducting this experiment.
Approximate Budget $10 (assuming you can find or borrow a gram scale). Timetable Approximately one week. (About one hour working time in
total; with one day needing to check on the experiment every two hours over a minimum of eight-hours waiting time.) You will need to start this experiment in the early morning. Step-by-Step Instructions
1. In the early morning just as the sun is coming out, begin to make a drying rack. Lay out four pieces of wood blocks or other material into a rectangle. Lay the netting half-way over the pieces. Tape the netting to each of the blocks. The netting should be taut (tight); you will probably need a helper to pull the wood while you tape the netting. 2. Cut one peach into thin slices. Cut as much of the peach as you can and place the slices on a piece of wax paper. 3. Leave the second peach on the counter, at room temperature. 4. Weigh the peach slices on the gram scale and note the weight. 5. Transfer all the peach slices onto the netting. 6. Bring the drying rack to a clear spot in the sun. Use two chairs, books, pots, or other props to set down the drying rack and keep it away from bugs. If you are in an Experiment Central, 2nd edition
Step 6: Bring the drying rack to a clear spot in the sun. ILL US TRA TI ON B Y TE MA H NEL SO N.
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Step 12: Check on both peaches every day for the next 6 days. I LLU ST RAT IO N BY TEM AH NEL SO N.
7.
8. 9. 10.
11. 12.
area where there are a lot of flying bugs, set a piece of netting over the fruit. Set it on the books or other material so that it does not touch the peaches. Check in on the peaches about every two hours. Turn the peaches over and make sure the drying rack remains in the sun. You may need to move it throughout the day. At the end of the day, bring the dried peaches inside and weigh them. Note the weight. Cut up the second peach and place the slices on the piece of wax paper. Weigh the peach slices. It should be similar to the weight of the first peach before it was dried. If it is not, take away or cut up more peach until the weights are similar. Place both peaches on a clean sheet of wax paper and set aside. They should be at room temperature. Check on both peaches every day for the next six days. Note any appearances of spoilage every day.
Summary of Results Compare the spoilage appearance and rates of the
two peaches. Subtract the starting and ending weight of the peach slices to determine how much water the dry peach lost. Was your hypothesis correct? Did the dried fruit show fewer signs of spoilage than the fruit that contained more water. Today, people dry food in a food dehydrator or an oven. Consider how the taste of the food would change with different food drying techniques. Write up a summary of your findings. You may want to include pictures. Modify the Experiment You can modify this experiment in several ways:
• Change the type of fruit, you can apples or bunches of smaller fruits, such as strawberries or grapes. 460
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• Change the amount of time you allow the fruit to dry: what happens if the fruit dries for only four hours compared to eight hours. • Change the environmental conditions the fruit is left out in.
Design Your Own Experiment How to Select a Topic Relating to this Concept Because food spoilage is a serious and
Troubleshooter’s Guide Below is a problem that may happen during this experiment, a possible cause, and a way to remedy the problem. Problem: The peach did not really lose that much water in the sun. Possible cause: The sun may not be strong enough, or it may not have been in the sun the entire day. Try to plan this experiment for a day that will be warm and sunny for the whole day. Also, make sure to move the drying rack so it is facing the sun throughout the day. When you think you will have a sunny day, repeat the experiment.
common problem, people have developed many methods of preserving foods. You can start thinking of ideas by identifying some common preservatives and techniques used in the foods you eat. Look Problem: Neither peach showed more appearat food labels to identify the preservative. You can ance of spoilage. separate the natural and synthetic preservatives. Possible cause: Depending upon the peaches Consider how leftovers are preserved in your home. and environment, you may need to leave the Check the Further Readings section and talk peaches out for a longer period of time. Look with your science teacher to learn more about for any brown spots, and continue monitorfood preservation. You could also talk with a ing the peaches. microbiologist for details on the microorganisms involved in spoilage. When experimenting with food, do not taste or eat any of the food items, and make sure to mark the item clearly to keep others away. When you conduct an experiment with food in the home, make sure you tell an adult. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. Experiment Central, 2nd edition
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• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are projects related to food preservation that are
inexpensive and waiting in the kitchen. You could conduct a project examining the uses of synthesized versus natural preservatives. You could explore how preservative delay spoilage for different types of foods. You could examine packaging that preserves food. How are the properties of different packaging materials designed to preserve specific foods. You could also use expiration dates to compare different food preservatives.
For More Information Dalton, Louisa. ‘‘What’s that Stuff?: Food Preservatives.’’ Chemical & Engineering News, November 11, 2002. http://pubs.acs.org/cen/science/8045/8045sci2. html (accessed on May 16, 2008). Information on various food preservatives. D’Amico, Joan and Karen Eich Drummond. The Science Chef Travels Around the World: Fun Food Experiments and Recipes for Kids. New York: John Wiley, 1996. Food experiments and recipes from around the world. Eating for Health. Vol. 3. Chicago: World Book Inc., 1993. Part of the ‘‘Growing Up’’ series, this volume provides thorough, interesting information about carbohydrates, vitamins, and minerals as well as metabolism, eating disorders, and processing. ‘‘Food: Nutrition, Safety and Cooking.’’ University of Nebraska Lincoln. http:// lancaster.unl.edu/food/myths ss/index.htm (accessed on May 18, 2008). Quiz and common myths on food safety. ‘‘From Farm to Table.’’ www.foodsafety.gov. http://www.foodsafety.gov/fsg/ fsgkids.html (accessed on May 18, 2008). Links to government sites on food safety and spoilage. ‘‘Kids World: Food safety.’’ N.C. Department of Agriculture and Consumer Services. http://www.ncagr.com/cyber/kidswrld/foodsafe/index.htm (accessed on May 18, 2008). Food safety facts and interactive question on spoilage.
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H
ave you ever wondered why bread rises? Or why some chocolates melt in your hand and others remain hard? Why does cooking change the color of some vegetables and cause meat to become more tender? The area of food science covers all of these questions and many more. Food science is a broad topic that applies scientific principles to foods in order to better understand them. We use the applications of food science every day in how we prepare and preserve foods. Food science helps us understand the nutrients in foods and how heat, cold, light, and air can affect them. It explores what foods are made of and looks at chemical reactions that occur when foods are combined. Food scientists also work to develop or improve a food’s flavor, texture, and nutrition. Chemistry, microbiology, and botany are some of the key areas food science covers.
Cooking and flavors Meat is one of the more apparent examples of a reaction that produces a lot of flavor: the Maillard reaction. The Maillard reaction is named after French chemist Louis Camille Maillard who began studying the reaction in 1912. Meats contain a lot of protein molecules, which are held together by bonds. Heat breaks the bonds and the protein unravels. This is called a denatured protein. The reaction between denatured proteins combines with natural sugars (a form of carbohydrates) in the meat. The reaction leads to changes in color and hundreds of flavors. The Maillard reaction is often referred to as the browning reaction, because meat does turn brown. The Maillard reaction also produces the toasty flavor on bread crust and the sweetness of browned onions. Researchers use the Maillard reaction to create many artificial flavors. If you have ever heated sugar and watched it brown you have witnessed another chemical process called caramelization. In caramelization, 463
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which is not related to the caramel candy, sugars move through a series of reactions at high temperature. Heating causes the sugar molecules to lose water and break down. The sugars turn brown and form new flavors. The Maillard reaction and caramelization reactions are so complex that researchers are still trying to understand exactly how they work. The rising of chemical leaveners Place a cake or bread dough in the oven and when it’s cooked, it is a lot higher. A leavening agent is any substance that causes dough or batter to rise, or increase in volume. In general the leavening agent makes food rise by producing air or gas that pushes the food ingredients apart, causing it to expand and increase in volume. In cooking, leavening agents work by chemical reactions and physical changes. Baking powder and baking soda are called chemical leavening agents because they work by chemical reactions. Baking soda is sodium bicarbonate. When moisture and an acid are added to sodium bicarbonate, it causes a reaction that releases the gas carbon dioxide. The bubbles of carbon dioxide push the food apart, causing its volume to increase. Like air, carbon dioxide also expands when heated. The reaction of baking soda starts to work immediately so cooks need to bake the food immediately. Baking powder is a mixture of sodium bicarbonate and an acid ingredient, such as tartaric acid (cream of tartar), along with other dry ingredients. Baking powder does not need an acid added because it is already in there. There are two types of baking powder. Single-acting baking powders start to react immediately with moisture, whether it is warm or cool. Double-acting baking powder reacts ‘‘double’’ because it releases gas in two reactions. Some gas is released immediately when moisture is added. Even more gas is released with heat. That means double-acting baking powder can still cause the recipe to rise even if it sits at room temperature for a period of time. The physical agents that lead to rising When making bread, the typical leavening agent is yeast. Yeast is a natural leavening agent that people have used for thousands of years. It is a live single-celled fungus. Yeast eat sugar in the form of starch, such as in flour, and release carbon dioxide gas and alcohol. Along with making dough rise, people use yeast to produce the alcohol in beer and wine. 464
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hydrophilic
Parts of the protein are attracted to water (hydrophilic or water-loving) and other parts avoid the water (hydrophobic or water-fearing).
hydrophobic air bubble
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Another method of leavening is whipped egg whites. Egg whites are about 90% water and 10% protein. Parts of the protein are attracted to water (hydrophilic or water-loving) and other parts avoid the water (hydrophobic or water-fearing). In its natural state, the hydrophobic parts of the proteins are curled up in the center and the hydrophilic parts are surrounded by water. Beating raw egg whites causes air bubbles to form and the protein molecules to uncurl. The uncurled protein molecules twist about so that the parts that don’t like water touch air. The result is a network of protein molecules that trap the air bubbles in place, causing the egg whites to froth and increase in volume and froth. Baking the frothy egg whites yeast eat sugar makes the bubbles become firm. and release alcohol Heating and change The best method of heating foods is another area of food science. Heating not only can kill harmful microorganisms, but it also affects the flavor, texture, and color of many foods.
Yeast eat sugar in the form of starch, such as in flour, and release carbon dioxide gas and alcohol. ILL US TRA TI ON B Y TE MA H NE LSO N.
alcohol
carbon dioxide
and carbon dioxide
Plants contain chlorophyll, the substance that gives plants its green color. The greener the vegetable, the more chlorophyll it contains. Experiment Central, 2nd edition
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WORDS TO KNOW Blanching: A cooking technique in which the food, usually vegetables and fruits, are briefly cooked in boiling water and then plunged into cold water.
yeasts, and mildews, that do not manufacture their own food. Hydrophilic: Having an attraction for water.
Caramelization: The process of heating sugars to the point at which they break down and lead to the formation of new compounds. Cell wall: A tough outer covering over the cell membrane of bacteria and plant cells. Chlorophyll: A green pigment found in plants that absorbs sunlight, providing the energy used in photosynthesis. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Hydrophobic: Having an aversion to water. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Leavening agent: A substance used to make foods like dough and batter to rise. Maillard reaction: A reaction caused by heat and sugars and resulting in foods browning and flavors. Pectin: A natural carbohydrate found in fruits and vegetables.
Fermentation: A chemical reaction in which enzymes break down complex organic compounds (for example, carbohydrates and sugars) into simpler ones (for example, ethyl alcohol).
Yeast: A single-celled fungi that can be used as a leavening agent.
Fungi: Kingdom of various single-celled or multicellular organisms, including mushrooms, molds,
Variable: Something that can affect the results of an experiment.
Chlorophyll lies in the plants’ cell and heat causes the cell walls to break down. This leads to changes in the chlorophyll, which leads to the vegetable turning browner. One method used to retain the color and texture of vegetables is blanching. In blanching, the food is briefly placed into boiling water and then plunged into cold water. The heat causes the air in the vegetables to expand and boil away, which leads to a more vibrant color. Carrots become more orange and green beans a richer green. The cold water immediately stops the cooking process. In the following two experiments, you will explore two aspects of food science. You will investigate how jelly becomes firm and how different leavening agents make foods rise. 466
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EXPERIMENT 1 Jelly and Pectin: How does acidity affect how fruit gels? Purpose/Hypothesis Pectin is what helps make
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
the gel in fruit gels, such as jellies and marma• the temperature of the mixture lades. Pectin is a type of carbohydrate found in • the amount of time the fruit is cooked plant cell walls. It is found in apples and citrus • the type of fruit fruits, such as limes and lemons, and is most • the amount of lemon juice plentiful in the skin and core. Pectin forms nat• the amount of time the gel is allowed to urally as the fruit ripen. cool When fruit is cooked, the heat causes the cell • the amount of fruit walls to break down and release the pectin. If the • the amount of sugar fruit is cooked in water the pectin moves into the In other words, the variables in this experiment water. The pectin molecules all have the same are everything that might affect the formation charge and so they repel one another. In order to of an apple jelly. If you change more than one make the pectin molecules bond, you need sugar variable, you will not be able to tell which varand the right acidity. Sugar pulls the water moliable had the most effect on the gelling of the ecules together and leaves the pectin on its own. apples. Adding an acidic substance gets rid of the pectin’s negative charges. The pectin can then bond to one another and form a gel. In this experiment you will make apple jam and test how the pH of the mixture affects the gelling of the jam. The pH is a measure of the acidity of a substance. A pH of 7 means the substance is neutral. Water is a neutral substance. The lower the pH, the higher its acidity. For the apple jam, the apples will supply the pectin and lemon juice will provide the acid. Lemons contain citric acid, which gives lemon a pH of approximately 2 to 3. You will make three jams: in one jam you will add lemon juice; the second jam you will add half the amount of lemon juice; and the third jam will not include any lemon juice. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of food science and gels. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change Experiment Central, 2nd edition
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How to Experiment Safely
• the variable you will measure • what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The apple jam with the most lemon juice will form the firmest gel.’’ In this case, the variable you will change will be the amount of lemon juice. The variable you will measure will be the firmness of the gel.
Be careful when handling the knife and working on the stove. Ask an adult for help when pouring the hot apple liquid into the strainer.
Level of Difficulty Moderate. Materials Needed
Step 1: Gather the sugar, lemon juice, and apples. I LLU ST RAT IO N BY T EM AH NEL SO N.
• • • • • • • • • • •
3 tart apples, about the same size (Macintosh or Jonathan work well) pot measuring cup strainer or colander bowl that fits under strainer or colander lemon juice teaspoons toothpicks plastic wrap stirring spoon cutting knife • spatula or stirring spoon • 3 small thick glass jelly jars, the same size (you could also use small bowls)
Sugar Lemon Juice
Approximate Budget $5. Timetable Approximately two hours (one hour
working time and one hour waiting). Step-by-Step Instructions
1. Label one glass (or bowl) ‘‘1 tsp. lemon;’’ the second glass ‘‘½ tsp;’’ and the third glass ‘‘0.’’ 468
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2. Cut the three apples into quarters and cut those quarters again. You should include the skins and cores. 3. Pour 3/4-cup water into a pot. Add the apple chunks and heat until the apple mixture is mushy. This should take about 20 minutes. 4. When the apples are soft, place the bowl under the colander and pour the applewater mixture into the colander. The colander should strain out the seeds and skin. You will need to press the apple mixture through the colander with a spoon or spatula. 5. Allow the mixture to cool for about 15 minutes and then divide the apple mixture evenly into thirds. 6. Place one-third of the mixture back in the pot. 7. Add 3 and ½-tablespoons of sugar. 8. Add 1 teaspoon of lemon juice. 9. Boil for approximately five to six minutes, stirring occasionally, until large bubbles appear. The droplets should be large and come together to form a ‘‘sheet.’’ (See illustration) 10. Pour the mixture into the 1 tsp jelly glass until the glass is about 3/4 full. Rinse out the pot 11. Repeat Steps 6 through 9 for each of the two remaining test jellies. Replace the 1 teaspoon of lemon juice with ½-teaspoon for the second jelly and no lemon juice for the third jelly. 12. Allow all the jellies to cool for at least an hour, until they have reached room temperature. 13. If a ‘‘skin’’ has formed on any of the jellies, carefully remove it. 14. Poke each jelly with a toothpick and note the results. 15. Cover the glass jars with plastic wrap and flip each jar upside. Note your observations. Summary of Results Look over your observa-
tions of each of the jellies. Was your hypothesis correct? Note any other differences between the Experiment Central, 2nd edition
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Step 4: You will need to press the apple mixture through the colander with a spoon or spatula. IL LU STR AT IO N BY TEM AH N EL SON .
Step 9: The droplets should be large and come together to form a ‘‘sheet.’’ IL LU STR AT IO N BY TE MA H NE LSO N.
Sheeting
Done
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, possible causes, and a way to remedy the problem. Problem: None of the jellies formed a gel. Possible cause: The fruit may have been too overripe, in which case the fruit does not contain enough pectin. Try the experiment again, using apples that are just slightly underripe. Possible cause: You may not have heated the apple mixture for enough time. When a cold metal spoon is placed in the mixture, the droplets should come together before falling off the spoon. Repeat the experiment, heating the mixture for 1 or 2 minutes longer.
jellies, such as the color or texture. Write a paragraph summarizing your results. Change the Variables You can conduct several
similar experiments by changing the variables. You can change the type of acid. You can also try peeling and coring the apple, to determine what parts of the apple contains the most pectin. You could also try altering the environment the jelly sets in.
EXPERIMENT 2 Rising Foods: How much carbon dioxide do different leavening agents produce? Purpose/Hypothesis Chemical leavening agents
need an acid and moisture to produce carbon dioxide. Double-acting baking powder releases carbon dioxide in two chemical reactions: with the addition of an acid and heat. In this experiment you will measure the amount of carbon dioxide produced by baking soda, baking powder, and double acting baking powder. After adding water, you will trap the carbon dioxide in a balloon. By measuring the balloon’s circumference (the distance around the balloon), you can determine the rate at which carbon dioxide is produced. For each of the leavening agents you will measure the amount of gas in the balloon with the leavening agent at room temperature and heated. Which leavening agent do you think will produce the greatest amount of carbon dioxide with heat? Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of food science and leavening. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
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A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The double acting baking powder will produce the greatest amount of carbon dioxide when heat is applied.’’ In this case, the variable you will change is the leavening agent. The variable you will measure is the circumference of the balloon as it fills with carbon dioxide. Level of Difficulty Moderate. Materials Needed
• • • • • • • • • • • •
• • • • •
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the time allowed for the leavening agent to produce gas • the type of leavening agent • the temperature of the water added to the leavener • the volume of the bottle • the type and shape of the balloon In other words, the variables in this experiment are everything that might affect the amount of carbon dioxide the leavening agent produces. If you change more than one variable at the same time, you will not be able to tell which variable affected the circumference of the balloon.
3 balloons, the same size and type string marker ruler or tape measure baking powder double acting baking powder baking soda vinegar or lemon juice measuring spoons bowl cup 3 small plastic or glass bottles, approximately 3 inches (7.6 centimeters) high and with a top small enough to pull a balloon over (small spray or lotion bottles work well); you can also use one bottle and rinse it out timer or clock with minute hand funnel wax paper (optional) small pan helper
Approximate Budget $10. Timetable 45 minutes. Experiment Central, 2nd edition
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Step-by-Step Instructions
How to Experiment Safely
1. Fill up the bowl with room temperature water. You will need about a cup. In this experiment you will be working with 2. Set several cups of water in the pot or boiling water. Be careful when pouring and kettle to boil. working around the water. 3. Stretch out all the balloons several times. Line up the balloons next to one another so that they are even. Mark a line on the balloons at the widest part, so that all the marks are even. This is the point where that should be the widest part; where you will measure the balloons circumference. 4. Place a teaspoon of baking soda in the bottle. Depending upon how large the bottle opening is, you may need to pour the baking soda onto wax paper and then fold the wax paper to direct the soda in. 5. With a helper, place the funnel in the balloon opening and pour in 3 tablespoons of the water from the bowl. If the balloon fills up, stretch it out and keep adding the water. When you are done the Step 6: With someone holding top of the balloon should not have water in it. the bottle, slip the balloon 6. With someone holding the bottle, slip the balloon opening over opening over the bottle top. IL LU STR AT ION BY the bottle top. Empty the water into the bottle and begin timing. TE MAH NEL SO N. 7. After one minute, wrap the string around the balloon at the marked spot (the widest part) and draw a line on the string where it has wrapped. 8. After two minutes wrap the string around the balloon at the same line and mark its circumference. Repeat after three minutes. 9. Pour boiling water into the cup until it is about half way full and set the bottle in the cup. Hold the bottle down so that the hot water surrounds the water inside the bottle. 10. Every minute for the next three minutes, place the string around the balloon and mark its circumference. Remember to 472
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line the string up with the mark on the balloon. 11. Repeat Steps 4–10 for the baking powder and then the double acting baking powder. For each leavening agent, use a new piece of string and line it up with the mark on the balloon. If you use the same bottle, make sure to rinse it well after each use. 12. Measure each of the marks on the three strings and record your data. Summary of Results Create a data table to record
your observations. You may want to graph your results, with the rate of expansion on one axis and the number of minutes on the other axis. Make a separate line or color for each of the leavening agents. Was your hypothesis correct? You may want to look through recipes to see which leavening agents are used for which types of foods. What are the other ingredients in the recipe that would activate the leavening agent? Change the Variables There are several ways that you can change this
experiment. You can focus on the leavening properties of baking soda and change the type of acid. Buttermilk and orange juice are two other acid solutions. You can also change the proportions of acid you mix with the baking soda. Using the same recipe, you can test how different leavening agents cause the food to rise. If you were making cookies, what results would each leavening agent produce?
Step 9: Hold the bottle down so that the hot water surrounds the water inside the bottle. ILL US TRA TI ON B Y TE MA H NEL SO N.
Step 10: Every minute for the next three minutes, place the string around the balloon and mark its circumference. IL LU STR AT IO N BY T EM AH NE LS ON.
Design Your Own Experiment How to Select a Topic Relating to this Concept
Food is such an important part of people’s lives that ideas to explore the science behind foods and how they work together are all around. You might want to look at the ingredients in your favorite food items or dishes. Think about what Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to fix the problem. Problem: The balloon did not expand much for any of the leavening agents. Possible cause: The leavening agent(s) may be too old to produce a reaction. To test whether the baking powder has expired, and a few pinches of baking powder to a couple tablespoons of room temperature water. The mixture should bubble and fizz. Replace the water with vinegar to test the baking soda. If the leavening agents are too old, buy a new baking powder or soda and repeat the experiment. Problem: The balloon kept tearing when placing it over the bottle. Possible cause: The balloon is probably too small and stretching may not help. Try finding a bottle with a smaller cap or a larger balloon. Make sure to stretch the balloon several times, and repeat the experiment.
the properties of all the ingredients add to the food. Consider your favorite meals, snacks, and drinks and you may want to explore how these foods are prepared and why. Check the Further Readings section and talk with your science teacher to gather information on food science questions that interest you. You may want to talk with someone you know who enjoys cooking. As you consider possible experiments, be sure to discuss them with a knowledgeable adult before trying them. Steps in the Scientific Method To do an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what your are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Recording Data and Summarizing the Results It’s always important to write down data and ideas you gather during an experiment. Keep a journal or record book for this purpose. If you keep notes and draw conclusions from your experiments and projects, other scientists could use your findings in their own research. Related Projects Food science experiments can go in many different
directions. For example, you might focus on the properties of one food 474
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type, such as milk or chocolate. How does this one food react to heat, cold, or with other commonly added substances? Does the order of ingredients make a difference in the finished texture or flavor? What chemical properties of the food cause it to react this way? You might also look at blending certain foods together. For example, why does salt alter the taste of certain dishes? Another possibility is to experiment with how cooking methods affect foods. Blanching, boiling, and baking all can affect the same food in different ways. You can look at techniques chefs use to preserve certain flavors while they are cooking foods.
For More Information Arnold Nick. Freaky Food Experiments. United Kingdom: Scholastic, 2007. Experiments with and about food. BBC. ‘‘Science of Cooking.’’ Science and Nature: Hot Topics. http:// www.bbc.co.uk/science/hottopics/cooking/ (accessed on May 21, 2008). Clear explanations, animations, and video of many cooking food science topics. Eating for Health. Vol. 3. Chicago: World Book Inc., 1993. Part of the ‘‘Growing Up’’ series, this volume provides thorough, interesting information about carbohydrates, vitamins, and minerals as well as metabolism, eating disorders, and processing. Exploratorium. Science of Cooking. http://www.exploratorium.edu/cooking/ (accessed on May 21, 2008). Recipes, illustrations and clear explanations of the science behind many foods, including pickles, candy, bread, and meat. Kids Health. Food and Nutrition. http://www.kidshealth.org/kid/nutrition/ index.html#All About Food (accessed on May 22, 2008). Series of easy to read articles on food and nutrients. Planet Science. The Planet Science Diner. http://www.planet science.com/ outthere/index.html?page=/outthere/diner/index.html (accessed on May 22, 2008). Clear information on many aspects of kitchen chemistry. Wolke, Robert L. What Einstein Told His Cook: Kitchen Science Explained. New York: W. W. Norton and Co., 2002. Answers to common questions about cooking and food science in a simple, clear style.
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hen food has spoiled it is usually noticeable to your senses of smell and sight. Spoilage is when food has taken on an undesirable color, odor, or texture. Eating spoiled food can result in food poisoning, which can cause vomiting, nausea, and more severe symptoms. There are two main causes of natural food spoilage: microscopic organisms and chemical changes. Attack of the microbes Leave food out on the kitchen countertop and within seconds it can become the home of microorganisms that are floating by in the air. When these microbes land on a suitable environment, they settle down and begin to grow. Many foods present an ideal environment. The three main types of microbes that cause food spoilage are yeasts, molds, and bacteria. Bacteria are single-celled organisms that grow under a wide range of conditions. Yeasts and molds are both types of fungi, a large grouping of organisms that have both plant and animal characteristics. These microorganisms cause beverages to sour, fuzz to grow, slime to form, and the color and smell of foods to change. Microorganisms are everywhere: in the air, water, soil, homes, and people. The majority of microorganisms are harmless or helpful to humans and all life on Earth. When they start living on food items though, they can quickly cause the food to spoil. The amount and rate of food spoilage increases as the number of microorganisms rise. And microorganisms grow, meaning they reproduce, at a speedy rate. Bacteria, for example, can reproduce once every twenty minutes under ideal conditions. That means, if there are no limitations, a food product that starts off with one bacterium will multiply to over five billion in about ten hours. If bacteria grew at this rate in real life they would soon overtake the planet. Fortunately, once too many bacteria live in one area, their food runs out and eventually they start dying. 477
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bacteria grow well in foods high in protein
molds can grow in foods with high acidity
Each type of microorganism has its own unique requirements for growth. GA LE GRO UP.
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yeasts grow well in sugary foods
The leftover that became a home Each type of microorganism has its own unique requirements for growth, but there are general conditions that most food-munching microbes need:
• Food: Each type—and species—of microbe thrives on different nutrients. Many bacteria thrive on proteins, such as meat; the fungi mold commonly grows on sugars and bread; and yeasts like simple sugars. • Moisture or water: Yeasts, molds, and bacteria all need water; some need more than others. Molds, for example, grow at lower levels of water than most bacteria. • Suitable temperature: Many microbes grow well at warm temperatures roughly equal to the inside of the human body. • Exposure to air: Yeasts and molds need air to grow. Most bacteria that cause food spoilage also need air to grow. One exception is the Clostridium bacterium, which is a common cause of canned food spoilage because it does not need air to live. • Suitable acidity level: Bacteria generally prefer mid- to low-acid foods such as vegetables and meat. Certain yeasts and molds grow in fruits that can tolerate a high-acid environment. • Time to grow: Even though bacteria can reproduce quickly, they still need time to grow. If food is consumed immediately after it is prepared, the bacteria won’t have time to cause spoilage. Slowing spoilage Long before people knew about microorganisms, ancient civilizations developed methods to prevent their food from spoiling. These techniques prevented microorganisms from living on the food in some way—either by making living conditions unpleasant or deadly, or by preventing the microorganisms from ever settling down on the food. Any substance added to food to give it a desired quality is called an additive. Preservatives are a type of additive that causes food to last longer without spoiling. There are both synthetic and natural preservatives. Natural preservatives were one of the earliest methods used to prevent spoilage. Spices are natural preservatives people have long valued. When Italian explorer Christopher Columbus (1451–1506) set sail for the New World, one of the items he was searching for was spices. Other natural Experiment Central, 2nd edition
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preservatives include vinegar, salt, and Vitamin C. Some foods contain a high concentration of these items, giving them a natural resistance to microbial growth. Antioxidants are substances that prevent spoilage by reducing the food’s exposure to air. Vitamin C and Vitamin E are natural antioxidants. Dehydration involves removing the water from food. When food is dehydrated, microorganisms no longer have the moisture they need to live. Ancient peoples dried strips of meat and other foods out in the sun. Dried snacks, such as fruits and raisins, are common dehydrated foods. Salting is another ancient method of preventing spoilage that combines the techniques of adding preservatives and dehydrating. Salt lowers the amount of water in the food and also removes water from the microbial cells, making it a harsh environment for organisms to live. Using salt to preserve food remains widespread in modern day. Pickles, meat, and fish are commonly salted. While salting can make food last longer, it also increases the sodium in food. Canning was another major breakthrough in food preservation. In the 1700s French leader Napoleon Bonaparte was searching for a method that would preserve foods for his troops. He offered a large cash prize to anyone who could develop a preservation method. In response a French candy maker came up with the idea of sealing foods in cans. Although the technique has changed over time, the basic process remains the same. The food is placed in a can, heated, and the can is quickly sealed. Modern canning techniques suck the air from the can before it is sealed. Chilling/heating: Microorganisms do not like it too hot or too cold. Temperatures that are outside the microorganisms’ living requirements will cause their growth to slow. Extreme hot and cold temperatures will kill the microbes. Before the refrigerator was invented, people Experiment Central, 2nd edition
Dried snacks, such as fruits and raisins, are common dehydrated foods. COP YR IGH T # KE LL Y A. QUI N.
Jars of home-canned vegetables. # CRA IG L OV EL L/C OR BI S.
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covering keeps new microbes gentle heating over time kills most organisms out, refrigerating slows growth
Pasteurization is a preservation technique that destroys most microbes by heating a liquid, then placing it in an airtight container. GAL E GR OU P.
wrapped foods in snow and ice. Refrigerators and freezers will slow or stop the growth, yet the low temperatures will not kill the microorganisms. When the food item is returned to a suitable environment the microorganisms will again start to grow. There are even bacteria that grow well in the cool refrigerator air. Boiling is another method of destroying microorganisms, yet boiling can change the taste and nutritional value of the food. Cooking food thoroughly also destroys microorganisms. French chemist Louis Pasteur (1822–1895) was the first person to demonstrate that microorganisms in the air produce food decay. In 1865, he developed a gentle heating method to destroy microorganisms in liquids and cause little change in the taste. After heating the liquid to 131˚F (55˚ Celsius), he placed the liquid in an airtight container. This process is known as pasteurization and in modern day, it uses slightly higher temperatures. Pasteurization destroys almost all the microorganisms without altering the composition, flavor, or nutritional value of the liquid. Most milk is treated this way. All by themselves Spoilage also can occur from natural chemical changes within the food without any help from microorganisms. Rancidity occurs when fats in the food break down, producing undesirable flavors and smells. For example, rancidity gives butter a strong, bitter taste. Salt in butter helps prevent the butter from turning rancid. Food can also decay on its own from natural proteins that begin to decompose or break down the food. 480
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WORDS TO KNOW Additive: A chemical compound that is added to foods to give them some desirable quality, such as preventing them from spoiling. Antioxidants: Used as a food additive, these substances can prevent food spoilage by reducing the food’s exposure to air. Bacteria: Single-celled microorganisms that live in soil, water, plants, and animals that play a key role in the decay of organic matter and the cycling of nutrients. Some are agents of disease. Canning: A method of preserving food using airtight, vacuum-sealed containers and heat processing. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
molds, yeasts, and mildews, that do not contain chlorophyll. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Pasteurization: The process of slow heating that kills bacteria and other microorganisms. Preservative: An additive used to keep food from spoiling. Rancidity: Having the condition when food has a disagreeable odor or taste from decomposing oils or fats. Spoilage: The condition when food has taken on an undesirable color, odor, or texture.
Dehydration: The removal of water from a material.
Spore: A small, usually one-celled, reproductive body that is capable of growing into a new organism.
Fungi: The kingdom of various single-celled or multicellular organisms, including mushrooms,
Variable: Something that can affect the results of an experiment.
EXPERIMENT 1 Preservatives: How do different substances affect the growth of mold?
Bread can get moldy very quickly. CO PYR IG HT # KEL LY A. QUI N.
Purpose/Hypothesis Mold is a type of fungi that
reproduces via spores. Spores are similar to plant seeds except they are microscopic. They move about in the air and when they land on a food source with a comfortable environment, they begin to grow. Once spores begin to grow, the mold releases more spores and the cycle continues. There are thousands of different kinds of molds. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of bread • the temperature • the amount of light • the additive • the amount of the additive • the quantity of the preservative in the additive In other words, the variables in this experiment are everything that might affect the mold’s growth. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on inhibiting mold growth.
Step 10: Place each damp slice of bread in its labeled bag and seal. GA LE GRO UP.
con t
rol
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘All the preservatives will inhibit the growth of fungi to some degree; salt will inhibit it the most.’’ In this case, the variable you will change is the substance sprayed on the bread. The variable you will measure is the amount of mold growth. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. For your control in this experiment you will spray plain water on the bread. At the end of the experige ment you can compare the control and the expern a r o t sal juice imental results. vin e
lemon
In this experiment you will examine how additives can act as preservatives for the bread. You will use different types of possible preservatives: vinegar, salt, vitamin C, and lemon juice. Molds grow well in a moist environment. You will spray the liquid preservatives on the bread to dampen the bread. For the salt, you will dampen the bread with water before you apply the salt. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of molds and spoilage. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
Level of Difficulty Moderate. ga r
Materials Needed
• water • 5 slices of nonpreservative white bread 482
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• spray bottle, such as one used to water plants • 5 plastic bags • graph paper marked in 0.05-inch or 1.0-millimeter increments • transparent paper • preservatives: white vinegar, lemon juice, table salt, nonpulp orange juice high in vitamin C (you can also select other, or additional, items to test) • marking pen • microscope or magnifying glass (optional)
How to Experiment Safely When conducting experiments with microorganisms, treat them all as if they could cause disease. Do not touch the mold or try to smell the bread. Never taste or ingest any of the bread.
Approximate Budget $10. Timetable 1 hour, 20 minutes setup; about 15 minutes daily for about
6 to 9 days. Step-by-Step Instructions
1. Lay out five slices of bread. 2. Label each of the bags with the name of one preservative; label one bag ‘‘Control.’’ 3. Prepare the preservatives by making sure each of the liquids flows easily through the spray bottle. If not, try to get a bottle with wider holes or dilute the liquid.
Surface Area Growth 1 day
2 days
3 days
4 days
5 days
6 days
Bread
control vinegar orange juice salt lemon
Data chart for Experiment 1. GA LE G RO UP.
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4. Pour a small amount of vinegar in the spray bottle. Spray the vinegar on a Troubleshooter’s Guide piece of bread to dampen it, counting the number of sprays it takes to dampen. Below are some problems that may arise during Do not soak it. this experiment, some possible causes, and some ways to remedy the problems. 5. Rinse the spray bottle thoroughly with water and repeat the process for the Problem: Mold did not grow on any of the lemon juice and orange juice, rinsing the breads. bottle out in between. Use the same numPossible cause: Make sure the bread you purchased has no preservatives in it. You may ber of sprays for each. want to buy fresh bread from a bakery. Once 6. Rinse out the sprayer and fill with water. you have bread that has no preservatives, 7. Spray the same number of sprays on the repeat the experiment. two remaining pieces of bread. Possible cause: You may have saturated the 8. On one piece of bread sprinkle salt lightly bread, not giving the fungi an environment over the damp bread. that promotes growth. Repeat the experi9. Allow the breads to sit on the counter for ment, lowering the number of sprays for each one hour. of the liquids to make sure the bread is only dampened. 10. Place each piece of bread in the appropriProblem: Mold grew at the same rate on the ate bag; put the water bread in the ‘‘ConControl slice as on one of the slices with the trol’’ bag. Seal the bags. preservative. 11. Set the bags in a dim area, such as in a Possible cause: There may not have been drawer. enough of the preservative in the additive, 12. Either trace or copy the graph paper on a such as if you used a juice that did not have a clear piece of transparency. high percentage of vitamin C or an imitation 13. Every day at roughly the same time, lemon juice. Make sure the additive contains examine each piece of bread for mold. the preservative you want to test, and repeat the experiment. Do not remove the bread from the bag. Possible cause: If you added water to the addiIf there is any mold, lightly place the tive, you may have diluted the additive too transparent graph over the bread and much. Repeat the experiment, using another determine the surface area of the mold liquid additive or a spray bottle with wider by counting the number of squares. holes as opposed to diluting the liquid. Note the results on a chart. 14. Continue examining each of the breads until mold has covered at least one of the slices. 15. If you have a magnifying glass or microscope, examine the mold(s) up close and note their descriptions. 16. After you have completed the summary, throw away the breads in their bags. 484
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Summary of Results Graph your data, labeling
‘‘Days’’ on the X-axis and ‘‘Surface Area’’ on the Y-axis. Use a different color pen or type of line for each of the substances on the bread, and mark the graph clearly. What was the substance that prevented mold growth for the greatest number of days? Once mold did begin to grow, how did the rate of growth compare to the first few days when there was no growth? If the growth rate increased rapidly, theorize why you think this occurred. Describe the mold or types of mold on the breads. Common types of molds that grow on bread are bluish-green or green molds; black or brown-black molds; and reddish or pink molds. By examining the molds and referring to a reference source you may be able to identify them.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the temperature of the milk • the milk’s exposure to heat • the amount of light • the type (wholeness) of the milk • the type of milk In other words, the variables in this experiment are everything that might affect the growth of bacteria. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the spoilage of the milk.
Change the Variables In this experiment you can
change the variables in several ways: • change the temperature, higher or lower • change the type of bread, using bread with preservatives or comparing brands • leave the breads out in both light and dark areas and compare growth • use a different growth substance, such as a type of fruit instead of bread
EXPERIMENT 2 Spoiled Milk: How do different temperatures of liquid affect its rate of spoilage? Purpose/Hypothesis The two main groups of bacteria in milk are Lactic
acids and Coliforms. Lactic acid is the natural bacteria present in milk and dairy products. Coliforms are the main reason for milk spoilage. Pasteurization kills almost all of the bacteria, but some of the bacteria that cause milk to spoil still remain. If these bacteria are given an environment that promotes growth, they will rapidly multiply. Experiment Central, 2nd edition
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In this experiment, you will be conducting two mini-trials in which you will determine how How to Experiment Safely temperature affects the rate of milk spoilage. You will examine the environmental temperatures When conducting experiments with microorthat affect milk by allowing glasses of milk to ganisms, treat them all as if they could cause disease. Do not touch the milk and, if you do, sit in cool, warm, and room-temperature enviwash your hands thoroughly. Do not taste or ronments. You will also determine how the temingest any of the milk. Be careful when working perature of the milk affects spoilage. One cup of at the stove. milk will be boiled, then left in a room-temperature environment. After three days, you will examine each of the milks. When milk spoils it changes in consistency, appearance, and smell. Spoiled milk also undergoes a chemical change. As the milk spoils, the bacteria produce acid. It is the acid that causes the milk to clot. You can compare the acidity of the test milks by using indicator strips. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of spoilage. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The milk in the warm area will spoil the quickest; the milk that was boiled will take the greatest amount of time to spoil.’’ In this case, the variable you will change is the temperature of the milk. The variable you will measure is the relative amount of spoilage of each milk. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. For the control for the boiled milk at room temperature, use the unboiled milk at room temperature. To compare milk spoilage among the test milks choose a standard among them, such as the milk at room temperature. Use the data from this standard to gauge the spoilage of the other test milks. 486
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Level of Difficulty Easy to Moderate. Materials Needed
• • • • • • • • • • • • •
whole milk refrigerator heat lamp, such as one used for plants 4 tall heat-resistant glasses plastic wrap 4 rubber bands pot spoon hot plate or stove measuring cup acid/base indicator strips masking tape marking pen
boiled room tempp
cold
warm
control
Steps 6 and 7: Place a rubber band around the plastic wrap and then place in its designated environment. G AL E GR OUP .
Approximate Budget $3 (not including lamp). Timetable 20 minutes setup; about 10 minutes daily for 4 to 5 days. Step-by-Step Instructions
1. Label each of the cups: ‘‘Cold,’’ ‘‘Warm,’’ ‘‘Room Temp/Control,’’ and ‘‘Boiled.’’ 2. Measure out 1 cup of milk and pour it in the glass labeled ‘‘Cold.’’ Pour another cup in the glass labeled ‘‘Warm,’’ and another cup in the ‘‘Room Temp/Control.’’ 3. Pour 1 cup in the pot and bring the milk to a low boil. 4. Stir continuously while letting the milk boil for one minute. 5. Pour the hot milk in the glass labeled ‘‘Boiled.’’ 6. Immediately, place plastic wrap over each of the glasses. 7. Wrap a rubber band around the plastic wrap to secure it to the glass. 8. Set the ‘‘Cold’’ glass in the refrigerator; the ‘‘Warm’’ glass near the heat lamp; and the remaining two glasses in an undisturbed area at room temperature. 9. Describe how each glass of milk appears each day for four to five days. Do not remove the plastic wrap or shake the glass. Experiment Central, 2nd edition
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: After several days, the milk at room temperature appeared to have the same amount of spoilage as the milk in the refrigerator.
10. At the end of the experiment, when at least one of the milks has separated, place an indicator strip in each glass and note the results—acid, base, or neutral— by comparing the color of the wet strips with the chart provided with the indicator strips. Summary of Results Examine your results and
note the acidity level of the milk(s) that spoiled at the fastest rate. How did the control milk comPossible cause: The room may be at a cool temperature and the bacteria could need pare to the boiled milk? Compare the appearance longer to grow. Continue the experiment for of the milk at the warm environment to the cool several more days. environment. How did the spoiled milk’s appearance change daily? When acid causes milk to curdle it forms solids called curds, and a liquid, called whey. Which of the test milks formed curds and whey? In an analysis of this experiment summarize what conclusions you can draw about the environment(s) that promote bacterial spoilage. After you keep the milk clot for a while, the clot shrinks and a yellow fluid (whey) is released. You can make this happen more quickly by squeezing a little lemon juice (acid) into a small amount of milk. The curds are the white caseins, or milk proteins, and they are sticky (people once used them as glue). If you touch them, remember to wash your hands. Change the Variables In this experiment you can change the variables
in several ways. You can change the fat content of the milk by comparing skim milk, whole milk, 2% milk, and other types. You can add a substance to the milk, such as sugar or chocolate, that may alter the speed of bacteria growth. Another way to change the experiment is to vary how much light the milk is exposed to by leaving the same type of milk out in a bright and dark area. You could also alter the food substance by using different beverages or solid foods instead of milk.
Design Your Own Experiment How to Select a Topic Relating to this Concept Food spoilage is a
common problem, with many possible project ideas. You could examine 488
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spoilage among different types of foods. You can also examine the steps taken to prevent spoilage, both in terms of additives and food handling. Check the Further Readings section and talk with your science teacher to learn more about spoilage. You could also talk with a microbiologist for details on the microorganisms involved in spoilage. When experimenting with food, do not taste or ingest any of the food items, and make sure to mark the item clearly to keep others away. Aside from causing food poisoning, some microorganisms that are attracted to food can cause diseases that are potentially deadly. If you conduct an experiment with food in the home, make sure you tell an adult. Steps in the Scientific Method To conduct an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Projects related to spoilage are numerous, inexpen-
sive, and waiting in the kitchen. You could conduct a project examining the uses of synthesized versus natural preservatives. Foods spoil Experiment Central, 2nd edition
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at different rates and under different environments. You could test different foods, all with the same main ingredient, for variables that affect the rate of spoilage. You could also examine how spoilage poses a serious health threat by examining potential diseases and illnesses from spoiled food. You could group certain foods together and determine if the rate of spoilage changes, depending on what the food is near. You could also examine expiration dates and conduct an experiment that tests how accurate the date is to when it begins to spoil. When working with food, make sure not to taste or ingest any of the food, and to always label it clearly as an experiment. Spoiled food contains microorganisms, some of which could be extremely harmful.
For More Information Dalton, Louisa. ‘‘What’s that Stuff?: Food Preservatives.’’ Chemical & Engineering News, November 11, 2002. http://pubs.acs.org/cen/science/ 8045/8045sci2.html (accessed on March 6, 2008). Information on various food preservatives. D’Amico, Joan, and Karen Eich Drummond. The Science Chef Travels Around the World: Fun Food Experiments and Recipes for Kids. New York: John Wiley, 1996. Food experiments and recipes from around the world. ‘‘Food: Nutrition, Safety and Cooking.’’ University of Nebraska Lincoln. http:// lancaster.unl.edu/food/myths ss/index.htm (accessed on March 8, 2008). Quiz and common myths on food safety. ‘‘From Farm to Table.’’ www.foodsafety.gov. http://www.foodsafety.gov/fsg/ fsgkids.html (accessed on March 8, 2008). Links to government sites on food safety and spoilage. ‘‘Kids World: Food safety.’’ N.C. Department of Agriculture and Consumer Services. http://www.ncagr.com/cyber/kidswrld/foodsafe/index.htm (accessed on March 8, 2008). Food safety facts and interactive question on spoilage.
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Forces
A
force causes or changes an object’s motion: It is a push or pull on an object. Forces have both a size and a direction. Forces also work in pairs: In order for a force to occur there must be an interaction between two objects. For example, when throwing a boomerang a person applies a force to the object that makes it move. Weightlifting exerts a force on the weight to pull it upward. These are forces that occur by physical contact between the two objects. Yet forces also occur upon a person who is standing still. Forces are, in fact, occurring on everyone and everything on Earth, along with celestial objects. In these forces, two interacting objects exert a push or pull with no physical contact between them. An example of this force is gravity. Gravity is the force of attraction between any two objects in the universe.
Guiding principles While there have been numerous contributors to people’s knowledge of forces, English scientist Isaac Newton (1642–1727) formulated the laws of motion, the rules that explain how forces work. As he was working on the laws of motion, Newton also explained the effect of gravity throughout the universe. In 1687 Newton published his landmark work Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), which gave people a new understanding of the universe and laid the foundation for the development of physics. Newton developed three laws of motion to explain forces: First law of motion: With no force, an object at rest will stay at rest, and an object moving in a certain direction and speed will remain moving in that same path and velocity. Velocity is the speed of an object in a particular direction. This resistance of an object to change its motion is called inertia. The greater the mass of an object is, the more force is needed for the object to overcome its inertia. For example, a toy train 491
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moving around a track would require relatively little force to make it move compared with the push a real train would need. Second law of motion: When a force acts upon an object it will accelerate. Acceleration is the rate of change in velocity. The acceleration of an object depends upon the size of the force and the mass of the object. The relationship between these variables in mathematical terms is: Force (F) = Mass of Object (m) x Acceleration of Newton’s second law of motion: Object (a), or F = ma, which can also be written a = F/m. As the force acceleration. For example, if increases, the acceleration will also increase. The more mass an object has, someone throws two balls with the lower the rate of acceleration. equal force, the ball with the lower mass will have greater An example of this law is evident when comparing the force needed acceleration. GA LE GRO UP. to throw two objects, such as two balls. If Ball 1 has 10 times the mass as Ball 2 and a pitcher throws the balls with equal force, then Ball 1 will accelerate at one-tenth the acceleration of the lighter ball. To make the two balls accelerate at the same rate, the pitcher will need to use ten times more force on Ball 1 than on Ball 2. Newton’s third law of motion: Third law of motion: For every action, there is an equal and opposite Forces always work in pairs. reaction. This law states that forces always work in pairs. When one force For example, when stepping off moving in a certain direction acts upon another force, then there must be of a boat there are multiple forces at work. GA LE GRO UP. a force of equal strength moving in the opposite direction. There is usually more than one force at work. For example, when a boat is sitting still downward force of gravity at the dock the force of gravity pulls with a downward force and the water responds with an equal and opposite upward force. A person who boards the boat and pushes it away from the dock exerts another force. The push starts the boat moving gradually away from the dock due to its inertia. Yet once moving, the boat will need forward force that same amount of force to stop it. When the boat stops and the boater steps back onto the backward force dock, that is another force. As the person steps off the boat with a push, the boat will move back in the opposite direction. upward force Round and round we go Newton’s laws of water explain both straight motion and circular 492
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motion. A force that causes an object to follow a circular path is called centripetal force. The word centripetal comes from the Latin words centrum and petere, meaning center seeking. (This force is often confused with centrifugal force, meaning center fleeing. Centrifugal force is not considered a true force, as there is no force acting upon the object; it is only the tendency of the object to continue in a straight line. See Ocean chapter.) Anytime there is a circular movement around a central point, then centripetal force is at work. Centripetal force is based on Newton’s first law of motion that states an object will travel along a straight path with constant speed unless a force acts upon it. Thus, for a circular motion to occur, there must be a constant force pulling the object towards the center of the circle. This force is always directed inward. For a planet orbiting the Sun, the force is gravity; for a ball twirling on a string, the force is the tension in the string; for a loop in a roller coaster ride, the force is applied by the curved track. An object moving in a circle is constantly accelerating because it is continuously changing its direction. This is true even if the object is moving at a uniform speed. (Acceleration is a change in velocity and velocity is the speed of an object in a particular direction.) The amount of centripetal force needed to keep an object moving in a circular path depends upon its acceleration, along with its mass. When the centripetal force is taken away, the object follows Newton’s first and third laws: Its inertia causes the object to move in a straight line and the force by which it moves outward is equal in strength and opposite in direction.
inward force forward path
In centripetal force, the inward force pulls the object or body away from its straight path to form a circular movement. GAL E GR OU P.
EXPERIMENT 1 Newton’s Laws in Action: How do water bottle rockets demonstrate Newton’s laws of motion? Purpose/Hypothesis The laws of motion explain how force affects the
movement of an object. Many objects such as trains, airplanes, and theme park rides demonstrate these laws. In this experiment, you will work with a water bottle rocket to observe Newton’s laws. After constructing a basic launcher you will use a plastic two-liter bottle and water to measure the Experiment Central, 2nd edition
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WORDS TO KNOW Acceleration: The rate at which the velocity and/or direction of an object is changing with respect to time. Centripetal force: A force that pushes an object inward, which causes the object to move in a circular path. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. First law of motion (Newton’s): An object at rest or moving in a certain direction and speed will remain at rest or moving in the same motion and speed unless acted upon by a force. Force: A physical interaction (pushing or pulling) tending to change the state of motion (velocity) of an object. Gravity: Force of attraction between objects, the strength of which depends on the mass
of each object and the distance between them. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Inertia: The tendency of an object to continue in its state of motion. Second law of motion (Newton’s): The force exerted on an object is proportional to the mass of the object times the acceleration produced by the force. Third law of motion (Newton’s): For every action there is an equal and opposite reaction. Variable: Something that can affect the results of an experiment. Velocity: The rate at which the position of an object changes with time, including both the speed and the direction.
force required to lift the rocket. By adding water to the rocket, you will increase its mass. A rocket exhibits all three of Newton’s laws of motion. Newton’s first law states that an object at rest will stay at rest, and an object in motion continues in motion. When the rocket is sitting on the launcher it is an object at rest. Once a force is applied to the rocket and it is in motion, it continues in motion. Newton’s second law explains that when a force acts upon an object it causes the object to accelerate. This is seen when force— in this case, the pressure of the air pumped in the bottle by the tire pump—is exerted on the rocket. The rocket launches and accelerates in upward motion. Newton’s third law refers to reactions, stating that for every action there is an equal and opposite reaction. When the rocket lifts, the air and water that filled the bottle are forced out of the spout in the opposite direction while propelling the rocket higher. 494
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The rocket will be your object, either at rest or in motion. The force is the pressure of the air pumped inside the launcher. As the rocket propels forward, the water will escape and cause the mass to change. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of rockets and Newton’s laws of motion. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The greater the amount of water in the rocket (bottle), the more air pressure (force) is required for launching.’’ In this case, the variable you will change is the mass (the amount of water in the rocket). The variable you will measure is the force (the air pressure in the rocket) required for liftoff. Level of Difficulty Difficult. Materials Needed To build launcher:
• 5 feet (1.5 meters) of 3/4-inch CPVC pipe (available in the plumbing section of home improvement or hardware stores). It is generally a yellowish color and is sold in 10-foot (3-meter) lengths. Use a saw or PVC cutters to cut. • 7 inches (18 centimeters) of ½-inch CPVC pipe • T-joint fitting with 3/4-inch ends and a ½-inch center for CPVC pipe • 45-degree elbow with 3/4-inch ends for CPVC pipe • 90-degree elbow with 3/4-inch ends for CPVC pipe Experiment Central, 2nd edition
A rocket exhibits all three of Newton’s laws of motion. (1) When the rocket is sitting on the launcher it is an object at rest. (2) Once a force is applied to the rocket and it is in motion, it continues in motion. (3) When the rocket lifts, propellants in the rocket are forced out in the opposite direction while propelling the rocket higher. AP/ WI DE W OR LD
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
• • • • •
• the amount of water in the bottle • the air pressure in the bottle
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• the tightness of the seal between bottle and launcher • thickness of the bottle • preciseness of gauge on tire pump In other words, the variables in this experiment are everything that might affect the mass of the rocket and the force applied by the compressed air inside. If you change more than one variable, you will not be able to tell which variable impacted the rocket liftoff.
• • • • • • •
two end caps for 3/4-inch CPVC pipe PVC primer (minimal amount) PVC glue/cement (minimal amount) roll of masking tape (½- or 3/4-inch wide) 2 inches (5 centimeters) of 5/8-inch inner diameter clear vinyl tubing (available at hardware or home improvement store) tire valve stem (ask at a local tire store and explain it’s for a science experiment; it may be possible to get a donation) saw or PVC cutting tool drill paring knife expandable pipe wrench; it needs to have the capacity to hold the 3/4-inch cap scrap wood block safety goggles protractor
For launch: •
• • • • • • •
• water bike tire pump with pressure gauge. Make sure it is a full-size pump. Small pumps that fit in a backpack may not create enough force. measuring cup 2-liter plastic soda bottle permanent marker paper towels or a drying rag tape measure open space partner and adult present when using tools
Approximate Budget $18 (not counting the bicycle pump). Timetable 1 hour to build; 30 minutes to dry; 30 minutes for experiment. Step-by-Step Instructions To build the launcher:
1. From the 5-foot (1.5-meter) piece of the 3/4-inch pipe cut two 6inch (15-centimeter) pieces and one 2-inch (5-centimeter) piece. 496
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2.
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The remaining piece should be approximately 46 inches (117 centimeters) long. How to Experiment Safely One person will clamp one of the 3/4-inch end caps with the wrench. Rest the cap on This is an involved experiment. It should be the scrap wood block to avoid drilling constructed and performed with the assistance through the workspace. Have the helper of another person. Have an adult present when working with the drill and saw or similar cutting drill a hole in the center of the PVC cap. device. Wear safety goggles during construcThe hole needs to be large enough for the tion. It is important to work in a well-ventilated tire stem to come part way through, area when working with PVC cement. The approximately 14 inch. Check to ensure rocket should be launched in a large open area. the tire valve is able to be pushed partway Do not attempt to catch the rocket. It is also through the hole. It may be necessary to important to only use plastic bottles and not glass bottles. trim away part of the rubber around the valve stem. This may be done with a paring knife. Glue the end cap to the 2-inch length of pipe: Push the valve stem partway through the 2-inch (5-centimeter) tube. Apply primer to the outside of the 2-inch (5-centimeter) pipe, the inside of the end cap, and a small amount to the base of the valve stem. Next, apply the glue over the primer. (Note: PVC glue dries very quickly and makes a lasting bond. Once the two pieces of CPVC touch, you have only a few seconds before they are connected forever.) Hold the valve stem partway out of the 2-inch (5-centimeter) piece of pipe and place it through the hole on the end cap. The valve stem should stick out of the hole in the cap. Pull firmly and slightly twist the valve stem, making sure it is secure. Wipe away excess glue. Connect the 46-inch (117-centimeter) piece of pipe to the 2-inch (5-centimeter) piece with the 45-degree elbow. Apply the primer and glue to the inside of the elbow and the outside of the long piece. Insert the pipe into the elbow. Next, apply to the other side of the elbow and the outside of the 2-inch piece. Firmly press the elbow on the 2-inch piece of pipe. Wipe away excess glue. Set aside to dry. Cut a 7-inch (18-centimeter) length of the ½-inch pipe. This will become your launching post. Connect the launching post to the T-joint fitting. Glue the two 3/4-inch CPVC pieces to the ends of the T-joint fitting. First apply the primer, then the glue again to the inside of the connector and
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Steps 2-4
hole in cap
tire stem apply primer and glue here
Steps 7-11
push vinyl down tube over tape
7" pipe launching post
glue and then tape 60 -70 angle
2" CPVC
Steps 2 to 4 and Steps 7 to 11: Constructing the launcher. GAL E GR OU P.
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the outside of the pipe. The 7-inch piece of ½-inch CPVC is then glued into the empty hole of the T-joint fitting. Tape masking tape around the connection of the 1/2 in PCVC post and the T. It will be necessary to make several wraps and tapering the tape slightly (about an inch or two) up the post. Next, push the 2-inch piece of clear vinyl tubing down the tube and over the tape. Use an extra piece of the 3/4-inch PCVC to assist in pushing the tubing down snugly over the tape. The tape and tubing will create a stopper for the bottle to fit on. Using your bottle, test to see if the tape and tubing will create a tight seal. If the seal is not tight, remove the tubing and add more tape. Glue the 90-degree elbow to the long piece made in the first five steps. Use your protractor to glue the T post to the 90-degree elbow. The post should create between a 70-degree and 60-degree angle with the ground, pointing away from the valve stem end of the launcher. Do not angle the post less than 45 degrees. Allow launcher to sit about 30 minutes to dry.
To launch: 1. In an open area, fill the 2-liter bottle with 2 cups (about 0.5 liter) of water. 2. Place the launch post in the bottle and push for a snug fit. Mark this spot with a permanent marker. (It works best to turn the launcher slightly on its side, and gently ‘‘roll’’ it back to its 498
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Steps 3 and 4: Pump the tire pump to fill the bottle with air. Keep pumping at a slow and steady pace until the rocket launches. GA LE GRO UP.
3. 4.
5. 6. 7. 8. 9.
standing position with the bottle on top. This way the water will not come out of the bottle.) Attach the tire pump to the valve nozzle. Pump the tire pump to fill the bottle with air. Keep pumping at a slow and steady pace until the rocket launches. The helper should note the gauge and record the pressure required for liftoff. Repeat launch for two more trials, noting the force (air pressure) and distance for each trial. Fill the 2-liter bottle with 3 cups (about 0.75 liter) of water. Repeat Steps 2 through 5. Fill the 2-liter bottle with 4 cups (about 1.0 liter) of water. Repeat Steps 2 through 5.
Summary of Results Examine your results to determine which amount of
water required the greatest amount of force for liftoff? Was your hypothesis correct? Hypothesize what would happen if you changed the bottle size, and maintained the water amount. What would occur if a cone top and wings were attached to the rocket? Write a brief summary of the experiment and your analysis.
Step 5: Data chart for rocket launch. GA LE GRO UP.
Data for Rocket Launch (averages) Pressure/Force
Change the Variables There are several ways you
can modify the experiment by changing the variables. You can change the sizes of the bottle and maintain the water amount. Another approach could include using various bottle Experiment Central, 2nd edition
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2 cups water 3 cups water 4 cups water
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The rocket will not take off.
sizes and filling each bottle to half of capacity, rather than a uniform water amount. If you have access to a football field, you could perform the experiment on the field and attempt to measure the distance of each launch. It may be beneficial to prop the launcher on a block of wood to create more of an angle (do not go less than 45 degrees).
Possible cause: Make sure your seal is tight. Wipe the stopper off after each launch. Check the tire pump to determine if it is attached appropriately. The pump may be too weak to perform the launch.
Modify the Experiment You can also explore Newton’s laws by conducting a simpler version of the rocket experiment. You will need a piece of wire several feet long. Gather together a balloon, tape measure, string, wide straw and masking tape. Slip the straw onto the wire so that it moves about freely, and securely tie the wire to two objects, such as two chairs.
Blow up the balloon, place a straw in it and tape the straw so that no air escapes. Bending the straw will help keep the air from escaping. Place a piece of masking tape on the end of the straw to seal the air inside. Tape the straw to the balloon. As you look at your experimental setup, think
Slip the straw onto the wire so that it moves about freely, and securely tie the wire to two objects, such as two chairs. I LLU ST RAT IO N BY TEM AH NEL SO N.
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about all the forces. The air, for example, is a force acting on the outside of the balloon. Now take the tape off the end of the straw. What happens as the air escapes? Newton’s third law of motion states that for every action force there is an equal and opposite reaction force. The air is the action and the movement of the straw is the opposite reaction. Measure how far your balloon moved along the wire. How can you make the straw move a shorter distance? How can you make it move farther? Experiment with blowing up the balloon different amounts. After each trial, write down the distance the straw moved.
EXPERIMENT 2 Centripetal Action: What is the relationship between distance and force in circular motion? Purpose/Hypothesis Centripetal force is any force that acts on an object
at a right angle to its path of motion. The constant right angle force results in the object moving in a circular path. In this experiment, you will examine how altering the force and radius will affect the acceleration of an object. Radius is the distance from the center to the outer point of a circle. The object’s mass will stay the same. A piece of string will have a mass attached to one end and washers creating the force attached to the other end. You will first alter the radius, and then alter the force. For a more accurate measure of how many times the mass completes a circle or revolution, you will count how many times it revolves in 30 seconds. That number will then be divided by 30 to give its revolutions per second. Another way to increase accuracy is to complete three trials of each experimental trial. Comparing the results to a control experiment will help you isolate each variable and measure the changes in the dependent variable. In this experiment there will be two variables that you will change, one at a time. Only one variable will change between the control and the experimental setup each time. In the first part, the distance will change when the radius increases. In the second part, the force will change. At the end of the experiment you can compare each of the results to the standard experiment. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of centripetal force. This educated Experiment Central, 2nd edition
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What Are the Variables?
guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the force • the radius • the mass In other words, the variables in this experiment are everything that might affect the acceleration of the mass. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on centripetal force.
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The greater the force, the greater the acceleration; the greater the radius; the lower the acceleration.’’ In this case, the variable you will change is the force and the distance, one at a time. The variable you will measure is the acceleration of the mass.
Level of Difficulty Easy to Moderate. Materials Needed
• • • • • • •
spool of thread with narrow hole ruler ten metal washers of equal size 3 feet (90 centimeters) of string masking tape watch with second hand bobbin, small spool of thread, rubber stopper or other lightweight object that can be easily tied • helper Approximate Budget $2. Timetable 30 minutes. Step-by-Step Instructions
1. Slide the string in the large spool of thread and move the spool up 2 feet (0.6 meters). 502
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2. On the long side of the string, attach four metal washers (this is the force) to the end How to Experiment Safely and secure with a knot. 3. Tie the bobbin or rubber stopper to the Be careful when swinging the mass and check to end of the short side of the string. This is ensure the knot is tight. Make sure you are working in an open area. the mass. 4. Wind a piece of tape about 1 inch (2.5 centimeters) below the spool to make sure it does not slide down and change the radius. Mark the string at the point above the tape. 5. Hold the washers with one hand and begin to swing the mass until it is moving parallel to the floor. Practice swinging at a steady rate. 6. While you are swinging, have your helper time 30 seconds and count the number of revolutions the bobbin makes. 7. Repeat Step 6 two more times so that you have three trials. This is your standard experiment. 8. Remove the tape and slide the spool down 1 foot (0.3 meters) towards the washers. Reattach the tape about 1 inch (2.5 centiSteps 5 and 6: Count the meters) below the spool. number of revolutions of the 9. Again, time the number of revolutions in a 30-second period, then mass in 30 seconds. GA LE repeat for two more trials. Note the results. GRO UP . 10. Return the spool to its beginning position, reattaching the tape at the marked point on the string. 11. Double the number of washers to eight. Support the washers until you have a steady swing and then have your helper time 30 seconds while you count the revolutions. Repeat two more times and note the results. Summary of Results Determine the time for
each revolution per second by dividing the total revolutions by 30. Once you have the revolutions per second for each trial, average the three trials. Make a chart of your data. Compare how long it took to complete a full circle when the radius lengthened. How much force would it take to have the revolutions of different radiuses Experiment Central, 2nd edition
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The radius looked like it was changing.
be the same. Look at how the increased force compares with the acceleration of the lesser force? What would happen to the acceleration if you halved the force? Hypothesize how the force and/or radius would need to change if the mass was doubled and you wanted to keep the acceleration equal.
Change the Variables You can continue to experiment on changing the variables in this experiment in new ways and new combinations. Try to halve the force and halve the radius. Look at what occurs if the radius is tripled and the force remains constant. You can also change the mass of the object, making it lighter or heavier. Make sure you secure the mass tightly to the string and try to work in an open area.
Possible cause: The paperclip might have slid loose. Use a tight paperclip and make sure it is attached firmly, then repeat the experiment.
Design Your Own Experiment How to Select a Topic Relating to this Concept Force is a broad topic that
A planet orbits a sunlike star. Astronomers depend on the principles of centripetal force to help them predict orbits and revolutions. # A FP/ CO RB IS.
has many possible experiments. To gather ideas on force, you can observe how force is applied in daily life. Look at sporting events and playground rides to see the application of Newton’s laws and centripetal force. You could also research how celestial bodies in the universe apply centripetal force. Check the Further Readings section and talk with your science or physics teacher to learn more about force. Steps in the Scientific Method To conduct an
original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. 504
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• Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data could include
charts and graphs to display your data. If included, they should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are many possible projects related to force. You
could construct simple machines to experiment with the amount of force required for work. These projects could explore how force varies with distance and mass. Astronomers depend on the principles of centripetal force to help them predict orbits and revolutions. You could examine how the planets, suns, and moons each have their own unique orbits due to the principles behind centripetal force. You could also explore the force of gravity with everyday objects.
For More Information Christianson, Gale E. Isaac Newton and the Scientific Revolution. New York: Oxford University Press, 1998. The personal life story of Newton and his work. Clark, John O. E. Physics Matters! Danbury, CT: Grolier Education, 2001. Provides a clear explanation of the science of physics with pictures and applications. ‘‘Newton’s Laws of Motion.’’ NASA Glenn Research Center. http:// www.grc.nasa.gov/WWW/K 12/airplane/newton.html (accessed on February 3, 2008). Explanations and illustrations of Newton’s laws of motion presented with different details for different grade levels. ‘‘Skateboard Science.’’ The Exploratorium. http://www.exploratorium.edu/ skateboarding (accessed on February 3, 2008). A look at the science of skateboarding and how it relates to centripetal force.
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ho, what, where, and when? At a crime scene, these are the pieces of information forensic scientists work to piece together. Forensic science is the application of science to the law. Often called forensics, it covers many areas of the sciences, included microbiology, physical science, and chemistry. Advances in the field of forensic science have shifted the way people solve crimes and the justice system. Evidence left at the crime scene includes the physical (such as a scrap of clothing or footprint) and biological (such as DNA). In many cases the evidence may be invisible to the naked eye. Fibers and strands of hair are examples. It took the development of high-powered microscopes in the nineteenth century to bring forward this area of forensics. Once crime solvers could see the object, they could study and compare it to possible suspects. Analysis techniques on blood, materials, and biological evidence have also revolutionized the field of forensics.
Fingering the evidence Hundreds of years ago people noticed that humans all have unique fingerprints. This observation was put to use officially in the late 1800s by Scottish doctor Henry Faulds. Credited with the first fingerprint identification, Faulds became interested in fingerprinting after noticing fingerprints on ancient clay pottery. Soon afterwards, his hospital was broken into. Faulds identified the thief from a greasy fingerprint on a surgical alcohol bottle. Fingerprints have become an important piece of criminal evidence. Over the years, technologies to analyze fingerprints have improved, but the basic idea of fingerprint analysis remains the same. People are all born with a unique fingerprint pattern—including identical twins. The pattern stays the same over the course of a person’s life, whether you are nine or 90 years old. There are three basic patterns used to categorize fingerprints: the loop, arc, and whorl. As its name says, the loop has a loop pattern, where the print starts and ends on the same side of the finger. An arc pattern rises 507
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and falls slightly, from one side of the finger to the other. The whorl forms circles around a central point. Looking at blood Blood found at a crime scene can provide key pieces of information to piece together how the crime happened. One forensic technique is called blood pattern or blood spatter analysis. A blood pattern can help investigators reconstruct the angle the blood came from, what direction it was traveling, and its velocity (speed).
People are all born with a unique fingerprint pattern. # E D BO CK/ CO RB IS.
The shape and size of the blood spatter provides clues as to the surface it landed on. Droplets that strike a hard surface, such as glass, will have a smooth circle. Blood droplets that hit wood spatter outwards. The direction of blood can trace the blood’s angle of origin. When a blood droplet strikes a surface straight down, perpendicular to the floor, it forms a clean circle. Blood that strikes a surface at an angle, such as 60 degrees, will have a tear drop shape. By knowing both the length and width of the blood drop investigators can calculate the impact angle. Even when there is no visible sign of blood, investigators can spot blood by spraying a substance called luminol. When luminol comes into contact with blood, it reacts with the iron in the blood. The reaction produces a blue glow that last for seconds before it fades. Investigators turn the lights off and look for the glow. Fiber evidence If a piece of material or thread is left at a crime scene, analyzing the fiber can help investigators identify where it came from. The fiber can come from a rug, clothing, or handbag. There are many types of fibers and each has its own characteristics. For example, each fiber will burn in a slightly different way. Some common types of fibers and their properties include: • Cotton: A plant fiber; the individual plant fibers that make up the yarn are relatively short compared to other fibers. When ignited, it burns with a steady flame and smells like burning leaves.
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Arch
Loop
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There are three basic patterns used to categorize fingerprints: the loop, arc, and whorl. IL LU STR AT IO N BY T EM AH NE LS ON.
• Linen: A plant fiber; the individual fibers that make up the yarn are relatively long. Linen takes longer to ignite than cotton. • Silk: A natural protein fiber made from worms. When burned, it burns quickly and smells like burning hair. • Wool: A protein fiber that comes from the fur of sheep. When burned, the flame is steady. • Acetate: Produced from cellulose (wood fibers). Acetate burns quickly with a flame that is relatively hard to put out. • Nylon: A synthetic (manmade) fiber made from petroleum products. Nylon melts and burns rapidly. It smells like burning plastic. • Polyester: A synthetic fiber, polyester melts and burns at the same time. The smoke from polyester is black with a sweetish smell. • Rayon: A synthetic fiber made from wood pulp, rayon burns rapidly and leaves only a slight ash. The burning smell is close to burning leaves. High tech evidence In the last half of the 90 twentieth century, scientific findings have led to key advances in forensics. DNA fingerprinting, 45 developed in 1984, is now a commonly used technique in forensics. All people have unique DNA—except identical twins—that is in almost 10 every cell in the body. DNA fingerprinting identifies sequences of DNA unique to each person. Experiment Central, 2nd edition
The direction of blood can trace the blood’s angle of origin. ILL US TRA TI ON B Y TE MA H NEL SO N.
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WORDS TO KNOW Blood pattern analysis: The study of the shape, location, and pattern of blood in order to understand how it got there.
DNA fingerprinting: A technique that uses DNA fragments to identify the unique DNA sequences of an individual.
Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Forensic science: The application of science to the law and justice system.
Deoxyribonucleic acid (DNA): Large, complex molecules found in the nuclei of cells that carry genetic information for an organism’s development; double helix. (Pronounced DEE-ox-see-rye-bo-noo-klay-ick acid)
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Luminol: A compound used to detect blood. Variable: Something that can affect the results of an experiment.
Investigators need only a tiny amount of DNA to analyze it. The DNA evidence can come from a hair root, saliva, or sweat. A DNA fingerprinting test can determine if the DNA from a crime scene matches the DNA of a suspect. It can also show if the DNA samples are from the same person or different people, and if the different people are related.
An example of a DNA fingerprint from the forensic department at the German Federal Police in Wiesbaden, central Germany. AP P HOT O/ MI CH AEL PR OBS T.
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There are many other techniques forensic scientists use. In the following experiments you will learn more about the forensic science techniques involved in fiber and blood pattern analyses.
EXPERIMENT 1 Fiber Evidence: How can scientific techniques be used to identify fiber? Purpose/Hypothesis What if a tiny piece of
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the cleanliness of the fiber • the type of fiber • the coating on the fiber • the length of the fiber • the environmental condition In other words, the variables in this experiment
material is found at a crime scene? How would are everything that might affect the identificayou identify it? In this experiment you will tion of the fiber. conduct several techniques to examine the properties of three to four fiber samples. You will first examine the fibers the materials are made out of with a microscope, magnifying glass, or from a digital photograph. You will then conduct a burn test on the fibers. On material samples, you will examine how each material absorbs water and if it dissolves in acetone (most fingernail polish removers contain acetone). Acetate dissolves in acetone; other fabrics do not. A fabric that contains acetate will partly dissolve. After you examine the properties of each Watch how the acetone effects type of fiber, you will identify a material sample the fabric. I LL UST RA TI ON BY from a ‘‘crime scene.’’ TEM AH N EL SON . Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of forensic science and the fiber. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change
(acetone)
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A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Fibers each have different properties, and if the properties of each sample are known, the sample can be identified.’’ In this case, the variable you will change is the type of fiber. The variable you will determine is the type of material. Water absorption step 1: Drop two drops of water on each fabric sample. I LLU STR AT IO N BY T EM AH NE LS ON.
Water absorption step 2: Note if the water absorbs into the fabric or stays bubbled on the
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Level of Difficulty Difficult. Materials Needed
• 1 to 2 spools of natural threads (cotton, linen, silk, or wool) • 1 to 2 spools of synthetic threads, which include acetate and either nylon or polyester (acetate can be 50% acetate; you can rip the acetate thread from the fabric) • fabric swatches that match the type of threads used, and which includes acetate; about 3 inches (7.6 centimeters) square (acetate can be 50% acetate) • candle in a holder • match • eyedropper • scissors • fingernail polish remover that contains acetone • 3 to 4 small plastic or glass containers • long tweezers, about 12 inches (30 centimeters) or longer (available at science supply sources or some hardware stores) • high-powered magnifying glass or microscope, or digital camera • sink • helper • aluminum foil Experiment Central, 2nd edition
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Approximate Budget $15 (assuming you can obtain a microscope or magnifying glass from another source). Timetable 2 hours. Step-by-Step Instructions Magnification:
How to Experiment Safely You will need to burn fibers in this experiment. Have an adult assist you in burning the fibers and be careful when disposing of the ashes.
1. Look at the material pieces under the microscope or magnifying glass. If you have a high-resolution digital camera, you can take a photograph and magnify the pictures. 2. Note any features in a chart, such as loose threads, if the threads are short or long; if there is a twist in the threads, the weave of the material; and if there are holes in the weave. Draw or sketch your observations. The Burn Test: 1. Wrap one thread around your closed hand five times and cut. Remove the clustered thread from around your hand and hold the two clusters together. The thread should be about 5 inches (13 centimeters) in length. 2. Use the tweezers to grasp one end of the thread cluster. 3. Light the candle and place it in sink. Set a piece of aluminum foil next to the sink. (If you do not have access to a sink you could conduct the test over a pan of water.) 4. Carefully, place the bottom of the thread into the candle flame. Observe it burn. Note if the flame is steady and how fast the flame moves. When the thread has finished burning, note any odor. 5. Conduct another trial with the same thread to make sure you have consistent results. 6. Repeat Steps 3–7 for each of the other threads.
The burn test. IL LUS TR ATI ON BY T EMA H NE LS ON.
Water Absorption: 1. Fill an eyedropper with water and lay out the fabric samples. Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The threads burn too quickly to identify anything. Possible cause: The threads may be too short. Wrap the threads around your hands another two to three times. You also may need to conduct the burn test several times for each thread, to compare how each thread burns relative to the others. Problem: I can’t see much detail through the magnifying glass. Possible cause: The magnification in your magnifying glass is not strong enough. You should be able to see the weave with a magnifying glass, or with your naked eye. Try to use a higher-powered magnifying glass if you want to see more detail, and repeat this test.
2. Drop two drops of water on each fabric sample. For each fabric sample, note if the water absorbs into the fabric or stays bubbled on the top. Dissolve in Acetone: 1. Fill three small plastic or glass containers about half full with acetone. (If you have four fabric samples you will need four containers, or to wait until one is completed.) 2. Cut about a half-inch square of fabric from each material sample. Drop one fabric sample into each of the containers of acetone. Wait 10 minutes. 3. Use the tweezers to remove the fabric onto the aluminum foil. Note if any of the materials partly dissolve. Material Matching: 1. Have a helper cut a small piece of a mystery fabric from one of the leftover swatches. Don’t look at which piece of fabric it is!
2. Repeat all the tests, pulling a piece of string from the material for the burn test. You can also have your helper hand you the matching string. Summary of Results Could you match the mystery material to one of the
tested fabrics? Did any of the tests not fit the properties you identified? You can try matching other fabrics, or having a helper try to match a fabric. Consider how these tests would be helpful in solving a crime. You may want to write up your results, including any pictures or drawings. Change the Variables If you want to change the variables in this experi-
ment you can use different fabrics. You could also use different types of fiber, such as threads from carpets or furniture materials. 514
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EXPERIMENT 2 Blood Patterns: How can a blood spatter help recreate the crime? Purpose/Hypothesis The impact of blood on an
object leaves forensic clues in its pattern and shape. This experiment focuses on investigating the angle of moving blood. You will test dropping artificial blood from different angles and evaluate the shape and pattern of the blood droplets. You will then use this knowledge to piece together where a ‘‘mystery’’ blood spatter came from. To begin this experiment, use what you know about forensic science and blood spatters to make an educated guess about how blood spatters can help reconstruct a crime. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the artificial blood • the surface the blood lands on • the force with which blood is spurted out • the height the blood is dropped from In other words, the variables in this experiment are everything that might affect the blood spatter. If you change more than one variable, you will not be able to tell which variable most affected the pattern of the blood.
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Blood that moves at an angle will have longer droplets than blood traveling straight up and down.’’ In this case, the variable you will change is the angle of the blood and then the direction of the moving blood, and the variable you will measure is the blood droplet shape. Level of Difficulty Moderate. Materials Needed
• brown paper rolls (available from craft store); you can also tape paper together if rolls are not available • eye dropper Experiment Central, 2nd edition
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How to Experiment Safely There are no safety hazards but this experiment has splattering, and it can be messy. You may want to wear old clothes.
• • • • • • • •
small hand scrubber white corn syrup ketchup or tomato paste bowl measuring cup stirring spoon protractor tape measure
• pencil • tape • wooden board or other object with a flat bottom, such as the back of a long pan, about 24 inches (61 centimeters) high • large flat working space outside • helper Approximate Budget $10. Timetable Approximately one hour. Step-by-Step Instructions Step 5a: Hold the eyedropper at the 90 degree mark and squeeze out a drop. I LL UST RA TIO N BY T EMA H NE LS ON.
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1. Lay the roll of paper down on a flat surface about 3 feet (91 centimeters) in length. 2. In a bowl, add 12 -cup of corn syrup and about 2 teaspoons of ketchup until it appears red. Stir. The ‘‘blood’’ should be thick enough to fall slowly from the spoon. 3. Tape the protractor to the flat board or object, approximately 10 inches (25 cm) above the ground. The 90 degree mark should be perpendicular to the ground. You can dangle the tape measure or a piece of string to the ground to make sure the 90 degree mark is perpendicular. 4. Fill up the eyedropper with the artificial blood. 5. Have the helper hold the board flat on the paper. Hold the eyedropper at the 90 Experiment Central, 2nd edition
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degree mark and squeeze out a drop. Label the drop 90 degrees. 6. Move the eye dropper to the 60 degree mark. Squeeze out a drop of blood. You may need to squeeze several spurts to get a good drop. Label the drop 60 degrees. Move the object holding the protractor slightly back on the paper so the drop will not mix with the previous drop. Hold the dropper at the 30 degree mark and shoot out several drops. Label the drops 30 degrees.
Step 5b: Label the drops. ILL US TRA TI ON B Y TE MA H
7. Repeat Step 6, moving the eye dropper to the opposite angle, at the 120 degree and 150 degree mark. You may need to fill up the eyedropper again and move the board with the protractor forward and backwards on the paper. Label each drop.
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8. Continue dropping blood at different angles until you can sketch the shape of a drop at each angle. Note its shape and characteristics. 9. Wet the bristles of the hand brush with the artificial blood. 10. Move the protractor holder to a clean area of paper. Stand back and turn away. Have your helper select an angle and splatter the blood at a specific angle. Your helper may choose to drop the blood from a greater height.
Step 10: Use the bristles of the hand brush to splatter the blood at a specific angle. IL LUS TR ATIO N BY TEM AH N EL SON .
11. Compare the splatter with the test splatters to reconstruct what angle the blood was moving. 12. You may also want to move the brush back and forth to see if you can determine the direction pattern of the blood spatter. Summary of Results Compare all the droplets
and spatter marks. Consider the tools that forensic specialists would use to collect and analyze the blood. Sketch the patterns of blood and summarize your results in writing. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise in this experiment, a possible cause, and a way to remedy it.
Design Your Own Experiment How to Select a Topic Relating to this Concept Forensic science covers a broad ranges
of fields and uses a wide range of techniques. Many of the techniques used by forensic investigators draw upon relatively new scientific advances. The techniques have opened up new Possible cause: The opening for the dropper is too small for the liquid. If you cannot find a forms of forensic evidence and improved the larger eyedropper, you can make the liquid traditional types, such as eyewitness recognition. thinner by adding more ketchup or water. If you are interested in investigating forensics, you may want to first explore all the different ways evidence is gathered. When you read or watch a mystery, consider the evidence at the crime scene and how forensic scientists could use it. Check the Further Readings section and talk with your science teacher to start gathering information on forensics that interest you. Problem: The artificial blood does not squirt out of the eye dropper.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your experiment can be
useful to others studying the same topic. When designing your experiment, develop a simple method to record your data. This method should be simple and clear enough so that others who want to do the experiment can follow it. 518
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Your final results should be summarized and put into simple graphs, tables, and charts to display the outcome of your experiment. Related Projects Experiments in forensics can cover collecting and ana-
lyzing physical and biological evidence. You may want to investigate evidence collection to determine how training can help people see ‘‘crime’’ details they might have previously missed. Face recognition is another area of forensics you can investigate. Footprints, tire tracks, and hand prints are other experiment ideas. There are also many experiments in fingerprinting, which can cover the best way to collect (‘‘lift’’) fingerprints and analyze them. For a research project, you can explore how advances in chemistry, microbiology, and other sciences have changed forensic science.
For More Information Gardner, Robert. Forensic Science Projects with a Crime Lab You Can Build. Berkeley Heights, NJ: Enslow, 2008. Projects related to forensic science. Harris, Tom. ‘‘How Luminol Works.’’ Virtual Museum of Canada. ‘‘Virtual Exhibit on Forensic Science.’’ http://www.virtualmuseum.ca/Exhibitions/ Myst/en/index.html (accessed on May 19, 2008). Detailed overview, timeline, and a game on forensic science. Human Genome Project Information. ‘‘DNA Forensics.’’ http://www.ornl.gov/ sci/techresources/Human Genome/elsi/forensics.shtml (accessed on May 19, 2008). Basic information on DNA fingerprinting. Layton, Julia. ‘‘How Crime Scene Investigations Works.’’ HowStuffWorks. http://science.howstuffworks.com/csi4.htm (accessed on May 19, 2008). Information on a range of forensic evidence. Rainis, Kenneth G. Hair, Clothing, and Tire Track Evidence: Crime-Solving Science Experiments. Berkeley Heights, NJ: Enslow, 2006. Science experiments related to forensic science.
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rom dinosaurs to prehistoric humans, fossils provide a glimpse into Earth’s past events, environment, and life forms. Fossils are the remains or traces of ancient organisms. Fossils can range in age from a mere ten thousand years to several billion years old. They can be microscopic or hundreds of feet long. From the Latin word fossilis, meaning something dug up, fossils are found on every continent. Scientists who study fossils are called paleontologists. Studying fossils has revealed a wealth of data about Earth’s 4.6 billionyear-old history, including its past geography, weather, animals, plants, biodiversity, and how life has changed over time. Fossils can provide information on past environmental conditions. Different types of plants, for example, require specific temperature, acidity, and amounts of water to live. By studying fossils, scientists can also determine an ancient animal’s age, health, eating habits, and movements. Unearthing 3.5 billion-year-old bacteria fossils led to theories on when life began and how it impacted the development of future life. Other fossil evidence shows how continents have shifted over time. Fossils can also create an understanding of modern Earth and how people can best preserve the planet. Until about two centuries ago, fossils were mysterious objects that cultures explained in varying ways. Some theorized that fossils were weapons left behind from the gods; others believed they were the seeds of adult animals, or the remains of animals that did not make it onto Noah’s ark. In the 1800s, scientists began turning up fossils of strange animals by the thousands: the giant reptilian ichthyosaur, the 40-foot (12meters)-long Megalosaurus, and teeth from the immense plant-eating Iguanodon. People began to understand what fossils were and, in the late 1800s, fossil hunting began in earnest. Ancient rock formations The vast majority of living organisms live, die, and decay without leaving behind any physical trace of their 521
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existence. Paleontologists estimate that only about 1 to 2% of all life forms ever become fossils. In order for a fossil to form, a number of conditions must occur simultaneously. Where an organism settles after death and its surroundings are the main factors that determine fossil formation. Fossils occur in rocks. The majority of fossils are found in a type of rock called sedimentary rock. Sedimentary rock forms when sediment particles—such as mud, sand, and gravel—settle and form rock. The sediments build up in layers. Thus, the oldest rocks normally lie on the bottom layer and the youngest at the top. Sedimentary rock is the type of rock most exposed at Earth’s surface. Shale, limestone, and sandstone are examples of sedimentary rock. One common fossilization process, called permineralization, creates a three-dimensional replica of the remains when minerals replace some or all of the organic matter. The first step in permineralization is for a dead organism to become buried in sediment quickly, before it is eaten or decomposed by other organisms. Over the next several hundred thousand years, layers of sediments cover the dead organism. The quicker a dead organism is covered with layers of sediment the greater its chance of being preserved. How quickly sediment covers a dead life form also determines the degree of preservation. Organisms are made up of soft parts, such as skin and tissue, which decompose quickly. Animals will eat them, microorganisms will break them down, and weather will erode them. In general, these parts decompose before they 1
Turning bone into rock: the fossilization process of permineralization. GA LE
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Animal dies. Soft tissue decomposes.
Sediment covers animal and turns to rock.
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Bones are replaced by minerals. New layers of rock form over millions of years.
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Shifting in Earth causes bones to come to the surface.
Permineralization continues. When the organic matter is completely replaced by minerals it is called petrifaction. GA LE GR OU P.
are protected by sediments, leaving only the hard parts of the dead organism, such as teeth, bones, and shells. As the sediment turns into rock, minerals and water from the rock seep into the remains. Slowly, these minerals fill in the open pore spaces of the organism’s remains. When the organic matter is completely replaced by minerals it is called petrifaction. The result is a duplicate of the structure made of rock. Petrifaction commonly occurs in wood. One of the largest examples of petrifaction is at the Petrified Forest National Park in Arizona, which holds acres of 200-million-year-old logs that have turned to stone. Even after a fossil is formed, a set of circumstances still must occur before it can be found. Shifting landmasses, weather eruptions, and natural disasters can destroy the fossil. The rock must also move towards a top layer of Earth in order for it to be exposed. This may occur over millions of years as the rock is pushed to the surface, or human activity can expose it. Forming other fossils Another type of fossil occurs when no part of the organism’s body remains. A fossil mold is an imprint of a bone, shell, or other hard body part. A mold forms when the dead organism settles in sediment and then decays, leaving an outline of its shape. If the mold fills with minerals it is called a cast. The rock cast has the same outer three-dimensional shape as the organism. Paleontologists often create casts of fossil molds by filling them with liquids, such as plaster, that harden. Body parts of ancient plants, insects, spiders, and other small animals are also found preserved in tree resin. Fossils form when one of these Experiment Central, 2nd edition
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creatures becomes trapped inside the sticky resin, which hardens to become a substance called amber. These life forms are often preserved with incredible detail. Some are so well preserved that scientists have attempted to extract the organism’s genetic material, the deoxyribonucleic acid (DNA) molecule.
The imprint of a 200-millionyear-old fossilized plant discovered in 2002. AP /W ID E WO RL D
Fossils that are not part of the animal or plant are called trace fossils. Examples of trace fossils include footprints, tunnels, and dung. Trace fossils provide evidence of the organism’s physical characteristics, eating habits, and activities. Examining fossilized droppings or dung, called coprolites, can supply evidence of where an animal lived and what it ate. A footprint can reveal an animal’s weight, size, and whether it hopped, sprinted, or walked. Because an animal sets down many hundreds of thousands of traces during its lifetime, but leaves only one body, paleontologists find trace fossils far more frequently than body fossils. The dating game In order to piece together a timeline of life on Earth, scientists need to understand a fossil’s age and how it relates to others. This information for all fossils is documented in the fossil record, a key source in understanding how species have evolved. Some organisms dominate the fossil record more than others because of certain physical characteristics. For example, fossils of animals without bones or shells are far more rare than those with hard parts. Marine animals are preserved more readily than land animals because they are more likely to be preserved in soft sediment. This is one reason why estimating the existence span of a species, its first appearance until its extinction, is one of the most challenging parts of the fossil record. One way to date a fossil is to determine its relative age, or how old it is in relation to other fossils or rocks. Unless the rock layers were overturned, fossils found in lower rock layers would be older than those found in upper layers. Fossilized rock with similar features and different locations are compared and placed relative to each other in the fossil record.
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Million Years Ago Homo sapiens
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apes, horses, elephants
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birds, dinosaurs, flowering plants, small mammals
early sharks, land plants, mollusks, corals, anthropods, invertebrates
single cell organisms
Absolute dating is a more precise approach that determines how many years old the fossil is from the current year. These methods were developed in the twentieth century with the findings of the known rate of decay of certain radioactive elements. Each element decays at its own constant and unique rate. Radioisotope dating techniques measure the amount of a certain element in nearby rocks to date the fossil. While relatively precise, absolute dating provides only an approximate date for the organism, accurate to hundreds of thousands of years. One type of absolute dating method examines the amount of the element carbon 14 found in the rock. All plant and animal life absorb carbon 14, and its rate of decomposition is known. This method is useful on material that is less than about 50,000 years old, which includes many human remains but excludes most fossils. For older fossils, scientists measure the amount of other radioactive elements left in rock, such as potassium, thorium, and uranium. Experiment Central, 2nd edition
The fossil record traces organisms through Earth’s history. G ALE GR OUP .
Discovered in the European nation of Georgia and dated by scientists at 1.7 million years, these partial humanlike skulls are the oldest human ancestral fossils ever found outside of Africa. AP / WID E WO RL D
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WORDS TO KNOW Absolute dating: The age of an object correlated to a specific fixed time, as established by some precise dating method.
Paleontologist: Scientist who studies the life of past geological periods as known from fossil remains.
Cast: In paleontology, the fossil formed when a mold is later filled in by mud or mineral matter.
Permineralization: A form of preservation in which mineral matter has filled in the inner and outer spaces of the cell.
Coprolites: The fossilized droppings of animals. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Fossil: The remains, trace, or impressions of a living organism that inhabited Earth more than ten thousand years ago. Fossil record: The documentation of fossils placed in relationship to one another; a key source to understand the evolution of life on Earth. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Mold: In paleontology, the fossil formed when acidic water dissolves a shell or bone around which sand or mud has already hardened.
Petrifaction: Process of turning organic material into rock by the replacement of that material with minerals. Radioisotope dating: A technique used to date fossils, based on the decay rate of known radioactive elements. Relative age: The age of an object expressed in relation to another like object, such as earlier or later. Sediment: Sand, silt, clay, rock, gravel, mud, or other matter that has been transported by flowing water. Sedimentary rock: Rock formed from compressed and solidified layers of organic or inorganic matter. Variable: Something that can affect the results of an experiment.
EXPERIMENT 1 Making an Impression: In which soil environment does a fossil most easily form? Purpose/Hypothesis Paleontologists have found fossils on every continent, yet some areas contain more fossils than others. One of the key factors leading to fossil formation is the type of sediment or material in which a dead organism settles. (Most organisms settle where they die; in some cases a river, wind, or animals can carry the organism to another location.) Scientist use fossils to study and determine the lifestyles and 526
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adaptations of plants and animals. The more details found in a fossil, the more information What Are the Variables? the scientists gain. In this experiment, you will determine how Variables are anything that might affect the the soil makeup of different geographical areas results of an experiment. Here are the main variables in this experiment: impacts the number of fossil casts formed. You will make three fossil casts in three soils of vary• the soil makeup ing moisture content. One of the soils will be dry • the consistency of the plaster of paris sand. Sand is made up of large particles and does • the object/organism not hold moisture. A second type of soil will be a • the depth the object is pressed mixture between sand and moist topsoil, which In other words, the variables in this experiment is made up of smaller soil particles that retain are everything that might affect the ability of water. The third soil will be a wet topsoil. the object to make an impression. If you change These soils will be the foundation layer for a more than one variable at the same time, you plaster of paris cast. Using one object, a shell, will not be able to tell which variable had the most effect on the impression. you will first press the organism into each soil to equal depths. The plaster of paris will form a cast from this mold. This cast will be the fossil. To begin this experiment, make an educated guess about the outcome of the experiment based upon your knowledge of fossils and sediment. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The moist soil will make the best fossil impression; the dry material will not be firm enough to cause a fossil to form.’’ Once you have gathered your soil bases you need to make your impressions. It is best to use a seashell with distinguishing qualities such as scallops, ridges, and possibly an erosion hole or chip. The variable you will change will be the soil. The variable you will measure will be the general shape and amount of detail of the impression. The item you use to make the impression should stay the same. Experiment Central, 2nd edition
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Level of Difficulty Easy to Moderate.
How to Experiment Safely Be careful when removing your fossil casts; plastic containers may break.
• • • • • • • • • • Step 6: Push the straw down until the mark on the straw is level with the soil. G AL E GRO UP.
Materials Needed
• plaster of paris (available at craft stores) • shell, preferably one with identifiable features such as a hole, chip, or alternate mark • 3 small disposable containers, such as a butter dish, large enough to fit the shell
water disposable spoons measuring spoon ruler straw tweezers marking pen bowl 3 cups (0.75 liters) of sand (available at garden store) 3 cups (0.75 liters) of moist, organic topsoil (available at garden store) Approximate Budget $5 to $10. Timetable 1 hour for the experiment; overnight
for the plaster of paris to harden. Step-by-Step Instructions
1. Make a sketch of your shell, noting the width, depth, and any identifiable features. 2. In a bowl, mix 1 cup (about 0.25 liters) of moist topsoil with 1 cup (about 0.25 liters) of sand. This is the moist soil. 3. Mix 2 cups (about 0.5 liters) of topsoil with 8 tablespoons (about 120 milliliters) water. This is the wet soil. 4. Label each container with the type of soil and place each soil type into the appropriate container. The soil should be at 528
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5. 6.
7. 8. 9.
10. 11. 12.
13.
least 2 inches (5 centimeters) deep. Even out the surface of the soil. Troubleshooter’s Guide Use the ruler to mark a line on the straw at 0.8 inches (2 centimeters). Below is a problem that may arise during this experiment, a possible cause, and a way to Place your shell in the soil with the ridges remedy the problem. facing down. Gently place the straw in the center of the shell. Push the straw down Problem: You have no fossils, only a lump of plaster. with your pointer finger until the mark on the straw is level with the soil. Possible cause: All of your soil samples may have been too loose. It may be necessary to Using tweezers, carefully remove your shell. choose a soil sample that has a more solid Wash and dry the shell. Repeat Step 6 for consistency. the other two soil samples. Mix enough plaster of paris to make a 1-inch-deep (2.5-centimeters) layer in each container. The plaster should be the consistency of thick pudding. Pour a layer of plaster of paris into each container. Allow plaster to harden overnight. Remove your fossil casts by slipping a butter knife or similar thin object in the side between the soil, fossil, and container. It may be necessary to break the plastic containers. Make sketches of each cast. (If a digital camera or Polaroid is available, you could take pictures.) Include any measurements of width and depth you are able to determine from your fossil cast.
Summary of Results Review the sketches of the casts compared to that of
the shell. Which soil type is best for making fossils? What qualities did you compare to determine the best soil? Note on the sketch or photograph where any information can be observed on the fossil. For example, a shell may have a hole in one point that can indicate erosion. What type(s) of environments do you feel are most suitable for fossils to form? From your conclusions, how would the environment impact the study of species through fossils? Change the Variables To change the variable in this experiment, you
could use different objects to make the cast. Try both heavier and lighter objects. You could also change the soil type, creating a wet mud soil and comparing that to the dry sand. Another way to alter the experiment is to vary the thickness of the soil layer. Experiment Central, 2nd edition
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EXPERIMENT 2 What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
Fossil Formation: What are the physical characteristics of an organism that make the best fossils?
• the hardness of the organism • the definable shape of the organism
Purpose/Hypothesis Organisms vary from the
microscopic and jelly-bodied to the mammoth and skeletal. The physical characteristics of the • force applied to make mold organism and its environment are two key factors • placement of the object on clay base in forming a fossil. Dating back about 3,500 milIn other words, the variables in this experiment lion years, the fossil record does not represent all are everything that might affect the organism’s types of organisms equally. Paleontologists theorize imprint. If you change more than one variable at that many groups of animals and plants have left the same time, you will not be able to tell which no fossil remains. There are some types of organvariable had the most effect on the physical isms that are more dominant in the record than characteristics of each organism’s mold. others. There are some organisms that have hard parts, some with only soft parts, and many with both. Examples of hard parts include bones, teeth, and wood; examples of soft parts include skin, muscle, and internal organs. In this experiment, you will examine how an organism’s characteristics determine the fossil remains left behind. You will create a fossil mold out of four different types of organisms or parts from organisms. You will begin by preparing a clay base for each of the items you are going to fossilize. Clay is a soft, moist substance similar to the watery sediment that preserves many fossils. You will first select four organisms to observe from four different categories: an exoskeleton, meaning skeletal bones on the outside; an endoskeleton, meaning an internal skeleton; an organism without a skeleton; and a plant. Examples of these four categories are a shell (exoskeleton), chicken bone (endoskeleton), feather (lacking a skeleton), and a leaf (plant). Each organism has physical characteristics that you can note before forming its imprint. Characteristics include if the organism has hard or soft parts, its shape, width, height, and any distinguishing features. To form an imprint you will drop a heavy book from the same height to make sure you use the same amount of pressure for each organism. After making an imprint of each organism, you can then compare the characteristics of the organism and the fossil imprint it makes. • the flexibility of the organism
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Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of fossilization. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
How to Experiment Safely Be careful when applying force using a heavy object.
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The feather will produce a poor fossil that is difficult to identify because it has no specific shape or form; the chicken bone will produce the best fossil imprint.’’ In this case, the variable you will change is the organism. The variable you will measure is the physical characteristics of the mold created by the organism. Level of Difficulty Moderate. Materials Needed
• • • • • • • • • • • •
modeling clay plant (leaf, fern) chicken bone, or another small bone shell (or other object to represent an endoskeleton) feather (or other object lacking a skeleton) heavy book ruler pencils magnifying lens wax paper tape four pieces of cardboard
Approximate Budget $8. Timetable 60 to 90 minutes. Experiment Central, 2nd edition
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Step-by-Step Instructions
shell hard/softness of organism sketch of organism's shape sketch of mold's shape features of organism features of mold height & width of organism height & width of mold
Step 1: Data chart for Experiment 2. GA LE GRO UP.
Step 6: Drop a heavy object from the same height onto each organism. GA LE GRO UP.
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1. Create a data chart, listing the organisms across the top columns and the observable feather fern characteristics down the sides. Make the chart boxes large enough to illustrate your observation and include descriptive words. 2. Feel each organism prior to making the fossil mold and note whether it is hard, soft, or both. 3. Draw a sketch of your organism. Measure the height and width and include in the sketch. 4. Cover each piece of cardboard with a sheet of wax paper, and then create four clay bases. Make the bases of equal size and thickness. The base should be about twice as high as the highest organisms, and be at least 1 inch (2.5 centimeter) larger in diameter than the largest object. 5. Gently place the first organism in the center of the first clay base. Do not apply pressure. 6. Place the clay base against a wall (or any flat, vertical object) and tape the ruler against the wall perpendicular to the base. Hold the book about 2 inches (5 centimeters) above the clay base with the organism on it, and drop the book. The height of the book above the organism does not have to be exactly 2 inches (5 centimeters); however, whatever the height is, use that same height for all organisms. 7. Remove the book and gently remove the organism. 8. Repeat Steps 5 through 7 for each organism. 9. Use the ruler to reexamine the same physical characteristics that you noted for the organism and note the results on your chart. Use the magnifying glass to observe any distinguishing features in the mold. Experiment Central, 2nd edition
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Summary of Results Examine your chart. Which qualities are the most varied among your organisms? Which mold provides the most accurate information? How does the detail of the mold relate to whether the organism is hard or soft? What are some other characteristics on the organism that the mold does not convey? Hypothesize what would occur to each material if you used a lighter book. Analyze what would happen to each organism if it was turned over and the imprint was made of the other side. Write a brief summary of the experiment and your analysis.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: There was no imprint on any or most of the objects. Possible cause: You may not have used enough force to press down on the object. Repeat the experiment, using a heavier book or raising the book to a higher measurement on the ruler.
Change the Variables There are several ways you
can modify the experiment by changing the variables. You can change the organisms you use. Try several different samples from the same class; for example, in the plants you could use a flower, a leaf, and a cactus. You can also alter the substance that sets the imprint formation. You could try dough made of a mixture of used coffee grounds, cold coffee, flour, and salt. How would this moist base impact your experiment? Another way to alter the variable is to change the force used to press down on the object in the clay. Modify the Experiment You can modify this experiment by filling the
impressions with Plaster of Paris. The Plaster of Paris represents the mud or sediment that will fill the form. Follow the experiment, noting the characteristics each of the four organisms leaves in the clay. Keep track of which clay model has which organism imprint. (It might be hard to tell them apart when they are covered with Plaster of Paris.) Mix up the Plaster of Paris, and spoon the plaster onto the clay until the impressions are filled. Allow the plaster to harden then carefully remove it from the clay. Use a magnifying glass to examine the mold. How do the imprints in the mold compare to the imprints in the clay?
Design Your Own Experiment How to Select a Topic Relating to this Concept Fossils open a window
into Earth’s life, geography, and environment that can reach back billions of years. To think of fossil-related projects, you can make a list of all Experiment Central, 2nd edition
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ancient events and people you have learned about and consider how fossils could have been used to gather the data. Check the Further Readings section and talk with your science teacher to learn more about fossils. You can also gather ideas for topics by visiting a natural history museum or science museum. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In any experiment you
conduct, you should look for ways to clearly convey your data. Your data
Paleontologists excavating a fossil bed in Utah. # JA MES L. A MO S/C OR BI S.
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should include charts and drawings such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are many project ideas that relate to fossils. If
there is a museum or university in the area in which you can see fossils, you can compare the different types of preservation, including petrifaction and fossils preserved in amber (these are sold by several companies). For a research project, you could explore the environmental conditions of areas that are rich with fossils, both in the United States and other parts of the world. You can explore fossil molds and imprints by examining how the environment or other factors play a part in the fossilization process. How paleontologists collect fossils is another area of study. Identifying and collecting fossils is a meticulous process that requires many skills. There are many organizations and companies that offer fossil hunts, complete with lessons on how to locate, unearth, and identify fossils. Dinosaurs are a popular topic for documentaries and movies. You can examine these films to look at how the filmmakers reached their representation of these creatures, how much of it was artistic freedom, and what was taken from the fossil record. For example, do paleontologists know that dinosaurs were certain colors? How do the more modern representations of dinosaurs differ from those made in the mid-1900s?
For More Information BBC. ‘‘Prehistoric Life’’ Science and Nature: Prehistoric Life. http://www.bbc. co.uk/sn/prehistoric life/index.shtml (accessed on March 13, 2008). Radio, animations, and explanations of prehistoric life and fossil evidence. ‘‘Fossil Gallery.’’ The Paleontology Portal. http://www.paleoportal.org/index. php?globalnav=fossil gallery§ionnav=main (accessed on March 13, 2008). Choose a time period to see images of fossils. Kittinger, Jo S. Stories in Stone: The World of Animal Fossils. New York: Franklin Watts, 1998. Photographs accompany information on various types of fossils and how they help people understand life on Earth. Experiment Central, 2nd edition
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‘‘Rocks and Layers.’’ U.S. Geological Survey. http://pubs.usgs.gov/gip/fossils/ rocks layers.html (accessed on March 13, 2008). Brief description of where fossils are found in rocks. San Diego Natural History Museum. ‘‘Finding Fossils.’’ Dinosaur Dig. http:// www.bbc.co.uk/sn/prehistoric life/index.shtml (accessed on March 13, 2008). Information on how to look for and identify fossils. ‘‘Tour of geologic time.’’ University of California Museum of Paleontology. http:// www.ucmp.berkeley.edu/exhibits/geologictime.php (accessed on March 13, 2008). Information on the geologic time periods of Earth. Trueit, Trudi Strain. Fossils. New York: Franklin Watts, 2003. What fossils look like, and how paleontologists use them to understand Earth.
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s a way of organizing living things, scientists have created five main classifications called kingdoms (some scientists use more than five). Each kingdom breaks down into smaller and smaller classifications. Plants and animals, for example, are two of these kingdoms. Fungi form another kingdom. There are thousands of types of fungi. They are both single-celled and multicelled; living on land and in water. They include the microscopic, such as yeasts, and the relatively mammoth, such as mushrooms. Scoop up a single teaspoon of topsoil and you will find about 120,000 fungi. One of the largest living organisms on Earth is a fungus. It is called the humongous fungus and extends about 3.5 miles (5.6 kilometers). Fungi play a vital role in Earth’s cycle of life. They decompose or break down dead bugs and plant material, such as leaves, converting their components into elements that living organisms can reuse. They are an essential source of food for plants and animals. Many plants depend on fungi for their nutrients. Fungi also have had a profound effect on human life. Take a look at a moldy fruit and you are observing a type of fungi that has transformed modern medicine. People eat fungi and use them to manufacture bread, wine, and flavorings. Fungi can also cause plant and animal diseases. In humans, dandruff and athlete’s foot are two widespread examples of disease caused by fungi.
It’s a plant . . . It’s an animal . . . It’s a . . . People once classified fungi as part of the plant kingdom. Years later they thought these creatures were part of the animal kingdom. As scientists learned more about this varied group of life, they found all fungi share characteristics that make them a unique kingdom. Fungi are eukaryotic (pronounced yoo-KAR-ee-ah-tic) organisms, meaning that their DNA or genetic material is enclosed in a nucleus. A nucleus is the round or oval structure inside a cell that is surrounded by a 537
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Fungi are one of the five kingdoms that scientists use to classify living organisms. GA LE GRO UP.
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protective envelope. Fungi need air, food, and water to live. They thrive in moist, warm environments, such as the underside of a rock or the space between a person’s toes. Most types of fungi do not depend on sunlight for energy, as plants do. Because of this, they thrive in dark areas, such as caves and in soil. Fungi do not manufacture their own food. To grow, fungi draw nutrients from the materials on which they live. Some fungi are decomposers, breaking down dead organic matter as they draw nutrients from it. A fungus that grows on a rotting tree or fallen leaves is an example of a decomposer. Fungi that grow on living animals and plants are called parasites. Parasites take the materials from the creature, or host, sometimes harming the organism in the process. A fungus that lives on a plant’s roots, for example, receives its food from the plant. Ringworm is an example of a human fungal parasite. Fruit that has mold on it, called a blight, is an example of a plant fungal parasite. One unique type of fungi is the lichen. Commonly found on rocks, trees, and buildings, lichens are composed of fungi living in partnership with one or more other types of organism. One common lichen unites fungi with green algae. In this lichen, algae produce food for the fungi and fungi provide an outer layer of protection for the algae. There are microscopic single-celled fungi, but the majority of fungi are more complex. Multicelled fungi string their cells together in long, threadlike strands called hyphae (pronounced HIGH-fee). The hyphae produce chemicals that break down the complex nutrients of its food source into simpler forms. These nutrients are absorbed through the walls of the hyphae, and flow between their cells. In search of food, hyphae spread outwards underneath the visible part of the fungi. The tangled mass of hyphae forms a network called a mycelium. Myceliums range in size from clumps of mold to systems that stretch for miles (kilometers). A fungus’s mycelium can expand quickly, adding up to a kilometer of new hyphae per day. Protists
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Reproducing styles Most fungi reproduce by releasing tiny particles called spores. Usually composed of a single cell, spores are smaller than dust particles and float through the air. A spore contains all the chemicals needed to make its fungus. Wind and water are the two main ways spores spread. Animals can also carry the spores. For example, the stinkhorn fungi produce an odor that attracts flies and beetles, which then carry the spores away. Spores can end up everywhere—they are in the air, on clothes, plants, and skin. When the spore encounters the right conditions it will grow and develop into the individual fungus. Fungi can also reproduce by growing and extending their hyphae. Hyphae grow as new cells form at the tips, creating ever-longer chains of cells. Many yeasts reproduce by budding. In budding, a parent yeast pushes out its cell to form a bud. In time, the bud pinches off and a new yeast cell is produced. Popular fungi Fungi can cause diseases in plants and animals. Yet there are many types of fungi that humans commonly use, from tasty treats to medicines. Mold: Mold is a type of fungi. It was a few of these stray mold spores that altered the treatment of bacterial diseases throughout the world. In 1928, British bacteriologist Alexander Fleming (1881–1955) was growing the Staphylococcus bacteria in his laboratory for study. Bacteria are a type of microscopic organism, some of which can cause disease. At that time, bacterial infections were sweeping throughout the world and killing millions of people. One day Fleming accidentally left a dish of bacteria uncovered on his lab bench before he took a vacation. When he returned Fleming noticed the mycelium dish was crowded with bacterial growth except for one clear area where a patch of mold was growing. The mold had produced a substance that stopped bacteria from growing. Fleming named the substance penicillin, after the Penicillium mold. Years later during World War II (1939–1945) scientists Howard Florey and Ernst Chain continued Fleming’s work. Bacterial infections were Experiment Central, 2nd edition
Fungi that grow on living animals and plants are called parasites. Fruit that has mold on it is an example of a plant fungal parasite. C OPY RI GHT # KE LL Y A. QUI N.
The tangled mass of hyphae forms a network called a mycelium. GA LE G RO UP.
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common in the war and were causing many soldiers to die. The scientists found penicillin effecspore tive against a wide range of harmful bacteria and they began to mass-produce it. Penicillin became the first antibiotic. Antibiotics weaken or destroy bacteria and other organisms that cause diseases. The success of penicillin led to the developments gills of many other antibiotics, such as streptomycin, that stop the spread of disease. Mushrooms: Mushrooms are one of the most familiar types of fungi. They can grow in Most fungi reproduce by damp soil and rotting wood. Although some mushrooms are edible to releasing spores that float humans, many of these fungi contain harmful poisons. Eating even a small through the air and grow when bite of some types, such as the white destroying angel mushroom, can kill a they find the right healthy adult. environment. GA LE GRO UP. The common mushrooms found in grocery stores produce their spores from gills located under their umbrella-like cap. A single mushroom can produce about two billion spores. The main part of the mushroom, its hyphae, lives underground. Cup-shaped mushrooms are part of another fungi group and they carry their spores in tiny pouches. Types of these Many yeasts reproduce by mushrooms are rare and highly valued, For exambudding. GA LE GRO UP. ple, truffles are delicacies that belong to this group. Truffles live completely underground. yeast cell bud Truffle hunters use highly trained pigs and dogs to sniff out their location. Yeast: Yeasts are single-celled fungi that belong to the same group as the truffles. These 1 2 cells look like little round or oval blobs under a nucleus microscope. Clusters of yeast create a white powdery appearance. They are commonly found on leaves, flowers, soil, and fruits. Bakers have long made use of a natural proc3 4 ess in yeast called fermentation. Yeasts eat a form original cell of sugar or starch. In fermentation, yeasts break down the sugars and starches into carbon dioxide gas and alcohol. The carbon dioxide gas bubbles, 5 causing an expansion or rising of the material new yeast cell around it. People use yeast to make bread rise, from budding and produce the alcohol in beer and wine. 540
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WORDS TO KNOW Antibiotic: A substance produced by or derived from certain fungi and other organisms, that can destroy or inhibit the growth of other microorganisms. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Eukaryotic: Multicellular organism whose cells contain distinct nuclei, which contain the genetic material. (Pronounced yoo-KAR-ee-ah-tic) Fermentation: A chemical reaction in which enzymes break down complex organic compounds (for example, carbohydrates and sugars) into simpler ones (for example, ethyl alcohol).
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Kingdom: One of the five classifications in the widely accepted classification system that designates all living organisms into animals, plants, fungi, protists, and monerans. Mycelium: In fungi, the mass of threadlike, branching hyphae. Nucleus: Membrane-enclosed structure within a cell that contains the cell’s genetic material and controls its growth and reproduction. (Plural: nuclei.)
Fungi: Kingdom of various single-celled or multicellular organisms, including mushrooms, molds, yeasts, and mildews, that do not manufacture their own food.
Spore: A small, usually one-celled, reproductive body that is capable of growing into a new organism.
Hypha: Slender, cottony filaments making up the body of multicellular fungi. (Plural: hyphae)
Variable: Something that can affect the results of an experiment.
In the following two experiments, you will explore how yeast breaks down food and in what environment it grows best. For an experiment on food spoilage and the fungi mold, see the Spoilage chapter.
EXPERIMENT 1 Decomposers: Food source for a common fungi Purpose/Hypothesis Decomposition is a critical part of Earth’s cycle of
life. In this experiment you will examine how fungi affect decomposition. You will use a banana as the food source for the fungi. This fruit provides a moist environment and other conditions that promote yeast growth. For the fungi you will use dry yeast that is used in cooking. The yeast Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the food source (fruit) • the type of fungi • environmental conditions, such as temperature and humidity • exposure to air In other words, the variables in this experiment are everything that might affect the decomposition of the fruit. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the decomposition.
becomes activated when it is given a source of moisture. You will place the yeast on a banana and then observe how it affects the fruit. Changes to the fruit can include changes in color, breaks in the skin, and odor. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of fungi and decomposition. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Yeast will cause the banana to decompose more rapidly than it would without the yeast.’’ In this case, the variable you will change is the addition of yeast to the banana. The variable you will measure is the description of the banana. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. For your control in this experiment you will use a plain banana. At the end of the experiment you can compare the control and the experimental results. Level of Difficulty Easy. Materials Needed
How to Experiment Safely Be careful when handling the knife. Do not taste or ingest any food in this experiment.
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• knife • marking pen Approximate Budget $3. Timetable 15 minutes setup; five minutes daily
for about a week. Step-by-Step Instructions
Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The banana pieces decomposed at equal rates. Possible cause: You may have used yeast that
was dead. Check the expiration date of your 1. Peel the banana and slice two pieces. (You yeast and, if necessary, purchase more. may want to cut it in half first Repeat the experiment using the new yeast. lengthwise.) 2. Place a slice of banana inside each plastic bag. 3. Sprinkle dry yeast on one slice. 4. Label the bag with the yeast ‘‘Yeast’’ and the bag without the yeast ‘‘Control.’’ 5. Seal or tie both bags shut and leave them in a warm place. 6. Observe the bags daily for one week. Each day write a brief description of how each banana appears. On the final day, note the difference, if any, between the two banana pieces. Observe changes in color, breaks in the skin, odors, and physical changes in the shape, size, or consistency (hard, soft, mushy) of the fruit.
Summary of Results Look at the description of your results. Which
banana slice shows the most and fastest decomposition? Was your hypothesis correct?
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Change the Variables There are several ways to
change the variables in this experiment. You can alter the fungi’s food source by using another fruit, fruit skin, or other item. Make sure the food source contains some moisture to activate the yeast. You can also use another type of fungi. If necessary, you can purchase a specific fungi from a biological supply company. Another way is to change the environment of the fruit, such as by placing one piece in a dark area and one in a bright area. Experiment Central, 2nd edition
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EXPERIMENT 2 Living Conditions: What is the ideal temperature for yeast growth? Purpose/Hypothesis People have long taken advantage of the natural
fermentation process of yeasts to produce foods, including alcohol and risen bread. (Ancient cultures’ use of fermentation is one of the earliest uses of biotechnology, which applies living organisms for human use.) Bakers commonly use the Saccharomyces cerevisiae yeast to produce carbon dioxide, which causes bread to rise. In this experiment you will examine in which conditions yeasts best live and grow. Yeasts kept in the most suitable living conditions will be the most active; those kept in less suitable conditions will not be as active. You will pour equal amounts of yeast into similar bottles and provide the yeast with water and a food source, sugar. Each bottle of yeast will be given a different growth environment: one warm and one cold. You will compare them to a third bottle kept at room temperature. You will measure the activity of the yeast by measuring the amount of carbon dioxide the yeast releases. You can do this in two ways. To measure the carbon dioxide, you will seal the opening of the bottle with an empty balloon. The carbon dioxide gas produced will cause the balloon to inflate. Every twenty minutes you will measure the amount of gas produced by measuring the circumference of the balloon. Another way to measure the carbon dioxide is to measure the acidity of the yeast solution. Carbon dioxide mixes with water in the yeast solution to form a weak acid, called carbonic acid. The more carbon dioxide produced, the more acidic the solution. You will use acid/base indicator strips to check the level of acidity after you remove the balloon. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of fungi. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one 544
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possible hypothesis for this experiment: ‘‘The yeast given the warmest environment will grow What Are the Variables? the most rapidly and produce the most carbon dioxide gas; the yeast in the coldest environment Variables are anything that might affect the will grow the least rapidly and produce the least results of an experiment. Here are the main variables in this experiment: gas.’’ In this case, the variable you will change is • temperature the temperature of the yeast’s environment. The • type of fungi (the yeast) variable you will measure is the amount of car• quantity of the fungi bon dioxide produced. • type of food source (the sugar) Conducting a control experiment will help • quantity of the food source you isolate each variable and measure the In other words, the variables in this experiment changes in the dependent variable. Only one are everything that might affect the amount of variable will change between the control and carbon dioxide produced from the yeast. If you your experiment. The control you will use for change more than one variable at the same this experiment is a room temperature environtime, you will not be able to tell which variable ment (water) for the yeast. Before you introduce had the most effect on the yeast’s growth. the yeast to its environment, you will measure the acidity of the plain sugar-water to have a control for the acidity level. At the end of the experiment you can compare the control results with the experimental results. Level of Difficulty Moderate. Materials Needed
• • • • • • • • • •
3 identical small glass or plastic bottles with narrow mouths 3 balloons 3 packets of dry yeast (not rapid-rising) about 9 teaspoons of sugar string tape ice cubes hot water 3 cups 2 clear bowls or rectangular containers, at least half the bottles’ height • tape measure • acid/base indicator strips • measuring cup, with spout preferably Experiment Central, 2nd edition
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• measuring spoons • funnel (optional) • thermometer or temperature gauge, should Fahrenheit range from 65–115 ˚ (18–46 ˚Celsius) (optional) • marking pen
How to Experiment Safely Have an adult present when handling hot water. Do not taste or ingest any of the solutions in the experiment.
Approximate Budget $8 Timetable 1 hour allowing water to sit; 1 hour and 45 minutes for experiment. Step-by-Step Instructions
1. To get room temperature water: In three separate cups, measure 3 /4 cup water. The water should not be hot or cold to the touch. Allow the water to sit for about one hour to reach room temperature. If you have a thermometer, the water should be at about 68–73.4˚Fahrenheit (20–23˚Celsius). 2. While waiting, label one bottle ‘‘Hot,’’ one bottle ‘‘Cold,’’ and one bottle ‘‘Control.’’ 3. Add 3 teaspoons of sugar to each cup and mix thoroughly. 4. Dip an indicator strip briefly in one of the sugar–water solutions. Compare the indicator color to the color chart. An acid should turn the indicator red, a base should turn the indicator blue. Note the results. 5. Pour the sugar-water into the three bottles. You may need a funnel for this. Clean the cups for later use. 6. Prepare a warm-water bath and a cold-water bath. For the warmwater bath, fill one of the two clear bowls or rectangular containers with warm water from the kitchen sink faucet. Let the water run until it gets fairly warm to the touch, but not scalding hot (about 104–113˚Fahrenheit [40–45˚Celsius]). For the cold-water bath fill the other bowl or container with cold water from the kitchen sink faucet and add ice cubes until the water gets cool to the touch (about 41–59˚Fahrenheit [5–15˚Celsius]). 7. Add one packet of dry yeast to each of the three bottles. 8. Securely place a balloon over the top of each bottle opening. Tape each balloon to the bottle to ensure no gas can escape. 9. Swirl each bottle gently to mix the contents. 546
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Step 10: Place yeast in hot, cold, and room temperature environments. G AL E GR OUP .
10. Place the bottle labeled ‘‘Hot’’ in the warm-water bath. Place the bottle labeled ‘‘Cold’’ in the cold-water bath. You may need to secure the bottles down with string and tape so that they sit firmly in the water and do not bob. 11. After 20 minutes, measure the circumference of each balloon. When you wrap the tape measure around the balloon make a small mark on the balloon with the pen above the measure to mark the spot. Note the results in a data chart. 12. Check to make sure the warm water is still warm. If it has cooled significantly, scoop some out and replace with fresh warm water. Add ice cubes to the cold water, if necessary 13. Continue measuring the balloons in 20-minute intervals until the balloons no longer expand. It should take about 60 minutes or more. 14. Remove the balloon from the ‘‘Cold’’ bottle and pour some of its contents into a clean cup. Dip an indicator strip briefly in the solution. Compare the indicator color to the color chart and note the results. 15. Repeat Step 14 for the bottles labeled ‘‘Hot’’ and ‘‘Control,’’ making sure to pour the contents into a clean cup each time. Note the results of each indicator strip. Experiment Central, 2nd edition
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Summary of Results Examine the data chart and graph the results of the circumference for each environmental condition. Label the measurements on one axis and the time on another. How does the balloon circumference of the yeast grown in a room temperature environment compare to that of the yeast grown in the cold-water and warm-water bath? Which bottle showed the greatest increase in balloon circumference? Which bottle was the most acidic? What do the results of the indicator convey about the growth of the yeast in each environment? Can you construct a hypothesis about the environmental conditions for all fungi from these results? Write a brief summary explaining your results and any conclusions you can draw from them. Change the Variables There are several ways to change the variable in this
experiment. You can alter the type of fungi. You can change different environmental conditions, such as the light level on the yeast. By using varying concentrations of acidic foods, such as lemon juice or vinegar instead of sugar water, you can alter the acidity level of the yeast. Modify the Experiment You can add to this experiment by examining the
fungi you grew up close. You will need access to a microscope and you may need an adult to help you use it. After you identified the ideal temperature for yeast growth, place a drop of the yeast solution onto a slide and cover. Yeast are single-celled organisms that divide by a process called budding. A yeast cell can divide in about 20 minutes. Sketch what you see under the microscope.
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Step 11: Note the circumferences of the balloons and acidity of the solutions in a data chart. GAL E GR OU P.
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If you do not have access to slides, you can purchase prepared yeast slides at a science supply store. You can also compare the reproduction rate of the yeast that was the most active to the yeast that was the least active. Does one divide slower than the other?
Design Your Own Experiment How to Select a Topic Relating to this Concept From the microscopic to the mam-
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: No balloons expanded and there was no indication of acidity in the solutions in the bottles labeled ‘‘Hot’’ and ‘‘Cold.’’ Possible cause: You may have used yeast that was no longer active. Check the expiration date of your yeast and, if necessary, purchase more. Repeat the experiment using this yeast.
moth, fungi are a wide and diverse kingdom of life. There are numerous projects related to Problem: The balloon on the bottle labeled fungi, from basic observation to exploring their ‘‘Hot’’ did not expand. living requirements. You could also explore funPossible cause: You may have used water that gi’s profound effect on Earth’s life cycle and was too hot, causing the yeast to die human life. instantly. Repeat the experiment, using warm water. Check the Further Readings section and talk with your science teacher to learn more about fungi. While some fungi may appear edible, remember to never eat any mushroom or other fungus you find unless you have had it identified by an expert in fungi. The mushroom may be poisonous or you could be allergic to it. Steps in the Scientific Method To conduct an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Experiment Central, 2nd edition
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Recording Data and Summarizing the Results Your data should include charts and
drawings such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of any fungi you worked with, the experimental setup, and results, which will help other people visualize the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. You may also want to include specimens, in a closed container, so that others can observe what you studied. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings.
Mushrooms are one of the most familiar types of fungi. FI EL D M ARK PUB LI CAT IO NS.
Related Projects Fungi are a broad kingdom filled with many possible experiments at hand because fungi grow on such a wide variety of sources. Different materials will grow different fungi. You could conduct a project on the differences among one group of fungi, such as molds. Most molds grow well on materials such as bread, used coffee-grounds, fruits, or other food items that are moist with no preservatives. You could isolate and grow the same type of fungi on a variety of food sources. Or you can keep the food source constant and grow different types of fungi on it. You could also perform a project on the reproduction of fungi. Examine the spores of fungi and the different methods fungi use to reproduce. For a research project, you could look at how fungi have had an effect on humans, in both positive and negative ways. You could look at how food manufacturers protect food against certain types of fungi and how fungi are a natural part of many foods.
For More Information Darling, Kathy. There’s a Zoo on You! Brookfield, CT: The Millbrook Press, 2000. A look at fungi, bacteria, viruses, and other microbes that affect humans. 550
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Fogel, Robert. Fun Facts About Fungi. http://www.herbarium.usu.edu/fungi/ FunFacts/factindx.htm (accessed on March 11, 2008). Fun facts and information on fungi. Ho, David. ‘‘Alexander Fleming.’’ Time.com. http://www.time.com/time/ time100/scientist/profile/fleming.html (accessed on March 11, 2008). A profile of Alexander Fleming, who was one of the principal discoverers of the antibiotic penicillin. LichenLand: Fun with Lichens. http://ocid.nacse.org/lichenland (accessed on March 11, 2008). Information and close up photographs of a wide range of lichens. Nardo, Don. Germs. San Diego, CA: KidHaven Press, 2002. Basic explanation of microbes. Pascoe, Elaine. Fungi. New York: PowerKids Press, 2003. Simple introduction to fungi with many pictures. Silverstein, Robert, Alvin, and Virginia. Fungi. New York: Twenty first Century Books, 1996. Clear details on the fungi kingdom. Volk, Tom. Tom Volk’s Fungi. http://botit.botany.wisc.edu/toms fungi (accessed on March 11, 2008). Information on fungi with links, pictures, and answers to frequently asked questions.
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Y
our genes play a major role in who you are: your features and even some personality traits come from your genes. Many other characteristics are produced from a combination of your genes and the environment. Genes are the basic units of heredity. They are passed from parent to offspring, and are carried in almost every cell of the body. Genetics is the science of genes and understanding how traits are passed down from parent to child.
A chunk of DNA Genes are segments of DNA that are housed in the nucleus (center) of cells. DNA is short for deoxyribonucleic acid. It is a long molecule shaped like a twisted ladder, which is called a double helix. In organisms that have two parents, like humans, half the DNA in the body comes from the father and half from the mother. All our DNA is packed so tightly in every cell, that if you attached all the molecules together it would stretch thousands of miles. What makes each person’s DNA unique is the order of the four chemical ‘‘letters’’ that make up the molecule. The chemicals are A, G, C, T, for short. Much like the meaning of words, the sequence of the letters determines its meaning. The letters AGCCT may produce a different characteristic than the CGCCT sequence. DNA sequences contain instructions to make proteins. Every organism has many thousands of different proteins, and it is the proteins that carry out the instructions. Each section of DNA that provides the instructions to manufacture a protein is called a gene. A gene determines the protein, and the protein carries out its specific function. In each cell, DNA is organized into structures called chromosomes. Species have different numbers of chromosomes. Humans have 23 pairs of chromosomes: 23 from the mother paired with 23 from the father, making a total of 46. Sperm and egg cells have 23 unpaired chromosomes. When the sperm and egg cells join, the child gets 23 chromosomes 553
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What makes each person’s DNA unique is the order of the four chemical ‘‘letters’’ that make up the molecule. ILLUSTRATION BY TEMAH NELSON.
When the sperm and egg cells join, the child gets 23 chromosomes from each parent, one of each. IL LUS TR ATI ON B Y TE MA H NE LS ON.
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from each parent, one of each. That means, except for the sex cells, you have two copies of every chromosome and thus, every gene. It starts with a pea No one knew about genes or DNA when the curiosity of Gregor Mendel (1822–1884) led to a turning point in the study of genetics. Mendel was an Austrian monk who was interested in science and mathematics. He failed his teaching examination, moved to a monastery and continued studying science. He also enjoyed gardening. Mendel wanted to understand the traits of pea plants, such as color and shape. Between 1856 and 1863 he bred numerous pea plants, carefully noting his experiments and the traits of each offspring. His results led him to several key genetic laws. One is the law of independent assortment, which says that parents’s traits are passed to the offspring independently of one another. Some scientists at the time theorized that traits were ‘‘blended’’ together, a mixture of both parents. In blending, the theory went, a pink flowering plant would spring from a cross between a red flowering and a white flowering plant. But Mendel showed that traits do not mix or blend. The red trait stays red and the white trait remains white. Parents pass down their traits intact. Even if the offspring does not appear to have the parents’s traits (a red or a white color, for example) they are still carrying these traits. The traits can appear in the next generation. Mendel showed this in his pea studies. A plant with wrinkled peas bred to another plant with wrinkled peas produced a plant that has a quarter of its peas smooth. This led Mendel to the idea of dominant and recessive genes. We have two forms of every gene: one from the mother and one from the father. These forms are called alleles. If a trait is dominant, you needs only one of the alleles for the trait to be visible, or ‘‘expressed.’’ Dimples, for example, are a dominant trait. If a child inherits the dimple gene from only one parent the child will dimple. If a Experiment Central, 2nd edition
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trait is recessive, you need both copies of the gene for it to be apparent. Red hair is a recessive trait. A child would need to inherit the red-hair gene from both the mother and father to be a red head. After Mendel, many researchers have made findings that have helped us better understand genetics. The identification of mutations was another major finding. A mutation is a change in the DNA of a gene. There are many different ways mutations can occur. Sometimes a mutation is repaired before it causes a trait to be expressed. And there are many mutations that have no negative effect. But there are also mutations that can cause health disorders. The sickle cell disease, for example, is a blood disorder that can cause pain and serious health problems. The sickle cell gene is recessive, and it occurs from a single ‘‘letter’’ mutation in the DNA. Altering the genes As researchers have learned how genes function and where they are located, it has led to techniques that recombine or modify genes. This technique is called genetic engineering or recombinant DNA technology. In simple form, genetic engineering first identifies a gene that expresses a desired trait. The gene is snipped out of the DNA and inserted into the DNA of another cell’s DNA in another organism. The ‘‘new’’ trait is then expressed in this organism. The first genetically engineered medicine was, in 1982, the hormone insulin. The gene for insulin was isolated from a person and inserted into bacteria cells. The bacteria cells, which rapidly reproduced, began producing insulin. Genetic engineering is now commonly used in research to ‘‘track’’ or see activity in the body. Researchers often use a gene that produces bioluminescence. Organisms that carry this gene, such as the firefly and certain fish, give off natural light. The gene is attached to a specific gene or compound in the body, which allows researchers to follow the light and see its activity. Today, genetic engineering is commonly used in research, medicine, and industry. There is ongoing research to learn more about what genes do and how they behave. In 2003, researchers finished a massive project to sequence the entire DNA of humans. This was called the Human Experiment Central, 2nd edition
Gregor Mendel used pea plants to experiment with genetics. GET TY I MA GES .
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spliced gene
Genome Project. By studying and understanding what genes do and how they function, researchers hope to answer many questions related to development and disease. There is also ongoing research to sequence the DNA of many other organisms. In the following experiment and project, you will explore more about genes and how they are inherited. If you want to learn more about DNA, see the DNA chapter.
EXPERIMENT 1 Genetic Traits: Will you share certain genetic traits more with family members than nonfamily members?
Gene splicing is also called genetic engineering or recombinant DNA technology. IL LUS TR ATI ON B Y TE MA H NE LS ON.
The allele for widow’s peak is dominant; straight hairline is recessive. IL LUS TR ATI ON BY TEM AH NEL SO N.
widows peak
In appearances, there are many broad traits humans share. But it is the unique set of characteristics that distinguishes people. Some physical characteristics are more common than others. A trait that only needs one allele to appear is a dominant trait; and a trait that needs both alleles to appear is recessive. There are many characteristics, such as hair color, that are due to a combination of multiple genes. Other characteristics, such as height, relate to a combination of genes and the environmental influences. There are also characteristics that researchers have traced to one or only a handful of genes. In this experiment, you will compare five genetic characteristics to family members and participants outside your family. You can then determine the percent of family members and non-family members who have the trait, and compare it to whether you have the trait. You will need a lot of family and non-family members. Try to observe the frequency of the followno widows peak ing characteristics in at least five to ten people. These features are due to only one or a few genes. • Widow’s peak or straight hairline: A widow’s peak gives the forehead hairline a downward dip, like a ‘‘V.’’ If there is no widow’s peak, the hairline is straight. The allele for widow’s peak is dominant; straight hairline is recessive.
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WORDS TO KNOW Alleles: One version of the same gene. Bioluminescence: Light produced by living organisms. Base pairs: In DNA, the pairing of two nucleotides with each other: adenine (A) with thymine (T), and guanine (G) with cytosine (C). Chromosome: A structure of DNA found in the cell nucleus. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Double helix: The shape taken by DNA (deoxyribonucleic acid) molecules in a nucleus. Gene: The basic unit of heredity; the genes contain a section of DNA that codes for a protein. Genetic engineering: A technique that modifies the DNA of living cells in order to make them change its characteristics. Also called genetic modification. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Nucleus: The central part of the cell that contains the DNA.
Dominant gene: A gene that passes on a certain characteristic, even when there is only one copy (allele) of the gene.
Pedigree: A diagram that illustrates the pattern of inheritance of a genetic trait in a family.
Deoxyribonucleic acid (DNA): Large, complex molecules found in the nuclei of cells that carry genetic information for an organism’s development; double helix. (Pronounced DEE-ox-seerye-bo-noo-klay-ick acid)
Protein: A complex chemical compound consisting of many amino acids attached to each other that are essential to the structure and functioning of all living cells.
DNA replication: The process by which one DNA strand unwinds and duplicates all its information, creating two new DNA strands that are identical to each other and to the original strand.
Recessive gene: A gene that produces a certain characteristic only two both copies (alleles) of the gene are present. Variable: Something that can affect the results of an experiment.
• Dimples versus no dimples: Dimples are from the dominant allele; no dimples is the recessive allele. • Earlobes: Detached or not detached: If the earlobes hang free they are detached. Detached earlobes are a dominant allele; attached earlobes are recessive. Earlobes are the dominant allele and attached earlobes are recessive. • Mid-finger hair: Hair on any of the middle-section of the fingers is a dominant allele. If the middle section of the fingers are hairless, it is from a recessive allele. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
To begin this experiment, make an educated guess about the outcome of the experiment based on your knowledge of genes and heredity. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
• the participants
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘I will share at least 50% of my characteristics with my family members.’’ Variables are anything you can change in an experiment. In this case, the variable you will change are the participants. The variable you will measure will be whether participants have the specific trait. Level of Difficulty Moderate (due to the number of participants needed). Materials Needed
• about 10 non family-member participants • family members, at least five • notepad and pen Detached earlobes are a dominant allele; attached earlobes are recessive.
Approximate Budget $0. Timetable Varies widely depending upon the
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number of participants. Each participant should take about five to 10 minutes to document.
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Step-by-Step Instructions
detatched ear
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1. Make two charts of each trait you will be observing, one for family members and one for non-family members. 2. Note whether you have each of the characteristics. 3. Begin testing family members and nonfamily members. For each person that has Experiment Central, 2nd edition
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the characteristic, make a mark if it matches you. For example, if you have a widow’s peak and your sister has a widow’s peak, make a mark. If your sister does not have a widow’s back, note the results separately. 4. When you have finished testing all participants, add up how many family members and non-family members you tested. Summary of Results For both the family and
absent
non-family member charts, divide the number of participants by the number of participants who share the same trait as you. This will give you what percent of people in each category share your traits. What percent do family members share your traits? Are there certain traits that you share equally or more with the people outside your family. You may want to graph your data, and write up a summary of your findings.
mid-digit hair
Hair on any of the middlesection of the fingers is a dominant allele. ILLUSTRATION BY TEMAH NELSON.
PROJECT 2 Building a Pedigree for Taste Purpose/Hypothesis It is not always practical or possible to breed organ-
isms the way Mendel did, and so scientists need other ways to understand how traits are passed down through the generations. A pedigree is a
My Traits
Family
non-Family
widow’s peak dimples earlobes detatched mid-finger hair % shared traits
Step 1: Make two charts of each trait you will be observing, one for family members and one for non-family members. IL LU STR AT IO N BY TE MA H NE LSO N.
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diagram that is similar to a family tree. The pedigree shows as many generations as possible Troubleshooter’s Guide and in genetics, it shows which family members have a particular trait. Looking at who inherits a This experiment is relatively straightforward and trait over several generations helps predict if a you should have no major troubles. The one problem you may have is to get enough particitrait is genetic and if it is recessive or dominant. pants to give you strong data. The number of The purpose of this project is to construct a family members and non-family participants pedigree of one trait. The trait you will follow is does not have to be the same, but the more if someone can taste or not taste PTC. PTC people you can collect data on for each group, stands for phenylthiocarbamide. This compound the more accurate your data will be. gives foods like broccoli and coffee a bitter flavor. By constructing a pedigree, it will help you determine if the trait is dominant or recessive. You will need three generations of family members for this project. For example, you and your siblings would be one generation; your parents would be another generation; and their parents would be a third generation. You do not need to use your family; you could make a pedigree of a friend’s family. All pedigrees have the same symbols. The basic symbols include: • • • • • • •
squares symbolize males circle symbolize females a line between male and female symbolizes mating individuals who show the trait have a dark circle or square individuals who do not show the trait have a white circle or square each generation is numbered to the left with Roman numerals Arabic numbers, from left to right, represent birth order
Level of Difficulty Easy/moderate (because of data collection). Materials Needed
• PTC paper (available from hobby and science supply sources); see Note below. • family members • paper/pencil Note: You could also construct pedigrees for other traits you are curious about; see Experiment 1 for other options. Approximate Budget $5. 560
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Timetable Varies widely depending upon finding family members. Step-by-Step Instructions
1. Use the symbols and the illustration as a guide to make a pedigree of the family you are going to analyze. Make sure to number and label the pedigree. 2. Have as many people as possible taste the PTC paper. If they can taste the PTC, color in the square or circle. 3. For any people you cannot test, place a question mark in the square or circle.
Step 2: Have as many people as possible taste the PTC paper. IL LU STR AT IO N BY T EM AH
Summary of Results When you have finished testing all the family
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members, study your pedigree. If only one parent has the trait, how does it affect the offspring? If no parents can taste PTC, do any of the offspring? The ability to taste PTC is a dominant trait. Can you tell this from your pedigree? You might want to construct pedigrees of different families, especially if the family you tested was a non-PTC tasting family.
Design Your Own Experiment How to Select a Topic Relating to this Concept The study of genetics can
reach into many different fields and areas. As researchers continue to understand genes, consider what answers genetics can give us. You may want to explore characteristics of certain animals, such as dogs, or how different animals are related to one another. You can also investigate technologies that scientists use to understand genetics. What are some ways that genes are manipulated, and how can this affect human life? Check the Further Readings section and talk with your science teacher to start gathering information on genetics questions that interest you.
A pedigree is a diagram that is similar to a family tree. ILL US TRA TI ON B Y TE MA H NEL SO N.
Steps in the Scientific Method To conduct an
original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, Experiment Central, 2nd edition
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what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
There should be no major problems in this project. The main issue will be finding enough family members to test if they can taste PTC. You may have to mail family members the PTC test strips. If it is not possible in your family, you can conduct the project on another family.
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Recording Data and Summarizing the Results Your data should include
charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. As DNA is difficult to visualize, you may also want to include photographs and drawings of your experimental setup and results. This will help others visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are several genetic techniques you can do that give more information on DNA and genes. Two commonly used techniques are gel electrophoresis and DNA fingerprinting. These techniques will require special equipment and help. (Check the Resources section for companies that sell kits.) You can also replicate an experiment of Mendel’s with pea plants. You can also focus on predicting genetic characteristics. There are some genetic traits that differ among males and females. The trait for color-blindness, for example, is carried on the female’s sex chromosomes and affects mostly males. You can conduct color-blind tests in a certain population (classmates and family) and determine if your sample matches the overall population. Advances in genetics and genetic manipulations has also brought many ethical questions and controversies. You could investigate one potential controversy, such as genetically manipulated food, and present different viewpoints. 562
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For More Information Cells Alive. Animal Cell Mitosis. http://www.cellsalive.com/mitosis.htm (accessed May 22, 2008). Interactive animation of chromosomes dividing into two cells. Cold Spring Harbor Laboratory. DNA from the Beginning. http:// www.dnaftb.org/dnaftb/3/concept (accessed on June 2, 2008). Clear explanation of genetic concepts with illustrations, animations, and audio. DNA From the Beginning. http://www.dnaftb.org/dnaftb (accessed on March 1, 2008). An animated introduction on the basics of DNA, heredity, and genetics. National Institute of General Medical Sciences. The New Genetics. http:// publications.nigms.nih.gov/thenewgenetics/index.html (accessed May 22, 2008). Comprehensive information with illustrations of how genes work. Ridley, Matt. Genome: The Autobiography of a Species in 23 Chapters. New York: HarperColllins, 2000. Each chapter looks at one gene on a human’s chromosome. The Tech Museum of Innovation. Understanding Genetics. http:// www.thetech.org/genetics (accessed on May 17, 2008). Online DNA exhibit includes images of cells and DNA. The University of Utah, Genetic Science Learning Center. Tour of the Basics. http://learn.genetics.utah.edu/units/basics/tour (accessed May 22, 2008). Basic information with illustrations of DNA and genes.
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Germination
T
he first stage in the development of a seed, when it grows from seed to seedling, is germination. Like humans, seeds are equipped with their own growing mechanisms. An embryo and a supply of food exist within these tiny life starters. But until they are exposed to certain conditions of temperature, moisture, oxygen, and in some cases light, seeds remain dormant, or inactive, for days, months, or even hundreds of years. For example, scientists found a North American Arctic lupine seed that was about 10,000 years old. It was the oldest seed found so far, and it eventually grew into a plant similar to today’s lupine. The seed waited 10,000 years and sprouted only when the right germination conditions were in place. Really old books about green things Botany, the study of plant life, had its beginnings in ancient Greece. Theophrastus (c. 372–287 B . C . E .) wrote two large botanical works that were so revolutionary they guided scientists for the next 1,800 years. In his books On the History of Plants and On Causes of Plants, Theophrastus set down a theory of plant growth, plant structure analysis, and the relationship of agriculture to botany. He also identified, classified, and described 550 plants.
Getting through the ground Germination begins with a seed’s activation underground and ends when the first leaves push through the soil. A seed may remain viable, that is, capable of germination, for many years. Temperature plays a big factor in germination. The most favorable temperature ranges from 59 ˚F to 100.4 ˚F (15 ˚C to 38 ˚C). Temperatures above or below this range slow down the germination rate. Absorbing water is a seed’s first activity. Every seed has a little helper called a micropyle, an opening that enables water to enter the seed more easily. Water kicks off the seed’s life processes, including respiration. Respiration is the process of oxygen from the air entering the seed and helping the cell use its stored food as energy. Too much water can literally 565
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In the first stages of a seed’s germination, the cotyledons start to use up stored food and its root system begins to grow. PH OT O RE SEA RC HE RS I NC.
drown out the necessary oxygen, so water has to be available in the right amount. The embryo, including one or two cotyledons, or seed leaves, starts to use up its stored food. Its cells begin to divide and grow, which causes the seed’s coat, or testa, to burst open. The seed’s root system, or radicule, starts to grow, threading its way through the testa into the soil. The cotyledon develops into the shape we call a seedling. It has two parts. The upper part supports an embryonic shoot at the end. This eventually pushes through the soil as a stem and leaves. The lower part contains the roots. As seeds grow, the stem and leaves push up. Food reserves provide the enormous energy they need to heave their way through soil. Seedlings have been known to push through tarred roads. Once they are above ground, chlorophyll usually begins to form in the leaves and stems. Germination is the process a dormant seed goes through when it wakes up to begin the growing process. Our lives depend on plants. Conducting germination experiments will take the mystery out of this important life process.
EXPERIMENT 1 As they grow, seedlings use up much energy. As a result, they can actually push through tarred roads while growing. PH OT O RE SEA RC HE RS I NC.
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Effects of Temperature on Germination: What temperatures encourage and discourage germination? Purpose/Hypothesis In this experiment you will investigate the ideal temperature needed to awaken a seed and stimulate it to grow. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of seed growth. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Experiment Central, 2nd edition
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WORDS TO KNOW Botany: The branch of biology involving the scientific study of plant life.
Micropyle: Seed opening that enables water to enter easily.
Chlorophyll: A green pigment found in plants that absorbs sunlight, providing the energy used in photosynthesis, or the conversion of carbon dioxide and water to complex carbohydrates.
Radicule: Seed’s root system.
Cotyledon: Seed leaves, which contain the stored source of food for the embryo. Dormant: The condition of a seed when its growing processes are inactive.
Respiration: The physical process that supplies oxygen to an animal’s body. It also describes a series of chemical reactions that take place inside cells. Seedling: A small plant just starting to grow into its mature form.
Embryo: The seed of a plant, which through germination can develop into a new plant.
Testa: A tough outer layer that protects the embryo and endosperm of a seed from damage.
Germination: The beginning of growth of a seed.
Variable: Something that can affect the results of an experiment.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Temperatures near or below freezing and those over 100˚F will prevent germination.’’ In this case, the variable you will change is the temperature, and the variable you will measure is the number of seeds that germinate. You expect those seeds stored in very hot and very cold temperatures will not germinate. Level of Difficulty Easy/moderate. Experiment Central, 2nd edition
Viable: The capability of developing or growing under favorable conditions.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the temperature of the surrounding air • the amount of water provided • the type of soil used In other words, the variables in this experiment are everything that might affect the germination of the seeds. If you change more than one variable, you will not be able to tell which variable had the most effect on the seeds’ germination.
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Materials Needed
How to Experiment Safely
• 15 seeds (Lima beans, kidney beans, and lentils are good seed choices; use only one The lamp can cause fires when not handled variety.) properly. Ask an adult to help you set it up. • water • 3 sponges • 3 plastic trays big enough to hold a sponge • 3 napkins big enough to hold a sponge • 3 thermometers (Fahrenheit or Celsius) • access to a refrigerator • a lamp with a 40-watt bulb Approximate Budget $10. (The seeds may be purchased at a supermarket
as dried beans or you may find them in your family’s kitchen. Try to borrow thermometers to reduce the cost.) Timetable 20 minutes to set up the experiment; one to two weeks to
complete it. Step-by-Step Instructions
1. Place a sponge into each of the plastic trays. 2. Place five seeds on top of each sponge.
Steps 1 and 2: Set-up of plastic tray with sponge and five seeds on top of sponge. GAL E GR OU P.
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Steps 3 to 5: Set-up of plastic tray with napkin over seeds and thermometer. G AL E GR OUP .
3. Pour water over the seeds and the sponge so that water collects in the tray. Do not pour too much. The seeds should not sit in the water. 4. Place a napkin over the seeds to keep them from drying out. 5. Place one tray indoors, away from a window or door. Place a thermometer under the napkin to record temperature. 6. Place another tray with seeds in the refrigerator. Again, place the thermometer under the napkin to record the temperature. 7. Place the third tray 10 to 12 inches (25 to 30 centimeters) away from the lamp and turn it on. 8. After about an hour, begin to record the temperature and condition of the seeds. Make up a data sheet with the headings Room Temperature and Location. Underneath add Date, Temperature, and Seed Activity. Then fill it in daily. Lift the napkin and diagram the changes in the seeds. Experiment Central, 2nd edition
Step 7: Placement of third tray underneath the lamp. GA LE GRO UP.
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The sponge dries out too quickly. Possible cause: There is not enough humidity. Cover the seeds with a loose layer of plastic wrap. This will increase humidity and prevent the seeds from drying out.
9. Make sure the sponge stays wet at all times and the seeds are not under water. Check on the seeds daily. Summary of Results Compare the data on your chart and summarize your findings. Did the results support your hypothesis? Which tray of seedlings grew the most? Which tray of seedlings did not grow at all? Change the Variables To further explore how
temperature affects germination, you can vary the experiment in the following ways: • Use different types of seeds and see if one type of seed is more tolerant of high or low temperatures than others. • Try growing seeds at different temperatures without watering them. Do any sprout? • Try growing seeds in the dark at different temperatures. Cover the seed trays to block all light from reaching the seeds. Does light seem to be a factor in germination?
EXPERIMENT 2 Comparing Germination Times: How fast can seeds grow? Purpose/Hypothesis Each seed type has an average germination time. The seed waits for the correct conditions to occur. For example, if a seed emerged after the first warm day in spring, it might get caught by a late frost and die. So the seed may wait for consistent conditions that are ideal for growth. In this experiment, the goal is to compare the germination time for two different varieties of seeds. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of seed growth. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen 570
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A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘When two different varieties of seeds are exposed to the same growing conditions, one group will consistently germinate before the other.’’ In this case, the variable you will change is the type of seed, and the variable you will measure is the time it takes to germinate. You expect one type of seed to germinate before the other. Level of Difficulty Easy/moderate. (Daily atten-
tion is required during the two-week experiment.)
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the types of seeds used • the temperature of the surrounding air • the amount of water provided • the type of soil used In other words, the variables in this experiment are everything that might affect the time it takes for the seeds to germinate. If you change more than one variable, you will not be able to tell which variable had the most effect on the germination time.
Materials Needed
• 12 seeds—two different varieties; six lima bean seeds and six radish seeds • 2 to 3 cups of potting soil • egg carton (dozen size) • water in a spray bottle • tray big enough to hold the egg carton • fork Approximate Budget $2 for seeds; borrow the spray bottle if possible. Timetable 15 minutes to set up and two weeks to run the experiment. Step-by-Step Instructions
1. Use the fork to poke holes in the bottom of the wells in the egg carton. This will allow drainage. Label the wells with the numbers one to 12—one to six along the back row and seven to 12 along the front row. 2. Place the six lima bean seeds in the back row (wells one to six) and the six radish seeds in the front row (wells seven to 12). 3. Fill the wells with soil to the top. (Each seed should have the same amount of soil in the well.) Place the egg carton on the tray. Experiment Central, 2nd edition
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Steps 1 and 2: Set-up of drainage holes and seeds in the egg carton. GAL E GR OU P.
4. Using the spray bottle, water each well with the same number of squirts. Make sure all the soil is wet. 5. Place the egg carton/tray on a window sill in a warm room. 6. Water daily, making sure the soil stays wet. 7. Perform a daily inspection of your seedlings. Record the results on a chart with your observations. Number across the top from one to 12, with columns underneath. Then number the days down the far left of the chart, from one to 10. Use symbols illustrated to depict the stage of germination that is occurring.
Step 7: Four views of egg carton wells as the seeds grow: no change, emergence of seedling, cotyledons open, and first true leaves open. GAL E GR OU P.
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Summary of Results The goal of this experiment
is to compare the average time of germination (from beginning to emergence of the first true leaves) for each seed species. Look at your results chart and determine the average number of days it took for the first true leaves to appear for each seed type. Which seeds germinated faster? Did one group consistently germinate before the other? Change the Variables To further explore seed
Troubleshooter’s Guide Here is a problem that may arise in your experiment, a possible cause, and ways to remedy it. Problem: The seeds have not done anything for two weeks. Possible cause: They may need more water. Try increasing the water and storing them in a warmer location. If that does not work, replace the seeds with new ones.
germination times, change the environmental conditions under which you try to sprout the seeds. In separate experiments, vary the amount of water, sunlight, or warmth provided for one type of seed, such as radish seeds. Do radish seeds sprout more quickly under certain environmental conditions? Then repeat the experiments with seeds of another type, such as bean seeds. Or you might expose identical trays of radish seeds and bean seeds to the same harsh environmental conditions (little water, cold temperatures) to see which seeds sprout first.
EXPERIMENT 3 Seed Scarification: Does breaking the seed shell affect germination time? Purpose/Hypothesis There are some plants that go through a period of
inactivity, called dormancy. Dormancy can protect the seed from harsh
Step 7: Sample seedling growth chart for Experiment 2. GA LE GR OU P.
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environmental conditions, such as cold. To help the seed stay dormant, some seeds have develWhat Are the Variables? oped a hard, thick seed coat. The coat keeps out water and nutrients. Variables are anything that might affect the Scarification is the process of cracking or results of an experiment. Here are the main variables in this experiment: opening the seed coat. In nature, seed scarification can happen several ways, such as the seed • the types of seeds falling from a tree or thawing after freezing. • the temperature of the surrounding air People can cause seed scarification by hand. In • the amount of water this experiment, you will look at how seed scar• the amount of light ification affects germination. Using the same • the type of soil used type of seeds, you will slightly nick open several In other words, the variables in this experiment of the seed coats. With another group of seeds, are everything that might affect the time it you will nick the seed coat and then allow the takes for the seeds to germinate. If you change seeds to soak in water. You can compare the more than one variable, you will not be able to germination time of these experimental seeds to tell which variable had the most effect on the a group of control seeds. germination time. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of what a seed needs to germinate and seed coats. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
Step 3: Gently make one or two nicks in the seed shell. Do not cut the seed too hard or it could injure the inner seed. I LLU STR AT IO N BY T EM AH NE LS ON.
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• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The group of seeds that are scarified will consistently germinate before the seeds not scarified.’’ In this case, the variable you will change is changing the seed shell, and the variable you will measure is the time it takes to germinate. You expect one type of seed to germinate before the other. Experiment Central, 2nd edition
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Level of Difficulty Moderate. Materials Needed
• 12 seeds—of the same type; sweet peas, moonflowers, or morning glories work well (the seeds should be relatively large with a thick outer shell) • 1 10-section peat pellet or similar type starter pot, with a cover (available at gardening stores); you can replace this with 2 to 3 cups of potting soil and an egg carton • water • 3 plastic bags • paper towel • plant labels • knife
How to Experiment Safely Have an adult help you cut the seeds. Because the seeds are small, your adult helper will need to handle the knife extremely carefully.
Approximate Budget $10. Timetable 30 minutes to set up over 24 hour
period; four to 10 days for germination.
Step 5: Wrap Scarification/ Moisture group of the seeds in a wet paper towel. ILLUSTRATION
Step-by-Step Instructions
BY TEMAH NELSON.
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Step 7: Cover the peat pellet (or carton) and set aside in a warm environment. I LL UST RA TI ON
con tro l
scarifi catio
n
BY T EMA H NE LS ON.
control
scarification
n to e ca ur if st ar o sc m
icatistounre scarifm o
1. Follow the direction for the peat pellet or add soil to the sections in the egg carton. 2. Separate the seeds into three groups, with two to four seeds in each group. Place one group of seeds into a plastic bag labeled ‘‘Control.’’ Place the second group of seeds into the bag labeled ‘‘Scarification,’’ and set the last group in a bag labeled ‘‘Scarification/Moisture.’’ 3. With the Scarification group, have an adult help you take a knife and gently make one or two nicks in the seed shell. Do not cut the seed too hard or it could injure the inner seed. Return the seeds to its plastic bag. 4. Repeat this same process with the Scarification/Moisture group.
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5. Wrap Scarification/Moisture group of the seeds in a wet paper towel. Wrap the Germination Time seeds in the towel and place it in a plastic 10 bag labeled Scarification/Moisture. 9 Allow these seeds to sit overnight 8 6. Plant each group of seeds separately. 7 Place about two to three seeds in each 6 section. Dig a small well in the soil, 5 plant and water. Label a marker with 4 the type of seed and insert. Repeat this 3 with the other two groups of seeds. Each 2 of the seeds should have the same amount 1 of water. control scarification scarification 7. Cover the peat pellet (or carton) and set moisture aside in a warm environment. 8. Check daily, making sure the soil stays Step 9: Sample graph to mark moist. when each of the seeds germinate. I LL UST RA TI ON BY 9. Set up a graph (see illustration) to mark when each of the seeds T EM AH NE LS ON. germinate. Summary of Results Take a look at your chart. Which group of seeds germinated faster? Did the seeds that were soaked in moisture geminate faster or slower than the seeds that were only nicked? Write a summary of your results.
Design Your Own Experiment How to Select a Topic Relating to this Concept Since germination is
dependent on so many variables, looking at variables may be the best place to start. For instance, cotyledons are the stored source of food for the growing embryo. What would happen if one cotyledon was removed? Or what would happen if a seed was cooked in boiling water for a minute? What would happen if the seed coat was removed before germination? Choose an aspect that interests you, then proceed with the research. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on germination questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be 576
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sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand.
Troubleshooter’s Guide Here is a problem that may arise in your experiment, a possible cause, and ways to remedy it. Problem: The seeds are not germinating, even after 10 days.
• State a testable hypothesis, an educated guess about the answer to your question.
Possible cause: They may need more water or the soil might not have any nutrients. Make sure you have nutrient-rich soil. You can purchase it at a gardening store. Give the seeds water and repeat.
• Decide how to change the variable you selected.
Problem: The seeds that were nicked with a knife did not germinate.
• Decide how to measure your results.
Possible cause: You may have cut and damaged the inside of the seed. Repeat the experiment, taking care to only nick the seeds.
Recording Data and Summarizing the Results
As a scientist investigating a question, you must gather information and share it with others. Bring all the data together and write a conclusion. Simplify the data into charts or graphs for others to understand easily. Related Projects When dealing with seeds, you
can take many different routes. You can try growing experiments or your investigation can be about seed anatomy, seed type (monocot or dicot), or methods of spreading the seeds.
Problem: There was no difference in any of the seeds’ germination. Possible cause: Not all seeds need scarification. You may have used a type of seed that did not. Try to purchase one of the recommended seed types, or ask for a recommendation at a gardening store for a type of seeds that needs scarification.
For More Information Andrew Rader Studios. ‘‘Plant Basics.’’ Rader’s Biology4kids.com. http:// www.biology4kids.com/files/plants main.html (accessed on February 8, 2008). Information on plant biology and structures. Burnie, David. Plant. London: Dorling Kindersley, 1989. Includes chapters on plant life processes such as ‘‘A Plant Is Born,’’ which covers germination. Missouri Botanical Garden. Biology of Plants. http://www.mbgnet.net/ bioplants/ (accessed on February 6, 2008). Basic information about plant biology and life. Experiment Central, 2nd edition
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United States Department of Agriculture. Plant’s Database. http:// plants.usda.gov (accessed on February 6, 2008). Provides a list of plants in every state, along with images of many plants. The Visual Dictionary of Plants. London: Dorling Kindersley, 1992. Offers an in depth overview of plants and their activities through text and clear, detailed photos.
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Gravity
E
arth orbits the Sun. The Moon orbits the Earth. But how do the planets stay in the sky? How do we stay on Earth’s surface? Englishman Sir Isaac Newton (1642–1727) figured out the answers to these questions while watching an apple fall in his orchard. Newton reasoned that the force that pulls the Moon into its curved path around Earth instead of a straight line was the same force that pulled the apple to the ground. Newton was a scientist and mathematician, and he wrote his theory on a scrap of paper, something he did with all his thoughts and formulas. The falling apple initiated his famous universal law of gravity, which states that the attracting force between any two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. It was published in his book Principia in 1687. Well, how do they stay up there? Danish scientist Tycho Brahe (1571–1630) developed a theory of planetary motions. Then, in 1609, Johannes Keppler used Brahe’s theory when he said that the planets orbited elliptically rather than in a circle. An elliptical orbit is a curved path similar to the shape of an egg. Newton’s laws unlocked many answers to questions scientists had been struggling with as they tried to figure out, among other things, what kept the planets orbiting in the first place. The planets orbit and position themselves according to a balanced set of natural laws. One law is called inertia, the tendency of objects to continue whatever motion is affecting them. In other words, a rotating planet continues to rotate; a stationary book remains sitting on a desk. These objects continue to do what they do until a force causes an acceleration or change in their state of motion. This was part of Newton’s First Law. In Newton’s Second Law, he said the greater the force, the greater the acceleration. He also introduced the concept of mass, the 579
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amount of atoms, in an object. The relationship between an object’s mass, acceleration, and the forces exerted on it was defined in his Second Law. Newton’s Third Law addressed gravity. For example, both the Moon and Earth are attracted to each other. But Earth has a much bigger mass, so it has a more powerful gravitational attraction that pulls the Moon into a curved path, or orbit, around Earth. The Sun exerts pulling forces as well. This attracting, pulling relationship exists between all the planets, moons, and stars. It keeps everything in the universe moving in an orderly fashion.
Sir Isaac Newton developed the theory of gravity as he watched an apple fall. L IBR AR Y O F C ONG RE SS.
High tide The gravitational forces of the Moon and Sun pull on Earth’s surface water, causing tides, or water surges, twice a day. The Moon has a stronger gravitational pull because it is closer to Earth than the Sun. Twice a month, when the Sun, Moon, and Earth are aligned, the force of their gravitational pull causes the highest tides, called spring tides. When the Sun and Moon are at right angles, they pull in different directions and have a weaker gravitational pull. Then lower tides, called neap tides, take place. What about me and the apple? What keeps your feet on the ground is Earth’s gravitational force pulling you down. The amount of gravitational force Earth exerts on an object, in this case you, depends on your mass. Earth has a very large mass, so its gravitational force is very strong. That is why we are not falling into space. You exert an attracting gravitational force on Earth as well, but the pull is very weak. If you are being pulled to the ground, it is easy to understand why Earth’s gravitational force also pulled Newton’s apple to the ground. Gravitational forces have a great effect on our lives. Conducting experiments makes us aware of their presence and influence, from keeping us from falling off the planet to allowing us to launch rockets.
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WORDS TO KNOW Acceleration: The rate at which the velocity and/ or direction of an object is changing with the respect to time.
Mass: Measure of the total amount of matter in an object. Also, an object’s quantity of matter as shown by its gravitational pull on another object.
Elliptical: An orbital path which is egg-shaped or resembles an elongated circle.
Universal law of gravity: The law of physics that defines the constancy of the force of gravity between two bodies.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Inertia: The tendency of an object to continue in its state of motion.
Variable: Something that can affect the results of an experiment. Weight: The gravitational attraction of Earth on an object; the measure of the heaviness of an object.
EXPERIMENT 1 Gravity: How fast do different objects fall? Purpose/Hypothesis In this experiment, you will determine the effect
that mass has on the gravitational pull exerted on a falling object. You will drop three pencils taped together at the same time as you drop a single pencil to see whether the heavier group falls faster. You will also drop two objects of about the same weight (a pencil and a Ping-Pong ball) but with different shapes to see which falls faster. According to the laws of physics, the falling rate for all objects is the same. Gravity does pull harder on objects with more mass. However, objects with more mass also have more inertia. Inertia causes objects to continue whatever motion is affecting them. That means objects at rest tend to stay at rest—they resist moving. The more mass an object has, the more inertia it has. The amount of force needed to overcome inertia balances out the pull of gravity, so objects with more mass fall at the same rate as objects with less mass. Falling rates can also be affected by air resistance, the force that air exerts on a moving object. Air resistance pushes up on a falling object, while Experiment Central, 2nd edition
The planets in the Andromeda Galaxy, M31, follow an elliptical orbit. P HOT O RES EA RC HER S I NC.
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the weight of each pencil • whether the pencils are dropped in a vertical or a horizontal position • the distance from which all objects are dropped • the amount of force used when the objects are dropped In other words, the variables in this experiment are everything that might affect the mass and shape of the objects. If you change more than one variable, you will not be able to tell which variable had the most effect on the speed with which the objects hit the floor.
Step 1: Tape three of the pencils together tightly. GA LE G RO UP.
gravity pulls down. The more surface an object has, the more air resistance it has and the more slowly it will fall. You can test this by crumpling a sheet of paper into a ball and dropping it at the same time as you drop a flat sheet of the same paper. The flat sheet has more air resistance and will fall more slowly. Before you begin the experiment, make an educated guess about the outcome based on your knowledge of gravity. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for the pencil experiment: ‘‘The group of pencils and the single pencil will fall at the same rate.’’ For the Ping-Pong ball experiment, your hypothesis might be this: ‘‘The Ping-Pong ball will fall more slowly than the pencil because its shape gives it more air resistance.’’ In this case, the variable you will change is the mass (pencils) and the shape (pencil and Ping-Pong ball) of the objects. The variable you will measure or observe is the time when each object hits the floor. Level of Difficulty Easy/moderate. Materials Needed
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4 wooden pencils, unsharpened masking tape 1 Ping-Pong ball 6-foot (1.8 m) step ladder Experiment Central, 2nd edition
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Approximate Budget $5 for pencils, tape, and
Ping-Pong ball. Timetable 20 minutes. Step-by-Step Instructions
How to Experiment Safely Ask an adult to climb the ladder so you can lie on the floor and observe when the objects hit the floor. No one should ever stand on the top step of a ladder.
1. Tape three of the pencils together tightly. 2. Place the taped pencils and the single pencil on the top of the ladder. 3. Ask your adult helper to climb the ladder. 4. Position yourself flat on the floor, about 6 feet (1.8 m) from the ladder so you can observe the pencils hitting the floor. 5. Have the adult pick up the taped pencils in one hand and the single pencil in his or her other hand. 6. Have the adult hold both sets of pencils at the same height from the floor, in a vertical position, and drop them. Your helper should not use any force, but simply let them both go at the same time. 7. Ask the adult to help you repeat this procedure with different groupings of pencils. Record your observations in a table similar to the one illustrated.
Steps 3 to 6: Adult drops pencils from ladder; student positioned for observation. GA LE GRO UP. Experiment Central, 2nd edition
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Step 7: Results chart for Experiment 1. GAL E GR OU P.
8. Have the adult repeat the procedure, dropping a single pencil, held vertically to reduce air resistance, and the Ping-Pong ball. Observe which object hits the floor first. Summary of Results Study the observations on your table and decide
whether your hypotheses were correct. Did the taped pencils and the single pencil hit the floor at the same time? If not, how would you explain the difference? (The larger group of pencils would have slightly more air resistance than the single pencil, even when dropped in vertical positions.) Did the single pencil hit the floor before the Ping-Pong ball? Why is that? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables Here are some ways you can vary this experiment:
• Vary the distance from which you drop the objects. Can you observe a difference in falling rates when the distance is longer or shorter? • Try dropping other objects with different amounts of mass or the same mass but different shapes. See how these changes affect their falling rates. 584
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PROJECT 2 Measuring Mass: How can a balance be made? Purpose/Hypothesis A useful measurement for
science is not the weight but the mass of an object. The mass is the amount of atoms that make up an object. Here is your hypothesis: ‘‘By creating a balance with counterweights, you will cancel out the effects of gravity and calculate the mass of an object.’’ The materials used as a counterweight can be varied if the mass is known. The balance you will create is accurate only for low-mass objects. Do not exceed 0.9 ounces (25 grams) or accuracy will diminish.
Step 2: Mark the ruler in the middle. G AL E GR OUP .
Level of Difficulty Moderate. Materials Needed
• • • • • • •
2 5-ounce (148-ml) cups plastic ruler, 1 foot (30 cm) long dried beans quarter, penny, nickel 30 small metal paper clips pencil Optional: dried split peas, Popsicle sticks
Approximate Budget $4 for the beans and wood. Timetable Approximately 30 minutes. Step-by-Step Instructions
1. Place the pencil on a level desk. If the pencil rolls, the desk is not level. 2. Mark the ruler in the middle. 3. Place the ruler over the pencil at right angles, as illustrated. 4. At each end of the balance place the 5-ounce (148 milliliter) paper cups. Draw rings to mark their positions. 5. Make sure the ruler is level, and neither side is touching the tabletop. Experiment Central, 2nd edition
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6. If a side is touching, very slightly move the ruler as it rests on the pencil. Try to balance it perfectly. 7. As a test material, place a quarter (0.19 oz or 5.5 grams) in one cup. 8. Place 1 nickel (0.175 oz. or 5 grams) and one paper clip (0.018 oz. or 0.5 grams) in the other cup. The balance should be level. 9. Continue to test other combinations of materials to determine which have equal mass. Below is a list of common materials and their mass: nickel: 0.175 oz. (5 grams) dime: 0.08 oz. (2.3 grams) penny: 0.087 oz. (2.5 grams) quarter: 0.19 oz. (5.5 grams) wooden Popsicle stick: 0.05 oz. (1.5 grams) one paper clip: 0.018 oz. (0.5 grams) dried split pea: 0.003 oz. (0.1 gram) Summary of Results You now have made an instrument of measurement.
It is important that you keep a record of the standard measurements and items for counterweights. Illustrated is a chart that you can make to keep track of the mass of tested objects. Modify the Experiment For a more in depth look at gravity and how air
pressure impacts gravity, you can do some simple experiments that will illustrate the relationship between these two forces.
Steps 3 and 4: Place the ruler over the pencil at right angles. At each end of the balance place the 5-ounce paper cups. GA LE GR OU P.
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In Experiment 1, you learned that air resistance, the force that air exerts on a moving object, affects the rate at which an object falls. Experiment with this idea further by using a plastic soda bottle and water. Using what you know about gravity and air resistance, predict what would happen if you added water to a soda bottle with holes and then change the air resistance in the bottle. What would happen to the water? How could air resistance prevent the water from spilling out of the holes? Carefully poke small holes in the bottom of a plastic bottle. Fill the bottle with water and twist on the cap. Hold onto the bottle cap and lift it above a sink, while making sure you are not squeezing the bottle. What happens? Now remove the cap and lift the bottle above the sink. What is happening to the water? How do the results show how air resistance can work against the force of gravity?
Troubleshooter’s Guide Below are some problems that may occur during this project, possible causes, and ways to remedy the problems. Problem: When you tested the quarter, it did not balance. Possible cause: The balance is not accurate to the 0.5 gram point. The actual mass of the quarter is 5.6 grams. Try adding one or two split peas to counter the weight. Problem: The balance keeps tipping and it does not seem to level out. Possible cause: Try using a pencil that has flattened sides to decrease sensitivity.
Design Your Own Experiment How to Select a Topic Relating to this Concept Gravity is a force of
nature that can be examined and studied in many different ways. Pretend to be Newton and make observations about what happens around you. Notice common events. Why does a coin fall through water more slowly than through air? Is gravity the same in water as it is in air? The study of gravity will lead you into other areas of physics such as friction, buoyant force, and acceleration.
Recording chart for Experiment 2. G AL E GR OUP .
Steps in the Scientific Method To do an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Experiment Central, 2nd edition
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Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording and Summarizing Results It is impor-
Air resistance working against the force of gravity. IL LUS TR ATI ON B Y TE MA H NE LS ON.
tant to be able to share your results with others. Put any data you collect into charts or graphs. Even Newton wrote down his measurements in journals. When summarizing the results, reflect on your question or purpose and describe how it was answered or proven. Look at your hypothesis and see if your initial idea was correct. Plot the results on graphs and charts. Make them easy for others to understand or follow. Related Projects One type of experiment that would be fun might be a
scale to measure weight. All you need is a spring, hook, and some cardboard. By hanging objects on the hook and hanging them on the spring, you can measure the pull of gravity on a mass.
For More Information Allaby, Michael, et al. The Visual Encyclopedia of Science. New York: Kingfisher, 1994. Includes illustrated science text and colorful photos that explain the gravity concept. Asimov, Isaac. Asimov’s Chronology of Science and Discovery. New York: Harper & Row, 1989. Offers a clear, direct explanation of gravity. Magill, Frank N. The Great Scientists. Danbury, CT: Grolier Education Corp., 1989. Contains a good background chapter about Isaac Newton, his discovery of gravity, and other scientific theories he introduced.
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Greenhouse Effect
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n 1827, a French mathematician named Jean-Baptiste-Joseph Fourier came up with an interesting theory. He said Earth’s atmosphere protected its inhabitants against the freezing temperatures of space. Fourier pointed out that Earth’s atmosphere acted as an insulator, an effect similar to what happens when heat is trapped within the glass walls and roof of a greenhouse. He called his theory the greenhouse effect. Today we know that the greenhouse effect takes place when sunlight passes through the atmosphere and is absorbed by land and water. The energy in the sunlight is converted to heat energy to warm the surface of Earth. Some of this heat energy is re-radiated out into the atmosphere in the form of infrared radiation. The infrared radiation has a longer wavelength than the sunlight and is absorbed by certain gases in the atmosphere, such as carbon dioxide. This traps the heat, keeping Earth’s surface warm. The greenhouse effect is actually a good thing. Without it, we would experience an average temperature of –2.2˚F (–19˚C), and we would all freeze. Perfecting a theory Two scientists in the nineteenth century expanded Fourier’s theory. In 1861, English physicist John Tyndall said that certain atmospheric gases, such as carbon monoxide and water vapor, warmed Earth’s surface. In 1896, Swedish scientist Svante Arrhenius made the greenhouse theory clearer in a scientific article. He stated that increased carbon dioxide levels in the atmosphere could trap more of the heat energy rising from Earth. More trapped heat energy meant warmer temperatures on Earth’s surface. Arrhenius was the first to understand the concept of global warming and climate changes because of the greenhouse effect.
We are all affected by the greenhouse effect The greenhouse effect has been in the news a lot lately. Why? Carbon dioxide levels began to rise during the late 1700s when machines began doing work that had 589
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A greenhouse traps the Sun’s heat within its glass walls and roof, just as carbon dioxide does in Earth’s atmosphere. PET ER ARN OL D IN C.
Global warming, caused by the greenhouse effect, causes polar ice caps and glaciers to melt faster. PHO TO R ES EAR CH ERS I NC.
previously been done by humans and animals. The machines needed fuel to work, and fossil fuels, such as coal and wood, were used. Fossil fuels contain carbon. Burning these fuels releases the carbon, which combines with the oxygen in air to form carbon dioxide. Back in the 1700s, this was not a big problem because there were not as many people or machines. But today, burning fossil fuels such as gasoline has caused a critical situation. Besides being used in vehicles—including cars, trucks, and planes—fossil fuels are used to produce electricity. Burning these fossil fuels releases billions of tons (metric tons) of carbon dioxide into the air every year. At the same time, many of the forests, which absorb carbon dioxide from the air, have been cut down. All of these factors increase the volume of heat-trapping carbon dioxide gas in our atmosphere. In addition, water vapor in the air and about thirty other gases also trap Earth’s heat, including gases from nitrogen-based fertilizers and methane emissions from decomposing vegetation.
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WORDS TO KNOW Atmosphere: Layers of air that surround Earth. By-products: Something produced in the making of something else. Combustion: Any chemical reaction in which heat, and usually light, are produced. The most common form of combustion is when organic substances combine with oxygen in the air to burn and form carbon dioxide and water vapor. Fossil fuels: A fuel such as coal, oil, gasoline, or natural gas that was formed over millions of years from the remains of plants and animals. Global warming: Warming of Earth’s atmosphere as a result of an increase in the concentration of gases that store heat, such as carbon dioxide. Greenhouse effect: The warming of Earth’s atmosphere due to water vapor, carbon dioxide, and other gases in the atmosphere that trap heat radiated from Earth’s surface.
Greenhouse gases: Gases that absorb infrared radiation and warm the air before the heat energy escapes into space. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Infrared radiation: Electromagnetic radiation of a wavelength shorter than radio waves but longer than visible light that takes the form of heat. Insulation: A material that is a poor conductor of heat or electricity. Microclimate: A unique climate that exists only in a small, localized area. Troposphere: Atmospheric layer closest to Earth where all life exists. Variable: Something that can change the results of an experiment.
These greenhouse gases absorb heat energy from Earth before it escapes into space. According to scientists, these heat-trapping gases will cause an average temperature rise of 3–8 ˚F (16–13 ˚C) in the next 60 years, which could cause destructive weather changes.
Nitrogen-based fertilizers contribute to the greenhouse effect. PHO TO R ES EAR CH ERS INC .
Conducting experiments and projects on how the greenhouse effect works will help you become aware of the delicate natural balance that maintains Earth’s environment as we know it. We have already experienced some of the problems caused by an overload of greenhouse gases, including air pollution, which causes respiratory problems. Being more aware of the greenhouse effect may make you want to help reduce these gases and help our planet. Experiment Central, 2nd edition
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EXPERIMENT 1 What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
Creating a Greenhouse: How much will the temperature rise inside a greenhouse?
Purpose/Hypothesis In this experiment you will measure the temperature inside a greenhouse. A greenhouse is a small enclosure that maintains • the amount of sunlight that passes a microclimate that is warmer than the climate through the glass or plastic outside it. A greenhouse is often used for growing • the amount of wind or rain plants in cold weather. It is made of plastic or • the color of the material under the glass that allows the Sun’s light energy to pass greenhouse through. When the light energy is absorbed by In other words, the variables in this experiment the soil and plants inside, it warms them. Some of are everything that might affect the temperathis energy is then re-radiated out into the greenture inside the greenhouse. If you change more house in the form of infrared radiation, or heat than one variable, you will not be able to tell which variable had the most effect on energy. Because the heat energy has a longer temperature. wavelength than the entering light energy, most of the energy is absorbed and trapped by the plastic or glass of the greenhouse walls and roof, just as the greenhouse gases in our atmosphere absorb and trap the heat energy from Earth. Although a small portion of the heat energy escapes, most of it is reflected or re-radiated back into the greenhouse to warm the air. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of greenhouses and the greenhouse effect. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen • the amount of sunlight reaching the greenhouse
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The more sunlight that shines on the greenhouse, the higher the inside temperature compared to the outside temperature.’’ 592
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In this case, the variable you will change (or let nature change) is the amount of sunlight that reaches the greenhouse, and the variable you will measure is the temperature inside the greenhouse compared to the outside temperature. If the difference between the inside temperature and outside temperature is greater on days when more sunlight reaches the greenhouse, you will know your hypothesis is correct.
How to Experiment Safely Goggles and adult supervision are required when hammering the nails. Wear gloves when handling the glass.
Level of Difficulty Easy/moderate. Materials Needed
• 2 thermometers • 4 wooden boards, roughly 1 x 6 x 20 inches (2.5 x 15 x 50 centimeters) • One 24 x 24-inch (60 x 60-centimeter) piece of transparent plastic or glass, 0.25 inch (0.5 centimeter) thick • Eight 2-inch (5-centimeter) nails • hammer • goggles • gloves
How a greenhouse works. GAL E GR OU P.
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Approximate Budget $10. (Use any lumber that
is cost-effective.) Timetable One week. (This experiment requires
a half-hour to assemble and one week to monitor.) Step-by-Step Instructions
Step 1: Carefully hammer two nails through each end of a piece of wood. GA LE GRO UP.
1. Hammer two nails through each end of a piece of wood, as illustrated. Repeat with a second piece of wood. Place the wood into a square with the two pieces with nails opposite each other. 2. Hold the wood in position and assemble the box by carefully driving the nails into the ends of the two remaining pieces of wood.
Step 6: Sample recording chart for Experiment 1. GA LE GR OU P.
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3. Place the piece of plastic or glass over the wood box. Be sure it completely overlaps the wood box so there are no gaps around the edges. 4. Place the greenhouse outside in a sunny spot. Put one thermometer inside the greenhouse and one outside the greenhouse close by. 5. Record the temperature inside and outside at the same time in the morning, afternoon, and evening for seven days. Record for a longer period if three or more days are mostly cloudy, windy, or rainy. 6. Record the general weather conditions during each day. See the results chart illustrated. Summary of Results Review the data collected at
the same time of day. Graph this data so you can compare temperatures inside and outside of the greenhouse. Note the general weather conditions for each day on the graph. Do your results confirm your hypothesis? Was the temperature inside the greenhouse higher on days when there was more sunshine? Was it consistently higher than the temperature outside? Was the difference between the inside temperature and the outside temperature greatest when there was more sunshine?
Troubleshooter’s Guide Here are some problems that may arise during this experiment, possible causes, and ways to remedy the problems. Problem: The temperature inside the greenhouse is going up too high, for example, 110˚F (43˚C). Possible cause: If you conduct this experiment during the warm summer months, the temperature inside the greenhouse will soar. Try placing a large piece of thin white paper on top of the greenhouse to block some of the Sun’s rays. Problem: The evening temperature inside the greenhouse is always much higher than the outside temperature. Possible cause: If you place the greenhouse on a dark surface, such as a brick patio or walkway, the dark materials will absorb heat during the day. That heat will remain trapped under the greenhouse to keep the inside warm in the evening, even when the outside temperature drops.
Change the Variables You can change the variables and repeat this experi-
ment. For example, you can vary the amount of sunlight reaching the greenhouse by placing one or more layers of thin tracing paper or wax paper over the glass. You can also vary the color of the material under the greenhouse by first placing the greenhouse on a white poster board and then on a black poster board. Does the black poster board absorb more incoming sunlight and make the temperature inside the greenhouse higher? If you place two bricks inside the greenhouse, will they absorb and retain enough heat to keep the greenhouse warm all night? To find out, you Experiment Central, 2nd edition
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would have to take temperature measurements at various times between sundown and sunrise. When you conduct further experiments, remember to change only one variable at a time or you will not be able to tell which variable affected the results.
EXPERIMENT 2 Fossil Fuels: What happens when fossil fuels burn? Purpose/Hypothesis Fossil fuels, such as oil, coal, and natural gas, are used to warm the world we live in and move the machines that make life easier. However, for every advantage there usually is a disadvantage. That is what this project will demonstrate. Many fossil fuels are hydrocarbons, which means they contain hydrogen and carbon. When these fossil fuels are burned during combustion, they combine with oxygen and other gases in the air to produce carbon dioxide, water vapor, and other by-products that may harm the environment or act as greenhouse gases. The combustion of fossil fuels is a major contributor to the greenhouse effect. In this project you will observe how carbon dioxide and water vapor are produced during combustion. You will also look for evidence of free carbon before it combines with oxygen to form carbon dioxide. Level of Difficulty Moderate. (The experimenter must be mature and Step 4: Carefully hold the rounded end of the spoon 1 inch (2.5 centimeters) above the flame. GA LE GRO UP.
responsible when performing this project.) Materials Needed
• • • • • • •
1 paraffin candle matches plate or candle holder metal spoon white index card goggles leather gloves
Approximate Budget $1 for the candle; other items will likely be found in the home. Timetable 10 minutes. 596
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Step-By-Step Instructions
1. Place the candle in the holder or on the How to Experiment Safely plate. Make sure it will not fall over. This project requires adult permission and 2. Remove all nearby flammable materials. supervision. Always use caution when handling 3. Using the matches, light the candle and matches and candles. Wear goggles, remove let it burn for a minute. (Ask for help if loose clothing, and tie back long hair. Do not try this project with any other fuel source. Gasoline, needed. An adult must be present.) kerosene, propane, lamp oil, and other fuels can 4. Wearing goggles and gloves, hold the be explosive and extremely dangerous. rounded end of the spoon 1 inch (2.5 centimeters) above the flame. Notice if anything accumulates on the spoon. Hold it there 10 seconds or less. Caution! The spoon will get hot. 5. Next, place the spoon directly into the flame for five to 10 seconds and remove. Notice if anything accumulates. Caution! The spoon will be very hot. 6. After the spoon has cooled, use your finger to transfer some of the black residue that has appeared on the spoon onto the index card. The residue is carbon produced by the combustion. Notice that the carbon was formed when the spoon was inside the flame. However, when you held the spoon above the flame, there was no black residue. A general formula for the combustion of paraffin-type hydrocarbons is illustrated above. During the first stage of combustion, the carbon and hydrogen molecules in the paraffin split apart. So, inside the flame, the carbon is free and has not bonded to the oxygen yet. That is why the carbon collected on the Step 6: The general formula for spoon held in the flame. Once the carbon rises out of the flame, it the combustion of paraffin-type joins with the oxygen in the air and becomes the invisible gas hydrocarbons. GAL E GR OU P. carbon dioxide. 7. Put on the goggles and gloves again and hold the glass upside down so the open end of the glass is even with the top of the candle, and the flame is inside the glass. Use both hands to hold the glass and keep it centered above the flame. Hold it there for 10 seconds or less. Caution! The glass will get hot. Watch for moisture accumulating inside the glass. This is the water vapor produced by the combustion. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy it. Problem: There was black residue on the spoon when held above the flame.
Summary of Results Make sure you keep a journal of your observations. Pay close attention to what is happening. If you do not give the project your full attention, you can miss events. You can diagram these events in a journal. Modify the Experiment In this experiment, you
built a greenhouse and measured the temperature inside and outside over a period of time. Possible cause: The spoon was too close to the You know that carbon dioxide is a greenhouse candle. Try again, holding the spoon at least an gas, and studies have shown that levels of carbon inch above the top of the flame. dioxide in the atmosphere have been rising. For a more advanced version of this experiment, you can explore how changing the carbon dioxide level will affect temperature. In modifying this experiment to introduce carbon dioxide, you will need to make two simple greenhouses. You can make the greenhouses from two plastic bottles. Cut the bottoms off and place a thermometer inside each bottle. Place a heat lamp over both the empty bottle and the bottle with the carbon dioxide. You can then add carbon dioxide into one of the bottles. One way to add carbon dioxide is with baking soda and vinegar. Baking soda mixed with vinegar creates a chemical reaction that produces carbon dioxide. Mix the baking soda and vinegar in a small container and immediately set the container inside one of the bottles. Turn on both heat lamps. Monitor the temperatures of both bottles over several hours and record your results. Compare the temperatures of the carbon dioxide bottle and its control. You can experiment with different concentrations of the baking soda and vinegar. You could also find other sources of carbon dioxide and see if they are more effective in producing a temperature change.
Design Your Own Experiment How to Select a Topic Relating to this Concept Since the atmosphere acts
as a giant greenhouse, sheltering life on Earth from harsh environments in space, the atmosphere is a good starting point for experiments and projects. For example, you might begin with an investigation into the layers of the atmosphere and how they help insulate the earth. You might 598
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Layers of the atmosphere surrounding Earth. GA LE GR OU P.
also identify which machines or sources of power generate the lowest levels of carbon dioxide and other greenhouse gases. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on greenhouse effect questions that interest you. As you consider possible experiments and projects, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of them might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Experiment Central, 2nd edition
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Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data on the green-
house effect can be put into charts or graphs or even photographed to enable the information to be shared with others. After the data is collected and analyzed, your final responsibility is to make a conclusion based on your experiment and decide whether your hypothesis was true. Related Projects For atmospheric experiments, it’s best to study the layer
closest to earth called the troposphere. This layer is where all life exists. For instance, you could design an experiment with plants and insects living in an environment that has an altered atmosphere.
For More Information Bilger, Burk. Global Warming. New York: Chelsea House Publishers, 1992. Examines the phenomenon of global warming, discussing the greenhouse effect in its positive, life giving form and again as this mechanism is knocked out of balance. U.S. Environmental Protection Agency. ‘‘Greenhouse Effect.’’ http:// www.epa.gov/climatechange/kids/greenhouse.html (accessed on January 17, 2008). Williams, Jack. The Weather Book. New York: Vintage Books, 1997. Includes diagrams and text on the greenhouse effect and other atmosphere related phenomena.
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T
he term groundwater sounds as if it refers to an underground lake or river, but relatively little groundwater is found in this form. Groundwater lies below the surface of the land; in fact, it is almost everywhere underground. Mostly it is found in the tiny pores, or spaces, between rocks and particles of soil and in the cracks of larger rocks. Where does groundwater come from? When rain falls, some of it flows along the surface of the ground into streams and lakes as runoff. Some of the rain evaporates into the atmosphere, some is taken up by plant roots, and some seeps into the ground to become groundwater. Aquifers are like big sponges Underground areas called aquifers collect much of this groundwater. An aquifer is composed of permeable rock, loose material that holds water. Permeable means ‘‘having pores that permit a liquid or a gas to pass through.’’ You might think of a groundwater aquifer as a big sponge that soaks up the rain that seeps below the surface. As water from the surface slowly seeps down, or percolates, through the soil, it eventually hits a solid, or impermeable, layer of rock or soil. The aquifer forms as groundwater collects in the area above this impermeable layer. The water table is the level of the upper surface of the groundwater. If the water table in an area is high, the upper surface of the groundwater is only a short distance below the surface of the ground. Confined or unconfined? Groundwater occurs in two conditions: confined and unconfined. A confined aquifer has a layer of impermeable clay or rock above it, and the water is held under pressure greater than the atmospheric pressure. When a well is drilled into a confined aquifer, it penetrates that impermeable, confining layer, allowing the water to rise under pressure. This is called an artesian well. An unconfined aquifer has no impermeable layer above it and is usually shallower than a confined aquifer. 601
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How groundwater forms. GA LE GR OU P.
How big is an aquifer? The size of an aquifer depends on the amount of rainfall and the composition of the underground rock and soil. The world’s largest aquifer is in the United States. Called the Ogallala, it spreads under eight western states, from South Dakota to Texas. The Ogallala formed millions of years ago and is still supplying water to cities, businesses, and farms. Unfortunately, people are using water from the Ogallala faster than it can be naturally replenished, and the water table is falling. Our most precious resource? Water is a natural but limited resource. Most of the water on Earth is saltwater; 97% of the world’s water supply is located in the oceans. That means that only 3% is freshwater, and twothirds of that is frozen in the polar icecaps, icebergs, and glaciers. Only the remaining 1% is groundwater or surface water in lakes, ponds, and streams. 602
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Where groundwater occurs. GA LE G RO UP.
Confined and unconfined aquifers. GA LE G RO UP.
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Today, about three-quarters of the cities in the United States depend on groundwater for part or all of their drinking water. Wells also withdraw groundwater to irrigate crops, keep golf courses green, and meet other recreational needs. When water is pumped out of an aquifer into a well, the water level drops. If rainfall does not replace that water, the aquifer becomes overdrawn. When water is pumped out faster than it is replaced, the ground may sink, creating sinkholes. Can aquifers become polluted? Contamination is another problem. Leaking underground storage tanks may seep petroleum products into groundwater. Inadequate septic systems, sewage treatment plants, fertilizer runoff from farms, salt runoff from highways, and chemicals discharged from factories are other sources of pollution that can make groundwater unsuitable for humans to drink or use. Where does your drinking water come from? PH OT O RE SEA RC HE RS I NC.
Pollution can come from specific, identified locations, called point sources, or from scattered areas, called nonpoint sources. Most groundwater pollution comes from nonpoint sources. Once an aquifer is polluted, it may remain that way for years. Wetlands provide homes for waterfowl and many other animal species. Low-lying wetlands may receive water from an aquifer. If the water is contaminated, it will pollute the wetlands, affecting all the wildlife that depends on these water habitats. As the human population continues to grow, the demand for fresh, clean water supplies grows too. Careful management and use are essential to maintain the quality of our groundwater and surface water. The following projects will help you understand how aquifers can become contaminated and how dirty water can be cleaned.
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Sources of water pollution. GA LE G RO UP.
PROJECT 1 Aquifers: How do they become polluted?
Pollution that enters rivers and streams may eventually end up in the groundwater. P HOT O RES EA RC HER S I NC.
Purpose/Hypothesis Many communities and
homeowners must rely on wells that pump groundwater from aquifers. Unfortunately, groundwater can be contaminated by improper use or disposal of harmful chemicals, such as lawn fertilizers and household cleaners. These chemicals can percolate down through the soil and rock into an aquifer and eventually be drawn into the wells. Such contamination can pose a significant threat to human health. Experiment Central, 2nd edition
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Pollution in groundwater aquifers can harm the wildlife in wetlands. P ETE R A RNO LD IN C.
In this project, you will build a model that shows how water is stored in an aquifer, how groundwater can become contaminated, and how this contamination can end up in a well. You will see that what happens above ground can affect the aquifers below ground—and the drinking water. Level of Difficulty Moderate, because of the time involved. Materials Needed
• 6 x 8-inch (15 x 20-centimeter) clear plastic container at least 6 inches (15 centimeters) deep • 1 pound (0.45 kilogram) modeling clay • 2 pounds (0.9 kilograms) play sand • 2 pounds (0.9 kilograms) aquarium gravel or pebbles, rinsed • plastic drinking straw • plastic spray bottle with a clear spray stem • green felt, 3 x 5 inches (7.6 x 12.7 centimeters) • 25 cup (59 milliliters) powdered cocoa • red food coloring • clean water • tape Approximate Budget $10 to $20 for the container, sand, clay, spray bottle, and other materials. 606
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WORDS TO KNOW Aeration: Mixing a gas, like oxygen, with a liquid, like water.
Nonpoint source: An unidentified source of pollution, which may actually be a number of sources.
Aquifer: Underground layer of sand, gravel, or spongy rock that collects water.
Percolate: To pass through a permeable substance.
Artesian well: A well in which water is forced out under pressure. Coagulation: A process during which solid particles in a liquid begin to stick together. Confined aquifer: An aquifer with a layer of impermeable rock above it where the water is held under pressure. Disinfection: Using chemicals to kill harmful organisms. Filtration: Removing impurities from a liquid with a filter. Groundwater: Water that soaks into the ground and is stored in the small spaces between the rocks and soil.
Permeable: Having pores that permit a liquid or a gas to pass through. Point source: An identified source of pollution. Pore: An opening or space. Runoff: Water that does not soak into the ground or evaporate, but flows across the surface of the ground. Sedimentation: A process during which gravity pulls particles out of a liquid. Surface water: Water in lakes, rivers, ponds, and streams. Unconfined aquifer: An aquifer under a layer of permeable rock and soil. Variable: Something that can affect the results of an experiment.
Impermeable: Not allowing substances to pass through.
Water table: The level of the upper surface of groundwater.
Impurities: Chemicals or other pollutants in water.
Wetlands: Areas that are wet or covered with water for at least part of the year.
Timetable 1 to 2 hours. Step-by-Step Instructions
1. Tape the straw vertically inside the plastic container along one side, as illustrated. Do not let the bottom end of the straw touch the bottom of the container. This will be the ‘‘well.’’ 2. Pour a 1.5-inch (3.8-centimeter) layer of sand on the bottom of the container. Experiment Central, 2nd edition
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3. Pour water into the sand, wetting it completely without creating puddles. The How to Experiment Safely water will be absorbed into the sand, surrounding the particles, much as it is Do not drink the water you are using in this stored in an aquifer. project. 4. Flatten the clay into a thin layer and cover half the sand with it, pressing the clay into three sides of the container. The clay represents the confining or impermeable layer that keeps water from passing through. 5. Pour a small amount of water onto the clay. Most should remain on top of the clay, with some flowing into the uncovered sand. 6. Cover the whole surface of the sand and clay with the aquarium rocks. On one side, slope the rocks to form a hill and a valley. 7. Fill the container with water until it is nearly even with the top of your hill. See how the water is stored around the rocks in the aquifer. Also notice a surface supply of water (a small lake). This model represents groundwater and surface water, both of which can be used for drinking. 8. Put a few drops of red food coloring into the straw to represent pollution. People often use old wells to dispose of farm chemicals, trash, and used motor oils. The food coloring will color the sand. This demonstrates one way that pollution can spread into and through an aquifer. 9. Place the green felt on the hill. Use a little clay to fasten it to the sides of the container.
Steps 1 to 7: How to build an aquifer. GAL E GR OU P.
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10. Sprinkle some cocoa on the hill, representing the improper use of materials Troubleshooter’s Guide such as lawn chemicals or fertilizers. 11. Fill the spray bottle with water. Make it Here is a problem that might arise, a possible cause, and a way to remedy the problem. rain on the hill and over the aquifer. The cocoa will seep through the felt and wash Problem: The straw is clogged with sand. into the surface water. This is another way Possible cause: The straw is too close to the that pollution reaches aquifers. bottom of the container. Make sure you put the 12. Check the area around the straw. The straw in first and leave a small space between it pollution has probably spread farther. and the bottom of the container. Then pour in Remove the top of the spray bottle and the sand. If sand still clogs the straw, gently insert the stem into the straw. Depress the blow through the straw to unclog it. trigger to pull up water from the well. Note its appearance. This is the same water that people would drink. It also is contaminated. Summary of Results From your model, you can easily see how pollution
spread into the surface water and the aquifer, contaminating the water supply. Write a paragraph about what you observed.
PROJECT 2 Groundwater: How can it be cleaned? Purpose/Hypothesis Surface water—water in lakes, rivers, and wet-
lands—often contains impurities that make it look and smell bad. It may also contain bacteria and other organisms that can cause disease. Consequently, this water must be ‘‘cleaned’’ before it can be used. Water treatment plants typically clean water by taking it through these processes: • aeration, which allows foul-smelling gases to escape and adds oxygen from the air • coagulation, which causes solid particles to stick together • sedimentation, which allows gravity to pull the solid particles out of a liquid • filtration, which removes more impurities with a filter • disinfection, which uses chemicals to kill harmful organisms This project will demonstrate the procedures that municipal water plants use to purify water. It’s important to maintain a clean water supply, Experiment Central, 2nd edition
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How to Experiment Safely Do not drink the water you are using in this project. Be careful using the scissors when you cut the tops and bottoms off the soda bottles.
• • •
• • • Step 5: Constructing a water filter. GA LE GRO UP.
• •
as this water often affects the quality of the groundwater used by people who depend on wells. Level of Difficulty Moderate. Materials Needed
• 5 pints (5 liters) of ‘‘swamp water’’ (or add 2.5 cups of dirt or mud to 10.5 pints of water) 3 large clear plastic soft-drink bottles: 1 with a cap; 1 with its top removed; 1 with its bottom removed 5-quart (1.5-liter) or larger beaker (or another clear plastic softdrink bottle bottom) 2 tablespoons (20 grams) alum (potassium aluminum sulfate; available from biological supply houses or ask your teacher for a source.) 5 pounds (0.7 kilograms) fine sand 5 pounds (0.7 kilograms) coarse sand 1 pound (0.5 kilograms) small pebbles (natural color aquarium rocks, washed) large (500 milliliter or larger) beaker or jar coffee filter • rubber band • stirrer • scissors Approximate Budget $10 for sand, pebbles, and
alum. Timetable 1 to 2 hours. Step-by-Step Instructions
1. Pour about 1.5 quart (1.5 liter) of the swamp water into the uncut soft-drink bottle. On a data sheet, describe the look and smell of the water. 2. To aerate the water, place the cap on the bottle and shake it vigorously for 30 610
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seconds. The shaking allows gases trapped in the water to escape and adds oxygen to the water. Then pour the water back and forth between the bottle with the cap and the cut-off bottle ten times. Describe any changes in the water. Pour the aerated water into the large beaker or bottle bottom. 3. To coagulate solid impurities in the water so they can be removed, add the alum crystals to the water. Slowly stir for five minutes. 4. To allow sedimentation, let the water stand undisturbed for 20 minutes. Observe it at five-minute intervals and write your observations about the changes in the water’s appearance.
Troubleshooter’s Guide Here is a problem that might arise during this project, a possible cause, and a way to remedy the problem. Problem: During sedimentation, the sediments mixed into the water that was being filtered. Possible cause: You might have poured the swamp water too quickly. Pour the contaminated water back into the sedimentation bottle and let it sit undisturbed again. Or pour it through the coffee filter and see if the sediment makes the water flow more slowly. The filter may not take all the sediment out, or it may become clogged with sediment, one of the many problems that occur during the actual water treatment process.
5. Construct a filter from the bottle with its bottom removed. First, attach the coffee filter to the outside of the neck of the bottle with a rubber band. Turn the bottle top upside down and pour in a layer of pebbles. The filter will prevent the pebbles from falling out. Pour the coarse sand on top of the pebbles. Pour the fine sand on top of the coarse sand. Clean the filter by slowly and carefully pouring through 10.5 pints (5 liters), or more, of clean tap water. Try not to disturb the top layer of sand as you pour. 6. To filter the swamp water, wait until a large amount of sediment has settled on the bottom of the bottle of swamp water. Then carefully— without disturbing the sediment—pour the top two-thirds of the swamp water through the filter. Collect the filtered water in a beaker or other container. 7. Compare the smell and appearance of the treated and untreated water. Note: The final step in water treatment is disinfection by adding chemicals to kill any harmful organisms. Because disinfectants must be handled carefully, this process is not included here. Do remember that the water you have treated is NOT safe to drink. Experiment Central, 2nd edition
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Summary of Results Write a report of your observations of the smell and
look of the water before and after treatment. Include the amount of time that it took for the sediments to form.
Design Your Own Experiment How to Select a Topic Relating to this Concept You have seen how water enters an aquifer, how it flows from the aquifer into wetlands, and how it is drawn into wells. Perhaps you wonder how long it takes to replenish the supply of groundwater that is removed from the aquifer. You can use the aquifer you built in Project 1 to design your own experiment to determine how long it takes to replace the water that is removed. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on groundwater questions that interest you. As you consider possible experiments, be sure to discuss them with a knowledgeable adult before trying them. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the two groundwater
projects, the results were not measurable. However, in designing your own experiment, you should decide how to record the data, how to measure much water you draw out, and how to determine how quickly the same amount of water is replenished. Related Projects You can undertake a variety of projects related to
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your community and what steps are being taken to prevent contamination. You might research the kinds of contaminants found most often in your community’s water and the probable sources of these contaminants. You might explore how flooding and drought each affect groundwater and its purity. If possible, compare the smell and appearance of surface water and groundwater—or water that has been treated by the city water division and water from a well. The possibilities just depend on your interests.
For More Information Dobson, Clive, and Gregor Gilpin Beck. Watersheds: A Practical Handbook for Healthy Water. Buffalo, NY: Firefly Books, 1999. Provides an overview of the fundamentals of ecology and the web of life through the water cycle. Kellert, Stephen, general editor. MacMillan Encyclopedia of the Environment. New York: Simon and Schuster, 1997. Provides information on the water cycle and related topics. U.S. Environmental Protection Agency Web Site. http://www.epa.gov/ seahome/groundwater Provides information on groundwater aquifers and projects and activities that help explain the water cycle and aquifers. Van Cleave, Janice. Janice VanCleave’s Ecology for Every Kid. New York: John Wiley & Sons, 1996. Provides projects and information on the water cycle and water pollution. U.S. Geological Survey. ‘‘Ground water aquifiers.’’ Water Science for Schools. http://ga.water.usgs.gov/edu/earthgwaquifer.html (accessed January 18, 2008). Provides information on groundwater aquifers and projects and activities that help explain the water cycle and aquifers.
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our feet are bare, and the Sun has been beating down on the sidewalk outside your home all day. You form a hypothesis or educated guess that the sidewalk is cool enough to allow you to walk on it without burning your feet. You decide to test your hypothesis, knowing that if you are wrong, you could be in for some painful moments! But how does heat from the sidewalk burn your feet? Heat is a form of energy produced by the motion of molecules that make up a substance. The faster the molecules move, the more heat they produce and the higher the temperature of the sidewalk or other substance. Temperature is the measure of the average energy of the molecules in a substance. Heat can travel from one body to another in three ways: by conduction, by convection, and by radiation. What is conduction? Conduction is the flow of heat through a solid. When you walk on a hot sidewalk, the concrete warms—or burns—your feet through conduction. When a warmer substance with quickly moving molecules (the sidewalk) comes into contact with a cooler substance with slowly moving molecules (your bare feet), the faster molecules bump into the slower ones and make them move faster, too.
The quickly vibrating molecules in the hot sidewalk can transfer their heat energy to your cool feet. KE LL Y A. QUI N.
As the slower molecules pick up speed, the cooler substance gets warmer. The warmer substance loses some of its heat energy and gets cooler. Heat energy is the energy produced when two substances that have 615
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different temperatures are combined. The greater the difference in temperatures, the faster both temperatures change. Some substances conduct or transfer heat better than others. In Experiment 1, you will test five substances to see which is the best conductor of heat. What is convection? The second way heat travels is by convection. Convection is the rising of warm air from an object, such as the surface of Earth. Convection allows heat to travel through both gases and liquids, moving from warmer areas to cooler areas. Heating the molecules in a gas or liquid makes them move farther apart, so the substance becomes lighter or less dense. The lighter air or liquid rises; it also cools off as heat energy escapes into the surrounding cooler air or liquid. As the molecules cool, they move closer together, and the substance becomes heavier or more dense and falls again. A burner heats the air inside the balloon. As the hot air rises into the cooler atmosphere, the balloon rises, too. PH OT O RE SEA RC HE RS I NC.
In Experiment 2, you will use colored water to create convection currents that show how heat moves through a liquid. A convection current is a circular movement of a fluid in response to alternating heating and cooling. What is radiation? Radiation is energy transmitted in the form of electromagnetic waves that travel through the vacuum of space at the speed of light. Infrared radiation consists of wavelengths that are shorter than radio waves but longer than visible light. Infrared radiation takes the form of heat. These heat rays are much like light rays except that we cannot see them. That hot sidewalk was heated by infrared radiation from the Sun. The Sun’s heat did not travel to the sidewalk by conduction or convection because the Sun and sidewalk are separated by the vacuum of space. The transfer of heat by radiation does not require that the hotter and cooler substances touch each other.
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Not only the Sun, but all hot objects give out infrared radiation. This radiation gives up its heat energy when it is absorbed by an object, but this energy can also be reflected back toward its source. If that sidewalk had been painted white, it would have reflected the Sun’s radiation, just as white clothing does. Why? The color white does not absorb light; it reflects it. Dark colors absorb light—and heat. What is heat capacity? Heat capacity is the measure of how well a substance stores heat. Specific heat capacity is the energy required to raise the temperature of 1 kilogram of a substance by 1 degree Celsius.
As warm air rises over land, convection causes cool air from the ocean to rush in and take its place. The result is wind. PHO TO R ES EAR CH ER S IN C.
All substances have the capacity to store heat but at different levels. For example, water has a high specific heat capacity. Water can store a large amount of energy before its temperature will rise. This is important as the high heat capacity of water works to stabilize ocean temperatures and maintain comfortable conditions for marine life. In Experiment 3, you will test three solutions to determine which one has the highest heat capacity.
Sunlight passes through the glass and heats the plants. The warm plants give off infrared radiation, but these rays are longer and cannot pass back through the glass. Trapped inside the greenhouse, the rays heat the air. Pollution in the atmosphere can trap heat close to Earth in the same way. This is called the greenhouse effect. GA LE G RO UP.
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WORDS TO KNOW Conduction: The flow of heat through a solid. Control experiment: A setup that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Heat energy: The energy produced when two substances that have different temperatures are combined. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Convection: The circulatory motion that occurs in a gas or liquid at a nonuniform temperature owing to the variation of its density and the action of gravity.
Infrared radiation: Electromagnetic radiation of a wavelength shorter than radio waves but longer than visible light that takes the form of heat.
Convection current: A circular movement of a fluid in response to alternating heating and cooling.
Radiation: Energy transmitted in the form of electromagnetic waves or subatomic particles.
Electromagnetic waves: Radiation that has properties of both an electric and a magnetic wave and that travels through a vacuum with the speed of light. Greenhouse effect: The warming of Earth’s atmosphere due to water vapor, carbon dioxide, and other gases in the atmosphere that trap heat radiated from Earth’s surface.
Radio wave: Longest form of electromagnetic radiation, measuring up to 6 miles (9.6 kilometers) from peak to peak. Specific heat capacity: The energy required to raise the temperature of 1 kilogram of the substance by 1 degree Celsius. Temperature: The measure of the average energy of the molecules in a substance.
Heat: A form of energy produced by the motion of molecules that make up a substance.
Thermal conductivity: A number representing a material’s ability to conduct heat.
Heat capacity: The measure of how well a substance stores heat.
Variable: Something that can affect the results of an experiment.
EXPERIMENT 1 Conduction: Which solid materials are the best conductors of heat? Purpose/Hypothesis In this experiment, you will test short lengths of five
different materials to compare their ability to conduct heat. Each length will have a dab of wax on one end holding a bead in place. You will heat the opposite end of the lengths with hot water. The time it takes for each bit of wax to melt and release its bead will tell you which material 618
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conducted heat the fastest. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of heat. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
• the topic of the experiment
• the types of conducting materials
• the variable you will change
• the air temperature during the experiment
• the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Copper will conduct heat faster than the four other materials; wood will be the slowest conductor.’’ In this case, the variables you will change are the conducting materials, and the variable you will measure is the time it takes each bit of wax to melt and release its bead. You expect the wax on the copper length to melt first, and the wax on the wood to melt last or not at all. You will also set up a control experiment to make sure that it is conducted heat from the water and not some other variable that melts the wax. To set up the control experiment, you will create an additional set of the five conducting materials, attach wax and beads to the ends, but not heat them. If the wax melts off the experimental copper length first and the experimental wood length last and if no wax melts off the control materials, you will know your hypothesis is correct.
• the amount of each conducting material that comes into contact with the water • the temperature of the water • the type of wax used • the amount of wax placed on the end of each conducting material • the size and type of beads In other words, the variables in this experiment are everything that might affect the time it takes for each bit of wax to release its bead. If you change more than one variable, you will not be able to tell which variable had the most effect on the rate at which the wax melted.
How to Experiment Safely Be sure to ask an adult to help you with this experiment. Handle the matches, lighted candle, and hot water carefully to avoid burns. Keep your clothing away from the flame. Dripping wax can also cause burns.
Level of Difficulty Moderate/high, because of safety factors; ask an adult
to help you complete this experiment. Experiment Central, 2nd edition
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Materials Needed
LEFT: Step 1a: Have an adult helper drip one drop of wax on one end of the conducting material. GA LE G RO UP. RIGHT: Step 1c: Use a piece of clay to attach the conducting material to the side of one bowl. Space the conducting materials evenly around the bowl and anchor them firmly with the clay so they will remain upright. GA LE GRO UP.
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• 2 4-inch (10-centimeter) lengths of 18-gauge copper wire • 2 4-inch (10-centimeter) lengths of 18-gauge aluminum wire • 2 4-inch (10-centimeter) lengths of 18-gauge steel wire • glass stirrer or solid glass rod • 13-inch (0.3-centimeter) diameter wooden dowel • 10 identical beads (glass or plastic) • candle • matches • 2 glass bowls (with straight sides, if possible) • very hot tap water • clay • stop watch or clock with a second hand Approximate Budget $4 for the wire, glass stirrer, dowel, and beads. The other materials should be available in most households. Timetable 30 minutes to set up and conduct the experiment.
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Step-by-Step Instructions
1. Use a match to light the candle. Then follow this procedure for each of the five conducting materials: a. Have your adult helper drip one drop of wax on one end of the conducting material. b. Quickly push a bead into the drop of wax and make sure it is securely lodged there. c. Use a piece of clay to attach the conducting material to the side of one bowl, as illustrated. Space the conducting materials evenly around the bowl and anchor them firmly with the clay so they will remain upright. Make sure each material extends the same distance into the bowl. 2. Repeat Step 1 to set up the control experiment in the second glass bowl. 3. Ask the adult to carefully pour about 2 inches (5 centimeters) of very hot tap water into the center of the experimental bowl. As the water level rises, it should touch the lower end of each conducting material. Make sure each material extends the same distance into the water.
Steps 4 and 5: Recording chart for Experiment 1. GA LE GRO UP .
4. Immediately start the stop watch. Record on a chart (see illustration) how long it takes for each bead to fall from its conducting material. 5. Observe the beads in your control experiment and record on the chart their position at the end of the experiment. Summary of Results Use the data on your chart to create a line graph
of your findings. The graph will indicate the time that lapsed before each bead fell. Then study your chart and graph and decide whether your hypothesis was correct. Did the bead on the experimental copper wire fall first, and the one on the wooden dowel fall last or not at all? Did the beads in the control experiment remain in place? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The bead on a different conductor fell before the bead on the copper conductor. Possible causes: 1. The hot water might have splashed against the conductors as you poured it, giving some conductors a head start in transferring heat. Try again, pouring slowly. 2. Some conductors may have more wax than the others, affecting the melting speed. Try again, making sure to drip the same amount of wax on all conductors. Problem: A conductor other than the wooden dowel was the last one to release its bead. Possible cause: See possible cause 2 above. Problem: A bead on a control conductor fell off, or most of the beads fell off immediately.
For your reference, here is a list of the materials in the experiment, plus a few more, with a number that represents their ability to conduct heat, called thermal conductivity. The higher the number, the better the material conducts heat: silver (58.2); copper (55.2); aluminum (29.4); steel (7.2); glass (0.12); wood (0.012); air (0.004); styrofoam (0.0034). Change the Variables You can conduct similar
experiments by changing the variables. For example, you can use other conducting materials, such as plastic, iron, or a stick of insulating foam. You can also place a different small object in the wax, such as a metal nail. Another way to measure conductivity is to use small containers made of different materials, such as a glass jar, an insulated cup, a plastic cup, and a steel can. Put an ice cube in each small container and place them all in a larger container holding a few inches of very hot water. To determine the best conductor, record how long it takes for the ice to melt in each small container.
Possible causes: 1. The beads are too large or heavy. Try again with smaller, lighter beads.
EXPERIMENT 2
2. The beads were not firmly attached. Try again, pushing the beads firmly into the wax.
Convection: How does heat move through liquids?
3. The room air temperature is too warm, helping to melt the wax. Move to a cooler location or repeat your experiment on a cooler day.
Purpose/Hypothesis In this experiment, you
will put tinted hot water into cold water and tinted cold water into hot water. In both cases, you will observe and record the movement of the water to determine how heat moves through liquids. Your experiment should cause convection currents to develop as heat moves through the water. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of heat. This educated guess,
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or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is a possible hypothesis for this experiment: ‘‘Hot water placed in cold water will rise, and cold water placed in hot water will fall.’’ In this case, the variable you will change is the temperature of the tinted water placed in the container and the water already in the container, and the variable you will measure is the motion of the tinted water. You expect the cold blue water will sink and the hot red water will rise. As a control experiment, you will also pour tinted room-temperature water into more room-temperature water to determine if it, too, moves in a certain pattern. During your experiment, if the hot water rises, the cold water falls, and the room-temperature water mixes together in no specific pattern, you will know your hypothesis is correct.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the temperatures of the water in different containers • the amount of water being dropped into water of a different temperature • whether the containers of water are stirred or otherwise disturbed If you change more than one variable, you will not be able to tell which one had the most effect on the movement of the water.
Step 1: Add 2 drops of the red (hot) water to the container of cold water. GA LE GRO UP.
Level of Difficulty Easy/moderate. Materials Needed
• 1 small container of very hot water, tinted red with food coloring • 1 large container of very hot water • 1 small container of icy cold water, tinted blue • 1 large container of icy cold water • 1 small container of room-temperature water, tinted green Experiment Central, 2nd edition
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• 1 large container of room-temperature water • 2 eye droppers
How to Experiment Safely Handle the hot water carefully to avoid burns. You might ask an adult to help you put the hot water into the containers.
Approximate Budget Less than $5 for food coloring and eye droppers. Timetable 20 minutes.
Step-by-Step Instructions
1. Using one eye dropper, add 2 drops of the red (hot) water to the large container of cold water. Observe and record the movement of the red water on a chart similar to the one illustrated. DO NOT STIR OR BUMP THE LARGE CONTAINER. Rinse the eye dropper. 2. Using the other eye dropper, add 2 drops of the blue (cold) water to the large container of hot water. Record the movement of the blue water on the chart. AGAIN, DO NOT STIR OR BUMP THE LARGE CONTAINER. 3. As a control experiment, use the rinsed, room-temperature eye dropper to add 2 drops of green (room-temperature) water to
Steps 1 to 3: Recording chart for Experiment 2. GAL E GR OU P.
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the large container of room-temperature water. Record what happens. Summary of Results Study the drawings on your
chart and decide whether your hypothesis was correct. Did the hot water rise, the cold water fall, and the room-temperature water mix in no specific pattern? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables Change the way that
water of a different temperature is introduced: immerse a glass tube that is open on both ends in a container of very warm (not burning) water colored red. Put your finger over the top of the tube, which should stop the water from flowing out either end. Now immerse the tube in a container of icy cold water. Hold the tube in a vertical position and take your finger off the end of the tube. Observe whether the red water flows out of the top or the bottom of the tube. Try the same experiment with cold, blue water in the tube and very warm water in the large container. From which end of the tube does the blue water flow?
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The tinted hot water (or the tinted cold water) simply spread throughout the water in the experimental large container, in no particular pattern. Possible cause: The difference between the water temperatures was too small. Make sure the cold water is icy and the hot water is very hot. Heat water in a microwave for a minute, if you wish, but ask an adult to help you handle it, using pot holders. Use containers that are microwave-safe. Problem: You could not clearly see the movement of the hot (or cold) water in the large container. Possible cause: The water was not tinted dark enough. Add more food coloring and try again.
EXPERIMENT 3 Heat Capacity: Which liquids have the highest heat capacity? Purpose/Hypothesis In this experiment, you will test the heat capacity of
three different liquids. You will use water, cream, and olive oil. Water has a relatively high heat capacity. Fats, on the other hand, cannot store a large amount of energy before a temperature rise. Each liquid will be heated in a hot water bath of 200˚F (93˚C) and temperature readings will be taken every minute for 10 minutes. You will then cool the liquid in a cold-water bath taking temperature readings every minute for 10 minutes. The time it takes to heat the liquids and the Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the types of liquids tested • the volume of the liquids tested • the starting temperature of the liquids • the temperature of the water baths • the length of time the liquids are heated
time it takes to cool the liquids will tell you which liquid has the highest heat capacity. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of heat. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is a possible hypothesis for this experiment: ‘‘The temperature of the cream will increase at a slower rate than the other two liquids.’’ The variables you will change are the three liquids being tested, and the variable you will measure is the change in temperature of the liquids over a period of 20 minutes. The control test you will measure against will be the temperature of the three liquids at room temperature.
In other words, the variables in this experiment are everything that might affect the temperature of the liquids during the testing period. If you change more than one variable, you will not be able to tell which one had the most effect on the temperature of the liquid tested.
Step 4: To the hot-water bath, add the glass filled with 1-cup of room temperature cream.
Level of Difficulty Moderate/Difficult, because of safety factors. Materials Needed
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water
O ive Oil
• 1 medium sized pot for hot-water bath • 1 medium sized pot for cold-water bath • 3 glass, heat-resistant measuring cups (or glass mason jars) • 2 thermometers with a clip that can attach to the side of the water bath • 1 cup room-temperature water • 1 cup room-temperature cream • 1 cup of room-temperature olive oil • stop watch or clock with a second hand Approximate Budget About $15.
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Timetable 30 minutes to set up and 60 minutes
to conduct the experiment Step-by-Step Instructions
How to Experiment Safely Ask an adult to help you with this experiment. Have an adult operate the stove. Handle the hot water bath and hot liquids carefully to avoid burns.
1. Measure out 1 cup of water, cream, and olive oil in separate containers. Set aside until they are at room temperature (about 72˚F, 22˚C). 2. Have an adult helper bring a medium pot filled half way with water to a temperature of 200˚Fahrenheit (93˚Celsius). Clip the thermometer to the side of the water bath, making sure it does not touch the sides. 3. Prepare a cold water bath. Fill a medium-sized pot a quarter full of cold water and add several cups of ice. 4. To the hot-water bath, add the glass filled with 1-cup of room temperature cream. 5. Place another thermometer in the cream, clipping it against the glass. Measure the temperature changes at one minute intervals for 10 minutes and record on chart (see illustration). 6. After 10 minutes remove the glass cup of cream with the thermometer from the hot-water bath and place in the cold-water bath. Record the temperature changes at one-minute intervals for 10 minutes. 7. Repeat this procedure, from the hot to the cold water bath, for the water and the min. cream olive oil. HOT COLD Summary of Results Graph the results of your
temperature reading for all three liquids. The graph will indicate the rate and rise of temperature of each liquid. How does the temperature rise compare to the room temperature? Decide whether your hypothesis was correct. Did the temperature of the cream rise at a slower rate than the water and olive oil? If not, which liquid did rise at the slowest rate? Write a paragraph summarizing your findings and explaining why or why not it supports your hypothesis. Experiment Central, 2nd edition
Step 5: Using this chart, record the temperature changes at one minute intervals for 10 minutes. I LL US TRA TI ON B Y TEM AH N EL SON .
water
olive oil
HOT COLD HOT COLD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
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Change the Variables You can conduct other heat capacity experiments by finding the heat capacity of different materials. You can use other household liquids or solid materials that change into liquids, such as paraffin wax or calcium chloride (ice melt). If you choose to use a solid material you must first melt or dilute the material so that you can measure the temperature of the material.
Design Your Own Experiment Step 6: After 10 minutes remove the glass cup of cream with the thermometer from the hot-water bath and place in the cold-water bath. I LL UST RA TI ON BY T EM AH NE LS ON.
How to Select a Topic Relating to this Concept You can explore many
other aspects of heat movement. For example, you might investigate the relationship between convection and wind, or you could find out how surface area affects the rate of heat conduction. For example, does water boil more quickly if it is in a wide pan or a narrow pan? Does ice melt more quickly if it is crushed into small pieces? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on heat questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Experimenting with heat is potentially dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. 628
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Recording Data and Summarizing the Results In
the heat movement experiments, your raw data might include charts, graphs, drawings, and photographs of the changes you observed. If you display your experiment, make clear your beginning question, the variable you changed, the variable you measured, the results, and your conclusions. Explain what materials you used, how long each step took, and other basic information. Related Projects You can undertake a variety of
projects related to the movement of heat. For example, you might explore which kinds of home insulation, insulated cups, or insulated gloves are most efficient at stopping the movement of heat through conduction. When a fireplace burns, how much of the heat escapes up the chimney through convection? Which colors are most efficient at reflecting radiated heat?
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The hot-water bath keeps changing temperature. Possible cause: The temperature of the stove is too high. Maintain a constant temperature by using a low to medium temperature setting and have cold water available to add to bath to maintain the 200 degrees. Problem: All three liquids showed the same results. Possible cause: The liquids might not have been at room temperature at the beginning of the experiment. Repeat the experiment, allowing the liquids to sit out for at least an hour longer and take the temperature of each of the liquids.
For More Information Friedhoffer, Robert. Molecules and Heat. New York: Franklin Watts, 1992. Explores scientific concepts involving heat and heat movement by turning them into ‘‘magic tricks.’’ Gardner, Robert, and Eric Kemer. Science Projects about Temperature and Heat. Hillside, NJ: Enslow Publishers, 1994. Provides detailed explanations of projects and the concepts they demonstrate. Gutnik, Martin. Experiments That Explore the Greenhouse Effect. Brookfield, CT: Millbrook Press, 1991. Outlines experiments that relate to the movement of heat as it causes the greenhouse effect. Wood, Robert. Heat FUNdamentals. New York: Learning Triangle Press, 1997. Offers more than 25 heat related activities and brief explanations.
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t’s easy to think humans are the major animals on our planet, but in reality, we are the minority. There are an estimated 10 quintillion insects alive at any time—that’s 10,000,000,000,000,000,000! They live in all different types of places: on water, on the tops of mountains, under rocks, and inside trees. Researchers have identified more than one million different species of insects, which make up about 80 percent of all known species in the world. And experts theorize there are millions more insect species not yet discovered. The study of insects is called entomology. Understanding how insects live and behave is important because they play such a large role in life on Earth. They pollinate (transfer pollen), break down animal waste, and are a major food source for animals. They also provide humans with products, such as honey and wax. The survival of animals—including people—depend upon these small creatures. Taking apart an insect There is a wide variety of insect shapes and sizes, yet there are certain characteristics all insects share. 1. Six legs: That leaves out the eight-legged spiders and the numerous-legged centipedes and millipedes. 2. An exoskeleton: A strong, hard skin on the outside of their body. The exoskeleton holds the muscles and protects the insect from outside elements. It also prevents the insect from growing once the exoskeleton has fully formed. 3. As insects grow, many need to shed their hard exoskeleton several times. This is called molting. Beneath the exoskeleton a new layer of skin forms. The insect becomes larger, which causes the exoskeleton to split and fall, making way for the new and larger exoskeleton. 631
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The three basic body segments all insects have are the head, thorax, and abdomen. I LLU STR AT IO N BY T EM AH NE LS ON.
Depending upon the insect, they can use antennae to sense smells, movements, and vibration. I LL UST RA TI ON BY T EM AH NE LS ON.
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4. Segmented bodies: An insect’s body is segmented (separated) into three distinct parts, which are all supported by the Head exoskeleton. The insect segments The three basic body Thorax segments all insects have are the head, thorax, and abdomen. The head is where the insects have Abdomen their antennae, mouthparts, and eyes. Antennae can be long, as in a grasshopper, or short, as in a fly. Depending upon the insect, they can use an antennae to sense smells, movements, and vibration. The mouth of an insect depends upon the species. There are a lot of ways insects can eat. Some of the ways they take in food includes sucking, chewing, piercing, lapping, or a combination. The type of eye an insect has depends upon the insect, but most insects have two compound eyes. Compound eyes are made up of thousands of different individual lens-like units in each eye. Unlike our eyes, they do not rotate or move. Each unit takes in a tiny visual and the brain puts them all together into the image. The middle segment of the insect body is the thorax. Each part of the thorax holds a pair of legs. If an insect has wings, they are attached to the thorax. The bottom insect segment is the abdomen. The abdomen is where digestion and reproduction take place. An insect also breathes through its abdomen through openings called spiracles. Insects on the go There are a lot of ways an insect can get around. Insects can hop, crawl, jump, fly or some combination. About 300 milantenna lion years ago, insects became one of the first creatures to fly. Flying allows insects to travel greater distances for food and escape predators quickly. Many insects, such as the grasshopper and bee, have two pairs of wings but only the back pair is used to fly. The front wings are smaller and protect the back pair. Insects such as the butterfly and beetle have linked their sets Experiment Central, 2nd edition
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Butterflies have linked their sets of wings together so that the pairs flap together. R OBE RT J. HUF FM AN. FI EL D MA RK PU BLI CA TI ONS .
of wings together so that the pairs flap together. The fly has a single pair of wings. For insects that don’t fly, and some that do, legs are how they move around. An insect leg is split into distinct sections. In some insects, such as ants, the legs are all about the same size and used mainly for walking. Insects with longer and more powerful back legs use their legs to jump. Grasshoppers and fleas are two types of insects that have powerful jumps. Some insect legs are designed to dig, cling, or capture food. The praying mantis has a large pair of spiked front legs that it uses to catch prey. Legs can also provide sensory experiences. A fly’s feet has tiny taste sensors that let the fly know if it should eat the substance it lands on. The busy cycle of life Insects live relatively short lives of less than a year in general. For example, flies can live about 15 to 30 days and butterflies for about a month or two. But there are a few insects that can live for years. The queen ants of some species can live for over 20 years! No matter the type of insect or length of time it lives, most insects pass through four life stages: 1) egg; 2) larva or nymph; 3) pupa; and 4) adult. Insects are born from eggs. The second stage, which can also be called other names, is the young immature insect. A caterpillar is in the larva stage. The caterpillar moves into the pupa stage when it goes through metamorphosis. In this type of metamorphosis (a complete metamorphosis), the insect goes through a distinct change Experiment Central, 2nd edition
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WORDS TO KNOW Abdomen: The third segment of an insect body. Bioluminescence: Light produced by living organisms. Ecosystem: An ecological community, including plants, animals and microorganisms, considered together with their environment. Entomology: The study of insects. Exoskeleton: A hard outer covering on animals, which provide protection and structure. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Insect: A six-legged invertebrate whose body has three segments.
Metamorphosis: The biological process in which an insect transforms from a larva into an adult, changing its appearance. Molting: A process by which an animal sheds its skin or shell. Pollinate: The transfer of pollen from the male reproductive organs to the female reproductive organs of plants. Pupa: The insect stage of development between the larva and adult in insects that go through complete metamorphosis. Spiracles: The openings on an insects side where air enters.
Invertebrate: An animal that lacks a backbone or internal skeleton.
Thorax: The middle segment of an insect body; the legs and wings are connected to the thorax.
Larvae: The immature stage between the egg and the pupa; this can also be called nymph.
Variable: Something that can affect the results of an experiment.
in appearance and structure. As a pupa, also called chrysalis, the caterpillar does not move or eat. When it emerges into its final adult stage, the caterpillar appears as a butterfly. Insects that look the same as adults and immature insects do not go through a complete metamorphosis. For these insects there is no pupa stage. Most insects live isolated lives but several groups are known as social insects. Ants, bees, and termites are among the social insects. Most social insects live in large colonies (groups) with distinct division of labors. In ant colonies, the ant nest is started by a queen who lays eggs. Some ants are assigned to defend the colony and others to build the nest. The insects in the colonies communicate with one another through chemical signals. Insects are a broad and fascinating group of animals. Each group of insects has its own unique characteristics, and you can learn a lot about insects by simply observing them. 634
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EXPERIMENT 1 Ant Food: What type of foods is one type of ant attracted to? Purpose/Hypothesis In this experiment, you will
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
investigate the food that most attracts one kind of • the type of ant ant. There are many types of ants and different • the item on the sponge ants prefer different foods. Ant diets include sug• the size of the sponge ary substances, seeds, and proteins (in the form of • where the sponge is set in relation to the other bugs and dead animals). You can find out ants the kind of food ants prefer by soaking a sponge • the environmental conditions in four to five liquid-form foods. By placing the In other words, the variables in this experiment food-soaked sponges in one outside area around are everything that might affect the amount of the same type of ant you can observe which food ants attracted to the food on the sponge. If you attracts the most ants. You can also observe how change more than one variable, you will not be ants communicate their food find to their fellow able to tell which variable had the most effect on attracting the ants to the sponge. ants. The foods you will use include: honey; beef broth; milk; and juice. Water will be the control. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of insects and ants. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The ants will be attracted primarily to the honey-soaked sponge and then the juice sponge.’’ In this case, the variable you will change will be the food substance on the sponge, and the variables you will measure will be the relative amount of ants on the sponge over a length of time. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental Experiment Central, 2nd edition
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How to Experiment Safely Do not touch the ants or disturb their living environment; simply observe them. Wash your hands after completing the experiment.
• • • • • • • • • •
tests, and that variable is the liquid food. For the control, you will soak the sponge in water. Level of Difficulty Moderate. Materials Needed
• sponge • scissors toothpicks with flags (for marking; you can make your own by attaching strips of paper to toothpicks) 1 beef bouillon cube or canned beef stock milk, about 3 tablespoons juice, such as orange juice, about 3 tablespoons honey, about 3 tablespoons 5 small cups or containers spoon tongs plastic forks large plate
beef stock
orange juice
milk
honey
water
Step 6: Place one sponge in each container. Allow the sponge to sit for at least 2 minutes and then flip over the sponge. I LLU ST RAT IO N BY TEM AH NEL SO N.
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• marking pen • outside clear area, with primarily one type of ant • a nice day Approximate Budget $10. Timetable 1 hour. Step-by-Step Instructions
1. Use the scissors to cut a sponge into 4 to 5 squares (depending upon if you are testing 4 or 5 food items), about 2 inches square. 2. On each of the flagged toothpicks, mark each of the foods you are using. Prepare each of the food items: 1. In container 1, pour about 3 tablespoons of milk. 2. In container 2, pour about 3 tablespoons of honey and stir in several drops of water to thin down the honey. 3. In container 3, add about 3 tablespoons of warm water to the bouillon. Use a spoon to crush and dissolve the cube. If you have beef stock pour about 3 tablespoons of the stock in the container. 4. In container 4, pour about 3 tablespoons of orange juice. 5. In container 5, pour about 3 tablespoons of water. 6. Place one sponge in each container. Allow the sponge to sit for at least two minutes and then flip over the sponge. Wait another two minutes. 7. Use plastic forks or tongs to place the sponge squares on the plate. As you set the sponge on the plate, place its matching marked toothpick in the sponge. If you use a pair of tongs, clean or wipe the tongs after you lift each sponge. Hold each sponge piece for a few seconds over the container until it no longer drips. Set it down, apart from the others, on the large plate. Make sure none of the food sources spread on any of the other sponges. 8. Carry the plate outside to the area where there is mainly one type of ant crawling about. 9. Set the sponge squares evenly spaced apart in a circle, with each sponge at least one foot apart from the next. Experiment Central, 2nd edition
Step 9: Set the sponge squares evenly spaced apart in a circle, with each sponge at least one foot apart from the next. ILL US TRA TI ON B Y TE MA H NEL SO N.
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Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can definitely be a learning experience. Here are some problems that may come up during this experiment, some possible causes, and some ways to remedy the problems. Problem: One of the foods attracted a lot of different types of ants or insects. Possible cause: You may have placed the foods in an area where there were too many insects, and one of the insects may have scared away the ants you were looking to track. Find another area, such as a porch or sidewalk, which is clear of other visible insects. Repeat the experiment. Problem: The honey and another, unexpected, food source both attracted about the same amount of ants. Possible cause: Some of the honey may have soaked into the other sponge when the sponges were on the plates and you were carrying it outside. Try the experiment again, this time place the sponges on separate plates, or using a large plate and being very careful none of the food dribbles onto its neighbor sponge.
10. Wait 20 minutes and note the relative amount of ants on each of the sponges. Does one sponge have a lot more ants than any of the others? 11. Over the next 15 to 30 minutes, observe the ants reaction to each sponge. Also, observe how the ants travel to the sponge they are attracted to. Look for lines of ants or possible ways ants may communicate to one another about the food. 12. When you have finished the experiment, use a plastic fork to throw away the sponges. (You may need to shake the sponges free of ants!) Summary of Results Look over your findings.
Was your hypothesis correct? Compare the foods they were not as attracted to? How did the control (water) sponge attract ants as compared to the sponge with milk, or orange juice? Could you see how ants communicated with one another about the food? Write up a summary of your findings. Change the Variables Here are some ways you
can vary this experiment:
• Test another type of ant: look around for another size or color of ant. • Focus on one food, such as the honey, and alter the concentration to determine how concentrated the food needs to be for the ant to sense it. • Change the foods, using all sweet items or protein sources, and see which attracts the most ants.
EXPERIMENT 2 Lightning Bugs: How does the environment affect a firefly’s flash? Purpose/Hypothesis There are hundreds of different types of fireflies. These insects, also called lightning bugs, are recognizable by their flashes 638
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of light. Fireflies are bioluminescent, meaning they produce light by a chemical reaction within What Are the Variables? the organism. Fireflies produce a chemical in their abdomen called luciferin. This substance Variables are anything that could affect the reacts with oxygen and another substance to give results of an experiment. Here are the main variables in this experiment: off light. How much oxygen the firefly breathes in determines the strength and pattern of the • the environment the firefly is in light flashes. • the type of firefly How often the firefly flashes depends upon • the time of day several factors, including the type of firefly, its • the vibration of the jar sex, and age. The flash of light can also depend • the amount of light upon the temperature, which can affect the amount of oxygen the firefly breathes. In this experiment, you can observe firefly flashes and measure if the rate of flashes changes depending upon the warmth or coolness of the firefly’s environment. You will need to catch a firefly and place it in a large jar. You can time the flashes and note the intensity of the light. You can then place the jar in cold and warm water in order to change the air temperature of the firefly, and again measure the flashes. To begin the experiment, use what you know about insects and fireflies to make an educated guess about how temperature will affect the bioluminescence. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The rate of light flashes from the firefly will increase and they will be brighter when it is warmer compared to when it is colder.’’ Experiment Central, 2nd edition
How to Experiment Safely Have an adult help you use the hammer (or any heavy block) and nail to poke holes in the lid of the jar. Treat the firefly gently, making sure not to leave it in the jar for more than a few hours. When you have finished observing the insect, release it back outside.
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In this case, the variable you will change is the temperature of the firefly’s environment, and the variable you will measure is the number and intensity of the its flashes. Level of Difficulty Moderate, due to working
with live insects. Materials Needed
Step 2: Try to catch one of the fireflies in the jar.
• large glass jar with a lid, such as a mason or large mayonnaise jar • hammer or mallet • nail • warm evening • plastic container • ice • clock with a minute hand • helper (optional) Approximate Budget $0. (Materials should be available in the average
household.) Step 4: Pour ice and cold water in the plastic container. Set the jar in the container so that it is partly submerged. I LL UST RA TI ON BY T EM AH NE LS ON.
Timetable Approximately 30 minutes experimental time; the time to collect fireflies will vary widely and you may want to spread out the three trials over three evenings. Step-by-Step Instructions
1. Have an adult help you use a hammer (or any heavy block) and a nail to poke small holes in the lid of the jar. This will allow air to enter the jar. 2. After the sun goes down, go outside to a dark area. Fireflies live in cities and open grassy areas but it is easier to spot their flashes away from streetlights or bright lights. It also helps to have someone with you when looking for and collecting the firefly. Fireflies are relatively slow fliers and they do not bite. When you see one, 640
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3.
4.
5.
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clap your hands over the insect. If you do not have a helper holding the jar, make sure the lid is open before you catch one in your hands. When a firefly is in the closed jar, bring it inside and darken the room so you can clearly see its flashes. Count the frequency of flashes over a period of time, such as two minutes. The exact time does not matter as long as it is the same in all the trials. Pour ice and cold water in the plastic container. Set the jar in the container so that it is partly submerged. Wait about 1 minute and time the flashes again. Note the intensity of the flashes. Replace the cold water in the container with warm water. Wait about a minute. Again, time the number of flashes over the two-minute time period (or what you used in the first trial) and note their intensity. Pour out the warm water. When you have finished observing the firefly, release it back outside. If desired, repeat the entire process for two more fireflies, one at a time. This will strengthen your findings and help you make sure the results are repeatable. Collect the fireflies in the same area so that you will have more chance of collecting the same type of firefly.
Troubleshooter’s Guide Experiments do not always work out as planned, especially when working with live organisms. Here are some problems that may arise during this experiment and ways to remedy the problems. • Problem: I can’t find any fireflies. • Possible causes: Adult fireflies only live about several weeks. When they mature into adults depends upon the area, but it is somewhere in the late spring or summer months. If you do not see any, ask an adult to help you research when they are expected in your area. And when looking for the insects, make sure you are in a dark area and be patient. • Problem: One of the fireflies gave far different results than the other two firefly trials. • Possible causes: There are hundreds of types of fireflies and each produces flashes in a certain pattern. It is possible you caught two different types of fireflies. You might also have collected a firefly that was too old, young, or sick. Repeat the experiment with another firefly. Make sure it is producing a steady rate of light flashes before placing the jar in a cool or warm environment.
Summary of Results If you conducted the experiment on more than one
firefly, average the frequency of the trials for the room temperature, cool, and warm environment. Was your hypothesis correct? How quickly did the flashes speed up or slow down when the firefly’s environment changed? Did the intensity of the flashes change also? Was there a certain pattern to the flashes? Write up a summary of your findings. You may Experiment Central, 2nd edition
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want to include pictures of the firefly, and some possible reasons why the firefly produces light. Change the Variables One way you can vary this experiment is by looking
at other factors that may affect the light a firefly produces. Would vibration or color affect the flash or intensity of a firefly? If you can collect different types of fireflies, you can see the unique lighting patterns in each. In general, male and female fireflies produce light at different frequencies. The male gives off a repeated signal and the female responds. You may want to observe firefly lighting in the wild before deciding on experiments.
Design Your Own Experiment How to Select a Topic Relating to this Concept Insects are all around you,
living on the sidewalks, in the grass, and often hiding inside homes. As you think about experiments and projects relating to insects, consider what insects you have questions about. Are there insects unique to your area? Think about insect interactions that you have observed. You can also consider when an insect turns into a pest, and how people use insect characteristics to develop pest controls. Check the Further Readings section and talk with your science teacher to start gathering information on insects and questions that interest you. You may want to speak with people who are knowledgeable about working or dealing with insects. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Remember that some insects can be harmful to people and you should research the insect before working with it. Work with someone familiar with the insect and plan how you will care for or handle insects that you collect or purchase. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. 642
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• Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question.
egg
adult larva
• Decide how to change the variable you selected. • Decide how to measure your results. pupa
Recording Data and Summarizing the Results
The most important part of the experiment is the information gathered from it. Think of how you can share your results with others. Charts, graphs, and diagrams of the progress and results of the experiments are helpful in informing others about an experiment. You may also want to take photographs or draw the insect.
Insects have four life stages. ILL US TRA TI ON B Y TE MA H NEL SO N.
Related Experiments You can do many experiments and projects with
insects through careful observation. You may want to collect your own insects and observe them over a period of time. One project that can help you learn about a variety of insects is by identifying the three body segments of different insects. How do the wings, lets, and antennae compare among different insects? You can also observe the four life cycles of insects. How does the timing of the life cycles compare among different types of insects? Are there certain environmental conditions that speed or slow down the change into one of the life cycles? You can experiment with how environmental conditions may speed or slow one of the life stages. Insect senses is another possible area of study. You can explore how different types of insects sense food, and threats. You can also experiment with groups of social insects, such as ants. Possible experiments include determining how they communicate with one another and how they build homes.
For More Information Bugbios. http://www.insects.org/entophiles/index.html (accessed on June 4, 2008). Comprehensive database of photographs and facts about a wide range of insects. Experiment Central, 2nd edition
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Butterflies and Moths of North America. http://www.butterfliesandmoths.org (accessed on June 6, 2008). Searchable database with photographs of butterflies and moths. ‘‘Camouflage.’’ BBC: Walking with Beasts. http://www.abc.net.au/beasts/ fossilfun/camouflage/camouflage.swf (accessed on May 11, 2008). An interactive game on animal camouflage. Doris, Ellen. Entomology. New York: Thames and Hudson, 1993. Describes different microorganisms, their functions, and purpose. Lang, S. Invisible Bugs and Other Creepy Creatures That Live With You. New York: Sterling Publishers, 1992. Describes different microorganisms, their functions, and purpose. Mound, Laurence. Insect. London, New York: DK Publishing, 2007. Parker, Steve. Ant lions, Wasps, and Other Insects. Minneapolis: Compass Point Books,, 2006. ‘‘Virtual Insects and a Spider.’’ 3D Insects. http://www.ento.vt.edu/sharov/3d/ virtual.html (accessed on June 4, 2008). Movies and information about different insects.
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A
ll animals go through changes during their lives. Some simply grow larger, while others completely change their forms. This kind of change is called metamorphosis, which means ‘‘change in form.’’
A caterpillar represents the larval stage in a complete metamorphosis. CO RB IS.
Some insects have no metamorphosis, simply growing larger and becoming able to reproduce. Others undergo an incomplete metamorphosis, in which the immature insects are known as nymphs. Nymphs, which often live in water, resemble the adult forms, but their wings are not fully developed and they have no reproductive organs. Nymphs gradually become adults by molting, or shedding their outermost layer. Other insects go through a complete metamorphosis, in which the immature stage is called a larva. Caterpillars, for example, are the larvae of butterflies. The larva becomes a pupa, which is mostly a resting stage. Finally, the pupa emerges as a full-fledged adult, such as a butterfly. Organisms in different stages of the life cycle often live in different habitats and eat different foods. What other organisms go through metamorphosis? Amphibians also go through a dramatic metamorphosis. You are probably familiar with the life cycle of the frog, which begins with a tadpole. You may have seen tadpoles in a pond or stream. An aquatic animal with a tail, the tadpole not only grows as it gets older, it also changes its form, growing legs, living at least partly on land, and losing its tail. 645
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WORDS TO KNOW Amphibians: Animals that live on land and breathe air but return to the water to reproduce. Complete metamorphosis: Metamorphosis in which a larva becomes a pupa before changing into an adult form. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Results from the control experiment are compared to results from the actual experiment. Ecologists: Scientists who study the interrelationship of organisms and their environments. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Incomplete metamorphosis: Metamorphosis in which a nymph form gradually becomes an adult through molting.
A ‘‘froglet’’ is one stage in the frog’s life cycle. PH OT O RE SEA RC HE RS I NC.
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Larva: Immature form (wormlike in insects; fishlike in amphibians) of an organism capable of surviving on its own. A larva does not resemble the parent and must go through metamorphosis, or change, to reach its adult stage. Metamorphosis: Transformation of an immature animal into an adult. Molting: Shedding of the outer layer of an animal, as occurs during growth of insect larvae. Nymph: An immature form in the life cycle of insects that go through an incomplete metamorphosis. Pupa: A stage in the metamorphosis of an insect during which its tissues are completely reorganized to take on their adult shape. Variable: Something that can affect the results of an experiment.
While tadpoles eat tiny aquatic vegetation, adult frogs eat just about any small animal that flies, jumps, or crawls past and can fit in their mouths. Why should we learn about metamorphosis? Many people are interested in the life cycles of animals. Farmers must know about insect life cycles in order to control harmful insects and encourage the helpful ones that help pollinate their plants, such as bees and butterflies. Ecologists are also interested in metamorphosis. Many amphibians are threatened with extinction due to the destruction of their habitat. Ecologists study metamorphosis to learn the needs of different stages of amphibian life cycles and better understand how to save them. Experiment Central, 2nd edition
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What questions do you have about life cycles? You will have an opportunity to explore life cycles in the following experiments. You will learn more about this natural phenomenon that can be so fascinating and dramatic to observe.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
EXPERIMENT 1
• the temperature of the water
Tadpoles: Does temperature affect the rate at which tadpoles change into frogs?
• the number of tadpoles in each bucket
Purpose/Hypothesis WARNING: Do not per-
• the age, size, and health of the tadpoles in each bucket • the tadpoles’ diet In other words, the variables in this experiment are everything that might affect the time it takes for the tadpoles to become frogs. If you change more than one variable, you will not be able to tell which variable had the most effect on the time for the tadpoles to metamorphose.
form this experiment unless you have a safe, approved spot to release live frogs once experiment is completed. You should be aware that it is illegal to release or dispose of live frogs in certain areas. If you are not sure about performing this experiment, ask your science teacher. In this experiment, you will discover how the water temperature in which tadpoles live affects how fast they grow and become adult frogs. Tadpoles are the larval form of frogs. They hatch from eggs laid by a female frog. Tadpoles live in the water and breathe through gills, but when they become frogs or toads, they breathe air and live mostly on land. Tadpoles eat only plants, while adult frogs eat insects and even small snakes. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of tadpoles. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The higher the water temperature, the faster tadpoles will become frogs.’’ In this case, the variable you will change will be the temperature of the water, and the variable you will measure will be the number of days it Experiment Central, 2nd edition
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How to Experiment Safely Be careful when handling live animals, and treat them with respect and care. Avoid touching the tadpoles because amphibians have extremely sensitive skin. Wash your hands before and after you touch the water. If you decide to find your own tadpoles in a pond or stream, ask an adult to help you. You should be aware that it is illegal to release or dispose of live frogs in certain areas. If you are not sure about performing this experiment, ask your science teacher.
takes for the tadpoles to become frogs. You expect the tadpoles in the warmest water to develop into frogs first. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental buckets, and that is the temperature of the water. For the control, you will use water at the air temperature outside (or at room temperature if your region is experiencing winter now). For the experimental buckets, you will have warmer and cooler water. You will measure the number of days it takes the tadpoles to become adult frogs. You will know they are fully adult when they completely lose their tails and have fully developed legs. If warmer water results in a faster metamorphosis, your hypothesis is correct.
Level of Difficulty Difficult, because of care required with live animals. Materials Needed
• 5 buckets or large glass jars with lids • water to fill the containers (Allow it to sit at least overnight to let any chlorine in it evaporate.) • a steady supply of boiled lettuce • 5 thermometers
Steps 1 and 2: Fill the five containers each with the same amount of water. Place five tadpoles in each container. GAL E GR OU P.
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Step 4: Recording chart for Experiment 1. GA LE G ROU P.
• large aquarium fish net • about 25 tadpoles (You can order tadpoles from a biological supply company, such as those listed in the Further Readings section, or you might find them in a stream or pond.) Approximate Budget $30 for thermometers and tadpoles. Timetable About 4 weeks. Step-by-Step Instructions
1. Fill each of the five containers with the same amount of water. Add a thermometer to each container. 2. Use the net to place five tadpoles in each container. 3. Place each container so that the water temperatures will be different. Leave one at room temperature. Place one outside as your Experiment Central, 2nd edition
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Step 7: Measure the size of the tadpoles in each container every week. GA LE GRO UP.
control. Place another under a lamp that will be left on constantly. Place one container in a cool, dark place, such as under a counter. Put the last one in the refrigerator. (Tadpoles in the wild often live in quite cold water.) 4. After an hour, record the water temperature in each container on a data sheet similar to the one illustrated. 5. Feed all your tadpoles about a silverdollar-sized piece of boiled lettuce every day or every other day. Do not overfeed because the lettuce will rot. Record how much food you put in the containers each day. 6. Change the water regularly, perhaps every other day. Use water that has been allowed to sit overnight and is at the same temperature as the water you are replacing. Putting tadpoles in water that is much warmer or cooler than they are used to could kill them. If any tadpoles die for any reason, remove them as soon as possible. 7. Record the water temperature in each container each day, and describe each group of tadpoles. You may want to sketch them. Measure their size each week and record it on your data sheet. 8. After a group of tadpoles becomes frogs, which could take several weeks, record the number of days and release them into an area where it is safe and legal to do so. You should be aware that it is illegal to release or dispose of live frogs in certain areas. If you are not sure about where to release your frogs, ask your science teacher. 9. Continue making observations and recording data until all the tadpoles have become frogs. Summary of Results Study the results on your chart. How many days did it take for the first group to become frogs? What was the water temperature in that container? Did tadpoles in cooler containers take longer to go through metamorphosis? Was your hypothesis correct? Summarize what you have found.
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Change the Variables You can vary this experi-
ment in several ways. For example, feed the tadpoles different amounts of food and keep the temperature of the water constant. Then you can determine how food availability impacts their growth rate. Or you might feed them different kinds of vegetation. You can also place different amounts of water in each container or a different number of tadpoles in each container. How does that affect their growth rate? Try varying the amount of sunlight that falls on each container. How does light affect tadpole growth?
EXPERIMENT 2 Insects: How does food supply affect the growth rate of grasshoppers or crickets?
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: All the tadpoles are going through metamorphosis at the same time. Possible cause: The water temperatures are too similar. Find warmer and cooler places to put the jars. Problem: Some of the tadpoles are dying. Possible causes: They are not getting enough to eat, or the water is too warm, too cold, or too dirty. Try feeding tadpoles more or make the water a little warmer or cooler in the jars where tadpoles are dying. Also, change the water regularly.
Purpose/Hypothesis WARNING:You should be
aware that it is illegal to release or dispose of live insects in certain areas. If you are not sure about performing this experiment, ask your science teacher. Insects such as grasshoppers and crickets go through an incomplete metamorphosis, where they gradually progress from eggs through several nymph stages to adulthood. In this experiment, you will explore how the amount of food available affects the growth rate of these insects from nymph to adulthood. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of insects. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The more food supplied to grasshoppers, the faster they will become adults.’’ Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of food you supply • the number of insects in each container • the age and health of the eggs you begin with • the temperature at which the insects are kept In other words, the variables in this experiment are everything that might affect the time it takes the grasshoppers to develop into adults. If you change more than one variable, you will not be able to tell which variable had the most effect on the grasshoppers’ growth rate.
In this case, the variable you will change will be the amount of food you feed the grasshoppers, and the variable you will measure will be the time it takes them to become adults. You expect the grasshoppers that are fed the most food will become adults first. Only one variable will change between the control experiment and the experimental containers, and that is the amount of food you supply. For the control, you will supply a medium amount of food. For the experimental insects, you will supply a greater and a lesser amount. You will measure how many days it takes from the egg stage to the adult stage. If the insects in the containers with the most food grow fastest, your hypothesis is correct. Level of Difficulty Difficult, because of care
required with live animals. Materials Needed
• 3 glass jars with lids • approximately 30 grasshopper or cricket eggs (You can obtain them from a biological supply company, such as those listed under Further Readings.) • fruit flies and a covered container to keep them in (You can also obtain fruit flies from a biological supply company.) • measuring tape (with millimeters) Approximate Budget $30, if you need to pur-
How to Experiment Safely
chase insects and food.
Always be careful with live animals and treat them with respect. Move their containers slowly. Wash your hands carefully before and after handling them. If any insects die, dispose of them. You should be aware that it is illegal to release or dispose of live insects in certain areas. If you are not sure about performing this experiment, ask your science teacher.
Timetable 2 to 3 weeks.
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Step-by-Step Instructions
1. Place an equal amount of eggs in each of the three jars. Label the jars ‘‘medium/control,’’ ‘‘small amount,’’ and ‘‘large amount.’’ 2. Place the jars in a warm, dry place out of the direct sun. Experiment Central, 2nd edition
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Step 1: Place an equal amount of eggs in each of the three jars. Label as shown. GA LE G RO UP.
3. When the eggs hatch, record the day and time on a data chart similar to the one illustrated. 4. Provide the amount of food named on the jar labels to each group of nymphs. It will be difficult to count the fruit flies you supply, but try to record the approximate number you give to each group. Or you might vary the number of times you feed each group each day. Feed the small group only once, the control group twice, and the large group three times. 5. Every day record the growth of your insects. Measure the length of at least one insect in each group each day. 6. The supply house probably provided information about how large these insects will be as adults. When the insects in any group reach that size, release them in an appropriate area. You should be aware that it is illegal to release or dispose of live insects in certain areas. If you are not sure about where to release your insects, ask your science teacher.
Step 5: Measure the length of at least one insect in each group each day. G AL E GR OUP .
7. Continue feeding and measuring until all groups have reached adulthood. Experiment Central, 2nd edition
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Recording chart for Experiment 2. GAL E GR OU P.
Summary of Results Study the results on your chart. How many days did it take your control group to reach adulthood? How many days did it take the group you fed the least? The most? Did food availability affect the growth rate of your insects? Was your hypothesis correct? Summarize what you have learned. Change the Variables You can vary this experiment in several ways. For
example, change the temperature where you keep the insects. How does heat or cold affect them? How about sunlight? Vary the number of eggs in each container. If some containers are very crowded, how does that affect the insects’ growth rate? Check the labels that came with your eggs for the different kinds of food the insects eat. Does a different diet affect their growth rate? Modify the Experiment In Experiments 1 and 2, you examined the
metamorphosis of a tadpole, and the grasshopper or cricket. If it is difficult for you to obtain and care for live animals, you can simplify these experiments by drawing or constructing representations of the animals’ life cycle. First, conduct research at your local library or on the Internet of an animal that undergoes a complete metamorphosis and one that goes 654
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through an incomplete metamorphosis. You can explore the life cycle of the tadpole, grasshopper, caterpillar, or cricket. In a notebook, keep track of your research and sketch the stages of the life cycles. For example, the monarch butterfly undergoes a complete metamorphosis. You can draw the unique stages of the caterpillar life cycle as it transforms into a butterfly. You could also sculpt the changes out of modeling clay, cut out paper figures, or mold the shapes out of pipe cleaners. Refer to your notebook and your representations to compare the life cycle of the two animals. List important features of each life stage.
Design Your Own Experiment How to Select a Topic Relating to this Concept If you are interested in life cycles, you
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The growth rate of the insects in all the containers seemed about the same. Possible cause: The amount you are feeding your insects is too similar. Try feeding one group several more times in a day than the other groups. Problem: Many of the insects appear to be dying. Possible causes: You are not feeding the insects enough, or the temperature is too cold. Try feeding more fruit flies, or check the information that came with the eggs to see if they need other kinds of food. Move them to a warmer place if the place you have been keeping them is rather cool.
could study the different stages (eggs, larvae, nymphs) and the organisms’ diets, habitats, sizes, forms, and activities. Perhaps you are interested in the transformation from caterpillars to butterflies. How long is each stage in the life cycle for various species? Where do they lay their eggs? What do they eat, if anything? Many butterflies, such as the monarch, migrate long distances. Where do they go? How can they fly so far, and how long do they stay there? Maybe you are more interested in the life cycles of amphibians, such as frogs, toads, salamanders, and newts. Investigate which ones live in your area and what time of the year you could best study the different stages of their life cycles. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on animal life cycle questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be Experiment Central, 2nd edition
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sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question.
The butterfly is the adult stage in the life cycle that begins as a caterpillar. P ETE R AR NO LD I NC.
• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts, such as the ones you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental setup and results. If you have done a non experimental project, explain clearly what your research question was and illustrate your findings. Related Projects Besides doing experiments, you could prepare a poster or model illustrating the life stages of a particular animal. Or you could research the migration patterns of a particular butterfly or study the effects of different stages of insects on agriculture. You could present your findings as a booklet, poster, or report. The possibilities are numerous.
For More Information Carolina Biological Supply Company, 2700 York Road, Burlington, NC 27215, 1 800 334 5551. http://www.carolina.com Frey Scientific, 100 Paragon Parkway, Mansfield, OH 44903, 1 800 225 FREY. http://www.freyscientific.com Goor, Ron, and Nancy Goor. Insect Metamorphosis: From Egg to Adult. New Jersey: Simon & Schuster, 1990. Discusses both complete and incomplete metamorphoses step by step with full color photographs. 656
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Kalman, Bobbie. Animal Life Cycles: Growing and Changing. New York: Crabtree Publishing, 2006. A simple explanation of the life cycle of different animals. Kneidel, Sally. Creepy Crawlies and the Scientific Method. Golden, CO: Fulcrum Resources, 1993. A series of informative chapters on insects and other small animals, experiments, and information on keeping those animals at home or school. Ruiz, Andres Llamas, and Francisco Arredondo. Metamorphosis (Cycles of Life Series). New York: Sterling Publications, 1997. Details concepts and processes of metamorphosis, focusing on frogs, butterflies, and dragonflies with colorful illustrations. Ward’s Natural Science Establishment, Inc., 5100 West Henrietta Road, PO Box 92912, Rochester, NY 14692, 1 800 962 2660. http://www. wardsci.com
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Light Properties
S Newton wrote about his experiments with a prism and compass in his manuscript Opticks, which was published in 1704. A RC HIV E PH OTO S.
cholars wondered about the properties of light as early as 600 B . C . E . in Miletus, which was part of the Greek empire. We now know that light is a form of energy that travels through the universe in waves. All light energy exists in an electromagnetic spectrum. The visible spectrum, what we see as light, is part of the electromagnetic spectrum.
Experiments with a shutter Isaac Newton (1642–1727), a brilliant English mathematician, had just received his bachelor’s degree at the University of Cambridge when the bubonic plague hit Great Britain. Because the plague spread faster in cities, Newton continued his graduate studies for two years at his countryside home. During this time, he conducted many experiments. Early in 1666, Newton darkened his room and made a small hole in his shutters. After positioning a triangular glass prism in front of this small beam of sunlight, he noticed a band of colors called a spectrum. He concluded that when the light hit the prism, it was bent, or refracted, to form many colors. He demonstrated how the colors in sunlight could be separated, then joined again to form white light. In his work, Newton proved three of the most important characteristics of light: that it travels in straight lines, that it can be reflected, and that it can be refracted, or bent. Newton also did an experiment showing sunlight’s reflection and refraction inside raindrops. He 659
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discovered that raindrops formed tiny transparent prisms that reflected and refracted the Sun to produce colorful rainbows. Making waves In 1801, Thomas Young, a London doctor, developed a theory that light traveled in waves and presented it to the Royal Society, a prestigious group of scientists. Christian Huygens of Holland had suggested the presence of light waves in his book published in 1690, but Young would go on to prove it with his experiments in 1803.
This spectrum is produced by a modern diffraction grating. PH OT O RE SEA RC HE RS I NC.
Young used a screen with one slit. In front of that, he placed another screen with two side-by-side slits, and watched how sunlight passed through. What he saw was bands of color fanning out and meeting each other on the other side. Young realized these bands of color called interference fringes could be made only by waves of light. Up to that time it was thought that there was no form to light and that it existed everywhere. Young’s experiment also showed diffraction. Diffraction occurs when an uninterruped wave of light hits an obstacle. The obstacle bends the wave into a shadow zone. This results in light and dark fringes outside the shadow’s edge. It glows in the dark Some substances produce visible light if excited by radiation, such as invisible ultraviolet light. Visible light that is produced only when the radiation source is present is called fluorescence. Certain chemicals in laundry soaps react with sunlight to produce a fluorescence that makes clothes look brighter. Visible light that is produced even after the radiation source is removed is called phosphorescence. Some plants and animals in the sea produce a phosphorescence. Great scientists throughout history came to their conclusions about light by experimenting. Conducting some projects will enable you to become familiar with some of light’s properties.
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WORDS TO KNOW Diffraction: The bending of light or another form of electromagnetic radiation as it passes through a tiny hole or around a sharp edge. Diffraction grating: A device consisting of a surface into which are etched very fine, closely spaced grooves that cause different wavelengths of light to reflect or refract (bend) by different amounts. Electromagnetic spectrum: The complete array of electromagnetic radiation, including radio waves (at the longest-wavelength end), microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays (at the shortest-wavelength end). Fluorescence: The emission of visible light from an object when the object is bombarded with electromagnetic radiation, such as ultraviolet rays. The emission of visible light stops after the radiation source has been removed. Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/or experiment. Interference fringes: Bands of color that fan out around an object. Light: A form of energy that travels in waves.
Phosphorescence: The emission of visible light from an object when the object is bombarded with electromagnetic radiation, such as ultraviolet rays. The object stores part of the radiation energy and the emission of visible light continues for a period ranging from a fraction of a second to several days after the radiation source has been removed. Radiation: Energy transmitted in the form of electromagnetic waves or subatomic particles. Reflected: The bouncing of light rays in a regular pattern off the surface of an object. Refracted: The bending of light rays as they pass at an angle from one transparent or clear medium into a second one of different density. Ultraviolet: Electromagnetic radiation (energy) of a wavelength just shorter than the violet (shortest wavelength) end of the visible light spectrum and thus with higher energy than the visible light. Variable: Something that can affect the results of an experiment. Visible spectrum: The range of individual wavelengths of radiation visible to the human eye when white light is broken into its component colors as it passes through a prism or by some other means.
PROJECT 1 Looking for the Glow: Which objects glow under black light? Purpose/Hypothesis Fluorescence is a scientific term that refers to some-
thing (usually a chemical compound) that reacts with light energy and glows brightly. In this project, you will examine compounds that react with ultraviolet light (UV), causing the compound to glow. When certain chemicals are exposed to UV light, the molecules absorb the light energy and then release it in the form of visible light. Experiment Central, 2nd edition
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Level of Difficulty Easy/moderate.
How to Experiment Safely
Materials Needed
The chemicals in many detergents can irritate the skin, so avoid contact with the skin and eyes. Always use caution when handling household chemicals. Normally UV light is considered dangerous and harmful to the eyes. However, the fixture you are using emits very long wavelength UV, which is safe to use.
• UV light, also called a ‘‘black light’’ (fluorescent fixture with black or dark purple lightbulb) • Wisk or Woolite brand laundry detergent • glow-in-the-dark plastic (can be a plastic toy) • calcite (mineral found in nature or rock stores) • white paper • objects to test (rocks and minerals, household detergents or cleaners, clothing, plants, etc.)
LEFT: Detergent needed for Project 1. GAL E GR OU P. RIGHT: Step 2: Place a small amount of Wisk or Woolite on a piece of white paper. GA LE
Approximate Budget
$20 for black light, $5 for detergents and for
calcite. Timetable 15 minutes.
GR OU P.
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Step-by-Step Instructions
1. Place the black light in a dark room and turn it on. 2. Place a small amount of Wisk or Woolite on a piece of white paper. Let the detergent dry a little and place the paper so that the light shines on it. Notice the color of the chemical. Wisk is blue/green. Woolite is green/yellow. 3. Place different objects in front of the black light, such as white socks, white or colored towels, or blue jeans. Record any color you notice. Test groups of objects such as rocks, minerals, household
Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: None of the objects emits light. Possible cause: The black bulb should glow a dark purple when on. If the bulb is not glowing, the light is not working. Turn the lights on in the room and unplug the black light from the wall outlet. Check to see if the lightbulb is firmly seated in its sockets on both ends. Repeat the project.
Step 4: Sample recording chart for Project 1. GA LE GRO UP. Experiment Central, 2nd edition
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detergents, flowers, fabric dyes, and plastic objects. 4. Repeat the test for each object. Record your observations. Summary of Results Keep a record or chart of the results of the project. It’s fun to discover how many things glow under UV light.
PROJECT 2 An example of light refraction using a glass of water. G AL E GRO UP.
A diffraction grating is a microscopically scratched plastic film that bends light as it goes around the scratched film, causing a spectrum to become visible. GA LE GRO UP.
Refraction and Defraction: Making a rainbow Purpose/Hypothesis Rainbows are a good example of refraction. Water
droplets are the first step in rainbow formation. The droplets form tiny transparent prisms that reflect and refract sunlight. Refraction or bending of sunlight, or white light, makes the spectrum colors of red, orange, yellow, green, blue, and violet spread out and become visible. Refraction can be made to occur in many transparent materials, including glass, plastic, or water. In this project, you will use a special plastic material to display the different spectrums found in colored light. The plastic material is called a diffraction grating. A diffraction grating is a microscopically scratched plastic film that bends light as it goes around the scratched film, causing a spectrum to become visible. Level of Difficulty Easy/moderate. Materials Needed
• diffraction grating (Local science and nature stores have these. They also may have toys called rainbow peepholes and rainbow makers, which contain diffraction gratings.) • colored lightbulbs (25-watt party lights in red, blue, green, yellow, purple, and orange.) • white lightbulb (any wattage) • light fixture or lamp that fits lightbulbs • colored markers 664
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Approximate Budget $30: $4 to $5 for each bulb
and $1 for a diffraction grating. (You might borrow colored Christmas lights.)
How to Experiment Safely
Timetable Approximately 30 minutes to per-
Do not stick your fingers into the light sockets. Make sure the fixture is unplugged before removing the bulb. Do not touch hot bulbs.
form and record the results. Step-by-Step Instructions
1. Insert the white light bulb into the lamp. Plug the lamp in and turn it on. 2. Turn off all other lights and darken the room as much as possible. 3. Hold the diffraction grating approximately 0.5 inch (1.25 cm) away from your eye and look through it. 4. Notice the colors of the visible spectrum. Use the colored markers to draw the spectrum on a piece of paper and label it. 5. Turn the lights back on, shut off the lamp, and allow the bulb to cool. 6. Unplug the lamp and remove the bulb. 7. Repeat Steps 1 through 6 with each colored light. Summary of Results Make a chart displaying the spectrums made by the
different colored bulbs. Compare your results. Write a summary of your findings.
Step 4: Use the colored markers to draw the observed spectrum on a piece of paper and label it. GA LE G RO UP.
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EXPERIMENT 3 Refraction: How does the material affect how light travels?
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
Purpose/Hypothesis In this experiment you will
determine how light refracts as it interacts with different materials. You will first observe the • the distance from the material reflection and transmission of light. Then you • the light beam will determine how different materials affect • the distance from the ruler light refraction. The materials you will test are In other words, the variables in this experiment plastic wrap, wax paper, a glue stick, and a glue are everything that might affect the passage of stick wrapped in aluminum foil. Aluminum foil the light. If you change more than one variable, traps the light, reflecting it back into the material. you will not be able to tell what had the most Light transmits or passes through clear materials. effect on how the material affected the light. As light passes through transparent materials it can refract, causing the light to bend. How much the light refracts depends upon the material. In order to find out how light travels, you will measure the diameter of the beam of light through the materials. Also, you can see how much light is moving through the material by noting the light’s intensity. For the light source, you will use an LED to determine the path of light as it travels. An LED stands for an light emitting diode. It is a small electronic device that lights up when electricity passes through. LEDs emit a bright colored light yet consume little energy. With an LED, you can determine how and where the light travels. Before you begin, make an educated guess about the outcome of this Step 2: Observe light reflection. experiment based on your knowledge of the materials and the properties IL LUS TR ATI ON B Y TE MA H of light. This educated guess, or prediction, is NE LS ON. your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen • the type of materials
Paper
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A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one Experiment Central, 2nd edition
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possible hypothesis for this experiment: ‘‘The glue stick wrapped in foil will cause less light to escape, leading to the strongest and narrowest beam of light.’’
How to Experiment Safely Avoid direct eye contact with the LED light.
In this case, the variable you will change will be the materials the light passes through. The variable you will measure will be the diameter and intensity of the LED beam. Level of Difficulty Moderate. Materials Needed
• LED, available at hardware or electronic stores • white paper • aluminum foil • wax paper • plastic wrap • glue stick • a ruler with exact markings • scissors • a dark room • a helper Approximate Budget $8–$12. Timetable Approximately 45 minutes. Step-by-Step Instructions
Step 3: Record the diameter of the spot and note the intensity of the light. IL LU STR AT IO N BY TEM AH N EL SON .
Step 6: Test light refraction by holding the LED above the ruler and measuring the diameter and intensity of the beam of light. ILL US TRA TI ON BY T EMA H NE LS ON.
1. Turn off all lights and darken the room as much as possible. 2. Observe light reflection: Place aluminum foil 6 inches (15 centimeters) in front of the LED light with white paper 6 inches behind the light. Have a helper turn on the LED and make a note of the location and intensity of the light. 3. Repeat this process, replacing the aluminum foil with a piece of plastic wrap. Experiment Central, 2nd edition
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Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The light did not change in diameter as expected. Possible cause: You may have moved the LED so that it was not the same from the ruler. Try having a friend place an object that is the same height as where you are holding the LED, and repeat the experiment. Problem: The beam of light was not visible many times. Possible cause: The room may not be dark enough. Try conducting the experiment in the evening, or block out more light from the windows.
4. Observe light transmission: Place a white piece of paper in front and in back of the aluminum foil. Record where you see the spot of light. Have a helper shine the LED toward the aluminum foil. (See illustration) 5. Observe light refraction: Hold the LED against a ¼-inch (0.64-centimeters) piece of glue stick and turn on the LED. Note the intensity of the light. Now cover the LED with a piece of aluminum foil and again turn on the LED. Record your observations. 6. Test light refraction; Hold the LED 3 inches (7.6 centimeters) above the ruler. It does not need to be exactly 3 inches (7.6 centimeters) above the ruler but you have to keep it the same distance for each material you test. 7. Shine the LED on the ruler. Measure the diameter of the beam of light and note the light’s intensity.
8. Place a piece of wax paper against the LED and shine the light. Measure the diameter of the spot on the paper. Record the data. 9. Repeat the process, replacing the wax paper one at a time with plastic wrap, ¼-inch (0.64-centimeter) piece of glue stick, and a ¼-piece (0.64-centimeters)of glue stick wrapped in foil. Each time, record the diameter of the spot and note the intensity of the light. Summary of Results Take a look at your data and notes. Was your
hypothesis correct? When the light was directed at the glue stick, how did it differ with and without the aluminum foil? Was there one or more materials that caused the light to lose intensity? What material led to the beam of light having the largest diameter? Write a paragraph on your findings. 668
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Change the Variables There are many variables you can change in this
experiment. For example, you can try passing the light through a variety of materials that are only solids, such as different metals. Or you can turn the light on in front of various liquids. You can also dye the same liquid, such as water, to measure how color plays a factor in light transmission. You can also change the type of light you are using.
Design Your Own Experiment How to Select a Topic Relating to this Concept There are many aspects of
the properties of light you can study, either as a project or as an experiment. One aspect you may want to study might be reflection. If you choose reflection, one question might be: How can I see into a puddle past my reflection? Check the Further Readings section for this topic, and talk with a teacher or with a librarian before finalizing your choice. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you’re answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the two properties of
light projects, your data might include drawings or photographs. If you exhibit your project, you need to limit the amount of information you offer, so viewers will not be overwhelmed by detail. Make sure the beginning question, the variable you measured, the results and your conclusions about light are clear. Viewers and judges will want to see how each experiment was set up. You might want to take a detailed photo at each stage. Label your photos clearly. Have colorful tables and charts ready with information and results. Experiment Central, 2nd edition
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Related Projects Your project does not have to be an experiment that
investigates or answers a question. It can also be a model, such as Newton’s original experiment with window shutters and a prism. Setting up such a model would be fun, and you would learn how this concept works.
For More Information Burnie, David. Light. London: Dorling Kindersley, 1992. Includes a chapter on how Newton split light and other interesting aspects of this phenomenon with great photos and illustrations. Davidson, Michael W. et al. ‘‘Light and Color; Molecular Expressions. http:// micro.magnet. fsu.edu/primer/lightandcolor/index.html (accessed on January 18, 2008). Hamilton, Gina L. Light: Prisms, Rainbows, and Colors. Chicago: Raintree, 2004.
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Magnetism
O The pattern of the iron filings in this demonstration shows the magnetic field of the bar magnet. PHO TO RE SE AR CHE RS I NC .
ne of the most mysterious phenomena we witness every day is magnetism, a fundamental force of nature caused by the motion of electrons in an atom. You put a note on a refrigerator door. You watch the speedometer in a car tell you how fast you are travelling. You listen to a tape of recorded music. All of these depend on magnetism, but how do these things work? How does the simple physics of the magnet make so much possible? Magnetism is a matter of alignment What turns an ordinary piece of iron into a magnet? A large iron bar actually contains millions of ‘‘mini-magnets,’’ small magnetized areas called domains. Each has a north pole and a south pole. If the poles of the iron’s domains are aimed in all different directions, their magnetic forces act against one another and cancel each other out. When all of the domains are facing the same way, the bar becomes a magnet because it now has a single, strong magnetic field, a space in which its magnetic force can be observed. How can we get all the domains facing the same way? This can be achieved by repeatedly rubbing the bar with one pole of another magnet in the same direction. Once the bar is magnetized, its magnetic field will exert enough force on the domains in nearby iron filings to temporarily magnetize them. Each filing has its own north and south poles, and those poles are attracted to or repelled by the magnet’s poles. (Remember that unlike poles attract and like poles repel.) 671
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When a metal’s domains face in all different directions, it has no overall magnetism. When they are lined up, as illustrated, they create a strong magnetic field. GAL E GR OU P.
Hans Christian Oersted studied the relationship between electricity and magnetism. PH OTO RE SEA RC HER S I NC.
The position of the domains in such a magnet is not permanent, however. Striking or jarring the bar will literally knock its domains out of alignment, and the bar will lose its magnetism. Even as time passes and the magnet sits in a drawer, it will slowly lose its magnetism as the domains shift back to their original positions. One way to preserve a magnet is to keep it in a magnetic circuit, in which each domain is held in place by the direction of the next domain. Placing a steel plate across the poles of a horseshoe magnet will complete the circuit: all the domains in the circuit will point in the same direction and will tend to remain that way. In the first experiment you will create a magnet and then test the effects on the magnet’s strength of heat, cold, jarring, and rubbing with another magnet. Electricity can also produce magnetism Electrical current flowing through a wire produces a magnetic field. If the wire is wound into a coil, it will produce a stronger magnetic field, similar to that of a bar magnet: each end of the coil will become a magnetic pole. This effect was discovered by Danish physicist Hans Christian Oersted (1777–1851). He noticed that electric current disturbed the normal functioning of magnetic compasses.
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WORDS TO KNOW Alignment: Adjustment in a certain direction or orientation. Alloy: A mixture of two or more metals with properties different from those metals of which it is made. Circuit: The complete path of an electric current including the source of electric energy. Control experiment: A setup that is identical to the experiment but is not affected by the variable that affects the experimental group. Domain: Small regions in iron that possess their own magnetic charges. Electron: A subatomic particle with a mass of about one atomic mass unit and a single electrical charge that orbits the nucleus of an atom. Electromagnetism: A form of magnetic energy produced by the flow of an electric current through a metal core. Also, the study of electric
and magnetic fields and their interaction with charges and currents. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Insulated wire: Electrical wire coated with a nonconducting material such as plastic. Magnetic circuit: A series of magnetic domains aligned in the same direction. Magnetic field: The space around an electric current or a magnet in which a magnetic force can be observed. Magnetism: A fundamental force in nature caused by the motion of electrons in an atom. Terminal: A connection in an electric circuit; usually a connection on a source of electric energy such as a battery. Variable: Something that can affect the results of an experiment.
Electromagnetism is a form of magnetic energy produced by the flow of an electric current through a metal core. It has many applications in our modern technology. Stereo speakers are one of the most common applications. Electrical signals pass through a coil, creating a varying magnetic field that pushes and pulls on another magnet attached to the speaker. This causes the paper speaker cone to move back and forth to produce sound. Some metals, including iron, can be made into electromagnets strong enough to lift tons of scrap steel. One advantage of electromagnets is that they can be turned on and off with the flip of a switch. In the second experiment, you will create a small electromagnet using an electric current and you will test the effect on the magnet when the strength of the current is varied. Experiment Central, 2nd edition
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EXPERIMENT 1 Magnets: How do heat, cold, jarring, and rubbing affect the magnetism of a nail? Purpose/Hypothesis In this experiment, you
The ‘‘keeper’’ placed across the positive and negative poles of this horseshoe magnet create a magnetic circuit that holds the domains in place and stops the magnet from losing its strength. GA LE GRO UP.
will first test the effect of rubbing a bar magnet on a steel or iron nail. The bar magnet should align the domains in the iron so that the nail becomes magnetized. You will then measure the effect of four actions upon the nail’s magnetic strength—heating, cooling, rubbing with a magnet in the opposite direction, and striking with a hammer. Each of the four actions will be tested on a different magnetized nail. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of magnetism. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Rubbing a magnetized nail with the opposite pole of the bar magnet that was used to magnetize it, striking or dropping it, and raising or lowering its temperature will decrease the strength of its magnetic field.’’ In this case, the variables you will change are the four actions you will take on identically magnetized nails, and the variable you will measure is the resulting strength of the nail’s magnetic field. You expect that all four actions will reduce the nail’s magnetic strength. Level of Difficulty Easy/moderate.
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Materials Needed
• bar magnet • 5 steel or iron nails about 3 inches (7.5 centimeters) long (iron is preferable; steel is an alloy containing other metals that cannot be magnetized) • hammer • 1 cup of hot tap water • 1 cup of cold tap water with ice added • 10 staples (separated and unused) • 10 steel paper clips • 10 plastic-coated paper clips • small wooden block • safety glasses Approximate Budget Less than $10 for the mag-
net. (Try to borrow the hammer and safety glasses, if you do not have them.) Timetable About 30 minutes. Step-by-Step Instructions
1. Rub one pole of the bar magnet lengthwise down one nail fifty times, always in the same direction. 2. Test the nail for magnetism by touching its point to a staple, then to a steel paper clip, then to a coated paper clip. 3. Observe and record on your data chart which objects the nail can lift. Carefully set the nail aside. Keep it several inches away from the other nails. 4. Repeat this procedure with three other nails, rubbing them the same number of times in the same direction with the same pole of the bar magnet. The magnetic strength of the nails should be almost the same. If one is significantly weaker, rub it with the magnet until the Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • type of metal in the nails • the size of the nails • the strength of the bar magnet used • the number of times the nail is rubbed with the bar magnet • the direction in which the nail is rubbed with the bar magnet • the actions performed on the nails (striking, heating, etc.) In other words, the variables in this experiment are anything that might affect the magnetic strength of the nails. If you change more than one variable for each nail, you will not be able to tell which variable had the most effect on the resulting magnetic strength of the nail. A fifth nail will be magnetized and tested without any action performed on it. This control experiment lets us know that any changes we see in magnetism result from the actions and not from some unseen factor.
How to Experiment Safely Safety glasses must be worn any time you are striking metal on metal. Do not strike the nail with great force, and be sure to rest the nail on the wooden block so it does not bend or snap when hit. Do not lift the hammer more than 6 inches (15 centimeters) from the block. (See illustration.)
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Step 4: Data chart for Experiment 1. GAL E GR OU P.
Step 7d: Rest the shaft of the nail flat on the block. G AL E GRO UP.
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strength of its field is similar to the others. Your data chart should look like the illustration. 5. To establish your control experiment, test the remaining nail for magnetism. If this nail picks up any of the test objects, it has somehow been magnetized. Do not be surprised if the nail does have a very weak magnetic field. Just the movements of nails against one another in a box can align a small percentage of the domains in the metal. To prove that rubbing the first four nails with the bar magnet caused them to become magnegtized, however, you must see a significant difference between their magnetic strength and that of the control nail. 6. Now rub the control nail the same number of times in the same direction. Check to be sure it is magnetized, record the results, and carefully set it aside away from the other nails. 7. Perform one action on each nail. (Remember not to disturb the control nail.) Experiment Central, 2nd edition
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a. Place the first nail in hot water and leave it for ten minutes. b. Place the second nail in the ice water and leave it for ten minutes. c. Rub the third nail with the same pole of the magnet used earlier, but in the opposite direction, twenty-five times. d. With everyone present wearing safety goggles, place the shaft of the fourth nail flat on the wooden block and strike it firmly three or four times. (Do not lift the head of the hammer any more than 6 inches [15 centimeters].) 8. Test the magnetic strength of each nail and note any changes on your chart. 9. Finally, check the control nail to make sure that nails do not lose their magnetic strength simply by sitting unused for several minutes. Record the strength of the control nail in the appropriate row on your chart.
Troubleshooter’s Guide This experiment is fairly straightforward. You should encounter little difficulty if you use the listed materials. When you are doing experiments with magnetism, results can be difficult to measure precisely. To compare the strengths of magnets, test their lifting power several times and average the results to achieve a greater degree of accuracy. Here are some problems that may arise during the experiment, some possible causes, and ways to remedy the problems. Problem: All of the nails are strongly magnetized to start with. Possible cause: They may have been exposed to a strong magnetic field prior to the experiment. Demagnetize them by striking each several times with the hammer. (It is not necessary to strike with great force. Remember to wear safety glasses and place the nails flat on a wooden block so they will not bend or snap.)
Summary of Results Compare your data from
Problem: The nails will not magnetize.
the four tests. Determine which of the actions demagnetized the nails and which did not. Check your findings against the predictions you made in your hypothesis. Which actions did you accurately predict would demagnetize the nails? Which actions did not have the effect you expected? Summarize your results in writing.
Possible causes:
Change the Variables By altering your variables,
you can make this experiment the basis of a series of interesting and informative investigations into magnetism. For example, how fast does magnetic strength weaken? Can we preserve a magnet longer by refrigerating it? Are the effects Experiment Central, 2nd edition
1. The nails are made of a metal or alloy that cannot be magnetized. Use iron or steel nails. (Iron is preferable.) 2. Your bar magnet is too weak. Check its strength and replace it if necessary. 3. You are changing the direction of the stroke as you rub the magnet on the nail, or you are accidentally switching poles as you rub the nail. Either mistake will sweep the nail’s domains in different directions. Follow this procedure carefully.
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of nail used • the number of batteries attached to the circuit, which is directly proportional to the current • the type and gauge of wire used • the shape and weight of the test objects used In other words, the variables in this experiment are everything that might affect the magnetic field strength of the electromagnet. If you change more than one variable, you will not be able to tell which variable had the most effect on the magnetic strength. Steps 1 to 3: Set-up of nail and D-cell battery. GAL E GR OU P.
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of demagnetization always reversible, or can domains be put permanently out of order?
EXPERIMENT 2 Electromagnets: Does the strength of an electromagnet increase with greater current? Purpose/Hypothesis In this experiment, you
will create an electromagnet and test the effect of varying levels of electric current on the strength of the magnetic field. You will increase the current by adding batteries to the circuit— the path of the electric current through a wire attached to the terminals of a source of electric energy. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of electromagnets. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The strength of an electromagnet’s magnetic field will increase when the current applied to the electromagnet is increased.’’ In this case, the variable you will change is the electrical current, and the variable you will measure is the resulting strength of the magnetic field of the electromagnet. You expect that a higher current will result in a higher magnetic field strength. Experiment Central, 2nd edition
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Level of Difficulty Easy/moderate. Materials Needed
• 2 feet (0.6 meter) of insulated, 16 to 18 gauge solid copper wire • 3 fresh D-cell batteries • iron or steel nail (iron is preferable) • electrical tape • 10 staples (separated and unused) • 10 steel paper clips • 10 plastic-coated paper clips • magnetic compass • wire strippers
How to Experiment Safely Do not change the number or type of batteries used in this experiment without first consulting a teacher. NEVER experiment with household current or car batteries! Both are dangerous and potentially life-threatening.
Approximate Budget Less than $15 for wire, batteries, and electrical tape.
(Try to borrow the wire strippers and compass, if necessary.) Timetable 15 to 20 minutes. Step-by-Step Instructions
1. Secure one of the D-cell batteries to a flat surface using a strip of electrical tape. 2. Coil the insulated copper wire ten or more times around the nail, starting at one end of the nail and working toward the other. Leave about 2 inches (5 centimeters) of straight wire at each end.
Step 6: Sample data chart for Experiment 2. GA LE G ROU P. Experiment Central, 2nd edition
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Troubleshooter’s Guide When doing experiments with magnetism, results can be difficult to measure precisely. To compare the strengths of magnets, test their lifting power several times and average the results to achieve a greater degree of accuracy. Here is a problem that may arise during the experiment, some possible causes, and ways to remedy the problems. Problem: The nail does not show any magnetism. Possible causes: 1. A connection is loose. Check your connections, especially where the copper wire meets the battery terminals. Secure them with electrical tape if necessary. 2. The nail is made of a metal or alloy that does not magnetize. Use an iron nail. 3. You are using uninsulated wire, causing the current to travel across the coil and disrupt the magnetic field. Use insulated wire. 4. Your batteries are dead. Check them with a flashlight and replace them if necessary.
3. Strip the insulation off both ends of the wire. Hold one end to the positive terminal on the battery, and the other end to the negative terminal. 4. Check the nail for a magnetic field by holding it over the compass. Does the compass needle always point along the same direction on the nail? Which end of the coil forms the north pole of the magnetic field, the one leading to the positive terminal or the one leading to the negative terminal? 5. Use the magnet to lift as many staples as possible. Repeat with the steel paper clips and with the coated paper clips. 6. Record on your data chart the number lifted each time. Your chart should look like the illustration. 7. Increase the voltage applied to the electromagnet by adding another D-cell battery to the circuit. This will double the electrical current. Secure the batteries firmly together with electrical tape, making sure the positive terminal of one is touching the negative terminal of the other. 8. Repeat the test of the magnet’s lifting power and record your observations on the chart.
9. Finally, repeat the tests once more with three batteries. This will triple the current. Do not use more than three D-cell batteries! Do not use any other type of battery without first asking your teacher. Summary of Results Your data from Steps 6, 8, and 9 should be recorded
on a chart. This chart should contain the information that will show whether your hypothesis is correct. Did changes in current strength affect the magnetic strength? You can increase the clarity of your results by converting the data into graph form. Summarize your results in writing. 680
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Change the Variables To further explore the topic of electromagnetism, you can vary this experiment in the following ways: • Use a different type of nail, such as copper or aluminum, or a heavier iron or steel nail • Try a heavier gauge copper wire • Vary the shape and weight of the items you try to pick up
One variation you must avoid is adding more than three batteries to the circuit or using a kind of battery other than D-cell. This can create enough electric current to be dangerous.
Design Your Own Experiment How to Select a Topic Relating to this Concept
If you look carefully around your house, you will discover that magnets play a hidden role in much of the technology we use today. You can investigate other uses of magnets and develop interesting ideas for experiments and demonstrations. Remember that magnetic particles make tape recordings and computer diskettes function. Magnets are at work in every electric motor you see. Magnetism also affects natural phenomena, such as the aurora borealis (northern lights) and the migratory patterns of birds. Check the Further Readings section and talk with your science teacher of school or community media specialist to start gathering information on magnetism questions that interest you. Remember that any experiment involving electricity should use no more than three 1.5-volt batteries, and any experiment proposal should be approved by your teacher.
The electromagnet is especially useful in the scrap yard because it can be easily switched on and off. P HOT O RE SE AR CHE RS INC .
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Experiment Central, 2nd edition
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Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the experiments included
here, and in any experiments you develop, try to display your data in accurate and interesting ways. When presenting your results to those who have not seen the experiment performed, showing photographs of the various steps can make the process more interesting and clear. Related Projects Simple variations on the two experiments in this
section can prove valuable and informative. The magnetic field created by an electromagnet has poles just like a permanent magnet. How could you discover which end of the coil is north and which is south? How does reversing the positive and negative contacts on the coil affect the field? What happens if you put an electromagnet coil around an already magnetized nail? Does it increase the strength of the field?
For More Information The Exploratorium. ‘‘Snacks about Magnetism.’’ The Exploratorium Science Snacks. http://www.explo ratorium.edu/snacks/iconmagnetism.html (accessed on February 19, 2008). A number of short experiments on magnetism. Gillett, Kate, ed. The Knowledge Factory. Brookfield, CT: Copper Beech Books, 1996. Provides some fun and enlightening observations on questions relevant to this topic, along with good ideas for projects and demonstrations. The Interactive Plasma Physics Education Experience! Electricity and Magnetism. http://ippex.pppl.gov/interactive/electricity/ (accessed on February 19, 2008). Information and animations on magnetism, and how it relates to electricity. Macaulay, David and Neil Ardley. The New Way Things Work. Boston: Houghton Mifflin, 1998. Detailed description of how machines work, including those that use electricity and magnetism. 682
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Ray, C. Claibourne. The New York Times Book of Science Questions and Answers. New York: Doubleday, 1997. Addresses both everyday observations and advanced scientific concepts on a wide variety of subjects. University of Maryland, Department of Electrical and Computer Engineering. Gallery of Electromagnetic Personalities. http://www.ece. umd.edu/taylor/ frame1.htm (accessed on February 19, 2008). Brief biographies of the people who make contributions to magnetism and electromagnetism.
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W
e live in a world filled with materials. There are materials that people have created, such as plastics, and others that come from nature, like wood. Our clothes, furniture, dishes, music players, sports equipment, and homes are all made of materials. Materials are a part of medicine in the threads for stitches and artificial hearts. Materials are key to space exploration in the astronaut’s spacesuits and the metals used in the spacecraft. The materials that make up packaging keep our food fresh and safe from harmful microorganisms. Materials science is the study of all these materials to better understand and use them. By understanding the properties, materials scientists can find ways to improve existing materials and develop new ones. Following nature’s lead The story of Velcro began when an electrical engineer, George de Mestral, noticed how burrs were sticking to his dog’s fur. An up-close look at the burr’s under a microscope showed him that the burr’s had natural hooks that were sticking to the fur. That led him to develop Velcro, a material that fastens with hooks on one side and loops on the other. The development of Velcro is an example of biomimetics. The science of developing materials inspired by nature is called biomimetics. Many organisms create materials with such amazing properties that scientists have long tried to mimic them for manmade materials. For example, scientists have long studied the silk a spider produces. Spider silk is so light and strong that if a thread of spider silk was the same weight as a thread of steel, the silk would be stronger. Spider silk can also stretch a long way without breaking. A material that could be manufactured having the same properties as spider silk would be useful for humans.
All types of materials There are several ways to categorize materials, and some materials can fall under more than one category. Different types of materials are: 685
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Electrical engineer, George de Mestral, noticed that burrs have natural hooks, leading to the development of Velcro. I LLU S-
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• Metals: These materials include metals or mixtures of metals. • Polymers: Polymers are long chains of repeating smaller units. Examples of polymers include plastic bottles, nylon, and polyester. • Textiles: Any type of cloth, yarn, or fabric is a textile. Spider silk is so light and strong that if a thread of spider silk was the same weight as a thread of steel, the silk would be stronger. ( C) LAY NE KE NNE DY/ CO RB IS.
• Ceramics: Glass, cement, and pottery all fall under ceramics, which is any material that is not metal and not organic (from living organisms). • Semiconductors: Material that have electrical properties inbetween a conductor and insulator. • New materials: Developments in science and technology are leading to new materials by mixing two or more materials together (composites) or by manipulating particles in current materials. Material properties With so many materials, there are a lot of material properties. Some properties can change with heat, cold, pressure, or other conditions. When developing and finding the best-suited materials, a few common properties that scientists look at include:
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• Strength: There are different types of measuring strengths for materials. Tensile compressional strength strength is one commonly used measure of strength. Tensile strength measures the point at which a material will break when it tensile strength is pulled. For materials that are pulled or stretched frequently, such as plastic bags, having a high tensile strength is an important feature. Compressional strength is another category, referring to the strength of a material when weight is pushing down or compressing the There are different types of measuring strengths for material. Materials where compressional strength is important materials: tensile strength and include steel and concrete. compressional strength. I LL US• Toughness: The toughness of a material is the amount of energy TRA TI ON B Y TE MA H NEL SO N. needed to break a material. A plastic spoon that easily snaps into two pieces would have far less toughness than a strip of wood that you can’t break. • Heat: Thermal properties relate to heat and include how well a material can hold, insulate, or conduct heat. Some materials, such as winter fabrics for the outdoors, are selected for their ability to insulate, not allowing heat to pass—either out or into the body. Flammability is a measure of how quickly a materials lights on fire and is a common test for many household materials. • Electrical: How well a material conducts electricity is a measure of its conductivity. Materials chosen for their ability to conduct electricity (electrons) include metals such as copper and silver. Other materials, such as rubbers and plastics, are selected because they do not conduct electricity. • Chemical: A material’s chemical properties are a measure of how the material will chemically change or react with other substances. When iron rusts, for example, that is a chemical change as the iron reacts with oxygen. • Biodegradable: Materials made of natural biological materials that are broken down by natural processes are called biodegradable. Materials made from primarily from plants—such as wool, corn, wood, and cotton—are examples of materials that could be biodegradable. Materials science is an interdisciplinary field. Professionals who work to develop materials could specialize in chemistry, engineering, or Experiment Central, 2nd edition
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WORDS TO KNOW Biodegradable: Capable of being decomposed by biological agents. Biomimetics: The development of materials that are found in nature. Conductivity: The ability of a material to carry an electrical current. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Electricity: A form of energy caused by the presence of electrical charges in matter. Flammability: The ability of a material to ignite and burn.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Insulator: A material through which little or no heat energy will pass. Polymer: Chemical compound formed of simple molecules (known as monomers) linked with themselves many times over. Tensile strength: The force needed to stretch a material until it breaks. Variable: Something that can affect the results of an experiment.
physics. In the experiments below, you will investigate two types of materials. As you conduct the experiments, consider what questions you have about materials and what you would like to explore.
EXPERIMENT 1 Testing Tape: Finding the properties that allow tape to support weight. Purpose/Hypothesis How would you develop a tape that supports a lot of
weight? There are a variety of properties that make tape support weight. One property is the adhesive on the tape. Some tapes have an adhesive that bonds tightly to an object while others are developed with a relatively weak adhesive. Another property of material strength is how much the tape can withstand tearing when it is pulled. This is called tensile strength. The higher the material’s tensile strength, the more pressure it can take before breaking. In this experiment, you will measure how a variety of tapes support weight to determine the properties of the tapes. You will first examine 688
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how each tape tears. You can then add an increasing amount of weight supported by the tape. Water will be the weight: One cup of water weighs approximately 8 ounces (0.24 milliliters). By measuring when the tape can no longer hold the weight, you can draw conclusions about the properties of the strongest tape. To begin this experiment make an educated guess, or prediction, of what you think will occur based on your knowledge of material science and tapes. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of bag • the bottle • the type of tape • the amount of tape used In other words, variables in this experiment are everything that might affect the amount of weight the tape can hold. If you change more than one variable, you will not be able to tell which variable impacted the tape’s strength.
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The more difficult a tape is to tear, the more weight it will support.’’ In this experiment the variable you will change will be the type of tape, and the variable you will measure will be the amount of weight the tape can hold before it breaks. Level of Difficulty Easy/moderate.
Materials needed for Experiment 1. I LL US TRA TI ON BY T EMA H NE LS ON.
Materials Needed
• • • • • • • •
5 small paper bags, lunch bags work well funnel scissors 2-liter soda bottle measuring cup water ruler 4 to 5 different types of tapes, including Duct, packing, and masking (clear
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How to Experiment Safely If you use the scissors to cut the bottle or bag, be careful. Check with an adult that you can stick tape to the wall. This experiment can be messy. If you have an outside area with a flat wall you may want to set up the experiment outside.
Step 6: Carefully add ¼ cup (about 2 ounces) of water to the bottle. When the tape can no longer support the bottle, write down the amount of weight the tape held. IL LU STR AT ION BY TE MAH NEL SO N.
household tape and painter’s tape are other types) • large container (to catch falling water) Approximate Budget $10. Timetable 30 minutes Step-by-Step Instructions
1. For each tape, tear off a piece about 6 inches (15 centimeters) using your hands. Note how difficult each tape is to rip crosswise. If you have to use scissors to tear the tape, write that down in a chart. 2. For each tape, tear the piece lengthwise and note how difficult each tape is to rip. 3. Tear a new piece of the first tape one inch less than the width of the bag and stick it on the bag with half the width of the tape on the bag. 4. Stick the bag on the wall and set the empty bottle in the bag. The bottle should be slightly higher than the bag. You may need to cut the top of the bottle or the bag with the scissors. 5. Set the large container underneath the bag/bottle and place the funnel in the bottle. 6. Carefully add ¼ cup (about 2 ounces) of water to the bottle, being careful not to drip any water on the bag. Continue adding water in ¼ cup increments, remembering to note how much water you are adding. When the tape can no longer support the bottle, write down the amount of weight the tape held. 7. Repeat Steps 3–6 with each of the tapes, using a new, dry bag in each set-up. Note your results. Summary of Results Look at your chart. You may want to graph the results with the amount of water on the y-axis and the tape on the x-axis.
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Did the tapes break at different weights? How did the ease or difficulty of tearing the tape relate to the tapes ability to hold weight? Consider other properties of the material that helped it withstand weight. If you were developing a tape that was stronger than the strongest tape you tested, what properties would you use? Write a summary of your results. Change the Variables You can vary this experi-
ment in several ways, depending on the goal of the material you want. If you want to continue testing strength, you can test the tape strength from another direction. You can also change the temperature, test the strength at both colder and warmer temperatures. If you wanted to focus on one tape, you could keep the weight the same and examine how the dimensions of the tape play a role in its strength.
EXPERIMENT 2 Developing Renewables: Can a renewable packing material have the same qualities as a nonrenewable material?
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The bag broke before barely any weigh was added. Possible cause: You may have dribbled some of the water on the bottom of the paper bag, which could have caused it to tear. Using a new, dry bag, repeat the test. Problem: The tape kept peeling off the wall. Possible cause: The surface may have a coating that is difficult to adhere to. Try to find a smooth, non waxy flat surface, and repeat the experiment. Problem: The bottle was filled with water and the tape did not break. Possible cause: That is a strong tape. If another bottle of any sort fits in the bag, insert it into the bottle and continue adding weight (water). You can also try using a larger paper bag that holds two bottles.
Purpose/Hypothesis Developing and testing renewable material is a
major area of material science. In general, renewable materials cause less harm to the environment than the counterpart materials. There are many issues to consider when developing a renewable material. For a renewable material to replace a non-renewable, it needs to show similar qualities as what it is meant to replace. Cost and manufacturing are two other issues involved in material development. In this experiment, you will work to develop a renewable packing material that can replace a non-renewable material. Packing peanuts are commonly made out of a form of polymer, such as Styrofoam, which can take hundreds of years to degrade. Properties that make Styrofoam a popular packing material include its lightness (it does not add weight to a Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of manufactured peanut • the item being tested • the amount of material tested • the height the egg is dropped In other words, the variables in this experiment are anything that might affect the protective properties of the corn-based material. If you change more than one variable, you will not be able to tell which variable had the most effect on material’s qualities.
• • • •
package) and its protective qualities. Styrofoam packing peanuts cushion objects to protect them from breaking. In this experiment you will focus on only matching the material’s qualities. You will produce and test renewable packing peanuts, made from corn. Corn-based packing peanuts dissolve in water. The goal is to produce a renewable material that has comparable qualities to the non-renewable packing peanut. You will vary the amount of water in your material before you test its protective qualities. By dropping a hard-boiled egg on both the renewable and non-renewable materials you can determine how they compare. Before you begin, make an educated guess about the outcome of the experiment based on your knowledge of renewables and material science. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘Materials made from corn will have the same protective qualities as the Styrofoam packing peanuts.’’ In this case, the variable you will change will be the main component of the material, and the variable you will measure will be the protective quality of the material. Level of Difficulty Moderate. Materials Needed
• Styrofoam packing peanuts, approximately 1 cup • yardstick • measuring cup 692
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• • • • • • • •
tablespoon hard boiled eggs, at least 4 to possibly 12 3 bowls, all the same size and shape microwave 2 microwave-safe mixing bowls spoon water cornstarch
How to Experiment Safely When you use the microwave, make sure the bowl is microwave-safe. Cornstarch can clog a garbage disposal so ask an adult how to dispose of it.
Approximate Budget $5; assuming you can find Styrofoam packing
peanuts in the household or school. Timetable 1 hour. Step-by-Step Instructions 1.) Making the corn-based packing material:
1. Pour 1 cup of cornstarch into the microwave-safe bowl. Add 4 tablespoons of warm water and stir. 2. Heat the bowl in the microwave for about 10 seconds. 3. Continue stirring the mixture. It should be the consistency of a thick paste. You may want to put it back in the microwave for another two to five seconds at a time. This is Material 1. 4. Repeat Steps 1–3, using a new bowl and adding 5 tablespoons of water to the cornstarch. This is Material 2. 5. Shape each of the corn paste into shapes that match the shape and size of the Styrofoam materials, keeping the two materials separate.
Step 1:5 Shape each of the corn paste into shapes that match the shape and size of the Styrofoam materials, keeping the two materials separate. IL LUS TR ATI ON B Y TE MA H NE LSO N.
2.) Testing the materials: 1. Set a yardstick against the wall; you may need to tape it or have a helper hold it. 2. Pour 1 cup of the Styrofoam peanuts into bowl 1. The peanuts should cover the bottom of the bowl and be at least 1-inch (2.5 centimeters) higher than bowl. The exact amount you use does not matter, as long as all the bowls have the same amount. Experiment Central, 2nd edition
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3. Pour 1 cup (or the matching amount) of the corn peanuts from Material 1 into the second clean bowl. Pour 1 cup (or the matching amount) of the corn peanuts from Material 2 into the third clean bowl. 4. Test how high you can drop the egg from in the Styrofoam peanut bowl before the shell cracks. Start at 6 inches and continue dropping the egg at 1-inch increments until you see or hear a crack. Note the height.
Step 2:5 Test how high you can drop the egg into the Styrofoam peanut bowl before the shell cracks. I LL UST RA TIO N BY
5. Drop a new hardboiled egg in the Material 1 bowl, starting at the same height you noted for the Styrofoam material. If the egg cracks, lower a new egg 1-inch and drop it again. Continue lowering the egg in 1-inch increments until the egg does not crack, using a new egg every time. If the egg does not crack, continue raising the egg in 1-inch increments until it cracks. Note the height. 6. Repeat this same process for Material 2, using new eggs.
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7. When you are done with the experiment, slowly pour water over the corn packing material and watch it dissolve. Summary of Results How do the three materials compare to each other in
terms of protecting the egg from cracking? If one material provided a far better cushion look at the materials and consider why. When producing the two corn-based packing materials, which of the materials was easier to make and shape? Which provided more of a cushion? Write a paragraph summarizing the challenges and testing of the renewable packing materials. You can hypothesize how you would improve upon the renewable material and other tests you would conduct. Change the Variables You can vary this experiment. Try using different
types of packing materials to test the renewable against. How does the corn-based material compare to bubble materials, for example? You can also add different ingredients to the corn-based material, such as a few drops of oil. 694
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Design Your Own Experiment How to Select a Topic Relating to this Concept
Materials are all around you. Consider if there is one item that you have seen change materials over time. Look around you at all the different objects in your house and school and see what properties interest you about these materials. Check the Further Readings section and talk with your science or engineering teacher to learn more about the properties of different materials. As you consider possible experiments, make sure to discuss them with your science teacher or another adult before trying them.
Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can definitely be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The corn paste keeps crumbling when it is shaped into a peanut. Possible cause: You may not have added enough water or mixed the water in thoroughly. Try again, microwaving before you stir and using your fingers to make sure the mixture is smooth.
Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
Problem: There was no noise but the eggs had a crack in them many times. Possible cause: The eggs might have started with small cracks. Before you drop the eggs, inspect each one thoroughly to make sure it is uncracked, and repeat the tests.
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In any experiment you
conduct, you should look for ways to clearly convey your data. You can do this by including charts and graphs for the experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. You might decide to Experiment Central, 2nd edition
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conduct an experiment that lasts several months. In this case, include pictures or drawings of the results taken at regular intervals. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are numerous possible experiments and projects you
can undertake related to materials science. For example, you can investigate how the materials for one sports item, such as skis or a tennis racquet, have changed over time. What properties set a professional, expensive tennis racquet apart from an everyday, less-expensive racquet? How have materials affected the sport? You can look at one property of clothing, such as waterproofing, weight, or insulation. Or you can experiment with recently developed fabrics, such as polyester or materials that are lightweight and warm. Does the warmth of a fabric relate to its weight? You could also test materials made from nature against similar, manmade materials.
For More Information BBC. The Science of Sport. http://www.bbc.co.uk/worldservice/sci tech/ features/science of sport (accessed April 24, 2008). Information on the role of science and materials in sports. Gardner, Robert. Science Projects about Chemistry. Hillside, NJ: Enslow Publishers, 1994. Describes many science projects, including separating and identifying substances and detecting unknown solids. Mueller, Tom. ‘‘Biomimetics: Design by Nature.’’ National Geographic.com. April 2008. Available online at http://ngm.nationalgeographic.com/2008/ 04/biomimetics/tom mueller text (accessed April 24, 2008). Peacock, Graham. Materials. New York: Thomson Learning, 1994. Basic activities on a range of materials. Polymer Science Learning Center, University of Southern Mississippi. The MacroGalleria. http://pslc.ws/macrogcss/maindir.html (accessed on April 14, 2008). Detailed site on all aspects of polymers, from studying them to everyday applications.
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hen you recall a particularly memorable event, think about what you remember. For example, what if you went to a great waterpark several years ago. You likely will remember your family or friends who you went with. You probably recall the rides, something you ate, and the thrill of the ride. But do you remember what you wore that day? What about where you parked or what you drank? Our brain processes so much information throughout a day—or event—that it picks and chooses what to file. The ability to store, retain, and recall information is memory. If someone had asked you on the way home from the hypothetical waterpark what you drank that day, it likely would have still been filed in your memory. And if every day you thought about what you drank at the waterpark, you would probably be able to recall it two years later. Where and how memories are stored tells a lot about how humans learn. Understanding memory can also lead researchers to help people retain their memories. Types of memory Memory is generally organized into three categories, depending upon the length of time it stays in the brain. • Sensory memory: Most of what we senses that gives us a picture of the scene around us is known as sensory memory. Sensory memory is fleeting, the brain can hold onto the information for seconds before it becomes lost. When you are taking a walk and spot a dog run by or a crack in the sidewalk, those scenes are sensory memory. • Short-term memory: When sensory memory moves into a longer form of storage it becomes short-term memory. This is also known as working memory. When you remember a shopping list, this is short term memory. Working memory allows us to link the past to the present. • Long-term memory: Once a memory is here, it is stored for days or decades. There are different types of long-term memory. One 697
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long term There are three types of memory: sensory, short term, and long term. IL LUS TR ATI ON B Y TE MA H NEL SO N.
type is how we remember to tie our shoes or ride a bike. This type of long-term memory records skills and facts that we have learned. The other type of long-term memory is the memory related to an episode or experience (this is called episodic memory). This is how we remember the sights, sounds, and emotions of an event years after it happened. How the filing system works The brain is made up of several different parts, which each have distinct functions. One area of the brain that plays an important role in memory is the hippocampus. The hippocampus, located deep inside the brain, is where new memories are formed. It is also important in directing the storage of memories to different parts of the brain. The hippocampus works with another part of the brain, the cerebral cortex. The cerebral cortex is the outer layer of the brain that is often linked to higher learning and processing information. It is also called the 698
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grey matter. Researchers theorize that memories are stored in different parts of the cerebral cortex. Memory problems Memory can falter or be harmed in several ways. Forgetting where you put your books or a math formula is common. But when memory is truly lost, it is called amnehippocampus sia. Because the brain stores and processes memory, if the brain is harmed it can cause amnesia. In some cases, such as a stroke or car accident, memories will return. In other cases, such as Alzheimer’s disease, memories may be permanently lost. Alzheimer’s is a disease that affects the hippocampus and as a result, affects the formation and storage of memories.
cerebral cortex
The hippocampus works with another part of the brain, the cerebral cortex. ILL US TRA TI ON BY T EMA H NE LS ON.
The major cause of amnesia in people who are not elderly is from some form of brain damage. Damage to different parts of the brain can lead to different types of amnesia. In one form of amnesia, a person cannot form new memories but the person can recall childhood memories. In another form of amnesia, a person will not be able to recall memories right before the injury but all other memories remain intact. When people remember an event that never happened or change the way it actually occurred it is called a false memory. False memories are not
PET scans comparing Alzheimer’s sufferer’s brain with healthy brain. The red color shows maximum, healthy blood flow, the yellow-green indicates less blood flow, while dark green and purple-blue areas indicate no flow. JONATHAN SELIG/COLLECTION/ GETTY IMAGES.
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WORDS TO KNOW Acronym: A word or phrase formed from the first letter of other words. Amnesia: Partial or total memory loss.
Long-term memory: The last category of memory in which memories are stored away and can last for years.
Cerebral cortex: The outer layer of the brain.
Memory: The process of retaining and recalling past events and experiences.
Control experiment: A setup that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Mnemonics: Techniques to improve memory.
False memory: A memory of an event that never happened or an altered memory from what happened.
Sensory memory: Memory that the brain retains for a few seconds.
Hippocampus: A part of the brain associated with learning and memory.
Short-term memory: Also known as working memory, this memory was transferred here from sensory memory.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Variable: Something that can affect the results of an experiment.
due to brain damage. They can occur when memories or suggestions are ‘‘planted’’ to a person, or when the brain is trying to make sense of a complex scene. In false memories people can truly believe the event occurred as they remember it. Keeping memory sharp Using what you have learned and stored in your memory is a way to keep it available. When people don’t use skills or knowledge for long periods of time, it can be hard for the brain to recollect it. There are also many ways to make memories ‘‘stick.’’ Mnemonics (pronounced ‘‘ne-mon-ics’’) are techniques or devices that help people retain memories. Different people have different mnemonic techniques that work for them. An examples of a visual mnemonic technique links an image to the item to be remembered. Creating a memorable acronym or phrase is another mnemonic device. An acronym is a word or phrase formed from the first letter of another word or name. ‘‘Roy G. Biv’’ is a well used acronym for the order of the colors in white light: red, orange, yellow, green, blue, indigo, and violet. ‘‘My Dear Aunt Sally’’ uses the first letter of each word to call to mind the math rule: multiply and divide before you add and subtract. Setting numbers or facts to song is another common memory technique. 700
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EXPERIMENT 1 Memory Mnemonics: What techniques help in memory retention? Purpose/Hypothesis One of the most famous
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
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mathematical concepts is pi (pronounced ‘‘pie’’). • the participants Pi () equals the distance around a circle (its cir• events or noise occurring in the cumference) divided by the distance across the background circle (its diameter). Pi is a constant, meaning it is • the amount of time given to participants always the same number no matter what the size of • the number to memorize the circle. And pi is a number that never ends. In In other words, the variables in this experiment shorthand, pi is commonly memorized as 3.14. are everything that might affect the ability of the Some people might know it is 3.14159. But the participants to memorize pi. If you change more decimal of pi goes on forever, and there is no than one variable, you will not be able to tell which variable had the most effect on memory. pattern to the numbers. Computers have calculated pi to over a trillion decimal places! And people have contests memorizing as many as they can. In this experiment, you can use pi to measure how different mnemonic devices help people remember up to 12 digits of pi. You can use two different mnemonics: Music, images, and repeating in patterns are three options. Because people have different abilities to memorize, it will help to find at least three people in each group so that you can find an average. Pi equals the distance around a The first group will set the numbers of pi to a song. The second group circle (its circumference) will relate patterns of numbers to images. The third group will be the divided by the distance across the circle (its diameter). control. This group will not use a mnemonic. All the groups will have the IL LU STR AT IO N BY T EM AH same amount of time to look at and memorize the number. The next day, NE LS ON. you will measure how many numbers of pi people in each group remembered. You will need to ask ce each person separately so one person does not ren fe influence another. (If finding a lot of people is difficult you can select one mnemonic devices and a control.) Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of memory and mnemonics. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
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How to Experiment Safely There are no safety hazards in this experiment.
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The people who use music will recall the most digits of pi, compared to the other mnemonic device and the control.’’ In this case, the variable you will change is the mnemonic device, and the variable you will measure is the amount of numbers the participants can recall. The participants who do not use a mnemonic device will serve as the control. If the people who set the numbers to song recall more digits on average than all other groups, you will know your hypothesis is correct. Level of Difficulty Moderate/difficult (because of the time and partic-
ipants involved). Materials Needed
Step 1: Think of a song you and the participants will know and set the 12 decimal places of pi to its tune. I LL UST RA TI ON BY T EM AH NE LS ON.
Twin-kle twin-kle
• • • •
the number pi (below) paper and pencil watch or timer participants, at least three in each group for a minimum of nine, with the more tested the stronger the experiment (if finding participants is difficult, you can select one mnemonic device to test. Participants will need to be available 20 minutes on Day 1 and about five minutes on Day 2)
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Approximate Budget $0. Timetable Approximately two hours over two
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days. The time will increase if participants in each group are tested separately or if each group is gathered on separate days. Each participant (group of participants) should have 20 minutes to remember the digits in pi on Day 1 and you Experiment Central, 2nd edition
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will need several minutes with each participant on Day 2. It does not matter what day each group is gathered, as long as the following day you test their recall. Step-by-Step Instructions
1. Think of a song you and the participants will know and set the 12 decimal places of pi to its tune. (See illustration.) The song can be as simple as ‘‘Happy Birthday to You’’ or a song that has a set rhythm. 2. Gather the first group of participants. Tell them you are conducting a memory experiment and have them all sing the song with the ‘‘pi’’ lyrics. Give them 20 minutes to sing the song. 3. Consider the second mnemonic device and come up with images for groups of numbers. The images can tell a story. For example, one set of images could be about a day at school where you are getting back a big math test. You look at the test and happily see you got 14 out of 15 correct (1415); the date on the calendar is September 26 (926); on a desk is a set of colored pencils, five of them are red, three are green, and five are orange (535); the window in the classroom has 8 out of the 9 windows dirty (89). Whatever the story or images are, sketch or print images that relate to each group of numbers. 4. Gather the second group of participants. After telling them you are conducting a memory experiment have them look at and say the numbers related to each image. Allow them to continue looking at the images and saying the numbers for 20 minutes. 5. For the control group, tell participants person 1 you are conducting a memory experiment person 2 and show them the numbers of pi, up to person 3 12 decimal places. Ask them to simply # of person 4 repeat the number and try to memorize digits person 5 it over the next 20 minutes. average 6. The day after working with Group 1, ask each participant individually in Group 1 Experiment Central, 2nd edition
Step 3: Come up with images for groups of numbers. For example, one set of images could be about a day at school where you are getting back a big math test. IL LUS TR ATI ON B Y TEM AH N EL SON .
Step 6: Make a note of how many numbers each person remembered. I LLU ST RAT IO N BY T EMA H NE LS ON.
Mnemonic Mnemonic (group 1) (group 2) Control
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Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The people in each group differed widely in how many numbers they recalled. Possible causes: The ability to memorize and retain information can differ among people. You may need a larger sample size to get a better average. If possible, increase your sample size to five people in each group and repeat the experiment. When you are calculating averages, do not use the highest and lowest numbers. Average only the three middle numbers for each group. There are generalities to the way people learn and memorize, but individuals have different learning styles. If possible, increase your sample size to five people in each group and repeat the experiment. When you are calculating averages, do not use the highest and lowest numbers. Average only the three middle numbers for each group. Problem: The people who put the numbers to lyrics could not recall as expected. Possible causes: Participants may not have been familiar with the song or tune. Find a song or tune each participant in the song group knows well, and set the pi numbers to that. Repeat the experiment.
to recite as many numbers of pi as they can recall. Start to hum the tune and ask again. Make a note of how many numbers each person remembered. 7. The day after working with Group 2, ask each participant individually to recite as many numbers of pi as they can recall. Show them the images you used. Note how many numbers each person recalled. 8. Repeat the same test for the control group one day after working with the control participants. Summary of Results Average the number of digits
each group recalled. (To calculate the average, add up the number of digits participants in each group remembered and divide by the total number of digits. If there were three participants and you tested 12 decimal places, the total number of digits would be 36. If there were four participants, the total digits would be 48.) Was your hypothesis correct? Could one group that used mnemonics recall the numbers of pi significantly better than the other group? How did the mnemonic groups compare to the control. Were there one or two participants who were especially good at recalling the numbers? Consider why certain mnemonic devices may help people with memory recall. Write a paragraph summarizing your findings and explaining whether they support your hypothesis.
Change the Variables Here are ways to vary this experiment:
• Use different types of mnemonic devices, such as associating each number with a letter or object. • Test the type of people, using the same memorizing device. Will children show better memory retention than adults? • Change what is memorized; use a group of words or science terms, such as the names of the bones in our skeleton. 704
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EXPERIMENT 2 False Memories: How can memories be influenced? Purpose/Hypothesis Sometimes, the brain can
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
lead people to remember things that did not actually occur. This is called false memory. One • the length of time witnesses are watchway a false memory can form is if a memory is ing the scene ‘‘planted’’ or suggested to the person who is • background noise and activity recalling the memory. In this experiment, you • the questions will test how false memories can be created. In other words, the variables in this experiment You will tell several helpers that you want to are everything that might affect the witnesses find out if you can recreate a crime scene from memory. their description. Set-up a scene in which there is activity and color: A person wearing colorful clothing and holding a bag comes into the room and places two to three items in the bag. The person will be wearing a large, colorful band-aid or other item on one hand. The ‘‘witnesses’’ will watch the scene. By asking some witnesses a leading question that suggests the band-aid was on the opposite hand, you can determine if each witness will retell the scene with the false memory. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of false memory. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘False memories can form from a misleading suggestions.’’ In this case, the variable you will change will be the planting of the memory, and the variable you will measure will be asking or not asking a leading question. You expect that when you ask a misleading question, you implant a false memory. Experiment Central, 2nd edition
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Level of Difficulty Easy/moderate.
How to Experiment Safely
Materials Needed
There are no safety hazards in this experiment.
• 6 witnesses, you can have more but try not to have less than 4 • 1 helper • bright shirt or other clothing for the helper
• bag or purse • pen and notebook • colorful accessory to place on helper’s arm (large band aid works well) Approximate Budget $0. Timetable Approximately 30 minutes, depending upon the number of
participants. Step-by-Step Instructions
1. Gather all your witnesses and tell them you want to see if they can recreate the scene and suspect for an experiment you are doing on forensics. 2. Have the helper put the colorful band aid in a prominent place on the right arm before entering the room. 3. Have the helper enter the room, place several small room items in the bag and leave. 4. Ask your witnesses not to talk about the scene and question each witness individually in a separate room. 5. Ask the first witness a series of questions: For example: What did the suspect take? In what order were the items taken? What color hair did the suspect have? What color clothes was s/he wearing? At the end of your questioning, ask: What color band-aid was the suspect wearing on his/her left arm? 6. Write down all the answers and repeat the answers, clearly stating the color of the band aid on the left arm, if the witness did not correct you. 7. Repeat these questions for half of the witnesses. 8. Repeat the questions for the other half of the witnesses, except in place of the misleading question ask directly: What arm was the band-aid on? What color was the band aid? 706
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9. When everyone is back together talk about what people remembered. Bring up the fact, if true, that some of the witnesses said the band aid was on the left arm. Do they still remember it that way? Summary of Results Did the witnesses who
were asked directly to recall the band aid remember it more accurately? Did the witnesses recall the color more than the placement? Were there certain memories that all the people recalled? When the witnesses were told that others remembered the placement of the band aid on a different arm, did they revise their memory? Write a summary of your results. Change the Variables You can vary this experiment in several ways.
Step 3: Have the helper enter the room, place several small room items in the bag and leave. I LL UST RA TIO N BY TEM AH N EL SON .
• Try varying the ages of the ‘‘witnesses.’’ Are younger people more likely to accept a false memory than adults? • Change the activity of the helper, to test how a more or less active scene will affect false memories. • Change the amount of time of the scene.
Design Your Own Experiment How to Select a Topic Relating to this Concept Memory is such a
fundamental part of our lives that studying it is important. You might decide to research the different forms of memories and what causes events to become memorable. Consider the ways that you use the different types of memory on a daily basis. When you instinctually step over a hole in the sidewalk, consider how your memory compares to what a small child would do? You might also what to investigate how memories are retained. Check the Further Readings section and talk with your science teacher to gather information on memory questions that interest you. You might also want to consider talking with someone who is a physician or involved in brain research. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure Experiment Central, 2nd edition
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Troubleshooter’s Guide There should be no major problems with this experiment. Recall can vary depending upon the person. The more people you conduct this experiment on, the better the chance you will have clear results.
what question you are answering, what your are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand.
• State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results It’s always important to write down data and ideas you gather during an experiment. Keep a journal or record book for this purpose. If you keep notes and draw conclusions from your experiments and projects, other scientists could use your findings in their own research. Related Projects Memory-related projects or experiments can go in
many different directions. For example, you might conduct experiments on what leads a sensory memory to transfer into a long-term memory. You might investigate what techniques help you or your classmates memorize facts or formulas. You could investigate how factors that relate to influencing memory. You could also experiment with memory in animals, such as cats, dogs, and insects. Do certain animals have longer memories than others? For a research project, you could also conduct a research project on memory loss: the types of amnesia and causes.
For More Information DiSpezio, Michael A. How Bright Is Your Brain?: Amazing Games to Play with Your Mind. New York: Sterling Pub. Co, 2004. Games and simple activities that explore the brain. The Exploratorium. Memory. http://www.exploratorium.edu/memory (accessed on May 19, 2008). Articles and webcasts from a museum exhibit. 708
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‘‘Memory Matters.’’ KidsHealth. http://www.kidshealth.org/kid/health problems/ brain/memory.html (accessed on May 21, 2008). Clear information on memory and the brain. Murphy, Pat, et al. The brain explorer: puzzles, riddles, illusions, and other mental adventures. New York: H. Holt, 1999 Brain based experiments and activities. PBS. ‘‘3 D Brain Anatomy.’’ The Secret Life of the Brain. http://www.pbs.org/wnet/ brain/3d (accessed on May 21, 2008). A three dimensional tour of the brain.
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n 1675, Anton van Leeuwenhoek (1632–1723), a Dutch merchant with an interest in science, looked through a microscope at a drop of stagnant water. He had originally built a simple microscope to examine textile threads for the draperies he made. Eventually, as a result of his scientific investigations, he built a more powerful microscope that could magnify objects 200 times. Under such a microscope, van Leeuwenhoek saw that the dirty water was full of tiny living creatures. Before his discovery, the smallest living creatures known were tiny insects. He called the life forms he looked at animalcules, but they would later become known as protozoa and bacteria. Other scientists would also find different life forms under the microscope and give them specific names. In time, the term microorganisms would be used to describe all microscopic forms of life.
Microorganisms come in a wide range of shapes but are too tiny to see with the naked eye. PH OTO RE SEA RC HER S I NC.
Connecting bacteria to disease Van Leeuwenhoek’s animalcules had an active life, scurrying around by means of small whip-like tails or by expelling streams of fluid. The bacteria he observed were quieter. They mostly lay about and multiplied. It was Louis Pasteur (1822–1895), a French chemist, who pieced together the connection between disease and these microorganisms. In the 1850s, while Pasteur was a professor and dean at the University of Lille in France, he helped a man who wanted to know why some of his sugar-beet juice, which was being distilled for alcohol, was going bad. What Pasteur discovered were rodlike organisms in the bad batches. They were bacteria, which multiply quickly. In his experiment, he found that heat killed these microorganisms. Pasteur applied his theory to the wine industry and showed wine growers in his hometown 711
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that bad-tasting wine occurred when bacteria fell into wine as it was being bottled. Pasteur advised them how to heat bottled wine just enough to kill bacteria. This method, known as pasteurization, is still used in the wine and milk industries. Between 1865 and 1870, Pasteur also discovered what was killing off France’s silkworms. Under a microscope, he saw microorganisms infecting the sick silkworms as well as the leaves they were eating. After Pasteur recommended that the infected silkworms and leaves be destroyed, the unaffected ones thrived. These incidents supported Pasteur’s germ theory of disease, that microorganisms cause diseases. He advanced the field of bacteriology, the study of different groups of bacteria.
Louis Pasteur discovered the link between disease and bacteria. L IBR AR Y O F C ONG RE SS.
Penicillin mold growing in a culture. PHO TO R ES EAR CH ERS I NC.
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These little guys do a lot Tiny microorganisms are basically everywhere—in the air, in your body, in your cat’s or dog’s fur, and in the soil. Bacteria are the smallest single-celled organisms. To help us see them, today’s microscopes can magnify subjects up to 2,000 times. That’s ten times stronger than the microscope van Leeuwenhoek developed, which was quite an accomplishment for his time. We usually group all microorganisms together as disease-carrying germs, but many are important to life functions. Microorganisms are categorized into five major groups: bacteria, such as salmonella; algae, such as blue-green algae; fungi, such as yeast; protists, such as amoebas; and viruses, such as chickenpox. Microorganisms are essential in the production of antibiotics, pickles, cheeses, and alcoholic beverages. Yeasts, which are in the fungi group, are used in bread and cheese making. The fungi group includes a mold called penicillin, which is an antibiotic. Bacteria, protozoa, and fungi feed on dead, decaying organisms, such as the organic material placed into composters. Experiment Central, 2nd edition
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We cannot see microorganisms with the naked eye unless they multiply. Conducting some experiments will put us in touch with these amazing living creatures.
EXPERIMENT 1 Microorganisms: What is the best way to grow penicillin? Purpose/Hypothesis Penicillin is a microscopic
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type and age of the fruit • the amount of bruising of the fruit • temperature of the environment • amount of light reaching the fruit
mold that grows on fruit. It looks green and • humidity of the environment powdery and is shaped like a small paint brush In other words, the variables in this experiment when viewed under a microscope. The word, are everything that might affect the growth of penicillin, in fact, means ‘‘small brush’’ in Latin. penicillin mold on the fruit. If you change more Early writing was often done with a small, finethan one variable, you will not be able to tell which variable had the most effect on mold pointed brush, and the English words pen and growth. Citrus fruits are the best source for this pencil are also derived from this Latin word. mold, so only citrus fruit will be used. In this experiment, you will determine the best growing conditions for the penicillin mold. You will place one set of fruit in a warm location and another set in a cool location. The difference in the amount of mold that grows will tell you whether temperature affects penicillin growth. To begin the experiment, use what you know about mold growth to make an educated guess about the effect of temperature. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: A moldy lemon (a small inset • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
shows how mold looks under a microscope). GA LE G ROU P.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Penicillin mold will grow more rapidly and produce more visible mold under warm conditions.’’ Experiment Central, 2nd edition
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WORDS TO KNOW Animalcules: Life forms that Anton van Leeuwenhoek named when he first saw them under his microscope; they later became known as protozoa and bacteria. Bacteria: Single-celled microorganisms that live in soil, water, plants, and animals and that play a key role in the decaying of organic matter and the cycling of nutrients. Some are agents of disease. Bacteriology: The scientific study of bacteria, their characteristics, and their activities as related to medicine, industry, and agriculture. Colony: A mass of microorganisms that have been bred in a medium. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Cultures: Microorganisms growing in prepared nutrients. Germ theory of disease: The belief that disease is caused by germs. Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/ or experiment.
Lactobacilli: A strain of bacteria. Medium: A material that contains the nutrients required for a particular microorganism to grow. Microbiology: Branch of biology dealing with microscopic forms of life. Microorganisms: Living organisms so small that they can be seen only with the aid of a microscope. Pasteurization: The process of slow heating that kills many bacteria and other microorganisms. Penicillin: A mold from the fungi group of microorganisms; used as an antibiotic. Protists: Members of the kingdom Protista, primarily single-celled organisms that are not plants or animals. Protozoa: Single-celled animal-like microscopic organisms that live by taking in food rather than making it by photosynthesis. They must live in the presence of water. Variable: Something that can affect the results of an experiment.
In this case, the variable you will change is the temperature of the environment, and the variable you measure is the amount of visible mold that grows. Level of Difficulty Easy/moderate. Materials Needed
• 2 cotton balls or small sponges • 2 oranges, about equally ripe • 2 lemons, about equally ripe 714
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• • • • • •
2 clear plastic bags (gallon size) bowl twist ties water use of a refrigerator microscopes and slides are optional
How to Experiment Safely Wash your hands after performing the experiment.
Approximate Budget $2 for fruit and bags. Timetable 20 minutes to set up, and one or two
weeks to complete. Step-by-Step Instructions
1. Bruise the fruit by rubbing it on the floor and dropping it. This helps the mold to invade the tough skin of the fruit. 2. Place the fruit in a bowl for one to three days. Leave the bowl out in the open where it will come into contact with mold in the air. 3. In one bag place one orange, one lemon, and one moist cotton ball. (The moist cotton ball raises the humidity.) 4. Repeat Step 3 for the other bag. 5. Tie each bag closed with a twist tie. 6. Place one bag in the refrigerator and the other in a warm place. 7. Every day, record any changes you observe. 8. After two weeks, open the bags and examine the fruit. 9. If you have access to a microscope, smear a small sample of mold on a slide and view it.
Steps 3 and 4: Place one orange, one lemon, and one moist cotton ball in clear plastic bag. GA LE GR OU P.
Step 8: After 2 weeks, open the bags and examine the fruit for mold. G AL E GR OUP .
Summary of Results Compare the mold growth
in each plastic bag. The bag in the warmer place should show considerably more growth because mold thrives in warm environments. Photograph your final results or draw a picture of what grew. Change the Variables You can conduct several similar experiments by changing the variables. For example, you can vary humidity by varying Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: Neither bag showed any mold growth after two weeks.
the number of soaked cotton balls or sponges. You could also change the fruit. Remember, if you change more than one variable at a time, you will not be able to tell which variable had the most effect on mold growth. Modify the Experiment This experiment exam-
ines the best temperature for mold growth. You can add to this experiment by measuring other Possible cause: There was not enough humidity environmental conditions that could affect mold present in the bags. Remoisten the cotton balls growth. Factors you can examine include light and allow the experiment to run for an addiand air. From what you know about how organtional two weeks. isms live and grow, make a hypothesis about how light and air will affect the amount of mold that will grow on the fruit. Follow Steps 1 and 2 in the experiment, adding four more oranges and four lemons. Prepare four addition bags containing an orange, lemon, and moist cotton ball. You should have six bags. In addition to placing bag 1 in the refrigerator and bag 2 in a warm place: Place bag 3 in a drawer or other dark area and bag 4 in a well-lit area, such as by a window; Wrap plastic wrap around each of the two fruits in bag 5 and leave bag 6 in a room temperature environment. The plastic wrap will seal the fruit from air. After two weeks examine the fruit in all the bags. Make a chart of each of the environments and note or draw the amount of mold growth in each setting. Was your hypothesis correct? You can measure mold growth on each of these environments separately using different fruits.
EXPERIMENT 2 Growing Microorganisms in a Petri Dish Purpose/Hypothesis Microbiologists often breed microorganisms in
large quantities called colonies. For this experiment you will prepare the medium needed to grow colonies of microorganisms. In this experiment you will change the source of the microorganisms. You will prepare the same medium for all samples. This medium is rich in nutrients needed by most microorganisms. You will then obtain microorganisms from different sources and observe their growth in the medium. To begin the experiment, use what you know about the source of microorganisms to make an educated guess about whether different types 716
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will grow in the same medium. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Different kinds of microorganisms can be obtained in many places, and all will thrive in a nutrient-rich medium to produce visible growth that varies in amount, color, and texture.’’ In this case, the variable you will change is the source of the microorganisms, and the variable you measure is the amount, color, and texture of the visible growth that appears.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of medium • the temperature of the environment • the humidity of the environment • the amount of light reaching the petri dishes • the sources of the microorganisms In other words, the variables in this experiment are everything that might affect the type and growth of microorganisms. If you change more than one variable, you will not be able to tell which variable had the most effect on the amount, color, and texture of the visible growth.
Level of Difficulty Moderate. (This experiment requires special attention to
cleanliness. Sterile conditions are ideal but almost impossible to obtain without training and special equipment.) Materials Needed
• 6 petri dishes and lids (If petri dishes are not available, use small bowls and clear plastic wrap.) • 1 package unflavored gelatin • ¼ cup (60 milliliters) sugar • 1 tablespoon (15 milliliters) salt • 1 tablespoon (15 milliliters) pork or beef, finely ground How to Experiment Safely • 1½ quart (1.5 liter) pot with a cover • 1 quart (1 liter) water This experiment requires boiling hot water to • tongs cook gelatin and to sterilize the equipment. Ask Approximate Budget $10 for petri dishes and
an adult to help you when using the stove or when handling boiling water.
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Timetable 90 minutes to prepare, and one to two weeks for results. Step-by-Step Instructions
Steps 1 and 2: When the water is boiling, use tongs to submerge the petri dishes into the water for 1 minute. GA LE GRO UP.
1. In the pot, boil one quart of water. 2. When the water is boiling, use tongs to submerge the petri dishes into the water for one minute. 3. Remove the petri dishes from the water. Place on the counter or table. Place the lids on top to keep the inside clean. Allow them to cool. 4. Follow directions on the package to prepare gelatin. 5. Add sugar, salt, and finely ground meat. 6. Bring gelatin to quick boil and remove from the heat.
Steps 10 to 12: Example of collecting microorganisms from the inside of the mouth. Be sure to collect samples from five different sources. GAL E GR OU P.
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Step 15: Examples of microorganism colonies from mouth samples in petri dish after two weeks. GA LE G RO UP.
7. Cover and cool for three to five minutes. 8. Ask an adult to help you fill the six petri dishes halfway with the gelatin medium. Cover each dish immediately. 9. Cool one hour before moving. 10. To collect microorganisms from the environment, gently wipe a surface with a cotton swab. Here are some suggestions for samples: doorknob, arm, inside of mouth, floor, used cup, leftover food, dirt. Wipe five different surfaces—one for each of five petri dishes. 11. Gently rub each used swab on the gelatin in a dish. Do not touch more than one swab to a dish. You will not be able to see the microorganisms on the cotton swab. Trust that something is there. 12. Mark each dish with the date and the source of the sample. Cover each dish and seal it with tape. 13. For a control experiment, leave one petri dish untouched. Label it ‘‘control’’ and seal it. 14. Keep the petri dishes together in a dark, warm area. Allow dishes to sit one to three weeks. 15. After the petri dishes show fuzzy gray mounds or slimy blobs, make a drawing of the microorganisms. 16. Do not open dishes or handle any microorganisms. Throw them away after the experiment. Summary of Results Because of the complexity and variety of micro-
organisms, you cannot identify specific species. However, you should draw and describe your findings to share with others. Write a summary. Did colonies of microorganisms develop in all of your petri dishes? Were Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
they different in color and texture? Did any growth appear in the control dish? Don’t be surprised if it did. Even the air contains microorganisms. Were you able to support your hypothesis?
Change the Variables After you have determined and recorded the amount, color, and texture of growth from various sources, repeat the experiPossible cause: The conditions they need to grow are not in place. If after two weeks no ment and change the amount of light or the growth is evident, try leaving the dishes in a temperature or the humidity. Do some microwarmer environment. organisms grow more or less than before? Do they appear different from before? Remember, if you change more than one variable at a time, you will not be able to tell which variable had the most effect on growth. Problem: The microorganisms are not growing.
Design Your Own Experiment How to Select a Topic Relating to this Concept Microorganisms are
everywhere. They are covering your body at this very moment, so you do not have to look far to find them. An experiment with microorganisms could include topics such as culturing or identifying their characteristics. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on microorganism questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of the microorganisms or procedures might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. 720
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• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results The most important part
of the experiment is the information gathered from it. Scientists working 400 years ago made discoveries in science that still help us today. In the fruit experiment, you cannot save the fruit to display or stop the decaying process with refrigeration. The results need to be recorded in drawings, photos, or notes. All these pieces of information you gathered then should be summarized into a conclusion or result. Related Experiments Microbes are simple organisms with simple needs,
such as air (in some cases not even air), water, warm temperatures, and food. By putting microorganisms on a petri dish and adding a drop of different chemical cleaners, you can find out what substances keep them from growing. If it is safe, you may want to use that chemical when you wash. That’s the idea behind antibacterial soaps.
For More Information American Museum of Natural History. ‘‘The Microbe Size O Meter.’’ Meet the Microbes! http://www.amnh.org/nationalcenter/infection/01 mic/01d size 01.html (accessed on March 2, 2008). A look at the sizes of different microorganisms relative to familiar objects. ‘‘Bacteria cam.’’ Cells alive! http://www.cellsalive.com/cells/bactcell.htm (accessed on March 2, 2008). Bacteria cell structure and images of real time bacteria growing. Dashefsky, H. Steven. Microbiology: 49 Science Fair Projects. Austin, TX: Tab Books, 1994. Outlines science projects that are well suited for this topic. Lang, S. Invisible Bugs and Other Creepy Creatures That Live With You. New York: Sterling Publishers, 1992. Describes different microorganisms, their functions, and purpose. ‘‘Penicillin: The true story?’’ Timeline Science. http://www.timelinescience.org/ resource/students/pencilin/pencilin.htm (accessed on March 2, 2008). A brief history of the many people who helped develop the antibiotic penicillin.
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Water and sand will appear stable and mixed when stirred, but over time the sand will settle out and some of the water will become clear again. PH OTO RE SEA RC HER S I NC.
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ost of the substances we see around us are mixtures, combinations of different elements or compounds. The components of some mixtures—such as sandy water, which consists of grains of sand suspended in water—can easily be separated or will naturally settle. Others, such as salty water, form more permanent mixtures. How can we separate different kinds of mixtures into their component parts? Mixtures that settle—separate out naturally—are called suspensions. Sandy water is a good example of a suspension. Stirring will mix the sand and the water, but over time, the denser sand will fall to the bottom of the container, and a clear layer of water will appear above it. A mixture whose parts remain stable and remain mixed over time is called a solution. Solutions commonly consist of a solid solute that is dissolved in a liquid solvent. The molecules of the solute are evenly dispersed and very small. Salt water, lemon juice, and antifreeze are all solutions. These mixtures will remain mixed even when left standing for a long time. A third type of mixture is a colloid, in which relatively large molecules of one substance remain mixed and stable due to electric charge repulsions. This repulsion occurs because colloidal particles contain an equal number of positive and negative ions (charged atoms), but the negative ions form a layer surrounding the particle. Thus, the particles are electrically neutral but still tend to repel one another to spread out evenly through the 723
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Although colloidal particles are electrically neutral, they possess an outer layer of negative ions and so repel one another. G AL E GRO UP.
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dispersing medium. Milk, gelatin, clay, and smoke are all colloids that combine solids, liquids, and gases in different ways. How mixtures can be separated It is often necessary to separate mixtures into their component parts. Separating a suspension can be fairly simple. Suppose you lose a ring in a bucket of sandy water. Once the denser sand and the ring have settled to the bottom of the bucket, you can carefully pour off the clear water into another container. This process is known as decanting. Next, you can pour the soupy mixture of sand, water, and your ring into a strainer large enough to let the sand and water pass through. This process, known as filtration, will separate the ring from the other components of the suspension. Another means of separating mixtures is the centrifuge, which spins the mixture at high speeds until the more-dense particles are forced outward by centrifugal force and separate from the less-dense solvent. Separating a solution is more difficult. For example, filtering salt out of seawater is possible only with extremely high pressure and very precise ‘‘molecular’’ filters. However, there are other ways to separate pure water from seawater. Raising the temperature of the solution until the water boils, capturing the steam and then cooling it until it condenses will yield pure liquid water and solid solute. This process is called distillation. Another process is called evaporation, which allows the vaporized water to escape, yielding only the solute. Colloids can also be separated into their component parts. When a colloid is heated, the repelling force between the colloidal particles is no longer great enough to keep the heated particles from bouncing into each other and bonding together. They gradually form clumps and settled out of the mixture. Causing colloidal particles to gather is called coagulation. It can be seen clearly in milk, which forms clumps of fat, called curds, when heated. Knowing how to separate mixtures into their component parts is crucial in both science and everyday life. Removing spaghetti from a pot of boiling water is not easy without filtration. Coagulation allows ionic or electrostatic cleaners to remove dust and soot from the air we breathe. A centrifuge is used to separate blood into its vital parts without Experiment Central, 2nd edition
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Distillation uses boiling and condensing to separate a solute from water. GAL E GR OU P.
damaging them. In the first experiment, you will identify various mixtures as suspension or solutions by applying different separation techniques. Although liquid colloids can often behave just like suspensions, there is a simple method for distinguishing between them. A light beam passing through a solution will not encounter any particles large enough to deflect it, and thus will not be visible. Colloidal particles are not dissolved and can be quite large compared to the particles in a suspension. A light beam passing through a colloid will be visible as it is dispersed by these particles. This phenomenon is called the Tyndall effect. In the second project, you will use the Tyndall effect to distinguish a colloidal mixture from a solution.
A light beam passing through a colloid will be visible, while one passing through suspension will not. This phenomenon is called the Tyndall effect. P HOT O RES EA RC HER S I NC.
EXPERIMENT 1 Suspensions and Solutions: Can filtration and evaporation determine whether mixtures are suspensions or solutions? Purpose/Hypothesis In this experiment, you will
attempt to separate the component parts of Experiment Central, 2nd edition
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WORDS TO KNOW Centrifuge: A device that rapidly spins a solution so that the heavier components will separate from the lighter ones. Coagulation: The clumping together of particles in a mixture, often because the repelling force separating them is disrupted. Colloid: A mixture containing particles suspended in, but not dissolved in, a dispersing medium.
smaller ones that can slip through the filter’s openings. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Ion: An atom or group of atoms that carries an electrical charge—either positive or negative— as a result of losing or gaining one or more electrons.
Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group.
Mixtures: Combinations of different elements or compounds.
Decanting: The process of separating a suspension by waiting for its heavier components to settle out and then pouring off the lighter ones.
Solute: The substance that is dissolved to make a solution and exists in the least amount in a solution, for example sugar in sugar water.
Distillation: The process of separating liquids from solids or from other liquids with different boiling points by a method of evaporation and condensation, so that each component in a mixture can be collected separately in its pure form.
Solution: A mixture of two or more substances that appears to be uniform throughout.
Electric charge repulsion: Repulsion of particles caused by a layer of negative ions surrounding each particle. The repulsion prevents coagulation and promotes the even dispersion of such particles through a mixtures.
Solvent: The major component of a solution or the liquid in which some other component is dissolved, for example water in sugar water. Suspension: A temporary mixture of a solid in a gas or liquid from which the solid will eventually settle out.
Evaporation: The escape of liquid vapor into the air, yielding only the solute.
Tyndall effect: The effect achieved when colloidal particles reflect a beam of light, making it visible when shined through such a mixture.
Filtration: The use of a screen or filter to separate larger particles that cannot slip through from
Variable: Something that can affect the results of an experiment.
several mixtures using two different methods. The result of each method will determine the nature of the mixture. One mixture will consist of sand in distilled water, and the other will be lemon juice in distilled water. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of mixtures. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: 726
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• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A solid mixed into a liquid may be separated by filtration if the mixture is a suspension, such as sand in water, or by evaporation if the mixture is a solution, such as lemon juice in water.’’ In this case, the variable you will change is the component mixed with water, and the variable you will measure is ability of a specific method to separate the components. You expect that filtration will separate the sand, thus showing it is a suspension, and evaporation will separate the lemon juice, thus showing it is a solution.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of mixtures tested • the purity of the mixed components • size of the openings in the filter • the temperature of the mixture In other words, the variables in this experiment are everything that might affect the ability of a component to be separated from a mixture. If you change more than one variable, you will not be able to tell which variable had the most effect on the separation. You will also set up a control experiment of pure water, with no substances mixed into it, to which you will apply the same methods of separation for comparison.
Level of Difficulty Moderate, because of the time
involved and the care required when using a heat source. Materials Needed
• • • • • • • • • • •
2 small saucepans, about 5 inches (12.5 centimeters) in diameter heat source (stove or a Bunsen burner) 4 clear 1-quart (1-liter) wide-mouth bottles 6 lemons 3 cups distilled water 1 cup (225 grams) of sand knife tablespoon funnel 3 conical paper coffee filters large wooden cutting board
Approximate Budget Less than $5, assuming a Bunsen burner or a stove
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How to Experiment Safely This experiment involves heat and boiling liquid. These steps should be performed with adult supervision and with proper protection, including potholders. Do not substitute other mixtures for those in this experiment without consulting your teacher. Many substances can ignite or give off toxic fumes when heated.
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Timetable The first stage of this experiment requires at least 1 hour for set-up, filtration, and partial evaporation by boiling. The second stage, evaporation without boiling, may take several hours or days, depending upon how much liquid remains in the saucepans. Step-by-Step Instructions
1. Carefully cut the lemons in half and squeeze their juice into a bottle. Do not remove any solid particles or seeds from the juice. Add 1 cup of distilled water and set the bottle aside. Pour 1 cup of distilled water into another bottle and stir in 3 tablespoons of sand. In a third bottle, place 1 cup of distilled water. This will be your control experiment. Filter the lemon juice. Place a coffee filter inside the funnel, hold the funnel over a bottle, and slowly pour the lemon juice into the funnel. The liquid that passes through the filter should appear uniform but will not be clear. Discard the used filter and clean the funnel and bottle, rinsing them with distilled water. Prepare a chart on which you will record your observations. Your chart should look something like the illustration. Stir each of the three samples, making sure to clean the spoon or stirrer after each one. Note the appearance of each sample on your chart. Allow the mixtures to settle for several minutes. In the next column on your chart, note any change in appearance. Line the funnel with another coffee filter and place it over the opening of the fourth bottle. Pour the mixture of water and sand into the funnel. Allow the liquid to filter into the bottle. Note any change in appearance on your chart. (See illustration.) Pour the lemon-juice mixture into a saucepan and place the saucepan on the heat source. Do not leave this sample unattended. Observe the sample as it evaporates. Do not allow the liquid to evaporate completely! When only a few tablespoons of the liquid remain, remove the saucepan from the heat and place it carefully on the wooden cutting board. (Remember to turn off the heat source when not using it and to be cautious around the saucepan, which will cool slowly.) Experiment Central, 2nd edition
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Step 5: Sample data chart for Experiment 1. GA LE G ROU P.
11. Repeat step 9 with your control liquid (the distilled water sample) in the second saucepan. 12. Place both saucepans in a safe place. Do not cover them. The liquids must continue to evaporate for you to see any dissolved solids. This final evaporation may take hours or even days, depending on how much liquid is left.
Step 8: Pour the mixture slowly and carefully into the funnel, as it may not drain quickly through the coffee filter. GA LE GRO UP .
13. Check the samples periodically. Once the liquid in the lemon juice has completely evaporated, note on your chart whether any visible solids have been left behind on the surface of the saucepan. Also monitor your control experiment. It should leave no significant solid residue in the pan. If it does, then your results cannot prove your hypothesis. Summary of Results Examine your results and determine whether your hypothesis is true. If a solid in a mixture is removed by your filtration method, then it was in suspension, and not in solution. If a solid is not removed by filtration Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The sand and water sample will not pass through the filter. Possible cause: The sand is preventing the water from passing through the funnel. Set the apparatus aside and allow time for the water to filter slowly through the sand and the filter. This may take awhile.
but is removed by evaporation, then the solid was in solution. Compare your results for the control, the sand mixture, and the lemon mixture. Write a summary of your findings. Change the Variables You can conduct similar
experiments by changing the variables. For example, try different mixtures. Do not use any solvent other than water. Compare your results for mixtures using salt, flour, gelatin, bouillon cubes, or effervescent antacid tablets. You can also experiment with the effect of temperature. Some solids, such as sugar, will dissolve more easily when the water is hot than when it is cool.
PROJECT 2 Colloids: Can colloids be distinguished from suspension using the Tyndall effect? Purpose/Hypothesis In this project, you will demonstrate how the Tyn-
dall effect can be used to show that a mixture that looks like a solution is actually a colloid. Level of Difficulty Moderate. Materials Needed
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flashlight black construction paper tape 5 pint (0.25 liter) heavy cream lemon juice 12-ounce (0.33-liter) soda 1 quart (1 liter) distilled water 5 teaspoon measuring spoon 5 clear glass jars
Approximate Budget $10 to $15. (Most materials may be found in the
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Timetable Less than 1 hour. Step-by-Step Instructions
1. Pour 1 cup of distilled water into each jar. Add 0.5 teaspoon of heavy cream to the first jar and stir vigorously. Clean the spoon with distilled water.
How to Experiment Safely Do not change the substances used in these mixtures without first checking with your teacher.
2. Add 0.5 teaspoon of lemon juice, salt, and soda to the second, third, and fourth jars respectively. Remember to stir each one and to wash the spoon to avoid mixing the samples. The fifth jar, the control, should contain only distilled water. 3. Curl a sheet of construction paper into a cone, leaving a 1-inch (2.5-centimeter) diameter opening. Tape the cone to the flashlight so it narrows the beam through the small opening. 4. Darken the room or an area of the room. (Total darkness is not necessary or safe.) Set the control jar of distilled water on a flat, clear surface. Shine the light through the jar from one side and observe that the light does not illuminate the water itself. 5. Try shining the light through the milk mixture. If the path of the beam is visible in the liquid, the mixture is a colloid. If the beam is not visible, the mixture is a solution.
Step 7: Construct a shield to block other illumination from reaching the jar. GA LE GR OU P.
6. Repeat Step 5 with the other mixtures. 7. If you find it difficult to determine when the light beam is being scattered, construct a shield to block other illumination from reaching the jar. Curl a sheet of construction paper into a tube. Cut an opening at the front through which you can observe, and a hole at the side through which you can shine the light beam. Place the tube over the jar and repeat Steps 4 and 5 to see the difference between a light beam when it is scattered and when it is not scattered. 8. Create a chart to show the results of your demonstration, noting which mixtures are colloids and which are solutions. Experiment Central, 2nd edition
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Step 8: Data chart for Project 2. GAL E GR OU P.
Summary of Results Remember that those who view your results may not have seen the project demonstrations performed, so you must present the information you have gathered in as clear a way as possble. Illustrations can show viewers the steps involved in determining whether a mixture is a solution or a colloid.
Design Your Own Experiment How to Select a Topic Related to this Concept The nature of mixtures
can provide topics for fascinating experiments and projects. Try measuring the changes that occur in the temperature at which water boils and when salt is added to it. You might test other methods of purification. Can you construct a simple centrifuge to separate suspensions? Can you purify salt water by freezing as well as by boiling? Finding the answers to these questions can become the basis for simple yet informative projects. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on mixture questions that interest you. Remember to check with a knowledgeable person before experimenting with unfamiliar materials. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. 732
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• State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In
the experiments included here and in any experiments you develop, you can try to display your data in more accurate and interesting ways. For example, in the colloid project, you could redesign the demonstration to show the light-beam test simultaneously for all of the jars. Remember that those who view your results may not have seen the experiment performed, so you must present the information you have gathered in as clear a way as possible. Including photographs or illustrations of the steps in the experiment is a good way to show a viewer how you got from your hypothesis to your conclusion. Related Projects The isolation of substances in
mixtures is an important and challenging part of chemistry. Other methods besides those described here can provide ideas for projects and experiments. For example, mixtures of two solids can be separated by using magnetism. Mixtures of two liquids that have different boiling points can be separated using distillation. Investigate these methods in the books listed in Further Readings, and try incorporating them into other projects.
Troubleshooter’s Guide This project is fairly simple, so not many problems should arise. However, when doing experiments involving mixtures, be aware that a number of unseen variables—such as temperature and impurity of substances— can affect your results. When mixing substances for a demonstration or experiment, you must keep the mixing containers and utensils clean. Even tiny impurities in a mixture can drastically alter your results. Any experiment you perform must be carefully designed to avoid letting unknown variations change the outcome and lead you to an incorrect conclusion. Here is a problem that may arise during this project, some possible causes, and ways to remedy the problem. Problem: All of the mixtures appear to scatter the light beam. Possible causes: 1. Too much light is reaching the back, top, or sides of the jar. Try isolating the jars by constructing the light shield described in step 7. 2. Your samples have become corrupted. Prepare new samples, making sure to clean the spoon between each mixture.
For More Information Andrew Rader Studios. ‘‘Mixture Basics.’’ Rader’s Chem4kids.com http:// www.chem4kids.com/files/matter mixture.html (accessed on February 18, 2008). Information on the chemistry of mixtures. Experiment Central, 2nd edition
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BBC. ‘‘Mixtures.’’Mixtures. Schools. Science: Chemistry. http://www.bbc.co.uk/ schools/ks3bitesize/science/chemistry/elements com mix 6.shtml (accessed on February 18, 2008). Basic information on the chemistry of mixtures. Gillett, Kate, ed. The Knowledge Factory. Brookfield, CT: Copper Beech Books, 1996. Provides some fun and enlightening observations on questions relevant to this topic, along with good ideas for projects and demonstrations. Kurtus, Ron. ‘‘Mixtures.’’ School for Champions. http://http://www.school for champions.com/chemistry/mixtures.htm (accessed on February 18, 2008). Basics of mixtures versus compounds. Ray, C. Claibourne. The New York Times Book of Science Questions and Answers. New York: Doubleday, 1997. Addresses both everyday observations and advanced scientific concepts on a wide variety of subjects. Wolke, Robert L. What Einstein Didn’t Know: Scientific Answers to Everyday Questions. Secaucus, NJ: Birch Lane Press, 1997. Contains a number of entries relevant to mixtures and solutions.
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f you were to view Earth from up high, you would see a planet covered with mountains. A mountain is an area that rises above its surrounding area and has a peak. It is estimated that about one-fifth of the Earth’s land contains mountains. There are even more mountains underwater. Mountains are an important source of our freshwater. They contain unique animals, plants, and ecosystems where many peoples make their homes and livelihood. Mountains also are a source of recreation and striking beauty.
Mountain stretches and peaks There is no defined height a landform needs to be before it is called a mountain. In general, a mountain is taller than a hill. Mountains exist in ranges, a chain of mountains that are next to one another. A mountain range can stretch for a few miles to thousands of miles. The height of a mountain is typically measured by how far it reaches above sea level. The longest mountain range in the world is the Andes. This chain of mountains in South America runs for approximately 4,500 miles (7,242 kilometers). The Rocky Mountains are North America’s longest mountain range. This series of mountains extends about 3,000 miles (4,828 kilometers), running from Alaska through Canada to New Mexico. There is a point in Colorado where the ‘‘Rockies’’ reach over 14,440 feet (4,401 meters). The Rockies are high, but the tallest mountains are located in Asia. Mount Everest is the world’s tallest mountain. Located along Nepal and Tibet, Mt. Everest has a peak that reaches more than 29,000 feet (8,839 meters). That’s over 5 miles (8 kilometers)! Tip-top formation Mountains all take shape from chunks of rock. The majority of mountains formed from the movement of Earth’s crust (the outer layer of the Earth). Scientists have divided the crust into seven large sections or plates that fit together like an eggshell. There are also many smaller plates. 735
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Mount Everest is the world’s tallest mountain. # AL IS ON WRI GH T/C OR BI S.
The plates can shift, overlap, or move against each other in what is called plate tectonics. The movement of the plates can push the crust upward, forming a mountain. How the plates move determines the shape of the mountain. For example, fold mountains occur when plates push against each other. The crust buckles or ‘‘folds,’’ much like wrinkles, as it lifts. As the folding continues, the mountains continue to grow higher and can take on ridgelike shapes. A fault-block mountain forms along a fault (a crack in the crust). The crust on one side of the fault moves apart from the crust on the other side. One side of the crust is forced upwards in an incline position, leaving one side of the mountain with a steep side and the other having a sloping side.
The crust buckles or ‘‘folds,’’ much like wrinkles, as it lifts. I LLU ST RAT IO N BY TEM AH NEL SO N.
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One side of the crust is forced upwards in an incline position, leaving one side of the mountain with a steep side and the other having a sloping side. IL LU STR AT IO N BY T EM AH NE LS ON.
Mountains are continuously changing shape due to natural weathering and erosion. In general, the taller the mountain, the younger it is. Rain, wind, and mountain rivers can erode (wear down) and move small bits of rocks on the mountain. Waterfalls, which often occur in mountains, will erode rocks. Over time, a sharp peak can become rounded and the mountain shape will change. Life on a mountain Mountains ecosystems generally share some climate rules. The higher you go up a mountain, the colder it becomes. Air molecules near the surface are packed together. As warm air rises above ground the air molecules begin to cool down. The more the air rises, the colder it gets. With more space for the air molecules to move around, the air becomes less dense (fewer air molecules in a certain area). Air higher in the atmosphere is often referred to as thinner. The cold air means mountain tops are cold. Mountains can also capture a lot of precipitation. Precipitation that falls in the form of rain on land will often be snow on the colder mountain top. Mountains can also affect the environment surrounding it. A large mountain can block the wind and rain on one side. It can also cause large shadows, which can lead to less plant and animal life. Rain flowing down a mountain is the source of freshwater rivers. Mountains are home to a diverse range of unique animals and plants. What lives on a mountain depends primarily upon where the mountain is located. The relative warmth makes life more Experiment Central, 2nd edition
MODIS image illustrating the dramatic rainshadow effect of the Andes Mountains in South America on rainfall and vegetation. At left is Chile, which appears quite lush, while Argentina (right) appears dry and brown. # N ASA /C OR BIS .
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WORDS TO KNOW Crust: The hard outer shell of Earth that floats upon the softer, denser mantle.
Leeward: The side away from the wind or flow direction.
Ecosystem: An ecological community, including plants, animals and microorganisms, considered together with their environment.
Mantle: Thick dense layer of rock that underlies Earth’s crust and overlies the core.
Erosion: The process by which topsoil is carried away by water, wind, or ice action. Fault mountain: A mountain that is formed when Earth’s plates come together and cause rocks to break and move upwards.
Mountain: A landform that stands well above its surroundings; higher than a hill. Precipitation: Any form of water that falls to Earth, such as rain, snow, or sleet. Rain shadow: Region on the side of the mountain that receives less rainfall than the area windward of the mountain.
Fold mountain: A mountain that is formed when Earth’s plates come together and push rocks up into folds.
Tectonic plates: Huge flat rocks that form Earth’s crust.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Variable: Something that can affect the results of an experiment.
plentiful at the bottom areas of the mountains. Some cultures live around or near the lower areas of mountains. Mountains in warmer climates, such as North America, are home to bears, lions, and cougars. At higher altitudes, goats, sheep, and smaller animals live. Birds, such as the eagle and condor, can also fly and live in high mountain areas. In the following experiments, you will explore more about mountain formation and about how mountains affect the surrounding climate.
EXPERIMENT 1 Mountain Plates: How does the movement of Earth’s plates determine the formation of a mountain? Purpose/Hypothesis Some mountains are created by the movement of tectonic plates. When these plates come together they can change the make-up of Earth’s surface features. Several elements are involved in affecting the features of a mountain, including the force with which the plates come together, the makeup of the Earth’s rocky outer crust, and the 738
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angle the plates meet. Mountains are often formed by folds or fault break movements. In a fold mountain, the movement of two plates forces rocks upwards into folds. Some rocks are brittle and will not fold or bend. A fault mountain occurs from a break or fracture in the plates. In this experiment you will create a simulation of plate movements and observe the flexibility of the terrain when plates collide in different ways. Plates can collide at even heights, uneven heights, and at angles. A strip of paper will represent a relatively flexible outer crust. A broom straw or spaghetti noodle will represent a hard and brittle outer crust. Which type of crust and movement will result in a fold versus a fault (a break)? To begin your experiment, use what you know about mountains and plate movement to make an educated guess about the formation of mountains. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
What Are the Variables? Variables are anything that might affect the results of the experiment. Here are the main variables in this experiment: • the terrain • the height of the plates • the thickness of the paper • the length of the paper • the force with which the plates move In other words, the variables in this experiment are everything that might affect the movement of the terrain. If you change more than one variable at a time, you will not be able to tell which variable had the most effect on the mountain formation.
How to Experiment Safely There are no safety concerns in this experiment.
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The plates which are even heights and with the paper will create a fold when they collide.’’ In this case, the variables you will change, one at a time, are the type of crust and the angle with which the plates come together. The variable you will measure is the shape of the mountain that forms when the plates meet. If Experiment Central, 2nd edition
Step 4: Slowly slide the books toward each other. IL LUS TR ATI ON B Y TE MA H NEL SO N.
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the paper forms a folded shape you will know your hypothesis is correct. Level of Difficulty Easy to Moderate. Materials Needed
• 6 or more hard bound books, 2 of which are the same height • 2 large paper clips • Strong tape, about 4 inches • Several pieces of broom straws (spaghetti noodles will also work) • 1, 8 ½ inch strip of paper, the weight of copy paper
Step 7: Repeat Steps 4–6, using a piece of straw. ILL US TRA TI ON B Y TE MA H NE LS ON.
Approximate Budget $5. Timetable Approximately 30 minutes. Step-By-Step Instructions
Summary of Results: Use sketches to observe how plates’ heights and movements affect the formation of a mountain. ILL US TRA TI ON B Y TE MA H NE LS ON.
Soft crust (paper) Even plates
Uneven plates
1. Tape a paperclip to the center of each of the two books that are the same width. 2. Lay the books flat on a table or desk about 7 inches (18 centimeters) apart. Have the sides with the paper clips face each other. The books are now representing your plates. 3. Insert the ends of the paper strip into each of the paper clips. 4. Slowly slide the books toward each other. The strip of paper is an area of Earth’s crust. Sketch a picture or make a note of what happens to the crust when the plates move toward each other. 5. Stack the books so that one stack is higher than the other, keeping the books with the paper clips on top. Repeat Steps 2–4. 6. Change the plates so that they are the same height. Repeat Steps 2–4 again, this time moving the plates at an angle as they come Hard crust (straw) together. 7. Repeat Steps 4–6, using a broom handle or spaghetti noodle as the ‘‘crust’’ on these trials.
Angles plates
Summary of Results Use your sketches and obser-
vations to determine how plates’ heights and 740
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movements as well as crust makeup, affects the formation of a mountain. Is a brittle crust more likely to form a fold or a fault? Which existing mountain ranges do your sketches represent? How is the shape of a mountain affected when the plates move towards each other at an angle? Write a paragraph showing your results. Change the Variables You can change one of the
Troubleshooter’s Guide Experiments do not always work out as planned. Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The paper does not form dips.
variables and repeat this experiment. You can change the force with which the plates move and observe how this affects the movement of the crust? You can also alter the crust by adding gravel or fabric between the plates.
Possible cause: If the paper only arches and does not create valleys your paper may be too thick. Try using a thinner paper and repeat the experiment.
EXPERIMENT 2
Possible cause: The noodles you are using may be too brittle. You can try steaming the noodles for a minute, or pluck some straws from a broom handle. Repeat the experiment.
Mountain Formations: How does the height of the mountain have an affect on desert formation?
Problem: The noodle keeps breaking before the plates move together.
Purpose/Hypothesis The formation of mountains can affect the surround-
ing climate and terrain (surface features) of the mountain area. Mountains are often found near deserts, because mountains often obstruct the airflow and ultimately rain in reaching the land bordering the leeward side of a mountain. How the mountain affects the surrounding terrain depends upon several factors, including the height of the mountain and the climate. In this experiment you will be looking at how warm moist air and mountain height affect the formation of a desert. Warm air, which contains moisture, rises into the atmosphere. As it rises, it cools and the moisture ultimately falls as a form of precipitation. Rain clouds often lose most of their moisture before the clouds completely cross the mountain range. In the case of tall mountain ranges, the precipitation can fall on one side of the mountain. The other side or, leeward side receives little to no rain, thus creating a dessert. This effect, called ‘‘rain shadow,’’ can produce a desert behind the mountain. In your experiment, you will create a flow of warm water to simulate the warm air rising and crossing the mountain range. You can observe how the warm air reacts in cool air, which is cool water placed in a dish with Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of the experiment. Here are the main variables in this experiment: • the width of the mountain • the temperature of the water In other words, the variables in this experiment are everything that might affect the size of the air that moves over the mountain. If you change more than one variable, you will not be able to tell which variable had the most effect on mountain formation.
Step 6: Slowly pour the half a cup of hot water into the cup placed in the corner.
‘‘mountains.’’ You will then change the height of the mountain. Does the height of the mountain have an affect on how much of the warm ‘‘air’’ is able to cross to the other side? To begin your experiment use what you know about mountains and deserts to make an educated guess about mountain formation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The height of a mountain has the greatest effect on if a desert is formed on the leeward side of the mountain.’’ In this case, the variable you will change is the height of the mountain, and the variable you will observe is the how great the mass of air is that moves over the mountain. If the mass is less with the taller mountain, you will know your hypothesis is correct. Level of Difficulty Easy to Moderate.
IL LU STR AT ION BY T EM AH N EL SON .
Materials Needed
• • • • • • •
9 13 glass baking dish 2 lbs of modeling clay food coloring (red) glass measuring cup paper cups yard stick hot and cold water
Approximate Budget $8. Timetable Approximately 1 hour. 742
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Step-By-Step Instructions
1. Use the modeling clay to create a ‘‘mounHow to Experiment Safely tain range’’ in the middle of the baking Be sure to use a pot holder and a measuring cup dish. Your first range should be approxiwith a handle for the warm water. mately 1.5 inches (3.8 centimeters) wide and reach half way up the baking dish. Stretch the mountains to either side of the glass dish. 2. Poke 10 holes in the sides of the cup near the bottom, no higher than the depth of the baking dish. 3. Fill the baking dish with cold water to about a half-inch from the top. 4. Add three drops of red food coloring to one-half cup of hot water. 5. Place the paper cup, with holes, in the corner of one side of the dish. 6. Slowly pour the half a cup of hot water into the cup placed in the corner. This is your ‘‘warm air mass.’’ 7. Observe if the water rises and crosses the mountain, or sinks and is unable to cross the mountain. Record your observations on a chart. Note about how much of the mass cross the mountain. 8. Empty the water from the baking dish. 9. Build a new mountain, this one should reach almost the top of the dish. Leave enough space so that water could still flow over the mountain, but not over flow the dish. Steps 7 and 14: Observe if the 10. Fill the baking dish with cold water until the mountain range is water rises and crosses the covered. mountain. I LLU STR AT IO N BY TEM AH N EL SON . 11. Add three drops of red food coloring to one-half cup hot water. 12. Place the paper cup, with holes, in the corner of one side of the dish. 13. Slowly pour the one-half cup of cold water into the cup placed in the corner. This is your warm airflow. 14. Observe if the water rises and crosses the mountain, or sinks and is unable to cross the mountain. Record your observations on the chart. Note about how much of the mass crosses the mountain. Experiment Central, 2nd edition
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Summary of Results Examine your data on the
Troubleshooter’s Guide Not all experiments work exactly as planned. Sometimes, what seems like a ‘‘mistake’’ will turn into a new learning experience. Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The cloud spreads out too much in the water to see where it moves. Possible cause: There may not be enough of a difference in the water temperatures. Your water may not have been hot or cold enough. Try the experiment again, making the hot water hotter and the cold water colder. Problem: It is too hard to measure how much of the cloud is moving. Possible cause: There may be too much water for your size dish. Try decreasing the amount of water you use to make your cloud, using a quarter of a cup, and try the experiment again.
different between how the warm water crossed over the low and high mountain range. Was your hypothesis correct? Consider how warm air might behave the same or different than the warm water. You might want to draw a picture of the results of your experiment and write a brief summary. Change the Variables Here are some ways you
can vary this experiment: • Build the mountain range out of rocks or pebbles, for a jagged mountain that is not as solid. • Build a mountain range with variation in its heights. • Conduct the experiment in different environmental conditions.
Design Your Own Experiment How to Select a Topic Relating to this Concept If
you have ever gone mountains climbing, hiking, or skiing, or visited a mountain, you have most likely come across some unique properties to mountains. You may have questions and ideas for experiments based on your experience. Did you come across any interesting animals or plants? Was it a rocky or grassy mountain? Are there mountain ranges that you are interested in, either locally or in other countries? If so, consider what type of mountain it is, its features, and life. Check the Further Readings section and talk with your science teacher or school or community media specialist to gather information on mountain questions that interest you.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. 744
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• Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Make drawings, graphs,
and charts to display your information for others. You might also draw conclusions about your findings. Which type of mountain seems to be the most common in your region? Why might that be? Related Projects If you are interested in mountains and want to discover more of their uses in your daily life, you might investigate how mountains erode over time, or mountains change the terrain in other ways aside from desert formation. You may want to conduct a research project on cultures that depend on mountains and the mountain life they use. You could also investigate extreme mountain climbing, how climbers prepare for the thinner atmosphere and other challenges.
For More Information Cox, Shirley. Earth Science. Vero Beach, FL: Rourke Publications, Inc., 1992. Chapters include how to choose geology projects. GMB Services. RocksForKids. http://www.rocksforkids.com (accessed February 7, 2008). Information on rock formation, identification, and collection. Knapp, Brian. Mountain. Danbury, CT: Grolier, 1992. Describes mountains and their makeup. Some chapters include experiments. The Mountain Institute. Learning about Mountains. http://www.mountain.org/ education/index.html (accessed on April 18, 2008). Comprehensive information about mountains, including formation, life, and weather. Parker, Steve. The Earth and How It Works. North Bellmore, NY: Marshall Cavendish, 1993. Outlines a variety of projects and experiments that examine Earth’s composition. U.S. Geological Survey. Geologic Provinces of the United States: Rocky Mountains. http://geomaps.wr.usgs.gov/parks/province/rockymtn.html (accessed on April 15, 2008). Information on features and geology of the Rocky Mountains. U.S. Geological Survey. Rocks and Minerals Site Contents. http://wrgis.wr.usgs. gov/parks/rxmin/index.html (accessed February 7, 2008). Provides information on rocks and minerals.
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anotechnology is a relatively new field of science that makes more headlines every year. It is a field that focuses on the small—the extremely small. In nanotechnology, people manipulate atoms and molecules to make new things. Those things can be materials or devices. Throughout history, people have made new things from altering or combining substances that already exist. But nanotechnology works the opposite way. In nanotechnology, researchers develop a substance from the small to the large by manipulating the basic building blocks of matter. The result could be miniature materials or devices that have completely unique properties. Science of the small The basic building blocks of nanotechnologies are atoms and molecules. All substances are made up of molecules. A drop of water, for example, is made up of millions of water molecules. If you were to keep dividing the drop into smaller droplets, you would end up with one molecule. That one water molecule would have the same properties as the drop of water. Molecules are made of atoms held together by chemical bonds. The water molecule consists of two hydrogen atoms and an oxygen atom. Diamonds are made up of a molecule of carbon atoms bonded together. Salt is made of the sodium chloride molecule, which is one sodium atom bonded to one chloride atom. Atoms and molecules are so small that a new prefix was coined to measure them: nano. The prefix ‘‘nano’’ comes from the Greek word for dwarf. Nano represents one billionth and so one nanometer is onebillionth of a meter. That’s about the size of one strand of the width of your hair split into about 50,000 pieces! It’s also about the size of ten hydrogen atoms. Things on the nanoscale are generally between 1 and 100 nanometers. Proteins in our bodies, viruses, and some particles in the air are nanosized. 747
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Seeing the small In order to work on the nanoscale, researchers needed to be able to see images of atoms and molecules. In 1981, the development of a powerful microscope allowed people to visualize the nanoscale on metals. Called the scanning tunneling microscope (STM), the microscope magnifies images of the shapes of atoms on the metal’s surface. Microscopes soon followed that allowed researchers to see images of atoms and molecules on other materials.
A drop of water, for example, is made up of millions of water molecules. I LL UST RA TI ON BY T EM AH NE LS ON.
Nanotechnology is not about simply making devices smaller. The field uses the fact that nanosize materials can have different properties than their larger counterparts. Color, hardness, melting point, and conductivity are all some of the properties that can change as the material become nanosized. One physical characteristic that can lead to these changes is the increased ratio of the surface area to volume. Surface area is all the area that is on the outside—surface—of the material. Volume is the amount of three-dimensional space taken up by a material. As a material shrinks, its surface area increases compared to its volume, In the nanosize, this ratio can increase dramatically, which can lead to different reactions. Gold nanoparticles, for example, can appear a reddish color and turn liquid at room temperature. dna
Things on the nanoscale are generally between 1 and 100 nanometers. I LL UST RA TI ON BY TE MA H NEL SO N.
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red blood cell
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dust mite
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head of a pin
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It is the arrangement of the atoms and molecules that gives materials its properties. Diamonds and the lead of pencils (graphite) are both made of up carbon molecules. In diamonds, the arrangement and bonds of the carbon atoms make it hard and clear. Graphite is dark and relatively soft. If researchers can pluck individual atoms and decide how to arrange them, they can determine the property of the material. One nanoscale material that was discovered in 1991 is also made of pure carbon. Carbon nanotubes are threads of carbon and the arrangement of its carbon makes it light, flexible, and stronger than steel. A nano-world of technologies There are high hopes that research in nanotechnology will translate into many products and devices that will help people. The technology will affect a wide range of fields, including transportation, sports, electronics, and medicine. Some of the current and future possibilities of nanotechnology includes: • Medicine: Researchers are working to develop nanorobots to help diagnose and treat health problems. Medical nanorobots, also called nanobots, could someday be injected into a person bloodstream. In theory, the nanobots would find and destroy harmful substances, deliver medicines, and repair damage. • Sports: Nanotechnology has been incorporated in outdoor fabrics to add insulation from the cold without adding bulk. In sports equipment, nanotech metals in golf clubs make the clubs stronger yet lighter, allowing for greater speed. Tennis balls coated with nanoparticles protect the ball from air, allowing it to bounce far longer than the typical tennis ball. • Materials Science: Nanotechnology has led to coatings that make fabric stain proof and paper water resistant. A car bumper developed with nanotechnology is lighter yet a lot harder to dent than conventional bumpers. And nanoparticles added to surfaces and paints could someday make them resistant to bacteria or prevent dirt from sticking. Experiment Central, 2nd edition
Swiss physicist Dr. Heinrich Rohrer, co-winner of the 1986 Nobel Prize in physics for his invention of the scanning tunneling microscope. AP PHO TO.
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• Electronics: The field of nano-electronics is working on miniaturizing and increasing the power of computer parts. If researchers could build wires or computer processing chips out of molecules, it could dramatically shrink the size of many electronics.
Graphite
Diamond
Diamonds and the lead of pencils (graphite) are both made of up carbon molecules. The arrangement and bonds of the carbon atoms cause the differences. I LL UST RA TI ON BY T EM AH NE LS ON.
Guarding the nano-future Much like other new technologies, nanotechnology has raised concerns and ethical questions. If devices become nanosize, people would not be able to see them. There is some concern these ‘‘invisible’’ devices could cause harm. If nanobots are developed, researchers would want them to selfreplicate like the cells in our body. These nanobots could potentially do many amazing things, such as pull trash apart into its microscopic molecules. But one question is what happens if there is a problem. What if nanorobots programmed to disassemble trash started taking apart other items? And what if these nanorobots multiplied endlessly? So far, nanobots are only theoretical and years in the future. The field of nanotechnology promises many future benefits, and people are working to develop guidelines that will help us deal with potential problems.
EXPERIMENT 1 Nanosize: How can the physical size affect a material’s properties? Purpose/Hypothesis As materials become smaller, the surface area to
volume ratio changes. Materials that are microscopic and nanosized have a much higher surface area to volume ratio compared to the same material you can see. Because you cannot see nano materials, in this experiment you will measure how the surface area to volume ratio changes the melting and freezing point of water. By freezing the water into large and small ice cubes, you can measure the surface area to volume ratio of each, and determine how long each size takes to melt and freeze. For a cube, the surface area is the area of the six square. The area of one square is the length the width, which are the same in a cube. The surface area (S) of the cube is the area of one side multiplied by six. If the length and width are represented by ‘‘a,’’ then S = 6 a a. The volume (V) of a cube is a a a. For a cube, the ratio of surface area to volume is then S/V, or 6/a (6:a). 750
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WORDS TO KNOW Atom: The smallest unit of an element, made up of protons and neutrons in a central nucleus surrounded by moving electrons. Bond: The force that holds two atoms together. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Molecule: The smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms.
Nanobots: A nanoscale robot. Nanometer: One-billionth of a meter. Nanotechnology: Technology that involves working and developing technologies on the nanometer (atomic and molecular) scale. Scanning tunneling microscope: A microscope that can show images of surfaces at the atomic level by scanning a probe over a surface. Surface area: The total area of the outside of an object. Variable: Something that can affect the results of an experiment. Volume: The amount of space occupied by a threedimensional object.
Before you begin, make an educated guess about the outcome of the experiment based on your knowledge of surface area to volume ratio and water. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The cubes with the smaller surface area to volume ratio will melt and freeze faster.’’ In this case, the variable you will change will be the surface area to volume ratio, and the variable you will measure will be the time it takes Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the size of the ice cubes • the material of the ice tray • the material the ice melts on • the temperature of the freezer • the room temperature In other words, the variables in this experiment are everything that might affect the melting and freezing of the ice.
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How to Experiment Safely
for the ice to freeze and melt. You expect a shorter freezing and melting time for the smaller ice than the larger ice cubes.
There are no safety issues in this experiment.
Level of Difficulty Easy/moderate (there is simple math involved). Materials Needed
• conventional, large ice cube trade • mini ice-cube tray (available at party stores) • 2 plates • freezer • clock with minute hand • toothpicks or other small pointy object • ruler with centimeters Step 1: Pour water into at least three of the cubes in both the large and small ice cube trays.
Approximate Budget $5. Timetable Approximately 3 hours. Step-by-Step Instructions
Step 4: Place two large ice cubes on one plate, and two mini ice cubes on the second plate. IL LUS TR ATI ON B Y TE MA H NE LS ON.
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1. Pour water into at least three of the cubes in both the large and small ice cube trays. 2. Place the trays in the freezer. Time for 30 minutes and poke each with a toothpick. If one set of ice cubes are frozen, note the time and leave them both in the freezer. Check back every five minutes until both sets are frozen and note the time for each. If neither ice cube tray is frozen solid, leave the trays in the freezer and check back every five minutes. 3. When all the ice cubes are frozen solid, remove them from the trays. On one of the large and mini ice cubes, use the ruler to measure the dimension for a side of each. Round off the measurement and note. 4. Place two large ice cubes on one plate, and two mini ice cubes on the second plate. Make sure the ice cubes are not Experiment Central, 2nd edition
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touching. Set the plates aside and wait at least 30 minutes. 5. Continue checking on the cubes at regular intervals. Note when the two small cubes and the two large cubes have completely melted. Summary of Results Was your hypothesis cor-
Troubleshooter’s Guide This experiment is straightforward and you should not have any major issues. The freezing time may vary from the protocol depending upon the temperature of the freezer and the size of the cubes. The melting time will also vary depending upon the size of the cubes.
rect? Did the mini cubes melt and freeze faster than its larger counterpart? Rounding off the measurements, you can calculate the surface area and volume of the large cube and the small cube. How do the different surface area to volume ratios relate to the melting and freezing point? Change the Variables If you want to vary this experiment, you can freeze
water and melt the cubes in extreme size differences. How would a pan of water compare to an ice cube? You can also change the substance and look at surface area to volume ratios in solid substances, such as salt or sugar.
EXPERIMENT 2 Nanosize Substances: How can the physical size affect the rate of reaction? Purpose/Hypothesis One reason that nanosize substances may behave
differently than the macrosize is due to the rate of reaction. Nanosize substances have a larger surface area compared to its larger counterpart. In this experiment, you will look at how increasing the surface area of a substance can affect its rate of reaction. You can use an antacid tablet and water. When antacid tablets react with water, the reaction produces carbon dioxide. In an enclosed container the carbon dioxide gas will push on the container and force its ‘‘top’’ into the air. You can compare the rate of reaction between a whole antacid tablet and two varying sizes of the crushed tablet. One tablet will be broken into chunks and the other will be crushed, which will result in more surface area. Before you begin, make an educated guess about the outcome of the experiment based on your knowledge of surface area to volume ratio and water. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the size of the ice cubes • the brand of antacid tablet • the size of the antacid tablet • the amount of water • the temperature of the water In other words, the variables in this experiment are everything that might affect the rate at which the reaction occurs.
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The greater the surface area, the faster the rate of reaction.’’ In this case, the variable you will change will be the surface area, and the variable you will measure will be the time it takes for the carbon dioxide to pop the top. Level of Difficulty Easy.
Materials Needed
Step 4: Quickly, snap on the top. IL LUS TR ATI ON BY T EM AH NEL SO N.
• 6 antacid tablets • 2 pieces of paper • spoon or any hard object • 3 film canisters (35 mm film) with lids that fit on the inside (as opposed to snap on the outside of the canister); you could also use 1 canister and rinse it out after each use • watch with minute hand • helper • outside area or clear, inside area than can get messy Approximate Budget $5. Timetable Approximately 15 minutes. Step-by-Step Instructions
1. Fill all three canisters half full with water that is about room temperature. (If you only have one canister, fill a cup with 754
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water and allow it to get to room temperature before pouring it in the canister.) 2. Go to the area where you want to set the canister down to time the reaction. As soon as you place the tablet in the canister, have your helper begin timing. 3. Drop a whole antacid tablet in the canister. (Your helper should start timing now.)
How to Experiment Safely Step back quickly when you put the top on the canister so that it does not hit you. This experiment can be messy. If possible, work outside or in an area that is easy to clean.
4. Quickly, snap on the top and set the canister down with the top on the bottom. 5. When the reaction occurs and the canister flies into the air, make a note of the time. 6. Place the second tablet on a piece of paper. Use a hard object, such as a book, to break the tablet into chunks. Carefully, drop the chunks into the second canister. Start timing! Firmly, place the top on the canister, flip it so the top is on the bottom and note the reaction time. Repeat this step with a crushed tablet. You will need to fold the paper and pour the crushed antacid into the container. 7. Repeat each of the trials. If one reaction time is far off from the same tablet size, you may want to repeat the trial a third time until you can get repeatable results. Summary of Results Look at the reaction times for each of the three
tablets with different surface areas. How does the amount of surface area relate to the reaction time? Was your hypothesis correct? Write a summary of your results, including how this experiment relates to nanostructures and substances.
Step 6: Place the second tablet on a piece of paper. Use a book to break the tablet into chunks. ILL US TRA TI ON B Y TE MA H NEL SO N.
Change the Variables Here are some ways you
can vary this experiment: • Change the temperature of the water. • Change the amount of water. • Use a different substance to measure the rate of reaction, such as sugar and dissolving rates. Experiment Central, 2nd edition
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Design Your Own Experiment Troubleshooter’s Guide Below is a problem that you may have during this experiment and a way to remedy the problem. Problem: The times for the two trials that were the same surface area were not at all close. Possible cause: You may have used different water temperatures. Warmer water can speed up a reaction. Try setting aside a large container of water. Wait for the water to come to room temperature and then use this water for all your trials.
How to Select a Topic Relating to this Concept
Nanotechnology is a wide and growing field that may be incorporated in materials and technologies you use. Most likely, it could be in a car you use, sunscreen, or even clothes you wear. You may want to look up products that were developed with nanotechnology and see if the products are familiar or readily available. Check the Further Readings section and talk with your science teacher to start gathering information on questions that interest you about nanotechnology. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what questions you’re answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Think of how you can
share your results with others. Charts, graphs, and diagrams of the progress and results of the experiments are very helpful in informing others about an experiment. Related Projects To experiment in nanotechnology, you can find prod-
ucts that are made using nanotechnology and compare those products to others. Some papers and clothing have a nanotech surface. Aside from surface area to ratio, you can experiment with other properties that make nanosize materials different than their larger counterparts. 756
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There are also many research projects you can do in nanotechnology. You can conduct a project on the major breakthroughs in the field or focus on one breakthrough, such as microscopes. You can also investigate the development and consequences of nanotechnology products in a certain field, such as medicine or sports equipment. Ethical issues and questions in the field of nanotechnology is another area of research.
For More Information Darling, David. Beyond 2000: Micromachines and Nanotechnology. Parsippany, NJ: Dillon Press, 1995. Johnson, Rebecca L. Nanotechnology. Minneapolis: Lerner Publications, 2006. Lawrence Hall of Science, University of California, Berkeley. Nanozone. http:// www.nanozone.org (accessed on May 17, 2008). Information, graphics, activities and videos on nanoscience. Northwestern University. ‘‘History of Nano Timeline.’’ Discover Nano http:// www.discovernano.northwestern.edu/whatis/History/# (accessed on May 17, 2008). Interactive timeline traces the history of nanotechnology from pre eighteenth century to modern day. Science Museum in London. Nanotechnology: small science, big deal. http:// www.sciencemuseum.org.uk/antenna/nano/index.asp (accessed on May 19, 2008). Information and an online game about nanotechnology from a science exhibit. The University of Wisconsin. ‘‘What is a Nanotechnologist?’’ Intro to Nanotechnology http://mrsec.wisc.edu/Edetc/technologist/index.html (accessed on May 17, 2008). Profiles of professionals in nanotechnology that explains what they do.
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Nutrition
T
he foods you eat affect whether you pay attention in class, how much energy you have for sports, and even whether you feel happy or sad. In fact, your meals and snacks affect how every cell in your body works. How do we know? Nutrition is the science of how the body uses nutrients to grow and function effectively. Nutrients are nourishing substances that the body needs. For example, the heart needs certain nutrients to help it pump blood. Our kidneys need nutrients to help rid our bodies of harmful wastes. Not surprisingly, deficiencies in certain nutrients can cause disease. Real men eat fruit Hardly anyone gets scurvy anymore, but this disease was common a few centuries ago, especially among the first explorers and the crews on their ships. No one knew what caused scurvy. People with it felt weak. Their gums, noses, and mouths bled, and their muscles ached. When the ship of French explorer Jacques Cartier became icebound on the St. Lawrence River in Montreal in 1535, 25 men became ill and died. Cartier was visited by local Native Americans. He mentioned his feelings of weakness and the bleeding symptoms of his men. The Native Americans went into the woods, brought back pine needles and bark from a tree, and told Cartier to boil them in water. Cartier and his men drank the tea and recovered. We now know the pine needles contained vitamin C, a substance also present in fruits and vegetables. Fruits and vegetables were rarely eaten on ships at that time. Storing them was a problem, and they were expensive to buy. In 1747, James Lind, a Scottish doctor, knew that many British sailors were dying from scurvy, but he had read a report that fruits and vegetables helped prevent the disease. The sailors recovered quickly when Lind added citrus fruit juices to their diet, so Lind suggested this remedy to the British navy. Still, it took several decades before this remedy was taken seriously. Eventually, scurvy was all but eliminated. 759
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Dr. James Lind suggested eating citrus fruits to prevent scurvy. BET TM ANN ARC HI VE.
Eating healthy foods helps people stay healthy. K ELL Y A. QU IN.
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Eat right to stay healthy It was not until the early 1900s that scientists began to understand how nutrient deficiencies affect the body. The body cannot make all the substances it needs, but those missing substances are found in food. Before we realized this, however, these substances were often removed from food. In the early 1900s, many foods were being processed. When rice processors removed the bran layers from whole rice to make white rice, they did not realize they were also removing a substance that was necessary for the body to function well. In regions where rice was the main food, a deficiency in this substance was causing a disease called beriberi. In 1911, Polish researcher Casimir Funk isolated this substance and discovered a type of chemical compound called an amine. He linked it with the Latin word vita, meaning ‘‘life,’’ and the new term vitamin was created. The vitamin in bran was named thiamine, a B vitamin that helps the body obtain energy from carbohydrates. As they learned more, scientists concluded that eating a variety of foods that are not processed, such as meats, fish, and fresh fruits and vegetables, helps our bodies stay healthy. And taking extra vitamins does not hurt either. The necessary nutrients Besides vitamins, what are the other main substances your body needs to work well? One is carbohydrates, which give your body energy. They are present in starches, including potatoes, rice, bread, peas, and beans. They are also in milk and fruit, as well as in fiber from grains and vegetables. Your body uses carbohydrates to manufacture the zip you need to win a race or hit a home run. Fats are necessary, too. Fats that come from olive oil, yogurt, nuts, and cheese help you grow and make your skin smooth. Fats also cushion body organs, keep your body warm, and help Experiment Central, 2nd edition
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you absorb vitamins. Extra fats are stored under the skin and become another source of energy when needed. Minerals, another kind of essential nutrient, help build bones and soft tissues. They act as regulators, keeping your blood pressure stable and your heart rate steady. They also keep your bones and teeth tough and help you digest your food. The six main minerals your body requires are calcium, magnesium, phosphorus, potassium, sodium, and sulfur. These minerals can be found in dairy products, fruit, vegetables, and meats. Other minerals, just as important but needed in smaller quantities, are known as trace elements. Some of the more important ones are iron, fluorine, iodine, and zinc. Your body needs help making cells as you grow and replacing cells that become worn out. That’s where proteins come in. Besides helping to build new cells, proteins trigger and speed up reactions within your body. Proteins also help form antibodies that ward off infections. Soybeans, beef, fish, beans, eggs, peas, and whole wheat are sources of protein. You might not think that water would be an important nutrient, but it is. Nutrients can be carried to where they are needed only in watery solutions. Good nutrition is essential for good health. Eating a variety of fresh, nonprocessed foods helps prevent diseases and sickness and gives you energy to work, think, and play. The projects that follow will help you analyze what you are actually eating on a day-to-day basis.
Peas and beans are good sources of carbohydrates. GR AN T HEI LM AN.
PROJECT 1 Energizing Foods: Which foods contain carbohydrates and fats? Purpose/Hypothesis This project will help you analyze a typical meal to
discover which foods provide the energy we need for our day-to-day activities. You will test for fats and for starches. Fats supply energy and are stored in the body for times when energy levels are low, such as when you exercise or miss a meal. The starches in carbohydrates also provide energy. Experiment Central, 2nd edition
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WORDS TO KNOW Amine: An organic compound derived from ammonia.
ture. As a nutrient, it helps build bones and soft tissues and regulates body functions.
Amino acid: One of a group of organic compounds that make up proteins.
Nutrient: A substance needed by an organism in order for it to survive, grow, and develop.
Antibody: A protein produced by certain cells of the body as an immune (disease-fighting) response to a specific foreign antigen.
Nutrition: The study of the food nutrients an organism needs in order to maintain well-being.
Antigen: A substance that causes the production of an antibody when injected directly into the body. Beriberi: A disease caused by a deficiency of thiamine and characterized by nerve and gastrointestinal disorders. Carbohydrate: A compound consisting of carbon, hydrogen, and oxygen found in plants and used as a food by humans and other animals.
Organic: Containing carbon; also referring to materials that are derived from living organisms. Protein: A complex chemical compound that consists of many amino acids attached to each other that are essential to the structure and functioning of all living cells. Scurvy: A disease caused by a deficiency of vitamin C, which causes a weakening of connective tissue in bone and muscle.
Fat: A type of lipid, or chemical compound used as a source of energy, to provide insulation and to protect organs in an animal body.
Thiamine: A vitamin of the B complex that is essential to normal metabolism and nerve function.
Inorganic: Not containing carbon; not derived from a living organism.
Trace element: A chemical element present in minute quantities.
Metabolism: The process by which living organisms convert food into energy and waste products.
Translucent: Permits the passage of light.
Mineral: An inorganic substance found in nature with a definite chemical composition and struc-
Vitamin: A complex organic compound found naturally in plants and animals that the body needs in small amounts for normal growth and activity.
Level of Difficulty Easy.
How to Experiment Safely Be careful not to get the iodine in your eyes. Ask an adult to help you use the iodine.
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Materials Needed
• iodine with dropper • brown paper bags cut into 10 or more 4-inch (10-centimeter) squares Experiment Central, 2nd edition
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• clear glass dinner plate • a typical meal (For example, a lunch consisting of a turkey and Swiss cheese sandwich with tomato, lettuce, and mayonnaise; milk; potato chips. Or a dinner of hamburger, pasta salad, corn bread, milk, and cake with icing) Approximate Budget $2 for iodine; other sup-
plies from meals. Timetable 1 hour; this project can be repeated
after each meal to determine eating trends.
Step 1: Create two 1 teaspoonsized samples of each food. GAL E GR OU P.
Step-by-Step Instructions
1. Create two 1 teaspoon-sized samples of each food, such as two samples of turkey, two of Swiss cheese, two of bread, and so on. 2. To test the foods for fat, rub a food sample on a square of brown paper. Remove the food sample, and allow the paper to dry. 3. Hold the paper up to the light and notice if it is translucent (if you can see light through it). Describe your observations on a data chart. Make a plus sign under a Fats heading for those foods that leave a translucent stain.
Steps 2 and 3: To test the foods for fat, rub a food sample on a square of brown paper. Remove the food sample, and allow the paper to dry. GA LE G RO UP. Experiment Central, 2nd edition
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Steps 4 and 5: Test food samples for starch by dripping four to five drops of iodine onto the food. GAL E GR OU P.
Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: Apples or pears do not stain black with iodine. Possible cause: These fruits contain cellulose, which is plant starch. Iodine turns black with more soluble, digestible starches, such as wheat, rice, and beans.
4. To test for starch, place a food sample on the glass dinner plate. Drip four to five drops of iodine onto the food. Allow 15 minutes for the iodine to penetrate. 5. On your data chart, make a plus sign under a Starch heading for foods that turn black from the iodine. 6. Repeat Steps 2 through 5 for each kind of food. Place each sample in a different spot on the paper and on the plate. Summary of Results Analyze your results. Figure out how many foods in your meal contain starch and/or fat. Consider what this says about the healthfulness of the meal and of your diet in general.
PROJECT 2 Nutrition: Which foods contain proteins and salts? Purpose/Hypothesis This project will help you identify proteins and
salts, nutrients needed for cell repair and daily maintenance. Proteins, present in every cell, are known as body builders. They help you grow and 764
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replace cells. Salts are minerals that your body uses to maintain water balance. Level of Difficulty Moderate. This experiment requires the purchase of two chemicals and the supervision of an adult.
How to Experiment Safely Ask an adult to help you with this project. Wear goggles or other eye protection and protective gloves when handling silver nitrate. Be careful with the silver nitrate, as it stains the skin.
Materials Needed
• silver nitrate (a salt-indicator solution, which can be purchased from science supply catalogs) • Biuret solution (a protein-indicator solution, also available from science supply catalogs) • glass test tubes or glass cups • test tube rack • food from one meal • water • goggles • rubber gloves Approximate Budget $20 for the silver nitrate and Biuret solutions,
depending on the quantity. The silver nitrate can be purchased as a crystal and dissolved in water.
Step 3: Place a food sample into each test tube. G AL E GR OUP .
Timetable 1 hour. Step-by-Step Instructions
1. Create ¼-teaspoon-size samples of each type of food from your meal. 2. Set test tubes in rack. 3. For the protein test, put a food sample into a test tube and add 10 drops of Biuret solution. 4. Wait 10 minutes. If the blue Biuret solution turns lavender, the sample contains protein. Record the result on a data chart. 5. For the salt test, put a food sample into a test tube and fill tube halfway with water. Shake gently. Add 10–20 drops of silver nitrate solution. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: None of my foods tested positive for salt. Possible cause: Insignificant amounts of salt may be present. Make a test tube sample of salt and water. Add silver nitrate to see if the solution turns white. If not, the silver nitrate may be contaminated.
6. Watch to see if the clear silver nitrate forms a milky white precipitation in the water. If so, salt is present. Record your results. 7. Repeat Steps 3 through 6 for each food sample, recording all your results on the data sheet. Summary of Results After testing a typical meal,
analyze your results. How many samples contained protein or salt? Do you see any pattern? Write a paragraph summarizing your findings.
PROJECT 3 Daily Nutrition: How nutritious is my diet? Purpose/Hypothesis This project will help you determine if you are
taking in the recommended nutrients and calories. A calorie is a unit of energy. The amount of energy and nutrients your body needs depends upon many factors, such as your age and if you are male or female. It also depends upon how much energy you ‘‘burn’’ every day through sports or simply moving around.
Steps 3 to 6: Testing food samples for either protein or salt content. GAL E GR OU P.
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Although everyone is different, there are general guidelines for the amount of nutrients How to Experiment Safely and total energy that people require. In this project, you can find out if you are taking in a There are no safely hazards in this project. healthy amount of energy and nutrients by determining your intake. The Nutrition Facts Label on food packages provides the calories and amounts of nutrients in each serving of food. The labels state the amount of nutrients both as a number and percentage of the Daily Value. The government chose an average daily value: 2,000 calories a day. If the percent Daily Value of carbohydrates lists 10%, that means the food gives 10% of the carbohydrates generally needed for the day. The percent Daily Values are calculated based on fat as 30% of total calories and carbohydrates as 60% of calories (protein is the other 10%). Some youths (and adults) will need more than that, and some will need less. In this project, you will measure the amount of energy, fats, and carbohydrates you consume. For some foods, you may have to estimate the amount you eat and nutrient information. If you eat lasagna, for example, you will need to look up the nutritional information for each serving for each ingredient and then add them together. You will also have to determine if you had one or more servings, as it is listed on the Nutrition Facts Label. By measuring the nutrition information over the course of three to five days, you can calculate the average to find out your typical nutrient intake. Level of Difficulty Moderate to Difficult, because of the time and
precision involved. Materials Needed
• • • • •
paper and pencil Nutrition Facts Labels from foods eaten throughout days of project measuring cup and spoons Internet access (optional) calculator (optional)
Approximate Budget $0. Timetable Approximately 30 minutes per day for three to five days. Experiment Central, 2nd edition
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Step-by-Step Instructions Food Servings Fat Carbohydrates Calories
1. If you have access to the Internet, visit the MyPyramid site listed below and write down how many calories and nutrients you should be consuming every day. If you do not have Internet access, you can ask a health professional or use the average of 2,000 calories. 2. Make a chart listing the food items and its major nutrients. See the illustration for an example.
TOTAL DAY 1:
Step 2: Make a chart listing the food items and its major nutrients. I LL UST RA TI ON BY T EM AH NE LS ON.
Step 3: Make sure you write down information from all the foods you are eating. IL LUS TR ATI ON B Y TE MA H NE LS ON.
3. For each food you eat, write in your chart the calories, fats, and carbohydrates listed on the Nutrition Facts Label. Make sure you look at the serving size and judge whether you are eating one serving. For many foods, such as breakfast cereals, it is easy to eat more than one serving size. You can use measuring cups to figure out how much is in your bowl or on your plate. If you eat two serving sizes, you will need to double the amount of calories and nutrients listed on the label. Also, make sure you write down information from all the foods you are eating, such as the milk and any fruit or sugar on your cereal. For fast food items, restaurants often provide nutritional information (you may have to ask). 4. At the end of the day, look at your chart and think about any foods you may have forgotten to list. If you did forget anything, such as snacks, add them to your chart. 5. Continue to measure your nutrient intake for three to five days. 6. When you have finished, add up the total calories and nutrients for each day. Calculate the average of the fats, carbohydrates, and calories. You can do this by adding up each item and dividing by the number of days. For example, if you ate 12,000 calories over five days, divide the calories by five. That means you
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consumed about 2,400 calories a day on average. 7. Compare the calories and nutrients you ate on average to your recommended intake. Summary of Results How does your recom-
mended intake compare to what you actually consumed? Are they close? Look at your chart and see if you are eating a healthful variety of food groups. Are there are a lot of high sugar and fat food? Are you eating more or less than the five or more servings of fruits and vegetables recommended each day? You can also continue this project by measuring your consumption of proteins, specific vitamins, and minerals throughout the day.
Design Your Own Experiment
Nutrition Facts
Serving Size 1 packet (43g) Servings Per Container 10 Amount per Serving
Calories Calories from Fat
160 20
Total Fat 2g Saturated Fat 0.5g
3% 2%
Trans Fat 0g Cholesterol 0g
0%
Sodium 240mg
10%
Total Carbohydrate 33g
11%
Protein 4g Vitamin A 20% Calcium 10%
Vitamin C 0% Iron 20%
How to Select a Topic Relating to this Concept
Diet is such a vital part of a healthy lifestyle that studying your eating habits is important. You might decide to research the major nutrients and learn more about how they can help improve your health. Check the Further Readings section and talk with your science teacher or school or community media specialist to gather information on nutrition questions that interest you. As you consider possible experiments, be sure to discuss them with a knowledgeable adult before trying them.
Step 6: Add up the total calories and nutrients for each day. Calculate the average of the fats, carbohydrates, and calories. IL LU STR AT ION BY TEM AH N EL SON .
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what your are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: It looks like I am not getting enough calories even though I am never hungry. Possible cause: You may have forgotten to list several foods. It is extremely hard to remember every food we eat in a day. Try taking your chart with you as you go about your daily activities, and jotting down the food item as soon as you eat it. You can calculate the nutritional information at a later time, but that will help you remember to include it. Problem: It looks like I am not getting enough nutrients even though I am never hungry. Possible cause: You may have forgotten to list several foods (see above) or you may actually not be consuming enough nutrients. If most of the foods you are eating are highly processed and contain a lot of fats and oils, these foods may be low in nutrients.
• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results
It’s always important to write down data and ideas you gather during an experiment. Keep a journal or record book for this purpose. If you keep notes and draw conclusions from your experiments and projects, other scientists could use your findings in their own research. Related Projects Nutrition-related projects or experiments can go in many different directions. For example, you might identify the types and quantity of nutrients you eat daily. You might decide to start regulating your intake of the lesshealthful foods. As a start, all you need to do is read the nutritional facts found on all food packages.
For More Information
Eating for Health. Vol. 3. Chicago: World Book Inc., 1993. Part of the ‘‘Growing Up’’ series, this volume provides thorough, interesting information about carbohydrates, vitamins, and minerals as well as metabolism, eating disorders, and processing. Food Standards Agency. ‘‘Vitamins and Minerals.’’ eatwell. http://www.eatwell. gov.uk/healthydiet/nutritionessentials/vitaminsandminerals/ (accessed on February 19, 2008). Information about vitamins, minerals, and where they are found. Kids Health. Food and Nutrition. http://www.kidshealth.org/kid/nutrition/ index.html#All About Food (accessed on February 19, 2008). Series of easy to read articles on food and nutrients. Levchuck, Caroline, and Michele Drohan. Healthy Living. Detroit: UXL, 2000. Contains chapters on nutrition, eating disorders, and other health issues. United States Department of Agriculture. MyPyramid Plan. http://www.mypyramid. gov/mypyramid/index.aspx (accessed on February 19, 2008). Customized food guide. United States Department of Agriculture. MyPyramid for Kids. http://www.fns. usda.gov/TN/kids pyramid.html (accessed on February 19, 2008). Nutritional information, a food tracking worksheet, and games.
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Oceans
I
f you were to look down at Earth from space you would see a planet that was covered in blue. That is because oceans cover almost three-quarters of the Earth’s surface and contain about 97% of the planet’s water supply. Life on Earth began in the ocean almost three-and-a-half billion years ago and life could not exist without a healthy ocean environment. Today, the oceans are home to an incredible variety of creatures, from the largest animal that ever lived, the blue whale, to microscopic organisms that can live in boiling waters. People depend on the oceans in many ways. Oceans have an important effect on weather patterns. They are essential for transportation, for both economic and military purposes. Many people throughout the world rely on the ocean for food and their livelihood. People also use the oil and minerals that come from beneath the ocean floor. The first voyage planned specifically to study the oceans was a British expedition that set out in 1872. In the twentieth century, interest in the oceans grew enormously. A new field evolved for oceanographers or people who study the ocean. Technological development allowed oceanographers to travel further and longer into the ocean depths. The discovery of previously unknown species and minerals in the ocean sparked further excitement and, today, the ocean is considered the last unexplored frontier.
A handful of seawater Earth’s oceans are all connected to one another. Until the year 2000, there were four recognized oceans: the Pacific, Atlantic, Indian, and Arctic. In 2000 the International Hydrographic Organization, the organization responsible for setting the oceans’ boundaries, recognized a new ocean, the Southern Ocean, encircling Antarctica. The main chemicals in ocean water are sodium and chlorine combined as sodium chloride, better known as ordinary table salt. Ocean waters also contain smaller amounts of many other chemicals. Salt, along with the other substances, flows into oceans from smaller bodies of water. 771
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Salt is a mineral that is found in soil and rocks. As river water flows, it picks up small amounts of salts from the rocks and soil. The S Chlorine 55.04% rivers carry it into the ocean where it remains. A L The salinity, or salt content, of ocean 30.61% T Sodium water varies across the oceans. Oceanographers Sulfate 7.69% report salinity in parts per thousand. On average, ocean salinity is thirty-five parts per thouMagnesium 3.69% sand. That means there are 35 pounds of salt for every 1,000 pounds of water, or 3.5% salt. Calcium 1.16% Changing properties On average, the Potassium 1.1% ocean extends about 2.3 miles (3.7 kilometers) downwards from the surface. Seawater has Remaining elements .71% different properties depending on its depth, (these include manganese, lead, gold, silver, iron, and zinc) from the surface to the ocean floor. As the water deepens, its pressure increases. The The main chemicals in ocean water near the ocean’s surface has very little water are sodium and chlorine water pressing down on it and so the water pressure is low. On the bottom combined as sodium chloride, of the ocean, the weight of all the water above presses down and the water better known as ordinary table pressure is high. At the deepest point in the ocean, the pressure is more than salt. GA LE GRO UP. 8 tons per square inch (1.1 metric tons per square centimeter)—equal to one person trying to support 50 jumbo jets. Sunlight gives the surface water warmth. On average, sunlight extends down to a depth of about 650 feet (250 meters). Water near the ocean floor gets no sunlight and is cold and dark. Both temperature and salinity affect the density of the water. Density is how much mass a certain volume of water contains. Molecules in warm water have more energy to move about. They spread farther apart, which results in less mass in a certain volume and therefore less density. Molecules in cold water have less energy and stay close together, resulting in a more mass in a certain volume and greater density. Water that is heavier or denser than the water around it sinks, while water that is less dense rises. Differences in density cause seawater to form layers in a process called stratification. A liquid will float on a liquid less dense than itself, such as oil on water. The layers formed in ocean waters can be incredibly stable and last for thousands of years. Rising and falling Currents are large streams of water flowing through the ocean. Currents occur in all bodies of salt water and can be caused by wind, salinity, heat content, the characteristics of the ocean’s
Concentrations of seawater minerals
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bottom, and Earth’s rotation. Currents in the top layer of the ocean are called surface currents and these are mainly caused by steady winds. Surface currents flow clockwise north of the equator and counterclockwise (in the opposite direction) south of the equator. The Gulf Stream runs along the east coast of the United States and is one of the strongest and warmest currents known. In some places it may travel more than 60 miles (96.6 kilometers) in a day. The currents carry the Sun’s heat from warmer regions to cooler areas, bringing mild weather to places that would otherwise be much cooler.
Increased pressure as water deepens
Currents also flow up and down within the water. These currents occur due to changes in seawater temperature and density and are called convection currents or density-driven currents. When warm surface water loses some of its heat to the air, the surface water becomes cooler and denser and starts to sink. This forces some of the water at lower levels to rise to form an up-and-down current. Deep ocean currents are important to marine life. Water at the ocean surface takes in oxygen from the air. Convection currents carry the oxygen down to the animals and plants that live in the bottom ocean regions. Minerals along the bottom of the floor are carried up to the sunlight layer, where animals use them. This process of lower-level, nutrientrich waters rising upward to the ocean’s surface is called upwelling.
Seawater has different properties depending on its depth from the surface to the ocean floor. As the water deepens, its pressure increases. GAL E GR OU P.
The waters in the ocean are constantly in motion. When wind blows over the ocean’s surface, it tries to pick up some of the water and creates waves. Waves are movements of water that rise and fall. The size of the wave depends on the wind’s power. Gentle breezes form tiny ripples along the surface; strong winds can create large waves. Even though it looks like waves push the water forward, the water actually moves very little. When a wave arrives it lifts the water particles up and forward. As the wave passes, each particle falls and flows backwards underwater to return to its starting point. That is why a bottle, or anything else, floating in the ocean will remain in roughly the same place as the waves pass. The highest point the waves reach is called the crest. The lowest point is called the trough. The distance from one crest to the next is the wavelength. Experiment Central, 2nd edition
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Tides are periodic rises and falls of large bodies of water. English mathematician and physicist Isaac Newton (1642–1727) was the first person to explain tides scientifically with his understanding of gravity. Gravity is a force of attraction between any two masses, such as the Sun and Earth.
pushed ater
lighter water pushes to surface
Tides are caused primarily by the gravitational pull of the Moon on Earth, and by the rotation of Earth. The tug of gravity from the Sun also affects the tides, but it has about half of the Moon’s force. The gravitational attraction causes the oceans to bulge out in the direction of the Moon. Another bulge occurs on the opposite water warms side of the Earth due to the water being thrown outward by the planet’s spin. These are high tides. hot area The areas between the tidal bulges experience low tide. (For a more detailed explanation of tides see Convection currents are caused when waters of different the Rotation and Orbits chapter.) temperatures and densities Sea life The oceans are filled with all types of amazing and bizarremeet. GA LE GRO UP. looking creatures. Although the Sun’s light only reaches a small layer of the seawater, the majority of animals and plants live in the top sunlight regions. Microscopic organisms called plankton are the main food supply in the ocean. They live at or near the surface of the water and many produce oxygen, much of which escapes into the air for humans to breathe. denser water sinks
Wavelength Crest Trough
Even though it may appear as though waves move the water forward, water moves in a circular motion. GAL E GR OU P.
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Tidal bulge caused by the gravitational pull of the moon and the sun
Tidal bulge resulting from the force of Earth's rotation
Tides are caused primarily by the gravitational pull of the Moon on Earth, and by the rotation of Earth. GAL E GR OU P.
In the lower ocean regions, deep-sea creatures have developed unique adaptations to survive in the dim, high-pressure, cold waters. Many deep-water fish are bioluminescent or they make their own light. The anglerfish uses a lighted ‘‘lure’’ on the top of its head to attract prey. The flashlight fish carries bioluminescent bacteria in pouches under its eyes that it can flash on and off at will to capture prey or find a mate. A shrimp heaves bioluminescent vomit onto an attacking fish, perhaps to blind the attacker and allow the shrimp to escape. Other deep-sea fish have expandable stomachs that can hold a fish much larger than themselves—a useful talent with the lack of food on the ocean floor. Fanglike teeth, hinged skulls, and large mouths are all traits that help these fish catch food. Some creatures attach themselves to the ocean floor, such as giant tube worms that can grow more than 10 feet (3 meters) long. In the 1970s, researchers discovered these worms, along with bacteria and giant clams, living in bubbling hot water with temperatures up to 650˚F (350˚C) spurting out from beneath the ocean floor.
A giant squid netted from the waters near Melbourne, Australia, in February 2001. Measuring 12 feet (4 meters) long, it is estimated its feeding tentacles would likely bring the size to 36 feet (12 meters). A P/ WID E WO RL D
EXPERIMENT 1 Stratification: How does the salinity in ocean water cause it to form layers? Purpose/Hypothesis Layers of seawater with
different densities can lead to stratification that can last for centuries. Anyone who has gone into Experiment Central, 2nd edition
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WORDS TO KNOW Bioluminescence: The chemical phenomenon in which an organism can produce its own light. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Convection current: Also called density-driven current, a cycle of warm water rising and cooler water sinking. Crest: The highest point of a wave. Currents: The horizontal and vertical circulation of ocean waters. Density: The mass of a substance compared to its volume. Gravity: Force of attraction between objects, the strength of which depends on the mass of each object and the distance between them. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Oceanographer: A person who studies the chemistry of the oceans, as well as their currents, marine life, and the ocean floor. Salinity: A measure of the amount of dissolved salt in seawater. Stratification: Layers according to density; applies to fluids. Tides: The cyclic rise and fall of seawater. Trough: The lowest point of a wave. (Pronounced trawf.) Upwelling: The process by which lower-level, nutrient-rich waters rise upward to the ocean’s surface. Variable: Something that can affect the results of an experiment. Wave: The rise and fall of the ocean water. Wavelength: The distance between one peak of a wave and the next corresponding peak.
the ocean and felt distinct layers of cold meeting the warm water has experienced the effect of stratification. Temperature and salinity are the two key factors determining density and, thus, ocean stratification. High salinity makes the water denser than low salinity, and cold water is denser than warm water. The denser the water relative to the water around it, the lower that water sinks. In this experiment you will examine how salinity affects stratification. You will make two saltwater solutions of different salinity concentrations: a 40 percent salinity solution and a 20% salinity solution. To visually observe the different densities, you will dye the water blue and place an object in the saltwater that is denser than fresh water—a small potato. You will then carefully place fresh water above the salt water and observe what happens. 776
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Before you begin, make an educated guess about the outcome of this experiment based on What Are the Variables? your knowledge of density and stratification. This educated guess, or prediction, is your Variables are anything that might affect the hypothesis. A hypothesis should explain these results of an experiment. Here are the main variables in this experiment: things: • the topic of the experiment • the temperature of the water • the variable you will change • the type of salt • the variable you will measure • the quantity of salt • what you expect to happen • the item placed in the water A hypothesis should be brief, specific, and In other words, the variables in this experiment measurable. It must be something you can test are everything that might affect the stratificathrough further investigation. Your experiment tion of the water. If you change more than one will prove or disprove whether your hypothesis is variable at the same time, you will not be able to tell which variable had the most effect on correct. Here is one possible hypothesis for this stratification. experiment: ‘‘Water that is higher in salinity is denser than water of lower salinity; the greater the difference between the densities, the more defined the stratification.’’ In this case, the variable you will change is the percentage of salt in the water. The variable you will measure is the density of the water. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control experiment and your experiment. For The tide is low along this your control in this experiment you will use a jar of fresh water. At the end Washington State beach. of the experiment you can compare the control and the experimental PHO TOG RA PH B Y CI NDY results. CLE ND ENO N. Note: When making a solid/liquid solution, it is standard to use weight/weight (grams/grams) or weight/volume (grams/milliliters). With water, 1 gram of water equals 1 milliliter. In this experiment, teaspoons and tablespoons are used to measure the solid. Level of Difficulty Easy to Moderate. Materials Needed
• water • 3 glass jars (mayonnaise jars work well) Experiment Central, 2nd edition
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How to Experiment Safely Have an adult present when handling hot water.
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container to hold water salt 3 small red potatoes measuring cup measuring spoons baster blue or red food coloring
• marking pen • masking tape Approximate Budget $5. Timetable 15 minutes for the initial setup; about two hours waiting time. Step-by-Step Instructions
Step 8: Dribble the water along the inside of the jar so that it does not mix up the solution. GA LE G RO UP.
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1. Use the masking tape to label each glass jar: ‘‘Control,’’ ‘‘40% salinity,’’ and ‘‘20% salinity.’’ 2. Pour 3 cups (700 milliliters) of hot water in each jar. 3. In the jar labeled ‘‘40% salinity,’’ add 8 tablespoons of salt. Stir vigorously. 4. In the jar labeled ‘‘20% salinity,’’ add 4 tablespoons of salt. Stir vigorously. 5. Add several drops of food coloring to the solution in each jar and stir. 6. Using one of the measuring spoons, carefully place a potato in each jar. 7. Allow the water to cool to room temperature. The jars should be about half full. If necessary, pour out some of the water at this point. 8. Fill up a container with plain water. Use the baster to carefully add this water to each jar until the jar is almost full. Dribble the water along the inside of the jar so that it does not mix up the solution. 9. Set the jars aside for 15 minutes and observe. Experiment Central, 2nd edition
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Summary of Results Write down or draw the results of the experiment. Was your hypothesis correct? Was there a difference in the stratification between the higher salinity water and the water of lower salinity? How does each compare to the control experiment? What does this tell you about the seawater where stratification occurs that lasts for hundreds or thousands of years? Name some reasons why stratification might occur for a short period of time. In the ocean both salinity and temperature affect density. As you write up your conclusions, hypothesize how changing the temperature of the salt water would affect the results. Change the Variables In this experiment you can
Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The water does not stratify and the potato sinks. Possible cause: Your tap water could have minerals in it, which would make it less dense. Try conducting the experiment again with purified water. Possible cause: You may not have thoroughly mixed the salt into the water. Try the experiment again, making sure to mix until the water is clear.
change the variables in several ways. You can alter the temperature of the water, mimicking the ocean conditions by using water of the same salinity and making the bottom layer cold and the top layer warm. You could make the salt water on the bottom warm and the fresh water cold. You can also use objects of differing densities to observe the relative density of the water. Modify the Experiment Bodies of water have varying levels of salinity. You can modify this experiment by measuring how different salinity levels affect ocean density. Collect several small, light objects, such as a the potato you used, a rubber band, button, tiny pebble, plastic bottle cap, small paperclip, or toothpick. If possible, collect two of each object. Fill three jars with warm water. In one jar, make a supersaturated solution of salt water. Stir in salt by the spoonful until the salt no longer dissolves in the water. Drop the items you have collected into the jar of plain water and stir. Wait a few moments and then collect only the items that sank to the bottom. If you have two of each item, leave them in the water jar. Now drop these items into the jar of salt water. Collect only the items that float. Use your third jar to measure how varying salinity levels affects density and items in the sea. Rinse off the items that sank in fresh water and floated in the supersaturated salt water. You should have at least two different objects. (You may need to test several more small items around Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the temperature of the water • the water contents • the quantity of hot or cold water placed in each jar • the quantity of the base water In other words, the variables in this experiment are everything that might affect the movement of the water. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on water’s density.
the house until you find ones that sink in water and float in the supersaturated salt water.) Place the items in the third jar and wait for them to sink. Mix into the water one tablespoon of salt at a time, stirring well after each addition. At what point does the salt water become denser than the items? Make a chart of the different objects and amount of salt you added until each item floats. If you know the amount of water, you can determine the percentage of salt. Is it more or less than the ocean?
EXPERIMENT 2 Currents: Water behavior in density-driven currents Purpose/Hypothesis One way that seawater
moves vertically is when a mass of water changes densities. These convection or density-driven currents occur at a slower rate than surface currents. Density-driven currents occur when water becomes less dense and begins to rise, or water becomes more dense and begins to sink. Either way, the moving water pushes the water below or above it to take its place. Density in ocean water is caused by both its salinity and temperature. This experiment focuses on how temperature differences help form density-driven currents. You will add liquids of different temperatures to various temperatures of water, and observe the behavior of the water. Dyes will allow you to observe the different temperature waters. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of density-driven currents. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one 780
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possible hypothesis for this experiment: ‘‘Colder water is denser than warmer water and will sink, How to Experiment Safely while the relatively warmer water will rise.’’ In this case, the variable you will change is Have an adult present when handling hot the temperature of the water. The variable you water. Either throw away the medicine or eyedropper or ask an adult to help you rinse out and will measure is the movement of the water. sterilize the dropper before putting it away. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control experiment and your experiment. For the control in this experiment, the temperature of the added liquid will be the same as the water already in the control jar. Level of Difficulty Easy. Materials Needed
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water 3 glass jars red and blue food coloring 2 cups for mixing 3 pieces of white paper or cardstock tea strainer or tongs eyedropper or medicine dropper ice-cube tray or small plastic cup
Approximate Budget $4. Timetable 15 minutes for the experiment; about one hour waiting time. Step-by-Step Instructions
1. Use the masking tape to label each jar: ‘‘Control,’’ ‘‘Hot,’’ and ‘‘Cold.’’ 2. Add several drops of blue dye to enough water to make two small, blue, ice cubes. Freeze. 3. When the blue water has frozen into ice, fill the ‘‘Cold’’ jar about two-thirds full with ice-cold water. 4. Fill the ‘‘Hot’’ jar about two-thirds full with hot water. Cover the jar to prevent the heat from escaping. 5. Fill the ‘‘Control’’ jar with room-temperature water. Experiment Central, 2nd edition
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Step 9: Use the tea strainer or tongs to hold one of the blue ice cubes and gently place it in the middle of the hot water in the ‘‘Hot’’ jar. GA LE GRO UP.
6. Fold the three pieces of paper or cardstock in half and place one in back of each jar. This will help you observe the experiment. 7. Let the water sit until completely still, about a minute. 8. While the water is sitting, add a small amount of red dye to about a quarter of a cup of hot water in a separate mixing cup. 9. Use the tea strainer or tongs to hold one of the blue ice cubes and gently place it in the middle of the ‘‘Hot’’ jar. 10. Use the eyedropper to release a small amount of the red-colored hot water in the middle of the cold water in the ‘‘Cold’’ jar. 11. Note the results. 12. In the ‘‘Control’’ jar, which has room-temperature water, gently place the second blue ice cube on the top of the water. Next, use the dropper to place a small amount of the hot, red-colored water deep in the water. Record the results. 13. For the control experiment, empty either the ‘‘Cold’’ jar or the ‘‘Hot’’ jar and refill with room-temperature water (allow the empty jar to return to room temperature before refilling). Use the dropper to place a small amount of room-temperature blue dye and room-temperature red dye in the water (rinse the dropper after placing the first color). Record the results. Summary of Results Examine the results of your experiment and draw the
movement of the water. Compare the results of the control to what you observed in the ‘‘Control’’ jar. How does what you observed relate to upwelling? In the ocean, both temperature and salinity affect the density of water; thus, both have an effect on density-driven currents. From what you have learned about seawater and density, write a paragraph on how adding salt to the dyed waters would affect the results. Change the Variables To change the variables in this experiment you can
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the ocean. You can also alter where the dyed water is placed in the jars. If a larger container was used you can vary the temperature of part of the water by using a heat lamp or heating the water from underneath.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem.
Design Your Own Experiment
Problem: The dyed water mixes into the jar’s water so quickly it is difficult to observe its movements.
How to Select a Topic Relating to this Concept The ocean is an immense subject with
Possible cause: You may have dropped or placed too much of the cold and/or hot water in the jar. Try the experiment again, using a smaller blue ice cube and only one large drop of the red water.
many possible projects that can branch from it. You could examine the properties of oceans and ocean life. You could also look at how oceans impact people’s lives. With oceanographers using incredible technological tools in their work, the study of the oceans is another possible topic to explore. Check the Further Readings section and talk with your science teacher to learn more about oceans. You can also gather ideas from following ocean explorers, who often show life footage or descriptions of their expeditions on the Internet. People who live near an ocean could consider taking a field trip to collect samples, look at sea life, or observe the ocean. If you do take a field trip, make sure to discuss your trip with an adult.
Problem: The results from the room-temperature water jar were the same as that of the Cold jar or Hot jar. Possible cause: The water in the jars may not have enough temperature variation between them. To make sure both the Control jar and the room-temperature jar have room-temperature water, allow lukewarm water to sit out for at least two to four hours. If you have a thermometer, it should be approximately 70–73˚ Fahrenheit (21–23˚ Celsius). Make sure the hot water is hot; 140–149˚ Fahrenheit (60–65˚ Celsius).
Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. Experiment Central, 2nd edition
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• State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts and drawings such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Many of the findings about oceans are relatively recent
and you can draw on this new information that oceanographers are discovering. The ocean is filled with life, from bacteria to fish to plants. You can explore the varied types of life and look at what lives in different parts of the ocean. Bioluminescence is one of the many adaptations that ocean creatures have developed. You can purchase bioluminescent organisms and observe their characteristics. Ocean plants differ from land plants in several ways. You can purchase an ocean plant and examine its characteristics. You could conduct a research project and study how the oceans support life suitable to that particular environment. You could also examine the physical properties of oceans. Waves and tides are two basic properties of oceans. You can create a small body of water in your bathtub or large container to examine the movements of waves. Place an object on the wave to examine if waves carry an object. Tides are dependent on geographic location and time of year. You can gather data on the Internet or reference books to predict the high and low tides of oceans around the world. Researching how scientists take the salt out of the ocean is another possible project.
For More Information Berger, Gilda, and Melvin Berger. What Makes an Ocean Wave? New York: Scholastic, 2001. Question and answer format about oceans and ocean life. 784
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‘‘Deep Ocean Creatures.’’ Extreme Science. http://www.extremescience.com/ DeepestFish.htm (accessed on March 14, 2008.) Nice pictures and facts on deep ocean creatures. Fleisher, Paul. Our Oceans: Experiments and Activities in Marine Science. Brookfield, CT: The Millbrook Press, 1995. Information on the physics and chemistry of the ocean with basic experiment ideas. Oceana. http://www.oceana.org (accessed on March 14, 2008). The ‘‘Beneath the Surface’’ area has lots of ocean information, live pictures, and interactive maps. ‘‘Ocean in Motion.’’ Office of Naval Research. http://www.onr.navy.mil/focus/ ocean/motion/tides1.htm (accessed on March 14, 2008). Brief explanation and animation of the tides. Pulley, Sayre, and April Pulley. Ocean. Brookfield, CT: The Millbrook Press, 1997. Description of the physical features, life, and use of the ocean. ‘‘Sea Dwellers.’’ Secrets of the Ocean Realm. http://www.pbs.org/oceanrealm/ seadwellers/index.html (accessed on March 14, 2008) Pictures of life in the ocean. ‘‘Water on the Move: The Ebbs and Flows of the Sea.’’ Museum of Science. http:// www.mos.org/oceans/motion/tides.html (accessed on March 13, 2008). From a museum ocean exhibit, includes real time tide data. Woods Hole Oceanographic Institute. Dive and Discover: Expeditions to the Seafloor. http://www.divediscover.whoi.edu (accessed on March 14, 2008). Follow ocean expeditions in this interactive web site.
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Optics and Optical Illusions
D
o you ever wonder how your eyes allow you to see? The science of light waves and how we see them is called optics. To understand optics, you must first understand a little about light itself.
A prism separates the colors in sunlight so we can see them. PH OTO RE SEA RC HER S I NC.
What is light made of? Visible light is a series of electromagnetic waves. These waves make up a small part of the electromagnetic spectrum, which includes many kinds of energy waves. You may be familiar with some of these, such as radio waves, microwaves, and X rays. Visible light is made of waves that are about 0.000014 to 0.000027 inches (360 to 700 nanometers) long. A nanometer is onebillionth of a meter. In this range are all the colors we can see; each color has a slightly different wavelength. Light does all kinds of interesting things. It can bounce off surfaces, particularly smooth surfaces. This is called reflection. It can also bend as it moves from one kind of material to another, such as from air to water. (That’s why a pencil sticking out of a glass of water looks bent.) This is called refraction. How do our eyes perceive light? The eye has a lens that focuses light onto a light-sensitive surface at the back of the eyeball, called the retina. The retina then sends nerve impulses to the brain, which the brain interprets as images. The lens in your eye is made of membranes and fluid, while the artificial lenses used in telescopes and cameras are glass or plastic. A lens must be made of a transparent material so that it can transmit a beam of light, forming an image. 787
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of lens being used • the focal length of the lens
What questions do you have about light and how we see it? You will have an opportunity to explore optics in the experiments that follow.
EXPERIMENT 1 Optics: What is the focal length of a lens?
Purpose/Hypothesis In this experiment, you will identify the focal point of different lenses and measure their focal lengths. When light rays • the distance from the object to lens pass through a lens, they converge at a single In other words, the variables in this experiment point, the focal point of the lens. The distance are everything that might affect the point at from the middle of the lens to the focal point is which the light focuses. If you change more than one variable, you will not be able to tell called the focal length. Every lens has its own which variable had the most effect on the focal focal length. length. The focal length of a lens indicates where the image will be focused and how powerful the lens is. In general, a lens has two rounded surfaces and its edges are fairly thin compared to its diameter. Focal length depends on the curvature of these surfaces. A convex lens has surfaces that curve outward, like a ball, while a concave lens has surfaces that curve inward, like the inside of a bowl. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of optics. This educated The focal length of a lens guess, or prediction, is your hypothesis. A hypothesis should explain indicates where the image will these things: be focused and how powerful the lens is. GA LE GRO UP. • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen • the angle at which you hold the lens relative to the light source
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The more convex the lens, the shorter the focal length.’’ 788
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WORDS TO KNOW Concave: Hollowed or rounded inward, like the inside of a bowl.
Nanometer: A unit of length; this measurement is equal to one-billionth of a meter.
Convex: Curved or rounded outward, like the outside of a ball.
Optics: The study of the nature of light and its properties.
Electromagnetic spectrum: The complete array of electromagnetic radiation, including radio waves (at the longest-wavelength end), microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays (at the shortest-wavelength end).
Prism: A piece of transparent material with a triangular cross-section. When light passes through it, it causes different colors to bend different amounts, thus separating them into a rainbow of colors.
Electromagnetic waves: Waves of energy that are part of the electromagnetic spectrum. Focal length: The distance of a focus from the center of a lens or concave mirror. Focal point: The point at which rays of light converge or from which they diverge.
Reflection: The bouncing of light rays in a regular pattern off the surface of an object. Refraction: The bending of light rays as they pass at an angle from one transparent or clear medium into a second one of different density.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Retina: The light-sensitive part of the eyeball that receives images and transmits visual impulses through the optic nerve to the brain.
Lens: A piece of transparent material with two curved surfaces that bend rays of light passing through it.
Variable: Something that can affect the results of an experiment.
In this case, the variable you will change will be the kind of lens, and the variable you will measure will be the focal length. You expect that lenses which are more convex will produce shorter focal lengths. Level of Difficulty Moderate, because of the materials needed. Materials Needed
• 3 or 4 different lenses, labeled for convexity and concavity (You might borrow them from school or buy them at a science museum shop.) • ruler or tape measure • large, white piece of paper or tagboard • small lamp Experiment Central, 2nd edition
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Approximate Budget $20 to purchase lenses.
How to Experiment Safely Do not drop the lenses, and try not to touch the lens surfaces with your fingers. Hands naturally have a lot of oils on them, which will affect how the lenses work.
Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can definitely be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: You cannot see an image at all. Possible cause: Your room is not dark enough or your object is not bright enough. Try darkening the room more or choosing a brighter light source. Problem: The focal length measurements are all alike. Possible causes: 1. Your lenses are too similar. Check the lens labels and make sure you have lenses with different characteristics. Someone at the store where you purchased them should be able to help. 2. You are not looking closely enough at the image to see where it is in focus. Sometimes the focus can be subtle. Look more closely at your cards.
Timetable 2 hours. Step-by-Step Instructions
1. Choose a room where you can dim the lights and set up the experiment. Place your lamp at least 3 feet (1 meter) away from your first lens. 2. In the dim light, hold the white card on the other side of the lens and look for the image of your object (the lamp). If you cannot see it, move the card closer to or farther from the lens until you can find it. Keep adjusting the distance of the card until your image is focused. 3. Set up a data chart, and describe what you see. How does the image look in comparison to the actual object? Write down any differences you observe. 4. Measure and record the distance between the lens and the card on which the focused image appears. Be sure to note which lens you were using. 5. Repeat the above steps with your other lenses. Record your findings on your chart. Summary of Results Study the results on your
chart. Which kind of lenses produced short focal lengths? Which produced longer ones? Was your hypothesis correct? Summarize what you have found. Change the Variables You can vary this experi-
ment in several ways. For example, try varying where you place the object on the other side of the lens. Measure and record what you find. You can also try placing two or more lenses next to each other and observe the effect on the image. Do 790
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the lenses add their effects together or do they cancel each other out? Does the image change size or direction? Record what you find.
EXPERIMENT 2 Optical Illusions: Can the eye be fooled? Purpose/Hypothesis After the lenses in your eyes
focus light, your brain must make sense of the images formed. This is not always easy. Optical illusions occur when the brain is tricked into thinking things are not as they are. These illusions use the way your brain processes optical information to fool you into seeing things that are not there. Examining how people react to optical illusions will help you understand how the eyes and brain work. In this set of experiments, you will explore how people perceive images. For each of the images illustrated, write a hypothesis about what people will see. For example, for the second picture, you will ask ten people this question: ‘‘Which figure is larger?’’ How do you think people will answer? Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of how your brain perceives images. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for the first image in this experiment: Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the image you are testing • the people you use as test subjects • the different ways the image can be seen • the lighting on the image • what you tell the test subject about the image before he or she views In other words, the variables in this experiment are everything that might affect how a person perceives the image. If you change more than one variable, you will not be able to tell which variable had the most effect on the test subject’s perception.
Optical illusion #1. G AL E GR OUP .
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‘‘Eight out of ten people will see non-parallel lines.’’ Write a hypothesis for the other images. In this case, the variable you will change will be the person viewing the image, and the variable you will measure will be how that person perceives the image. For the first image, you expect that most, but not all, of the people will perceive that the lines are not parallel. Remember, the more people you test, the more accurate your results will be. After you complete these experiments, you will draw some conclusions about how the mind perceives visual images. Level of Difficulty Difficult, because of the need
to gather test subjects. Materials Needed Optical illusion #2. G AL E GRO UP.
• images provided throughout Experiment 2 • at least 10 people as test subjects • paper and pencil • a well-lighted room Approximate Budget $0.
Optical illusion #3. G AL E GRO UP.
Timetable Depends on the subjects’ availability. Step-by-Step Instructions
1. Find at least 10 people who are willing to participate in your project. Explain the task to them. 2. Photocopy the images illustrated throughout Experiment 2, enlarging them if possible. Make sure the copies are clear. 3. Prepare a question for each of the images. 4. List the images on a data sheet, number them, and record the question you will ask for each one. Make a column where you 792
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will write each subject’s answer. Make a copy of the data sheet for each subject. 5. Conduct your interviews with one subject at a time. Carefully record their answers on a data sheet. Summary of Results Study your findings care-
fully. Did people have similar reactions to the images, or were they varied? What conclusions, if any, can you draw about the way the eyes and the brain work together on perception? Were any or all of your hypotheses correct? Change the Variables You can vary this experi-
ment in several ways. For example, locate other optical illusions and test people’s reactions. How does this add to what you learned about perception in the first set of experiments? Does it change your ideas, or confirm them? Or you can try testing a different set of people. Ask young children, older people, or another group. Do their responses change? Can you draw any conclusions about the way people perceive things as they get older? Modify the Experiment You can make this experiment more difficult by testing what reasons could influence people seeing illusions. In order to do this, you will need to focus on only one of the images provided. Think about some reasons why the brain may cause people to see an illusion, and then form a hypothesis. For example, familiarity of a picture may lead people to draw conclusions about an image that looks like the familiar image. A person may need more time to process certain images. If a test person were warned beforehand that there is something odd about an image, does the person still perceive the illusion? If the test person were given 60 seconds to study the image, instead of 10 seconds, what is the result? What if a contrasting color were placed behind the image? After you come up with a series of possible factors that may influence the perception of a test person, write them down in a chart. Select Experiment Central, 2nd edition
Optical illusion #4. GAL E GRO UP .
Optical illusion #5. GA LE GR OU P.
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How to Experiment Safely There are no hazards associated with this experiment.
Troubleshooter’s Guide Experiments using people can be difficult. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: Subjects look at images for a long time and say they can see it in many ways.
the one you hypothesize will play the largest role in perception and start testing people. You will need a lot of test subjects, because you will only be able to test one hypothesis for each group of ten people. For example, if you are testing how looking at an image for a longer amount of time will affect subjects’ perception, you will need to show the image to ten subjects for a relatively long amount of time. Compare those results with the results from Experiment 1. Then, you will need another set of ten subjects to test out another hypothesis.
Design Your Own Experiment How to Select a Topic Relating to this Concept If you are interested in optics, you
could further investigate kinds of lenses. You could examine reflection and refraction with mirrors or prisms, which bend light and separate out the different wavelengths so you can see different colors. You could study the effects of Problem: It is difficult to draw conclusions from polarizers, which line up different wavelengths of the many different answers subjects gave. light, creating interesting effects, like the polarPossible cause: Everyone perceives things a izing filters used on cameras. little differently. Study how your subjects If you are interested in optical instruments, responded, think about what you see, and try to you can build your own camera or investigate telethink of reasons why people may see things scopes, microscopes, and magnifying lenses. You differently. Do you think it has to do with their can explore illusions involving color, movement, eyes? Their brains? Their past experience? You and three-dimensional objects. Or you could may decide that you cannot draw any conclusions from the data you collected. That often explore the work of M.C. Escher, who drew pichappens in the field of science. tures that confuse the mind. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on optics questions that interest you. Possible cause: Explain clearly that you are trying to explore the way perception works and so you want their first reaction. Tell them not to spend too much time analyzing what they see.
Steps in the Scientific Method To do an original experiment, you need to
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what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results
Your data should include charts, such as the ones you did in these experiments, that are clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental set-up and results. If you are preparing an exhibit for a science fair, display any optical instruments you built or copies of the illusions you worked with. If you have done a nonexperimental project, explain clearly what your research question was and illustrate your findings.
The lens in a camera focuses light from a subject you are photographing onto the camera film. U. S. GEO LO GIC AL SUR VE Y.
Related Projects There are also other ways you can explore the topic of
optics, such as building models of optical instruments or studying their history. If you are interested in perception, you could explore the connections between perception and art and research artists who have studied how the mind perceives images. All of these ideas would lead to fascinating projects.
For More Information Ardley, Neil. Science Book of Light. Burlington, MA: Harcourt Brace, 1991. Simple experiments demonstrating principles of light. Experiment Central, 2nd edition
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Armstrong, Tim. Make Moving Patterns: How to Make Optical Illusions of Your Own. Jersey City, NJ: Parkwest Publications, 1993. Ideas for creating your own series of optical illusions. Davidson, Michael W., and The Florida State University. Science, Optics & You. http://micro.magnet.fsu.edu/optics/index.html (accessed on January 14, 2008). Levine, Shar, Leslie Johnstone, and Jason Coons. The Optics Book: Fun Experiments with Light, Vision & Color. New York: Sterling Publications, 1998. Informative book on light, vision, and optical instruments, with experiments, explanations, and drawings. Seckel, Al. Optical Illusions: The Science of Visual Perception. Buffalo, NY: Firefly Books, 2006. Collection of optical illusions, with information on the science of visual perception.
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Osmosis and Diffusion
G The smell of vanilla quickly diffuses in all directions. K ELL Y A . Q UIN .
as and liquid molecules are always in motion. They move randomly in all directions and bounce around and into each other. As they move, molecules have a tendency to spread out, moving from areas with many molecules to areas with fewer molecules. This process of spreading out is called diffusion. You have probably noticed diffusion in your home. If you opened a bottle of vanilla in your kitchen, for example, you probably could soon smell the vanilla in all parts of the room. The vanilla spread through the air from an area of high concentration of vanilla molecules to areas of less concentration. They diffused throughout the room—and perhaps throughout the house. Osmosis (pronounced oz-MO-sis) is a kind of diffusion. Osmosis occurs when a substance diffuses across a semipermeable membrane from an area of high concentration to an area of low concentration. A semipermeable membrane lets some substances through but not others. What are some examples of diffusion? Diffusion takes place constantly in our bodies and is vital to cell functioning. Cell walls are selectively permeable, meaning that certain substances can pass through them, but others cannot. Diffusion allows certain materials to move into and out of cell walls, from a higher concentration to a lower concentration. For example, oxygen diffuses from the air sacs in your lungs into your blood capillaries because the concentration of oxygen is higher in the air sacs and lower in the capillary blood. 797
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Oxygen enters blood cells by diffusing from areas of high concentration to areas of low concentration. PH OTO RES EA RC HER S I NC.
Different kinds of membranes allow differing amounts of diffusion to occur. Think about a helium balloon. It starts out full of helium and floats upwards, but over a period of a day or two it loses helium until it is no longer lighter than air and cannot float any more. Why does this happen? The balloon allows the helium atoms to pass through it into the atmosphere. Helium atoms slowly diffuse from an area of high concentration (inside the balloon) to an area of lesser concentration (the great outdoors). How does osmosis work? When materials move into and out of a cell at equal rates, the cell is said to be balanced, or in dynamic equilibrium. An isotonic solution has a concentration of materials the same as that inside a cell. If a cell is placed in an isotonic solution, molecules will still move into and out of the cell, but the cell will be in dynamic equilibrium. If a substance is in lower concentration outside a cell than inside the cell, the substance will leave the cell through osmosis. Likewise, the substance will move into the cell if the situation is reversed. A hypotonic solution, where the concentration of substances is lower than that in the cell, draws substances out of the cell. What do you think will happen if the cell is in a hypertonic solution, where the concentration of materials in the solution is higher than that inside the cell? We see examples of osmosis and diffusion all around us. When you add water to a wilted plant, for example, it soon stands up straight. You have just seen osmosis in action! Do you have questions of your own about osmosis? You will have an opportunity to explore osmosis and diffusion in the following experiments.
EXPERIMENT 1 Measuring Membranes: Is a plastic bag a semipermeable membrane? Purpose/Hypothesis In this experiment, you will find out how a thin
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WORDS TO KNOW Concentration: The amount of a substance present in a given volume, such as the number of molecules in a liter.
Hypotonic solution: A solution with a lower concentration of materials than a cell immersed in the solution.
Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Isotonic solutions: Two solutions that have the same concentration of solute particles and therefore the same osmotic pressure.
Diffusion: Random movement of molecules that leads to a net movement of molecules from a region of high concentration to a region of low concentration.
Molecule: The smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms.
Dynamic equilibrium: A situation in which substances are moving into and out of cell walls at an equal rate. Hypertonic solution: A solution with a higher concentration of materials than a cell immersed in the solution. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Osmosis: The movement of fluids and substances dissolved in liquids across a semipermeable membrane from an area of its greater concentration to an area of its lesser concentration until all substances involved reach a balance. Semipermeable membrane: A thin barrier between two solutions that permits only certain components of the solutions, usually the solvent, to pass through. Variable: Something that can affect the results of an experiment.
some kinds of molecules to pass through but not others. For example, the plastic might allow small molecules to pass through, but not larger ones. You will test two solutions—iodine and starch, each with a different size molecule—to see what happens. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of osmosis. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
A helium balloon is a semipermeable membrane. PHO TO R ES EAR CH ERS IN C.
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of solution • the kind of membrane • the thickness of the membrane • the temperature of the solutions • the color of the solutions • the volume of the solution inside the bag and in the measuring cup In other words, the variables in this experiment are everything that might affect whether a solution passes through a membrane. If you change more than one variable, you will not be able to tell which variable had the most effect on the passage of the solution through the membrane.
Step 3: Water baggie in the measuring cup. GAL E GR OU P.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘Iodine will cross through the plastic membrane, while starch will not.’’ In this case, the variable you will change will be the solutions. The variable you will measure will be changes in the solutions in the bag and in the measuring cup that holds the bag. You expect the iodine solution to pass through the plastic baggie, while the starch solution will not. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental set-up, and that is the solution in the plastic bag. For the control, you will use a bag of water. For your experiment, you will use a bag of starch solution. You will put both bags into iodine solutions in measuring cups. After you allow the solutions time to diffuse through the bag, you will observe the color and the volume of water in both the plastic bags and the measuring cups. A color change may occur because when iodine comes into contact with starch, the starch solution turns bluish-black. If the starch solution in the bag turns bluish-black, you will know that iodine solution in the measuring cup has crossed through the plastic membrane and entered the bag. If the blue iodine solution in the measuring cup turns black, you will know that starch has crossed through the membrane into the cup. If the solution in the bag turns black, but the cup solution does not, you know your hypothesis is correct: iodine crossed through the plastic membrane, but the starch did not. Level of Difficulty Moderate.
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Materials Needed
• 2 quart-size (1-liter size) measuring cups • a smaller measuring cup or graduated cylinder • small sealable plastic bags • cornstarch • water • iodine with dropper • masking tape • measuring spoons and cups • goggles
How to Experiment Safely Wash your hands before, during, and after the experiment, so you do not transfer the starch or iodine on your hands. Wear goggles so you do not get the iodine in your eyes. Be careful with all glassware.
Approximate Budget Less than $10. (Most of these materials should be available in the average household.) Timetable 2 days, leaving experiments overnight. Step-by-Step Instructions
1. Prepare your solutions. Add 1 tablespoon (15 milliliters) of cornstarch for each cup of water to make the starch solution. Add 10 drops of iodine for each cup of water to make the iodine solution. You will probably need a total of 10 to 12 cups of each solution. 2. For your control, fill one baggie with water. Seal it tightly to prevent leakage. Place 2 to 3 cups iodine solution in one large measuring cup. Record the exact amount of solution in the cup, using the measuring lines on the side of the cup.
Steps 7 and 8: ‘‘Control’’ and ‘‘Experiment’’ measuring cups. GA LE G RO UP.
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Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The iodine solution changed color right away. Possible cause: Starch solution leaked out or was on the outside of the bag. Seal your bag tighter and wash the outside carefully. Problem: There was no change in color. Possible cause: Those plastic baggies are not permeable to either solution. Try a thinner baggie or a different brand. Problem: There is no change in volume. Possible cause: The solutions are not strong enough. Try adding more cornstarch or iodine to your solutions.
3. Fill another measuring cup with 2 cups (500 milliliters) of plain water. Place the water baggie in this cup and record how much the water level rises. The difference in the water level is the volume of the water in your baggie. 4. Place the water baggie in the cup of iodine solution you prepared. Label the cup ‘‘control’’ with masking tape and set it aside. 5. Fill another baggie with starch solution and seal it. Measure and record its volume, as in Step 3. Carefully rinse the outside of the bag with water to wash off any starch solution. 6. Place 2 cups (500 milliliters) of iodine solution in another large measuring cup. Record the exact volume. 7. Lower the bag of starch solution into the iodine solution. Label this cup ‘‘experiment.’’ 8. Let the control and experimental cups sit overnight. 9. The next day, check the solutions in the bags and in the cups. What colors are they? Measure and record the volume of water in the cups and the bags.
Step 9: Data chart for Experiment 1. GAL E GR OU P.
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Summary of Results Study the results on your
chart. Did the color of the solutions change? Remember that if the starch solution in the bag turned black, iodine entered through the plastic membrane. If the iodine solution in the cup turned black, starch must have leaked out of the bag. If the volume of solution in the bag increased, you know that molecules were entering the bag, but few were leaving. Was your hypothesis correct? What have you discovered? What happened in the control cup? Change the Variables You can change thevariables
and repeat this experiment. For example, try adding more iodine and cornstarch to create stronger solutions. See how that affects the change in volume and/or the rate of osmosis. (Or try using weaker solutions.) You can also try using different varieties of plastic bags or different materials altogether. See which ones allow certain solutions through and how quickly.
EXPERIMENT 2
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • type of solution in balloon • thickness of balloon • the temperature of the water • amount of water in the bucket and the balloon In other words, the variables in this experiment are everything that might affect the movement of water across the membrane. If you change more than one variable, you will not be able to tell which variable had the most effect on the movement across the membrane.
Step 2: Funneling fresh water into a balloon. GAL E GR OU P.
Changing Concentrations: Will a bag of salt water draw in fresh water? Purpose/Hypothesis In this experiment, you will see osmosis in action. You will place a balloon filled with salt water into a bucket of fresh water and watch what happens. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of osmosis. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Experiment Central, 2nd edition
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A hypothesis should be brief, specific, and measurable. It must be something you can test How to Experiment Safely through observation. Your experiment will prove or disprove your hypothesis. Here is one possible There are no safety hazards in this experiment. hypothesis for this experiment: ‘‘A balloon filled with salt water will expand when placed in fresh water.’’ In this case, the variable you will change will be the kind of water you put in the balloon and the variable you will measure will be how much water enters the balloon as reflected by changes in the volume of the balloon. You expect the balloon filled with salt water will absorb fresh water and expand. Only one variable will change between the control experiment and the experimental balloon, and that is the kind of solution inside the balloon. For the control, you will use fresh water. For your experimental balloons, you will use two different concentrations of salt water. You will measure how much water is in the balloons after they soak in fresh water. If the experimental balloons gain water when they have salt water in them, and the control balloon does not, then your hypothesis will be supported. Level of Difficulty Easy. Materials Needed
• salt • at least three thin balloons or sealable baggies • 3 buckets or other large containers
Steps 2 to 5: Balloons in labeled buckets. GAL E GR OU P.
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• • • • •
funnel measuring cup measuring spoons 2 bowls stirrer
Approximate Budget $3 for balloons. Timetable 1 hour to set up the experiment; 1 day to view the results. Step-by-Step Instructions
1. Measure 12 cups (6 pints or 2.8 liters) of water into each bucket. 2. Use the funnel to pour 1 cup (.5 liter) of fresh water into a balloon. Tie the balloon tightly and place it in a bucket labeled ‘‘control.’’ 3. Use the bowls to prepare two salt solutions with different concentrations. For Solution 1, add 3 teaspoons of salt to 2 cups of water. For Solution 2, add 9 teaspoons of salt to another 2 cups of water. Stir both solutions until the salt dissolves. 4. Use the funnel to pour one cup of Solution 1 into one balloon and tie it tightly. Rinse the funnel. Then use the funnel to pour one cup of Solution 2 into another balloon and tie it tightly. 5. Place each balloon into its own bucket, labeled ‘‘Solution 1’’ and ‘‘Solution 2.’’ 6. Leave all three buckets overnight.
Step 7: Data chart for Experiment 2. GA LE G ROU P. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: No volume change occurred at all. Possible causes: 1. You have used a very thick balloon that is not permeable. Try a different kind of balloon or baggie. 2. Your solutions were not well mixed. Try adding more salt and stirring longer. Problem: One or more of the balloons exploded.
7. The next day, examine all three balloons. Measure the change in volume by placing each one in a large (1000-milliliter) measuring cup filled with 2 cups (500 milliliters) of water. Record how high the water rises. The difference is the volume in the balloon. Summary of Results Study the results on your chart. Compare the change in volume for each balloon to any change in your control. The more volume the balloons gained, the greater amount of osmosis occurred. What did you find? Was your hypothesis correct? Write a paragraph summarizing and explaining your findings.
Change the Variables There are several ways you can vary this experiment. For example, try other salt concentrations. Add more salt or less. Or try sugar or starch solutions and see what effect those have on amount of osmosis that occurs. You can also experiment with different membranes, such as thicker or thinner balloons or baggies or balloons made of Mylar. See what kind of effect these have on osmosis. Finally, you can see how long osmosis takes under the different conditions you are testing.
Possible cause: The balloon membrane is very thin and too much water entered. Try using weaker salt solutions or not leaving the balloon in the water for as long.
EXPERIMENT 3 Changing Sizes: What effect does molecule size have on osmosis Purpose/Hypothesis In this experiment, you will see how molecules of
certain sizes can move through a membrane through osmosis. A semipermeable membrane allows smaller molecules, such as water, to move through the membrane. Larger molecules, such as sugar, that are too large to move through the membrane cannot pass. The membrane you will use will be the membrane of an egg. The solutions you will use will be water and corn syrup, which contains sugar. You will first need to dissolve the shell to expose the membrane. The acid in vinegar will dissolve the eggshell. Vinegar contains about 5 percent 806
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acid. In order to speed up the experiment, you can strengthen the concentration of the acid What Are the Variables? by boiling off some of the water. Then you will observe osmosis with the egg membrane in disVariables are anything that might affect the tilled water and another egg membrane in corn results of an experiment. Here are the main variables in this experiment: syrup. Before you begin, make an educated guess • the type of solution about the outcome of this experiment based on • the temperature of the solution your knowledge of osmosis. This educated guess, • the type of egg or prediction, is your hypothesis. A hypothesis In other words, the variables in this experiment should explain these things: are everything that might affect the movement • the topic of the experiment of the solution through the egg membrane. If • the variable you will change you change more than one variable, you will not be able to tell which variable had the most • the variable you will measure effect on the movement of the solution across • what you expect to happen the membrane. In this experiment, you will A hypothesis should be brief, specific, and compare the two eggs against one another. measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The smaller the molecular size the more readily the solution will move through the membrane and the more the egg will weigh.’’ In this case, the variable you will change will be the size of the molecules that surround the egg membrane. The variable you will measure will be the weight of the egg, both before and after the egg is immersed in the water and corn syrup. Level of Difficulty Moderate. Materials Needed
• corn syrup • white vinegar • 2 glass containers, just large enough to fit an egg • 2 large slotted spoons • 2 eggs • distilled water • pot • stove or hot plate Experiment Central, 2nd edition
How to Experiment Safely Have an adult help you simmer the vinegar, and be careful when handling any hot solutions. Wash your hands after handling the egg or vinegar.
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• measuring cup • gram scale Approximate Budget $10. Timetable 30 minutes to set up the experiment; three to five days to complete. Step-by-Step Instructions
Step 2: Pour the concentrated vinegar over the egg. ILL US TRA TI ON B Y TE MA H NE LS ON.
Steps 4 and 9: Weigh the eggs on a gram scale and note their weight. I LL UST RA TI ON BY T EM AH NE LS ON.
1. Simmer 4 cups of vinegar on a hot pot or stove until the vinegar boils down to 1 cup. Cool completely. 2. Place each egg in a small glass jar. Pour enough of the concentrated vinegar over each egg until the egg is completely covered. Set aside. 3. After two days, the shell should be dissolved completely. If it’s not, set aside for another day. Using a slotted spoon, carefully scoop out the egg. Rinse each egg under running water until it is clean. 4. Weigh the egg on a gram scale and note its weight. 5. Rinse and wipe dry the two glass jars. Label one jar ‘‘Distilled Water.’’ Label the second jar ‘‘Corn Syrup.’’ 6. Place one shelled egg in each of the glass jars. 7. In the jar labeled ‘‘Distilled Water,’’ immerse the egg with distilled water. In the jar labeled ‘‘Corn Syrup,’’ immerse the egg with corn syrup. Set aside. 8. After one day, look at the eggs and note the description. 9. Using a slotted spoon, carefully scoop out each egg and weigh. Note the weight of each egg. Summary of Results Compare the appearance
and weight of the eggs. Did both the corn syrup and distilled water move through the membrane? How did the size of the molecules in the water and corn syrup play a role in 808
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osmosis? Was your hypothesis correct? Write a paragraph summarizing and explaining your findings. Change the Variables There are several ways you
can vary this experiment. For example, try other sugary liquids, such as different types of maple syrup or sugar water. You can also try various types of eggs, to test if the membranes are different. You can change the temperature also, repeating the experiment in a cold or warn water bath.
Design Your Own Experiment How to Select a Topic Relating to this Concept
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The egg shell is not dissolving. Possible causes: There may not be enough acid in the vinegar or you did not wait long enough for the eggshell to dissolve. Try immersing the egg in vinegar again and waiting slightly longer. Problem: The solution did not move into or out of the membrane. Possible cause: The membrane was too dirty with the shell remains. Repeat the experiment, rinsing off the egg thoroughly with warm water until the egg is completely smooth to the touch.
If you are interested in osmosis and diffusion, you might study their effects on living organisms or the effects of different solutions on plants or on simple one-celled organisms, such as a paramecium. Are you interested in rates of diffusion? Try timing how long different solutions take to diffuse throughout water. Or create solutions using different-size molecules and higher and lower concentrations. You might separate solutions and then watch what diffuses through membranes. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on osmosis questions that interest you.
Step 7: In the jar labeled ‘‘Distilled Water,’’ immerse the egg with distilled water. In the jar labeled ‘‘Corn Syrup,’’ immerse the egg with corn syrup. I LLU STR AT IO N BY TEM AH N EL SON .
Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
distille d water
corn syrup
• State the purpose of—and the underlying question behind—the experiment you propose to do. Experiment Central, 2nd edition
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• Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts, such as the ones you did in these experiments. All charts should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental set-up and results. If you are preparing an exhibit for a science fair, display your results, such as any experimental set-ups you built. If you have done a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects You can design projects that are similar to these experi-
ments, involving trials and charts of data to summarize your results. You could also prepare a model that demonstrates a point you are interested in with regard to osmosis or diffusion. Or you could investigate the effects of osmosis in a certain environment. There are many options.
For More Information Gardner, Robert. Experimenting with Water. New York: Franklin Watts, 1993. Fascinating experiments that explore the strange properties of water. Vancleave, Janice Pratt. Janice Vancleave’s Biology for Every Kid: One Hundred One Easy Experiments That Really Work. New York: John Wiley & Sons, 1989. Basic principles of biology of plants and animals through informative text and experiments.
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o you know what rusting metal, photographic processes, battery operation, and clothes bleaching have in common? They are all examples of an important and common kind of chemical reaction called an oxidation-reduction reaction. This kind of reaction involves the transfer of electrons, which are tiny particles in atoms. During oxidation, a substance’s atoms lose electrons. During reduction, a substance’s atoms gain electrons.
Rust destroys millions of dollars in property every year. PH OTO R ES EA RCH ER S IN C.
What actually happens during oxidation? To understand oxidation, it is important to understand how atoms work. All atoms have three kinds of tiny particles—electrons, protons, and neutrons. Electrons have negative electrical charges, while protons have positive charges. Neutrons are neutral—neither positive nor negative. The sum of the electrical charges in each atom are balanced, so atoms is electrically neutral. The oxidation state of an atom is the sum of its positive and negative charges, and the oxidation state of any atom is zero. Oxidation reactions involve a change in the oxidation state of the atoms involved, caused by a loss or gain of electrons. During oxidation, an atom loses electrons and becomes a positively charged ion. (An ion is an atom or a group of atoms that carries an electrical charge, either positive or negative.) Metal atoms tend to undergo oxidation easily. In an oxidation reaction, the metal loses one, two, or three electrons and becomes positively charged. The other substance, a nonmetal, gains electrons, becoming a negatively charged ion. The nonmetal is thus reduced. Remember that oxidation cannot occur without a corresponding reduction reaction. 811
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WORDS TO KNOW Atom: The smallest unit of an element, made up of protons and neutrons in a central nucleus surrounded by moving electrons. Control Experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Results from the control experiment are compared to results from the actual experiment. Corrosion: An oxidation-reduction reaction in which a metal is oxidized (reacted with oxygen) and oxygen is reduced, usually in the presence of moisture. Electron: A subatomic particle with a mass of about one atomic mass unit and a single negative electrical charge that orbits the nucleus of an atom. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment Ion: An atom or groups of atoms that carries an electrical charge—either positive or negative—as a result of losing or gaining one or more electrons. Neutron: A subatomic particle with a mass of about one atomic mass unit and no electrical charge that is found in the nucleus of an atom.
Oxidation: A chemical reaction in which oxygen reacts with some other substance and in which ions, atoms, or molecules lose electrons. Oxidation-reduction reaction: A chemical reaction in which one substance loses one or more electrons and the other substance gains one or more electrons. Oxidation state: The sum of an atom’s positive and negative charges. Oxidizing agent: A chemical substance that gives up oxygen or takes on electrons from another substance. Proton: A subatomic particle with a mass of about one atomic mass unit and a single positive electrical charge that is found in the nucleus of an atom. Reduction: A process in which a chemical substance gives off oxygen or takes on electrons. Variable: Something that may affect the results of an experiment.
What are some examples of oxidation? One common example of an oxidation reaction is the one that occurs between sodium, a soft metal, and chlorine, a gas. When these elements exchange one electron, a violent reaction occurs, and a new substance, sodium chloride, is formed. We know it as the hard, white substance often found on the kitchen table: salt. Here is what happens: both sodium (Na) and chlorine gas (Cl2) are electrically neutral. When they combine, sodium undergoes oxidation, loses an electron, and becomes positively charged. Chlorine undergoes reduction and becomes negatively charged. Because atoms do not ‘‘like’’ to be charged, the sodium and the chlorine are attracted to their opposite charges and combine to create salt. 812
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Oxidation reactions play an important role in many processes of modern life; the results are all around us. One of the most common places you see the results of oxidation is in the process of corrosion, particularly involving iron and steel. Iron oxide flakes off in what we call rust. An oxidizing agent is anything that causes another substance to lose electrons. Bleaches are one example. Bleaches remove electrons that are activated by light to produce colors. What kind of questions do you have about oxidation-reduction? You’ll have an opportunity to explore oxidation in the following experiments and think about designing your own experiments on this important and far-reaching topic.
EXPERIMENT 1
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of solution being used • the cleanliness of the pennies prior to the experiment • the time allowed for the pennies and nails to soak in the solution • the color of the pennies and the nails after they have soaked in the solution In order to test your hypothesis, you can change only one variable at a time. If you change more than one, you will not be able to tell which factor caused a change in the outcome of your experiment.
Reduction: How will acid affect dirty pennies? Purpose/Hypothesis In this experiment, you will find out how an acid
leads to a reducing reaction, and you will explore the movement of atoms during the reaction. Acids are important reducing agents, involved in many common chemical reactions in our daily lives. Pennies are coated with copper oxide (CuO), which forms when copper combines with oxygen from the air. Pennies look dirty when they are coated copper oxide. In this experiment, you will immerse pennies into a mixture of vinegar or lemon juice and salt—which dissolves copper oxide. (Vinegar and lemon juice are weak acids; the salt helps the reaction.) When you put the dirty pennies into the solution, the copper oxide and copper will dissolve into the water. Some of the copper atoms will leave their electrons behind and float in the water as positively charged copper ions, missing two electrons. They have been reduced. When you put steel nails into the same solution, the salt and vinegar dissolve some of the iron from the nails. When the iron atoms leave, they also leave electrons behind just as the copper did. Now you will have positively charged iron ions floating around in the solution with the positively charged copper ions. Since the nails will now have extra electrons left on them from the iron atoms that dissolved into the Experiment Central, 2nd edition
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solution, the nails are negatively charged. What happens when there are positive and negative How to Experiment Safely charges near each other? They attract! What do you think will happen to the copper ions as they Wash your hands before and after handling the get near the negatively charged nails? dirty pennies and other materials. Wear goggles and rubber gloves to avoid eye and skin contact Do you have an educated guess about what with the acid solutions. Be careful in handling will happen to the pennies and the nails in the the nails to avoid cuts or punctures. acidic solution? That educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘An acidic solution will cause the pennies to become clean and copper to coat the nails.’’ Variables are anything that can be changed in an experiment. In this case, the variable you will change will be the acid in your solution, and the variable you will measure will be the color (a measure of cleanliness) of the pennies and the color of the nails after they have soaked in the solution. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental bowls, and that variable is the kind of solution you use to immerse the pennies and nails. For the control, you will use plain water. For your experimental bowls, you will use lemon juice and vinegar.
Steps 1 to 5: Bowl set-up with pennies. GAL E GR OU P.
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Step 3: Data sheet for Experiment 1. GA LE G ROU P.
You will record the color of the pennies and the nails both before and after you immerse them in the solutions. If the pennies become cleaner and brighter, and the nails become copper-colored, your hypothesis is supported. Level of difficulty Moderate. Materials Needed
• • • • • • • • • •
45 equally dirty pennies ¼ cup lemon juice ¼ cup white vinegar ¼ cup water 2 teaspoons salt 3 glass or ceramic bowls 6 clean steel nails (not galvanized nails) paper towels goggles rubber gloves
Step 9: Place a nail in each bowl. Lean a second nail against the side of the bowl so only about half of it is in the solution. G AL E GR OUP .
Approximate Budget Up to $5. (Try to borrow
the goggles from your school.) Timetable 2 hours. Step-by-Step Instructions
1. Put water in one bowl, lemon juice in another, and vinegar in a third. Label Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are some problems that may occur during the experiment, possible causes, and ways to remedy the problems.
2.
3.
Problem: The pennies did not change color in any of the solutions.
4.
Possible causes: 1. Your pennies were not dirty enough. Find dirtier pennies and repeat the experiment. 2. Your solutions are not acidic enough. Check the expiration dates on your bottles of vinegar and lemon juice, and replace them, if necessary.
5. 6.
Problem: The nails did not pick up any copper at all.
7.
Possible causes: 1. Make sure your nails are steel and clean. Impurities can affect the oxidation reaction. 2. You may not have left them in solution long enough, or if the pennies did not have much copper oxide on them, little copper will be in solution. Run the experiment again with dirtier pennies and leave the nails for a longer time.
8. 9.
10. 11.
each bowl if you need help telling them apart. Add 1 teaspoon salt to the vinegar solution and to the lemon juice, and stir until it dissolves. Examine the color of the pennies carefully. Describe the color on your data sheet, illustrated. Place one penny in each bowl. Describe what happens on your data sheet. Place 14 more pennies in each bowl. Watch what happens to them. After five minutes, remove the pennies from one bowl. Rinse them thoroughly under running water and place them on a paper towel to dry. Write the kind of solution they were soaking in on the paper towel. Repeat Step 6 with the pennies from the other two bowls. Examine the nails carefully and describe their color on your data sheet. Place a nail in each bowl. Lean a second nail against the side of the bowl so only about half of it is in the solution. After 10 minutes, examine the nails. Record the colors on your data sheet. Leave the nails for an hour and then examine them again.
Summary of Results Study the results on your chart. What have you discovered? What color changes took place? Why? Was your hypothesis correct? Write a paragraph to summarize and explain your findings. Change the Variables You can vary this experiment. Here are some
possibilities: • Try different solutions to see how they affect the oxidation/reduction reaction, such as baking soda, bleach, or tomato juice. Or try 816
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diluting the solutions with water to vary the ratio of water to acid. Be sure to record how much of each you use. Again, be careful in handling these liquids. Wear goggles and gloves and work in a ventilated area, especially when using bleach. • Vary the time you leave the pennies and nails in the solution. What happens?
What Are the Variables? Variables are anything that could affect the results of an experiment. Here are the variables in this experiment: • the amount of water in jars • the amount of air in each jar • the material used in water
EXPERIMENT 2 Oxidation and Rust: How is rust produced? Purpose/Hypothesis One of the most common
• the type of steel wool • the type of candles • the time the candles burn after the steel wool is removed In order to test your hypothesis, you can change
oxidation reactions is the production of rust, only one variable at a time. If you change more than one, you will not be able to tell which factor caused otherwise known as corrosion. Iron readily coma change in the outcome of your experiment. bines with water and oxygen to form rust. In this experiment, you will explore the process of iron oxidation, which produces rust. You will see the result of the depletion of oxygen as this element is removed from the air to combine with iron. Do you have an educated guess about how water will affect a piece of steel wool? What might happen to a candle burning in the same container as the steel wool? That educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘Wet steel wool will oxidize to form rust when left for several days. This process removes oxygen from the air, so a candle placed in the same space will burn for a shorter amount of time.’’ Experiment Central, 2nd edition
How to Experiment Safely Be careful handling glass jars to avoid breakage. As with all fire, be extremely careful handling matches. You are strongly urged to have an adult help you light the candles. Have water or a fire extinguisher close by in case of an accident.
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Step 1: Set-up of ‘‘wet’’ and ‘‘dry’’ jars. GA LE GRO UP.
Steps 3 and 4: Dropping lit candle into experimental jar. GA LE GRO UP.
In this case, the variable you will change will be whether the steel wool is exposed to water. The variable you will measure will be the amount of rust on the steel wool and the length of time the candle burns. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental jar, and that is whether the steel wool is exposed to moisture. For the control, you will use dry steel wool. For your experimental jar, you will use damp steel wool. You will measure how much oxidation or rust occurs and how long the candles burn. If the control shows no rust while your experimental jar shows some, AND the candle burns for a shorter amount of time in the experimental jar, your hypothesis is supported. Level of Difficulty Easy/moderate; ask an adult
to help you light the candles. Materials Needed
• 2 equal-sized pieces of steel wool (Do not use scouring pads that contain soap.) • 2 identical glass jars with metal lids • water • 2 small birthday candles • matches • a small amount of modeling clay • stopwatch
Data chart for Experiment 2. GAL E GR OU P.
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Approximate Budget $5 to $7 if you need to purchase steel wool, modeling clay and/or candles. Timetable 3 days. Step-by-Step Instructions
1. Wet one piece of steel wool and place it in one of the jars. In the other jar, place a dry piece of steel wool. Label each jar carefully. 2. Close both lids tightly and place the jars in a cool, dark place for three days. 3. Have an adult light one of the candles. 4. Open the experimental jar and have the adult drop in the candle. Quickly close the jar again. 5. Use the stopwatch to time how long the candle burns. Record the time on a chart like the one illustrated. 6. Repeat Steps 3 to 5, having your adult helper drop the other lighted candle in the control jar. 7. After both candles have burned, remove the steel wool from both jars and record what you find.
Troubleshooter’s Guide Below are some problems that may occur during this experiment, possible causes, and ways to remedy the problems. Problem: No rust showed on the either piece of steel wool. Possible causes: 1. You did not put enough water on the experimental steel wool. Try wetting it more, or putting a small amount of water in the base of the jar before leaving it. 2. You did not leave the jars long enough. Try leaving both jars for several more days. Problem: The candles burned the same length of time. Possible cause: You let in too much outside air when you opened the jars. Open and close the jars as quickly as possible so little outside air will have an opportunity to mix with the air in the jars.
Summary of Results Study your results, comparing the amounts of rust
on each piece of steel wool and the times the two candles burned. The more rust you observe, the more oxidation occurred. The shorter time the candles burned, the less oxygen was present in the jars, showing that more oxidation occurred. What did you discover? Was your hypothesis supported? Write a paragraph summarizing and explaining your results. Change the Variables You can vary this experiment. Here are some
possibilities: • Try using other kinds of metal, such as screws and nails, tinfoil, painted steel wool, or even different brands of steel wool, to see what oxidizes more readily. See if you can isolate factors that cause more rust than others, such as the amount of exposed surface area or the shape, size, or color of the metal. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
• See what happens when you leave the experimental set-up for several more days. How much more rust do you find? Can you make any additional predictions about the effect of oxidation on other objects?
• the type of acid being used
EXPERIMENT 3
• the cleanliness of the copper
Oxidation Reaction: Can acid change the color of copper?
• exposure to the atmosphere • the concentration of acid being used In order to test your hypothesis, you can change only one variable at a time. If you change more than one, you will not be able to tell which factor caused a change in the outcome of your experiment.
Purpose/Hypothesis In this experiment, you will examine how an acid can form a bluegreen solid in an oxidation/reduction reaction with copper. The acid you will use is vinegar, which is about 5% acetic acid. When acetic acid is added to copper (Cu), the copper loses two electrons. The acetic acid gains two electrons. The metal copper gets oxidized and the acetic acid gets reduced. The result is copper acetate, which is a blue-green solid. Copper acetate dissolves in acid but not in water. You will use a sheet or coil of copper and add acetic acid. In order to speed up the reaction, you will need to make the acid stronger than 5%. The more acetic the vinegar, the faster the reaction occurs. You will use two different concentrations of vinegar so that you can compare the reaction speed. You can do this by carefully heating the vinegar and boiling off some of the water. (The water boiling point is lower than
Steps 1–8: Label the three jars appropriately, placing the copper item in the jar and filling with liquid.
control
25% acetic aci d
50% ac etic acid
I LLU ST RAT IO N BY TEM AH NEL SO N.
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the acetic acid boiling point, and so water will boil of first.) The reaction also needs air and time. Make an educated guess about what will happen to the copper when it is bathed in acidic acid? That educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
How to Experiment Safely Be extremely careful when heating the vinegar and ask for an adult to help. Do not touch the vinegar.
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘Acetic acid will cause the copper to turn blue-green’’. Variables are anything that can be changed in an experiment. In this case, the variable you will change will be the acid in your reaction, and the variable you will measure will be the color (a measure of cleanliness) of the copper and the solid that is formed from the reaction. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental copper reaction. The variable you will change is the acid used to immerse the copper. For the control, you will use distilled water. You will record the color of the copper before the experiment and the solid that forms on top of the copper.
Step 11: After approximately a week, the surface of the copper item will have changed. ILL US TRA TI ON B Y TE MA H NEL SO N.
Level of Difficulty Moderate. Materials Needed
• 3 copper items that are the same, such as wires or thin sheets (available at hardware or craft stores) • white vinegar • hot pot or stove • 3 wide mouth small jars, such as baby jars • potholder Experiment Central, 2nd edition
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Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The copper did not change.
• • • • • •
measuring cups bowl distilled water plastic knife wax paper or paper plate magnifying glass (optional)
Approximate Budget $5.
Possible causes: You did not allow enough time for the change to occur, or the copper was not exposed to enough air. Try placing the copper in a widermouth jar and letting it sit for more time.
Timetable 2 hours to set up the experiment; 2
days to a week to see results. Step-by-Step Instructions
1. Label the three jars: ‘‘control.’’ ‘‘25% acetic acid.’’ ‘‘50% acetic acid.’’. Possible cause: 2. Place the copper item in each jar. You may not have been using pure copper. Pur3. Pour 1 cup of vinegar into the pot and chase more copper and ask if it is 100%copper simmer until the vinegar boils down to ¼ before trying the experiment again. cup. You will probably have to pour it into the measuring cup and back into the pot until it is at ¼ cup. Remember to use a potholder. 4. Using a potholder, pour the acetic acid into a bowl to cool. 5. Pour another 1 cup of vinegar into the pot and simmer. 6. When the vinegar boils to ½ cup, allow it to cool. Step 12: Using a plastic knife, 7. Pour enough of the ¼ cup of vinegar into the jar labeled ‘‘25% gently scrape the blue-green solid acetic acid.’’ until the solution just covers the copper. Pour the ½ off the copper onto wax paper or a paper plate. I LLU STR AT IO N cup acetic acid solution into the jar labeled ‘‘50% acetic acid.’’ BY T EM AH NE LS ON. until it just covers the copper. 8. In the control jar, cover the copper with distilled water. 9. Set the jars aside. Do not cover. The vinegar will evaporate over time. 10. After two days, examine all three jars. Note any changes to the surface of the copper. 11. Every day continue to examine all three jars. After approximately a week, if the surface of the copper has changed, carefully pour the acetic acid of each jar down the sink. Wait Problem: The copper only darkened.
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another day until the solution has all evaporated. 12. Using a plastic knife, gently scrape the blue-green solid off the copper onto wax paper or a paper plate. If you have a magnifying glass you can take a closer look at the newly-formed solid. Summary of Results Describe the blue-green
copper acetate that has formed. Study the results on your chart. Compare the change in the copper immersed in distilled water to the copper items in the acetic acid. Did one reaction occur faster than the other two? Did the copper turn blue-green or did the copper change into another solid? Was your hypothesis correct? Write a paragraph summarizing and explaining your findings. Change the Variables There are several ways that you can vary this experiment. For example, you can try other acetic acid concentrations. You can test lower and higher concentrations (carefully and with adult help). You can also experiment with different metals or copper alloys. A copper alloy is copper blended with other metals, such as bronze, zinc or lead.
You can see rust on metal fences all over the world. PE TER ARN OL D IN C.
Design Your Own Experiment How to Select a Topic Relating to this Concept Oxidation-reduction
reactions take place all around you every day. Are you interested in corrosion of metals? Try experimenting with different kinds of metals to see which ones corrode faster and what happens to them when they corrode. Or investigate bleaching action, involving electrons activated by light. Another reaction involving light is that of photo-chromic glass, which causes eyeglasses to darken in direct sunlight because of photooxidation. Perhaps you are interested in how batteries work. Most of them involve oxidation-reduction reactions with various compounds such as ammonium chloride, silver oxide, mercury, or nickel/cadmium. If Experiment Central, 2nd edition
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you experiment with batteries, use extreme caution because they contain potentially toxic compounds. Oxidation-reduction reactions are involved in photosynthesis, metabolism, nitrogen fixation, fuel combustion, and many other things. The possibilities for investigation are endless. Think about your interests and check the Further Readings section. Talk with your teachers or librarians about how you can get further information on the topics that interest you. Batteries work by an oxidation/ reduction reaction. PH OT O RE SEA RC HE RS I NC.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through before you do it. Otherwise you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts, such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental setup and results. If you are preparing an exhibit, you may want to display your results, such as rusted metals or bleached fabrics clearly labeled as to what you did with them. These materials will make your exhibit more interesting for viewers. If you have done a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects You can design projects that are similar to these experi-
ments, involving trials and charts of data to summarize results. You could also prepare a model that demonstrates the point that interest you with 824
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regard to oxidation-reduction and its effects in everyday life. Or you could do a research project investigating how oxidation-reduction is involved in acid rain or other environmental problems. You could explore the history of scientists who have studied oxidation-reduction and the kinds of experiments that led them to discoveries. The possibilities are numerous.
For More Information Burns, George, and Nancy Woodman. Exploring the World of Chemistry. Danbury, CT: Franklin Watts, 1995. Outlines several experiments in oxidation. Fitzgerald, Karen. The Story of Oxygen. Danbury, CT: Franklin Watts, 1996. Explores the history, chemistry, and uses of oxygen. Gutnik, Martin. Experiments that Explore Acid Rain. Millbrook Press, 1992. Investigates how oxidation reactions affect acid rain, among other experiments. Mebane, Robert, Thomas Rybolt, and Ronald Perkins. Adventures with Molecules: Chemistry Experiments for Young People. Enslow Publishers, 1987. Outlines more ways to explore oxidation reduction reactions.
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Periodic Table
C
onsidered one of the most important chemistry reference tools, the periodic table is a familiar sight around the world. The periodic table is an arrangement of the elements by their properties. An element is a substance in pure form, meaning that it cannot be broken down into any other substance. The smallest particle of an element is an atom. With one glance, the periodic table can provide a great deal of information on both individual elements and groups of them. A person familiar with the table can extract an element’s relative mass, basic properties, and how it compares with its neighbors without knowing any facts about the element itself.
Elemental developments All matter on Earth is made up of elements. There are only a finite number of natural elements, although others are synthesized or manufactured by people. (As of 2008, there were 118 officially named elements.) The periodic table leaves spaces for unknown elements still to be discovered. The desire to categorize elements goes back to the fifth century B . C . E . when ancient Greeks theorized that all matter falls under four elements: Earth, air, fire, and water. In 1789 French chemist Antoine Lavoisier (1743–1794) published the definition and first set of thirtythree chemical elements. Lavoisier grouped them into four categories on the basis of their chemical properties: gases, nonmetals, metals, and earths. As more elements were discovered, many scientists worked on classifying them. The turning point came when Russian chemist Dmitri Mendeleev (1834–1907) made up cards of each of the elements and worked on arranging them in patterns. At that time there were sixty-three known elements. He found that there were repeating or periodic relationships between the properties of the elements and their atomic weights. By arranging the elements in order of increasing atomic weight, the 827
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Russian chemist Dmitri Mendeleev created the basic structure of the periodic table. THE LI BRA RY OF C ONG RE SS.
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properties of the elements were repeated periodically. The arrangement of elements in this manner was called the periodic table. In 1869 Mendeleev published the first periodic table. In his table, rows (across) and columns (down) each shared certain properties. Mendeleev’s table even left placeholders for elements that had yet to be identified. Over the next two decades, more elements were discovered, including gallium, scandium, and germanium. When these elements fit into the predicted spaces, the table gained acceptance. Over the next century the periodic table changed in several ways, yet its basic structure set down by Mendeleev remained. Blocks of data Each block in the periodic table contains the name and properties of that element. The letters are the abbreviation or atomic symbol of the chemical element. Each element has a one- or two-letter abbreviation as its symbol, often taken from the Latin word for a description, place, or name. For example, the atomic symbol for gold, Au, comes from the first two letters of the Latin word aurum, meaning shining dawn. Mercury’s symbol, Hg, comes from the Latin hydragyrum, meaning liquid silver, and lead’s symbol, Pb, comes from the Latin plumbum, meaning heavy. Above the symbol is the atomic number of the element. The atomic number represents the number of protons, or positively charged particles, in an atom of that element. The number of protons in an atom equals the number of electrons, negatively charged particles, which move around the center of the atom. The number and arrangement of protons and electrons in an atom determines the chemical behavior of the element. The number below the symbol is the atomic mass, the average mass of an element. Also known as atomic weight, atomic mass is given in atomic mass units (amu). An atom’s atomic mass is the weight of its protons and neutrons. A neutron is a particle that has no charge and is located in the center of the atom. Across and down Each row of elements across the table is called a period. Rows in the periodic table are read left to right. All of the elements Experiment Central, 2nd edition
Periodic Table
in a period have the same number of shells. A shell is the number of areas an atom needs to hold its electrons. The first shell holds two electrons, the second shell holds up to eight, and the atomic 6 third shell can hold up to eighteen electrons. The number maximum number of shells found around any atom is seven. Thus, there are seven periods. For example, carbon (C) atoms have six electrons: two electrons in the first shell and the remaining four are in the second shell. HydroCarbon atomic symbol gen (H), which has one electron, needs only one 12.01 shell. Helium (He), which has two electrons, is the only other element with one shell and the two elements share a row by themselves. Calatomic mass cium (Ca) and Magnesium (Mg) each have two shells and, thus, are in the second row. Each column of elements down the periodic table is called a group or family. Elements in a Each block in the periodic table group have the same number of electrons in their outer shell. The group provides information on a at the left edge of the periodic table has one electron in its outer shell. particular element. GA LE Every element in the second column has two electrons in its outer shell, GRO UP . and so on. Groups are numbered from left to right. There are two sets of groups: the A and B groups. The A groups run along the high columns of the table and have similar properties. The B groups in the middle section of the table are called transition elements. Transition elements have common properties; they are hard, strong metals that conduct heat and electricity well. These elements also have their electrons arranged in a complex arrangement, which is lacking in the A group. Periodic patterns Both periods and groups supply information on the element’s characteristics and behavior. In a period, as the atomic mass increases from left to right the atomic size decreases. (The more electrons there are, the more they are pulled towards the center and the atom tightens.) Metals are on the left and middle sections of the periods with the most active metal in the lower left corner. Nonmetals are located on the right side. With the exception of hydrogen, the first element in a period is a solid, and the last element in a period is always a gas that does not react with other elements. Elements that share the same number of electrons in their outer shell, the groups, share many of the same behaviors. Examples of shared
C
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6 protons (+)
electrons (-)
shells
Carbon Atom Electrons encircle the center of the atom in shells. G AL E GRO UP.
characteristics include their stability, boiling point, and conductivity. For example, the elements on the far right of the table is called the noble gases. Noble gases are colorless gases that are all nonreactive because their outermost shell is full. When the outermost shell is full the atom is completely stable and does not react. The groups on the far left also share many properties with each other. With few electrons in their outer shells, these metals are highly reactive and react strongly with nonmetals. Although the properties in groups are similar, they change as you move up or down the column. For example, chemical activity generally increases as you go down a metal group and decreases as you move down a nonmetal group.
EXPERIMENT 1 Metals versus Nonmetals: Which areas of the periodic table have elements that conduct electricity? Purpose/Hypothesis Conductivity is one of the properties that relates to
the position of the element in the periodic table. Conductivity relates to the electron configuration in the element’s atoms. Atoms are constantly working to get a full count of atoms in their outer shell. They can do this by losing or gaining electrons. A full count gives the atom stability and, thus, it does not need to react with other atoms. Elements in the lownumber groups have atoms with one or few electrons in their outer shell. This causes these atoms to lose electrons easily. Their electrons move among all the atoms in the substance. Atoms in the highest groups have a full or almost-full outer shell and usually gain electrons. Their electrons do not move about freely. The periodic table is composed of two main groups: metals and nonmetals. Metals are on the left and middle of the table; nonmetals make up parts of groups IIIA to VIIIA. Almost all metals are solids (mercury, a liquid, is the exception). Nonmetals can be solids, liquids, or gases. In this experiment you will determine what areas of the periodic table have elements that are electrical conductors. A conductor provides a path that allows electricity to flow from a battery’s positive terminal to its 830
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7
6
5
4
3
2
1
1
.00794
*
57-70
Ra radium
Fr
francium
88
barium
(223)
cesium
87
Ba
Cs (226)
lawrencium
Lr
† Actinides
(26 )
Db
105
tantalum
Ta
40.
5
(262
Th thorium
Ac actinium
232.038
cerium
90
(227)
lanthanum
89
58 Ce
38.9055
La
57
rutherfordium dubnium
Rf
hafnium
104
(262)
103
Hf
80.9479
niobium
78.49
73
92.90638
72
Nb
41 95.94
Tc
43 (98)
manganese
40.90765
Nd
60 44.24
bohrium
Bh
107 (264)
86.207
rhenium
Re
75
(23 )
U
92 238.0289
protactinium uranium
Pa
91
praseodymium neodymium
Pr
59
seaborgium
Sg
106 (263)
83.85
tungsten
W
74
molybdenum technetium
Mo
42
Mn
54.9305
VII B 25
VI B 5 .996
7
6
chromium
Cr
24
radon
Rn
86 (222)
0 .07
55.847
( 45)
(265)
90.2
(237)
neptunium
Np
93
promethi m promethium
Pm
61
hassium
Hs
108
osmium
Os
76
ruthenium
Ru
44
iron
Fe
26
8
02.90550
(268)
92.22
62 50.36
(244)
plutonium
Pu
94
samarium
Sm
06.42
58.69
ununnilium
Uun
110 (269)
95.08
platinum
Pt
78
palladium
Pd
46
nickel
Ni
10 63.546
IB
unununium
(272)
96.96654
07.8682
Uuu
111
gold
Au
79
silver
Ag
47
copper
Cu
29
11
63 5 .965
(243)
americium
Am
95
europium
Eu
64
57.25
curium
Cm
96
(247)
gadolinium
Gd
2.4
65.39
II B
12
(247)
berkelium
Bk
97
terbium
Tb
65
58.92534
ununbiium
Uub
112 (277)
200.59
ercury mercury
Hg
80
cadmium
Cd
48
zinc
Zn
30
Inner–Transition Metals
meitnerium
Mt
109
iridium
Ir
77
rhodium
Rh
45
cobalt
Co
27 58.93320 28
VIII B
9
Atomic weight
Transition Metals
Atomic number Symbol Name
50.94 5
VB
vanadium
V
23
5
zirconium
Zr
lutetium
*Lanthanides
†
89-102
*Lu
71 74.967
ytt ium yttrium
37.327
strontium
32.90543
56
55
rubidium
Y
Sr
Rb
9 .224
titanium
40
88 90585
scandium
39
85.4678
calcium
37
38
Ti
47.88
potassium
Sc
22
IV B 0
III B 21 44.9559
Ca 87.62
40.078
4
3
K
20
magnesium
39.0983
sodium
19
Mg
24.3050
Na
11 22.989768 12
beryllium
9.0 2 82
II A
lithium
4 Be
6.94
2
Li
3
hydrogen
H
IA
1
Main–Group Elements
13 26.98 539
204.3833
62.50
(25 )
californium
Cf
98
dysprosium
Dy
66
thallium
Tl
81
indium
In
49 4.82
69.723
gallium
G Ga
31
aluminum
Al
6
(289)
207.2
8.7 0
30.973762
einsteinium
Es
(257)
67.26
fermium
Fm
100 (252)
erbium
Er
68
bismuth
Bi
5.9994
VI A
16
35.4527
iodine
tellurium
(289)
No
102
(2 0)
73.04
(259)
ytterbium
Yb
70
astatine
At
mendelevium nobelium
Md
101
(258)
68.9342
thulium
Tm
69
ununhexium
Uuh
116
polonium
Po
85
I
26.90447
Te (209)
27.60
53
79.904
bromin bromine
Br
35
chlorine
Cl
17
fluorine
8.9984032
VII A
52
78.96
32.066
F
9
17
selenium
Se
34
sulfur
S
16
oxygen
O
8
83 208.98037 84
antimony
Sb
51
2 .75
74.92 59
arsenic
As
33
phosphorus
P
15
holmium
4.93032 64.93032
4.00674
VA
nitrogen
N
7
15
99
Ho
67
ununquadium
Uuq
114
lead
Pb
82
tin
Sn
50
germanium
Ge
32 72.6
28.0855
silicon
Si
14
carbon
C
2.0
IV A
0.8
III A
boron
B
5
14
13
Main–Group Elements
4.002602
(293)
(222)
3 .29
83.80
ununoctium
Uuo
118
radon
Rn
86
xenon
Xe
54
krypton
Kr
36
39.948
20. 797
argon
Ar
18
neon
Ne
10
helium
He
2
18
VIII A
Periodic Table
Period
In the periodic table, groups and periods share certain properties. G ALE GRO UP .
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WORDS TO KNOW Alkali metals: The first group of elements in the periodic table, these metals have a single electron in the outermost shell. Atom: The smallest unit of an element, made up of protons and neutrons in its center, surrounded by moving electrons. Atomic mass: Also known as atomic weight, the average mass of the atoms in an element; the number that appears under the element symbol in the periodic table. Atomic number: The number of protons (or electrons) in an atom; the number that appears over the element symbol in the periodic table. Atomic symbol: The one- or two-letter abbreviation for a chemical element. Control experiment: A setup that is identical to the experiment, but is not affected by the variables that affects the experimental group. Electron: A subatomic particle with a mass of about one atomic mass unit and a single electrical charge that orbits the center of an atom.
the table. A family of chemical compounds share similar structures and properties. Group: A vertical column of the periodic table that contains elements possessing similar chemical characteristics. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Neutron: A particle that has no electrical charge and is found in the center of an atom. Noble gases: Also known as inert or rare gases; the elements argon, helium, krypton, neon, radon, and xenon, which are nonreactive gases and form few compounds with other elements. Period: A horizontal row in the periodic table. Periodic table: A chart organizing elements by atomic number and chemical properties into groups and periods. Proton: A positively charged particle in the center of an atom.
Element: A pure substance composed of just one type of atom that cannot be broken down into anything simpler by ordinary chemical means.
Shell: A region of space around the center of the atom in which electrons are located.
Family: A group of elements in the same column of the periodic table or in closely related columns of
Variable: Something that can affect the results of an experiment.
negative terminal. You will test the electrical conductivity of several elements by placing each one in the path of the electricity, and connecting the path to a small light. If the light comes on, the flow of electricity is passing through the element; if the light remains off, then the element did not pass the flow of electricity. There are many elements you can test. Options are provided in the materials section. To begin this experiment make an educated guess, or prediction, of what you think will occur based on your knowledge of the periodic 832
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table. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Elements in the middle and left of the periodic table will conduct electricity, and the light will come on; elements on the right side of the table will not be good conductors, and the light will not come on.’’ In this experiment the variable you will change will be the element; the variable you measure will be whether electricity is conducted to the light. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental trials. The control experiment will test for a complete circuit. The positive and negative wires will carry the electric current directly to the light bulb.
Gold is a transition metal. Will it conduct electricity? # CH ARL ES O’R EA R/ COR BI S.
Level of Difficulty Moderate. Materials Needed
• • • • • • • • • •
periodic table wire strippers (such as a knife) pliers scissors or wire cutters 2 1.5-volt batteries battery holder, (wires should be attached to holder) 6 insulated alligator clips insulated copper wire (about 2 feet or 61 centimeters) small light bulb and light bulb socket, less than 3 volts Elements: aluminum (foil, wire); silver (jewelry, silverware, wire); gold (jewelry); zinc (penny made after 1982, which is made of 97.5% zinc, the remaining 2.5% is copper); copper (wire; penny
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the element
dated 1962 to 1982, which is 95% copper and 5% zinc); carbon (lead in pencil, diamond on piece of jewelry); silicon (glass) Approximate Budget $12–$20. Timetable 1 hour Step-by-Step Instructions
• the battery voltage In other words, the variables in this experiment are everything that might affect whether electricity is conducted to the light. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on conducting the electricity.
1. Insert the two batteries in the battery holder so the positive and negative ends are opposite to one another. 2. Cut three pieces of wire, each 6 to 12 inches (15 to 30 centimeters) long. 3. Strip about 0.5 inch (1.3 centimeters) of the insulation off both ends of each piece of wire. 4. Insert each end of the wire through the How to Experiment Safely hole in the alligator clip and twist. There should now be three pieces of wire with Make sure there is no water nearby as water will clips on each end. carry the electricity. Be careful when cutting wire. If the wire gets hot to the touch at any 5. Twist or press the light bulb into the base. point, immediately disconnect the wire from the 6. Assemble the control experiment. With battery. Make sure the wire is fully insulated. one wire, attach one clip to the exposed end of the battery wire and the clip on the other side to the light socket. Repeat with a second wire on the other side of the light socket. Note the results. 7. Remove one clip from the socket, and attach the third wire’s clip in place of that clip. 8. Attach the clip of the free end of the third wire to one of the test elements. Attach the free end of the second wire to the other end of the element. When the path is complete, note whether the light glows. 9. Repeat Step 8, replacing the element with each test element one at a time. Note the results for each. Summary of Results Create a chart of your results, writing down whether
each element was a conductor or nonconductor. Examine the results. What elements conducted electricity and where are they located in the periodic 834
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table? Air is made up of gases, mostly oxygen and nitrogen. Look at the periodic table and examine why gases do not conduct electricity. Examine the number of electrons in the elements you used. Look up how many electrons are in their outer shell. Write a brief summary of the experiment, explaining why some elements would make better conductors than others. Change the Variables To change the variable in
this experiment, you can use a different voltage battery. You can also use a light with a different voltage.
EXPERIMENT 2 Soluble Families: How does the solubility of an element relate to where it is located on the periodic table?
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The light bulb does not light as expected. Possible cause: The wire to the alligator clip may not be securely fastened to the element, or the alligator clip may not be touching the exposed wire. Repeat the experiment, scraping off enough plastic and checking that the exposed wires connect with each other. Problem: The control light does not light for any element. Possible cause: See ‘‘possible cause’’ above. Also, the battery may be dead and have no charge. Repeat the experiment with a fresh battery.
Purpose/Hypothesis Groups are columns run-
ning down the periodic table. In this experiment you are determining an element’s solubility. Solubility is the ability of a substance to dissolve in a liquid. For example, sugar dissolves in water and is therefore called soluble in water. Chocolate chips mixed with water do not dissolve and are called insoluble in water. Solubility is one of the properties that relates to the location of the element in the periodic table. In this experiment you will determine what areas of the periodic table have the property of being soluble in water. You will use substances made from elements in the first two families of the periodic table. The first group on the left, Group 1A, is the Alkali Metals. Group 2A is called Alkali Earth Metals. These elements will form salts when a metal combines with a nonmetal. For example, sodium and chloride combine to make table salt. By mixing these salts Experiment Central, 2nd edition
Step 8: Attach the clips to the test element and note if the current flows to the light. GA LE GRO UP .
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of salt • the temperature of water • the quantity of salt • the size of the salt particles In other words, the variables in this experiment are everything that might affect whether the salts are soluble in water. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on solubility.
in water, you can then determine if either is soluble. To begin this experiment make an educated guess, or prediction, of what you think will occur based on your knowledge of the periodic table, solubility, and groups. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Salts made from elements in the Alkali Metals will dissolve in water more readily than salts in the Alkali Earth Metals.’’ In this experiment the variable you will change will be the type of salt; the variable you measure will be the solubility of the salt. Note: When making a solid-liquid solution (solid/liquid), it is standard to use weight/weight (grams/grams) or weight/volume (grams/milliliters). With water, 1 gram of water equals 1 milliliter. In this experiment, teaspoons and tablespoons are used to measure the solid.
Level of Difficulty Easy to Moderate. Materials Needed
• washing soda (sodium carbonate: available at many supermarkets in the detergent section) • potassium carbonate (available at chemical supply houses: an adult must order this) • chalk (calcium carbonate; active ingredient in many antacids) • water • measuring spoons • metal spoon 836
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• • • • •
measuring cup plastic gloves three glasses masking tape marking pen
Approximate Budget $15.
How to Experiment Safely Be careful when working with potassium carbonate. Wear plastic gloves during this experiment. Do not ingest it or get it near your eyes. Wash your hands thoroughly after the experiment.
Timetable 30 minutes. Step-by-Step Instructions
1. Pour 1 cup (about 0.25 liters or 250 milliliters) of room-temperature water into each glass. Label each glass with the name of one of the salts. 2. Crush the calcium carbonate into a powder by wrapping a small piece of chalk or tablet in plastic wrap and pressing down on it with a spoon. 3. Measure out 1 teaspoon of the crushed calcium carbonate and stir it thoroughly in the water in the glass labeled ‘‘calcium carbonate’’ for at least one minute. You may need to stir for up to two minutes. 4. Examine the bottom of the glass for any powder residue and note the solubility. 5. Repeat Steps 4 and 5 for the other two salts using the other two glasses of water. Summary of Results Was your hypothesis cor-
rect? Why are the salts of Alkali Metals more soluble than Alkali Earth Metals? Determine the electron configuration of the three salts. Write up a brief description of the experiment, analyzing your conclusion.
Step 3: Stir each of the salts in the water to determine its solubility. GA LE G RO UP.
Change the Variables It is difficult to find pure
elements as most are naturally found mixed with other elements. To change the variable in this experiment, you can try to change the water temperature. You can hypothesize what the combination of other salts would be Experiment Central, 2nd edition
sodium potassium
calc um
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Periodic Table
and then conduct research to verify your hypothesis.
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The powder did not dissolve as expected.
EXPERIMENT 3 Active Metals: What metals give off electrons more readily than others?
Possible cause: The salt particles may be too large to dissolve. The particles should be a fine powder. Try repeating the experiment, crushing the chalk or tablets completely and stirring thoroughly.
Purpose/Hypothesis Some metals are more active than others, meaning they let go of their electrons more easily than other metals. In general, the activity of different elements relates to its position in the periodic table. Elements that are larger are Problem: The salt does not completely dissolve generally more likely to lose their outer electrons where it theoretically should dissolve. than the smaller elements). Possible cause: See ‘‘possible cause’’ above. In this experiment you will determine which The metallic element you used may not be of two metals is more active: zinc or copper. In pure. Make sure you are not using colored chalk. You can also try purchasing real chalk order to help the metals give off electrons, you will or use another antacid tablet. boil each in a salt and vinegar solution. Vinegar is a weak acid that helps loosen the electrons, and salt acts like a bridge for the electrons to move. The metal that loses electrons more readily will get plated, meaning a thin layer of metal will deposit on it. When the electrons move from one metal onto the more active metal, it will cause a visual change. By trying this experiment with both metals, you will be able to determine which metal is more active. To begin this experiment make an educated guess, or prediction, of what you think will occur based on your knowledge of the periodic table, metals, and groups. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Zinc is more active than copper and therefore will lose its electrons when placed in an acidic solution.’’ 838
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In this experiment the variable you will change will be the type of metal. The variable you measure will be the visual changes to the metals. Level of Difficulty Moderate. Materials Needed
• • • • • • •
white vinegar table salt 2 small glass bowls small pan measuring cup measuring spoon copper wire, small gage, approximately 20 feet (6 meters), tightly wound into ball (copper wire for jewelry works well, found at craft stores) • 4 zinc washers (found at hardware stores) • steel wool • tongs or fork
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of metal • the length of time the metal is boiled • the length of time the metal is placed in acid solution • the purity of the metal tested • the amount of salt in the solution In other words, the variables in this experiment are everything that might affect the activity of metals in the solution. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the metal’s activity.
Approximate Budget $10. Timetable Approximately 2 hours Step-by-Step Instructions
1. Pour 1 cup of white vinegar and one tablespoon of table salt into a small pan. 2. Place the copper wire into the pan. 3. Boil the wire in the vinegar solution for 15 minutes. 4. While the vinegar solution is coming to a boil, clean the zinc washer with steel wool until scratching is visible. 5. Place the zinc washer in a glass bowl. 6. Once the vinegar solution has boiled for 15 minutes, pour only the solution into the glass bowl. Use a pair of tongs or fork to remove the copper wire. Make sure the solution covers the washer. 7. Observe and record changes to the zinc washer at 15 minute intervals for 45 minutes. Experiment Central, 2nd edition
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Periodic Table
How to Experiment Safely Be careful when boiling the vinegar and salt solution. Have an adult helper assist you with this part of the experiment. Allow the metals to cool before you touch them after they are taken out of the boiling solution.
8. Repeat all the steps above, switching the two metals. Replace the copper wire with three zinc washers. Make sure to make a new vinegar and salt solution. After boiling the zinc washers for 15 minutes, pour only the solution into a glass bowl that holds copper wire. 9. Observe and record changes to the copper wire at 15 minute intervals.
Summary of Results Compare the appearance of the zinc washers and
Step 1: Gather your materials (salt, vinegar, copper wire, and zinc washer). I LLU STR AT IO N BY T EM AH NE LS ON.
copper wire that were in the glass bowls. Was your hypothesis correct? Did the zinc accept more electrons and change color? How do the results relate to their placement in the periodic table? Write a summary of the experiment, explaining which of the metals was more active. You might want to include pictures and notes from your observations. Change the Variables To change the variable in this experiment, you can
use alkali earth metals such as magnesium and calcium found in common antacid medications. You can experiment with different metals and changing the temperature of the vinegar and salt solution.
Design Your Own Experiment How to Select a Topic Relating to this Concept
SALT
V ineg a r
There are many ways to categorize and group the elements in the periodic table. All matter is made up of elements, yet it is difficult to find elements in their pure form. When experimenting with the properties of elements, look for the active ingredient on major products. Check the Further Readings section and talk with your science teacher to learn more about the periodic table and the elements. Steps in the Scientific Method To conduct an
original experiment, you need to plan carefully and think things through. Otherwise, you might 840
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not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Step 3: Boil the wire in the vinegar solution for 15 minutes. I LL UST RA TIO N BY TEM AH N EL SON .
Recording Data and Summarizing the Results Your data should include
charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings.
Step 6: Once the vinegar solution has boiled for 15 minutes, pour only the solution into the glass bowl with the zinc washer. IL LU STR AT ION BY T EMA H NE LSO N.
Related Projects For projects related on the peri-
odic table, you can compare a variety of metals with one another to determine their differences and similarities. Some properties you can look at are the metal’s relative softness, conductivity, and how it is affected by oxygen. Because elements are difficult to come across in their pure form, you can theorize on the properties of other metals and then conduct research. Certain groups of elements also react with bases, such as baking soda. If you order elements from a lab supply house, make sure you follow all the Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The metals did not change.
necessary safety precautions. Scientists are continuing to discover elements in the laboratory. For a research project you could look at the history of the periodic table and the story of the discoveries.
For More Information
Andrew Rader Studios. ‘‘Elements.’’ Rader’s Chem4Kids.com. http://www. chem4kids.com/ files/elem intro.html (accessed on February 18, 2008). Detailed information about the periodic table, elements, metals, and other subjects for Possible cause: The copper wire may not have intermediate and advanced students. lost enough electrons. Make sure the vinegar Baum, Rudy. ‘‘The Periodic Table of the Elements.’’ solution is brought to a rolling boil for at least Chemical & Engineering News. http://pubs.acs.org/ 15 minutes. You may want to boil the copper cen/80th/elements.html (accessed on February 18, wire for 20 minutes. 2008). Possible cause: The copper’s electrons were BBC. ‘‘Mixtures.’’ Chemical Symbols: The Periodic not able to move onto the zinc washer. Table. Schools. Science: Chemistry. http://www. There may not have been enough salt in the bbc.co.uk/schools/ks3bitesize/science/chemistry/ vinegar solution. Make sure you add 1 elements com mix 2.shtml (accessed on tablespoon of salt and stir well. February 18, 2008). Basic information on the chemistry of mixtures. Emsley, John. ‘‘The Development of the Periodic Table.’’ Chem.Soc: the ASC’s Chemical Science Network. http://www.chemsoc.org/viselements/pages/history. html (accessed on February 18, 2008). The history of the development of the periodic table. Heiserman, David L. Exploring Chemical Elements and their Compounds. Blue Ridge Summit, PA: Tab Books, 1992. A basic introduction to chemical elements. PeriodicTable.com http://periodictable.com/ (accessed on February 18, 2008). Information about the periodic table suited to different audiences. ‘‘The Periodic Table of Comic Books.’’ Department of Chemistry, University of Kentucky. http://www.uky.edu/Projects/Chemcomics (accessed on February 18, 2008). An informative and amusing collection of information about various chemical elements and their properties as found in the pages of comic books. Sacks, Oliver. Uncle Tungsten: Memories of a Chemical Boyhood. New York: Vintage Books, 2002. Autobiography of Sacks tells of early chemistry experiments and learning about the elements. Possible cause: The wire may not have a high enough copper content. Make sure you are using real copper wire. You can also use a piece of copper. Repeat the experiment.
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pesticide is any substance that prevents, repels, or kills pests. The definition of a pest is a relative one. A pest is an organism that is unwanted by humans at a specific time or in a specific place. Pests can range from cockroaches and mice, to fungi and plants. In modern day, pesticides are an integral part of food production and household use. The use of pesticides has a long history. There is evidence that ancient Romans and Chinese, for example, used various minerals and plant extracts as pesticides. Manufactured chemical pesticides began in the 1930s and dramatically increased after World War II (1939–45). The widespread use of chemical pesticides led to an increased concern for how pesticides were affecting the environment, animals, and people. Over the years, pesticides have undergone much advancement, including the development of natural substances and improvements on the traditional.
Pest control Pesticides are categorized according to what type of pests they affect. Some common types of pesticides include insecticides for insects, herbicides for weeds, fungicides for fungi, and rodenticides for rodents. A pesticide can be a natural or a chemically synthesized substance. Chemical pesticides are toxic, meaning they contain poisons. Natural pesticides do not use poisons to affect pests. Both types of pesticides have positives and negatives. These pesticides control pests by physically, chemically, or biologically disrupting a pest’s life cycle or behavior. There are hundreds of different synthetic chemicals used in pesticides. How each pesticide works depends on its active ingredient(s). Some pesticides have similar properties based on their chemical structure. There are several groups of synthetic chemical pesticides that interrupt a pest’s nerves from communicating with each other and from activating certain muscles. Organophosphates, for example, are a group of long-lasting pesticides that affect the central nervous system (brain) and peripheral 843
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transmitting nerve cell nerve signals
Organophosphates, one type of synthetic pesticide, prevent the nerves from signaling to the muscles that control the pest’s breathing, resulting in suffocation and death. GAL E GR OU P.
cannot receive
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nervous system (nerves found outside of the brain or spinal cord). In one pesticide, for example, the organophosphates prevent the nerves from signaling to the muscles that control the pest’s breathing, resulting in suffocation and death. The possible health effects for humans associated with an excess of chemical pesticide exposure include headaches, dizziness, muscle twitching, nausea, and damage to the central nervous system and kidneys. Biopesticides are pesticides produced from substances found in nature; these do not use poison to affect pests. There are three main categories of biopesticides. One category includes those in which the active ingredient occurs in nature. For example, pheromones are chemical scents animals use to communicate, attract mates, and mark territory. If a pheromone-based pesticide is released into the air at a time when insects are looking for each other to mate, the insects will become confused. Less mating and far fewer offspring will result. Other types of this biopesticide include garlic, mint, and red peppers. The active ingredient in another type of biopesticide is microorganisms or microbes, such as bacteria and fungi. Microbes produce substances that destroy a range of other microbes. For example, there are fungi that control weeds, and other fungi that kill specific insects. The most widely used microbial insecticide is the soil-dwelling bacterium Bacillus 844
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bacteria DNA
flower DNA
flower DNA with bacteria gene spliced in
By splicing bacteria DNA into the plant’s DNA, scientists can create a genetically engineered plant that destroys specific pests. GA LE G RO UP.
thuringiensis, also known as Bt. When certain insects ingest the bacteria during the larvae stage, the bacteria interfere with the insect’s digestion and cause the insect to starve. One of the fastest-growing categories of biopesticides includes pesticide products that are genetically engineered or modified. Developed in the 1970s, genetic engineering is based on the understanding that genes are responsible for a species’ characteristics. Genes are segments of deoxyribonucleic acid (DNA), a molecule in every organism’s cell that carries genetic information for its development. Many organisms have genes that are responsible for producing substances that kill or prevent the growth of other organisms. This technique inserts the gene of one species into the DNA of the same or another species. The genetically modified organism then produces a desired trait. For example, scientists have taken the pestfighting gene out of the Bt bacteria and inserted it into a corn plant’s genetic material. The Bt corn then manufactures the substance that destroys the corn borer or another hungry insect. The good, the bad, and the pesty Pesticides both directly and indirectly hold many benefits for people. They increase agricultural yields by eliminating pests and weeds, providing more food and income for people around the world. They protect crops from disease that can devastate food supplies. In the mid-1800s, for example, a fungus spread quickly through Ireland’s potato crops, resulting in the starvation of more than a million people and causing mass emigration. Shielding plants from disease also lessens disease in plant-eating livestock and, ultimately, in humans who would eat that plant or livestock. For the nonfarmer, the use of pesticides has become commonplace. Insect repellents, flea and tick pet Experiment Central, 2nd edition
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A cotton farmer in India points to genetically modified Bt cotton infected with bollworms, January 2003. Bt cotton has failed to prevent bollworm attacks, for which it was designed. A P/W ID E WO RL D
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collars, weed killers, and mildew cleaners are just a few of the household products that contain pesticides. Yet because pesticides are designed to control living organisms, some affect organisms they are not targeted to control, called nontarget organisms. The result can harm humans, animals, and the environment. The pesticide dichlorodiphenyltrichloroethane (DDT) is the classic example of how pesticides can cause unintended effects. DDT was discovered to be an effective insecticide in 1939 and within a few years it became one of the most widely used pesticidal chemicals in the United States. Farmers used it on their crops, and the government used it to protect people against disease-carrying insects, such as mosquitoes that carried malaria. For years scientists warned about the possible harmful effects of DDT; then in 1962 Rachel Carson’s book Silent Spring was published. Her book mapped out how DDT was harming wildlife, the environment, and people. In one scenario, DDT sprayed on plants was eaten by small animals, which were then consumed by birds. The pesticide harmed both the adult birds and their eggs. The eggs’ shells were so thin they were often crushed when the mother sat on them during their incubation period. Eggs that were not crushed often did not hatch. The book stimulated widespread public concern, and in 1973 the chemical was banned in the United States (it is still used in other countries). A balancing act The danger of pesticides to humans and the environment depends upon the pesticide and its mechanism for pest control. Some factors that determine a pesticide’s potential harm are its toxicity, specificity in its targets, and how long it remains in the environment before it breaks down or degrades. Pesticides can enter nontarget plants, insects, and other organisms in several ways. Pesticides do not always stay where they are put down. Wind Experiment Central, 2nd edition
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pesticide particles volatilization
leaching runoff
Pesticides can spread through the environment through volatilization, runoff, and leaching. GA LE G RO UP.
or rain can carry the pesticide into bodies of water. There, it can affect sea life and contaminate water. It can move through or leach into the soil. Leaching is the movement of dissolved chemicals with water downward through the soil. Water not absorbed into the soil also causes pesticides to travel. When this water moves over a sloping surface it is called runoff; the runoff picks up and carries the pesticides. Leaching and runoff cause pesticides to travel into unintended locations, sometimes winding up in groundwater, lakes, oceans, or neighboring areas. In a process called volatilization, some pesticides convert into a gas and move in the air. These pesticides can travel long distances before they settle down into waters or on land. One of the most important factors that affects the risk of pesticide leaching is the amount of time it takes for the pesticide to degrade. Pesticides degrade into substances that are usually less toxic. Pesticides can attach to soil particles and remain in effect long after the manufacturers intended. The longer a pesticide lasts, the greater the chance it will accumulate in an unintended area or nontarget organism. DDT was an example of a long-lasting pesticide. The advantage of biopesticides is that they have a low danger level (toxicity) to organisms they are not targeted for and to humans. Low toxicity means less risk to water supplies and life. Many of these biopesticides also degrade relatively rapidly. The drawback to biopesticides is that they are not as powerful as conventional chemical pesticides. Because these pesticides degrade Experiment Central, 2nd edition
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A swarm of locusts surrounds a Filipino farmer. A locust infestation of rice and sugar farms in Tarlac, Philippines, in 1994 caused major crop and financial losses for farmers. # RE UTE RS NEW ME DI A/C OR BI S.
quickly, they have only a short time period where they can be used. In addition, certain microbial pesticides can become inactive if exposed to extreme environmental conditions, such as too much heat or dryness. Some environmental and citizens groups are also concerned about genetically modified organisms. They say that these plants may produce unintended consequences to people, the environment, and animals. The U.S. federal government evaluates and regulates pesticide use. Regulations on pesticides applied to foods have especially strict safety standards. Pesticides are labeled as to their level of toxicity. Washing and cooking foods are ways that people can reduce pesticide residue.
EXPERIMENT 1 Natural versus Synthetic: How do different types of pesticides compare against a pest? Purpose/Hypothesis Many plants produce substances that prevent or
harm pests. Some of these substances kill their insect predators and others repel them. For example, a plant can emit an odor that prevents pests from approaching. Yet while biopesticides are generally safer to the environment and carry fewer risks to people, chemicals remain the 848
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WORDS TO KNOW Biopesticide: Pesticide produced from substances found in nature.
Pesticide: Substance used to reduce the abundance of pests.
Control experiment: A setup that is identical to the experiment, but is not affected by the variables that affects the experimental group.
Runoff: Water not absorbed by the soil; moves downward and picks up particles along the way.
Degrade: Break down.
Synthesized: Prepared by humans in a laboratory; not a naturally occurring process.
Deoxyribonucleic acid (DNA): Large, complex molecules in cells that carries genetic information for an organism’s development.
Synthetic: A substance that is synthesized, or manufactured, in a laboratory; not naturally occurring.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Toxic: Poisonous.
Leaching: The movement of dissolved chemicals with water that is percolating, or oozing, downward through the soil.
Variable: Something that can affect the results of an experiment.
Pest: Any living thing that is unwanted by humans or causes injury and disease to crops and other growth.
Volatilization: The process by which a liquid changes (volatilizes) to a gas.
pesticide of choice for the vast majority of professionals. Because pesticides are so important to society, people are continuously searching for the most effective substance that will cause the least harm. In this experiment you will examine how biopesticides compare to a synthetic pesticide. The two natural pesticides are a spray made from chili peppers and one made from garlic. These are commonly used among gardeners as repellents. With chili, it is the hot chilies that make the most effective repellent. Garlic’s strong odor can also act as a repellent. With the synthetic insecticides, look for one that works against general pests, such as aphids, caterpillars, beetles. Evidence of these pests can be seen in the holes they bore or bits of leaves that they have munched. Aphids will leave a sticky residue on the leaves. Once you have made a spray of the natural substances, you can apply all the pesticides to the same type of plant and set outside. To measure the effectiveness of each pesticide you can examine the plant’s general health, count holes in the leaves and pests on the plant, and feel the leaves. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of plant • the pests in the environment • the type of pesticide • the climate
Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of synthetic pesticides and biopesticides. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
In other words, the variables in this experiment are everything that might affect the amount of pests that are attracted to the plant. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the pesticide’s effectiveness.
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The synthetic pesticide product will better prevent pests from harming the plants than the biopesticides.’’ In this case, the variable you will change is the type of pesticide sprayed on the plant. The variable you will measure is the amount of damage to the plant caused by pests. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. For your control in this experiment you will not apply any pesticide to a plant. At the end of the experiment you can compare the control plant to the experimental plants.
Level of Difficulty Moderate. Materials Needed
• 4 small plants of the same type, preferably broad leafed (coleus works well) • 1 hot chili pepper (haban~eros work well) • 1 garlic bulb (five cloves) or crushed garlic • spray bottle • chemical pesticide (available from hardware store, drugstore, or greenhouse) 850
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• • • • • • • • •
outside area water 2 bowls marking pen chopping knife cheesecloth funnel rubber gloves several nice days
Approximate Budget $15.
How to Experiment Safely Have an adult present for this experiment. Be careful when working with hot water and chili peppers. The pepper’s seeds and juices can burn, so wear rubber gloves and avoid touching your face; never directly ingest the peppers or touch your eyes. Make sure you apply the chemical pesticide outside and follow the directions and warnings carefully. Wear a longsleeved shirt and long pants when applying and wash your hands afterwards.
Timetable 45 minutes setup; overnight waiting;
10 minutes every three days for about two weeks. Step-by-Step Instructions
1. Label the plant containers: ‘‘Pepper,’’ ‘‘Garlic,’’ ‘‘Chemical,’’ and ‘‘Control.’’ 2. Prepare the chili pepper spray: Chop one chili and place the pieces in a bowl. Boil 1 cup (about 240 milliliters) of water and pour over the chopped peppers. Set aside overnight. 3. The next day, prepare the garlic spray: Finely chop about five cloves of garlic and add 1 cup (about 240 milliliters) of hot water. Set aside for two hours until cool. 4. When the solutions are ready, use the cheesecloth to strain out the garlic and the peppers. Use the funnel to pour one of the solutions into the spray bottle. 5. In an open area outside, spray the first solution on the plant labeled for that pesticide. After each application, set the plant in a distant area to keep each pesticide isolated from the other plants. Make sure to wash out the spray bottle thoroughly between the pepper and garlic spray (save each solution in a covered and labeled container). Repeat with the other two solutions. Do not spray anything on the control. garlic
Materials needed to compare different pesticides in Experiment 1. G AL E GR OUP .
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The natural sprays did not stick to the plant leaves. Possible cause: The mixtures adhere to the leaves of some plants more than others. Try adding a drop of nondetergent dishwashing soap and mixing well, then reapply. Problem: None of the plants had much evidence of pests. Possible cause: This experiment works best when there are many insects around, often during the spring and summer months. Try to set your plants down in a wooded area or one that has a large quantity of plants and then continue your observations.
6. Set the four plants outside in the same general area, leaving enough room between the plants so they do not touch one another. 7. Every three days for the next 15 days observe the plants and note any pests or effects of pests. Reapply the sprays if it rains. If you reapply, again make sure to isolate each plant when you spray. Summary of Results Was your hypothesis cor-
rect? Look at your data and determine how the pesticides compared to one another. Was there one type of pest that was on one plant more than another? Some types of insects, such as aphids, gather on the underside of leaves. Note the relative amount of any different type of pests on each plant. How did the control plant compare to the experimental plants? Change the Variables In this experiment you can
• • • • •
change the variables in several ways: change the type of plant use the same pesticide and set the plants down in different environments, such as near lush plant growth or in an open space apply different types of synthetic pesticides make up and apply different natural pesticides, such as pesticides made from onions, soaps, neem oil, and molasses. use the same pesticide and see how close you need to apply it to the plant for it to be effective.
EXPERIMENT 2 Moving through Water: How can pesticides affect nontarget plant life? Purpose/Hypothesis Leaching and runoff can cause pesticides to move
away from their target location. When pesticides mix with rain or irrigation water, they can seep into the soil and travel to another area where they can affect the plant, animals, and environment. In this experiment, you 852
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will examine the effects of pesticides on new growth. You will plant a lettuce seed and nurture it with water that has insecticide in it. Planting three sets of seeds, you will add two varying amounts of insecticide to the water and compare them to lettuce grown in unaltered water. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of leaching, runoff, and pesticides. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of plant • the environment • the amount of pesticide • the type of pesticide In other words, the variables in this experiment are anything that might affect the growth of the plant. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the plant’s health.
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Water with the greatest amount of pesticide will result in stunted or no plant growth.’’ In this case, the variable you will change is the amount of insecticide in the water. The variable you will measure is the plant health. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. For the control in this experiment you will give the lettuce plant plain water. At the end of the experiment, you can compare the results from the control experiment with the experimental plants. Level of Difficulty Easy to Moderate. Materials Needed
• • • •
15 lettuce seeds peat pots, with moist to dry soil (available at garden stores) water liquid synthetic insecticide
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• • • • • • • • • •
How to Experiment Safely Have an adult present for this experiment. Be careful when working with the pesticide. Measure the pesticide outside or in a sink. Follow the warnings carefully and wash your hands afterwards. Make sure you throw away the disposable cups and spoons that come into contact with the pesticide. Keep younger children away from the cups containing the pesticide mixtures.
marking pen masking tape ruler area with light paper towels plastic wrap two rubber bands plastic teaspoon measuring cup three disposable plastic cups
Approximate Budget $7. Timetable 20 minutes setup; about 5five minutes
daily for eight to 12 days (longer if desired). Step-by-Step Instructions
Step 9: Note the number of sprouts in each pot and measure the height of the plants. G ALE G RO UP.
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1. Label the disposable cups: ‘‘Low Pesticide,’’ ‘‘High Pesticide,’’ and ‘‘Control.’’ Label each peat pot ‘‘Low,’’ ‘‘High,’’ and ‘‘Control.’’ The dirt should be dry to moist. 2. In the Low Pesticide cup, use the plastic spoon to place 2 teaspoons (about 10 milliliters) of the pesticide in the cup. 3. In the High Pesticide cup, use the plastic spoon to place 5 teaspoons (about 25 milliliters) of the pesticide in the cup. 4. Measure and pour 0.5 cup (about 125 milliliters) of water into each of the cups. The Control cup should have plain water. Use plastic spoons to stir the High and Low cups, making sure to throw the spoons away when you have finished. 5. In each peat pot, plant five lettuce seeds per the instructions on the package. 6. Working over a sink or paper towels, pour the High pesticide water into the peat pot labeled High. Pour enough water to saturate the lettuce seeds. Water will start to drip out the bottom control when you have poured enough. 7. Repeat with the Low water, and the Control water. Set the plants on a plastic Experiment Central, 2nd edition
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container or holder to catch the water dripping out the bottom. 8. To seal in the water, tightly cover the disposable cups (not the peat pots) with plastic wrap and wrap a rubber band around the plastic. Place the water cups aside near the plants and make sure labeling is clearly visible. 9. After the seeds sprout (about five days), start daily observations of the plants. Count how many sprouts there are in each pot and measure the height. Make your measurements at the same time every day. 10. When the seeds need more water, use the water from its designated cup until the water is gone. (You may need to restir.) Summary of Results Examine the height and
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: None of the plants grew. Possible cause: Make sure you are following instructions as to the amount of light and warmth the seeds need. You may also have bought defective seeds. Try the experiment again with a new packet, making sure to follow the instructions. Problem: There was not much difference between the two groups of seeds watered with the pesticides. Possible cause: All the pesticide water may not have soaked into the plants. Make sure you stir the water thoroughly before applying it to the seeds, and repeat the experiment.
number of sprouts from each peat pot. Average the heights of each group and graph the results. Is there a difference between the experimental trials and the control? Are there any other physical characteristics that are different among the groups of lettuce sprouts? Write up a brief summary of the experiment. Change the Variables You can change the variables in this experiment in
several ways: • Change the brand of insecticide; try to find one with different main ingredients than the one you used • Alter the type of pesticide, to a herbicide or fungicide • Compare different types of plants, such as peas, tomatoes, and a flower
Design Your Own Experiment How to Select a Topic Relating to this Concept Pesticides are a contin-
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pesticides. You can compare organic fruits and vegetables to chemically treated foods. You can also look at the impact pesticides have had on food production throughout the world. When experimenting with pesticides, always make sure to work in an open area and take proper safety precautions. Check the Further Readings section and talk with your science teacher to learn more about pesticides. You could also speak with a professional at a local greenhouse or nursery, or any knowledgeable gardener. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects With so many pesticide options, there are many possible project ideas. You can explore the biology of how pesticides work on insects. Choose one or two groups of chemical pesticides, then compare the effect of these to the substances that plants produce to ward off insects. How do herbicides affect plants? The amount of time pesticides remain in 856
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the soil and on plants is another area of study. An experiment can look at how often a pesticide needs to be reapplied for effectiveness. You can also conduct a project that looks at how different pesticides move through the soil. Determining if a pesticide is on soil or in water is usually determined through chemical analysis. One home technique to find out where pesticides are would be to compare the test samples against a standard. Measure the standard by setting a pesticide-sprayed plant outside for a certain length of time and noting the results. You can then spray the water with possible pesticide in it and compare the results to the standard. For a research project, you can explore the use of pesticides on food products, how pesticides have changed over the years, and the precautions that are taken on the foods. How do organic products compare in size and yield? Compare the United States to other countries’ use of pesticides.
For More Information ‘‘About Pesticides.’’ U.S. Environmental Protection Agency. http://www.epa.gov/ pesticides/about (accessed on February 3, 2008). Provides answers to frequently asked questions about pesticides. ‘‘50 Ways Farmers Can Protect Their Groundwater: 24. Determine the Soil Pesticide Interaction Rating.’’ University of Illinois Extension: College of Agricultural, Consumer, and Environmental Sciences. http://www.thisland. uiuc.edu/50ways/50ways 24.html (accessed on February 3, 2008). This site is intended primarily for farmers, but offers good explanations of how pesticides get into soil and their effects. Nancarrow, Loren, and Janet Hogan Taylor. Dead Snails Leave No Trails. Berkeley, CA: Ten Speed Press, 1996. Natural pest control information and recipes. ‘‘Pesticides As Water Pollutants.’’ Food and Agriculture Organization. http://www. fao.org/docrep/W2598E/w2598e07.htm#historical%20development%20of %20pesticides (accessed on February 3, 2008). Information on how pesticides can pollute groundwater.
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he numerical measurement of acids and bases in a solution is called pH (the abbreviation for potential hydrogen). Acids and bases are groups of chemicals. When dissolved in water, all acids release hydrogen atoms with a positive electric charge (H+). These atoms are known as hydrogen ions. The term pH means the strength of the hydrogen ions. The p is derived from the Danish word potenz meaning strength; H is the symbol for hydrogen. When dissolved in water, bases produce negatively charged hydroxide ions (OH–). When mixed together in the right proportions, acids and bases neutralize each other and form a water and a salt. In 1909, Danish scientist Soren Peter Lauritz Sorensen, whose wife Margarethe Hoyrup Sorensen assisted him in much of his work, developed the concept of pH for determining hydrogen ion concentration.
Blue litmus paper turns pink in the presence of the acid in this lemon. P HO TO RE SE AR CHE RS I NC .
Scaling it down The pH scale ranges from 0 to 14. Very acidic substances are at the lower end of the scale, with 0.0 being the most acidic, and very basic substances are at the upper end of the scale, with 14.0 being the most basic. A pH of 7.0 indicates a substance that is neutral—neither acidic nor basic. They’re everywhere Acids and bases are present in our daily lives more than we realize. We could not digest food without the diluted hydrochloric acid in our stomachs. Eight special amino acids in the protein foods we eat are necessary for good health. Acetic acid is found in vinegar. Sulfuric acid is used in dyes, drugs, explosives, car batteries, and fertilizer. Among the most commonly known bases are ammonia and sodium hydroxide, which is used to make soap. Are you blue? No, I’m acid Measuring pH is important to chemists, biologists, bacteriologists, 859
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A digital pH meter measures pH. PHO TO R ES EAR CH ER S I NC.
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and agriculture experts as well as others in science, medicine, and industry. Your life depends on the right pH of your body fluids, including your blood and digestive juices. Determining soil pH can help a farmer grow better crops because some plants thrive in acidic soils, while others grow better in alkaline (basic) soils. Lime is spread on fields to neutralize soil that is too acidic. The hydrangea plant actually communicates the type of soil it grows in by the color of its flowers. If the soil is alkaline, this plant blooms red. If the soil is acid, it blooms blue. Quick! Get the litmus paper But what if you are not a hydrangea plant? How do you determine the pH of a solution? By using an indicator. Indicators are pigments that change color when they come into contact with acidic or basic solutions. Litmus paper is an indicator. By dipping litmus paper into liquids and watching the change in color, chemists can tell whether a liquid is an acid or a base. To determine the pH of a solution, scientists also use a machine called a digital pH meter, which has an electric probe connected to it. The probe is dipped into a solution and measures its pH. A large dial on the meter shows the pH reading. To calculate the total amount of acid or base in a solution, the chemist uses a process called titration. Titration is a method of analyzing the makeup of a solution by adding known amounts of a standard solution until a reaction occurs, such as a color change. It all falls down Remember the lime the farmer spread on the acidic field? Sometimes lime is added to a lake or stream that has become too acidic because of acid rain. Acid rain, an environmental problem that became much worse beginning in the 1950s, is rain, snow, or sleet made unnaturally acidic by sulfur dioxide and nitrogen oxide emissions. The emissions, which mix with air masses, come from the smokestacks of electric power plants that burn coal or from companies that burn high sulfur oil for fuel. Rainfall with a pH of 4, which occurs in the worst acid rain areas, is about one-tenth as acidic as vinegar. Acid rain damages trees and crops and even corrodes stone buildings and statues. Fish are not able to reproduce when their habitat Experiment Central, 2nd edition
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becomes too acidic. Some larger aquatic plants cannot tolerate the acid and die. Strong acids can damage metals and human skin. Some weaker acids are used as drugs, including aspirin. Strong bases, such as lye, can blind a person. Baking soda, which is used in baking, toothpaste, and as a cleaner, is a weak base. Measuring a substance’s pH can give you valuable information about its structure and makeup.
EXPERIMENT 1 Kitchen Chemistry: What is the pH of household chemicals? Purpose/Hypothesis The pH scale is used by
chemists to determine the ratio of acids to bases present in a solution. The scale ranges from 0 to 14 and indicates whether the solution is more acidic or more basic. In this experiment you will use an universal indicator to determine the pH of several common household chemicals, including vinegar, baking soda, lemon juice, water, and ammonia. Universal indicators, which change color in the presence of acids and bases over a broad range of the pH scale, exist in nature and are found in a few plants. Red
A scientist tests rain samples for acidity. PET ER A RN OLD INC .
The pH scale ranges from 0 to 14 and indicates whether the solution is more acidic or more basic (alkaline). GA LE G RO UP. Experiment Central, 2nd edition
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WORDS TO KNOW Acid: A substance that when dissolved in water is capable of reacting with a base to form salts and release hydrogen ions.
Ion: An atom or group of atoms that carry an electrical charge—either positive or negative—as a result of losing or gaining one or more electrons.
Acid rain: A form of precipitation that is significantly more acidic than neutral water, often as the result of industrial processes and pollution.
Neutralization: A chemical reaction in which the mixing of an acidic solution with a basic (alkaline) solution results in a solution that has the properties of neither an acid nor a base.
Base: A substance that when dissolved in water is capable of reacting with an acid to form salts and release hydrogen ions. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Indicator: Pigments that change color when they come into contact with acidic or basic solutions.
pH: (The abbreviation for potential hydrogen.) A measure of acidity or alkalinity of a solution referring to the concentration of hydrogen ions present in a liter of a given fluid. Titration: A procedure in which an acid and a base are slowly mixed to achieve a neutral substance. Variable: Something that can affect the results of an experiment.
cabbage, grape juice, radish skin, and violet flowers all contain a pigment or coloring that changes in the presence of different chemicals. The red cabbage ‘‘juice’’ used in this experiment is extracted during the boiling process. This solution is chemically neutral (pH 7), but when added to another substance, the color changes to indicate whether the substance contains a high concentration of an acid or a base. If the substance is an acid, the red cabbage solution will turn pink. If the substance is neutral, the solution will remain purple. If the substance is basic, the solution will become blue, green, or yellow. Yellow indicates a strong base, which may burn your skin on contact. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of pH. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • • 862
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A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Vinegar and lemon juice are acids, baking soda and ammonia are bases, and water is neutral.’’ In this case, the variable you will change is the substance being tested, and the variable you will measure is the color of the indicator solution. You expect the indicator solution to show that vinegar and lemon juice are acids, baking soda and ammonia are bases, and water is neutral. Level of Difficulty Difficult, because of the care
required in using a heat source and in handling ammonia and other chemicals. Materials Needed
• red cabbage indicator solution (boil six to eight cabbage leaves in 1 cup of water for five minutes, retain only the colored solution and allow to cool)
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the substance being tested • the age or freshness of the substance • the concentration of the acidic or basic components of the substance • the presence and amount of any contaminants in the substance • the age or freshness of the pH indicator • the experimenter’s ability to distinguish colors In other words, the variables in this experiment are everything that might affect the pH of the substance and the resulting color of the indicator solution. If you change more than one variable, you will not be able to tell which variable had the most effect on the pH or color.
Materials for Experiment 1. GA LE G RO UP.
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How to Experiment Safely Adult supervision is necessary for this experiment. Treat each chemical as if it were dangerous, and do not inhale the odors, especially from the ammonia. Do not eat or drink while conducting this experiment. Wear goggles to prevent eye injury. Wash your hands immediately if they come in contact with any of the chemicals. Consult your science teacher before you substitute any chemicals for the ones listed in this experiment.
• household chemicals: vinegar, baking soda, lemon juice, water, ammonia, white or clear detergent, etc. • cups (3.5-ounce clear plastic) or test tubes (glass or plastic) • measuring spoons • goggles • paper towels (for cleanup) Approximate Budget $2 for the red cabbage,
which is necessary for this experiment. Timetable 1 hour. Step-by-Step Instructions
Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can definitely be a learning experience. Be aware of contamination. Always make sure the utensils and cups are clean. Use only fresh chemicals that have not spoiled. If you are not getting the desired results, place a scoop of baking soda (sodium bicarbonate) into a cup that has been washed, rinsed, and dried. Make sure you use a clean spoon. Pour in some indicator solution and stir. The resulting color should be blue, indicating a base.
1. Place a small amount (approximately ½ teaspoon) of one chemical into the cup. Wash the measuring spoon. 2. Place an equal amount of indicator solution (red cabbage water) in the same cup. Again, wash the measuring spoon. 3. Record the resulting color change of the indicator solution. 4. Determine the chemical property of the substance—acid, base, or neutral. 5. In clean cups, repeat this procedure for each of the other chemicals. Summary of Results Record your results in a
journal or notebook. Go back to your hypothesis and determine whether your original guesses were correct. Write a paragraph summarizing your findings. Here is a general rule of thumb for acids and bases: • Acids are corrosive but lose their acidity when combined with bases. • Bases feel slippery when they come in contact with the skin; they lose their alkalinity when mixed with acids. (But do not test bases by touching them; they can burn your skin.) • Salts are formed when acids and bases react. 864
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Change the Variables You can vary this experi-
ment in several ways. Try comparing different brand-name items or testing items that have spoiled. For instance, milk when fresh is base but when spoiled is an acid.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the variables for this experiment:
Modify the Experiment One reason this experiment is difficult is that you need to boil cabbage to make a universal indicator. You can simplify this experiment by purchasing a pH indicator. Also called litmus paper, pH indicator strips are commonly sold at drug stores and places that sell science supplies. Litmus papers are available in different sensitivity. Commonly available litmus papers will turn either blue or red, depending up if the solution is a base or acid.
• the acid or base being tested
If you want to explore pH more, you can compare the results of the litmus paper to your universal indicator. How close are the two indicators?
• the experimenter’s ability to distinguish colors
EXPERIMENT 2 Chemical Titration: What is required to change a substance from an acid or a base into a neutral solution?
• the age or freshness of the acid and base • the concentration of the acidic or basic components (many acids are diluted in water) • the presence and amount of any contaminants in the acid and base • the amount of acid added to the base, and vice versa • the age or freshness of the pH indicator
In other words, the variables in this experiment are everything that might affect the pH of the substance and the resulting color of the indicator solution. If you change more than one variable, you will not be able to tell which variable had the most effect on the pH or color.
Purpose/Hypothesis After you understand how to use indicators, you can
begin testing and manipulating chemicals. Here is a general description of how acids and bases mix and the results. Acids produce a H+ particle called a hydrogen ion. Bases produce an OH–particle called a hydroxide ion. These H+ and OH–ions can join to form H2O or water, a neutral substance. The leftover substance is a salt. The chemical formula for a typical acid-base reaction between hydrochloric acid and sodium hydroxide. GAL E GR OU P.
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How to Experiment Safely Adult supervision is necessary for this experiment. Treat each chemical as if it were dangerous. Do not eat or drink while conducting this experiment. Wear goggles to prevent eye injury. Wash your hands immediately if they come in contact with any of the chemicals. Consult your science teacher before you substitute any chemicals for the ones listed in this experiment. When acids and bases react to form a salt, the reaction can be violent. Gases, flames, heat, and other forms of energy can be released. In other words, use caution!
The chemical formula for a typical acid-base reaction between hydrochloric acid and sodium hydroxide is illustrated. The resulting products of this reaction are neutral sodium chloride (salt) and water. When an acid and a base combine to form a neutral solution, the procedure is called a titration reaction. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of pH. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A basic substance can be neutralized by the addition of an acid, and vice versa.’’
Materials for Experiment 2. GAL E GR OU P.
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In this case, the variable you will change is the amount of acid being added to the base (or base to acid), and the variable you will measure is the color of the indicator solution. You expect the indicator solution to show a color indicating the basic pH changes to a neutral pH with the addition of an acid, and vice versa. Level of Difficulty Difficult, because of the care required in using a heat
source and in handling chemicals. Materials Needed
• red cabbage indicator solution (refer to Experiment 1 for instructions) • vinegar • baking soda • stomach antacids (such as Tums) • baking powder • clear plastic cups • measuring spoons • goggles
Step 4: Slowly pour vinegar into the cup and watch the violent acid-base reaction. GAL E GR OU P.
Approximate Budget $2 to $10. Timetable 1 hour. Step-by-Step Instructions
1. In a cup place 1 teaspoon of baking soda. 2. In the same cup place an equal amount of indicator solution, and then stir. 3. Note the color of the solution. 4. In the same cup slowly pour some vinegar. Watch the violent acid-base reaction, and stop when the solution turns purple. 5. If you add too much vinegar, the solution may turn pink. Slowly sprinkle more baking soda into the cup until the purple color reappears. Experiment Central, 2nd edition
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Summary of Results When the baking soda (a base) was added to the
indicator, the color changed from purple to blue indicating the presence of OH–ions (a base) with a pH of greater than 7. When the vinegar (an acid) was added, the H+ ions reacted with the OH–ions and produced water (a purple neutral solution, with a pH of 7). The gas CO2 was produced during the reaction. When an acid and a base are joined equally, the resulting solution is neutral. You have caused a titration reaction. Summarize the results of your experiment in writing. Change the Variables You can vary this experiment in several ways. Try
adding substances such as antacids to vinegar and indicator solutions. Test the pH of baking powder, which is an acid and a base in a powdered mixture.
Design Your Own Experiment How to Select a Topic Relating to this Concept Here is your chance to create a fun experiment about a topic that interests you. Chemistry is a great topic to experiment in because it is part of your everyday life. Everything from the detergent that washes your clothes to the vinegar in salad dressing is made up of chemicals, and so are you! Find an area of chemistry that interests you and start to investigate it. Cleaners, cosmetics, medicine, and food are some areas that you may want to examine. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on pH questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some chemicals can be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure of what question you are answering, what you are or should be measuring, or what your findings may prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. 868
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• State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Keep a journal and record
your notes and measurements in it. Your experiment can then be utilized by others to answer their questions about your topic. Related Projects After you have chosen a topic to examine, develop an experiment to go with it. For example, you might want to investigate the power of detergents or cleaners. Since grass stains on jeans are common, your experiment could be to determine what detergent works best to remove them.
For More Information Adams, Richard, and Robert Gardner. Ideas for Science Projects. New York: Franklin Watts, 1996. Well organized science projects for middle grade students. Andrew Rader Studios. ‘‘Acids and Bases are Everywhere.’’ Rader’s Chem4kids.com. http://www.chem4kids.com/files/react acidbase.html (accessed on March 13, 2008). Information on the chemistry of mixtures. Newmark, Ann. Eyewitness Science: Chemistry. London: Dorling Kindersley, 1993. Great visual examples and interesting facts that include pH. U.S. Environmental Protection Agency. ‘‘What is pH?’’ Acid Rain. http:// www.epa.gov/acidrain/measure/ph.html (accessed on March 13, 2008). Brief explanation of the pH scale.
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T Jan Ingenhousz discovered that sunlight stimulates photosynthesis in plants. CO RB IS- BE TTM AN N.
o get our food, we go to the supermarket, pick vegetables or fruit from our gardens, or cast a rod in our favorite fishing hole. A plant, however, makes its own food using sunlight as its major energy source in a process called photosynthesis. In fact, the term photosynthesis means ‘‘putting together by light.’’ Shining the light on vegetables In the eighteenth century, Jan Ingenhousz, a Dutch physician and plant physiologist, proved that sunlight was essential to the life activities of green plants. In 1779, he published experiments showing that plants have two respiratory cycles. At night, plants absorb oxygen and exhale carbon dioxide, just as animals do, but during the day the cycle is reversed. Another eighteenth-century scientist, Englishman Joseph Priestley, made similar discoveries about plant respiration; but it was Ingenhousz who proved through his vegetable experiments that it was only in the presence of light that plants absorbed carbon dioxide and gave off oxygen. This was a major discovery because until then most people thought the soil was the only source of a plant’s nutrients. How it works Think of a plant’s leaf as a solar panel. Just like the flat glass panels you see on rooftops, a leaf’s flat surface makes it an efficient sunlight absorber. Within each leaf cell are up to a hundred disc-shaped chloroplasts. Chloroplasts have a green pigment called chlorophyll, which traps light. 871
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We know that sunlight is actually a spectrum of many colors that have different wavelengths. The pigments in plants absorb different wavelengths of the sunlight spectrum. Chlorophyll is not the only pigment in plants, but it is the most plentiful pigment. It reflects the green part of the spectrum, which makes plants look green to the human eye, but absorbs other parts of the spectrum. Other pigments, such as carotene and xanthophyll reflect yellow-orange and yellow spectrum colors. These pigments act as a support team to chlorophyll. Sunlight supplies the energy. Chlorophyll turns the switch that powers a plant’s chemical reactions. Those reactions include taking carbon dioxide from the atmosphere, plus water and inorganic chemicals from the soil, and converting them into oxygen and glucose. Glucose is needed in every part of the plant. Cellulose, the tough, fibrous part of the plant, is formed from glucose. Starch, another glucose by-product, is stored within the roots, leaves, or stems of plants. Pores on the underside of the leaf let gases in and out. Tubes called xylem carry water throughout the plant; tubes called phloem distribute the food. Light intensity, temperature, and water supply are some of the key factors that affect the rate of photosynthesis. In rain forests, plants grow in abundance,because the weather there is rainy and warm, and the Sun’s rays are more intense. Need oxygen? Get a plant The carbon dioxide given off by animals is consumed by plants. Plants on land and in the sea replace the oxygen taken in by animals. That is why there is so much concern for preserving forests, green spaces, and oceans. Besides being animal habitats, they are oxygen producers. Without plants, we would all die. Interestingly, most of Earth’s photosynthesis does not take place on land. Over 75% of photosynthesis processes on Earth actually takes place in our oceans. Chlorophyll is the vital link in photosynthesis in marine plants as well. But these underwater organisms have larger concentrations of other pigments than their plant ‘‘cousins’’ on land. Because little light Experiment Central, 2nd edition
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penetrates below a depth of 330 feet (100 meters), photosynthesis takes place in the upper part of the ocean called the euphotic zone. Plants that live in this zone are called phytoplankton. During photosynthesis, plants consume carbon dioxide produced by animals and replace oxygen consumed by animals. Unlocking the keys of this balanced activity through experiments will help you appreciate the hidden benefits of our national parks, nature preserves, and oceans. Plants are not green things that just sit there, but vital, living organisms that help us stay healthy.
EXPERIMENT 1
Phytoplankton are underwater plants that utilize photosynthesis to produce oxygen. P ETE R A RNO LD I NC .
Photosynthesis: How does light affect plant growth? Purpose/Hypothesis This experiment deals with the concept of photo-
synthesis and how different wavelengths of light affect plant growth. Plants contain different pigments, including chlorophyll, carotene, and xanthophyll, so they can respond to different wavelengths. In this experiment, three different colors of light will be used to grow plants. The three colors will represent different wavelengths of light: red— long; yellow—medium; and violet or blue—short. A fourth plant will be grown under a white light, which contains all wavelengths. The amount of growth for each plant will demonstrate which color light promotes the most plant growth. To begin your experiment, use what you know about photosynthesis to make an educated guess about light color and plant growth. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one Experiment Central, 2nd edition
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WORDS TO KNOW Carotene: Yellow-orange pigment in plants. Chlorophyll: A green pigment found in plants that absorbs sunlight, providing the energy used in photosynthesis for the conversion of carbon dioxide and water to complex carbohydrates. Chloroplasts: Small structures in plant cells that contain chlorophyll and in which the process of photosynthesis takes place. Euphotic zone: The upper part of the ocean where sunlight penetrates, supporting plant life, such as phytoplankton. Glucose: A simple sugar broken down in cells to produce energy. Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/ or experiment. Phloem: Plant tissue consisting of elongated cells that transport carbohydrates and other nutrients. Photosynthesis: Chemical process by which plants containing chlorophyll use sunlight to manufacture their own food by converting carbon dioxide
and water to carbohydrates, releasing oxygen as a by-product. Physiologist: A scientist who studies the functions and processes of living organisms. Phytoplankton: Microscopic aquatic plants that live suspended in the water. Pigment: A substance that displays a color because of the wavelengths of light it reflects. Respiration: The physical process that supplies oxygen to an animal’s body. It also describes a series of chemical reactions that take place inside cells. In plants, at night or in the dark, the process is the same as in animals. In light, plants absorb carbon dioxide to use in photosynthesis, and give off oxygen. Xanthophyll: Yellow pigment in plants. Xylem: Plant tissue of elongated, thick-walled cells that transport water and mineral nutrients. Variable: Something that can affect the results of an experiment.
possible hypothesis for this experiment: ‘‘Plants grown under white light will grow the most because white light contains all the wavelengths that plants can use in photosynthesis and most closely duplicates natural sunlight.’’ In this case, the variable you will change is the color, or wavelength, of light, and the variable you will measure is the amount of plant growth over a period of several weeks. If the plants under the white light grow more than those under the colored lights, you will know your hypothesis is correct. Level of Difficulty Moderate, since the plants in this experiment may
require daily attention for a few weeks. 874
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Materials Needed
• scissors • 4 lamps (desk lamps with reflectors are best) • 4 cardboard boxes, 18 inches (46 centimeters) square • 4 light bulbs (25-watt), in white, red, yellow, and violet or blue • 4 pots filled with soil • 40–80 bean or corn seeds (These seeds sprout and grow rapidly, so results can be seen in two weeks. Use the same type of seeds in all pots.) Approximate Budget $3 or each light bulb and
$3 for bean and corn seeds. Timetable Approximately 4 weeks, during which
15 minutes of daily attention is required, plus 1 hour to set things up.
What Are the Variables? Variables are anything that might affect the results of the experiment. Here are the main variables in this experiment: • the types of plants chosen • the color of light • the intensity of light • the amount of water provided to each plant • the type of soil • the surrounding air temperature In other words, the variables in this experiment are everything that might affect the growth of the plants. If you change more than one variable, you will not be able to tell which variable had the most effect on plant growth.
Step-By-Step Instructions
1. Plant 10 to 20 seedlings in each pot. Water generously and allow the water to drain.
The spectrum and wavelength of different colors. GAL E GR OU P.
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2. Cut a hole into the top of your boxes. The hole should be 2 inches (5 centimeters) How to Experiment Safely smaller in diameter than the diameter of the lamp. Try to place the hole in the center Use caution when handling hot lamps. Be sure of the box top. Cut a door in the side of the lamps and light bulbs are not touching the boxes or plants. Turn off the lights and move each box so that the door can be closed the lamps aside before watering the plants to during the day to block outside light. avoid a possible electrical shock. 3. Locate the boxes side-by-side on a table away from windows in a warm, but not hot, room. Place a lamp with a different color light bulb over each box. Label each box as illustrated. 4. Place a plant inside each box under the light. 5. Plug in the lamps and turn them on. 6. After the seeds sprout, open each door every day and record the height of each plant on your results chart. 7. Leave the lights on each day for approximately eight to 12 hours. Turn them on in the morning, and shut them off at night. Remember to keep the doors in Materials for Experiment 1. the boxes closed. GA LE GRO UP. 8. Sprinkle water over the soil every other day. Never allow the soil to completely dry out. Remember to turn the lights off and move the lamps aside before watering the plants to avoid a possible electrical shock. Replace the lamps when you are finished.
Steps 3 and 4: Place a lamp with a different color light bulb over each box. Label each box as illustrated. Place a plant inside each box under the light. GA LE GR OU P.
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9. After two to four weeks, study your charted results and summarize them. Summary of Results After the experiment is fin-
ished, collect the final data and organize it into usable statistics and charts. Graph the plant heights for a visual comparison of plant growth. Determine which wavelength/color affects growth the most. Reflect on your hypothesis. Which color/wavelength of light was most beneficial for plant growth? Change the Variables Different plant species contain varying amounts of pigments. Instead of varying the color of light, you could vary the plant being tested—either by growing different seeds or by using different small house plants. You could also test the effect of varying the intensity of light, which is what you can do in Experiment #2.
Troubleshooter’s Guide Here is a problem you may encounter, some possible causes, and ways to fix the problem. Problem: All the plants are starting to wilt, turn yellow, or fall over. Possible causes: 1. The plants may be in shock from being removed from their normal environment. Grow the plants outside the box, indoors, for one week before starting the experiment again. 2. The lamps are too close to the plants, causing them to wilt from the heat. Raise the lamp a few inches and try again.
EXPERIMENT 2 Light Intensity: How does the intensity of light affect plant growth? Purpose/Hypothesis This experiment deals with the amount of light
required for photosynthesis and growth. In this experiment, three wattages of light bulbs—40 watt, 25 watt, and 5 watt—will be used to determine how the different amounts of light intensity affect plant growth. A fourth plant will have no light bulb. In general, the more light present, the better a plant responds in its growth and vigor. However, light can also scorch or burn a plant if it is too intense. To begin the experiment, use what you know about photosynthesis to make an educated guess about how light intensity will affect plant growth. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the types of plants chosen • the intensity of light • the amount of water provided to each plant • the type of soil • the surrounding air temperature In other words, the variables in this experiment are everything that might affect the growth of the plants. If you change more than one variable, you will not be able to tell which variable had the most effect on plant growth. Plants can be categorized into those having a low, medium, or high preference for light. For this experiment, an ivy was chosen because it has a medium light preference.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A 25-watt light bulb will promote the most plant growth because its intensity is neither too dim nor too bright.’’ In this case, the variable you will change is the intensity of the light, and the variable you will measure is the amount of plant growth over a period of several weeks. If the plant under the 25-watt light bulb grows the most, you will know your hypothesis is correct. Level of Difficulty Moderate because of the dura-
tion of the experiment. (It takes approximately four weeks to cause a noticeable result.) Materials Needed
• scissors • 3 lamps (desk lamps with reflectors are best) • 4 cardboard boxes, 18 inches (46 centimeters) square • 3 light bulbs: one 40-watt, one 25-watt, one 5-watt • 4 potted ivy plants
Step 2: Cut a door into each box. Door should be 10 inches wide on all sides; only three sides are cut with the fourth side acting as a hinge. GA LE GR OU P.
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Approximate Budget $20 for light bulbs and
plants. Timetable 4 weeks, including 5 minutes a day
for watering and recording growth, plus one hour for set up. Step-By-Step Instructions
How to Experiment Safely Use caution when handling hot lamps. Be sure the lamps and light bulbs are not touching the boxes or plants. Do not use bulbs with an intensity greater than 40 watts to avoid the possibility of fire. Turn off the lights and move the lamps aside before watering the plants to avoid a possible electrical shock.
1. Cut a hole into the top of three boxes. The hole should be 2 inches (5 centimeters) smaller in diameter than the diameter of the lamp. Try to place the hole in the center of the box top. Do not cut a hole in the top of the fourth box. 2. Cut a door into each box, following the diagram illustrated. 3. Place a lamp with a light bulb over each box with a hole in it. Label each box. 4. Place a potted plant inside each of the four boxes. 5. Record the health of each plant. Measure its approximate size. 6. Plug in lamps and turn them on. 7. Keep the lights on for eight to 12 hours daily. Keep the doors closed to block outside light. 8. Water the plants every other day. Remember to turn off the lights and move the lamps aside before watering the plants to avoid a possible electrical shock. 9. Check on the plants daily. Record any changes in health, such as loss of leaves, plants turning brown, or plants growing toward light. Mark the headings Week 1, 2, 3, and 4, and record the changes in each plant. 10. After 4 weeks, the plant with no light will probably be dead and the experiment will be concluded.
Steps 3 and 4: Place a lamp with a light bulb over each box with a hole in it and label each box. Place a potted plant inside each of the four boxes. GA LE GRO UP .
Summary of Results After the experiment is completed, collect your data and display it for others to view. Make drawings of plants to demonstrate the effects of light intensity. Reflect on your hypothesis and draw some conclusions. What was the Experiment Central, 2nd edition
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Step 9: Each week record the changes in each plant. Illustration shows the likely outcome after four weeks. GA LE GR OU P.
best wattage or light intensity for the plants? If your hypothesis was that the 25-watt light would be best, and it turned out that the 40-watt light was actually the best, you weren’t wrong—you just got a different result than predicted. You still learned something from the experiment. Change the Variables Just as in Experiment #1, one way to change the
variables is to change the plants being tested. Go to a plant nursery and find a type of plant that likes a low intensity light. Repeat the experiment to see which wattage bulb produces the best growth with the new plant.
Design Your Own Experiment How to Select a Topic Relating to this Concept Photosynthesis is essential
for a plant’s survival and growth. Air, water, light, nutrients, and temperature are crucial elements that play a part in photosynthesis. You can select from the elements needed for photosynthesis to conduct an experiment. For example: temperature affects the function of the pigments responsible for photosynthesis. You can experiment to determine at what temperature photosynthesis stops in trees, that is, when they go into dormancy. 880
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Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on photosynthesis questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of them might be dangerous. Steps in the Scientific Method Here is your
Troubleshooter’s Guide Here is a problem you may encounter, a possible cause, and a way to solve the problem. Problem: All the plants lost their leaves. Possible cause: The plants are in shock. Grow them outside the box inside the house for a week or two before starting the experiment.
chance to answer questions or discover new facts. Design an experiment about a topic that interests you. To do this, you must follow some guidelines to help you stick to your goal and get useful information. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Experimenting is a means
by which we discover the answers to our questions. It is important to record all the changes in the experiment as well as conclusions drawn from it. Others may use your experiment to answer questions or solve related problems regarding your topic. Related Projects If you decide to test temperature and its effects, you may
want to choose a plant that drops its leaves, known as deciduous, and monitor the temperature outside. In this sample experiment, all you have to do is choose a plant species, such as white oak, and monitor the average temperature when it drops its leaves.
For More Information Bonnet, Robert L., and G. Daniel Keen. Botany: 49 Science Fair Projects. Blue Ridge Summit, PA: Tab Books, 1989. Features seven projects on photosynthesis in Chapter 3. Experiment Central, 2nd edition
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Groleau, Rick. ‘‘Illuminating Photosynthesis.’’ Nova Online. http://www.pbs. org/wgbh/nova/methuselah/photosynthesis.html# (accessed on March 1, 2008). Interactive animations on photosynthesis. Lammert, John M. Plants: How to Do A Successful Project. Vero Beach, FL: Rourke Publications, Inc., 1992. Includes a chapter on photosynthesis. ‘‘Photosynthesis: How Life Keeps Going.’’ FT Exploring. http://www.ftexploring. com/photosyn/photosynth.html (accessed on March 2, 2008). Comprehensive information on photosynthesis and energy.
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lants come in all shapes and sizes, from floating water plants about the size of a pencil dot to trees towering hundreds of feet high. Travel to anywhere on Earth and you will spot some type of plant, even in the extreme cold and hot environments. All animals, from bugs to people, depend upon plants to live. They supply oxygen and food, both directly and indirectly. There are an estimated 500,000 different types of plants with a wide variety of features. But in general, plants share a similar anatomy (structure).
Roots are how most plants absorb water and nutrients. IL LU STR AT ION BY T EM AH NE LS ON.
At the root of it The root of a plant is an organ that plays many roles. In general, most plant roots lie underground. They anchor the plant, keeping it from being tossed into the air on gusty days. Roots are how most plants absorb water and nutrients. Nutrients in the soil dissolve in water. The root hairs, hundreds of fine hairs on the root, absorb the water through a process called osmosis. Osmosis is the movement of water from an area where there is a high concentration of water to an area of low water concentration through a cell membrane. The membrane encircles the cell and allows only some substances to pass into the cell. Roots also take in oxygen. Although plants produce oxygen, they also need some oxygen to live in a process called respiration. Soil contains pockets of oxygen. In some plants, roots lie near the ground where there is a richer supply of oxygen. Trees that live in or near the mud, where there is little oxygen, sometimes have roots above ground to gather oxygen. Plants that have their roots in the air are called epiphytes. Epiphytes often live on another 883
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Cacti store water in its stem and use it little by little in order to survive the dry conditions of the desert. F IE LD M ARK PUB LI CAT IO NS.
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plant, collecting water and nutrients from the runoff or rain. Epiphytes that live in humid environments can take in the water and nutrients from the air. Some epiphytes have adapted to slow their growth when there is little water. Other plants have shallow roots that thread out extensively so they can quickly suck up water close to the surface. Holding it all together Stems pick up where the root meets the ground, holding the plant up and supporting its structure. The larger the plant, the thicker the stem. Larger plants can also have multiple stems, with shoots branching off from one another. Stems can be soft and flexible, allowing the plant to bend. Other plants, such as trees, have stems that are hard and woody. Water and nutrients absorbed from the roots move through the stem and up the plant through tube-like structures. The tubes that carry the water are called xylem. The xylem is made of dead cells and has thick walls. The tubes that carry the food are called phloem. The phloem is made of living cells and have thin walls. Stems can also store water and food. Many cacti, for example, store water in its stem and use it little by little. In some plants, stems act as reproductive shoots. Potatoes grow from the underground parts of a stem, acting as food storage and reproductive organs. Making food and oxygen The point at which the leaf joins the stem is called the node. The water and nutrients move from the root into the veins of the leaves. The substances move from the larger leaf veins to smaller offshoots in the leaf. Leaves are where the plant produces its food in a process called photosynthesis. To make its food or energy, plants need water, carbon dioxide (a gas in the air), and energy from the sun. The same compound in plants that supplies its green color, chlorophyll, is also responsible for collecting the sun’s energy. The products of photosynthesis results in sugars and oxygen. The sugars are what the plant uses for food and the oxygen is released into the Experiment Central, 2nd edition
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air. In photosynthesis, plants take in more carbon dioxide and release more oxygen than the amount of oxygen they need in respiration. That means plants end up producing more oxygen than they consume.
releases oxygen
sunlight
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A leaf ’s surface has microscopic openings called stomata, named after the Greek word for mouth. The stomata open and close regularly to exchange gases, such as oxygen and carbon dioxide. The plant will also lose its water in the form of water vapor when the stomata are open. In plants, this loss of water is called transpiration. For most plants transpiration occurs primarily on the leaves. Water can also escape from leaves in the form of liquid. When a plant takes in too much water, the water can escape through pores in the leaves. All shapes and sizes The structure and type of leaf depends upon the plant’s environment. Cacti are found in deserts, which are extremely dry. Leaves of a cactus are few and small to keep it from losing water. Shaped like sharp needles, the leaves also keep hungry or thirsty animals away.
To make its food or energy, plants need water, carbon dioxide (a gas in the air), and energy from the sun. ILL US TRA TI ON B Y TE MA H NEL SO N.
Where a leaf sits on the stem helps determine how much sunlight it will get. In some plants the leaves spiral up a stem and in others they sit on opposite sides of the stem. Another leaf arrangement, called the whorl, is when several leaves shoot out from the same point. Because capturing the sun’s energy is essential for a plant’s survival, plants living in low sunlight areas have made several adaptations. These can be plants that live low to the ground or deep inside a lush forest. In some plants, the stalks of the lower leaves reach longer than the ones above it. This is one reason why there are many cone-shaped plants, such as pine trees. Some leaves on upper parts have holes or notches that allow the sunlight to shine through. Leaves can arrange themselves into mosaics, such as an ivycovered wall or leaves growing around trees. In these leaf patterns the arrangement allows each leaf to be exposed to the sun. There are other plants that have adapted to the shade by growwhorled ing wide, large leaves. Experiment Central, 2nd edition
Where a leaf sits on the stem helps determine how much sunlight it will get. ILL US TRA TI ON B Y TE MA H NEL SO N.
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WORDS TO KNOW Anatomy: The study of the structure of living things. Chlorophyll: A green pigment found in plants that absorbs sunlight, providing the energy used in photosynthesis. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Osmosis: The movement of fluids and substances dissolved in liquids across a semi-permeable membrane from an area of greater concentration to an area of lesser concentration until all substances involved reach a balance. Photosynthesis: Chemical process by which plants containing chlorophyll use sunlight to manufacture their own food by converting carbon dioxide
and water into carbohydrates, releasing oxygen as a by-product. Phloem: The plant tissue that carries dissolved nutrients through the plant. Respiration: The process of an organism using oxygen for its life processes. Root hairs: Fine, hair-like extensions from the plant’s root. Stomata: Pores in the epidermis (surface) of leaves. Transpiration: Evaporation of water in the form of water vapor from the stomata on the surfaces of leaves and stems of plants. Variable: Something that can affect the results of an experiment. Xylem: Plant tissue consisting of elongated, thickwalled cells that transport water and mineral nutrients. (Pronounced ZY-lem.)
EXPERIMENT 1 Plant Hormones: What is the affect of hormones on root and stem growth? Purpose/Hypothesis Gibberellic acid is a group of growth hormones that are
produced naturally in plants. Gibberellic acid plays a role in how plants develop and grow. In this experiment, you will test the affect of giving plants Gibberellic acid at different points of its life cycle to evaluate how the hormone affects the root and stem growth. You will apply Gibberellic acid during the seed stage for one experimental set-up and shortly after the plant has sprouted for the second set-up. By measuring the stem length and comparing root growth, you will be able to see how the hormone has affected development. Because Gibberellic acid is dissolved is in a water solution, this experiment will also help you observe how plants take in essential nutrients through water. 886
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Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plant growth and hormones. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • environmental temperature • time given for experiment • type of plant • how the growth hormone is applied
A hypothesis should be brief, specific, and • soil nutrient content measurable. It must be something you can test In other words, the variables in this experiment are through further investigation. Your experiment everything that might affect the growth of the will prove or disprove whether your hypothesis is plant. If you change more than one variable at the correct. Here is one possible hypothesis for this same time, you will not be able to tell which variexperiment: ‘‘Plants that receive hormones at the able impacted the plant’s root and stem growth. youngest stage, as a seed, will show more stem and root growth than the other plants.’’ In this case, the variable you will change is the stage in the growth cycle that Gibberellic acid is given to the plant. The variable you will measure is the plant stem and root growth. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental plants, and that is the Gibberellic acid. For the control, you will not apply any Gibberellic acid to the plant. At the end of the experiment you will compare this group of plants to the others. Level of Difficulty Moderate, due to the time involved. Materials Needed
• 1 packages of seeds: radishes, peas, and geraniums work well • 1 peat pellet or similar type starter pot, with a cover (available at gardening stores); or 3 small pots with potting soil • Gibberellic acid (available at some gardening stores or science supply stores) • fingernail polish remover (with acetone) • 2 plastic bottles • distilled water Experiment Central, 2nd edition
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• ruler • 2 stirring spoons
How to Experiment Safely
• measuring cup There are no safety hazards in this experiment. Wash your hands and clean up your work area after you have planted the seeds.
Approximate Budget $15. Timetable 20 minutes preparation time; five
minutes daily for approximately six weeks. Step-by-Step Instructions
1. Mark one pot ‘‘Group 1;’’ the second pot ‘‘Group 2;’’ and the third pot ‘‘Control.’’
Step 2: Add two to four drops of fingernail polish to each bottle and swirl until the Gibberellic acid is dissolved. I LL UST RA T IO N BY T EM AH NE LS ON.
2. Tear two small pieces of wax paper and place a large pinch of Gibberellic acid (GA) on each sheet. Try to have the same amount of GA on each sheet. If you have a sensitive gram scale you can weigh the sheets to make sure they are equal. Pour one pinch of GA in one bottle and the second pinch of GA in the second bottle. Add two to four drops of fingernail polish to each bottle and swirl until the Gibberellic acid is dissolved. 3. Add a cup of distilled water to the first bottle and mix with a spoon. This is the GA solution you will use to water Group 1. 4. Add a cup of distilled water to the second bottle and set aside. This is the GA solution you will use to water Group 2. 5. Plant the seeds as directed. You should plant at least two seeds in each Group and in the Control group. 6. Water Group 1 as directed using the mixed GA solution. Water Group 2 and the Control seeds with plain water. 7. Cover (if you have one) and set aside in a warm environment. Continue watering the seeds as needed. Use the GA solution for Group 1 until all the water is used and then use only water.
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8. When the seeds germinate, use a ruler to measure the growth. You may want to sketch the growth.
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9. When Group 2 has grown approximately 0.79 in (2 centimeters), mix the second bottle of GA solution with a spoon and begin watering these young plants with the GA water. Continue watering Group 2 with its GA solution until the solution is gone and then switch back to plain water. 10. Check on the plants every day and water when needed. After approximately five to six weeks measure stem and root growth. 11. To measure stem growth: Use a ruler to compare the height of each stem and make a note.
12. To measure root growth: Carefully, lift the Group 1 plants out of the pots and immerse in a container of warm water. Allow the plants to soak for 15 minutes and gently rub the soil off the roots. Set these plants aside and mark them as Group 1. Repeat this same process for the Group 2 and Control plants.
Step 9: Mix the second bottle of GA solution with a spoon and begin watering these plants with the GA water. I LLU ST RATIO N BY TEM AH N EL SON .
13. Use a ruler to measure the longest roots for each of the plants. You may want to draw the root growth. 14. When you have finished with your analysis and experiment, you can replant the plants and continue growing them. Summary of Results If you had two plants grow
Step 13: Use a ruler to measure the longest roots for each of the plants. IL LU STR AT IO N BY TEM AH N EL SON .
in each group, average the stem height for the group. Look at how the two experimental plants compare to the Control plants. If you have made sketches or drawings during the experiment, compare how each of the groups compares to the control during the experiment. You may want to create a graph to record the germination and height of each group. Did the seeds given Gibberellic acid show more or less growth than the young plants? If you want to continue following the plant’s growth, you can measure Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: All the plants grew about the same and at the same rate. Possible cause: The Gibberellic acid may not have been dissolved in the water. Gibberellic acid does not dissolve in water but it does dissolve in acetone (fingernail polish remover) or alcohol. Make sure the nail polish remover you used contains acetone. If it does not, you can use several drops of rubbing alcohol and mix it thoroughly with the GA. Problem: None of the seeds sprouted. Possible cause: There can be several reasons why your plants did not grow. Check to make sure you are using nutrient-rich soil and make sure you did not over water them. You may want to ask the advice of a friend or adult who grows plants. If none of the seeds germinated the seeds may all have been unhealthy. Purchase another bag of seeds and repeat the experiment.
flowering and leaf growth. You may need to transfer the young plants to a larger pot. Change the Variables One variable you can
change is the type of plant. Not all plants respond the same way to Gibberellic acid. Choose plants that flower, for example, and measure how the growth hormone affects flowering? You could also change the concentration of Gibberellic acid, using both more and less concentrated GA solutions. Another variable you could change is how the growth hormone is applied. In this experiment you added it to the soil. What would happen if you sprayed the water on the leaves?
EXPERIMENT 2 Water Uptake: How do different plants differ in their water needs? Purpose/Hypothesis The amount of water plants
need to live depends upon the type of plant. Different plants take in different amount of water at various times. Some plants need a constant supply of water and cannot survive in extremely dry soil. Other plants take in their water in spurts, drying out before they need more water. In this experiment, you will be measuring how different plants take in water through its roots. You will use a form of potometer, which can measure the rate of water uptake. The main reason for water uptake by a plant is transpiration. You will test young plants with different size leaves: One has broader, larger leaves relative to the other plant, which has small little leaves. When testing different plants, you will need to try and keep the plants as similar as possible, in both size and leaves. To begin this experiment, use what you know about plant anatomy to make an educated guess about how the different plants will take up water. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change
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• the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The plant with the broadest and largest leaves will take up the most water.’’ In this case, the variable you will change is the type of plant, and the variable you will measure is the amount of water taken up by the plant, during the day and night, over several days. Level of Difficulty Moderate to Difficult. (This
experiment takes patience and an attention to detail.) Materials Needed
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of plant • the amount of plant used • the amount of sun or temperature • the amount of time before water uptake is measured • the humidity • the amount of wind In other words, the variables in this experiment are everything that might affect the water uptake of the plants. If you change more than one variable, you will not be able to tell which variable most affected the plants’ need for water.
• 2 clamps (available at hardware stores) • pothos seeds (also called devil’s ivy; you can try other plants with large, broad leaves) • sweat pea seeds (you can also try other plants with small leaves) • 1, 10-section peat pellet or similar type starter pot with a cover (available at gardening stores); you can replace this with 2 to 3 cups of potting soil and an egg carton • ring stand (available at science supplies stores; a vertical wooden paper towel holder also works well.) • plastic tubing with a 1/4-inch diameter opening, about 3 feet (available at hardware stores) • scissors • 1 ml. plastic pipette, 1/4-inch diameter (available from science supply stores) • Vaseline (petroleum jelly) • plastic wrap • small bowl • knife or scissors • toothpicks • copper wire, chopsticks, or other thin long item Experiment Central, 2nd edition
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Approximate Budget $20.
How to Experiment Safely Be careful when cutting the tubing with the scissors. Have an adult help you cut the plastic pipette with a knife or scissors
Timetable Approximately two hours working
time; total time three to four weeks. Note: this experiment asks for measurements in 12-hour increments. Try to begin the experiment in the morning or evening.
Step-by-Step Instructions
Step 9: Carefully set the plant’s roots into the tube. I LL UST RA T IO N BY T EM AH NE LS ON.
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1. Follow the direction for the peat pellet or add soil to the sections in the egg carton and plant several seeds of both plants. 2. Continue caring for the plant according to the instructions until at least one of each type of plant is approximately 2 to 3 inches (5–8 centimeters) tall. (The second experimental plant will have three more days to grow so it can be a slightly smaller than the first experimental plant.) 3. Fill a small bowl with warm water. Gently, lift the section of soil holding one of the plants and set it in the bowl. Use your fingers to carefully remove the dirt, making sure not to harm the roots. 4. Attach both clamps to the ring stand, one towards the top and one in the middle. 5. Cut the plastic pipette about half an inch from the bottom to widen it. You made need to have an adult use a knife. 6. Place the pipette into the plastic tube. It should fit snugly and not move around. 7. Attach the pipette to the middle clamp and the plastic tube to the top clamp. The plastic tube should go to about the top of the ring stand. Cut off any extra tubing. 8. Fill the tube with water until water moves up to the 1ml. mark on the pipette. 9. Carefully set the plant’s roots into the tube. You may need a toothpick or other small object to poke down the roots. 10. To seal the plant from the air, tape plastic wrap around the opening between the roots and tube. Spread petroleum jelly Experiment Central, 2nd edition
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on any openings between the plant and the plastic wrap. Make sure the water mark is at the 1 ml. mark and there are no bubbles. You may need to add more water if any spilled. Use a long, thin utensil or wire to poke in the water and pop any bubbles. Set a small plastic cup or deep bottle cap on the end of the open end of the pipette. Note the time and water level on a chart. In 12-hour increments, note the water level over the next two to three days. Repeat Steps 8–14 for the second type of plant. Try to match the number of leaves and height of the first plant.
Summary of Results Graph the water uptake for each of the plants,
broken into the 12-hour periods of day and night. Did the plant with the larger leaf need more water? Was there a pattern to when either plant took in water? Summarize your results in writing. Change the Variables There are many ways you
can vary this experiment. Once you have the setup for the potometer, you can examine how environmental conditions affect water uptake and loss. You can use a fan for wind, or test humidity. How does the amount of indoor light or Sun affect different plants?
Step 10: Tape plastic wrap around the opening between the roots and tube. I LL UST RA TIO N BY TEM AH N EL SON .
Step 14: In 12 hour increments, note the water level over the next 2 to 3 days. IL LUS TR ATIO N BY TEM AH N EL SON .
Design Your Own Experiment How to Select a Topic Relating to this Concept There are many aspects of plant anat-
omy you can further explore, either as a project or as an experiment. Look around at what plants are growing in your local area. Consider how plants growing near streets and human activity differ from the plants growing in more remote Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise in this experiment, a possible cause, and a way to remedy it. Problem:The water was almost used up. Possible cause: The seal that locked the plant stem into the tube may not have been tight, which would have allowed water to evaporate into the air. Try the experiment again, making sure to use enough plastic wrap and Vaseline. Problem:The two tests were extremely different. Possible cause: There may have been bubbles in the liquids. Bubbles are air that take the place of the water. Repeat the experiment, looking carefully for bubbles as you fill the tubing and making sure to pop all bubbles.
areas. As you observe the different types of plants, examine the properties of the leaves and stems. Check the Further Readings section for this topic, and talk with a teacher or gardener to help you formulate a topic. You might want to visit a local greenhouse (nursery) to see a wide variety of plants. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you’re answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Plant anatomy is a broad topic. You can take advantage
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one aspect of the anatomy. You could compare the characteristics and behavior of a desert plant, such as a cactus, with a water plant. You could study the adaptations of the leaves and roots of different plant species. You could also investigate in more detail how water transpires from leaves by examining a plant under a microscope. Another related project could focus on how water allows a plant to acquire its essential nutrients. Plants will usually get their nutrients from the soil, once the nutrients dissolve in water and are pulled into the plant. Some plants do not need soil to get their nutrients. Hydroponics is the technique of growing plants in water that contains dissolved nutrients. A hydroponics experiment could vary the nutrients in the water or the plants.
For More Information Andrew Rader Studios. ‘‘Plant Basics.’’ Rader’s Biology4kids.com. http://www. biology4kids.com/files/plants main.html (accessed on April 9, 2008). Information on plant biology and structures. Black, David, and Anthony Huxley. Plants. New York: Facts on File, 1985. Readable scientific introduction to plants. Bruce, Anne. ‘‘Water movement through a plant.’’ Microscopy UK. http://www. microscopy uk.org.uk/mag/artmar00/watermvt.html (accessed on April 9, 2008). Explains how water moves through plants; includes informative pictures. Missouri Botanical Garden. Biology of Plants. http://www.mbgnet.net/bioplants (accessed on April 9, 2008). Basic information about plant biology and life. PlantingScience. http://www.plantingscience.org (accessed on April 9, 2008). Examples of student research projects, images, and resources to collect plant information. Suzuki, David and Kathy Vanderlinden. Eco-Fun. Vancouver: BC: Greystone Books, 2001. Project and experiments related to plants and the environment. Taylor, Barbara. Inside Guides: Incredible Plants. New York: DK Publishing, 1997. Large illustrations and clear information on the parts of a plant.
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P Water enters a plant through the plant’s root hairs. The root hairs absorb the water through a process called osmosis. CO PY RI GHT # KEL LY A. QUI N.
lants are a diverse group of organisms that include over 250,000 species. They live in a range of environmental conditions, from mountaintops to the ocean floor. They can claim the world’s largest organism, a redwood tree that can stretch to a height of 364 feet (110 meters), and the world’s oldest organism, the 4,700-year-old bristlecone pine tree. Without plants, life on Earth as it is now could not exist. Plants make their own food by photosynthesis, a process that uses the energy of the Sun to make sugar and oxygen. Humans and other organisms use the oxygen released by photosynthesis to survive. Plants are also used for food, shelter, and protection by organisms in every known environment. Plants depend on water for several essential functions. Water is needed for photosynthesis and to help transport nutrients through a plant’s system. Most growing plants contain about 90% water. This water maintains the plant’s internal temperature and provides it structure. Without water or with too much water, a plant dies. How plants take in water and what they do with it is essential for their survival. Rooting water flow Water enters a plant through the plant’s root hairs, hundreds of fine hairs that extend out from the root. These hairs suck in the water that lies between the soil particles. Most of the nutrients that a plant needs are dissolved in this water. The root hairs absorb the water through a process called osmosis. Osmosis 897
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Osmosis is the movement of water through the cell membrane from an area of high water concentration to an area of low water concentration. GA LE GRO UP.
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is the movement of water from an area where there is a high concentration of water to an area of low water concentration through the cell membrane, the layer that encircles and holds the parts of a cell together. The cell’s membrane is semipermeable, meaning it allows some things to pass through the membrane and prevents others from passing. Once inside the root hair, the plant uses osmosis to move the water into the xylem (pronounced ZY-lem). The xylem are long tubes or vessels made up of bundles of dead cells with tough cell walls. Xylem vessels transport water to all parts of the plant, from the root to the leaves. Water in the xylem is mainly drawn upwards through osmosis because there is a continual need for water in the outer leaves of a plant. Water in leaves is constantly evaporating or turning into water vapor. Water vapor is water in its gas state. The low concentration of water in the leaves pulls the water upwards. In plants, this loss of water is called transpiration. For most plants transpiration occurs primarily on the leaves. A leaf’s surface has tiny pores called stomata that open and close regularly to exchange gases, such as oxygen and carbon dioxide. When stomata are open, the plant loses water or transpires. Like evaporation, transpiration occurs more rapidly in hot, dry weather. In most plants there are more stomata located on the underside of the leaves. This ensures the plant will not lose too much water since it is transpiring on the side facing away from the sun. Some plants have tiny hairs that protect them from transpiring too much. Other plants are protected from excess less water inside than water loss by a waxy film covering the outer layer outside of the leaves. Desert plants have thorns in place of leaves to avoid losing too much water. Standing up straight Aside from providing a plant’s basic food and water requirements, water maintains a plant cell’s structure and water molecules shape. The visible sign that a plant has taken in enough water is when it stands up straight and shows no sign of limpness. less water In a plant cell the membrane is surrounded by a outside than rigid cell wall. Inside the cell wall in the center of the inside plant cell there is a large, liquid compartment called a vacuole (pronounced VAK-yoo-ole). Vacuoles transport and store nutrients, waste products, and other molecules. A vacuole is also the area in the cell Experiment Central, 2nd edition
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where water collects. When water enters the vacuole, it causes pressure to build inside the cell. The pressure of the vacuole pushing outwards on transpires the cells is called turgor pressure. The strong cell through leaves walls keep the buildup of water from bursting the cell, which results in increased pressure. Turgor pressure of all the neighboring cells is what allows a plant to stand upright. If a plant does not have enough water in its cells there is water absorbed nothing pressing against the cell walls. This phethrough root hairs moves up nomenon causes plasmolysis, meaning when a through xylem cell has lost its water, and wilting results. Plasmolysis frequently occurs in plants left in hot sunny windows and not given enough water. As long as the cells are still living the turgor pressure can be increased. Watering the plant will cause The plant uses osmosis to move the cells to take in water and the vacuoles again press against the wall to the water into the xylem. Xylem straighten the plant. vessels transport water to all Turgor pressure also impacts transpiration as it affects whether the parts of the plant, from the roots to the leaves. GA LE stomata (singular: stoma) open. A stoma is surrounded by two guard cells. GRO UP . When water enters these surrounding cells, the turgor pressure causes them to swell and creates an opening between them, which is the stoma. When the turgor pressure decreases, the cells relax and the stomata close. Adapting to dry environments In places where water is a rare resource, such as deserts, plants have had to adapt to survive in the dry, hot environment. These plants usually have special methods of storing Turgor pressure is what allows and conserving water. The desert cacti, for example, have few or no leaves, a plant to stand upright. GA LE GRO UP . which reduces transpiration. Some desert plants have deep roots to pull up water deep in the sand. Other plants have shallow roots that thread out extensively so they can quickly suck up water turgor pressure vacuole close to the surface. Desert plants can store water in their stems, cell leaves, or thick roots. For example, the old man wall cactus has a layer of hair that helps it to store water. This hair can also keep it from losing not enough water increased water water by lessening the drying effects of the wind. causes the cell causes vacuole to push to deflate against cell wall Some desert plants are dormant, not active, during dry periods, and then spring to life when Experiment Central, 2nd edition
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it rains. To avoid the heat of the Sun, many plants move into action during the night hours. For example, the Sonoran Desert’s saguaro only opens its white flowers at night. Some desert plants have adapted by having smaller or no leaves. On others leaves will have a thick covering that is coated with a waxy substance to reduce water loss. Hair on the leaves of plants helps to reduce the evaporation of moisture from the surface of leaves by reflecting sunlight.
A wilting plant is a sure sign of plasmolysis, meaning the plant is in need of water. CO PY RI GHT # KE LLY A . QU IN.
EXPERIMENT 1 Water Flow: How do varying solutions of water affect the amount of water a plant takes in and its turgor pressure?
Purpose/Hypothesis To maintain a stable environment, plants move water in and out of their cells until the concentration of water molecules is equal on both sides of the cell membrane. Osmosis causes the water to flow from a region of high concentration to a region of low concentration. As the plant cells takes in more water, the turgor pressure increases; when the plant cells take in less water, the turgor pressure decreases. Changing the concentration of the particles, or solutes, dissolved in water will change the amount of water present. Adding salt to water, for example, makes the water have a high concentration of solutes, which is Turgor pressure causes guard called a hypertonic solution. A low-solute concentration is called a cells to open the stoma, causing hypotonic solution. In osmosis, cells will try to equalize the concentration transpiration to occur. G AL E of the solute molecules. A cell placed in a hypoGRO UP. tonic solution will draw water into its cells to equalize the solute molecules. A cell in a hypertonic solution will move water out of the cell to make the solutes more equal. In this experiment, you will examine the movement of water in a plant. This experiment will investigate how varying concentrations of guard cell stoma salt water affect the amount of water that enters or leaves a plant’s cells. You will place a flower in water molecule three colored-water solutions, two of which contain different concentrations of salt. You will 900
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WORDS TO KNOW Cell membrane: The layer that surrounds the cell, but is inside the cell wall, allowing some molecules to enter and keeping others out of the cell. Cell wall: A tough outer covering over the cell membrane of bacteria and plant cells. Dormant: A state of inactivity in an organism. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Osmosis: The movement of fluids and substances dissolved in liquids across a semi-permeable membrane from an area of greater concentration to an area of lesser concentration until all substances involved reach a balance. Photosynthesis: Chemical process by which plants containing chlorophyll use sunlight to manufacture their own food by converting carbon dioxide and water into carbohydrates, releasing oxygen as a by-product.
Plasmolysis: Occurs in walled cells in which cytoplasm, the semifluid substance inside a cell, shrivels and the membrane pulls away from the cell wall when the vacuole loses water. Root hairs: Fine, hairlike extensions from the plant’s root. Stomata: Pores in the epidermis (surface) of leaves. Transpiration: Evaporation of water in the form of water vapor from the stomata on the surfaces of leaves and stems of plants. Turgor pressure: The force that is exerted on a plant’s cell wall by the water within the cell. Vacuole: An enclosed, space-filling sac within plant cells containing mostly water and providing structural support for the cell. Variable: Something that can affect the results of an experiment. Xylem: Plant tissue consisting of elongated, thickwalled cells that transport water and mineral nutrients. (Pronounced ZY-lem.)
measure the movement of water in three ways: observing the plant’s turgor pressure, observing the water movement in the plant, and weighing the flowers before and after they are placed in the water. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plant cells and turgor pressure. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
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A hypothesis should be brief, specific, and measurable. It must be something you can test What Are the Variables? through further investigation. Your experiment will prove or disprove whether your hypothesis is Variables are anything that might affect the correct. Here is one possible hypothesis for this results of an experiment. Here are the main variables in this experiment: experiment: ‘‘Water with a low concentration of salt will flow into a plant’s cells and cause an • the amount of salt increase in turgor pressure and weight; water • the type of plant with a high concentration of salt will flow out • the water of a plant’s cells and cause a decrease in turgor • time of experiment pressure and weight.’’ • environmental conditions In this case, the variable you will change is the In other words, the variables in this experiment amount of salt in the water. The variable you will are everything that might affect the amount of measure is how much water the plant has drawn into water the plant draws in or out of its cells. If you its cells. change more than one variable, you will not be Conducting a control experiment will help able to tell which variable impacted the water you isolate each variable and measure the changes uptake. in the dependent variable. Only one variable will change between the control and the experimental plants, and that is the amount of salt. For the control, you will place the flower in plain water. At the end of the experiment you will compare this plant with each of the others. Note: When making a solid-liquid solution (solid/liquid), it is standard to use weight/weight (grams/grams) or weight/volume (grams/milliliters). With water, 1 gram of water equals 1 milliliter. In this experiment, teaspoons and tablespoons are used to measure the solid. Step 9: Leave the flowers undisturbed eight to twelve hours. GAL E GR OU P.
Level of Difficulty Easy to Moderate. Materials Needed
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4 clear plastic cups 3 white carnation flowers blue food coloring, concentrated salt measuring spoons scale sharp knife or plant shears marking pen Experiment Central, 2nd edition
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Approximate Budget $7. Timetable 45 minutes for setup and followup; 8
to 12 hours waiting. Step-by-Step Instructions
How to Experiment Safely Handle the knife or scissors carefully when cutting the stems.
1. Make a 40% weight/weight (gram/gram) solution of salt water. One gram of water equals 1 milliliter of water. Add 7 tablespoons (96 grams) of salt to 1 cup (240 milliliters or 240 grams) of warm water. If you have a gram scale you can measure 40 grams of salt and add that with 100 grams of warm water. Add the salt slowly and stir after each addition. The salt should be completely dissolved in the water. Label the cup ‘‘40%.’’ 2. To make a 20% solution of salt water, add 3.5 tablespoons (46 grams) of salt to 1 cup (240 milliliters or 240 grams) of warm water. If you have a gram scale you can measure 20 grams of salt and add that to 100 grams of water. Label the cup ‘‘20%.’’ 3. Allow the water to cool to room temperature. 4. Fill up a cup with plain water. Label the cup ‘‘Control.’’ 5. Stir several drops of blue dye into each cup for a strong blue color. 6. Carefully cut each carnation’s stem under cool running water. 7. Dry off the stems and weigh each flower. Step 10: Data chart for 8. Place one carnation in each of the cups of water. Experiment 1. G AL E GR OUP . 9. Leave the flowers undisturbed 8 to 12 hours. 10. In a chart, describe the turgor pressure of each flower relative to the 20 percent salt Flowers concentration. Weigh each flower and 40% 20% control note in the chart. Examine the blue starting water’s movement and note whether the weight water has entered each flower. final weight
Summary of Results Examine the chart. Has the
water entered some flower or flowers more than others? If the blue water is not visible in the white flower of the carnation, you may want to carefully cut the bottom part of the stem to see if the water has entered the flower. Observe the stem’s bottom of each flower and the petals of Experiment Central, 2nd edition
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Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem.
the carnations. Look at the before and after weights of each flower. How do the test flowers compare to the control flowers? In any flower that took up the water, describe how the water entered the petals. Write a paragraph describing your results and explanations of what occurred.
Problem: The water did not go move at all or barely moved into any of the carnations.
Change the Variables You can vary this experi-
Troubleshooter’s Guide
Possible cause: You may have started out with a flower that was dead. Purchase another flower and repeat the experiment. Possible cause: You may have crushed the stem when you cut it. Try the experiment again, making sure to cut the stem under cool water. Cutting under water prevents the flowers from taking in air instead of water. Problem: The flower was heavier and the turgor pressure increased but water did not go appear to enter the plant. Possible cause: The water may have moved into the plant but you were not able to see it because the color was not strong enough. Make sure you are using a nonsweetened concentrated dye. Blue ink works well also. Repeat the experiment, making sure the water is a rich blue color.
ment several ways: • Change the type of flower or plant you use. Celery stalks, with leaves, and white-colored flowers with large stems work well. • Alter the solute you put in the water to another substance, such as sugar. • Decrease or increase the amount of time the plant is sitting in the solution. • Change the environmental conditions of the plant by placing one flower under a heat lamp or out in the sun, and another in a cool, dark place.
EXPERIMENT 2 Transpiration: How do different environmental conditions affect plants’ rates of transpiration? Purpose/Hypothesis All plants transpire. The
rate of transpiration depends on a plant’s physical properties and its environmental conditions. As transpiration occurs mainly on the leaf, a general rule is that plants with larger leaves will transpire more than plants with smaller leaves. In this experiment, you will examine the environmental factors that affect a plant’s transpiration rate. Using the same type and size plants, you will vary the amount of heat and wind each plant receives. You will place one plant in a warm environment, a second plant in a windy environment, and a third plant in a cool, calm environment. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plants and transpiration. This 904
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educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • environmental conditions, temperature
A hypothesis should be brief, specific, and and wind measurable. It must be something you can test • time given for experiment through further investigation. Your experiment • type of plant will prove or disprove whether your hypothesis is • leaf size correct. Here is one possible hypothesis for this • leaf shape experiment: ‘‘Plants that receive more heat and • soil content wind will transpire at a greater rate than plants in In other words, the variables in this experiment a cool, calm environment.’’ are everything that might affect the amount of In this case, the variable you will change is the water that the plant transpires. If you change environment of the plant. The variable you will more than one variable at the same time, you measure is the amount of water the plant transpires. will not be able to tell which variable impacted Conducting a control experiment will help the plant’s rate of transpiration. you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental plants, and that is the change to its environment. For the control, you will place the plant in a standard indoor environment. At the end of the experiment you will compare this plant with each of the others. Level of Difficulty Moderate. Materials Needed
• four potted plants with large leaves; make sure the leaves are not waxy or hairy: geraniums, caladiums, coleus, and philodendrons work well • four plastic sandwich bags • wire ties • small fan • four small dry sponges • scale Approximate Budget $15. Experiment Central, 2nd edition
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Timetable 1 hour preparation time; 24 hours
waiting.
How to Experiment Safely This experiment poses no safety hazards. For the plants’ health, when you have completed the experiment remove the plastic sandwich bags and care for the plant as directed.
2. 3.
4. 5. 6. 7.
Step-by-Step Instructions
1. Assign each plant a number. On each plant, place a sandwich bag over a group of three to four leaves. Choose leaves that are of equal dimensions. Fasten each bag securely on the stem with a wire tie. Place one plant in the direct sunlight or under a heat lamp. Place one plant in a dark, covered area. Place the third plant in front of the fan and turn the fan on low. Leave the control plant indoors and set it aside. After 24 hours note the results of any water in the bags. Weigh a dry sponge and record the weight. Carefully, soak up all the water in the bag with the sponge. Reweigh the sponge and record the weight. Repeat Steps 5 and 6 for every plant, using a new sponge each time.
Summary of Results Create a data table to record your observations.
Subtract the weight of the dry sponge from the final weight of the wet
control
Step 3: Place each plant in a different environmental condition. GAL E GR OU P.
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sponge to calculate the weight of the water each plant transpired. Was your hypothesis correct? For additional information, you could determine the area of each of the leaves and calculate the rate of transpiration for the entire plant. Hypothesize what adaptations outside plants could make to transpire less, compared to the characteristics of indoor plants. Change the Variables There are several ways that
you can change this experiment. One variable you can change is the type of plant. Choose another plant with a broader leaf. With a larger bag, you can also conduct the transpiration experiment on trees. You can lengthen the amount of time the plants transpire. You can also alter the environmental conditions, such as producing a humid environment or a dry environment.
Design Your Own Experiment
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: Some of the bags did not contain moisture. Possible cause: The bags may not have been sealed tightly and the water vapor escaped. You can try to seal the bag with a rubber band or fasten the tie tightly. Repeat the experiment, checking that there are no leaks or holes in the bag. Problem: It looked like there was water in the bags, but it weighed nothing. Possible cause: Your scale may not be sensitive enough to register the weight. If possible, borrow a more sensitive scale from your school and repeat the experiment. You could also note the results visually.
How to Select a Topic Relating to this Concept
You come into contact with plants every day through your diet and environment. Observe the plants that are around you as you prepare to design an experiment. You could also visit a greenhouse and examine the different species of plants available. Check the Further Readings section and talk with your science teacher to learn more about plants and water. You could also talk with a botanist in your area or a professional who works with plants. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. Experiment Central, 2nd edition
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• State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results
Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Desert plants, such as the organ pipe cactus, have developed special methods of storing and conserving water to survive in the dry, hot environment. F IEL D M ARK PUB LI CAT IO NS.
Related Projects You can take advantage of the
many species of plants to conduct an experiment with plants and water. For example, you could compare the characteristics and behavior of a desert plant, such as a cactus, with a water plant. How does transpiration differ in the two species of plants? You could study the adaptations related to transpiration in a variety of plant species. Covering one side of a leaf with petroleum jelly will allow you to determine where transpiration occurs in a plant’s leaves. You could also investigate in more detail how water flows into a plant by examining parts of a plant’s stem, leaves, roots, and cells under a powerful microscope. Another related project could focus on how water allows a plant to acquire its essential nutrients. Plants will usually get their nutrients from the soil, once the nutrients dissolve in water and are pulled into the plant. Some plants do not need soil to get their nutrients. Hydroponics is the technique of growing plants in water that contains dissolved nutrients. A hydroponics experiment could vary the nutrients in the water or the plants.
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For More Information Andrew Rader Studios. ‘‘Plant Basics.’’ Rader’s Biology4kids.com. http://www. biology4kids.com/files/plants main.html (accessed on February 8, 2008). Information on plant biology and structures. Black, David, and Anthony Huxley. Plants. New York: Facts on File, 1985. Readable scientific introduction to plants. Bruce, Anne. ‘‘Water movement through a plant.’’ Microscopy UK. http://www. microscopy uk.org.uk/mag/artmar00/watermvt.html (accessed on February 12, 2008). Explains how water moves through plants; includes informative pictures. ‘‘Cell Expansion and Differentiation.’’ Ohio State University: Horticulture and Crop Science in Virtual Perspective. http://www.hcs.ohio state.edu/hcs300/ cell3.htm (accessed on February 12, 2008). Illustrations on turgor pressure and the cell wall. Missouri Botanical Garden. Biology of Plants. http://www.mbgnet.net/bioplants (accessed on February 6, 2008). Basic information about plant biology and life. United States Department of Agriculture. Plant’s Database. http://plants.usda. gov/ (accessed on February 6, 2008). Provides a list of plants in every state, along with images of many plants. United States Department of Agriculture Forest Service. Celebrating Wildflowers. http://www.fs.fed.us/wildflowers/index.shtml (accessed on February 16, 2008). Variety of information on a wide range of plants.
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Polymers
P
olymers are everywhere, both inside us and around us. The word comes from the Greek words poly, meaning ‘‘many,’’ and meros, meaning ‘‘parts.’’ A polymer is a material composed of long string of repeating molecular units. They can contain a chain of hundreds to thousands of these units, in the shape of a single straight chain or multiple branching chains. The type and number of the repeating units, along with how the polymer connects to other polymers, determine the physical properties of that polymer. Polymers are valuable in both nature and industry because they can have great strength and durability, yet be lightweight. There are both natural and synthetic, or manmade, polymers. Proteins, silk, and starches are polymers found in nature. Understanding how polymers function in the natural world has led not only to advancements in biology, but also to the development of synthetic polymers that have revolutionized numerous products and fields. Space science depends on synthetic polymers for their space vehicles and equipment. In medicine polymers are used in heart valves, artificial skin, and organ replacements. Plastic bags, nylon, rugs, and fabrics are examples of synthetic polymers that people commonly use. Chain properties One of the first polymers created was due to the popular sport of billiards in the late 1800s. At that time, billiard balls were made of ivory, a material in short supply even then. An American inventor won a contest to find a material to replace the ivory. He took the basic structural material that makes up plant cell walls and treated it with chemicals. The result was the polymer celluloid—a shiny, hard material that could be molded when hot. This type of plastic became commonly used in X-ray film and motion picture film. In the early 1900s the first synthetic polymer from a nonnatural substance was developed. That was soon followed by the first synthetic fiber, rayon. Companies 911
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Silly Putty is a synthetic rubber polymer. A P/W ID E WO RL D
Monomers string together like beads on a string to form a polymer. GA LE GRO UP.
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began to get involved in developing polymers, and the study of polymers began in earnest. Polymers start off from tiny units called monomers. To make a polymer, monomers are strung together like beads to form a long polymer chain. A polymer can be made up of billions or trillions of monomers. The chemical reaction that makes polymers from monomers is called polymerization. Each bead on the chain is the basic unit. In many cases, the chain links on a polymer are made up of only carbon atoms. The carbon-carbon bond is a strong one and this gives these polymers strength. In other cases, the chain units are made of nitrogen, oxygen, and/or silicon. Many classes of polymers are made of just carbon and hydrogen. In these polymers, carbon makes up the basic links in the chain, and hydrogen atoms are bonded along the carbon backbone. For example, the common plastic polyethylene, which is found in grocery bags, juice containers, and bottles, is one such polymer. Composed of the monomer ethylene, polyethylene is composed of a chain of carbon atoms bonded together, with each carbon atom attached to two hydrogen atoms. What kind is it? Because there are so many different kinds of polymers, there are also many different ways to classify them, depending on their properties. There are some polymers that Monomers are flexible and others are that are hard. Elastomers are polymers that have an elastic or rubbery behavior. They can be stretched or bent, but spring back to their original shape. Other polymers, such as a fishing line, are hard and difficult to stretch. Some polymers can be heated and reheated repeatedly. Others will undergo a permanent chemical change if they are heated, which will alter their properties. One way polymers are differentiated is according to their mechanical properties, such as tensile strength. A polymer’s tensile strength is the force needed to stretch a material until it breaks. Elongation is another mechanical Experiment Central, 2nd edition
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property. A polymer’s elongation is the percentage increase in length that occurs before it breaks under tension. Physical properties of polymers are another way to group them. The chain length of a polymer plays a major role in the polymer’s physical properties and behavior. One factor that affects tensile strength is the chain length or the molecular weight. As a general rule, polymers with a higher molecular weight produce stiffer, stronger, and denser materials. The greater the molecular weight, the higher the tensile strength.
Polyethylene
How the chains are arranged also affects the physical properties of a polymer. The chains in a polymer can tangle up with each other, like a plate of spaghetti. This makes many polymers incredibly durable. The chains can be either linear (straight), branched, or cross-linked.
Many polymers are made of hydrogen atoms bonded along a carbon backbone. GAL E GRO UP .
Getting rid of polymers The positive qualities in polymers—their durability, strength, and lightness—bring with them the challenge of how to get rid of many of these products. Enormous quantities of disposable, synthetic polymers are produced every year in the United States alone.
Plastic wrap, food containers, and bags are synthetic polymers commonly used in the average household. C OP YRI GH T # KE LL Y A. QUI N.
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The production of these materials is causing concerns for the environment. Many of the products are plastics and are linear not biodegradable, meaning that they do not break down naturally and quickly into the raw materials of nature. Plastic soda can rings, for example, can take an estimated 400 years to break down! Recycling these plastics will help reduce the branched amount of garbage in the environment. When plastics are recycled they are reprocessed and made into new products. Yet different methods are used to recycle different materials, and there can be multiple polymers in a person’s garbage. Most plastics and bottles are made from six polymers. The plastics industry has developed a cross-linked chart to distinguish the six polymers from each other: A specific number is written in a threeThe arrangement of a polymer arrow triangle that is imprinted on most plastic products. Polymers’ chain has an impact on its physical properties, such as density, are also used to separate the different physical properties. G AL E types. People are encouraged to recycle and separate their plastic containGRO UP. ers. In the meantime, researchers are working to develop polymers with improved biodegradability.
EXPERIMENT 1 Polymer Strength: What are the tensile properties of certain polymers that make them more durable than others? Purpose/Hypothesis Tensile strength is one key test that researchers
conduct on polymers. A polymer’s tensile strength depends on what molecules make up the polymer, as well as the orientation of the polymers. Polymers align themselves as long chains. These chains are aligned parallel to each other and tangle together in many synthetic polymers. When pulled lengthwise, these chains can stretch a great distance before breaking. However, widthwise it is only the entanglements that hold the polymers together. In this direction the polymer will break much more easily. Companies make many synthetic polymers by manufacturing the long chains of polymers parallel to each other along the length of the 914
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product. This results in a strong bond lengthwise, from top to bottom, and a weak bond widthwise, from left to right. In this experiment you will test in what direction the orientation of the polymer is strongest: lengthwise or widthwise. The polymer you will use will be any plastic bag. Most plastic bags are made of the polymer polyethylene. To test a polymer’s tensile strength, one end of the polymer is held stationary while a force is applied to the other end until the sample breaks. Before the sample breaks it elongates, or lengthens. Tensile testing is usually done on samples shaped like a ‘‘dogbone.’’ The size of the sample can vary, but the shape is important. Almost all the elongation will occur in the narrow section of the dogbone. Elongation occurs in the thinnest section because it is the weakest. You will test plastic samples in both directions by taping one end of the samples to a stationary object and attaching a weight to the opposite end. You will increase the weight incrementally, measuring the plastic’s elongation after each addition of the weight, until the plastic breaks. Samples should always break in the thinnest section, the middle of the dogbone. For increased accuracy, you will conduct three trials for both the lengthwise and widthwise direction. To begin this experiment make an educated guess, or prediction, of what you think will occur based on your knowledge of polymer strength and orientation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
A mound of plastic products awaits reprocessing at a Des Moines, Iowa, recycling facility. AP /WI DE W OR LD
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The plastic bag cut in the Experiment Central, 2nd edition
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WORDS TO KNOW Biodegradable: Capable of being decomposed by biological agents. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Elastomers: Any of various polymers having rubbery properties. Elongation: The percentage increase in length that occurs before a material breaks under tension. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of plastic bag (polymer) used • the amount of weight
Monomer: A small molecule that can be combined with itself many times over to make a large molecule, the polymer. Polymer: Chemical compound formed of simple molecules (known as monomers) linked with themselves many times over. Polymerization: The bonding of two or more monomers to form a polymer. Synthetic: Something that is made artificially, in a laboratory or chemical plant, but is generally not found in nature. Tensile strength: The force needed to stretch a material until it breaks. Variable: Something that can affect the results of an experiment.
lengthwise direction will support far more weight than the sample cut widthwise.’’ In this experiment the variable you will change will be the orientation of the polymer chains, and the variable you will measure will be the amount of weight the polymer can hold before it breaks. Level of Difficulty Difficult.
• the direction the polymer is cut • the size of the cut polymer • the shape of the cut polymer In other words, variables in this experiment are everything that might affect the amount of weight the polymer can hold. If you change more than one variable, you will not be able to tell which variable impacted the polymer’s strength.
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Materials Needed
• bar to hold the clothes hanger or plastic sample (clothing rod works well). • sturdy clothes hanger with a stiff, straight section across the bottom (wood or very stiff metal) • 2 plastic garbage bags (white or light color) • scissors Experiment Central, 2nd edition
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• • • • • • • • •
wide duct tape a 2-liter empty plastic bottle How to Experiment Safely string Be careful when using the scissors. wastebasket or bucket to catch plastic bottle water funnel measuring cup piece of 8.5-inch by 11-inch (216-millimeter by 280-millimeter) paper marking pen Step 1: The dogbone template. GA LE G RO UP.
Approximate Budget $8. Timetable 1 hour. Step-by-Step Instructions
1. Trace the template of the dogbone (refer to the illustration) on the paper and cut out the paper. 2. To determine the lengthwise direction of the bag, stretch the bag gently in each direction and determine which way has the least pull. This is the lengthwise direction. It is not always the top-to-bottom direction of the bag. Mark the ‘‘top’’ and the ‘‘bottom’’ with the marking pen. 3. Lay the plastic bag in the lengthwise, topto-bottom, direction and place the paper template over the bag. Cut out the plastic bag, making sure the cuts are smooth. 4. Repeat Step 3 two more times so that you have three dogbone-shaped pieces of plastic. Mark each piece with an ‘‘L’’ for lengthwise. 5. Repeat Steps 2 and 3 in the crosswise direction. Mark each piece with a ‘‘C’’ for crosswise. Experiment Central, 2nd edition
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6. On each of your samples draw a line across the beginning and end of the mid-section of the bone. This will be the area you will measure.
Measuring area
7. Attach one end of a plastic sample to the hanger with duct tape, wrapping the tape firmly around the hanger. 8. Attach another piece of duct tape to the bottom of the plastic. In the center of this bottom piece of duct tape make a small hole. Put a string around the neck of the 2-liter bottle and attach the other end of the string through the hole. Tie with a double knot.
Steps 7 and 8: Setup for Experiment 1. GA LE GRO UP.
9. Measure the length between the top and bottom marks on the bag and write it down. 10. Place the wastebasket or bucket on the floor directly under the bottle. Carefully pour ¼ cup of water (60 milliliters) into the bottle using a funnel. Measure the length between the top and bottom marks on the bag again and write it down. 11. Continue adding ¼ cup (60 milliliters) of water, measuring the stretch or elongation of the sample after every water addition until the sample breaks. Note your results. 12. Repeat Steps 7 through 11 for each of the remaining five sample bags. Summary of Results Average the three trials of elongation for both the
lengthwise and crosswise polymer orientations. Construct a chart where Column 1 is the weight of the water, Column 2 is the length of the sample, and Column 3 is the percent elongation. The percent elongation is the length of the end sample minus the original length of the sample divided by the original length of sample. Multiply that number times 100 to get the percent. Percent elongation = [(finished sample length–original sample length) divided by original sample length] 100. Plot a graph of the results with the amount of water on the y-axis and the percent elongation on the x-axis. Did the samples break at different weights? Clearly label your graph. Did the samples break at different 918
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weights? Did the lengthwise or crosswise sample break first? Write a brief explanation of your results. Change the Variables You can vary this experi-
ment in several ways. Try using different types of plastic, such as a food wrapper compared to a thick plastic garbage bag. You could experiment with cutting the bag in the diagonal direction. Cut out different sizes of the dogbone, using the same direction and plastic. Does this impact the plastic’s elongation?
EXPERIMENT 2 Polymer Slime: How will adding more of a polymer change the properties of a polymer ‘‘slime’’? Purpose/Hypothesis The objective of this
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The plastics break at the top or bottom. Possible cause: There could be a slight tear or cut in the plastic. If it breaks anywhere but the middle you will need to repeat the experiment. Problem: The widthwise-labeled dogbone was stronger. Possible cause: You may have mislabeled the plastics when you first stretched the bag to determine the lengthwise direction. Repeat the experiment, making sure to pull gently on the bag to determine which direction pulls the least amount. Problem: The elongation for the three trials varied greatly.
experiment is to create a cross-linked polymer Possible cause: You may have changed more and observe the physical properties of adding than one variable. Make sure you used the increased polymer chains. Guar gum is used as same sturdy hanger for each trial. Was one a a thickening agent in foods. The guar contains a thin metal hanger that bent? Could you have polymer called polysaccharide. Polysaccharide is mismeasured the water or spilled some as you a large molecule composed of carbon, oxygen, were pouring? Repeat the experiment, makand hydrogen atoms joined together in long ing sure all the variables are equal. chains, which makes it long and flexible. Because it is a linear polymer that is not cross-linked, guar gum pours like a thick solution. In order to form a ‘‘slime’’ the linear polysaccharide must be crosslinked to form a three-dimensional network. This creates stronger bonds between the separate chains. Borax has sodium borate as the active ingredient. Sodium borate is the cross-linking agent, meaning that it creates the interconnecting bonds between the carbon and oxygen atoms that link the linear polymer chains together. In this experiment you will determine how the amount of a polymer alters the properties of a mixture. You will make three different polymer slimes with varying amounts of polysaccharide. The borax will cross-link Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of borax used • the amount of guar gum • the amount of water used • the temperature of the mixture • any added food coloring In other words, the variables in this experiment are everything that might affect the properties of the slime. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the slime’s physical properties.
the polysaccharides. After you have made the three different slimes, you will conduct tests to compare the firmness and elasticity of the slimes. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of polymers and their properties. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Increasing the amount of polymer in the slime will give the polymer greater firmness and elasticity.’’ In this case, the variable you will change is the amount of polymer you add to your slime. The variables you will measure are the slime’s firmness and elasticity. When making a solid-liquid solution (solid/liquid), it is standard to use weight/weight (grams/grams) or weight/volume (grams/milliliters). With water, 1 gram of water equals 1 milliliter. In this experiment, teaspoons and tablespoons are used to measure the solid.
Level of Difficulty Moderate. Materials Needed
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borax (found in supermarkets in the laundry section) guar gum (a thickener agent; found in health food stores) water four stirring rods or spoons measuring spoons scale or measuring cup resealable bags food coloring (optional) Experiment Central, 2nd edition
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• four clear mixing bowls [to see if the materials dissolved] • marking pen • masking tape • latex gloves Approximate Budget $10.
How to Experiment Safely Borax is a weak bleaching agent. Avoid contact with your eyes and face. Use latex gloves when handling the slime as a precaution. Do not ingest any of the slimes. Wash all the bowls, spoons, and other utensils afterwards.
Timetable 45 minutes. Step-by-Step Instructions
1. Pour one-half of a cup (120 milliliters or 120 grams) of water into a bowl. 2. Add 1 teaspoon of borax (sodium borate) to the water and stir until completely dissolved. The solution should be clear. 3. Label the solution ‘‘Borax.’’ 4. Measure out one-third of a cup (80 milliliters or 80 grams) of water into a second bowl or measuring cup. 5. Add ¼ teaspoon of guar gum to the solution while stirring. Continue stirring until completely dissolved. The guar gum will suspend in the liquid so this solution will not be clear. 6. Label the solution on the tape: ‘‘¼ teaspoon Guar gum.’’ 7. If you want to make colored slime, add a specific amount of the desired color to the solution. You will need to add this exact color and amount to each of the mixtures.
3/4 t guar gum
1/4 t g uar
1/2 t guar gum gum
Step 10: When finished making the three slimes, lay each on the counter; one at a time, determine its firmness by measuring its diameter. GA LE GR OU P.
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8. Add 1 teaspoon of the borax solution to the guar gum solution. Stir for one Troubleshooter’s Guide minute and then let sit for at least two minutes. Below are some problems that may arise during this experiment, some possible causes, and 9. Repeat the previous steps to make two ways to remedy the problems. more mixtures, replacing the¼ teaspoon guar gum with 12 teaspoon and 34 teaspoon Problem: The slime is not a uniform consistency. guar gum respectively. Label the two mixPossible causes: The borax is not dissolved well. tures accordingly. When mixing the borax make sure to stir continuously until the mixture is clear. Mix 10. When finished making the three slimes, the guar gum continuously. lay each on the counter; one at a time, Problem: The slime is too firm or loose. determine its firmness by measuring its Possible causes: You may have mixed up the diameter. Note your results in a chart. stirring spoons between the borax and guar 11. Hold each in your hand and describe the gum. Make sure to use separate spoons or slime’s firmness, using the ‘‘¼ guar gum’’ rinse thoroughly between measurements. as the standard of comparison. 12. Hold one of the slimes to an edge and let it hang down. Time one minute; determine its elasticity by measuring its length, or if it breaks apart. Note your results. Repeat for two other slimes. Summary of Results Examine the chart of your data and observations.
Data chart for Experiment 2. GA LE GRO UP.
Which amount of guar gum made the polymer the most firm? How do the physical properties of the slimes with the lowest and highest amount of guar gum compare with each other? What does measuring the diameter show? What can you conclude about the slime if it had a longer stretch than the others? What if it broke during the stretch? If you want to display the results of your slime experiment, the slime can be stored in a resealable bag. You can demonstrate the slime’s firmness by having people feel it and experiment with it themselves.
Firmness Diameter
1/4 tsp. guar 1/2 tsp. guar 3/4 tsp. guar
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Elasticity Length
Breaks Apart
Change the Variables There are many ways to
vary this experiment. Here are some suggestions: • Keep the amount of guar gum equal and vary the amount of borax. • Keep the amount of guar gum and borax equal and vary the amount of water used. Experiment Central, 2nd edition
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Does using more or less water give the slime added bounce? • Place the slime in different temperature environments after you have made three mixtures that use the same measurements. Put one in the refrigerator, one at room temperature, and one in a hotwater bath.
How to Experiment Safely Be careful when you are cutting the plastic into small pieces. Ask an adult to help cut containers that are tough. Work carefully around the boiling water. Have an adult help you remove the plastics from the boiling water.
PROJECT 3 Polymer Properties: How are the properties of hard plastics different? Purpose/Hypothesis The plastic containers that hold liquids, foods, and
numerous other everyday items are all polymers. There are many different types of plastics. One way to identify plastics is by the numbers code on the bottom of containers. The numerical code is for recycling. Because plastics have different properties, including melting points, they are sorted according to type. The recycling codes divide plastics into seven types. Some of the plastics can keep their shape after being heated and some cannot. Plastics that are polypropylenes (PP), for example, contain crystals that prevent the polymers from softening in boiling water. These crystals are hard and rigid. Density is another property that is different among the plastic types. Plastics denser (heavier) than water will sink; plastics lighter than water will float. Alcohol is less dense than water. In this project, you will test the properties of at least four types of plastics to better understand the different properties of polymers. You can examine if the plastics retain their shape and color after being boiled in water. You can also measure the relative density of the plastics. By testing the density of plastics in both water and alcohol, you will be able to identify how plastics that appear similar have unique properties. Level of Difficulty Moderate. Materials Needed
• at least 4 plastic containers with different recycling numbers, include at least one numbered 1 or 2 and at least one numbered 6 or 7 Experiment Central, 2nd edition
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Step 1: Make a chart. I LLU ST RAT IO N BY TEM AH NEL SO N.
• • • • • • • • • Step 2: Cut four of the same shapes out of each plastic container. I LL UST RA TI ON BY T EM AH NE LS ON.
rubbing alcohol (70%) vinegar scissors pot hot plate or stove 4 plastic spoons paper towels tongs 4 small glasses
Approximate Budget $5, assuming you can use household containers that
are going to be recycled. Timetable about 1 hour. Step-by-Step Instructions
1. Make a chart similar to the illustration. 2. Decide on four different shapes, such as a triangle or diamond. Each shape should be about the size of your thumb. Cut four of the same shapes out of each plastic container. The different shapes will help you identify the plastics from one another. 3. Note the shape of each plastic. 924
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4. Test the flexibility of each plastic by placing a plastic between your thumb and finger. Try to bend the plastic and write down the results in your chart. Reaction to heat 1. Boil a pot of hot water. Reduce to a simmer and place one of each plastic type in the pot. 2. Allow the plastics to simmer for about five minutes. 3. Use the tongs to remove the plastics and place them on a paper towel. Note any changes in shape on the chart, such as curled edges. 4. Wait a few seconds for the plastics to cool and then try to bend each of the shapes again. Write down if the boiled plastic bends easier or harder than its corresponding plastic. Density 1. Pour rubbing alcohol into a cup until it is about half-full. Place one of the unused plastic shapes into the liquid. Use a plastic spoon to gently press the plastic to the bottom. Remove the spoon and see if the plastic rises. Note the results on your chart. 2. Repeat this step for each of the three other types of plastics. 3. Fill another cup with water. Repeat the same steps for each of the four plastics, using new pieces of plastic. Note the results on your chart. Summary of Results Take a look at your chart. How do the four types of
plastics differ? Look at what each type of plastic container was used for and its properties. Can you draw conclusions about what types of plastics are used for long-term storage or heating. Consider how the properties of the plastic play a role in what it contains. You can also test the other types of plastic and compare your results.
Step 4: Test the flexibility of each plastic by placing a plastic between your thumb and finger. I LLU STR AT IO N BY TEM AH N EL SON .
Design Your Own Experiment How to Select a Topic Relating to this Concept Polymers are everywhere. They are in
your kitchen, clothes, and many disposable products that you purchase. You could examine Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem. Problem: All the plastics sank in both water and alcohol. Possible cause: You may have pressed down on the plastic too hard, causing the pieces to stick to the bottom. Repeat the density tests, pressing down each plastic slowly until it nears the bottom of the cup, and then remove the spoon. It is also possible you selected plastics that were denser than both alcohol and water. You can try the experiment again, using a different type of plastic. Problem: The results were different when a test was repeated. Possible cause: You have mixed up the plastics! Make sure the shapes are unique enough that you can identify each shape easily, and write down the corresponding plastic type as soon as you cut out the shape.
how polymers have changed over history or how they impact people’s lives. Check the Further Readings section and talk with your science teacher to learn more about polymers. Because polymers are so diverse, there are many different types of polymer chemists. Ask family, teachers, and friends if they know a polymer chemist you can talk with. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question.
• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. 926
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Related Projects You can use the many different physical and mechanical properties of polymers for further experiments and projects. For example, you could investigate the biodegradability of plastics by composting a number of materials. You could first compare the biodegradability of the six different types of polymers. You probably have several different types of plastic products (as determined by the number in the three-arrow triangle printed on a product) in your house already. You could then compare the breakdown of a specific plastic and determine how it relates to both other plastics and nonpolymer materials, such as an organic material like a food item or dead insect. You could compare synthetic polymers’ properties to synthetic nonpolymer materials, such as aluminum foil or specific fabrics. To determine the specific polymer in the product you can look at the ingredients listed on the packaging or call the toll-free number. You could also look at polymers in a specific industry, such as the medical or space field, and explore how polymers have impacted the industry, everyday life, and products related to that field.
For More Information American Chemistry Council. plastics 101. http://www.americanchemistry.com/s plastics/sec learning.asp?CID=1571&DID=5957 (accessed on February 26, 2008). This industry page has loads of basic information and news on plastics. The Chemical Heritage Foundation. ‘‘What Do those Triangles Mean?’’ Faces in the Molecular Science: Faces in Polymer. http://www.chemheritage.org/ EducationalServices/faces/poly/readings/rec.htm (accessed on February 26, 2008). Descriptions of the recycling codes on plastic containers. Energy Information Administration. ‘‘Recycling Plastics.’’ Energy Kid’s Page. http://www.eia.doe.gov/kids/energyfacts/saving/recycling/solidwaste/ plastics.html (accessed on February 27, 2008). Information on how plastics are produced, labeled, and recycled. Polymer Science Learning Center, University of Southern Mississippi. The MacroGalleria. http://pslc.ws/macrogcss/maindir.html (accessed on February 26, 2008). Detailed site on all aspects of polymers, from studying them to everyday applications.
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E
nergy is involved in nearly everything we do. It is defined as the ability to do work, to set an object in motion. There are several different kinds of energy. Kinetic energy is the energy an object has when it is in motion. Vibration, forward motion, turning, and spinning are all examples of kinetic energy. Kinetic energy is directly proportional to the mass of an object. If two objects move at the same speed, and one has twice the mass of the other, the object with twice the mass will have twice the kinetic energy. Potential energy is the energy an object has because of its position; it is energy waiting to be released. For example, a weight suspended above the ground has potential energy because it can be set in motion by gravity. Compressed or extended springs also have potential energy.
The position of the boulder atop the cliff gives it potential energy. CO RB IS .
Thermal energy is the kinetic energy of atoms vibrating within matter. The faster the atoms move, the hotter the object becomes. Electrical energy is the kinetic energy resulting from the motion of electrons within any object that conducts electricity. Chemical energy is the potential energy stored in molecules. Thermal, electrical, and chemical energy are all forms of kinetic or potential energy. What laws control energy? One of the most fundamental laws of physics is that energy cannot be created or destroyed, only transformed from one form into another. For example, if a suspended weight falls, its potential energy becomes kinetic energy. When a car burns fuel, the fuel’s chemical energy is transformed into thermal energy, which in turn, is transformed into kinetic energy by the engine to make the car move. 929
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WORDS TO KNOW Chemical energy: Potential energy stored in molecules.
Kinetic energy: The energy of an object or system due to its motion.
Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Results from the control experiment are compared to results from the actual experiment.
Mass: Measure of the total amount of matter in an object.
Electrical energy: Kinetic energy resulting from the motion of electrons within any object that conducts electricity. Energy: The ability to cause an action or to perform work. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
As one ball hits another, it transfers some of its kinetic energy to that ball. PH OT O RE SEA RC HE RS I NC.
Potential energy: The energy of an object or system due to its position. Thermal energy: Kinetic energy caused by the movement of molecules due to temperature. Variable: Something that can affect the results of an experiment. Work: The result of a force moving a mass a given distance. The greater the mass or the greater the distance, the greater the work involved.
Energy can also be transferred from one object to another. Think about a game of pool. When a moving ball hits a still one, the moving ball stops and the still one begins to move. The majority of the first ball’s kinetic energy has been transferred to the second ball, while a small amount has been converted to thermal energy by the collision. If you could measure the temperature on the surface of each ball, you would find there was a slight rise in temperature at the point of contact. The total amount of energy involved—kinetic and thermal—remains the same. No energy was created or destroyed by the collision. Who wrote these laws? The person who laid the groundwork for the study of energy was English mathematician and physicist Isaac Newton (1642–1727). Newton developed the laws of motion, which describe how objects are acted upon by forces. Newton’s ideas formed the basis for much of physics, in fact. He studied at Cambridge University, where he excelled in
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mathematics and developed the field of calculus while he was still a student. Newton later became a professor at Cambridge, where he built the first reflecting telescope and studied optics. He published his most important work in 1687, the Principia Mathematica. This book describes Newton’s three laws of motion and the law of gravitation, which are a major part of the foundation of modern science. Newton also had an interesting life. He became Master of Mint in England, where he supervised the making of money, and later became the first scientist to be knighted. What questions do you have about energy? In the following experiments, you will have a chance to explore the topics of potential and kinetic energy. You will learn more about how these forms of energy affect us and everything we do.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the mass of the ball • the material it is made of • the surface on which it bounces • the height from which it is dropped • the force with which it is dropped • the height to which it bounces back In other words, the variables in this experiment are everything that might affect the rebound height of the ball. If you change more than one variable, you will not be able to tell which variable had the most effect on the rebound height.
EXPERIMENT 1 Measuring Energy: How does the height of an object affect its potential energy? Purpose/Hypothesis In this experiment, you will
How to Experiment Safely In selecting your bouncing location, choose a place where you will not knock over or break anything.
drop a rubber ball and measure its rebound height. When you pick up the ball and raise it to a certain height, your body is performing work, and the ball is gaining potential energy as a result. When you release the ball, this potential energy changes to kinetic energy as the force of gravity causes the ball to gain speed. When the ball hits the ground, its kinetic energy changes back to potential energy as the ball comes to a stop and is compressed by the impact. A split second later, the potential energy of this compression propels the ball back into the air, giving it kinetic energy again. Finally, as the ball reaches the maximum height of its rebound, its kinetic energy is converted back into potential energy, as measured by its height above the ground. To begin the experiment, use what you know about potential and kinetic energy to make an educated guess about the relation between the Experiment Central, 2nd edition
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ball’s initial drop height and its rebound height. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
Steps 1 and 2: Measure 3 feet up a wall and mark; tape the measuring tape to the wall with the ‘‘zero’’ end at the floor. GA LE GRO UP.
Step 3: Hold the ball slightly away from the wall at the 3-foot height and simply drop it. GA LE GRO UP.
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The higher the height from which the ball falls, the greater its potential energy and the higher it will bounce.’’ In this case, the variable you will change will be the height from which you drop the ball. The variable you will measure will be the height it reaches when it bounces back. If the height of the ball’s rebound increases as you increase the drop height, you will know your hypothesis is correct. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and the experimental bounce, and that is the height from which you drop the ball. For the control, you will drop the ball from 3 feet (about 1 meter) high. For the experiment, you will change the height for each drop. You will measure the height to which the ball bounces back each time. If the ball dropped from higher distances bounces back to higher heights, your hypothesis is correct. Level of Difficulty Easy. Materials Needed
• rubber ball • flat wood or concrete floor on which to bounce the ball • paper and pencils • masking tape • measuring tape, about 6 feet (2 meters) long 932
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Recording chart for Experiment 1. GA LE G RO UP.
Approximate Budget $3 for a rubber ball. Timetable About 1 hour. Step-by-Step Instructions
1. With your measuring tape, measure up a wall 3 feet (about 1 meter) from the floor and mark this level with a piece of masking tape. This will be your control height. 2. Tape your measuring tape to the wall with the ‘‘zero’’ end at the floor. You will use it to measure the heights of the bouncing ball. 3. Hold the ball slightly away from the wall at the 3-foot height and simply drop it. Do not use any force, as it will affect your results. Watch closely and use the measuring tape to determine how high the ball bounced. Repeat the drop several times and average the bounce heights. Record the height from which you dropped it and the average height to which it bounced. 4. Now drop the same ball several times from at least 12 inches (30 centimeters) higher or lower than the control level. Record its bounce heights, taking an average for each dropping height. 5. Repeat this procedure for at least five different heights, recording each height and averaging each bounce height. Experiment Central, 2nd edition
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Summary of Results Study the results on your
Troubleshooter’s Guide Below are some problems that may occur during this experiment, possible causes, and ways to remedy the problems. Problem: It is difficult to accurately measure the bounce height. Possible causes: • You are measuring the bounce against a wall that is too close to the color of the ball. Try bouncing with a ball that is significantly darker or lighter than the wall you are measuring against. • Your measuring tape is difficult to read. Try marking off heights with chalk or masking tape so that they are easier to read. Problem: The ball bounces so high you cannot see where the bounce ends. Possible causes: • The ball you are using is too rubbery. Try using a slightly less bouncy ball. • You are exerting force when you drop the ball. Do not push down when you drop the ball. Simply let it fall from your hand.
chart. Did the drop height affect how high the ball bounced back? Was your hypothesis correct? Did the ball rebound as high as the drop height? If not, why not? Be sure to summarize what you discovered. Change the Variables You can vary this experi-
ment in several ways. For example, instead of changing the height, change the weight (mass) of the ball. Use a rubber ball that is much heavier and one that is much lighter, all dropped from the same height. (Change only one variable at a time.) Weigh each ball before you drop it. Use the ball from this experiment as your control. Record each bounce height again. What do you find? You can also try using different kinds of balls, such as tennis balls or golf balls. How are they affected? What do you think makes the difference?
EXPERIMENT 2 Using Energy: Build a roller coaster Purpose/Hypothesis Potential energy, provided
by the force of gravity pulling on an object, is converted into kinetic energy as an object falls from a height. The amount of potential energy an object has is revealed by the speed with which it moves once released. You can calculate potential energy using the formula PE = mgh, where m is mass, g is the acceleration of gravity 32.2 feet/second2 (9.8 meters/second2), and h is the height of the object in feet (meters). You can calculate kinetic energy using the formula KE=(0.5)mv2, where m is mass, and v is the velocity of the object in feet/second (meters/second). The speed with which the object moves and the height to which it returns also indicate how much potential energy is being converted into kinetic energy and back to potential energy. You can explore this idea by watching a roller coaster. 934
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In this experiment, you will build your own roller coaster and roll a marble on it to demonstrate potential and kinetic energy. Do you have an idea about how a marble will behave on a homemade roller coaster? Where will it move the fastest? Will it have enough energy from rolling down one hill to roll up the next hill? To begin the experiment, use what you know about potential and kinetic energy to make an educated guess about how the marble will behave. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the height of the first hill and the second hill • the amount of friction between the track and the marble • the amount of force or ‘‘push’’ you apply to the marble when you release it In other words, the variables are anything that might affect the height the marble will reach on the second hill. If you change more than one variable, you will not be able to tell which variable had the most effect on the results.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The higher the first hill of the roller coaster, the higher the marble will climb on the second hill.’’ In this case, the variable you will change will be the height of the first hill, and the variable you will measure will be the height the marble climbs on the second hill. If the marble climbs higher on the second hill when the height of the first hill is raised, you will know your hypothesis is correct. Only one variable will change between the control and experimental set-up, and that is the height at which the marble starts to roll. For the control, you will start your marble from a hill at 2 feet (0.6 meters) above ground. For your experiments, you will vary the heights of the first hill. You will measure the heights that the marble climbs on the second hill to compare the amount of kinetic energy produced by the potential energy of the initial drop.
A roller coaster has both potential and kinetic energy. COR BI S.
Level of Difficulty Moderate. Experiment Central, 2nd edition
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Materials Needed
How to Experiment Safely Choose your experiment location carefully to avoid the marble rolling into places where it cannot be retrieved. Do not release the marble from very high heights, as it could jump off the roller coaster track and hit someone.
• 2 pieces of garden hose or other flexible tubing, each approximately 6 feet (1.8 meters) long • 1 large marble • books, bricks, or wooden blocks • masking tape • chair • tape measure or ruler
Approximate Budget $20 if you need to buy a garden hose or other
tubing. Timetable Approximately 2 hours. Step-by-Step Instructions
1. To make the roller coaster track, lay the two pieces of garden hose or tubing side by side on a flat surface and tape them together across the upper side, so the tape does not show on the lower side. Place tape about every 6 inches (15 centimeters). Flip the taped hose or tubing over so the untaped side is up. The two pieces of hose should form a channel in which the marble can roll. (You can also form the roller coaster from a single uncut length of hose by making a sharp u-bend in the middle and taping the two halves together.)
Step 1: How to assemble roller coaster track. GAL E GR OU P.
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Steps 2 and 3: How to create the roller coaster. G ALE GRO UP .
2. Place one end of the hose track on a chair 24 inches (60 centimeters) off the ground. Let the other end fall to the ground. 3. Let the hose track follow the ground for a short distance and then place two to three bricks under the other end, creating a second hill. 4. Record the height of both hills on a data sheet (see illustration). You have created your roller coaster. 5. To make the heights easier to read, attach a tape measure or ruler vertically on the bricks that form the second hill. Be sure to put the ‘‘zero’’ end on the floor.
Step 4: Recording chart for Experiment 2. GA LE G ROU P. Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are some problems that may occur during this experiment, possible causes, and ways to remedy the problem. Problem: The marble jumped over the second hill. Possible causes: • Your second hill is not high enough. Use more blocks or bricks to make it higher. The height of the hill does not matter as long as you record the height the ball reaches accurately. • Your first hill is too high. Lower it until you can release the marble and it stays on the second hill. Problem: The marble does not stay on the hose track. Possible cause: The marble is too large or too small for the hose. Try using a different size marble that fits well into the track.
6. Place the marble at the top of the first hill and release it. Do not push it, but simply let it go. Sight across your tape measure or ruler to determine the height the marble reaches on the second hill. You might ask a friend to help you note the highest height before the marble begins to roll back again. 7. Repeat this procedure several times and record the average height the marble reaches on the second hill. 8. Now raise the height of the first hill by adding a book or block on the chair. Record the new height of the first hill. 9. Release the marble from the higher first hill several times, taking an average of the heights it reaches on the second hill. Record the average height. 10. Repeat the procedure, raising and lowering the height of the first hill. Be sure to record each hill height and the height the marble reaches on the second hill. Summary of Results Study the results on your
chart. Compare the heights of the first hills and the heights the marble reached on the second hill. Did higher initial heights give your marble more potential energy, which created more kinetic energy to climb the second hill? Was your hypothesis correct? If you want to calculate the potential energy, use the formula described and record the number for each of your hill heights. Change the Variables You can vary this experiment several ways. For
example, remember that potential energy depends partially on the weight of the object. Try using a heavier or lighter marble. What is the effect? You can also try making the second hill steeper or more gradual. What is the effect? How high does the marble rise? Make your first hill higher and create a number of smaller hills with your hose. Can you build up enough potential energy to get your marble over more than one hill? What conditions will allow the marble to do that? 938
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Design Your Own Experiment How to Select a Topic Relating to this Concept If you are interested in
kinetic energy, you could explore the energy in vibrations, in rotational movement, or in objects moving in straight lines or up and down. Or you could investigate the use of kinetic energy in heat or electricity. If you are interested in potential energy, you could study the effects of springs. How does the size or flexibility of the spring affect its potential energy? How much weight can a spring move? You could study the swing of a pendulum (using a backyard swing) as its potential energy is converted to kinetic energy and back again. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on potential and kinetic energy questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or other knowledgeable adult before trying them. Some might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through before you do it. Otherwise you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts, such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental setup and results. If you have done a nonexperimental project, explain clearly what your research question was and illustrate your findings. Experiment Central, 2nd edition
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Related Projects Besides completing experiments, you could prepare a model that demonstrates a point you are interested in with regard to kinetic and potential energy. Or you could investigate the uses of energy in industry, cooking, music, medicine, or dancing. You could explore the history of the study of energy, going all the way back to Newton and Galileo, or you could look at the future of energy, exploring nuclear and fusion energy. There are numerous possibilities.
For More Information Bennet, Bob, Dan Keen, Alex Pang, and Frances Zweifel. Science Fair Projects: Energy. New York: Sterling Publications, 1998. Simple activities and ideas about science fair projects related to energy and using simple materials. Doherty, Paul, and Don Rathjen. The Cool Hot Rod and Other Electrifying Experiments on Energy and Matter. New York: John Wiley & Sons, 1996. Collection of twenty two experiments on all aspects of energy, with drawings, photos, and sidebars. Leary, Catherine, and Michael Anthony DiSpezio. Awesome Experiments in Force & Motion. New York: Sterling Publications, 1998. Provides exciting ideas for kinetic energy projects. National Energy Education Development Project. Scientific Forms of Energy. http://www.eia.doe.gov/kids/energyfacts/science/formsofenergy.html (accessed February 3, 2008). Nova. Newton’s Dark Secrets. http://www.pbs.org/wgbh/nova/newton/legacy. html (accessed February 3, 2008).
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R
enewable energy is energy from sources that are unlimited or replenish in a relatively short amount of time. Long before electricity, renewable energy sources powered people’s daily needs. People captured the Sun’s rays for warmth, burned wood to cook, and used wind to pump water. In the modern day, scientists have developed many systems to harness and transform the energy from renewable sources into energy that people can use.
Heating it up Renewable energy has become a major issue in the modern day. The main energy sources we use today come from fossil fuels. The three main fossil fuels are coal, oil, and natural gas. Fossil fuels are non-renewable. It took hundreds of thousands of years for fossil fuels to form. They are called fossil fuels because they formed from the ‘‘fossils’’ of plants and animals hundreds of millions years ago. Fossil fuels all contain carbon. Burning these fuels releases the carbon, which combines with the oxygen in air to form carbon dioxide. Fossil fuels are used to power cars, planes, and produce electricity. Every year the worldwide demand for energy grows and more fossil fuels are burned. The greenhouse effect occurs when gases such as carbon dioxide trap heat moving away from Earth. The trapped heat warms Earth’s surface, leading to warmer temperatures and a shifting climate. By replacing fossil fuels with renewable energy, we can greatly reduce the emissions of greenhouse gasses. In order for a renewable energy to replace the use of fossil fuels in modern day, the energy needs to be transformed into a form of energy that people use. That energy usually takes the form of electrical energy— electricity. Availability, cost, and the ability to capture the energy source are all issues in transforming renewable energy into usable energy. 941
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Rotor blade
Gearbox & generator
Tower
Underground electrical connections
Wind turbines capture the wind’s energy. I LLU STR AT IO N BY T EM AH NE LS ON.
Where renewables come from There are many sources of renewable energy. The sources most commonly used are: • Wind energy: Wind can be a powerful force. Wind is the result of radiation from the Sun that heats the atmosphere unevenly. The first windmills were developed thousands of years ago. The windmills were used to grind grain and pump water. By the turn of the twentieth century, people had developed small systems that generate electricity from the movement of wind. Wind turbines or blades capture the wind’s energy. The turbines are placed high in the air and are spread apart, like a pinwheel. The wind turns the blades, which causes an electric generator to spin. The generator produces electricity. Groups of wind machines that produce electricity are called wind farms.
• Solar energy: Each day, the Sun provides Earth with vast amounts of energy. We use solar energy every day. Plants need the Sun’s energy to live, and animals and people eat plants. The sun is used for warmth and heat. Researchers have developed several ways to capture the Sun’s energy. To read more about solar energy see the Solar Energy chapter. • Biomass: Biomass is renewable organic matter, such as trees. Plants are considered renewable because new plants can grow relatively quickly (compared to the formation of fossil fuels). When a tree is burned the energy inside the plant transforms into heat energy. People have long used wood to heat their homes. In modern day, wood is the largest biomass energy resource. To transform the plant materials are transformed into electricity by first burning them. The heat produced boils water, which produces steam. The steam turns turbines, which cause a generator to spin and the generator produces electricity. Many other sources of biomass are also used as renewable sources. Crops such as corn can produce oils. The oils can be used to fuel vehicles. Even the fumes from landfills can be used as a biomass
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Glen Canyon Dam harnesses the energy from the water and converts it into electricity. # ATLANTIDE PHOTOTRAVEL/ CORBIS.
energy source. Methane gas, produced from animal manure, is another potential source of biomass. Biomass can produce about the same amount of carbon dioxide as fossil fuels, but because plants remove carbon dioxide from the atmosphere regrowing plants can offset the carbon dioxide produced. • Hydropower: Moving water can contain a lot of stored energy. When that energy is put to use, it is called hydropower. In the United States, hydropower is the most commonly used renewable energy source. Electricity is produced—hydroelectricity—by the force of falling water. Dams collect and move the water to create a large amount of force. The water turns the blades of a turbine, which spin a generator and produces electricity. More renewables Another source of renewable energy that is available but not yet as commonly used is the energy deep inside Earth. This is called geothermal energy. Earth’s core (center) is continuously generating heat. Thousands of feet below ground Earth’s temperature is hot enough to boil water. Capturing this energy as steam spins a turbine, which in turn powers an electric generator. In the experiments that follow, you will investigate two types of renewable energy sources: wind energy and hydropower. For experiments related to solar energy, see the Solar Energy chapter. As you conduct the Experiment Central, 2nd edition
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WORDS TO KNOW Biomass: Organic materials that are used to produce usable energy. Efficiency: The amount of power output divided by the amount of power input. It is a measure of how well a device converts one form of power into another. Fuel cells: A device that uses hydrogen as the fuel to produce electricity and heat with water as a byproduct. Generator: A device that converts mechanical energy into electrical energy,
other gases in the atmosphere that trap heat radiated from Earth’s surface. Hydropower: Energy produced from capturing moving water. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Solar energy: Any form of electromagnetic radiation that is emitted by the Sun.
Geothermal energy: Energy from deep within Earth.
Turbine: A spinning device used to transform mechanical power from energy into electrical energy.
Greenhouse effect: The warming of Earth’s atmosphere due to water vapor, carbon dioxide, and
Variable: Something that can affect the results of an experiment.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of wind • the size of the boat • the distance the boat travels
experiments, consider what questions about renewable energy you would like to explore further.
EXPERIMENT 1 Capturing Wind Energy: How does the material affect the amount of wind energy harnessed?
• the size of the sail • the length of the mast • the material the sail is made from In other words, the variables in this experiment are everything that might affect the speed of the boat. If you change more than one variable at a time, you will not be able to determine which variable had the most effect on the amount of wind energy.
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Purpose/Hypothesis People have used wind as
an energy source for thousands of years. In order for wind to supply energy, the wind must be collected. One way to collect wind would be from a sail, such as on a boat. The sail creates a resistance for the wind and thus, powers the boat forward. In this experiment you will be testing different types of materials on sailboats to determine Experiment Central, 2nd edition
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how the material affect the amount of wind energy harnessed. You will be looking at how How to Experiment Safely materials create a resistance with wind. The wind pushes on the material (the sail) and its Have an adult use the saw to cut the wood. energy moves the boat forward. The materials Have an adult help you use the drill. you will use are netting, flexible plastic, and broadcloth, which is a thick, sturdy fabric. During the experiment, you should also consider how materials need to withstand the force of the wind and not tear due to the resistance. To begin the experiment, use what you have learned about solar energy to make a guess about how the material will affect the wind energy it captures. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The boat with the sail made out of broadcloth will capture the most wind energy and so move the boat the fastest.’’ In this case, the variable you will change is the material the sail is made of and the variable you will measure is the speed with which the boat moves. If the wind moves the boat with the cloth the fastest, your hypothesis is correct.
Step 1: Draw the base of the boat on wood. I LL UST RA TIO N BY T EMA H NE LS ON.
Level of Difficulty Moderate. Materials Needed
• pine wood, 6 3 1 inches (15 8 2.5 centimeters) • 2, one-quarter inch (0.64 centimeters) dowels, both 16 inches (40 centimeters) long • construction paper Experiment Central, 2nd edition
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• netting (also called tulle), 12 inch by 12 inch (30 30 centimeters) piece (available at fabric stores) • broadcloth, 12 inch by 12 inch piece (available at fabric stores) • plastic bag, 12 inch by 12 inch piece • 11, 3-inch (8-centimeter) zip ties • drill with one-quarter inch bit (the bit should be the diameter of the dowels) • hot glue gun and glue sticks • electric fan with at least two speeds • stop watch or watch with second hand • small saw • a still, wind-less day (if you are conducting the experiment outside) • water area, at least 6 feet (1.8 meters) in length (a bathtub works well)
3 inches
Approximate Budget $15. Step 5: Attach the cross bar centered on the mast and crisscross two zip ties to secure the cross bar to the mast. IL LUS TR ATI ON B Y TE MA H
Timetable About 40 minutes for setup; 30 minutes to complete and record results. Step-by-Step Instructions
NE LS ON.
Step 9: Place the boat in a body of water. I LL UST RA TI ON BY T EM AH NE LS ON.
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1. Draw the base of the boat on wood. (See illustration). 2. Have an adult cut out the boat base with a saw. 3. Drill a small and shallow hole in the center of the boat. Do not drill all the way through the wood. This hole is for inserting the mast. 4. Use hot glue to insert and hold the one piece of doweling in the hole. This is the boat’s mast. 5. After the glue has dried, attach the cross bar centered on the mast about 3 inches (7.6 centimeters) from the bottom of where the mast and boat meet. Crisscross two zip ties to secure the cross bar to the mast. Trim the cross bar to leave 6 inches (15 centimeters) on each side of the mast. Experiment Central, 2nd edition
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6. Make a pattern for a sail out of construction paper, using a 12-inch (30-centimeter) triangle. 7. Use the pattern to cut a sail out of each of the three types of material: the netting, broadcloth, and plastic. 8. Attach one of the sails to the boat using zip ties on all three corners (at the mast and cross bar ends). 9. Place the boat in a body of water. If you are using a bathtub place the boat on one end. If you are using a natural body of water, mark a place where you are setting the boat and note a spot about 6 feet (1.8 meters) away. 10. Aim the fan at the boat and turn it on the low speed. If the boat does not move across the water with the low speed, turn the fan on the higher speed. 11. Use the stopwatch to time how long it takes for the boat to cross the body of water (or reach a set mark if the boat is on a long stream or other natural body of water). Record the time. Repeat the test for two more trials. 12. Repeat Steps 8–10, attaching the two remaining sails of different materials each time.
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The mast keeps falling down. Possible causes: 1. The hole may be too large or too shallow. The dowel should fit snugly in the hole. If it is loose, try using a smaller drill bit. If the dowel fits snugly, try drilling the hole slightly deeper into the wood, without drilling through the wood. Repeat the tests. Problem: The boat tips over in the water. Possible cause: 1. The sails may be too large for the boat. Try making the sails 2 inches (5 centimeters) smaller and repeat. Possible cause: The wind from the fan may be too strong. 1. If you are conducting the experiment outside, make sure it is not a windy day. Use the lowest setting on the fan and move the fan farther away from the boat.
Summary of Results After you average the three
trials for each of the materials, analyze your data to determine if the type of material affected the amount of wind that the sail collected. Was there one material that gathered more wind energy than others? Is it possible to gather too much wind? Consider if some materials might be better for certain strengths of wind. Write a paragraph summarizing your results. You may want to include pictures or drawings. Change the Variables You can vary this experiment by changing the shape
of the sail to determine if certain shapes capture greater amounts of wind. How does a square shape capture wind energy, for example? You can test Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of the experiment. Here are the main variables in this experiment:
different sizes as well as shapes. You can also try varying the wind speed to explore how the material can withstand greater amounts of wind energy. In order to increase accuracy of results, complete three time trials of each sail type and average the results?
• the amount of pressure • the number of spoons • the size of the spoons • the size of the water wheel • the construction of the water wheel • the distance of the water wheel from the water energy source
EXPERIMENT 2 Hydropower: How does water pressure affect water energy? Purpose/Hypothesis Water is a source of energy
that has existed for thousands of years. Ancient cultures used water to move ships and grind grain. In the modern day, hydropower is a major source of electricity. An important aspect of hydropower is the pressure caused by the movement and also, the weight of the water. The more stored water in a set area, the more water there is to push downwards. The downward pressure of the water can create a lot of force. In hydropower, the moving water is harnessed and used to produce usable energy. In this experiment you will look at how the pressure of stored water affects the amount of energy the water produces. The water will exit onto a water wheel. You can measure how the force of moving water affects the amount of energy harnessed by counting the revolutions of a water wheel. To begin your experiment, use what you know about hydropower and renewable energy to make an educated guess about water pressure and energy. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
In other words, the variables in this experiment are everything that might affect the movement of the water wheel. If you change more than one variable, you will not be able to tell which variable had the most effect on the water energy.
Steps 1: 3 and 4: Insert spoons about an 1 to 1.5 inches apart. In the same slot, insert the straw or stirrer. I LL UST RA TI ON BY T EM AH NE LS ON.
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A hypothesis should be brief, specific, and measurable. It must be something you How to Experiment Safely can test through observation. Your experiment will prove or disprove whether your Have an adult assistant you in using the knife. hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘An increase in stored water increases the energy harnessed in water, which will make the wheel spin faster.’’ In this case, the variable you will change is the amount of stored water. If the water wheel makes more revolutions with the greater amount of water you will know your hypothesis is correct. Level of Difficulty Moderate. Materials Needed
• 2 gallon or larger container (an extra large liquid laundry detergent container works well) • 5 or more gallons of water • swim noodle with a hollow center • 6 plastic spoons • utility knife • stop watch or clock with second hand • 12 inch piece of dowel • pitcher • permanent marker • colored straw or coffee stirrer • 2 to 3 helpers
Step 2:6 Pull the plug and pour water into the container at a steady rate to maintain the water at the 1 gallon mark. ILL US TRA TI ON B Y TE MA H NEL SO N.
2 gallons
Approximate Budget $10. Timetable Approximately 90 minutes. Step-By-Step Instructions 1.) Create the water
wheel 1. Have an adult cut off a 2 inch (5 centimeters) section of the swim noodle. This will be the center of your water wheel. 2. Break off the handles of the spoons. Experiment Central, 2nd edition
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3. Make a slit in the noodle and insert a spoon. Continue around the circle, placing spoons about an 1 to 1.5 inches (2.5–3.8 centimeters) apart. Five to six spoons should fit around the circle. All spoons should be facing the same way. 4. In the same slot as one of the spoons, insert the straw or stirrer. 2.) Force of water energy 1. Mark three lines on the container at 1, 1.5, and 2 gallons. 2. Poke a hole in the side of the container with a pencil, 1 inches (2.5 centimeters) up from the base; it should be on the narrowest side. Place a pencil in the hole to plug the hole until you are ready to start the trials. 3. Slide the water wheel on the dowel. 4. Hold the dowel and wheel below the container and out approximately 6 inches (15 centimeters). You will need to allow some water to come out of the hole to determine the best point to hold the wheel. The best point is where the water wheel moves free and consistently. Once this is determined, tape the wheel in place so it is consistent for all trials. 5. Fill the container to the 1 gallon mark.
1 gallon # of rotations
1.5 gallons
2 gallons
Trial 1
Trial 2
Trial 3 Step 2:8 Record the results. I LLU ST RAT IO N BY TEM AH NEL SO N.
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6. Have a helper ready with a pitcher of water. Once the plug is pulled, the Troubleshooter’s Guide helper will need to pour water into the container at a steady rate to mainIn any experiment, problems can occur. Sometain the water at the 1 gallon mark. times, experiments that do not work perfectly can turn out to be helpful. Here is one problem This will keep the water pressure you may encounter, some possible causes, and steady. ways to fix the problem. 7. Pull the plug on the water and time for Problem: The wheel is not moving freely. one minute. 8. Use the colored straw or stirrer to count Possible cause: The spoons may be facing the the number of revolutions the wheel wrong way. Turn the spoons so they are facing the opposite way If the wheel is still not moving makes in one minute with one gallon of freely, you may want to purchase a pinwheel water. Record the results. and try the experiment again. 9. Conduct two more trials at this level of water and note the revolutions for each trial. 10. Repeat Steps 6–9, filling the container first to the 1.5 gallon mark and then to 2 gallons. For each amount of water, conduct three trials and note the results. Summary of Results After the experiment is finished, average the number
of revolutions for each amount of water. Analyze your data table to determine the affect of water pressure on energy. Does more pressure result in more harnessed energy? Change the Variables You can change several variables in this experi-
ment. Try moving a toy boat or another object rather than the water wheel. You can also change the shape or size of the water wheel. Does temperature affect the water energy?
Design Your Own Experiment How to Select a Topic Relating to this Concept Consider all the different
types of renewable energy. Think about what aspect of renewable energy you are interested in, such as ways to use this energy or how a certain renewable is generated into electricity. You might want to investigate whether pollution is changing the effects of renewable energy on our world. You may want to look around where you live or go to school to see if any homes, schools, or businesses use renewable energy sources. Experiment Central, 2nd edition
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Check the Further Readings section and talk with your science teacher or community media specialist to start gathering information on renewable energy questions that interest you. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise you might not be sure which question you are answering, what you are or should be measuring, and what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Every good experiment
should be documented so that other people can understand the procedures and results. Make diagrams, charts, and graphs of any information that is useful. You might also want to include small scale models related to your renewable energy experiment or project. Your experiment, whether it proves or disproves your hypothesis, is information that others can learn from. Related Projects Renewable energy sources are all around us. What
types of renewable energy have you used or would you like to use? You can design and build small generators, powered by a renewable energy source. You can also conduct a project in energy efficiency in your home or school. Can you shift any part of the energy system into a renewable energy source? Compare carbon emissions both before and after the change. How does cost play a role in selecting renewable energy sources?
For More Information Asimov, Issac. The Sun and Its Secrets. Milwaukee, WI: Gareth Stevens Publishing, 1994. Discusses the Sun’s origins, content, and historical facts. 952
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Energy Information Administration. ‘‘Renewable Energy.’’ Energy Kid’s Page. http://www.eia.doe.gov/kids/energyfacts/sources/renewable/renewable.html (accessed July 24, 2008). Answers to basic questions about renewable energy types and sources. ‘‘The Energy Story.’’ Energy Quest. http://www.energyquest.ca.gov/story/chapter17. html (accessed on April 13, 2008). Information and projects related to renewable energy. ‘‘Renewable. Energy.’’ Energy Kid’s Page. http://www.eia.doe.gov/kids/ energyfacts/sources/renewable/renewable.html (accessed on April 13, 2008). Basic information on different forms. ‘‘Solar Energy Animation.’’ Ocean Motion. http://oceanmotion.org/html/ resources/solar.htm (accessed on March 18, 2008). Information demonstrates how the intensity of the energy from the sun varies with location and time. Suzuki, David and Kathy Vanderlinden. Eco-Fun. Vancouver: BC: Greystone Books, 2001. Project and experiments related to the environment. U.S. Department of Energy. Kids Saving Energy. http://www.eere.energy.gov/ kids/ (accessed on April 13, 2008). Information on renewable energy sources and energy saving tips.
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Rivers
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he Carson begins in California, rushing northward from the headwaters on Sonora Peak in the Sierra Nevada Mountains, then rambling through gorges and alpine meadows. After leaving California, its next destination is the desert plain of Nevada. The Carson is a river, a main course of water into which many smaller bodies of water flow. The longest river in North America is the Mississippi. At 2,280 miles (3670 kilometers), it’s the tenth longest on Earth. The Nile River, the world champion in length, winds 4,145 miles (6670 kilometers) from the equator to the Mediterranean Sea.
The Niagara River and its falls have carved out a 100-foot (30-meter) deep plunge pool. PH OTO RE SEA RC HER S I NC.
First things first The source of a river’s waters, in fact, all the waters of the world, is the hydrologic cycle, which circulates and distributes the fresh water on Earth. To examine this cycle, we might begin with the sea. The Sun warms the ocean water, causing some of the surface water to evaporate and rise into the air as water vapor. Upon meeting cooler air above, this water vapor condenses and forms rain droplets, or it freezes into ice crystals. The droplets or crystals eventually fall again as precipitation: rain, snow, or hail. Some precipitation falls back into the sea, while some falls on land where it sinks into the ground, or runs into rivers, lakes, ponds, and streams. French scientist Claude Perrault was one of the first to describe the hydrologic or water cycle. In 1674, he measured the precipitation that fell into the upper Seine River’s basin and compared it with the estimated amount of water flowing into the Seine from streams and smaller rivers. The precipitation added about six times as much water as the streams. This was a significant discovery because previously scientists had thought that all rivers were fed by underground springs. 955
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Mapping out the journey Rivers begin in mountains as several streams. These streams are formed from runoff consisting of rain, melted snow, sleet, and hail, as well as underground water that rises to the surface. Smaller streams gather into larger streams until they form a river. The river makes its home in a channel, a shallow trench carved into the ground from the pressure, volume, and movement of the water. The journey of a river is rarely straight. Wide, shallow rivers with pebbly islands in the middle are called braided rivers. The islands split the river into many streams, which then come together again, just like braided hair. Lowland rivers that twist and turn before flowing to the sea are called meandering rivers. The term originated from the Latin word maeander. For example, the Menderes River in Turkey is famous for its windy course. Scotland’s Deveron River meanders 26 miles (42 kilometers) back and forth across the land, but its actual straight-line length is only 6.5 miles (10.5 kilometers).
The Nile River plays an important part in the hydrologic cycle. PE TER AR NO LD I NC.
The power of water Where does a river’s energy come from? The elevation of the land triggers its push, even in areas where the slope is gentle. The speed and volume of a river descending a steep slope can reshape Earth’s surface, picking up soil and rocky debris and then dropping it when the water slows down and loses some of its energy. Rivers have gouged out canyons, built mud and stone landforms, and sculpted solid rock into pillars and arches. An example of how powerful a river’s force can be is the Niagra River, which runs through Canada and the United States. As it courses downslope on its 35-mile (56-kilometer) trail, the water pounds everything along its way. The cliff that creates its falls is a ridge made of dolomite, a very tough limestone. The river has worn down the ridge’s overlying rock, creating a lower area that focuses the fall of the water. In the following two experiments, you will explore ways that water changes the shape of our environment. The experiments will help you
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WORDS TO KNOW Braided rivers: Wide, shallow rivers with multiple channels and pebbly islands in the middle.
precipitation and back to the atmosphere through evaporation and transpiration.
Channel: A shallow trench carved into the ground by the pressure and movement of a river.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Meandering river: A lowland river that twists and turns along its route to the sea.
Deposition: Dropping of sediments that occurs when a river loses its energy of motion.
River: A main course of water into which many other smaller bodies of water flow.
Glacier: A large mass of ice formed from snow that has packed together and which moves slowly down a slope under its own weight.
Sediment: Sand, silt, clay, rock, gravel, mud, or other matter that has been transported by flowing water.
Hydrologic cycle: Continual movement of water from the atmosphere to Earth’s surface through
Variable: Something that can affect the results of an experiment.
Moraine: Mass of boulders, stones, and other rock debris carried along and deposited by a glacier.
appreciate how rivers and streams have influenced the shape of your own community.
EXPERIMENT 1 Weathering Erosion in Glaciers: How does a river make a trench? Purpose/Hypothesis In this experiment you will investigate the effects that
glaciers, rivers of ice, have on the landscape, such as forming trenches and moraines, arc-shaped ridges of rocky debris. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of glaciers. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • size of the ice flow • size of pieces of sediment • temperature surrounding ice flow • duration of the experiment In other words, the variables in this experiment are everything that might affect the sediment erosion. If you change more than one variable, you will not be able to tell which variable had the most effect on erosion.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Ice flow causes sediment erosion.’’ In this case, the variable you will change is the presence of an ice flow, and the variable you will measure is the movement of soil in the ice flow’s path. You expect the ice flow to cause erosion. As a control experiment, you will set up one tray of sand with no ice flow in it. That way, you can determine whether the sand moves even with no ice flow. If the sand moves under the ice flow, but not in the control tray, your hypothesis will be supported. Level of Difficulty Moderate. Materials Needed
Step 1: Screening over the bucket. GA LE GRO UP.
• 10 pounds (4.5 kilograms) play sand for sandboxes • 24-inch (60-centimeter) square of window screening • two 8 24-inch (20 61-centimeter) plastic trays (Liners for window boxes are ideal.) • water • freezer • ruler • bucket Approximate Budget $15. Timetable 30 minutes to set up; 5 minutes a day
to add water over a 30-day period. Step-by-Step Instructions
1. Place the screening over the bucket and sift the sand by pouring it through the screen. Save any sand that remains on the screen. Discard any sand that goes through the screen. 958
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2. Pour the sand that remained on the screen into both plastic trays. 3. Using the side of the ruler, smooth the surface of the sand in the trays and measure the depth of the sand. Make sure the sand is the same depth in both trays. 4. Using your finger, make a well in the sand at one end of both plastic trays. 5. Place the trays inside the freezer and prop up the ends with the well about 1 inch (2.5 centimeters). 6. Pour 0.25 cup (60 milliliters) of water into the well of one tray (the experimental tray) and close the door. The control tray will have no water—and thus no ice. Add another 0.25 cup (60 milliliters) of water to the experimental tray daily for 30 days.
Step 5: Place the trays inside the freezer and prop up the ends with the well about 1 inch. GAL E GR OU P.
7. After 30 days, record the length of the ice flow that formed in the experimental tray. 8. Carefully remove both trays from the freezer. 9. Allow the ice flow to melt six to 12 hours. 10. Diagram the pattern the ice caused in the sand; describe the sand pattern in the control tray. 11. Measure the depth of the sand in the trench and at the end of the ice flow in the experimental tray. Measure the sand depth at both ends of the control tray. Record your findings.
Steps 10 and 11: Tray showing pattern left by ice flow. GA LE GR OU P.
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, some possible causes, and ways to remedy the problem. Problem: After 10 days, there is no ice accumulation near the well in the experimental tray. All the water flows quickly through the sand to the bottom of the tray.
Summary of Results Organize your data on a chart that shows the sand levels in both trays at the beginning and the end of the experiment. Compare your end results. Did the ice flow move sediment? Did erosion take place in the control tray? Write a paragraph summarizing what you found. Change the Variables You can change the vari-
1. The angle is too steep. Lower both trays to a very gentle slope.
ables in this experiment by using different soils. You might try top soil or a more rocky soil. Also, you can change the angle of the slope and see how the depth of the trench is affected. Gravity plays a large role in soil movement. The steeper the slope, the greater the pull of gravity.
2. The sand is too coarse. Try a finer mesh screen and use smaller grains of sand.
EXPERIMENT 2
Possible causes:
Stream Flow: Does the stream meander? What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of soil being used (size and composition) • the flowrate of water used • the slope of the landscape • the duration of the water flow In other words, the variables in this experiment are everything that might affect the stream pattern. If you change more than one variable, you will not be able to tell which variable had the most effect on the pattern.
How to Experiment Safely Handle the bricks carefully to prevent injury.
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Purpose/Hypothesis Rivers and streams can
carve patterns into Earth’s surface. This experiment will simulate the force that water can have in an environment. Will a water travel in a straight path down a slope? Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of stream patterns. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A gentle flow of water across a downward sloping landscape will create a meandering stream Experiment Central, 2nd edition
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path, while a more forceful flow will create a straighter path.’’ In this case, the variable you will change is the velocity of the water flow, and the variable you will measure is the resulting stream pattern. You expect the stream to meander for low flows and be straighter for higher flows. Level of Difficulty Easy. Materials Needed
• flat outdoor area • hose and water supply • 24-inch (61-centimeter) long shallow pan, such as a plant tray • 5 pounds (2.2 kilograms) sand for a sandbox • 5 pounds (2.2 kilograms) gravel • 2 bricks or wooden blocks for support
Steps 1 to 3: Set-up of sand and gravel tray. G ALE GRO UP .
Approximate Budget $8 for sand and gravel. Timetable 45 minutes. Step-by-Step Instructions
1. Pour equal amounts of gravel and sand into the tray and mix well. Make the surface level and smooth from one end to the other. 2. Lift one end approximately 6 inches (15 centimeters) high and place a brick underneath. Place the other brick in front of the lower end to keep it from sliding. 3. Place the end of the hose at the high end of the box. 4. Turn the hose on for two minutes, allowing a very soft flow of water to run over the sand. 5. After two minutes, turn off the water and diagram the pattern of water. 6. Turn the water on again for two more minutes; then turn it off and diagram the pattern again. Experiment Central, 2nd edition
Step 5: Diagram the pattern of water flow after 2 minutes. G AL E GR OUP .
Step 6: Diagram the pattern of water flow after 4 minutes. GA LE G RO UP.
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The sand or gravel did not move or show a pattern in the first two minutes. Possible cause: Not enough water was applied. Allow the water to flow longer, until a stream bank begins to form.
7. Smooth the surface of the sand and gravel and repeat Steps 4 through 6 with a higher water flow rate. Summary of Results Study your diagrams and the tray of sand. Which size particle of sand or gravel moved the most? As the stream flowed longer, how were the patterns affected? Did your stream begin to meander at the lower flowrate and go straighter at the higher flowrate? Write a paragraph summarizing your results and explaining them. Change the Variables To vary this experiment,
experiment with the angle of the slope or the size of the particles in the streambed.
EXPERIMENT 3 River Flow: How does the steepness and rate of water flow affect river erosion? Purpose/Hypothesis Rivers are found in many elevations and they flow
at varying rates. Water racing down a steep incline will erode materials in a different way than water slowly moving down a shallow incline. The rate at which the water flows also plays a role in erosion. In this experiment, you will make a mini-river and place sediment on the bottom of it. By varying the rivers steepness and water rate, one at a time, you can measure how each factor affects erosion. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of rivers and erosion. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis 962
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for this experiment: ‘‘The steepest river with the highest rate of water flow will cause the most erosion, while the shallowest river with the lowest water rate will cause the least erosion.’’ In this case, the variables you will change is the river steepness and water rate, one at a time, and the variable you will measure is the remaining sediment. Level of Diffculty Moderate. Materials Needed
• 24 cups of dirt • 2 strips of wood, between 6 to 8 feet long (12 inches or 24 inches) • measuring cup • container that holds 4 cups • protractor • 2 funnels, with one spout width about 50% wider than the other (you could make a and taping a plastic, such as a pastry sheet) • tape measure • Duct tape • plastic tarp, shower curtain, or garbage bags • marker • 2 to 4 helpers • an outside area
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • elevation of the river • width of the river source • amount of water • type of sediment • placement of sediment • amount of sediment In other words, the variables in this experiment are everything that might affect the sediment erosion. If you change more than one variable, you will not be able to tell which variable had the most effect on erosion.
funnel by rolling
Step 1: Tape one side of the plastic to one strip of wood. IL LU STR AT IO N BY T EM AH NE LS ON.
Approximate Budget $10. Timetable about 1 hour and 30 minutes. Step-by-Step Instructions
To Make the ‘‘River:’’ 1. Tape one side of the plastic to one strip of wood. See illustration. 2. Tape the second side of the plastic to the other strip of wood. Experiment Central, 2nd edition
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3. Roll the wood over the plastic several times, if needed. This will create your How to Experiment Safely river. You will be able to adjust the width of the river by rolling the plastic in or out. This experiment poses no safety hazards but it 4. Have two people on each side hold the can get messy. boards firmly. Your river bed should be at least 10 inches wide. It should have a little slack in it. Make sure you maintain the same width throughout each test. 5. Mark a pour point at the top of the river. This will be the point where the water flow will begin for each trial. 6. Use tape or a marker to mark off a two to three foot section of the river about 3 feet from the bottom. This will be where you will spread the sediment each trial. To test for erosion: 7. Lift the top of the river to 18 inches and hold it tight. Use the protractor to measure the angle of elevation at the end of the river (where the river meets the ground). 8. Spread out 4 cups of dirt or sand between the marked points. 9. Pour 4 cups of water into a container.
sediment
Steps 10 and 11: Using the narrow funnel, pour the container of water into the funnel at the pour point down the river. Observe the erosion pattern. IL LU STR AT IO N BY
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10. Using the narrow funnel, pour the container of water into the funnel at the pour Smallest incline point down the river. River angle 11. Observe the erosion pattern. You may N row Nar w Wide Funnel Funnel want to sketch the pattern. 12. Use your measuring cup to measure the Angle amount of dirt left in the river. Try to Height measure all the remaining sediment. 13. Record your results on a table similar to Length the illustration. a constant 14. Starting with a clean river, lift the top of Initial the river to 24 inches. Repeat Steps 2–7, sediment using fresh dirt. Note the angle of elevaFinal sediment tion with the protractor. 15. Lift the top of the river to 36 inches (91 centimeters), and repeat Steps 2–7. Again, use fresh dirt and measure the angle of elevation. 16. Repeat the test at the three incline heights, using the wider funnel, thus increasing the rate of water flow. Match the angle of elevation for each incline.
Medium incline angle
Greatest incline angle
Narrow Wide Narrow Wide Funnel Funnel Funnel Funnel
Mark the results in a chart. ILL US TRA TI ON B Y TE MA H NEL SO N.
Summary of Results Analyze your data to determine how the incline angle affects the erosion process. How would erosion differ in a mountain river versus a plains river? Does the steepness changes in a river disturb the water flow and thus, change the water path at different points? Does the angle of the river or the amount of water flow have more of an impact on erosion? Change the Variables There are several ways you can change the variables
in this experiment. You can add natural debris to the sediment, such as leaves or twigs. Determine if natural debris positively or negatively impacts erosion. You can also add small pebbles and stones. The length of the river may also plays a factor in river erosion. Try changing the length to a shorter and longer river.
Design Your Own Experiment How to Select a Topic Relating to this Concept Rivers of water have
carved Earth’s landscape, whether flowing in streams and rivers or creeping slowly as glaciers. You can try other experiments relating to rivers, involving topics such as water velocity and turbidity (amount of mud in the water) or Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: Water is leaking from the ‘‘river.’’ Possible cause: The plastic is not taped well enough. Be sure to tape the back of the bags (or other material) with Duct tape so that there are no holes. Problem: All the dirt keeps washing away. Possible cause: If all dirt is washing off the river, decrease your heights of elevation and try the experiment again. Problem: The river keeps moving during the trials. Possible cause: If it is too difficult to hold the river width tight, try using a detached playground slide or piece of guttering for the sides of the river. You could also build a smaller river.
a river’s rates of erosion, deposition, and weathering. You might also investigate underground rivers or cave-forming rivers. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on river questions that interest you. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question.
• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results It is important that your
data be kept organized in graphs or charts. When you finish your experiment, you must summarize the data and record your results. Reflect on the original question you wanted to answer. Write a paragraph explaining what happened and why so others can learn from your research. Related Projects To develop an experiment on this topic, think about a
question that you want answered. Where does the water flow the fastest? What is the largest size rock that can be carried by a river? Where does the water come from and go to? Investigate ways to measure and analyze rivers in order to answer your questions. 966
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The Maruia River on South Island, New Zealand, is a meandering river. COR BI SBE TTM AN N.
For More Information BBC. ‘‘Rivers and Water Management.’’ Schools. Science: Geography. http:// www.bbc.co.uk/schools/gcsebitesize/geography/riverswater/ riverprocessesrev2.shtml (accessed on March 15, 2008). Basic information on river erosions. Knapp, Brian. River. Danbury, CT: Grolier Educational Corp., 1993. Offers facts about rivers, including how they work and rivers of the world. Includes simple experiments. Pringle, Lawrence. Rivers and Lakes. New York: Time Life Books, 1985. Explains how rivers change the landscape and how their energy is harnessed. Good chapter about organisms and wildlife that depend on rivers for their survival. U.S. Geological Survey. ‘‘Earth’s Water.’’ Water Science for Schools. http://ga. water.usgs.gov/edu/mearth.html (accessed on March 12, 2008). Information and illustrations about the properties of water.
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A
ccording to archaeologists (scientists who study the past remains of human activities), the Copper, Bronze, and Iron Ages were named for the main minerals that were being used in tools during those time periods, which spanned 10,000 B . C . E . to 2,000 B . C . E . Minerals are natural, nonliving solids—tiny particles arranged in definite patterns. Rocks are solid mixtures of minerals. If you look at a rock with a magnifying lens, you can often see the distinct grains of several different minerals.
Earth is a living machine At the end of the eighteenth century, James Hutton (1726–1797), a Scottish doctor, met once a week in Edinburgh to talk with other visionary men about new ideas. The Industrial Revolution was just beginning, and the men he met included James Watt, inventor of the steam engine, and Joseph Black, the chemist who discovered carbon dioxide. Hutton was interested in the rock and soil of his homeland and discussed his theories with this group. Certain cliffs overlooking the North Sea, called Siccar Point, particularly fascinated Hutton. The upper part of the cliffs is red sandstone in horizontal layers, while the lower half is a dark rock tilted almost vertically. He knew the cliffs did not just magically appear in this form. After years of study, Hutton concluded that Earth was like a living machine, driven by heat within. He theorized that over thousands of centuries, the heated material within Earth’s core erupted and formed deposits on the ocean bottom. Over time, these deposits rose to form new land. Then rains eroded them, sending some of the soil and rock particles back into the oceans. It was part of a continual cycle of creation and destruction. In 1788, Hutton presented his ideas to the Royal Society of Edinburgh. He was not entirely correct, but his theory was accepted at the time and represented the beginning of modern geology, the science of rocks, volcanoes, earthquakes, and the history of Earth. 969
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James Hutton (right) founded modern geology by studying rocks such as those at Siccar Point in Scotland. LI BR ARY O F C ONG RE SS.
Shake, rattle, and roll Earth’s very hot, solid inner core is the machine that Hutton envisioned. Earth’s inner core is surrounded by an outer core, a hot layer of liquid metal. After that comes a layer called the mantle, which produces the liquid rock of volcanoes. Earth’s crust is the top layer, the one on which we live. Huge, moving blocks of rock called plates make up Earth’s crust. Their fit is similar to the pieces of a cracked eggshell. The boundaries where the pieces meet are called seismic belts. Cracks along these belts allow heat from the upper mantle to escape. Within seismic belts, movement, heat, and eruptions combine to form various minerals, each kind with a specific crystal form. Some valuable minerals are located by mining near seismic belts. Classifying this old rock Rocks vary enormously because of the way they are formed. Geologists, scientists who study rocks, classify them into three categories: igneous, sedimentary, and metamorphic rocks. Igneous (pronounced IG-knee-us) rocks are formed when rock material cools from a hot, liquid state called magma. Magma is a thick substance like melted glass. When it reaches Earth’s surface, usually through volcanic eruptions, it is called lava.
The molten lava from this Hawaiian volcano is a form of rock that shot up from the depths of Earth’s mantle. PHO TO R ES EAR CH ER S IN C.
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Sedimentary rocks are formed from particles that have broken away from other rocks and have been washed down and deposited on the bottoms of lakes or oceans. These particles may become mixed with fragments of dead plants or seashells. Over millions of years, these deposits may get buried under other rocks and soil. The pressure of tons of earth above the particles packs them together in layers and hardens them into rock. Metamorphic (pronounced meta-MORE-fic) rocks are formed from sedimentary and igneous rock that become deeply buried in Earth. They are not formed from melting. Instead, the combination of intense heat and pressure changes them into different minerals. Metamorphic, in fact, means ‘‘changed in shape.’’ When you think about it, Earth really is a living machine that forms the rocks and minerals that serve as the foundation of our daily lives. In the two projects that follow, you will examine rocks and minerals closely to learn more about them.
PROJECT 1
Mountains may include rocks of many types. P HOT O RES EA RC HER S I NC.
Mineral Testing: What kind of mineral is it? Purpose/Hypothesis In this project, you will determine the character-
istics of mineral samples, such as hardness, luster, and color. Each mineral has specific characteristics, or properties, that distinguish it from other minerals and can help you identify it. Level of Difficulty Moderate/difficult. Materials Needed
• white ceramic tile • hammer • magnifying lens Experiment Central, 2nd edition
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WORDS TO KNOW Cleavage: The tendency of a mineral to split along certain planes. Crust: The hard, outer shell of Earth that floats upon the softer, denser mantle. Fracture: A mineral’s tendency to break into curved, rough, or jagged surfaces. Geology: The study of the origin, history and structure of Earth. Igneous rock: Rock formed from the cooling and hardening of magma. Inner core: Very dense, solid center of Earth.
Metamorphic rock: Rock formed by transformation of pre-existing rock through changes in temperature and pressure. Mineral: An inorganic substance found in nature with a definite chemical composition and structure. Most have a crystal form. Outer core: A liquid core that surrounds Earth’s solid inner core; made mostly of iron. Plates: Large regions of Earth’s surface, composed of the crust and uppermost mantle, which move about, forming many of Earth’s major geologic surface features. Rock: Naturally occurring solid mixture of minerals.
Lava: Molten rock that occurs at the surface of Earth, usually through volcanic eruptions.
Sedimentary rock: Rock formed from the compressed and solidified layers of organic or inorganic matter.
Luster: A glow of reflected light; a sheen.
Seismic belt: Boundaries where Earth’s plates meet.
Mantle: Thick, dense layer of rock that underlies Earth’s crust and overlies the core.
Streak: The color of the dust left when a mineral is rubbed across a rough surface.
• glass plate or cup (used, since you will be scratching it as part of the experiment) • penny • 4 samples of unpolished minerals (gathered outdoors or purchased at a store; avoid polished samples because they lose some of their natural properties) • 4 index cards • goggles Approximate Budget Less than $10 for a tile, minerals, and a mag-
nifying lens. Timetable 20 minutes. 972
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Step-by-Step Instructions
How to Experiment Safely 1. Prepare an index card, as illustrated, to record data for each of your samples. Wear goggles at all times when testing miner2. Number each sample and write the same als. Mineral fragments and dust can irritate your number on an index card. eyes. 3. Determine and record the color or colors of each sample. 4. Check the streak. The streak of a mineral is the color of the dust left when the mineral is rubbed across a rough surface. Using the underside of the ceramic tile, firmly rub the mineral across the tile. Record the color of any residue left on the tile. 5. Examine the luster or shine of the mineral. If the mineral is shiny gold, silver, or grey, it is considered metallic. If it is not shiny, it is considered nonmetallic. Describe the luster of each mineral (metallic or nonmetallic) on its card. 6. Determine how each mineral breaks apart when struck. Cleavage is a mineral’s tendency to break in along smooth, flat planes. Fracture is a Step 1: Index card set-up. GA LE mineral’s tendency to break into curved, rough, or jagged surfaces. GRO UP.
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Step 4: Using the underside of the ceramic tile, firmly rub the mineral across the tile. G AL E GRO UP.
Wearing your goggles, strike the mineral with a hammer and break it. Using the magnifying lens, observe how many flat surfaces exist on the broken pieces. Draw your findings on the data card. 7. Check each mineral’s hardness, using the Moh’s Hardness Scale. The scale ranges from 1 (softest mineral, such as talc) to 10 (hardest mineral, such as a diamond). To determine the hardness of each mineral, see what it scratches. For instance, if the mineral scratches glass, it registers a 5.5–5.6 on the Moh’s Hardness Scale; if it scratches a penny, but does not scratch glass, it registers 3.5–5.5 on the Scale; if it scratches a fingernail, but does not scratch a penny or glass, it registers 2.5–3.5 on the Scale; if it does not scratch a fingernail, penny, or glass, it registers 1.0–2.5 on the Scale. 8. Some minerals have special properties, such as being magnetic or dissolving in water. Some have a different smell, taste funny, react with acid, or glow under ultraviolet light. If you notice any special properties for each mineral, record them on its card. Summary of Results Compare your results. What colors were your
samples? Did the color of the streaks surprise you because they were different from the mineral? Could you tell if the samples were metallic or nonmetallic? How did the samples compare in hardness? If you wish, use a mineral identification guide and the properties you identified to
Step 6: Determine how each mineral breaks apart when struck. Wear your goggles! GA LE GR OU P.
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determine the name of each sample. Set up a display of your samples and their data cards.
PROJECT 2
How to Experiment Safely Wear goggles at all times and use the hammer outside, away from others.
Rock Classification: Is it igneous, sedimentary, or metamorphic? Purpose/Hypothesis This project will give you the basic knowledge
needed to classify igneous, sedimentary, and metamorphic rocks. Level of Difficulty Moderate. Materials Needed
• • • • • • •
hammer 12 rock samples of different colors, sizes, and textures flat, hard surface—old table or board egg carton permanent marking pen goggles magnifying lens
Step 1: Carefully crack each rock sample with the hammer to expose a fresh surface. GA LE GRO UP .
Approximate Budget $0. If possible, gather rock
samples outdoors and borrow a hammer and goggles. Other materials should be available in the average household. Timetable 1 hour. Step-by-Step Instructions
1. Using the hammer outside on the table or board, carefully crack each rock sample to expose a fresh surface. 2. Place a sample of each rock into the egg carton wells. 3. Use the marking pen to label each sample with a number from 1 to 12. 4. Construct a data sheet to log all observations (see illustration). Experiment Central, 2nd edition
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Step 5: Examples of igneous, metamorphic, and sedimentary rocks. GAL E GR OU P.
5. Using a magnifying lens, examine each rock. Look for characteristics such as: a. Igneous rocks (formed from cooled, liquid rock): Contain large or small crystals; appears glassy with seashell pattern when cracked. b. Metamorphic rocks (derived from pre-existing rock that was changed by heat and pressure): Layers that appear wavy. c. Sedimentary rocks (formed from pre-existing rock fragments or seashells or dead plants or animals): Include fossils—preserved
Data sheet for Project 2. GA LE GR OU P.
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plant or animal remains; contains pebbles, sand, silt, or clay particles; contains carbon or coal; contains layers. Summary of Results Examine your data sheet.
Based on the visible properties, place each rock in one of the three categories. Remember, you must see some evidence to justify your conclusion. For example, sample 3 in the illustration, fossilized limestone, has sand grains as well as small sea shell fragments, so it must be sedimentary rock.
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: You cannot see any visible characteristics in some of the samples. Possible cause: Some samples may be too small. A larger sample may be needed. For example, layers in metamorphic rock may be hard to see in a small sample.
Modify the Project To further your understandProblem: A sample seems to possess properties ing of rocks and make this project more challengof two groups, such as metamorphic layers and ing, you can experiment with how rocks break sand grains. down. We know that wind, rain, rivers and rock Possible cause: Since metamorphic rock is slides can change the shapes of rocks. Rocks are derived from other types of rocks, a sample may also broken apart by repeated freezing and thawpossess properties from other categories. ing. As the water in a rock freezes it expands, producing cracks in the rock. Over time these cracks will push the minerals apart and the rock will separate Into pieces. What type of rock is more likely to crack due to freezing and thawing? In Project 2, you classified rocks into three categories, igneous, sedimentary and metamorphic. Using what you know about the characteristics of each type of rock, make a prediction about which type is more As the water in a rock freezes it likely to break apart after freezing and thawing. Place your igneous, expands, producing cracks in sedimentary and metamorphic rocks in separate plastic containers. the rock. I LLU ST RAT IO N BY TEM AH N EL SON . Cover the rocks with water and place all the containers in the freezer. When the water has frozen remove container from the freezer and allow the water to melt. Look closely at the rocks do you see any cracks? Repeat this process of freezing and thawing four to six times. Was your hypothesis right? Which type of rock has changed the most? Record your data and consider what would happen if you soaked the rocks overnight in the water before freezing. Would this make a difference in your results and Experiment Central, 2nd edition
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if so why? Consider that some rocks may absorb more water than others and therefore may have a higher water content upon freezing.
Design Your Own Experiment How to Select a Topic Relating to this Concept Rocks and minerals are
present in your daily life, from the rocks in the cement of our sidewalks to the minerals in bath powder. Choose a type of rock or mineral to study. Minerals used in household cleaning and rocks used in industry are just two leads you can investigate. Check the Further Readings section and talk with your science teacher or school or community media specialist to gather information on rock and mineral questions that interest you. As you consider possible experiments, be sure to discuss them with a knowledgeable adult before trying them. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Make drawings, graphs,
and charts to display your information for others. You might also draw conclusions about your findings. Which minerals seem to be the most common in your region? Why might that be? Related Projects If you are interested in rocks and minerals and want to
discover more of their uses in your daily life, you might investigate how rocks are used to prevent erosion or what consistency is the best for plaster, whose main ingredient is minerals. The possibilities are almost as endless as our supply of rocks and minerals. 978
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For More Information Barrow, Lloyd H. Adventures with Rocks and Minerals. Hillside, NJ: Enslow Publishing, 1991. Describes geological experiments. Chapters include what causes minerals to break and what freezing does to rocks. Cox, Shirley. Earth Science. Vero Beach, FL: Rourke Publications, Inc., 1992. Chapters include how to choose geology projects. GMB Services. RocksForKids. http://www.rocksforkids.com/ (accessed February 7, 2008). Information on rock formation, identification, and collection. Parker, Steve. The Earth and How It Works. North Bellmore, NY: Marshall Cavendish, 1993. Outlines a variety of projects and experiments that examine Earth’s composition. U.S. Geological Survey. Rocks and Minerals Site Contents. http://wrgis.wr.usgs. gov/parks/rxmin/index.html (accessed February 7, 2008). Provides information on rocks and minerals.
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arth, like all the planets in our solar system, is in constant motion. All of the planets revolve or orbit around the Sun. An orbit is when one object in the universe goes round another one without touching it. For Earth, it takes about 365 days to complete one orbit around the Sun. Without Earth’s rotation and orbit, the world would be a far different place. The rotation gives Earth its night and day. That allows the many life forms on Earth to remain at a comfortable temperature, warming during the sunlight hours and cooling down at the night. It affects the direction of wind and the ocean’s daily tides. The orbit and tilt of rotation also give Earth its four seasons. All the planets in the solar system also rotate, or spin, as they orbit the Sun. On average, Earth rotates once every 24 hours—or more precisely, 23 hours, 56 minutes, 4.091 seconds. The complete rotation of an object with respect to the stars is called a sidereal (pronounced sy-DEER-ee-awl) day. Renaissance rules Today’s knowledge of planets’ rotations and orbits evolved during the sixteenth and seventeenth centuries in what is known as the Renaissance age. Scientists at that time were building telescopes and were able to observe how celestial objects behaved in detail for the first time. In 1543 Polish astronomer Nicolaus Copernicus (1473–1543) published his theory that Earth spins on its axis once daily and revolves around the sun annually. The widespread belief at that time was that the Sun and other planets revolved around Earth. Copernicus’ theory caused great controversy and most people did not accept it. Some scientists did believe Copernicus however, including German astronomer Johannes Kepler (1571–1630). In the early 1600s Kepler worked out three laws that applied to planetary motion. One of the laws stated that Earth orbits the Sun in an elliptical path. With this knowledge, astronomers could predict the movement of other planets through observations and mathematical calculations. 981
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Each planet revolves as it orbits the Sun. GA LE GRO UP.
All of the planets in the solar system revolve, or orbit, around the Sun; the planets also rotate, or spin, as they orbit the Sun. GA LE GRO UP.
*Earth time Mercury Venus Earth Mars Jupiter
Saturn Uranus Neptune Pluto
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Around and around There are many orbits in the solar system. Planets and other objects orbit around the Sun. Moons orbit around their planets. The main reason why objects orbit around another object is due to gravity. Gravity is the force pulling all matter together. In the seventeenth century, English scientist Isaac Newton (1642–1727) realized the revolutionary idea of gravity when he was just twentythree years old. Newton explained that the force of gravitation makes every pair of bodies attract and applies to all objects in the universe. This gravitational force relates to why objects fall to Earth as well as the motion of the moon and the planets in orbit. (For further information on gravity, see the Force chapter.) The pull of gravity is stronger from heavier objects, and so lighter objects orbit the heavier one. The Sun is the heaviest object in the solar system. It is about a thousand times heavier than the largest planet, Jupiter, and more than 300,000 times heavier than Earth. The gravity of the Sun keeps Earth and all the planets in their orbits. The gravity of Earth pulls our Moon into its orbit around Earth. Why we spin All the planets in the solar system rotate on their axis. A planet’s axis is an imaginary line drawn through its Period of Period of center from the North to South Pole. The Earth’s revolution* rotation axis is tilted at a 23.45˚ angle from vertical. Other 88 days 59 days planets rotate at different angles. Except for Venus and Uranus, all planets rotate in the same direc225 days 243 days tion that they orbit the Sun—from west to east. 365 days 24 hours Earth’s continuous rotation began as the 687 days 25 hours planet was formed, an estimated 4.6 billion years ago. The solar system formed from clouds 12 years 10 hours of dust and gases that were spinning around the Sun. When these materials collapsed together 29 years 10 hours they formed a larger and larger object that eventually formed a planet. Since these materials 84 years 18 hours were already spinning, they began to spin faster as they collapsed inwards. This phenomenon is 165 years 18 hours similar to an ice skater spinning. When the ice skater brings his or her arms closer to the body, 248 years 6.4 days he or she will spin faster. Experiment Central, 2nd edition
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Astronomers theorize that a large object collided with the newly formed planet, setting Northern hemisphere experiences summer Earth spinning at a faster rate. The collision also may have tilted Earth’s axis to its 23.45˚ angle. The seasons are caused by this angle of rotation. Since the axis is tilted, different parts of the planet are oriented towards the Sun at different times of the year. For example when Earth is equator at a certain place in its orbit, the northern hemisphere (the half of the planet north of the equator, including the United States) is tilted toward the Sun. During this portion of Earth’s orbit, the northern hemisphere experiences the summer season. Six months later Earth is on the opposite side of the Sun. The northern hemisphere is tilted away from the Sun and experiences the winter season. The Earth spins continuously because there is no force in space to make it stop. One of the laws of motion states that a force is required to slow or stop a moving object. For example, when you roll a ball along the ground it will eventually stop due to the friction with the ground and the force of the air pushing against the ball. For Earth rotating on its axis, there is no force to counteract the rotation. That means it does not require any energy to keep it rotating. Rotation’s moving effects Earth’s daily tides are caused both by gravity and our planet’s spinning movements. Both the Sun and Moon produce a gravitational pull on Earth. Yet because the Moon is closer to Earth than the Sun, it has about double the gravitational force as that of the Sun, which means it has about double the influence on the tides. caused by centrifugal force As the Moon revolves around Earth, the earth and Moon are revolving together, like one unit, around a common point located within Earth. This point is called the center of gravity or the center of mass. At this center of gravity, the gravitational forces of Earth and the Moon pull out on each other equally. As the two objects rotate as one system, everything in and on Earth experiences centrifugal force. (While Experiment Central, 2nd edition
Northern hemisphere experiences winter
Sun
The tilt of the Earth on its axis, and its rotation, causes the four seasons. GA LE G RO UP.
Centrifugal force is caused by an object’s tendency to keep moving in a straight line. This outwardpull effect occurs in all rotating objects. GAL E GR OU P.
center of gravity
caused by gravitational pull
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Leaves fall from the trees in autumn as a prelude to the coming winter season. FI EL D M ARK PUB LI CAT IO NS.
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centrifugal force actually acts on all matter, only the water is free to move about.) Centrifugal force is actually not a force, but the absence of a force. A force is a push or pull. Centrifugal force is caused by an object’s tendency to keep moving in a straight line. This outward-pull effect occurs in all rotating objects. For example, when a car turns sharply the passenger will seem to be pushed to the outside of the curve. The centrifugal force that the rider is experiencing is not due to an actual push: The passenger’s body is trying to keep moving forward in the same direction. Centrifugal force causes Earth’s water to be pulled away from the center of the spin. On the side of Earth closest to the Moon, the Moon’s gravity is strong enough to overcome the centrifugal force. The total or net gravitational force is in the direction of the Moon and causes a bulge or tide that is pulled towards the Moon. (For further information on tides, see the Ocean chapter.) On the side of Earth opposite the Moon, the Moon’s gravity is not strong enough to overcome the centrifugal force. The net gravitational force is away from Earth, causing a second bulge or tide to occur on the opposite side of the Moon. At any one time there are two bulges of water of roughly equal size, one towards and one away from the Moon. Low tides are created in areas about halfway between these two high-tide bulges when the water withdraws. Curving around Another effect caused by Earth’s rotation causes large moving bodies on or above Earth’s surface to curve instead of moving in a straight path. Called the Coriolis force, this bending movement is named after French mathematician Gustave-Gaspard Coriolis. In 1835, he explained mathematically that this phenomenon is due to the object’s course relative to the rotation of Earth. The direction the object will curve depends on whether it is located north or south of the equator. In the northern hemisphere an object will turn to the right of its direction of movement; in the southern hemisphere, to the left. At the equator moving objects do not turn at all. Experiment Central, 2nd edition
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The circumference or distance around Earth at the equator is larger than it is at the poles. What Are the Variables? Since the whole Earth rotates once every 24 hours, the surface of the earth at the equator Variables are anything that might affect the moves faster than it does at the poles. People results of an experiment. Here are the main variables in this experiment: living at the equator might not feel it, but they are rotating at a rate of about 1,000 miles per • the length of the pendulum’s cord hour (1,609 kilometers per hour). As the equator • the amount of time the pendulum swings moves more quickly to the east than other points • wind on Earth, objects traveling away from the equaIn other words, the variables in this experiment tor are deflected to the east. are everything that might affect the pendulum’s The Coriolis force is a relatively weak one for swing. If you change more than one variable at most objects and is not noticeable. In large the same time, you will not be able to tell which objects that move over a length of time, the variable had the most effect on the pendulum’s swing. Coriolis force can have a significant effect. For example, winds naturally move in ways that equalizes their warmth. Warm winds located at the equator move towards cold air at the poles; cold air at the poles moves toward the equator. The Coriolis force causes these winds to follow a curved path as they move.
EXPERIMENT 1
The rotation of the Earth causes the Coriolis force. G ALE GR OU P.
Foucault Pendulum: How can a pendulum demonstrate the rotation of Earth? Purpose/Hypothesis In 1851, French physicist
Jean-Bernard-Leon Foucault (1819–1868) proved that Earth rotates on its axis through a demonstration with a pendulum. A pendulum consists of a free-swinging cord set at a fixed point with a weight hanging from it. A pendulum swings at a constant rate and direction if there is no force moving against it. Foucault hung a pendulum from a high ceiling and noted that the path of the pendulum’s swing slowing changed its direction of swing. Since there was no force acting on the pendulum, he concluded that Earth had to be rotating beneath it. Experiment Central, 2nd edition
Northern Hemisphere Equator Southern Hemisphere
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In this experiment you will make a simple Foucault pendulum. When a pendulum is moving freely in air, the air resistance causes the pendulum to slow down and eventually stop. A heavy weight and tall pendulum will reduce the effect of friction. (Foucault’s original pendulum consisted of a 62-pound (28-kilogram) iron ball suspended on a 220-foot (67-meter) steel wire.) You will use a bag of sand as the pendulum’s weight, and then note how the sand moves as it trickles from the bag. To observe results from the pendulum it should swing for at least 30 to 60 minutes. After that time, note the apparent change in the direction in which the pendulum is swinging. To begin this experiment, make an educated guess about the outcome of the experiment based on your knowledge of Earth’s rotation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
The first picture of Earth and Moon in a single frame, taken September 18, 1977, by Voyager 1. TH E NA TIO NA L AE RON AU TIC S AN D SP AC E ADM IN IS TRA TI ON.
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the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The lines of sand falling from the Foucault pendulum will shift slightly over time as Earth is continuously rotating.’’ In this experiment, the variable you will change is time. The variable you will measure will be the appearance of the pendulum’s swing. Level of Difficulty Moderate to Difficult (because of the difficulty in keeping the swing straight). Materials Needed
• 13 feet (4 meters) of nylon cord or strong string • cloth or canvas sack 986
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WORDS TO KNOW Axis: An imaginary straight line around which an object, like a planet, spins or turns. Earth’s axis is a line that goes through the North and South Poles. Centrifugal force: The apparent force pushing a rotating body away from the center of rotation. Circumference: The distance around a circle. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Coriolis force: A force that makes a moving object appear to travel in a curved path over the surface of a spinning body.
Gravity: Force of attraction between objects, the strength of which depends on the mass of each object and the distance between them. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Orbit: The path followed by a body (such as a planet) in its travel around another body (such as the Sun). Rotate: To turn around on an axis or center. Sidereal day: The system of time to measure a day based on the motion of the stars. Variable: Something that can affect the results of an experiment.
• ladder at least 12 to 15 feet (3.5 to 4.5 meters) high, high swing set, or other tall stable outdoor structure • fine, dry sand (available at hardware stores or greenhouses) • calm, nonwindy day • large garbage bag • watch or timer • tape • sharp nail • chair Approximate Budget $8. Timetable 75 minutes. Step-by-Step Instructions
1. Fill the sack with sand. Make sure there are no leaks in the bag by holding it over a clean surface and moving it gently. 2. Tie the open end of the sack together with the cord or string, and stand on a chair to hang the bag from the top of the ladder or other stand. You may need an adult’s help with this. Experiment Central, 2nd edition
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3. Use the nail to punch a small hole in the bottom of the sand bag. The hole should How to Experiment Safely be slightly larger than the tip of a pen, to allow the sand to fall out slowly. Hold the Make sure the pendulum stand you are using is bag up to make sure that sand drops out securely attached to the ground and will not tip over. Be careful when handling the sharp nail. at a visible rate. When it is flowing propAlso, be careful when you are attaching the erly, seal the hole with a piece of tape. string to the tall structure. Ask an adult to either 4. Lay out the garbage bag on the ground help you balance or attach the string for you. under and around the pendulum. 5. Make sure the bag of sand hangs straight down and is not tilted. If it is, adjust either the sack or the cord. 6. Keep the cord tight and pull the bag straight back about 4 feet (1.2 meters) high. Remove the tape and carefully set the pendulum in motion. Make sure you swing in a straight line and do not have an elliptical swing. 7. Over the next 45 to 60 minutes, carefully give the cord an extra swing when it slows down. Try to keep the pendulum swinging for 60 minutes. Make sure you simply push the swing in the direction Step 6: Carefully release the it is moving and do not shift the cord at all. This experiment may sack so that the pendulum take more than one attempt. moves in a straight line. GA LE GRO UP.
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Summary of Results Draw the pattern of the sand. Explain the results, including how the Coriolis force influences the direction of the sand lines. For example, a Foucault pendulum set in motion in the northern hemisphere traces out a line that is always shifted toward the right. How many degrees the pendulum shifts depends on where it is geographically located or its latitude. Latitude identifies the north-to-south position of a point on Earth The equator is 0˚ latitude; the north and south poles are each 90˚ latitude. At the equator the pendulum would not shift at all. At either of the poles the pendulum’s swing would complete a circle in about 24 hours. You can figure out the rate of rotation where you live by finding your latitude and figuring out the following equation through longhand or a Experiment Central, 2nd edition
Rotation and Orbits
calculator. Mathematically, the pendulum’s rate of shift is equal to the rate of rotation of Earth multiplied by the sine of the number of degrees of latitude: n = 360 degrees x sine (latitude), where n equals the number of degrees of rotation. The sine of latitude represents the angular distance of a place from the equator. Change the Variables By increasing the time you
keep the pendulum swinging, the more the sand lines will shift and the better you will be able to observe Earth’s rotation. You can attempt to find an even taller structure from which to hang your pendulum. Keeping the pendulum swinging manually is challenging because of any inadvertent shifting of the swing’s direction. One way to increase the swing time of a Foucault pendulum is to build a mechanical device that automatically pushes the cord back and forth. There are several such designs available. See the Further Readings section, talk to your teacher, or research the topic independently.
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The bag is moving in a circular, elliptical path. Possible cause: You may not have pushed the bag in a straight line for the first push or any subsequent pushes. Try practicing a straightline push with the tape on the bag, and then repeat the experiment. Problem: There was no shift in the lines of sand. Possible cause: You may have set the cord slightly off-kilter during one of your pushes, or the pendulum may not have swung long enough. Try practicing a straight-line push with the tape on the bag, and then repeat the experiment, making sure to keep the pendulum swinging for at least 60 minutes.
EXPERIMENT 2 Spinning Effects: How does the speed of a rotating object affect the way centrifugal force can overcome gravity? Purpose/Hypothesis The term centrifugal force comes from the Latin meaning ‘‘center-fleeing’’ or ‘‘away from the center,’’ which explains the outward movement of an object experiencing centrifugal force. Centrifugal force can overcome the effects of gravity. One of the factors that affect centrifugal force depends on the speed of rotation or an object’s velocity. The greater the speed of the object, the greater the force. In this experiment you will observe centrifugal force occurring with different velocities, and see how each overcomes the effects of gravity. You will measure the outward pull of water in a small container that is revolving. The faster you spin the container, the higher its velocity. You will spin the container at two different speeds, each for the same length of time. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of centrifugal force and gravity. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • length of string
This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
• speed of rotation
A hypothesis should be brief, specific, and measurable. It must be something you can test • mass of spinning object through further investigation. Your experiment will prove or disprove whether your hypothesis is In other words, the variables in this experiment correct. Here is one possible hypothesis for this are everything that might affect the way the water moves. If you change more than one experiment: ‘‘At higher speeds, the water will be variable at the same time, you will not be able to pushed further outwards.’’ tell which variable had the most effect on cenIn this case, the variable you will change is trifugal force. the velocity of a spinning object. The variable you will measure is the distance the water was pushed outwards. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable Step 5: Swing the container overhead. GA LE GRO UP. will change between the control and the experimental trials. Your control experiment will use no centrifugal force and, thus, will only have the effects of gravity. At the end of the experiment you can compare your observations from the control with the experimental trials. • shape of container
Level of Difficulty Easy. Materials Needed
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5 feet (1.5 meters) of string shallow Styrofoam or thin plastic cup single hole puncher clear area outside tape measure small cloth rag water watch with second hand partner Experiment Central, 2nd edition
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Approximate Budget $5. Timetable 20 minutes. Step-by-Step Instructions
How to Experiment Safely Be careful that your partner or anyone else is not too close when you are swinging the cup. You may get wet so wear the appropriate clothes.
1. Punch two holes on opposite sides of the plastic cup and thread the string through the holes. 2. Punch holes all around the sides of the container. 3. Stand in an open area outside and use an object to mark where you are standing. 4. Wet the rag with water until it is dripping wet, and place it in the cup. This is the control. Wait a few seconds and note your observations of what happens to the water. 5. Wet the rag again and replace it the container. Slowly swing the container in an arc until you get a slow circular motion over your head. 6. Have your partner time you and count the number of complete revolutions you make in 10 seconds. 7. Increase the speed of the revolutions and again count the number of revolutions you make in 10 seconds. 8. Find the mid-point of where the water landed in the circle for the first set of revolutions. Measure from that point to the mark where you were standing. Troubleshooter’s Guide 9. Repeat the measurement at the midpoint of where the water landed for the first Below is a problem that may arise during this higher-speed revolutions. experiment, a possible cause, and a way to Summary of Results Construct a chart with your
results and graph the data. Examine how the outward force of the water changes with the velocity of the spinning object. How does gravity affect the control experiment? The experimental setups? What does the velocity of the revolving container illustrate about the speed of rotation and planets? Experiment Central, 2nd edition
remedy the problem. Problem: The water stopped coming out of the container before the revolutions stopped. Possible cause: The rag may not have been wet enough. Try pouring a little water in the container to a point below where the holes start. Dump the rag in water, place it in the container, and repeat the experiment.
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Change the Variables To change the variables in this experiment you
can alter the weight of the revolving object. Fill up a container with different amounts of water and weigh each object before you start spinning. You can also change the spinning object to a solid material, such as a marble or a rock. Another variable that you can change is the length of the string.
Design Your Own Experiment How to Select a Topic Relating to this Concept The movements of
celestial objects have fascinated people long before there were any astronomical gadgets. For projects related to rotation and orbits, you can think about how the movements of the Sun and Moon have an effect on Earth. You can also visit a local planetarium to view how objects in our solar system move. Check the Further Readings section and talk with your science teacher to learn more about rotations and orbits of celestial objects. Remember that if you conduct a project where you observe celestial objects, never look directly at the Sun to avoid damage to your eyes. Steps in the Scientific Method To conduct an original experiment,
you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you
At any one time there are two bulges of water (or high tide) of roughly equal size, one towards and one away from the Moon. Low tides are created in areas about halfway between these two high-tide bulges. Here, boats docked near the shore are beached during low tide. # NI K W HEE LE R/C OR BI S.
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are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and drawings such as the one you did for the experiments in this chapter. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of the experimental setup, models of any celestial setup, and the results, which will help other people visualize the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are multiple projects related to the orbits and
rotations of celestial bodies. You can focus on the Moon’s orbit through the sky, recording its phases throughout a month and its effect on Earth. There are certain celestial bodies that are held together by mutual gravitational attraction, such as the Earth and the Moon. You can examine other planet-moon systems, determine the point at which the bodies orbit around, and map out the orbit of each body. Another factor relating to orbits is the relationship between the time it takes a planet to complete one orbit and its distance from the Sun. You can explore how mass and distance affect a celestial body’s orbit. Another project could be to focus on the basic shapes of planetary orbits. Each planet has its own unique orbital path; some are close to circular and others are far more elliptical. You can map out the paths of the orbits on paper or construct a model. To further explore tides, you could examine how the Sun impacts tides and map the high and low tides in your area. Ocean tides are not exactly twelve hours apart. Another Experiment Central, 2nd edition
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possible project is to explore what causes the time between tides, look up tidal information in a certain area, and then predict the high and low tides for the next month. Scientists have found that a planet’s rotation affects its shape. You can explore this principle on Earth and other celestial bodies. For a research project, you can look at the many people and discoveries that led to the understanding that Earth orbits and rotates around the Sun.
For More Information Arnett, Bill. The Eight Planets. http://www.nineplanets.org (accessed on February 16, 2008). Overview of the history, mythology, and science of the planets, moons and other objects in our solar system. ‘‘Coriolis Force.’’ Department of Atmospheric Sciences at the University of Illinois at Urbana-Champaign. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/ crls.rxml (accessed on February 16, 2008). Brief explanation of the Coriolis force with a video. Curious about Astronomy. http://curious.astro.cornell.edu/index.php (accessed on February 17, 2008). Clear answers to many astronomy questions and the chance to ask questions. Groleau, Rick. ‘‘What Causes the Tides?’’ PBS: Nova. http://www.pbs.org/ wgbh/nova/venice/tide nf.html (accessed on February 17, 2008). PBS’s Nova site illustrates the centrifugal force that causes tides. NASA Observatorium. http://observe.arc.nasa.gov/nasa/space/centrifugal/ centrifugal index.html (accessed on February 16, 2008). Detailed explanation of centrifugal force. National Aeronautics and Space Administration. The Space Place. http:// spaceplace.jpl.nasa.gov/en/kids/ (accessed on February 16, 2008). Answers to space related questions, activities, and clear space science explanations. Scagell, Robin. Space Explained: A Beginner’s Guide to the Universe. New York: Henry Holt & Company, 1996. Look at how the universe was created; includes lots of illustrations. Simon, Seymour. Our Solar System. New York: William Morrow & Co., 1992. Simple description of the origins, characteristics, and future of the solar system, with lots of illustrations.
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W
hat gives ocean water its salty taste? The answer lies in its salinity, the total salt content of the water. Saline (salty) substances are present in all water, even rain water, but sodium and chlorine are the two most abundant saline substances dissolved in ocean water.
Get out the yardstick In 1872, the H.M.S. Challenger began its worldwide ocean expedition from Portsmouth, England. On board were 240 sailors and scientists, including four naturalists and their support team. Originally built as a warship, the ship was converted into a floating scientific lab by the British government to study the biology of the sea, as well as the chemical and physical properties of the water. Between 1872 and 1876, the ship sailed 68,890 miles (110,908 kilometers) and made 492 stops. Nearly 5,000 new species, including giant worms and deep-sea shrimp almost as big as lobsters, were brought on board and identified.
In 1872, the crew of the H.M.S. Challenger were the first to measure ocean salinity. NO RTH WI ND P IC TUR E AR CH IVE .
Samples of seawater were also collected and analyzed for their chemical composition. The main substances present included bicarbonates and sulfates, as well as salts such as calcium, magnesium, potassium, sodium, and chloride. Sodium and chloride were the most abundant. While the samples showed that different salinity measurements existed, the average salinity of all the samples was about 3.5%, or 35 pounds (kilograms) of salt per 1,000 pounds (kilograms) of seawater. Scientists today still use this average salinity figure, and the Challenger’s salinity samples are still the only worldwide set of analyzed seawater. In fact, this voyage helped launch modern oceanography. John Murray, one of naturalists onboard, later supervised the publication of 50 volumes of Challenger Reports based on the expedition’s discoveries. 995
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WORDS TO KNOW Buoyancy: The upward force exerted on an object placed in a liquid. Calibration: To standardize or adjust a measuring instrument so its measurements are correct. Density: The mass of a substance compared to its volume. Density ball: A ball with the fixed standard of 1.0 gram per milliliter, which is the exact density of pure water.
Nansen bottles: Self-closing containers with thermometers that draw in water at different depths. Oceanography: The study of the chemistry of the oceans, as well as their currents, marine life, and the ocean bed. Salinity: The amount of salts dissolved in water. Specific gravity: The ratio of the density of a substance to the density of pure water.
Hydrometer: An instrument that determines the specific gravity of a liquid.
Standard: A base for comparison.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Variable: Something that can affect the results of an experiment.
The Red Sea has a salinity level of 27 percent. P ETE R A RN OLD INC .
Where did the salt come from? Millions of years ago, one ocean covered Earth. This vast ocean was just barely salty. Over time, land formed, and rain washed salt and minerals from the land into the ocean. Salt also came from rocks and sediments on the ocean floor, and from undersea volcanic activity that literally erupted salts into the water. All these accumulated salts made ocean water heavier, that is, gave it a greater density than fresh water. The discoveries made on the Challenger gave us an average salinity for oceans, but this number can vary quite a bit. For example, the Baltic Sea near Sweden has a salinity content of 1%; while the Red Sea near Egypt has a salinity content of 27%. Salinity increases through evaporation, which begins as the surface water of the ocean is warmed by the Sun. The heated water becomes water vapor and rises into the atmosphere, leaving the salt behind. Generally, waters in climates with strong sunlight and high temperatures, such as the region
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around the Red Sea, tend to have a higher salinity level because the surface water there evaporates at a faster rate. In the Baltic Sea region, rain, fresh water from adjoining rivers, and melting ice keep the salinity level low. The colder weather there also reduces the evaporation rate. Getting the evidence Two instruments used to analyze ocean water are hydrometers, which measure seawater density, and Nansen bottles. Nansen bottles are more sophisticated versions of those collection bottles used on the H.M.S. Challenger. The bottles are self-closing containers with thermometers; they can draw in water at different depths. Through their use, scientists have learned that the sea has different layers of water with specific salinity levels and temperatures. In the two experiments that follow, you will learn more about salinity by measuring it in different ways.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of water in the sample • the amount of salt in the water • the temperature of the water • the accuracy of the hydrometer measurements In other words, the variables in this experiment are everything that might affect the specific gravity of the water. If you change more than one variable at a time, you will not be able to determine which variable had the most effect on the specific gravity.
EXPERIMENT 1 Making a Hydrometer: How can salinity be measured? Purpose/Hypothesis In this experiment, you will create a scientific
instrument called a hydrometer. A hydrometer is used to measure the specific gravity of water, comparing the density of one water sample to that of pure water. Pure water has a density of 1.000 grams/milliliter. If any salts or chemicals are added, they will dissolve and their added mass will increase the density of the water. This will increase the specific gravity. The greater the specific gravity, the greater the salinity. A hydrometer works on the Archimedes Principle of buoyancy, which states that a liquid exerts an upward buoyant force on an object equal to the amount of liquid displaced by the object. Thus if an object floats partially submerged in water, the downward weight of the object must be counterbalanced by the upward buoyant force, which is equal to the weight of the water displaced. Otherwise, the object would sink to the bottom. If you add salt to the water, the downward weight of the object will displace less water because the water is now denser—that is, it has more Experiment Central, 2nd edition
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mass for a given volume. As a result, the object will float higher in the water, with less of it submerged. If you place measurement graduations along the surface of the object where the water touches, you have created a hydrometer. The hydrometer measurements can then be equated to the specific gravity, and in turn to the amount of salt in the water, or salinity. To begin the experiment, use what you have learned about salinity to make a guess about what will happen to the specific gravity of water when salt is added. This educated guess is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Steps 1 and 2: Making a hydrometer. GA LE G RO UP.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The more salt in the water, the higher its specific gravity.’’ In this case, the variable you will change is the amount of salt in the water, and the variable you will measure is the water’s specific gravity. If the specific gravity increases with an increase in salt, your hypothesis is correct.
Materials for Experiment 1. GAL E GR OU P.
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Level of Difficulty Moderate/difficult because
accurate measurements and adjustments are required. Materials Needed
How to Experiment Safely Be sure to handle glass carefully.
• one 1-quart (1-liter) graduated cylinder filled with distilled water at room temperature • one 5-inch (12.7-centimeter) test tube • one 6-inch (15.2-centimeter) glass rod • 1 rubber test tube stopper with a single hole that fits the glass rod • 2 tablespoons (30 milliliters) sand • 1 to 3 cups (250 to 750 milliliters) table salt • small amount of petroleum jelly • fine tip permanent marker • measuring spoons • stirring rod
Steps 3 to 8: Hydrometer in graduated cylinder of distilled water with different water levels marked. GA LE GRO UP.
Approximate Budget $0 to $10. Ideally, you can borrow most of the materials from school. Ask your science teacher for help. Timetable About 1 hour. Step-by-Step Instructions
1. Place a small dab of petroleum jelly on the end of the glass rod. Push the glass rod through the stopper until it reaches the bottom of the stopper. 2. Place a pinch or two of sand into the test tube and place the stopper into it. You have made a hydrometer. 3. Place the test tube hydrometer into the graduated cylinder of distilled water. 4. Add or remove some of the sand from the test tube until the hydrometer floats vertically in the water with approximately 1 inch (2.5 centimeters) of the glass rod above the water. Experiment Central, 2nd edition
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5. Use the marker to write 1.000 on the glass rod at the level of the surface of the water.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The test tube does not float vertically in the water. Possible cause: There is not enough weight in the bottom of the tube to keep it upright. Use more sand or substitute a denser material instead of sand, such as small roller bearings.
6. Remove the hydrometer from the water and stir in 3 tablespoons of salt. This is equivalent to about 3.5 ounces (100 grams) of salt. Stir until all of the salt is dissolved. 7. Place the hydrometer in the water and mark the new water level. It should be lower on the rod because the water is denser and the hydrometer is now floating slightly higher. The increased water density, compared to the density of pure water, means the salty water has a higher specific gravity.
8. Add another 3 tablespoons of salt and mark the water level again. The hydrometer should float even higher in the water as the density (and specific gravity) of the water increases. Summary of Results Study the marks on your hydrometer. Do they
support your hypothesis? Did the specific gravity increase each time you added more salt to the water? What does this tell you about the salinity of the water? Write a paragraph describing and explaining your results. Change the Variables You can change the variables in this experiment in
several ways. For example, you can chill the water by placing it in a refrigerator to determine the effect of water temperature on salinity. You could also use a different kind of salt—for example, potassium chloride instead of sodium chloride.
EXPERIMENT 2 Density Ball: How to make a standard for measuring density Purpose/Hypothesis This experiment is designed to create a standard.
A standard is an object or instrument that has a fixed value. In this experiment, you will create a standard for measuring the density of a solution, called a density ball. A density ball has the fixed standard of 1.0 gram/milliliter, which is the exact density of pure water. You will then 1000
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determine if your standard can accurately indicate if a water sample’s density is greater than or How to Experiment Safely equal to pure water. This experiment is similar to Experiment Be sure to handle glass safely. #1, except here you will determine density by watching whether the density ball standard is suspended or floats. To begin the experiment, use what you know about the density of pure water to make an educated guess about how a density ball will work. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘By creating a standard for the density of pure water, you will be able to determine whether a solution has a density greater than or equal to 1.0 gram/milliliter.’’ In this case, the variable you will change is the amount of salt in the water, and the variable you will measure is how your density ball reacts to changes in density. If your density ball accurately predicts whether a water sample is greater than or equal to the density of pure water, you will know your hypothesis is correct. What are the Variables? Variables are anything
Materials for Experiment 2. GAL E GR OU P.
that might affect the results of an experiment. Here are the main variables in this experiment: • • • •
the amount of water in the sample the amount of salt in the water the temperature of the water the behavior of the density ball
In other words, the variables in this experiment are everything that might affect the density reading indicated by the density ball. If you change more than one variable, you will not be Experiment Central, 2nd edition
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able to determine which variable had the most effect on the density reading. Level of Difficulty Moderate, because delicate adjustments are required for this experiment. Materials Needed
• one 1-quart (1-liter) graduated cylinder filled with distilled water at room temperature • one 5-inch (12.7-centimeter) test tube • 1 rubber test tube stopper without a hole • 2 tablespoons (30 milliliters) sand • 1 to 2 cups (250 to 500 milliliters) salt • measuring spoons • stirring rod Step 4: Test tube freely suspended in water. G AL E GRO UP.
Approximate Budget $0 to $10. See if you can
borrow the lab materials from your science teacher. You probably have salt and perhaps sand at home. Timetable 30 minutes. Step-by-Step Instructions
Step 4: What to do if test tube sinks to bottom or floats to surface. GA LE GRO UP.
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1. Place a pinch or two of sand in the test tube. 2. Place the stopper in the opening of the test tube securely. This is your density ball. 3. Place the test tube into the graduated cylinder of distilled water. 4. Wait 15 to 20 seconds and note where the test tube is positioned. If it is suspended freely in the water without floating to the surface or sinking to the bottom, it has the same density as water at room temperature: 1.0 gram/milliliter. If the test tube sinks to the bottom, remove some sand and try again. If it floats to the surface, add some sand. Experiment Central, 2nd edition
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5. Remove the test tube and stir 3 tablespoons—about 3.5 ounces (100grams)— of salt into the water. 6. Place the test tube back into the water and note its position. (It should float now because the added salt makes the water denser than the ball.) Summary of Results Did your density ball indi-
cate the density of the water and support your hypothesis? Write a paragraph explaining what you have learned during this experiment. How did your density ball behave in different solutions? What does this tell you about the solutions?
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The test tube sinks and rests on the bottom. Possible cause: The test tube is too heavy. Remove a pinch of sand from it and try again. Problem: The test tube floats at the surface. Possible cause: The test tube is not heavy enough. Add a pinch more sand and try again.
Change the Variables You can change the vari-
ables and conduct other similar experiments. For example, try your 1.0 grams/milliliter standard density ball in another liquid, such as corn oil or vinegar, to determine if those liquids are more or less dense than pure water. How is the density of these liquids affected if you add salt?
Design Your Own Experiment How to Select a Topic Relating to this Concept If you are interested in
salinity or its effects, there are many fascinating experiments you can explore. For example, how is salt used in the human body? Why does salt cause metal corrosion? How do marine animals adapt to their environment? These are all possible questions you can explore. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on salinity questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of the materials or procedures might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Experiment Central, 2nd edition
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Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts that are labeled and easy to read. You may also want to include photos, graphs, and drawings of your set-up and results. When working with salinity, you may be able to set up your experiment as a demonstration model. Do not forget to share what you have learned about salinity. Related Projects You might do an experiment on how salinity affects
plants. Another possibility is to find the corrosion rate on metals exposed to salts. You may also want to explore the use of salts in chemistry and manufacturing. Be sure to talk with your teacher before starting a project.
For More Information ‘‘Deep Ocean Creatures.’’ Extreme Science. http://www.extremescience.com/ DeepestFish.htm (accessed on March 14, 2008.) Nice pictures and facts on deep ocean creatures. Lambert, David. The Kingfisher Young People’s Book of Oceans. New York: Kingfisher, 1997. Includes nine ocean topics with related subjects. Describes how the oceans formed and the composition of seawater. ‘‘Ocean Water: Salinity.’’ Office of Naval Research. http://http://www.onr.navy. mil/Focus/ocean/water/salinity1.htm (accessed on March 14, 2008). Brief explanation and animation of the tides. Rothaus, Don P. Oceans. Chanhassen, MN: The Child’s World Inc., 1997. Describes the characteristics of the world’s oceans including the chemistry of seawater.
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W
hen you encounter a problem, how do you solve it? Do you consider what you already know about the problem, think of a possible answer, and then see if your answer is correct? If so, you are using the scientific method. The scientific method is a way of carefully collecting evidence about a question or problem, using that evidence to form a possible answer, and then testing the answer to see if it is accurate. You can use this method as a tool for solving problems in science class and in many other areas of your life. For example, it could help you figure out why your pencils keep disappearing, how to wrap your sandwich so it does not dry out by lunchtime, or why your dog no longer likes his favorite food. What are the steps in the scientific method? The scientific method has six steps, described below. They will help you solve all kinds of problems, in and out of school. Step 1: State a problem or ask a question. Step 2: Gather background information. Step 3: Form a hypothesis. Step 4: Design and perform an experiment. Step 5: Draw a conclusion. Step 6: Report the results.
Step 1: State a problem or ask a question. To begin using the scientific method, think about the world around you. You may see something that makes you curious, such your sandwich drying out by lunchtime on some days but not on others. You might see an unexplained light in the sky. You might hear a statement that you are not sure is true. For example, a friend might tell you that wearing glasses makes your eyes become weaker. Put your curiosity into the form of a problem or question, such as these: • Why does my sandwich dry out some days but not others? • What is that light in the sky? 1005
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• Does wearing glasses make your eyes weaker?
You do not have to be a scientist to use the scientific method. PH OT O RE SEA RC HE RS I NC.
Step 2: Gather background information. Read more about the problem or question. Observe it closely. Step 3: Form a hypothesis. Now use what you know about the situation to think of a possible answer for your question. This answer, or guess, is your hypothesis. A hypothesis is an idea in the form of a statement that can be tested by observations and/or experiment. You will use what you already know about the situation to form a hypothesis. Here are possible hypotheses to answer the questions above: • Plastic bags that seal keep more moisture in bread than waxed paper or plastic bags without seals do. • That light in the sky is an airplane. • Wearing glasses does not make your eyes become weaker. All of these hypothesis are testable: You can make observations, do research, or set up experiments to determine whether each hypothesis is correct. Here are some examples of hypotheses that are vague and untestable: • Sandwiches taste better when you seal them in plastic bags. How can you measure ‘‘taste better?’’ • The light in the sky might be a reflection or something. How can you measure ‘‘might be’’ or ‘‘something?’’ • Wearing glasses might make your eyes weaker, if you wear them long enough. How long is ‘‘long enough?’’ The ancient Greeks often hypothesized about the causes of natural events. However, they assumed they could figure out the correct explanations just by thinking about the situation long enough. They usually did not experiment to find out whether their explanations were accurate. Aristotle, a famous Greek philosopher, developed theories that led to many discoveries, but his theories were based mostly on reasoning, not experimentation. For example, he hypothesized that the flies that he found on rotting fruit just appeared out of the air. He did not experiment to find out whether his hypothesis was true. Step 4: Design and perform an experiment. In this step, you go beyond the ancient Greeks: you prove or disprove your hypothesis. You might be
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Hypotheses: Is the light in the sky just an airplane—or something else? PHO TO RE SE AR CHE RS I NC .
able to establish whether your hypothesis is accurate by research, such as checking the local airport to see if an airplane flew over your house at a certain time last night. Or you might gather expert opinions about how wearing glasses affects people’s eyesight. For the sandwich problem, the best approach is an experiment. An experiment is a controlled observation. The experimenter carefully changes one condition at a time, such as the type of sandwich wrapping, and observes what happens. In most experiments, a control experiment is set up with the same conditions as the actual experiment. The conditions remain the same in the control experiment but are changed in the actual experiment, one condition at a time. If something happens only in the actual experiment and not in the control, it is clear that it was caused by changing a condition in the actual experiment. The control experiment for our sandwiches might be leaving a slice of bread unwrapped to see what happens to it and comparing it to those in various wrappings. Conditions that change during an experiment and affect the results are called variables. The variables in our sample experiment include the type of bread, how fresh it is, the size of the piece of bread being wrapped, any fillings used with the bread, the length of time the bread is wrapped, the temperature of the wrapped bread during the experiment, and the type of sandwich wrapping. Only one variable is changed at a time during Experiment Central, 2nd edition
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Is your sandwich still fresh at lunchtime? K ELL Y A . QU IN.
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the experiment. The variable being changed is called the independent variable, which in our experiment is the type of sandwich wrapping. What might happen if we change two variables at a time, such as wrapping wheat bread with waxed paper and putting rye bread in a sealed plastic bag? If the rye bread is fresher than the wheat bread at the end of the experiment, we cannot be sure which variable is the cause—the type of bread or the type of wrapping. The condition that changes during an experiment is called the dependent variable. In our example, the dependent variable is the amount of moisture in the bread. Results of experiments must be measurable, so we need a way to measure this moisture. We decide to weigh each slice of bread before and after the experiment. The difference in the weight would be the amount of moisture that evaporated. Experiments must also be repeatable. We must write down our procedure and follow it carefully, so that someone else could carry out the same procedure and see if the same results occur. Step 5: Draw a conclusion. The next step in the scientific method is to graph or chart our results, analyze them, and determine whether our hypothesis was correct. For some experiments, we might have quite a bit of data to analyze. For our sample experiment, we compare the loss in weight of each bread slice after the wrapping is removed. What is our conclusion? Did our results support our hypothesis? Even if the results did not support our hypothesis, we have learned something just by asking the question and doing the experiment. Often there is no ‘‘right’’ answer when we use the scientific method. Instead, we simply gather more information about the problem, which is valuable in itself. Step 6: Report the results. Reporting our results allows other scientists to build on our work—and to repeat our experiment to see if they get the same results. Without the sharing of results, little scientific progress would be made. Scientists publish their findings in scientific journals as a way of sharing what they have learned. In the two experiments that follow, you will use information you gather to identify mystery powders, and you will use the scientific Experiment Central, 2nd edition
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WORDS TO KNOW Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Dependent variable: The variable in an experiment whose value depends on the value of another variable in the experiment. Experiment: A controlled observation.
Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/or experiment. Independent variable: The variable in an experiment that determines the final result of the experiment. Scientific method: Collecting evidence and arriving at a conclusion under carefully controlled conditions. Variable: Something that can change the results of an experiment.
method to prove or disprove Aristotle’s hypothesis that fruit flies appear out of thin air.
EXPERIMENT 1 Using the Scientific Method: What are the mystery powders? Purpose/Hypothesis In this experiment, you will begin with three mys-
tery powders and ask yourself, ‘‘What are these powders?’’ Then you will gather information from a chart that shows how three kinds of powder react when mixed with water, iodine, and vinegar. Next, you will hypothesize the identity of each mystery powder. Then you will test how each powder reacts with water, iodine, and vinegar. You will compare your results with the chart and draw a conclusion about the identity of each powder. Then you will know whether your hypothesis was correct. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Level of Difficulty Easy/moderate. Experiment Central, 2nd edition
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Materials Needed
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the purity of the sample of each powder • the amount of water, iodine, and vinegar that is added to each powder • the accuracy of your observations In other words, the variables in this experiment are everything that might affect how each powder reacts to the water, iodine, and vinegar.
• 3 ounces (85 grams) of baking soda in its original container • 3 ounces (85 grams) of cornstarch in its original container • 3 ounces (85 grams) of flour in its original container • 6 small labels • 6 small dishes • 3 spoons • water • iodine (the kind used to prevent infections) • vinegar • eye dropper
• black paper • magnifying lens • goggles or other eye protection Approximate Budget Up to $10; most materials available in the average
household. Timetable Approximately 30 minutes. Step-by-Step Instructions
1. Turn three of the small dishes upside down and attach a label to each bottom that says baking soda, cornstarch, or flour. 2. Turn the three dishes right side up. 3. Put about 3 ounces (85 g) of the powder on the label (baking soda, cornstarch, or flour) into each dish. Make sure the amounts are equal. After the dishes are filled, you should no longer be able to read the labels on the bottom. 4. Move the dishes around until you no longer know which powder is which. (You might ask another person to do this while you wait in another room.) 5. Add a label to the side of each dish that says A, B, or C. 6. Gather information by studying Table 1 (see illustration). Notice how each powder looks or feels and how it reacts with water, iodine, and vinegar. Iodine will turn a powder black if the powder 1010
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7.
8.
9. 10.
11.
contains starch. Vinegar, an acid, will make a powder bubble or fizz if the powHow to Experiment Safely der is a base. The acid and base react with each other to produce carbon dioxide. Wear goggles to prevent the iodine, vinegar, or Create a table similar to the one illusany of the powders from getting in your eyes. Never taste substances you are using in an trated above. You will fill in the table as experiment. you test each powder. Pour a small amount of Powder A on the black paper, and carefully observe it with the magnifying lens. Repeat with Powders B and C. Do you notice any slight variations in color or any other differences? Add your observations to Table 2. Feel each powder, rinsing your hands after touching each one. Record your observations on Table 2. Based on your observations, make a hypothesis about the identities of Powders A, B, and C. Remember that a hypothesis is a clear, testable statement of your educated guess about the identity of the unknown powders. Here is a possible hypothesis: ‘‘Powder A is baking soda. Powder B is flour. Powder C is cornstarch.’’ Fill an empty dish with about 2 ounces (60 ml) of water. Add about 12 ounce (14 grams) of Powder A and stir with a spoon. Notice whether the powder dissolves in the water and the water
Step 6: Table 1, Characteristics of Three Powders G AL E GR OU P.
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12.
13. 14. 15.
16.
17.
remains clear, or whether the powder does not dissolve and the water becomes cloudy. Record your observations in Table 2. Throw away the powder sample you just tested. Rinse and dry the spoon and small dish. Use the same spoon and dish each time you test Powder A. Repeat Steps 11 and 12 with Powder B and Powder C, using the other two dishes. Record your observations. Place about 12 ounce (14 grams) of Powder A into its empty dish. Use the eye dropper to add 1 to 2 drops of iodine to Powder A. Observe what happens and record the results in your table. If Powder A contains starch, the iodine will turn it black or purple. Repeat Steps 14 and 15 with Powder B and Powder C. When you are finished, rinse out the eye dropper. Record what you observed in Table 2. Repeat Steps 14 and 15 with each of the powders, adding 1–2 drops of vinegar this time. Add your observations to Table 2. If the powder is a base, the acidic vinegar will mix with it and form fizzling carbon dioxide gas.
Summary of Results Compare the results in Table 2 with the character-
istics in Table 1. Can you use your test results to establish the identity of
Step 7: Create a Chart of Reactions for Experiment 1. GAL E GR OU P.
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each powder? Then pick up each dish of powder and read the label on the bottom. Were you correct? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables You can vary this experi-
ment in these ways:
Troubleshooter’s Guide Below is a common problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: All of the powders reacted the same in the tests.
• Use other powders, such as salt, granuPossible cause: Your samples might have lated sugar, or powdered sugar. become contaminated if the spoon, dish, and eye dropper were not cleaned before each test. • Set up the experiment for someone else, This contamination will affect your test results. perhaps a younger student, and see if he Try the experiment again, being careful to keep or she can identify a mystery powder you your equipment clean. have selected. • With an adult’s help, place a sample of baking soda, cornstarch, and flour, separately, on a square of aluminum foil and heat the sample with a candle. Notice which powders melt and which turn black. Use this information to help identify mystery powders. Step 15: Add 1 to 2 drops of iodine to Powder A. G AL E • Mix each powder with a little water and GR OU P. test it with red and blue litmus (pH) paper. If the powder is acidic, blue litmus paper will turn red. If the powder is basic, red litmus paper will turn blue. If the paper does not change color, the powder is neutral. This test provides one more characteristic to help identify the powders.
EXPERIMENT 2 Using the Scientific Method: Do fruit flies appear out of thin air? Purpose/Hypothesis In this experiment, you
will test Aristotle’s assumption that fruit flies are created spontaneously—from nothing. You will determine whether the flies are present in all air and can appear anywhere or whether they are attracted from other places by rotting fruit. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the ripeness of the banana slices (this variable will be controlled by taking all the slices from the same banana) • the temperature of the air around both sets of banana slices (flies are more active in warm temperatures) • whether the container with the experimental slices is tightly sealed • the opportunity for flies to be attracted to the fruit (in a sealed, air-conditioned room, flies are unlikely to be near enough to be attracted to the bananas) The independent variable, the one you will change, is whether the bananas are in a sealed container or exposed to the air around them. The dependent variable, the one you will measure, is the presence or absence of fruit flies.
First, form a hypothesis about the outcome of this experiment based on your understanding of fruit flies and bananas, the fruit you will use in this experiment. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is a possible hypothesis for this experiment, one that Aristotle thought was true: ‘‘Fruit flies will appear on bananas even if they are kept in a covered container.’’ In your experiment, you will place several slices of a ripe banana in a covered container. As a control experiment, you will leave several other slices of the same banana exposed to the air. If flies appear on both the covered and the exposed banana slices, you will know that your hypothesis is correct.
Level of Difficulty Easy/moderate. Materials Needed
• • • • • • •
1 very ripe banana, unpeeled, with no obvious rotten spots clear container that can be completely sealed small, shallow bowl table knife magnifying lens water for cleaning the banana a warm, shaded area outside (or a warm area inside that is near a window or door)
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Timetable 15 minutes to set up; five minutes to
record observations each day for a week to 10 days.
How to Experiment Safely
Step-by-Step Instructions
Ask permission before beginning this experiment, as it is likely to attract flies. Handle the table knife with caution.
1. Gently rinse the unpeeled banana to clean off any fly eggs that might already be on it. 2. Peel the banana, and use the table knife to cut it into about ten slices. 3. Put half of the slices in the clear container and seal it tightly. 4. Put the rest of the slices in the uncovered, shallow dish. 5. Place the sealed container and the shallow dish in a warm, shady spot, outside if possible. 6. Starting the next day, use the magnifying lens to check for fruit flies. Record your observations in Table 3 each day for seven to 10 days, or until flies appear.
Summary of Results Study the data on your table and decide whether your hypothesis was correct. Did flies appear in the sealed container? Did they appear on the slices in the shallow dish? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. If your hypothesis was not supported, what did you learn?
Steps 3 and 4: Place some slices in a covered container, and more in an uncovered container. GA LE GRO UP.
Step 6: Observe containers for the presence of fruit flies. GAL E GRO UP.
Change the Variables Here are some ways you
can vary this experiment: • Use a different kind of fruit or try raw meat, such as hamburger. • Put both containers in a warmer or a cooler place to see how that affects the results of the experiment. • Put a banana that has obvious rotten areas on it inside a sealed container to see if flies appear from eggs already on the banana. Experiment Central, 2nd edition
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Modify the Experiment You can often change
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: Flies appeared on the slices in the sealed container. Possible cause: The banana must have already contained fly eggs. Try the experiment again, choosing a banana that is not so ripe and rinsing it thoroughly before you start. Problem: No flies appeared anywhere. Possible cause: The area around your experiment is just too clean! Try placing both containers outside, if the weather is warm, or inside in a place that is well traveled. Both containers must be exposed to the same environment.
the level of difficulty of an experiment by adding to or simplifying it. Sometimes, this involves altering your hypothesis. Whenever you modify an experiment, make sure that you still isolate only one variable at a time. You could add another part to this experiment, for example, by testing the theory of spontaneous generation among different items. Are there certain items that attract organisms more than others? It may help you understand why the theory of spontaneous generation was believed for so long. Test a series of items, preferably outside in a warm environment. You can test food items, such as an apple or soda, along with other items, such as a plastic cup. Make sure each item is clean. For each item, your control will be the same clean item sealed in a clear container.
Make a note of your results in a chart, noting the food item and any organisms that appear. You could also try to isolate what part of the item attracted the organisms. For example, if ants began hovering around a cookie, you can isolate the different items in the cookie (sugar, flour, milk) and see which of the items attracts the ants again.
Table 3 for Experiment 2. GA LE GR OU P.
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Design Your Own Experiment How to Select a Topic Relating to this Concept You can explore many
questions using the scientific method. What has always intrigued you? For example, you could use this method to see which brand of a product gets the best results, which studying techniques help you or others learn more, or how long microwave popcorn should cook in order to pop all the kernels and burn none. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some materials or procedures are dangerous to use. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure which question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In your unknown powder
and fruit fly experiments, your raw data might include tables, drawings, or photographs of the changes you observed. If you display your experiment, make clear the question you are trying to answer, the variable you changed, the variable you measured, the results, and your conclusions. Explain what materials you used, how long each step took, and other basic information. Related Projects You can undertake a variety of projects related to the
scientific method. For example, you might find out how much sunlight a day produces the fastest growing seedlings, which kind of software is the Experiment Central, 2nd edition
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easiest to learn how to use, or how to speed up the life cycle of a fruit fly. Many, many of the questions that occur to you can be answered using the scientific method!
For More Information Gardner, Robert. Science Projects about Chemistry. Hillside, NJ: Enslow Publishers, 1994. Describes many science projects, including separating and identifying substances and detecting unknown solids. VanCleave, Janice. A+ Projects in Chemistry. New York: Wiley, 1993. Outlines many experiments and includes information about the scientific method.
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S
hells are familiar sights in nature. In general, a shell is a hard protective covering that encloses a variety of animals and fruits. Eggshells protect unborn birds. Plants produce seeds that have coverings to keep their fruit and seeds safe. Coconuts and peanuts are example of shelled foods. Insects have an exoskeleton, a hard outer covering, which protects their bodies. Seashells are the shells, or protective coverings, of marine animals. Shells from the sea come in all sizes, shapes, and colors and house a variety of animals. To understand seashells, we need to look at the animals that made them.
Who has shells? Animals such as birds, fish, reptiles, and mammals have internal skeletons or backbones that provide structure and support to protect the animal. There are also animals that have a hard outer covering or shell to protect their soft bodies from predators. Snails, crabs, and lobsters are animals with an outer shell. These animals are called invertebrates and they have an exoskeleton (or external skeleton), like many insects. Most invertebrates do not have an internal skeleton or backbone. Exceptions to this include tortoises and turtles, who have both an internal skeleton (backbone) and an outer shell. The largest group of shelled creatures is the mollusks. Mollusk means ‘‘soft-bodied.’’ There are approximately 75,000 species of mollusks, which include the snail, oyster, and octopus. These animals have evolved over time to live in many different environments. The snail, for example, is a mollusk that lives in the ocean, freshwaters, and on land. (Slugs are similar to snails except they do not carry a shell.) Most mollusks have shells with the exception of the octopus, squid, and slug. Mollusks can be grouped into many categories depending upon the characteristics of the animal. Some of the more common categories are the gastropod and bivalve. Gastropod comes from the Greek words ‘‘foot’’ and ‘‘stomach.’’ Snails are gastropods and in their spiral shaped 1019
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One type of mollusk is the invasive zebra mussels, a bivalve mussel. AP PHO TO/ U. S. D EPA RT ME NT O F AG RI CUL TU RE.
Some of the more common categories of mollusks are the gastropod and bivalve. IL LUS TR ATI ON B Y TE MA H NE LS ON.
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shell they use their foot (the fleshy part of their body that protrudes from the shell) to propel themselves forward. Bivalve uses the prefix ‘‘bi,’’ which means two, because bivalve organisms have a two-part shell. The two shells in a bivalve connect to cover the animal. Common bivalves are the clam, oyster, and scallop shells. Another group of animals that have a hard shell-like outer covering is the crustaceans. Crustaceans are invertebrates. They have a segmented body with a hard exoskeleton. Some common crustaceans are crabs, lobsters, crayfish, and shrimp. How shells are made The shells of gastropods and bivalves are made of calcium carbonate. Mollusks take in calcium that they find in their environment from food and the water they live in to create their shell. When baby mollusks hatch from their eggs, they have a tiny shell that grows with them. They use a part of their body called the mantle (soft tissue that is located between the shell and its inner organs) to continually produce layers of calcium carbonate crystals to their shell. Adding calcium carbonate enlarges and strengthens the shell. Each species of mollusk forms a shell with a unique shape and color. However, within a particular species there are differences in shells due to the environment, food, and climate. For example, color differences among shells can be due to the diet of the animal that lives inside it and the water quality of its environment. The shells of crustaceans are made out of a substance called chitin. When lobsters, crabs, and other crustaceans hatch from eggs, they are born with a hard layer of skin that serves as an exoskeleton. A chitin exoskeleton is strong yet flexible, allowing the animals to move their legs and claws. Crustacean shells are segmented to cover the entire body but also allow for moveBivalve ment, much like a suit of armor. As the crustacean grows, it sheds the old skin and grows a new one. This shedding process is called molting. An adult lobster will molt his skin yearly. During this molting time a crustacean is vulnerable to Experiment Central, 2nd edition
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WORDS TO KNOW Bivalve: Bivalves are characterized by shells that are divided into two parts or valves that completely enclose the mollusk like the clam or scallop.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Internal skeleton: An animal that has a backbone.
Calcium carbonate: A substance that is secreted by a mollusk to create the shell it lives in. Chitin: Substance that makes up the exoskeleton of crustaceans. Camouflage: Markings or coloring that help hide an animal by making it blend into the surrounding environment.. Crustacean: A type of arthropod characterized by hard and thick skin, and having shells that are jointed. This group includes the lobster, crab, and crayfish. Exoskeleton: A hard outer covering on animals, which provide protection and structure. Gastropod: The largest group of mollusks; characterized by a single shell that is often coiled in a spiral. Snails are gastropods.
Invertebrate: An animal that lacks a backbone or internal skeleton. Mantle: Soft tissue that is located between the shell and an animal’s inner organs. The mantle produces the calcium carbonate substance that create the shell of the animal. Mollusk: An invertebrate animal usually enclosed in a shell, the largest group of shelled animals. Molting: A process by which an animal sheds its skin or shell. Shell: A hard outer covering that protects an animal that lives inside. Variable: Something that can affect the results of an experiment.
predators as its outer shell is not yet hardened. In order to protect itself, the crustacean will often hide until its shell is hard. Shells for survival Shells provide many ways that help the soft bodied animals inside them survive. The hard exterior shell is an obvious protection from a predator but the shape of the shell is also useful to the mollusk. Some shell shapes are designed to make it easy to burrow into the sand to hide. There are bivalves with deep ridges in the shell that helps the shell anchor itself to the bottom of their environment. Other shells grow long spiny spikes that collect seaweed and help to hide the animal. Shells are often used as camouflage. They often blend into their environment appearing the same color as sand or rocks. The cowry shell is a brightly colored shiny shell whose animal is also brightly colored but with a different pattern. When threatened by a predator the animal will retreat into its shell, thus confusing the predator. Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of shell • the force with which the wood is dropped • the height of the wood block In other words, the variables in this experiment are everything that might affect the amount of water the plant draws in or out of its cells. If you change more than one variable, you will not be able to tell which variable affected the shell breaking.
Shells are vital to the existence of the animals that live inside them. In the experiment and project to follow, you will test the strength of two different shells and classify various seashells. The activities will highlight the characteristics unique to shells, and help you think of your own experiments relating to seashells.
EXPERIMENT 1 Shell Strength: Which shell is stronger: a clam shell or lobster shell? Purpose/Hypothesis A strong shell offers an
animal protection from other animals and the environment. Clam shells and lobster shells are In this case, the variable you will change is the composed of two different types of materials. A type of shell. The variable you will measure is clam shell is primarily made of calcium carbowhich shell breaks first. nate. A lobster shell is made of chitin, a type of carbohydrate, along with protein. A clam shell is formed over time by the mollusk that lives inside it and the lobster shell is repeatedly replaced as the lobster grows. The A lobster is a crustacean. # BRO WN IE H AR RI S/C OR BI S. clam shell is hard and rigid and can become thick. The lobster shell is a segmented hard skin-like covering with some flexibility at the joints. Given the properties of these two shells, what shell do you think is stronger? In this experiment, you will test the strength of both shells by dropping a weight onto the shells from various heights. The weight will be a block of wood, and you will create a pulley system to repeatedly and evenly drop the wood. The shell that remains intact the longest from the weight dropping is the stronger shell. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of shells and material strength. This educated guess, or prediction, is your 1022
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hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
How to Experiment Safely Have an adult help you nail together the pieces of the pulley system. If you need to cook a lobster, have an adult help with the cooking and meat extraction.
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The wooden block will cause the clam shell to break first as it is more rigid than the lobster shell.’’ Level of Difficulty Moderate/difficult (due to the materials and building
the pulley system). Materials Needed
• lobster shell tail, fresh with lobster meat extracted (available from fish markets, who may give you the tail shell for free) When purchasing lobster try to have the store steam it. If this is not possible then you will need an adult to help you steam or boil the lobster and remove the meat prior to the experiment. • clam shell, approximately 2–3 inches (5–7.5 centimeters) in width (use found shells or available from online stores) • 4 pieces of wood, about 28 inches (71 centimeters) long, 2 inches (5 centimeters) wide, and 1 inch (2.54 centimeters) in depth • 1 piece of wood, 18 inches long, 1 inch wide, and 1 inch in depth • block of wood, about 7 inches (18 centimeters) long, 3 inches (7.5 centimeters) wide, and 1 inch in depth • 1-inch pulley (available at hardware stores) • string, about 6 feet (1.8 meters) • 1 screw hook • marker • 1 foot (0.3 meters) of thin wire • 2 nails Experiment Central, 2nd edition
Building the pulley. IL LU STR AT IO N BY T EM AH NE LS ON.
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• hammer • pliers (to cut and secure wire) Gastropod
Bivalve
Size
Other
Approximate Budget $20–30 (use found shells
and scrap wood if possible).
Color
Timetable Approximately 45 minutes.
Weight
Step-by-Step Instructions 1.) Building the
Geography
pulley: Use the chart to track your findings. I LL UST RA TI ON BY T EM AH NE LS ON.
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3. 4. 5. Step 2:1: Mark a line on the string at the point you want to stop. I LL UST RA TI ON BY
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1. Use the four long pieces of wood (28 x 2 x 1) to build two pieces shaped like the letter ‘‘A.’’ For each wood ‘‘A.’’ shape, cross the ends of two pieces of wood over each other and secure them together with a nail. Take the length of wood measuring 18 x 1 x 1 and place it across the two ‘‘A.’’ frames at the top. Secure both ends of this piece of wood onto the ‘‘A.’’ frames using wire and pliers. You should now have a frame that will stand by itself on a table. Attach the pulley to the middle of the frame at the top with another piece of wire. Take the block of wood and attach the screw hook in the middle of the width of the block. The block should hang down lengthwise. Take the string and pull it through the top of the pulley. On one end tie a knot with a loop in it. Attach the block with the screw hook onto this loop. You should now have a block of wood attached to a string that runs through the pulley.
T EM AH NE LS ON.
2.) Testing for strength: 1. Place a clam shell directly under the block of wood. Pull the string against the edge of your work table to raise the block of wood about a third of the way up from the bottom of the pulley. Mark a line on the string at the point you want to stop. The exact height does not matter as you have the mark so that it is repeatable. 2. Release the string to let the wood drop. Note the results. 1024
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3. Repeat this step with the lobster shell, pulling the string to the same mark to Troubleshooter’s Guide drop it from the same height. 4. If neither shell is broken, place the clam Here are some of the problems that may arise shell under the block of wood again. Pull during this experiment, some possible causes, and ways to remedy the problems. the string against the edge of your work table to raises the block of wood about Problem:The clam shell did not break. two thirds of the way up from the bottom Possible cause: The clam shell could be too large of the pulley. Mark a line on the string. and thick, try a smaller shell. The height of the 5. Release the string to let the wood drop. block when dropped was too low, try a higher Note the results. height. Change the position of the shell, make 6. Repeat this step with the lobster shell, sure that it is directly under the wooden block. pulling the string to the same mark to Problem:The lobster shell breaks too easily. drop it from the same height. Possible cause:The lobster was too dry. Use the 7. If neither shell is broken, drop the block lobster shell within 24 hours of when the meat is from a higher point on both shells. removed. Repeat the same process of dropping the wood block, pulling the string against the edge of the table to raise the block of wood about two thirds of the way up. 8. If the shells are still intact, raise the block to the top of the pulley. Continue dropping the block, counting each drop, until each shell breaks. Note the number of times it took to break. Summary of Results What were your results? Was your hypothesis
correct? Consider how the strength of a shell can help an animal survive. Do you think there could be a negative side to having a strong shell? Write a paragraph of your findings. You may want to chart your results.
Step 2:2 Release the string to let the wood drop. ILL US TRA TI ON BY T EMA H NE LS ON.
PROJECT 2 Classifying Seashells Purpose/Hypothesis In this project, you will
gather found and/or purchased seashells and classify them given what you already know about seashells. When scientists classify a group of animals, rocks, or in this case seashells, they are looking for similarities in the animals that Experiment Central, 2nd edition
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live in the shell or in the shell itself. Classification is important because it means that there is a universal system for identifying or naming something. You will group the shells into categories: gastropod, bivalve, crustacean, and echinoderms. You will then classify each of the groups into its characteristics. If you come across a shell that is difficult to classify, conduct some research about the shell and determine where it belongs. Level of Difficulty Easy/moderate Materials Needed
• 30–50 shells, found and/or purchased, try to find shells of all shapes and sizes (available from online seashell sellers or from your own collection). • poster board • containers: glass canning jars and shoe boxes work well • gram scale (optional) • tape measure(optional) Approximate Budget $15 for purchasing shells; $0 if use found shells. Timetable one to two hours to sort through and organize shells by characteristic. Consider this project as an ongoing hobby that you can continue as you find and collect new shells. Step-by-Step Instructions
1. Find a large space, table or area on the floor and spread out all the shells. 2. Organize the shells by shape. Determine if the shell falls into one of the four categories below: gastropod, bivalve, crustacean, or echinoderm • Gastropod: Cone-like or spiral shell. • Bivalve: Two shells that are identical and hinged together to form a complete covering for the animal that lived inside. • Crustacean: Hard outer covering that is segmented with flexible joints. • Echinoderm: Spiny or spiky outer covering of animal like a sea urchin or live sand dollar. Star fish are unique in that they have five distinct arms, like a star. 3. Put aside any shells that do not fit into the four categories. 1026
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1 2
4. Separate each of the groups into smaller groups of the animals that lived inside the shells, such as snails, clams, scallops, and crabs. 5. There are many ways you can further classify the shells in each group. You can group them by:
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• Size: Use a tape measure to determine the length of the shells; for the volume you can measure the amount of water each shell holds. • Color: If there is more then one color, categorize by the main color or you can group by patterns. • Weight: Weigh each on a gram scale. • Geography: Separate the general location of where the shell was found, such as in the Northeast or Southeast of the United States.
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Step 5: Use a tape measure to determine the length of the shells. I LLU STR AT IO N BY TEM AH N EL SON .
6. You can display your shells by gluing them to paper and writing the name of the shell or type of shell under it. You can also group them by type into containers: jars or boxes. Summary of Results Examine the physical characteristics of the shells in
each groups. Do some shells have ridges, for example, and others do not? Choose how to display each category of shells, on a poster board or in containers. Consider what each characteristics tells about the group of shells. Write what you know about each type of shell. Researchers still have many questions about seashell characteristics. You can look to see if your questions are some of the same questions scientists are exploring.
Design Your Own Experiment How to Select a Topic Relating to this Concept Seashells are products of
their environment. Consider why and how different environments yield different shells. Water temperature and acidity, types of shoreline: sandy vs. rocky are just some of the factors that can affect a shell’s development. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on seashells and questions that interest you. Experiment Central, 2nd edition
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Seashells
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results It is important to docu-
ment as much information as possible about your experiment. Part of your presentation should be visual, using charts and graphs. Remember, whether or not your experiment is successful, your conclusions and experiences can benefit others. Related Projects Seashell formation and characteristics encompass animals, the environment, geography, and other sciences. There are many experiments and projects you can do to get more information about seashells. For instance, scientists are finding that some scallop shells have ridges that can determine the age of the shell and the environment the shell lived in, such as water temperature. Also, you could consider how shells differ by geography and why. Do warmer waters produce more or fewer shells, or different colored shells? You can also explore how increased carbon dioxide in the atmosphere could affect the acidity of the oceans and its resulting effect on seashells.
For More Information Arthur, Alex. Shell. New York: Alfred A. Knopf, 1989. Provides a good overview of different types of shells focusing on aspects of camouflage and collection ‘‘Conchologists of America, Inc.’’ COA Kid’s. http://www.conchologistsofamerica. org/kids/inicial/default.asp (accessed May 23, 2008). Facts, games, and activities on shells. Dance, S. Peter. The World’s Shells. New York: McGraw Hill Book Company, 1976. A guide for collectors of the world’s shells. 1028
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National Geographic. Science and Space. http://science.nationalgeographic.com/ science/earth (accessed May 23, 2008). Provides up to date articles on the oceans and seashells San Diego Natural History Museum. ‘‘Frequently Asked Questions about Marine Invertebrates.’’ Marine Invertebrates. http://www.sdnhm.org/research/marine inverts/marifaq.html (accessed May 23, 2008). Answers to basic questions about seashells and collecting shells.
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Separation and Identification
M
ost natural and manufactured materials are mixtures, not pure substances. In a mixture, each of the substances has its own chemical properties. Salt water, gravel, and cookies are a few examples of mixtures. People can use physical means to separate mixtures into their component parts. Separating mixtures is important because it allows people to identify the substances that make up the mixture. Separating the components in a substance is usually one of the first steps in identifying its components. All mixtures can be separated and identified by the distinguishing chemical or physical properties of the components. The separation technique chosen depends on the type of mixture and its characteristics. After a mixture is separated, one or all of its components can be identified. Researchers can match the properties of the unknown substance to those properties of a known substance. Appearance and the way the unknown substance reacts with other substances are ways to identify a substance. Separation and identification techniques are used for all types of different purposes. If there are pollutants in the water, scientists first separate and identify the pollutants to clean the water. Forensic scientists, people who work in criminal investigations, use the techniques to identify evidence, such as fabrics or blood. Research scientists will separate unknown biological samples to identify the molecules in the sample. In blood tests doctors may need to identify and then separate iron or another component out of the blood.
Mixing it up Anything a person can combine is a mixture. Mixtures with varying compositions are called heterogeneous, meaning that they have different appearance and properties at different points in the mixture. For example, a mixture of oil and water is a heterogeneous mixture. The two substances form layers because of their different chemical properties, and one part of the mixture will have a higher concentration 1031
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When mixed together, oil and water form a heterogeneous mixture. Here, a layer of olive oil floats atop a layer of water. # K ELL Y A . QU IN.
Doctors often need to separate and identify components in patients’ blood—for example, iron—in order make a diagnosis. # TO M AN D DE E A NN M CCA RT HY/ CO RB IS.
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of oil, while another part of the mixture will have a higher concentration of water. Solutions are a type of mixture in which all the substances are evenly distributed, or homogeneous. A solution has the same appearance and properties throughout the entire mixture. When sugar is mixed into a cup of hot tea, for example, the sugar molecules dissolve and are spread evenly throughout the cup. The sugar-tea mixture is a solution. The sugar molecules are called the solute molecules. The substance it dissolved in, the tea water, is called the solvent. Separating by size Size is one method used to separate many simple mixtures. If the parts of a heterogeneous mixture are large enough, the mixture can be separated by hand or by a sieve. A sieve has holes in it that are small enough for some of the solid substance or substances to pass through and the larger particles will remain above the holes. Soil, for example, is sifted through a sieve to separate out the chunks of rock and gravel from the fine soil particles. Filtration is a commonly used separation technique similar to a sieve except it separates undissolved solid particles from a liquid. In filtration, a mixture passes through a filter, a material with spaces in it that holds back the particles. Filters are used frequently to clean water, make coffee, and purify air. Other simple separation techniques include settling and evaporation. Settling is when the larger, heavier components will sink or settle to form distinct layers. When muddy water sits for a period of time, for example, the dirt will sink to the bottom. In evaporation, the liquid is heated until it becomes a gas and leaves behind the solid particles. Separating by speed One widely used method that scientists use to identify the parts in a solution is known as chromatography. Chromatography is a technique that separates components based on the rate each moves over a specific material. Each component has properties that determine its movement. Chromatography has many uses. It is commonly used in Experiment Central, 2nd edition
Separation and Identification
laboratories to isolate new compounds, analyze water solute oil solute differences between environmental samples, and molecules molecules identify drugs from urine or blood samples. In chromatography, a gas or liquid mixture travels over an unmoving substance. The unmovcoffee ing substance chosen depends on the type of mixsolute molecules ture. Paper chromatography is one of several types of chromatography that are all based on the same principles. In paper chromatography the unmovHeterogeneous Homogeneous ing substance is paper. The components in the mixture move at different rates over the paper In a homogenous mixture, based on their attraction to the paper. Some large-sized components may solute molecules are evenly stick to the paper and hobble along; other small-sized components may glide distributed; in a heterogeneous over the paper and travel quickly. For example, to separate the colors in a mixture, molecules are dye, the dye is made into a preparation. A spot of the dye preparation is unevenly distributed and can be visually distinguished from placed on the end of a piece of chromatography paper. Different colors that one another. GAL E GR OU P. make up the dye then travel at varying rates along the paper. Paper chromatography is one of the most basic types of chromatography. Other types include gas chromatography and liquid chromatography. Gas chromatography has a gaseous mixture while liquid chromatography uses liquids. Each is used in many ways including detecting explosive materials, analyzing fibers and blood, and testing water for pollutants. What is it? Over the years scientists have gathered and compiled the many properties of individual substances. To identify an unknown substance in a mixture, scientists try to match the properties of the unknown substance to those of known substances. While there are numerous properties used in identification, there are some routine techniques that test for common properties. A substance’s shape and color is one of the first pieces of evidence scientists note. Its solubility or its ability to dissolve in another substance is another first step in identification. Because water is a common and known substance, it is the standard for many tests. A substance that dissolves in water is called soluble in water, and one that does not is called insoluble in water. Another common method used to identify a liquid is to determine its pH, or the measure of its acidity. The pH scale goes from 0 to 14. The lower the pH, the more acidic the solution. For example, lemons are acidic and so would have a lower pH than soaps, which are basic. At the midway point, where the pH is 7, the substance is neutral. Water is an example of a neutral substance. Experiment Central, 2nd edition
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The effect of heating a substance can also provide several pieces of information. The temperature where a solid substance turns into a liquid is called its melting point. The temperature where a liquid turns into a gas is called its boiling point. Different substances also give off unique colors when placed in a flame. Potassium, for example, gives off a violet flame when heated in a flame; sodium emits a yellow-colored flame. In the following two experiments, you will use separation and identification techniques to identify a mixture.
EXPERIMENT 1 Chromatography: Can you identify a pen from the way its colors separate?
A chromatography machine is commonly used in laboratories to isolate new compounds, analyze differences between environmental samples, and identify drugs from urine or blood samples. CUS TOM
Purpose/Hypothesis Chromatography is a common technique used to identify substances, from drugs in blood samples to a type of pen used in a crime. The word chromatography comes from the Greek word chromato, which means color.
In this experiment, you will use paper chromatography to separate the colors out of four different types of black ink. The color black is a mixture of several colors. Different types of pens mix together varying amounts of colored inks to produce black ink. Once the colors are separated you will have a partner select one of the black pens as
M ED IC AL S TOC K PH OT O
A pH scale ranges from 0 to 14 and is used to determine a solution’s acidity. With 7 being neutral, a pH of 0 is the highest acid value and a pH of 14 is the highest base value. GA LE
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Water
Bases
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WORDS TO KNOW Boiling point: The temperature at which a substance changes from a liquid to a gas or vapor. Chromatography: A method for separating mixtures into their component parts (into their ‘‘ingredients’’) by flowing the mixture over another substance and noting the differences in attraction between the substance and each component of the mixture. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Filtration: The mechanical separation of a liquid from the undissolved particles floating in it. Heterogeneous: Different throughout. Homogenous: The same throughout. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Mixture: A combination of two or more substances that are not chemically combined with each other and that can exist in any proportion. pH: A measure of a solution’s acidity. The pH scale ranges from 0 (most acidic) to 14 (least acidic), with 7 representing a neutral solution, such as pure water. Solubility: The tendency of a substance to dissolve in some other substance. Solute: The substance that is dissolved to make a solution and exists in the least amount in a solution; for example, sugar in sugar water. Solution: A mixture of two or more substances that appears to be uniform throughout except on a molecular level. Soluble: A substance that can be dissolved in some other substance.
Insoluble: A substance that cannot be dissolved in some other substance.
Solvent: The major component of a solution or the liquid in which some other component is dissolved; for example, water in sugar water.
Melting point: The temperature at which a substance changes from a solid to a liquid.
Variable: Something that can affect the results of an experiment.
the unknown. You will then identify the unknown pen based on the pattern of the colors. Paper chromatography identifies the parts of a mixture by first treating the paper with a solvent, a liquid that can dissolve other substances, and then observing how those substances travel different distances over the paper. How far each substance travels depends on the attraction it has for the paper. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of chromatography and separation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment • type of paper will prove or disprove whether your hypothesis is • time allowed for separation correct. Here is one possible hypothesis for this • concentration of alcohol and water experiment: ‘‘Different colors will separate out • type of ink used in the pens from each other by traveling different distances In other words, the variables in this experiment on the stationary phase. The pattern of the separe everything that might affect the ink colors arated colors can then be used for identification.’’ moving over the paper. If you change more In this case, the variable you will change is the than one variable at the same time, you will not be able to tell which variable had the most type of black ink. The variable you will measure is effect on color separation. the pattern of how the ink’s colors separate. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental trials. Your control experiment will use an ink of one color, either red or blue. Level of Difficulty Moderate to Difficult. Materials Needed Step 8: Experiment 1 setup. Make sure the ink dots are not submerged in the liquid. G ALE
• 4 paper coffee filters • pencil
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control
Pen #1 Pen #2
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• 4 different kinds of black pens, permanent ink • red or blue pen (control) • 91% isopropyl alcohol • water • ruler • measuring cups • 2 small glasses about 4 inches (10 centimeters) tall • 3 paperclips • scissors • marking pen Experiment Central, 2nd edition
Separation and Identification
Approximate Budget $10. Timetable 2 hours.
How to Experiment Safely
Step-by-Step Instructions
Be careful when handling alcohol; do not ingest it and keep it away from your face.
1. Cut the coffee filter paper into four strips measuring 2 inches by 4 inches (5 centimeters by 10 centimeters). One paper will hold the control ink, one the unknown ink, one the two black inks, and one the other two black inks. 2. Assign each of the four black pens a number, 1 through 4. 3. On each strip of paper, draw a line about 0.75 inches (2 centimeters) from the end of the paper with a pencil (NOT a pen). This end will be the bottom of the strip. 4. To separate the four unknown pen inks: Take two of the strips of filter paper. On the pencil line, about 0.5 inches (1.3 centimeters) Step 14: Different types of pens in from the edge of the paper, make a large dot with Pen 1. The mix together varying amounts of dot should be about the size of an eraser on a pencil. On the same colored inks to produce black ink. Measure from the top of every new pencil line on the opposite edge of the paper make a dot with Pen color to the pencil line to determine 2. Use the pencil to label each dot below the line (between the line how far the separate colors traveled and the bottom of the strip) with the pen number. (For example, up the strip G AL E GR OUP . the dot made with pen number 1 should be labeled ‘‘1.’’) On a fresh strip of filter paper, repeat this process for Pen 3 and Pen 4. 5. To separate the control ink: On the pencil line in the middle of a fresh strip of paper, make a large dot with the control ink. The control is a single color ink of red or blue. Label the dot ‘‘Control.’’ 6. Stir together ¼ cup (60 milliliters) of the top of alcohol with ¼ cup (60 milliliters) of color #2 water. Pour this mixture into each of the two glasses so that the liquid sits below top of color #1 the 2-centimeter line. It should be about halfway to the line. Unknown Pen 7. Straighten the two paperclips. Push one paperclip carefully through the top (the end without the dots) of two labeled Experiment Central, 2nd edition
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strips of paper, and push the second paperclip through the top of the third Troubleshooter’s Guide strip of paper. 8. Rest each straightened paper clip across Below are some problems that may arise during this experiment, some possible causes, and the top of one glass, with the bottom of some ways to remedy the problem. the paper strips hanging down into the liquid. There will be two strips of paper in Problem: The spot disappeared off of the paper. one glass and a third strip of paper in the Possible cause: The liquid level is too high and is over the line. The ink dot could have dissecond glass. The ink dots should be close solved into the liquid. Repeat the experiment to the surface of the liquid, but NOT with less liquid in the glass, making sure the submerged in it. dots are not submerged in the liquid. 9. Wait 30 minutes. Problem: The ink spot does not spread. 10. While you are waiting, turn away and Possible cause: The ink is not soluble in the liquid. have a partner select one of the four pens Repeat the experiment using a different type tested. This will be the ‘‘Unknown’’ ink. of ink. 11. To separate the unknown ink: On the pencil Problem: The black ink did not separate into its different components. line in the middle of a fresh strip of paper make a large dot with the unknown pen. Possible cause: The paper may not be able to separate all the components. Repeat the Label the dot ‘‘Unknown.’’ Push a straightexperiment using a filter paper of a finer grade ened paperclip carefully through the top. or of a different weave. You can also purchase 12. Remove the first three strips of paper after chromatography paper from a lab supply house. the 30 minutes, and rest the paperclip Problem: The unknown ink did not match any holding the ‘‘Unknown’’ pen along the of the inks already separated. top of one of the glasses. This strip should Possible cause: There may have been a probalso sit in the liquid 30 minutes. lem during the experiment for any of the reasons above, or you may have changed 13. Allow the first three strips of paper to dry more than one variable, which is the (about 30 minutes). When the unknown unknown pen. Check that the mixture prepink has been submerged for 30 minutes, aration was given the same amount of time to remove and let dry. move up the paper. Make sure the paper was 14. For each of the known inks, measure the same. If you prepared a different mixture preparation, that could also have altered the from the top of every new color to the results. Repeat the experiment, making sure pencil line to determine how far the septhat all the other variables are equal. arate colors traveled up the strip. Write your results in a table, noting the description and measurement for the four pens. 15. Repeat the measurements for the separated colors of the unknown ink. Identify the unknown pen by comparing its measurements and pattern to the four black pens. 1038
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Summary of Results Examine the results of the table compared to that of
the unknown pen. How closely does the unknown pen match the pattern of one of the inks? Scribble a few lines with each of the black pens and label the scribble with the associated pen number. Compare each of the pen’s patterns with its associated color black. Can you see a difference between the shades of each black pen? Look at the color of each black pen again and re-examine the table. Evaluate whether the black inks that appear more similar also have a greater likeness in their patterns. Change the Variables Changing some of the variables may lead to
interesting results. Try changing the type of paper you are using to a coffee filter paper or a finer grade of white paper. You could also change the mobile phase. Try using water without adding alcohol or alcohol without adding water. Mix the two in different amounts and record what your results. You can also change the color and types of pen you use.
EXPERIMENT 2 Identifying a Mixture: How can determining basic properties of a substance allow you to identify the substances in a mixture? Purpose/Hypothesis Because the components in a mixture keep their
own chemical properties, scientists can identify the substances in a mixture by knowing the properties of its components. In order to identify a substance, its components are isolated and tested. In this experiment, you will determine different properties of several substances that are similar in appearance. You will then have a partner create a mixture with two of the substances. Using the properties of the substances that you determined, you will identify the composition of the mixture. The substances you will use are three household items: flour, sugar, and baking soda. The properties you will determine for each substance are its appearance, solubility in water, solubility in vinegar, and pH. To determine pH you will use red cabbage. The chemicals that give red cabbage its red/purplish color also can act as a pH indicator. The red cabbage pH indicator does not determine an exact pH number, but it can distinguish between acid (pH of 0 to 6), neutral (pH near 7), and base (pH of 8 to 14). When the juice of red cabbage is added to an acid, such as vinegar or lemon juice, it will become pink to red; when it is added to a Experiment Central, 2nd edition
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base, it will turn blue or green. If the solution turns purple, it indicates that the substance is What Are the Variables? neutral, neither an acid nor a base. To begin this experiment make an educated Variables are anything that might affect the guess about what you think will occur based on results of an experiment. Here are the main variables in this experiment: your knowledge of mixtures. This educated guess, or prediction, is your hypothesis. A hypothesis • the substance should explain these things: • the solvent • the topic of the experiment • the quantity of each component in the • the variable you will change mixture • the variable you will measure • the temperature of the solvent • what you expect to happen • the pH indicator A hypothesis should be brief, specific, and In other words, variables in this experiment are measurable. It must be something you can test anything that might affect the identification of through further investigation. Your experiment the components in the mixture. If you change will prove or disprove whether your hypothesis is more than one variable, you will not be able to tell which variable impacted the determination correct. Here is one possible hypothesis for this of the substance’s properties and, thus, the experiment: ‘‘A mixture can be identified by mixture’s composition. determining the properties of the individual substances in the mixture.’’ In this experiment the variable you will change will be the substances that might possibly make up the mixture. The variable you will measure will be the mixture’s properties. Level of Difficulty Moderate. Materials Needed
• • • • • • • • • • • • 1040
clear plastic cups (at least six, as many as twenty) water vinegar white flour (about a cup) white sugar (about a cup) baking soda (about a cup) measuring spoons measuring cups mixing spoons red cabbage sealable sandwich bag knife Experiment Central, 2nd edition
Separation and Identification
• measuring cups • marking pen
How to Experiment Safely
Approximate Budget $12.
Be careful when handling alcohol; do not ingest it and keep it away from your face. Handle the knife carefully when cutting. Even though you are working with food products, never ingest any of the experimental solutions because one might contain alcohol. Throw away each solution in the sink and clean the cups thoroughly if you are going to reuse them.
Timetable 2 hours. Step-by-Step Instructions
1. Prepare a chart with four columns down and four rows across. Label the columns with the headings of ‘‘Flour,’’ ‘‘Sugar,’’ ‘‘Baking Soda,’’ and ‘‘Unknown.’’ Label the rows: ‘‘Appearance,’’ ‘‘Soluble with water,’’ ‘‘Soluble with vinegar,’’ and ‘‘Acid/Base/Neutral.’’ 2. Label one clear plastic cup ‘‘Flour,’’ a second ‘‘Sugar,’’ and a third ‘‘Baking Soda.’’ The cups may be reused throughout the experiment by rinsing them thoroughly with water and drying. 3. Put 1 teaspoon of each of the three substances in the appropriate plastic cup. 4. Record the color and description of the substance’s appearance on the chart (for example, powder, grainy, etc.)
Flour
Sugar
Baking Soda
Unknown
Appearance Soluble with Water Soluble with Vinegar Acid, Base, or Neutral
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Step 1: Prepare a chart to record the results of Experiment 2. GAL E GR OU P.
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Step 5: Stir completely before you note if the mixture is soluble or not soluble G AL E GRO UP.
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5. Add ¼ cup (about 60 milliliters) of water to each of the cups and stir vigorously for 30 to 60 seconds. Allow the mixtures to stand for 15 minutes, then record whether each substance is soluble in water. If the solvent is clear it is soluble; if the solvent is cloudy and most of the substance remains at the bottom of the cup, it is insoluble. 6. In a clean cup, repeat Step 4 and Step 5, using vinegar in place of water. 7. Prepare a pH indicator: Chop red cabbage into small pieces and measure ½ cup of the pieces. Put the pieces into a sealable sandwich bag. Add ½ cup (about 120 milliliters) of very warm water to the cabbage. Close the bag and mix gently by squeezing. Let the water and cabbage sit for five minutes, mixing occasionally. Pour the purple water into a separate plastic cup. 8. In a clean cup, add 1 teaspoon of each of the substances into the appropriate cup. 9. Place 2 teaspoons (10 milliliters) of the purple pH indicator into each of the three cups and stir. Note whether the substance is an acid (solution turns pink to red), a base (solution turns blue or green), or neutral (solution remains purple). 10. Turn away and have a partner mix two of the three substances together, using 2 tablespoons of each of the substances into a clean cup. Have your partner write down the two substances he or she selected. 11. Follow the procedures in Steps 4 through 9 to test the mixture for the properties defined in the chart. (You can use the same pH indicator made in Step 7.) For example, after recording the appearance of the mixture, add vinegar and stir the mixture to determine if it is soluble in water, and so on. Remove 1 teaspoon of the mixture each time you test for a specific property.
FLOU Sugar
Summary of Results Use the data you have collected for each property to identify which of the substances made up the unknown mixture. When you have reached a conclusion check with your partner. How did each of the properties enable you to narrow down the identification of Experiment Central, 2nd edition
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the mixture? Hypothesize how a mixture of another two substances would have reacted. Record your results and list the steps you took to identify your mixture. Change the Variables There are numerous ways you can change the variables in this experiment. You can use different food substances that have the same powdery appearance as the ones given. Cream of tartar, powdered sugar, and cornstarch are some examples. You can change the look of the materials completely and use any substances that appear similar. You can also examine how other liquids react with these substances. Make sure you change only one variable at a time for each test, and keep careful records of your results.
Design Your Own Experiment
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: Some of the substance will not dissolve. Possible cause: The mixture may need to be stirred further, or more solvent should be added to the substance. Repeat the test, stirring the solution thoroughly. Problem: The solvent has turned a slight color. Possible cause: The substance you are using may not be pure and some small part of the substance may be soluble in the solvent. Make sure you are using pure white flour and white sugar, and repeat the test. Possible cause: You may not have rinsed the cups thoroughly. Repeat the test, washing the cup again or using a fresh plastic cup.
How to Select a Topic Relating to this Concept
Separation techniques and identification are used in many professions for a variety of reasons. Wherever there is a mixture, there is some way to separate it. Check the Further Readings section and talk with your science teacher to learn more about separation and identification. You can examine the CRC Handbook of Chemistry and Physics, listed in Further Readings, which provides detailed tables of chemicals’ behaviors and characteristics. Using this book as a guide could provide ideas on how to separate and identify substances. If you construct a project that uses heat or flames, make sure you have adult supervision. Steps in the Scientific Method To conduct an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Experiment Central, 2nd edition
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Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include charts and graphs such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. For any unknown substance you may want to have a sample out so that people can note the characteristics of the substance. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Separation and identification is a broad topic that can
branch out to many projects. You can use paper chromatography to analyze the makeup of other liquid mixtures, such as candy or the pigments in vegetables. To identify the makeup of solid substances, you can examine rocks and minerals. Rocks are made of minerals and minerals each have specific properties. Certain minerals will dissolve in an acid like vinegar, for example, and others will not. You can also explore how different fields of study use separation and identification techniques, and what techniques they use. You can select one profession to focus and conduct an experiment related to that area of study. Or you can research the many techniques and uses used by a range of professions. For example, the biotechnology field performs separation techniques on many biological substances to identify the molecules. Astronomers use separation and identification techniques to analyze any chunks of rocks or other materials that have landed on Earth from space. Examples of other professions you can explore include art conservators, archaeologists, and food scientists. 1044
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For More Information BBC. ‘‘Mixtures.’’Mixtures. Schools. Science: Chemistry. http://www.bbc.co.uk/ schools/ks3bitesize/science/chemistry/elements com mix 6.shtml (accessed on February 18, 2008). Basic information on the chemistry of mixtures. Kurtus, Ron. ‘‘Mixtures.’’ School for Champions. http://http://www.school for champions.com/chemistry/mixtures.htm (accessed on February 18, 2008). Basics of mixtures versus compounds. Lide, David R, ed. CRC Handbook of Chemistry and Physics, 83rd edition. Boca Raton, FL: CRC Press, 2002. This authoritative reference provides properties of chemical substances. ‘‘Separating and Purifying.’’ Journal of Chemical Education. http://jchemed.chem. wisc.edu/JCESoft/CCA/CCA6/MAIN/1ChemLabMenu/Separating/MENU. HTM (accessed on February 18, 2008). Somewhat technical description of separation techniques.
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W
hen most people envision machines, the image probably does not include a simple screwdriver or pencil sharpener. Yet these devices are also machines. A machine is any object that makes work easier by altering the way in which the work is accomplished. Put another way, a machine can use a smaller force to overcome a larger force. In physics, work is defined as force applied over a distance. For example, a person does work when pushing a shopping cart down an aisle, yet does no work when pushing against a closed door. Simple machines have few moving parts, or sometimes none at all. They are the building blocks for machines of all levels of complexity and all mechanical devices. People have been using simple machines for thousands of years. Zippers, staplers, nails, and scissors are just a few examples of common modern-day machines. Machines can enlarge and change the direction of a force, yet all machines must follow the principles of the conservation of energy. This principle states that the work or amount of energy coming out of a machine is equal to the amount of energy put into the machine. Work is made up of the amount of force applied and the distance over which the force is maintained. Effort is the force applied. In mathematical terms, work equals force times distance w = fd. Put another way, a machine that uses half the force to lift an object, must then double the distance it applies the force. Simple machines include the inclined plane, wedge, screw, lever, pulley, and wheel and axle.
Incline at work An inclined plane, also called a ramp, decreases the amount of force needed to lift a load or weight by increasing the distance the load travels. For example, an inclined plane that covers twice the distance of the vertical side will need half the amount of effort to lift a 1047
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p am of r e c tan dis
of unt mo a s ine erm det
Full Effort
In a ramp or inclined plane, the greater the distance, the less effort. GAL E GR OU P.
weight than if the weight was lifted straight up. The amount of work remains the same. Historians theorize that ancient Egyptians used long, shallow ramps to help them carry five-ton stones up pyramids that soared hundreds of feet tall. Driveways, slides, and car ramps are modern-day examples of machines that make use of inclined planes. A wedge looks like an inclined plane, yet it does work by moving (an inclined plane always remains still). A wedge changes the direction of a force. When a wedge comes into contact with an object, the wedge changes the direction of the force and causes it to move at a right angle. Wedges are often used to push things apart. The force needed for the wedge depends upon the size of the wedge angle. The smaller the angle of the wedge, the less force is needed yet the greater the distance it must be pushed. The pointed end of the nail is an example of a wedge. As the nail is pounded down with a force, the wood is pushed apart sideways. A narrow nail with a small angle must be moved more distance than that of a thick nail with a larger angle. Less force is needed for the thin nail yet it must move a greater distance. Doorstops, the tines on a fork, and knives are other examples of wedges. A screw is basically an inclined plane wrapped around a cylinder. The length of the screw is the height of the plane, and the distance traveled is determined by the amount of threads on the screw. While turning, a screw converts a rotary motion into a forward or backward motion. The spiral ridges, or threads, around the screw cause the screw to turn many 1048
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times to move forward a short distance. This is similar to moving an object up an inclined plane or ramp. The width between the threads, or pitch, is similar to the angle of the inclined plane. The closer together the threads are around the screw, the more it needs to turn to move the same distance, making it less effort to turn. Screws with threads spaced farther apart travel less distance and take more force to turn. The screw’s spiral threads act like wedges. Each thread produces a force at right angles to its rotation. Pulley power A pulley consists of a rope or other cord pulled over a steadied wheel. At one end of the rope is the object or load to be lifted; the other end is where the force is applied. A single, fixed pulley changes the direction of a force. The force needed to lift the load still equals the weight of the load, yet it can feel easier if a person is pulling down instead of pushing up. Using two or more pulleys connected together can decrease the amount of effort needed to lift the same load. If using two pulleys, the rope leading to each individual pulley can hold half as much weight. With the load weighing half as much, a person need apply only half the force. The tradeoff is that the rope needs to be pulled twice the distance. The force is cut in half but the distance the rope must be pulled has doubled. Lever lifts A lever is any bar-type object free to move or pivot about at a fixed point. The point at which the lever pivots is called the fulcrum. A downward motion at one end results in an upward motion on the opposite side. In a lever, the fulcrum’s relationship to its load and the force applied, or effort, determines the work of the lever. Levers are categorized by where the fulcrum is located in relation to the load and effort. There are three basic types of levers. A first-class lever has its fulcrum placed between its load and the effort. One end is forced down and the other end moves up. When the fulcrum is in the center of the lever, the amount of effort pushed down on one side equals the amount of load lifted on the Experiment Central, 2nd edition
Slides of all kinds are examples of inclined planes. # K EL LY MOO NE Y PH OTO GR APH Y/ COR BI S.
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spiral groove
ramp
Screws are examples of simple machines. The closer together the threads are around the screw, the more it needs to turn to move the same distance, making it less effort to turn. Screws with threads spaced farther apart travel less distance and take more force to turn.
distance between grooves determines amount of effort
tighter grooves increase distance, and lessen effort
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other side. If the distance from the effort to the fulcrum increases by two, then only half as much pushing effort is needed to raise the same load. If the load doubles, then the distance from the fulcrum to the load must also double in order for the same effort to move it. Pliers, a person’s jaw, and a seesaw are examples of this type of lever.
downward force on one end results in upward force on other end
Fulcrum A seesaw is an example of a lever where the fulcrum is equally centered between load and effort. GAL E GR OU P.
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equal distance from center
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A fulcrum at one end with the load in the middle and the effort at the far end is a secondclass lever. This type of lever, such as a wheelbarrow, increases the force needed to lift the load, but decreases the distance it has to move. A third-class lever has the fulcrum at one end, the effort in the middle, and the load at the far end. Tweezers and fishing rods are examples of this type of lever. A wheel and axle machine rotates around a fixed point and works in a similar way to a revolving lever. The axle is the object that attaches to the wheel. The wheel moves the axle. When the wheel revolves it moves a greater distance than the axle. The larger the diameter of the wheel, the less effort needed to turn it, but the greater distance needed for the same work. In reverse, a greater force applied to the axle will turn the wheel a greater distance. Doorknobs, pencil sharpeners, screwdriver handles, and steering wheels all use a wheel and axle.
A wheelbarrow is an example of a lever where the fulcrum (in this case, the wheel) is at one end with the load (the bucket) in the middle and the effort (person lifting the handles) at the far end. # KE LL Y A. QUI N.
EXPERIMENT 1 Wheel and Axle: How can changing the size of the wheel affect the amount of work it takes to lift a load? Purpose/Hypothesis A wheel and axle can be used to do work using less
force. In a wheel and axle, both parts move together. In this experiment you will construct a wheel and axle that also incorporates the pulley. You will join two spools together, one the wheel and the other the axle. The axle will hold a load and you will apply force to the wheel. Washers will be the load and also apply the force. This experiment will use three wheels of different diameters. By changing the diameter of the wheel, you will find out how the relationship in size between the wheel and the axle determines how easy it is to lift the load. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of work and machines. This Experiment Central, 2nd edition
In a pencil sharpener, the wheel turns the axle, which is attached to a blade. The more turns you have to make, the less effort it takes. GA LE G RO UP.
axle
wheel
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WORDS TO KNOW Conservation of energy: The law of physics that states that energy can be transformed from one form to another, but can be neither created nor destroyed.
Machine: Any device that makes work easier by providing a mechanical advantage. Pulley: A simple machine made of a cord wrapped around a wheel.
Control experiment: A setup that is identical to the experiment, but is not affected by the variables that affects the experimental group.
Screw: A simple machine; an inclined plane wrapped around a cylinder.
Effort: The force applied to move a load using a simple machine.
Simple machine: Any of the basic structures that provide a mechanical advantage and have no or few moving parts.
Friction: A force that resists the motion of an object, resulting when two objects rub against one another.
Variable: Something that can affect the results of an experiment.
Fulcrum: The point at which a lever arm pivots.
Wedge: A simple machine; a form of inclined plane.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Inclined plane: A simple machine with no moving parts; a slanted surface.
Wheel and axle: A simple machine; a larger wheel(s) fastened to a smaller cylinder, an axle, so that they turn together. Work: Force applied over a distance.
educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Given that the axle stays constant, the larger the wheel, the less force will be needed to lift the load.’’ In this case, the variable you will change is the diameter of the wheel. The variable you will measure is the amount of force needed to lift the load. 1052
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Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental setup, and that is the diameter of the wheel. For the control, you will use a wheel that is of equal size to the axle. At the end of the experiment you can compare the results of the control to the experimental trials. Level of Difficulty Easy to Moderate. Materials Needed
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the diameter of the wheel • the weight of the cups • the diameter of the axle • the load In other words, the variables in this experiment are everything that might affect the amount of force needed. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on getting the work done.
• 2 small paper or plastic cups • metal washers all of equal size, at least 20 • dowel (should fit through spools to allow spools to spin) • masking tape • ruler • hole puncher • marking pen • string (optional) • 2 full thread spools of equal size (wheel and axle) • 3 cylindrical objects of varying sizes: (full thread spools or ribbon spools work well). Use the thread spool as a guide when collecting these objects: find one about half its size, one about twice its diameter, and one about three or four times its diameter). Approximate Budget $3. Timetable 20 minutes. Step-by-Step Instructions
1. Measure and note the diameters of the two equal-size cylinders in a data chart. 2. Set up a wheel and axle control by placing the dowel into the two cylinders of the same size: the wheel and axle. Tape the spools together so they move as one unit. Experiment Central, 2nd edition
How to Experiment Safely There are no safety hazards in this experiment.
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Set the dowel on a table with the wheel and axle hanging just over the edge, then tape the dowel firmly to the table at the far end and several points along the dowel. The wheel is the outside cylinder. 3. Label the cups ‘‘A’’ and ‘‘B.’’ Punch two holes in each of the cups on opposite sides near the open upper rim. Cut two pieces of string slightly larger than the diameter of the cup. Tie each end of the string to a hole on the outside of the cup so that it is slightly loose.
B force
A
load
Step 7: Apply force by placing washers in cup B, one at a time, until cup A has been raised and is sitting just below the axle. GA LE G RO UP.
4. Pull down 20 inches (51 centimeters) of thread from the axle and attach cup A to the thread. Use several inches of the thread from the wheel to attach cup B. (Note: If you are not using thread spools or the thread is weak, then tape a piece of string to the center of the cylinder.) 5. Wrap the thread around the wheel until cup B is sitting just below the thread. 6. Place eight washers in cup A. 7. Apply force by placing washers in cup B, one at a time, until cup A has been raised and is sitting just below the axle. Note the force needed by counting the amount of washers. Record your results. 8. Remove the wheel; cup A will fall back in its starting point.
diameter wheel
axle
load
force
control wheel 1 wheel 2 wheel 3
Data chart for Experiment 1. GAL E GR OU P.
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9. Measure the diameter of a second spool. Slide this wheel on the dowel and firmly attach it to the axle. Pull down the string (or ribbon) and reattach cup B to the new spool, making sure it is at the same starting point just below the spool. 10. Again, apply force by placing washers in cup B, one at a time, until cup A is sitting below the axle. Note the results. 11. Repeat Steps 7 through 10 for the next two wheels. Summary of Results Examine your chart.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The load only lifted part of the time. Possible cause: The wheel and axle may have come loose at some point during the experiment. Check to make sure that the two cylinders are firmly attached and they are moving as one unit. You may need to use electrical tape or some other stronger tape. Repeat the experiment.
Compare the ratio of the diameters between the wheel and axle, and the ratio between the load and force for each wheel. How do they relate to each other, and how do they relate to the control? What size wheel made the work of lifting the load the easiest? In your wheel and axle, look at what other type of machine is in use? How does changing the direction of the force provide an additional mechanical advantage? Change the Variables To change the variable in this experiment, you can
alter the diameter of the axle instead of the wheel. You can also use more or less weights as the load.
EXPERIMENT 2 Lever Lifting: How does the distance from the fulcrum affect work? Purpose/Hypothesis A lever is a bar that pivots on a fulcrum. The mass
placed on a lever is called the load. In a first-class lever, the fulcrum sits in between the two loads. The load presses down on the lever with a force or effort. In this experiment, you will vary the distances between the applied force, or effort, and the fulcrum to determine how to make the load easier to lift. You will use a ruler as the lever, metal washers as the load, and a small narrow object as the fulcrum. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of levers and machines. Experiment Central, 2nd edition
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What Are the Variables?
This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the mass of the load
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
• the distance from load to fulcrum
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘More force is needed when it is applied closer to the fulcrum than farther from the fulcrum.’’ In this case, the variable you will change is the distance from the fulcrum. The variable you will measure is the force needed to lift the load.
In other words, the variables in this experiment are everything that might affect the work of the lever. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the work.
Level of Difficulty Easy. Materials Needed
• 12-inch (30-centimeter) flat ruler • ten metal washers of the same size • narrow flat object, such as a pencil or domino Approximate Budget $2. Timetable 20 minutes. Step-by-Step Instructions
How to Experiment Safely There are no safety hazards in this experiment.
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1. Make a lever by placing the narrow object that serves as a fulcrum, such as a domino, under a ruler at the 6-inch (15-centimeter) mark. 2. Place four washers at one end of the ruler. Add washers on the opposite end of the ruler until the load is lifted and the lever is Experiment Central, 2nd edition
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balanced. Note the number of washers and the distance. 3. Remove the washers on the 12-inch (30-centimeter) mark so that the opposite side lies on the table. 4. Place washers one at a time on the 10inch (25.4-centimeter) mark, until the lever is balanced. Note the number of washers and the distance.
force
load
5. Remove the washers on the 10-inch mark and repeat, placing the washers on the 8inch (20.3-centimeter) mark.
Step 5: Place the washers closer to the fulcrum to determine how many it takes to lift the load. GA LE G RO UP.
Summary of Results Examine your results and compare the different
loads required to accomplish the same amount of work: lifting the load. For each trial, complete the equation work equals force times distance, where force is the number of washers needed to push down one side, and distance is the distance from the fulcrum. Predict how many washers you would need at several different points along the ruler. Change the Variables To change the variable in this experiment you could alter the position of the fulcrum. Keep the number of washers on one side the same, move the fulcrum, and then determine how much force is needed to lift the load.
EXPERIMENT 3 The Screw: How does the distance between the threads of a screw affect the work? Purpose/Hypothesis The screw is a simple
machine that is a modification of an inclined plane. The threads (or grooves) wrapped around a cylinder are an incline. It is this incline that helps the screw move into an object. The distance between the threads around the cylinder determines the steepness of the incline. The Experiment Central, 2nd edition
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The washers keep falling off. Possible cause: Your fulcrum may be too high. Use a smaller object, such as a flat pencil, and repeat the experiment.
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incline affects the distance the screw moves into an object after one full turn.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • circumference of screws • the number of threads • the diameter of the screwdriver • the type of screw • the type of wood In other words, the variables in this experiment are everything that might affect the work of the screw. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the work.
This experiment will use three screws with different threads. Fewer threads will give a steeper incline. By changing the distance between the threads, you will find out how the steepness of the threads’ incline determines the amount of work needed to turn the screw into a piece of wood. You can estimate work through distance and force. Work equals force applied over a distance. All the screws will be moved the same distance. For the purposes of this experiment, you can estimate how much force each screw takes to turn by measuring the number of turns. Some screws may take more effort to turn than others. As you conduct the experiment, consider difficulty of turning each screw compared to one another.
Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of simple machines and screws.
Screw 1
Screw 2
Screw 3
Thread width Number of revolutions Step 2: Fill in the distance on a chart. IL LU STR AT IO N BY TE MA H NEL SO N.
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This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
How to Experiment Safely Hold the screwdriver firmly in your hands and be careful not to let it slip. Do not attempt to pull the screw out without adult help.
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘More work is needed to turn a screw with fewer threads into an object compared to a screw that has more grooves. In this case, the variable you will change is the distance between the grooves. The variable you will measure is the work needed to twist the screw. Level of Difficulty Moderate. Materials Needed
• 3 screws that are 2-inches (5-centimeters) long, each with a different number of threads; they should all be either flat or Phillips • 1 block of 2x4 pine wood • screw driver, flat or Phillips depending on type of screw • painters tape • ruler with centimeters and millimeters • marker or pen
Steps 3 and 4: Wrap a piece of tape one-half inch from the point of each screw. Mark a line on the tape to help you count the revolutions. I LLU ST RATIO N BY TEM AH N EL SON .
Approximate Budget $8. Timetable 20 minutes. Step-by-Step Instructions
1. Use the marker to mark three lines on the wood where the screws will be inserted. 2. Measure the distance between the threads on each screw in centimeters or millimeters. Fill in the distance on a chart similar to the illustration. Experiment Central, 2nd edition
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3. Wrap a piece of tape one-half inch from the point of each screw. 4. Mark a line on the tape to help you count the revolutions.
Step 5: Turn the first screw into the wood, counting the rotations. I LL UST RA TIO N BY T EMA H NE LS ON.
5. Turn the first screw into the wood. You will need to count the number of rotations made by the screw. Continue with the twisting until the screw is into the wood 0.5 inches (1.3 centimeters), where the mark was placed on the tape matches with the line on the wood. 6. Turn the second and then third screws into the wood. Note the number of turns each screws until it reaches the mark on the tape. 7. Analyze chart to determine which screw required the least amount of revolutions, greatest amount of revolutions. Summary of Results Consider how easy or hard each screw was to turn.
How does the amount of effort relate to the distance between the threads. Using the data on your chart consider when it be better to use a screw with a larger thread distance versus a shorter thread distance? Think about some ways that the principles behind screws are incorporated into common devices. Change the Variables One way to change the variable in this experi-
ment is to use screws with the same threads but different thicknesses. Try using an extremely wide screw compared to a thin one. You can also use different types of screws and compare the effort involved.
Design Your Own Experiment How to Select a Topic Relating to this Concept To choose a topic related
to simple machines and mechanics you can look at the objects that you use every day. Select several items and identify the type(s) of simple machines that it utilizes. You can use these tools to model the design of your machines. Check the Further Readings section and talk with your science teacher to learn more about machines and mechanics. 1060
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Steps in the Scientific Method To conduct an
original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
Troubleshooter’s Guide You should not encounter many problems during this experiment. Below is one problem that may arise, and a way to remedy the problem. Problem: The screw won’t turn into the wood.
• State the purpose of—and the underlying Possible cause: You may not be using soft pine or you may be screwing into a particularly question behind—the experiment you hard section of the wood. Try using a fresh propose to do. piece of pine wood and repeat. • Recognize the variables involved and select one that will help you answer the question at hand. Did you know that your jaw is • State your hypothesis, an educated guess about the answer to your a simple machine? The jaw acts question. as a first-class lever when you • Decide how to change the variable you selected. are chewing food. # K EL LY A . • Decide how to measure your results. QUI N. Recording Data and Summarizing the Results
Your data should include charts and drawings such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. You may also want to include specimens, in a closed container, so that others can observe what you studied. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Because simple machines are all
around, finding materials and ideas related to simple machines is relatively simple. As machines Experiment Central, 2nd edition
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are linked with force, you can investigate the principles behind force that are at work in a machine. A project idea can be to take one simple machine and use the same force in many different setups. You can take apart common household simple machines (with an adult’s permission, of course) and compare the differences and similarities between machines that use the same principles. Compare one type of simple machine, such as a screwdriver, to its different types. Look at what features each machine has to make its work easier. You can also build or take apart complex machines, and sketch the simple machines that it uses. For a research project, you can investigate the history of simple machines and how they have impacted people’s lives.
For More Information ‘‘Background Information for Simple Machines.’’ Canada Science and Technology Museum. http://www.sciencetech.technomuses.ca/english/ schoolzone/Info Simple Machines.cfm (accessed on February 29, 2008). Informative site explaining various simple machines, including levers, pulleys, and more. Lafferty, Peter. Force & Motion. New York: EyeWitness Books, Dorling Kindersley, 2000.With photographs and many graphics, this book describes the science of force and motion and their applications in simple machines. Macaulay, David, and Peter Lafferty. The Way things Work. Boston: Houghton Mifflin, 1988. Clear text with many illustrations describes the principles behind numerous inventions and tools. Museum of Science, Boston. Exploring Leonardo. http://www.mos.org/sln/ Leonardo/LeoHomePage.html (accessed on February 29, 2008). Exhibit on Leonardo da Vinci’s work with machines. ‘‘Simple Machines.’’ BrainPOP. http://www.brainpop.com/technology/ simplemachines/ (accessed on February 29, 2008). Animations, activities, and explanations of simple machines. University of Utah. ‘‘Simple and Complex Machines.’’ ASPIRE. http://sunshine. chpc.utah.edu/javalabs/java12/machine/index.htm (accessed on February 29, 2008). Illustrated explanations with lab activities of various machines.
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ommonly called dirt, soil is a central ingredient for life on Earth. Soil is the thin, outer layer of material on the surface of Earth, ranging from a fraction of an inch to several feet thick. Plants depend on soil for their nutrients and growth. These plants are then consumed and used by animals, including people. Soils provide shelter and a home for insects and small animals. Microscopic organisms flourish in soil, breaking down dead matter, which returns nutrients into the soil for new life. People use soils directly as a material to build on and grow crops in. Soils also reveal a historical record of an area’s past life and geography. Understanding the properties of a soil is a key to determining how the soil will function for a particular use. The specific makeup of soil depends on its location, yet all soils share the same basic composition: minerals, water, air, and organic matter, meaning matter that contains carbon and comes from living organisms. Minerals are naturally occurring inorganic or nonliving substances that come from Earth’s crust. Different types and combinations of these components form multiple types of soil. In the United States alone, researchers have identified over seventy thousand different soils. Soils are characterized by many features, including their structure, texture, living organisms, and acidity.
The scoop on dirt Soil is a dynamic material that Earth is constantly manufacturing. The highest percent of any given soil is made of minerals, which all come from the same material: rocks. Nature churns rocks into new soil regularly and slowly. A rock is a mixture of minerals that stays together under normal conditions. Rocks can be hard, relatively soft, small, or large. Over time, rocks get weathered or worn down naturally by their environment. Several factors contribute to how fast the rock weathers. The rock’s composition, climate, surrounding organisms, and location are all key 1063
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factors. Weathering also needs time. It can take 100 years to more than six hundred years to form one inch of topsoil. The rocks that form soil are called the parent material. When some rocks weather, their min25% erals react with other elements to form different water chemicals from the original parent material. 45% minerals Other rocks retain the same composition of the parent material. The makeup of the parent material determines many properties of the resulting 25% soil. air The mineral content of the parent material can be acidic, neutral, or alkaline. The acidity of soil is measured on a pH scale from 0 to 14. On 5% this scale, a pH of 7 is neutral, above 7 is alkaline, organic matter and below 7 is acidic. The acidity of the soil is a key factor in determining the types of plants and other organisms that thrive there. Iron, for Basic composition of soil. G AL E example, is an acidic mineral in which azaleas and blueberries grow GRO UP. well. Elm, yucca, and sycamore grow in nonacidic soils. Soil life also depends upon minerals for essential nutrients, which come from the specific mineral content in the parent material. Calcium, phosphorus, and potassium are examples of familiar minerals soil life needs. Winds, rain, sunshine, and temperature shifts all play a part in weathering. Water slips into the cracks of a rock. Varying temperatures
Climate and location are two factors that cause rocks to break down and form soil. GA LE
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freeze and thaw the water repeatedly, expanding the cracks and fragmenting the rock. Rain pounds against a rock, wearing it down into increasingly smaller particles. Winds beat against the rock’s surface, tearing away its outer layers. In general, a moist, warm climate causes rocks to break down more quickly than a cool, dry climate. The surface features of an area also impact soil formation and its erosion. Water that flows over land can carry soil with it and expose new rocks to weathering. Soils on slopes and hills have a high rate of water flow. Here, soils are carried by the water flow at a faster rate than soils on flat surfaces, which have more time to form. Along with the weather, a warm climate also hastens the weathering process because it provides a comfortable environment for life. Organisms that live in and on the soil affect soil’s formation in several ways. Plant roots stretch into the soil and break up small fragments. Burrowing animals wriggle through soil and move rock fragments to cause crumbling. Animals stomp on the soil and split up rock pieces. Some microscopic organisms that produce acid, such as fungi and lichens, break up the minerals within rocks. Size matters Soils are generally made up of one of three mineral particles: sand, silt, or clay. The type of particles is another major factor in determining the life in and on the soil. Water and air, needed by both plants and animals, sit in the spaces between the particles. Almost all soils have some combination of these particles, and it is the relative percentage of one over the other that determines its category. Sand particles are relatively large, ranging in size from 0.002 inches to 0.08 inches (0.05 millimeters to 2 millimeters) in diameter. Sandy particles feel gritty to the touch. The particles have large air spaces between them, causing water to run through easily. Because they do not retain moisture, sand is loose and crumbly. Water that runs through sand can cause minerals necessary for growth to drain or leach out of the soil. Leaching is the movement of dissolved particles downward through the soil. Silt is the next largest soil particle, ranging in size from 0.00008 inches to 0.002 inches (0.002 millimeters to 0.05 millimeters) in diameter. Silt particles are fine and hold in some water. Silt particles feel soft and can hold together well when moist. When they are dry they are easily blown away by wind. Experiment Central, 2nd edition
Nature churns rocks into new soil regularly and slowly. COR BI S.
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sand
Soils are generally made up of one of three mineral particles: sand, silt, or clay. GA LE
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clay
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Clay particles are the smallest type of soil. Clay particles have little air space between them. They hold the highest amount of water and keep other soil particles together. Moist clay packs tightly together and can be molded. When clay particles are dry they harden, which can slow the growth of plant roots. Dirty layers As the weathering process continues over time, it causes soil to develop into layers that have distinct characteristics. A vertical slice of two or more of these layers is known as a soil profile. The layers are known as soil horizons and are named O, A, B, and C. How thick each horizon is depends upon its location. Soil horizon properties differ in their color, texture, consistency, life, and acidity. The uppermost soil layer, the O layer, is filled with organic matter. As this matter gets decomposed from soil-dwelling creatures it forms a darkbrown, organic material called humus. Most humus comes from plant materials, such as dead leaves, twigs, and stems that fall to the ground. Dead animals in the soil and above it also contribute to humus. Humus retains water and contains nutrients for life to grow. Sitting right below this layer is the A layer, called topsoil. Topsoil contains decaying plant and animal remains, along with a wealth of microscopic organisms such as bacteria. With all of its humus and organic matter, topsoil is usually the darkest and most fertile layer in the soil. Soil animals, such as earthworms and ants, live comfortably in 1066
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this layer, using the plant and animal remains for food. Plant roots stretch out in this region to suck up the water and nutrients. Subsoil is the middle, or B, soil layer. It is usually lighter in color than topsoil because it does not contain as much humus, making it less fertile. Denser and with less nutrients than topsoil, relatively few animals and plants are found here. Some plants with long roots reach down into the subsoil to get at the water stored between the particles. The C layer, or horizon, contains partially disintegrated parent material and its minerals. It is far less altered and weathered than the layers above it and has none of the organic matter life needs to grow. Beneath this layer is the bottom region below the soil called bedrock. This layer contains bits of rock similar to the parent material. Life in the dirt lane Soils are teeming with life, from the microscopic bacteria and fungi to the visible small animals and plants. Live organisms promote growth and new life in soil. Once dead, organisms contribute to the amount of decayed organic matter in soil, which influences its characteristics. Pick up a handful of soil and you are holding billions of microscopic organisms. These microbes decompose organic matter and return vital nutrients into the environment. Plant roots hold soil particles together and prevent them from blowing away. Animals that burrow into the soil, such as squirrels and moles, create holes that allow air and water to enter. Insects such as beetles, ants, spiders, and snails eat organic matter and begin the decaying process. Worms tunnel through the soil, creating air pockets and turning over the soil.
O horizon humus
A horizon topsoil
B horizon subsoil
C horizon
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In a soil horizon the soil particles get gradually larger. GAL E GR OU P.
EXPERIMENT 1 Soil Profile: What are the different properties of the soil horizons? Purpose/Hypothesis Soil is composed of three main categories of particles: sand, silt, and clay. Each of these particles has distinct properties Experiment Central, 2nd edition
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Earthworms tunnel through the soil, creating air pockets and turning over the soil. # SA LLY A. M OR GA N; E COS CE NE/ CO RB IS.
including its feel, texture, color, nutrients, and size. While these three particles can form many different combinations in a soil, the proportion of each changes in each horizon. In this experiment, you will take a soil profile and determine the properties of three different horizons. Because the depth of each soil horizon depends on location, the depth suggested to dig is a guide. You may need to dig farther down than suggested to find three unique horizons, or you may not have to dig as deep. Once you have the three samples you will examine their characteristics in several ways. Using a kit, you will test each sample for nutrients. By feeling the soil and pressing it together you can determine its texture and feel. You will then estimate the relative proportions of sand, silt, and clay by measuring the point at which each layer settles in water. Larger particles will settle first; the smallest particles will settle last. Another varying characteristic among the horizons is the amount of microorganisms, which decompose organic matter and create the humus. An optional part to this experiment is to determine the amount of microorganisms in each horizon by placing chopped organic matter in each sample and examining the results. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of soil horizons and soil particles. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The soil horizons at lower 1068
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WORDS TO KNOW Alkaline: A substance that is capable of neutralizing an acid, or basic. In soil, soil with a pH of more than 7.0, which is neutral.
Parent material: The underlying rock from which soil forms. Rock: Naturally occurring solid mixture of minerals.
Bedrock: Solid layer of rock lying beneath the soil and other loose material. Clay: Type of soil comprising the smallest soil particles. Control experiment: A setup that is identical to the experiment, but is not affected by the variables that affects the experimental group. Humus: Fragrant, spongy, nutrient-rich decayed plant or animal matter. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Leach: The movement of dissolved minerals or chemicals with water as it percolates, or oozes, downward through the soil. Mineral: An nonorganic substance found in nature with a definite chemical composition and structure. Organic: Made of, or coming from, living matter.
Sand: Granular portion of soil composed of the largest soil particles. Silt: Medium-sized soil particles. Soil: The upper layer of Earth that contains nutrients for plants and organisms; a mixture of mineral matter, organic matter, air, and water. Soil horizon: An identifiable soil layer due to color, structure, and/or texture. Soil profile: Combined soil horizons or layers. Topsoil: Uppermost layer of soil that contains high levels of organic matter. Variable: Something that can affect the results of an experiment. Weathered: Natural process that breaks down rocks and minerals at Earth’s surface into simpler materials by physical (mechanical) or chemical means.
depths will contain more sand, be grittier, lighter, and have less minerals and organic matter than the soil of the top horizon.’’ In this case, the variable you will change is the depth of the soil. The variable you will measure is the soil’s properties, including its particle makeup, organic matter, color, and mineral content. Level of Difficulty Difficult (because of the digging and the multiple parts). Materials Needed
• area with soil that you can dig (another option is to find an area already dug; see also Change the Variables) Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the patch of soil you choose • the depth you dig • the amount the jar is shaken • the type of organic matter present In other words, the variables in this experiment are everything that might affect the soil horizons. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the properties of each horizon.
• shovel • plastic container that can hold about 2 cups (500 milliliters) • grasses, flowers, leaves (optional part) • yardstick • ruler • three self-sealing bags • three 1-quart (about 1-liter) straight jars with lids • water • marking pen • nutrient testing kit (available from garden or hardware stores) Approximate Budget $18. Timetable Varies because of digging; 3 hours experiment time; 24 hours waiting. Optional part will take 3 weeks; 15 minutes per week.
How to Experiment Safely
Step-by-Step Instructions
1. Find a clear area of soil and dig to a depth of about 30 inches (76 centimeters). Place the ruler in the hole to measure depth. 2. Label the self-sealing bags ‘‘Soil A,’’ ‘‘Soil B,’’ and ‘‘Soil C.’’ 3. Use the plastic containers to collect three samples at different depths. (Examine the soil profile for differences in color and texture and use this as your collection indicators. The following measurements are guidelines.) Collect the first soil sample by placing the top of the container at 2 inches (5 centimeters) down and scooping dirt inside the container. When filled, place the soil in Soil A bag and note the depth on a data chart. Collect the next soil sample at roughly 15 inches (38 centimeters). Place the soil in Soil B bag and note the depth. Collect the third soil sample at 30 inches (76 centimeters). Place the soil in Soil C bag and note the depth. Remove any visible insects from the soil samples.
This is a messy experiment; be sure to wash your hands thoroughly after collecting the soil. Watch out for any insects in the soil.
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4. Note the color(s) of each sample on your data chart.
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5. Determine the texture of each layer: Collect a small ball of soil in your hand from Soil A and spray it with water so that it is damp. (If it is already damp leave as is.) Rub the soil between your fingers and feel if the texture is floury (silt), sticky (clay), or gritty (sand).
s
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6. Use that same ball to determine if the soil sticks together. Press the soil between your thumb and forefinger to make a ribbon. Note whether the soil forms a ribbon without breaking, forms a ribbon with breaking, or does not form a ribbon.
so il A
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Step 3: Collect soil samples from three horizons. GA LE
7. Repeat Steps 5 and 6 for Soil B and Soil C.
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8. Estimate the relative percentage of clay, sand, and silt particles: Place 1 cup of Soil A in a labeled jar and add water until the jar is almost full. Repeat with the other two soils, adding the same amount of water in each jar and making sure the jars are labeled. Cover the jars and shake for at least two minutes. 9. After one minute, make a mark on the jar at the level the particles have settled to the bottom. This is the sand. Measure up to the mark with the ruler.
Texture Depth
Color
Feel
Ribbon
% Sand, Silt, Clay
Nutrients
soil A soil B soil C
Data chart for Experiment 1. GA LE G RO UP.
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10. Let the jars sit undisturbed. After two to three hours, mark and measure the thickness of the next layer. This is the silt. 11. Wait at least 24 hours to measure the last level, which is the clay. 12. Divide the thickness of each layer by the total height of all three layers. Multiply that number by 100 for a rough percentage of each type of particle. Note the results. 13. Test for nutrients: Follow the directions on the nutrient kit to determine the level of nutrients in each soil sample. silt sand Steps 9 to 11: Measure each layer of particle. GAL E GRO UP.
14. (Optional) Determine the relative amount of microorganisms in each samclay ple: Leave 1 cup (about 240 milliliters) of each soil sample in the bag and add enough water to moisten (the rest of the soil can be returned to ground). Seal the bag and poke small holes in the top. 15. Chop up organic matter, such as leaves, grass, and/or flowers. Add 2 tablespoons (30 milliliters) of the chopped organic matter to each bag. Spray each soil so each is the same moistness and place bags in a dark environment, such as a drawer. Every five to seven days add another tablespoon of water (15 milliliters) to each of the soils. Every week for two to three weeks, note the decomposition of the organic matter and any visible life, such as fungi. Summary of Results Examine your chart of the three soils. What is the
most striking difference in soil properties between them? How did Soil A compare to Soil C in texture and color? How do the differences in the estimated soil particles relate to the soils color and whether it sticks together? Determine if any of your soils showed the property of only one type of soil particle? Hypothesize would happen if you grew the same plant in each soil. Based on your results, how does each soil hold water? Write a brief summary of the experiment and your analysis. 1072
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Change the Variables The main way to change
the variable in this experiment is to alter the type of soil. If digging is not possible in your area, you can purchase different soil types in a garden shop and repeat the same steps for each soil. To change the variable in the microorganisms part, you can use the same type soil and alter the kind of organic matter. Modify the Experiment You can conduct a sim-
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The soil horizons were very similar. Possible cause: You may not have dug down deep enough when you collected the samples. There should be a change in texture and color marking the different horizons. Repeat the experiment, digging down another 12 inches (30 centimeters) or more.
plified version of this experiment that will take less time (and less mess) by comparing the soil composition from two locations. First, consider Problem: The organic matter did not what two areas you want to collect soil. Try to decompose. find soils that have different characteristics, such Possible cause: You may not have allowed as color or if plants grow in it. Make a hypothesis enough time for the microorganisms in the if one soil contains more sand, silt, or clay than soil to decompose it. It is also possible that the other sample. you have few microorganisms in any of your Using a spade, collect a sample of each soil soils. Repeat with another sample from the same location, and use a soil as a control that type. Scrape away the first couple inches of the is a rich, dark brown color from the top layer soil and then place about a cup of the soil in a of the soil. plastic bag. Make sure to label the bag with the soil location. Spread out each sample and remove any pebbles, leaves, or other debris. You can do this by hand or with a colander. You will need two narrow glass jars with lids, a measuring cup, liquid soap, and a ruler. Place a cup of soil from one location in the first glass jar and a cup of soil from the second location in the second jar. Add a drop of liquid soap (this will separate the soil particles). Fill the jars with water and shake for at least two minutes. Set the jars down and watch the particles settle to the bottom. After a couple minutes, use a ruler to measure the amount of sand that settled. Sand is the heaviest soil particle. After another 15 minutes, measure the particles that have settled. Measure the buildup of particles over a set time period, comparing the two jars. When you have finished, you can graph the amount of particles that settled in each sample for each time period. Did one sample have more sand? Are there still clay particles floating about in the water? Was your hypothesis correct? Think about how the area and soil life, if anything, relates to the soil sample. Experiment Central, 2nd edition
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EXPERIMENT 2 Soil pH: Does the pH of soil affect plant growth? Purpose/Hypothesis A soil’s pH is a measure of how acidic or basic it is.
A soil that is basic is called alkaline. Alkaline soils are often referred to as sweet; acidic soils are referred to as sour. Soil pH is measured on a pH scale. The pH scale ranges from 1 to 14, with 7 being neutral, neither acid nor alkaline. Water, for example has a pH of 7. Acidic soils have a pH less than 7; the lower the number, the more acidic the soil. Alkaline soils have a pH above 7; the higher the number, the more alkaline the soil. Most plants prefer a neutral to slightly acidic soil, with a pH between 6 and 7, yet some plants prefer acidity whereas others grow best in alkaline soil. Potatoes, gardenias, and blueberries grow best in acidic soils. Geraniums, asparagus, and mint grow best at higher pH levels. The pH of the soil also affects how available the nutrients are for plants to absorb. For example, nitrogen, potassium, and phosphorous are key nutrients that plants needs to grow. In soil that is highly acidic or alkaline, plants cannot get phosphorus. Potassium is most available in soils with high pH and unavailable at low pH. Nitrogen becomes available to plants with a pH of roughly 5.5 or above.
To ensure proper growth of crops or other plants, it is important to know the pH level of the soil before planting. FI ELD MA RK P UBL IC ATI ON S.
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In this experiment, you will test how acidity affects plant growth by growing the same type of plant in both an acidic and an alkaline soil. To make soil more alkaline, gardeners add calcium carbonate (limestone). This is referred to as liming. For a quick way to make soil more alkaline you can add baking soda, which is also alkaline. To increase the acidity of the soil you will add vinegar (gardeners use sulfur or aluminum sulfate). To determine the soil pH’s effect, you can measure height, number of leaves, how fast the plants grow, leaf color, and number of flowers. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of soil and acidity. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of soil • the nutrients in the soil • the type of plant • the pH of the soil In other words, the variables in this experiment are everything that might affect the growth of the plant. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the plant’s growth.
• the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The plant will grow best in one type of soil pH; plants grown in the other two pH soils will not be as healthy.’’ In this case, the variable you will change is the pH of the soil. The variable you will measure is the health of the plant. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental setup, and that is the soil pH. For the control, you will use a neutral potting soil, between pH of 6 and 7. At the end of the experiment you can compare the results of the control to the experimental trial. Level of Difficulty Moderate. Experiment Central, 2nd edition
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Materials Needed
How to Experiment Safely There are no safety hazards in this experiment.
• • • • • • • • •
• • • • •
15 seeds of one plant type 3 plant pots, such as plastic containers potting soil white vinegar baking soda
cheesecloth small bucket that cheesecloth can fit over rubber band or string (to fit around container) ruler container that holds 8 cups (about 2 liters), such as a soda bottle pH test kit or strips (available at garden or hardware store) measuring spoons measuring cup marking pen
Approximate Budget $10. Timetable Varies depending on the plant selected and soil; an estimated 1
hour for setup, then 10 minutes every five days for six weeks. Step-by-Step Instructions
Steps 7 and 8: Measure how pH affects the plants’ health. G ALE G RO UP.
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1. Measure the pH of the Control soil and note the results. It should be somewhere between 6 and 7. 2. Prepare acidic soil: The soil should be dry to moist. Make a solution of 1 tablespoon (15 milliliters) vinegar with 8 cups (about 2 liters) of water in the bottle or container and shake it. 3. Secure the cheesecloth over the top of the small bucket with a rubber band or string. Put the soil on top of the cheesecloth. One cup at a time, pour the vinegar-water solution over the soil until it is saturated, then test the pH. Have the soil reach a pH of roughly 5.0. Depending on the soil, you may need to add more of the vinegar solalkaline ution. If more acidity is needed, wait until the soil becomes dry to moist (try putting it in the Sun), then again pour the vinegarwater solution over the soil. Retest the pH Experiment Central, 2nd edition
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of soil. When the pH is at the right level for the experiment, note the pH on a chart. 4. Prepare alkaline soil: The soil should be dry to moist. Make up a solution of 1 tablespoon baking soda with 4 cups (about 1 liter) of water and shake it. 5. Repeat Step 3, replacing the vinegarwater solution with the baking sodawater solution. Have the soil reach a pH of roughly 8.0. Depending on the soil, you may need to make the soil more alkaline. Wait until the soil becomes dry to moist, then pour more of the baking soda-water solution over the soil. Retest the pH of soil and when it is alkaline enough note the number.
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: The soil did not turn very acidic or alkaline. Possible cause: The soil may not have been dry enough for it to soak up the vinegar or baking soda. Make sure you wait long enough so that when you press the soil together it falls apart, then add the solution.
6. Label each of the containers: ‘‘Alkaline,’’ ‘‘Acidic,’’ and ‘‘Control.’’ 7. Plant five seeds in each container, using the indicated soil, and care for as indicated. 8. Every five days (this may vary depending on your plant) measure the height of the plant, number of leaves, flowers/buds, or any other characteristic of your plant. Summary of Results When the control plants have reached full height,
examine your results. Was your hypothesis correct? How did each of the other plants compare to the control? Are there specific characteristics of the plant that were especially different than the control? Once you have determined the best pH of your plant, research what nutrients are available to your plant in that soil. What nutrients are lacking? Change the Variables There are a few ways that you can change the
variables in this experiment. You can alter the type of plant you grow, or you may want to grow several different types at once. (Some plants display interesting differences in a range of soil pHs, such as hydrangeas, which have a visible petal-color change.) You can also choose a soil with a low amount of nutrients, then add different nutrients to the soil to determine each one’s effect on plant growth. Nutrient-testing kits are available at garden or hardware stores. Experiment Central, 2nd edition
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Design Your Own Experiment How to Select a Topic Relating to this Concept Whether it is bought or
dug, soil offers many possible project ideas. Check the Further Readings section and talk with your science teacher to learn more about soil. You may want to visit a garden store or greenhouse to look at the different varieties of soils available. Look around at the types of soils in your area and the kinds of plants that grow in them. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data could include
charts and graphs to display your data. If included, they should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to bring samples of any soil samples you used, and display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Soils’ diversity and significance offer a range of project
ideas. You could further compare the properties of soil particles by measuring how different types of soils hold water. The amount of water soils hold relates to pesticides and fertilizers that people put in the soil. A project could explore what happens to these products when they are 1078
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placed in soils of various types. This could lead to a project on leaching and nutrient deficiencies in the soil. You could also explore the properties of parent materials and the process of weathering. A project could look at why certain parts of the world have distinct soils, such as deserts. You may be able to collect or purchase rock samples and compare their characteristics with one another. How does the soil composition in certain geographic areas impact their economy, environment, and agriculture? You could also look at the methods scientists have developed to replenish the soil of minerals, nutrients, and other vital properties.
Backyard
Playgroun d
For More Information Bial, Raymond. A Handful of Dirt. New York: Walker and Company, 2000. Explains what soil is made of and what lives in it. ‘‘The Dirt on Soil: What’s Really Going on Under the Ground?’’ Discovery Education. http://school.discoveryeducation.com/schooladventures/soil/ (accessed on March 11, 2008). Information and pictures of soil layers and life, along with a game. Soil Science Education Home Page. http://soil.gsfc.nasa.gov/index.html (accessed on March 11, 2008). Basic information, featured soils, and learning activities about soil. Stell, Elizabeth P. Secrets to Great Soil. Pownal, VT: Storey Publishing Book, 1998. Comprehensive book on soil properties and how to create fertile soil.
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Compare the properties of soil particles by measuring how different types of soils hold water. The amount of water soils hold relates to pesticides and fertilizers that people put in the soil. IL LU STR AT IO N BY TEM AH N EL SON .
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S
unlight has been recognized as a powerful source of energy since ancient times. ‘‘Burning glasses’’ that dated back to 7 B . C . E . have been found in the ruins of Nineva (now part of Iraq). These glasses were similar to magnifying lens and could concentrate sunlight into a beam hot enough to start a fire. Each day, Earth receives about 4 quadrillion kilowatt-hours of solar energy, generated by nuclear reactions deep inside the Sun’s mass. While we receive a lot of solar energy, it is not easy to harness. Environmental concerns and our limited supply of fossil fuels make finding ways to gather and concentrate solar energy efficiently an urgent challenge. Hot! Hot! Hot! Think of the Sun as a constantly active hydrogen bomb: a swirling, mass with eruptions that give off great amounts of energy. Within the Sun’s center, the temperature is about 25,000,000˚F
Solar eruptions like this one could provide us with enough power for thousands of years— if we could harness the energy. GA LE G RO UP.
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These solar collectors turn to catch the Sun’s rays throughout the day. P HOT O R ES EAR CH ER S I NC.
This plant in the Pyrenees Mountains in France uses mirrors to capture solar energy. PH OT O RE SEA RC HE RS I NC.
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(14,000,000˚C). About 700 million tons (635 million metric tons) of hydrogen fuse into 695 million tons (630 million metric tons) of helium each second. What happens to the missing five million tons of material? It is converted into solar energy. Besides heating and illuminating the Sun itself, some of this energy travels to Earth as sunlight. How is some of this energy collected? One way is through the use of solar collectors, flat devices made of aluminum, copper, or steel panels painted black. The black color helps to absorb the heat energy. The glass or plastic covering these panels enables light to enter, but prevents most of the heat from bouncing back into the atmosphere. The heat is then stored in a layer of pebbles or salt surrounded by a thick layer of insulation behind the black panel. This type of solar energy collection is an active solar energy system. An active system requires a separate collector, as well as a storage device and pumps or fans that draw heat when needed. Passive solar energy systems use the design of the building or natural materials to collect the Sun’s energy. One example is buildings with large windows that face south, allowing the Sun’s heat to spread throughout the structure during the day. This process is similar to the greenhouse effect, in which the Sun’s energy gets trapped near Earth’s surface by gases and other atmospheric matter. Various forms of passive solar energy systems have been applied for centuries. For example, buildings were constructed with thick walls of stone, sod, and adobe to absorb the Sun’s heat during the day and release it at night. Greenhouses were used in the early 1800s to capture the Sun’s heat so plants could be grown during cold weather. Solar reflections The Pyrenees Mountains, near Odeille in southern France, seem like an unlikely place for a solar reflector, but one has existed there since the 1950s. It towers over a meadow of wildflowers and features 63 separate mirrors that reflect sunlight onto a curved, mirrored wall. Electric motors move the mirrors to track sunlight and direct it to a central receiving tower. This method generates the intense heat Experiment Central, 2nd edition
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WORDS TO KNOW Active solar energy system: A solar energy system that uses pumps or fans to circulate heat captured from the Sun.
used, and stored by means of the design of a building and the materials from which it is made.
Efficiency: The amount of power output divided by the amount of power input. It is a measure of how well a device converts one form of power into another.
Photoelectric effect: The phenomenon in which light falling upon certain metals stimulates the emission of electrons and changes light into electricity.
Greenhouse effect: The warming of Earth’s atmosphere due to water vapor, carbon dioxide, and other gases in the atmosphere that trap heat radiated from Earth’s surface.
Photovoltaic cells: A device made of silicon that converts sunlight into electricity. Solar collector: A device that absorbs sunlight and collects solar heat.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Solar energy: Any form of electromagnetic radiation that is emitted by the Sun.
Passive solar energy system: A solar energy system in which the heat of the Sun is captured,
Variable: Something that can affect the results of an experiment.
needed for industrial use. It also produces steam in boilers, which is used to produce electricity. Other solar energy collectors include photovoltaic (pronounced photo-vol-TAY-ic) cells, developed by three Bell Telephone scientists in 1954 as a way to produce electric power from sunlight. Also known as solar cells, they convert sunlight energy into electrical energy. They have been used to provide electric power during space exploration, but are most commonly used to light billboards and power irrigation pumps. Because the energy output of solar cells is small, many are needed to produce a significant amount of electricity. However, newer cells now operate at about a 40% efficiency, a good rate compared to the efficiency of burning fossil fuels, which is about 34%. As the demand for less expensive and sustainable solar energy increases, scientists are developing new ways to create more efficient solar cells. sola In the experiments and project that follow, you will learn about two uses of solar energy: helping plants grow, powering electric motors, and heating a home. The experiments and project will help you appreciate all the ways that solar energy can—or could—affect our lives. Experiment Central, 2nd edition
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EXPERIMENT 1 Capturing Solar Energy: Will seedlings grow bigger in a greenhouse? Purpose/Hypothesis A greenhouse is a passive solar collector, allowing
light energy to pass through while blocking the escape of heat. The locked-in heat and moisture from watering create a warm, humid environment similar to a rain forest. In this experiment, you will build a greenhouse and determine whether it helps seedlings grow faster and bigger. Clear plastic will be used as the walls of the greenhouse because it allows the light in and traps the heat. To begin the experiment, use what you have learned about solar energy to make a guess about how the greenhouse will affect the seedlings. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible
Greenhouse model. GA LE GR OU P.
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hypothesis for this experiment: ‘‘The trapped solar energy in a greenhouse will cause seedlings to grow faster and larger than identical seedlings grown in the same environment without a greenhouse.’’ In this case, the variable you will change is whether seedlings are inside or outside the greenhouse, and the variable you will measure is the growth rate of the seedlings. If the seedlings inside the greenhouse grow more than those outside the greenhouse, your hypothesis is correct. Level of Difficulty Easy/moderate. Materials Needed
• 4 wooden boards, roughly 1 6 20 inches (2.5 15 50 centimeters) • 1 piece of transparent plastic or glass, 24 24-inch (60 60-centimeter) and 0.25 inch (0.5 centimeter) thick • Eight 2-inch (5-centimeter) nails • 10 marigold or radish seeds • 10 small plastic pots, or 10 plastic yogurt containers, or 10 bottoms cut from 1quart (1-liter) milk cartons • soil • hammer • goggles • gloves
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of sunlight reaching all the seedlings • the type of plants • the temperature outside the greenhouse • the color of the material under the greenhouse • the water and care given to the seedlings In other words, the variables in this experiment are everything that might affect the growth of the seedlings. If you change more than one variable at a time, you will not be able to determine which variable had the most effect on the growth rate.
How to Experiment Safely Goggles and adult supervision are required when hammering the nails. Wear gloves when handling the glass.
Approximate Budget $12. (Use any lumber that is cost-effective.
When formed into a box, the lumber must be tall enough for the pots to fit under the glass or plastic and still have room for the seedlings to grow.) Timetable 2 to 3 weeks. (This experiment requires 30 minutes to
assemble the greenhouse and 2 to 3 weeks to monitor the plant growth.) Experiment Central, 2nd edition
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Step-by-Step Instructions
Step 1: Nails positioned on wood for assembling the greenhouse. GA LE GRO UP.
1. Hammer two nails through each end of a piece of wood, as illustrated. Repeat with a second piece of wood. Place the wood into a square with the two pieces with nails opposite each other. 2. Hold the wood in position and assemble the box by carefully driving the nails into the ends of the two remaining pieces of wood. 3. Place the piece of plastic or glass over the wood box. Be sure it completely overlaps the wood box so there are no gaps around the edges. 4. Place the greenhouse outside in a sunny spot or inside near a sunny window. 5. Plant the seedlings in the ten pots. Place five pots inside the greenhouse and five next to the greenhouse. Water each pot when the soil feels dry. 6. Measure and record the growth rate of each group of seedlings every day on a chart similar to the one illustrated. Continue your experiment for 2 weeks or longer.
Step 6: Growth chart for Experiment 1. GAL E GR OU P.
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Summary of Results Study the results on your
growth chart. Can you see a difference between the seedlings inside and outside the greenhouse? Which ones are growing faster? Which ones look healthier? Was your hypothesis correct? Did the heat and humidity in the greenhouse affect the plants’ growth rate? Write a paragraph summarizing and explaining your findings. Change the Variables You can vary this experi-
ment by using different kinds of seeds or using small, identical plants. You can also try growing plants under a ‘‘ceiling’’ of plastic, with the sides open to the air. Does this arrangement still trap enough heat to make a difference in the growth? Does the difference in humidity affect plant growth?
PROJECT 2 Solar Cells: Will sunlight make a motor run? Purpose/Hypothesis In this project, you will be
working with photovoltaic cells, or solar cells, which utilize the photoelectric effect to convert solar energy into electricity. This project will allow you to determine if you can operate a small electric motor with solar cells. It will also let you determine how many cells and how much sunlight it takes to operate the motor. Level of Difficulty Easy/moderate.
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The seedlings inside and outside the greenhouse are growing slowly. Possible causes: 1. The time of year makes a difference, especially in the northern area of the country. During the winter, the Sun’s rays are less intense, and all the seedlings will grow more slowly. You will still see a difference. It will just take a little more time. 2. The spot does not get enough sun. Move the greenhouse and the other seedlings to a sunnier spot. 3. There is a gap between the box and the glass or plastic, which allows the warm air and humidity inside the greenhouse to escape. Seal the gap with tape. Problem: The seedlings inside the greenhouse withered and died after they sprouted. Possible cause: During the summer, the temperature inside the greenhouse can soar to 110˚F (43˚C) or more in direct sun. Move the greenhouse and all ten pots to a less sunny location or cover the glass or plastic with a large sheet of thin white paper to block some of the Sun’s rays.
Materials Needed
• 3 solar cells (.5-volt rating each) • 1 DC motor (l.5-volt rating) • 4 jumper wires with alligator clips on each end—three about 4 inches (10 centimeters) long, and one about 12 inches (30 centimeters) long Experiment Central, 2nd edition
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How to Experiment Safely Handle solar cells carefully. They are fragile and break easily.
• stopwatch or clock • marking pen • posterboard or a small table to support the experiment • cardboard to provide shade, about 24 inches (60 centimeters) square Approximate Budget $25. (Supplies can be pur-
Troubleshooter’s Guide Below is a problem that may arise during this project, a possible cause, and a way to remedy it.
chased at an electronics store.) Timetable About 30 minutes. Step-by-Step Instructions
Problem: The motor does not rotate under any condition.
1. Place the jumper wires with alligator clips on the + and - terminals of the solar cells, as Possible cause: The connections may be loose. illustrated. Attach the other ends to the Check them connections and try again. motor terminal. Be careful to match the + or - connections. Place the experiment on a piece of posterboard or a small table so you can move it around. 2. Make a small mark on the shaft of the electric motor with the marking pen. 3. Test the ability of the solar cells to power the motor under different lighting conditions, such as the following: outside on a sunny day; outside on a sunny day, but shaded by the cardboard; inside on a sunny day, but out of direct sunlight; inside in a dark room; inside at night under an incandescent and/or fluorescent light bulb.
Step 1: Set-up of three-cell circuit. GAL E GR OU P.
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Step 4: Sample performance chart for Project 2. GA LE GR OU P.
4. Record how many rotations the motor makes in 10 seconds—or if it runs at all—under each condition, using a chart similar to the one illustrated. Summary of Results Study your results. Under which conditions did the
solar cells operate the motor? How many rotations could you record? Write a paragraph summarizing and explaining your findings. Experiment Central, 2nd edition
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EXPERIMENT 3 What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the amount of heat generated from the heat lamp
Retaining the Sun’s heat: What substance best stores heat for a solar system? Purpose/Hypothesis Solar energy is often used
in homes as a source of heat. The solar energy system (solar panels) captures and stores the heat • the amount of time the container is left of the sun during the sunny hours. The heat is under the heat lamp then re-circulated in the home when needed, • the length of black plastic tubing and during the night or on cloudy days. Storing the therefore the volume of the substance heat of the sun is a major component of a solar put into the tube. energy system. In other words, the variables in this experiment Some storage devices use Glauber’s salt are everything that might affect the air tem(sodium sulfate decahydrate) in their storage perature in the containers. If you change more than one variable at a time, you will not be able systems. Glauber’s salt has the ability to store to determine which variable had the most effect more heat in its liquid state than water or other on the temperature. substances. In this experiment you will test Glauber’s salt along with two other substances to measure which one stores heat longer and would be most useful in a solar energy system. A heat lamp will provide the ‘‘Sun’s’’ energy. You will place three different substances: water, Glauber’s salt, and iodized salt in three clear plastic containers and place under a heat lamp for 12 hours. Once the heat lamp is turned off, you can begin to measure which substance best retains heat. To begin the experiment, use what you have learned about solar energy to make a guess about what substance will retain heat the longest. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The Glauber’s salt will retain heat longer than the water and table salt after being placed under a heat lamp.’’ 1090
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In this case, the variable you will change is the substance in the plastic containers. The variable you will measure is the air temperature in each of the containers. If the air temperature in the container with the substance containing the Glauber’s salt remains higher than the other containers, your hypothesis is correct.
How to Experiment Safely The heat lamp can get hot. Be careful when handling the lamp; you may want an adult to help.
Level of Difficulty Moderate to Advanced (because of the time and detail
involved). Materials Needed
3 clear plastic containers with lids, approximately 2 6 6 inches 1 heat lamp (150 watts) with a clip 60 grams (about one-quarter cup) of water 60 grams iodized salt (table salt) 60 grams Glauber’s salt (sodium sulfate decahydrate, available from a science supply store; you may need to ask your teacher for help ordering) • a container big enough to hold all three containers, an empty aquarium works well • tape • 3 digital thermometers small enough to be placed inside plastic container. If testing one substance at a time, then only 1 thermometer is needed (if you only have 1 thermometer, you can test each item separately) • • • • •
Approximate Budget $15 (assuming you have or can borrow a heat lamp
and large container). Timetable approximately 30 minutes to set-up; 12 hours waiting; 2 hours
monitoring results Step-by-Step Instructions
1. Place 60 grams of Glauber’s salt (in crystal form) in one plastic container. Label the container ‘‘Glauber’s.’’ 2. Place 60 grams of water in the second container, and 60 grams of iodized salt in the third container. Label each container with the substance it contains. Experiment Central, 2nd edition
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3. Tape one thermometer on the side of each container so that the temperature readings are visible. 4. Place all three labeled containers in the large container and clip the heat lamp onto the side of container. Make sure the heat lamp shines on all three containers evenly. Glauber Salt
5. Record the starting temperature of containers on a chart. 6. Turn on the heat lamp. Leave the lamp on for 12 hours.
Step 3: Tape one thermometer on the side of each container so that the temperature readings are visible. I LL UST RA TIO N BY TE MA H NE LS ON.
Step 6: Turn on the heat lamp. Leave the lamp on for 12 hours. IL LUS TR ATI ON B Y TE MA H
7. Turn off the heat lamp and record the temperature every 15 minutes for two hours. You can keep recording every 30 minutes until the air returns to the starting temperature. Summary of Results Study the results of your
temperature readings. You may want to graph the data. Can you see a difference between the rate at which the Glauber’s salt and table salt cooled? How did these substances compare to the water temperature reading? Which substance cooled down the fastest and which took the longest to cool? Was your hypothesis correct? Write a paragraph summarizing and explaining your findings.
NE LS ON.
Change the Variables You can change the var-
iables in this experiment several ways. You can vary the substances within the containers to measure what stores heat more than others. Instead of using a heat lamp, you could place the containers out in the sun. Depending upon where you live and the season, you can place the containers in a sunny spot, and record the temperatures after the sun has gone down. How does this compare with using a heat lamp? How high do the temperatures get? 1092
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Design Your Own Experiment How to Select a Topic Relating to this Concept
First, define what aspect of solar energy you are interested in, such as ways to use this energy. You might want to investigate whether pollution is changing the effects of solar energy on our world. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on solar energy questions that interest you. As you consider possible experiments, be sure to discuss them with a knowledgeable adult before trying them. Some of the materials or processes may be dangerous. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise you might not be sure which question you are answering, what you are or should be measuring, and what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Troubleshooter’s Guide It’s common for experiments to not work exactly as planned. Learning from what went wrong can also be a good experience. Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: Temperature changes between the three substances did not differ. Possible causes: The heat lamp may not be hot enough. Check your heat lamp; it should be at least 150 watts. If it is 150 watts, the containers may not be receiving the same amount of heat. Try heating one container at a time with the heat lamp directly over the container. Problem:The thermometer is not taking readings. Possible causes:The thermometer may have fallen into the liquid in the container and is wet. Make sure the thermometer is anchored to the container and check that the thermometer is working. Repeat the experiment. Problem: The Glauber’s salt did not melt completely. Possible cause: The salt may not be getting enough heat. Try heating one container at a time with the heat lamp directly over the container. You also can increase the number of hours you leave on the heat lamp. If you increase the hours, make sure to keep it the same for the other substances. Even in a partial liquid state Glauber’s salt will retain heat. You can take your temperature readings and see the outcome.
Recording Data and Summarizing the Results Every good experiment
should be documented so that other people can understand the procedures and results. Keep diagrams, charts, and graphs of any information Experiment Central, 2nd edition
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that is useful. Your experiment, whether successful or not, is important information to be shared with others. Related Projects Solar energy is available on a daily basis (except on
cloudy days), so take advantage of this free resource. For example, you could design and build a solar oven for cooking, a solar battery to run toys, or a radiometer to measure solar intensity. Explore the possibilities!
For More Information Aldous, Scott. ‘‘How Solar Cells Work.’’ HowStuffWorks. http:// www.howstuffworks.com/solar cell.htm (accessed on March 18, 2008). Explanation of solar cells. Asimov, Issac. The Sun and Its Secrets. Milwaukee, WI: Gareth Stevens Publishing, 1994. Discusses the Sun’s origins, content, and historical facts. Edelson, Edward. Clean Air. New York: Chelsea House Publishers, 1992. Explores the devastating effects of population growth and industry on air quality and ways to clean up the air including using solar energy as a solution. Energy Information Administration. ‘‘Solar Energy: Energy from the Sun.’’ Energy Kid’s Page. http://www.eia.doe.gov/kids/energyfacts/sources/ renewable/solar.html (accessed on March 18, 2008). Basic information on solar energy. ‘‘Energy Story: Solar Energy.’’ Energy Quest. http://www.energyquest.ca.gov/ story/chapter15.html (accessed on March 18, 2008). Information and science projects related to solar energy. ‘‘Solar Energy Animation.’’ Ocean Motion. http://oceanmotion.org/html/ resources/solar.htm (accessed on March 18, 2008). Information demonstrates how the intensity of the energy from the sun varies with location and time.
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ou hear sound when vibrations enter your ears and send signals through your nerves to your brain. These vibrations are caused by disturbances in the air. For example, when you hit a drum, the top of it vibrates, causing a disturbance in the molecules in the air. This vibration, or sound wave, travels through the air in all directions, eventually reaching your ears. If you could see sound waves, they would look much like the waves you see when you drop a stone onto a calm water surface.
Sound waves are usually described with two measurements: frequency and amplitude. GAL E GR OU P.
How do we hear? Sound waves travel through air at about 1,088 feet (332 meters) per second. When the sound waves or vibrations reach your ears, they push on your eardrums and cause them to vibrate. Each eardrum pushes against a series of three tiny bones in your middle ear. These tiny bones push against another membrane, which causes waves in a fluid inside your inner ear. Here, special cells pick up the differences in pressure from the waves and transform them into electrical signals that travel along nerves to your brain. When these signals reach the brain, you hear the sound and usually recognize its source. How is sound measured? Sound waves are usually described with two measurements: frequency and amplitude. Frequency means the number of waves passing a given point in a given period of time. This is usually measured in hertz, abbreviated Hz. One hertz equals 1 cycle per second. Humans can usually hear sounds with frequencies from 20 Hz to 20,000 Hz. The faster a wave vibrates, the higher its frequency and the higher a sound it produces. The highness or lowness of a sound is its pitch. A high-frequency sound has a high pitch. The amplitude of the sound is its power or loudness. The taller the sound wave, the higher 1095
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As the drum vibrates, it pushes on molecules in the air, causing them to vibrate in the same way. This vibration, or sound wave, travels through the air in all directions, eventually reaching your ears. PE TER AR NO LD I NC.
its amplitude and the louder the sound it produces. We usually measure amplitude in decibels. For example, leaves rustling in the wind might produce a sound of about 20 decibels, while a jet taking off creates a sound of at least 140 decibels, loud enough to damage your hearing. Listening to very loud sounds for a long time, including loud music, will damage the tiny nerves in your ears and can lead to a permanent hearing loss. Many rock musicians have discovered that they already have hearing problems. How long have people wondered about sound? People have been experimenting with sound for a long time. Pythagoras (572–497 B . C . E .) experimented with strings to determine how sounds changed with changes in the lengths of the strings. Historians credit him with the development of the musical scale. In about 1700, French physicist Joseph Sauveur first used the word acoustics to describe music and the way sound works. He worked on the mathematics of sound and studied how strings made different sounds depending on their length. Hermann von Helmholtz (1821–1894) discovered much about sound in the 1800s, especially the connections between mathematics and music. He also built one of the first sirens. Sound, and the way humans and other animals perceive it, is a fascinating topic. What kind of questions do you have about sound? You will have an opportunity to explore different aspects of sound in the following experiments.
EXPERIMENT 1 Wave Length: How does the length of a vibrating string affect the sound it produces? Purpose/Hypothesis In this experiment, you will find out how the length
and tightness of a plucked string affects the sounds it produces. Before you begin, make an educated guess about the outcome of the experiment 1096
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WORDS TO KNOW Acoustics: The science concerned with the production, properties, and propagation of sound waves.
Hertz (Hz): The unit of measurement of frequency; a measure of the number of waves that pass a given point per second of time.
Amplitude: The maximum displacement (difference between an original position and a later position) of the material that is vibrating. Amplitude can be thought of visually as the highest and lowest point of a wave.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Decibel (dB): A unit of measurement for the amplitude of sound.
Wave: A regular disturbance that carries energy through matter or space without carrying matter.
Frequency: The rate at which vibrations take place (number of times per second the motion is repeated), given in cycles per second or in hertz (Hz). Also, the number of waves that pass a given point in a given period of time.
Variable: Something that can affect the results of an experiment
Pitch: A property of a sound, determined by its frequency; the highness or lowness of a sound.
Vibration: A regular, back-and-forth motion of molecules in the air. Volume: The amplitude or loudness of a sound.
based on your knowledge of sound. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
Waves spread out from the source of the disturbance in wider and wider circles. K EL LY A. Q UI N.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The longer the string, the higher the pitch of the sound produced by that string.’’ In this case, the variable you will change will be the length of the string, and the variable you will measure will be the pitch of the sound. You expect a longer string to produce a higher pitch sound. Experiment Central, 2nd edition
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Level of Difficulty Easy.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of string • the length of the string • the tightness or tension of the string • the strength with which the string is plucked • the pitch of the sound • the experimenter’s ability to detect different pitches In other words, the variables in this experiment are everything that might affect the perceived pitch of the sound. If you change more than one variable, you will not be able to tell which variable had the most effect on the pitch.
How to Experiment Safely Be careful handling the scissors.
Steps 1 and 2: Set-up of experimental instrument. G AL E GRO UP.
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• a sturdy cardboard box, such as one for copy paper • thin, strong string • scissors • hole-puncher • ruler Approximate Budget $5, if you need to buy
string; other materials should be available in the average household. Timetable 1 hour. Step-by-Step Instructions You will be working
with the top edge of two sides of the box; the edges join to make a V. 1. Use the hole puncher or the tip of your scissors to make ten small holes along each side of the V, placing the holes opposite from each other, as shown. 2. Tie a length of string through each pair of holes, pulling it tightly before tying it to the other edge of the box. You should end up with strings of 10 lengths, as illustrated. 3. Using your ruler, measure the length of each string from knot to knot. Record these lengths on your data sheet. 4. Pluck each string several times and listen carefully. What do you hear? Describe it on your data sheet. You may want to play the strings for other people, so you are not depending on only your own ears. 5. If possible, bend the cardboard angle a little outward to pull the strings tighter and increase the tension. Repeat sStep 4. How do the sounds change? Experiment Central, 2nd edition
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6. Try plucking the strings harder and softer. Record what you hear on your data sheet. Summary of Results Study the results on your
chart. Did the longer strings produce higher pitches or lower pitches? Why? Was your hypothesis correct? Did increasing the tension change the pitch of the sound? Write a paragraph summarizing and explaining what you have found. Change the Variables You can vary this experi-
ment. Try using different materials, such as piano wire, fishing line, thicker string, or rubber bands. See how the pitch of the sound is affected.
EXPERIMENT 2
Troubleshooter’s Guide Experiments do not always work out as planned. Even so, figuring out what went wrong can definitely be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: You cannot hear a clear sound from the strings. Possible cause: Your strings are not tied tightly enough. Try again, trying them tightly. Problem: All the strings sound the same. Possible cause: Your cardboard box is not big enough to allow markedly different lengths of strings. Find a bigger box so the lengths of the strings vary more and try again.
Pitch: How does the thickness of a vibrating string affect sound? Purpose/Hypothesis In this experiment, you will explore how the thick-
ness of the vibrating object affects the pitches it produces. You will use different sizes of rubber bands to test this effect. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of sound. The educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment
Step 3 and 6: Data sheet for Experiment 1. G AL E GR OUP .
• the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘Thicker bands will produce lower pitches.’’ Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables for this experiment: • the thickness of rubber bands • the length of bands
In this case, the variable you will change will be the thickness of the rubber band, and the variable you will measure will be the pitch of the sound. You expect a thicker band to produce a lower pitch sound. Level of Difficulty Easy. Materials Needed
• the strength with which the band is plucked • the sound produced by plucking • the experimenter’s ability to detect different pitches In other words, the variables in this experiment are everything that might affect the pitch of the sound. If you change more than one variable, you will not be able to tell which variable had the most effect on the pitch.
How to Experiment Safely Try not to snap yourself with the rubber bands.
• 8-inch-square (20-centimeter square) metal baking pan with straight sides • 5 rubber bands of different thickness but the SAME length • ruler Approximate Budget $5, if you need to purchase
rubber bands; other materials should be available in the average household. Timetable 1 hour. Step-by-Step Instructions
1. Arrange the rubber bands in order from thinnest to thickest. 2. Measure the width of each rubber band with your ruler. Record these numbers on your data sheet, as illustrated.
Step 2 and 5: Data sheet for Experiment 2. GAL E GR OU P.
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3. Keep the bands in order, stretch each one over the pan, which acts as a sound box. Be sure to stretch them the same amount so the portion of the band over the open part of the pan is under the same tension as the rest of the band. See illustration. 4. Pluck each band, beginning with the thickest one, and listen carefully to the pitch it produces. 5. Describe each tone as you pluck the band and record on your data sheet what you hear.
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: You cannot hear the differences in the pitches. Possible cause: Your rubber bands are too similar in size. Try to find bands that are several millimeters different in width. Check an office supply store or an art supply store. Problem: You cannot hear much sound at all.
Summary of Results Study the results on your
Possible cause: The pan is absorbing the vibra-
chart. How did the thickness of the band affect tions. Be sure the pan is metal, with straight sides, the pitch it produced? Did a thick band produce and deep enough so the bands are free to vibrate. a lower pitch or a higher pitch? Thick bodies vibrate more slowly than small ones, and slower vibrations produce lower pitches. Is this what happened in your experiment? Was your hypothesis correct? Write a paragraph summarizing what you learned.
Step 3: Keeping the rubber bands in order, stretch each one over the pan, which acts as a sound box. G AL E GR OUP . Experiment Central, 2nd edition
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Change the Variables You can vary this experi-
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the loudness of the sound • the distance of the sound from the experimenter • the material covering the sound device • the thickness of the material covering the sound device
ment in several ways. Try using bands with even greater differences in thickness. Record their width and see what happens. Try putting the same size bands on a larger pan and plucking the two instruments next to each other. What do you hear? Experiment with different size pans and you can create an entire orchestra. What is the effect of length on the sounds you produce? You can also use a box made from something else, such as wood or plastic. Repeat the experiment and record what you learn.
• the enclosure of the sound device • the experimenter’s ability to detect the loudness In other words, the variables in this experiment are everything that might affect the perceived loudness of the sound. If you change more than one variable, you will not be able to tell which variable had the most effect on the sound.
EXPERIMENT 3 Soundproofing: How do different materials affect sound? Purpose/Hypothesis How sound waves travel
through a gas, liquid, or solid depends upon the properties of the matter. When sound waves pass through materials, they may move easily through the material, be absorbed, or be reflected. It is likely that some combination will happen. The more a sound is absorbed, the better the material is at sound insulation. In this experiment, you will measure how different solid materials affect sound. You can test several materials, including cardboard, plastic, aluminum foil, Styrofoam, felt, and rubber. The thickness of a material also affects the amount of sound waves that pass through the material. For this reason, you will need to have all the materials at about the same thickness. Which of the materials will best absorb the sound waves? You will need a helper to carry out this experiment. Your helper will make sure the listener does not see the materials being tested, which will help avoid bias. Your helper will also serve as a second listener, so you can have two sets of data to draw upon. Before you begin, make an educated guess about the outcome of the experiment based on your knowledge of sound and the materials. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
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• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
How to Experiment Safely You may need to cut the Styrofoam to make it the same thickness as the other materials. Be careful handling the scissors.
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘The rubber material will absorb the sound more than the other materials.’’ In this case, the variable you will change will be the material covering the sound, and the variable you will measure will be the loudness of the sound. In this experiment, your control will be the reference for you to compare each sound. The control in this experiment will be the metronome sound moving through air, not enclosed by any solid material. Throughout the experiment you will compare the control against the experimental test materials. Level of Difficulty Moderate. Materials Needed
• piece of cardboard, about 1/8 inch thick, large enough to cover the box opening • aluminum baking sheet, about 1/8 inch thick, large enough to cover the box opening • felt fabric • Styrofoam (available at hardware or craft stores) • rubber floor mat (car mats work well) • masking tape • scissors • metronome, you could also use an alarm clock, watch that ticks loudly, or other device with a constant sound • shoe box, large enough to fit the metronome or other sound device • ruler • helper • headphones (optional) Approximate Budget $10, most materials should be available in a
household. Experiment Central, 2nd edition
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Timetable 45 minutes. Step-by-Step Instructions
Step 2: Place the shoebox on a table or countertop and set the metronome (or other device) inside. I LL UST RA TI ON BY
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T EM AH NE LS ON.
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6. Step 5: Completely cover the box opening with one of the materials. I LLU ST RAT IO N BY TE MA H NE LSO N.
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1. Using the ruler, make sure the felt and Styrofoam are the same thickness as the other materials. You may need to fold over the felt and cut the Styrofoam. 2. Place the shoebox on a table or countertop and set the metronome (or other device) inside. 3. Stand back several feet from the box, at a distance where you can hear the sound. Use the tape to mark the spot on the floor where you are standing. Place the shoebox on a table or countertop and set the metronome (or other device) inside. Stand at the tape and turn around so you cannot see the box. Have your helper start the metronome. This is the loudness you will compare the test materials against. While you cover your ears with headphones (if available), have your helper completely cover the box opening with one of the materials. You should not know which of the materials your helper is using. The material may need to be taped to the box so that the opening is sealed. After your helper has given you a signal, uncover your ears and listen. Note how the loudness compares to the Control sound in a chart (see the sample chart). Still keeping your back turned, have your helper listen to the sound device uncovered before moving on to the next material. This will help you compare the sound against each test material. 8. Repeat Steps 6–8, using all the materials. Make sure you cover your ears while your helper places the material over the box opening. Do not turn around. After you listen to each sound, write down how the loudness compares to the Control. 9. When you have tested all the materials, you and your helper switch places. Make another chart. Have your helper stand at Experiment Central, 2nd edition
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the tape mark on the floor, facing away from the box. Repeat the process, with you placing each material over the box opening in any order. Summary of Results Look at the results on the
two charts. Are they the same? Was there one material that you both thought significantly affected the loudness of the sound? Were there any materials that made the sound louder? Were you or was your helper surprised at the results? While analyzing your results, consider the properties of each material. Write a paragraph summarizing and explaining what you have found. Change the Variables There are many ways you
can vary this experiment to explore soundproofing. You can focus on one of the materials, such as the fabric, and test different types. You can test velour, silks, and felt. You can test different types of metals. If you test different types of one material, make sure the thicknesses are about the same. But you also can use one material and change the thickness. You could try combining certain materials together to test for soundproofing. You may want to research the materials that buildings or musicians use to soundproof rooms, and test how these materials affect sound.
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: You had different results than your helper. Possible cause: It is likely that there will be some difference in how you and your helper perceive the loudness. If the results are extremely different, it may be that one of you is not completely covering the box opening. Compare how you are both placing the material against the box opening? Are you both sealing the box completely? When you have found a consistent setup, try again. Problem: The sounds were all muffled about the same amount. Possible cause: You may be standing too far away from the sound to make a noticeable difference. Stand far enough away that you can hear the sound clearly without anything covering the box opening, and repeat the experiment.
Design Your Own Experiment How to Select a Topic Relating to this Concept Are you interested in the
frequency of vibrations and the pitches they produce, how to amplify sound to make it louder, or how to direct where the sound waves go? Maybe you are interested in how sound waves travel through different materials, such as gases, water, and solids. Would you like to make your own instruments and experiment with the sounds they make? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information about sound questions that interest you. Experiment Central, 2nd edition
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Structure of the human ear. GAL E GR OU P.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise you may not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts, such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental set-up and results. If you are preparing an exhibit, display the sound-producing devices you create to help explain what you did and what you discovered. Observers could even test them out themselves. If you have done a 1106
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nonexperimental project, you will want to explain clearly what your research question was and illustrate your findings. Related Projects There are many uses of sound in modern technology. You could investigate how acoustics work in a large concert hall or how speakers and amplifiers work in your home sound system. You could also see how sound is used in modern medicine, in ultrasound machines, for example. These machines help doctors observe things that are difficult to see by turning sound into pictures.
For More Information Dale, Jeremy W., and Simon F. Park. Molecular Genetics of Bacteria. New York, NY: John Wiley & Sons, 2004. De Pinna, Simon, and Chris Fairclough. Sound (Science Projects). Austin, TX: Raintree/Steck Vaughn, 1998. Provides ideas for science fair projects involving the principles of sound. Harris, Tom. ‘‘How Hearing Works.’’ HowStuffWorks. http://www.howstuffworks.com/ hearing.htm (accessed on March 13, 2008). Clear explanation of hearing and sound. Kaner, Etta. Sound Science. Toronto: Kids Can Press, 1991. Explores the nature of sound using games, puzzles, fun facts and experiments. ‘‘Science of Music.’’ Exploratorium. http://www.exploratorium.edu/music/ (accessed on March 13, 2008). The science of the sounds of music. Trun, Nancy Jo, and J.E. Trempy. Fundamental Bacterial Genetics. Oxford, UK: Blackwell Science, 2003. Van Cleave, Janice. Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. New York: John Wiley & Sons, 1991. Presents step by step experiments using household materials and scientific explanations. ‘‘ZoomSci.’’ PBS Kids. http://pbskids.org/zoom/activities/sci/ (accessed on March 13, 2008). Simple science experiments on sound.
Experiment Central, 2nd edition
Ultrasound scan of a fetus. PHO TO R ES EAR CH ER S IN C.
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P
eople’s fascination with space goes back hundreds of years to simple stargazing and trying to understand the heavens. Today’s astronomers use a wealth of tools to study space. Most astronomers are involved in measuring things, such as the speed, distance, and mass of objects in the universe. Knowing these facts can lead to further knowledge, such as the object’s origin or composition. To measure things astronomers use observations and laws of the universe. Much of what we know about space comes from the study of light given off by objects in space. The change from observing objects with the naked eye to powerful instruments was one of the major advances in astronomy. Telescopes are one of the main tools astronomers use to gather light. Understanding the physical laws of how light and objects move also fueled astronomers’ knowledge of the universe. Merging the visual data with calculations has led to awesome findings on stars, planets, galaxies, and solar systems that are far, far away. Mountains on the Moon Peer through the right telescope on Earth and it is possible to view something in space that is a billion light years away—just one light year is about 5,865,696,000,000 miles (9,460,800,000,000 kilometers)! The telescope was the first groundbreaking tool used in astronomy. With the telescope, astronomers could study the motions of celestial objects that were previously undetectable. The telescope was invented in the Netherlands in the early 1600s. Soon afterwards, Italian scientist Galileo Galilei (1564–1642) became the first person to use this new instrument to study the sky. He made a series of remarkable discoveries. Among his observations was that the Moon had mountains and craters on it and was not smooth as previously believed. He observed four bright objects orbiting or revolving around Jupiter, what is now known as Jupiter’s moons. He also saw that the Sun 1109
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had spots, which rotated. His observations led him to conclude that objects rotated and that they revolved around other objects. In modern day astronomers use telescopes of all shapes and sizes. Some are located on Earth and others sit in space. One of the most famous telescopes in space is the Hubble Space Telescope. The Hubble was launched into space in 1990 and has transmitted up-close views of celestial objects that are billions of light years away. One of the largest optical telescopes in the world is the W. M. Keck telescope in Hawaii. It measures 33 feet (10 meters) in diameter. # ROG ER R ES SM EY ER/ CO RB IS.
The Hubble Space Telescope was launched into space in 1990 and has transmitted upclose views of celestial objects that are billions of light years away. UPI /B ETT MA NN.
How they work In the way that they collect and magnify the light, telescopes make objects appear larger than they are. There are two basic types of telescopes: refractor telescopes and reflector telescopes. Each goes about enlarging an image in different ways. The amount of light a telescope can collect relates to the size of the lens or mirror used to gather light. Telescopes that have a larger lens or mirror will generally collect more light, and so will detect much fainter objects. The Galileo-style of telescope is a refractor telescope and it uses two types of lenses to gather and bend or refract the light. The lens in the front of the telescope, the objective lens, gathers the light from the object. In a refracting telescope the objectives lens is a convex lens, a lens that is thicker in the middle and curves outward. Convex lenses make objects appear larger but blurry. This is the type of lens used in a magnifying glass. In one type of refractor telescope the second lens, called the eyepiece lens, uses a smaller concave lens. A concave lens caves or curves inward in the middle. This focuses the light from the objective lens and magnifies it. A long tube, or series of tubes, holds the lenses in place at the correct distance from one another. The reflector telescope uses mirrors instead of lenses to collect light. The primary mirror that collects and focuses the light is usually a concave mirror. The light reflects off the primary mirror to another mirror, which directs the light to the eyepiece. Each type of telescope has strengths and weaknesses. Most of the largest telescopes
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Incoming light
eyepiece
A refractor telescope uses two types of lenses to gather and bend or refract the light. GA LE
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in the world are reflectors. Large mirrors cost less and are easier to support than lenses. The deeper astronomers look into space, the farther back in time they are looking. It takes so long for light traveling through space to reach Earth that astronomers scanning the edges of the universe are seeing objects as they were billions of years ago. Shifty light Astronomers take observations gathered from telescopes and apply their knowledge of how light travels to theorize on the past, present, and future behavior of objects in space. The Doppler effect or Doppler shift is one way that astronomers make measurements on the light they observe. Astronomers use the Doppler effect to calculate the speed of an object and its movements. Although they are not visible, light energy travels in waves. Water and sound energy also travel in waves. A wave is a vibrational disturbance that
eyepiece primary mirror
Incoming light
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A reflector telescope uses mirrors instead of lenses to collect light. GA LE G RO UP.
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travels through a material or space. Light waves can travel through matter or a vacuum, such as space. Every wave has a high point called a crest. Red The distance from one crest to the next crest is called the wavelength. Orange Visible light is made up of seven basic colors— crest red, orange, yellow, green, blue, indigo, and Yellow violet. Each color has its own unique wavelength. For example, blue light waves are shorter than red Green light waves. The frequency is the number of waves that pass a point in space during any time interval. What a person sees as color is actually Blue the frequency of the light. Because red has a longer wavelength, something red has a lower Violet frequency than something blue. The Doppler shift occurs because there is an apparent shift in the wavelength depending on whether an object is moving towards or away Light travels in waves; each from the observer. As objects in space move away, or recede, from Earth, color has its own wavelength. the wavelengths appear stretched or longer. This is called a redshift, GA LE GRO UP. because the light appears to have a lower frequency. If the object moves towards Earth, the wavelengths appear compressed or shorter. This makes the light appear to have a higher frequency and a blueshift occurs. When an object approaches a In a vacuum, such as space, all the wavelengths in light travel at one person, waves bunch together speed. If scientists know the amount and colors of light that an object and there is a blueshift; when gives off, they can measure the amount of color shift. Since the wavean object recedes, waves spread length of each color is known, the color shift will determine the direction out and there is a redshift. and speed of the object. GA LE GRO UP. The Doppler effect can be used by astronomers to gather information about how fast object approaching stars, galaxies, and other astronomical objects (blueshift waves) object moving away move toward or away from Earth. Using the (redshift waves) Doppler shift, astronomers calculated that the more distant galaxies are moving away from Earth more rapidly than the ones that are closer. This finding led to the theory that the universe is expanding, and to the origins of the solar system. direction of car In the following two experiments you will explore the Doppler effect and telescopes. wavelength
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WORDS TO KNOW Blueshift: The shortening of the frequency of light waves toward the blue end of the visible light spectrum as they travel towards an observer; most commonly used to describe movement of stars towards Earth. Concave lens: A lens that is thinner in the middle than at the edges. Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Convex lens: A lens that is thicker in the middle than at the edges. Crest: The highest point reached by a wave. Doppler effect: The change in wavelength and frequency (number of vibrations per second) of either light or sound as the source is moving either towards or away from the observer. Focal length: The distance from the lens to the point where the light rays come together to a focus.
Objective lens: In a refracting telescope, the lens farthest away from the eye that collects the light. Redshift: The lengthening of the frequency of light waves toward the red end of the visible light spectrum as they travel away from an observer; most commonly used to describe movement of stars away from Earth. Reflector telescope: A telescope that directs light from an opening at one end to a concave mirror at the far end, which reflects the light back to a smaller mirror that directs it to an eyepiece on the side of the tube. Refractor telescope: A telescope that directs light through a glass lens, which bends the light waves and brings them to a focus at an eyepiece that acts as a magnifying glass. Telescope: A tube with lenses or mirrors that collect, transmit, and focus light. Variable: Something that can affect the results of an experiment.
Frequency: The rate at which vibrations take place (number of times per second the motion is repeated), given in cycles per second or in hertz (Hz). Also, the number of waves that pass a given point in a given period of time.
Wave: A motion in which energy and momentum are carried away from some source; a wave repeats itself in space and time with little or no change.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Wavelength: The distance between the crest of a wave of light, heat, or energy and the next corresponding crest.
EXPERIMENT 1 Telescopes: How do different combinations of lenses affect the image? Purpose/Hypothesis Telescopes take advantage of the properties of light
to enlarge and focus images. The basic design of a telescope aligns two Experiment Central, 2nd edition
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Powerful telescopes allow scientists to observe parts of space that the human eye never could, such as this cluster of thousands of stars. SP AC E TEL ES COP E SC IE NC E I NS TIT UT E
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lenses a set distance from each other. In general, the objective lens is relatively large in diameter so that it can gather light; the eyepiece is smaller and stronger. For this experiment, you will test different combinations of convex (curving outward) and concave (curving inward) lenses. If possible, try to gather several different strengths and sizes of lenses; the listed sizes are only suggestions. Check the Further Readings section for places to find lenses. The objective lens will always be a convex lens. This lens should be larger in diameter and weaker than the eyepiece lens. The thinner a lens is in the center, the weaker it is. Use an eyepiece lens that is smaller and more powerful than the objective lens. You can determine a lens’ power by its focal length, the distance required by the lens to bring the light to a focus. In general, as the focal length of a lens decreases, the power of the lens increases. You will use both a convex and a concave eyepiece lens. Cardboard, or construction paper, tubes that slide in and out from each other will hold the lenses. The distance between the two lenses should be about the sum of the focal lengths of the lenses. Using a convex and a concave lens will produce a right-side-up image. Using two convex lenses will produce an upside-down image. (When viewing celestial objects, astronomers do not care that much whether the object is upside down or not.) You can also calculate the magnification power of your telescope if you know the focal lengths of your lenses. The magnification power equals the focal length of the objective lens divided by the focal length of the eyepiece lens. For example, if the focal length of the objective lens is 50 centimeters, and the focal length of the eyepiece is 5 centimeters, your telescope will magnify the object ten times the actual size of the object. If the focal length of that same telescope had a focal length of 1 centimeter, the telescope would magnify the object 50 times its actual size. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of telescopes. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: Experiment Central, 2nd edition
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• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Two convex lenses will produce a larger but blurrier image than a convex and a concave lens combination.’’ In this case, the variable you will change is the type of eyepiece lens. The variable you will measure is the size and sharpness of the image produced.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the thickness of the lens • the size of the lens • the curvature of the lens • the distance between the lenses In other words, the variables in this experiment are everything that might affect the magnified image. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on seeing the image.
Level of Difficulty Moderate. Materials Needed
1. 1 convex lens for the objective lens (can be about 2 to 4 inches [5 to 10 centimeters] in diameter, and over 500 millimeters in focal length). (Lenses are available from scientific supply houses and hobby stores. You could also try to find lenses around the house, such as from magnifying glasses or old eyeglasses, as well as asking an eyeglass store if they have any lenses they are going to discard.) 2. 1 convex lens for the eyepiece, smaller in diameter than the objective lens (can be 1 to 1.5 inches [2.5 to 3.5 centimeters] in diameter, focal length of less than 20 to 50 millimeters) 3. 1 concave lens for the eyepiece, (can be 1 to1.5 inches [2.5 to 3.5 centimeters] in diameter, focal length of less than 20 to 50 millimeters) 4. sturdy tape, such as masking tape 5. scissors 6. ruler 7. 2 cardboard tubes, one that slides inside the other: The tubes should be about the same size as the lenses. If you do not have tubes, you can roll up thick construction paper and tape to make them. Experiment Central, 2nd edition
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8. helper 9. picture or news article to view 10. other concave and convex lenses of different sizes (optional)
How to Experiment Safely If you use the telescope outside, never look directly at the Sun. The Sun’s rays are so powerful they can cause permanent eye damage.
Approximate Budget $15. Timetable 1 hour.
Step-by-Step Instructions
Step 7: Tape the objective lens to the far end of the telescope, and the eyepiece lens to the near side. GA LE GRO UP.
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1. Tape the picture or printed piece of paper on a wall. 2. Begin with the smaller, stronger convex lens to use as the eyepiece, and the larger, less powerful convex lens for the objective lens. Hold the objective lens towards the picture at arms length. 3. Hold the eyepiece near your eye, in front of the objective lens. 4. Move the eyepiece closer and farther away to the objective lens while focusing on the picture. 5. When the object is in focus, have your helper measure the distance between the two lenses. (If you know the focal length of your lenses, the distance of the tubes should about equal the sum of the focal lengths of the lenses.) 6. Place the smaller tube inside the larger tube. The tubes should fit snugly inside each other, with the inner tube able to slide. Extend the tubes and cut them so the combined length of the tubes is slightly greater than the distance between the lenses. If you are rolling tubes out of thick construction paper, make sure you roll the paper into tubes where the openings are roughly equal to the size of the lenses. 7. Tape the objective lens to the far end of the telescope, and the eyepiece lens to the near side. 8. Look at the picture through the telescope, sliding the tubes until the object comes into focus. 9. Note whether the image is right side up or inverted, and the relative size of the image. objective lens (convex) 10. Remove the eyepiece lens and repeat Steps 2 through 7 using the concave lens as the eyepiece. Experiment Central, 2nd edition
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11. If you have other lenses of differing sizes and thickness, repeat the process to compare the results. Old glasses and magnifying glasses are a couple inexpensive sources for lenses. Record whether the lens is thicker or thinner than the one you already used when you note the results. If you know the focal lengths of the lenses, calculate the magnification power. Summary of Results Was your hypothesis cor-
Troubleshooter’s Guide Below is a problem that may arise during this experiment, some possible causes, and some ways to remedy the problem. Problem: The picture is blurry. Possible cause: The distance between the two lenses may be too short or long. The distance should be equal to the sum of the focal lengths of the two lenses. Building a telescope involves some trial and error to get the correct distance and focus. Take careful measurements when holding the lenses up and try to gather several different lenses to investigate telescopes thoroughly.
rect? What does sliding the inner tube in and out do to the image? If you tried using other lenses, how did these compare to the first set? Think about what change the eyepiece made in the appearance of the image once you placed it in front of the objective lens. If you want to continue the project to view celestial objects, go outside at night. Pick one particular light in the night sky and compare the image using each of the telescopes. Change the Variables To change the variables in this experiment you can
change the type of lens you use, the thickness of the lens, or the length between the lenses. Modify the Experiment You can simplify this experiment by testing two
magnifying glasses by themselves. Try to find two magnifying glasses that are different sizes. If you do not have two magnifying glasses, you can use other lenses around the house, such as eyeglasses. You need to make sure that one of the lenses is convex (thicker in the middle). Find a well-lit object or picture that you can focus on. Hold the more powerful magnifying glass up close to your eye. This is the eyepiece lens. Hold the weaker magnifying glass between the eyepiece lens and the object. This lens should be convex. Move this lens back and forth until the object become clear and in focus. How does moving the lens change the look of the object? What happens when you take the lens away and only look through the eyepiece lens? Keep the eyepiece lens the same and experiment with convex lenses you can find that are different strengths. How does this magnify the object? Experiment Central, 2nd edition
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EXPERIMENT 2 What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
Doppler Effect: How can waves measure the distance and speed of objects? Purpose/Hypothesis Astronomers use the Dop-
• the sound
pler effect to determine whether an object in space is moving towards or away from Earth and how fast it is moving. However, the Doppler • the direction the object is moving—either effect was first discovered using sound waves, not towards or away from the person holding light waves. The perception of both light and the microphone sound is from the waves emitted. Waves coming In other words, the variables in this experiment from an object moving away from an observer are everything that might affect the sound of have a lower frequency than those from an object the noise maker. If you change more than one moving toward the observer. variable at the same time, you will not be able to tell which variable had the most effect on the In sound, pitch is determined by how many distance and speed of the object. waves per second reach the ear. The more sound waves a person hears, the higher the pitch. When an object moves toward a person, it takes less and less time for each wave to reach the person. The waves crowd together. The person gets more waves per second and it results in an increase in pitch. When the sound moves away from a person, the waves spread out. A person gets fewer waves per second and the person hears a decrease in pitch. In this experiment, you will determine how the Doppler effect relates to sound waves. You will record the sound of an alarm clock or noisemaking device that is approaching and moving past you at varying speeds. You can then draw conclusions about the relative distance and speed of the object from listening to the increase and decrease in pitch. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of the Doppler effect and waves. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen • the speed of the object (in this case, the bicycle)
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will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this How to Experiment Safely experiment: ‘‘The object moving at the fastest speed will emit a pitch that quickly increases, Be careful when biking. Find an empty area with then decreases, as it passes a stationary person.’’ little or no traffic before you begin. In this case, the variable you will change is the speed of the moving object. The variable you will measure is the pitch of the sound. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental setup, and that is the movement of a noisy object. For the control in this experiment you will record the sound of an unmoving object, which will release its sound waves at a steady pitch. Level of Difficulty Easy. Materials Needed
• an assistant to help perform experiment • bicycle • wind-up alarm clock with continuous sound or other portable noise-making appliance, such as a kitchen timer • tape recorder with microphone • helper Approximate Budget $0 (assuming that you have the tape recorder
and bike).
Step 3: Tape record the sound of the alarm clock as it approaches and moves past you.
Timetable 20 minutes.
GAL E GR OU P.
Step-by-Step Instructions
1. For the control: Stand at the side of a low-traffic area with the tape recorder. Start the alarm clock or buzzer and record the noise as you hold it for about five to 10 seconds. When finished recording, say the word ‘‘control’’ into the microphone to identify what is happening on the tape. Experiment Central, 2nd edition
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2. One person will hold the tape recorder and one will ride the bike. Have your Troubleshooter’s Guide helper (or you) walk a set distance away with the tape recorder; when the biker is Below is a problem that may arise during this ready to ride, he or she should turn the experiment, a possible cause, and a way to remedy the problem. alarm clock or buzzer on. 3. The person at the side of the road begins Problem: There was no difference between the ‘‘Slow’’ tone and the ‘‘Fast’’ tone. tape recording, as the biker slowly rides the bike past the tape recorder. The biker Possible cause: The biker may not have been riding at a significantly slower speed that the should keep at a steady, slow pace, by fast speed. Try biking at two different speeds counting the rotations of each pedal. as you steadily count, matching your count4. Say the word ‘‘Slow’’ into the microing to each pedal rotation. Practice for the phone after the bike stops. slow and fast speeds, then repeat the experiment. 5. Repeat the bike ride, returning to the set distance, this time riding at a steady quick pace past the tape recorder with the alarm clock on. 6. Say the word ‘‘Fast’’ into the microphone after the bike stops. 7. Turn off the noise and listen to the tape recordings. Summary of Results Write a brief description of each recording. How did
the control sound compare to the fast sound? Did you hear the sound increasing in pitch? By using the data on both the fast and slow sounds, and the set distance, what conclusions can you draw on the relative speed at which each object was traveling? How does this help you draw conclusions on the relative distance the object was from you? Write a summary of the experimental results and how these results relate to astronomical measurements. Change the Variables You can change the variable in this experiment by
changing the speed of the moving object. You can physically throw the sound maker, or move it around in a ball or a string. You can also see what happens when the person with the microphone runs alongside the bike at the same speed.
Design Your Own Experiment How to Select a Topic Relating to this Concept There are many types of
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further experiment with the telescope and the Doppler effect, or explore other tools. Check the Further Readings section and talk with your science or physics teacher to learn more about space measurements. You may also want to visit a planetarium or science museum to get some ideas. There are also many amateur astronomy groups and organizations you could join. Steps in the Scientific Method To conduct an original experiment, you
need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data could include
charts and graphs to display your data. If included, they should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help other people visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects Space observations and calculations is a broad topic with many related projects. Every day, astronomers are learning new information produced from tools on Earth and in space. There are many different types of telescopes with varying combinations of lenses and mirrors. You can explore the strengths and weaknesses of the different types. Once you have built a standard telescope, you can experiment with building telescopes of varying powers and materials. Experiment Central, 2nd edition
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You could explore the data from telescopes and how humans’ view of space has changed over the past several centuries. A project related to space measurement could involve identifying stars with a telescope that you have constructed. You could also look at how computer calculations have influenced people’s knowledge of space. The Doppler effect also has many commonplace usages that you could examine.
For More Information Freudenrich, Craig. ‘‘How Telescopes Work.’’ How Stuff Works. http://science. howstuffworks.com/telescope1.htm (accessed on February 3, 2008). Simple explanation of telescopes. ‘‘Galileo’s Biography.’’ The Galileo Project. http://galileo.rice.edu/bio/index. html (accessed on February 8, 2008). Details of Galileo’s life and work. ‘‘How Telescopes Work.’’ Yes Mag. http://www.yesmag.bc.ca/how work/ telescope.html (accessed on February 8, 2008). Brief, clear explanation of how telescopes work, with references. Kerrod, Robin. The Night Sky. Austin, TX: Raintree Steck Vaughn Publishers, 2002. A look at the history of the exploration of the sky, with graphics and illustrations. ‘‘Telescopes.’’ Astro-Tom.com. http://www.astro tom.com/telescopes/ telescopes.htm (accessed on February 8, 2008). Explanation of telescopes along with lots of other astronomy information.
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Galileo Galilei confirmed that a huge collection of stars make up the Milky Way. CO RB IS CO RP .
he first myth about the stars in the night sky probably came from the Chinese 5,000 years ago. They described stars as a heavenly river. The two brightest stars lived on either side of the river. They were known as Vega, a princess who wove beautiful clothes, and Altair, a herdsman. One night each year, a bridge of birds would span the river, allowing Vega and Altair to meet. We now know that stars are not princesses, herdsmen, gods, or goddesses, but vast clumps of hydrogen gas and dust that exist in space millions of miles (kilometers) away. Scientists who study the positions, motions, and composition of stars, planets and other objects in space are known as astronomers.
What’s up there? Ancient people were intrigued by what we now call the Milky Way. What was this band of light that stretched across the skies, they wondered. According to Greek legend, droplets of milk spilt upwards when Juno breastfed the infant Hercules. That’s why this light became known as the Milky Way. Democritus, a Greek philosopher, realized the truth in the fifth century B . C . E . He suggested that countless stars, too faint to be seen individually, make up the Milky Way. In 1609, when the Italian astronomer Galileo Galilei (1564–1642) focused the telescope he had made, the immense number of stars he saw staggered him. Galileo confirmed that the Milky Way is made up of innumerable stars grouped in clusters. A star is born How does a star begin? First, hydrogen, helium, dust, and ashes of stars that 1123
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The Orion Nebula is the birthplace of at least 700 young stars. PH OTO RE SEA RC HER S I NC.
Sirius is the brightest star in the sky. PHO TO R ES EAR CH ER S I NC.
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have died form swirling nebula, the Latin word for ‘‘cloud.’’ When a dense accumulation of these nebula gathers, the mass becomes a spawning ground for stars. As this mass of gas and dust heats up, gravity causes it to clump together, and a new star is formed. But only after nuclear fusion takes place at the star’s core does it produce enough light for us to see it. This process takes about 50 million years. A star stays in the same spot during its lifetime. We do see stars in different positions over the course of a month, but this apparent movement of the stars is caused by Earth moving around the Sun. Certain stars lie in patterns called constellations. Of the eighty-eight constellation patterns, some form shapes that look like animals, women, warriors, or objects. Constellation patterns sparked the star myths told by ancient people. Astronomers use light-years to measure the distance between stars. A light-year is the distance light travels in one year: roughly 5.9 trillion miles (9.5 trillion kilometers). How vast are the distances between stars? The star Proxima Centuri is 25 trillion miles (40 trillion kilometers) away—or 4.29 light-years. And that’s the closest star. The brightest and the biggest Sirius, 8.6 light-years away, is the brightest star in the sky, twenty-six times brighter than the Sun, which is also a star. How was this determined? In 1912, astronomer Henrietta Swan Leavitt (1868–1921) discovered that stars increase and fade in brightness over time. By studying a sequence of photographs of stars, analyzing their changes, and applying mathematical formulas, Leavitt came up with a way for astronomers to calculate the true brightness of stars. Stars are just one part of a galaxy, which also includes gas, dust, and planets, all drawn together by gravity. The Milky Way is not the only galaxy. The Andromeda Galaxy, which has about 300 trillion stars, and the Milky Way, with about 200 billion stars, are the two biggest and most important in a cluster of thirty galaxies called The Local Group. Improved technologies are helping astronomers detect galaxies that were Experiment Central, 2nd edition
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WORDS TO KNOW Astronomers: Scientists who study the positions, motions, and composition of stars and other objects in the sky.
Light-year: Distance light travels in one year in the vacuum of space, roughly 5.9 trillion miles (9.5 trillion kilometers).
Constellations: Patterns of stars in the night sky. There are eighty-eight known constellations.
Milky Way: The galaxy in which our solar system is located. Nebula: Bright or dark cloud, often composed of gases and dust, hovering in the space between the stars.
Fusion: Combining of nuclei of two or more lighter elements into one nucleus of a heavier element; the process stars use to produce energy to produce light and support themselves against their own gravity.
Star: A vast clump of hydrogen gas and dust that produces great energy through fusion reactions at its core.
Galaxy: A large collection of stars and clusters of stars containing anywhere from a few million to a few trillion stars.
The Local Group: A cluster of thirty galaxies, including the Milky Way, pulled together by gravity.
unknown just decades ago. Scientists estimate that there are over 100 billion galaxies in the visible universe. The two projects that follow will help you learn more about the stars over our heads.
PROJECT 1 Tracking Stars: Where is Polaris? Purpose/Hypothesis Stars do not move in space, but the planets, includ-
ing Earth, rotate on their axis and revolve around stars like our Sun. While stars appear to be in different places in the sky from one night to the next, what has really happened is that Earth has shifted its position. In this project, you will use a camera to follow the stars. Normally when a picture is taken, the film is exposed to light for only a fraction of a second. In this experiment, the film will be exposed for 1200 seconds. To obtain a clear picture and avoid over-exposing the film, you must take the pictures at night in dark surroundings (no overhead lighting including street lights) with a clear sky and a view of the North Star (Polaris). Level of Difficulty Moderate, because of the camera operation. Experiment Central, 2nd edition
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Materials Needed
• single-lens reflex 35-mm manual camera, such as a Pentax K-1000 (your school This project poses no hazards. However, you may use this type in photography classes) might ask a knowledgeable adult to help you • 1 roll 35-mm film, 1000 speed, 12 to 24 operate the camera. exposures • shutter bulb (Keeps the shutter open for prolonged exposures. You can purchase one in a photography store.) • tripod stand for camera • compass (optional) • ruler and protractor
How to Experiment Safely
Approximate Budget Less than $20 for film and shutter bulb. (Try to
borrow all other supplies.) Timetable 1 to 2 hours. Step-by-Step Instructions
1. Properly load the film in the camera. If necessary, ask for help. 2. Set the shutter speed to the manual setting (M). Some cameras have a different symbol. Use the setting that keeps the shutter open as long as you press the shutter button.
Steps 2 to 5: Parts of a camera. GAL E GR OU P.
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3. Set the film speed at 1000. 4. Attach the shutter bulb by screwing the end into the shutter button. 5. Set the aperture to the highest number. 6. Screw the tripod into the bottom of the camera 7. Set the tripod on firm ground. 8. Locate Polaris, the North Star, in the northern sky, using the pointer stars of the Big Dipper. 9. Position the camera so the North Star is visible through the eyepiece. 10. Squeeze the bulb to open the shutter. Hold it open by adjusting the screw near the bulb. 11. Leave the shutter open for one hour. 12. Close the shutter by loosening the screw or releasing the bulb. 13. Advance the film and repeat steps 10 through 12 on different nights. 14. Remove the roll of film and get it developed. 15. Using a pen, draw lines on each photo from the North Star (the only star that did not move) to the ends of one or two star trails. 16. Using a compass, measure the angle of the two lines. The angle should measure 15 degrees for each hour the film is exposed.
Step 8: Locate Polaris, the North Star, in the northern sky, using the pointer stars of the Big Dipper. G ALE GR OUP .
Step 16: Compass over photo with lines drawn to North Star from an angle. GAL E GR OU P. Experiment Central, 2nd edition
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Here is a problem that may arise during this project, some possible causes, and ways to remedy the problem.
Summary of Results Record your angle measurements and the date on each photo. All angles should be 15 degrees for each hour of exposure because Earth revolves 15 degrees each hour. What seemed to happen to all the stars except the North Star? How can you explain this?
Problem: The photo is too hazy, and the star trails are not visible.
PROJECT 2
Troubleshooter’s Guide
Possible causes: The sky was not clear enough, or there were too many lights that overexposed the film. Try the project again, away from houses and streets.
Tracking the Motion of the Planets: Can a planet be followed? Purpose/Hypothesis Planets sometimes reflect
light from the Sun, which makes them shine like stars. But unlike the stationary stars, Earth and the other planets move through the sky as they orbit the Sun. As the other planets orbit the Sun, Earth continues through its orbit. The combination of these movements can make the apparent path of the planets in Earth’s sky resemble an s-shaped pattern. In this project, you will examine this phenomenon. Level of Difficulty Moderate. (You need to be familiar with the star
positions.)
Steps 3 to 5: Example of plotting the position of a planet on Day 1 and 2, related to the Orion Constellation. GA LE GR OU P.
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Materials Needed
• a star map for your area and time of the year • binoculars or telescope (optional)
How to Experiment Safely Always stay on level ground when star gazing. Have an adult with you.
Approximate Budget $2 for a star map. (Consult
local papers or magazines for current monthly maps.) Timetable 15 to 20 minutes per night for 10 to 15 nights. Step-by-Step Instructions
1. Examine your local star map. Most star maps should be held upside down and over your head. 2. Choose a planet that should be visible in your night sky. Locate its position on the map. 3. With or without using binoculars, try to find this planet in the night sky. Planets are usually the brightest objects in the sky and do not twinkle like stars. 4. On your star map, record the position and time you located the planet. 5. Repeat this procedure every night for 10 to 15 nights. 6. Connect the marks on the star map and trace the path of the planet.
Step 6: Example of graphing a planet’s motion relative to the Orion Constellation. GA LE GR OU P.
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Summary of Results Record your results on a star
Troubleshooter’s Guide Here are some problems that may arise during this project, some possible causes, and ways to remedy the problems.
map like the one illustrated. Be sure to label each star and the daily positions of the planet. After 10 to 15 nights of observations, were you able to notice the motion of the planet among the stars?
Problem: You cannot see the planets or stars.
Design Your Own Experiment
Possible cause: The sky is too overcast. Try coming out again an hour or two later.
How to Select a Topic Relating to this Concept
Problem: You cannot find the new position of the planet. Possible cause: You might be unfamiliar with the night sky. Ask a knowledgeable adult for help, or look on the Internet for a daily star map. Locate the planet and transfer its position to your star map.
Example of apparent motion of star and planets. G AL E GRO UP.
Space is an infinite frontier sparsely filled with objects. Comets, stars, meteors, asteroids, moons, and planets are just a few of the objects visible in space. Before you begin making observations or experimenting, ask yourself questions. What is an asteroid? What is the difference between a meteor and a meteorite? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on star questions that interest you.
Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
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Recording Data and Summarizing the Results As a scientist investigating
a question, you must gather information and share it with others. Observations, researched facts, and data can be diagrammed or charted. Once you have gathered your information, study it, draw a conclusion, and share your results with others. Related Projects Binoculars and telescopes can improve your view of the nighttime sky. When choosing a topic such as comets, make sure you have the proper instruments to observe the object. You may want to choose a phenomenon or event that is easily observed, such as a meteor shower. When a meteor shower is predicted, you might try to calculate the number of shooting stars you see in one hour.
For More Information Matloff, Gregory L. The Urban Astronomer. New York: John Wiley, 1991. Describes interesting objects you can see in a city sky. McSween, Jr., Harry Y. Stardust to Planets. New York: St. Martin’s Press, 1993. Provides a good survey of the solar system. National Aeronautics and Space Administration. NASA: For Students. http:// www.nasa.gov/audience/forstudents/index.html (accessed on January 10, 2008). Van Cleave, Janice. Astronomy for Every Kid. New York: John Wiley, 1991. Outlines more than one hundred simple experiments that demonstrate the principles of astronomy.
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Y
ou experiment with static electricity every time you shuffle across a rug and touch a metal door handle. Static electricity is a form of electricity produced by friction (the rubbing of one object against another) in which the electric charge does not flow in a current but stays in one place. Electricity is a form of energy caused by the presence of electrical charges in matter. Matter is anything that has mass and takes up space. All matter, including you and this book, is made of tiny particles called atoms. An atom is the smallest particle of which an element can exist. Each atom, in turn, contains positively charged protons in its nucleus, or center core, and negatively charged electrons orbiting around its nucleus. How does an object become electrically charged? An increase or decrease in the number of electrons in an object gives it an electrical charge. When an object gains electrons, it becomes negatively charged. When it loses electrons, it becomes positively charged. In some materials, such as copper and silver, electrons can move around freely. These ‘‘free’’ electrons make these two metals good conductors. A conductor is a substance that is able to carry an electrical current. In other materials, electrons are tightly bound to their atoms. These materials, such as glass, rubber, and dry wood, do not conduct electricity easily, so they are good insulators and can be used as protective layers around conductors. Some materials have a stronger attraction for electrons than other materials. When two different materials are rubbed together, electrons move from the material that has the weaker attraction for them to the material that has the stronger attraction. For example, a balloon will usually not stick to a sheet of paper. However, you can make it stick by rubbing them together. As you rub, electrons move from the paper, which has a weak attraction for electrons, to the balloon, which has a stronger 1133
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attraction. Because the paper has lost some electrons, it now is positively charged. The balloon has gained electrons, so it is now negatively charged. When it comes to electrical charges, opposites attract. A material with a positive charge attracts a material with a negative charge, and vice versa. However, materials that both have a positive charge repel (are resistant to) each other, as do materials that both have a negative charge.
Rubbing does not create new electrons. It just causes them to move from the paper to the balloon. GA LE GRO UP.
When you place the negatively charged balloon near the positively charged paper, they will now cling together. As they cling, however, some of the electrons move from the balloon back to the paper. When the electrons are evenly distributed again, the balloon and paper are no longer electrically charged, so they will stop clinging together. What is static electricity? As you placed the charged balloon near the charged paper, you might have seen or heard a small crackle of static electricity. When an object with a strong negative charge is placed near one with a strong positive charge, the attraction of these opposites is so
Benjamin Franklin was the first to use the words ‘‘positive’’ and ‘‘negative’’ to describe electric charges. PHO TO R ES EAR CH ER S IN C.
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great that the air between them becomes electrically charged. It forms a path over which the electrons can move. As the electrons jump from the negative object to the positive one, they create static electricity. After the jump, the electrons are balanced again, so both objects lose their electrical charge. American scientist and political leader Benjamin Franklin (1706–1790) was one of the first to experiment with static electricity. You may remember his famous and dangerous kite experiments with lightning, which is a form of static electricity. Scientists still do not know exactly how lightning occurs, but they do know that a negative charge in one cloud repels electrons on the ground beneath it or in another cloud. As these electrons are repelled, the surface of the ground or the other cloud facing the negative cloud ends up with an excess of protons, giving it a positive charge. When the difference between the negative and positive charges reaches a certain point, lightning flashes from the negatively charged cloud to the positively charged ground or to the other cloud. This powerful burst of static electricity balances the electrons at both locations. In the first experiment, you will build an electroscope, a device that determines whether an object is electrically charged, and you will use it to test objects for electrical charges. In the second experiment, you will determine whether wool or nylon creates a stronger electrical charge.
Lightning is a form of static electricity. P ETE R A RNO LD INC .
EXPERIMENT 1 Building an Electroscope: Which objects are electrically charged? Purpose/Hypothesis In this experiment, you will build an electroscope
and use it to determine whether objects have an electric charge. An electroscope has two metal strips that hang down. When you hold a negatively charged object near the strips, the excess electrons move into Experiment Central, 2nd edition
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WORDS TO KNOW Atom: The smallest unit of an element, made up of protons and neutrons in a central nucleus surrounded by moving electrons.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Conductor: A substance able to carry an electrical current.
Insulator: A material through which little or no electrical current will flow.
Control experiment: A setup that is identical to the experiment but is not affected by the variable that will be changed during the experiment.
Matter: Anything that has mass and takes up space.
Current: A flow of electrical charge from one point to another. Electricity: A form of energy caused by the presence of electrical charges in matter. Electron: A subatomic particle with a single electrical charge that orbits around the nucleus of an atom. Electroscope: A device that determines whether an object is electrically charged. Friction: The rubbing of one object against another.
Nucleus: The central core of an atom, consisting of protons and (usually) neutrons. Proton: A subatomic particle with a single positive charge that is found in the nucleus of an atom. Static electricity: A form of electricity produced by friction in which the electric charge does not flow in a current but stays in one place. Variable: Something that can affect the results of an experiment.
the strips, causing them both to have a negative charge. Because they both have the same charge, they will repel each other and move apart. When you remove the charged object, the strips will lose their negative charge and hang down, as before. An electroscope responds in the same way if a positively charged object is brought near the strips. The positively charged object attracts electrons from the strips, giving them both a positive charge. This time the strips move apart because they are both positively charged. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of static electricity. This educated guess, or prediction, is your hypothesis. A hypothHow to Experiment Safely esis should explain these things: Be careful in handling the glass materials and in using the scissors.
• the topic of the experiment • the variable you will change
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• the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A glass test tube and a plastic comb that have been rubbed will hold an electric charge, but identical objects that have not been rubbed will not hold a charge.’’ In this case, the variable you will change is whether the objects have been rubbed, and the variable you will measure, using the electroscope, is the electric charge of the objects. You expect the objects to have a charge only after they have been rubbed. The unrubbed objects will serve as a control experiment, showing whether the objects have an electric charge if they have not been rubbed. If only the rubbed objects have an electric charge, you will know your hypothesis is correct. Level of Difficulty Easy/moderate. Materials Needed
• 1 wide-mouth jar • cardboard circle cut to cover the jar opening • 2 strips of aluminum foil, each 0.5 inches x 2 inches (1.3 centimeters x 5 centimeters) • large paper clip • sharpened pencil • masking tape • scissors • clean, dry cloth • 2 identical pairs of objects to test, such as two glass test tubes and two plastic combs Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • whether the experimental and control objects are identical • which objects are rubbed • how long and in what manner the objects are rubbed • whether the test objects touch each other (keep those you rubbed—the experimental objects—separate from those you did not rub—the control objects—so electrons will not move from one to the other before you test them) • the humidity level of the air (electric charges can leak away in humid air and change the results of your experiment) In other words, the variables in this experiment are everything that might affect the electric charges of the objects. If you change more than one variable, you will not be able to tell which variable had the most effect on each object’s electric charge.
Steps 2 and 3: Preparing aluminum foil strip and paper clip. G AL E GR OUP .
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Approximate Budget $0 to $5. The materials
should be available in most households. Timetable 15 minutes to build the electroscope;
10 minutes to test the objects. Step-by-Step Instructions
Step 4: Set-up of cardboard circle and paper clip. G AL E GRO UP.
1. Choose a day with low humidity to do your experiment. (If the air feels damp, it has just rained, or you seem to perspire easily, the humidity is too high for this experiment.) 2. Use the pencil to make a small hole in one end of each foil strip. 3. Open the paper clip so that it becomes a loop with two hooks at the bottom. 4. Use the scissors to cut two slots in the cardboard circle. Slip the sides of the paper clip into the slots. 5. Hang each foil strip on a paper clip hook. If the strips do not move freely, enlarge the holes in them.
Step 8: Recording chart for Experiment 1. GAL E GR OU P.
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6. Use masking tape to secure the cardboard circle to the top of the jar. Your electroscope is ready to use. 7. Hold one of the control objects near the top of the paper clip loop that is sticking out of the cardboard circle. Do not touch the clip with the object. 8. Move the object away. Use a chart such as the one illustrated to record whether the aluminum strips moved apart. 9. Repeat Steps 7 and 8 with the other control object. 10. Rub one test object vigorously with the dry cloth and repeat Steps 7 and 8. 11. Rub the other test object vigorously with the cloth and repeat Steps 7 and 8. Summary of Results Use the data on your chart
to create a line or bar graph of your findings. Then study your chart and graph and decide whether your hypothesis was correct. Did the aluminum strips move apart only for the rubbed objects? What does this show? Write a paragraph summarizing your findings and explaining whether they support your hypothesis.
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The aluminum strips did not move for any objects. Possible causes: 1. The air is too humid. Wait for a drier day and try again. 2. The holes in the strips are too small, preventing movement. Enlarge the holes and try again. 3. The test objects were not charged. Rub them longer or try rubbing them with a wool scarf. Problem: The strips moved for all of the objects. Possible cause: The control objects were charged accidentally. Touch them to something metal to release any electric charge in them and test them again.
Change the Variables You can vary this experiment in several ways. For example, use different pairs of objects, including copper or silver objects that are good conductors. You can also put an object that you know has a positive charge near the paper clip. For example, you might use paper after it has been rubbed against a balloon. Do the aluminum strips respond in the same way?
EXPERIMENT 2 Measuring a Charge: Does nylon or wool create a stronger static electric charge? Purpose/Hypothesis In this experiment, you will create an electric charge
in nylon, which is a synthetic fiber, and in wool, a natural fiber. Then you Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the types of cloth used and the size of the pieces • whether the pairs of control and experimental cloth squares are identical • which cloth squares are rubbed • how long the cloth squares are rubbed and what they are rubbed against
will measure the strength of each charge, using the electroscope you built in Experiment 1 or using an alternative procedure. Before you begin, make an educated guess about the outcome of this experiment based on your understanding of static electricity. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
• whether the rubbed cloth squares touch anything before they are tested
A hypothesis should be brief, specific, and measurable. It must be something you can test • the humidity level of the air (electric through observation. Your experiment will prove charges can leak away in humid air and or disprove whether your hypothesis is correct. change the results of your experiment) Here is one possible hypothesis for this experiIn other words, the variables in this experiment ment: ‘‘Wool will create a stronger static electric are everything that might affect the strength of charge than nylon.’’ the static electric charge. If you change more In this case, the variable you will change is than one variable, you will not be able to tell the material being rubbed, and the variable you which one had the most effect on the strength will measure is the strength of the electrostatic of the static charge. charge, as measured on your electroscope. You expect the wool will have a stronger charge. As a control experiment, you will also test squares of wool and nylon that have not been rubbed. The control experiment will determine whether these unrubbed cloth squares also have a charge and, if so, how strong it is. If the rubbed wool has a stronger charge than the rubbed nylon and if the unrubbed cloth squares have little or no static charge, you will know your hypothesis is correct. Level of Difficulty Easy/moderate. Materials Needed
• two 5-inch (12.7-centimeter) squares of wool • two 5-inch (12.7-centimeter) squares of nylon • plastic comb 1140
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Step 2: Recording chart for Experiment 2. GA LE G ROU P.
• electroscope from Experiment 1 (or a clean, empty margarine tub with a clear lid and some dry, lightweight cereal, such as puffed rice) • ruler
Step 3: Hold an empty margarine container about 1 inch (2.5 centimeters) above the lid of cereal. GA LE GRO UP.
Approximate Budget $3 for cloth. (The other
materials should households.)
be
available
in
most
Timetable 20 minutes. Step-by-Step Instructions To use an electro-
scope to measure the strength of a static charge: 1. Choose a dry day to do your experiment. Be careful not to rub the control squares of cloth against anything. 2. Place the control wool square near the paper clip loop. Observe the response of the aluminum strips. If they move, use the ruler to estimate the distance between the lower edges of the two strips. Record Experiment Central, 2nd edition
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the results on a chart like the one illustrated.
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: None of the cloth squares held a static charge. Possible causes: 1. The air is too humid. Wait for a drier day and try again. 2. The experimental squares were not charged. Rub them longer, making sure to rub both kinds of cloth in the same way. Problem: All of the cloth squares held a charge. Possible cause: The control squares might have been charged accidentally as you prepared for your experiment. Touch them to something metal to release any electric charge in them and test them again. Problem: The pieces of cereal flew all around. Possible cause: The cereal had already been charged, perhaps by being shaken and rubbed inside the box. Try a different box of cereal and try not to let the pieces rub together.
3. Repeat Step 2 with the control nylon square. 4. Rub the experimental wool square vigorously against the comb. Then, without touching the cloth to anything, hold it near the paper clip loop. Observe and record how the aluminum strips respond. 5. Repeat Step 4 using the experimental nylon square, rubbing it in the same way and as long as you rubbed the wool square. To use an alternative testing procedure: Rubbing a plastic margarine container with a cloth square will give the container a static electric charge that will draw lightweight cereal toward the container. Rubbing causes electrons to leave the cloth and move to the plastic tub. The negatively charged tub then repels the electrons in the cereal and attracts the protons, drawing the cereal upward. 1. Choose a day with low humidity for your experiment. 2. Place about 15 pieces of cereal in the tub lid.
3. As a control experiment, hold the empty margarine container about 1 inch (2.5 centimeters) above the lid of cereal. Observe whether any cereal pieces move upward toward the bottom of the container, and record your findings on a chart. 4. With one hand inside the container, rub the outside vigorously with a square of wool. Then remove the wool and hold the container above the cereal. Record how the cereal pieces respond and how many respond. 5. Repeat Step 4 with the nylon square, rubbing in the same way and for the same length of time. Record the results. 1142
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Summary of Results Use the data on your charts
to create a line or bar graph of your findings. Then study your charts and graph and decide whether your hypothesis was correct. Did the wool square create more static electricity than the nylon square, either causing the aluminum strips to move farther apart or causing more cereal to cling to the bottom of the margarine container? Did the unrubbed cloth squares exert no noticeable static charge, according to your electroscope? Or did the unrubbed container not pull the cereal upward? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables You can change the var-
iables and conduct other interesting experiments. For example, use different kinds of synthetic and natural fabrics, such as rayon, polyester knit, cotton, or silk. You can also change the length of time you rub a cloth square to see if the strength of the electric charge increases the longer you rub. Another way to vary the experiment is to rub a cloth square against the plastic comb, and hold the comb near the paper clip in the electroscope instead of the cloth. The comb should also hold a static charge, although it will be negative, while the cloth should be positive. (The electroscope should respond in the same way because both aluminum strips will still receive the same kind of charge and move apart.) Instead of using cereal in the alternative electroscope design, you can put salt and pepper or tiny pieces of paper in the margarine container.
An electroscope can determine whether an object holds an electric charge. PE TER AR NO LD INC .
Modify the Experiment This experiment tested whether nylon or wool
has a stronger static electric charge. You can make this experiment more challenging by testing a variety of materials and creating a Triboelectric Series. Triboelectricity relates to electricity that comes from friction. A Triboelectric Series is a list of materials showing which are more likely to let go of their negative charges (electrons) and becomes positively charged, and which are more likely to attract electrons and becomes Experiment Central, 2nd edition
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negatively charged. Some materials, such as steel, are not likely to give up electrons at all. If a material does not have a charge, it is called neutral. You will first need to gather a variety of materials found in the house, such as leather, glass, wool, paper, plastic, wood, and plastic wrap. You can also test your hair and skin. Test each object with the electroscope as described in the experiment, and measure the distance between the aluminum strips. Write up a summary of your results. When you are done, you can see how your Tribolectric Series compares to others. The electroscope in this experiment will show that there is a charge, not whether the charge is positive or negative. You can carry this experiment even further by exploring the charge of each material. Knowing what you do about static electricity and electricity, how would you sort which of the items in your Tribolectric Series are positively or negatively charged? If you start out with an item that you know has a certain charge, how would that help?
Design Your Own Experiment How to Select a Topic Relating to this Concept You can explore many
other aspects of static electricity. For example, why does static electricity occur in some situations and not in others? What kinds of materials are more likely to have a positive or a negative charge? How does the humidity in the air affect static electricity? How do static charges affect electrical equipment? As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. While static electricity usually involves a small electric charge (except for lightning!), experiments with electricity are potentially dangerous. NEVER experiment with lightning or the electric current that comes from electrical outlets. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on static electricity questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. 1144
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Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the static electricity experiments, your raw data might include not only charts and graphs of the responses of control and electrically charged objects, but also drawings or photographs of these responses. If you display your experiment, make clear your beginning question, the variable you changed, the variable you measured, the results, and your conclusions. You might include photographs or drawings of the steps of the experiment. Explain what materials you used, how long each step took, and other basic information. Related Projects You can undertake a variety of projects related to static
electricity. For example, you might explore products that claim to stop static cling on clothes. Does one product work better than another? You might see how many times you can transfer a static charge from one object to another, or if you can use static electricity to move objects without touching them.
For More Information Bonnet, Robert. Science Fair Projects with Electricity and Electronics. New York: Sterling Publishing, 1996. Outlines nearly fifty projects designed for science fairs. Energy Information Administration. ‘‘Electricity: A Secondary Energy Source.’’ Energy Kid’s Page. http://www.eia.doe.gov/kids/energyfacts/sources/ electricity.html (accessed on February 12, 2008). Explanation of electricity includes information on static electricity. Garner, Robert. Science Projects about Electricity and Magnets. Hillside, NJ: Enslow Publishers, 1994. Provides detailed explanations of projects and the concepts they demonstrate. Gibson, Gary. Understanding Electricity. Brookfield, CT: Copper Beech Books, 1995. Explains basic concepts and includes experiments. Experiment Central, 2nd edition
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Kurtus, Ron. ‘‘School for Champions.’’ Materials that Cause Static Electricity. http://www.school for champions.com/science/static materials.htm (accessed on February 9, 2008). List and explanation of the Triboelectric Series. Van Cleave, Janice. Spectacular Science Projects: Electricity. New York: Wiley & Sons, 1994. Describes twenty science projects, explaining how to carry them out and what they prove. Wood, Robert. Electricity and Magnetism FUNdamentals.New York: Learning Triangle Press, 1997. Offers instructions for experiments on the nature of electricity and magnetism and the relationship between them.
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R
ight now, at least one area of the world is experiencing some type of powerful storm. Storms are periods of extreme bad weather that can bring powerful winds and torrential rains. Storms can rip buildings apart, toss cars through the air, cause deaths, and spark forest fires. Every day there are as many as fifty thousand storms occurring throughout the world. They can stretch for hundreds of miles, or remain isolated to a few hundred yards. Either way, storms can cause enormous devastation. Some of the more common types of storms are thunderstorms, tornadoes and hailstorms.
How air works Storms all begin by the movement of air. Air is made up of a mixture of different gases, mainly oxygen and nitrogen with about four times as much nitrogen. Air is constantly moving around as it changes temperatures. The movement of air causes wind. (For more details on how air works, see Air chapter.) When air gets warmer its particles start to move about quickly and expand. The warm air particles take up more room in a given space. This makes the warm air rise because it is lighter than the air around it. Cooler air particles move closer together and take up less room. That makes cooler air heavier than the air around it and causes it to sink. As the Sun heats the air around Earth’s surface, this warm air moves upwards and the cooler air sinks. The faster that air is warmed and rises, the faster the winds. Clouds a brewing Thunderstorms need three basic ingredients to form. The first is moisture in the air or water vapor, which forms clouds and rain. The second is a column of unstable air, which provides relatively warm, moist air on the bottom layers with cold, dry air high above it. And lastly, a thunderstorm needs some kind of force to lift the air upwards. When the moist, warm air rises it eventually meets colder air and begins to cool. That forms the beginning of a cloud. Inside a cloud, 1147
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cool air causes water vapor to condense
sun heats surface, warming air
The process of cloud formation. GA LE GRO UP.
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currents of air move up and down quickly. This air is filled with tiny particles of dust. Water vapor is pushed upwards by the warm air. When it comes into contact with cooler air, the warm, moist air rises water vapor condenses. Condensation is when a gas (or vapor) changes into a liquid. The condensed drops of water will then surround a dust particle. Clouds form where millions of waterdust droplets gather together. Each of the particles in a cloud has a positive and a negative electrical charge. These small, puffy clouds grow increasingly larger as more warm air rises from the ground. If the cloud gets large enough, it may continue to rise into the ever-colder air. Strong winds can blow the top of the cloud downwind, and this gives the top of the cloud an anvil shape. This thunderstorm cloud is called a cumulonimbus cloud and it can extend upwards for miles. Shocking sights, loud noises To be called a thunderstorm there must be thunder. Thunder is caused by lightning, and lightning begins in the cumulonimbus clouds. Lightning is an intense discharge of electricity. Scientists estimate that about a hundred lightning flashes occur each second around the world. The electricity flowing within a lightning bolt is so powerful that it can kill instantly, split trees, and spark fires. The average flash of lightning could turn on a 100-watt light bulb for more than three months. As a storm advances, strong winds blow the particles of dust and water in the cloud and cause them to hit each other. Each particle contains positive and negative charges, which are attracted to each other under normal conditions, but collisions cause the positive and negative charges to separate. Positive charges tend to move towards the top of a cloud and negative charges move towards the bottom. Both types of charges hold energy. Charges that are alike repel each other and charges that are opposites pull together. When enough charges and time build up, the negative charge in the cloud reach out towards the positive charges on the ground. The result is a burst of electricity, or a lightning bolt. Every lightning flash produces thunder. In just a fraction of a second a lightning flash can heat up the air to 50,000˚F (28,000˚C)—a temperature hotter that the surface of the Sun. The burst of heat causes the air molecules around it to expand quickly away from the lightning’s flash. As Experiment Central, 2nd edition
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this hot air cools, it contracts. This quick expansion and contraction of air causes the air molecules to shake or vibrate, making sound waves that create the sound of thunder.
+ + + + + + + + + + + + + + _ _ _ _ _ + _ _ _ _ _ _ _ _ _ _
Thunder and lightning occur simultaneously, yet people will always see lightning before _ they hear thunder because light and sound travel + ++ + at different speeds. Light travels at about 186,000 miles per second (299,800 kilometers per second). The speed of sound is only about 0.2 miles per second (0.3 kilometers per second). That means a person will see lightning almost instantly, but won’t hear the thunder for several seconds. Knowing this allows any storm watcher to calculate the distance of the lightning strike. Count the number of seconds between the lightning and the thunder, and divide the number of seconds by five to calculate the miles distance; divide the number of seconds by three to calculate the kilometers distance.
_
_ _
Lightning forms when the negative charges in the cloud are attracted to the positive charges on the ground. GAL E GRO UP .
Twisting about Tornadoes are swirling columns of air that have enormous power. They have a short life span, from a few minutes to over an hour, yet are one of the most ferocious storms. They develop on land Fujita Tornado Scale
F-Scale
Winds
Type of Damage MINIMAL DAMAGE:
F0
40-72 mph 64-116 km/h
F1
73-112 mph 117-180 km/h
Automobiles overturned, carports destroyed, trees uprooted.
F2
113-157 mph 181-253 km h
Roofs blown off homes, sheds and outbuildings demolished, mobile homes overturned.
F3
158-206 mph 254-332 km/h
F4
207-260 mph 333-418 km/h
F5
261-318 mph 419-512 km/h
Some damage to chimneys, TV antennas, roof shingles, trees and windows.
MODERATE DAMAGE:
MAJOR DAMAGE:
SEVERE DAMAGE: Exterior walls and roofs blown off homes. Metal buildings collapsed or are severely damaged. Forests and farmland flattened.
DEVASTATING DAMAGE: Few walls, if any, standing in well-built homes. Large steel and concrete missiles thrown far distances.
INCREDIBLE DAMAGE: Homes leveled with all debris removed. Schools, motels, and other larger structures have considerable damage with exterior walls and roofs gone.
Experiment Central, 2nd edition
Developed by Dr. T. Theodore Fujita in 1971, the Fujita Tornado Scale, or F-Scale, classifies tornadoes according to the damage caused. G ALE GR OU P.
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B
A
warm co ol a
air
ir
The formation of a tornado. (A) formation of vortex; (B) when the funnel cloud touches the ground it becomes a tornado. GA LE GRO UP.
and come from the energy released in a thunderstorm. This energy is concentrated in a small funnel cloud area, such as the size of a football field, and moves across the ground at speeds of 20 to 40 vortex miles per hour (32 to 64 kilometers per hour). On average, the United States gets about a thouupdrafts sand tornadoes each year. The most violent tornadoes can reach wind speeds of over 250 miles per hour (400 kilometers per hour) and can slice a path of destruction more than 1 mile (1.6 kilometers) wide and 50 miles (80 kilometers) long. Tornadoes are often called ‘‘twisters’’ because of their rapidly spinning, funnel-shaped clouds. Only a small percentage of thunderstorms will turn into a tornado, and scientists have different theories on what exactly causes a tornado to form. One widespread theory says tornadoes form mainly due to wind. When winds at two different heights move at two different speeds this can create a horizontal spinning column of air. Thunderstorms supply the rising warm air or updrafts that a tornado needs to form. The updraft tilts the spinning air from the horizontal to the vertical direction. This whirling air is called a vortex and it causes the funnel cloud to form. When the warm air gets pulled up and meets the cold air, the moisture in the air condenses. Water droplets get swept into
Using special equipment, storm chasers gather data on tornadoes to help scientists learn more about this powerful, destructive form of storm. # CO RB IS S YG MA
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the mass of whirling air, starting at the top of the vortex where the temperature is lowest. This begins to form the tornado’s visible funnel cloud.
Hail growing Colder Air
Strong updrafts will cause the funnel cloud to narrow, which causes it to spin faster. This principle works much as an ice skater spinning. When an ice skater brings his or her arms closer to the body, he or she will spin faster. The funnel extends downwards from the cloud to the land as a tornado forms. A funnel cloud that touches land becomes a tornado. Some funnel clouds are hard to spot until they strike. As they pick up dirt and other materials from the ground these materials swirl about and cause the funnel cloud to darken and become more visible. Scientists are still working to answer several questions on tornadoes. One of the key questions is why updrafts in some thunderstorms become twisting funnel clouds, while those in similar thunderstorms do not. Some of the people who are helping to answer questions on tornadoes and other storms are storm chasers. Storm chasers seek out storms for study or adventure. They often use special equipment and can capture the spectacular sights and sounds of these violent storms.
Warmer (Moist) Air
The formation of hail stones. ILL US TRA TI ON B Y TE MA H NEL SO N.
Hailstorms Hailstorms, like lightening and tornadoes, are a product of strong thunderstorms. Hail can create massive damage to property and crops, and harm people who are caught in them. Hail tends to fall along paths, which can vary in size from a few acres to larger areas 10 miles (16 kilometers) wide by 100 miles (160 kilometers) long. Hail is formed during thunderstorms when tiny particles are swept into strong currents of rising and falling air in a storm cloud. The particle, called the nucleus, can be dust, salt, pollutants or ice crystals. The nucleus attracts water droplets around it that freeze as it moves into colder temperatures. A gust of downward moving air causes the nucleus to move into warmer temperatures where it picks up more water. The water forms into ice when an updraft (rising air) lifts it higher. The cycle of moving down and up through the air, gaining water that freezes, creates layers of ice. The longer the cycle continues, the larger the hail stone. Experiment Central, 2nd edition
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WORDS TO KNOW Air: Gaseous mixture that envelopes Earth, composed mainly of nitrogen (about 78%) and oxygen (about 21%) with lesser amounts of argon, carbon dioxide, and other gases.
Storm: An extreme atmospheric disturbance, associated with strong damaging winds, and often with thunder and lightning.
Condense: When a gas or vapor changes to a liquid.
Storm chasers: People who track and seek out storms, often tornadoes.
Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group.
Tornado: A violently rotating, narrow column of air in contact with the ground and usually extending from a cumulonimbus cloud.
Cumulonimbus cloud: The parent cloud of a thunderstorm; a tall, vertically developed cloud capable of producing heavy rain, high winds, and lightning.
Updraft: Warm, moist air that moves away from the ground.
Updraft: A strong current of upward moving air.
Variable: Something that can affect the results of an experiment.
Funnel cloud: A fully developed tornado vortex before it has touched the ground.
Vortex: A rotating column of a fluid such as air or water.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Water vapor: The change of water from a liquid to a gas.
The size of a hailstone, generally, is also determined by the strength of the updraft. The stronger the updraft, the more ice layers will accumulate as it travels up and down in the cloud. The hailstone will eventually fall to earth when it becomes too heavy to stay in the air. Most hailstones are smaller than a dime and often melt before they reach the ground. However, severe thunderstorms can produce extremely large hailstones, golf ball size and larger.
EXPERIMENT 1 Lightning Sparks: Explore how separating charges causes an attraction between objects Purpose/Hypothesis Lightning that is produced during a storm is simply
a massive electric spark, which is called static electricity. Friction causes the particles to separate into positive and negative charges. These opposite 1152
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charges attract one another, and when the electric charges are separated they look for a way to get back together. In a storm, the jump of numerous negative charges reaching out towards the positive charges produces a bolt of lighting. A miniature version of static electricity will produce sparks and an attraction between charged objects. In this experiment you will explore what happens when you cause charges to separate. You will use friction to create electrical charges on a balloon, and observe how three different objects react to these charges. The three objects you will use are: salt and pepper, water, and another balloon. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of lightning and charges. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the object that is charged • the degree of friction • the material that produces the friction • the distance from the balloon to the objects In other words, the variables in this experiment are everything that might affect the charge of the balloon. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the action of the charged particles.
• the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘If enough charges are separated, the balloon will attract different objects and create electricity.’’ In this case, the variable you will change is the separation of the negative and positive charges on the balloon. The variable you will measure is how the balloon’s charges are attracted to other objects. Having a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental setup, and that is the amount of charged particles. At the end of the experiment you will compare the charged balloon with the neutrally charged balloon. Level of Difficulty Easy. Experiment Central, 2nd edition
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Materials Needed
How to Experiment Safely
• • • • •
This project poses little hazards, but remember you are experimenting with electricity, however small. Do not conduct this experiment if there are any flammable vapors in the air, such as gasoline from an open container.
2 balloons salt and pepper access to sink small plate wool cloth or nylon (optional)
Approximate Budget $2. Timetable 30 minutes. Step-by-Step Instructions
Step 5: Hold the balloon close to, but not touching, the stream of water. GA LE GRO UP.
1. Sprinkle some salt and pepper on a plate. 2. Inflate both balloons. For the control, do not rub one balloon. Place the balloon about 1 inch (2.5 centimeters) above the salt and pepper. Then place the balloon about 1 inch (2.5 centimeters) away from a trickle of water from the faucet. Note the results. 3. Rub the second balloon briskly against a piece of wool or your hair. 4. Hold this balloon about 1 inch (2.5 centimeters) above the salt and paper. Note what you see and hear. 5. Hold the balloon about 1 inch (2.5 centimeters) from a trickle of water. Note the results. 6. Darken the room. Rub both balloons against a cloth or your hair, and place them together. Note what you see and hear. 7. Place your hand gently over the section of the balloon that you rubbed. Again place the two balloons together and note the results. Summary of Results Create a data chart that
describes the results of each trial. Compare the results to the control experiment. What did placing your hand over the balloon do to the charges in the balloon? Write a paragraph explaining your conclusions. Include how powerful bolts of lightning relate to this experiment. Change the Variables You can change the vari-
ables in this experiment in several ways. You can use different types of material to create friction, 1154
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and determine if this produces less or more attraction. You can also create charges on different objects, such as a comb. Try creating sparks or picking up different objects.
EXPERIMENT 2
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
Tornadoes: Making a violent vortex
Problem: There was no difference between the control and the experimental balloon.
Purpose/Hypothesis Tornadoes occur when air
Possible cause: You may not have created
masses clash and result in a spinning vortex. enough friction, in which case not enough The air in the vortex becomes stretched and narcharges would separate. Try rubbing the balloon vigorously against your hair, and rower with time. As the shape of the funnel repeat the experiment. gradually narrows, it creates an increase in the rotation speed, resulting in a twist similar to that of a spinning skater. In this experiment you will observe the relationship between the intensity of a vortex and its shape. You will create a vortex using water; a vortex of fluids behaves similar to that of air. A whirlpool and the water in a draining bathtub are examples of a vortex in liquids. The vortex forms when spinning water, or air, is pulled downwards, in this case by gravity. The funnel of water narrows as it is pulled down. You will fill two bottles with water, create a vortex, and observe the water movement from one bottle to another. You will control the
A tornado rips across the countryside in Jarrell, Texas, in May 1997. A P/W ID E WO RL D Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the size of the hole • the shape of the bottles • the size of the bottles • the temperature of the liquid
narrowness of the vortex by placing two different size holes between the two bottles. Observing small colored materials placed in the water will provide a way to measure the speed of the water’s rotation. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of tornadoes and vortexes. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
• the type of liquid In other words, the variables in this experiment are everything that might affect the vortex. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the water’s speed.
• • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The speed of the water will increase as the vortex becomes increasingly narrow.’’ In this case, the variable you will change is the size of the vortex hole, and the variable you will measure is the speed of the water. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and each of your vortexes. For the control, you will observe the water’s speed without narrowing the hole. At the end of the experiment you will compare the intensity of the control with each of the experimental vortexes.
Level of Difficulty Easy. Materials Needed
• • • • •
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2 identical 2-liter clear plastic soda bottles scissors duct tape or electrical tape water sparkles or any other small visible material that does not dissolve in water, such as oregano Experiment Central, 2nd edition
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• 2 washers the same outside diameter as the mouth of the bottles, one with a small center hole and one with a larger center hole • marking pen
How to Experiment Safely There are no safety hazards in this experiment.
Approximate Budget $5. Timetable 30 minutes. Step-by-Step Instructions
1. 2. 3. 4. 5.
6.
7.
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Label one bottle ‘‘A’’ and the other ‘‘B.’’ For your control: Fill Bottle A about two-thirds full of water. Sprinkle in some of the sparkles or other visible material. Place bottle B upside down on top of bottle A. Tape the mouths of the two bottles tightly together with the tape, aligning the openings up exactly. Test for leakage by carefully tilting the bottles. Turn the bottles over so that bottle A (with the water in it) is on top of bottle B, and quickly swirl the bottles several times, just like you would spin a hula-hoop. Set the bottles down and observe the water, noting the shape and speed of the swirling water. Untape the bottles and tape the washer with the larger hole to the mouth of bottle A. Do not cover the washer hole with tape. Again, tape the two bottles tightly together, lining up the mouths exactly. Quickly turn the bottles over and swirl. Note the description of the shape and B speed of the vortex. Repeat Steps 7 and 8, taping the washer with the smaller hole to bottle A. Note the results.
Step 5: Line up the two bottles exactly and tape together. GA LE GRO UP .
Summary of Results Evaluate your results. Was
your hypothesis correct? How does the water relate to the actions of a tornado? Compare the results of the two experimental trials with the control experiment. Write a summary of the Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: There was no vortex. Possible cause: You may not have lined up the washer exactly with the mouths of the bottles, or the tape may have covered some of the circular opening. Repeat the experiment, making sure the opening is clear. Problem: It was difficult to gauge the speed of the vortex. Possible cause: Determining the speed of the water is an estimate based on how quickly the sparkles are swirling. You may need to place less sparkles in the bottle. Select the same point on the bottle for every experiment to focus on the swirl.
experiment that explains your results. You may want to include drawings of the shape and speed of each vortex. Change the Variables To alter this experiment you can change several of the variables, one at a time, and again observe the flow pattern of the water. You can use bottles of different shapes and sizes. You can also try changing the type of liquid you use and the temperature of the liquid. Would the experiment give the same results with a thick liquid substance as opposed to one that has greater flow? Different swirling techniques may also provide interesting results.
EXPERIMENT 3 Forming Hailstones: How do temperature differences affect the formation of hail? Purpose/Hypothesis Hailstones form when a
particle cycles up and down in a cloud. The extreme temperature difference between the cold, high air and the warmer air below leads to layers of ice forming around the nucleus In this experiment, you will explore how extreme temperature differences affect the formation of a hailstone. For the extremely cold temperature, you will use dry ice. Dry ice is frozen carbon dioxide. It has a temperature of about -109˚Fahrenheit (-78˚Celsius). Dry ice and alcohol is a slightly warmer temper than dry ice alone. For the relatively warm temperature, you will use dry ice and water. A glass bead will act as the hail’s nucleus. In one trial, you will form a hailstone by having the nucleus move through all three temperatures. In a second trial, you will only use the two relatively warm temperatures. The amount of time forming the hailstones should be approximately the same. By comparing the formation of the hailstone, you can measure the affect of temperature differences on hail formation. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of how hail is produced in a cloud. 1158
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This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the variables in this experiment: • the size of the glass bead
• the temperatures of the baths A hypothesis should be brief, specific, and • the time that the bead spends in the measurable. It must be something you can test baths through further investigation. Your experiment will prove or disprove whether your hypothesis In other words, the variables in this experiment are everything that might affect the accumulais correct. Here is one possible hypothesis for tion of ice on the glass bead. If you change more this experiment: ‘‘The nucleus that passes than one variable at the same time, you will not through more extreme temperatures will accube able to tell which variable had the most mulate more ice and form a larger hailstone than effect on the properties of the hailstone. the nucleus that moves through the relatively warmer temperatures.’’ In this case, the variable you will change is the temperatures that the nucleus will move through as it forms a hailstone. The variable you will measure is size and shape of the hailstone.
Level of Difficulty Moderate Materials Needed
• 1 pound (0.45 kilgrams) of dry ice (You will need adult help in purchasing dry ice) • 1 cup of isopropyl alcohol (rubbing alcohol) • 4 plastic containers • 1 cup of water • 2 glass beads, approximately 14 inch (0.64 centimeters) in diameter • thread to string the bead, approximately 10 inches (24 inches) long • thick, insulated gloves to handle dry ice • tongs to handle dry ice • pencil • clock with second hand
Step 2: Set up three temperature baths: 1) container of dry ice; 2) container of isopropyl alcohol and dry ice; and 3) a container of water and dry ice. ILL US TRA TI ON B Y TE MA H NEL SO N.
er dr y ice + wat
dry ice + alcohol
Approximate Budget $12 Experiment Central, 2nd edition
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Timetable 45 minutes.
How to Experiment Safely
Step-by-Step Instructions
1. Take the glass bead and string it on thread. Make sure it is securely tied onto the thread. 2. Set up three temperature baths: 1) container of dry ice; 2) container of isopropyl alcohol and dry ice; and 3) a container of water and dry ice Dry ice usually comes in a cardboard box or insulated container. For the dry ice container, you can leave it in the box or container. For the dry ice/alcohol mixture: Place two plastic containers inside of each other. Fill the container with one cup of isopropyl alcohol and add three to four chunks of dry ice. Make sure the mixture becomes slushy and thick, add more dry ice if needed as it melts. For the dry ice/water mixture: Place two plastic containers inside of each other, as in the previous step, and add 1 cup of water. To the water add two chunks of dry ice. Mixture should become bubbly and foggy. Keep adding dry ice as it melts. Place all three ice baths on a tray to protect the table or countertop. To create a hailstone using three temperatures: Use the pencil to push the glass bead into the dry ice until it covers the bead. Have the bead sit in the dry ice for one minute. Use the string to pull out the bead and dip it into the dry ice and alcohol mixture for 10 seconds. 9. Dip the bead into the dry ice/ water mixture for three seconds. 10. Repeat the cycle, but place the bead on top of the dry ice instead of submerging it so you do not dislocate any ice that is forming. Leave the bead in the dry ice for 30 seconds. 11. Repeat Steps 7–9 for seven to eight cycles and record your observations. 12. To create a hailstone using two temperatures: use the pencil to push a glass bead into the dry ice until it covers the bead.
Dry ice is a dangerous substance, have an adult assist you in purchasing and using it during the experiment. Never touch dry ice with your bare hands. Always wear gloves and use tongs when handling.
3. 4.
5.
6. 7. Step 7: Use the pencil to push the glass bead into the dry ice until it covers the bead. I LLU ST RAT IO N BY T EM AH NEL SO N.
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Have the bead sit in the dry ice for one minute. 13. Use the string to pull out the bead and dip it into the dry ice and alcohol mixture for 30 seconds. 14. Dip the bead into the dry ice and water mixture for three seconds. 15. Repeat the process of dipping the bead into the dry ice/alcohol and into the dry ice/water for nine to 10 cycles. The amount of time forming the two hailstones should be approximately the same.
dr y ice + wate
r
dr y ice + alcohol
Summary of Results Look at the two pieces of
hail you formed. How do the sizes of the hailstones compare to one another? Was your hypothesis correct? How does the ice accumulate on the bead as it passes through the different temperature baths? Write a summary of the experiment that explains your results. You may want to include drawings of how the ice forms on the bead over time.
Step 8: Use the string to pull out the bead and dip it into the dry ice and alcohol mixture for 10 seconds. I LL US TRA TI ON BY TEM AH N EL SON .
Change the Variables To alter this experiment you can change one or
more of the variables. You could use a nucleus other than a glass bead, such as a pebble or small ball. If you change this variable think about what materials maintain a cold temperature: glass, plastic, metal? You can experiment with dipping the bead in the ice baths for varying lengths of time, or change the order of baths that you dip the bead into. For example, start the bead in the dry ice and alcohol bath and then place it into the dry ice and then the dry ice and water. How does this affect the build up of ice?
Design Your Own Experiment How to Select a Topic Relating to this Concept To select a related project,
you can create models of weather phenomena and collect information from observing. An experiment with storms could include observing collecting data before and during a thunderstorm. You can also use the information meteorologists and storm chasers have gathered on tornadoes. The tools used to measure storms opens up another branch of related projects. Experiment Central, 2nd edition
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Troubleshooter’s Guide Below are problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: Ice did not accumulate on the glass bead. Possible cause: The bead did not get cold enough initially to sustain the formation of ice. Make sure there are still chunks of dry ice in the water bath. Keep the bead submerged in dry ice for one full minute before moving it into the alcohol and water baths. Problem: Ice built up on the bead but was lost in water bath. Possible cause: The water and dry ice bath serves the purpose of adding water to the bead. But if the bead is submerged in the water and dry ice too long it will melt the ice that has accumulated. Make sure that you dip the bead briefly into this bath. You can try two seconds instead of three. Also, make sure that you are replacing the dry ice that melts in the water. The dry ice serves to keep the water cold, and as it melts the temperature increases.
Check the Further Readings section and talk with your science teacher to learn more about storms. You may also want to contact a local weatherperson in your area to talk about his or her work and possible project ideas. Steps in the Scientific Method To conduct an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Recording Data and Summarizing the Results If appropriate, your data
should include charts and graphs. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. If you are observing or reporting on a weather phenomena, you may want to include a series of drawings or photographs taken over a set period of time. Make sure you note the time each picture occurred. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. 1162
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Related Projects You can design your own experiments on storms. Investigate methods that meteorologists use to measure storms and how these tools have changed over history. How far in advance can meteorologists predict a storm and how accurate are these predictions? You can also conduct a project related to storm safety and how people should behave in a storm. Scientists have broken down each storm into stages. You could create models of each of the stages and provide explanations for each one. There still remain many questions about how tornadoes form. You can look at differing theories of what causes a tornado and evaluate the evidence for these theories. Where are tornadoes most likely to form and why? With lightning, there are theories on how lightning is attracted to some types of trees more than others. You can investigate what lightning hits and the cause of attraction of each object.
For More Information ‘‘The Disaster Area.’’ FEMA for Kids. http://www.fema.gov/kids/dizarea.htm (accessed on February 18, 2008). Simple instructions and explanations of storms by the Federal Emergency Management Agency. DryiceInfo.com. www.dryiceinfo.com (accessed on February 18, 2008). Background and searchable database on where to purchase dry ice. Grazulis, Thomas P. Significant Tornadoes 1680 1991. St. Johnsbury, VT: Environmental Films, 1993. Comprehensive listing of significant tornadoes and their effects. Kahl, Jonathan, D. Thunderbolt: Learning about Lightning. Minneapolis, MN: Lerner Publishing Group, 1993. Simple explanations, photographs, and charts related to lightning. Kramer, Stephen. P. Lightning. Minneapolis, MN: Lerner Publishing Group, 1993. Lots of illustrations and color to explain this phenomena. Moore, Gene. Chase Day. www.chaseday.com/hail.html (accessed on February 18, 2008). Information and photographs of hailstorms and hailstones. ‘‘Thunderstorms.’’ Met Office. http://www.metoffice.gov.uk/education/ secondary/students/thunderstorms.html (accessed on February 20, 2008). Thunderstorms leaflet includes illustrations. ‘‘Tornadoes: The Most Ferocious Storm.’’ The Why Files. http://whyfiles.org/ 013tornado/ (accessed on February 20, 2008). Interactive animations showing the formation and effects of a tornado.
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H
umans have been busy building structures for almost as long as we have existed. The structures that we build, however, have changed dramatically over the last thousand years. We have learned to construct buildings that extend thousands of feet up, and we can build bridges that safely support tons of weight over immense stretches of water. What have we learned that enables us to build what our ancestors would have thought impossible? The answer lies mainly in concepts about the nature of force and motion that Sir Isaac Newton (1642–1727) developed over three hundred years ago. Newton proposed a set of ‘‘laws’’ that clearly explain why and how objects move or remain still. These laws apply to the planning of structures like buildings and bridges because they must be designed to remain fixed in place and not be moved by the forces that act upon them.
Different forces can act upon one object One of Newton’s laws tells us that different forces can act on a single object at the same time, as when two soccer players kick the ball at the same time. One has exerted force on the ball toward the goal; the other has exerted force in another direction. If the two players kick with precisely the same energy in exactly opposite directions, then the ball will remain motionless. Two kicks that are not equal in energy and not opposite in direction, however, will send the ball flying sideways off the field. This combined force is called a resultant. Standing a single playing card on its edge is nearly impossible. Two cards, however, can be stood on edge quite easily. This is because the two cards can be made to exert two equal and exactly opposite forces upon each other. As long as this force stays balanced, the cards will remain standing. When different forces add up to a resultant of zero, this state is called equilibrium. If you increase the force on one side without increasing the force on the other, the resultant is no longer zero; equilibrium has 1165
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WORDS TO KNOW Arch: A curved structure that spans an opening and supports a weight above the opening. Beam: A straight, horizontal structure that spans an opening and supports a weight above the opening.
Force: A physical interaction (pushing or pulling) tending to change the state of motion (velocity) of an object. Platform: The horizontal surface of a bridge on which traffic travels.
Compression: A type of force on an object where the object is pushed or squeezed from each end.
Resultant: A force that results from the combined action of two other forces.
Equilibrium: A balancing or canceling out of opposing forces, so that an object will remain at rest.
Rigidity: The amount an object will deflect when supporting a weight. The less it deflects for a given amount of weight, the greater its rigidity.
been disrupted, and the cards will fall in the direction exerted by the stronger force. A card house can stand because the forces acting on it add up to a resultant of zero. COR BI S-B ET TMA NN.
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The science of architecture and engineering is largely the analysis of force: how to distribute and direct the many forces acting on a structure to ensure that it remains in equilibrium. The arch redistributes forces to maintain equilibrium One early development in architecture that uses the principle of distribution of force is the arch. The arch directs the downward force of the supported weight around the arch and into the ground. In a stone arch, for example, each stone has slightly tapered sides. The weight on the top stone causes it to push out and down on the next stone, and so on around the curve of the arch until it reaches the ground. An arch can support greater weight than a straight beam across an opening, even when the beam and arch are built of the same materials. This is because the force in an arch squeezes, or compresses, the material in the arch, rather than bending it the way it does in a beam. Most materials are stronger in compression than they are in bending. The greatest bending force in a beam takes place in the center, Experiment Central, 2nd edition
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where it is unsupported. Over time, the bending force on the beam could cause it to crack. The same principle applies to bridges. The platform of a bridge, the flat surface over which vehicles travel, can be supported either by a beam or by an arch. A simple beam bridge can extend only a limited distance before its weight and the weight of the traffic upon it would cause the beam to fail. An arch bridge more effectively transfers the force of this weight out to the ground. Many large bridges today use arches as part of their design. In the first project, you will construct two bridges—one using a beam and one using an arch—and determine whether the arch can support more weight. In the second project, you will see if you can increase the strength of the beam design by increasing the vertical height of the beam.
RIGHT: The arch is an effective design because it distributes the downward force around the arch and into the ground. G ALE GR OUP . LEFT: The beam design is limited in the weight it can bear because the middle section is unsupported. G AL E GR OUP .
How to Experiment Safely PROJECT 1 Arches and Beams: Which is strongest? Purpose/Hypothesis In this project, you will
Use only iron fishing sinkers for weights in this experiment. If only lead sinkers are available, substitute coins or some other easily measurable form of weights. Lead is toxic and should not be handled without proper protection.
construct one bridge using an arch and one Experiment Central, 2nd edition
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Steps 4 and 6: Set-up of arch bridge. GAL E GR OU P.
using a beam. The bridges will use the same vertical supports and platforms, and the arch and beam will be of identical thickness. You will test the bridges to determine how much weight each one can support. Level of Difficulty Easy/moderate. Materials Needed
• • • • • •
1 sheet of red poster board, 14 x 22 inches (36 x 56 cm) 1 sheet of white poster board, 14 x 22 inches (36 x 56 cm) scissors ruler 10 iron fishing sinkers, 0.5-ounce (14-gram) each 4 stacks of textbooks, each approximately 5 inches (12 cm) tall
Steps 5 and 6: Set-up of beam bridge. GAL E GR OU P.
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Approximate Budget $15 for poster board and
sinkers. Timetable Approximately 40 minutes. Step-by-Step Instructions
Troubleshooter’s Guide Here is a problem you may encounter, some possible causes, and ways to solve the problem.
Problem: The accordion folds of the beams tend 1. Cut two pieces of white poster board, 14 to flatten out, decreasing the vertical height of x 4 inches (36 x 10 centimeters). These the beam. will be the platforms of your bridges. Possible causes: 2. Cut two pieces of red poster board, 14 x 5 inches (36 x 12 centimeters). These will 1. Your tape is not holding. Try folding the edges of the white platform around the be the support designs (beam and arch) of beam and then taping the assembly. your bridges. 2. Your poster board is not rigid enough. 3. Place two stacks of textbooks about 8 Use thicker poster board. inches (20 centimeters) apart. Do the same with the other two stacks. These will be the vertical supports of your bridges. 4. Bend one piece of red poster board into an arch and place it between one pair of vertical supports. This will be the arch of one bridge. The peak of the arch should be the same height as the vertical supports. Adjust the distance between the vertical supports until the peak of the arch is even with the top of the two stacks. 5. Lay the other red piece across the second pair of vertical supports. This will be the beam of the other bridge. Adjust the distance between the vertical supports until it is the same as the distance on the arch bridge. 6. Measure and mark the centers of the two pieces of white poster board. Lay each of the white pieces across a pair of vertical supports so that the center mark is halfway across the opening. These will be the platforms of your bridges. The weights must be placed on or near the centerpoints you marked on the platforms. Your bridges should look like the illustrations. 7. Measure the height of the platforms (at the center) and record this height on a data chart. Place one weight on the center point of each bridge. Measure any distance the center of the platform has dropped. Record this on your data chart. Add another weight as close to the first as possible and measure the height again. 8. Continue adding weights to the bridges. Measure and record the distance each platform drops after each new weight is added. Repeat this process until both of the bridges have collapsed. Experiment Central, 2nd edition
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Summary of Results Examine your data and compare the results of the tests for the two designs. Did your predictions prove true? Which design proved to be the sturdier one? Summarize your results in writing. Change the Project By altering the project, you can investigate other
questions about bridges. How does doubling the thickness of the arch or the beam affect its strength? What if you construct the arch bridge with two arches instead of one? Also consider changing the materials. Is rigidity always a good thing? See which supports more weight, a slightly flexible design made of cardboard, or an identical design made of wooden hobby sticks.
PROJECT 2 Beams and Rigidity: How does the vertical height of a beam affect its rigidity? Purpose/Hypothesis Rigidity is a measure of how much an object, such as
a bridge, will deflect when supporting a weight. Bridges must not only be strong, but they must also be fairly rigid to keep the platform level without sagging. In this project, you will construct three beam-support bridges using beams of different vertical heights. You will test each one and compare the results to determine whether increasing the height of a beam can make this bridge design more rigid. Level of Difficulty Moderate. Materials Needed
• 1 sheet of red poster board, 14 x 27 inches (36 x 68 centimeters) or the equivalent with 2 sheets • 1 sheet of white poster board, 14 x 22 inches (36 x 56 centimeters) • scissors How to Experiment Safely • tape Use only iron fishing sinkers for weights in this • ruler experiment. If only lead sinkers are available, • 10 iron fishing sinkers, 0.5-ounce substitute coins or some other easily measurable (14-gram) each form of weights. Lead is toxic and should • 6 stacks of textbooks, each approximately not be handled without proper protection. 5 inches (12 centimeters) tall 1170
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Approximate Budget $15 for poster board and
sinkers. Timetable Approximately 40 minutes. Step-by-Step Instructions
1. Cut three pieces of white poster board, all 14 x 4 inches (36 x 10 centimeters). These will be the platforms of your bridges. 2. Cut three pieces of red poster board, 14 x 6 inches (36 x 15 centimeters), 14 x 9 inches (36 x 23 centimeters), and 14 x 12 inches (36 x 30 centimeters). These will be used to make the beams of your bridges. 3. Place the stacks of textbooks in three pairs. The stacks should be about 10 inches (25 centimeters) apart. These will be the vertical supports of your bridges. 4. On the 14 x 6-inch piece of red poster board, measure and mark the board so the 6-inch (15-centimeter) width is divided into six 1-inch (2.5-centimeter) segments. Fold the board carefully along these marks so it looks like the illustration. 5. Divide the 14 x 9-inch poster board into six 1.5-inch- (3.8 centimeter-) wide segments and divide the 14 x 12-inch poster board into six 2-inch- (5-centimeter-) wide segments. Carefully fold each one into an accordion shape. 6. Lay the three folded red pieces across the three pairs of vertical supports. These will be the beams of the bridges. 7. Measure and mark the centers of the three pieces of white poster board. These will be the platforms of your bridges. The weights must be placed on or near the centerpoints you marked on the platforms. 8. Attach the platforms to the beams using tape. Place the beam/platform assemblies across the three pairs of vertical supports with the beam-side down. Your bridges should look like the illustration. 9. Measure the vertical height of each bridge, from the bottom of the folded beam to the Experiment Central, 2nd edition
Step 4: Illustration of accordion-fold beam. GAL E GRO UP.
Steps 6 to 8: Set-up of beam bridge. GA LE G RO UP.
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Troubleshooter’s Guide Here is a problem you may encounter during this project, some possible causes, and ways to solve the problem. Problem: One of the bridges tends to twist and dump its weight before collapsing. Possible causes: 1. Your weights are off center. Place your weights as close to the center mark as possible. 2. Your poster board is not rigid enough. Use thicker poster board.
top of the platform. Record this information on a data chart. 10. Measure the height of the platforms at the center and record this height on your data chart. Place one weight on the center point of each bridge. Measure the distance the center of the platform has dropped. Record this on your data chart. Add another weight as close to the first as possible and measure again. 11. Continue adding weight to the bridges. Measure and record the distance each platform drops after each new weight is added. Repeat this process until both of the bridges have collapsed. Summary of Results Examine your data and
compare the results of the tests for the three beams. Did your predictions prove true? How much does each increase in vertical beam height increase the beam’s ability to support weight? Summarize your findings in writing. Change the Project By altering the project, you can determine whether it
is preferable to construct a wide bridge with a low vertical height or a narrow bridge with a greater vertical height. Which is stronger, a bridge 4 feet (1.2 meter) wide and 2 feet (0.6 meter) high, or a bridge 2 feet (0.6 meter) wide and 4 feet (1.2 meter) high? Also consider changing the materials. Is rigidity always a good thing? See which supports more weight, a slightly flexible design made of cardboard or an identical design made of wooden hobby sticks.
Design Your Own Experiment How to Select a Topic Relating to this Concept Watching the way your bridge designs reacted to the weight placed on them may have already given you ideas for improving them. Architecture and design engineering encompasses a wide range of structures and products you see and use every day. Can you think of a way to make something work better or keep people safer? Testing ideas in miniature is a vital tool for trying out new ideas. 1172
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Think about combining the ideas and designs used in these projects. Can you think of a way to use the strongest beams in the second project to make a stronger arch? Can you build a bridge that uses both a beam and an arch? If you are doing a project as a group, try holding a competition for bridge designs. If you want to do an experiment or a project, check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on structure and shape questions that interest you.. As you consider possible experiments or projects, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of them might be dangerous. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure which question you are answering, what you are or should be measuring, and what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do.
This modern-day bridge combines the arch and the beam designs. GAL E GR OU P.
• Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the projects included here and in any experiments or projects you develop, you can look for ways to display your data in more accurate and interesting ways. For example, can you think of a better way to measure the weight sustained by Experiment Central, 2nd edition
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the bridge? Should you test the structures by distributing the weight across the span? Remember that those who view your results may not have seen the experiment performed, so you must present the information you have gathered in as clear a way as possible. Including photographs or illustrations of the steps in the experiment is a good way to show a viewer how you got from your hypothesis to your conclusion. Related Projects To develop other experiments or projects on this topic,
take a look at the structures and shapes of things you see around you every day. Take different design options and test them in miniature. Consider ways you could reinforce the bridges you built to enable them to hold more weight. Can you think of a better way to construct new models?
For More Information Briscoe, Diane. Bridge Building: Bridge Designs and How they Work. Bloomington, MN: Red Brick Learning, 2004. Gibson, Gary. Making Shapes. Brookfield, CT: Copper Beech Books, 1995. Demonstrates a variety of structural shapes and how they are applied in construction. Hawkes, Nigel. Structures: The Way Things are Built. New York: MacMillan Publishing Company, 1990. Looks at ancient and modern structures and describes how they were built. National Aeronautics and Space Administration (NASA). Newton’s Laws of Motion. http://www.grc.nasa.gov/WWW/K 12/airplane/newton.html (accessed on February 6, 2008). Descriptions and graphics of Isaac Newton’s three laws of motions. Slafer, Anna, Keven Cahill, and the National Building Museum. Why Design?: Activities and Projects from the National Building Museum. Chicago: Chicago Review Press, 1995. Stevenson, Neil. Architecture: The World’s Greatest Buildings Explored and Explained. New York: DK Publishing, 1997. Examines in depth the history, design, and construction of fifty buildings and structures from around the world. The Visual Dictionary of Buildings. New York: DK Publishing, 1992. Clearly illustrates and provides terminology for numerous architectural features from ancient to modern times. WGBH Educational Foundation. Building Big. http://www.pbs.org/wgbh/ buildingbig/index.html (accessed on February 6, 2008). Information and activities on bridges, domes, skyscrapers, dams, and tunnels.
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nyone who has ever raced to finish an activity knows the importance of time. In modern day, people monitor time by the minute. Yet thousands of years ago, keeping track of time was not important. People went about their work and play when the Sun was in the sky and they slept when the Sun was down. Over the years, people began to notice patterns in the Sun’s rising and falling. Eventually these patterns led to a system of keeping time that was accepted throughout the world. The natural rhythms of the Sun and Moon established the time concepts of year, month, and day. Other timekeeping classifications— weeks, hours, minutes, and seconds—are manmade inventions. The concept of time has intrigued some of the most prominent scientists. It has also led to the development of several major discoveries. Breaking up time Ancient Egyptians noticed that the Sun rose at different positions on the horizon depending on the season. In the warmer season when the crops grew, the Sun rose farther to the north. In the cooler season after the last harvest, the Sun rose farther to the south. They noted the position of the sunrise on a particular morning and tracked this position through the seasons. They found it took 365 sunrises before the Sun returned to the same position. Today people know that 365 days is the time it takes Earth to orbit around the Sun. We call that length of time a year. Technically, a year is 365 days, 5 hours, 48 minutes, and 46 seconds.
The ancient Egyptians also noticed a full moon occurred once every 2912 days—which is what we now call a month, from the Greek and Latin words for moon. The Egyptians chose to split up a month into groups of seven days. Historians theorize they could have selected the number seven because ancient peoples believed (wrongly) that seven heavenly bodies revolved around Earth. 1175
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It takes 365 days—one year— for Earth to orbit around the Sun. N AS A.
As Earth revolves around the Sun, the planet also rotates. A day is the amount of time it takes for Earth to complete one rotation. As it spins, half of Earth faces the Sun and has light; the other half faces away from the Sun and is dark. When a day exactly begins depends upon one’s point of view. Ancient Egyptians began their day at dawn; Babylonians, Jews, and Muslims began at dusk; and Romans began their day at midnight. A solar day is the time it takes the Sun to return to its highest point in the sky. While the average day in a year measures twenty-four hours, lengths of individual days vary. After Earth has completed one rotation it must spin for about an extra four minutes around the Sun for the Sun to reach the same point in the sky. Astronomers measure a day by the length of time it takes for Earth to make a complete turn with respect to the stars, which is constant throughout the year. This is called a sidereal day and it lasts 23 hours 56 minutes and 4.1 seconds of average solar time. 1176
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Hours came about when Egyptians studied the movement of the stars at night. They noted a regular motion of the stars and divided the night into twelve equal parts, based on the rising of a particular star or stars in the night sky. They then decided to divide the day into the same number of parts, known as hours. To measure daylight’s hours, they used a sundial to track a shadow as the Sun moved across the sky (actually as Earth revolved beneath the Sun). A sundial has an upright part in the center called a gnomon. The gnomon casts a shadow across a surface that is divided into twelve equal parts. As the Sun moves across the sky, the tip of the gnomon’s shadow creeps across the twelve sections. The sundials in Egypt were probably fairly accurate because this area is relatively close to the equator. Near the equator the position of the Sun is always high overhead throughout the year, and the length of time the sun is up each day is almost constant. Farther north or south from the equator, the time the sun is up can be very long or very short depending on the season. For example, in northern Alaska the Sun never sets in mid-summer and never rises during mid-winter. Under those conditions, sundials would not be of much value in keeping time. The water clock was another type of time measurement that ancient people used. The water clock did not depend on an area’s location or the changing rhythms of the Sun. In a water clock, a bowl with a small hole in the bottom was filled with water. Lines were marked on the inside of the bowl to symbolize the hours. As the water dripped slowly out the bottom, the water level sank, revealing the lines in the bowl. A water clock worked steadily at all times of the night and day, but someone had to refill the supply of water when it was empty. Swing time A revolution in science that began in the sixteenth century had a significant impact on time. First, Polish mathematician Experiment Central, 2nd edition
Sundials tell time by the position of the sun. CO RBI SBET TM ANN .
The water clock was another type of time measurement that ancient peoples used. GA LE GRO UP .
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In the late 1500s, Galileo Galilei was the first to begin experimenting with the concepts of a pendulum and oscillation. T HE L IBR AR Y O F C ONG RE SS.
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Nicolas Copernicus (1473–1543) found that Earth rotates around the Sun, not the other way around as was previously believed. His work caused a great deal of controversy because it was generally accepted at the time that Earth was the center of the universe. Eventually, the Copernican theory became accepted, and people could know Earth’s location when they calculated time. Then in 1581 Italian teenager Galileo Galilei (1564–1642) made a significant finding. The story goes that while Galileo was attending a church service, he began to watch a heavy lamp swinging from a chain attached to the ceiling. He used his pulse as a timepiece to note how long it took for each swing or oscillation. Whether the length of the swings was long or short, each swing always took the same amount of time. Galileo began experimenting with a pendulum, a free-swinging weight, usually consisting of a heavy object attached to the end of a long rod or string, suspended from a fixed point. He found that the amount of time it takes a pendulum to complete one full swing had nothing to do with the weight of the pendulum or how far the pendulum swings. The length of time it takes for the pendulum to go back and forth depends only on the length of the pendulum. Galileo designed a simple pendulum timepiece, but he never built it. In 1656 Dutch scientist Christian Huygens (1629–1695) used Galileo’s ideas of oscillation to build the first pendulum clock. Inside this clock the regular movements of the pendulum turned wheels that controlled the hands of the clock. It was accurate to within one minute a day. A mess of times Until the late 1800s, the world was a jumble of times. Countries, cities, and even neighboring towns were using their own local time, setting their clocks to noon when the Sun was directly overhead. Four o’clock in one city could be seven minutes past four in a town a short distance away. As travel, industry, and communication began to grow, it was decided there should be a standard time throughout the world. In 1884 the world was officially divided into 24 time zones, like 24 segments of an orange. There was one zone for each hour of the day, and the time within each zone was the same. The starting point for the time zones was an imaginary north-south line that ran through Greenwich, Experiment Central, 2nd edition
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1 AM
2 AM
3 AM
4 AM
5 AM
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7 AM
8 AM
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2 PM
3 PM
4 PM
5 PM
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ARCTIC O CEAN
Moscow
Los Angeles
Chicago Denver
Toronto New York
PACIFIC O CEAN
Tehran Cairo Karachi Mumbai
Delhi
Seoul
Tokyo
Shanghai
Kolkata Guangzhou Bangkok
Abidjan Lima
Monday Sunday
Beijing Tianjin
Rome
ATLANTIC O CEAN
Honolulu Mexico City
Novosibirsk
Paris
World Time Zones Nonstandard time
Jakarta
Kinshasa Rio de Janeiro São Paulo
Prime Meridian (Greenwich Time)
International Date Line
London
I N DI A N OC E A N 0 0
2000 2000
Perth
Brisbane
4000 mi.
4000 km
There are twenty-four time zones worldwide, one for each hour of the day. G ALE GRO UP.
England. The east–west distance around the world from this imaginary line determined each area’s time zone. This system of time is called Greenwich Mean Time (GMT). Space-time: It’s all relative Moving into the past and future has long been a favorite theme of science fiction authors, but the subject of moving in time has also fascinated scientists. For years people thought that time was an absolute: It could not be stretched or condensed. In 1887 two scientists found that the speed of light—how fast light travels in a vacuum—appeared unchanged by the movement of its source or that of the observer. The speed of light is rounded off to186,000 miles per second (297,600 kilometers per second). Then in the early 1900s physicist Albert Einstein (1879–1955) changed people’s view of time and space. Where something is located is its place in space. Einstein said that time combines with space to form space-time, and that it is not absolute: How fast time moves depends on how fast the person measuring time is moving in space. Einstein’s theory showed that time is relative, and so his theory is called the Theory of Special Relativity. The faster an object travels, the more slowly time passes for that object. This would only be noticeable at speeds approaching the speed of light. A simple theoretical example would be how you would perceive time if you were looking at a clock while moving away from it on a rocket traveling at the speed of light. When you first look back at the clock, you see that it reads 2 hours, 20 minutes, and 11 seconds. This image of the Experiment Central, 2nd edition
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12 3
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Amount of time passing for astronaut
The theory of special relativity says that time is relative: Less time will pass for the person in the fast-moving rocket than for a person moving relatively slowly. GAL E GR OU P.
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Rocket finishes flight
Rocket takes off
clock is being carried to you through space on a beam of light traveling at the speed of light—the same speed as your rocket. When you look back at the clock five seconds later, you discover that the clock still reads the same time as it did before because the beam of light is just barely able to keep up with your rocket, so the image you see does not change. Therefore time does not change for you either. Atomic time Over the years scientists have broken up time into increasingly smaller bits. To divide time with such precision, researchers again turned to something found in nature—an atom. The negative charges in atoms vibrate at a regular rhythm. Atomic clocks tell time by measuring ‘‘ticks’’ inside a cesium atom. One second is defined as the time it takes a cesium atom to ‘‘tick’’ 9,192,631,770 times. The first atomic clock was developed in the 1940s and scientists keep improving its accuracy. This clock is so accurate that it loses no more than one second about every 20 million years.
EXPERIMENT 1 Pendulums: How do the length, weight, and swing angle of a pendulum affect its oscillation time? Purpose/Hypothesis The swing of a pendulum led to one of the first accurate timepieces ever developed. There are three main factors in a pendulum: the weight hanging on the pendulum, the length of the pendulum from the point of suspension to the weight, and the distance 1180
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WORDS TO KNOW Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Gnomon: The perpendicular piece of the sundial that casts the shadow. Greenwich Mean Time (GMT): The time at an imaginary line that runs north and south through Greenwich, England, used as the standard for time throughout the world. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Oscillation: A repeated back-and-forth movement. Pendulum: A free-swinging weight, usually consisting of a heavy object attached to the end of a long rod or string, suspended from a fixed point.
Solar day: Called a day, the time between each arrival of the Sun at its highest point. Sidereal day: The time it takes for a particular star to travel around and reach the same position in the sky; about four minutes shorter than the average solar day. Sundial: A device that uses the position of the Sun to indicate time. Theory of special relativity: Theory put forth by Albert Einstein that time is not absolute, but it is relative according to the speed of the observer’s frame of reference. Water clock: A device that uses the flow of water to measure time. Variable: Something that can affect the results of an experiment.
or angle of the pendulum’s swing. In this experiment, you will predict what factors affect the amount of time it takes a pendulum to complete one full back-and-forth motion, or oscillation. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of pendulums. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The time it takes a pendulum to complete an oscillation is only affected by the length of the pendulum: the shorter the length, the less time it takes.’’ Experiment Central, 2nd edition
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In this case, the variables you will change, one at a time, are the weight you hang on the What Are the Variables? pendulum, the length of the pendulum, and the angle of its swing. The variable you will measure Variables are anything that might affect the is the time it takes for the pendulum to complete results of an experiment. Here are the main variables in this experiment: an oscillation. Conducting a control experiment will help • the weight of the substance on the you isolate each variable and measure the pendulum changes in the dependent variable. Only one • the length of the string or twine variable will change between the control experi• the angle of the pendulum’s swing ment and each of your pendulum trials. To In other words, the variables in this experiment change only one variable at a time, it is important are everything that might affect the pendulum’s to always begin the pendulum’s swing at the oscillation. If you change more than one variasame point, and to use the same weight and ble at the same time, you will not be able to tell which variable had the most effect on the time it string length. Then you will change one variable. takes to make one oscillation. The pendulum in your control experiment will always have a length of 16 inches (40 centimeters), start at a 45-degree angle, and have a weight of two washers. You will complete three tests in this experiment. You will measure how a pendulum’s oscillation is affected by the pendulum’s swing angle, weight, and length. For each variable you will use a stopwatch to note the Step 3: Data chart for exact time it takes for the pendulum to complete one back-and-forth Experiment 1. G ALE GRO UP . swing, or oscillation. To lessen the effect of human error, you will conduct three trials of each test, then average the times. Time Trial 1 Angle
45 60 75 Weight 2 washers 4 washers 6 washers Length 8 inches 16 inches 24 inches
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Trial 3
Average
Level of Difficulty Easy to Moderate (because of
the number of trials needed). Materials Needed
• stopwatch • 6 metal washers • a 16-inch (40-centimeter) piece of string or twine • a 24-inch (60-centimeter) piece of string or twine • a paperclip Experiment Central, 2nd edition
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• pendulum support: any stable object at least 3 feet (91 centimeters) high, such as a table • pencil • protractor • masking tape
How to Experiment Safely Make sure the pendulum stand you are using will not tip over.
Approximate Budget $5 (not counting stopwatch. If you do not have a stopwatch, try using a precise timer that you can start and stop). Timetable 45 minutes. Step-by-Step Instructions
1. Tape the pencil onto the table so that half the pencil hangs over the edge of the table (or other pendulum support). 2. Pull a paperclip slightly apart to make a hook and tie the end of the 16-inch (40-centimeter) long piece of string tightly to the closed end of the paperclip. Tie the other end of the string to the pencil. Place two washers on the paperclip hook. 3. Create a chart with a column listing the control, the varying weights, angles, and lengths. List the time it takes for one oscillation across the top row for three trials and the average time. 4. Tape the protractor to the edge of the table, directly in back of the pendulum so that the 0˚ mark lines up with the string. 5. Control Swing: Pull the pendulum back to the 45˚ mark. Using your stopwatch, time how long it takes for the pendulum to complete one full swing. Repeat two more times, noting the times for each swing in the control row for each variable. 6. Swing Angle: Repeat Step 5, pulling the pendulum back to 60˚ and 75˚. Write down the time it takes for each trial. 7. Weight: Add two more washers so there are a total of four washers on the paperclip. Pull the pendulum back to the 45˚ mark and time one complete swing. When you have completed the three trials, add another two washers and repeat. Experiment Central, 2nd edition
Step 5: Pull the pendulum back to the 45˚ mark. G AL E GR OU P.
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Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: One of my trials came out with a much different time than the other two trials. Possible cause: This experiment requires careful attention to detail. This could be due to human error. Make sure you always reset the stopwatch after every trial. Redo the three trials again. If you have trouble accurately measuring the time of one swing, measure the time of two swings and divide the time you measured by 2 before recording it on your chart. Problem: The pendulum is swinging erratically and not moving in a smooth, flat arc. Possible cause: Make sure the pendulum stand is on a flat surface and the pencil is flat on that surface. There could also be outside factors effecting the swing, such as wind, the jostling of the pendulum stand, or brushing the string with your hand while swinging. Problem: The washers are falling off the paperclip. Possible cause: Try using either smaller, flatter washers or a larger paperclip. The washers should be of equal size and weight for all trials, but what they weigh will not affect the experiment.
8. Length: Remove the string from the pencil and cut the string in half. Tie the 8inch (20-centimeter) string to the pencil. Return to the standard weight, two washers, and pull back to the standard 45˚ angle. Time one full swing for the three trials. 9. Construct the standard pendulum except with the 24-inch (60 centimeter) piece of string: Attach the paperclip with two washers and tie to the pencil. Pull the weight back to 45˚ and time one full swing. Repeat two more trials. Note the results in a chart. Summary of Results Either with a calculator or
by hand, average the three times for each trial and note them on your chart. (In this case, you add up the three times and divide the total by three to get the average.) Compare the data from the nine different tests. Determine which of the variables affected the time of the pendulum’s swing—the swing angle, the weight, or the length. How did this variable affect the time? Check your findings against the predictions you made in your hypothesis. You can create three separate graphs of the data, each conveying the results of one variable, and compare them to each other. The y-axis can represent the change in the variable and the x-axis can represent the amount of time it takes to complete an oscillation.
Change the Variables Using the same materials and methods, you can
change the variables by combining the different variables you tested. Does using a heavy weight and a short angle cause the time of a pendulum’s swing to differ between a light weight and a long angle? Would an oscillation of a short cord and a heavy weight take more, less, or the same amount of time than an oscillation of a long chord and a light weight? Make sure you change only one variable at a time so that you can determine which variable is causing the change. For example, 1184
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if you are looking at the heavy weight/short angle versus the light weight/long angle, conduct an experiment first timing the oscillation of a heavy weight/short angle, a heavy weight/long angle, a light weight/short angle, and a light weight/long angle.
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • The temperature of the water
EXPERIMENT 2
• The size of the containers
Water Clock: Does the amount of water in a water clock affect its accuracy?
• The size of the hole in the container
Purpose/Hypothesis Unlike sundials, water
• The number of containers the water flows through • The amount of water used In other words, the variables in this experiment
clocks do not depend on the daylight hours or are everything that might affect the drip rate of a sunny day. This fact made water clocks useful the water. If you change more than one variable at the same time, you will not be able to tell timekeeping devices among ancient cultures. which variable had the most effect on the water There are many different versions of water clock’s accuracy. clocks. Ancient water clocks used one container with markings on it. A later water clock design has water drip at a constant rate from one container into another container below it. The height of the water in the bottom container indicates the amount of time that has passed since the clock was started. One challenge in designing an accurate water clock relates to the rate at which the water flows or drips out of the container. The quantity of water in a container is one factor that can affect the drip rate of the water. In a container of water, all the water pushes downwards, causing pressure on the water at the bottom. A greater quantity of water will cause a greater quantity of pressure pushing downwards; less water will result in less pressure. In this experiment you will investigate how the amount of water can affect a water clock’s accuracy. You will first make a simple water clock and measure a specific period of time with the water always remaining at a constant level. This will be your control. You will then use three different levels of water that will each drip into the container: a quarter, half, and three-quarters filled. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of water clocks and timekeeping. Experiment Central, 2nd edition
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How to Experiment Safely This project poses very few hazards. Be careful with the thumbtack. If you are concerned about spilling water, place old newspapers on the floor under the area where you are conducting the experiment.
This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘As the amount of water in a water clock decreases, the accuracy of the water clock will also decrease.’’ In this case, the variable you will change is the amount of water in the water clock. The variable you will measure is the clock’s ability to measure time. At the end of the experiment you will examine the water’s ability to keep time compared to the control. Having a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control experiment and the experimental water clocks, and that is the amount of water in the container. For the control experiment you will use a full container that will have level water pressure and time one minute. At the end of the experiment you will compare the one-minute markings with the markings of the experimental clocks. Level of Difficulty Moderate. Materials Needed
• • • • • • • • • • 1186
thumbtack or pin watch with second hand ruler water rectangular plastic container (roughly 1 gallon or 3.7 liters) cylindrical tall glass jar 2 chairs, with flat seats masking tape cup marking pen Experiment Central, 2nd edition
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Approximate Budget $10. Timetable 45 minutes. Step-by-Step Instructions
Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
1. Measure the height of the rectangular plastic container and draw a mark at the oneProblem: The water ran out before it completes the five minutes. quarter, one-half, and three-quarters points. Possible cause: The pinhole may be too large 2. Use the thumbtack to punch a small hole or your plastic container may not be large in the bottom of the plastic container in the enough. Repeat the experiment, using a center. Position the container so that each smaller pin or thumbtack. You could also side rests on a chair, with the middle open. shorten your time measurement, but the experiment works best if timed for at least 3. Place the cylindrical glass on the floor three minutes. directly beneath the hole. 4. Hold your finger tightly over the hole in the plastic container and completely fill the container with water. Have a cup of water nearby to keep the container full as the water drips out. 5. Take your finger off the hole and let the water drip out into the glass on the floor for one minute. While the water is dripping, refill the container with water so that it remains completely full. 6. After one minute place your finger over the hole and empty the container in a sink. Place a piece of masking tape lengthwise along the cylindrical glass and draw a small line on the tape at the water level. 7. Use the ruler to precisely measure the height of the water in the glass. Setup of Experiment 2: Making This measurement equals one minute. From the one-minute mark a water clock. GAL E GR OUP . measure four more one-minute marks. You should have five evenly spaced lines along the masking tape, one for each minute. 8. Return the plastic container to its position on the chairs. Hold your finger over the hole and fill the water level to the onequarter mark. Remove your finger and time how long the water takes to reach each of the marks on the tape. Do not put more water in the container. Note your results in a chart. Experiment Central, 2nd edition
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9. Repeat the process with the starting water level at the one-half point and the three-quarters point. Note your results. Summary of Results Examine your chart of the times. Was your hypoth-
esis correct? How did the starting water level at the one-quarter mark compare to the control minute? How did the times change as a result of the water level? Plot your results with the time on one axis and the starting water level on the other axis. Can you think of ways to make your water clock remain accurate? Write a summary of your results and conclusions.
Design Your Own Experiment How to Select a Topic Relating to this Concept The topic of time has
many angles that you can explore. You could examine areas related to the mechanical property of time, such as in a watch or grandfather clock. Other topics you could explore include cultural differences in keeping time, the inventions of keeping time and how they have impacted everyday life; and the theory of time travel. Check the Further Readings section and talk with your science or physics teacher to learn more about time. If you want to build something for an experiment, such as a timekeeping device, make sure to check with an adult before using any tools. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In any experiment you
conduct, you should look for ways to clearly convey your data. You can do this by including charts and graphs for the experiments. They should 1188
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be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. You might decide to conduct an experiment that lasts several months. In this case, include pictures or drawings of the results taken at regular intervals. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects The subject of time is a broad one and can include many
projects. You could examine how different timekeeping devices work, such as a watch and a solar watch, by carefully taking them apart. You could also investigate solar time by building a sundial. There are many different types of sundials. You can build a sundial with the goal to tell time to within minutes or build a sundial to examine how keeping time with it changes over the seasons. Other timekeeping devices you could explore include a shadow clock, a sand clock, and different types of water clocks. You could also examine the idea of time and relativity. There are scientists who hypothesize that moving backwards or forwards in time is theoretically possible, and there are other scientists who disagree. You could explore this debate and make your own conclusions.
For More Information ‘‘Albert Einstein: Person of the Century.’’ Time.com. http://www.time.com/ time/time100/poc/home.html (accessed February 3, 2008). Albert Einstein was named Time magazine’s Person of the Century; site includes articles, links, and the runners up. Ganeri, Anita. The Story of Time and Clocks. New York: Oxford University Press, 1996. Explores the development of recording and measuring time. MacRobert, Alan M. ‘‘Time and the Amateur Astronomer.’’ Sky & Telescope. http://skyandtelescope.com/howto/basics/article 259 1.asp (accessed February 3, 2008). Summary of the different time systems used from ancient to modern day. National Institute of Standards and Technology. ‘‘A Walk Through Time.’’ http://physics.nist.gov/GenInt/Time/ (accessed February 3. 2008]. A look at time from ancient calendars to modern day. Skurzynski, Gloria. From Seasons to Split Seconds. Washington D.C.: National Geographic Society, 2000. The history and science of time and timekeeping. Snedden, Robert. Time. New York: Chelsea House, 1996. Looks at scientists involved with time and time’s role in the universe. Experiment Central, 2nd edition
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W Charles Darwin, who helped us understand evolution, also studied plant growth. LI BRA RY OF CON GR ESS .
hy do plants grow toward light? How far will plants stretch to reach light? These questions fascinated the famous British biologist Charles Darwin (1809–1882), who is best known for formulating the theory of natural selection. Also called survival of the fittest, natural selection is the process by which plants and animals best adapted to their environment to survive and pass their traits on to their offspring. Darwin studied tropism, which includes the bending of plants toward light, because he believed that this trait helped plants reach the light they needed to survive. In 1880, Darwin performed experiments showing how the growing tip of a plant bends toward a light source. This behavior is called phototropism. Photo means ‘‘light,’’ and tropism means ‘‘the growth or movement of a plant toward or away from a stimulus.’’ Thus, phototropism means ‘‘the tendency of a plant to grow toward a source of light.’’ At the same time, Darwin noticed that some shade-loving plants turn away from light, a behavior called negative phototropism. Darwin also discovered another kind of tropism: geotropism, meaning ‘‘a bending toward Earth.’’ He found that the roots of plants are sensitive to gravity, the attraction of Earth’s mass on objects, and grow toward the center of gravity, which is the planet’s core. Auxins hold the key In 1926, Dutch botanist Fritz W. Went discovered that a group of plant hormones called auxins strongly affect plant growth. Hormones are chemicals produced in the 1191
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Auxins have caused the shady side of the plant stems to grow more quickly than the sunny side, turning the plant toward the light. PHO TO R ES EAR CH E RS I NC.
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cells of plants and animals that control bodily functions. Stem cells with a large supply of auxins grow faster than stem cells with just a little of these hormones. Auxins are repelled (turned away) by sunlight, so when light shines on one side of a stem, the auxin moves toward the shady side. Thus, growth slows or stops on the side facing the light. While the shady side of the stem grows more quickly, the sunny side remains nearly the same. In time, the longer side of the stem arcs over the shorter side, bending the plant toward the light. Roots’ reaction to gravity is also controlled by the hormone auxin. However, although auxin speeds the growth of cells in plant stems, it slows the growth of cells in roots. For example, if a plant in a pot is turned on its side, gravity pulls the auxin to the underside of the root, where it slows growth. Then the top side of the root grows more quickly. As the top side grows longer than the underside, the root is forced downward toward Earth. This behavior makes sure that the roots grow deep into the soil, anchoring the plant. At the same time, the stem of the plant grows away from gravity, a negative geotropism. This behavior exposes the leaves to sunlight, which the plant needs for photosynthesis. Reaching out—to water and fence posts Two growing behaviors do not seem to be controlled by auxins. A behavior called hydrotropism causes roots to grow toward a water source. This behavior is controlled by cells in the growing areas of the roots that are sensitive to the presence of water. The root cells grow at different rates, bending the root in the direction of the water. Growing toward water increases the plant’s chances of survival. The second behavior occurs in vines and climbing plants and is called thigmotropism. Thigmo- means ‘‘touch’’; thigmotropism is the tendency for a plant to grow toward a surface it touches. Vines and climbing plants have delicate stems called tendrils. When a tendril touches a solid object, such as a fence post, plant cells on the side away from the post grow very quickly, pushing the tendril toward the post and making it curl around it. That is how plants such as sweet peas, beans, and morning glories climb fences. Experiment Central, 2nd edition
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Why are scientists interested in tropisms? Researchers have created chemical growth substances based on auxins that offer many benefits. These artificial auxins can be sprayed or dusted on stored potatoes to slow the growth of eyes or on fruit and flower petals to stop them from falling too soon. They can also be used as herbicides to kill broad-leaved weeds. In addition, these ‘‘fake’’ auxins encourage root growth in plant cuttings. Food webs, interconnected sets of food chains, depend on plants. People are part of food webs, so the world’s population also depends on plants. For this reason, we need to learn as much as possible about plant growth to feed our expanding population. Your own experiments can interest and educate others about this vital topic.
EXPERIMENT 1 Phototropism: Will plants follow a maze to reach light?
Auxins cause roots to grow longer on their top side, pushing the root toward the ground. GAL E GR OU P.
Purpose/Hypothesis In this experiment, you
will find out whether plants will grow sideways through a maze to reach light. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plant growth. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
A hypothesis must be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this Experiment Central, 2nd edition
What Are the Variables? Variables are anything that might affect the results of an experiment. The main variables in this experiment are: • the type and health of the plants • the position and strength of the light • the distance from the plant to the light • the temperature where the plants are placed • the amount of water they receive In other words, the variables in this experiment are everything that might affect plant growth. If you change more than one variable during the experiment, you will not be able to tell which variable had the most effect on plant growth.
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WORDS TO KNOW Auxins: Plant hormones that strongly affect plant growth.
Hydrotropism: The tendency of roots to grow toward a water source.
Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Food webs: Interconnected sets of food chains, which are a sequence of organisms directly dependent on one another for food.
Photosynthesis: The process by which plants use sunlight to convert carbon dioxide and water into food and oxygen.
Geotropism: The tendency of roots to bend toward Earth.
Phototropism: The tendency of a plant to grow toward a source of light.
Gravity: The attraction of Earth’s mass on objects.
Thigmotropism: The tendency for a plant to grow toward a surface it touches.
Heliotropism: The tendency of plants to turn towards the Sun throughout the day.
Tropism: The growth or movement of a plant toward or away from a stimulus.
Hormones: Chemicals produced in the cells of plants and animals that control bodily functions.
Variable: Anything that might affect the results of an experiment.
experiment: ‘‘A plant will grow sideways through a maze to reach a light that is about 10 inches (25 centimeters) away.’’ In this case, the variable you will change is the position of the light, and the variable you will measure is the plant’s growth toward the light. You expect the plant to grow sideways through the maze toward the light positioned at the other end of the maze. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control plant, which is not being ‘‘experimented on,’’ and the experimental plant. That variable is the position of the light. The light will continue to be overhead for the control plant, as usual. It will be coming from the side for the experimental plant. You will measure the direction of growth for the experimental plant and the control plant. If the experimental plant grows sideways while the control plant continues to grow upright, you will know your hypothesis is correct. Level of Difficulty Moderate, because of the time involved. 1194
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Materials Needed
• • • • • • • • • •
2 small potatoes with eyes (buds) How to Experiment Safely 2 small planting pots with saucers Be careful as you use the scissors to cut a section potting soil out of the shoe box. scissors an empty shoe box with a top 3 strips of cardboard, each about 5 inches (12.5 centimeters) long and as wide as the height of the shoe box masking tape ruler water a warm, sunny spot
Approximate Budget $2 for the potatoes and planting materials. Timetable 1 to 2 weeks for the potato plants to sprout; plus 1 to 2 weeks
for the experiment once the plants have sprouted. Step-by-Step Instructions
1. Allow the potatoes to sit in a warm, sunny place for a week or two until their buds (eyes) start to grow. 2. Plant each potato in a pot with the eye or eyes just above soil level. Water both pots. 3. Take the cover off the shoe box. Cut a section about 2 inches (5 centimeters) square out of one end. (See illustration.) 4. Follow these steps to form a maze inside the box: a. Tape one cardboard strip to the right side and bottom of the box about 2 inches (5 centimeters) from end. (It should end about 2 inches [5 centimeters] from the left side of the box.) b. Tape another strip to the left side and bottom of the box about 2 inches (5 centimeters) from the first strip. (It should end about 2 inches [5 centimeters] from the right side of the box.) Experiment Central, 2nd edition
Steps 3 to 5: Set-up of shoe box maze. G AL E GR OUP .
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Step 7: Recording chart for Experiment 1. GAL E GR OU P.
c. Repeat for the third strip, taping it to the right side and bottom of the box, as shown in illustration. d. Leave space at the far end of the box for a potato plant. 5. Place one potato plant in the far end of the box. This is your experimental plant. Place the other potato plant outside of—but near—the box, where it will get the same amount of sun as the box. This second plant is your control experiment. 6. Water both plants, if needed, and put the lid on the shoe box. 7. Every day, take the lid off the shoe box. Use the ruler to measure the growth and direction of growth of both plants. Record this information on a chart (see illustration). Also make sketches of the growth. Keep the lid on the box the rest of the time. Water both plants whenever the soil feels dry. Summary of Results Create a chart like the one shown to record your findings. Be sure to record your observations every day. Make the chart easy to read, as it will become part of your display. After the plant has been growing in the box for a week or two, study your chart and sketches and decide whether your hypothesis is correct. Did the experimental plant grow through the maze to reach the light? Did the control plant grow upward toward the light, as plants usually do? 1196
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Write a paragraph summarizing your findings and explaining whether your hypothesis was correct and how you know. Change the Variables You can vary this experi-
ment by changing the variables. For example, use rooted avocado pits or sunflower or bean seedlings. Just make sure the experimental and control plants are identical and healthy. You can also move the position of the light. Construct identical mazes in two shoe boxes. Then place one box flat, as in this experiment, and one on end with the light hole at the top. Put a plant at the far end of the first box and at the bottom of the second box. See whether plants move faster through the maze when they are growing up or growing sideways. Finally, you can change the distance of the light from the plants. Construct more elaborate mazes to test the limits of a plant’s efforts to reach the light.
EXPERIMENT 2 Geotropism: Will plant roots turn toward the pull of gravity? Purpose/Hypothesis In this experiment, you
will find out whether plant roots change the direction they are growing as their position is changed in relation to the pull of gravity. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plant growth. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen Experiment Central, 2nd edition
Troubleshooter’s Guide Problem: One or both plants are not growing at all. Possible cause: The plant may have been diseased or infested with insects. Repeat the experiment with different plants. Problem: The control plant is growing sideways, too. Possible cause: The light might have been coming from a low position, perhaps blocked by a window blind. Remove any obstructions and make sure the light comes from overhead. The control plant should begin growing upright. Problem: The experimental plant is growing straight up and pushing against the top of the box. Possible causes: 1. Light might have been seeping in through cracks in the box, drawing the plant upward. Cover the box with a towel, making sure not to cover the light hole at the end. Also, make sure to replace the box lid immediately after making your daily growth measurements. 2. The light source might not have been strong enough. Place both plants in a sunnier spot or remove one cardboard strip to let in more light. Problem: By the end of a week, the experimental plant has barely started to grow through the maze. Possible causes: You might not have allowed enough time, or the plant may be growing slowly because of cool temperatures or too little light. If you remedy these problems, the plant should continue to grow or grow faster.
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A hypothesis must be brief, specific, and measurable. It must be something you can test through What Are the Variables? observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is Variables are anything that might affect the one possible hypothesis for this experiment: ‘‘Roots results of an experiment. Here are the main variables in this experiment: will change the direction they grow as their position is changed in relation to the pull of gravity.’’ • the type of seeds and their germination rate In this case, the variable you will change is the • the amount of light and water the seeds receive direction of the pull of gravity, and the variable you • the temperature where the seeds are placed will measure is the direction of root growth. You • the direction of the pull of gravity expect the roots to grow toward the pull of gravity. In other words, the variables in this experiment are Setting up a control experiment will help everything that might affect the direction of root you isolate one variable. Only one variable will growth. If you change more than one variable change between the control seeds, which are not during the experiment, you will not be able to tell being ‘‘experimented on,’’ and the experimental which variable had the most effect on the roots. seeds. That variable is the direction of the pull of gravity, the attraction of Earth’s mass on objects. Gravity will continue to pull from the bottom for the control seeds as they remain with their roots pointing down. Gravity will seem to pull from Steps 4 to 7: Set-up of control different directions as you turn the experimental seeds so their roots point and experimental glass pane in various directions. ‘‘sandwiches.’’ GA LE GRO UP. You will record the direction of root growth for the experimental seeds and the control seeds. If the roots of the experimental seeds grow in different directions as you turn them, while the control seeds’ roots continue to grow straight down, you will know your hypothesis is correct. The experimental roots will be turning toward the direction of the pull of gravity. Level of Difficulty Moderate, because of the time
involved. Materials Needed You can complete this experi-
ment using small panes of glass held together with rubber bands and set in cake pans. As an alternative, you can use large glass jars with lids. The panes are easier to turn to encourage roots to grow in a circle. However, glass panes are more 1198
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expensive and require careful handling to avoid accidents. • four 10-inch (25-centimeter) squares of glass with the edges taped for safety • 8 large rubber bands • 2 cake pans or other flat containers, large enough to hold the squares of glass standing on an edge • bean or sunflower seeds • paper towels • water • eyedropper • warm, sunny spot • optional: camera and film
How to Experiment Safely The edges of glass panes can be razor sharp. Ask an adult to wrap all edges of the glass with tape to prevent cuts. Then be careful in handling the glass so it does not break.
Approximate Budget $16 for four 10-inch (25-centimeter) squares of
double-strength glass (or $8 for the same amount of single-strength glass); about $1 for seeds. Timetable 2 to 3 weeks for the roots to complete a circle. Step-by-Step Instructions
Step 10: Experimental ‘‘sandwich’’ with roots formed into a circle. G ALE GRO UP .
1. Cut five or six layers of paper towels to form a 10-inch (25-centimeter) square pad. 2. Place the pad on one glass square and cover the pad with enough water to moisten it. 3. Arrange six to eight seeds in a circle on the pad. 4. Carefully place another square of glass on top, so the pad and seeds are like the filling in a sandwich. 5. Place four rubber bands around the ‘‘sandwich,’’ at the top, bottom, and both sides, to hold it together. Alternative method: Fill a jar with damp, crumpled paper towels. Then carefully place the seeds in a row around the inside of the jar between the towels and the glass. Experiment Central, 2nd edition
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6. Repeat Steps 1 through 5 to create a control experiment. 7. Place the cake pans side by side in a warm, sunny spot. Stand each ‘‘sandwich’’ vertically in a cake pan, propping it up with books or other supports, if necessary. If you are using the alternative method, place the jars side by side in a warm, sunny spot. 8. Leave the control sandwich (or control jar) in this position throughout the experiment. 9. Use the eyedropper to moisten the towels if they dry out. 10. After the roots have grown about 1 inch (2.5 centimeters), turn the experimental sandwich (or jar) once, resting it on its side. Now the roots should point to the side. In a few days, the roots should bend downward toward the pull of gravity again. Then turn the sandwich once again, so the top is the bottom. When the roots point down again, turn the sandwich again. Continue until the roots form a circle. 11. Every day, record the root growth you see in both experimental and control seeds on a chart (see illustration). If possible, take photographs of the two sandwiches (or jars) together each time you turn the experimental one.
Step 11: Recording chart for Experiment 2. GAL E GR OU P.
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Summary of Results Create a chart like the one illustrated to record your findings. Be sure to record your observations every day. Make the chart easy to read, as it will become part of your display. Study your chart and decide whether your hypothesis was correct. Did the roots of the experimental seeds change direction as you changed the position of the roots in relation to the pull of gravity? Did the roots of the control seeds continue to grow downward, as they usually do? Write a paragraph summarizing your findings and explaining whether your hypothesis was correct and how your measurements and observations support it. Change the Variables There are several ways you
can vary this experiment. For example, try different seeds like mustard, radish, or other seeds. You can also change the light. Light one seed sandwich from the top and one from the bottom to see if the position of the light affects how the roots grow. Finally, you can change the amount of water the seeds receive. Set up two seed sandwiches, as in this experiment, then use the eyedropper to water only one section of the paper towels for the experimental seeds. The moisture will spread somewhat, but the farthest, driest roots should turn toward the moisture. This demonstrates hydrotropism, growing toward water.
EXPERIMENT 3 Heliotropism: How does the Sun affect the movement of certain plants? Purpose/Hypothesis Heliotropism is the ten-
dency of plants to follow the movement of the Sun throughout a day. ‘‘Tropism’’ means turning and ‘‘helio’’ comes from the Greek meaning Experiment Central, 2nd edition
Troubleshooter’s Guide Experiments do not always work out as planned. However, figuring out what went wrong can definitely be a learning experience. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: One or both sets of seeds did not sprout and/or grow roots. Possible causes: 1. The seeds may have been diseased or exposed to freezing temperatures or other adverse conditions. Dispose of them, clean the glass panes or jars thoroughly, and repeat the experiment with different seeds. 2. The seeds might have dried out or they might be too cold. Try adding more water or putting the seeds in a warmer spot. Or start again with new seeds. Problem: The roots of the experimental plant did not form a circle. Possible cause: They needed more time to grow between turns. Try again, allowing more time. Problem: The stems of the new plants became tangled in the roots. Possible cause: As roots grow toward gravity, stems grow away from it. Every time you turned the sandwich or jar, the stem also responded to the change in the pull of gravity. You might try seeds that grow less vigorous plants, such as mustard or radish seeds (which are also smaller and harder to handle). You can point out the stems’ response to gravity as part of your experiment as well.
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the type of sunflower • the amount of water • the placement of the sunflowers • the age of the sunflowers In other words, the variables in this experiment are everything that might affect the sunflower reacting to the Sun. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on plant movement.
• • • •
sun. In heliotropic plants, flowers, leaves, and stems can all move in the direction of the Sun. Sunflowers are a heliotropic species. In this experiment you will observe and measure how sunflowers move in relation to the Sun. You will need to grow the sunflower plants because generally sunflowers have more of a tendency to be heliotropic when they are young. By comparing the movement of sunflowers left alone in the Sun to sunflowers moved away and blocked from the Sun, you can measure how the Sun’s movement affects the plants throughout the day. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of sunflowers and heliotropism. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
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Step 3: In the morning, note or draw the plants direction in relation to the sun. Look at the leaves, stem, and any flower buds. IL LU STR AT IO N BY TE MA H NEL SO N.
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A hypothesis should be brief, specific, and measurable. It must be something you can test How to Experiment Safely through further investigation. Your experiment will prove or disprove whether your hypothesis is There are no safety hazards in this experiment. correct. Here is one possible hypothesis for this experiment: ‘‘The sunflowers moved away from the Sun will either stop moving or move towards the Sun while the plants left alone will move towards the Sun throughout the day.’’ In this case, the variable you will change is the availability of the Sun to the sunflower. The variable you will measure is the movement of the sunflowers. Level of Difficulty Easy to Moderate, due to the time involved. Materials Needed
• • • • • •
sunflower seeds, at least eight (avoid giant or tall sunflowers) potting soil 3 pots or dishes to grow flowers large tree or other object outside that can block sun open sunny area several warm, sunny days
Approximate Budget $5. Timetable 20 minutes setup time; several minutes every day to care for the plants, and approximately 45 minutes every day for the last several days to week.
Step 4: At midday, turn one of the pots sitting in the sunny area around in a half-circle. Place one pot in the shade. ILL US TRA TI ON B Y TE MA H NEL SO N.
Step-by-Step Instructions
1. Plant two seeds (in case one does not grow) in each pot and water. Follow the directions on the packet. Sunflowers need sun, so you will likely need to find a sunny spot for the pots. 2. When the young plants begin to sprout leaves and are about to bud, set the pots outside near one another in an open, sunny area. A good time to do this is when you have at least two days you can Experiment Central, 2nd edition
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Troubleshooter’s Guide Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
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Problem: None of the sunflowers are moving towards the Sun. Possible cause: The sunflowers may be too young for you to notice. If they have only just germinated, allow them to grow until you see some leaf shoots and the beginnings of a flower bud, and then begin your observations. Problem: The sunflowers are not growing. Possible cause: Sunflowers need a lot of sun and water. Make sure your soil is rich in nutrients. Purchase another bag of sunflower seeds, or you can buy young sunflowers and continue the experiment.
5.
6.
observe the plants at three different times throughout the day. In the morning, note or draw the plants direction in relation to the Sun. Look at the leaves, stem, and any flower buds. At midday, turn one of the pots sitting in the sunny area around in a half-circle. Again note or draw how the plants in each of the pots face in relation to the Sun. In the late afternoon, before the Sun sets, note the direction each of the plants face in relation to the Sun. For the next week, continue the experiment by repeating Steps 3–5. You may want to shorten or lengthen the experiment depending upon your schedule and observations.
Summary of Results Examine your drawings and notes. How did the direction of the leaves, stems, and buds that only had afternoon shade differ from the plants in the pot you turned around. Did the sunflowers you left alone move with the Sun? Was your hypothesis correct. Consider some advantages for plants to always face the Sun. What would be some disadvantages for some plant types, such as desert plants. Write a summary of your findings. You may want to include drawings or pictures. Change the Variables One of the ways you can vary this experiment is to
test heliotropism in different types of plants. You can ask at a gardening store or nursery what plants you could test. You can also investigate if certain desert plants would move to avoid the Sun. Another variable you can change is the free movement of the plants. What would happen if you prevented the sunflowers from moving for part of the day? How would it affect growth or direction?
Design Your Own Experiment How to Select a Topic Relating to this Concept Whether your interest in
plants is old or new, plants offer fascinating questions to explore through science experiments. Consider what puzzles you about plants. What have 1204
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you wondered about? For example, if you cut the growing tip off a plant, will the remaining stem still turn toward the light? What if you turn a potted plant upside down and put the light source underneath the plant? Will the stem grow downward, toward the light? Do roots grow differently if the seeds are planted upside down? What happens if you cut the tip off roots? Will they still turn toward the pull of gravity? Which way would roots grow in a zero-gravity environment? How might tropisms affect plants growing in a space station? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on tropism questions that interest you. Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
Thigmotropism is the behavior that causes this green bean vine to grow up and around the wire support. PH OTO RE SEA RC HERS IN C.
Recording Data and Summarizing the Results In the two tropism experi-
ments, your raw data might include not only charts of measurements of plant or root growth, but also drawings or photographs of these changes. If you display your experiment, you need to limit the amount of information you offer, so viewers will not be overwhelmed by detail. Make clear your beginning question, the variable you changed, the variable you measured, the results, and your conclusions about plant Experiment Central, 2nd edition
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growth. Viewers—and judges at science fairs—will want to see how each experiment was set up, including the shoe-box maze or seed sandwiches you created. The plants or seeds or a photograph or drawing of the plant or root growth at several stages during the experiment would be valuable and interesting. Be sure to label everything you include clearly to show how it fits together. Viewers will want to know what kinds of plants or seeds you used, how long each step took, and other basic information. Related Projects There are a variety of projects relating to plants and plant
growth that you can undertake. You can make a paper or clay model of the reproductive parts of flowers, or you can collect and display different kinds of plants that have been equally exposed to acid rain. Or you can demonstrate how a process works, such as showing how water circulates through a plant from the roots up the stem and out through the leaves.
For More Information Alvin, Virginia, and Robert Silverstein. Plants. New York: Henry Holt, 1996. Explains the plant kingdom classifications and specific kinds of plants, from the first seed plants to edible plants. Capon, Brian. Plant Survival: Adapting to a Hostile World. Portland, OR: Timber Press, 1994. Covers ways that plants have adapted to adverse conditions, such as cold or hot temperature and too much or too little precipitation. Catherall, Ed. Exploring Plants. Austin, TX: Steck Vaughn, 1992. Provides information and projects relating to plant structures, functions, reproduction, and growth. Cochrane, Jennifer. Nature. New York: Warwick Press, 1991. Examines how plants have invaded seemingly inhospitable land and managed to thrive there. Hangarter, Roger P. ‘‘Plant Tropic Responses.’’ Plants-In-Motion. http:// plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/ tropisms.html (accessed February 25, 2008). Brief movies of different plants showing tropics responses. Kerrod, Robin. Plant Life. New York: Marshall Cavendish, 1994. Information about plant biology, groups, and habitats. Parker, Steve. Science Project Book of Plants. New York: Marshall Cavendish, 1989. Features more experiments and explanations about plants and their growth. Tesar, Jenny. Green Plants. Woodbridge, CT: Blackbirch Press, 1993. Includes information on the metabolism, reproduction, and growth of plants, plus their reactions to the environment and role in the food web. Van Cleave, Janice. Plants: Mind-Boggling Experiments You Can Turn into Science Fair Projects. New York: Wiley, 1997. Illustrates possible projects, along with lots of information about plants and plant processes. 1206
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our grandmother proudly shows you an African violet she has grown from seed. Its flower is really unusual: pink with tiny red dots. She grew this plant by pollinating a pink African violet with a red one and planting the seeds that resulted. You remember that pollination is the transfer of pollen from the male reproductive organs to the female reproductive organs of plants. It is a form of sexual reproduction. Only one of your grandmother’s seedlings produced dotted flowers. She knows that if she pollinates this special plant with pollen from a different violet, she might not get any more plants with dotted flowers. Pollinated seeds, like the fertilized eggs of animals, contain the characteristics of both parents. The flower-color characteristics of the other violet may be stronger than the ones in the special plant. If so, none of the seedlings from this pollination will have dotted flowers. Still, your grandmother is smiling. She knows how to grow more of these special plants without using pollen or seeds. She will use vegetative propagation.
Pollination mixes the characteristics of two parent plants. G AL E GR OUP .
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Pollination has produced African violets of many colors in this greenhouse. PET ER ARN OL D IN C.
Auxins can speed up plant growth or slow it down. G AL E GRO UP.
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What is vegetative propagation? Vegetative propagation is a form of asexual reproduction, a reproductive process that does not involve the union of two individuals in the exchange of genetic material. In sexual reproduction, genetic material transfers characteristics from both parents to their offspring. But plants produced by vegetative propagation, or asexual reproduction, have only one parent, so they have the genetic material of only that parent. They are identical to that parent. Grandma does not want any new characteristics in her seedlings, just the ones from her special parent plant, so she will grow new violets from that plant’s leaf cuttings. Growing plants from leaf cuttings is one form of vegetative propagation. In Experiment 1, you will grow new plants from leaf and stem cuttings. How can a plant grow from a leaf or stem? In many plants, cells in the stem tips, root tips, leaves, and certain other areas of the plant are capable of becoming different kinds of plant tissue. These cells allow the stem of a plant to produce roots. They allow the eye, or bud, of a potato to produce both roots that grow downward and shoots that grow upward and become the stems and leaves of a new potato plant. You will explore the growth of potato eyes during Experiment 2. Experiment Central, 2nd edition
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Plant hormones help control this growth. A hormone is a chemical produced in living cells that regulates the functions of the organism. Auxins are a group of plant hormones responsible for patterns of plant growth. When a stem begins to grow horizontally, gravity causes auxin to accumulate on the lower side of the stem. This hormone makes the cells on that side grow longer. This forces the growing tip of the stem to turn upward. Auxin has the opposite effect on roots. A concentration of auxin on the lower side of roots stops growth there. As the top side of the root continues to grow, the root tip turns downward. English scientist Charles Darwin (1809–1882) noticed that plants’ tendency to bend toward light increased the chances of their survival. He figured out that the growing tip of the plant controlled this bending, but it was not until 1926 that the Dutch botanist (one who studies plants) Fritz W. Went isolated the hormone auxin in the growing tip. Since then, scientists have produced artificial auxins. They are used to improve root growth and produce seedless fruits by stimulating the growth of fruit without pollination. These hormones can also stop fruit from falling from trees before it is ripe. In addition, the hormones slow the ripening of fruit that will be shipped long distances and help preserve potatoes, onions, and other vegetables that will be stored for an extended period. Auxins can also kill weeds by speeding up their growth cycle. Learning about plant growth can help you increase your plant collection. More importantly, it can enable you to better understand the plants that we depend on for our existence. Without plants, also called producers, the plant-eaters or herbivores starve. Without herbivores, the meat-eaters or carnivores go hungry, too.
Whether you are a strict vegetarian or live from hamburger to hamburger, you need plants! PET ER A RN OLD INC .
EXPERIMENT 1 Auxins: How do auxins affect plant growth? Purpose/Hypothesis In this experiment, you will try to produce new
plants from stem and leaf cuttings. You will treat half of the cuttings with the plant hormone auxin, while the other half will not be treated. The difference between the two groups of cuttings in root, leaf, and stem Experiment Central, 2nd edition
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WORDS TO KNOW Asexual reproduction: A reproductive process that does not involve the union of two individuals in the exchange of genetic material.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Auxins: A group of plant hormones responsible for patterns of plant growth.
Pollination: The transfer of pollen from the male reproductive organs to the female reproductive organs of plants.
Carnivore: A meat-eating organism. Control experiment: A setup that is identical to the experiment but is not affected by the variable that will be changed during the experiment. Genetic material: Material that transfers characteristics from a parent to its offspring. Herbivore: A plant-eating organism. Hormone: A chemical produced in living cells that regulates the functions of the organism. Humidity: The amount of water vapor (moisture) contained in the air.
Producer: An organism that can manufacture its own food from nonliving materials and an external energy source, usually by photosynthesis. Sexual reproduction: A reproductive process that involves the union of two individuals in the exchange of genetic material. Tuber: An underground, starch-storing stem, such as a potato. Variable: Something that can affect the results of an experiment. Vegetative propagation: A form of asexual reproduction in which plants are produced that are genetically identical to the parent.
growth will tell you whether auxin makes any difference. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plant propagation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Stem cuttings treated with auxin will 1210
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grow more roots, taller stems, and more leaves, and treated leaf cuttings will grow more new plants than will untreated stem and leaf cuttings.’’ In this case, the variable you will change is the auxin treatment, and the variable you will measure is root, stem, and leaf growth for the stem cuttings and the number of new plants grown by the leaf cuttings. Your untreated cuttings will serve as a control experiment to allow you to measure any difference in growth. If the treated cuttings grow more than the untreated ones, you will know your hypothesis is correct. Level of Difficulty Moderate, because of the time
and materials involved. Materials Needed
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the types and health of the plants from which the cuttings are taken • the size of the plant cuttings and the locations from which they are taken on the parent plants • the light, water, soil, and temperature conditions under which the cuttings are grown • treatment with the hormone auxin In other words, the variables in this experiment are everything that might affect the growth of the cuttings. If you change more than one variable, you will not be able to tell which variable had the most effect on growth.
• stem cuttings from several plants, including geranium, coleus, petunia, fuchsia, dieffenbachia, dracena, philodendron, and ivy • leaf cuttings from several plants, including African violet, gloxinia, rex begonia, piggyback plant, peperomia, sansevieria, and succulents (such as a jade plant) • rooting hormone powder, such as Rootone or Hormodin • pruning shears or scissors • two 4-inch-diameter (10-centimeter-diameter) pots with saucers for each kind of cutting you plan to make (one pot for the treated cuttings and one for the untreated cuttings) • potting soil (if possible, mix vermiculite or perlite, two kinds of soil conditioners, into the soil) • pot labels and a marker • pencil • water • clear plastic bags big enough to fit over each pot • ruler Experiment Central, 2nd edition
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Approximate Budget Costs will depend on
How to Experiment Safely Be very careful in using the shears or scissors to make the cuttings. You might ask an adult to help you. Also try not to get the rooting hormone on your skin or especially in your eyes. Wash your hands after setting up the experiment.
whether you need to buy plants or can take cuttings from available plants. Pots cost about $1 each. Potting soil is $3 to $4 for a large bag. A container of Rootone will be $4 to $5. Timetable 3 weeks for the cuttings to sprout and
grow. Step-by-Step Instructions
1. Label each pair of pots ‘‘Experimental’’ and ‘‘Control,’’ along with the name of the plant. 2. Fill each pot with soil, leaving 1 inch (2.5 centimeters) or so at the top of pot. 3. Take the cuttings. Make at least two cuttings of each plant for the experimental pot and two identical cuttings of the same plant for the control pot. (You will need extra cuttings in case some die.) For stem cuttings from each plant you selected: a. Take four 3- to 4-inch (7.5 to 10 centimeter) cuttings from the plant. Slice at an angle to expose as many special growing cells in the stem as possible. Cut just below where a leaf is attached. b. Pull off any leaves close to the bottom of the cuttings. c. Use the pencil to make two holes 2 inches (5 centimeters) deep in each pot. d. Dip about 1 inch (2.5 centimeters) of the end of two cuttings into the container of rooting hormone. Tap the stem to remove excess powder. e. Gently put the stem of each treated cutting into a hole in the experimental pot without rubbing off the powder. Pat the soil around the cutting. f. Put the two untreated cuttings into holes in the control pot, and pat the soil around them. 4. For leaf cuttings from each plant you selected: a. Cut four healthy leaves from the plant. The leaves might have stems attached or not, but make the cuttings identical. b. Use the pencil to make two shallow grooves in the potting soil of each pot. 1212
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c. Dip the bottom edge (and any stem) of two leaves into the container of rooting hormone. Tap the leaves to remove excess powder. d. Gently place each treated leaf into the soil in the experimental pot without rubbing off the powder. Pat the soil around it. e. Put the two untreated leaves into the control pot, and pat the soil around them. 5. Water all the cuttings and place the pots in a warm, light spot, but not in direct sunlight. 6. Place a plastic bag loosely over each pot to keep the humidity level high around the cuttings. Humidity is the amount of water vapor (moisture) contained in the air. The cuttings will all have a better chance of taking root and growing if the air around them is moist. 7. Observe and record any visible growth on a chart similar to the one illustrated. Stem cuttings may grow taller and grow more leaves. Leaf cuttings may sprout tiny leaves at their base. 8. Check the soil in each pot twice a week and water any pots that feel dry. 9. At the end of Week 3, gently pull each cutting out of its pot, shake off the soil, and record the number and length of any roots that have grown.
Steps 3d and 3e: Dip cuttings into root hormone and then gently plant them in experimental pot. GA LE GRO UP .
Summary of Results Use the data on your chart to create some or all of
these graphs: • a line graph comparing the height of the experimental and control stem cuttings at the end of each week • a line or bar graph comparing the leaf growth of the two groups of stem cuttings at the end of each week • a bar graph comparing the number of new plants growing on the leaf cuttings at the end of each week • a chart comparing the final root growth of all cuttings, carefully labeling the stem and leaf cuttings Then study the graphs and your growth chart and decide whether your hypothesis was correct. Did the experimental stem cuttings show more stem, leaf, and root growth than the control cuttings? Did the experimental leaf cuttings grow more tiny new plants than the control Experiment Central, 2nd edition
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Step 7: Recording chart for Experiment 1. GAL E GR OU P.
cuttings? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables Here are some ways to vary this experiment:
• Use cuttings from plants that are harder to root, such as woody stem cuttings from a rose bush.
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• Try a variation on leaf cuttings: cut rex begonia leaves into wedge-shaped pieces or cut sansevieria leaves horizontally into short lengths. Dip the bottom edges of some pieces into rooting hormone, and plant in potting soil. • Treat all cuttings with rooting hormone and experiment with the amount of humidity around the cuttings to see how that affects their growth. • Root the cuttings in water instead of soil. Cover the top of the water containers with clear plastic wrap or aluminum foil and make a hole for each cutting. Stir rooting hormone into the water of some cuttings to see if it improves root growth under these conditions. • Sprinkle seeds with rooting hormone before planting them. Compare their growth with that of untreated seeds. Modify the Experiment In this experiment you
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: All or most of the cuttings rotted. Possible cause: The humidity was too high. Try again, watering the cuttings less or not using the plastic bags. Problem: All or most of the cuttings dried up. Possible causes: 1. The cuttings needed more water. Try again, checking every other day to see if the soil has dried out. 2. The cuttings received too much direct sun. Place them where they will receive light but not direct sun. Problem: The control cuttings from one kind of plant grew more than the experimental cuttings from another kind of plant.
looked at how auxins effect plant growth. Possible cause: Different types of plants have Researchers now know that auxin activity is different growth rates. Focus on whether cutaffected by the time of day. Like people, plants tings from the same plant grew better when go through a natural cycle every 24 hours. Plants they were treated with the rooting hormone. may produce more auxins at night, for example, because that is when water is most available and the plants are preparing for daylight. You can modify this experiment and increase the level of difficulty by experimenting with auxins and the day-night cycle. By using lights, you will not let the plants experience a nighttime. Make a hypothesis about how depriving plants of nighttime will effect growth. You will need two more pots and two grow lights. (If you only have one light you could conduct the two experimental cuttings one after another.) For each of your trial experiments, set up one more pot and label it ‘‘Experimental/Daylight.’’ You should have three pots for each of the cuttings. Prepare the Experimental/Daylight cuttings at the same time and the same way as the ‘‘Control’’ setup. Experiment Central, 2nd edition
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During the day, place all the pots in an area where they receive light. Every night, turn a grow light on over the ‘‘Experimental/Daylight’’ pots. Make sure the pots are far away from the Experimental and Control pots so these plants can experience darkness. In the morning, you can turn off the lights and turn them back on in the evening. Over the next three weeks observe and record any visible growth. How do the cuttings of the daylight trials compare to the Control and Experimental cuttings? Was your hypothesis correct? What can you learn from this experiment about when plants may produce auxins and how that affects plant growth?
EXPERIMENT 2 Potatoes from Pieces: How do potatoes reproduce vegetatively? Purpose/Hypothesis In this experiment, you will cut up potatoes and plant different parts of them to determine which parts can be used for vegetative propagation. The potatoes we eat are actually tubers, which are underground, starch-storing stems. The eyes, or buds, on one potato can develop into several identical new plants through vegetative propagation. The starch stored in the potato or tuber provides food for the new plant until it develops its own root system. Here are the questions to investigate: Do only the eyes of potatoes develop into new plants? What about chunks of potato without eyes? And will eyes grow without any potato attached? To find out, you will plant some chunks of potato with eyes, some chunks without eyes, and some eyes without potatoes attached. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of plant propagation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Only chunks of potatoes with eyes will develop into new potato plants.’’ 1216
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In this case, the variable you will change is whether the potato has an eye, and the variable you will measure is the presence or absence of new growth. Your control experiment will consist of planting potato chunks without eyes and planting eyes without potato chunks attached to them. If only the chunks with eyes sprout, you will know that your hypothesis is correct. This result will prove that the special cells in plant stems and leaves that can develop into different kinds of plant tissue are also present in potato eyes. However, the eyes require the starch food in potatoes in order to reproduce successfully. Level of Difficulty Moderate, because of the time
involved. Materials Needed
• 2 or 3 seed potatoes (available at garden supply stores or farmers’ markets) or other potatoes that have not been treated to stop the growth of eyes • three 5- or 6-inch- (12- or 15-centimeter) diameter pots and saucers • pot labels and a marker • potting soil (if possible, mix vermiculite or perlite into the soil) • sharp knife and cutting board • water • ruler
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the kind of potatoes used • the light, water, soil, and temperature conditions under which the potato parts are grown • the presence of eyes in the potato chunks • whether the eyes have potato attached In other words, the variables in this experiment are everything that might affect the growth of new potato plants. If you change more than one variable, you will not be able to tell which variable had the most effect on the new plant growth.
How to Experiment Safely Take care in cutting the potatoes into chunks. You might ask an adult to help you.
Approximate Budget $6 for potatoes, pots, and potting soil. Timetable 3 weeks. Step-by-Step Instructions
1. Locate the green or white eyes on the potatoes. If there are no eyes yet, place the potatoes in a shallow dish that contains about 1 inch Experiment Central, 2nd edition
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Steps 4 and 5: Set-up of three pots with soil and potato chunks. GAL E GR OU P.
(2.5 centimeters) of water. Leave the dish in a sunny place for several days, and eyes should appear. 2. Carefully cut up the potatoes, creating two or three chunks with eyes attached. Also create two or three chunks that do not have eyes. One surface of these chunks should be covered with potato skin. 3. Use your fingernail to gently separate two or three eyes from a potato. 4. Mark the three pots Chunks with eyes,Chunks without eyes, and Eyes only.
Step 7: Recording chart for Experiment 2. GAL E GR OU P.
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5. Fill each pot about half full of soil and place the appropriate chunks or eyes on the soil. Cover with more soil. 6. Water all pots and place them in a warm, sunny location. 7. Observe and record any growth you see, using a chart like the one illustrated. Feel the soil every other day and add water when it seems dry. Summary of Results Study the findings on your
chart and decide whether your hypothesis was correct. Did only the potato chunks with eyes sprout? Did the eyes without potato attached sprout and then die? Write a paragraph summarizing your findings and explaining whether they support your hypothesis. Change the Variables Here are ways to vary this
experiment:
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: Nothing in any of the pots sprouted. Possible causes: 1. The pots might have been too cold or the soil too dry. Try again, providing good growing conditions for all the pots. 2. The potatoes might have been old or diseased. Try again with new potatoes. Problem: Some of the chunks without eyes sprouted. Possible cause: Perhaps they contained eyes that had not yet broken through the potato’s skin. Take the chunks out of the soil and see if eyes have developed. If so, eliminate them from your experiment.
• Use a different type of potato, such as baking, red, or sweet potatoes, to see if Problem: Some of the eyes without potato the experiment results change. attached are growing. • Leave different amounts of potato Possible cause: A small amount of potato might attached to the eyes to determine how be attached, providing a temporary source of much potato results in the best growth. food. Continue the experiment to see if the eyes keep growing. (They might, if they develop • Sprinkle a rooting hormone on potato roots quickly enough.) chunks, with and without eyes, to see if it changes the results of the experiment. (Versions of the growth hormone auxin are often sprayed on potatoes to slow the growth of eyes. Auxin can both promote and discourage plant growth, depending on how much is used and when it is applied.)
Design Your Own Experiment How to Select a Topic Relating to this Concept You can explore many
other aspects of vegetative propagation. Consider what you would like to know about this topic. For example, you might investigate growing new Experiment Central, 2nd edition
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plants by using runners (strawberries and spider plants), suckers (succulents such as aloe), or air-layering (dieffenbachia and dracena). Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on plant growth questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of the chemicals or procedures might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure which question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the plant growth experi-
ments, your raw data might include charts, graphs, drawings, and photographs of the changes you observed. If you display your experiment, make clear the question you were answering, the variable you changed, the variable you measured, the results, and your conclusions. Explain what materials you used, how long each step took, and other basic information. Related Projects You can undertake a variety of projects related to
vegetative propagation. For example, how small a piece of a leaf will produce new plants? Will all parts of a leaf produce new plants equally well? Will a bulb (an underground stem, like a potato) produce two identical plants if it is cut in half and both parts are planted? Which will bloom first, a plant grown from seed or a plant reproduced vegetatively?
For More Information Alvin, Virginia, and Robert Silverstein. Plants. New York: Twenty First Century Books, 1996. Offers a general description of the plant kingdom and its 1220
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classification system, along with discussion of specific kinds of plants, such as poisonous ones. Bleifeld, Maurice. Botany Projects for Young Scientists. New York: Franklin Watts, 1992. Contains a collection of activities and experiments, exploring photosynthesis, plant structures, and growth. Hershey, David. Plant Biology Science Projects. New York: Wiley, 1995. Outlines plant related science projects that will interest young adults. Missouri Botanical Garden. Biology of Plants. http://www.mbgnet.net/ bioplants/ (accessed on February 6, 2008). Basic information about plant biology and life. Tocci, Salvatore. Experiments with Plants. New York: Children’s Press, 2001. Van Cleave, Janice. Spectacular Science Projects with Plants. New York: Wiley, 1997. Presents facts and experiments relating to plants.
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Vitamins and Minerals
V
itamins and minerals are substances that are essential for people to grow, develop, and remain healthy. Vitamins are organic, meaning that they contain carbon and come from living organisms. Minerals are inorganic, meaning that they do not contain carbon or come from living organisms. Except for two vitamins, humans cannot make any of their own vitamins and minerals. People must get these nutrients from foods. Diseases characterized by lack of nutrients are called deficiency diseases. There are hundreds of vital functions that require proper vitamins and minerals. Maintaining strong bones and muscles, ensuring good vision, healing wounds, providing energy, and fighting infections are a few examples of how the body uses these substances. For years researchers focused their work on determining the amount of each vitamin and mineral needed to avoid any health problems. The Recommended Daily Allowance (RDA) are guidelines formulated by the U.S. government for the amount of each substance a person needs every day. Researchers also are exploring how vitamins and minerals can prevent and treat disease.
An alphabet of vitamins The discovery of vitamins is a story of many people working to understand disease symptoms. In England during the 1700s, it was common for sailors traveling on long voyages to develop bleeding gums, loose teeth, and bruised skin. Some symptoms were more severe and caused many sailors to die. A Scottish naval doctor found that citrus fruits cured the sick sailors, and prevented others from getting ill. The substance in these fruits was unknown at the time. The disease, called scurvy, is now known to be caused by a lack of vitamin C, also called ascorbic acid. Other physicians around the world were recognizing how the changes in a person’s—or animal’s—diet affected health. For the deadly disease beriberi, it was a study of chickens that furthered vitamin research. When 1223
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Vitamin A for healthy vision
A combination of vitamins and minerals gives strong bones and muscles
Vitamins and minerals perform many functions in the body and are essential for good health. GA LE GRO UP.
Vitamins are categorized into two types: water soluble and fat soluble. GA LE GRO UP.
fat soluble vitamins stored in liver and fat until needed
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a group of chickens started coming down with beriberi-like symptoms, it was discovered they Fluorine gives had been fed white rice instead of their usual strong enamel, which prevents cavities brown rice. Upon switching them back to the brown rice, the chickens recovered. This led to Vitamin K the theory that patients were not falling ill from clots blood when cut something they took in, but from something they were missing from their diet. In 1913, scientists isolated the first vitamin, vitamin A, and named it after the first letter of the alphabet. Vitamin B1, or thiamine, was the first B vitamin found and is the vitamin in brown rice that prevents beriberi, a deficiency disease involving the nervous system. As more vitamins were isolated, scientists continued to name them with letters. The human body needs thirteen different vitamins. These vitamins serve many functions vital to good health. For example, one of vitamin A’s main roles is in the production of retinal. Eyes need retinal to sense light, and it is manufactured with the help of vitamin A. Even today, vitamin A deficiency causes blindness in millions around the world, and is a major cause of childhood blindness. Vitamin B12 maintains healthy nerve cells and red blood cells, and is also needed to make DNA, the genetic material in all cells. People’s bodies can only make two vitamins—vitamin K and vitamin D. The sunlight reacts with a chemical in the skin to produce vitamin D, which is necessary for hard bones. About half of the vitamin K a person water soluble vitamins travel needs is made in the intestines, from the bacteria in bloodstream that live there. Vitamin K helps make blood clot when there is a cut, preventing too much blood from flowing out of the body. People need to get the rest of the required vitamin K, and all the excess vitamins eliminated other vitamins, through foods. Fats and water Vitamins are also divided into two categories: fat-soluble and water-soluble. The fat-soluble vitamins dissolve in fats. These vitamins are stored in the body’s fat Experiment Central, 2nd edition
Vitamins and Minerals
Vitamins
Major functions
A (fat soluble)
helps night vision and color vision, growth, healthy skin, fights sickness
B1 - thiamine (water soluble)
strong muscles, growth
Major sources apricots, nectarines, carrots, liver, eggs, milk, broccoli, pumpkin brown breads, beans, grain, cereals, nuts, peas
B2 - riboflavin (water soluble)
helps eyesight; heals cuts, bruises; involved in making red blood cells
milk, cheese, eggs, leafy vegetables, meat, brown breads
C - absorbic acid (water soluble)
repairs broken bones, strong gums and teeth, fights infections
green vegetables, berries, tomatoes, oranges, lemons, grapefruit, and citrus juices
D (fat soluble)
strong bones, teeth
body makes this with sun; tunafish, eggs; added to milk
E (fat soluble)
protects eyes, skin, liver; protects lungs from pollution; helps store Vitamin A
vegetable oils, leafy green vegetables, peanuts
K (fat soluble)
clots blood when wounded
leafy green vegetables, cabbage, cheese, broccoli
Calcium
strong teeth, bone; crucial roles in nerve and muscle cells
milk, yogurt, cheeses, fortified in some juices
Iron (trace mineral)
transports oxygen in red blood cells
red meat, poultry, fish, dried beans, apricots, raisins
Zinc (trace mineral)
heals cuts, helps body grow
seafood, liver, eggs, peanuts, grain food, dark meat of chicken
Fluorine (trace mineral)
strong tooth enamel
sardines, salmon, apples, eggs; added to water
Magnesium (macromineral)
strong bones, controls body temperature
milk, eggs, cheese, yogurt, meats, seafood, molasses
Potassium (macromineral)
keeps the heart strong
bananas, potatoes, raisins, melons, broccoli, beef
Minerals
A selection of the roles some vitamins and minerals play and their sources. GA LE G RO UP.
tissues and liver until the body needs them. Fat-soluble vitamins can remain in storage from a few days to a year. Vitamins A, D, E, and K are all fat-soluble vitamins. Water-soluble vitamins dissolve in water and travel through the bloodstream. They move quickly through the blood and need to be replenished often. As the vitamins stream through the body, organs and tissues pick up the vitamins they need. Whatever the body does not use comes out in urine. Water-soluble vitamins include Vitamin C and the B vitamins. Mind your minerals Minerals originate in the ground and are taken in by plants and animals. Water in the ground soaks up such minerals as calcium (Ca), magnesium (Mg), and iron (Fe). This natural, mineral-rich Experiment Central, 2nd edition
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Brown rice and other grains are a good source of vitamin B1, which helps build muscle. C OPY RI GH T # KE LL Y A. QU IN.
water is called hard water. Animals get their minerals when they eat the plants. Plants absorb minerals from the water in the soil. People ingest the majority of minerals directly from foods. They either eat plants directly or consume the animals that have eaten the plants. People need a smaller amount of minerals than vitamins. These minerals play a number of crucial roles. They help build strong bones and teeth, transmit nerve signals, maintain a regular heartbeat, metabolize food, and many other functions. Minerals are categorized into two types based on how much of the mineral a person needs for good health. The two groups are macrominerals and trace minerals. The body needs a larger amount of macrominerals than trace minerals, although both types are essential. The macromineral group is made up of calcium, phosphorous, magnesium, sodium, potassium, and chloride. Trace minerals include iron, manganese, copper, iodine, zinc, chromium, fluoride, and selenium. Food sources Vitamins and minerals are found in a variety of foods. Each type of food contains a certain amount of vitamins and minerals. Some foods are a rich source of these nutrients, such as broccoli, and others, such as soda, are not a significant source. For most people, eating a well-balanced diet with a wide variety of foods supplies the necessary amounts of vitamins and minerals. People who are ill or do not get their nutrients through food take supplements, or additional vitamins and minerals. Many foods are fortified or enriched with essential vitamins and minerals. Water, for example, is fortified with additional mineral fluorine. Vitamin D is added to milk after it is heated to kill germs, which causes it to lose Vitamin D in the process. Many cereals and juices are also fortified with vitamins and minerals. Packages list the RDA for the vitamins and minerals they contain. There are RDAs provided for children, teenagers, and adults. The RDA listed on food packaging is the amount that an average, healthy adult should consume each day.
EXPERIMENT 1 Vitamin C: What juices are the best sources of vitamin C? Purpose/Hypothesis Vitamin C is a water-soluble vitamin that is essen-
tial for human growth and health. In this experiment, you will explore the 1226
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relative quantity of vitamin C in different juices. To measure the amount of vitamin C you will What Are the Variables? observe the chemical reaction of vitamin C with iodine. Variables are anything that might affect the results of an experiment. Here are the main Iodine mixed with water forms ions, which variables in this experiment: are charged particles. When ions mix with starch they produce a compound that has a blue color. • the type of juice Ascorbic acid, or vitamin C, breaks up the bond • the freshness of the juice between the ions and the starch, reversing the • the temperature of the juice color change. The more vitamin C in a subIn other words, the variables in this experiment stance, the quicker the bonds will be broken, are anything that might affect the speed at and the faster the liquid will turn clear. which the vitamin C breaks up the bond. If you change more than one variable at the same You will test the vitamin C content of time, you will not be able to tell which variable orange, grapefruit, and apple juice. Make sure has the highest concentration of vitamin C. all the juices are fresh—not from concentrate. You can use your imagination and test a variety of other juices also, such as tomato, grape, and carrot. You will first create a bond between a starch solution and iodine. You will then slowly add juice to the solution to determine the amount it takes for the juice to break the bond, turning the solution clear. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of vitamin C. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these Minerals in the earth are taken things: in by plants, which are then ingested by animals. Humans can get their required minerals by eating plants and animals.
• the topic of the experiment • the variable you will change • the variable you will measure
G AL E GR OUP .
• what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The orange juice will contain more vitamin C than the other two juices.’’ In this case, the variable you will change is the type of juice. The variable you will Experiment Central, 2nd edition
Mg
Ca
Fe
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WORDS TO KNOW Control experiment: A setup that is identical to the experiment, but is not affected by the variable that acts on the experimental group. Deficiency disease: A disease marked by a lack of an essential nutrient in the diet. Fat-soluble vitamins: Vitamins such as A, D, E, and K that can be dissolved in the fatof plants and animals. Fortified: The addition of nutrients, such as vitamins or minerals, to food. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Inorganic: Made of or coming from nonliving matter. Macrominerals: Minerals needed in relatively large quantities. Minerals: Inorganic substances that originate in the ground; many are essential nutrients.
Organic: Made of, or coming from, living matter. Scurvy: A disease caused by a deficiency of vitamin C, which causes a weakening of connective tissue in bone and muscle. Supplements: A substance intended to enhance the diet. Trace minerals: Minerals needed in relatively small quantities. Variable: Something that can affect the results of an experiment. Vitamins: Organic substances that are essential for people’s good health; most of them are not manufactured in the body. Water-soluble vitamins: Vitamins such as C and the B-complex vitamins that dissolve in the watery parts of plant and animal tissues.
measure is the relative amount of juice it takes to make the solution clear. Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and your experiment. For your control in this experiment you will use a solution of pure vitamin C. At the end of the experiment you can compare the results of the control with the experimental results. Level of Difficulty Moderate. Materials Needed
• paper towel • spoon 1228
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• 500-milligram vitamin C tablet • cornstarch • 4 small clear glasses or jars, such as baby food jars • iodine (available at drug stores) • apple juice • orange juice • grapefruit juice • other juices: tomato, carrot, or grape (optional) • dropper • measuring cup • measuring spoons • paper towel • marking pen • 2 mixing cups
How to Experiment Safely Be careful when handling iodine: It is a poison and can stain your skin, clothing, and countertops.
Approximate Budget $10. Timetable 1 hour. Step-by-Step Instructions
1. Write the name of the juice to be tested on each of the jars. Label one jar ‘‘Vitamin C.’’
iodine
vitamin c
grapefruit
orange
Experiment Central, 2nd edition
starch solution
apple
Step 6: Add one drop of iodine to each jar. Cap the jar and swirl. GAL E GR OU P.
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2. To prepare the starch solution, mix ½ teaspoon (2.5 milliliters) of cornstarch in Troubleshooter’s Guide 1 cup (0.25 liters) warm water. Stir thoroughly until the cornstarch dissolves. Below is a problem that may arise during this experiment, a possible cause, and a way to 3. Crush the vitamin C tablet in a folded remedy the problem. paper towel. 4. Dissolve the crushed tablet in 2 cups Problem: The pure vitamin C took as many drops as a juice to turn clear. (0.5 liters) of warm water. The vitamin C Possible cause: You may not have crushed and solution is now 500 milligrams/milliliters, dissolved the vitamin C thoroughly. Make or 1 milligram/milliliter. Allow to cool to sure the tablet is in a fine powder before you room temperature. pour it in the water, then mix briskly and 5. Put 2 tablespoons (30 milliliters) of the repeat the experiment. starch solution into each jar. 6. Add one drop of iodine to each jar. Cap the jar and swirl. The solution should turn blue-black. 7. Test the control solution: Add 1 drop of the vitamin C solution to its jar and swirl. Add another drop, if needed, until the blue-black color has disappeared. Note the results in a chart. 8. Test each juice: Add 1 drop of the orange juice to its jar and swirl. Continue to add drops, swirling after each drop, until the blue color clears completely. Note the number of drops in the chart. 9. Repeat with the apple and the grapefruit juices. Note your results. Summary of Results Examine how many drops it took for each juice to
dissolve the bond and clear the color. Graph the results of your experiment. Which juice had the highest concentration of vitamin C? How did this juice compare to the test standard, pure vitamin C? Hypothesize how the vitamin C content of other types of beverages—vegetable juice, carrot juice, soda, and sports drinks—would compare the juices you tested. Change the Variables In this experiment you can change the variables in
several ways. You can use the same type of juice, such as orange juice, and vary the brands. You could also test the vitamin C content in different solid foods by blending a set quantity of each food with a set amount of water. Length of storage, heat, light, and oxygen can all affect the amount of vitamin C in beverages and food. You could change each of these variables for one kind of food or beverage. With one type of juice you could also vary the freshness. For example, you could test one frozen 1230
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concentrate orange juice, one store-bought refrigerated orange juice, and one freshly squeezed orange juice.
EXPERIMENT 2 Hard Water: Do different water sources have varying mineral content? Purpose/Hypothesis Water that contains miner-
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the water source • the amount of soap • the type of soap • the mineral added
als in it is called hard water. The hardness or level In other words, the variables in this experiment of the mineral content varies from location to are everything that might affect the amount of location. In this experiment, you will examine soap scum the water produces. If you change the mineral content of various waters by mixing more than one variable at the same time, you the water with soap. will not be able to tell which variable had the Two common elements in hard water are most effect on the soap scum. magnesium and calcium. These minerals can lessen the cleaning ability of soap by preventing the lathering action. Hard-water minerals readily bind to the soap molecules, forming a large and heavy compound that sinks. The result is a soap scum that does not dissolve in water. (Water softeners remove the hard minerals.) To determine the hardness of varying water sources, you will mix water with soap. You will use tap water, rainwater, and chalk-water. Chalk is a form of limestone, which is composed of calcium. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of minerals and hard water. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The water highest in minerals will be the chalk water; the water least high in minerals will be the rainwater.’’ Experiment Central, 2nd edition
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In this case, the variable you will change is the water source. The variable you will measure How to Experiment Safely is the hardness of the water. Conducting a control experiment will help If you are not using a disposable eyedropper, you isolate each variable and measure the make sure to wash the dropper thoroughly to remove all traces of the soap. Be careful when changes in the dependent variable. Only one handing the hot water. variable will change between the control and your experiment. For your control you will use distilled water, water that has no minerals in it. At the end of the experiment you can compare the control and the experimental results. Level of Difficulty Easy to Moderate. Materials Needed
• • • • • • •
Step 8: After placing two drops of liquid soap in each of the bottles, shake each bottle and examine the amount of soap scum. GA LE GRO UP.
eyedropper liquid soap 4 small plastic bottles with caps measuring cup (with spout preferably) funnel (optional) piece of chalk (calcium) tap water • rain water • distilled water • spoon • cup or bowl to collect rain water • marking pen Approximate Budget $5. Timetable 45 minutes (not counting the time it takes to wait for rain).
control
ta p
rain calcium
Step-by-Step Instructions
1. On a day when rain is forecast, place a bowl outside to collect at least 1 cup of rainwater. 1232
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2. Over a measuring cup, scrape about 1 teaspoon (5 milliliters) of chalk into powder using the edge of a spoon. 3. Measure 1 cup (240 milliliters) of hot distilled water into the cup. Stir the ground chalk and water thoroughly. Cool to room temperature. 4. Label the bottles: ‘‘Calcium,’’ ‘‘Tap,’’ ‘‘Control,’’ and ‘‘Rain.’’ 5. Pour the chalk water into its designated bottle. (There may be some chunks left over on the bottom so pour slowly.) You may need to use a funnel for this. Rinse out the measuring cup. 6. Measure out 1 cup (240 milliliters) of tap water and carefully pour into its bottle. Rinse the cup and repeat with the distilled and rain water.
Troubleshooter’s Guide Below are some problems that may arise during this experiment, some possible causes, and some ways to remedy the problems. Problem: The chalk did not dissolve in the water. Possible cause: You may not have scraped the chalk into a fine enough powder. Chalk will dissolve better in warmer water than cooler water. Repeat the experiment, making sure to use hot water and a fine powder. Problem: There was no difference in the amount of scum between the calcium water and the tap water. Possible cause: Try allowing the bottles to sit for another 15 minutes to determine if there is a difference as the soap bubbles disappear.
7. Using the eyedropper, place two drops of the liquid soap into each of the bottles. 8. Shake each of the bottles and examine the amount of soap scum. Note a description of the results. 9. Allow the bottles to sit for 15 minutes and, again, note the results. Summary of Results Examine the results of your experiment. Was your
hypothesis correct? How does the rainwater compare to the control? The ability of soap and detergent to lather directly affects their ability to clean. Hypothesize why water softeners are popular in some areas of the country more than others. What would be the result of simply adding more soap or detergent? Write an analysis of the experiment, including an explanation of your results for each type of water. Change the Variables In this experiment you can change the variable by
altering the water source. You can focus on one type of water, such as tap water or mineral water. Different geographic locales will have varying amounts of mineral in the water. You can also try the experiment on different brands of mineral water. Experiment Central, 2nd edition
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Modify the Experiment
In order to keep in top physical shape, athletes require the proper balance of vitamins and minerals. AP/ WI DE W OR LD.
You can modify this experiment by increasing the level of difficulty and experimenting with water softeners. Water softeners inactivate the minerals in water. Adding water softener to hard water can lead to less soap scum and more lather. You will need to gather three cups, three bottles, and a laundry water softener. Follow the experiment procedures, making sure to save the soapy water in the bottles. After you have determined which water is highest in minerals, make three more cups of this hard water. Pour one cup of hard water into each of the three bottles. Place two drops of liquid soap into each of the bottles. In two of the bottles, drop in a different amount of water softener. You could add two drops in one bottle and four drops in the second bottle. The third bottle will be the control. Make sure you label each of the bottles. Shake each of the bottles and note the results. How much lather or soap scum did each bottle make? How do the results compare to the natural rain water? Try using different amounts of water softener. Is there an amount you can use that will give results similar to the rainwater? You might want to graph your findings and summarize your results.
Design Your Own Experiment How to Select a Topic Relating to this Concept There are many possible projects related to vitamins and minerals. As almost all foods contain some amounts of vitamins and minerals, you can work with food and beverages. You can also focus on where vitamins and minerals are derived from, and their effect on various life forms. Check the Further Readings section and talk with your science or nutrition teacher to learn more about vitamins and minerals. You can also
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gather ideas from examining the vitamin and mineral contents listed on the packaging of the foods you eat. Steps in the Scientific Method To conduct an
original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved and select one that will help you answer the question at hand. • State your hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results.
For most people, eating a wellbalanced diet with a wide variety of foods supplies the necessary amounts of vitamins and minerals. CO PY RI GHT # KE LL Y A. QUI N.
Recording Data and Summarizing the Results Your data could include
charts and drawings, such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photographs and drawings of your experimental setup and results, which will help others visualize the steps in the experiment. If you are preparing an exhibit, you may want to display your results, such as any experimental setup you designed. If you have completed a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects There are many possible project ideas related to vitamins
and minerals. You can examine the vitamins and minerals that you and people you know take in by adding up the foods you eat and charting the results. Compare the numbers to the Recommended Daily Allowances (RDA). You can also experiment with removing the minerals from certain types of food. You could also examine how other species, besides humans, use vitamins and minerals. Different animals produce certain vitamins that humans do not. You could look at what elements these animals produce Experiment Central, 2nd edition
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and how vitamins and minerals impact an animal’s health. Vitamin and mineral deficiency is also a serious health problem in many parts of the world. A project on deficiency diseases could include examining several of these diseases and possible foods people of that area could easily attain to stop or prevent the disease. You could also conduct a research project on the history of the discovery of vitamins and minerals, and the work of finding more of these elements.
For More Information ‘‘All About What Vitamins and Minerals Do.’’ KidsHealth. http://kidshealth. org/kid/stay healthy/food/vitamin.html (accessed on February 19, 2008). Easy to read explanation of vitamins and minerals. Centers for Disease Control and Prevention. Fruits & Veggies More Matters. http://www.fruitsandveggiesmatter.gov/ (accessed on February 19, 2008). Provides benefits and recommended amounts of fruits and vegetables. Food Standards Agency. ‘‘Vitamins and Minerals.’’ eatwell. http://www.eatwell. gov.uk/healthydiet/nutritionessentials/vitaminsandminerals (accessed on February 19, 2008). Information about vitamins, minerals, and where they are found. Kalbacken, Joan. Vitamins and Minerals. San Francisco, CA: Children’s Press, 1998. Simple, basic information about vitamins and minerals. United States Department of Agriculture. Search the USDA National Nutrient Database for Standard Reference. http://www.nal.usda.gov/fnic/foodcomp/ search (accessed on February 19, 2008). Search for the vitamin and mineral content of specific foods.
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O
n August 24, in 79 A . D ., the citizens of Pompeii, in what is now Italy, woke up to a warm, sunny day. Some probably went to sit outside their beautiful villas to sit and admire the fruit trees, ornamental wall paintings, and statues in their enclosed gardens. Many of the villas overlooked the sparkling Bay of Naples. Businesses were opening and some were already bustling with activity. But life in Pompeii ended abruptly that morning when nearby Mount Vesuvius erupted. Pompeii and the neighboring town of Herculaneum were destroyed. More than 2,000 people were suffocated by the gas and ash that spewed from Vesuvius and covered Pompeii or by the lava flow of molten rock that leveled Herculaneum. Pliny the Younger, a Roman historian, saw the terrible event from the nearby town of Miseneum and wrote the first written, eyewitness account of a volcano’s eruption.
This gold pin, with the head of a ram at the tip, was found in Pompeii. C ORB IS .
Today Vesuvius is still an active volcano, a conical or domelike mountain of lava, ash, and cinders that forms around a vent leading to molten rock deep within Earth. When volcanoes erupt, they literally blow their top, ejecting tons of rock and debris into the air, as well as sending clouds of toxic gases and steam and rivers of lava down the sides of the mountain. Get the drift? After the Americas were discovered, scientists observed that Earth’s continents fit together like the pieces of a jigsaw puzzle. The scientists believed that the continents had once been joined together in one land mass and then violently separated. In 1912, German meteorologist Alfred Wegener (1880–1930) proposed that the continents were moving apart slowly at a predictable rate. 1237
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Alfred Wegener’s theory about continental drift was a first step in discovering the dynamics of a volcano. C OR BI S CO RP.
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He coined the term continental drift and conducted much research to support his theory. Many thought Wegener’s idea was radical, but his suggestion that some force caused the continents to move eventually became the key to unlocking the dynamics of a volcano. After Wegener died, the geologists who agreed with his theory took it a step further. They proposed that the radioactive decay of naturally occuring elements deep within Earth produced tremendous heat. The heat was so intense that it melted rock, forming a vast caldron of liquid that boiled and swirled in vast amounts. This bubbling mass generated convection currents, currents of molten rock. The scientists suggested that these molten rock currents pushed up under ridges in the ocean and through active volcanoes—moving the continents. How does a volcano blow its top? Deep under a volcano is Earth’s mantle, a layer that lies between the the Earth’s crust or outermost layer, which extends 25 miles (40 kilometers) down, and Earth’s core. The further down, the hotter the temperature gets. Earth’s inner core can reach 13,000˚F (7,000˚C). At the top of the mantle, around 30 miles (45 kilometers) down, magma can be found. Magma is liquid rock that consists of gases and silica; this substance collects and forms pools known as a magma chambers,—which are the volcano’s furnace. The gases bubble through the magma, making the liquid hotter and lighter than surrounding rocks, and this helps push this volatile liquid mixture up through a volcano’s vent. Even the slight strain of tides can affect the inner pressure of a volcano and cause it to blow. Most often, though, the cause is the movement of tectonic plates, large flat pieces of rocks that form Earth’s outer crust and fit together like pieces of a cracked eggshell. Grinding or overlapping can melt some of the plate rock, which pushes it up into the magma chamber, where it causes a magma surge. If the dome over a volcano’s vent is obstructed with rock or dirt, pressure builds up even more, causing a more violent eruption. The same basic principles that govern tectonic plate movement can cause both earthquakes and volcanic Experiment Central, 2nd edition
Volcanoes
WORDS TO KNOW Continental drift: The theory that continents move apart slowly at a predictable rate. Convection currents: Circular movement of a fluid in response to alternating heating and cooling. Crust: The hard outer shell of Earth that floats upon the softer, denser mantle. Lava: Molten rock that occurs at the surface of Earth, usually through volcanic eruptions. Magma: Molten rock deep within Earth that consists of liquids, gases, and particles of rocks and crystals. Magma underlies areas of volcanic activity and at Earth’s surface is called lava. Magma chambers: Pools of bubbling liquid rock that are the source of energy causing volcanoes to be active.
Magma surge: A swell or rising wave of magma caused by the movement and friction of tectonic plates, which heats and melts rock, adding to the magma and its force. Mantle: Thick dense layer of rock that underlies Earth’s crust and overlies the core. Seismograph: A device that records vibrations of the ground and within Earth. Seismometer: A seismograph that measures the movement of the ground. Tectonic plates: Huge flat rocks that form Earth’s crust. Volcano: A conical mountain or dome of lava, ash, and cinders that forms around a vent leading to molten rock deep within Earth.
eruptions, so it is not surprising that both can be detected by the same instrument. While seismographs are used mostly for detecting earthquakes, they can also detect vibrations deep within Earth that indicate the gradual rise of magma. Sometimes there’s a good side to a down side The citizens of Pompeii and others who died because of volcanic eruptions would certainly disagree that there is any positive side to this natural disaster; but volcanic eruptions do have some good effects. If an eruption produces a layer of ash less than 8 inches (20 centimeters) thick, farmers get a free, nutritient-rich natural fertilizer blanketing their land. For example, the ash from Mount Vesuvius helps the grapes grow in that area’s wine region. Although the 20 feet (6 meters) of ash that covered Pompeii smothered every living thing, the ash also preserved the city, its artifacts, and its inhabitants. Archeological findings have shown us in detail the civilization of an ancient people who were lively, cultured, and gifted. In the following projects you will be able to learn more about volcanoes. Experiment Central, 2nd edition
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PROJECT 1 How to Experiment Safely Do not activate the volcano’s eruption without adult supervision. Wear goggles to do it. Always handle scissors carefully.
Model of a Volcano: Will it blow its top? Purpose/Hypothesis In this activity you will
construct a working model of a volcano. This model will demonstrate the dynamics of magma flow and the gaseous buildup that causes a volcano to blow.
Level of Difficulty Moderate. Materials Needed
Step 3: Set-up of plastic tube and straws. GA LE GRO UP.
• glue • 8-inch (20-centimeter) long plastic tube, 1.5 inches (3.8 centimeter) in diameter • 4 plastic straws • newspaper • masking tape • scissors • 4 rolls plaster of Paris gauze (or papier-mache´ mix and newspaper) • empty film container • effervescent antacid tablets • water • goggles or other eye protection • brown and red water-based or acrylic paint • cornstarch • baking soda • vinegar • red food coloring Approximate Budget $10 to $15. Timetable 2 to 3 hours. Step-by-Step Instructions
1. Place about six sheets of newspaper over the surface you will be working on. 1240
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2. Poke four holes in the plastic tube between 1 and 2 inches (2.5 to 5 centimeters) from the bottom. Make sure the straws can fit through the holes. 3. Glue the straws into the tube’s holes, making sure the glue does not clog the straws’ openings. 4. Twist a sheet of newspaper into a stick shape. Repeat with several sheets. 5. Wrap the sticks around the tube, making sure the straws stick out, and tape into place. The bottom should be wide and the top narrower, just like a volcano. 6. Gently moisten the plaster of Paris strips and wrap them around the volcano. Make sure you cover all the newspaper. 7. Allow to dry for 30 minutes. Trim the straws that are protruding out of the volcano. 8. Paint the surface with brown and red water-based or acrylic paint and allow to dry. 9. Using leftover material, create a cap that covers the top of the plastic tube. Make sure it’s removable but snug. 10. Remove the volcano cap. 11. Place one to five antacid tablets inside the plastic film container. 12. Pour 1 tablespoon of water into the container. Snap the top on and drop into the plastic tube opening at the top of the volcano. 13. Place the volcano cap back on quickly, stand back, and watch it blow! 14. Remove the volcano cap. 15. Mix 1 cup (224 grams) of cornstarch with 0.75 cup (178 milliliters) of water. Add ten drops of red food coloring. Add 0.25 cup (56 grams) baking soda mix and add 0.25 cup (56 grams) of vinegar. 16. Pour the mixture into the plastic tube and observe. The magma mixture will swell inside the volcano and cause a bubbling eruption. Slowly the magma will creep Experiment Central, 2nd edition
Steps 4 and 5: Wrap newspaper sticks around the tube, making sure the straws stick out, and tape into place. GAL E GR OU P.
Step 16: The magma mixture will swell inside the volcano and cause a bubbling eruption. Slowly the magma will creep out of the volcano and become lava. G ALE GRO UP .
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out of the volcano and become lava. Lava should also slowly come out of the straw vents on the side.
Troubleshooter’s Guide Here are some problems that may arise during this project, possible causes, and ways to remedy the problems. Problem: The magma/lava flow did not come out of the straws.
Summary of Results Write a paragraph explain-
ing what you witnessed when the volcano erupted and the magama/lava flowed. Research how Mount Vesuvius blew and compare your volcano with how that volcano erupted. Make a diagram of the internal structure of the volcano.
Possible cause: The tubes are clogged. Stick a pipe cleaner through the straws to make sure the tubes are open. Add more vinegar and baking soda to the mix and try again.
PROJECT 2
Problem: The film container did not blow the top off the volcano.
Looking at a Seismograph: Can a volcanic eruption be detected?
Purpose/Hypothesis Seismometers are instruments that detect disturbances in Earth’s crust. Used mostly for earthquake detection, they can also measure the turbulence of a volcano’s magma activity. The disturbance or activity is recorded on a seismograph, a sheet of paper that shows the intensity of the activity. For this project you will construct a seismograph that will simulate the types of disturbances that indicate volcanic activity.
Possible cause: You need more antacid. Try adding more to the container and do not forget to wear your goggles.
Level of Difficulty Easy. Steps 1 to 3: Set-up of shoe box and coil toy. GA LE G RO UP.
Materials Needed
• shoe box • metal coil toy (like a Slinky) • metal block (or a stone), 2 by 2 inches (5 x 5 centimeters) • pencil • roll of adding machine tape • scissors • tape Approximate Budget $2 to $5 for purchase of coil toy and adding machine tape. 1242
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Timetable Less than 30 minutes. Step-by-Step Instructions
How to Experiment Safely
1. Cut a 2.5 to 3-inch (6 to 7-centimeter) Handle scissors carefully. slit on each side of a shoe box. 2. With scissors cut the coil toy in half. 3. Poke a hole in the top of the box and pull a few coils of the toy through. 4. Tape the metal block to the spring. 5. Tape the pencil to the block. Face the tip toward the back and make sure the tip touches the back wall. 6. Carefully feed the paper through both slits cut in the side walls. Do not tear the paper. You have now built the seismograph. 7. Place your seismograph on a table. 8. Place any heavy object on top of the seismograph to hold it in place. 9. Ask a friend to help by gently shaking the table or lifting it off the ground a half inch. 10. As your friend is causing the disturbance, slowly and gently pull the paper through the hole. Summary of Results Examine your seismic data. The tape records the
magnitude of seismic disturbances in Earth’s crust that can lead to a magma surge. Mark your tape with observations of what may have happened if a volcano really erupted. Refer to the illustration of the sample seismograph paper for ideas.
Steps 4 to 6: Set-up of the seismograph. GAL E GR OU P. Experiment Central, 2nd edition
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Design Your Own Experiment Troubleshooter’s Guide
How to Select a Topic Relating to this Concept These projects are simple models that
Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems.
will familiarize you with some of the important dynamics of a volcano. If you wish to investigate further, research the type, sizes, and places of volcanoes. Or lava flows, properties of lava, or the effects of volcanic ash may interest you. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on volcano questions that interest you.
Problem: The pencil does not move up and down. Possible cause: The coil toy is too tight. Either try a heavier coil toy or gently stretch the coil toy until the coils no longer touch each other. Problem: The pencil is not making clear marks on the seismograph paper.
Steps in the Scientific Method To do an original
experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question.
Possible cause: The pencil is not touching the paper. Adjust it or try using a marker with a fine tip.
Sample seismograph paper with observations recorded. How does your paper compare? GA LE GR OU P.
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• Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results
In any experiment, you should keep notes and data organized so that others can utilize and understand it. Charts, graphs, and pictures are excellent ways to share and summarize your results. Related Projects Besides constructing a model of
a volcano and simulating its eruption, you could investigate the environmental effects of eruptions or past climate changes due to eruptions. Start by asking a question you want answered. Then construct an investigation around that question.
For More Information North Dakota and Oregon Space Grant Consortia. Volcano World. http://volcano.und.edu (accessed on January 12, 2008). Rubin, Ken. Volcano & Earthquakes. New York: Simon & Schuster Books for Young Readers, 2007. Van Rose, Susanna. Volcano & Earthquake. New York: Knopf, 1992. Photographs and text explain the causes and effects of volcanoes and earthquakes and examine specific occurrences throughout history.
Experiment Central, 2nd edition
Mount Tolbachik in Russia’s Kamchatka Peninsula erupted on July 6, 1975, spewing lava that gushed at a speed of 550 feet (168 meters) per second. AP/ WI DE W OR LD PH OT OS.
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W
ater is found not only in oceans, rivers, streams, ponds, swamps, puddles, and similar places. It is also stored in the soil, in polar ice caps, and in underground areas called aquifers. Some water is actually in the air as water vapor. The water cycle, sometimes called the hydrologic cycle, is the continuous movement of water between the atmosphere, land, and bodies of water. Rainstorms are the major way that water gets from the atmosphere to Earth. Then the rain seeps into the soil or runs over land into streams, rivers, and oceans. Over time, water evaporates from lakes, ponds, swamps, rivers, oceans, and even soil, changing from a liquid to a gas called water vapor. This water vapor rises into the atmosphere again, where it cools and condenses around dust or salt particles in the air, turning back into droplets of liquid. When the droplets get too heavy to remain in the air, they fall as precipitation: rain, snow, sleet, or hail. Water vapor is often invisible, but on a warm summer day, you can feel water vapor. The air often feels damp because it contains a lot of water vapor.
How much water can the air hold? There is a limit to how much water vapor air can hold. When the air becomes saturated with water vapor, the excess water vapor condenses into droplets of water. Water vapor high in the atmosphere forms clouds, large masses of droplets. When these clouds are close to the ground, we call them fog. You have probably also seen water vapor condense on windows or on cold drink glasses. Is the water cycle a new idea? The water cycle is driven by the Sun and gravity and affects climate, soils, erosion, habitat, transportation, and so on. This cycle has been recognized and studied by scientists for thousands of years. Leonardo da Vinci wrote about it in the 1400s. The founders of modern hydrologic study were Pierre Perroult (1608–1680), 1247
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Illustration of global water cycle. GAL E GR OU P.
Edme Mariotte (1620–1684), and Edmund Halley (1656–1742). Today, people who study the water cycle are called hydrologists. People can affect the water cycle. For example, paving land with concrete decreases the amount of water that can enter the soil. Using dams to create artificial lakes or reservoirs increases evaporation. What other factors affect the water cycle? How do temperature and surface area affect the rate at which water changes into water vapor? You will have an opportunity to explore these questions in the following two experiments. When it is really cold outside you can see your breath. What you see is water vapor. GRA NT H EIL MA N.
EXPERIMENT 1 Temperature: How does temperature affect the rate of evaporation? Purpose/Hypothesis Evaporation occurs when
liquid water turns into water vapor, a gas. The more water that evaporates and then condenses back into water droplets in the atmosphere, the more rain that falls. In this experiment, you will determine how water temperature affects the rate of evaporation. Before you begin, make an educated guess about the outcome of this experiment based on your 1248
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WORDS TO KNOW Aquifer: Underground layer of sand, gravel, or spongy rock that collects water. Condense/condensation: The process by which a gas changes into a liquid. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that affects the experimental group. Results from the control experiment are compared to results from the actual experiment. Evaporate/evaporation: The process by which liquid changes into a gas. Hydrologists: Scientists who study water and its cycle. Hydrology: The study of water and its cycle. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Precipitation: Water in its liquid or frozen form when it falls from clouds in the atmosphere as rain, snow, sleet, or hail. Saturated: Containing the maximum amount of a solute for a given amount of solvent at a certain temperature. Surface area: The area of a body of water that is exposed to the air. Variable: Something that can affect the results of an experiment. Water (hydrologic) cycle: The constant movement of water molecules on Earth as they rise into the atmosphere as water vapor, condense into droplets and fall to land or bodies of water, evaporate, and rise again. Water vapor: Water in its gaseous state.
knowledge of evaporation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • • • •
the topic of the experiment the variable you will change the variable you will measure what you expect to happen
The water cycle is important to all life forms because it brings water continuously to land and removes many impurities along the way. A P I MAG ES .
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The warmer the water temperature, the more evaporation will occur.’’ In this case, the variable you will change will be the temperature of the water, and the variable Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the temperature of the water • the temperature of the surrounding air • the amount of water in each container at the beginning and end of the experiment • the surface area of the water • the amount of humidity or water vapor in the air In other words, the variables in this experiment are everything that might affect the rate of evaporation of the water. If you change more than one variable, you will not be able to tell which variable had the most effect on the evaporation.
you will measure will be the amount of water left in your containers at the end of the experiment. You expect the container with the warmer water will have less water left because more has evaporated into the air. Setting up a control experiment will help you isolate one variable. Only one variable will change between the control and your experimental containers, and that is the water temperature. The control container will remain at room temperature. You will make the water in the experimental containers cooler or warmer than room temperature. You will record the amount of water you put into your containers and the amount of water left after the containers spend a day at different temperatures. If the container with the hotter water has less water left in it, your hypothesis is correct. Level of Difficulty Easy.
Materials Needed
• 3 containers of the same size, shape, and material • 6 cups (3 pints or 1.4 liter) water • ice cubes
Step 2: Set-up of three containers. GAL E GR OU P.
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• an insulated container large enough to hold one of the three containers above (an ice chest would work) • thermometer • measuring cup • graduated cylinder • flexible lamp
How to Experiment Safely If your containers are made of glass, handle them carefully. Also be careful not to touch the light bulb in the lamp.
Approximate Budget Less than $15. (Most of these materials should be available in the average household.) Timetable 1 to 2 hours to set up and take the initial data, plus another 24
hours to take the final data. Step-by-Step Instructions
1. Measure 2 cups (1 pint or 0.4 liters) of water into two containers. Fill the third container to the same level with a mixture of water and as many ice cubes as will fit. Mark the water level on the side of each container. 2. Label one container ‘‘control,’’ the second one ‘‘warm,’’ and the third one with the ice ‘‘cool.’’ 3. Place all three containers in a room where the temperature is about 70 to 72˚F (21 to 22˚C). Use the thermometer to take the temperature, and record it on your data sheet. 4. Leave the control container as is. Place the cool container inside the insulated container. Take the water temperature and record it.
Data sheet for Experiment 1. GA LE G RO UP.
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Troubleshooter’s Guide Experiments do not always work out as planned. However, figuring out what went wrong can definitely be a learning experience. Here is a problem that may arise during this experiment, a possible cause, and ways to remedy the problem. Problem: The containers all lost about the same amount of water. Possible cause: The water temperatures were not different enough. Use more ice in the cool one, and place the light bulb closer to the warm one.
5. Place the flexible light so it shines directly on the warm container but does not warm the other two containers. After an hour or so, take the water temperature and record it. 6. Leave your containers in place for 24 hours. 7. The next day, use the graduated cylinder to measure the amount of water remaining in each container. Record your findings. Summary of Results Study your results. How did
the air temperature affect the amount of evaporation from each container? Was your hypothesis correct? Summarize what you found.
Change the Variables You can change the variables and repeat this
experiment to learn more. Try controlling the temperature more closely so you can measure the change in evaporation rate that occurs with a smaller temperature difference. You can also see if any changes in the results occur when you change the size or shape of your containers. What do you notice? Modify the Experiment This experiment examines how the temperature
of water affects its evaporation rate. Wind speed also can have a significant affect on evaporation. You can make this experiment more challenging by measuring how wind speed compares to temperature in affecting the rate of evaporation. In order to measure wind speed, you will need two small fans that are the same size. You can use the same three containers you used to test temperature differences. Again, fill each of the containers with two cups of water. Set one fan to a low speed and place it near the first container. Set the second fan on a high speed and place it near the second container. The third container will be your control. Leave the containers alone for 24 hours, and then use the graduated cylinder to measure the remaining water in each container. Compare your data for wind speed and temperature variations. The results only measure how two specific wind speeds compare to 1252
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specific temperatures. In actuality, wind and temperature would vary and they would play How to Experiment Safely a role together. You can experiment with different wind speeds and temperatures to find There are no safety hazards in this experiment. the highest or lowest evaporation rate. You can also look at humidity, another key weather event that affects evaporation rate. Humidity is the amount of water vapor in the air. You can experiment with humidity by using a humidifier, and placing a container of water in an enclosed area, such as a closet.
EXPERIMENT 2 Surface Area: How does surface area affect the rate of evaporation? Purpose/Hypothesis In this experiment, you will fill containers of
different sizes with the same amount of water to explore how their surface area affects the rate of evaporation. For example, if you poured a certain amount of water in a tall, thin test tube with a small surface area, and the same amount in a short, broad cake pan with a large surface area, which container would have the greater rate of evaporation? Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of evaporation. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A greater surface area will lead to faster evaporation.’’ In this case, the variable you will change will be the surface area of your trays. The variable Experiment Central, 2nd edition
Which body of water do you think experiences the most evaporation? PE TE R AR NO LD INC .
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • surface area of the water • amount of water • length of the experiment • temperature of the water • the temperature of the surrounding air • the amount of humidity or water vapor in the air In other words, the variables in this experiment are everything that might affect the rate of evaporation of the water. If you change more than one variable, you will not be able to tell which variable had the most effect on the evaporation.
you will measure is amount of evaporation that occurs. For the control experiment, you will use a medium-sized tray. For the experimental containers, you will use larger and smaller trays. You will measure how much evaporation occurs by monitoring the water level in the trays over time and measuring the amount of water left. If the tray with the largest surface area shows the fastest rate of evaporation, then your hypothesis is correct. Level of Difficulty Easy. Materials Needed
• 3 metal or plastic square or rectangular watertight trays or containers of different sizes • ruler or tape measure • water • graduated cylinder
Approximate Budget Less than $5. (Most of these materials should be
available in the average household; try to borrow the graduated cylinder.)
Step 1: Figuring the surface area of the tray. GAL E GR OU P.
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Data sheet for Experiment 2. GA LE G RO UP.
Timetable About 5 days. Step-by-Step Instructions
1. With your ruler, measure both sides of each tray. Multiply the two sides together to get the surface area of the tray. Record these numbers on your data sheet (see illustration). 2. Measure exactly the same volume of water into each tray. The amount is not important, as long as you know how much it is and put the same amount in each tray. 3. Place the trays side by side under the same conditions. They should either all be exposed to sunlight or all be in the dark, for example.
Steps 2 and 3: Set-up of the three trays. Place the trays side by side under the same conditions. GAL E GR OU P. Experiment Central, 2nd edition
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Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: No evaporation occurred. Possible cause: Your containers did not receive enough light or heat for measurable water to evaporate. Try putting all of them in direct sunlight. Problem: Evaporation seemed the same in all the containers. Possible cause: There is not enough difference in the surface areas of your containers. Try using larger trays and smaller trays.
4. After the trays sit for a day, pour the water from each tray into the graduated cylinder and measure it. Record this information on your data sheet, and pour the water back into the same tray. Be careful not to lose any water as you pour. 5. Repeat Step 4 every day for five days. Summary of Results To find out how much water evaporated each day, subtract the amount of water left each day from the amount from the previous day. Compare your findings. What have you discovered? Did the tray with the largest surface area lose the most water to evaporation? Did the tray with the smallest surface area lose water to evaporation at the slowest rate? Was your hypothesis correct? Summarize what you have found.
Change the Variables You can vary this experiment in several ways. For
example, you can use pans that are really big and really small. Compare the evaporation rates. What does this tell you about evaporation from lakes, ponds, and oceans? You can also experiment with the effect of temperature. Try moving all your pans to a very warm or very cool place, such as a refrigerator. What happens then? Be sure to record the temperature in the places you put the pans. Finally, you can use containers with similar surface area but different depths. Determine the effect of depth on the evaporation rate.
Design Your Own Experiment How to Select a Topic Relating to this Concept If you are interested in
the water cycle, you could study the evaporation rate when water is moving and still, investigate the evaporation differences between saltwater and fresh water, or compare how concrete and soil affect the rate of evaporation. If you are more interested in condensation, you could try making your own clouds and studying the effects of water temperature, air temperature, and sizes of water bodies. Or you may want to study the 1256
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surfaces on which rain falls on and measure how long it takes to evaporate or seep into the soil. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on water cycle questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise you might not be sure what question you are answering, what your are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Your data should include
charts, such as the one you did for these experiments. They should be clearly labeled and easy to read. You may also want to include photos, graphs, or drawings of your experimental setup and results. If you are preparing an exhibit, draw diagrams of your procedure and display your containers. If you have done a nonexperimental project, explain clearly what your research question was and illustrate your findings. Related Projects In addition to completing experiments, you could prepare
models that demonstrate the water cycle or you could research how the water cycle is being affected by human actions, globally or locally. You might study the amounts of rainfall in different parts of the country and how landforms affect rainfall. You might go in many directions with your interests.
For More Information Hooper, Meredith, and Christopher Coady. The Drop in My Drink: The Story of Water on Our Planet. New York: Viking Children’s Books, 1998. Detailed information on the water cycle, interesting facts about water, and important environmental information. Experiment Central, 2nd edition
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‘‘Hydrologic Cycle.’’ Earthscape. http://www.und.edu/instruct/eng/fkarner/ pages/cycle.htm (accessed on March 2, 2008). Explanation of the water cycle process along with activities. National Aeronautics and Space Administration. Droplet and the Water Cycle. http://kids.earth.nasa.gov/droplet.html(accessed on March 2, 2008). A game were users follow the cycle of a water droplet. U.S. Geological Survey. ‘‘The Water Cycle.’’ Water Science for Schools. http:// ga.water.usgs.gov/edu/watercycle.html (accessed on March 2, 2008). Information and illustrations on the water cycle. Walker, Sally M. Water Up, Water Down: The Hydrologic Cycle. Minneapolis, MN: Carolrhoda Earth Watch Book, 1992. Descriptions of the water cycle, historically important experiments, and the water cycle’s importance to all life on Earth.
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W
ithout water, the life forms we see on Earth could not possibly exist. This simple combination of three atoms—one oxygen, two hydrogen—acts in complex ways that can turn a barren, dusty planet into a thriving biological community. What are the properties of water that make it so versatile and vital? How can we measure and compare water’s properties to those of other liquids? A number of observable properties of water result from its molecular structure, meaning not only the atoms that make up water, but also the shape of the water molecule. The bonds between the one oxygen and two hydrogen atoms do not form a straight line but form an angle like a wide V. This shape gives the molecule a positive electric charge on one side and a negative electric charge on the other. This charge gives water the properties of adhesion, the tendency to stick to certain other substances and cohesion, the tendency to stick to itself.
The molecular structure of water. GAL E GR OU P.
Adhesion and cohesion in everyday life The properties of adhesion and cohesion can be easily observed by watching raindrops on a windowpane. Adhesion holds the drops to the glass. Even if the window is tilted forward, some drops will cling to the underside of the pane. Cohesion can be seen if you trace the path of drops down the pane. Drops close to one another will be drawn together by cohesion, forming larger drops. Observe carefully and you will see that drops will far more readily join together than split apart. Splitting a water drop requires some energy or change to loosen the bonds that hold the molecules together. Cohesion, as you might predict, results from the attraction of one water molecule’s positive side to another water molecule’s negative side. 1259
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Cohesion creates surface tension, which enables water bugs to ‘‘skate’’ along the water’s surface without sinking. The first experiment will demonstrate that surface tension can keep afloat an object that is denser than water. You will then compare the surface tension of two other liquids to that of water. Forces affecting adhesion Adhesion, water’s tendency to cling to certain substances, creates capillary action. In extremely narrow spaces, such as inside water vessels in the stem of a plant, water will actually rise against gravity by the force of adhesion. This capillary action helps plants pull water up from the soil. Observe the surface of water in a straw: the water can be seen ‘‘climbing’’ the wall of the straw. This bowing of the water’s surface is called the meniscus, and it is caused by the strength of the water’s adhesion to the solid around it. In liquids that have much stronger cohesion than adhesion, such as mercury, the meniscus bows upward at the middle and down at the edges. Water’s adhesive force causes its meniscus to rise up the walls of the straw. Mercury’s cohesive force causes it to bow away from the walls of the straw and toward itself. PH OT O RE SEA RC HE RS I NC.
Adhesion in water depends upon the structure of the second substance’s molecules. Some substances are hydrophilic, attracted to water, and some are hydrophobic, not attracted to water. This explains why water will easily clean a salty film off your hands, but will not efficiently remove grease without using detergent. Salt is hydrophilic, but grease is normally hydrophobic. Detergent acts as a link between the water molecules and the grease. The molecules of the detergent possess one end that bonds with the grease and another end that bonds with water. When these detergent molecules coat the grease, they change it from hydrophobic to hydrophilic (see illustration). In the first experiment, you will demonstrate the strength of the cohesive force of water by floating a metal object (one that ordinarily would not float) on its surface. In the second experiment, you will measure the adhesive force between water and a solid by determining how much weight is required to break the strength of adhesion. You will
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WORDS TO KNOW Adhesion: Attraction between two different substances.
Hydrophilic: A substance that is attracted to and readily mixes with water.
Buoyancy: The tendency of a liquid to exert a lifting effect on a body immersed in it.
Hydrophobic: A substance that is repelled by and does not mix with water.
Capillary action: The tendency of water to rise through a narrow tube by the force of adhesion between the water and the walls of the tube.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment.
Cohesion: Attraction between like substances.
Meniscus: The curved surface of a column of liquid.
Density: The mass of a substance compared to its volume.
Variable: Anything that might affect the results of an experiment.
then predict how coating the solid with a hydrophobic substance such as grease or petroleum jelly will affect the strength of adhesion.
EXPERIMENT 1 Cohesion: Can the cohesive force of surface tension in water support an object denser than water? Purpose/Hypothesis In this experiment, you will first demonstrate the
strength of the cohesive force of water by floating a metal object on its surface. Then you will test the relative cohesive force of two other liquids by attempting to float the same object and others on them. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of the properties of water. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
Surface tension of a paper clip floating on water. PH OTO RES EA RC HER S I NC.
A hypothesis should be brief, specific, and measurable. It must be something you can test Experiment Central, 2nd edition
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What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the composition of the liquids • the purity of the liquids • the type of objects used to test surface tension • the method by which the objects are placed on the liquids In other words, the variables in this experiment are everything that might affect the surface tension of the liquid. If you change more than one variable, you will not be able to tell which variable had the most effect on surface tension.
through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘We can determine from observation of surface tension whether other liquids have greater or lesser cohesion than water.’’ In this case, the variable you will change is the liquid, and the variable you will measure is whether the object floats or sinks. You expect that you will be able to observe the differences in surface tension between liquids. Level of Difficulty Easy/moderate. Materials Needed
• 3 wide-mouth glass jars or drinking glasses • corn oil • isopropyl alcohol • distilled water • 3 unused staples (make sure they are clean of any adhesive) • 3 small sewing needles • 3 small steel paper clips • 3 large steel paper clips • tweezers • safety goggles
How to Experiment Safely Do not substitute any other liquids in this experiment without checking with your teacher first. Always wear goggles when experimenting with alcohol and work in a well-ventilated room. Keep the alcohol away from your nose and mouth.
Approximate Budget $1 to $10. (Most materials may be found in the average household.) Timetable 10 to 20 minutes.
Step-by-Step Instructions
1. Pour 2 inches (5 centimeters) of water into jar 1. Fill jar 2 to the same level with alcohol, and fill jar 3 to the same level with oil. 2. If you are using objects other that those in the materials list, make sure none of them is less dense than the liquid, which would make them float due to buoyancy and not due to 1262
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cohesion and surface tension. To find out, push each object to the bottom of the liquid. If it floats to the top, then you must replace it with something denser. 3. Using the tweezers, carefully place a staple flat on the surface of the water. You should have little difficulty floating the staple on the water. 4. Remove the staple and try the needle and the paper clips. Do not put two objects in the cup at the same time, and let any ripples settle before trying the next object. 5. On your chart, describe what each object does. Your chart should look something like the illustration. 6. Repeat Steps 3, 4, and 5 with jar 2 and jar 3. Summary of Results Examine your chart and
Troubleshooter’s Guide When doing experiments in adhesion and cohesion, be aware that unintended impurities can greatly affect your results. Natural oil from your fingers can alter the behavior of a small object on water, and an invisible soap film on the inside of a glass can easily spoil your results. Here is a problem that may arise during this experiment, some possible causes, and ways to remedy the problem. Problem: When any object is placed on the surface of the water, it sinks. Possible causes: 1. None of your objects is light enough. Try using a staple and a sewing needle. 2. Your water has been contaminated. Dump it out, clean the glass, and make sure the glass is rinsed clean of any soap residue.
compare the results of the tests for each liquid. Did your predictions prove true? Were you able to get meaningful results for each liquid? Which liquid had the strongest cohesion? The weakest? How did the cohesive force of alcohol and oil compare to the cohesion of water?
Step 5: Sample data chart for Experiment 1. GA LE G ROU P. Experiment Central, 2nd edition
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Change the Variables You can change the vari-
• the type of substance applied to the object
ables and conduct similar experiments. For example, what happens to the surface tension if you dissolve salt in the water? That is, does salty seawater have a different surface tension than fresh water? You can also change the temperature of the water—either cooling or heating it—to determine the effect on surface tension. Warning: Do not try heating the alcohol, as it may burn with an almost-invisible flame and cause injury or damage.
• the amount of substance applied to the object
EXPERIMENT 2
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the purity of the water • the shape of the object used to test adhesion
In other words, the variables in this experiment are everything that might affect the surface tension of the liquid. If you change more than one variable, you will not be able to tell which variable had the most effect on surface tension.
The materials pictured will serve to test your hypothesis, but you might wish to construct a sturdier set-up for demonstrations or repeated tests. GA LE G RO UP.
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Adhesion: How much weight is required to break the adhesive force between an object and water? Purpose/Hypothesis In this experiment, you will
first determine the strength of the adhesive force between a flat piece of wood and the surface of water. Then you will measure the effect of altering the adhesion between the two by adding a hydrophobic substance. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of the properties of water. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘A coating of a hydrophobic substance on an object will measurably reduce the adhesive force between that object and water.’’ In this case, the variable you will change is the coating on the object, and the variable you Experiment Central, 2nd edition
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will measure is amount of weight (force) it takes to overcome the surface tension. You expect that a hydrophobic coating on an object will reduce the weight required to overcome surface tension. Level of Difficulty Easy/moderate.
How to Experiment Safely Do not substitute any other substances in this experiment without checking with your science teacher first. If you decide to construct a sturdier balance, remember that you must wear safety glasses when hammering nails.
Materials Needed
• 9 x 12-inch (23 x 30-centimeter) pan • block of balsa wood, approximately 6 inches (15 centimeters) square and less than 1 inch (2.5 centimeters) thick, available in most hobby stores) • 12-inch (30-centimeter) or longer wooden dowel • wooden ruler with three holes (to fit a three-ring binder) • plastic container with two holes punched near the lip • thumb tacks • string • pencil • distilled water • ¼-cup of a hydrophobic substance such as cooking oil, grease, or petroleum jelly • 5 rolls of pennies (or enough to fill the container) Approximate Budget $10 to $15. (Most materials may be found in the
average household.) Timetable 1 to 2 hours.
Steps 1 to 3: The assembled balance should look like this. GAL E GR OU P.
Step-by-Step Instructions
1. Assemble your balance. a. Measure and mark the exact center of the block of wood (draw two diagonals from corner to corner). Cut a 30-inch (76-centimeter) length of string and tie a small loop in one end. Push a thumb tack partway into the center mark. Twist the loop of string around the Experiment Central, 2nd edition
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The action of detergent between water and grease. G AL E GRO UP.
tack, and push the tack as far into the wood as possible, securing the string. b. Cut a 24-inch (60-centimeter) length of string and loop the end through the two holes in the lip of the plastic container. Then tie the end onto the length of string about 4 inches (10 centimeters) up from the container. c. Cut a 6-inch (15-centimeter) length of string and tie it firmly around the dowel, 2 inches (5 centimeters) from the end. If necessary, put a tack next to the loop of string to keep it from slipping off. Tie the other end of the string through the center hole of the ruler. d. Place the dowel on a desk so the ruler is suspended at least 6 inches (15 centimeters) out over the floor. Attach the wooden block’s string to one of the outside holes on the ruler. Make sure that when the ruler is held level, the block is suspended 1 inch (2.5 centimeters) from the floor. 2. Attach the plastic container to the other end of the ruler and begin filling it with pennies until the weight is balanced. Record how many pennies equals the weight of the wood block. 3. Place the pan on the floor beneath the wood block. Fill the pan with water until the block is resting on the water’s surface. The ruler should remain at or close to level. (You may need someone
Step 4: Sample data chart for Experiment 2. GAL E GR OU P.
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to steady the ruler so it does not shift from side to side during this step.) 4. Begin adding pennies to the plastic container until the downward force of the weight overcomes the force of adhesion and lifts the block off the surface of the water. Record the number of pennies added on a chart like the one illustrated. 5. Wipe the block and let it sit in a warm place for several hours until it is dry. Coat the underside of the block with your hydrophobic substance. (Note: Once you have coated the block, you will not be able to repeat Step 4. Some of the substance may remain permanently on the wood, changing the adhesive force. If you wish to do repeated tests, you must use two blocks.) 6. Remove enough pennies so the block is balanced once more, and place the block back on the water’s surface. Repeat Step 4. Record the number of pennies necessary to lift the block clear of the water.
Troubleshooter’s Guide When doing experiments in adhesion and cohesion, be aware that unintended impurities can greatly affect your results. Natural oil from your fingers can alter the behavior of a small object on water, and an invisible soap film on the inside of a container can easily spoil your results. Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: The block breaks free of the adhesive force after the addition of very little or no weight. Possible cause: The tack in the block is not properly centered. Pulling upward on one side of the block will overcome the adhesive force more easily. Center the tack. Problem: The plastic container is full and the block still has not been balanced or lifted. Possible causes: 1. Your container is too small. 2. Your block is too heavy. Use balsa wood (and not a hardwood).
Summary of Results Examine your data and com-
pare the results of the tests with your hypothesis. Did your hypothesis prove true? Compare the number of pennies necessary to balance the block in Step 2 to the number necessary to break the surface tension in Step 4. The difference between these two numbers shows the strength of the surface tension. Note on your chart the exact number of pennies. Change the Variables You can vary this experiment to investigate differ-
ent aspects of adhesion and cohesion. Try altering the test materials to determine whether different solids have different levels of adhesion to water. Repeat the experiment using a block wrapped in plastic and another wrapped in aluminum foil. Hypothesize whether the two will Experiment Central, 2nd edition
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show different levels of adhesion and test your hypothesis. Be sure to check with your teacher before testing with new materials. Modify the Experiment Hydrophobic substan-
Cohesion, the bonding of water molecules to one another, enables this water bug to ‘‘skate’’ over the water’s surface without sinking. PE TER AR NO LD I NC.
ces, such as soap and oil, affect the surface tension of water. You can conduct a simple experiment with adhesion and surface tension with liquid soap and a small object, such as a staple. Take four or five small plastic widemouth glasses or bowls. Fill all the glasses about half way with water. Use the results of Experiment 1 to find an object that floats, such as a staple or small paperclip. With tweezers, carefully place the staple (or other object) in the first glass so that it floats. You should have at least five of the same object. In the second glass, add a drop of liquid soap and stir. Wait for the water to settle and then slowly place a clean staple (or other object) into the glass. Does it float? Write down the number of soap droplets and the results on a chart. Now add two drops of soap to the third glass and stir. Again, place a clean staple carefully on top of the water and note the results. Continue add one more drop to each glass until the object no longer floats. If you reuse the glasses or objects, make sure you wash and dry them thoroughly. How does breaking the cohesive forces of water depend upon the amount of a hydrophobic substance? You can repeat this experiment with different size and shape objects.
Design Your Own Experiment How to Select a Topic Relating to this Concept The simple experiments
described here touch on only a few aspects of adhesion and cohesion. Many experiments on the nature of hydrophilic and hydrophobic substances can be performed with inexpensive, readily available materials. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on water property questions that interest you. 1268
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Steps in the Scientific Method To do an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment:
• State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results In the experiments
included here and in any experiments you develop, you can look for ways to display your data in more accurate and interesting ways. Diagrams would be especially useful in Experiment 2. Remember that those who view your results may not have seen the experiment performed, so you must present the information you have gathered in as clear a way as possible. Including photographs or illustrations of the steps in the experiment is a good way to show a viewer how you got from your hypothesis to your conclusion. Related Projects To develop other experiments on this topic, think about
adhesion and cohesion in everyday life. Why does a coaster stick to the bottom of a wet glass? Investigate the function of capillary action in plants. Think of ways you could demonstrate the reason oil spills are so damaging to our ecosystem. Investigate how oil spills are cleaned up without polluting the water with detergents.
For More Information Environment Canada. ‘‘Properties of Water.’’ The Nature of Water. http:// www.ec.gc.ca/WATER/en/nature/prop/e prop.htm (accessed on March 2, 2008). Lots of brief explanations about the different properties of water. Kyrk, John. ‘‘Animated Essentials of Water and pH.’’ http://www.johnkyrk. com/H2O.html (accessed on March 2, 2008). Animations of the chemical properties of water. Experiment Central, 2nd edition
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Ray, C. Claibourne. The New York Times Book of Science Questions and Answers. New York: Doubleday, 1997. Addresses both everyday observations and advanced scientific concepts on a wide variety of subjects. U.S. Geological Survey. ‘‘Water Properties.’’ Water Science for Schools. http:// ga.water.usgs.gov/edu/waterproperties.html (accessed on March 2, 2008). Information and illustrations about the properties of water. Van Cleave, Janice. Chemistry For Every Kid. New York: John Wiley and Sons, Inc., 1989. Contains a number of simple and informative demonstrations and investigations into properties of water, including cohesion, the meniscus, and capillary action.
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The Sun’s rays shine directly on the equator, so that region gets very warm. The rays hit the North and South Poles at an angle, so the same amount of heat spreads over a wider area, thus these regions stay cool. GA LE G RO UP.
eather is the state of the troposphere at a particular time and place. The troposphere is the lowest layer of Earth’s atmosphere, ranging to an altitude of about 9 miles (15 kilometers) above Earth’s surface. Weather differs from climate. Climate is the average weather that a region experiences over a long period. A change in the weather can mean a rain shower. A change in climate might consist of a year-round warming trend that affects how crops grow in a region. All weather starts with the Sun’s heat, but the Sun does not heat Earth’s surface evenly. The Sun’s direct rays make the equator regions much warmer than other areas, while the tilt of Earth’s axis causes the hemisphere that is tilted toward the Sun to be warmer than the hemisphere that is tilted away from the Sun. The elements of weather include temperature, humidity, cloudiness, precipitation (rain, snow, hail), wind, and air pressure. These elements interact to spread the Sun’s heat more evenly around Earth. Without them, the equator region would get much hotter than it does, while the pole regions would get colder. Air moves because of differences in both temperature and air pressure, also called atmospheric pressure. Atmospheric pressure is the pressure exerted by the atmosphere at Earth’s surface due to the weight of the air. As the Sun heats Earth’s surface, the surface heats the air above it. As the air molecules warm up, they move farther apart. This reduces the density or heaviness of the air and creates an area of low air pressure. On the other hand, molecules in cool air are closer together, making that air denser and heavier. Cool air creates an area of high air pressure. 1271
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Recognizing different types of clouds can help you predict the weather. FI EL D MA RK P UBL IC ATI ON S.
Air moves from areas of high pressure to areas of low pressure, creating wind. During Project 1, you will build an anemometer (pronounced an-eh-MOM-eter), a device that measures the speed of wind. As warm air rises into the atmosphere, it carries with it water vapor, which is water in its gas form. As the air cools, the gas molecules move closer together and condense around very small particles of dust or salt in the air. The water vapor turns into its liquid form, water droplets. Clouds are huge masses of condensed water vapor. As warm, light air rises, cooler, heavier air rushes in to take its place, creating windy conditions. CO RB IS.
As the droplets bump into each other, they join to form larger drops. In time, they are large and heavy enough to fall as rain. One rain drop can contain a million cloud droplets! An English naturalist named Luke Howard gave cloud groups these Latin names in 1803: Cirrus (pronounced SEAR-us, from the Latin word for ‘‘curl of hair’’); Stratus (from the Latin word for ‘‘layer’’); Cumulus (pronounced CUME-u-lus, from the Latin word for ‘‘heap’’); and Nimbus (from the Latin word for ‘‘rain’’). Since then, meteorologists have used Howard’s names to describe 10 types of clouds at three levels.
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High-level clouds about 20,000 feet (6.0 kilometers) above Earth include Cirrus, wispy clouds that precede bad weather; Cirrostratus, layers of clouds that signal rain; and Cirrocumulus, rippled clouds that signal unsettled weather Middle-level clouds about 7,000 to 17,000 feet (2.1 to 5.2 kilometers) above Earth include Altocumulus, flat gray-white clouds that precede a summer storm; Altostratus, layers of gray clouds that indicate it will rain soon; and Nimbostratus, thick dark-gray clouds that signal rain or snow. Low-level clouds less than 7,000 feet (2.1 kilometers) above Earth include Stratocumulus, gray or white rolls that indicate dry weather; Stratus, layers of gray clouds that often bring precipitation; Cumulus, fluffy white puffs seen on hot summer days; and Cumulonimbus, dark, towering clouds that bring storms. Weather affects what we wear, what we eat, the kinds of work we do, how we have fun, and, most importantly, the ecosystem in which we live. Learning more about the weather helps us better understand the world in which we live.
This cup anemometer is connected to instruments inside the weather station that record how many times the cups spin in a certain period of time. The spinning rate indicates the wind speed. P HOT O R ES EAR CH ER S IN C.
PROJECT 1 Wind: Measuring wind speed with a homemade anemometer Purpose/Hypothesis In this project, you will make a simple anemometer
and compare the wind speed measured by your anemometer with the wind speed measured in your region by the National Weather Service. The National Weather Service gathers wind speed and other weather information every one to six hours from about 1,000 land stations throughout the United States and its possessions. Meteorologists at the Weather Service use this information to make weather predictions, which are then broadcast over radio and television. The Service’s weather stations use cup anemometers to measure wind speed. Some television stations provide a live broadcast of the current wind speed; you might even see the speed change during the forecast. If you can tune in to one of these broadcasts, you can make your wind speed measurements simultaneously, thus eliminating the time variable. Experiment Central, 2nd edition
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WORDS TO KNOW Anemometer: A device that measures wind speed. Atmospheric pressure: The pressure exerted by the atmosphere at Earth’s surface due to the weight of the air. Climate: The average weather that a region experiences over a long period. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment. Density: The mass of a substance compared to its volume. Ecosystem: An ecological community, including plants, animals, and microorganisms, considered together with their environment.
Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Humidity: The amount of water vapor (moisture) contained in the air. Meteorologists: Scientists who study weather and weather forecasting. Troposphere: The lowest layer of Earth’s atmosphere, ranging to an altitude of about 9 miles (15 kilometers) above Earth’s surface. Variable: Something that can affect the results of an experiment. Water vapor: Water in its gas form. Weather: The state of the troposphere at a particular time and place.
Level of Difficulty Easy/moderate. Materials Needed
• • • •
metal or plastic protractor Ping-Pong ball 8 inches (20 centimeters) of strong thread transparent tape
Approximate Budget Less than $5. (Most or all of these materials should be available in the average household.) Timetable 15 to 20 minutes. Step-by-Step Instructions
1. Tape one end of the thread firmly to the Ping-Pong ball. 2. Tie the other end of the thread to the middle of the flat side of the protractor, as illustrated. The ball should hang down so the thread 1274
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3.
4.
5. 6.
7.
crosses the rounded side of the protractor. The numbers (angles) marked on the rounded side will indicate wind speed. Determine when the weather will be broadcast over a local radio or television station and whether it includes a live broadcast of wind speed. At the same time as a live weather broadcast or about two hours before a taped broadcast, take your anemometer outside. Stand in an open area, away from trees, buildings, and traffic. Hold the anemometer by one corner, with the flat side parallel to the ground. As the wind blows, note the angle of the farthest movement of the thread. Record it on a chart similar to the one illustrated. Use the scale provided to convert the angle to miles per hour (mph) and record it on your chart:
Angle= mph 90˚ angle= 0 mph 80˚ angle= 15 mph 70˚ angle= 20 mph 60˚ angle= 25 mph 50˚ angle= 30 mph 40˚ angle= 35 mph 30˚ angle= 40 mph 20˚ angle= 50 mph
Steps 1 and 2: Set-up of PingPong ball and protractor. GA LE GRO UP .
Step 6: Data chart for Project 1. G AL E GR OUP .
8. Take a second wind-speed measurement and record it on the chart. 9. Add the wind speed from the radio or television broadcast to your chart. 10. Repeat Steps 4 to 9 on two more days and record the results. Summary of Results Use the data on your chart
to create a triple-bar graph comparing the three Experiment Central, 2nd edition
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Troubleshooter’s Guide Here is a problem that may arise during this project, some possible causes, and ways to remedy the problem. Problem: Your wind speed reading was much higher or lower than the one broadcast on radio or television. Possible causes: 1. You took your reading in a spot that is protected from the wind or a spot that serves as a natural wind tunnel, increasing its speed and force. Try again in a different spot. 2. You took your reading at a different time from the reading that was broadcast. Try calling the radio or television station and see if the forecaster or someone else will give you the current wind speed. Then quickly do your own reading.
readings on each day. Then study your graph and chart and how accurately your anemometer measured wind speed. Were your own measurements on any day within 5 miles per hour (8 kilometers per hour) of those given in the radio or television broadcast? Write a paragraph summarizing your findings. Modify the Project In this project you built an anemometer to measure wind speed. You can add to this project by also measuring wind direction. Using both an anemometer and a wind vane will give you two key measurements used to forecast the weather.
There are many materials you can use to build a simple wind vane. The finished wind vane will look similar to a ‘‘T’’ shape, with an arrowhead on one end and a tail on the other (see illustration). The top of the ‘‘T,’’ the rod, is parallel to the ground and able to spin freely on a rod. The arrow points in the direction of the wind.
One way to build a wind vane is to attach a straw to a dowel or pencil. You can use a long tack to attach the straw in the middle point. Spin the straw around several times to make sure it spins freely. Cut out an arrow and tail from card stock. Ask an adult to help you cut slits into the straw and slip the paper into the straw. You may need tape. You will need a compass to determine north and south. Attach the dowel to a solid, wide base, such as a large plastic container that is weighted down. Tape a compass or write the direction points on the base. For a sturdier rod, you could use a dowel in place of a straw. You will need an adult to help you attach the rod into the larger dowel using a drill and screw. The adult helper can also cut small slits in both sides of the rod where you can slide the arrow and tail. Place the wind vane in an open area with the anemometer. When you measure the wind speed, note the wind direction. Why is knowing both wind direction and speed important? Follow the weather reports 1276
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and compare your measurements and weather predictions to the reports.
EXPERIMENT 2 Clouds: Will a drop in air temperature cause a cloud to form? Purpose/Hypothesis In this experiment, you
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • how much the air pressure increases and then drops inside the bottle
will create a cloud in a bottle by making water • whether the bottle contains smoke parvapor condense around tiny smoke particles in ticles and how many particles are present the air. To make the vapor condense, you will • whether the bottle is tightly sealed suddenly reduce the air pressure, allowing the • the amount of water in the bottom of the water vapor molecules to move farther apart bottle and cool off. • the air temperature outside the bottle But is it the drop in temperature that causes In other words, the variables in this experiment the cloud to form? And will a cloud form withare everything that might affect the formation of out tiny particles in the air? To find out, you will a cloud. If you change more than one variable, also try the experiment without a drop in temyou will not be able to tell which variable had the most effect on the cloud formation. perature and without smoke particles in the air. (You might need a helper to complete these experiments.) Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of clouds. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Here is one possible hypothesis for this experiment: ‘‘A cloud will form only after a drop in temperature and only when particles are present in the air.’’ In this case, the variable you will change in the first part of the experiment is the air pressure (and hence the air temperature), and the variable you will change in the second part of the experiment is the presence of smoke particles in the bottle. The variable you will measure in both parts of the experiment is the presence of a cloud. You expect the cloud will form only when the temperature drops and particles are present. Experiment Central, 2nd edition
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How to Experiment Safely Ask an adult to help you light and handle the matches.
You will complete two control experiments. In one, you will determine whether a cloud will form without a drop in temperature. In the other control experiment, you will see if a cloud will form without smoke particles in the air. If a cloud forms only when the temperature drops and when particles are present, you will know that your hypothesis is correct. Level of Difficulty Easy/moderate—but you may
need someone to help you manipulate the materials. Materials Needed
• three 1-quart (1-liter) plastic soda bottles, empty and clean, with caps • matches Steps 3 to 7: Set-up of cloud experiment. GA LE G RO UP.
• • • •
flashlight labels and a marker measuring cup water
Approximate Budget Less than $5. (Most materials should be available in
the average household.) Timetable 1 hour. Step-by-Step Instructions Step 9: Data chart for Experiment 2. GA LE GRO UP.
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1. Label one bottle ‘‘Experimental’’ and two bottles ‘‘Control.’’ 2. Pour 1 cup of water into each bottle. 3. Drop two lighted matches into the Experimental bottle and quickly screw on the cap. 4. Let the matches burn until the water puts them out. 5. Shake the bottle to make the air inside moist. 6. With the bottle upright, squeeze the bottle to increase the air pressure inside. Experiment Central, 2nd edition
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7. Place the flashlight so it shines into the bottle (or have your helper hold the flashlight). 8. Quickly unscrew the cap to lower the pressure inside the bottle and cool off the water vapor. 9. Check to see if a cloud forms. If it does, it will last only a few seconds. Record your observations on a chart similar to the one illustrated. 10. Using one of the Control bottles, repeat Steps 3 through 9, omitting Step 8. (Do not unscrew the cap, so the air pressure and temperature of the water vapor inside the bottle do not change.) 11. Observe this Control bottle for at least three minutes to see whether a cloud forms. Record your observations. 12. Using the other Control bottle, repeat Steps 5 through 9. (This time, you do not perform Steps 3 and 4 so the bottle contains no smoke particles.) 13. Observe the second Control bottle for at least three minutes to see whether a cloud forms. Record your observations. Summary of Results Study the findings on your chart and decide whether your hypothesis was correct. In which bottles did a cloud form? Write a paragraph summarizing your findings and explaining whether they support your hypothesis.
Troubleshooter’s Guide Here are some problems that may arise during this experiment, some possible causes, and ways to remedy the problems. Problem: A cloud did not seem to form inside the Experimental bottle. Possible causes: 1. The air pressure did not get high enough inside the bottle. Try again, squeezing the bottle harder. 2. You unscrewed the cap too slowly, allowing the air to cool so slowly that the water vapor did not condense. Try again, unscrewing it as quickly as possible. 3. The bottle did not contain enough smoke particles. Try again, dropping in three or four lighted matches. 4. You did not look into the bottle quickly enough and missed the cloud. Try again, and have a helper unscrew the cap so you can observe what is happening. Problem: A cloud formed in the Control bottle that contained no smoke particles. Possible cause: The air in the bottle already contained other tiny particles. Rinse the bottle and try again.
Change the Variables Here are some ways you can vary this experiment:
• Try increasing or reducing the amount of smoke particles, or try adding dust to the air inside the bottle instead of smoke particles. • Experiment with the amount of water in the bottle. Try the experiment with no water at all. Experiment Central, 2nd edition
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• Complete the experiment using saltwater and no smoke particles. Shake the bottle vigorously to release salt from the water into the air. (Most cloud particles actually form around salt released into the air from ocean waves.) • Try doing the experiment outside on a chilly day. Instead of unscrewing the cap, see if the air outside the bottle chills the air inside enough to form a cloud.
Design Your Own Experiment How to Select a Topic Relating to this Concept You can explore many other aspects A weather vane can determine wind direction. I LLU STR AT IO N BY T EM AH NE LS ON.
of weather. Consider what you would like to know about this topic. For example, you might want to find out how Earth’s rotation affects wind direction. Or you might try your hand at predicting the weather by observing clouds. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on weather questions that interest you. As you consider possible experiments, be sure to discuss them with your science teacher or another knowledgeable adult before trying them. Some of the materials or procedures might be dangerous. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure which question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. 1280
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Recording Data and Summarizing the Results In your wind speed and cloud-making experiments, your raw data might include charts, graphs, drawings, and photographs of the changes you observed. If you display your experiment, make clear the question you are trying to answer, the variable you changed, the variable you measured, the results, and your conclusions. Explain what materials you used, how long each step took, and other basic information. Related Projects You can undertake a variety of projects related to weather. For example, you might find out how seeding clouds produces rain. Or you could try an experiment with a pan of flour that will show you the different sizes of raindrops. Now that you have an anemometer, you might make a weather vane to determine wind direction, a rain gauge to keep track of rainfall, and a hydrometer to measure the humidity in the air.
For More Information Ahrens, C. Donald. Meteorology Today: An Introduction to Weather, Climate, and the Environment. New York, NY: Brooks Cole, 2002. Burt, Christopher C., and Mark Stroud. Extreme Weather: A Guide and record Book. New York, NY: W.W. Norton & Company, 2004. Edheads. Weather. http://www.edheads.org/activities/weather/ (accessed on February 19, 2008). Interactive animations on weather and stories about professionals in the field. The National Oceanic and Atmospheric Administration (NOAA) National Weather Service. Jetstream: Online School for Weather. http:// www.srh.weather.gov/jetstream/ (accessed on February 18, 2008). Information and pictures of weather phenomena. Web Weather for Kids. http://www.eo.ucar.edu/webweather/ (accessed on February 19, 2008). Information, activities, and safety information on weather.
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Anemometers record wind speed. PH OTO RE SEA RC HER S I NC.
Weather sleuths everywhere Thousands of weather stations throughout the world communicate weather observations and data to international weather centers every three hours where the information is analyzed by meteorologists, who study the weather and the atmosphere. The weather stations consist of outdoor shelters, known as Stevenson screens, that house instruments such as thermometers, which measure air temperature, and anemometers, which record wind speed. All instruments at these stations are of the same type and accuracy. Weather stations also record many other weather elements, including types of clouds, humidity, air pressure, precipitation (rainfall or snowfall), and visibility. Instruments and equipment that record weather in the upper atmosphere include radar, satellites, radiosonde balloons, and planes. Radar tracks the path of storms, while satellites send back pictures of entire weather systems. The radiosonde balloons carry instruments that record weather conditions in the upper atmosphere and send the data back by radio. Planes with special meteorological equipment track storms and their weather patterns. A supercomputer collects all this information, calculates how air pressure, moisture, and winds might affect each other, and produces a forecast for the next 24 hours. Weather forecasting before computers The first weather forecasting guide was written about 2,000 years ago. A Greek naturalist named Theophrastus wrote the Book of Signs, a collection of 200 natural signs that indicated the type of 1283
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Tornado watches are posted for a region when weather conditions are likely to form these destructive storms. CO RB IS.
weather that was on its way. In 1687, John Tulley of Saybrook, Connecticut, published a farmers’ almanac that included the first weather forecast made in the United States. In 1792, Robert Bailey Thomas of West Boyleston, Massachusetts, began writing an annual almanac, which he eventually called The Old Farmer’s Almanac. Along with humorous stories, Thomas offered some of the nation’s earliest long-range weather forecasts. Instruments such as the weathervane, which indicates wind direction, were used at least 2,000 years ago in Athens, Greece. In the seventeenth century, more precise weather instruments emerged that could indicate humidity, temperature, and barometric pressure, as well as wind direction and rainfall. The real science of meteorology (pronounced ME-tee-or-ology), the study of the atmosphere and weather, began during this era. Measuring the air’s ups and downs One of the most important meteorological instruments was the barometer, which measures air pressure changes with a column of mercury that rises and falls. Air pressure differences between two adjoining areas of the atmosphere cause winds, and the barometer made it possible to predict wind velocity patterns. Many people worked on the design and theory of the barometer, but Evangelista Torricelli of Italy (1608–47) is generally credited with developing the first one in 1644.
Satellites can track deadly hurricanes, such as Hurricane Katrina, and alert those people who live in their path. AP I MA GE S.
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Dewpoint temperature chart. GA LE G RO UP.
Weather maps and computers Weather maps have isobars, continuous lines that connect areas with the same air pressure. Meteorologists use isobars to observe the development of high and low pressure areas. A high pressure area is surrounded by winds that blow clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. It usually brings dry weather. A low pressure area is surrounded by winds that blow counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. It usually brings cloudy, wet, and windy weather. Meteorologists also study the formation and movements of fronts, the front edges of moving masses of air. When cold air lies behind the edge, it is known as a cold front. When warm air lies behind, it is a warm front. Computer forecasting techniques were first developed in the 1950s. The computer evaluates current weather conditions in a large area and then predicts changes that will occur in the next 10 minutes. This generates a new set of weather conditions, and the predictions continue until the computer has created a forecast for the next day’s weather. With today’s supercomputers, the several billion computations required for a single forecast can be worked out very quickly. Experiment Central, 2nd edition
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WORDS TO KNOW Barometer: A device that measures air pressure. Condensation: The process by which a gas changes into a liquid. Control experiment: A set-up that is identical to the experiment but is not affected by the variable that will be changed during the experiment. Dewpoint: The point at which water vapor begins to condense. Front: The front edges of moving masses of air. High air pressure: An area where the air is cooler and more dense, and the air pressure is higher than normal. Hypothesis: An idea in the form of a statement that can be tested by observation and/or experiment. Isobars: Continuous lines that connect areas with the same air pressure.
Low air pressure: An area where the air is warmer and less dense, and the air pressure is lower than normal. Meteorologist: Scientist who studies the weather and the atmosphere. Radiosonde balloons: Instruments for collecting data in the atmosphere and then transmitting that data back to Earth by means of radio waves. Variable: Something that can affect the results of an experiment. Weather forecasting: The scientific predictions of future weather patterns. Weather forecasting: The scientific prediction of weather patterns, may look simple when we watch a television weather forecast on the local news, but it’s not. That forecast was based on data collected and analyzed from many sources.
Warning people of hurricanes and tornadoes is an important function of weather forecasting. Understanding weather terms and the formation of storms can help you avoid surprises and stay safe. In the experiment that follows, you will learn more about why and when condensation forms. The project will enable you to build your own barometer to help you make your own weather forecasts.
EXPERIMENT 1 Dewpoint: When will dew form? Purpose/Hypothesis This experiment deals with a principle of weather
called dewpoint. Dew is the moisture that forms on plants and other objects when air is cooled sufficiently for the water vapor in the air to condense into liquid. The temperature at which dew forms is called the dewpoint temperature. If the dewpoint temperature is close to the air 1286
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temperature, there is a high possibility of fog, rain, or snow during the next few hours. What Are the Variables? In this experiment, you will first determine the dewpoint temperature for that day. Then you Variables are anything that might affect the will use what you have learned to guess or predict results of an experiment. Here are the main variables in this experiment: whether dew will form on a cold glass left outdoors. Before you begin, make an educated guess • the amount of water vapor present in the about the outcome of this experiment based on atmosphere your knowledge of weather. This educated guess, • the current weather conditions, including air temperature or prediction, is your hypothesis. A hypothesis should explain these things: • how fast the thermometer is swung during the experiment • the topic of the experiment • the variable you will change In other words, the variables in this experiment are everything that might affect the dry bulb • the variable you will measure and wet bulb temperatures (and hence the • what you expect to happen dewpoint temperature). If you change more A hypothesis should be brief, specific, and than one variable, you will not be able to tell measurable. It must be something you can test which variable had the most effect on the through observation. Your experiment will prove dewpoint. or disprove your hypothesis. Here is one possible hypothesis for this experiment: ‘‘If the dewpoint temperature is close to 32˚F (0˚C), dew should develop on a glass of ice water.’’ Materials for Experiment 1. In this case, the variable you will change is the temperature of the glass, GAL E GR OU P. and the variable you will measure is the formation of dew. You expect dew to form on the glass of ice water if the dewpoint temperature for that day is near freezing. As a control experiment, you will set up one glass of water at air temperature. That way, you can determine whether dew forms no matter what the temperature of the glass. If dew forms only on the cold glass, your hypothesis will be supported. Level of Difficulty Easy. Materials Needed
• thermometer (for safety, use an alcohol thermometer with red fluid inside) • dewpoint temperature chart (illustrated) Experiment Central, 2nd edition
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• • • • •
How to Experiment Safely Always use caution when handling thermometers. If a thermometer should break, ask an adult for assistance in cleaning it up.
1-inch (2.5-centimeter) square of cloth small rubber band water (at air temperature) ice 2 plastic or glass drinking cups (any size)
Approximate Budget About $10, if thermome-
ters need to be purchased. Timetable 30 minutes each day; experiment can be repeated each day for
a week, if you wish. Step-by-Step Instructions
Step 2: Thermometer with cloth banded to the bottom. Wet cloth thoroughly. G AL E GRO UP.
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1. Using the thermometer, take a reading of the outside air temperature and record it on a data sheet. This will be the ‘‘dry bulb temperature.’’ 2. Place the cloth around the bulb at the bottom of the thermometer and wrap the rubber band around to hold the cloth securely. Wet the cloth thoroughly with tap water. 3. Wave the thermometer with the wet cloth in the air for one minute. Be sure to hold the thermometer at the top, at the opposite end of the cloth. Do not touch the thermometer stem. 4. Record the temperature shown on the thermometer. This will be the ‘‘wet bulb temperature.’’ 5. On the data sheet, write the difference between the wet bulb and dry bulb temperatures. Example: Dry Bulb Temperature is 61˚F (16˚C). Wet Bulb Temperature is 50˚F (10˚C). The difference is 11˚F (6˚C). 6. Using the data you have collected, refer to the dewpoint temperature chart. Locate the dry bulb temperature in the left column. Locate the difference in wet and dry bulb temperatures across the top of the chart. Find where the two points intersect and record that number as the dewpoint temperature. Experiment Central, 2nd edition
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7. Fill one cup with water and ice cubes. The approximate temperature of the water will be 32˚F (0˚C). Fill the second cup (your control experiment) with water at normal tap water temperature. 8. Leave both cups outdoors in the shade for 30 minutes. 9. Check the outside of both cups for condensation. Record whether your hypothesis is correct. (The cup with ice water should always be below the dewpoint temperature and collect condensation. The cup at air temperature should remain dry unless the air temperature matches the dewpoint temperature.)
Troubleshooter’s Guide Here is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem. Problem: Condensation does not form on either glass. Possible cause: The air does not contain enough water vapor. Place the cups in a different spot (outside or inside) or repeat the experiment on a different day.
Summary of Results Create a chart to organize your results. If you repeat
this experiment for several days, notice if dew has formed on the cup surfaces each morning. Replace the ice every day. Change the Variables You can vary this experiment in several ways. The
air temperature and the amount of water vapor in the air change from day to day. If you change the locations or seasons in which you try this experiment, you can see different results. During spring and fall, high water vapor tends to be present. Indoor environments during the winter months often have less water vapor present.
PROJECT 2 Air Pressure: How can air pressure be measured? Purpose/Hypothesis Changes in the atmosphere are the cause of most of
our weather. The purpose of this project is to build a barometer that shows changes in air pressure. When air is warmed, it rises and the air pressure decreases. If the air is cooled, it sinks and air pressure increases. Low air pressure usually indicates stormy weather, and high air pressure usually indicates fair weather. By observing air pressure trends, you will be able to predict upcoming weather conditions. Level of Difficulty Easy. Experiment Central, 2nd edition
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When air is warmed, it rises and the air pressure decreases. If the air is cooled, it sinks and air pressure increases. GA LE GR OU P.
Materials Needed
• • • • • •
wide-mouth jar without a lid 7-inch (17.5-centimeter) diameter round balloon plastic straw index card rubber cement scissors
Approximate Budget $1 for balloon. Timetable 20 minutes to prepare barometer; 1 to 2 weeks to observe
changes in air pressure.
Materials for Project 2. GA LE GR OU P.
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Step-by-Step Instructions
How to Experiment Safely 1. Cut end off the balloon and stretch the balloon over the mouth of the jar. Use caution in handling the scissors. 2. Use the rubber band to attach the balloon securely to the jar. 3. Rubber cement the straw horizontally to the center of the balloon, so most of it extends over the edge of the jar. 4. Prop up the index card behind the straw. Line up the straw with the middle of the index card, but not touching it. 5. Draw a line behind the straw and label it ‘‘baseline.’’ 6. Draw a line 0.5 inch (1 centimeter) above the baseline and label it ‘‘high pressure—fair weather.’’ 7. Draw a line 0.5 inch (1 centimeter) below the baseline and label it ‘‘low pressure—poor weather.’’ 8. Place the barometer outdoors in the shade and watch for changes in air pressure. 9. Record your observations along with daily weather conditions. Summary of Results Can you explain changes in the readings on your
barometer? (If the air pressure outside increases, it presses on the balloon and causes the straw to rise. If the air pressure outside drops below the pressure in the jar, the balloon swells, and the straw points downward.) For a fun experiment, try monitoring the environment inside your home. Leave the barometer in different rooms and record the results.
Illustration of completed barometer. GAL E GR OU P. Experiment Central, 2nd edition
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Modify the Project You can extend this project
by detailing the relationship between specific weather conditions and your barometer. After you do so for several weeks, you can use your Here is a problem that may arise during this barometer to predict the weather. experiment, a possible cause, and a way to remedy the problem. Follow the instructions for making your barometer. For the barometer in the project, you Problem: The straw on the balloon does not drew a 0.5 inch mark both above and below the move. baseline. Use the ruler to add lines every onePossible cause: If no change is noticeable, test eighth of an inch both below and above the basethe barometer by using a hair dryer to warm up line. Make a chart listing wind speed, temperthe air in the jar. Adjust the balloon until the ature, and precipitation. straw dips down. Place your barometer outside in a safe spot where it can stay for several weeks. Every day note the change in the barometer and the weather conditions. Before and after any weather change, try to make a precise note of the mark on the barometer. News programs and weather Web sites can tell you the exact wind speed and temperature. If it rains, find out the amount it rained in your area and write it down in your chart. After about a month take a look at your chart. What does the air pressure tell you about wind, temperature, and precipitation? Using your chart as a guide, use only the barometer to forecast the weather over the next week. How close can you come to actual weather events?
Troubleshooter’s Guide
Design Your Own Experiment How to Select a Topic Relating to this Concept The day’s weather conditions affect your daily routine and sometimes your mood. Since weather is always changing and is different around the globe, it presents many study possibilities. Possible weather topics include precipitation, humidity, air masses, hurricanes, tornadoes, and El Nin~o. Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on weather forecasting questions that interest you. Steps in the Scientific Method To do an original experiment, you need to
plan carefully and think things through. Otherwise, you might not be sure what question your are answering, what you are or should be measuring, or what your findings prove or disprove. 1292
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Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. • State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results Experiments help us
answer questions, so it is important to save your experiment results; keep a journal and jot notes and measurements in it. Your experiment can then be used by others and help answer their questions. Related Projects When thinking about experimenting in weather, focus
on one specific field. For example, if you decide to examine similarities in weather between New York City and London, England, you might compare weather patterns. When you start exploring possible projects, you will be amazed at the range of experiments and projects available.
For More Information BBC. ‘‘Become a Weather Detective.’’ BBC Weather. http://www.bbc.co.uk/ weather/weatherwise/activities/weatherstation (accessed on February 6, 2008). Information and activities on weather forecasting. Kerrod, Robin. Young Scientist Concepts & Projects: Weather. Milwaukee, WI: Garth Stevens Publishing, 1998. Offers a fact file and learn it yourself project book. McVey, Vicki. The Sierra Club Book of Weather Wisdom. Boston: Little, Brown and Company, 1991. Includes dramatic weather stories from around the world, weather facts, and hands on activities, games, and experiments. National Oceanic and Atmospheric Administration. National Weather Service. http://www.nws.noaa.gov (accessed on February 6, 2008). Provides local weather conditions and forecasts. Peacock, Graham. Meteorology. New York: Thompson Learning, 1995. Provides interesting information about weather and climate. Taylor, Barbara. Weather and Climate. New York: Kingfisher Books, 1993. Outlines weather and geography facts and experiments.
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long with providing oxygen and beauty, trees also supply people with wood. Wood is the tissue of trees. We use wood to build houses, make paper, and provide fuel. It is a natural resource that has great use because of its strength and durability.
The hardwoods versus the softwoods There are two main group for categorizing different types of woods: hardwood or softwood. The difference between the two types of woods relates to how the tree reproduces. Hardwoods are angiosperms, which are flowering plants. Angiosperm trees have their seeds within the flowers, and the seeds are protected by the ovary. A few examples of angiosperm trees are apple, oak, and walnut. A peach, apple, or other fruit from a tree develops around the seeds. Most hardwood trees are deciduous, meaning they lose their leaves when the season turns cool and they grow back when the weather warms. Deciduous trees have broad leaves. Softwoods are trees that have their seeds exposed. These trees are called gymnosperms, which means ‘‘naked seed.’’ Conifer trees are the most common types of gymnosperms and are often referred to as evergreens. These trees produce cones that contain the seeds and have needle-like leaves that can stay on the tree during cold weather. When the seeds do fall, they are exposed to air. Pine, spruce, and fir are examples of softwood trees. A common rule of thumb is that a hardwood tree is harder and denser than a softwood. (The density of a wood is its mass for a certain volume.) But there are many exceptions to this rule. Balsa wood, for example, is categorized a hardwood yet it is one of the lightest woods in the world. It is commonly used to make model airplanes and other toys. Inside the wood Outside of the tree is a layer of bark. The bark is made up of dead tissue that protect the tree from pests, harsh environment, and other possible damage. The ‘‘woody’’ inside tissue of trees carries water and nutrients throughout the tree. The layer directly next to 1295
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The oak tree is an example of an angiosperm tree. FI EL D MA RK P UBL IC ATI ON S.
the bark is the phloem, which are living cells. The cells of the phloem form thin tubes that transport nutrients throughout the tree. The neighboring inside layer to the phloem is the cambium. The cambium is where the tree’s growth occurs. The cells in part of the cambium form the phloem, and the cells in the other part of the cambium form the wood tissue on the other side. As a tree grows and expands, the cambium layer move further from the center of the tree. The wood tissue next to the cambium is also made up of layers. On the outer layer of the wood tissue is the sapwood. The sapwood transports the sap throughout the tree and it is usually a lighter color. When the sapwood cells die, they eventually become heartwood, the inner wood tissue of the tree. Although heartwood is dead, it is strong and provides the tree with support. Water does not move through the heartwood. Substances that form in the heartwood protect the wood from decay and also give the wood its distinctive color. Wood properties The properties of wood mainly depend upon the type of tree. Yet even trees that are the same type can produce woods with different characteristics. The properties that people look for in wood depends upon the use of the wood. Common characteristics are wood color, strength, grain, and density. Some woods are more resistant to pests, and this would be important for wood that is outside. Flexibility can also be an important characteristic. 1296
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heartwood
sapwood cambium phloem
outer bark
The wood tissue next to the cambium is also made up of layers. I LLU STR AT IO N BY TE MA H NE LSO N.
When selecting woods, wood strength is an important characteristic. The strength of wood depends upon the wood and the direction of the fibers. Wood fibers stretch up and down the tree and are visible from looking at the grain. The strength of wood is relatively high parallel to the grain, and relatively low perpendicular (across) the grain. Woods can also have a windy, curly grain. In general, the denser the wood, the stronger it is. The fibers or grain of the wood also determines the pore size. Pores are the ends of the wood fibers. Some woods are open grain or porous, meaning they have large pores. Porous woods include oak and ash. Other types of wood are closed grain, and the pores are less visible. Closed-grain woods include cherry and maple. Wood veneering and products Wood is considered a renewable resource because new trees can be grown. But some woods come from trees that take hundreds of years to fully mature. Veneering is one way to have the appearance of a unique or exotic wood while using only a sliver Experiment Central, 2nd edition
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Endgrain
Longgrain
Wood grain. I LLU STR AT IO N BY T EM AH NE LS ON.
of the wood. A veneer is a thin slice of wood. The veneer is glued onto materials that are more available, such as plywood, giving the wood the appearance of the veneer wood type. Plywood is a commonly used wood product that uses the principles of veneering. Plywood is made from gluing together many sheets of veneer with the veneer grains going in opposite directions. This produces an extremely strong material. In the two experiments that follow, you will examine two properties of different woods: water absorption and hardness.
EXPERIMENT 1 Water Absorption: How do different woods absorb water? Purpose/Hypothesis When wood absorbs water—from precipitation or
moisture in the air—it can cause the wood to expand, then dry and possibly crack. How woods absorb water and how much each absorbs are key properties that help people select a type of wood. In this experiment, you will look at three or more types of woods. First you will examine how grain direction relates to water movement through the wood. You can place a piece of wood in dyed water, and measure if the water moves along the grain or across it (the end grain). Do you think the water will move in the same direction on each of the pieces of wood? After you test water direction on each piece of wood, the dyed water will allow you to more easily examine the grain of each of the woods. Which wood is more open grain or closed grain? You will use this information to hypothesize which type of wood will absorb the most water. You can measure your hypothesis by weighing each piece of wood, before and after soaking the woods in water for 24 hours. To begin the experiment, use what you know about wood and water to make an educated guess about how the water will move. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things: • the topic of the experiment • the variable you will change 1298
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WORDS TO KNOW Angiosperm: A flowering plant that has its seeds produced within an ovary. Cambium: The tissue below the bark that produces new cells, which become wood and bark. Coniferous: Refers to trees, such as pines and firs, that bear cones and have needle-like leaves that are not shed all at once. Deciduous: Plants that lose their leaves during some season of the year, and then grow them back during another season. Density: The mass of a substance divided by its volume. Hardwood: Wood from angiosperm, mostly deciduous, trees. Heartwood: The inner layer of wood that provide structure and have no living cells.
Hypothesis: An idea phrased in the form of a statement that can be tested by observation and or experiment. Mass: Measure of the total amount of matter in an object. Also, an object’s quantity of matter as shown by its gravitational pull on another object. Phloem: The plant tissue that carries dissolved nutrients through the plant. Relative density: The density of one material compared to another. Sapwood: The outer wood in a tree, which is usually a lighter color. Softwood: Wood from coniferous trees, which usually remain green all year. Variable: Something that can affect the results of an experiment. Veneer: Thin slices of wood.
• the variable you will measure • what you expect to happen A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘Water will move along the grain for all the woods, and the wood type with the most open grain will absorb the most water.’’ How to Experiment Safely In this case, the variables you will change are If the wood needs to be cut into pieces, have an the types of wood, and the variable you will adult cut the wood to size. You will be working measure is how water direction moves and with dyed water so this experiment can be which type of wood absorb the most water. slightly messy. Wash your hands after working with the dye.
Level of Difficulty Moderate. Experiment Central, 2nd edition
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Materials Needed
What Are the Variables? Variables are anything that could affect the results of an experiment. Here are the main variables in this experiment: • the type of wood • the environment in which the wood is kept • the dryness of the wood • the amount of time the wood is exposed to water In other words, the variables in this experiment are everything that might affect the ability of the wood to absorb water. If you change more than one variable, you will not be able to tell which variable had the most effect.
Step 1a: Start with 3 (or more) blocks of different types of wood. I LL UST RA TI ON BY T EM AH NE LS ON.
• • • • • • •
• 3 (or more) blocks of different types of wood, approximately 3 inches (7.6 centimeters) wide by 6 inches (15 centimeters) long, and 34 of an inch thick. Oak, poplar, and pine work well; other wood types are walnut, cherry, and mahogany. (Available from building supply stores or scraps from a lumber yard or school shop. If you find wood that needs to be cut, have an adult cut the wood to size. The wood should all be approximately the same size but they do not need to match exactly.) Note: Avoid woods from trees you find outside as they likely contain more moisture than woods in stores. • plastic container, large enough to fit the blocks of wood • food coloring or dye, a dark color such as blue or green
ruler watch or clock with a minute hand plastic or wooden stirrer gram scale wax paper gloves (optional) magnifying glass (optional) Approximate Budget Less than $5. (Assuming
you can find the wood as scraps and you have or can borrow a gram scale.) Timetable Approximately 45 minutes working
time; 24 hours total time. Step-by-Step Instructions
1. Place a piece of wax paper on the scale and weigh each of the three woods. Note the weight on a chart. 1300
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2. Fill the container about half way with warm water. Add several drops of the dye or food coloring. Stir and continue adding the dye until the water is a dark color. 3. At the same time, set each of the three pieces of wood in the water with the grain (length) facing up and down. Start timing for one minute. 4. Observe the water movement in each of the woods, looking at both the end grain and long grain. After one minute, measure where the water has reached in each of the woods. Measure on both the end and long grain. Note the results. (If you have gloves, you could wear them to avoid getting dye on your hands, or you could handle the wood with wax paper). 5. Set the woods back in the water and wait two more minutes, or until the water has reached close to the top of a wood. Measure how far the water traveled along the long and end grain, on each of the woods. 6. Set all the wood on a piece of wax paper. Examine each of the woods’ grains up close or with a magnifying glass. 7. Form a hypothesis as to which type of wood will absorb the most water. 8. Set all the woods back in the container so they lie flat (with the long side left to right). The water should cover the pieces of wood. If it does not, add more water. 9. Wait about 24 hours. 10. Carefully drain the water. 11. Place a piece of wax paper on the scale. Hold one piece of wood above the container until it no longer drips and set the wood on it. You may want to pick the wood up with wax paper or wear gloves so as to not get dye on your hands. Note the weight of the wood. Experiment Central, 2nd edition
Step 1b: Weigh each of the three woods. I LLU STR AT IO N BY TEM AH N EL SON .
Steps 3 and 4: Set each of the three pieces of wood in the water with the grain (length) facing up and down and observe the water movement. ILL US TRA TI ON B Y TE MA H NEL SO N.
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Troubleshooter’s Guide Here is one problems that may arise during the experiment and a way to remedy it.
12. Weigh each of the pieces of wood, holding the pieces so they no longer drip before placing them on a fresh piece of wax paper.
Summary of Results Subtract the end weight of the wood from the starting weight. Which of the woods gained the most weight from the water? Possible causes: The wood may have been too Did it relate to whether the wood had an open or moist to start with. Woods are usually dried for closed grain? Was your hypothesis correct? How long periods of time before they are available did the water travel along the grain of the wood? for use. Try another piece of wood, making sure Did it differ depending upon the type of wood? it is not freshly cut, and repeat the experiment. Consider how water absorption would affect selecting a wood for a home or piece of furniture. Write a summary of your findings. You might want to sketch pictures of the water movement. Problem: One of the woods did not take up the dyed water at all.
Change the Variables You can vary this experiment in several ways. You
can focus on one type of wood, such as oak, and examine the water absorption properties of different types of oak. You can also change the amount of water available to each wood, to measure how much water the end grain or long grain can absorb. Another way to vary the experiment is to change the environmental temperature. How does humidity or cold affect water absorption?
EXPERIMENT 2 Wood Hardness: How does the hardness of wood relate to its building properties? Purpose/Hypothesis In general, hardwoods are harder and denser than
softwoods. The structure of the wood depends on the thickness and makeup of the cell walls. Many hardwoods have thicker cell walls (fibers) than softwoods. How hard or soft a wood is affects how the wood is used. For some soft woods, builders can pound nails into the wood without the wood cracking. A nail inserted into a hard wood may crack, and builders will use a drill before nailing wood together. You can use a nail to determine the relative hardness or softness of three to four different woods. The woods you test will be a mix between hardwoods and softwoods. In order to compare them, you will need to 1302
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use the same force when inserting the nail into the woods. The deeper the nail is driven into the wood, the softer the wood. To form a hypothesis, you can first compare the heaviness of each wood to one another. Using this information, you can then make a hypothesis as to which nail will go in the least. You will then finish driving the nail into the wood with a hammer. To begin the experiment, use what you know about wood and hardness to make an educated guess about how the heaviness of the wood will determine its hardness. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
What Are the Variables? Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment: • the wetness of the wood • the force with which the weight hits the nail • the heaviness of the weight • the size of the nail In other words, the variables in this experiment are everything that might affect how far the nail is driven into the wood.
• the topic of the experiment • the variable you will change • the variable you will measure • what you expect to happen
How to Experiment Safely Be careful when using the hammer and nails.
A hypothesis should be brief, specific, and Have an adult help you with the hammering to make sure the wood cannot move around. measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: ‘‘The nail will move deeper into the woods that are lighter compared to the heavier woods, which may crack.’’ In this case, the variable you will change is the type of wood, and the variable you will measure is the depth the wood moves into the wood. Level of Difficulty Moderate. Materials Needed
• 3 or more different pieces of wood, minimum 34-inch thick and approximately 6 inches (15 centimeters) square: at least 1 softwood (pine, cedar) and 1 hardwood (poplar, balsa, oak) • 3 nails 34-inch long with point, all the same diameter Experiment Central, 2nd edition
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Step 6: Set the tubing in the middle of the lightest piece of wood and trace the circle onto the wood. I LL UST RA TI ON BY T EM AH NE LS ON.
Steps 7 and 8: Line up the paper circle over the wood circle. Place the nail on the center mark of the wood. IL LUS TR ATI ON B Y TE MA H
• cardboard or plastic tube, at least 30 inches (76 centimeters) long (wrapping paper rolls works well); if tubing is not available you can make tubing by taping together several sheets of thick paper • full can or water bottle that fits tightly into the diameter of the tube • hammer • marker • sharp pencil • piece of paper • scissors • ruler with 0.06-inch increments Note: The exact size of the wood is not important but when the tubing is on the wood there should be at least 2 inches (5 centimeters) of wood around the tube and the nail should be slightly shorter than the thickness of the wood. Approximate Budget Less than $5. (Most, if not all, materials may be
found in the average household.) Timetable Approximately 30 minutes.
NE LS ON.
Step-by-Step Instructions
1. Lift each of the wood samples one at a time, then compare one to another in each hand. Place the woods in order, from the lightest to the heaviest. 2. Measure how long the nail is and note its length on a chart. 3. Use the marker and ruler to make small lines on each nail at 0.06-inch increments, about 34 way up the nail. 4. Set the tubing on the paper and trace the circle. Follow your tracing to cut out the circle. 5. To find the center of the circle, fold the circle in half and then in half again. 1304
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6.
7.
8.
9. 10.
11. 12. 13.
14.
Unfold and mark a dot where the fold lines intersect. Set the tubing in the middle of the lightest piece of wood. Use the pencil to trace the circle onto the wood. Repeat this process with the other wood samples. Line up the paper circle over the wood circle. Poke a small hole in the paper with the pencil to mark the middle of the circle on the wood. Place the nail on the center mark of the wood and gently hammer it in until it reaches the second mark. The nail should be standing straight and not wobbling. If you can easily push the nail to its side, hammer it in to the next mark. Set the wood on the floor. Place the tubing on the circle mark. Hold the can or other circular object even with the top of the tubing and release. Retrieve the object and drop the can four more times, for a total of five times. Repeat Steps 6–10 on the remaining types of wood. Measure how far each nail went into the wood by measuring how much of the nail did not go into the wood. Note your results. Finish driving the nail into the wood with the hammer. Hammer the nails gently and have an adult help you make sure the piece of wood is secure. Note if any of the woods starts to crack.
Step 10: Hold the can or other circular object even with the top of the tubing and release. ILL US TRA TI ON B Y TE MA H NEL SO N.
Summary of Results Subtract how much of the nail was still exposed from
the length of the nail. Was your hypothesis correct? Was the lightest wood also the wood that the nail went into furthest? Compare the difference between the two types of the hardwood or softwood. Did any of the heavy woods crack or begin to crack? Write a summary of your results. Change the Variables You can vary this experiment. Here are some
possibilities. Try different types of either hardwood or softwood to compare them against one another. You could even try different types Experiment Central, 2nd edition
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Troubleshooter’s Guide Here are some problems that may arise during the experiment, some possible causes, and ways to solve the problem. Problem: The nail fell over when the weight was dropped. Possible causes: 1. The nail may have been too thin. Try using a slightly thicker nail with a sharp point, and repeat the experiment. 2. The weight may have hit the nail at an angle. The can, water bottle, or other circular object should fit snugly in the tube opening so that it cannot move around and hit the nail straight. Change the tube or object to there is no room for the can to move, and repeat the experiment. Problem: The nail hardly went into the wood. Possible cause: The weight you dropped is not heavy enough. If you are using a can or bottle, make sure it is full. See if you can find a heavier object that is the same diameter. You may also want to try a larger tube, and a larger (heavier) can, bottle, or other object.
of the same wood, such as oak. You can also experiment with driving the nail into the end grain instead of the long grain.
Design Your Own Experiment How to Select a Topic Relating to this Concept
There are many experiments you could design to investigate the properties of wood and how people use it. Take a look at the wooden furniture, toys, sports equipment, or other pieces in your home or school and try to identify what type of wood it is. What about the home itself? Consider the properties of each piece. Can you see the grain or pores in the wood? Think about what woods you are curious about or you may want to investigate familiar wooden items. Why is a wooden bat, for example, made with a certain type of wood and how does this affect the bat’s ability to hit a ball? Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on questions relating to wood that interest you. You also may want to visit a lumberyard or store that sells different woods. Steps in the Scientific Method To conduct an
original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove. Here are the steps in designing an experiment: • State the purpose of—and the underlying question behind—the experiment you propose to do. • Recognize the variables involved, and select one that will help you answer the question at hand. 1306
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• State a testable hypothesis, an educated guess about the answer to your question. • Decide how to change the variable you selected. • Decide how to measure your results. Recording Data and Summarizing the Results It is important to docu-
ment as much information as possible about your experiment. Part of your presentation should be visual, using charts and graphs. You can also include samples of the woods. Remember, whether or not your experiment is successful, your conclusions and experiences can benefit others. Related Projects If you are interested in experimenting more with wood
and its properties, you can start collecting and examining different types of wood. You may want to start collecting woods you find outside and then purchase samples of other wood types. Compare properties of the different woods to one another. You can conduct an experiment on what gives wood its unique colors. Some woods, such as purpleheart, change or fade over time. How might oxygen or sunlight affect the color of wood? You can also explore the affect of disease and bugs on wood. In some cases, disease, worms, and bugs can leave marks that increase its beauty and value. Another aspect related to wood you may also want to explore is wood finishes. Finishes can protect and affect the appearance of woods. Try an experiment in finishing the same type of wood with different finishes, such as a wax, oil, and shellac. How does each change the appearance and ability of the wood to withstand water? For a project, you can make different types of paper out of wood.
For More Information Burnie, Davis. Tree. New York: DK Publishing, 2005. Information on trees and wood. Gardner, Robert. Science Projects Ideas about Trees. Springfield< NJ: Enslow Publishers, 1997. Describes tree related projects for young people. Wolke, Robert L. What Einstein Didn’t Know: Scientific Answers to Everyday Questions. Secaucus, NJ: Birch Lane Press, 1997. Contains a number of interesting entries on the nature of water. ‘‘Wood Cells.’’ Nikon. http://www.microscopyu.com/galleries/confocal/ woodcells.html (accessed on May 2, 2008). Close up images of wood.
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Budget I nde x
Chapter name in brackets, followed by experiment name. The numeral before the colon indicates volume; numbers after the colon indicate page number. LESS THAN $5
[Air] Air Density: Does warm air take up less room than cool air? 1:36 [Animal Defenses] Camouflage: Does an animal’s living environment relate to the color of the animal life? 1:63 [Annual Growth] Tree Growth: What can be learned from the growth patterns of trees? 1:74 [Bones and Muscles] Muscles: How does the strength of muscles affect fatigue over time? 1:120 [Chemical Properties] Slime: What happens when white glue and borax mix? 1:167 [Crystals] Cool Crystals: How does the effect of cooling impact crystal growth? 2:252 [Density and Buoyancy] Buoyancy: Does water pressure affect buoyancy? 2:264 [Dyes] Applying Dyes: How does the fiber affect the dye color? 2:301 [Earthquakes] Detecting an Earthquake: How can movement of Earth’s crust be measured? 2:314 [Earthquakes] Earthquake Simulation: Is the destruction greater at the epicenter? 2:317 [Eclipses] Simulating Solar and Lunar Eclipses 2:327 [Flight] Helicopters, Propellers, and Centripetal Force: Will it fly high? 3:418 lxxxv
BUDGET INDEX
[Food Spoilage] Spoiled Milk: How do different temperatures of liquid affect its rate of spoilage? 3:485 [Forces] Centripetal Action: What is the relationship between distance and force in circular motion? 3:501 [Fungi] Decomposers: Food source for a common fungi 3:541 [Genetics] Building a Pedigree for Taste 3:559 [Germination] Comparing Germination Times: How fast can seeds grow? 3:570 [Gravity] Gravity: How fast do different objects fall? 3:581 [Gravity] Measuring Mass: How can a balance be made? 3:585 [Greenhouse Effect] Fossil Fuels: What happens when fossil fuels burn? 3:596 [Heat] Conduction: Which solid materials are the best conductors of heat? 3:618 [Heat] Convection: How does heat move through liquids? 3:622 [Insects] Lightning Bugs: How does the environment affect a firefly’s flash? 3:638 [Memory] False Memories: How can memories be influenced? 4:705 [Memory] Memory Mnemonics: What techniques help in memory retention? 4:701 [Microorganisms] Microorganisms: What is the best way to grow penicillin? 4:713 [Nutrition] Daily Nutrition: How nutritious is my diet? 4:766 [Nutrition] Energizing Foods: Which foods contain carbohydrates and fats? 4:761 [Oceans] Currents: Water behavior in density-driven currents 4:780 [Optics and Optical Illusions] Optical Illusions: Can the eye be fooled? 4:791 [Osmosis and Diffusion] Changing Concentrations: Will a bag of salt water draw in fresh water? 4:803 [Oxidation-Reduction] Reduction: How will acid affect dirty pennies? 4:813 [pH] Kitchen Chemistry: What is the pH of household chemicals? 4:861 [Potential and Kinetic Energy] Measuring Energy: How does the height of an object affect its potential energy? 5:931 [Rocks and Minerals] Rock Classification: Is it igneous, sedimentary, or metamorphic? 5:975 lxxxvi
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BUDGET INDEX
[Scientific Method] Using the Scientific Method: Do fruit flies appear out of thin air? 5:1013 [Simple Machines] Lever Lifting: How does the distance from the fulcrum affect work? 5:1055 [Simple Machines] Wheel and Axle: How can changing the size of the wheel affect the amount of work it takes to lift a load? 5:1051 [Space Observation] Doppler Effect: How can waves measure the distance and speed of objects? 6:1118 [Stars] Tracking the Motion of the Planets: Can a planet be followed? 6:1128 [Static Electricity] Building an Electroscope: Which objects are electrically charged? 6:1135 [Static Electricity] Measuring a Charge: Does nylon or wool create a stronger static electric charge? 6:1139 [Storms] Lightning Sparks: Explore how separating charges causes an attraction between objects 6:1152 [Tropisms] Phototropism: Will plants follow a maze to reach light? 6:1193 [Volcanoes] Looking at a Seismograph: Can a volcanic eruption be detected? 6:1242 [Water Cycle] Surface Area: How does surface area affect the rate of evaporation? 6:1253 [Weather] Clouds: Will a drop in air temperature cause a cloud to form? 6:1277 [Weather] Wind: Measuring wind speed with a homemade anemometer 6:1273 [Weather Forecasting] Air Pressure: How can air pressure be measured? 6:1289 [Weather Forecasting] Dewpoint: When will dew form? 6:1286 [Wood] Water Absorption: How do different woods absorb water? 6:1298 [Wood] Wood Hardness: How does the hardness of wood relate to its building properties? 6:1302 $5–$10
[Acid Rain] Acid Rain and Animals: How does acid rain affect brine shrimp? 1:5 [Acid Rain] Acid Rain and Plants: How does acid rain affect plant growth? 1:9 Experiment Central, 2nd edition
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BUDGET INDEX
[Acid Rain] Acid Rain: Can acid rain harm structures? 1:12 [Adhesives] Adhesives in the Environment: Will different environmental conditions affect the properties of different adhesives? 1:26 [Adhesives] Material Adhesion: How do various glues adhere to different materials? 1:22 [Air] Convection Currents: How can rising air cause weather changes? 1:39 [Air and Water Pollution] Eutrophication: The effect of phosphates on water plants. 1:55 [Air and Water Pollution] Pollutant Bioindicators: Can lichens provide clues to an area’s air pollution? 1:51 [Annual Growth] Lichen Growth: What can be learned from the environment by observing lichens? 1:79 [Bones and Muscles] Bone Loss: How does the loss of calcium affect bone strength? 1:116 [Caves] Cave Formation: How does the acidity of a substance affect the formation of a cave? 1:132 [Caves] Cave Icicles: How does the mineral content of water affect the formation of stalactites and stalagmites? 1:135 [Cells] Investigating Cells: What are the differences between a multicellular organism and a unicellular organism? 1:141 [Cells] Plant Cells: What are the cell differences between monocot and dicot plants? 1:145 [Cells] Yeast Cells: How do they reproduce? 1:147 [Chemical Energy] Rusting: Is the chemical reaction exothermic, endothermic, or neither? 1:152 [Chemosenses] Smell and Taste: How does smell affect the sense of taste? 1:186 [Chemosenses] Supertasters: Is there a correlation between the number of taste buds and taste perception? 1:180 [Chlorophyll] Plant Pigments: Can pigments be separated? 1:193 [Comets and Meteors] Meteor Impact: How do the characteristics of a meteorite and its impact affect the shape of the crater? 2:221 [Composting/Landfills] Composting: Using organic material to grow plants 2:237 [Composting/Landfills] Living Landfill: What effect do the microorganisms in soil have on the decomposition process? 2:232 lxxxviii
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BUDGET INDEX
[Crystals] Crystal Structure: Will varying shape crystals form from varying substances? 2:246 [Density and Buoyancy] Density: Can a scale of relative density predict whether one material floats on another? 2:260 [DNA (Deoxyribonucleic Acid)] The Stuff of Life: Isolating DNA 2:289 [Dyes] Holding the Dye: How do dye fixatives affect the colorfastness of the dye? 2:304 [Eclipses] Phases of the Moon: What does each phase look like? 2:329 [Enzymes] Finding the Enzyme: Which enzyme breaks down hydrogen peroxide? 2:362 [Enzymes] Stopping Enzymes: Does temperature affect enzyme action? 2:368 [Erosion] Erosion: Does soil type affect the amount of water that runs off a hillside? 2:377 [Erosion] Plants and Erosion: How do plants affect the rate of soil erosion? 2:381 [Flight] Lift-Off: How can a glider be made to fly higher? 3:415 [Flowers] Sweet Sight: Can changing a flower’s nectar and color affect the pollinators lured to the flower? 3:431 [Fluids] Spinning Fluids: How do different fluids behave when immersed in a spinning rod? 3:444 [Fluids] Viscosity: How can temperature affect the viscosity of liquids? 3:441 [Food Preservation] Drying Foods: Does drying fruits help prevent or delay spoilage? 3:458 [Food Preservation] Sweet Preservatives: How does sugar affect the preservation of fruit? 3:454 [Food Science] Jelly and Pectin: How does acidity affect how fruit gels? 3:463 [Food Science] Rising Foods: How much carbon dioxide do different leavening agents produce? 3:470 [Food Spoilage] Preservatives: How do different substances affect the growth of mold? 3:481 [Forensic Science] Blood Patterns: How can a blood spatter help recreate the crime? 3:515 [Fossils] Fossil Formation: What are the physical characteristics of an organism that make the best fossils? 3:530 Experiment Central, 2nd edition
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BUDGET INDEX
[Fossils] Making an Impression: In which soil environment does a fossil most easily form? 3:526 [Fungi] Living Conditions: What is the ideal temperature for yeast growth? 3:544 [Genetics] Genetic Traits: Will you share certain genetic traits more with family members than non-family members? 3:556 [Germination] Effects of Temperature on Germination: What temperatures encourage and discourage germination? 3:566 [Germination] Seed Scarification: Does breaking the seed shell affect germination time? 3:573 [Greenhouse Effect] Creating a Greenhouse: How much will the temperature rise inside a greenhouse? 3:592 [Groundwater Aquifers] Groundwater: How can it be cleaned? 3:609 [Insects] Ant Food: What type of foods is one type of ant attracted to? 3:635 [Magnetism] Electromagnets: Does the strength of an electromagnet increase with greater current? 4:678 [Magnetism] Magnets: How do heat, cold, jarring, and rubbing affect the magnetism of a nail? 4:674 [Materials Science] Developing Renewables: Can a renewable packing material have the same qualities as a non-renewable material? 4:691 [Materials Science] Testing Tape: Finding the properties that allow tape to support weight. 4:688 [Microorganisms] Growing Microorganisms in a Petri Dish 4:716 [Mountains] Mountain Formations: How does the height of the mountain have an affect on desert formation? 4:741 [Mountains] Mountain Plates: How does the movement of Earth’s plates determine the formation of a mountain? 4:738 [Nanotechnology] Nanosize Substances: How can the physical size affect the rate of reaction? 4:753 [Nanotechnology] Nanosize: How can the physical size affect a material’s properties? 4:750 [Oceans] Stratification: How does the salinity in ocean water cause it to form layers? 4:775 [Osmosis and Diffusion] Changing Sizes: What effect does molecule size have on osmosis 4:806 xc
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BUDGET INDEX
[Osmosis and Diffusion] Measuring Membranes: Is a plastic bag a semipermeable membrane? 4:798 [Oxidation-Reduction] Oxidation and Rust: How is rust produced? 4:817 [Oxidation-Reduction] Oxidation Reaction: Can acid change the color of copper? 4:820 [Periodic Table] Active Metals: What metals give off electrons more readily than others? 4:838 [Pesticides] Moving through Water: How can pesticides affect nontarget plant life? 4:852 [pH] Chemical Titration: What is required to change a substance from an acid or a base into a neutral solution? 4:865 [Photosynthesis] Photosynthesis: How does light affect plant growth? 4:873 [Plants and Water] Water Flow: How do varying solutions of water affect the amount of water a plant takes in and its turgor pressure? 5:900 [Polymers] Polymer Properties: How are the properties of hard plastics different? 5:923 [Polymers] Polymer Slime: How will adding more of a polymer change the properties of a polymer ‘‘slime’’? 5:919 [Polymers] Polymer Strength: What are the tensile properties of certain polymers that make them more durable than others? 5:914 [Renewable Energy] Hydropower: How does water pressure affect water energy? 5:948 [Rivers] River Flow: How does the steepness and rate of water flow affect river erosion? 5:962 [Rivers] Stream Flow: Does the stream meander? 5:960 [Rocks and Minerals] Mineral Testing: What kind of mineral is it? 5:971 [Rotation and Orbits] Foucault Pendulum: How can a pendulum demonstrate the rotation of Earth? 5:985 [Rotation and Orbits] Spinning Effects: How does the speed of a rotating object affect the way centrifugal force can overcome gravity? 5:989 [Salinity] Density Ball: How to make a standard for measuring density 5:1000 [Salinity] Making a Hydrometer: How can salinity be measured? 5:997 Experiment Central, 2nd edition
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BUDGET INDEX
[Scientific Method] Using the Scientific Method: What are the mystery powders? 5:1009 [Separation and Identification] Chromatography: Can you identify a pen from the way its colors separate? 5:1034 [Simple Machines] The Screw: How does the distance between the threads of a screw affect the work? 5:1037 [Soil] Soil pH: Does the pH of soil affect plant growth? 5:1074 [Sound] Pitch: How does the thickness of a vibrating string affect sound? 5:1099 [Sound] Soundproofing: How do different materials affect sound? 5:1102 [Sound] Wave Length: How does the length of a vibrating string affect the sound it produces? 5:1096 [Storms] Tornadoes: Making a violent vortex 6:1155 [Time] Pendulums: How do the length, weight, and swing angle of a pendulum affect its oscillation time? 6:1180 [Time] Water Clock: Does the amount of water in a water clock affect its accuracy? 6:1185 [Tropisms] Heliotropism: How does the Sun affect the movement of certain plants? 6:1201 [Vegetative Propagation] Auxins: How do auxins affect plant growth? 6:1209 [Vegetative Propagation] Potatoes from Pieces: How do potatoes reproduce vegetatively? 6:1216 [Vitamins and Minerals] Hard Water: Do different water sources have varying mineral content? 6:1231 [Vitamins and Minerals] Vitamin C: What juices are the best sources of Vitamin C? 6:1226 [Water Cycle] Temperature: How does temperature affect the rate of evaporation? 2:1248 [Water Properties] Cohesion: Can the cohesive force of surface tension in water support an object denser than water? 6:1261 $ 11 – $ 15
[Animal Defenses] Ladybug Threats: How do ladybugs defend themselves when they feel threatened? 1:65 [Chemical Properties] Chemical Patination: Producing chemical reactions on metal 1:173 [Chemical Properties] Chemical Reactions: What happens when mineral oil, water, and iodine mix? 1:170 xcii
Experiment Central, 2nd edition
BUDGET INDEX
[Comets and Meteors] Comet Nucleus: Linking a Comet’s Composition to its Properties. 2:218 [DNA (Deoxyribonucleic Acid)] Comparing DNA: Does the DNA from different species have the same appearance? 2:291 [Electricity] Batteries: Can a series of homemade electric cells form a ‘‘pile’’ strong enough to match the voltage of a D-cell battery? 2:340 [Electricity] Electroplating: Using electricity to move one metal onto another metal 2:344 [Enzymes] Tough and Tender: Does papain speed up the aging process? 2:365 [Ethnobotany] Coiling Reeds: How does the tightness of the coil affect the ability to hold materials? 2:396 [Groundwater Aquifers] Aquifers: How do they become polluted? 3:605 [Heat] Heat Capacity: Which liquids have the highest heat capacity? 3:625 [Light Properties] Refraction: How does the material affect how light travels? 4:666 [Mixtures and Solutions] Colloids: Can colloids be distinguished from suspension using the Tyndall effect? 4:730 [Mixtures and Solutions] Suspensions and Solutions: Can filtration and evaporation determine whether mixtures are suspensions or solutions? 4:725 [Periodic Table] Soluble Families: How does the solubility of an element relate to where it is located on the Periodic Table? 4:835 [Pesticides] Natural versus Synthetic: How do different types of pesticides compare against a pest? 4:848 [Plant Anatomy] Plant Hormones: What is the affect of hormones on root and stem growth? 5:886 [Plants and Water] Transpiration: How do different environmental conditions affect plants’ rates of transpiration? 5:904 [Renewable Energy] Capturing Wind Energy: How does the material affect the amount of wind energy harnessed? 5:944 [Rivers] Weathering Erosion in Glaciers: How does a river make a trench? 5:957 [Seashells] Classifying Seashells 5:1025 Experiment Central, 2nd edition
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BUDGET INDEX
[Seashells] Shell Strength: Which shell is stronger: a clam shell or lobster shell? 5:1022 [Separation and Identification] Identifying a Mixture: How can determining basic properties of a substance allow you to identify the substances in a mixture? 5:1039 [Solar Energy] Retaining the Sun’s heat: What substance best stores heat for a solar system? 5:1090 [Space Observation] Telescopes: How do different combinations of lenses affect the image? 6:1113 [Storms] Forming Hailstones: How do temperature differences affect the formation of hail? 6:1158 [Structures and Shapes] Arches and Beams: Which is strongest? 6:1167 [Structures and Shapes] Beams and Rigidity: How does the vertical height of a beam affect its rigidity? 6:1170 [Volcanoes] Model of a Volcano: Will it blow its top? 6:1240 [Water Properties] Adhesion: How much weight is required to break the adhesive force between an object and water? 6:1264 $ 16 – $ 20
[Bacteria] Bacterial Resistance: Can bacteria gain resistance to a substance after exposure? 1:95 [Color] Color and Flavor: How much does color affect flavor perception? 1:207 [Color] Temperature and Color: What color has the highest temperature? 1:210 [Dissolved Oxygen] Goldfish Breath: How does a decrease in the dissolved oxygen level affect the breathing rate of goldfish? 2:279 [Electromagnetism] Electromagnetism: How can an electromagnet be created? 2:354 [Electromagnetism] Magnetism:How can a magnetic field be created and detected? 2:351 [Ethnobotany] Plants and Health: Which plants have antibacterial properties? 2:392 [Flowers] Self versus Cross: Will there be a difference in reproduction between self-pollinated and cross-pollinated plants of the same type? 3:427 [Forces] Newton’s Laws in Action: How do water bottle rockets demonstrate Newton’s laws of motion? 3:493 [Forensic Science] Fiber Evidence: How can scientific techniques be used to identify fiber? 3:511 xciv
Experiment Central, 2nd edition
BUDGET INDEX
[Nutrition] Nutrition: Which foods contain proteins and salts? 4:764 [Optics and Optical Illusions] Optics: What is the focal length of a lens? 4:788 [Periodic Table] Metals versus Nonmetals: Which areas of the periodic table have elements that conduct electricity? 4:830 [Photosynthesis] Light Intensity: How does the intensity of light affect plant growth? 4:877 [Plant Anatomy] Water Uptake: How do different plants differ in their water needs? 5:890 [Potential and Kinetic Energy] Using Energy: Build a roller coaster 5:934 [Soil] Soil Profile: What are the different properties of the soil horizons? 5:1067 [Stars] Tracking Stars: Where is Polaris? 6:1125 [Tropisms] Geotropism: Will plant roots turn toward the pull of gravity? 5:1197 $ 2 1– $ 25
[Bacteria] Bacterial Growth: How do certain substances inhibit or promote bacterial growth? 1:90 [Biomes] Building a Desert Biome 1:108 [Biomes] Building a Temperate Forest Biome 1:107 [Chemical Energy] Exothermic or Endothermic: Determining whether various chemical reactions are exothermic or endothermic 1:156 [Dissolved Oxygen] Decay and Dissolved Oxygen: How does the amount of decaying matter affect the level of dissolved oxygen in water? 2:274 [Fish] Fish Breathing: How do different fish take in oxygen? 3:404 [Fish] Fish Movement: How do fins and body shape affect the movement of fish? 3:407 [Light Properties] Looking for the Glow: Which objects glow under black light? 4:661 [Solar Energy] Capturing Solar Energy: Will seedlings grow bigger in a greenhouse? 5:1084 [Solar Energy] Solar Cells: Will sunlight make a motor run? 5:1087 $ 2 6– $ 30
[Electricity] Electrolytes: Do some solutions conduct electricity better than others? 2:335 Experiment Central, 2nd edition
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[Life Cycles] Insects: How does food supply affect the growth rate of grasshoppers or crickets? 4:651 [Life Cycles] Tadpoles: Does temperature affect the rate at which tadpoles change into frogs? 4:647 [Light Properties] Refraction and Defraction: Making a rainbow 4:664 $ 31 – $ 35
[Chlorophyll] Response to Light: Do plants grow differently in different colors of light? 1:197
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Experiment Central, 2nd edition
Level of Difficulty Index
Chapter name in brackets, followed by experiment name. The numeral before the colon indicates volume; numbers after the colon indicate page number. EASY
Easy means that the average student should easily be able to complete the tasks outlined in the project/experiment, and that the time spent on the project is not overly restrictive. [Air] Air Density: Does warm air take up less room than cool air? 1:36 [Air and Water Pollution] Eutrophication: The effect of phosphates on water plants. 1:55 [Bones and Muscles] Muscles: How does the strength of muscles affect fatigue over time? 1:120 [Chemosenses] Smell and Taste: How does smell affect the sense of taste? 1:186 [Electromagnetism] Electromagnetism: How can an electromagnet be created? 2:354 [Flight] Helicopters, Propellers, and Centripetal Force: Will it fly high? 3:418 [Flight] Lift-Off: How can a glider be made to fly higher? 3:415 [Fungi] Decomposers: Food source for a common fungi 3:541 [Nanotechnology] Nanosize Substances: How can the physical size affect the rate of reaction? 4:753 [Nutrition] Energizing Foods: Which foods contain carbohydrates and fats? 4:761 [Oceans] Currents: Water behavior in density-driven currents 4:780 xcvii
LEVEL OF DIFFICULTY INDEX
[Osmosis and Diffusion] Changing Concentrations: Will a bag of salt water draw in fresh water? 4:803 [Potential and Kinetic Energy] Measuring Energy: How does the height of an object affect its potential energy? 5:931 [Rivers] River Flow: How does the steepness and rate of water flow affect river erosion? 5:962 [Rivers] Stream Flow: Does the stream meander? 5:960 [Rotation and Orbits] Spinning Effects: How does the speed of a rotating object affect the way centrifugal force can overcome gravity? 5:989 [Simple Machines] Lever Lifting: How does the distance from the fulcrum affect work? 5:1055 [Sound] Pitch: How does the thickness of a vibrating string affect sound? 5:1099 [Sound] Wave Length: How does the length of a vibrating string affect the sound it produces? 5:1096 [Space Observation] Doppler Effect: How can waves measure the distance and speed of objects? 6:1118 [Storms] Lightning Sparks: Explore how separating charges causes an attraction between objects 6:1152 [Storms] Tornadoes: Making a violent vortex 6:1155 [Volcanoes] Looking at a Seismograph: Can a volcanic eruption be detected? 6:1242 [Water Cycle] Surface Area: How does surface area affect the rate of evaporation? 6:1253 [Water Cycle] Temperature: How does temperature affect the rate of evaporation? 6:1248 [Weather Forecasting] Air Pressure: How can air pressure be measured? 6:1289 [Weather Forecasting] Dewpoint: When will dew form? 6:1286 E A S Y / M O D E R AT E
Easy/Moderate means that the average student should have little trouble completing the tasks outlined in the project/experiment, and that the time spent on the project is not overly restrictive. [Air] Convection Currents: How can rising air cause weather changes? 1:39 [Bones and Muscles] Bone Loss: How does the loss of calcium affect bone strength? 1:116 xcviii
Experiment Central, 2nd edition
LEVEL OF DIFFICULTY INDEX
[Caves] Cave Formation: How does the acidity of a substance affect the formation of a cave? 1:132 [Chemical Properties] Slime: What happens when white glue and borax mix? 1:167 [Chemosenses] Supertasters: Is there a correlation between the number of taste buds and taste perception? 1:180 [Composting/Landfills] Living Landfill: What effect do the microorganisms in soil have on the decomposition process? 2:232 [Dissolved Oxygen] Decay and Dissolved Oxygen: How does the amount of decaying matter affect the level of dissolved oxygen in water? 2:274 [Dissolved Oxygen] Goldfish Breath: How does a decrease in the dissolved oxygen level affect the breathing rate of goldfish? 2:279 [Dyes] Applying Dyes: How does the fiber affect the dye color? 2:301 [Earthquakes] Earthquake Simulation: Is the destruction greater at the epicenter? 2:317 [Eclipses] Phases of the Moon: What does each phase look like? 2:329 [Eclipses] Simulating Solar and Lunar Eclipses 2:327 [Enzymes] Finding the Enzyme: Which enzyme breaks down hydrogen peroxide? 2:362 [Enzymes] Tough and Tender: Does papain speed up the aging process? 2:365 [Fluids] Spinning Fluids: How do different fluids behave when immersed in a spinning rod? 3:444 [Food Spoilage] Spoiled Milk: How do different temperatures of liquid affect its rate of spoilage? 3:485 [Forces] Centripetal Action: What is the relationship between distance and force in circular motion? 3:501 [Fossils] Making an Impression: In which soil environment does a fossil most easily form? 3:526 [Genetics] Building a Pedigree for Taste 3:559 [Genetics] Genetic Traits: Will you share certain genetic traits more with family members than non-family members? 3:556 [Germination] Comparing Germination Times: How fast can seeds grow? 3:570 [Germination] Effects of Temperature on Germination: What temperatures encourage and discourage germination? 3:566 Experiment Central, 2nd edition
xcix
LEVEL OF DIFFICULTY INDEX
[Greenhouse Effect] Creating a Greenhouse: How much will the temperature rise inside a greenhouse? 3:592 [Heat] Convection: How does heat move through liquids? 3:622 [Light Properties] Looking for the Glow: Which objects glow under black light? 4:661 [Light Properties] Refraction and Defraction: Making a rainbow 4:664 [Magnetism] Electromagnets: Does the strength of an electromagnet increase with greater current? 4:678 [Magnetism] Magnets: How do heat, cold, jarring, and rubbing affect the magnetism of a nail? 4:674 [Materials Science] Testing Tape: Finding the properties that allow tape to support weight. 4:688 [Memory] False Memories: How can memories be influenced? 4:705 [Microorganisms] Microorganisms: What is the best way to grow penicillin? 4:713 [Mountains] Mountain Formations: How does the height of the mountain have an affect on desert formation? 4:741 [Mountains] Mountain Plates: How does the movement of Earth’s plates determine the formation of a mountain? 4:738 [Nanotechnology] Nanosize: How can the physical size affect a material’s properties? 4:750 [Oceans] Stratification: How does the salinity in ocean water cause it to form layers? 4:775 [Oxidation-Reduction] Oxidation and Rust: How is rust produced? 4:817 [Periodic Table] Soluble Families: How does the solubility of an element relate to where it is located on the Periodic Table? 4:835 [Pesticides] Moving through Water: How can pesticides affect nontarget plant life? 4:852 [Plants and Water] Water Flow: How do varying solutions of water affect the amount of water a plant takes in and its turgor pressure? 5:900 [Scientific Method] Using the Scientific Method: Do fruit flies appear out of thin air? 5:1013 [Scientific Method] Using the Scientific Method: What are the mystery powders? 5:1009 [Seashells] Classifying Seashells 5:1025 c
Experiment Central, 2nd edition
LEVEL OF DIFFICULTY INDEX
[Seashells] Shell Strength: Which shell is stronger: a clam shell or lobster shell? 5:1022 [Simple Machines] Wheel and Axle: How can changing the size of the wheel affect the amount of work it takes to lift a load? 5:1051 [Solar Energy] Capturing Solar Energy: Will seedlings grow bigger in a greenhouse? 5:1084 [Solar Energy] Solar Cells: Will sunlight make a motor run? 5:1087 [Static Electricity] Building an Electroscope: Which objects are electrically charged? 6:1135 [Static Electricity] Measuring a Charge: Does nylon or wool create a stronger static electric charge? 6:1139 [Structures and Shapes] Arches and Beams: Which is strongest? 6:1167 [Time] Pendulums: How do the length, weight, and swing angle of a pendulum affect its oscillation time? 6:1180 [Tropisms] Heliotropism: How does the Sun affect the movement of certain plants? 6:1201 [Vitamins and Minerals] Hard Water: Do different water sources have varying mineral content? 6:1231 [Water Properties] Adhesion: How much weight is required to break the adhesive force between an object and water? 6:1264 [Water Properties] Cohesion: Can the cohesive force of surface tension in water support an object denser than water? 6:1261 [Weather] Clouds: Will a drop in air temperature cause a cloud to form? 6:1277 [Weather] Wind: Measuring wind speed with a homemade anemometer 6:1273 MODERATE
Moderate means that the average student should find tasks outlined in the project/experiment challenging but not difficult, and that the time spent on the project/experiment may be more extensive. [Acid Rain] Acid Rain and Animals: How does acid rain affect brine shrimp? 1:5 [Acid Rain] Acid Rain and Plants: How does acid rain affect plant growth? 1:9 [Acid Rain] Acid Rain: Can acid rain harm structures? 1:12 [Adhesives] Adhesives in the Environment: Will different environmental conditions affect the properties of different adhesives? 1:26 Experiment Central, 2nd edition
ci
LEVEL OF DIFFICULTY INDEX
[Adhesives] Material Adhesion: How do various glues adhere to different materials? 1:22 [Air and Water Pollution] Pollutant Bioindicators: Can lichens provide clues to an area’s air pollution? 1:51 [Animal Defenses] Camouflage: Does an animal’s living environment relate to the color of the animal life? 1:63 [Animal Defenses] Ladybug Threats: How do ladybugs defend themselves when they feel threatened? 1:65 [Annual Growth] Lichen Growth: What can be learned from the environment by observing lichens? 1:79 [Annual Growth] Tree Growth: What can be learned from the growth patterns of trees? 1:74 [Biomes] Building a Temperate Forest Biome 1:107 [Caves] Cave Icicles: How does the mineral content of water affect the formation of stalactites and stalagmites? 1:135 [Chemical Energy] Exothermic or Endothermic: Determining whether various chemical reactions are exothermic or endothermic 1:156 [Chemical Energy] Rusting: Is the chemical reaction exothermic, endothermic, or neither? 1:152 [Chemical Properties] Chemical Patination: Producing chemical reactions on metal 1:173 [Chemical Properties] Chemical Reactions: What happens when mineral oil, water, and iodine mix? 1:170 [Chlorophyll] Plant Pigments: Can pigments be separated? 1:193 [Chlorophyll] Response to Light: Do plants grow differently in different colors of light? 1:197 [Color] Color and Flavor: How much does color affect flavor perception? 2:207 [Color] Temperature and Color: What color has the highest temperature? 2:210 [Comets and Meteors] Comet Nucleus: Linking a Comet’s Composition to its Properties. 2:218 [Comets and Meteors] Meteor Impact: How do the characteristics of a meteorite and its impact affect the shape of the crater? 2:221 [Composting/Landfills] Composting: Using organic material to grow plants 2:237 cii
Experiment Central, 2nd edition
LEVEL OF DIFFICULTY INDEX
[Crystals] Cool Crystals: How does the effect of cooling impact crystal growth? 2:252 [Crystals] Crystal Structure: Will varying shape crystals form from varying substances? 2:246 [Density and Buoyancy] Buoyancy: Does water pressure affect buoyancy? 2:264 [Density and Buoyancy] Density: Can a scale of relative density predict whether one material floats on another? 2:260 [DNA (Deoxyribonucleic Acid)] The Stuff of Life: Isolating DNA 2:289 [Dyes] Holding the Dye: How do dye fixatives affect the colorfastness of the dye? 2:304 [Earthquakes] Detecting an Earthquake: How can movement of Earth’s crust be measured? 2:314 [Electricity] Batteries: Can a series of homemade electric cells form a ‘‘pile’’ strong enough to match the voltage of a D-cell battery? 2:340 [Electricity] Electrolytes: Do some solutions conduct electricity better than others? 2:335 [Electricity] Electroplating: Using electricity to move one metal onto another metal 2:344 [Electromagnetism] Magnetism:How can a magnetic field be created and detected? 2:351 [Enzymes] Stopping Enzymes: Does temperature affect enzyme action? 2:368 [Erosion] Erosion: Does soil type affect the amount of water that runs off a hillside? 2:377 [Erosion] Plants and Erosion: How do plants affect the rate of soil erosion? 2:381 [Ethnobotany] Coiling Reeds: How does the tightness of the coil affect the ability to hold materials? 2:396 [Ethnobotany] Plants and Health: Which plants have antibacterial properties? 2:392 [Fish] Fish Breathing: How do different fish take in oxygen? 3:404 [Fish] Fish Movement: How do fins and body shape affect the movement of fish? 3:407 [Flowers] Self versus Cross: Will there be a difference in reproduction between self-pollinated and cross-pollinated plants of the same type? 3:427 Experiment Central, 2nd edition
ciii
LEVEL OF DIFFICULTY INDEX
[Fluids] Viscosity: How can temperature affect the viscosity of liquids? 3:441 [Food Preservation] Drying Foods: Does drying fruits help prevent or delay spoilage? 3:458 [Food Preservation] Sweet Preservatives: How does sugar affect the preservation of fruit? 3:454 [Food Science] Jelly and Pectin: How does acidity affect how fruit gels? 3:467 [Food Science] Rising Foods: How much carbon dioxide do different leavening agents produce? 3:470 [Food Spoilage] Preservatives: How do different substances affect the growth of mold? 3:481 [Forensic Science] Blood Patterns: How can a blood spatter help recreate the crime? 3:515 [Fossils] Fossil Formation: What are the physical characteristics of an organism that make the best fossils? 3:530 [Fungi] Living Conditions: What is the ideal temperature for yeast growth? 3:544 [Germination] Seed Scarification: Does breaking the seed shell affect germination time? 3:573 [Gravity] Gravity: How fast do different objects fall? 3:581 [Gravity] Measuring Mass: How can a balance be made? 3:585 [Greenhouse Effect] Fossil Fuels: What happens when fossil fuels burn? 3:596 [Groundwater Aquifers] Aquifers: How do they become polluted? 3:605 [Groundwater Aquifers] Groundwater: How can it be cleaned? 3:609 [Insects] Ant Food: What type of foods is one type of ant attracted to? 3:635 [Insects] Lightning Bugs: How does the environment affect a firefly’s flash? 3:638 [Light Properties] Refraction: How does the material affect how light travels? 4:666 [Materials Science] Developing Renewables: Can a renewable packing material have the same qualities as a non-renewable material? 4:691 [Microorganisms] Growing Microorganisms in a Petri Dish 4:716 civ
Experiment Central, 2nd edition
LEVEL OF DIFFICULTY INDEX
[Mixtures and Solutions] Colloids: Can colloids be distinguished from suspension using the Tyndall effect? 4:730 [Mixtures and Solutions] Suspensions and Solutions: Can filtration and evaporation determine whether mixtures are suspensions or solutions? 4:725 [Nutrition] Nutrition: Which foods contain proteins and salts? 4:764 [Optics and Optical Illusions] Optics: What is the focal length of a lens? 4:788 [Osmosis and Diffusion] Changing Sizes: What effect does molecule size have on osmosis 4:806 [Osmosis and Diffusion] Measuring Membranes: Is a plastic bag a semipermeable membrane? 4:798 [Oxidation-Reduction] Oxidation Reaction: Can acid change the color of copper? 4:820 [Oxidation-Reduction] Reduction: How will acid affect dirty pennies? 4:813 [Periodic Table] Active Metals: What metals give off electrons more readily than others? 4:838 [Periodic Table] Metals versus Nonmetals: Which areas of the periodic table have elements that conduct electricity? 4:830 [Pesticides] Natural versus Synthetic: How do different types of pesticides compare against a pest? 4:848 [Photosynthesis] Light Intensity: How does the intensity of light affect plant growth? 4:877 [Photosynthesis] Photosynthesis: How does light affect plant growth? 4:873 [Plant Anatomy] Plant Hormones: What is the affect of hormones on root and stem growth? 5:886 [Plants and Water] Transpiration: How do different environmental conditions affect plants’ rates of transpiration? 5:904 [Polymers] Polymer Properties: How are the properties of hard plastics different? 5:923 [Polymers] Polymer Slime: How will adding more of a polymer change the properties of a polymer ‘‘slime’’? 5:919 [Potential and Kinetic Energy] Using Energy: Build a roller coaster 5:934 [Renewable Energy] Capturing Wind Energy: How does the material affect the amount of wind energy harnessed? 5:944 Experiment Central, 2nd edition
cv
LEVEL OF DIFFICULTY INDEX
[Renewable Energy] Hydropower: How does water pressure affect water energy? 5:948 [Rivers] Weathering Erosion in Glaciers: How does a river make a trench? 5:957 [Rocks and Minerals] Rock Classification: Is it igneous, sedimentary, or metamorphic? 5:975 [Salinity] Density Ball: How to make a standard for measuring density 5:1000 [Separation and Identification] Identifying a Mixture: How can determining basic properties of a substance allow you to identify the substances in a mixture? 5:1039 [Simple Machines] The Screw: How does the distance between the threads of a screw affect the work? 5:1057 [Soil] Soil pH: Does the pH of soil affect plant growth? 5:1074 [Sound] Soundproofing: How do different materials affect sound? 5:1102 [Space Observation] Telescopes: How do different combinations of lenses affect the image? 6:1113 [Stars] Tracking Stars: Where is Polaris? 6:1125 [Stars] Tracking the Motion of the Planets: Can a planet be followed? 6:1128 [Storms] Forming Hailstones: How do temperature differences affect the formation of hail? 6:1158 [Structures and Shapes] Beams and Rigidity: How does the vertical height of a beam affect its rigidity? 6:1170 [Time] Water Clock: Does the amount of water in a water clock affect its accuracy? 6:1185 [Tropisms] Geotropism: Will plant roots turn toward the pull of gravity? 6:1197 [Tropisms] Phototropism: Will plants follow a maze to reach light? 6:1193 [Vegetative Propagation] Auxins: How do auxins affect plant growth? 6:1209 [Vegetative Propagation] Potatoes from Pieces: How do potatoes reproduce vegetatively? 6:1216 [Vitamins and Minerals] Vitamin C: What juices are the best sources of vitamin C? 6:1226 [Volcanoes] Model of a Volcano: Will it blow its top? 6:1240 cvi
Experiment Central, 2nd edition
LEVEL OF DIFFICULTY INDEX
[Wood] Water Absorption: How do different woods absorb water? 6:1298 [Wood] Wood Hardness: How does the hardness of wood relate to its building properties? 6:1302 MODERATE/DIFFICULT
Moderate/Difficult means that the average student should find tasks outlined in the project/experiment challenging, and that the time spent on the project/experiment may be more extensive. [Bacteria] Bacterial Growth: How do certain substances inhibit or promote bacterial growth? 1:90 [Biomes] Building a Desert Biome 1:108 [Cells] Investigating Cells: What are the differences between a multicellular organism and a unicellular organism? 1:141 [Cells] Plant Cells: What are the cell differences between monocot and dicot plants? 1:145 [Cells] Yeast Cells: How do they reproduce? 1:147 [Flowers] Sweet Sight: Can changing a flower’s nectar and color affect the pollinators lured to the flower? 3:431 [Heat] Conduction: Which solid materials are the best conductors of heat? 3:618 [Heat] Heat Capacity: Which liquids have the highest heat capacity? 3:625 [Memory] Memory Mnemonics: What techniques help in memory retention? 4:701 [Nutrition] Daily Nutrition: How nutritious is my diet? 4:766 [Plant Anatomy] Water Uptake: How do different plants differ in their water needs? 6:390 [Rocks and Minerals] Mineral Testing: What kind of mineral is it? 6:971 [Rotation and Orbits] Foucault Pendulum: How can a pendulum demonstrate the rotation of Earth? 6:985 [Salinity] Making a Hydrometer: How can salinity be measured? 6:997 [Separation and Identification] Chromatography: Can you identify a pen from the way its colors separate? 6:1034 [Solar Energy] Retaining the Sun’s heat: What substance best stores heat for a solar system? 6:1090 Experiment Central, 2nd edition
cvii
LEVEL OF DIFFICULTY INDEX
DIFFICULT
Difficult means that the average student wil probably find the tasks outlined in the project/experiment mentally and/or physically challenging, and that the time spent on the project/experiment may be more extensive. [Bacteria] Bacterial Resistance: Can bacteria gain resistance to a substance after exposure? 1:95 [DNA (Deoxyribonucleic Acid)] Comparing DNA: Does the DNA from different species have the same appearance? 2:291 [Forces] Newton’s Laws in Action: How do water bottle rockets demonstrate Newton’s laws of motion? 3:493 [Forensic Science] Fiber Evidence: How can scientific techniques be used to identify fiber? 3:511 [Life Cycles] Insects: How does food supply affect the growth rate of grasshoppers or crickets? 4:651 [Life Cycles] Tadpoles: Does temperature affect the rate at which tadpoles change into frogs? 4:647 [Optics and Optical Illusions] Optical Illusions: Can the eye be fooled? 4:791 [pH] Chemical Titration: What is required to change a substance from an acid or a base into a neutral solution? 4:865 [pH] Kitchen Chemistry: What is the pH of household chemicals? 4:861 [Polymers] Polymer Strength: What are the tensile properties of certain polymers that make them more durable than others? 5:914 [Soil] Soil Profile: What are the different properties of the soil horizons? 5:1067
cviii
Experiment Central, 2nd edition
Timetable Index
Chapter name in brackets, followed by experiment name. The numeral before the colon indicates volume; numbers after the colon indicate page number. LESS THAN 15 MINUTES
[Greenhouse Effect] Fossil Fuels: What happens when fossil fuels burn? 4:596 15 T O 2 0 M I N U T E S
[Air] Air Density: Does warm air take up less room than cool air? 1:36 [Air] Convection Currents: How can rising air cause weather changes? 1:39 [Chemosenses] Smell and Taste: How does smell affect the sense of taste? 1:186 [Density and Buoyancy] Buoyancy: Does water pressure affect buoyancy? 2:264 [Enzymes] Finding the Enzyme: Which enzyme breaks down hydrogen peroxide? 2:362 [Flight] Helicopters, Propellers, and Centripetal Force: Will it fly high? 3:148 [Fluids] Spinning Fluids: How do different fluids behave when immersed in a spinning rod? 3:444 [Heat] Convection: How does heat move through liquids? 3:622 [Light Properties] Looking for the Glow: Which objects glow under black light? 4:661 cix
TIMETABLE INDEX
[Magnetism] Electromagnets: Does the strength of an electromagnet increase with greater current? 4:678 [Nanotechnology] Nanosize Substances: How can the physical size affect the rate of reaction? 4:753 [Rocks and Minerals] Mineral Testing: What kind of mineral is it? 5:971 [Rotation and Orbits] Spinning Effects: How does the speed of a rotating object affect the way centrifugal force can overcome gravity? 5:989 [Simple Machines] Lever Lifting: How does the distance from the fulcrum affect work? 5:1055 [Simple Machines] The Screw: How does the distance between the threads of a screw affect the work? 5:1057 [Simple Machines] Wheel and Axle: How can changing the size of the wheel affect the amount of work it takes to lift a load? 5:1051 [Space Observation] Doppler Effect: How can waves measure the distance and speed of objects? 6:1118 [Static Electricity] Measuring a Charge: Does nylon or wool create a stronger static electric charge? 6:1139 [Volcanoes] Looking at a Seismograph: Can a volcanic eruption be detected? 6:1242 [Water Properties] Cohesion: Can the cohesive force of surface tension in water support an object denser than water? 6:1261 [Weather] Wind: Measuring wind speed with a homemade anemometer 6:1273 30 TO 45 MINUTES
[Annual Growth] Tree Growth: What can be learned from the growth patterns of trees? 1:74 [Caves] Cave Formation: How does the acidity of a substance affect the formation of a cave? 1:132 [Chemical Energy] Rusting: Is the chemical reaction exothermic, endothermic, or neither? 1:152 [Flight] Lift-Off: How can a glider be made to fly higher? 3:415 [Food Science] Rising Foods: How much carbon dioxide do different leavening agents produce? 3:470 [Forces] Centripetal Action: What is the relationship between distance and force in circular motion? 3:501 [Gravity] Gravity: How fast do different objects fall? 3:581 cx
Experiment Central, 2nd edition
TIMETABLE INDEX
[Gravity] Measuring Mass: How can a balance be made? 3:585 [Heat] Conduction: Which solid materials are the best conductors of heat? 3:618 [Light Properties] Refraction and Defraction: Making a rainbow 4:664 [Light Properties] Refraction: How does the material affect how light travels? 4:666 [Magnetism] Magnets: How do heat, cold, jarring, and rubbing affect the magnetism of a nail? 4:674 [Materials Science] Testing Tape: Finding the properties that allow tape to support weight. 4:688 [Memory] False Memories: How can memories be influenced? 4:705 [Mountains] Mountain Plates: How does the movement of Earth’s plates determine the formation of a mountain? 4:738 [Periodic Table] Soluble Families: How does the solubility of an element relate to where it is located on the Periodic Table? 4:835 [Rivers] Stream Flow: Does the stream meander? 5:960 [Salinity] Density Ball: How to make a standard for measuring density 5:1000 [Scientific Method] Using the Scientific Method: What are the mystery powders? 5:1009 [Solar Energy] Capturing Solar Energy: Will seedlings grow bigger in a greenhouse? 5:1084 [Solar Energy] Solar Cells: Will sunlight make a motor run? 5:1087 [Sound] Soundproofing: How do different materials affect sound? 5:1102 [Static Electricity] Building an Electroscope: Which objects are electrically charged? 6:1135 [Storms] Forming Hailstones: How do temperature differences affect the formation of hail? 6:1158 [Storms] Lightning Sparks: Explore how separating charges causes an attraction between objects 6:1152 [Storms] Tornadoes: Making a violent vortex 6:1155 [Structures and Shapes] Arches and Beams: Which is strongest? 6:1167 [Structures and Shapes] Beams and Rigidity: How does the vertical height of a beam affect its rigidity? 6:1170 [Time] Pendulums: How do the length, weight, and swing angle of a pendulum affect its oscillation time? 6:1180 Experiment Central, 2nd edition
cxi
TIMETABLE INDEX
[Time] Water Clock: Does the amount of water in a water clock affect its accuracy? 6:1185 [Vitamins and Minerals] Hard Water: Do different water sources have varying mineral content? 6:1231 [Wood] Wood Hardness: How does the hardness of wood relate to its building properties? 6:1302 1 HOUR
[Animal Defenses] Ladybug Threats: How do ladybugs defend themselves when they feel threatened? 1:65 [Bones and Muscles] Muscles: How does the strength of muscles affect fatigue over time? 1:120 [Cells] Investigating Cells: What are the differences between a multicellular organism and a unicellular organism? 1:141 [Cells] Plant Cells: What are the cell differences between monocot and dicot plants? 1:145 [Cells] Yeast Cells: How do they reproduce? 1:147 [Chemical Energy] Exothermic or Endothermic: Determining whether various chemical reactions are exothermic or endothermic 1:156 [Chemical Properties] Slime: What happens when white glue and borax mix? 1:167 [Chemosenses] Supertasters: Is there a correlation between the number of taste buds and taste perception? 1:180 [Color] Temperature and Color: What color has the highest temperature? 2:210 [Comets and Meteors] Meteor Impact: How do the characteristics of a meteorite and its impact affect the shape of the crater? 2:221 [Density and Buoyancy] Density: Can a scale of relative density predict whether one material floats on another? 2:260 [DNA (Deoxyribonucleic Acid)] The Stuff of Life: Isolating DNA 2:289 [Earthquakes] Detecting an Earthquake: How can movement of Earth’s crust be measured? 2:314 [Earthquakes] Earthquake Simulation: Is the destruction greater at the epicenter? 2:317 [Eclipses] Simulating Solar and Lunar Eclipses 2:327 cxii
Experiment Central, 2nd edition
TIMETABLE INDEX
[Electricity] Batteries: Can a series of homemade electric cells form a ‘‘pile’’ strong enough to match the voltage of a D-cell battery? 2:340 [Electricity] Electrolytes: Do some solutions conduct electricity better than others? 2:335 [Electricity] Electroplating: Using electricity to move one metal onto another metal 2:344 [Fish] Fish Breathing: How do different fish take in oxygen? 3:404 [Forensic Science] Blood Patterns: How can a blood spatter help recreate the crime? 3:515 [Fossils] Fossil Formation: What are the physical characteristics of an organism that make the best fossils? 3:530 [Insects] Ant Food: What type of foods is one type of ant attracted to? 3:635 [Materials Science] Developing Renewables: Can a renewable packing material have the same qualities as a non-renewable material? 4:691 [Mixtures and Solutions] Colloids: Can colloids be distinguished from suspension using the Tyndall effect? 4:730 [Mixtures and Solutions] Suspensions and Solutions: Can filtration and evaporation determine whether mixtures are suspensions or solutions? 4:725 [Mountains] Mountain Formations: How does the height of the mountain have an affect on desert formation? 4:741 [Nutrition] Energizing Foods: Which foods contain carbohydrates and fats? 4:761 [Nutrition] Nutrition: Which foods contain proteins and salts? 4:764 [Oceans] Currents: Water behavior in density-driven currents 4:780 [Periodic Table] Metals versus Nonmetals: Which areas of the periodic table have elements that conduct electricity? 4:830 [pH] Chemical Titration: What is required to change a substance from an acid or a base into a neutral solution? 4:865 [pH] Kitchen Chemistry: What is the pH of household chemicals? 4:861 [Polymers] Polymer Properties: How are the properties of hard plastics different? 5:923 [Polymers] Polymer Slime: How will adding more of a polymer change the properties of a polymer ‘‘slime’’? 5:919 Experiment Central, 2nd edition
cxiii
TIMETABLE INDEX
[Polymers] Polymer Strength: What are the tensile properties of certain polymers that make them more durable than others? 5:914 [Potential and Kinetic Energy] Measuring Energy: How does the height of an object affect its potential energy? 5:931 [Renewable Energy] Capturing Wind Energy: How does the material affect the amount of wind energy harnessed? 5:944 [Rocks and Minerals] Rock Classification: Is it igneous, sedimentary, or metamorphic? 5:975 [Rotation and Orbits] Foucault Pendulum: How can a pendulum demonstrate the rotation of Earth? 5:985 [Salinity] Making a Hydrometer: How can salinity be measured? 5:997 [Sound] Pitch: How does the thickness of a vibrating string affect sound? 5:1099 [Sound] Wave Length: How does the length of a vibrating string affect the sound it produces? 5:1096 [Space Observation] Telescopes: How do different combinations of lenses affect the image? 6:1113 [Vitamins and Minerals] Vitamin C: What juices are the best sources of vitamin C? 6:1226 [Weather] Clouds: Will a drop in air temperature cause a cloud to form? 6:1277 2 HOURS
[Chlorophyll] Plant Pigments: Can pigments be separated? 1:193 [Electromagnetism] Electromagnetism: How can an electromagnet be created? 2:354 [Electromagnetism] Magnetism:How can a magnetic field be created and detected? 2:351 [Ethnobotany] Coiling Reeds: How does the tightness of the coil affect the ability to hold materials? 2:396 [Fluids] Viscosity: How can temperature affect the viscosity of liquids? 3:441 [Food Science] Jelly and Pectin: How does acidity affect how fruit gels? 3:467 [Forces] Newton’s Laws in Action: How do water bottle rockets demonstrate Newton’s laws of motion? 3:493 [Forensic Science] Fiber Evidence: How can scientific techniques be used to identify fiber? 3:511 cxiv
Experiment Central, 2nd edition
TIMETABLE INDEX
[Groundwater Aquifers] Aquifers: How do they become polluted? 3:605 [Groundwater Aquifers] Groundwater: How can it be cleaned? 3:609 [Heat] Heat Capacity: Which liquids have the highest heat capacity? 3:625 [Oceans] Stratification: How does the salinity in ocean water cause it to form layers? 4:775 [Optics and Optical Illusions] Optics: What is the focal length of a lens? 4:788 [Oxidation-Reduction] Reduction: How will acid affect dirty pennies? 4:813 [Periodic Table] Active Metals: What metals give off electrons more readily than others? 4:838 [Potential and Kinetic Energy] Using Energy: Build a roller coaster 5:934 [Renewable Energy] Hydropower: How does water pressure affect water energy? 5:948 [Rivers] River Flow: How does the steepness and rate of water flow affect river erosion? 5:962 [Seashells] Classifying Seashells 5:1025 [Seashells] Shell Strength: Which shell is stronger: a clam shell or lobster shell? 5:1022 [Separation and Identification] Chromatography: Can you identify a pen from the way its colors separate? 5:1034 [Separation and Identification] Identifying a Mixture: How can determining basic properties of a substance allow you to identify the substances in a mixture? 5:1039 [Stars] Tracking Stars: Where is Polaris? 6:1125 [Water Properties] Adhesion: How much weight is required to break the adhesive force between an object and water? 6:1264 3 HOURS
[Adhesives] Adhesives in the Environment: Will different environmental conditions affect the properties of different adhesives? 1:26 [Air and Water Pollution] Pollutant Bioindicators: Can lichens provide clues to an area’s air pollution? 1:51 [Annual Growth] Lichen Growth: What can be learned from the environment by observing lichens? 1:79 Experiment Central, 2nd edition
cxv
TIMETABLE INDEX
[Comets and Meteors] Comet Nucleus: Linking a Comet’s Composition to its Properties. 2:218 [Erosion] Erosion: Does soil type affect the amount of water that runs off a hillside? 2:377 [Fish] Fish Movement: How do fins and body shape affect the movement of fish? 3:407 [Fungi] Living Conditions: What is the ideal temperature for yeast growth? 3:544 [Nanotechnology] Nanosize: How can the physical size affect a material’s properties? 4:750 [Volcanoes] Model of a Volcano: Will it blow its top? 6:124 6 HOURS
[Color] Color and Flavor: How much does color affect flavor perception? 2:207 [Dissolved Oxygen] Goldfish Breath: How does a decrease in the dissolved oxygen level affect the breathing rate of goldfish? 2:279 [Enzymes] Stopping Enzymes: Does temperature affect enzyme action? 2:368 1 DAY
[Adhesives] Material Adhesion: How do various glues adhere to different materials? 1:22 [Eclipses] Phases of the Moon: What does each phase look like? 2:329 [Enzymes] Tough and Tender: Does papain speed up the aging process? 2:365 [Fossils] Making an Impression: In which soil environment does a fossil most easily form? 3:526 [Osmosis and Diffusion] Changing Concentrations: Will a bag of salt water draw in fresh water? 4:803 [Plants and Water] Transpiration: How do different environmental conditions affect plants’ rates of transpiration? 5:904 [Plants and Water] Water Flow: How do varying solutions of water affect the amount of water a plant takes in and its turgor pressure? 5:900 [Solar Energy] Retaining the Sun’s heat: What substance best stores heat for a solar system? 5:1090 [Water Cycle] Temperature: How does temperature affect the rate of evaporation? 6:1248 [Wood] Water Absorption: How do different woods absorb water? 6:1298 cxvi
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TIMETABLE INDEX
2 D A YS
[Bacteria] Bacterial Growth: How do certain substances inhibit or promote bacterial growth? 1:90 [Flowers] Sweet Sight: Can changing a flower’s nectar and color affect the pollinators lured to the flower? 3:431 [Genetics] Genetic Traits: Will you share certain genetic traits more with family members than non-family members? 3:556 [Memory] Memory Mnemonics: What techniques help in memory retention? 4:701 [Osmosis and Diffusion] Measuring Membranes: Is a plastic bag a semipermeable membrane? 4:798 [Soil] Soil Profile: What are the different properties of the soil horizons? 5:1067 3 D A YS
[Animal Defenses] Camouflage: Does an animal’s living environment relate to the color of the animal life? 1:63 [Chemical Properties] Chemical Patination: Producing chemical reactions on metal 1:173 [Chemical Properties] Chemical Reactions: What happens when mineral oil, water, and iodine mix? 1:170 [DNA (Deoxyribonucleic Acid)] Comparing DNA: Does the DNA from different species have the same appearance? 2:291 [Dyes] Applying Dyes: How does the fiber affect the dye color? 2:301 [Dyes] Holding the Dye: How do dye fixatives affect the colorfastness of the dye? 2:304 [Ethnobotany] Plants and Health: Which plants have antibacterial properties? 2:392 [Genetics] Building a Pedigree for Taste 3:559 [Insects] Lightning Bugs: How does the environment affect a firefly’s flash? 3:638 [Oxidation-Reduction] Oxidation and Rust: How is rust produced? 4:817 5 D A YS
[Food Spoilage] Spoiled Milk: How do different temperatures of liquid affect its rate of spoilage? 3:485 [Nutrition] Daily Nutrition: How nutritious is my diet? 4:766 Experiment Central, 2nd edition
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TIMETABLE INDEX
[Osmosis and Diffusion] Changing Sizes: What effect does molecule size have on osmosis 4:806 [Water Cycle] Surface Area: How does surface area affect the rate of evaporation? 6:1253 6 D A YS
[Bacteria] Bacterial Resistance: Can bacteria gain resistance to a substance after exposure? 1:95 1 W E EK
[Acid Rain] Acid Rain and Animals: How does acid rain affect brine shrimp? 1:5 [Crystals] Crystal Structure: Will varying shape crystals form from varying substances? 2:246 [Dissolved Oxygen] Decay and Dissolved Oxygen: How does the amount of decaying matter affect the level of dissolved oxygen in water? 2:274 [Food Preservation] Drying Foods: Does drying fruits help prevent or delay spoilage? 3:458 [Food Preservation] Sweet Preservatives: How does sugar affect the preservation of fruit? 3:454 [Fungi] Decomposers: Food source for a common fungi 3:541 [Germination] Seed Scarification: Does breaking the seed shell affect germination times? 3:573 [Greenhouse Effect] Creating a Greenhouse: How much will the temperature rise inside a greenhouse? 3:592 [Optics and Optical Illusions] Optical Illusions: Can the eye be fooled? 4:791 [Oxidation-Reduction] Oxidation Reaction: Can acid change the color of copper? 4:820 [Tropisms] Heliotropism: How does the Sun affect the movement of certain plants? 6:1201 8 TO 12 DAYS
[Bones and Muscles] Bone Loss: How does the loss of calcium affect bone strength? 1:116 [Caves] Cave Icicles: How does the mineral content of water affect the formation of stalactites and stalagmites? 1:135 [Food Spoilage] Preservatives: How do different substances affect the growth of mold? 3:481 cxviii
Experiment Central, 2nd edition
TIMETABLE INDEX
[Pesticides] Moving through Water: How can pesticides affect nontarget plant life? 4:852 10 DAYS
[Acid Rain] Acid Rain: Can acid rain harm structures? 1:12 [Air and Water Pollution] Eutrophication: The effect of phosphates on water plants. 1:55 [Microorganisms] Growing Microorganisms in a Petri Dish 4:716 [Scientific Method] Using the Scientific Method: Do fruit flies appear out of thin air? 5:1013 2 WE EK S
[Acid Rain] Acid Rain and Plants: How does acid rain affect plant growth? 1:9 [Crystals] Cool Crystals: How does the effect of cooling impact crystal growth? 2:252 [Erosion] Plants and Erosion: How do plants affect the rate of soil erosion? 2:381 [Germination] Comparing Germination Times: How fast can seeds grow? 3:570 [Germination] Effects of Temperature on Germination: What temperatures encourage and discourage germination? 3:566 [Microorganisms] Microorganisms: What is the best way to grow penicillin? 4:713 [Pesticides] Natural versus Synthetic: How do different types of pesticides compare against a pest? 4:848 [Stars] Tracking the Motion of the Planets: Can a planet be followed? 6:1128 [Tropisms] Geotropism: Will plant roots turn toward the pull of gravity? 6:1197 [Weather Forecasting] Air Pressure: How can air pressure be measured? 6:1289 [Weather Forecasting] Dewpoint: When will dew form? 6:1286 3 TO 4 W EE K S
[Life Cycles] Insects: How does food supply affect the growth rate of grasshoppers or crickets? 4:651 [Life Cycles] Tadpoles: Does temperature affect the rate at which tadpoles change into frogs? 4:647 Experiment Central, 2nd edition
cxix
TIMETABLE INDEX
[Plant Anatomy] Water Uptake: How do different plants differ in their water needs? 5:890 [Rivers] Weathering Erosion in Glaciers: How does a river make a trench? 5:957 [Tropisms] Phototropism: Will plants follow a maze to reach light? 6:1193 [Vegetative Propagation] Auxins: How do auxins affect plant growth? 6:1209 [Vegetative Propagation] Potatoes from Pieces: How do potatoes reproduce vegetatively? 6:1216 4 W E EK S
[Photosynthesis] Light Intensity: How does the intensity of light affect plant growth? 4:877 [Photosynthesis] Photosynthesis: How does light affect plant growth? 4:873 6 W E EK S
[Plant Anatomy] Plant Hormones: What is the affect of hormones on root and stem growth? 5:886 [Soil] Soil pH: Does the pH of soil affect plant growth? 5:1074 6 T O 1 4 WE E KS
[Chlorophyll] Response to Light: Do plants grow differently in different colors of light? 1:197 [Flowers] Self versus Cross: Will there be a difference in reproduction between self-pollinated and cross-pollinated plants of the same type? 1:423 4 MONTHS
[Composting/Landfills] Composting: Using organic material to grow plants 2:237 [Composting/Landfills] Living Landfill: What effect do the microorganisms in soil have on the decomposition process? 2:232 6 MONTHS
[Biomes] Building a Desert Biome 1:108 [Biomes] Building a Temperate Forest Biome 1:107
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Experiment Central, 2nd edition
General Subject Index The numeral before the colon indicates volume; numbers after the colon indicate page number. Bold page numbers indicate main essays. The notation (ill.) after a page number indicates a figure.
A groups (periodic table), 4: 829 A layer (soil), 5: 1066 67, 1067 (ill.) Abscission, 1: 192 Absolute dating, 3: 525 Acceleration bottle rocket experiment, 3: 493 501, 495 (ill.), 498 (ill.), 499 (ill.) build a roller coaster experiment, 5: 934 38, 935 (ill.), 936 (ill.), 937 (ill.) centripetal force experiment, 3: 501 5, 503 (ill.) centripetal force in, 3: 493, 493 (ill.) Newtonian laws of motion on, 3: 492, 492 (ill.) of planetary orbits, 3: 579 80 Acetate, 3: 509, 511 14, 511 (ill.), 512 (ill.), 513 (ill.) Acetic acid, 1: 165, 4: 820 23, 820 (ill.), 821 (ill.), 822 (ill.) Acetone, 3: 511 14, 511 (ill.), 512 (ill.), 513 (ill.) Acid/base indicators, 4: 860 cave formation experiment, 1: 134, 134 (ill.) pH of household chemicals experiment, 4: 861 65, 861 (ill.), 863 (ill.) Acid rain, 1: 1 17, 17 (ill.) brine shrimp experiment, 1: 5 8, 7 (ill.) damage from, 1: 1 3, 4: 860 61 design an experiment for, 1: 15 16 formation of, 1: 1, 164 pH of, 1: 1, 2 (ill.), 3 (ill.), 4: 860 61, 861 (ill.)
plant growth experiment, 1: 9 12, 11 (ill.) structure damage experiment, 1: 12 15, 14 (ill.), 15 (ill.), 16 Acidity in food preservation, 3: 452 in food spoilage, 3: 478 measurement of, 1: 1 neutralization of, 1: 4 for separation and identification, 5: 1033, 1034 (ill.) of soil, 5: 1064 soil pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) See also pH Acids acid copper reduction experiment, 4: 813 17, 814 (ill.), 815 (ill.) cave formation experiment, 1: 132 35, 134 (ill.) chemical properties of, 1: 164 chemical titration experiment, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) copper color change experiment, 4: 820 23, 820 (ill.), 821 (ill.), 822 (ill.) electricity conduction by, 2: 334 pH of, 4: 859 61 uses for, 4: 859, 860 See also Lemon juice; Vinegar Acoustics, 5: 1096 Acronyms, 4: 700 Actions, reactions to every, 3: 492, 494 cxxi
GENERAL SUBJECT INDEX
Active solar energy systems, 5: 1082 Adaptation, 1: 87 Additives, food, 3: 453 Adenine, 2: 286 87 Adhesion of water, 6: 1259 61, 1260 (ill.) water adhesion and weight experiment, 6: 1264 68, 1265 (ill.), 1266 (ill.) Adhesives, 1: 19 32, 20 (ill.), 21 (ill.) design an experiment for, 1: 31 32 environmental conditions experiment, 1: 26 30, 27 (ill.), 28 (ill.), 29 (ill.) glue adherence experiment, 1: 22 25, 23 (ill.), 24 (ill.) tape strength experiment, 4: 688 91, 689 (ill.), 690 (ill.) types of, 1: 19 22 Aeration, 3: 609 12, 610 (ill.) Aerobic decomposition, 2: 231 African violets, 6: 1207, 1207 (ill.) Agar, 1: 90 95, 92 (ill.), 93 (ill.), 95 100 Agriculture, 2: 229 30, 4: 646 Air, 1: 33 44, 35 (ill.), 36 (ill.), 43 (ill.), 45 composition of, 1: 33, 34 (ill.) convection current experiment, 1: 39 42, 41 (ill.) density of, 1: 34 36, 35 (ill.), 36 (ill.), 4: 737 design an experiment for, 1: 42 44 in food spoilage, 3: 478 in soil, 5: 1063, 1064 (ill.) warm air vs. cool air experiment, 1: 36 39, 36 (ill.), 38 (ill.) water vapor content of, 6: 1247 Air currents convection, 1: 36, 36 (ill.) convection current experiment, 1: 39 42, 41 (ill.) in storm formation, 6: 1147 in weather, 6: 1272 Air masses, 1: 34 39, 35 (ill.), 36 (ill.), 38 (ill.) Air pollution, 1: 45 60, 46 (ill.) acid rain from, 1: 1 from coal, 1: 46, 164 design an experiment for, 1: 58 59 from gases, 1: 45 46 greenhouse effect, 1: 46, 47 (ill.) indoor, 1: 48 cxxii
lichen bioindicator experiment, 1: 51 55, 52 (ill.), 54 (ill.), 82 lichen bioindicators for, 1: 74 from particulate matter, 1: 45, 46 47, 59 prevention of, 1: 50 Air pressure barometric measurement of, 1: 34, 43 44, 6: 1284 build a barometer experiment, 6: 1289 92, 1290 (ill.), 1291 (ill.) flight and, 3: 422 fluids and, 3: 439, 439 (ill.) in weather, 1: 33 34, 6: 1271, 1272 (ill.) on weather maps, 6: 1285 wind and, 1: 33 34 Air resistance, 3: 581 82 Airplanes, 3: 413 15 Alcohol in bread making, 2: 359 isolation and extraction experiment, 2: 289 91, 289 (ill.), 290 (ill.) safety for handling, 2: 290, 293 species differences in DNA experiment, 2: 291 95, 293 (ill.) yeast in, 3: 540 Algae, 1: 131, 3: 538, 4: 712 chlorophyll in, 1: 191 in eutrophication, 1: 49 50, 55 58 in lichens, 1: 51, 73 74, 75 (ill.), 3: 538 photosynthesis by, 1: 74, 75 (ill.) Alkali earth metals, 4: 835 38, 835 (ill.), 837 (ill.) Alkali metals, 4: 835 38, 835 (ill.), 837 (ill.) Alkaline solutions. See Bases Alkalinity pH measurement of, 1: 1 of soil, 5: 1064 soil pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) Alleles, 3: 554 Allergies, food, 1: 187 Altair, 6: 1123 Altitude air density changes from, 1: 36, 36 (ill.), 4: 737 dissolved oxygen level changes from, 2: 272, 273 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Altocumulus clouds, 6: 1273 Altostratus clouds, 6: 1273 Alum crystal formation experiment, 2: 246 50, 246 (ill.), 249 (ill.) fixatives for colorfastness experiment, 2: 304 7, 306 (ill.), 307 (ill.) Aluminum acidity reaction of, 1: 164 build an electroscope experiment, 6: 1135 39, 1137 (ill.), 1138 (ill.) decomposition of, 2: 231 glue adherence experiment, 1: 22 25, 23 (ill.), 24 (ill.) heat conduction experiment, 3: 618 22, 620 (ill.), 621 (ill.) light refraction experiment, 4: 666 69, 666 (ill.), 667 (ill.) soundproofing materials experiment, 5: 1102 5, 1104 (ill.) Aluminum sulfate. See Alum Alzheimer’s disease, 4: 699 Amazon Basin, 1: 105 Amber, 3: 535 Amino acids, 2: 286 Ammonia comet composition experiment, 2: 218 21, 220 (ill.) copper patina experiment, 1: 173 75, 174 (ill.), 175 (ill.) pH of household chemicals experiment, 4: 861 65, 861 (ill.), 863 (ill.) safety for, 1: 173 Ammonium, 1: 157 59, 157 (ill.), 158 (ill.), 159 (ill.), 164 Amnesia, 4: 699 Ampere, Andre´ Marie, 2: 333, 334 (ill.) Amperes (amps), 2: 333 Amphibians acid rain damage to, 1: 1 2 life cycle of, 4: 645 46, 646 (ill.) tadpoles and temperature experiment, 4: 647 51, 648 (ill.), 649 (ill.), 650 (ill.) Amplitude, 5: 1095 (ill.) Anaerobic decomposition, 2: 231 Andes, 4: 735 Experiment Central, 2nd edition
Andromeda Galaxy, 6: 1124 Anemia, sickle cell, 2: 287, 3: 555 Anemometers, 6: 1273 77, 1273 (ill.), 1275 (ill.), 1283 (ill.) Angel fish, 3: 407 9, 409 (ill.), 410 Angiosperms, 3: 423, 6: 1295, 1296 (ill.) Angle of impact, 2: 221 25, 224 (ill.) Anglerfish, 4: 775 Angraecum sesquipedale, 3: 426 Aniline, 2: 300 Animal defenses, 1: 61 69, 62 (ill.), 63 (ill.) camouflage experiment, 1: 63 65, 64 (ill.) design an experiment for, 1: 68 69 ladybug experiment, 1: 65 68, 66 (ill.), 67 (ill.) overview of, 1: 61 63 Animals cave, 1: 130 31 color perception, 2: 214 desert biome, 1: 104 5 enzymes from, 2: 360 living on mountains, 4: 738 minerals from, 6: 1226 ocean, 4: 774 75 Annual growth, 1: 71 83 design an experiment for, 1: 82 83 lichen growth experiment, 1: 79 82, 81 (ill.) by lichens, 1: 72 74, 74 (ill.) tree growth experiment, 1: 74 79, 78 (ill.) by trees, 1: 71 72, 72 (ill.), 73 (ill.) See also Plant growth Antacids build a model volcano experiment, 6: 1240 42, 1240 (ill.), 1241 (ill.) chemical titration experiment, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) nanosize and reaction rate experiment, 4: 753 55, 754 (ill.), 755 (ill.) Antennae (insects), 3: 632, 632 (ill.) Anthocyanin, 1: 192 Antibiotic resistance, 1: 88 90, 95 100, 97 (ill.) Antibiotics, 1: 89 90, 3: 539 40, 4: 712 anti bacterial plant experiment, 2: 392 95, 394 (ill.), 395 (ill.) growing penicillin experiment, 4: 713 16, 713 (ill.), 715 (ill.) cxxiii
GENERAL SUBJECT INDEX
Ants, 1: 62, 3: 634 food for ants experiment, 3: 635 38, 636 (ill.), 637 (ill.) queen, 3: 633, 634 Appert, Nicholas, 3: 452 Apple jelly, 3: 467 70, 468 (ill.), 469 (ill.) Apple juice, 6: 1226 31, 1229 (ill.) Apples, falling, 3: 579, 580 Aquarium projects. See Fish tank projects Aquatic plants. See Water plants Aquifers, groundwater. See Groundwater aquifers Arches, 6: 1166 67, 1167 70, 1167 (ill.), 1168 (ill.), 1173 (ill.) Archimedes, 2: 259 (ill.) Archimedes Principle, 2: 259 Architecture. See Buildings; Structures Arctic Ocean, 4: 771 Aristotle, 5: 1006, 1013 Arm muscles, 1: 115 16, 116 (ill.) Arrhenius, Svante, 3: 589 Artesian wells, 3: 601 Ascorbic acid. See Vitamin C Asexual reproduction, 6: 1208 Ashes, volcanic, 6: 1239 Astronomers, 6: 1109 Atlantic Ocean, 4: 771 Atmosphere, 1: 33 34, 35 (ill.), 3: 589 600, 599 (ill.) Atmospheric pressure. See Air pressure Atomic clocks, 6: 1180 Atomic mass, 4: 828, 829 Atomic number, 4: 828 Atomic symbol, 4: 828 Atomic weight, 4: 827 28 Atoms chemical energy of, 1: 151 in crystals, 2: 244, 245 (ill.) density of, 2: 257 electrons in, 2: 349 in nanotechnology, 4: 747 48 shells of, 4: 829, 830, 830 (ill.) Automobiles. See Cars Autotrophs, 1: 74 Autumn, 1: 192 cxxiv
Auxins leaf/stem cuttings and auxins experiment, 6: 1209 16, 1213 (ill.), 1214 (ill.) in phototropism, 6: 1191 92, 1193, 1193 (ill.) in vegetative propagation, 6: 1208, 1209 Avery, Oswald, 2: 286 (ill.) Axles. See Wheel and axle machines
B groups (periodic table), 4: 829 B layer (soil), 5: 1067, 1067 (ill.) Babylonia, 2: 325 26, 375 Bacillus thuringiensis (Bt), 4: 844 45 Bacteria, 1: 85 102, 86 (ill.), 101 (ill.), 4: 712 anti bacterial plant experiment, 2: 392 95, 394 (ill.), 395 (ill.) bacterial resistance experiment, 1: 95 100, 97 (ill.) blue green, 1: 51 in caves, 1: 129, 131 for cleaning oil spills, 1: 50 for decomposition, 2: 273 design an experiment for, 1: 100 101 diet of, 1: 87 88 discovery of, 1: 85, 4: 711 12 DNA, 2: 286 enzymes from, 2: 362 extremophile, 1: 88, 88 (ill.), 101 in food, 1: 101 food spoilage by, 3: 477 80, 478 (ill.) growth inhibition/promotion experiment, 1: 90 95, 92 (ill.), 93 (ill.) microorganisms and decomposition experiment, 2: 233 35, 234 (ill.), 235 (ill.), 236 safety for, 1: 91, 96 spoiled milk and temperature experiment, 3: 485 88, 487 (ill.) structure of, 1: 86 87, 86 (ill.) uses for, 1: 101, 4: 712 See also Antibiotics Bacterial diseases, 1: 85 86, 3: 539 40, 4: 711 12, 712 (ill.) Bacterial resistance, 1: 88 90, 95 100, 97 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Baking powder, 3: 464 chemical titration experiment, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) leavening agents and carbon dioxide experiment, 3: 470 73, 472 (ill.), 473 (ill.), 474 Baking soda cave formation experiment, 1: 133 35, 134 (ill.) as a leavening agent, 3: 464 leavening agents and carbon dioxide experiment, 3: 470 73, 472 (ill.), 473 (ill.), 474 mystery powder identification experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) pH of household chemicals experiment, 4: 861 65, 861 (ill.), 863 (ill.) soil pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) stalagmites and stalactite experiment, 1: 135 39 unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) vinegar reaction, 1: 165 Balance/counterweight scale, 3: 585 87, 585 (ill.), 586 (ill.), 587 (ill.), 588 (ill.) Balloons, radiosonde, 6: 1283 Balls, falling, 5: 931 34, 932 (ill.), 933 (ill.) Balsa wood, 2: 257, 258, 258 (ill.), 6: 1295 Baltic Sea, 5: 996, 997 Bark (tree), 2: 299, 6: 1295 96 Barometers, 6: 1284 build a barometer experiment, 6: 1289 92, 1290 (ill.), 1291 (ill.) experiments for, 1: 43 44 mercury, 1: 34 Barometric pressure. See Air pressure Barringer Meteor Crater, 2: 217, 221 Bases (basic solutions) chemical properties of, 1: 164 chemical titration experiment, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) for neutralization, 1: 4 pH of, 4: 859 61 uses for, 4: 859, 860 Baskets, 2: 390 91, 396 99, 398 (ill.), 399 (ill.) Bats, 1: 130, 131 (ill.), 3: 425 27 Experiment Central, 2nd edition
Batteries, 2: 334 35, 4: 824 (ill.) build a multicell battery experiment, 2: 340 44, 341 (ill.), 342 (ill.) electromagnet strength experiment, 4: 678 81, 678 (ill.), 679 (ill.) Beams, 6: 1166 67, 1167 (ill.) rigidity of beams experiment, 6: 1170 72, 1171 (ill.) strength of arches vs. beams experiment, 6: 1167 70, 1168 (ill.) Bean seeds, 3: 566 70, 568 (ill.), 569 (ill.), 570 73, 572 (ill.) Bedrock, 5: 1067, 1067 (ill.) Beef aging meat experiment, 2: 365 68, 366 (ill.), 367 (ill.) ant food experiment, 3: 635 38, 636 (ill.), 637 (ill.) Bees, 3: 426, 426 (ill.) Beet dyes, 2: 301 4, 302 (ill.), 303 (ill.), 304 7, 306 (ill.), 307 (ill.) Beriberi, 4: 760, 6: 1223 24 Bernoulli, Daniel, 3: 413, 415 Betta fish, 3: 404 6, 405 (ill.) Billiard balls, 5: 911 Biodegradability, 4: 687, 691 94, 693 (ill.), 694 (ill.), 5: 914, 927 Bioindicators, 1: 51 55, 52 (ill.), 54 (ill.), 82 Bioluminescence, 3: 555, 638 42, 640 (ill.), 4: 775, 784 Biomass, 5: 942 43 Biomes, 1: 103 12 desert, 1: 103, 104 5, 104 (ill.) desert biome experiment, 1: 108 11, 109 (ill.), 110 (ill.), 111 (ill.) design an experiment for, 1: 111 12 rainforest, 1: 105 6, 105 (ill.) taiga, 1: 103 4, 104 (ill.) temperate forest experiment, 1: 106 (ill.), 107 8, 107 (ill.), 108 (ill.) Biopesticides, 4: 843, 844 46, 847 52, 851 (ill.) Birds, 1: 50, 104, 105, 3: 425 27, 4: 846 Bitter taste, 1: 177, 180, 182 86 Bivalves, 5: 1019 20, 1020 (ill.), 1021, 1025 27, 1027 (ill.) cxxv
GENERAL SUBJECT INDEX
Black ink, 1: 63, 5: 1034 39, 1036 (ill.), 1037 (ill.) Black light, 4: 661 64, 662 (ill.), 663 (ill.) Blanching, 3: 466 Bleach, 4: 812, 823 "Blending in," 1: 61 62 Blindness, 2: 205 6, 6: 1224 Blood, 1: 113, 4: 797, 798 (ill.) Blood spatter analysis, 3: 508, 509 (ill.), 515 18, 516 (ill.), 517 (ill.) Blue green bacteria, 1: 51 Blueshift, 6: 1112, 1112 (ill.) Boats, sail, 5: 944 48, 945 (ill.), 946 (ill.) BOD5, 2: 273 Boiling point, 4: 748, 752 (ill.), 5: 1034 Bonds, 1: 20, 151 Bone loss, 1: 115 20, 119 (ill.) Bone marrow, 1: 114 Bone tissue, 1: 113 Bones, 1: 113 25, 114 (ill.) apatite crystals in, 2: 243 bone loss experiment, 1: 116 20, 119 (ill.) composition and function, 1: 113 14, 115 (ill.), 116 (ill.) design an experiment for, 1: 123 25 fossil formation experiment, 3: 530 33, 532 (ill.) fossil molds of, 3: 523 muscle strength and fatigue experiment, 1: 120 23, 122 (ill.) Bony fish, 3: 401, 402, 402 (ill.), 403 (ill.) Book of Signs (Theophrastus), 6: 1283 84 Borax polymer slime experiment, 5: 919 23, 921 (ill.), 922 (ill.) white glue reaction, 1: 167 70, 168 (ill.), 169 (ill.) Boreal forest, 1: 103 4, 104 (ill.) Botany, 3: 565 Boussingault, Jean Baptiste, 2: 229 Bracken Cave, 1: 130 Brahe, Tycho, 3: 579 Braided rivers, 5: 956 Brain hearing sounds, 5: 1095 memory and, 4: 698 99, 699 (ill.) seeing optical illusions experiment, 4: 791 94, 791 (ill.), 792 (ill.), 793 (ill.) cxxvi
Bran, 4: 760 Branches, 1: 71, 74 79 Bread mold on, 3: 478 moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) yeast in, 2: 359, 3: 464 65, 465 (ill.), 540, 544 Breathing. See Respiration Bridges, 6: 1165, 1173 (ill.) rigidity of beams experiment, 6: 1170 72, 1171 (ill.) strength of arches vs. beams experiment, 6: 1167 70, 1168 (ill.) Brightness, 2: 206 7, 6: 1124, 1124 (ill.) Brine shrimp, 1: 5 8, 7 (ill.) Bromelain, 2: 368 72, 370 (ill.), 371 (ill.) Bronze Age, 2: 231, 5: 969 Browning reaction. See Maillard reaction Bt (Bacillus thuringiensis), 4: 844 45 Budding, 1: 143 44, 3: 539, 540 (ill.) Buds, 1: 72, 72 (ill.), 73 (ill.) Building materials, 2: 321 Buildings, 6: 1165 acid rain damage to, 1: 3, 12 15, 14 (ill.), 15 (ill.), 16 building properties of wood experiment, 6: 1302 6, 1304 (ill.), 1305 (ill.) earthquake destruction experiment, 2: 317 21, 319 (ill.), 320 (ill.), 321 (ill.) See also Structures Buoyancy, 2: 257 69, 257 (ill.), 259, 259 (ill.) design an experiment for, 2: 267 69 make a hydrometer experiment, 5: 997 1000, 998 (ill.), 999 (ill.) relative density and floating experiment, 2: 260 64, 262 (ill.), 263 (ill.) water pressure experiment, 2: 264 67, 265 (ill.), 266 (ill.) Burn test, 3: 513, 513 (ill.) Burrs, 4: 685, 686 (ill.) Butter, rancid, 3: 480 Butterflies life cycle of, 3: 633 34, 4: 645, 656 (ill.) mimicry by, 1: 62 pollination by, 3: 425 27 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
C layer (soil), 5: 1067, 1067 (ill.) Cabbage, purple, 2: 304 7, 306 (ill.), 307 (ill.) Cactus, 5: 899 900, 908, 908 (ill.) desert biome experiment, 1: 108 11, 109 (ill.), 110 (ill.), 111 (ill.) saguaro, 1: 105, 5: 900 water storage by, 5: 884, 884 (ill.), 885 Calcite, 1: 129 30, 4: 862 Calcium bone loss experiment, 1: 115 20, 119 (ill.) in bones, 1: 114 hard water sources experiment, 6: 1231 34, 1232 (ill.) for nutrition, 4: 761, 6: 1226 periodic table location for, 4: 829 in soil, 5: 1064 in water, 6: 1225 26 Calcium carbonate bone loss experiment, 1: 116 20, 119 (ill.) seashells of, 5: 1020, 1022 soil pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) solubility of elements experiment, 4: 835 38, 835 (ill.), 837 (ill.) stalagmites and stalactite experiment, 1: 135 39, 137 (ill.) Calcium chloride, 1: 157 59, 157 (ill.), 158 (ill.), 159 (ill.) Calories, 4: 766 69, 768 (ill.), 769 (ill.) Cambium, 6: 1296, 1297 (ill.) Camera lenses, 4: 795 (ill.) Cameras, 6: 1125 28, 1126 (ill.), 1127 (ill.) Camouflage, 1: 61 62, 63 65, 64 (ill.), 5: 1021 Canals, 2: 375 Cancellous bone, 1: 114 Canned food, 3: 452 53, 479, 479 (ill.) Capillary action, 6: 1260 Carbohydrates dietary carbohydrate sources experiment, 4: 761 64, 763 (ill.), 764 (ill.) muscle strength and fatigue experiment, 1: 123 for nutrition, 4: 760, 761 (ill.) Experiment Central, 2nd edition
Carbon, 2: 230, 246 (ill.), 4: 749, 829, 5: 912 Carbon carbon bonds, 5: 912 Carbon dating, 3: 525 Carbon dioxide in air, 1: 33 in bread making, 2: 359 burning fossil fuels experiment, 3: 596 98, 596 (ill.), 597 (ill.) in cave formation, 1: 127 29, 128 (ill.) comet composition experiment, 2: 218 21, 220 (ill.) in dry ice, 2: 220 from fish, 3: 402 greenhouse effect, 1: 46, 47 (ill.), 3: 589 90, 5: 941 from leavening agents, 3: 464 leavening agents and carbon dioxide experiment, 3: 470 73, 472 (ill.), 473 (ill.), 474 nanosize and reaction rate experiment, 4: 753 55, 754 (ill.), 755 (ill.) in plant respiration, 4: 871, 872 from power plants, 1: 46 temperature for yeast growth experiment, 3: 544 49, 547 (ill.), 548 (ill.) from yeast, 2: 359, 3: 540 41 Carbon monoxide, 1: 45, 2: 231 Carbon nanotubes, 4: 749 Carbonic acid, 1: 127 29, 128 (ill.), 132 35, 134 (ill.), 3: 544 Cardboard soundproofing, 5: 1102 5, 1104 (ill.) Cardiac muscles, 1: 115, 115 (ill.) Carlsbad Caverns, 1: 129 Carotene, 1: 192, 201 (ill.), 4: 872 Cars, 1: 3 4, 46, 3: 590 Carson, Rachel, 4: 846 Carson River, 5: 955 Cartier, Jacques, 4: 759 Cartilage, 1: 114 Cartilaginous fish, 3: 401 Casts, fossil, 3: 523, 526 29, 528 (ill.) Catalase, 2: 361 (ill.), 362 65, 363 (ill.), 364 (ill.) Catalysts, 2: 359 60, 360 (ill.) Catalytic converters, 1: 3 4 Caterpillars, 3: 633 34, 4: 645 Caventou, Joseph Biernaime, 1: 191 Caverns. See Caves cxxvii
GENERAL SUBJECT INDEX
Caves, 1: 127 40, 140 (ill.) cave formation experiment, 1: 132 35, 134 (ill.) design an experiment for, 1: 139 40 formation of, 1: 127 29, 128 (ill.) life forms in, 1: 130 31, 131 (ill.) sea, 1: 129, 129 (ill.) stalagmites and stalactite experiment, 1: 135 39, 137 (ill.) stalagmites and stalactite formation, 1: 129 30, 130 (ill.) Cell division, 1: 143 44 Cell membrane, 1: 142 bacteria, 1: 86, 87 (ill.) diffusion through, 4: 797, 798 (ill.) osmosis through, 4: 798, 5: 898 Cell nucleus, 1: 86, 142 43, 2: 285, 289 91, 289 (ill.), 290 (ill.) Cell theory, 1: 141 42 Cells, 1: 141 50, 142 (ill.) design an experiment for, 1: 148 50 microscopes for, 1: 141, 141 (ill.) monocot vs. dicot plant experiment, 1: 145 47, 145 (ill.), 146 (ill.), 147 (ill.), 148 multicellular/unicellular experiment, 1: 144 45, 144 (ill.) osmosis, 5: 898 99, 898 (ill.), 899 (ill.) reproduction of, 1: 143 44 structure of, 1: 142, 142 (ill.) yeast reproduction experiment, 1: 147 48, 147 (ill.), 148 (ill.), 149 (ill.), 150 Cellulose, 4: 872 Cement, contact/rubber, 1: 20, 22 25 Centrifugal force, 5: 983 83, 983 (ill.), 989 92, 990 (ill.) Centrifuge, 4: 724 25 Centripetal force, 3: 492 93, 493 (ill.) distance/force relationship experiment, 3: 501 5, 503 (ill.) helicopter and propeller experiment, 3: 418 21, 418 (ill.), 419 (ill.), 420 (ill.) orbits and, 3: 493, 504 (ill.), 505 Ceramics, 4: 686 Cerebral cortex, 4: 698 99, 699 (ill.) CFCs (Chlorofluorocarbons), 1: 46 Chain, Ernst, 3: 539 40 cxxviii
Chalk acid rain damage to, 1: 12 15, 14 (ill.), 15 (ill.), 16 cave formation experiment, 1: 132 35, 134 (ill.) hard water sources experiment, 6: 1231 34, 1232 (ill.) solubility of elements experiment, 4: 835 38, 835 (ill.), 837 (ill.) Chanute, Octave, 3: 414 Chase, Martha, 2: 286 Chemical energy, 1: 151 61, 152 (ill.) definition of, 1: 151, 5: 929 design an experiment for, 1: 160 61 endothermic vs. exothermic experiment, 1: 156 60, 157 (ill.), 158 (ill.), 159 (ill.) production of, 1: 151 52 rusting experiment, 1: 152 56, 155 (ill.) Chemical pesticides, 4: 843 44, 844 (ill.), 848 52, 851 (ill.) Chemical properties, 1: 163 76, 164 (ill.), 165 (ill.), 4: 687 in chemical reactions, 1: 163 66, 164 (ill.) copper patina experiment, 1: 173 75, 174 (ill.), 175 (ill.) design an experiment for, 1: 175 76 mineral oil, water and iodine experiment, 1: 170 73, 170 (ill.), 171 (ill.), 172 (ill.) white glue and borax experiment, 1: 167 70, 168 (ill.), 169 (ill.) Chemical reactions chemical properties in, 1: 163 66, 164 (ill.) copper patina experiment, 1: 173 75, 174 (ill.), 175 (ill.) definition of, 1: 163 design an experiment for, 1: 160 61, 175 76 endothermic, 1: 151, 152, 165 endothermic vs. exothermic experiment, 1: 156 60, 157 (ill.), 158 (ill.), 159 (ill.) energy from, 1: 151 enzymes in, 2: 359 60, 360 (ill.), 361 (ill.), 362 65, 363 (ill.), 364 (ill.) examples of, 1: 164 exothermic, 1: 151 52, 152 (ill.), 165, 165 (ill.) in food spoilage, 3: 451 of leavening agents, 3: 464 65 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
mineral oil, water and iodine experiment, 1: 170 73, 170 (ill.), 171 (ill.), 172 (ill.) mystery powder identification experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) nanosize and reaction rate experiment, 4: 753 55, 754 (ill.), 755 (ill.) process of, 1: 164 65 rusting experiment, 1: 152 56, 155 (ill.) safety for, 1: 158 synthesis, 1: 163 taste as, 1: 179 white glue and borax experiment, 1: 167 70, 168 (ill.), 169 (ill.) Chemosenses, 1: 177 90 design an experiment for, 1: 189 90 smell, 1: 177, 179 80, 179 (ill.), 180 (ill.) smell taste relationship experiment, 1: 186 89, 187 (ill.) supertaster experiment, 1: 180 86, 184 (ill.) taste, 1: 177 79, 178 (ill.) Chili peppers, 4: 848 52, 851 (ill.) China, 2: 389, 6: 1123 Chitin exoskeleton, 5: 1020 21, 1022 25, 1023 (ill.), 1024 (ill.), 1025 (ill.) Chloride, 5: 995, 6: 1226 Chlorine, 4: 812 Chlorofluorocarbons (CFCs), 1: 46 Chlorophyll, 1: 191 201, 191 (ill.) color change from cooking, 3: 465 66 color change in leaves, 1: 192, 192 (ill.), 201 (ill.) in cyanobacteria, 1: 74 design an experiment for, 1: 200 201 light colors and plant growth experiment, 1: 197 200, 197 (ill.), 199 (ill.), 200 (ill.) in photosynthesis, 1: 191 201, 191 (ill.), 4: 871 72, 5: 884 85 pigment separation experiment, 1: 193 97, 195 (ill.), 196 (ill.) Chloroplasts, 1: 191, 4: 871 72 Chromatography, 5: 1032 33, 1034 (ill.) paper chromatography and ink experiment, 5: 1034 39, 1036 (ill.), 1037 (ill.) plant pigment separation experiment, 1: 193 97, 195 (ill.), 196 (ill.) Chromium, 6: 1226 Experiment Central, 2nd edition
Chromosomes, 3: 553 54, 554 (ill.) Chrysalis, 3: 634 Cilia, 1: 179 Circles, pi of, 4: 701 4, 701 (ill.), 702 (ill.), 703 (ill.) Circular motion, 3: 492 93, 493 (ill.), 501 5, 503 (ill.) Cirrocumulus clouds, 6: 1273 Cirrostratus clouds, 6: 1273 Cirrus clouds, 6: 1272, 1273 Citric acid, 2: 334, 340 44, 341 (ill.), 342 (ill.) Clam shells, 5: 1022 25, 1023 (ill.), 1024 (ill.), 1025 (ill.) Clay density of, 2: 257, 258, 258 (ill.) in soil, 5: 1065, 1066, 1066 (ill.) soil horizon properties experiment, 5: 1067 73, 1071 (ill.), 1072 (ill.) soil type and runoff experiment, 2: 377 80, 378 (ill.), 379 (ill.) Clean Air Act, 1: 50 Clean Water Act, 1: 50 Cleaning products, 1: 164 Climate, 4: 741 44, 742 (ill.), 743 (ill.), 6: 1271 Climate change, 1: 46, 72, 3: 589 Climbing plants, 6: 1192, 1205 (ill.) Clocks, 6: 1177 78 atomic, 6: 1180 pendulum, 6: 1178 water, 6: 1177, 1177 (ill.), 1185 88, 1187 (ill.) Clostridium, 3: 478 Clouds, 6: 1271, 1272 73 formation of, 6: 1147 48, 1148 (ill.), 1272 funnel, 6: 1150 51, 1150 (ill.) lightning formation in, 6: 1135 temperature and cloud formation experiment, 6: 1277 80 types of, 6: 1272 73, 1272 (ill.) Coagulation, 3: 609 12, 610 (ill.), 4: 724 Coal, 1: 1, 3, 46, 164 Coatings, 4: 749 Cohesion, 6: 1259 61, 1261 64, 1261 (ill.), 1263 (ill.), 1268 (ill.) Coiling reeds, 2: 396 99, 398 (ill.), 399 (ill.) Cold fronts, 1: 35, 6: 1285 Cold packs, 1: 152, 152 (ill.), 160, 161 (ill.) cxxix
GENERAL SUBJECT INDEX
Cold temperature adhesives experiment, 1: 26 30, 27 (ill.), 28 (ill.), 29 (ill.) cool temperature and crystal growth experiment, 2: 250 53, 252 (ill.) for food preservation, 3: 453, 453 (ill.), 479 80 magnetic strength effect experiment, 4: 674 78, 674 (ill.), 676 (ill.) mountain altitude and, 4: 737 Coliform bacteria, 3: 485 Collagen, 1: 114, 2: 368 72, 370 (ill.), 371 (ill.) Colloids, 4: 723 24, 724 (ill.), 725, 725 (ill.) separation of, 4: 724 25 Tyndall effect experiment, 4: 730 32, 731 (ill.), 732 (ill.) Colonies, bacteria, 1: 87 Color blindness, 2: 205 6 Colorfastness of dyes, 2: 300, 304 7, 306 (ill.), 307 (ill.) Colors, 2: 203 14, 203 (ill.), 204 (ill.), 205 (ill.) as animal defenses, 1: 65 68, 66 (ill.), 67 (ill.) animals perception of, 2: 214 camouflage, 1: 61 62, 63 65, 64 (ill.) cooking changes in, 3: 465 66 copper color change experiment, 4: 820 23, 820 (ill.), 821 (ill.), 822 (ill.) design an experiment for, 2: 213 14 in dyes, 5: 1033 fiber type and dye color experiment, 2: 301 4, 302 (ill.), 303 (ill.) heat absorption and reflection by, 3: 617 how we perceive them, 2: 205 6, 205 (ill.) hue, saturation and brightness of, 2: 206 7, 214 interference fringes, 4: 660 leaves changing, 1: 192, 192 (ill.), 200 (ill.) light colors and plant growth experiment, 1: 197 200, 197 (ill.), 198 (ill.), 199 (ill.), 4: 873 77, 875 (ill.), 876 (ill.) make a rainbow experiment, 4: 664 65, 664 (ill.), 665 (ill.) in nanotechnology, 4: 748 overview, 2: 203 7 paper chromatography and ink experiment, 5: 1034 39, 1036 (ill.), 1037 (ill.) pollinators attracted by, 3: 426, 431 35, 433 (ill.) primary, 2: 205 in separation and identification, 5: 1033 cxxx
taste perception experiment, 2: 207 10, 208 (ill.), 209 (ill.) temperature of different colors experiment, 2: 210 12, 211 (ill.), 212 (ill.), 213 testing mineral characteristics experiment, 5: 971 75, 973 (ill.), 974 (ill.) of visible light, 6: 1112 See also Pigments Columbus, Christopher, 3: 462 Coma (comet), 2: 216 Combustion, 1: 152, 3: 596 98, 596 (ill.), 597 (ill.) Comets and meteors, 2: 215 27, 216 (ill.), 217 (ill.), 218 (ill.) composition and properties experiment, 2: 218 21, 220 (ill.) composition of, 2: 215, 216, 216 (ill.) crater shape experiment, 2: 221 25, 224 (ill.) craters from, 2: 217, 218 (ill.) design an experiment for, 2: 225 27 models of, 2: 227 orbital path of, 2: 215 16, 216 (ill.) Complex craters, 2: 217, 218 (ill.) Composting, 2: 229 41, 230 (ill.) design an experiment for, 2: 239 40 microorganisms and decomposition experiment, 2: 232 35, 234 (ill.), 235 (ill.) organic waste for plant growth experiment, 2: 235 39, 236 (ill.), 238 (ill.), 239 (ill.) process of, 2: 230, 230 (ill.), 231 (ill.) Compound eyes, 3: 632 Compound microscopes, 1: 141, 141 (ill.) Compressional strength, 4: 687, 687 (ill.) Computers, 4: 750, 6: 1283, 1285 Concave lens, 4: 788 91, 788 (ill.), 6: 1110, 1113 17, 1114 (ill.), 1116 (ill.) Condensation, 6: 1272 Conduction conductivity of elements experiment, 4: 830 35, 833 (ill.) of electricity, 4: 687, 6: 1133 of heat, 3: 615 16 heat conduction experiment, 3: 618 22, 620 (ill.), 621 (ill.) Cones (eye), 2: 205, 205 (ill.) Confined aquifers, 3: 601, 603 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Conifers, 1: 103, 104 (ill.), 6: 1295 Conservation of energy, 5: 1047 Constellations, 6: 1124 Contact cement, 1: 20 Continental drift, 6: 1237 38 Contractions, muscle, 1: 115 16, 116 (ill.), 120 23, 122 (ill.) Control experiment, 5: 1007 Convection box, 1: 44 Convection currents in air, 1: 36, 36 (ill.) air currents experiment, 1: 39 42, 41 (ill.) for heat transfer, 3: 615, 616 ocean currents experiment, 4: 780 83, 782 (ill.) in oceans, 4: 773, 774 (ill.) in water, 1: 44 Convex lens, 4: 788 91, 788 (ill.), 6: 1110, 1113 17, 1114 (ill.), 1116 (ill.) Cooking, 1: 194, 3: 463 64, 465 66 Cool air, 6: 1147 48, 1271 convection current experiment, 1: 39 42, 41 (ill.) transpiration rate and environment experiment, 5: 904 7, 906 (ill.) warm air vs. cool air experiment, 1: 36 39, 36 (ill.), 38 (ill.) See also Cold temperature Copernicus, Nicolaus, 5: 981, 6: 1178 Copper acid copper reduction experiment, 4: 813 17, 814 (ill.), 815 (ill.) conductivity of, 6: 1133 construct a multicell battery experiment, 2: 340 44, 341 (ill.), 342 (ill.) copper color change experiment, 4: 820 23, 820 (ill.), 821 (ill.), 822 (ill.) electrons released by metals experiment, 4: 838 40, 840 (ill.), 841 (ill.), 842 electroplating experiment, 2: 344 45, 344 (ill.), 345 (ill.) heat conduction experiment, 3: 618 22, 620 (ill.), 621 (ill.) hydrochloric acid reaction, 1: 165 for nutrition, 6: 1226 patina reaction experiment, 1: 173 75, 174 (ill.), 175 (ill.) Experiment Central, 2nd edition
Copper Age, 5: 969 Coprolites, 3: 524 Coral snakes, 1: 62 Coriolis, Gustave Gaspard, 5: 984 Coriolis force, 5: 984 85 Corn, genetically engineered, 4: 845, 846 (ill.) Corn oil, 5: 942 Cornstarch, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) Corona, 2: 326 Corrosion. See Rusting Cotton, 3: 508 Cotyledons, 3: 566, 566 (ill.) Counterweights, 3: 585 87, 585 (ill.), 586 (ill.), 587 (ill.), 588 (ill.) Cowry shell, 5: 1021 Cows, 1: 48 Craters, meteor impact, 2: 217, 218 (ill.), 221 25, 224 (ill.), 227 Cream heat capacity, 3: 625 28, 626 (ill.), 627 (ill.), 628 (ill.) Cream of tarter. See Tartaric acid Crest, 4: 773, 774 (ill.) Crick, Francis, 2: 286 87, 287 (ill.) Crickets, 4: 651 55, 653 (ill.), 654 (ill.) Crime scene blood spatter analysis experiment, 3: 515 18, 516 (ill.), 517 (ill.) DNA fingerprinting, 2: 296, 3: 509 10, 510 (ill.) forensic techniques for, 3: 507 11 Cross pollination, 3: 424 25, 425 (ill.), 427 31, 430 (ill.) Crust. See Earth’s crust Crustaceans, 5: 1020 21, 1022 (ill.) classifying seashells experiment, 5: 1025 27, 1027 (ill.) strength of shells experiment, 5: 1022 25, 1023 (ill.), 1024 (ill.), 1025 (ill.) Crustose lichens, 1: 52, 52 (ill.) Crystal lattice, 2: 243 Crystals, 2: 243 55, 246 (ill.) artificial, 2: 245 46 cool temperature and crystal growth experiment, 2: 250 53, 252 (ill.) design an experiment for, 2: 254 55 cxxxi
GENERAL SUBJECT INDEX
formation of, 2: 245 46 forming different crystal shapes experiment, 2: 246 50, 246 (ill.), 249 (ill.), 254 (ill.) shape and structure of, 2: 243, 244 45, 244 (ill.), 245 (ill.), 254 (ill.) uses for, 2: 243 44, 244 (ill.) Cultures (social), 2: 389, 391 Cumulonimbus clouds, 6: 1148, 1273 See also Thunderstorms Cumulus clouds, 6: 1272, 1273 Curing food, 3: 452 Currents. See Air currents; Convection currents; Ocean currents Curves, 5: 984 85 Cuttle fish, 1: 63 Cyanoacrylate glue, 1: 20, 21, 22 25, 24, 24 (ill.) Cyanobacteria, 1: 74, 75 (ill.) Cytology, 1: 142 Cytoplasms, 1: 86, 142 Cytosine, 2: 286 87
D cell batteries, 2: 334 35, 340 44, 341 (ill.), 342 (ill.) da Vinci, Leonardo 3: 413, 422 (ill.), 6: 1247 Daily Value, 4: 767 Darwin, Charles, 6: 1191, 1191 (ill.), 1209 Data recording, 1: 16, 31, 43 Dating techniques, 3: 524 25 Days, 6: 1175, 1176 DDT (Dichlorodiphenyltrichloroethane), 4: 846, 847 Dead zones, 2: 271, 273 Decanting, 4: 724 Decay. See Decomposition Decibels, 5: 1096 Deciduous trees, 1: 107 8, 107 (ill.), 192 Decomposition aerobic, 2: 231 anaerobic, 2: 231 bacteria for, 1: 85, 101 (ill.), 2: 273 BOD5 needed for, 2: 273 chemical reaction, 1: 163 in composting, 2: 229 30 cxxxii
decay and dissolved oxygen changes experiment, 2: 274 79, 276 (ill.), 277 (ill.) dissolved oxygen level changes from, 2: 272 73, 273 74 in fossil formation, 3: 522 23, 522 (ill.) fungi for, 3: 537, 538, 538 (ill.) in landfills, 2: 231, 232 35, 234 (ill.), 235 (ill.) in radioactive decay, 3: 525, 6: 1238 yeast decomposition experiment, 3: 541 43, 543 (ill.) Deep ocean currents, 4: 773 Deep sea life, 4: 775 Defense mechanisms. See Animal defenses Deficiency diseases, 6: 1223, 1224 Defraction grating, 4: 664 65, 664 (ill.), 665 (ill.) Democritus, 6: 1123 Denatured proteins, 3: 463 Density, 2: 257 69, 257 (ill.), 259 (ill.) of air, 1: 34 36, 35 (ill.), 36 (ill.), 4: 737 of balsa wood, 2: 257, 258, 258 (ill.), 6: 1295 of clay, 2: 257, 258, 258 (ill.) convection current experiment, 1: 39 42, 41 (ill.) definition of, 1: 36, 2: 257 density ball measurement experiment, 5: 1000 1003, 1001 (ill.), 1002 (ill.) design an experiment for, 2: 267 69 of fluids, 3: 439 mountain altitude and, 4: 737 ocean convection currents experiment, 4: 780 83, 782 (ill.) relative, 2: 258 59, 258 (ill.), 260 64, 262 (ill.), 263 (ill.) relative density and floating experiment, 2: 260 64, 262 (ill.), 263 (ill.) salinity and, 4: 772 salinity and stratification experiment, 4: 775 80, 778 (ill.) of seawater, 4: 772 temperature and, 4: 772 warm air vs. cool air experiment, 1: 34 39, 35 (ill.), 36 (ill.) water pressure and buoyancy experiment, 2: 264 67, 265 (ill.), 266 (ill.) of wood, 6: 1295 Density ball, 5: 1000 1003, 1001 (ill.), 1002 (ill.) Density driven currents. See Convection currents Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Deoxyribonucleic acid. See DNA Dependent variable, 5: 1008 Desert biome, 1: 103, 104 5, 104 (ill.) desert biome experiment, 1: 108 11, 109 (ill.), 110 (ill.), 111 (ill.) mountains and desert formation experiment, 4: 741 44, 742 (ill.), 743 (ill.) Desert plants, 1: 105, 5: 898, 899 900, 908, 908 (ill.) Detergents action of, 6: 1260 borax in, 1: 167 DNA isolation and extraction experiment, 2: 289 91, 289 (ill.), 290 (ill.) enzymes in, 2: 362 eutrophication from, 1: 55 species differences in DNA experiment, 2: 291 95, 293 (ill.) Deveron River, 5: 956 Dewpoint temperature, 6: 1285 (ill.), 1286 89, 1287 (ill.), 1288 (ill.) Diamonds, 2: 243, 244, 246 (ill.), 4: 747, 749, 750 (ill.) Dichlorodiphenyltrichloroethane (DDT), 4: 846, 847 Dicot plants, 1: 145 47, 145 (ill.), 146 (ill.), 147 (ill.), 148 Diesel vehicles, 1: 46 Diet of bacteria, 1: 87 88 dietary carbohydrate and fat sources experiment, 4: 761 64, 763 (ill.), 764 (ill.) dietary proteins and salt sources experiment, 4: 764 66, 765 (ill.), 766 (ill.) how good is my diet experiment, 4: 766 69, 768 (ill.), 769 (ill.) vitamins and minerals in, 6: 1226, 1235 (ill.) See also Food; Nutrition Diffraction of light, 4: 660 Diffusion. See Osmosis and diffusion Digestion, 1: 85, 164, 2: 359, 360 Digital pH meter, 4: 860, 860 (ill.) Dimples, 3: 554 55, 556 59, 558 (ill.), 559 (ill.) Dinosaurs, 1: 85 Dioscorides, 2: 389 Dirt. See Soil Experiment Central, 2nd edition
Diseases, 1: 85 86, 86, 88 90, 3: 539 Dishwasher detergents. See Detergents Disinfection, 3: 609 12, 610 (ill.) Dissolved oxygen, 2: 271 84, 272 (ill.), 273 (ill.), 274 (ill.) decay and dissolved oxygen changes experiment, 2: 274 79, 276 (ill.), 277 (ill.) design an experiment for, 2: 282 84 factors effecting levels of, 2: 271 73 goldfish breathing rate experiment, 2: 279 84, 281 (ill.), 282 (ill.), 283 Distance, 3: 501 5, 503 (ill.), 5: 1047 Distillation, 4: 724, 725 (ill.) DNA (Deoxyribonucleic acid), 2: 285 97, 286 (ill.), 295 (ill.), 3: 553 54 bacteria, 1: 86, 87 cell nucleus, 1: 142 43 design an experiment for, 2: 295 96 of different species, 2: 287 88 isolation and extraction experiment, 2: 289 91, 289 (ill.), 290 (ill.) mutations, 3: 555 replication of, 2: 287, 288 (ill.) sequencing, 2: 287 88, 295 (ill.), 3: 553 species differences in DNA experiment, 2: 291 95, 293 (ill.) structure of, 2: 286 87, 287 (ill.), 3: 554 (ill.) DNA fingerprinting, 2: 296, 3: 509 10, 510 (ill.), 562 DNA transformation, 2: 296 Dolphins, 3: 402 Dominant inheritance, 3: 554 55 Doppler effect, 6: 1111, 1112, 1112 (ill.), 1118 20, 1119 (ill.) Double acting baking powder, 3: 464, 470 73, 472 (ill.), 473 (ill.), 474 Double helix structure, 2: 286 87, 287 (ill.), 3: 554 (ill.) Dried food, 3: 451, 479, 479 (ill.) food drying experiment, 3: 458 61, 458 (ill.), 459 (ill.), 460 (ill.) process of, 3: 453 Drinking water, 3: 604, 605 9, 608 (ill.), 609 12, 610 (ill.) Drugs, plant based, 2: 389 90, 390 (ill.) See also Antibiotics cxxxiii
GENERAL SUBJECT INDEX
Dry cell batteries, 2: 334 Dry environments, 5: 899 900 See also Desert Dry ice, 2: 220, 6: 1158 61, 1159 (ill.), 1160 (ill.), 1161 (ill.), 1162 Dung, 3: 524 Dust in cloud formation, 6: 1148 in comets, 2: 218 21, 220 (ill.) in star formation, 6: 1123 24 Dust Bowl, 2: 375, 375 (ill.) Dust tail (comet), 2: 216 Dutchman’s pipe, 3: 427 Dyes, 2: 299 309, 299 (ill.), 300 (ill.) colorfastness experiment, 2: 304 7, 306 (ill.) design an experiment for, 2: 308 9 fiber type and dye color experiment, 2: 301 4, 302 (ill.), 303 (ill.) fixatives for, 2: 300 301, 300 (ill.), 304 7, 306 (ill.), 307 (ill.) natural, 2: 299, 301 4, 302 (ill.), 303 (ill.), 304 7, 306 (ill.), 307 (ill.), 391 separation of colors in, 5: 1033 synthetic, 2: 299 300, 304 7, 306 (ill.), 307 (ill.) Dynamic equilibrium, 4: 798
Eardrum, 5: 1095, 1106 (ill.) Earlobes, 3: 556 59, 558 (ill.), 559 (ill.) Ears, 3: 403, 5: 1095, 1106 (ill.) Earth centrifugal force and gravity experiment, 5: 989 92, 990 (ill.) circumference of, 5: 985 formation of, 5: 982 83 geologic history of, 5: 969 70, 970 (ill.) gravity, 3: 579, 580 pendulum rotation experiment, 5: 985 89, 988 (ill.) rotation and orbit of, 5: 981 85, 982 (ill.), 983 (ill.), 984 (ill.), 985 (ill.), 986 (ill.) Earthquakes, 2: 311 23, 322 (ill.) build a seismograph experiment, 2: 314 16, 315 (ill.), 316 (ill.) cxxxiv
design an experiment for, 2: 322 23 epicenter destruction experiment, 2: 317 21, 319 (ill.), 320 (ill.), 321 (ill.) epicenter of, 2: 312 measurement of, 2: 312 13 Earth’s axis, 5: 982, 983 Earth’s core, 5: 969 70, 6: 1238 Earth’s crust, 5: 970 earthquake movement experiment, 2: 314 16, 315 (ill.), 316 (ill.) in mountain formation, 4: 735 37, 737 (ill.) mountain formation experiment, 4: 738 41, 739 (ill.), 740 (ill.) Earth’s mantle, 5: 970, 6: 1238 Earthworms, 2: 230, 231 (ill.) Echinoderms, 5: 1025 27, 1027 (ill.) Eclipses, 2: 325 32, 325 (ill.) design an experiment for, 2: 330 32 eclipse model experiment, 2: 327 29, 328 (ill.), 329 (ill.) history of, 2: 325 26 lunar, 2: 326, 326 (ill.), 327 29, 328 (ill.), 329 (ill.) phases of the moon experiment, 2: 329 30, 330 (ill.), 331 (ill.) solar, 2: 325 29, 325 (ill.), 328 (ill.), 329 (ill.) Ecosystem, 2: 381, 4: 737 38 See also Biomes Eels, electric, 1: 63, 63 (ill.) Effort, 5: 1047 Egg whites, 3: 465, 465 (ill.) Eggs, 4: 806 9, 808 (ill.), 809 (ill.) Eggshells, 4: 806 9, 808 (ill.), 809 (ill.), 846, 5: 1019 Egyptians, 2: 389, 5: 1048, 6: 1175, 1177 Einstein, Albert, 6: 1179 Elasticity, 2: 321, 5: 912 Electric eels, 1: 63, 63 (ill.) Electric motors, 2: 358 (ill.), 5: 1087 89, 1088 (ill.), 1089 (ill.) Electric power plants, 1: 1, 46, 3: 590 Electricity, 2: 333 47, 334 (ill.) conduction of, 4: 687, 6: 1133 conductivity of elements experiment, 4: 830 35, 833 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
construct a multicell battery experiment, 2: 340 44, 341 (ill.), 342 (ill.) definition of, 5: 929 design an experiment for, 2: 346 47 electrolyte solution experiment, 2: 335 40, 337 (ill.), 338 (ill.), 339 (ill.) electromagnet creation experiment, 2: 354 57, 354 (ill.), 356 (ill.) electromagnet strength experiment, 4: 678 81, 678 (ill.), 679 (ill.) electroplating experiment, 2: 344 45, 344 (ill.), 345 (ill.) magnetic field creation experiment, 2: 351 54, 353 (ill.) in magnetism, 2: 349 50, 4: 672 73 production of, 2: 333 34, 349 from renewable sources, 5: 941 43 safety for, 2: 352, 358 from solar energy, 5: 1083 Volta Pile, 2: 335 (ill.), 344 See also Static electricity Electrodes, 2: 333, 334 Electrolytes construct a multicell battery experiment, 2: 340 44, 341 (ill.), 342 (ill.) for electricity conduction, 2: 333 34 electrolyte solution experiment, 2: 335 40, 337 (ill.), 338 (ill.), 339 (ill.) Volta Pile, 2: 344 Electromagnetic spectrum, 2: 203, 350, 350 (ill.), 4: 659, 660 (ill.), 787 Electromagnetic waves, 2: 203, 204 5, 204 (ill.), 350, 350 (ill.), 3: 616 17 Electromagnetism, 2: 349 58, 349 (ill.), 350 (ill.), 357 (ill.), 358 (ill.), 4: 672 73, 681 (ill.) design an experiment for, 2: 356 57 electricity in, 2: 349 50, 4: 672 73 electromagnet creation experiment, 2: 354 57, 354 (ill.), 356 (ill.) electromagnet strength experiment, 4: 678 81, 678 (ill.), 679 (ill.) magnetic field creation experiment, 2: 351 54, 353 (ill.) production of, 2: 349 50 Electronics, 4: 750 Experiment Central, 2nd edition
Electrons in electricity, 2: 333, 349 electrons released by metals experiment, 4: 838 40, 840 (ill.), 841 (ill.), 842 in oxidation reduction reactions, 4: 811 in static electricity, 6: 1133 35, 1134 (ill.) Electrophoresis, gel, 3: 562 Electroplating, 2: 335, 344 45, 344 (ill.), 345 (ill.) Electroscope, 6: 1135 39, 1137 (ill.), 1138 (ill.), 1140 Electrostatic cleaners, 4: 724 Elements conductivity of elements experiment, 4: 830 35, 833 (ill.) periodic table of, 4: 827 42 properties of, 4: 828 solubility of elements experiment, 4: 835 38, 835 (ill.), 837 (ill.) Elevation. See Altitude Elliptical orbits, 3: 579, 5: 981 Elongation, 5: 912 13, 915, 919 Embryos, plant, 3: 565 Emeralds, 2: 243 Endoskeleton, 3: 530 Endothermic reactions, 1: 151, 152, 165 from cold packs, 1: 152, 152 (ill.), 160, 161 (ill.) design an experiment for, 1: 160 61 vs. exothermic, 1: 156 60, 157 (ill.), 158 (ill.), 159 (ill.) rusting experiment, 1: 152 56, 155 (ill.) Energy conservation of, 5: 1047 food, 1: 160 laws of, 5: 929 32 See also Chemical energy; Heat; Kinetic energy; Potential energy; Renewable energy; Solar energy Energy Information Administration, 2: 231 Entomology, 3: 631 Environmental conditions adhesives experiment, 1: 26 30, 27 (ill.), 28 (ill.), 29 (ill.) camouflage experiment, 1: 63 65, 64 (ill.) extreme, 1: 88, 101 pollution effects, 1: 45 cxxxv
GENERAL SUBJECT INDEX
Environmental Protection Agency (EPA), 2: 271 Enzymes, 2: 359 73 aging meat experiment, 2: 365 68, 366 (ill.), 367 (ill.) in chemical reactions, 2: 359 60, 360 (ill.), 361 (ill.), 362 65, 363 (ill.), 364 (ill.) design an experiment for, 2: 372 73 in digestion, 2: 359, 360 discovery of, 2: 359 60 DNA isolation and extraction experiment, 2: 289 91, 289 (ill.), 290 (ill.) hydrogen peroxide break down experiment, 2: 361 (ill.), 362 65, 363 (ill.), 364 (ill.) production of, 2: 360 62 species differences in DNA experiment, 2: 291 95, 293 (ill.) temperature and enzyme action experiment, 2: 368 72, 370 (ill.), 371 (ill.) EPA (Environmental Protection Agency), 2: 271 Epicenter, 2: 312, 317 21, 319 (ill.), 320 (ill.), 321 (ill.) Epiphytes, 5: 883 84 Epoxies, 1: 20 Epsom salts, 1: 135 39, 2: 246 50, 246 (ill.), 249 (ill.) Equator, 5: 985 Equilibrium, 4: 798, 6: 1165 66 Erosion, 2: 375 88, 375 (ill.), 376 (ill.), 386 (ill.), 5: 1065 design an experiment for, 2: 386 87 glacier erosion trench experiment, 5: 957 60, 958 (ill.), 959 (ill.) of mountains, 4: 737 plants and the rate of erosion experiment, 2: 381 86, 382 (ill.), 383 (ill.), 384 (ill.) river erosion experiment, 5: 962 65, 963 (ill.), 964 (ill.), 965 (ill.), 966 soil type and runoff experiment, 2: 377 80, 378 (ill.), 379 (ill.) Eruptions. See Volcanoes Ethics, 2: 296, 3: 562, 4: 750 Ethnobotany, 2: 389 400, 390 (ill.) anti bacterial plant experiment, 2: 392 95, 394 (ill.), 395 (ill.) coiling reeds experiment, 2: 396 99, 398 (ill.), 399 (ill.) cxxxvi
design an experiment for, 2: 399 400 plants as medicine, 2: 389 90, 390 (ill.), 400 tools from plants, 2: 390 92, 392 (ill.), 400 Eukaryotes, 3: 537 38 Euphotic zone, 4: 873 Eutrophication dissolved oxygen level changes from, 2: 273, 274 (ill.), 278 79 nutrients in, 1: 49 50, 50 (ill.) process of, 1: 55 58 Evaporation evaporation and surface area experiment, 6: 1253 56, 1253 (ill.), 1254 (ill.), 1255 (ill.) evaporation and temperature experiment, 6: 1248 53, 1250 (ill.), 1251 (ill.) of mixtures, 5: 1032 in PVA glue, 1: 20 21 of seawater, 4: 724 stalagmites and stalactite experiment, 1: 135 39, 137 (ill.) suspensions vs. solutions experiment, 4: 725 30, 729 (ill.) in the water cycle, 6: 1247 wind and, 6: 1252 53 Evidence, 3: 507 11, 508 9, 511 14, 511 (ill.), 512 (ill.), 513 (ill.) Excavations, 2: 230 31 Exhaust, car. See Cars Exoskeleton chitin, 5: 1020 21, 1022 25, 1023 (ill.), 1024 (ill.), 1025 (ill.) fossils of, 3: 530 of insects, 3: 631, 5: 1019 seashells as, 5: 1019 21, 1020 (ill.) Exothermic reactions, 1: 151 52, 152 (ill.), 165, 165 (ill.) design an experiment for, 1: 160 61 vs. endothermic, 1: 156 60, 157 (ill.), 158 (ill.), 159 (ill.) rusting experiment, 1: 152 56, 155 (ill.) Experiments, 5: 1006 8 Extinction, 3: 410 11 Extreme environments, 1: 88, 88 (ill.) Extremophiles, 1: 88, 88 (ill.), 101 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Eyes color vision by, 2: 205 6, 205 (ill.) compound, 3: 632 of fish, 3: 403 perception of light, 4: 787 seeing optical illusions experiment, 4: 791 94, 791 (ill.), 792 (ill.), 793 (ill.)
Fabrics fiber evidence from, 3: 508 9, 511 14, 511 (ill.), 512 (ill.), 513 (ill.) nanotechnology for, 4: 749 natural vs. synthetic, 2: 301 4, 302 (ill.), 303 (ill.) properties of, 4: 696 soundproofing materials experiment, 5: 1102 5, 1104 (ill.) Falling objects, 3: 579, 580, 581 84, 582 (ill.), 583 (ill.), 584 (ill.) See also Gravity False memory, 4: 699 700, 705 7, 707 (ill.) Family genetics, 3: 556 59, 558 (ill.), 559 (ill.) Farming, 2: 229 30, 4: 646 Fat soluble vitamins, 6: 1224 25, 1224 (ill.) Fatigue, 1: 120 23, 122 (ill.) Fats, 4: 760 64, 763 (ill.), 764 (ill.) Faulds, Henry, 3: 507 Fault block mountains, 4: 736 Faults (earthquake), 2: 311, 322 (ill.) Feathers, 3: 530 33, 532 (ill.) Fermentation, 3: 540 41, 544 49, 547 (ill.), 548 (ill.) Ferns, 1: 131 Fertilizer, 1: 49, 55, 2: 279, 386 Fiber evidence, 3: 508 9, 511 14, 511 (ill.), 512 (ill.), 513 (ill.) Fibers, natural vs. synthetic, 2: 301 4, 302 (ill.), 303 (ill.) Filtration for separating mixtures, 4: 724, 5: 1032 suspensions vs. solutions experiment, 4: 725 30, 729 (ill.) water cleaning experiment, 3: 609 12, 610 (ill.) Experiment Central, 2nd edition
Fingerprinting, DNA, 2: 296, 3: 509 10, 510 (ill.), 562 Fingerprints, 3: 507 8, 508 (ill.), 509 (ill.), 519 Fins, 3: 402 3, 407 9, 409 (ill.), 410 Fir trees, 1: 103, 104 (ill.) Fireballs, 2: 217 Fireflies, 3: 638 42, 640 (ill.) Fireworks, 1: 165, 165 (ill.) First class lever, 5: 1049 50 First law of motion, 3: 491 92, 494, 579 Fish, 3: 401 11, 402 (ill.) acid rain damage to, 1: 1 2 bioluminescent, 4: 775, 784 characteristics of, 3: 401 2, 402 (ill.) defense mechanisms of, 1: 61, 63 design an experiment for, 3: 409 11 dissolved oxygen changes experiment, 2: 279 84, 281 (ill.), 282 (ill.), 283 dissolved oxygen levels for, 2: 271, 272, 273 fish breathing experiment, 3: 404 6, 405 (ill.) how they breathe, 3: 402, 403 (ill.) how they move, 3: 402 3, 403 (ill.) movement of fish experiment, 3: 407 9, 410 ocean, 4: 774 75 senses of, 3: 403 4 water pollution and, 1: 50, 3: 411 Fish tank projects desert biome experiment, 1: 108 11, 109 (ill.), 110 (ill.), 111 (ill.) dissolved oxygen changes experiment, 2: 279 84, 281 (ill.), 282 (ill.), 283 fish breathing experiment, 3: 404 6, 405 (ill.) movement of fish experiment, 3: 407 9, 409 (ill.), 410 temperate forest biome, 1: 106 8, 106 (ill.), 107 (ill.), 108 (ill.) Fish tanks, care of, 3: 406 Fixatives for dyes, 2: 300 301, 300 (ill.), 304 7, 306 (ill.) Flagella, 1: 87 Flammability, 1: 164 Flashlight fish, 4: 775 Flavor, 2: 207 10, 208 (ill.), 209 (ill.), 3: 463 64 See also Taste cxxxvii
GENERAL SUBJECT INDEX
Fleas, 3: 633 Fleming, Alexander, 3: 539 Flight, 3: 413 22, 414 (ill.) centripetal force experiment, 3: 418 21, 418 (ill.), 419 (ill.), 420 (ill.) design an experiment for, 3: 421 22 history of, 3: 413 15, 415 (ill.), 422 (ill.) by insects, 3: 632 33 making gliders fly experiment, 3: 415 18, 416 (ill.), 417 (ill.) Floating density and buoyancy in, 2: 257 (ill.), 259, 259 (ill.) relative density and floating experiment, 2: 260 64, 262 (ill.), 263 (ill.) water pressure and buoyancy experiment, 2: 264 67, 265 (ill.), 266 (ill.) water surface tension cohesion experiment, 6: 1261 64, 1261 (ill.), 1263 (ill.) Florey, Howard, 3: 539 40 Flour mystery powder identification experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) Flowers, 3: 423 37, 424 (ill.) attracting pollinators experiment, 3: 431 35, 433 (ill.) design an experiment for, 3: 435 37 parts of, 3: 423 24, 424 (ill.), 426 (ill.), 436 37 pollination of, 3: 423 27, 425 (ill.), 426 (ill.) self pollination vs. cross pollination experiment, 3: 427 31, 430 (ill.) Fluids, 3: 439 49 categories of, 3: 440 41 design an experiment for, 3: 447 48 properties of, 3: 439 40, 439 (ill.), 440 (ill.) spinning rod experiment, 3: 444 47, 446 (ill.), 447 (ill.) viscosity and temperature experiment, 3: 441 44, 442 (ill.), 443 (ill.) Fluorescence, 4: 660, 661 64, 662 (ill.), 663 (ill.) Fluoride, 6: 1226 Fold mountains, 4: 736 Foliose lichens, 1: 52, 52 (ill.) cxxxviii
Food acidic, 1: 164 allergies, 1: 187 bacteria and, 1: 87 88, 101 canned, 3: 452 53, 452 (ill.), 479, 479 (ill.) chlorophyll production of, 1: 192 curing, 3: 452 decay and dissolved oxygen changes experiment, 2: 274 79, 276 (ill.), 277 (ill.) dietary carbohydrate and fat sources experiment, 4: 761 64, 763 (ill.), 764 (ill.) dietary proteins and salt sources experiment, 4: 764 66, 765 (ill.), 766 (ill.) dried, 3: 451, 453, 458 61, 458 (ill.), 459 (ill.), 460 (ill.), 479, 479 (ill.) food supply and growth rate experiment, 4: 651 55, 653 (ill.), 654 (ill.) frozen, 3: 451, 453 fungi as, 3: 537 heating, 3: 465 66 how good is my diet experiment, 4: 766 69, 768 (ill.), 769 (ill.) organic, 4: 855 56 pesticides on, 4: 848 processed, 4: 760 salting, 3: 452, 452 (ill.) smell taste relationship experiment, 1: 186 89, 187 (ill.) supertaster experiment, 1: 180 86, 184 (ill.) taste of, 1: 177 79, 178 (ill.) See also Diet; Nutrition; Taste Food additives, 3: 453 Food coloring, 2: 207 10, 208 (ill.), 209 (ill.) Food energy, 1: 160 Food poisoning, 3: 477 Food preservation, 3: 451 62 design an experiment for, 3: 461 62 food drying experiment, 3: 458 61, 458 (ill.), 459 (ill.), 460 (ill.) history of, 3: 478 80 methods of, 3: 451 53, 452 (ill.), 453 (ill.) moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) sugar fruit preservation experiment, 3: 454 57, 455 (ill.), 456 (ill.) vinegar for, 3: 452, 452 (ill.), 479 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Food preservatives, 3: 452, 453, 462, 478 79, 481 85, 481 (ill.), 482 (ill.), 483 (ill.) Food science, 3: 463 75 design an experiment for, 3: 473 75 heating food, 3: 465 66 jelly and pectin experiment, 3: 467 70, 468 (ill.), 469 (ill.) leavening agents, 3: 464 65, 465 (ill.) leavening agents and carbon dioxide experiment, 3: 470 73, 472 (ill.), 473 (ill.), 474 Maillard reaction in, 3: 463 64 Food spoilage, 3: 477 90 design an experiment for, 3: 461 62, 488 90 food drying experiment, 3: 458 61, 458 (ill.), 459 (ill.), 460 (ill.) microorganisms in, 3: 451 53, 477 80, 478 (ill.) moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) prevention of, 3: 478 80, 479 (ill.), 480 (ill.) process of, 3: 451, 477 78 spoiled milk and temperature experiment, 3: 485 88, 487 (ill.) sugar fruit preservation experiment, 3: 454 57, 455 (ill.), 456 (ill.) Food webs, 6: 1193 Footprints, 3: 524 Forces, 3: 491 505, 492 93, 504 (ill.) arch distribution of, 6: 1166 67 bottle rocket experiment, 3: 493 501, 495 (ill.), 498 (ill.), 499 (ill.), 500 (ill.) centripetal force experiment, 3: 501 5, 503 (ill.) design an experiment for, 3: 504 5 effect on structures, 6: 1165 66, 1166 (ill.) machines can change, 5: 1047 Newtonian laws of motion, 3: 491 93, 492 (ill.), 493 (ill.), 579 80 planetary orbits and, 3: 579 80 wheel size and effort experiment, 5: 1051 55, 1054 (ill.) Forensic science, 3: 507 19 blood spatter analysis experiment, 3: 515 18, 516 (ill.), 517 (ill.) design an experiment for, 3: 518 19 DNA fingerprinting, 2: 298, 3: 509 10, 510 (ill.), 562 Experiment Central, 2nd edition
fiber evidence experiment, 3: 511 14, 511 (ill.), 512 (ill.), 513 (ill.) techniques for, 3: 507 11, 508 (ill.), 509 (ill.), 510 (ill.) Forests acid rain damage to, 1: 2, 3 (ill.) biomes, 1: 103 4 boreal, 1: 103 4, 104 (ill.) carbon dioxide absorbed by, 3: 590 temperate forest experiment, 1: 106 (ill.), 107 8, 107 (ill.), 108 (ill.) See also Rainforests; Trees Fossil casts, 3: 523, 526 29, 528 (ill.) Fossil fuels acid rain from, 1: 1, 2 (ill.), 4 burning fossil fuels experiment, 3: 596 98, 596 (ill.), 597 (ill.) efficiency of, 5: 1083 greenhouse gases from, 3: 590, 5: 941 Fossil molds, 3: 523, 535 Fossils, 3: 521 36, 524 (ill.), 525 (ill.), 534 (ill.) collection of, 3: 535 dating techniques for, 3: 524 25 design an experiment for, 3: 533 35 formation of, 3: 521 24, 522 (ill.), 523 (ill.) fossil formation experiment, 3: 530 33, 532 (ill.) soils for fossil casts experiment, 3: 526 29, 528 (ill.) Foucault, Jean Bernard Leon, 5: 985 Fourier, Jean Baptiste Joseph, 3: 589 Franklin, Benjamin, 6: 1134 (ill.), 1135 Franklin, Rosalind, 2: 287 Freeze drying, 3: 453 Frequency, 2: 350, 5: 1095 (ill.), 6: 1112, 1112 (ill.) Fresh Kills landfill, 2: 231 Freshwater. See Water Friction, 6: 1133 lightning sparks experiment, 6: 1152 55, 1154 (ill.) static electricity from, 6: 1133 34, 1134 (ill.) Frogs leaf, 1: 61 62 life cycle of, 4: 645 46, 646 (ill.) tadpoles and temperature experiment, 4: 647 51, 648 (ill.), 649 (ill.), 650 (ill.) cxxxix
GENERAL SUBJECT INDEX
Fronts (weather), 1: 34 35 Frozen food, 3: 451, 453 Fruit food drying experiment, 3: 458 61, 458 (ill.), 459 (ill.), 460 (ill.) how fruit flies appear experiment, 5: 1013 16, 1015 (ill.), 1016 (ill.) jelly and pectin experiment, 3: 467 70, 468 (ill.), 469 (ill.) for scurvy, 4: 759, 760 (ill.) sources of vitamin C experiment, 6: 1226 31, 1229 (ill.) sugar fruit preservation experiment, 3: 454 57, 455 (ill.), 456 (ill.) yeast decomposition experiment, 3: 541 43, 543 (ill.) Fruit flies, 5: 1013 16, 1015 (ill.), 1016 (ill.) Fruticose lichens, 1: 52, 52 (ill.) Fulcrum, 5: 1049 51, 1050 (ill.), 1055 57, 1057 (ill.) Full moon, 6: 1175 Fungal diseases, 3: 539 Fungi, 3: 537 51, 538 (ill.), 539 (ill.), 550 (ill.), 4: 712 as biopesticides, 4: 844 45 in caves, 1: 131 design an experiment for, 3: 549 50 in lichens, 1: 51, 73 74, 75 (ill.) microorganisms and decomposition experiment, 2: 233 35, 234 (ill.), 235 (ill.), 236 reproduction by, 3: 539, 540 (ill.) safety for, 1: 81 sugar fruit preservation experiment, 3: 454 57, 455 (ill.), 456 (ill.) temperature for yeast growth experiment, 3: 544 49, 547 (ill.), 548 (ill.) types of, 3: 537, 538 uses for, 3: 537, 538, 539 41, 4: 712 yeast decomposition experiment, 3: 541 43, 543 (ill.) Fungicides, 4: 843 Funk, Casimir, 4: 760 Funnel clouds, 6: 1150 51, 1150 (ill.) cxl
Galaxies, 6: 1123, 1124 25 Galileo Galilei, 6: 1109, 1123, 1123 (ill.), 1178, 1178 (ill.) Garbage, 2: 230 31, 232 35, 234 (ill.), 235 (ill.) See also Landfills Garlic, 2: 392 95, 394 (ill.), 395 (ill.), 4: 848 52, 851 (ill.) Gas chromatography, 5: 1033 Gases in air, 1: 33 air pollution, 1: 45 46 in comets, 2: 216 as fluids, 3: 439 41 greenhouse, 1: 46, 47 (ill.), 48, 3: 589 91 noble, 4: 830 Gastropods, 5: 1019 20, 1025 27, 1027 (ill.) Gecko, 1: 19, 20 (ill.) Gel, 3: 467 70, 468 (ill.), 469 (ill.) Gel electrophoresis, 3: 562 Gelatin, 1: 92, 97 how color affects taste experiment, 2: 207 10, 208 (ill.), 209 (ill.) medium preparation experiment, 4: 716 20, 718 (ill.), 719 (ill.) temperature and enzyme action experiment, 2: 368 72, 370 (ill.), 371 (ill.) Gemstones, 2: 243 Genes, 3: 553 Genetic engineering, 3: 555, 556 (ill.), 562, 4: 845, 846 (ill.), 848 Genetic traits, 3: 554 55, 556 59, 558 (ill.), 559 (ill.), 562 Genetics, 3: 553 63, 554 (ill.), 555 (ill.) color blindness, 2: 206 cross pollination, 3: 425, 425 (ill.) design an experiment for, 3: 561 62 genetic traits experiment, 3: 556 59, 558 (ill.), 559 (ill.) pedigree for taste experiment, 3: 559 61, 561 (ill.) pollination, 3: 425, 425 (ill.), 6: 1207, 1207 (ill.), 1208 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
smell, 1: 179 80, 189 taste, 1: 180 vegetative propagation, 6: 1208, 1208 (ill.) Geology, 5: 969 70, 970 (ill.) Geometric patterns (crystals), 2: 243, 244 45, 244 (ill.) Geothermal energy, 5: 943 Geotropism, 6: 1191, 1192, 1197 1201, 1198 (ill.), 1199 (ill.), 1200 (ill.) Germ theory of disease, 1: 86, 4: 712 Germination, 3: 565 78, 566 (ill.) design an experiment for, 3: 576 77 germination time experiment, 3: 570 73, 572 (ill.) process of, 3: 565 66 seed scarification experiment, 3: 573 76, 574 (ill.), 575 (ill.), 576 (ill.) temperature for germination experiment, 3: 566 70, 568 (ill.), 569 (ill.) Gibberellic acid, 5: 886 90, 888 (ill.), 889 (ill.) Gills, 3: 401, 402, 404 6, 405 (ill.) Glaciers, 5: 957 60, 958 (ill.), 959 (ill.) Glass, 2: 231, 3: 618 22, 620 (ill.), 621 (ill.), 4: 823 Glauber’s salt, 5: 1090 92, 1092 (ill.), 1093 Gliders, 3: 414, 415 18, 416 (ill.), 417 (ill.) Global warming, 1: 46, 3: 589, 590 (ill.) Glucose, 4: 872 Glues, 1: 19 21 glue adherence experiment, 1: 22 25, 23 (ill.), 24 (ill.) light refraction experiment, 4: 666 69, 666 (ill.), 667 (ill.) Glutamate, 1: 177 GMT (Greenwich Mean Time), 6: 1179 Gnomon, 6: 1177 Gold, 4: 828 Goldfish, 2: 279 84, 281 (ill.), 282 (ill.), 283 Golgi bodies, 1: 142 Grain, wood, 6: 1297, 1298 (ill.) Grapefruit, 6: 1226 31, 1229 (ill.) Graphite, 2: 244, 246 (ill.), 4: 749, 750 (ill.) Grasses, 2: 381 86, 382 (ill.), 383 (ill.), 390 91 Grasshoppers, 3: 633, 4: 651 55, 653 (ill.), 654 (ill.) Gravity, 3: 579 88, 580 (ill.) build a roller coaster experiment, 5: 934 38, 935 (ill.), 936 (ill.), 937 (ill.) center of, 5: 983 Experiment Central, 2nd edition
centrifugal force and gravity experiment, 5: 989 92, 990 (ill.) definition of, 3: 491 in density determination, 2: 259 design an experiment for, 3: 587 88 geotropism effect, 6: 1191, 1192 height of objects experiment, 5: 931 34, 932 (ill.), 933 (ill.) measuring mass experiment, 3: 585 87, 585 (ill.), 586 (ill.), 587 (ill.), 588 (ill.) Newtonian laws of motion on, 3: 492, 579 80 orbits, 5: 982 root growth and gravity experiment, 6: 1197 1201, 1198 (ill.), 1199 (ill.), 1200 (ill.) specific, 2: 258, 5: 997 1000, 998 (ill.), 999 (ill.) speed of falling objects experiment, 3: 581 84, 582 (ill.), 583 (ill.), 584 (ill.) star formation, 6: 1124 tides, 4: 774, 775 (ill.) Grease, 6: 1260 Greeks, ancient, 2: 389, 3: 565, 4: 827, 5: 1006, 6: 1123 Green algae, 3: 538 Greenhouse effect, 3: 589 600, 590 (ill.), 591 (ill.), 599 (ill.) burning fossil fuels experiment, 3: 596 98, 596 (ill.) design an experiment for, 3: 598 600 from fossil fuel combustion, 3: 590, 5: 941 gases in, 1: 46, 47 (ill.), 48, 3: 589 91 greenhouse temperature increase experiment, 3: 592 96, 593 (ill.), 594 (ill.) history of, 3: 589 90 how it works, 1: 46, 47 ll, 3: 589, 617 (ill.) particulate matter in, 1: 46 47 Greenhouses, 5: 1082, 1084 87, 1084 (ill.), 1086 (ill.) Greenwich Mean Time (GMT), 6: 1179 Groundwater aquifers, 3: 601 13, 603 (ill.) aquifer contamination experiment, 3: 605 9, 608 (ill.) design an experiment for, 3: 612 13 formation of, 3: 601, 602 (ill.), 603 (ill.) pollution of, 3: 604 5, 605 (ill.), 606 (ill.) water cleaning experiment, 3: 609 12, 610 (ill.) cxli
GENERAL SUBJECT INDEX
Growth of bacteria, 1: 90 95, 92 (ill.), 93 (ill.) of crystals, 2: 245 46, 250 53, 252 (ill.) insect food supply and growth rate experiment, 4: 651 55, 653 (ill.), 654 (ill.) See also Annual growth; Plant growth Guanine, 2: 286 87 Guar gum, 5: 919 23, 921 (ill.), 922 (ill.) Gulf Stream, 4: 773 Guppies, 3: 404 6, 405 (ill.) Gymnosperms, 6: 1295
Hailstones, 6: 1151 52, 1151 (ill.), 1158 61, 1159 (ill.), 1160 (ill.), 1161 (ill.), 1162 Hair, mid finger, 3: 556 59, 559 (ill.) Hair dyes, 2: 300 Hairline, straight, 3: 556 59, 556 (ill.), 559 (ill.) Halley, Edmond, 2: 215 16, 216 (ill.), 326, 6: 1248 Halley’s Comet, 2: 215 16, 216 (ill.) Han Hsin, 3: 413 Hard water, 6: 1226, 1231 34, 1232 (ill.) Hardness, 4: 748, 5: 971 75, 973 (ill.), 974 (ill.) Hardwood, 6: 1295, 1302 6, 1304 (ill.), 1305 (ill.) Hawkmoths, 3: 426 Health effects of pesticides, 4: 844 of pollution, 1: 59 of vitamins and minerals, 4: 761, 6: 1223 36, 1224 (ill.), 1225 (ill.), 1226, 1227 (ill.), 1234 (ill.), 1235 (ill.) Hearing, 5: 1095, 1106 (ill.) Heartwood, 6: 1296 Heat, 1: 151 52, 3: 615 29, 615 (ill.), 616 (ill.) conduction in solids experiment, 3: 618 22, 620 (ill.), 621 (ill.) convection in liquids experiment, 3: 622 25, 623 (ill.), 624 (ill.) for cooking food, 3: 465 66, 479 80 definition of, 3: 615, 5: 929 design an experiment for, 3: 628 29 endothermic reactions, 1: 165 cxlii
endothermic vs. exothermic experiment, 1: 156 60, 157 (ill.), 158 (ill.), 159 (ill.) exothermic reactions, 1: 165 heat capacity experiment, 3: 625 28, 626 (ill.), 627 (ill.), 628 (ill.) magnetic strength effect experiment, 4: 674 78, 676 (ill.) movement of, 3: 615 17, 616 (ill.), 617 (ill.) for separation and identification, 5: 1034 solar heat storage experiment, 5: 1090 92, 1092 (ill.), 1093 from sunlight, 3: 589 temperature of different colors experiment, 2: 210 12, 211 (ill.), 212 (ill.), 213 thermal properties of materials, 4: 687 transfer of, 3: 615 16, 5: 930 wood for, 5: 942 Heat capacity, 3: 617, 625 28, 626 (ill.), 627 (ill.), 628 (ill.) Heat energy. See Heat Heat lamp safety, 1: 28 Heavy metals, 1: 49 Helicopters, 3: 413, 418 21, 418 (ill.), 419 (ill.), 420 (ill.) Heliotropism, 6: 1201 4, 1202 (ill.), 1203 (ill.) Helium, 4: 829, 6: 1123 24 Helmholtz, Hermann von, 5: 1096 Heng, Chang, 2: 312 13 Herbal medicine, 2: 389 90, 390 (ill.), 400 Herbicides, 1: 49, 4: 843 Heredity. See Genetics Hershey, Alfred, 2: 286 Heterogeneous mixtures, 5: 1031 32, 1032 (ill.), 1033 (ill.) High tide, 4: 774, 5: 984, 992 (ill.) Hippocampus, 4: 698 99, 699 (ill.) H.M.S. Challenger, 5: 995, 995 (ill.), 996 Homogenous mixtures, 5: 1032, 1033 (ill.) Honey ant food experiment, 3: 635 38, 636 (ill.), 637 (ill.) viscosity and temperature experiment, 3: 441 44, 442 (ill.), 443 (ill.) Hooke, Robert, 1: 141 Hormones, plant. See Plant hormones Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Horned lizards, 1: 63 Hot environments adhesives experiment, 1: 26 30, 27 (ill.), 28 (ill.), 29 (ill.) transpiration rate and environment experiment, 5: 904 7, 906 (ill.) Hot springs, 1: 88 Hours, 6: 1177 Household chemicals, 4: 861 65, 861 (ill.), 863 (ill.) Howard, Albert, 2: 229 Howard, Luke, 6: 1272 Hubble Space Telescope, 6: 1110, 1110 (ill.) Hue (color), 2: 206 7 Human Genome Project, 3: 555 56 Humans, 1: 85, 2: 287, 288, 3: 553 55, 555 56 Humidity adhesives experiment, 1: 26 30, 27 (ill.), 28 (ill.), 29 (ill.) in weather, 6: 1271, 1284 Humonogous fungus, 3: 537 Humus, 2: 229, 230, 5: 1063, 1066, 1067 (ill.) Hunting weapons, 2: 391 Hurricanes, 6: 1284 (ill.), 1286 Hutton, James, 5: 969, 970 (ill.) Huygens, Christian, 4: 660 Hydrangea, 4: 860 Hydrocarbons, 3: 596 Hydrochloric acid, 1: 164, 165, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) Hydrogen density of, 2: 257 nanotechnology, 4: 747 periodic table location for, 4: 829 in polymers, 5: 912 in star formation, 6: 1123 24 in water molecules, 1: 20, 21 (ill.), 4: 747, 748 (ill.), 6: 1259 Hydrogen ions, 1: 1, 2: 334, 4: 859, 865 Hydrogen peroxide, 1: 163, 2: 361 (ill.), 362 65, 363 (ill.), 364 (ill.) Hydrogen sulfide, 1: 129 Hydrologic cycle. See Water cycle Hydrologists, 6: 1248 Hydrometers, 5: 997 1000, 998 (ill.), 999 (ill.) Experiment Central, 2nd edition
Hydrophilic substances, 3: 465, 465 (ill.), 6: 1260 Hydrophobic substances attraction to water, 6: 1260 proteins, 3: 465, 465 (ill.), 6: 1260 water adhesion and weight experiment, 6: 1264 68, 1265 (ill.), 1266 (ill.) Hydroponics, 5: 895 Hydropower, 5: 943, 943 (ill.), 948 51, 948 (ill.), 949 (ill.), 950 (ill.) Hydroxide ions, 4: 865 Hypertonic solutions, 4: 798 Hyphae, 3: 538, 539, 539 (ill.), 540 Hypothesis formation, 5: 1006, 1007 (ill.) Hypotonic solutions, 4: 798
Ice in comets, 2: 215, 216, 218 21, 220 (ill.) dry, 2: 220 Ichthyosaur, 3: 521 Igneous rocks, 5: 970, 975 78, 975 (ill.), 976 (ill.), 977 (ill.) Iguanodon, 3: 521 Imperfect flowers, 3: 424 Incandescent lights, 1: 198, 198 (ill.) Inclined plane, 5: 1047 48, 1048 (ill.), 1049 (ill.) Independent assortment, law of, 3: 554 Independent variables, 5: 1008 Indian Ocean, 4: 771 Indicators, pH. See Acid/base indicators Indigo, 2: 299 Indoor air pollution, 1: 48 Indore method, 2: 229 Industrial chemicals, 1: 49 Inertia, 3: 491 92, 493, 494, 579, 581 Information gathering, 5: 1006 Infrared radiation, 3: 589, 616 17 Ingenhousz, Jan, 4: 871, 871 (ill.) Inheritance, dominant vs. recessive, 3: 554 55 See also Genetics Inhibition, zone of, 1: 90 91 Ink, 1: 63, 5: 1034 39, 1036 (ill.), 1037 (ill.) Insecticides, 4: 843 cxliii
GENERAL SUBJECT INDEX
Insects, 3: 631 44 ant food experiment, 3: 635 38, 636 (ill.), 637 (ill.) characteristics of, 3: 631 32, 632 (ill.) design an experiment for, 3: 642 43 dyes from, 2: 299 exoskeleton of, 3: 631, 5: 1019 food supply and growth rate experiment, 4: 651 55, 653 (ill.), 654 (ill.) fossils of, 3: 523 24 life cycle of, 3: 633 34, 643 (ill.), 4: 645, 645 (ill.), 646 lightning bug experiment, 3: 638 42, 640 (ill.) movement by, 3: 632 33, 633 (ill.) natural adhesives from, 1: 19 pheromones, 4: 844 pollination by, 3: 425 27 social, 3: 634 taiga biome, 1: 104 temperate forest biome, 1: 108 Insulin, 3: 555 Interference fringes, 4: 660 International Hydrographic Organization, 4: 771 Invertebrates, 5: 1019 Involuntary muscles, 1: 115 Iodine mineral oil, water and iodine experiment, 1: 170 73, 170 (ill.), 171 (ill.), 172 (ill.) mystery powder identification experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) for nutrition, 6: 1226 plastic bag membrane experiment, 4: 798 803, 799 (ill.), 800 (ill.), 801 (ill.), 802 (ill.) sources of vitamin C experiment, 6: 1226 31, 1229 (ill.) Ion tail, 2: 216 Ionic cleaners, 4: 724 Ionic conduction, 2: 333 34 Ions, 2: 244, 245 (ill.) Iron for bacteria, 1: 88 magnetized, 4: 671 72, 671 (ill.), 672 (ill.) for nutrition, 6: 1226 oxidation reduction reactions, 4: 812 rusting, 1: 151, 152 (ill.), 163, 165, 4: 812 rusting experiment, 1: 152 56, 155 (ill.) in soil, 5: 1064 cxliv
steel wool rust experiment, 4: 817 20, 818 (ill.) synthesis reactions, 1: 163 in water, 6: 1225 26 Iron Age, 5: 969 Iron oxide, 1: 151, 152 56, 155 (ill.), 4: 812 Irrigation, 2: 375 Isobars, 6: 1285 Isotonic solutions, 4: 798 Ivory, 5: 911
Janssen, Hans, 1: 141 Janssen, Zacharius, 1: 141 Jawless fish, 3: 401, 402 (ill.) Jelly, 3: 467 70, 468 (ill.), 469 (ill.) Jellyfish, 1: 149 Joints, 1: 113 14 Juices, fruit, 6: 1226 31, 1229 (ill.) Jumping spiders, 1: 62 Jumps, 3: 633 Jupiter (planet), 6: 1109
Kangaroo rats, 1: 105 Kepler, Johannes, 3: 579, 5: 981 Kinetic energy, 5: 929 40, 930 (ill.) build a roller coaster experiment, 5: 934 38, 935 (ill.), 936 (ill.), 937 (ill.) design an experiment for, 5: 939 40 height of objects experiment, 5: 931 34, 932 (ill.), 933 (ill.) laws of, 5: 929 31 Kingdoms, 3: 537 Kites, 3: 413 Koch, Robert, 1: 86 Kuhne, Willy, 2: 359 60
Labyrinth, 3: 404 6, 405 (ill.) Lactic acid, 3: 485 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Ladybugs, 1: 65 68, 66 (ill.), 67 (ill.) Lady’s Slipper, 3: 426, 427 (ill.) Lakes acid rain damage to, 1: 1 2 dissolved oxygen in, 2: 271 84 eutrophication of, 1: 49 50, 50 (ill.), 55 58, 57 (ill.) neutralization of, 1: 4 water pollution, 1: 48 Landfills, 2: 229 41, 231 (ill.) biomass energy from, 5: 942 43 decomposition in, 2: 231 design an experiment for, 2: 239 40 history of, 2: 230 31 microorganisms and decomposition experiment, 2: 232 35, 234 (ill.), 235 (ill.) sanitary, 2: 231 Langley, Samuel Pierpont, 3: 414 Larva, 3: 633 34, 4: 645 Lattice, crystal, 2: 243 Laundry detergents. See Detergents Lava, 5: 970 Lava caves, 1: 129 Lavoisier, Antoine, 4: 827 Law of independent assortment, 3: 554 Laws of motion. See Newtonian laws of motion Leaching, 4: 847, 847 (ill.), 851 55, 854 (ill.) Lead air pollution, 1: 45, 46 atomic symbol for, 4: 828 density of, 2: 257, 258, 258 (ill.) safety for handling, 6: 1167 Leaf cuttings, 6: 1208, 1209 16, 1213 (ill.), 1214 (ill.) Leaf frog, 1: 61 62 Leaf litter, 2: 381 86, 382 (ill.), 383 (ill.) Leather dyes, 2: 300 Leavening agents, 3: 464 65, 465 (ill.), 470 73, 472 (ill.), 473 (ill.), 474 See also Baking powder; Baking soda; Yeast Leaves, 5: 885, 885 (ill.) chlorophyll in, 1: 191 201, 191 (ill.) color change by, 1: 192, 192 (ill.), 201 (ill.) falling in autumn, 1: 192 fossil formation experiment, 3: 530 33, 532 (ill.) in photosynthesis, 4: 871 72, 5: 884 85 Experiment Central, 2nd edition
pigment separation experiment, 1: 193 97, 195 (ill.), 196 (ill.) transpiration rate and environment experiment, 5: 904 7, 906 (ill.) water in, 5: 898 LED (Light emitting diode), 4: 666 69, 666 (ill.), 667 (ill.) Leeuwenhoek, Anton van, 1: 85, 141, 4: 711 Legs (insect), 3: 631, 633 Lemon juice acid copper reduction experiment, 4: 813 17, 814 (ill.), 815 (ill.) construct a multicell battery experiment, 2: 340 44, 341 (ill.), 342 (ill.) copper patina experiment, 1: 173 75, 174 (ill.), 175 (ill.) electrolyte function, 2: 334 electrolyte solution experiment, 2: 335 40, 337 (ill.), 338 (ill.), 339 (ill.) jelly and pectin experiment, 3: 467 70, 468 (ill.), 469 (ill.) moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) pH of, 4: 859 (ill.) pH of household chemicals experiment, 4: 861 65, 861 (ill.), 863 (ill.) Lenses camera, 4: 795 (ill.) focal length of lens experiment, 4: 788 91, 788 (ill.) telescope, 6: 1110 telescope lenses experiment, 6: 1113 17, 1114 (ill.), 1116 (ill.) Levers, 5: 1049 51, 1050 (ill.), 1055 57, 1057 (ill.) Lichens air pollution experiment, 1: 51 55, 54 (ill.) annual growth of, 1: 72 74, 74 (ill.) fungi in, 1: 51, 73 74, 75 (ill.), 3: 538 growth experiment, 1: 79 82, 81 (ill.) structure of, 3: 538 types of, 1: 52, 52 (ill.) Life cycle, 4: 645 57, 656 (ill.) of amphibians, 4: 645 46, 646 (ill.) design an experiment for, 4: 655 56 cxlv
GENERAL SUBJECT INDEX
food supply and growth rate experiment, 4: 651 55, 653 (ill.), 654 (ill.) of insects, 3: 633 34, 643 (ill.), 4: 645, 645 (ill.), 646 pesticide disruption of, 4: 843 tadpoles and temperature experiment, 4: 647 51, 648 (ill.), 649 (ill.), 650 (ill.) Lift (airplane wing), 3: 413, 415 18, 416 (ill.), 417 (ill.) Lifting loads inclined plane for, 5: 1047 48, 1048 (ill.), 1049 (ill.) lever lifting experiment, 5: 1055 57, 1057 (ill.) levers for, 5: 1049 51, 1050 (ill.), 1051 (ill.) wheel size and effort experiment, 5: 1051 55, 1054 (ill.) Ligaments, 1: 113 14 Light, 4: 659 70, 659 (ill.) bending, 2: 203 5, 205 (ill.) black, 4: 661 64, 662 (ill.), 663 (ill.) black light experiment, 4: 661 64, 662 (ill.), 663 (ill.) colors as, 2: 203 5 design an experiment for, 4: 669 70 electromagnetic spectrum, 2: 203, 4: 659, 660 (ill.), 787 focal length of lens experiment, 4: 788 91, 788 (ill.) how we view it, 4: 787 light colors and plant growth experiment, 1: 197 200, 197 (ill.), 199 (ill.), 200 (ill.), 4: 873 77, 875 (ill.), 876 (ill.) lightning bug experiment, 3: 639 42, 640 (ill.) make a rainbow experiment, 4: 664 65, 664 (ill.), 665 (ill.) passing through colloids, 4: 725, 725 (ill.) in photosynthesis, 4: 871 73 phototropism effect, 6: 1191 93 properties of, 4: 659 60 red, 2: 203, 204 5, 210 12, 211 (ill.), 212 (ill.), 213, 4: 873 77, 875 (ill.), 876 (ill.) refraction experiment, 4: 666 69, 666 (ill.), 667 (ill.) in space, 6: 1109, 1111 12, 1112 (ill.) speed of, 6: 1149, 1179 cxlvi
splitting, 2: 244 45 telescope magnification of, 6: 1110 temperature of different colors experiment, 2: 210 12, 211 (ill.), 212 (ill.), 213 Tyndall effect experiment, 4: 730 32, 731 (ill.), 732 (ill.) violet, 2: 203, 204 5, 210 12, 211 (ill.), 212 (ill.), 213, 4: 873 77, 875 (ill.), 876 (ill.) visible, 4: 659, 660, 787, 6: 1112 white, 2: 203 5, 205 (ill.), 4: 873 77, 875 (ill.), 876 (ill.) yellow, 4: 873 77, 875 (ill.), 876 (ill.) Light bulbs incandescent, 1: 198, 198 (ill.) light intensity and plant growth experiment, 4: 877 80, 878 (ill.), 879 (ill.), 880 (ill.) Light emitting diode (LED), 4: 666 69, 666 (ill.), 667 (ill.) Light sensitivity, 1: 164 Light years, 6: 1124 Lightning formation of, 6: 1135, 1135 (ill.), 1148 49, 1149 (ill.) lightning sparks experiment, 6: 1152 55, 1154 (ill.) Lightning bugs, 3: 638 42, 640 (ill.) Lilienthal, Otto, 3: 414, 414 (ill.) Lime, 1: 4, 4: 860, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) Limestone acid rain damage to, 1: 3, 12 15, 14 (ill.), 15 (ill.), 16, 17 (ill.) caves, 1: 127 29, 128 (ill.), 132 35, 134 (ill.) stalagmites and stalactite experiment, 1: 135 39, 137 (ill.) stalagmites and stalactite formation, 1: 129 30, 130 (ill.) See also Chalk Lind, James, 4: 759, 760 (ill.) Linen, 3: 509 Lippershey, Hans, 1: 141 Liquid chromatography, 5: 1033 Liquids density of, 2: 259 electricity conduction through, 2: 333 34 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
as fluids, 3: 439 41 heat capacity experiment, 3: 625 28, 626 (ill.), 627 (ill.), 628 (ill.) heat convection experiment, 3: 622 25, 623 (ill.), 624 (ill.) relative density and floating experiment, 2: 260 64, 262 (ill.), 263 (ill.) viscosity and temperature experiment, 3: 441 44, 442 (ill.), 443 (ill.) Lisbon, Portugal earthquake of 1755, 2: 311 12, 312 (ill.) Litmus paper, 4: 860 Litter, 1: 50 Liver, 2: 361 (ill.), 362 65, 363 (ill.), 364 (ill.) Lizards, 1: 19, 20 (ill.), 63, 104 5 Lobsters, 5: 1022 25, 1022 (ill.), 1023 (ill.), 1024 (ill.), 1025 (ill.) Lockyer, Joseph Norman, 2: 326 (ill.) Long term memory, 4: 697 98, 698 (ill.) Low tide, 4: 774, 5: 984, 992 (ill.) Luciferin, 3: 639, 640 (ill.) Luminol, 3: 508 Lunar eclipse, 2: 326, 326 (ill.), 327 29, 328 (ill.), 329 (ill.) Lungfish, 3: 402 Luster of minerals, 5: 971 75, 973 (ill.), 974 (ill.)
Machines. See Simple machines Macrominerals, 6: 1226 Macroorganisms, 2: 230, 231 (ill.) Magma, 5: 970, 6: 1238, 1239 Magnesium chemical properties of, 1: 165 hard water sources experiment, 6: 1231 34, 1232 (ill.) for nutrition, 4: 761 periodic table location for, 4: 829 in water, 6: 1225 26 Magnetism, 4: 671 83, 671 (ill.), 681 (ill.) design an experiment for, 4: 681 82 domain alignment for, 4: 671 72, 672 (ill.) Experiment Central, 2nd edition
electricity in, 2: 349 50, 4: 672 73 electromagnet creation experiment, 2: 354 57, 354 (ill.), 356 (ill.) electromagnet strength experiment, 4: 678 81, 678 (ill.), 679 (ill.) magnetic strength experiment, 4: 674 78, 674 (ill.), 676 (ill.) production of, 2: 349 50, 4: 672 73 See also Electromagnetism Magnifying lens, 5: 1081 Maillard, Louis Camille, 3: 463 64 Maillard reaction, 3: 463 64 Malnutrition, 4: 759 60 Mammals, 1: 50, 104, 3: 524 See also Animals Manganese, 6: 1226 Manure, 2: 229, 5: 943 Marble, 1: 12 15, 14 (ill.), 15 (ill.), 16 Marine mammals, 1: 50, 3: 524 Mariotte, Edme, 6: 1248 Mass acceleration and, 3: 492 atomic, 4: 828, 829 center of, 5: 983 density determination, 2: 257, 259 of fluids, 3: 439 gravity’s effect on, 3: 580, 581 inertia and, 3: 491 92 measuring mass experiment, 3: 585 87, 585 (ill.), 586 (ill.), 587 (ill.), 588 (ill.) second law of motion on, 3: 579 80 Materials science, 4: 685 96, 686 (ill.) design an experiment for, 4: 695 96 nanosize and properties experiment, 4: 750 53, 752 (ill.) nanotechnology in, 4: 749 properties of materials, 4: 686 87, 687 (ill.) renewable packing material experiment, 4: 691 94, 693 (ill.), 694 (ill.) soundproofing materials experiment, 5: 1102 5, 1104 (ill.) tape strength experiment, 4: 688 91, 689 (ill.), 690 (ill.) types of materials, 4: 685 86 Mauve, 2: 300 cxlvii
GENERAL SUBJECT INDEX
Meandering rivers course of, 5: 956, 967 (ill.) stream pattern experiment, 5: 960 62, 961 (ill.), 964 (ill.), 965 (ill.), 966 Meap tides, 3: 580 Meat aging meat experiment, 2: 365 68, 366 (ill.), 367 (ill.) ant food experiment, 3: 635 38, 636 (ill.), 637 (ill.) cooking, 3: 463 64 curing, 3: 452 safety for, 2: 366 Meat tenderizer aging meat experiment, 2: 365 68, 366 (ill.), 367 (ill.) DNA isolation and extraction experiment, 2: 289 91, 289 (ill.), 290 (ill.) species differences in DNA experiment, 2: 291 95, 293 (ill.) Mechanical bonding, 1: 20 Medicinal plants, 2: 389 90, 390 (ill.), 400 Medicine, 2: 389 90, 390 (ill.), 400, 4: 749 See also Health effects Medium, for microorganisms, 4: 716 20, 718 (ill.), 719 (ill.) Megalosaurus, 3: 521 Melanin, 1: 200 Melting point, 4: 748, 752 (ill.), 5: 1034 Membranes cell, 1: 86, 87 (ill.), 142, 4: 797, 798, 798 (ill.), 5: 898 semipermeable, 3: 452, 4: 797, 798 803, 799 (ill.), 800 (ill.), 801 (ill.), 802 (ill.), 806 9, 808 (ill.), 809 (ill.) Memory, 4: 697 709 design an experiment for, 4: 707 8 false, 4: 699 700, 705 7, 707 (ill.) how it works, 4: 698 99, 699 (ill.) make a false memory experiment, 4: 705 7, 707 (ill.) memory mnemonics experiment, 4: 701 4, 701 (ill.), 702 (ill.), 703 (ill.) problems with, 4: 699 700, 699 (ill.) techniques to help, 4: 700 types of, 4: 697 98, 698 (ill.) cxlviii
Mendel, Gregor, 3: 554, 555 (ill.) Mendeleev, Dmitri, 4: 827 28, 828 (ill.) Meniscus, 6: 1260 Mercury, 4: 828 Mercury barometers, 1: 34 Mestral, George de, 4: 685, 686 (ill.) Metals, 4: 686 conductivity of elements experiment, 4: 830 35, 833 (ill.) electricity conduction through, 2: 333 electrons released by metals experiment, 4: 838 40, 840 (ill.), 841 (ill.), 842 glue adherence experiment, 1: 22 25, 23 (ill.), 24 (ill.) heavy, 1: 49 oxidation reduction reactions in, 4: 811 (ill.) periodic table location for, 4: 829 See also Copper; Iron Metamorphic rocks, 5: 971, 975 78, 975 (ill.), 976 (ill.), 977 (ill.) Metamorphosis amphibians, 4: 645 46, 645 (ill.) insects, 3: 633 34 tadpoles and temperature experiment, 4: 647 51, 648 (ill.), 649 (ill.), 650 (ill.) Meteor showers, 2: 218, 218 (ill.), 227 Meteorites, 2: 217, 217 ll, 218 (ill.) Meteoroids, 2: 216 17, 217 (ill.) Meteorologists, 1: 34, 6: 1284 Meteors. See Comets and meteors Methane, 1: 46, 48, 2: 231, 5: 943 Mexican free tail bats, 1: 130 Michell, John, 2: 312 Microclimates, 3: 592 96, 593 (ill.), 594 (ill.) Microorganisms, 4: 711 21, 711 (ill.) as biopesticides, 4: 844 45 for composting, 2: 229 design an experiment for, 4: 720 21 discovery of, 4: 711 12, 712 (ill.) in food spoilage, 3: 451 53, 477 80, 478 (ill.) growing penicillin experiment, 4: 713 16, 713 (ill.), 715 (ill.) in landfills, 2: 231, 232 35, 234 (ill.), 235 (ill.) medium preparation experiment, 4: 716 20, 718 (ill.), 719 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
in soil, 2: 229, 5: 1063, 1067 types of, 4: 712 See also Bacteria; Fungi Microscopes compound, 1: 141, 141 (ill.) development of, 1: 85, 141 for forensic science, 3: 507, 511 for microorganisms, 4: 711 for nanotechnology, 4: 748 scanning tunneling, 4: 748 Mid finger hair, 3: 556 59, 558 (ill.), 559 (ill.) Milk ant food experiment, 3: 635 38, 636 (ill.), 637 (ill.) pasteurization of, 3: 480, 485 spoiled milk and temperature experiment, 3: 485 88, 487 (ill.) Milky Way, 6: 1123, 1124 Mimicry, 1: 62 Mineral oil, 1: 170 73, 170 (ill.), 171 (ill.), 172 (ill.) Minerals, 5: 969 79, 970 (ill.), 6: 1223 36, 1234 (ill.) in bones, 1: 113, 114 crystalline, 2: 243, 244 definition of, 5: 969 design an experiment for, 5: 978, 6: 1234 36 dyes from, 2: 299 formation of, 5: 970 in fossil formation, 3: 523 hard water sources experiment, 6: 1231 34, 1232 (ill.) health effects of, 4: 761, 6: 1223 36, 1224 (ill.), 1225 (ill.), 1226 (ill.), 1227 (ill.), 1234 (ill.), 1235 (ill.) in soil, 5: 1063, 1064, 1064 (ill.) stalagmites and stalactite experiment, 1: 135 39, 137 (ill.) testing mineral characteristics experiment, 5: 971 75, 973 (ill.), 974 (ill.) trace, 6: 1226 in water, 6: 1225 26 Mini biomes, 1: 106 8, 106 (ill.), 107 (ill.) Miniaturization, 4: 750 Mirrors, 6: 1110 11 Mississippi River, 5: 955 Experiment Central, 2nd edition
Mixtures and solutions, 4: 723 34, 723 (ill.) design an experiment for, 4: 732 33 hypertonic vs. hypotonic, 4: 798 osmosis of, 4: 798 separation of, 4: 724 25, 725 (ill.), 5: 1031 34, 1032 (ill.) suspensions vs. solutions experiment, 4: 725 30, 729 (ill.) Tyndall effect experiment, 4: 730 32, 731 (ill.), 732 (ill.) types of, 4: 723 24, 724 (ill.), 5: 1031 32, 1033 (ill.) unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) Mnemonics, 4: 700, 701 4, 701 (ill.), 702 (ill.), 703 (ill.) Moh’s Hardness Scale, 5: 974 Molds antibiotics from, 3: 539 40, 4: 712 diffusion of, 4: 797 food spoilage by, 3: 477 80, 478 (ill.) growing penicillin experiment, 4: 713 16, 713 (ill.), 715 (ill.) moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) Molecules carbon, 4: 749 crystals, 2: 244 molecule size and osmosis experiment, 4: 806 9, 808 (ill.), 809 (ill.) in nanotechnology, 4: 747 48 salt, 4: 747 water, 1: 20, 21 (ill.), 4: 747, 748 (ill.), 6: 1259, 1259 (ill.) Mollusks, 5: 1019 20, 1020 (ill.), 1021 Molting, 3: 631, 5: 1020 21 Monocot plants, 1: 145 47, 145 (ill.), 146 (ill.), 147 (ill.), 148 Monosodium glutamate (MSG), 1: 177 Months, 6: 1175 Moon gravity and, 3: 579, 580 of Jupiter, 6: 1109 lunar eclipse, 2: 326, 326 (ill.), 327 29, 328 (ill.), 329 (ill.) mountains on, 6: 1109 cxlix
GENERAL SUBJECT INDEX
orbit of, 5: 982, 986 (ill.) phases of, 2: 329 30, 330 (ill.), 331 (ill.) tides and, 4: 774, 775 (ill.), 5: 983 84 in timekeeping, 6: 1175 Mordants, 2: 300 301, 300 (ill.), 304 7, 306 (ill.), 307 (ill.) Mosses, 1: 131 Motion circular, 3: 492 93, 493 (ill.), 501 5, 503 (ill.) three laws of, 3: 491 93, 492 (ill.), 493 (ill.) Motors, electric, 2: 358 (ill.), 5: 1087 89, 1088 (ill.), 1089 (ill.) Mount Everest, 4: 735, 736 (ill.) Mount Vesuvius, 6: 1237, 1237 (ill.), 1239 Mountain range, 4: 735 Mountains, 4: 735 45, 736 (ill.) air density and, 1: 36, 36 (ill.) desert formation experiment, 4: 741 44, 742 (ill.), 743 (ill.) design an experiment for, 4: 744 45 ecosystem of, 4: 737 38 formation of, 4: 735 37, 736 (ill.), 737 (ill.) on the moon, 6: 1109 mountain formation experiment, 4: 738 41, 739 (ill.), 740 (ill.) Mouths (insect), 3: 632 Movement by fish, 3: 402 3, 403 (ill.), 407 9, 409 (ill.), 410 of heat, 3: 615 17, 616 (ill.), 617 (ill.) water bottle rocket experiment, 3: 493 501, 495 (ill.), 498 (ill.), 499 (ill.), 500 (ill.) See also Motion MSG (Monosodium glutamate), 1: 177 Mucus, 1: 179 Multicellular organisms, 1: 141, 144 (ill.) Municipal water supply, 3: 609 12, 610 (ill.) Murray, John, 5: 995 Muscle contractions, 1: 115 16, 116 (ill.), 120 23, 122 (ill.) Muscle fibers, 1: 115, 115 (ill.), 124 Muscle strength, 1: 115 16, 115 (ill.), 120 23, 122 (ill.) Muscles, 1: 113 25 design an experiment for, 1: 123 25 muscle strength and fatigue experiment, 1: 120 23, 122 (ill.) strength of, 1: 115 16, 115 (ill.) cl
Mushrooms, 1: 81, 108, 3: 540, 550 (ill.) Music, 4: 700, 701 4, 701 (ill.), 702 (ill.), 703 (ill.) Mutations, DNA, 3: 555 Mycelium, 3: 538, 539 (ill.) Mystery powders experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.)
Nails, magnetized, 4: 674 78, 674 (ill.), 676 (ill.) Nanometers, 4: 787 Nanorobots (nanobots), 4: 749, 750 Nanotechnology, 4: 747 57, 748 (ill.), 749 (ill.) building blocks of, 4: 747 48, 748 (ill.), 750 (ill.) design an experiment for, 4: 756 57 nanosize and properties of materials experiment, 4: 750 53, 752 (ill.) nanosize and reaction rate experiment, 4: 753 55, 754 (ill.), 755 (ill.) uses for, 4: 749 50 Nansen bottles, 5: 997 Napoleon Bonaparte, 3: 452, 479 Nares, 3: 403 4 National Weather Service, 6: 1273, 1275 (ill.) Native American baskets, 2: 390 91, 396 Natural dyes, 2: 299, 301 4, 302 (ill.), 303 (ill.), 304 7, 306 (ill.), 307 (ill.), 391 Natural fibers, 2: 301 4, 302 (ill.), 303 (ill.) Natural pesticides, 4: 843, 844 46, 847 52, 851 (ill.) Natural pollutants, 1: 48 Nebula, 6: 1124, 1124 (ill.) Nectar, 3: 425 26, 431 35, 433 (ill.) Needles (tree), 1: 103 Nervous system, 4: 843 44, 844 (ill.) Neutralization, 1: 4, 4: 860 Neutrons, 4: 828 Newton, Isaac energy, 5: 930 31 gravity, 5: 982 laws of motion, 3: 491, 579, 580 (ill.), 6: 1165 light, 2: 203 5, 203 (ill.), 205 (ill.), 4: 659 60, 659 (ill.) tides, 4: 774 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Newtonian fluids, 3: 440 41, 444 47, 446 (ill.), 447 (ill.) Newtonian laws of motion, 3: 491 93, 492 (ill.), 493 (ill.) bottle rocket experiment, 3: 493 501, 495 (ill.), 498 (ill.), 499 (ill.), 500 (ill.) planetary orbits and, 3: 579 80 on structures, 6: 1165 Niagara River, 5: 955 (ill.), 956 Nickel electroplating, 2: 344 45, 344 (ill.), 345 (ill.) Nile River, 5: 955, 956 (ill.) Nimbostratus clouds, 6: 1273 Nimbus clouds, 6: 1272 Nitrates, 1: 49 Nitric acid, 1: 164 Nitrogen, 1: 33, 85, 2: 230, 386 Nitrogen dioxide, 1: 45 Nitrogen oxides, 1: 1, 46 Noble gases, 4: 830 Non Newtonian fluids, 3: 440 41, 444 47, 446 (ill.), 447 (ill.) Nonpoint source pollution, 3: 604, 605 (ill.) Nontarget organisms, 4: 846 Nontasters, 1: 180 86 North Star, 6: 1125 28, 1126 (ill.), 1127 (ill.) Notes, sticky, 1: 22, 22 (ill.), 26 30, 27 (ill.), 28 (ill.), 29 (ill.) Nuclear fusion, 6: 1124 Nucleation, 2: 246 Nucleotides, 2: 286 87, 291 Nucleus cell, 1: 86, 142 43, 2: 285, 289 91, 289 (ill.), 290 (ill.) comet, 2: 216 Number, atomic, 4: 828 Nutrients dissolved oxygen level changes from, 2: 272 73, 279 in eutrophication, 1: 49 50, 50 (ill.) how good is my diet experiment, 4: 766 69, 768 (ill.), 769 (ill.) needed for health, 4: 760 61, 761 (ill.) for plants, 5: 883, 895 role of, 4: 759 Experiment Central, 2nd edition
Nutrition, 4: 759 70, 760 (ill.) design an experiment for, 4: 769 70 dietary carbohydrate and fat sources experiment, 4: 761 64, 763 (ill.), 764 (ill.) dietary proteins and salt sources experiment, 4: 764 66, 765 (ill.), 766 (ill.) essential nutrients in, 4: 760 61, 761 (ill.) how good is my diet experiment, 4: 766 69, 768 (ill.), 769 (ill.) muscle strength and fatigue experiment, 1: 123, 124 (ill.) vitamins and minerals in, 6: 1223 26, 1224 (ill.), 1225 (ill.), 1226 (ill.), 1227 (ill.), 1234 (ill.), 1235 (ill.) Nutrition Fact Labels, 4: 767 69, 768 (ill.), 769 (ill.) Nylon, 3: 509, 6: 1139 44, 1141 (ill.), 1143 (ill.) Nymphs, 4: 645
O layer (soil), 5: 1066, 1067 (ill.) Observation, controlled, 5: 1007 Occluded fronts, 1: 35 Ocean currents, 4: 772 74, 774 (ill.), 780 83, 782 (ill.) Ocean water. See Seawater Ocean waves, 4: 773, 774 (ill.), 784 Oceanographers, 4: 771 Oceans, 4: 771 85 biome, 1: 103 convection current experiment, 4: 780 83, 782 (ill.) design an experiment for, 4: 783 84 eutrophication experiment, 1: 55 58, 57 (ill.) life in, 4: 774 75, 775 (ill.) photosynthesis in, 4: 872 73, 873 (ill.) salinity and stratification experiment, 4: 775 80, 778 (ill.) seawater properties, 4: 771 72, 772 (ill.), 773 (ill.) size of, 1: 48, 4: 772 See also Tides cli
GENERAL SUBJECT INDEX
Octopi, 1: 63 Odors as animal defenses, 1: 62 63, 62 (ill.), 65 68, 66 (ill.), 67 (ill.) pollinators attracted by, 3: 426 27 smell taste relationship experiment, 1: 186 89, 187 (ill.) See also Smell, sense of Oersted, Hans Christian, 4: 672, 672 (ill.) Ogallala aquifer, 3: 602 Oil pollution, 1: 48 49, 49 (ill.), 58 Oil power plants, 1: 1, 46 Oil spills, 1: 48 49, 49 (ill.), 50 Oils heat capacity experiment, 3: 625 28, 626 (ill.), 627 (ill.), 628 (ill.) viscosity and temperature experiment, 3: 441 44, 442 (ill.), 443 (ill.) Old Farmers Almanac, 6: 1284 Olfactory cells, 1: 179, 179 (ill.), 189 Olive oil, 3: 625 28, 626 (ill.), 627 (ill.), 628 (ill.) Onions, 2: 392 95, 394 (ill.), 395 (ill.) Oobleck, 3: 448 Oort cloud, 2: 215 Opossums, 1: 61 Optics and optical illusions, 4: 787 96, 787 (ill.), 795 (ill.) design an experiment for, 4: 794 95 focal length of lens experiment, 4: 788 91, 788 (ill.) light and how we view it, 4: 787 88 seeing optical illusions experiment, 4: 791 94, 791 (ill.), 792 (ill.), 793 (ill.) See also Light Orange juice ant food experiment, 3: 635 38, 636 (ill.), 637 (ill.) sources of vitamin C experiment, 6: 1226 31, 1229 (ill.) Orbits, 5: 981 94, 982 (ill.), 983 (ill.), 984 (ill.), 985 (ill.), 992 (ill.) centrifugal force and gravity experiment, 5: 989 92, 990 (ill.) centripetal force in, 3: 493, 504 (ill.), 505 of comets, 2: 215 16, 216 (ill.) design an experiment for, 3: 505, 5: 992 94 clii
discovery of, 5: 981 82, 6: 1109 10 elliptical, 3: 579, 5: 981 of the moon, 5: 982, 986 (ill.) Newtonian laws of motion and, 3: 579 80 pendulum rotation experiment, 5: 985 89, 988 (ill.) star movement and, 6: 1124 Organelles, 1: 86, 142 Organic farming, 2: 229 30 Organic food, 4: 855 56 Organic matter, 5: 1063, 1066 Organic waste, 2: 229, 230, 235 39, 236 (ill.), 238 (ill.), 239 (ill.) Organisms, nontarget, 4: 846 Organophosphates, 4: 843 44, 844 (ill.) Orion nebula, 6: 1124 (ill.) Oscillation, 6: 1180 85, 1182 (ill.), 1183 (ill.) Osmosis and diffusion, 4: 797 810, 797 (ill.) design an experiment for, 4: 809 10 molecule size experiment, 4: 806 9, 808 (ill.), 809 (ill.) of nutrients, 5: 883 plastic bag membrane experiment, 4: 798 803, 799 (ill.), 800 (ill.), 801 (ill.), 802 (ill.) process of, 4: 797, 798 salt water osmosis experiment, 4: 803 6, 803 (ill.), 804 (ill.), 805 (ill.) through semipermeable membranes, 3: 452, 4: 797 of water for plants, 4: 798, 5: 897 98, 898 (ill.), 899 (ill.) Osteoporosis, 1: 114, 116 (ill.) Overfishing, 3: 411 Oxidation-reduction reactions, 4: 811 25, 811 (ill.), 823 (ill.), 824 (ill.) acid copper reduction experiment, 4: 813 17, 814 (ill.), 815 (ill.) copper color change experiment, 4: 820 23, 820 (ill.), 821 (ill.), 822 (ill.) design an experiment for, 4: 823 25 examples of, 4: 812 13 process of, 1: 164, 4: 811 rusting experiment, 1: 152 56, 155 (ill.) rusting process as, 1: 151, 152 (ill.), 4: 812, 823 (ill.) steel wool rust experiment, 4: 817 20, 818 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Oxygen in air, 1: 33 altitude and, 1: 36 for composting, 2: 230 diffusion in blood, 4: 797, 798 (ill.) for fish, 3: 402, 404 6, 405 (ill.) in landfills, 2: 231 from photosynthesis, 5: 884 85 in plant respiration, 4: 871, 872, 5: 883 rust reaction, 1: 163, 165 in water molecules, 1: 20, 21 (ill.), 4: 747, 748 (ill.), 6: 1259, 1259 (ill.) See also Dissolved oxygen Ozone, 1: 46
Pacific Ocean, 4: 771 Packing peanuts, 4: 691 94, 693 (ill.), 694 (ill.) Packing tape, 1: 21 Paleontologists, 3: 521, 534 (ill.), 535 Palmieri, Luigi, 2: 313 Papain, 2: 360, 365 68, 366 (ill.), 367 (ill.) Papaya, 2: 360, 365 68, 366 (ill.), 367 (ill.) Paper chromatography, 5: 1033, 1034 39, 1036 (ill.), 1037 (ill.) Papillae, 1: 178, 179, 181 Papyrus, 1: 19 Parasites, 3: 538 Parents, genetics from, 3: 553 55 Parrot fish, 1: 61 Particulate matter, 1: 45, 46 47, 59 Pascal, Blaise, 1: 34 Pascal (unit of measure), 1: 34 Passive solar energy systems, 5: 1082, 1084 87, 1084 (ill.), 1086 (ill.) Pasteur, Louis, 1: 86, 3: 452, 4: 711 12, 712 (ill.) Pasteurization, 3: 480, 480 (ill.), 485, 4: 712 Patinas, 1: 173 75, 174 (ill.), 175 (ill.) Patterns, camouflage, 1: 61 62 Pea plants, 3: 554 Pectin, 3: 467 70, 468 (ill.), 469 (ill.) Pelletier, Pierre Joseph, 1: 191 Pencil lead. See Graphite Experiment Central, 2nd edition
Pendulums pendulum oscillation time experiment, 6: 1180 85, 1182 (ill.), 1183 (ill.) pendulum rotation experiment, 5: 985 89, 988 (ill.) in timekeeping, 6: 1178 Penicillin discovery of, 3: 539 40, 4: 712, 712 (ill.) growing penicillin experiment, 4: 713 16, 713 (ill.), 715 (ill.) Pennies, 4: 813 17, 814 (ill.), 815 (ill.) Pepsin, 2: 360 Perception, 4: 791 94, 791 (ill.), 792 (ill.), 793 (ill.) Perfect flowers, 3: 424 Periodic table, 4: 827 42, 831 (ill.) conductivity of elements experiment, 4: 830 35, 833 (ill.) design an experiment for, 4: 840 42 development of, 4: 827 28, 828 (ill.) electrons released by metals experiment, 4: 838 40, 840 (ill.), 841 (ill.), 842 how to read, 4: 828 30, 829 (ill.), 830 (ill.) solubility of elements experiment, 4: 835 38, 835 (ill.), 837 (ill.) Perkin, William Henry, 2: 299 300, 299 (ill.) Permineralization, 3: 522, 522 (ill.), 523, 523 (ill.) Perrault, Claude, 5: 955 Perroult, Pierre, 6: 1247 48 Pesticides, 4: 843 57, 846 (ill.), 848 (ill.) benefits and dangers of, 4: 845 48 chemical, 4: 843 44, 844 (ill.) degradation of, 4: 847 design an experiment for, 4: 855 57 natural, 4: 843, 844 46, 847 48 natural vs. chemical pesticides experiment, 4: 848 52, 851 (ill.) safe handling of, 4: 851 water movement of pesticides experiment, 4: 851 55, 854 (ill.) water pollution by, 1: 49, 4: 846 47, 847 (ill.) Pests, definition of, 4: 843 Petals, 3: 424, 424 (ill.) Petri dishes, 4: 716 20, 718 (ill.), 719 (ill.) Petrifaction, 3: 523, 535 Petrified Forest, 3: 523 cliii
GENERAL SUBJECT INDEX
pH, 4: 859 69 of acid rain, 1: 1, 2 (ill.), 3 (ill.), 4: 860 61, 861 (ill.) brine shrimp experiment, 1: 5 8, 7 (ill.) chemical titration experiment, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) definition of, 1: 1, 4: 859 design an experiment for, 4: 868 69 dye colorfastness and, 2: 307 household chemicals pH experiment, 4: 861 65, 861 (ill.), 863 (ill.) jelly and pectin experiment, 3: 467 70, 468 (ill.), 469 (ill.) measurement of, 4: 859 60, 859 (ill.), 860 (ill.) microorganisms and decomposition experiment, 2: 233 35, 234 (ill.), 235 (ill.), 236 neutral, 1: 9 plant growth experiment, 1: 9 12, 11 (ill.) rate of erosion experiment, 2: 386 for separation and identification, 5: 1033, 1034 (ill.) soil, 4: 860, 5: 1064 soil pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) pH indicators. See Acid/base indicators pH meter, digital, 4: 860, 860 (ill.) Phenylthiocarbamide (PTC), 3: 559 61, 561 (ill.) Pheromones, 4: 844 Phloem, 4: 872, 5: 884, 6: 1296 Phosphates, 1: 49, 55 58, 57 (ill.) Phosphorescence, 4: 660 Phosphorus, 1: 55, 2: 386, 4: 761, 5: 1064 Photo chromic glass, 4: 823 Photosynthesis, 4: 871 82, 871 (ill.), 872 (ill.), 873 (ill.) by algae, 1: 74, 75 (ill.) chlorophyll in, 1: 191 201, 191 (ill.), 4: 871 72, 5: 884 85 design an experiment for, 4: 880 81 discovery of, 4: 871 dissolved oxygen from, 2: 271 72 light colors and plant growth experiment, 1: 197 200, 197 (ill.), 199 (ill.), 200 (ill.), 4: 873 77, 875 (ill.), 876 (ill.) cliv
light intensity and plant growth experiment, 4: 877 80, 878 (ill.), 879 (ill.), 880 (ill.) process of, 1: 191 201, 191 (ill.), 4: 871 72, 5: 884 85, 885 (ill.), 897 Phototropism, 6: 1191 93, 1192 (ill.), 1193 (ill.) auxins in, 6: 1191 92, 1193, 1193 (ill.), 1209 phototropism maze experiment, 6: 1193 97, 1195 (ill.), 1196 (ill.) Photovoltaic cells, 5: 1083, 1087 89, 1088 (ill.), 1089 (ill.) Physical changes, 1: 163, 164 (ill.) Physical properties, 1: 163 Phytoplankton, 4: 873, 873 (ill.) Pi, 4: 701 4, 701 (ill.), 702 (ill.), 703 (ill.) Pickling, 3: 452, 452 (ill.) Pigments colors, 2: 205 in leaves, 1: 192 light colors and plant growth experiment, 1: 197 200, 197 (ill.), 199 (ill.), 200 (ill.) plant pigment separation experiment, 1: 193 97, 195 (ill.), 196 (ill.) Pill bugs, 1: 68 Pineapple, 2: 368 72, 370 (ill.), 371 (ill.) Pistil, 3: 423 24, 424 (ill.) Pitch (sound), 5: 1095 (ill.), 1099 1102, 1100 (ill.), 1101 (ill.) Planetary orbits. See Orbits Plankton, 2: 279, 4: 774 Plant anatomy, 5: 883 95, 883 (ill.), 884 (ill.), 885 (ill.) design an experiment for, 5: 893 95 in photosynthesis, 5: 884 85, 885 (ill.) plant hormones and growth experiment, 5: 886 90, 888 (ill.), 889 (ill.) for pollination, 3: 423 27, 425 (ill.), 426 (ill.), 427 (ill.) water uptake experiment, 5: 890 93, 892 (ill.), 893 (ill.) Plant cells. See Cells Plant growth, 5: 1084 87, 1084 (ill.), 1086 (ill.) acid rain experiment, 1: 9 12, 11 (ill.) annual, 1: 71 74, 72 (ill.), 73 (ill.), 74 (ill.) auxins in, 6: 1191 92, 1209 design an experiment for, 1: 82 83 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
heliotropism and plant movement experiment, 6: 1201 4, 1202 (ill.), 1203 (ill.) lichen growth experiment, 1: 79 82, 81 (ill.) by lichens, 1: 72 74, 74 (ill.) light colors and plant growth experiment, 1: 197 200, 197 (ill.), 199 (ill.), 200 (ill.), 4: 873 77, 875 (ill.), 876 (ill.) light intensity and plant growth experiment, 4: 877 80, 878 (ill.), 879 (ill.), 880 (ill.) organic waste for plant growth experiment, 2: 236 39, 236 (ill.), 238 (ill.), 239 (ill.) phototropism effect on, 6: 1191 93, 1192 (ill.), 1193 (ill.) phototropism maze experiment, 6: 1193 97, 1195 (ill.), 1196 (ill.) plant hormones and growth experiment, 5: 886 90, 888 (ill.), 889 (ill.) soil pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) tree growth experiment, 1: 74 79, 78 (ill.) by trees, 1: 71 72, 72 (ill.), 73 (ill.) water movement of pesticides experiment, 4: 851 55, 854 (ill.) Plant hormones leaf/stem cuttings and auxins experiment, 6: 1209 16, 1213 (ill.), 1214 (ill.) in phototropism, 6: 1191 92, 1193, 1193 (ill.) plant hormones and growth experiment, 5: 886 90, 888 (ill.), 889 (ill.) in vegetative propagation, 6: 1208, 1209 Plants acid rain damage to, 1: 2 anti bacterial plant experiment, 2: 392 95, 394 (ill.), 395 (ill.) cave, 1: 131 climbing, 6: 1192, 1205 (ill.) color perception, 2: 214 cultural uses of, 2: 389, 390 92, 392 (ill.), 400, 5: 897 desert, 1: 105, 5: 898, 899 900, 908, 908 (ill.) dicot, 1: 145 47, 145 (ill.), 146 (ill.), 147 (ill.), 148 enzymes from, 2: 360 fossils of, 3: 524 (ill.) genetic engineering of, 4: 845, 846 (ill.), 848 heliotropic, 6: 1201 4, 1202 (ill.), 1203 (ill.) Experiment Central, 2nd edition
how they stand up, 5: 898 99, 899 (ill.) medicinal, 2: 389 90, 390 (ill.), 400 minerals absorbed by, 6: 1226 monocot vs. dicot, 1: 145 47, 145 (ill.), 146 (ill.), 147 (ill.), 148 nutrients for, 5: 883, 895 organic waste for plant growth experiment, 2: 235 39, 236 (ill.), 238 (ill.) pigment separation experiment, 1: 193 97, 195 (ill.), 196 (ill.) rainforest, 1: 106 respiration by, 4: 871, 872, 5: 883, 898 shade, 5: 885, 6: 1191 wilting, 5: 899, 900 (ill.) See also Flowers; Photosynthesis; Pollination; Water plants Plants and water, 5: 897 909, 897 (ill.), 900 (ill.), 908 (ill.) design an experiment for, 5: 907 9 in dry environments, 5: 899 900 osmosis for, 4: 798, 5: 897 98, 897 (ill.), 898 (ill.), 899 (ill.) rate of erosion experiment, 2: 381 86, 382 (ill.), 383 (ill.), 384 (ill.) transpiration rate and environment experiment, 5: 904 7, 906 (ill.) turgor pressure experiment, 5: 900 904, 900 (ill.), 902 (ill.), 903 (ill.) Plasmolysis, 5: 899 Plastics adhesives from, 1: 19 decomposition of, 2: 231 glue adherence experiment, 1: 22 25, 23 (ill.), 24 (ill.) light refraction experiment, 4: 666 69, 666 (ill.), 667 (ill.) litter, 1: 50 plastic bag membrane experiment, 4: 798 803, 799 (ill.), 800 (ill.), 801 (ill.), 802 (ill.) polymer strength experiment, 5: 914 15, 917 (ill.), 918 (ill.) properties of different plastics experiment, 5: 923 25, 924 (ill.), 925 (ill.), 926 recycling, 5: 923 See also Polymers clv
GENERAL SUBJECT INDEX
Plate tectonics earthquakes, 2: 311 formation of, 5: 970 mountain formation, 4: 735 37, 736 (ill.), 737 (ill.) mountain formation experiment, 4: 738 41, 739 (ill.), 740 (ill.) volcanic eruptions, 6: 1238 39 Playing dead, 1: 61, 65 68, 66 (ill.), 67 (ill.) Plywood, 6: 1298 Pnematocyst, 1: 149 Point source pollution, 3: 604, 605 (ill.) Poisoning, food, 3: 477 Polaris (North Star), 6: 1125 28, 1126 (ill.), 1127 (ill.) Poles, magnetic, 4: 671 72 Pollen, 3: 424, 425, 426, 437 Pollination of flowers, 3: 423 27, 425 (ill.), 426 (ill.), 427 (ill.) genetics of, 3: 425, 425 (ill.), 6: 1207, 1207 (ill.), 1208 (ill.) self pollination vs. cross pollination experiment, 3: 427 31, 430 (ill.) Pollinators, 3: 425 27, 431 35, 433 (ill.) Pollution. See Air pollution; Water pollution Polyester, 3: 509 Polyethylene, 5: 912, 914 15, 917 (ill.), 918 (ill.) Polymerization, 5: 912 Polymers, 4: 686, 5: 911 27, 912 (ill.), 913 (ill.) adhesives from, 1: 19, 21 chains of, 5: 911 12, 912 (ill.), 913, 913 (ill.), 914 15, 914 (ill.), 917 (ill.), 918 (ill.), 919 design an experiment for, 5: 925 27 polymer slime experiment, 5: 919 23, 921 (ill.), 922 (ill.) properties of, 5: 912 13 properties of different plastics experiment, 5: 923 25, 924 (ill.), 925 (ill.), 926 synthetic, 5: 911 12 tensile strength experiment, 5: 914 19, 917 (ill.), 918 (ill.) Polysaccharides, 5: 919 23, 921 (ill.), 922 (ill.) Polyvinyl acetate (PVA), 1: 20, 22 25, 23 (ill.), 167 70, 168 (ill.), 169 (ill.) clvi
Pombal, Marquis de, 2: 312 Pomo Indians, 2: 390 91, 396 Pompeii, 6: 1237, 1237 (ill.), 1239 Pores, 3: 601 Potassium, 4: 761, 5: 1034, 1064, 6: 1226 Potassium carbonate, 4: 835 38, 835 (ill.), 837 (ill.) Potatoes, 6: 1208, 1216 19, 1218 (ill.) Potential energy, 5: 929 40, 929 (ill.) build a roller coaster experiment, 5: 934 38, 935 (ill.), 936 (ill.), 937 (ill.) definition of, 5: 929 design an experiment for, 5: 939 40 height of objects experiment, 5: 931 34, 932 (ill.), 933 (ill.) Potometers, 5: 890 93, 892 (ill.), 893 (ill.) Potter, Beatrix, 1: 73 Power plants, 1: 1, 46, 3: 590 Precipitation mountain ecosystems, 4: 737 mountains and desert formation experiment, 4: 741 44, 742 (ill.), 743 (ill.) in the water cycle, 5: 955, 6: 1247 in weather, 6: 1271 See also Rain Predators, 1: 61 63 Preservation of food. See Food preservation Pressure. See Air pressure; Turgor pressure; Water pressure Priestley, Joseph, 4: 871 Primary colors, 2: 205 Prisms, 2: 204, 205 (ill.), 210 12, 211 (ill.), 212 (ill.), 213 Processed food, 4: 760 Products, of chemical reactions, 1: 151, 164 65 Prokaryotes, 1: 86 Prominences, solar, 2: 326 Propagation. See Vegetative propagation Propellers, 3: 418 21, 418 (ill.), 419 (ill.), 420 (ill.) Proteins denatured, 3: 463 dietary protein sources experiment, 4: 764 66, 765 (ill.), 766 (ill.) DNA isolation experiment, 2: 289 91, 289 (ill.), 290 (ill.) in food spoilage, 3: 478 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
hydrophilic vs. hydrophobic, 3: 465, 465 (ill.) for nutrition, 4: 761 temperature and enzyme action experiment, 2: 368 72, 370 (ill.), 371 (ill.) Protists, 4: 712 Protons, 2: 349, 4: 828 Protozoa, 4: 711, 712 PTC (Phenylthiocarbamide), 3: 559 61, 561 (ill.) Puffer fish, 1: 63 Pulleys, 5: 1049, 1051 55, 1054 (ill.) Pupa, 3: 633 34, 4: 645 Purple cabbage, 2: 304 7, 306 (ill.), 307 (ill.) Purple dyes, 2: 299 PVA (Polyvinyl acetate), 1: 20, 22 25, 23 (ill.) Pyramids, 5: 1048 Pythagoras, 5: 1096
Quadricep muscles, 1: 120 23, 122 (ill.) Quarters (coin), 2: 344 45, 344 (ill.), 345 (ill.) Queen ants, 3: 633, 634
Radiation of heat, 3: 615, 616 17 infrared, 3: 616 17 Radioactive decay, 3: 525, 6: 1238 Radioactivity (chemical reaction), 1: 164 Radioisotope dating, 3: 525 Radiometers, 1: 43 Radiosonde balloons, 6: 1283 Radish seeds, 3: 570 73, 572 (ill.) Radon, 1: 48 Rain dissolved oxygen level changes from, 2: 272 mountain effect on, 4: 737 normal pH level, 1: 1, 2 (ill.) in the water cycle, 5: 955, 6: 1247 See also Acid rain Rain shadow, 4: 741 44, 742 (ill.), 743 (ill.) Rainbows, 2: 204 (ill.), 205, 4: 664 65, 664 (ill.), 665 (ill.) Experiment Central, 2nd edition
Raindrops, 4: 659 60, 6: 1272 Rainforests, 1: 105 6, 105 (ill.), 2: 390 Ramps, 5: 1047 48, 1048 (ill.), 1049 (ill.) Rats, kangaroo, 1: 105 Rayon, 3: 509, 5: 911 RDA (Recommended Daily Allowance), 6: 1223, 1226 Reactants, 1: 151, 164 65 Reactions, chemical. See Chemical reactions Reactions, for every action, 3: 492, 494 Reaumur, Rene Antoine de, 2: 359 Recessive inheritance, 3: 554 55 Recombinant DNA technology, 3: 555 Recommended Daily Allowance (RDA), 6: 1223, 1226 Recycling, 2: 231, 240, 5: 914, 915 (ill.), 923 Red cabbage juice chemical titration experiment, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) pH of household chemicals experiment, 4: 861 65, 861 (ill.), 863 (ill.) unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) Red hair, 3: 555 Red light bending, 2: 204 5 light colors and plant growth experiment, 4: 873 77, 875 (ill.), 876 (ill.) temperature of different colors experiment, 2: 210 12, 211 (ill.), 212 (ill.), 213 wavelength of, 2: 203 Red Sea, 5: 996 97, 996 (ill.) Redshift, 6: 1112, 1112 (ill.) Reduction reactions. See Oxidation reduction reactions Reeds, 2: 390 91, 396 99, 398 (ill.), 399 (ill.) Reflection, in raindrops, 4: 659 60 Reflector telescopes, 6: 1110 11, 1111 (ill.) Reflectors, solar, 5: 1082 83 Refraction light refraction experiment, 4: 666 69, 666 (ill.), 667 (ill.) make a rainbow experiment, 4: 664 65, 664 (ill.), 665 (ill.) in raindrops, 4: 659 60 Refractor telescopes, 6: 1110, 1111 (ill.) clvii
GENERAL SUBJECT INDEX
Refrigeration, 3: 453, 479 80 Relative age dating, 3: 524 Relative density, 2: 260 64, 262 (ill.), 263 (ill.) Relativity, special, 6: 1179, 1180 (ill.) Renaissance age, 5: 981 Renewable energy, 5: 941 53 design an experiment for, 5: 951 52 hydropower and water pressure experiment, 5: 948 51, 948 (ill.), 949 (ill.), 950 (ill.) sources of, 5: 942 43, 942 (ill.), 943 (ill.) wind energy experiment, 5: 944 48, 945 (ill.), 946 (ill.) See also Solar energy Renewable materials, 4: 691 94, 693 (ill.), 694 (ill.), 6: 1297 98 Rennin, 2: 360 Reproduction asexual, 6: 1208 by bacteria, 1: 87 cellular, 1: 143 44 sexual, 6: 1207 by yeast, 1: 143 44, 147 48, 147 (ill.), 148 (ill.), 149 (ill.), 150 Resins, tree, 3: 523 24 Resistance, bacterial, 1: 88 90, 95 100, 97 (ill.) Respiration dissolved oxygen changes experiment, 2: 279 84, 281 (ill.), 282 (ill.), 283 by fish, 3: 402, 403 (ill.), 404 6, 405 (ill.) in germination, 3: 565 66 by plants, 4: 871, 872, 5: 883, 898 Resultants, 6: 1165 Results of experiments, 5: 1008 Retina, 2: 205, 205 (ill.), 4: 787 Retinal, 6: 1224 Revolving levers, 5: 1051, 1051 (ill.) Ribosomes, 1: 86 Rice, 4: 760, 6: 1223 24, 1226 (ill.) Richter, Charles F., 2: 312 (ill.), 313 Richter Scale, 2: 312 (ill.), 313 Rings, tree, 1: 71 72 Ringworm, 3: 538 Rivers, 5: 955 67, 955 (ill.), 967 (ill.) course of, 5: 956, 967 (ill.) design an experiment for, 5: 965 66 clviii
dissolved oxygen in, 2: 271 84 glacier erosion trench experiment, 5: 957 60, 958 (ill.), 959 (ill.) river erosion experiment, 5: 962 65, 963 (ill.), 964 (ill.), 965 (ill.), 966 stream pattern experiment, 5: 960 62, 961 (ill.) water pollution of, 1: 48 Rocket launcher, 3: 495 98, 498 (ill.), 499 (ill.), 500 (ill.) Rockets, water bottle, 3: 493 501, 495 (ill.), 498 (ill.), 499 (ill.), 500 (ill.) Rocks, 5: 969 79, 970 (ill.), 971 (ill.) classification of, 5: 970 71 classifying rocks experiment, 5: 975 78, 975 (ill.), 976 (ill.), 977 (ill.) crystalline, 2: 243, 244, 255 definition of, 5: 969 design an experiment for, 5: 978 igneous, 5: 970, 975 78, 975 (ill.), 976 (ill.), 977 (ill.) lichen on, 1: 74, 79 metamorphic, 5: 971, 975 78, 975 (ill.), 976 (ill.), 977 (ill.) molten, 6: 1238 sedimentary, 3: 522, 5: 971, 975 78, 975 (ill.), 976 (ill.), 977 (ill.) in soil formation, 5: 1063 65, 1064 (ill.), 1065 (ill.) weathering of, 5: 1063 65 Rocky Mountains, 4: 735 Rodale, J. I., 2: 229 Rodenticides, 4: 843 Rodents, desert, 1: 104 5 Rods (eye), 2: 205, 205 (ill.) Rohrer, Heinrich, 4: 749 (ill.) Roller coasters, 5: 934 38, 935 (ill.), 936 (ill.), 937 (ill.) Romans, 2: 389 Rooting hormones, 6: 1209 16, 1213 (ill.), 1214 (ill.) Roots acid rain experiment, 1: 9 12, 11 (ill.) annual growth of, 1: 71 plant hormones and growth experiment, 5: 886 90, 888 (ill.), 889 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
plant water uptake experiment, 5: 890 93, 892 (ill.), 893 (ill.) plants and the rate of erosion experiment, 2: 381 86, 382 (ill.), 383 (ill.), 384 (ill.) role of, 5: 883 84, 883 (ill.) root growth and gravity experiment, 6: 1197 1201, 1198 (ill.), 1199 (ill.), 1200 (ill.) tropism effect on, 6: 1192 water absorbed by, 5: 897 98, 897 (ill.), 898 (ill.) Rotation, 5: 981 94, 982 (ill.), 983 (ill.), 984 (ill.), 992 (ill.) centrifugal force and gravity experiment, 5: 989 92, 990 (ill.) Coriolis force, 5: 984 85, 985 (ill.) design an experiment for, 5: 992 94 effect on tides, 5: 983 84 pendulum rotation experiment, 5: 985 89, 988 (ill.) in timekeeping, 6: 1176, 1178 velocity of, 5: 985, 985 (ill.) Rubber adhesives, 1: 20, 22 25, 24 (ill.) Rubbing. See Friction Runoff of pesticides, 4: 847, 847 (ill.), 851 55, 854 (ill.) Rusting process of, 1: 151, 152 (ill.), 4: 812, 823 (ill.) steel wool rust experiment, 4: 817 20, 818 (ill.) synthesis reaction, 1: 153 54, 155 (ill.), 163
Saccharomyces cerevisiae, 3: 544 49, 547 (ill.), 548 (ill.) Sachs, Julius von, 1: 191 Safe Water Drinking Act, 1: 50 Saguaro cactus, 1: 105, 5: 900 Sail boats, 5: 944 48, 945 (ill.), 946 (ill.) Sailors, 4: 759, 6: 1223 Salinity, 5: 995 1004, 995 (ill.), 996 (ill.) acid copper reduction experiment, 4: 813 17, 814 (ill.), 815 (ill.) copper patina experiment, 1: 173 75, 174 (ill.), 175 (ill.) density ball experiment, 5: 1000 1003, 1001 (ill.), 1002 (ill.) Experiment Central, 2nd edition
design an experiment for, 5: 1003 4 dissolved oxygen level changes from, 2: 272 electrons released by metals experiment, 4: 838 40, 840 (ill.), 841 (ill.), 842 make a hydrometer experiment, 5: 997 1000, 998 (ill.), 999 (ill.) ocean convection currents experiment, 4: 780 83, 782 (ill.) salinity and turgor pressure experiment, 5: 900 904, 900 (ill.), 902 (ill.), 903 (ill.) salt water osmosis experiment, 4: 803 6, 803 (ill.), 804 (ill.), 805 (ill.) of seawater, 4: 771 72, 772 (ill.), 5: 995 97, 995 (ill.), 996 (ill.) solar heat storage experiment, 5: 1090 92, 1092 (ill.), 1093 Saliva, 1: 178 Salt attraction to water, 6: 1260 crystal formation experiment, 2: 246 50, 246 (ill.), 249 (ill.), 254 (ill.) dietary salt sources experiment, 4: 764 66, 765 (ill.), 766 (ill.) for food preservation, 3: 452, 452 (ill.), 479, 480 formation of, 4: 812, 5: 996 moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) molecules of, 4: 747 for nutrition, 4: 761 See also Salinity Salt water. See Seawater Salty taste, 1: 177, 179, 182 86 San Andreas Fault, 2: 322 (ill.) Sand in soil, 5: 1065, 1066 (ill.) soil horizon properties experiment, 5: 1067 73, 1071 (ill.), 1072 (ill.) soil type and runoff experiment, 2: 377 80, 378 (ill.), 379 (ill.) soils for fossil casts experiment, 3: 526 29, 528 (ill.) Sandy water, 4: 723, 723 (ill.) Sanitary landfills, 2: 231 Sapwood, 6: 1296 Satellite images, 2: 376 Saturation of colors, 2: 206 7, 214 clix
GENERAL SUBJECT INDEX
Sauveur, Joseph, 5: 1096 Scallop shells, 5: 1028 Scanning tunneling microscope (STM), 4: 748 Scarification of seeds, 3: 573 76, 574 (ill.), 575 (ill.), 576 (ill.) Scents. See Odors; Smell, sense of Schleiden, Matthias, 1: 142 Schwann, Theodor, 1: 142 Scientific method, 5: 1005 18, 1006 (ill.), 1007 (ill.), 1008 (ill.) design an experiment for, 5: 1017 18 how fruit flies appear experiment, 5: 1013 16, 1015 (ill.), 1016 (ill.) mystery powder identification experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) steps in, 5: 1005 8 Screws, 5: 1048 49, 1050 (ill.), 1057 60, 1058 (ill.), 1059 (ill.), 1060 (ill.) Scurvy, 4: 759 60, 760 (ill.), 6: 1223 Sea anemones, 1: 149 Seabirds, 1: 50 Seashells, 5: 1019 29, 1020 (ill.), 1022 (ill.) cave formation experiment, 1: 133 35, 134 (ill.) classifying seashells experiment, 5: 1025 27, 1027 (ill.) design an experiment for, 5: 1027 28 formation of, 5: 1020 21 fossil casts experiment, 3: 526 29, 528 (ill.) fossil formation experiment, 3: 530 33, 532 (ill.) strength of shells experiment, 5: 1022 25, 1023 (ill.), 1024 (ill.), 1025 (ill.) Seasons, 5: 981, 983, 983 (ill.), 984 (ill.) Seawater amount on the Earth, 3: 602 density of, 4: 772 freshwater from, 4: 724 25 properties of, 4: 771 72, 772 (ill.), 773 (ill.) salinity and stratification experiment, 4: 775 80, 778 (ill.) salinity of, 4: 771 72, 772 (ill.), 5: 995 97, 995 (ill.), 996 (ill.) stratification of, 4: 772 Second class lever, 5: 1051, 1051 (ill.) Second law of motion, 3: 492, 492 (ill.), 494, 579 80 Sediment, 3: 522, 524, 526 29, 528 (ill.) clx
Sedimentary rocks, 3: 522, 5: 971, 975 78, 975 (ill.), 976 (ill.), 977 (ill.) Sedimentation, 3: 609 12, 610 (ill.) Seed crystals, 2: 246 Seedlings, 3: 566, 566 (ill.), 5: 1084 87, 1084 (ill.), 1086 (ill.) Seeds development of, 3: 423 germination of, 3: 565 78, 566 (ill.) germination time experiment, 3: 570 73, 572 (ill.) seed scarification experiment, 3: 573 76, 574 (ill.), 575 (ill.), 576 (ill.) shells of, 5: 1019 temperature for germination experiment, 3: 566 70, 568 (ill.), 569 (ill.) Seesaws, 5: 1050 (ill.) Seismic belts, 5: 970 Seismic waves, 2: 311 Seismographs build a seismograph experiment, 2: 314 16, 315 (ill.), 316 (ill.) detecting volcanic eruptions experiment, 6: 1242 44, 1242 (ill.), 1243 (ill.), 1244 (ill.) for earthquakes, 2: 313 for volcanic eruptions, 6: 1239 Seismology, 2: 312 Selenium, 6: 1226 Self pollination, 3: 424, 425 (ill.), 427 31, 430 (ill.) Semiconductors, 4: 686 Semipermeable membranes molecule size and osmosis experiment, 4: 806 9, 808 (ill.), 809 (ill.) osmosis through, 3: 452, 4: 797 plastic bag membrane experiment, 4: 798 803, 799 (ill.), 800 (ill.), 801 (ill.), 802 (ill.) Sensory memory, 4: 697, 698 (ill.) Sepals, 3: 424, 424 (ill.) Separation and identification, 4: 724 25, 725 (ill.), 5: 1031 45, 1032 (ill.), 1033 (ill.) design an experiment for, 5: 1043 44 paper chromatography and ink experiment, 5: 1034 39, 1036 (ill.), 1037 (ill.) techniques for, 5: 1032 34, 1034 (ill.) unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Settling (separation technique), 5: 1032 Sewage, 1: 49 Sexual reproduction, 6: 1207 Shade plants, 5: 885, 6: 1191 Sharks, 3: 402 Shear stress, 3: 441 Shells of atoms, 4: 829, 830, 830 (ill.) of eggs, 4: 806 9, 808 (ill.), 809 (ill.), 846, 5: 1019 of seeds, 5: 1019 See also Seashells Shelter, 2: 391 Ships, 2: 257 (ill.), 259 See also Sail boats Shooting stars. See Comets and meteors Shoreline extension, 2: 231 Short term memory, 4: 697, 698 (ill.) Shrimp, 1: 5 8, 7 (ill.), 4: 775 Shutters, 4: 659 Sickle cell anemia, 2: 287, 3: 555 Sidereal day, 5: 981, 6: 1176 Sieve, 5: 1032 Silent Spring (Carson), 4: 846 Silk, 3: 509, 4: 685, 686 (ill.) Silkworms, 4: 712 Silt, 5: 1065, 1066 (ill.), 1067 73, 1071 (ill.), 1072 (ill.) Silver, 6: 1133 Simple craters, 2: 217, 218 (ill.) Simple machines, 5: 1047 62, 1061 (ill.) design an experiment for, 5: 1060 62 examples of, 5: 1047 51, 1048 (ill.), 1049 (ill.), 1050 (ill.), 1051 (ill.) lever lifting experiment, 5: 1055 57, 1057 (ill.) screw thread size experiment, 5: 1057 60, 1058 (ill.), 1059 (ill.), 1060 (ill.) wheel size and effort experiment, 5: 1051 55, 1054 (ill.) Single acting baking powder, 3: 464 Sirius (star), 6: 1124, 1124 (ill.) Skeletal muscles, 1: 115, 115 (ill.), 120 23, 122 (ill.) Skeletons, 1: 113, 114 (ill.), 5: 1019 Skunks, 1: 62 63, 62 (ill.) Experiment Central, 2nd edition
Slugs, 5: 1019 Smell design an experiment for, 1: 189 in fish, 3: 403 4 how it works, 1: 177, 179 80, 179 (ill.), 180 (ill.) smell taste relationship experiment, 1: 186 89, 187 (ill.) vanilla, 4: 797 See also Odors Smith, Robert Angus, 1: 3 Smog, 1: 47, 48 (ill.) Smoke, 1: 165 Smooth muscles, 1: 115, 115 (ill.) Snails, 2: 299, 5: 1019 Snakes, 1: 62, 104 5 Snow, 4: 737 Snowflakes, 2: 245 Soaps, 1: 95 100, 97 (ill.), 6: 1231 34, 1232 (ill.) See also Detergents Social insects, 3: 634 Sodium, 4: 812, 5: 995, 1034, 6: 1226 Sodium borate. See Borax Sodium carbonate, 4: 835 38, 835 (ill.), 837 (ill.) Sodium chloride. See Salinity; Salt Sodium hydrocarbonate, 1: 157 59, 157 (ill.), 158 (ill.), 159 (ill.) Sodium hydroxide, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) Sodium sulfate decahydrate (Glauber’s salt), 5: 1090 92, 1092 (ill.), 1093 Softwood, 6: 1295, 1302 6, 1304 (ill.), 1305 (ill.) Soil, 2: 232 35, 5: 1063 79 bacteria in, 1: 85 composition of, 5: 1064, 1064 (ill.), 1065 66, 1066 (ill.) design an experiment for, 5: 1078 79 formation of, 5: 1064 (ill.), 1065 (ill.) humus in, 2: 229, 230, 5: 1063, 1066 layers of, 5: 1066 67, 1067 (ill.) life in, 5: 1067, 1068 (ill.) microorganisms and decomposition experiment, 2: 232 35, 234 (ill.), 235 (ill.) microorganisms in, 2: 229, 5: 1063, 1067 oxygen pockets in, 5: 883 clxi
GENERAL SUBJECT INDEX
pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.) pH of, 4: 860, 5: 1064 properties of soil horizons experiment, 5: 1067 73 soil horizon properties experiment, 5: 1071 (ill.), 1072 (ill.) soil type and runoff experiment, 2: 377 80, 378 (ill.), 379 (ill.) soils for fossil casts experiment, 3: 526 29, 528 (ill.) terraces, 2: 386 uses of, 5: 1063 Soil erosion. See Erosion Soil horizons, 5: 1066 67, 1067 73, 1067 (ill.), 1071 (ill.), 1072 (ill.) Soil profile, 5: 1066, 1067 73, 1067 (ill.), 1071 (ill.), 1072 (ill.) Soil test kit, 2: 386 Solar (photovoltaic) cells, 5: 1083, 1087 89, 1088 (ill.), 1089 (ill.) Solar collectors, 5: 1082, 1082 (ill.) Solar days, 6: 1176 Solar eclipse, 2: 325 29, 325 (ill.), 328 (ill.), 329 (ill.) Solar energy, 5: 942, 1081 94, 1081 (ill.) design an experiment for, 5: 1093 94 heat storage substances experiment, 5: 1090 92, 1092 (ill.), 1093 seedling growth in greenhouses experiment, 5: 1084 87, 1084 (ill.), 1086 (ill.) solar cells to run a motor experiment, 5: 1087 89, 1088 (ill.), 1089 (ill.) ways to collect it, 5: 1082 83, 1082 (ill.) where it comes from, 5: 1081 82, 1081 (ill.) Solar reflectors, 5: 1082 83 Solar system, 2: 215, 5: 982 83 Solids density of, 2: 259 heat conduction experiment, 3: 618 22, 620 (ill.), 621 (ill.) relative density and floating experiment, 2: 260 64, 262 (ill.), 263 (ill.) Solubility separation techniques for, 5: 1033 solubility of elements experiment, 4: 835 38, 835 (ill.), 837 (ill.) unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) clxii
Solutions. See Mixtures and solutions Solvents, 5: 1032 Songs, 4: 700, 701 4, 701 (ill.), 702 (ill.), 703 (ill.) Sorensen, Margarethe Hoyrup, 4: 859 Sorensen, Soren Peter Lauritz, 4: 859 Sound, 5: 1095 1107, 1095 (ill.), 1096 (ill.), 1106 (ill.) design an experiment for, 5: 1105 7 Doppler effect experiment, 6: 1118 20, 1119 (ill.) measurement of, 5: 1095 96, 1095 (ill.) soundproofing materials experiment, 5: 1102 5, 1104 (ill.) speed of, 6: 1149 string length and sound experiment, 5: 1096 99, 1097 (ill.), 1098 (ill.) string thickness and sound experiment, 5: 1099 1102, 1100 (ill.), 1101 (ill.) Soundproofing, 5: 1102 5, 1104 (ill.) Sour taste, 1: 177 Southern Ocean, 4: 771 Space observation, 6: 1109 22 bacteria in, 1: 88 design an experiment for, 6: 1120 22 Doppler effect experiment, 6: 1118 20, 1119 (ill.) light in, 6: 1109, 1111 12, 1112 (ill.) telescope lenses experiment, 6: 1113 17, 1114 (ill.), 1116 (ill.) telescopes for, 6: 1109 10, 1110 (ill.), 1111 (ill.) Space time, 6: 1179 80, 1180 (ill.) Special relativity, theory of, 6: 1179, 1180 (ill.) Species DNA differences, 2: 287 88, 291 95, 293 (ill.) Specific gravity, 2: 258, 5: 997 1000, 998 (ill.), 999 (ill.) Spectrum, electromagnetic, 2: 203, 350, 350 (ill.), 4: 659, 660 (ill.), 787 Speed centrifugal force and gravity experiment, 5: 989 92, 990 (ill.) in chromatography, 5: 1032 33 crater shape experiment, 2: 221 25, 224 (ill.) of fluids, 3: 441 of light, 6: 1149, 1179 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
measuring wind speed experiment, 6: 1273, 1275 (ill.) Newtonian laws of motion on, 3: 491 92 of sound, 6: 1149 speed of falling objects experiment, 3: 581 84, 582 (ill.), 583 (ill.), 584 (ill.) of wind, 6: 1273 (ill.), 1283 (ill.) Speleology, 1: 127, 132 Spelunking, 1: 132 Sperm cells, 3: 423, 424 Spices, 3: 462 Spiders, 1: 62, 108, 4: 685, 686 (ill.) Spinning rod experiment, 3: 444 47, 446 (ill.), 447 (ill.) Spoiled food. See Food spoilage Spores, 3: 481, 539 Sports equipment, 4: 749 Spring tides, 3: 580 Springs, hot, 1: 88 Spruce trees, 1: 103, 104 (ill.) Squats (exercise), 1: 120 23, 122 (ill.) Squid, giant, 4: 775 (ill.) Stalactities, 1: 129 30, 130 (ill.), 135 39, 137 (ill.) Stalagmites, 1: 129 30, 130 (ill.), 135 39, 137 (ill.) Stamen, 3: 423, 424, 424 (ill.) Staphylococcus bacteria, 3: 539 Starches dietary carbohydrate sources experiment, 4: 761 64, 763 (ill.), 764 (ill.) for nutrition, 4: 760 in photosynthesis, 4: 872 plastic bag membrane experiment, 4: 798 803, 799 (ill.), 800 (ill.), 801 (ill.), 802 (ill.) Stars, 6: 1123 31, 1124 (ill.) design an experiment for, 6: 1130 31 discovery of, 6: 1123, 1123 (ill.) formation of, 6: 1123 24 for timekeeping, 6: 1177 tracking the North Star experiment, 6: 1125 28, 1126 (ill.), 1127 (ill.) tracking the planets experiment, 6: 1128 30, 1128 (ill.), 1129 (ill.), 1130 (ill.) Stars, shooting. See Comets and meteors Experiment Central, 2nd edition
Static electricity, 6: 1133 46, 1135 (ill.) build an electroscope experiment, 6: 1135 39, 1137 (ill.), 1138 (ill.) design an experiment for, 6: 1144 45 how to make it, 6: 1133 34, 1134 (ill.) in lightning, 6: 1135, 1135 (ill.), 1148 49 lightning sparks experiment, 6: 1152 55, 1154 (ill.) measuring the charge experiment, 6: 1139 44, 1141 (ill.), 1143 (ill.) Statues, 1: 12 15, 14 (ill.), 16, 17 (ill.) Steel, 4: 812 heat conduction experiment, 3: 618 22, 620 (ill.), 621 (ill.) steel wool rust experiment, 4: 817 20, 818 (ill.) Stems, 5: 884, 884 (ill.) leaf/stem cuttings and auxins experiment, 6: 1209 16, 1213 (ill.), 1214 (ill.) plant hormones and growth experiment, 5: 886 90, 888 (ill.), 889 (ill.) water storage in, 5: 899 Stereo speakers, 4: 673 Stevenson screens, 6: 1283 Sticky notes, 1: 22, 22 (ill.), 26 30, 27 (ill.), 28 (ill.), 29 (ill.) STM (Scanning tunneling microscope), 4: 748 Stomachs, expandable, 4: 775 Stomata, 5: 885, 898, 899 Storm chasers, 6: 1150 (ill.), 1151 Storms, 6: 1147 63 design an experiment for, 6: 1161 63 formation of, 6: 1147 48 hail, 6: 1151 52, 1151 (ill.) hailstone formation and temperature experiment, 6: 1158 61, 1159 (ill.), 1160 (ill.), 1161 (ill.), 1162 lightning sparks experiment, 6: 1152 55, 1154 (ill.) thunderstorms, 6: 1147 49, 1149 (ill.) tornadoes, 6: 1149 (ill.), .1150 (ill.), 1155 (ill.) water vortex experiment, 6: 1155 58, 1157 (ill.) Stratification, 4: 772, 775 80, 778 (ill.) Stratocumulus clouds, 6: 1273 Stratus clouds, 6: 1272, 1273 Strawberries, 3: 454 57, 455 (ill.), 456 (ill.) Streams, 1: 1 2, 4, 2: 271 84 See also Rivers clxiii
GENERAL SUBJECT INDEX
Strength of materials, 4: 687, 687 (ill.) polymer strength experiment, 5: 914 19, 917 (ill.), 918 (ill.) of polymers, 5: 912 seashell strength experiment, 5: 1022 25, 1023 (ill.), 1024 (ill.), 1025 (ill.) tape strength experiment, 4: 687 (ill.), 688 91, 689 (ill.), 690 (ill.) of wood, 6: 1297 String and sound experiments, 5: 1096 99, 1097 (ill.), 1098 (ill.), 1099 1102, 1100 (ill.), 1101 (ill.) Structures, 6: 1165 74 acid rain damage to, 1: 3, 12 15, 14 (ill.), 15 (ill.), 16 arches in, 6: 1166 67, 1167 (ill.), 1173 (ill.) building properties of wood experiment, 6: 1302 6, 1304 (ill.), 1305 (ill.) design an experiment for, 6: 1172 74 earthquake destruction experiment, 2: 317 21, 319 (ill.), 320 (ill.), 321 (ill.) forces acting on, 6: 1165 66, 1166 (ill.) rigidity of beams experiment, 6: 1170 72, 1171 (ill.) strength of arches vs. beams experiment, 6: 1167 70, 1168 (ill.) Styrofoam, 4: 691 94, 693 (ill.), 694 (ill.), 5: 1102 5, 1104 (ill.) Subatomic particles, 2: 257 Subliming, 2: 216 Subsoil, 5: 1067, 1067 (ill.) Substrate, 2: 360 Sugar caramelization of, 3: 463 64 crystal formation experiment, 2: 246 50, 246 (ill.), 249 (ill.), 254 (ill.) for food preservation, 3: 452 in food spoilage, 3: 478 from photosynthesis, 5: 884 85 in solutions, 5: 1032 sugar fruit preservation experiment, 3: 454 57, 455 (ill.), 456 (ill.) unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) Sulfur, 1: 88, 4: 761 clxiv
Sulfur dioxide, 1: 1, 3, 17 (ill.), 45 Sulfuric acid in acid rain, 1: 164 for cave formation, 1: 129 endothermic vs. exothermic reaction experiment, 1: 157 (ill.), 158 59, 158 (ill.), 159 (ill.) Sumerians, 2: 375, 389 Summer season, 5: 983 Sun and sunlight food drying experiment, 3: 458 61, 458 (ill.), 459 (ill.), 460 (ill.) heat energy from, 3: 589 heliotropism and plant movement experiment, 6: 1201 4, 1202 (ill.), 1203 (ill.) ocean penetration by, 4: 772 orbits around, 5: 982 in photosynthesis, 4: 871 73 solar eclipse, 2: 325 29, 325 (ill.), 328 (ill.), 329 (ill.) solar energy from, 5: 1081 82, 1081 (ill.) tides and, 5: 983 84, 993 94 for timekeeping, 6: 1175, 1176 in weather, 6: 1271, 1271 (ill.) Sun prints, 2: 329 30, 330 (ill.), 331 (ill.) Sundials, 6: 1177, 1177 (ill.), 1189 Sunflowers, 6: 1201 4, 1202 (ill.), 1203 (ill.) Superglue. See Cyanoacrylate glue Supersaturated solutions, 2: 246 Supertasters, 1: 180 86, 184 (ill.) Surface area evaporation and surface area experiment, 6: 1253 56, 1253 (ill.), 1254 (ill.), 1255 (ill.) nanosize and properties experiment, 4: 750 53, 752 (ill.) in nanotechnology, 4: 748 Surface currents, 4: 773 Surface tension, 3: 440 (ill.), 441, 448, 6: 1261 64, 1261 (ill.), 1263 (ill.) Suspensions, 4: 723, 724, 725 suspensions vs. solutions experiment, 4: 725 30, 729 (ill.) Tyndall effect experiment, 4: 730 32, 731 (ill.), 732 (ill.) Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Sweet taste, 1: 177, 182 86 Swim bladder, 3: 402, 403, 403 (ill.) Synthesis reactions, 1: 163 Synthetic dyes, 2: 299 300, 304 7, 306 (ill.), 307 (ill.) Synthetic fibers, 2: 301 4, 302 (ill.), 303 (ill.) Synthetic polymers, 5: 911 12
Tadpoles, 4: 645 46, 646 (ill.), 647 51, 648 (ill.), 649 (ill.), 650 (ill.) Taiga biome, 1: 103 4 Tails (comet), 2: 216 Tape (adhesive), 1: 21 22 environmental effects experiment, 1: 26 30, 27 (ill.), 28 (ill.), 29 (ill.) tape strength experiment, 4: 688 91, 689 (ill.), 690 (ill.) Tartaric acid, 3: 464 Taste design an experiment for, 1: 189 in fish, 3: 403 4 genetics of, 1: 180 how color affects taste experiment, 2: 207 10, 208 (ill.), 209 (ill.) how it works, 1: 177 79, 178 (ill.) pedigree for taste experiment, 3: 559 61, 561 (ill.) smell taste relationship experiment, 1: 186 89, 187 (ill.) supertaster experiment, 1: 180 86, 184 (ill.) Taste buds, 1: 177 79, 178 (ill.), 180 86, 184 (ill.) Taste cells, 1: 177 79 Tasters, 1: 180 86 Tectonic plates. See Plate tectonics Telescopes, 6: 1110 11, 1111 (ill.) combination of lenses experiment, 6: 1113 17, 1114 (ill.), 1116 (ill.) development of, 6: 1109, 1123 for space observation, 6: 1109 10, 1110 (ill.), 1111 (ill.) Temperate forest biome, 1: 106 8, 106 (ill.), 107 (ill.), 108 (ill.) Temperature adhesives experiment, 1: 26 30, 27 (ill.), 28 (ill.), 29 (ill.) Experiment Central, 2nd edition
cloud formation and temperature experiment, 6: 1277 80, 1280 (ill.) cool temperature and crystal growth experiment, 2: 250 53, 252 (ill.) desert biome experiment, 1: 108 11, 109 (ill.), 110 (ill.), 111 (ill.) dewpoint, 6: 1285 (ill.), 1286 89, 1287 (ill.), 1288 (ill.) dissolved oxygen level changes from, 2: 272, 273 (ill.) enzyme action and temperature experiment, 2: 368 72, 370 (ill.), 371 (ill.) evaporation and temperature experiment, 6: 1248 53, 1250 (ill.), 1251 (ill.) in food spoilage, 3: 478 for germination, 3: 565 germination temperature experiment, 3: 566 70, 568 (ill.), 569 (ill.) greenhouse temperature increase experiment, 3: 592 96, 593 (ill.), 594 (ill.) hailstone formation and temperature experiment, 6: 1158 61, 1159 (ill.), 1160 (ill.), 1161 (ill.), 1162 ocean convection currents experiment, 4: 780 83, 782 (ill.) radiometers for, 1: 43 salinity and stratification experiment, 4: 775 80, 778 (ill.) spoiled milk and temperature experiment, 3: 485 88, 487 (ill.) tadpoles and temperature experiment, 4: 647 51, 648 (ill.), 649 (ill.), 650 (ill.) temperate forest biome, 1: 108 temperature of different colors experiment, 2: 210 12, 211 (ill.), 212 (ill.), 213 transpiration rate and environment experiment, 5: 904 7, 906 (ill.) viscosity and temperature experiment, 3: 441 44, 442 (ill.), 443 (ill.) warm air vs. cool air experiment, 1: 36 39, 36 (ill.), 38 (ill.) in weather, 6: 1271, 1284 See also Cold temperature Tenderizer. See Meat tenderizer Tendrils, 6: 1192 Tennis balls, 4: 749 clxv
GENERAL SUBJECT INDEX
Tensile strength of materials, 4: 687 polymer strength experiment, 5: 914 19, 917 (ill.), 918 (ill.) of polymers, 5: 912 tape strength experiment, 4: 687 (ill.), 688 91, 689 (ill.), 690 (ill.) Terraces, soil, 2: 386 Tetra fish, 3: 407 9, 409 (ill.), 410 Textiles, 4: 686, 696 Thales of Miletus, 2: 325 Theophrastus, 3: 565, 6: 1283 84 Theory of special relativity, 6: 1179, 1180 (ill.) Thermal energy. See Heat Thermal inversion, 1: 47, 47 (ill.) Thermal pollution, 1: 49 Thermal properties, 4: 687 Thermometers, 1: 151 Thiamine, 4: 760 Thickness, 5: 1099 1102, 1100 (ill.), 1101 (ill.) Thigmotropism, 6: 1192, 1205 (ill.) Third law of motion, 3: 492, 492 (ill.), 494, 580 Thomas, Robert Bailey, 6: 1284 Thorax, 3: 632 Threads, 5: 1048 49, 1050 (ill.), 1057 60, 1058 (ill.), 1059 (ill.), 1060 (ill.) Thunder, 6: 1148 49 Thunderstorms, 6: 1147 49, 1149 (ill.), 1150, 1151, 1151 (ill.) Thyme, 2: 392 95, 394 (ill.), 395 (ill.) Thymine, 2: 286 87 Tides, 3: 580, 4: 777 (ill.), 784, 5: 992 (ill.) Earth’s rotation effect, 5: 983 84 moon’s effect on, 4: 774, 775 (ill.), 5: 983 84 Sun’s impact on, 5: 983 84, 993 94 Time, 6: 1175 89, 1176 (ill.), 1178 (ill.) design an experiment for, 6: 1188 89 devices for measuring, 6: 1177 78, 1177 (ill.) history of, 6: 1175 78 pendulum oscillation time experiment, 6: 1180 85, 1182 (ill.), 1183 (ill.) space time, 6: 1179 80, 1180 (ill.) water clock experiment, 6: 1185 88, 1187 (ill.) Time zones, 6: 1178 79, 1179 (ill.) Titan Arum, 3: 423, 427 clxvi
Titration, 4: 860, 865 68, 865 (ill.), 866 (ill.), 867 (ill.) Tomatoes, 1: 164 Tools, 2: 390 92, 400, 5: 969 Topsoil, 5: 1064, 1066 67, 1067 (ill.) erosion of, 2: 375, 375 (ill.) soils for fossil casts experiment, 3: 526 29, 528 (ill.) See also Soil Tornadoes, 6: 1149 51, 1149 (ill.), 1150 (ill.), 1155 (ill.), 1284 (ill.) water vortex experiment, 6: 1155 58, 1157 (ill.) weather forecasting of, 6: 1286 Torricelli, Evangelista, 1: 34, 6: 1284 Tortoises, 5: 1019 Toughness of materials, 4: 687 Toxicity, 1: 164 Trace fossils, 3: 524 Trace minerals, 6: 1226 Traits, genetic, 3: 554 55, 556 59, 558 (ill.), 559 (ill.), 562 Transfer of energy, 5: 930, 930 (ill.) Transformation of energy, 5: 929 Transforming factor (DNA), 2: 285 86 Transpiration transpiration rate and environment experiment, 5: 904 7, 906 (ill.) of water, 5: 885, 890, 892 (ill.), 893 (ill.), 898, 899 Tree resins, 3: 523 24 Trees angiosperm, 6: 1295, 1296 (ill.) annual growth of, 1: 71 72, 72 (ill.), 73 (ill.) coniferous, 1: 103, 104 (ill.), 6: 1295 deciduous, 1: 107 8, 107 (ill.), 192 growth pattern experiment, 1: 74 79, 78 (ill.) lichen on, 1: 79 rainforest, 1: 105 6 structure of, 6: 1295 96, 1297 (ill.) wood from, 6: 1295 See also Forests Troglobites, 1: 130 Troglophiles, 1: 130 31 Trogloxenes, 1: 130 Tropical forests, 2: 376 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Tropisms, 6: 1191 1206 design an experiment for, 6: 1204 6 geotropism, 6: 1191 heliotropism and plant movement experiment, 6: 1201 4, 1202 (ill.), 1203 (ill.) phototropism, 6: 1191 93, 1191 (ill.), 1192 (ill.), 1193 (ill.), 1209 phototropism maze experiment, 6: 1193 97, 1195 (ill.), 1196 (ill.) root growth and gravity experiment, 6: 1197 1201, 1198 (ill.), 1199 (ill.), 1200 (ill.) thigmotropism, 6: 1192, 1205 (ill.) Troposphere, 1: 33, 35 36, 3: 600, 6: 1271 Trough, 4: 773, 774 (ill.) Troy (ancient city), 2: 230 31 Truffles, 3: 540 Tsunamis, 2: 322 Tube worms, 4: 775 Tulley, John, 6: 1284 Tundra, 1: 103 Tunnels, trace fossils of, 3: 524 Turgor pressure role of, 5: 899, 899 (ill.), 900 (ill.) salinity and turgor pressure experiment, 5: 900 904, 900 (ill.), 902 (ill.), 903 (ill.) Turtles, 5: 1019 Twigs, 1: 72, 72 (ill.), 74 79 Tyndall, John, 3: 589 Tyndall effect, 4: 725, 725 (ill.), 730 32, 731 (ill.), 732 (ill.)
Ultraviolet rays, 1: 46, 4: 661 64, 662 (ill.), 663 (ill.) Umami, 1: 177 Unconfined aquifers, 3: 601, 603 (ill.) Unicellular organisms, 1: 141, 144 (ill.) Unit cells, 2: 243 Upwelling, 4: 773
Vacuoles, 1: 142, 5: 898 99, 899 (ill.) Vacuum seal, 3: 453 Experiment Central, 2nd edition
Van der Waals’ force, 1: 20, 21 (ill.) Vanilla, 4: 797 Variables, 5: 1007 8 Vega (star), 6: 1123 Vegetables color change by cooking, 3: 465 66 composting, 2: 230, 236 39, 236 (ill.), 238 (ill.), 239 (ill.) for scurvy, 4: 759 Vegetative propagation, 6: 1207 21, 1207 (ill.), 1208 (ill.), 1209 (ill.) design an experiment for, 6: 1219 20 genetics of, 6: 1208, 1208 (ill.) leaf/stem cuttings and auxins experiment, 6: 1209 16, 1213 (ill.), 1214 (ill.) potato reproduction experiment, 6: 1216 19, 1218 (ill.) Vehicles. See Cars Velcro, 4: 685, 686 (ill.) Velocity, 3: 441, 491 92, 493, 5: 985, 985 (ill.) See also Speed Veneer, 6: 1297 98 Venomous snakes, 1: 62 Vibrations for sound conduction, 3: 403, 5: 1095, 1096 (ill.) string length and sound experiment, 5: 1096 99, 1097 (ill.), 1098 (ill.) string thickness and sound experiment, 5: 1099 1102, 1100 (ill.), 1101 (ill.) Vinegar acid copper reduction experiment, 4: 813 17, 814 (ill.), 815 (ill.) baking soda reaction, 1: 165 bone loss experiment, 1: 117 20, 119 (ill.) brine shrimp experiment, 1: 5 8, 7 (ill.) chemical titration experiment, 4: 865 68, 865 (ill.), 866 (ill.), 867 (ill.) copper patina experiment, 1: 173 75, 174 (ill.), 175 (ill.) electrolyte solution experiment, 2: 335 40, 337 (ill.), 338 (ill.), 339 (ill.) electrons released by metals experiment, 4: 838 40, 840 (ill.), 841 (ill.), 842 for food preservation, 3: 452, 452 (ill.), 479 clxvii
GENERAL SUBJECT INDEX
moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) molecule size and osmosis experiment, 4: 806 9, 808 (ill.), 809 (ill.) mystery powder identification experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) pH of household chemicals experiment, 4: 861 65, 861 (ill.), 863 (ill.) rusting experiment, 1: 152 56, 155 (ill.) safety for, 1: 119 soil pH and plant growth experiment, 5: 1074 77, 1074 (ill.), 1076 (ill.), 1079 (ill.) structure damage experiment, 1: 12 15, 14 (ill.), 15 (ill.), 16 unknown mixtures experiment, 5: 1039 43, 1041 (ill.), 1042 (ill.) Vines, 6: 1192, 1205 (ill.) Violet light bending, 2: 204 5 light colors and plant growth experiment, 4: 873 77, 875 (ill.), 876 (ill.) temperature of different colors experiment, 2: 210 12, 211 (ill.), 212 (ill.), 213 wavelength of, 2: 203 Virchow, Rudolf, 1: 142 Viscosity, 3: 439 41, 441 44, 442 (ill.), 443 (ill.) Visible light, 4: 659, 660, 787, 6: 1112 Vision, color, 2: 205 6, 205 (ill.) Vitamin A, 6: 1224 Vitamin B, 6: 1224 Vitamin C for food preservation, 3: 479 moldy bread experiment, 3: 481 85, 481 (ill.), 482 (ill.), 483 (ill.) for scurvy, 4: 759, 6: 1223 sources of vitamin C experiment, 6: 1226 31, 1229 (ill.) Vitamin D, 6: 1224, 1226 Vitamin K, 6: 1224 Vitamins, 4: 760, 6: 1223 36, 1224 (ill.), 1225 (ill.), 1226 (ill.), 1234 (ill.), 1235 (ill.) design an experiment for, 6: 1234 36 discovery of, 6: 1223 24 clxviii
fat soluble vs. water soluble, 6: 1224 25, 1224 (ill.) sources of vitamin C experiment, 6: 1226 31, 1229 (ill.) Volatilization, 4: 847 Volcanoes, 6: 1237 45, 1237 (ill.), 1245 (ill.) build a model volcano experiment, 6: 1240 42, 1240 (ill.), 1241 (ill.) design an experiment for, 6: 1244 45 eruptions of, 5: 969 70, 970 (ill.), 6: 1237, 1238 39 formation of, 6: 1237 38 natural pollutants from, 1: 48 seismographs for eruptions experiment, 6: 1242 44, 1242 (ill.), 1243 (ill.), 1244 (ill.) Volta, Alessandro, 2: 334, 335 (ill.) Volta Pile, 2: 335 (ill.), 344 Voltage, 2: 334 Voltmeters, 2: 334, 337 (ill.) construct a multicell battery experiment, 2: 340 44, 341 (ill.), 342 (ill.) electrolyte solution experiment, 2: 335 40, 337 (ill.) Volume in density determination, 2: 257 of fluids, 3: 439 nanosize and properties experiment, 4: 750 53, 752 (ill.) surface area ratio, 4: 748, 750 53, 752 (ill.) Voluntary muscles, 1: 115 Vortex, 6: 1150 51, 1150 (ill.), 1155 58, 1157 (ill.)
Waals, Johannes Diderik van der, 1: 20 Walking stick insect, 1: 62 Warm air convection current experiment, 1: 39 42, 41 (ill.) in storm formation, 6: 1147 48 thermal inversion, 1: 47, 47 (ill.) warm air vs. cool air experiment, 1: 36 39, 38 (ill.) Warm climate, 5: 1065 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Warm fronts, 1: 35, 6: 1285 Washing soda, 4: 835 38, 835 (ill.), 837 (ill.) Waste, organic, 2: 229, 230, 235 39, 236 (ill.), 238 (ill.), 239 (ill.) Water adhesion and weight experiment, 6: 1264 68, 1265 (ill.), 1266 (ill.) adhesion by, 6: 1259 61 cave formation, 1: 127 29, 128 (ill.), 135 39, 137 (ill.) cohesion of, 6: 1259 61, 1268 (ill.) comet composition experiment, 2: 218 21, 220 (ill.) dead zones in, 2: 271, 273 design an experiment for, 6: 1268 69 drinking, 3: 604, 605 9, 608 (ill.), 609 12, 610 (ill.) electricity conduction through, 2: 333 electrolyte solution experiment, 2: 335 40, 337 (ill.), 338 (ill.), 339 (ill.) evaporation and surface area experiment, 6: 1253 56, 1253 (ill.), 1254 (ill.), 1255 (ill.) evaporation of, 1: 20 21, 6: 1247 in food spoilage, 3: 478 for germination, 3: 565 66 hard, 6: 1226, 1231 34, 1232 (ill.) heat capacity experiment, 3: 625 28, 626 (ill.), 627 (ill.), 628 (ill.) heat capacity of, 3: 617 heat convection experiment, 3: 622 25, 623 (ill.), 624 (ill.) mineral oil, water and iodine experiment, 1: 170 73, 170 (ill.), 171 (ill.), 172 (ill.) minerals in, 6: 1225 26 molecules of, 1: 20, 21 (ill.), 4: 747, 748 (ill.), 6: 1259, 1259 (ill.) mystery powder identification experiment, 5: 1009 13, 1011 (ill.), 1012 (ill.), 1013 (ill.) nanosize and properties experiment, 4: 748, 752 (ill.) plant growth experiment, 1: 9 12, 11 (ill.) plant water uptake experiment, 5: 890 93, 892 (ill.), 893 (ill.) properties of, 3: 440, 6: 1259 70, 1259 (ill.), 1260 (ill.) Experiment Central, 2nd edition
relative density compared to, 2: 258 salt water osmosis experiment, 4: 803 6, 803 (ill.), 804 (ill.), 805 (ill.) sandy, 4: 723, 723 (ill.) from seawater, 4: 724 25 in soil, 5: 1063, 1064 (ill.) solar heat storage experiment, 5: 1090 92, 1092 (ill.), 1093 solubility in, 5: 1033 solubility of elements experiment, 4: 835 38, 835 (ill.), 837 (ill.) specific gravity of, 5: 997 1000, 998 (ill.), 999 (ill.) surface tension cohesion experiment, 6: 1261 64, 1261 (ill.), 1263 (ill.) surface tension of, 3: 440 (ill.), 441, 448 transpiration of, 5: 885, 890, 892 (ill.), 893 (ill.), 898, 899 tree growth experiment, 1: 78 79 van der Waals’ force in, 1: 20, 21 (ill.) water absorption by wood experiment, 6: 1298 1302, 1300 (ill.), 1301 (ill.) water vortex experiment, 6: 1155 58, 1157 (ill.) See also Water properties Water bottle rocket experiment, 3: 493 501, 495 (ill.), 498 (ill.), 499 (ill.), 500 (ill.) Water clocks, 6: 1177, 1177 (ill.), 1185 88, 1187 (ill.) Water cycle, 5: 955, 6: 1247 58, 1248 (ill.), 1249 (ill.) design an experiment for, 6: 1256 57 evaporation and surface area experiment, 6: 1253 56, 1253 (ill.), 1254 (ill.), 1255 (ill.) evaporation and temperature experiment, 6: 1248 53, 1250 (ill.), 1251 (ill.) Water lilies, 3: 427 Water plants dissolved oxygen levels for, 2: 271, 273 74, 278 79 eutrophication, 1: 49 50, 50 (ill.), 55 58, 57 (ill.) photosynthesis by, 4: 872 73 Water pollution, 1: 45 60, 46 (ill.) aquifer contamination experiment, 3: 605 9, 608 (ill.) design an experiment for, 1: 58 59 dissolved oxygen level changes from, 2: 272 73 clxix
GENERAL SUBJECT INDEX
eutrophication experiment, 1: 55 58, 57 (ill.) fish effected by, 1: 50, 3: 411 of groundwater aquifers, 3: 604 5, 605 (ill.), 606 (ill.) from nutrients, 1: 49 50, 50 (ill.) from oil, 1: 48 49, 49 (ill.), 58 from pesticides, 1: 49, 4: 846 47, 847 (ill.) prevention of, 1: 50 water cleaning experiment, 3: 609 12, 610 (ill.) water movement of pesticides experiment, 4: 851 55, 854 (ill.) Water pressure, 4: 772, 773 (ill.), 5: 948 51, 948 (ill.), 949 (ill.), 950 (ill.) Water properties, 6: 1259 70, 1259 (ill.), 1260 (ill.), 1268 (ill.) adhesion and weight experiment, 6: 1264 68, 1265 (ill.), 1266 (ill.) design an experiment for, 6: 1268 69 of Newtonian fluids, 3: 440 surface tension cohesion experiment, 6: 1261 64, 1261 (ill.), 1263 (ill.) Water soluble vitamins, 6: 1224 25, 1224 (ill.) Water supply, 3: 602, 609 12, 610 (ill.), 4: 771 Water vapor burning fossil fuels experiment, 3: 596 98, 596 (ill.), 597 (ill.) in cloud formation, 6: 1148, 1272 evaporation and temperature experiment, 6: 1248 53, 1250 (ill.), 1251 (ill.) greenhouse effect from, 3: 590 91 temperature and cloud formation experiment, 6: 1277 80, 1280 (ill.) in thunderstorms, 6: 1147 48 in the water cycle, 5: 955, 6: 1247 Water wheels, 5: 948 51, 948 (ill.), 949 (ill.), 950 (ill.) Waterfalls, 5: 956 Watson, James D., 2: 286 87, 287 (ill.) Wavelength electromagnetic waves, 2: 349 (ill.), 350, 350 (ill.) of light, 6: 1112, 1112 (ill.) ocean waves, 4: 773, 774 (ill.) clxx
string length and sound experiment, 5: 1096 99, 1097 (ill.), 1098 (ill.) Waves electromagnetic, 2: 203, 204 5, 204 (ill.), 350, 350 (ill.), 3: 616 17 ocean, 4: 773, 774 (ill.), 784 sound, 5: 1095, 1095 (ill.) Wax paper, 4: 666 69, 666 (ill.), 667 (ill.) Weapons, 2: 391, 392 (ill.) Weather, 6: 1271 81, 1273 (ill.), 1285 (ill.) air masses in, 1: 34 36, 35 (ill.) air pressure and, 1: 33 34, 6: 1271, 1272 (ill.) causes of, 1: 33 36, 6: 1271 72 convection current experiment, 1: 39 42, 41 (ill.) design an experiment for, 1: 42 44, 6: 1280 81 fronts, 1: 34 35, 6: 1285 measuring wind speed experiment, 6: 1273 77, 1275 (ill.) sun in, 6: 1271, 1271 (ill.) temperature and cloud formation experiment, 6: 1277 80 thermal inversions in, 1: 47, 47 (ill.) warm air vs. cool air experiment, 1: 36 39, 36 (ill.), 38 (ill.) See also Storms Weather forecasting, 6: 1283 93, 1283 (ill.), 1284 (ill.) build a barometer experiment, 6: 1289 92, 1290 (ill.), 1291 (ill.) computers and, 6: 1283, 1285 design an experiment for, 6: 1292 93 dewpoint temperature experiment, 6: 1286 89, 1287 (ill.), 1288 (ill.) history of, 6: 1283 84 Weather maps, 6: 1285 Weather stations, 6: 1283 Weather vanes, 6: 1280 (ill.), 1284 Weathering glacier erosion trench experiment, 5: 957 60, 958 (ill.), 959 (ill.) mountains, 4: 737 in soil formation, 5: 1063 65 Weaver ants, 1: 62 Weaving, 2: 399 Experiment Central, 2nd edition
GENERAL SUBJECT INDEX
Wedges, 5: 1048 Wegner, Alfred, 6: 1237 38, 1238 (ill.) Weight atomic, 4: 827 28 crater shape experiment, 2: 221 25, 224 (ill.) tape strength experiment, 4: 688 91, 689 (ill.), 690 (ill.) water adhesion and weight experiment, 6: 1264 68, 1265 (ill.), 1266 (ill.) Weissenberg effect, 3: 444 47, 446 (ill.), 447 (ill.) Wells, 3: 601, 604 Went, Fritz W., 6: 1191 92, 1209 Wetlands, 3: 604, 606 (ill.) Whales, 3: 402 Wheel and axle machines, 5: 1051 55, 1051 (ill.), 1054 (ill.) Wheelbarrows, 5: 1051, 1051 (ill.) Whirlpools, 6: 1155 Whirly toys, 3: 418 21, 418 (ill.), 419 (ill.), 420 (ill.) White glue, 1: 20, 22 25, 23 (ill.), 167 70, 168 (ill.), 169 (ill.) White light, 2: 203 5, 205 (ill.), 4: 873 77, 875 (ill.), 876 (ill.) WHO (World Health Organization), 2: 390 Widow’s peak, 3: 556 59, 556 (ill.), 559 (ill.) Wilting plants, 5: 899, 900 (ill.) Wind air pressure and, 1: 33 34 anemometers for, 6: 1273 (ill.), 1283 (ill.) direction of, 6: 1280 (ill.), 1284 evaporation and, 6: 1252 53 measuring wind speed experiment, 6: 1273 77, 1275 (ill.) for pollination, 3: 425 in storm formation, 6: 1147 transpiration rate and environment experiment, 5: 904 7, 906 (ill.) in weather, 6: 1271 Wind energy, 5: 942, 942 (ill.), 944 48, 945 (ill.), 946 (ill.) Wind turbines, 5: 942 Windmills, 5: 942 Wings airplane, 3: 413, 414, 414 (ill.) insect, 3: 632 33, 633 (ill.) Experiment Central, 2nd edition
Winter season, 5: 983, 984 (ill.) Wolffia, 3: 423 Wood, 6: 1295 1307, 1296 (ill.), 1297 (ill.) building properties experiment, 6: 1302 6, 1304 (ill.), 1305 (ill.) density of, 6: 1295 design an experiment for, 6: 1306 7 elasticity of, 2: 321 glue adherence experiment, 1: 22 25, 23 (ill.), 24 (ill.) grain, 6: 1297, 1298 (ill.) for heat, 5: 942 heat conduction experiment, 3: 618 22, 620 (ill.), 621 (ill.) petrifaction of, 3: 523 properties of, 6: 1296 97 types of, 6: 1295 water absorption experiment, 6: 1298 1302, 1300 (ill.), 1301 (ill.) water adhesion and weight experiment, 6: 1264 68, 1265 (ill.), 1266 (ill.) Wood finishes, 6: 1307 Wool, 3: 509, 6: 1139 44, 1141 (ill.), 1143 (ill.) Work, definition of, 5: 1047 World Health Organization (WHO), 2: 390 Worms, tube, 4: 775 Wright, Orville, 3: 413 15, 415 (ill.) Wright, Wilbur, 3: 413 15, 415 (ill.)
Xanthophyll, 1: 192, 201 (ill.), 4: 872 Xerophytes, 1: 105 Xylem, 1: 71 72, 4: 872, 5: 884, 898
Years, 6: 1175, 1176 (ill.) Yeast in bread making, 2: 359, 360 (ill.), 3: 464 65, 465 (ill.), 540, 544 carbon dioxide from, 2: 359, 3: 540 41 in food spoilage, 3: 477 80, 478 (ill.) production of, 2: 360, 362 clxxi
GENERAL SUBJECT INDEX
reproduction, 1: 143 44, 147 48, 147 (ill.), 148 (ill.), 149 (ill.), 150 temperature for yeast growth experiment, 3: 544 49, 547 (ill.), 548 (ill.) uses for, 3: 540 41 yeast decomposition experiment, 3: 541 43, 543 (ill.) Yellow light, 4: 873 77, 875 (ill.), 876 (ill.) Yellowstone National Park, 1: 88, 88 (ill.) Yogurt, 1: 101 Young, Thomas, 4: 660
clxxii
Zinc chemical properties of, 1: 165 construct a multicell battery experiment, 2: 340 44, 341 (ill.), 342 (ill.) electrons released by metals experiment, 4: 838 40, 840 (ill.), 841 (ill.), 842 for nutrition, 6: 1226 Zone of inhibition, 1: 90 91
Experiment Central, 2nd edition
