second edition Greg Rickard Nici Burger Warrick Clarke David Geelan Dale Loveday Stewart Monckton Geoff Phillips Peter Roberson Cherine Spirou Kerry Whalley
Sydney, Melbourne, Brisbane, Perth, Adelaide and associated companies around the world
Contents Acknowledgements
v
Series features
vi
How to use this book
CHAPTER
1
CHAPTER
2
CHAPTER
3
CHAPTER
4
viii
Syllabus correlation
x
Verbs
xi
Being a scientist
2
Unit 1.1 Science and safety
3
Unit 1.2 Equipment
9
Unit 1.3 Observations and measurement
17
Unit 1.4 Reporting
25
Unit 1.5 Working scientifically
29
Chapter review
33
Solids, liquids and gases
34
Unit 2.1 The particle model
35
Science focus: Observation and discovery
43
Unit 2.2 Changes of state
45
Unit 2.3 Expansion
51
Unit 2.4 Density
57
Chapter review
63
Mixtures and their separation
64
Unit 3.1 Types of mixtures
65
Unit 3.2 Separating insoluble substances
73
Unit 3.3 Separating soluble substances
80
Unit 3.4 Water supply and sewage
86
Chapter review
92
Classification
94
Unit 4.1 Why classify?
95
Unit 4.2 Living or non-living?
102
Unit 4.3 From kingdom to species
110
Science focus: Grouping living things
114
Unit 4.4 Classification of animals
117
Unit 4.5 Plants and other kingdoms
127
Chapter review
135
iii
CHAPTER
5
CHAPTER
6
CHAPTER
7
CHAPTER
8
CHAPTER
9
iv
Cells
137
Unit 5.1 Cells and the microscope
138
Unit 5.2 Plant cells
149
Unit 5.3 Animal cells
155
Unit 5.4 Single cells, groups of cells
158
Science focus: Stem cells
163
Chapter review
166
Heat, light and sound
167
Unit 6.1 Energy
168
Unit 6.2 Heat
176
Unit 6.3 Light
188
Unit 6.4 Sound
196
Chapter review
203
Forces
205
Unit 7.1 What are forces?
206
Unit 7.2 Friction
212
Unit 7.3 Gravity
218
Unit 7.4 Balanced and unbalanced forces
224
Unit 7.5 Forces in water
231
Unit 7.6 Magnetic forces
236
Chapter review
242
Earth in space
244
Unit 8.1 Earth’s movement in space
245
Unit 8.2 The Moon
250
Unit 8.3 The Sun
257
Unit 8.4 The solar system
262
Science focus: Early astronomy
275
Chapter review
279
Our planet Earth
280
Unit 9.1 Our Earth
281
Unit 9.2 Rocks and minerals
286
Unit 9.3 Types of rocks
292
Unit 9.4 Weathering and erosion
301
Unit 9.5 The atmosphere
306
Science focus: Global climate change
313
Unit 9.6 Weather
316
Chapter review
322
Sci Q Busters
324
Index
328
Acknowledgements We would like to thank the following for permission to reproduce copyright material. The following abbreviations are used in this list: t = top, b = bottom, l = left, r = right, c = centre. AAP Image: pp. 231tr, 258r, 314l, 314r. Alamy: p. 19. Auscape/John Carnemolla: p. 294bl. Auscape/Reg Morrison: p. 293l. Bureau of Meteorology: p. 301l. Corbis: pp. ivb, 35, 169bcl, 169tcl, 224, 283, 296. CSIRO Minerals: p. 76r. CSIRO: p. 313t. Dorling Kindersley: pp. 46 both, 47t, 145t, 145c. Dorling Kindersley/Clive Streeter: p. 47b. Dorling Kindersley/Colin Keates Courtesy of the Natural History Museum, London: p. 287br. Dreamstime: pp. 87, 179tc, 179tr, 198, 293r. Fairfax photos/Vince Caligiuri: p. 206. Getty Images: pp. iii c top, 2, 45, 47, 102t, 121t, 163b, 231br, 280. iStock Photo: pp. 4, 57, 68 all, 80 b, 128l, 129tl, 159br, 172, 175, , 231 l, 245, 252, 253, 257bl, 286bc, 286br, 292t, 313b. Jupiter Images: p. 250. The Kobal Collection/New Line Cinema: p. 281b. Lin, Mike: p. 163t. Melbourne Arts Centre, The, Concert Hall: p. 199b. NASA: pp. ivcb , 218b, 251br, 251tr, 257t, 260, 263, 264, 265, 266 all, 267, 268t, 269, 275l, 275r, 278, 306, 317, 318br. Opitz, Bernd: p. 214bl. Pearson Australia: pp. 144, 191. Pearson Australia/Elizabeth Anglin: 142b. Pearson Australia/Alice McBroom: pp. 85, 258l. Photodisc: pp. iiicb, 29, 51, 64, 65, 73, 80t, 149, 160, 188 all, 207cr, 213r, 236. Photolibrary.com: pp. ivt, 9, 17, 43, 66, 75 both, 76l, 82r, 95t, 103b, 104c, 104b, 105bl, 106 both, 111b, 114, 115t, 117, 118t, 118b, 119r, 120tr, 120br, 122 all, 123 all, 127r, 128br, 129r, 130 both, 137, 138 all, 140 both, 141, 142cl, 142t, 143 all, 145b, 150, 155l, 158 both, 159t, 159c, 159bl, 164, 166, 168l, 178, 189br, 196, 199t, 214t, 220, 232, 244, 268b, 276, 277 both, 286tl, 286tr, 287bl, 288b, 289 both, 294br, 295l, 297, 302, 303t, 310, 319. Photos.com: pp. 25 both, 200, 282. Picture Source, The/Terry Oakley: p. 67t. Rickard, Greg: p. 294t. Science and Society Picture Library: p. 139. Science Photo Library: pp. 142cr, 151b. Shutterstock: pp. iiit, ivct, 3 all, 37, 43l, 53, 66l, 67b, 74 both, 74r, 94, 95 b, 96 all, 97 all, 81, 82l, 100 all, 102b, 103t, 104t, 105t, 105br, 107, 110, 111 all, 112 both, 115b, 118c, 119l, 120bl, 121b, 127l, 129 bl, 155r,167, 168r, 169 all, 170 all, 171l, 176, 179tl, 179b, 181 both, 189tl, 189tr, 189bl, 207tl, 207tr, 207cl, 207bl, 207br, 212 both, 214br, 216 all, 218t, 219, 225, 237, 251l, 257bc, 257br, 262, 281t, 286bl, 287t, 288tr all, 288bl, 292r, 294c, 295r, 301r, 303c, 303b, 316, 318l all, 324, 325 both, 326 both. Sydney Water: p. 86. Every effort has been made to trace and acknowledge copyright. However, if any infringement has occurred, the publishers tender their apologies and invite the copyright holders to contact them.
v
Series features
Science Focus Second Edition
The Science Focus Second Edition series has been designed for the revised NSW Science Syllabus, Stages 4 and 5. This fresh and engaging series is based on the essential and additional content.
Student books with student CD
NENTW ENT O
C The student book consists of chapters with the following features: • A science context at the beginning of each chapter encourages students to make meaning of science in terms of their everyday experiences. • Science Clip boxes contain quirky and fascinating science facts and provide opportunity for further exploration by students. • Unit and chapter review questions are structured around Bloom’s Taxonomy of Cognitive Processes. Questions incorporate the key verbs, so that students can begin to practise answering questions as required in later years. • Investigating sections incorporate ICT and research skills. These tasks are designed to push students to apply the knowledge and skills they have developed within the chapter. • Practical activities are placed at the end of each unit to allow teachers to choose when and how to incorporate the practical work. • Science Focus spreads use a contextual approach to focus on the outcomes of the prescribed focus area. Student activities on these pages allow for further investigation into the material covered. Each student book includes an interactive student CD containing: • an electronic version of the student book • a link to Pearson Places for extensive online content.
Homework books
NENTW ENT
CO The homework book has a fresh new design and layout and provides the following features: • A syllabus correlation grid links each worksheet to the NSW Science Syllabus. • Updated worksheets cover consolidation, extension and revision activities with explicit use of syllabus verbs so that students can begin to practise answering questions as required in later years. • Questions are clearly graded within each worksheet, allowing students to move from lower-order questions to higher-order questions. • A crossword for every chapter spans across a double-page spread so students can easily read the clues and instructions. • Sci-words are listed for each chapter in an easy-to-follow tabulated layout.
vi
Teacher editions (including teacher edition CD and student CD)
NEW
The innovative teacher edition contains a wealth of support material and allows a teacher to approach the teaching and learning of science with confidence. Teacher editions are available for each student book in the series. Teacher editions include the following features: • pages from the student book with wrap-around teacher notes covering the learning focus, outcomes and a pre-quiz for every chapter opening • approximately 10 different learning strategies per unit in addition to the activities provided in each unit of the student book • assessment ideas • answers to student book questions • practical activity support including a safety spot, common mistakes, possible results and suggested answers to practical activity questions • Teacher Resource boxes highlighting additional resources available, such as worksheets, online activities and practical activities. Each Science Focus Second Edition Teacher Edition CD includes: • student book answers • homework book answers NEW Pearson Places • chapter tests and answers • curriculum grids www.pearsonplaces.com.au • teaching program for each chapter Pearson Places is the online • student risk assessments destination that is constantly evolving ng • lab technician risk assessments to give you the most up-to-date educational • safety notes content on the Web. Visit Pearson Places to • lab technician checklist and recipes. access educational content, download lesson material, use rich media and connect with students, educators and professionals around W NE LiveText™ DVD Australia. • Pearson Reader The LiveText™ DVD is designed More than an eBook, Pearson Reader for use with an interactive provides unique online student books whiteboard or data projector. that allow teachers and students to It consists of an electronic harness the collective intelligence of version of the student book all who participate. Search for a unit of with component links, some of work and contribute by adding links and which are unique to LiveText™. sharing resources. The features include one-touch • Student Lounge zoom and annotation tools that One location for student support allow teachers to customise ise material—interactives, animations, lessons for students. revision questions and more! • Teacher Lounge One location for teacher support material—curriculum grids, chapter tests and more!
For more information on the Science Focus Second Edition series, visit the Bookstore at: www.pearsonplaces.com.au
vii
How to use this book
Science Focus 1 Second Edition
Science is a fascinating, informative and enjoyable subject. Science encourages us to ask questions and helps us understand why things happen in our daily lives, on planet Earth and beyond. Scientific knowledge is constantly evolving and challenges us to think about the world in which we live. Science shows us what we knew, what we now know and helps us make informed decisions for our future. Science Focus 1 Second Edition has been designed for the revised NSW Science Syllabus. It includes material that addresses the learning outcomes in the domains of knowledge, understanding and skills. Each chapter addresses at least one prescribed focus area in detail. The content is presented through many varied contexts to engage students in seeing the relationship between science and their everyday lives. The student book consists of nine chapters with the following features: Unit
4
Classification
Prescribed focus area:
The key prescribed focus area addressed within the chapter is clearly emphasised.
The nature and practice of science
Key outcomes
Additional
Essential
4.2, 4.8.1, 4.8.2
s
Living things are classified according to their structural features.
s
A range of plants and animals can be identified using simple keys.
s
Animals are classified first as vertebrates and invertebrates.
s
Vertebrates are then classified as mammal, bird, reptile, amphibian or fish.
s
Invertebrates are then classified into the main groupings of arthropods, worms, molluscs or cnidarians.
s
Plants are classified first as vascular plants or bryophytes.
s
Organisms survive by producing their own food (autotrophic organisms) or by eating other organisms (heterotrophic organisms).
s
Organisms can be classified by designing simple keys.
s
Five important kingdoms are animal, plant, fungi, monera and protists.
s
Species is the most specific grouping that an organism can belong to.
s
Members of the same species are so similar that they can reproduce and produce fertile young.
The learning outcomes relevant to the chapter are clearly listed. A clear distinction between essential and additional outcomes is presented in student-friendly language.
Units Context The context section appears at the beginning of each unit to encourage students to make meaning of science in terms of their everyday experiences.
Unit
4.1
context
4.1
context
3 State which of the groups in Question 2 has the most detailed description of the organisms in it.
14 A mnemonic is a silly sentence that helps remind you of something. You could, for example, remember the order in organism are classified (kingdom—phylum—class— which organisms order—family— order—family—genus—species) by, instead, remembering ‘Kind people can often find green shoes!’ Create your own mnemonic to re represent the order of classification from kingdom to spec species.
4 Organisms are grouped into five kingdoms. List them.
15 The complete classification cl of a human is:
2 List these groups from the one that contains the greatest ms to the group that contains the least: number of organisms m, genus, order, class. family, species, phylum, kingdom,
5 State the structural feature that splits animals into twoo phyla.
Kingdom: Anima Animal
6 State the two major groups into which plants are classified. ed.
4.3
Phylum: Chorda Chordata (vertebrate)
QUESTIONS Understanding
Class: Mammali Mammalia (mammal) Order: Primata ((primates)
7 Explain how you know a terrier and a poodle belong to the same species.
Family: Hominid Hominidae (hominids)
8 Explain how you know that a horse and a donkey are different species.
Genus and spec species: Homo sapiens Use this and inf information from the text to construct a table s that shows the similarities between a human with a dog and the differences bbetween them.
9 Describe how the unique scientific name for every living thing is created.
Remembering 10 A subphylum represents a group smaller than a phylum but
166 You have just discovered di a new species! You must now report your findings to the AS4NT (The Australian Society for Things) Naming Things).
bigger than a class. Use this information to explain what you
1 State the meanings of terms taxonomy and taxonomist. thinkthe a subclass represents.
a Outline the ccharacteristics of your new organism. Be creative!
2 List these groupsApplying from the one that contains the greatest 11 The scientific name of the Tasmanian devil is Sarcophilus number of organismsharrisii. to Identify the group that contains the least: its:
b Construct a diagram d or model of your new species. c Classify your organism by placing it in a kingdom.
a genus
family, species, phylum, kingdom, genus, order, class. b species. Identify important characteristics shared by all animals in the 3 State which of the12groups 2 has the most detail genus Felis in (the Question cat family). description of theAnalysing organisms in it.
d Further class classify your organism by giving it a name using the binomial naming system.
13 Four native plants found in the Blue Mountains are Banksia anksia
4 Organisms are grouped into fivepunctata, kingdoms. Listandthem. d Banksia ericifolia, Eucalytpus Acacia floribunda marginata. Analyse this information to:
5 State the structural feature that ofsplits animals a State the number species this represents. ents.into two phyla b Name the plants that are in the same ame genus.
6 State the two major cgroups into which plants are classified. Predict if botanists couldd ever cross any of these plants to
Understanding
edlings. make new seedlings.
113
Investigating The investigating activities can be set for further exploration and assignment work. These activities may also include a variety of structured tasks that fall under the headings of reviewing and e - xploring.
planets as terrestrial, gas giants or dwarfs; and geologists classify rocks as igneous, sedimentary or metamorphic. Biologists have the most difficult classification job of all— they need to be able to classify every living thing, placing every organism into groups that are similar in some way.
Classification makes life a lot easier for everyone, not just scientists. At the supermarket, items are hey organised by type or by the way they are packaged. Canned fish is in one nd aisle, pasta in another and sauces and bread somewhere else. Canned vegetables are in one place, the fresh ones in another and the frozen ones in the freezer. Classification in the supermarket helps you find what youu want. If you need some chocolate syrup for your ice cream, then you will sert probably find it with the other dessert kely toppings. Likewise, soy sauce is likely uce. to be found near the tomato sauce.
W
Scientists need to be abl many different tasks. On important is classificatio the organisation of differ groups of related types. elements as metals, non metalloids; astronomers
Creating
1 State the meanings of the terms taxonomy and taxonomist.t
2002 and beyond
Classification
Unit
QUESTIONS
Remembering
Voyager 1 & 2
The solar system
Why classify?
Scientists need to be able tto carry out many different tasks. One of o the most important is classification. Classification is the organisation of different differen things into Chemists classify groups of related types. Ch non-metals or elements as metals, non-m astronomers classify the metalloids; as me tronomers cla
4.3
4.3
Chapter opener
creating questions. Questions incorporate a variety of verbs, including the syllabus verbs. All verbs have been bolded so students can begin to practise answering questions as required in examinations in later years.
Fig 4.1.2 Goods at the supermarket are
19 Much of the information we know about the outer uter planets came from the Voyager 1 and 2 missions. Use the information in the table to construct a scaled timeline for each mission. N Date
Mission
20 August 1977
Voyagerr 2
5 September 1977
Voyagerr 1
5 March 1979
Voyagerr 1
9 July 1979
Voyagerr 2
12 November 1980
Voyagerr 1
25 August 1981
Voyagerr 2
24 January 1986
Voyagerr 2
25 August 1989
Voyagerr 2
1998
Voyagerr 1
2002 and beyond
8.4 8 4
What happened? Launches
8.4 8 4 Launches
Flies by Jupiter
INVESTIGATING INVESTIG INVE STIGATIN STIG ATING ATIN G
Flies by Jupiter Flies by Saturn
Flies by Saturn Flies by Uranus
Investigate your available resources (e.g. textbook, Flies by Neptune Most distant human-made encyclopaedias, Internetobject etc.) to: Exploring past Pluto 1 Find out what or who each planet was named after.
Voyagerr 1 & 2
Construct a booklet that summarises this information, including pictures of each planet and the person or object the planet was named after. L
INVESTIGATING INVESTIGAT INVESTI GAT ATING ATIN NG N G
2 Find out what the given statement means. Money spent on space exploration would be better spent on e -xploring
Investigate your available resources (e.g. textbook, encyclopaedias, Internet etc.) to: 1 Find out what or who each planet was named after.
things like medical research and aid programs.
mation, Construct a booklet that summarises this information, including pictures of each planet and the personn or object the planet was named after. L 2 Find out what the given statement means.
To find ou out more about the solar system, a list of web destinations can be found oon Science Focus 1 second edition Student Lounge. There, you will also find a link to a website that allows you to construct a model of a spac space probe, such as the Cassini spacecraft that was sent to explore Saturn.
Organise a class debate on this issue. L
etter spent on Money spent on space exploration would be better things like medical research and aid programs. Organise a class debate on this issue. L
272
classified to make them easier to find.
Libraries have their own classification system, organising their books by types, subject and author. Textbooks on the same subject are going to be in roughly the same place, novels by the same author will be grouped together, and encyclopaedias will be in their own section.
Practical activities
Fig 4.1.1 Although it may look like something from science fiction, this Hercules beetle is a very real living thing. Biologists need to be able to classify all living things, even Hercules beetles.
95
Unit content
g
y
y
Making a pasta key
Aim
To construct a key to classify pasta.
4.1
PRACTICAL ACTIVITIES VIT VI TIE T IE IES ES
1
Aim
Unit
The unit includes illustrations, photos and content to keep students engaged and challenged as they learn about science. A homework book icon appears within the unit indicating a related worksheet from the Worksheet supporting homework book.
Practical activities are placed at the end of each unit, allowing teachers to choose when and how to best incorporate practical work into the teaching and learning. A practical activity icon will appear throughout the unit to signal suggested times for practical work. Within some practical activities a safety box 4.1 appears that lists very importantt 2 Constructing keys ur safety information. Some practical activities are design ! your own (DYO) tasks and others may be conducted using ed to a data logger. Icons are inserted indicate these options.
4 When en you get to the poin point where you are at a particular type, draw the pasta or paste a sample of it in that place on your key.
5 Gather all the pasta togeth together again and decide on a new set of To construct different types of keys to classify collect Equipment eristics by which tto reclassify your pasta. Once again, characteristics A sample of at least five different kinds of uncooked pasta (e.g. spiral pasta, tubes, shells, bows, spaghetti etc.) in a beaker or cup.
Safety Method
uct a dichotomous key. construct
Questions ns
1 Identify fy the main feature of a dichotomous key.
1 Pour the contents of the beaker onto your bench.
2 Look at the keys designed by other groups. State whether
2 As aplants group, decide(e.g. on the characteristics (e.g. shape, size etc.)rhus)they Some oleander and are used the same chara characteristics that you did. you will use to classify your sample of pasta. 3 Evaluate uate the different key keys you constructed. Which do you 3 In your workbook, construct a dichotomousin key tosome classify nk was better? Why? think cause allergic reactions people. your pasta. pasta
Equipment
A collection of at least ten of one of the following: Fig 4.1.15 s LEAVES COLLECTED FROM DIFFERENT TREES AND SHRUBS school Start off your key like this.
Unit questions
viii
A set of questions related to the unit are structured around Bloom’s Taxonomy of Cognitive Processes. The questions move from straightforward, lower-order remembering, understanding and applying questions, through to more complex, higher-order evaluating, analysing and
2
C Constructing Constructi t ting g keys k
Aim
Method
To construct different types of keys to classify collected objects.
!
Safety
Some plants (e.g. oleander and rhus) are known to cause allergic reactions in some people.
Equipment
A collection of at least ten of one of the following: s LEAVES COLLECTED FROM DIFFERENT TREES AND SHRUBS AROUND THE school s PIECES OF COMMON LABORATORY GLASSWARE AND EQUIPMENT s OBJECTS FROM A PENCIL CASE
?
1 As a group, decide on the characteristics you will use to classify your ten objects.
2 Group the objects according to the characteristics you chose. 3 Construct a dichotomous key and a tabular key that would allow others to classify your ten objects in exactly the same way as you did.
Questions
1 Outline some practical advantages of classifying different EQUIPMENT USED IN THE LABORATORY 2 Compare the dichotomous keys you constructed with your tabular keys. Which was easiest to construct? Suggest why.
101
DYO
1 List three examples of each of the following: a organisms b vertebrates
c Identify a feature of birds that resembles re a feature of those long-extinct dinosaurs.
c invertebrates d endotherms
8 Identify whether the following ques questions are dichotomous:
e ectotherms
a Does the animal have a backbone?
f angiosperms
CHAPTER REVIEW g conifers h fungi
i protists.
1 List three examples each of the following: b the three main of orders of mammals c the four main classes of invertebrates
a organisms d the five main orders of arthropods
e the five main classes of vascular plants. b vertebrates
Understanding invertebrates Explain why.
e ectotherms 5 Clarify the meanings of the following terms: a respiration f angiosperms b excretion
g conifersc h fungi
stimulus
d response species
g vertebrate
a the person b the lion. 10 Identify whether the he following pairs of animals belong to the same species: a a Lebanese mann and a Chinese w woman c a greyhound and nd a poodle d a lizard and a crocodile e a donkey and a horse. 11 You are standing ng by a campfire, list listening to the rustle of the he bushes, the crackle of the fire and the laughter possums in the of your friends. all of the things mentioned in nds. Identify whether al this sentence nce are alive. Do any of the non-living things show any of the Explain. he characteristics of life? Ex
a Identify some of the other ways in which they classify the music.
h exoskeleton
heterotroph. a the five imain classes of vertebrates
b the
d What type of animal is that?
12 Electronic ronic music storage systems ssuch as iTunes classify the music usic they contain in a number of different ways (e.g. by artist).
e taxonomy
i protists.f
c Did you feed the dog?
b a tiger and a gorilla rilla
3 Explain why scientists classify things.
d endotherms 4 Cells were unknown before the invention of the microscope.
2 State:
b What colour is your T-shirt?
9 You watch somebody run across a field being chased by a hungry lion. Identify characteristics of life are shown dentify which character by:
2 State: Remembering a the five main classes of vertebrates
c
b Recent research has indicated th that many (if not all) dinosaurs were warm blooded aand that birds may have evolved from them. Use this info information to classify dinosaurs, placing them in the correct animal kingdom. c
6 Plants and animals both use cellular respiration for energy. threeExplain main orders ofundergo mammals Explai o photosynthesis. why only plants can
Applying Ap plying ying th f Appl i l
fi
t b t
7 Until recently, it was thought that dinosaurs were reptiles. a If this was correct, list the kind of features you would expect dinosaurs to have.
b Explain the advantages of using ddifferent keys to classify the same music.
Analysing Ana 13 Classify the following as angiosper angiosperm, conifer, fern or bryophyte: a pine b tree fern c apple tree d liverwort.
135
Fact File Mars
Fig 8.4.7 Mars showing red earth and polar caps.
Mass
0.107 times that of Earth
Moons
Two (Phobos—diameter 23 km, Deimos—diameter 10 km)
Diameter
6794 km ( = 0.53 × Earth’s diameter)
Surface
Soft red soil containing iron oxide (rust), ( ), giving g g the pplanet its red appearance. Cratered regions, large volcanoes, a large canyon and possible possibl dried-up water channels. Polar caps of frozen carbon dioxide and water.
Atmosphere Atmo
Very thin, mainly carbon dioxide
Gravity Gr
0.376 times that on Earth
Surface temperature
–120 °C to 25 °C
25.2°
1.52 AU (228 million km)
Time to orbit Sun (year)
687 Earth days
Scale model (Sun = 300 mm) Diameter
1.4 mm
Distance from Sun
49.1 m
Mars
Fig 8.4.8 The Mars Phoenix mission. The landing system syste stem on Phoenix allows the spacecraft to touch down within 10 kilometres etres res of its targeted landing area.
The asteroid belt The asteroid belt is made up of thousands ds of small ound the Sun rocky metallic bodies and dust in orbit around Sun. ameter of about The largest asteroid is Ceres, having a diameter 1000 kilometres. Researchers have found several nearEarth asteroids, but none are predicted to crash into Earth in the near or distant future.
Two (Phobos— Deimos—diam
Diameter
6794 km ( = 0 diameter)
Fig 8.4.9 Thousands of asteroids lie in a belt between Mars and Jupiter. One is Ida, an asteroid big enough too have a gravitational field that has trapped its own orbiting moon,, Dactyl.
266
Worms
Polyps Polyps are cnidarians that att attach themselves to something like a rock. Corals and anemones are examples of polyps.
There are three different phyla of worms—roundworms, flatworms, and segmented worms. Roundworms Roundworms have long cylindrical bodies that are in one piece without segments. They have a digestive tube with a mouth and anus. Some roundworms are parasitic, living off (and weakening) other living animals. Others live ‘free’ in water or damp soil. Examples of roundworms are threadworms, hookworms and the parasitic roundworms found in the intestines of humans, dogs, pigs and horses.
Science
Science Clip features contain quirky information related to the topic that students will find interesting.
Clip
What do I do?
Flatworms Flatworms are similar to roundworms in that they also can be parasitic or ‘free’. They differ in that they have flat bodies instead of round ones. If they have a digestive system, it has only one opening, which acts as both mouth and anus. Flukes and tapeworms are examples of flatworms.
Fig 4.4.18 Coral polyps olyps are living ng things th called cnidarians.
opening acts as both mouth and anus
Medusas Medusas are cnidarians nidarians that can swim about freely. Jellyfish are medusas. Many ar are harmless, whereas some, ellyfish, can kill. kill The stinging cells of like the box jellyfish, others, such as bluebottles, in inject a mix of chemicals that leave painful, raised red w welts wherever they touch the skin.
It is currently recommended that bluebottle stings are soaked for about 20 minutes in hot water (say under a hot shower or
4.4
0.107 times th
Moons
hooks anchor the worm to the internal wall of the gut
Segmented worms Also known as annelids, segmented worms can be found both on land and in water. They have welldeveloped body systems and bodies with multiple segments. Examples are leeches and earthworms.
Ask
Sci cii Q B Busters Bu us team
Chalk talk
Fig 4.4.19 Jellyfish are medusas, a type of cnidarian.
The big Moon Worksheet 4.3 Classifying
Fig 4.4.21 The segments are clear on the body of this leech.
Hot versus cold
Prac 2 p. x
and ancient skeletons, such as this fossilised dinosaur skull.
Chalk talk
The big Moon
115
Hi Isabella, If a piece of chalk is held incorrectly, it first sticks to the blackboard and then suddenly crumbles. The chalk then slips and vibrates, causing the loud squeal. As the vibrations die down and the chalk dust falls out of the way, friction between the chalk and the board increases until the chalk sticks once again and the cycle is repeated.
That’s one theory anyway. There is another, which is based on impurities in the chalk stick. These small hard bits of grit scratch against the blackboard much like your fingernails would. And what about the solution? Well, you can ask your teacher to try these: s 3NAP THE CHALK IN TWO 4HIS SHOULD DOUBLE THE frequency of the sound and therefore should not be heard.
s AT WHAT ANGLE IT IS HELD
s 0USH DOWN HEAVIER ONTO THE BLACKBOARD This should rub the grit off quickly and the lesson should be squeak free.
s HOW TIGHTLY THE PIECE OF CHALK IS HELD
s 5SE THE WHITEBOARD
s THE LENGTH OF THE PIECE OF CHALK
Or maybe you could experiment yourself, and then pass on the results to your teacher.
s WHERE THE CHALK IS HELD BY THE FINGERS
Career Profile boxes appear throughout the book, covering information about specific careers in science.
Hot versus cold
Hi Q Busters, I was at school yesterday when there was a loud squeal coming from the chalk as the teacher wrote on the blackboard. What causes this? Can you suggest anything I can pass on to our teacher so she doesn’t do it again? It’s driving the whole class mad! Best wishes, Isabella
The frequencies of the squealing chalk depend on the following things:
! PALAEONTOLOGIST EXAMINES CLASSIFIES AND animal and plant fossils found in sedimen This helps us understand the history of lif
Geologist
For example, if the chalk is held just above the blackboard contact point and at right angles to it, the frequencies are higher than if the chalk is held at a 45° angle. In the first case, vibrations are generated along the length of the chalk. In the second case, the chalk vibrates by bending.
Pic of full moon?
Another way to prove it is to look at the low Moon though a rolled-up piece of paper. This will block out the surroundings and the illusion should vanish. Happy moon gazing! The Q Busters Team
Hot versus cold Dear Q Busters Someone at school said she heard on the TV that hot water freezes faster that cold water. This can’t be true, can it? Please help as I am now confused about freezing water. Regards, Alexandra REPLY
Hi Alexandra,
Dear Q Busters, The other night when we had a full moon it looked enormous just as it rose, but then got smaller later in the night. How can this be? I thought the Moon was the same distance away from the Earth all of the time! From Rachel REPLY
Hi Rachel,
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One theory suggests that the mind judges the size of an object based on its surroundings. With a low Moon the trees and houses near you appear smaller against the moon which, in turn, makes it appear bigger than it really is.
This would seem to be completely wrong by what you have been taught so far in Science. This phenomenon, where hot water appears to freeze faster than cold water, actually has a special name. It’s called the Mpemba effect. It is named after the Tanzanian high school student, Erasto Mpemba, who, in 1963, discovered it when experimenting at school.
Happy chalking! The Q Busters Team
The big Moon
Many, theories have been put forward, and many, experiments have been conducted. The findings suggest thats it’s only an optical illusion.
until the Moon is higher in the sky. Measure it again, compare your measurements, and you’ll find it’s more or less the same size no matter where it happens to be in the sky.
To prove this for yourself, hold a ruler at arm’s length and measure the Moon as it rises. Make a note of this measurement, and then wait a while
There is still great debate out there over whether this is fact or fiction, but here are the two main theories at present.
the surface. Well, this is removing most of the dissolved gases in the water. The gases actually reduce water’s ability to conduct heat. Therefore, with less dissolved gas in the water, it can cool faster. But we still don’t know for certain. Happy freezing! The Q Busters Team
1. Evaporation. As you know, when hot water is placed in an open container it begins to cool with steam coming off. This will reduce the amount of water in the container. With less water to freeze, the process can take less time. 2. Dissolved gases. When you are boiling water, Alexandra, you know that it’s boiling because you can see the bubbles rising and popping on
Insert pic?
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ACCURATE RECORDS AND PREPARE s KEEP KEEP ACCURATE RECORDS AND PREPARE REPORTS SAFELY IN A NUMBER OF DIFFERENT ENV s WORK WORK SAFELY IN A NUMBER OF DIFFERENT ENVIRONMENTS
299
Case study boxes cover an in depth exploration of a single case or topic.
Case study
1.2
Case study
Fig 9.3.15 Geologists studying sedimentary rock layers in the field.
Unit
Geologists study the composition and structure of the Earth. This allows them to locate materials and minerals. Geologists work in laboratories and in the field, usually as part of a team. Fieldwork can involve spending time in remote deserts, or in tropical or Antarctic areas. Geologists can be involved in: s ADVISING ON SUITABLE LOCATIONS FOR TUNNELS AND BRIDGES s EXAMINING ROCK SAMPLES USING ELECTRON MICROSCOPES s STUDYING THE NATURE AND EFFECTS OF NATURAL EVENTS LIKE weathering, erosion, earthquakes and volcanoes s TAKING ROCK SAMPLES FOR ANALYSIS s FINDING THE AGE OF ROCKS AND FOSSILS A good geologist will be able to: s WORK AS A TEAM MEMBER OR ALONE
Stormy weather
Palae
ladies, mare’s fart, hound’s piss, open arse, bum-towel and pissabed. Using his binomial system, they became Taraxacum officinale.
Chalk talk
REPLY
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9.3
Fig 9.3.14 One of the jobs of a palaeontologist is to inspect fossils
Career Profile
Career Profile
Palaeontologists can be involved in: s LOCATING LOCATING SITES WHERE FOSSILS MAY BE FOUND SITES DIG s CAREFULLY CAREFULLY DIGGING FOSSILS OUT OF THE ROCKS IN WHICH they are fou found s PREPARING PREPARING FOSSILS FOR DISPLAY OR STORAGE FO s DATING DATING FOSSILS TO WORK OUT THEIR AGE IN s USING USING INFORMATION ABOUT FOSSILS TO STUDY OTHER THINGS SUCH A SUCH AS OIL EXPLORATION OR THE HISTORY OF LIFE ON THE Earth. A goo good palaeontologist will: AB s BE BE ABLE TO WORK SAFELY AS A TEAM MEMBER OR ALONE AB s BE BE ABLE TO WORK VERY CAREFULLY AND PATIENTLY AS IT CAN take yyears to remove fossils from rocks A s HAVE HAVE A GOOD EYE FOR DETAIL FO s LOVE LOVE FOSSILS
Fig 4.3.9 Until Linnaeus, common dandelions were known as naked
Sci Sc Sci ci Q Bus Buster B Bu uste us ters tter ers er
What do I do?
Unit U
! PALAEONTOLOGIST EXAMINES CLASSIFIES AND DESCRIBES animal and plant fossils found in sedimentary rocks. This helps us understand the history of life on Earth.
Linnaeus and Cuvier proposed their kingdoms and classes based on the information they had available at the time. The development of the microscope, however, revealed characteristics of organisms that had never been seen before, particularly in plants and microorganisms such as bacteria. With this new information, new kingdoms were needed and others could be re-organised.
Sci Q Busters appears after Chapter 9 and provides answers to student questions. Students are able to email questions that come up during class time to the Q Busters team at
[email protected]
Cereal sounds
Palaeontologist
north of Finland in 1732, Linnaeus nearly fell into an icy crevasse. He saved himself from near-death and went on to discover 100 new plant species on this expedition.
microscope (SEM) of the head of a dog’s parasitic tapeworm.
p Clilip Clip
Some leeches are used in medicine to suck out blood from clots and to encourage blood flow into newly attached limbs after microsurgery.
Career Profile
Arguments in science
Fig 4.3.7 While on a scientific expedition to the far
Fig 4.4.20 An image obtained by a scanning electron
nce enc cience cie cien SScience Sc
It is currently recommended that bluebottle stings are soaked for about 20 minutes in hot water (say under a hot shower or in a bath). The traditional vinegar solution does little since the bluebottle injects a chemical irritant that is neither acid nor base.
Linnaeus originally left room in his kingdoms for mythical animals such mermaids, satyrs, unicorns and ‘monstrous humans’. Room was left for
Unit
Mass
for unicorns (white horses with single long, spiralled horns growing from their foreheads), unicorn-like horns are found on narwhals (rare arctic mammals that resemble dolphins) and some seahorses.
Homo ferus (humans Many students of Linnaeus who walked on all fours went on to explore the world like dogs) and Homo for new plants and animals. caudatus (humans who One, Daniel Solander, had a tail)! accompanied Captain James Cook on his first journey (on which he discovered the east coast of Australia in 1770). He and Joseph Banks brought back to Europe the first ever collection of Australian plants. Botany Bay (originally called Stingray Bay, then Botanist Bay) in Sydney was also named by them. Although some changes were made by the French zoologist Georges Cuvier in the early 1800s, the basic system as developed by Linnaeus is still used today.
Indigenous Australian classification Aborigines traditionally classify animals according to their usefulness, where they live or how they were used. Penguins and emus, for example, are placed in the same category as kangaroos—both are ground-dwelling sources of meat and so they are grouped together. Other birds are placed in the ‘flying food source’ category. In some instances, an animal has no Aboriginal name because it was not used for anything. Some Aboriginal tribes in northern Australia name plants according to their uses or their locations, such as a swamp. In these tribes, fish (guya) are also classified according to where they live. This gives five categories: garrwarpuy living near the surface ngopuy living near the bottom mayangbuy living in rivers raypinbuy living in freshwater gundapuy living among rocks and reefs.
Clip
Monstrous humans! Fig 4.3.8 Although there is no evidence
Pearson Places icons direct students to the Science Focus 1 Second Edition Student Lounge on Pearson Places. The Student Lounge contains animations, video clips, web destinations, drag-and-drop interactives and revision questions.
1.03 Earth days
Distance from Sun
The Laps are the indigenous people of Scandinavia. Reindeer are important to them and so they have more than 107 different categories for them! Their native Saami language classifies them according to their age, condition, body shape and the shape of their antlers!
Science
Aboriginal flag icons denote material that is included to cover Indigenous perspectives in science.
Fact File
Tilt of axis
Clip
107 Reindeers!
Clip
Carl Linnaeus In 1735, the Swedish naturalist Carolus (Carl) Linnaeus (1707–1778) proposed a systematic way of grouping and naming living things. He classified all living things as either animal or plant. He then further divided all animals into six classes: Mammalia (mammals), Aves (birds), Amphibia (amphibians and reptiles), Pisces (fish), Insecta (insects) and Vermes (all the other invertebrates). In recognition of his pioneering work, Linnaeus was made a noble in 1761. From then on, he was known as Carl von Linne.
Scientists still argue over how many kingdoms there should be. Some claim that the protists should not have their own kingdom and that, instead, they should be split amongst the animal, plant and fungi kingdoms. Recent research suggests that the monera kingdom could also be split to form Science two new kingdoms. Although the argument continues, most accept that there are five basic kingdoms Penis worms! (animal, plant, fungi, protists and Science Focus 1 presents monera). nine main classes of animals, Scientists also argue about how but there are other obscure many phyla and classes there are. animals with their own specialised classes. Sponges, There is no hard-and-fast definition for example, have their own for a phylum and so scientists also class (ponifera), whereas argue about its definition, too, starfish belong to another sometimes merging the idea of class class called echinoderms. and phyla together. For these Another small class is called reasons, there may be up to 89 priapulida, otherwise known as penis worms! different classes.
Go to icons direct students to a unit within the same stage of the NSW curriculum. This unit reference allows students to revisit or extend knowledge. Go to
Science Period of rotation (day)
Science
Likewise, shellfish and crustaceans (maypal) have at least ten categories. These are determined by how they attach to rocks, how they move about and whether they live amongst rocks or on a reef. Four distinct subgroups are: gundapuy attached to reefs or rocks warranggulpuy move over the outer surface of rocks lirrapuy move around the edges of rocks djinawapuy attached beneath rocks or inside coral.
Literacy and numeracy icons appear throughout to indicate an emphasis on literacy or numeracy. N L
Science Fact File boxes contain essential science facts relevant to the topic.
Science
On each continent, indigenous peoples established their own keys to classify the living things around them. Many early keys were based on whether the animals or plants were useful as a food source, a source of fur or natural fibres that could be woven or whether they were part of their spirituality. Animals, for example, were sometimes classified as wild or domesticated. Other classification keys were based on whether the animal lived on the land or in the sea. The term ‘fish’, for example, used to refer to anything swimming or anything that lived in the sea. Even today, creatures such as jellyfish, shellfish, crayfish and starfish include ‘fish’ in their names, despite them now being classified as creatures other than fish.
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Other features or icons The solar system
Grouping living things
Prescribed Focus Area: The history of science
4.3
Remembering
Unit
Chapter review questions follow the last unit of each chapter. These questions are structured around Bloom’s Taxonomy of Cognitive Processes and cover the chapter learning outcomes in a variety of question styles to allow students the opportunity to consolidate new knowledge and skills.
CHAPTER REVIEW
Science Focus
and current research and development. The features allow students to explore science in further detail through a range of student activities.
Chapter review
The medicine man
British GP, Dr Harold Shipman killed an estimated 236 23 of his patients between 1974 and 1998. His visits to sick, elderly people were often followed by a worsening off their ailment and then what seemed to be an ious death. Dr Shipman would return and wri unsuspicious write th out the death certificate and alter the records to say that the person was so sick that they were close to death. at the doctor was actually giving Very few suspected that ction. his patients a lethal injection. However, in 1986 he killed a healthy elderly lady and st will and testament that fabricated a poorly worded last made him the sole beneficiary. The police investigated the forged will and then exhumedd (dug up) her body. They also exhumed the bodies of Shipman’s other und in each of patients. Traces of morphine were found aths. Shipman’s them—the probable cause of their deaths.
computer system became vital evidence as the date of every file he modified was recorded. The files for many of the deaths showed that they were modified on the day the patients died, uncovering many more likely murders. Shipman was convicted and given 15 life sentences, but he committed suicide in custody, leaving many questions unanswered. The motives for his crimes remain a mystery.
Fig 1.2.8 Dr Harold Shipman killed at least 236 patients. A poorly forged will led to his capture.
The m Clip
Science
Plastic money Australia was the first to use the plastic banknote—a banknote— $10 commemorative note introduced in January 1988 tto coincide with the Australian Bicentenary. Plasticc banknotes are m more durable than paper ones, lasting four to five times imes longer. A paper pap $5 note had an average life of about six months, lasts more than nths, a plastic one la three years. Note Printing Australia ralia (NPA) is owned by the Reserve
British GP, Dr Harold Shipman killed an est of his patients between 1974 andQUESTIONS 1998. His ON NS S sick, elderly people were 1.2 often followed by a of their ailment and thenRemembering what seemed to be 1 List five documents that a criminal might try to falsify. 2 State what indicated that hat the Hitlerretur diaries were fake. unsuspicious death. Dr Shipman would 3 State what can be used to determine which typewriter was ansom note. used for a ransom out the death certificate and alter the record 4 List the advantage(s) of Australian banknotes being printed plastic. the person was so sick thatonthey were close t 5 List the features that usually give away fake banknotes. V f d h h d
The Science Focus 1 Second Edition package
Bank of Australia and prints all Australian banknotes. It has also produced plastic banknotes for Thailand, Indonesia, Papua New Guinea, Kuwait, Western Samoa, Singapore, Brunei, Sri Lanka and New Zealand. NPA also sells plastic blank notes to government printers in other countries so that they can print their own money. Old and ‘worn-out’ Australian plastic money is recycled into plastic objects such as plumbing fittings and compost bins.
Understanding 6 Investigators generally ignore the slant and spacing of letters in a handwritten document. Explain why. 7 Describe how a computer printer can be identified from a fake letter.
Don’t forget the other Science Focus 1 Second Edition components that will help engage and excite students in science: Science Focus 1 Second Edition Homework Book
8 Explain how inks can be identified using: a fluorescence b chromatography 9 Describe the following: a intaglio printing b microprinting c a water mark
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Science Focus spreads appear throughout the book. These are special features on various aspects of science including history, the impact of science on society and the environment
Science Focus 1 Second Edition Teacher Edition, with CD Science Focus 1 Second Edition Pearson Reader Science Focus 1 Second Edition LiveText™
ix
Stage 4
Syllabus Correlation chapter
1 2 3
Outcomes
Being a scientist
Solids, liquids and gases
Mixtures and their separation
Science Focus 1
4 5 6 7 8 9 Classification
Cells
Heat, light and sound
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4.1 4.2 4.3 4.4 4.5
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▲ indicates the key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Areas.
Our planet Earth
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Earth in space ▲
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4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27
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Forces
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Verbs Science Focus Second Edition uses the following verbs in the chapter questions under the headings of Bloom’s Taxonomy of Cognitive Processes. The verbs in black are the key verbs that have been developed to help provide a common language and consistent meaning in the Higher School Certificate documents. All other verbs listed below feature throughout the book and are provided here for additional support to teachers and students.
Remembering
Analysing
List Name Present Recall Record Specify State
Analyse
write down phrases only without further explanation present remembered ideas, facts or experiences provide information for consideration present remembered ideas, facts or experiences store information and observations for later state in detail provide information without further explanation
Understanding Account Calculate
Clarify Define Describe Discuss Explain Extract Gather Modify Outline Predict Produce Propose Recount Summarise
account for: state reasons for, report on. Give an account of: narrate a series of events or transactions ascertain/determine from given facts, figures or information (simply repeating calculations that are set out in the text) make clear or plain state meaning and identify essential qualities provide characteristics and features identify issues and provide points for and/or against relate cause and effect; make the relationships between things evident; provide why and/or how choose relevant and/or appropriate details collect items from different sources change in form or amount in some way sketch in general terms; indicate the main features of suggest what may happen based on available information provide put forward for consideration or action retell a series of events express, concisely, the relevant details
Applying Apply Calculate
use, utilise, employ in a particular situation ascertain/determine from given facts, figures or information Demonstrate show by example Examine inquire into Identify recognise and name Use employ for some purpose
identify components and the relationship between them; draw out and relate implications Calculate ascertain/determine from given facts, figures or information (requiring more manipulation than simply applying the maths) Classify arrange or include in classes/categories Compare show how things are similar or different Contrast show how things are different or opposite Critically (analyse/evaluate) add a degree or level of accuracy/depth, knowledge and understanding, logic, questioning, reflection and quality to (analyse/evaluate) Discuss identify issues and provide points for and/or against Distinguish recognise or note/indicate as being distinct or different from; to note differences between Interpret draw meaning from Research investigate through literature or practical investigation
Evaluating Appreciate Assess
make a judgement about the value of make a judgement of value, quality, outcomes, results or size Critically (analyse/evaluate) add a degree or level of accuracy/depth, knowledge and understanding, logic, questioning, reflection and quality to (analyse/evaluate) Deduce draw conclusions Draw draw conclusions, deduce Evaluate make a judgement based on criteria; determine the value of Extrapolate infer from what is known Investigate plan, inquire into and draw conclusions Justify support an argument or conclusion Propose put forward (for example a point of view, idea, argument, suggestion) for consideration or action Recommend provide reasons in favour Select choose one or more items, features, objects
Creating Construct Design Investigate Synthesise
make; build; put together items or arguments provide steps for an experiment or procedure plan, inquire into and draw conclusions about put together various elements to make a whole
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1
Being a scientist
Prescribed focus area: The nature and practice of science
Essential skills
Key outcomes 4.2, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19, 4.22
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Different pieces of laboratory equipment are used for different purposes.
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Use the correct piece of equipment for the correct task.
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Metric units must be included with all measurements.
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Care must be taken when measuring to minimise errors.
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Experiments need to be planned in detail before you begin.
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Each experiment should test only one variable at a time.
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Risks need to be identified before starting an experiment.
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Ways to minimise these risks need to be thought of at all times.
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Tables are a good way of recording your experimental results.
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Graphs are a good way of showing any patterns that may exist in your results.
Unit
1.1
context
Science and safety
Scientists ask questions about how the physical and living world around us works. These might be about how animals like ants breathe, how rainbows are formed, why sunsets are red or what affects the rate at which fruit rots. To
performing experiments. An experiment is simply a test on a small part of the world.
Science: Asking questions The answers to questions that scientists ask often can be found in textbooks, encyclopaedias or on the Internet. Sometimes the questions that scientists ask have never been asked before and that is when scientists need to find the answers themselves by
investigate the world, scientists carry out experiments. Many of these experiments can be extremely dangerous and so a set of laboratory safety rules is needed to reduce the risks involved.
Quick Quiz
Prac 1 p. 7
The branches of science Science covers many areas. So many, in fact, that science is split into branches or disciplines.
Astronomy: astronomers ask questions about the planets, stars and the universe, like ‘What causes an eclipse?’
Biology: biologists ask questions about living things. They might study why mosquito and ant bites itch.
Chemistry: chemists investigate materials, chemicals and chemical reactions and how they can be used. They might ask why wood burns but steel doesn’t.
Ecology: ecologists study how living things affect each other and the environment in which they live. They might ask about what animals are likely to become extinct if world temperatures increase.
Geology: geologists study rocks, the Earth, earthquakes, volcanoes and fossils. They might ask what causes earthquakes to happen.
Physics: physicists ask questions about how and why things move and the forces and energy involved. They might ask questions about how to make bike helmets safer.
Fig 1.1.1 Six of the many branches of science.
3
Science and safety
Safety in science In science you will need to deal with many potential dangers. You will work with intense heat, acids and other corrosive substances. It is particularly dangerous if any chemicals get splashed into your eyes. Other chemicals are poisonous and can make you extremely ill or can kill. Broken glass and equipment pose the risk of cutting you or of fragments entering your eyes if they shatter.
Safety rules The science laboratory can be a dangerous place, but it becomes far safer if everyone follows a set of safety rules. Each laboratory is different and so is every class. This means that one set of rules cannot be used by everyone. Each class needs to develop their own set of rules with their teacher to keep everyone safe. Common sense is a good start. If something has the potential to hurt someone then DON’T DO IT! Always look for potentially unsafe activities in the lab and report these immediately to your teacher.
Fig 1.1.2 Working safely in the laboratory is the most important skill you will learn this year in Science.
Fig 1.1.3 The students here are doing something potentially dangerous. What are they doing wrong? What rules would you make to minimise the risk to themselves and to others in the lab?
Fig 1.1.4 The students here are doing the right thing. What are they doing right and what risks are they avoiding? Worksheet 1.1 Laboratory safety
4
Unit
QUESTIONS
Remembering
1.1
1.1
Applying
1 List six of the main branches of science.
6 The following scientists are working in different branches or disciplines of science. Identify which branch each is working in:
2 Make a list of four safety DOs and four DON’Ts in the laboratory.
a Johanna is studying the eating habits of a cheetah.
3 Use your common sense to state whether the following rules are good ones or silly ones likely to cause injury:
b Yianni is developing a new type of plastic. c Lauren is studying the crystals embedded in a rock.
a It is OK to pour all substances down the sink after an experiment.
d Brigid is studying the movement of the planets. e Gary is investigating what animals might be affected when a new dam is built.
b Running and pushing people in the laboratory is never allowed.
f Ying is studying the flow of electricity through an electronic circuit.
c It is OK to eat and drink in the laboratory. d Spilt chemicals can be left unattended.
7 Within each branch of science are sub-branches. Identify whether the sub-branches below belong in astronomy, biology, chemistry or ecology.
e The teacher always must be told if something goes wrong. f Safety glasses are optional when we use chemicals in the laboratory.
a Optics: the study of light
g Chemicals should never be tasted or smelled.
b Entomology: the study of insects
h Always point test tubes away from yourself and others.
c Vulcanology: the study of volcanoes
i It is good science to mix unknown chemicals together.
d Zoology: the study of animals. 8 Identify five injuries that can happen in a science laboratory if simple safety rules are not obeyed.
Understanding 4 Describe four dangers that you might have to deal with in a science laboratory.
9 Identify another simple experiment in which the following senses would be too dangerous to use:
5 Eye injuries are common in science laboratories. Explain what could cause these injuries and describe what could be done to minimise the risk of them.
a sight b hearing c taste. 10 Sometimes it is too dangerous to use some of our senses. Complete this table by identifying which senses should and should not be used.
Experiment
Senses that you would use
Sense that would give the most information
Senses that you would NOT use
Testing the ability of strong acids to clean a sheet of metal Testing how long milk takes to go off Testing how long it takes for six tomatoes to ripen Studying lava flowing from a volcano Testing a new pesticide
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5
Science and safety
Evaluating
12 Propose what you should do if:
11 Inspect the safety signs shown in Figure 1.1.5 and propose what each one might be warning you about.
a You accidentally break something in the laboratory. b You smell gas. c A hissing sound is heard coming from a Bunsen burner that is not lit. d You need to leave a Bunsen burner to collect some extra equipment? 13 Propose a reason why some of the safety rules in Science are different from those in other subjects, such as design and technology, food technology and PDHPE.
Creating 14 Without using any words, design a simple two-colour sign to tell people that: a There is a slippery surface ahead. b Crocodiles are in the waterways. c Earmuffs must be used in this area. d You should not eat centipedes. 15 Design a series of simple signs to inform students of the science safety rules. The signs must be in only two colours and use only a few words.
Fig 1.1.5
1.1
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find and draw the symbols commonly used to label these types of chemicals: a flammable b corrosive c explosive.
2 Define what these terms mean and write a definition for each: L a toxic b caustic c flammable. 3 Outline what these sub-branches of science study: a botany b microbiology c paleontology d acoustics e seismology.
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Unit
Group A International
Group B Australian
a Describe his or her work. b Explain why the scientist’s work was an important development for science or society in general.
Marie Curie
Karl Kruszelnicki
c Identify dates that were important in the scientist’s life. Explain why these dates were important.
Frank Macfarlane Burnett
Helen Alma Newton Turner
d Present your information as either a poster, a PowerPoint presentation or a diary as if written by the scientist.
Galileo Galilei
William Bragg
Robert Gallo
Richard Daintree
Anne Dollin
Nancy Burbridge
Stephen Hawking
John Cornforth
Alfred Nobel
Peter Doherty
Rosalind Franklin
Howard Florey
Isaac Newton
Fred Hollows
William Herschel
Mark Oliphant
Luc Montagnier
Andy Thomas
Charles Darwin
Sister Elizabeth Kenny
Albert Einstein
Barry Marshall
Ernest Rutherford
Tim Flannery
Thomas Edison
Sir Gustav Nossal
James Watson
David Unaipon
1.1 1
1.1
4 Find information about two of the scientists in the table below. Select one scientist from each group. L
e -xploring To find out more about the branches of science, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
We b Desti nation
PRACTICAL ACTIVITIES
The mysterious case of the stolen sausages
Scientists need to use all of their five senses to make detailed observations. The main sense a scientist uses is sight. They will also use hearing, smell, taste and touch, although sometimes it will be far too dangerous to use some of these. In a way, a scientist is like a detective trying to solve a puzzling case. Clues must be gathered through careful observation of all the evidence. The various clues can then be linked together until a conclusion can be drawn about the case. In science, we don’t always get it right the first time—sometimes more experiments and observations are required.
Aim To act a set of observations to work out whom most likely stole the sausages.
Method 1 Carefully read the story on the next page. 2 Prepare a list of observations as you read the story. 3 Draw lines between observations that seem related in some way. 4 In groups, try and work out all the details of this mysterious case … who stole the sausages, when, why and how! 5 Check with other groups to see if they agree with you.
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Science and safety
After a beautiful sunny morning, the weather on this fateful day has turned terrible, with torrential downpours of rain and howling wind. You arrive home at 3.17 p.m. and are surprised to notice that the neighbour’s lawn has been mowed. You are surprised since, from experience, you know that wet grass is very hard to cut. You enter the house. The sausages that you left defrosting on the kitchen table are gone! You enter the lounge room. The front window has been shattered! Pieces of broken glass are lying everywhere. There is now nothing interrupting the view of next door’s garden and lawn. Mum’s favourite vase on the mantelpiece is lying in pieces on the floor. You remember that every time your neighbour dropped in she always said, ‘Why don’t you get rid of that old vase? It’s so ugly!’. The curtains are all messed up and the carpet is soaking wet and marked and smudged with mud! Some strands of blond hair are stuck on the windowsill. But what’s this? A small stone has been placed in the middle of the coffee table … the calling card of the sausage burglar? Later that night you notice that Fritz, the golden retriever, hasn’t touched the food in his bowl.
Questions 1 State what you want to know about the case or what you are trying to investigate. Scientists call this the aim. 2 List the observations you have made. 3 Identify the suspects in this case. 4 Explain what evidence there is to link them to the crime scene. 5 In conclusion, identify: a who you think stole the sausages b who or what broke the window c when it probably happened d who or what broke the vase e the order it all happened in. In the case above, you have used many of the skills a scientist needs. To have successfully solved the case you needed to: • Be clear about what you were trying to find out. • Make an educated guess of what you hoped to find out. • Make careful observations of what happened. • Take careful measurements, if possible. • Infer reasons about why the investigation went as it did. • Draw logical conclusions about what was found out.
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Unit
1.2
context
Equipment
As a scientist, you will use a lot of different pieces of equipment. You need to know the name of each piece and how to use it safely and accurately.
Everyday laboratory equipment Equipment is used in science to help carry out experiments and to make observations more accurate. Chemistry experiments, for example, are commonly run in beakers and conical flasks. Measuring cylinders are used to accurately measure volumes of liquid and thermometers are used to measure temperature. Stopwatches and electronic timers are more accurate than normal watches and clocks, and can be used for better timing. Other equipment magnifies very small objects that might normally be difficult to measure. Microscopes magnify extremely small objects, whereas telescopes magnify objects that are far away. Microphones and electronic amplifiers allow you to hear sounds that otherwise cannot be heard. You will use a lot of different pieces of equipment in the school science laboratory. As with all equipment, there are special rules for using each piece. Your teacher will instruct you on how to safely use each one. Fig 1.2.1 The Bunsen burner is one of the most important pieces of equipment you will use in science.
250
spatulas
thermometer
230
test tube
210 190 170
measuring cylinder
beaker
150 130 110 90
conical flask
70 50
watch-glass
30
or to take accurate measurements
or to run experiments in to measure out materials
test-tube rack with drying posts
safety glasses
bosshead clamp retort stand
Fig 1.2.2
tongs
or for keeping us safe clay triangle
or for holding things
Commonly used laboratory equipment.
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Equipment
Scientific drawing Diagrams of scientific equipment must be easy to draw and easy to read. You don’t need to be an artist, but you do need to follow certain rules so that your diagrams can be understood by another scientist. Scientists draw their equipment as a cross-section— they ‘split’ the equipment down the middle. The drawings are simple lines and curves, normally without any shading or colouring. These diagrams are known as two-dimensional (2D) scientific diagrams and are used by scientists all around the world.
Collar: controls the amount of air that enters the burner and controls the heat and colour of the flame. The hole must be closed before lighting.
barrel
airhole (gas jet inside)
Worksheet 1.2 Laboratory equipment
gas hose
base
Worksheet 1.3 Wordfind
Fig 1.2.4 Parts of the Bunsen burner Worksheet 1.5 The Bunsen burner
Pyrex
Using the Bunsen burner Pyrex filter paper and funnel
test tube
beaker
conical flask
Fig 1.2.3 Always draw scientific equipment as a simple 2D cross-section. Worksheet 1.4 Scientific apparatus
The collar controls the amount of air that enters the burner and controls the heat and colour of the flame. The collar must be turned so that the airhole is closed whenever a Bunsen burner is lit. Very little air is then able to mix with the gas and so the gas will not burn well. It produces an easily visible, pale yellow flame that is relatively cool. It is also a dirty flame because it leaves a layer of carbon on anything that is heated in it. This flame is called the safety flame because it is the coolest flame and is the easiest to see. If the collar is turned so that the airhole is open then a lot of air will enter. The gas will burn efficiently with no smoke and will be extremely hot (about 1500°C). Although difficult to see, this flame is blue in colour and noisy.
Prac 1 p. 13
light blue
The Bunsen burner
dark blue
hottest part of the flame cone of unburnt gas
A potentially dangerous piece of equipment you will use in the laboratory is the Bunsen burner. It is used to heat chemicals. Your safety depends upon using it correctly. I n t e r a c t i ve
Fig 1.2.5 There is a small cone of unburnt gas at the very base of a Bunsen burner flame. The hottest part of the flame is just above this cone.
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Prac 2 p. 14
Prac 3 p. 14
Unit
1.2
evaporating dish
clay triangle Bunsen burner
tripod and gauze mat
retort stand, bosshead and clamp
bench mat
crucible and lid
Fig 1.2.6 The Bunsen burner gets so hot that special equipment is needed to safely hold objects when heating them.
Prac 4 p. 15
Science
Prac 5 p. 16
Fact File
People in science: Robert Bunsen (1811–1899) The German chemist Robert Bunsen invented many different pieces of laboratory equipment but the Bunsen burner was not one of them. It is likely that Bunsen’s laboratory assistant, Peter Desdega, developed it in 1855, possibly from earlier designs by the English scientist Michael Faraday (1791–1867). This presents a few questions: Who should get the credit? Who does the work in science? Bunsen worked on explosive arsenic compounds, which almost killed him, and he lost one eye when a glass container exploded. Working with the German physicist Gustav Kirchhoff (1824–1887), Bunsen discovered two new elements—caesium and rubidium.
Science
Clip
Smelly Bunsen! Bunsen was a bachelor for all his life. He developed a number of strange personality quirks, including not bathing! International Bunsen day is celebrated each year on Bunsen’s birthday of March 31.
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Equipment
1.2
QUESTIONS
Remembering 1 State what each piece of equipment is used for: a clay triangle b beaker c safety glasses d test tube
c A physicist wants to accurately measure the time it takes for a stone to drop 2 metres. d An astronomer wants to study the surface of the Moon. 11 The Bunsen burner can be extremely dangerous if not treated carefully. Identify what each of the students in Figure 1.2.7 might be doing wrong.
e thermometer f measuring cylinder g tongs. 2 Recall the following pieces of equipment by drawing their correct 2D scientific diagrams: a beaker b a conical flask c a test tube d a tripod and gauze mat. 3 List the characteristics of: a the safety flame b the blue flame.
Understanding 4 Clarify the purpose of the collar in a Bunsen burner.
Analysing 12 Compare the following pieces of equipment by listing their similarities:
5 Explain why a yellow flame is called a safety flame when it is still hot enough to seriously burn you.
a a beaker and a conical flask
6 Explain why the gas must be turned on after the match is lit.
c tongs, a peg and a clamp
7 Explain why a Bunsen burner should be left for awhile before it is packed away.
d a clay triangle and a gauze mat
8 Propose why you should not use a piece of burning paper to light a Bunsen burner.
Applying 9 Identify a piece of equipment that you would use to: a Measure the temperature of boiling water. b Measure out exactly 55 mL of salt water.
b a beaker and a measuring cylinder
e a test tube and an evaporating dish.
Creating 13 Construct a labelled 2D scientific diagram that shows the setup used for boiling water. You will need to show the bench mat, tripod and gauze mat, Bunsen burner and beaker. 14 Construct a plan of your school laboratory that shows where the following special safety equipment is located:
c Transfer a small amount of solid onto a balance.
a fire blanket
d Pour liquid into a conical flask.
b fire extinguishers (Is there more than one type?)
10 Identify a piece of equipment that would assist these scientists in making the following observations:
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Fig 1.2.7
c eyewash d broken glass container
a A microbiologist wants to study extremely small bacteria that have been causing infections.
e bucket (maybe containing sand or another chemical to soak up spills)
b A chemist is measuring the heat generated by a chemical reaction.
f first aid cabinet g safety signs.
Unit
1.2
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to find what these pieces of equipment look like and state what they are used for: a pipette b burette
1.2
INVESTIGATING
e -xploring To find out more about Bunsen burners, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
We b Desti nation
c micrometer d barometer e mortar and pestle f ammeter.
1.2
PRACTICAL ACTIVITIES
1 What is it? Aim To draw, classify and name common laboratory equipment.
Measuring equipment
Pouring equipment
Storage equipment
Equipment to run chemical reactions in
Safety equipment
Holding equipment
Cleaning equipment
Mixing equipment
Equipment A range of everyday scientific equipment.
Method 1 In your science workbook construct a table with eight sections, as shown opposite. 2 Each piece of equipment you have been provided with must be drawn under one of the headings. Draw each piece: a as realistically as you can b as a scientific diagram. 3 Write the name of each piece of equipment under the diagram.
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Equipment
2 Lighting a Bunsen burner
4 Open the airhole by turning the collar and observe the blue flame produced.
Aim
5 Turn off the Bunsen burner by turning off the gas.
To correctly and safely light a Bunsen burner.
6 Light the Bunsen burner again, but this time in front of your teacher, showing them you know what to do.
!
Safety 1 Tie long hair back and wear safety glasses. 2 Never turn your back on a lit Bunsen burner. 3 When not using the Bunsen burner, close the airhole (producing a yellow safety flame) or turn it off. 4 Allow the Bunsen burner to thoroughly cool before packing it away.
Equipment • • • •
Questions 1 List your observations of the flame when the airhole is half open. 2 Identify the colour of the flame when the airhole is open completely. 3 Explain why the airhole should be open or shut when lighting a Bunsen burner.
Bunsen burner bench mat matches safety glasses
Method 1 Place a Bunsen burner on a bench mat and connect its hose up to the gas outlet. 2 Ensure the hose is flat on the bench and not twisted. 3 Follow the instructions in the Science Fact File opposite to light the Bunsen burner.
3 Investigating the flame
Fact File
How to light a Bunsen burner 1 Make sure the airhole in the collar is closed. 2 Light a match or a taper and place it close to the top of the barrel. Don’t get it too close. 3 Turn on the gas tap. 4 A flame should light. This flame should be yellow–orange in colour and is known as the safety flame. 5 If a hotter flame is needed then open the airhole. The flame should turn blue and become noisier.
Part 1: Flame temperature
Method
Aim To investigate the flame of a Bunsen burner.
!
Science
Safety Do not hold the gauze mat or porcelain in the flame with your bare hands—use tongs.
1 Set up and light the Bunsen burner. 2 Set it to the yellow flame. 3 With tongs, hold the gauze mat vertically in the flame so that it touches the top of the burner.
Equipment • • • • • • • •
14
Bunsen burner bench mat matches safety glasses old and ‘bald’ gauze mat pin tongs small piece of broken white porcelain Fig 1.2.8
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Unit
5 Carefully draw diagrams of any heat markings that you see.
Questions
1.2
4 Now set the flame to blue and repeat the experiment.
1 State whether your match lit up. 2 Predict the relative temperature of the flame at its centre.
Questions 1 Discuss whether the yellow flame is hot enough to make the gauze mat go red.
3 Describe your observations of the pin, particularly at its edges.
2 Describe the markings caused by the blue flame.
4 Compare the heat at the centre with the heat at the edges of a Bunsen burner.
3 Sketch a diagram of a flame and label where the flame is hottest and where it is ‘coolest’.
Part 3: Dirty and clean
Method
Part 2: Matches that won’t light!
1 Hold a small piece of porcelain in a pair of tongs.
Method 1 Set up the Bunsen burner. 2 Place a pin carefully straight through an unlit match, a little under its head. 3 Balance the pin on the top of the Bunsen burner so that the match head is in the centre of the barrel.
2 Hold the porcelain in a blue flame and record your observations. 3 Hold the porcelain in the yellow flame and record what you see. 4 Copy the table below into your workbook and then complete it.
Questions
4 Light the burner as usual. 5 Quickly turn the collar so that you get a blue flame. flame
1 Describe what happened to the porcelain in the yellow flame and the blue flame. 2 State which flame could be called ‘dirty’. 3 Identify whether the ‘dirty’ flame was cool or hot.
inner cone of cold unburnt gas pin safety match
Fig 1.2.9 The match head should be just above the top of the Bunsen burner.
Noise of flame
Airhole
Colour of flame
Coloured diagram of flame
Coloured diagram of What happened to the gauze mat held in flame porcelain held in the flame?
Closed Half open Open
4 How hot is hot? Aim To accurately measure an amount of water and heat using different flames.
!
Safety Boiling water will burn badly if spilt. Treat it and the hot beaker with care.
Equipment • • • • • • •
Bunsen burner bench mat matches safety glasses tripod and gauze mat retort stand bosshead and clamp
• 100 mL measuring cylinder • 250 mL beaker • stopwatch or clock with seconds markings
>> 15
Equipment
Method 1 Set up the equipment for boiling water, as shown in Figure 1.2.10. bosshead clamp
2 Accurately measure 80 mL of tap water using the measuring cylinder and pour it into a 250 mL beaker. 3 Time how long it takes for the water to boil when using a blue Bunsen burner flame. Boiling will be obvious when the water begins to bubble vigorously. 4 Repeat the experiment with a yellow flame only.
thermometer retort stand beaker
Questions 1 State how long it took for the beaker of water to boil in each case. 2 Identify in which case the beaker boiled first.
gauze mat tripod Bunsen burner
box of matches
3 Identify the flame colour that was the hottest. 4 Explain how you can tell which flame is the hottest. 5 Explain how you can control the heat and colour of a Bunsen burner flame. 6 Explain why it is important to use the same quantity of water in each part of the experiment.
bench mat
Fig 1.2.10
5 Heating a test tube Aim To safely heat a liquid in a test tube.
!
Safety 1 Use tongs to hold the test tube because the glass will get very hot. 2 Point the test tube away from everyone, including yourself.
Equipment • • • • • • •
Bunsen burner bench mat matches safety glasses test tube test-tube rack wooden tongs or peg
Method 1 Adjust a Bunsen burner to get a blue flame. 2 Fill the test tube to about one-third with water. 3 With tongs, hold the test tube near its top.
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4 Point the test tube away from people, including yourself. 5 Heat the test tube carefully near the bottom. 6 Move the test tube in and out of the flame until the water starts to bubble. 7 Put the hot test tube in the test-tube rack.
Fig 1.2.11 Constantly move the test tube in and out of the flame to ensure that all parts of its base is heated.
8 Record your observations.
Questions 1 Explain why pointing test tubes at people is dangerous. 2 Outline why test tubes must always be kept moving in a flame. 3 Explain why tongs need to be kept near the top of the test tube and not the bottom. 4 Explain why test tubes should never be laid flat on a bench.
Unit
1.3
context
Observations and measurement
You are constantly observing and interacting with the world around you— you hear the lunch bell, you smell your classmate’s tuna sandwich and you see that it’s raining outside. As a scientist you
will need to make detailed observations and to think about what you have just observed. Measurements can make your observations more detailed and allow you to see any patterns that may exist.
Fig 1.3.1 Not all scientists make their observations and measurements in the laboratory.
Qualitative and quantitative observations Scientists make two types of observations. Observations can be qualitative. This means that the observations are being written down in words only. Qualitative observations could be made about the noise a bird makes, the taste of ice-cream or a description of what happens when water is boiled. Other observations are quantitative. These observations involve measurements and are stated as numbers. Examples are: the temperature of a room recorded as 25°C, the time being 12.45 p.m., the volume of a liquid in a can of soft drink being measured as 375 mL, and the memory of an iPod Prac 1 p. 22 being 8 GB.
Inferring and predicting Once you have observed something, you can then make a logical explanation (known as an inference) as to what happened and why it happened. You may then be
able to predict what might happen in the future. Predictions must be logical and based on the observations made in your earlier experiments. You make observations, inferences and predictions every day, probably without knowing it. Consider: Observation Inference Prediction
The dog barked. That possum is back again. The barking will frighten it away.
Sometimes the same observation can lead to different inferences and predictions: Observation Inference Prediction or Observation Inference Prediction
The leaves are turning brown. The tree is dying. I will have to get a new one. The leaves are turning brown. It is a deciduous tree that loses its leaves in autumn. It will get new leaves in spring.
In this case, a calendar could assist you in deciding which is correct.
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Observations and measurement
Measurement Measurements are extremely important in science because they improve the accuracy of your observations. Measurements can also be arranged in tables and can be used to construct graphs. Tables and graphs are very useful in science because they make it much easier to see any patterns that may exist in the measurements.
Units Scientists use the units of the metric system for their measurements. Grams are used for measurements of small masses, like the mass of a coin or a mouse, whereas kilograms or tonnes are used for heavier objects. Centimetres, metres and kilometres are used for length. Seconds, minutes and hours are used for time. Measurement
Abbreviations mm, cm, m, km
Mass (sometimes incorrectly called weight)
milligram, gram, kilogram, tonne
mg, g, kg, t
Time
second, minute, hour
s, min, h
Speed
kilometres per hour, metres per second
km/h (sometimes shown on road signs as kph), m/s
Volume of a liquid
millilitres, litres, megalitres
mL, L, ML
Temperature
degrees Celsius, kelvin
°C, K
Whoops! In 1999 NASA sent three space probes to land on and explore the surface of Mars. All three failed. One is thought to have failed because NASA scientists did not write the units down for a series of measurements. One group of scientists thought the measurements were in older Imperial units, whereas another group thought they were metric. This caused the spacecraft to be programmed wrongly so that it ‘thought’ it was higher than it actually was. The spacecraft crashed into the surface!
20°C C
Fig 1.3.2 You cannot always be sure of measurements exactly.
millimetre, centimetre, metre, kilometre
Clip
Is the temperature shown here 23.4°C, 23.5°C or 23.6°C?
10°C
Length, height and distance
Science
18
Commonly used metric units
30°C
Sometimes measurements fall between the lines on a device and some guesswork is needed. This causes a reading error in your measurement.
Science
Clip
Give ’em an inch and they’ll take a mile! Some older Australians still use Imperial units (e.g. pounds, inches, feet, yards and miles) for their measurements. These are the units they grew up with and the units they are most used to. People in the USA (but not the scientists) also use Imperial units (including degrees Fahrenheit for their temperatures) for everyday measurements.
Errors and mistakes You will always have errors in your Just right: person B will read this measurements, regardless of how measurement most accurately as 20 careful you are. Errors are not B C A mistakes. Mistakes can be avoided Too low: Too high: with care. Errors are slight person A will person C will changes in measurements that read this as 18.2 read this as 21.5 cannot be avoided regardless of how careful you are. A reading error, for example, is always made whenever you must guess the measurement because it 0 5 10 15 20 falls between markings on your 25 30 35 measuring instrument. Another important error is caused by not having your eye directly in line with the measurement. This is called Fig 1.3.3 Parallax error is caused by reading a measurement from an angle. parallax error.
A beam balance is often used in the school laboratory to measure the mass of an object. The mass is a measure of how much matter there is in an object and is sometimes incorrectly called weight.
Taking accurate measurements You need to minimise errors and make no mistakes if you are to take accurate measurements. Scientists do this by following these rules or conventions: • Minimise parallax errors by always reading measuring devices from directly in front. • Minimise zero errors by checking that the measuring device has the correct starting point (usually zero). • Always write down measurements as soon as they are taken. Do not try to remember measurements. • Always write down the units of the measurements. • Always use correct abbreviations for units. For example, always use g for grams (not G or gms) and mL for millilitres (not ML or mls). • If possible, write all measurements in a table. • When working in a group, always make sure you have a copy of the results before you leave the laboratory. • Always measure quantities in metric units. • Do not use fractions such as ½ or ¼ in measurements. Use decimals instead. For example, 9.5 kg is acceptable but 9½ kg is not.
1.3
An important measuring device: The beam balance
Unit
A common problem when using measuring devices is called zero error. This is when the device reads some value even though nothing is being measured. An example is a weighing scale that measures 0.12 kg when nothing is on it.
Fig 1.3.5 A laboratory beam balance is used for measuring mass.
Mass is usually measured in the laboratory in grams, abbreviated as g. Larger masses are usually measured in kilograms (kg). For increased accuracy, an electronic balance is Prac 5 Prac 3 Prac 4 sometimes used. p. 24 p. 23 p. 23
Worksheet 1.6 Measurement
Go to
Science Focus 2 Unit 1.3
Prac 2 p. 22
Measure from the bottom of the meniscus if it curves downwards.
70 mL
Measure from the top of the meniscus if it curves upwards.
70 mL
65
65
Science
Fact File
Measuring curvy water 60
60
55
55
50
50
reading = 67 mL
reading = 66 mL
Liquids in narrow tubes, such as measuring cylinders, often have a curve at their surface. This curve is called a meniscus. When you need to measure the volume of a liquid that has a meniscus, follow these rules: • Measure from the bottom of the meniscus if it curves downwards. • Measure from the top of the meniscus if it curves upward.
Fig 1.3.4 Liquids in thin tubes often form a curved surface or meniscus.
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Observations and measurement 0
100
200
300
400
500
600
0
10
20
30
40
50
60
70
80
90
100
0
1
2
3
4
5
6
7
8
9
10
Fig 1.3.6 A beam balance reading 200 + 70 + 3.5 = 273.5 g
1.3
QUESTIONS
Remembering 1 State the correct metric unit for: a mass b length. 2 State the abbreviation for each of the following metric units: a b c d e f
grams kilogram litre millilitre seconds degrees Celsius.
Understanding 3 Define the following terms: L a qualitative b quantitative c meniscus d mistake e error. 4 Copy the following into your workbook and modify any incorrect statements so they become true. a A qualitative observation is one where numbers are involved. b If we use a thermometer, we are making a qualitative observation. c The colour of a leaf is an example of a quantitative measurement. d An inference is a logical explanation about what happened in an experiment. e A prediction is a logical guess about what might happen in the future. f Metric units are never used by scientists for measurements. g The kilometre is an example of an Imperial unit. h Seconds could be used to measure the distance that a sprinter runs.
i There is 375 ML in a normal soft drink can. (Be careful!) j Mistakes are the same as errors. 5 Describe the following types of errors: a reading error b parallax error c zero error.
Applying 6 Identify four observations about samples of: a salt b milk c talcum powder d a $1 coin e the gas you breathe out. 7 Identify each sentence below as an observation, inference or prediction: a The missing fish were eaten by the cat. There will be no fish left in the pond after a while. The cat is on the edge of the fishpond. b One Olympian is bigger than the other. The bigger Olympian will win the event. One can lift a heavier weight than the other. c The fish will be a big one. I’ve caught a fish. The line is taut and the fishing rod is bending. 8 The gas you breathe out contains carbon dioxide. Identify this statement as an observation or prediction. 9 Identify what is wrong with the following measurements: a Mass of a mouse = 150 1_4 g b The car was travelling at 100. c The wind speed was 10 miles per hour. d A full bottle of soft drink contains 1.25 mL. e Evan’s height = 158 m.
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>>
Unit
Type of empty container
Mass of container
Folded piece of paper
1.2 g
Watch-glass
13.7 g
11 Identify whether NASA made an error or a mistake in its failed 1999 missions to Mars. Explain your reasoning.
Analysing
Beaker
12 Analyse these measuring devices and state their measurements. a
7
b 40
c
300
6
d
4
30
200
20
100
10
Mass of container + substance
Salt
34.5 g
Crystals Water
Mass of substance
18.6 g 275.0 g
195.1 g
13 Jill is performing an experiment incorrectly in Figure 1.3.8. Before Jill passed out, she wrote down everything that she saw, heard and smelt in this experiment. Analyse what happened and list all the qualitative observations that Jill would have made.
5 30
Type of substance that was added
1.3
10 Fred measured the mass of some substances that could not be held in the pan of a beam balance. He needed to put the substances in containers instead. Complete the table (opposite) of his results by calculating the missing values. N
3 20
e
f
2
0
100
200
300
400
500
600
0
10
20
30
40
50
60
70
80
90
100
0
1
2
3
4
5
6
7
8
9
10
0
100
200
300
400
500
600
0
10
20
30
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50
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80
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100
0
1
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3
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5
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10
g
j
h 60
100
200
14 While in hospital, Jill made some inferences and predictions about the experiment. Classify which are inferences and which are predictions. a A chemical reaction happened between the metal and the acid.
15
45
Fig 1.3.8
0
300
30
b The dissolved metal turned the liquid green. c The reaction caused the brown gas.
i
d A different acid might not produce brown gas. 16
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e A different metal might not dissolve.
18
50 40
f Brown gas makes people pass out. k
l
g More metal would have made more brown gas.
20
55 0
10 0
900
0
100 200
800 700 600
Fig 1.3.7
500
300 400
50
5
10
45 15 40 20 35 30 25
h Stronger acid would give us more brown gas.
Creating 15 Rob’s poorly recorded results for an experiment are shown in Figure 1.3.9. Construct a table and present the results as they should look. Fig 1.3.9
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Observations and measurement
1.3
PRACTICAL ACTIVITIES
The burning question!
1
1 Melt a little of the wax at the bottom of the candle and use it to stick the candle to the lid or Petri dish.
Aim To observe a burning candle.
Equipment • • • • •
Method
a candle gas jar or beaker metal or plastic lid or Petri dish matches access to electronic scales
Fig 1.3.10
2 Find the mass of the candle and lid or dish on the electronic scales. Record your result. 3 Light the candle. 4 Use all your senses (except taste) to write as many observations as you can. (Michael Faraday, the 19th century scientist, made 53!) 5 Now cover the candle with a gas jar or beaker. 6 Record more observations. 7 Again, find the mass of the candle and lid.
Questions 1 How many different observations did you make? For each observation, state whether it was qualitative or quantitative. 2 Compare the two masses. If they were different, propose a reason why.
2
Taking measurements
Aim To measure various items with a range of measuring devices.
Equipment • access to a range of instruments and pieces of equipment that all show different quantities (e.g. 250 mL beaker filled half-way with water, thermometer in a flask of cold water) • a sheet of A4 paper next to each piece of equipment
Method 1 In your workbook, construct a table similar to that shown right. 2 Next to each piece of equipment is a piece of paper. Write your measurement in your table and on the piece of paper.
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Questions 1 Compare all the results on the paper from each group and state any differences. 2 If you got all different measurements, does this mean that everyone is wrong? 3 Identify any results that were significantly different from the rest. 4 State a conclusion for this experiment. 5 Propose reasons why scientists may not get exactly the same measurements. Name of piece of equipment
What is being measured
My measurement
Unit it is measured in
Unit
DYO
Aim To develop a method that measures things without accurate measuring instruments.
Equipment • small box of Smarties or M&Ms (with mass on box or on packet) • a stack of identical sheets of A4 paper • 30 cm ruler • access to a clock (not a stopwatch) • access to a calculator
Method 1 You have been given a very restricted range of equipment for this experiment. In groups, design your own way of measuring each of the following:
1.3
3 Oddball measuring
?
a the mass of a Smartie or an M&M without using any weighing device b the thickness of a single piece of A4 paper with a normal ruler c the time it takes for one heartbeat to happen. 2 Use your method to take/calculate each measurement.
Questions 1 Your methods probably measured the thickness of many Smarties/M&Ms, sheets of paper or heartbeats. Explain why it would be physically impossible to measure just one of each with the equipment you were given. 2 Identify the assumption you made in each of your methods.
4
How massive?
Aim To use a beam balance correctly to find the mass of various objects.
Equipment • access to beam balances • objects to weigh • 50 g mass
Method
5 Repeat this step for all the sliding masses until you finish with the lightest sliding mass. 6 When you have successfully got the pointer at 0, record the measurement in your table and on the paper next to each balance.
Questions
1 Construct a table in your workbook with the column headings Object being measured, Mass and Units.
1 State what the reading of a beam balance should be when nothing is in its pan.
2 Move all the sliding masses to 0 on the beam balance.
2 State the mass that you obtained for the 50 g ‘standard’ mass.
3 The arm should now be balanced and reading 0. If this does not happen, adjust the balance screw on the edge of the arm.
3 Explain why a 50 g ‘standard’ mass might not be exactly 50 g in an experiment.
4 Add the object to be measured and slide the heaviest sliding mass until the arm drops below 0. Then pull the sliding mass back one notch.
4 Describe three errors that might be present in these measurements.
23
Observations and measurement
5
Measurements and predictions
0.7
Aim
0.6
To find the mass of various lengths of spaghetti. 0.5
• beam balance • four different lengths of uncooked spaghetti • ruler with 1 mm markings
Method 1 Break each length of spaghetti into three pieces so that you have a wide range of sizes and so that you end up with nine different lengths.
Mass (g)
Equipment
0.4 0.3 0.2 0.1 0 10
2 Construct a table in your workbook or set up an Excel spreadsheet with headings Length and Mass. 3 Measure the length and mass of each piece of spaghetti and record it in your table. 4 Use this information to draw a line graph and draw a line of best fit through your points or generate the graph using your Excel spreadsheet. N 5 Mark on your graph a length that you did not measure. 6 Use the graph to estimate its mass. 7 Get another length of spaghetti and break it at the length you chose in step 6 above. 8 Measure and record the mass of the spaghetti you used in step 7.
24
20
30 40 50 Length (mm)
60
Fig 1.3.11 Line of best fit for mass of spaghetti versus length
Questions 1 Explain what is a line of best fit. 2 Compare your predicted value for the mass of the piece of spaghetti with the actual value. 3 State a conclusion about the link between mass and length of an item.
Unit
1.4
context
Reporting
Scientists need to record their methods, observations and measurements so that other scientists can repeat their
experiments. To do this, they need to write a scientific report.
Equipment or materials This is a list of all equipment and chemicals needed in the experiment. The sizes of the various pieces of equipment must also be included.
Risk assessment (safety guidelines) This can be a short statement on how you intend to minimise risks when performing the experiment. Any safety equipment you intend to use should also be included here. For many experiments, for example, you would list safety glasses and a lab coat or apron.
Fig 1.4.1 Your observations must be recorded as you go. Otherwise, you might forget some of them.
Scientific reports A scientific report should contain the following sections: • aim • hypothesis (optional) • equipment or materials • risk assessment (safety guidelines) • method • results (observations and measurements) • discussion (analysis of results) • conclusion.
Fig 1.4.2 Multiple observations are made in experiments and scientists need to record all of them in the results section of their report.
Aim This is what you intended to do in the experiment, what you were trying to investigate or what you hoped to achieve.
Hypothesis (optional) You probably have an idea of what might happen or what you might find out in an experiment. This ‘educated guess’ is called your hypothesis.
Method This is a detailed list of what was done in the experiment. To allow another scientist to be able to repeat the experiment, you must include what quantities were used and the exact order in which the experiment was performed. This is often presented as a numbered list. A diagram of the experiment (with all the equipment connected, not separate) can be very useful.
25
Reporting Results (observations and measurements)
It can also include calculations and graphs and improvements and ideas for future experiments.
You must include a complete list of measurements and observations that you took in the experiment. Results are easier to read if they are presented in a table. Always include headings and units (e.g. m, s or kg) in your table. For example, if you were heating water to boiling point, you might contruct a table with temperature (°C) and time (min) as its headings.
Conclusion
Discussion (analysis of results) This is where you: • Answer questions given in the prac. • Describe any problems you encountered in the experiment and what you did to overcome those problems. • Discuss what you think your results show about the experiment. • State what you have found about the experiment from other sources, such as textbooks, the Internet or encyclopaedias.
This is where you summarise what you have found out in the experiment. The conclusion should be short and must relate directly to the aim.
Common mistakes made in scientific reports Writing a scientific report is sometimes difficult and students make mistakes frequently. Tony ran an experiment during which he tested the flexibility and stretch of a fishing line. His scientific report is shown below.
Prac 1 p. 27
Prac 2 p. 28
Date? Apparatus? Materials?
No label What length?
Spacings should be equal, and increase by the same amount Points are too big
What weights? No units
Put units in headings
A diagram would help here
Units changed The conclusion does not match the aim
Units changed
26
Fig 1.4.3 Tony’s report had many mistakes in it, which are highlighted here.
Go to
Science Focus 2 Unit 1.4
What was actually found out here?
Unit
QUESTIONS
Remembering
1.4
1.4
c needs to be added to the graph d is missing from two measurements in his table.
1 List the sections required in a good scientific report. 2 State two things that must always be included in result tables. 3 State what graphs must always have on their axes.
7 Use the aim of Tony’s experiment to re-write his conclusion so that it matches.
Analysing
Understanding 4 In your own words, describe what is meant by the term aim.
8 Tony’s hypothesis was excellent. Analyse why.
5 Explain the difference between an inference and a hypothesis.
9 Analyse the Mysterious case of the stolen sausages on page 8 and identify your:
Applying
a aim
6 Referring to Tony’s report, identify what:
b hypothesis
a section is missing
c observations
b is missing from his method
d conclusion.
1.4 1
PRACTICAL ACTIVITIES
Spreading puddles
eyedropper
Aim To measure the area of water droplets and see if there is a pattern in their sizes.
Equipment • glass microscope slide • eyedropper • graph paper
glass microscope slide
graph paper
Method
Fig 1.4.4 Count the number of squares covered by each drop.
1 Construct the table below in your workbook. 2 Collect a clean glass slide, an eyedropper and a piece of graph paper and place the graph paper under the slide. 3 Drop one drop of water onto the slide.
4 Estimate the area covered by the drop by counting the squares on the graph paper underneath. Count half-covered squares as full and less than half-covered as empty. 5 Add another drop of water, being careful to keep it the same size, and estimate the area covered.
Number of drops 1
2
3
4
5
6
7
8
9
10
Predicted area (squares) Actual area (squares)
>> 27
Reporting 6 Repeat for three drops. 7 Predict the size for four, five and six drops. N 100
8 Check your predictions by counting the squares for four, five and then six drops on the slide.
1 Compare the actual area to your predicted area and comment on your prediction. 2 Describe any pattern you see connecting the number of drops with the area covered. 3 Predict the size for seven, eight, nine and ten drops. N
Area (squares)
Questions
80 60 40 20 0
4 Present your results as a line graph, with Area on the vertical axis and Number of drops on the horizontal axis. N
2
3
4 5 6 7 8 Number of drops
5 State a conclusion for this experiment.
Fig 1.4.5
2
5 Measure the temperature of the water every two minutes until the water boils, recording your results in your workbook.
Does salt make a difference?
Aim To investigate if salt makes a difference to the boiling point of water.
!
Safety 1 Tie long hair back and wear safety glasses. 2 Never turn your back on a lit Bunsen burner. 3 When not using the Bunsen burner, close the air hole (producing a yellow safety flame) or turn it off. 4 Allow the Bunsen burner and other equipment to thoroughly cool before packing it away.
Equipment • • • • •
two 250 mL beakers Bunsen burner tripod gauze mat bench mat
• thermometer • teaspoon or large spatula • glass stirring rod
9
Temperature (˚C)
10
Time (min)
6 In another beaker, measure out another 150 mL of water. 7 To this water, add two teaspoons or two large spatulas of salt. Use the glass stirring rod to dissolve the salt. 8 Once again, use a blue flame to heat this beaker of salty water until it boils, recording its temperature every two minutes.
Fig 1.4.6
Questions 1 Write up the experiment, using the headings of Aim, Hypothesis, Equipment, Method, Results and Conclusion.
1 Set up your equipment to boil water.
2 Compare the boiling point of the salty water with the unsalted water. Put your answer in the Discussion section of your report.
2 Use the markings on the side of the beaker to measure out 150mL of water.
3 Construct a line graph of your results to show the difference (if any) of the rise in temperature for both solutions.
3 Use the thermometer to measure the temperature of the water. Record this temperature in your workbook.
4 State a conclusion for this experiment.
Method
4 Carefully light the Bunsen burner and use a blue flame to heat the water.
28
1
5 Cooks often add salt when they cook rice or pasta. Use the conclusion from this experiment to propose a reason why.
Unit
1.5
context
Working scientifically
Scientists rarely start with an experiment, but normally with observations made in everyday life or even possibly by accident. Their observations lead them to
ask questions like ‘What caused that?’ or ‘Why did that happen?’. They then design experiments to answer their questions.
(the dog will probably be bluffed). Your conclusion probably confirmed that dogs are easily bluffed, at least on the first few tries. Another example of observations leading to experiments comes from Joe, Year 7 scientist. Joe noticed that when he washed dishes he sometimes made lots of froth and at other times he made almost none. Joe has a problem. He’s about to solve it scientifically.
Fig 1.5.1 Observations can trigger questions that eventually lead to an experiment.
Observations can lead to experiments Most likely, you have already run an experiment based on observations you have made about the world. It might be as simple as throwing a ball to a dog. Throw the ball and they fetch it. This observation has probably led you to wonder what would happen if you pretended to throw the ball. Although it doesn’t look much like an experiment, it definitely is. It has a clear aim (to test if a dog can be bluffed by a pretend-throw) and hypothesis
Fig 1.5.2 Joe wondered why so much froth was produced in the kitchen sink.
Fair tests and variables Things happen due to lots of different factors, but it is sometimes difficult to determine which factor has the biggest effect and which ones have no effect at all. Any test that a scientist carries out must be a fair one. To be fair, you must change only one factor at a time. These factors are called variables and are anything that may affect the results of an experiment.
29
Working scientifically Joe thought about it carefully and came up with a list of factors that could affect the amount of froth produced: Prac 1 • the amount of detergent used p. 31 • the amount of water in the sink • the speed of the water coming from the tap • the temperature of the water. These were his variables. From their observations, scientists then make a hypothesis. This is a prediction or ‘educated guess’ about what they may find in an experiment or what might have caused the observations. Joe had noticed that more froth was produced when faster tap water was added and when more detergent was used. He thought that these variables would have a great effect, but didn’t think the temperature of the water in the sink would have any effect at all. This was his hypothesis.
Planning experiments Scientists change only one factor or variable at a time. Otherwise they would not be able to work out which variable caused the effect. All the other variables must be kept exactly the same or constant. Go to
30
Science Focus 2 Unit 1.1
Joe then designed and ran two experiments that he thought could solve his problem. Experiment 1: He put three drops of detergent in the sink each time. He ran hot water in very slowly at first, then repeated with hot but faster water. He repeated the experiment with very fast but equally hot water. Each time he filled the sink half-way. Experiment 2: He put one drop of detergent in the sink and turned the tap on high until the sink was half full. He then repeated the experiment with two drops of detergent, then three and then four. To make sure you design an effective experiment you should know: • the problem you are trying to solve (the aim) • exactly what you are going to measure (called the dependent variable) • what you are going to change (called the independent variable) • what you are going to keep the same (called the controlled variable) • anything else that might affect the experiment but you cannot control (e.g. air pressure).
Prac 2 p. 32
Prac 3 p. 32
Unit
QUESTIONS e Outline how Joe could measure the amount of froth produced.
Understanding 1 Define the term variable. 2 Recall why only one variable should be changed at a time in an experiment.
d Outline as a series of dot-points a detailed method that he could use.
a the growth of a plant b the time taken to cook a potato
e Construct a table for the expected results.
c the number of times you go to the toilet in a day
6 Joe then wanted to test whether the temperature of the water had any effect on the froth. For this new experiment:
d your test results for this topic. 4 a Joe thought of four variables that may have affected the amount of froth produced. List the four variables.
a State an aim. b List the equipment he would need.
b Identify the variable that Joe didn’t think was important.
c State a risk assessment for the experiment. d Outline as a series of dot-points a detailed method that he could use.
c Predict which variable will have the most effect on the experiment.
e Construct a table for the expected results.
d Identify two other variables that Joe didn’t think of.
PRACTICAL ACTIVITIES
Froth production
?
Aim To interpret another student’s experiment and write a report correctly.
Equipment • • • • •
a State its aim. c State a risk assessment for the experiment.
3 Identify variables that are likely to affect:
1
5 For one of Joe’s experiments: b List the equipment he would need.
Applying
1.5
1.5
1.5
dishwashing detergent with dropper ruler access to tap large beaker/bucket/ice-cream container thermometer
DYO
Part 2 3 Test one of the variables that Joe did not test. 4 Once again, write up the experiment.
Questions 1 State the variables that Joe tested. 2 Explain why Joe kept the variables the same in both experiments. 3 List three other variables that could have been tested. 4 Describe which variable you think would have the most effect.
Method Part 1 1 Repeat one of Joe’s experiments. 2 Write up the experiment, following the rules for writing a report.
31
Working scientifically
? DYO
Answering a question with an experiment
2
Travis noticed that when he dropped a ball, it never bounced back to the same height from which it was dropped.
Aim To identify variables and design a simple experiment.
Equipment • tennis ball • metre ruler
Method 1 Identify all the variables that you think will have some effect on the bounce. 2 Decide which variable you are going to keep the same.
Fig 1.5.3
Questions 1 Identify which variables:
3 Design your own experiment that would test Travis’s observation. You will need to collect at least five different measurements.
a affected the bounce height b did not significantly affect the bounce height. 2 State two conditions that would combine to produce:
4 Perform the experiment.
a a high bounce
5 Construct a table of your results.
b a low bounce.
6 Make suggestions on how you could improve your experiments.
? 3
Investigating variables
DYO
Aim To design your own experiment and report on it.
Equipment Prepare a list of the equipment you intend to use.
!
Safety Once you have decided on your topic and method, write your own risk assessment, listing all the possible dangers that may be involved and what can be done to minimise them.
Method 1 Read the following investigations and choose one of them to run as an experiment. Whichever investigation you choose: a Identify three variables that are likely to have an effect on the results. List them in order from what you consider to be the most important to what you consider to be the least.
32
b Choose one important variable and design your own experiment that could test it. c Prepare a risk assessment for your method and present it to your teacher for approval. 2 Once approved, run the experiment and collect the necessary results. 3 Write up your experiment using the normal headings of Aim, Equipment, Method etc.
Possible topics • Nikki liked sweet coffee so she always added lots of sugar. She often noticed, however, that a lot of it remained undissolved at the bottom of the cup. She wanted to find out why the amount on the bottom differed each time. • George heard an old tale that if you want an avocado to ripen quickly, you should place it in a brown paper bag with a banana! He thought this sounded weird and wanted to see if it was true. • Samira liked to blow bubbles and wanted to find out how she could make bigger ones.
CHAPTER REVIEW 1 State six of the common branches of science and recall what each branch studies. 2 State the use for each of the following pieces of equipment:
Applying 8 For each of the following, identify whether the following observations are quantitative or qualitative: a The apple is red.
a spatula
b There is 200 mL of water in this beaker.
b beaker
c The packet of sugar states that it is 200 g but when you hold it, it feels a lot lighter.
d tripod e evaporating basin f Bunsen burner. 3 Recall equipment used in the laboratory by drawing 2D scientific diagrams for the following pieces of equipment:
d The thermometer reads that the temperature of the room is 25°C. 9 Identify four observations you could make about: a a glass of tomato juice b an ice cube
a a beaker used to boil 200 mL of water
c rain
b a 50 mL measuring cylinder
d grass.
c a tripod with wire gauze d a Bunsen burner. 4 List the steps you need to follow to light a Bunsen burner. 5 State the correct metric units for: a mass b time c length d temperature. 6 List the subheadings needed when writing a scientific report.
Understanding 7 Explain why a Bunsen burner’s yellow flame is known as the safety flame.
Analysing 10 Compare a Bunsen burner’s blue flame and its safety flame by listing their similarities and differences.
Evaluating 11 Propose a reason why a Bunsen burner’s blue flame is hotter than the safety flame.
Creating 12 You have often wondered whether your cup of hot chocolate will cool down faster in a glass cup or a polystyrene cup. Design an experiment to test this idea. Worksheet 1.7 Crossword Ch
pt
a
Worksheet 1.8 Sci-words
s
c measuring cylinder
on
Remembering
er R sti ev i ew Q u e
33
2
Solids, liquids and gases
Prescribed focus area: The nature and practice of science
Key outcomes
Additional
Essentials
4.2, 4.7.1, 4.7.2, 4.7.3
•
Scientists construct models based on experimental evidence to help explain things that can’t be observed directly.
•
Matter is made up of particles that are moving continuously.
•
Matter expands when heated and contracts when cooled.
•
The pressure of a gas increases as the number of collisions increases.
•
Properties of solids, liquids and gases can be described by a simple particle model.
•
Changes of state occur by adding or removing energy to the particles in a substance.
•
The particle model can be used to explain a wide range of characteristics of a substance.
•
Diffusion occurs due to the random movement of particles.
•
Sublimation occurs when a solid changes directly to a gas or a gas changes directly to a solid—without first forming a liquid.
Unit
2.1 The particle model
context
Water is one of the few substances on Earth that you can see every day as a solid, liquid and a gas—liquid water runs from the tap, water vapour comes from a boiling kettle and solid ice cubes are in the freezer. Although the same type of particles make up ice, steam and tap water, the three materials behave very
differently. The particles that make up solids, liquids and gases are far too small to be seen (even with a microscope) and so scientists use a model to explain their various properties.
Scientists, architects and engineers also use physical models of things such as buildings, ships, aircraft and landscapes. These models can be used to test how a skyscraper might respond in an earthquake or how a flood may affect the shape of a river valley. Likewise, a model aircraft can be tested in a wind tunnel to see how a newly shaped wing cuts through the air. Sometimes scientists use a model to describe an idea or concept that helps them explain how something works. This type of model is particularly useful when they are investigating something that cannot be seen, such as the structure of the atom (the atomic model). The model might not be exactly right but it can be used to understand and predict how things behave and react—just like a model aircraft helps designers better understand the real thing. For example, scientists cannot see individual particles of water, but they can observe how water (and ice and steam) behaves. From these observations scientists have developed the particle model to better understand different forms of water and other solids, liquids and gases.
The particle model Fig 2.1.1 Liquid water, solid ice and the water vapour in this man’s breath are all the same substance.
Models in science Quick Quiz Scientists often use models to help them understand the world and the way it works. Computer models, for example, are commonly used to simulate weather patterns and to predict the movements of the planets, tides and tsunamis, and the effects of earthquakes.
Matter is the basic building material from which substances are made. Everything in the universe is made of matter—from stars to spiders, galaxies to geckos and planets to people. Matter has mass and takes up space. There are three states of matter—solids, liquids and gases. Ice, water and steam, for example, are all water, but in different states, or phases. To explain the behaviour of solids, liquids and gases scientists use a model known as the particle model. This model proposes that all matter is made up of tiny, invisible particles and explains the different states in terms of how these I n t e r a c t i ve particles move and stick together.
35
The particle model
Particles in solids: s STRONGLY BONDED TO EACH OTHER s VIBRATE A LITTLE BUT NOT MUCH COMPARED TO LIQUIDS AND GASES s VIBRATE FASTER WHEN HEATED
Properties of solids: s HAVE A DEFINITE SHAPE s DO NOT FLOW s VIRTUALLY IMPOSSIBLE TO COMPRESS s EXPAND IF HEATED BUT USUALLY LESS THAN LIQUIDS AND GASES solid
Particles in liquids: s WEAKLY BONDED TO EACH OTHER s BREAK THEIR BONDS EASILY s VIBRATE AND MOVE MORE THAN THOSE IN A SOLID s MOVE FASTER WHEN HEATED
Properties of liquids: s NO DEFINITE SHAPE s CAN FLOW TO TAKE THE SHAPE OF THE BOTTOM OF A CONTAINER s VERY DIFFICULT TO COMPRESS VIRTUALLY INCOMPRESSIBLE
liquid
Gas particles: s ARE @FREE HAVING NO BONDS BETWEEN THEM s HAVE MUCH MORE ENERGY THAN THOSE OF A SOLID OR LIQUID s FLY AROUND BOUNCING OFF EACH OTHER AND THE WALLS OF THEIR CONTAINER
Properties of gases: s NO FIXED SHAPE s GASES SPREAD OR DIFFUSE TO COMPLETELY FILL A CONTAINER s GASES ARE EASILY COMPRESSED
I n t e r a c t i ve
gas
Fig 2.1.2 The particles in a solid are in fixed positions but jiggle back and forth on the spot. The particles in liquids and gases all vibrate too. These particles can move about freely though, giving liquids and gases the ability to flow and move about. Prac 1 p. 41
Solids Solids come in many different types. Iron, plastic, wood and sponge are all solids with very different characteristics. All solids, however, share some common characteristics, which are known as the physical properties of solids. The particle model explains these properties by imagining that the particles within the solid are bonded strongly to each other and packed very closely together.
Properties of solids
Particle model of solids
Solids have a defined shape and do not flow.
The particles are strongly bonded to their neighbours, so their position is fixed.
Solids are virtually incompressible.
There is very little space between the particles, so they cannot be pushed any closer together.
Solids expand when heated and contract when cooled.
Heating causes the particles to vibrate faster, pushing them further apart and causing the solid to expand. The reverse happens when the solid is cooled.
Science
Clip
Viscosity and quicksand Viscosity describes how easily a liquid flows. Water flows easily and so has a low viscosity, whereas honey, which does not flow as easily, has a high viscosity. Quicksand is an unusual substance because its viscosity increases when you try to move through it quickly, making it ‘thicker’ and harder to move through. The best way of getting out is to move through it slowly and smoothly.
36
Prac 2 p. 41
Unit
Gases
Water, oil, honey and mercury are all Prac 3 Prac 4 very different liquids, but they, too, p. 41 p. 42 share some common physical properties. These properties can also be explained by the particle model. In this model, the particles in a liquid are packed very close together and can move around freely.
Although most gases are invisible, they are extremely important to life on Earth. The air Prac 5 p. 42 you breathe is a mixture of gases and whenever you smell something, your nose is detecting gas particles. In the particle model, gas particles are not bonded to each other at all. This allows them to move around freely anywhere within their container.
Properties of liquids
Particle model of liquids
Liquids flow to take the shape of their container.
The particles are weakly bonded to their neighbours. This allows the particles to move freely within the liquid.
Liquids are virtually incompressible.
There is very little space between the particles, so they cannot be pushed together any further.
Most liquids expand when heated and contract when cooled.
Heating causes the particles to vibrate faster, forcing them further apart and causing the liquid to expand. The reverse happens when the liquid is cooled.
Fig 2.1.3 Liquids take the shape of their containers.
2.1
Liquids
Animati on
Science
Clip
The longest experiment of all time According to the Guinness Book of Records, the University of Queensland holds the title for the longest running experiment. The experiment began in 1927 and is still running! The aim of the experiment is to determine the viscosity of pitch, a black liquid that is so viscous it appears to be solid—even brittle. Professors John Mainstone and Thomas Parnell began the experiment by putting some pitch into a large funnel and started counting the drops oozing from its tip. Today, the ninth drop is only just starting to form! This suggests that pitch is 100 billion times more viscous than water.
Properties of gases
Particle model of gases
Gases have no fixed shape and will spread to fill their container.
The particles are not bonded to each other and so are free to move anywhere within their container.
Gases are compressible.
Lots of space between the particles allows them to be pushed closer together easily.
Gases expand dramatically when heated and contract when cooled.
Gas particles are constantly moving. Heating a gas causes the particles to move faster and move further apart. This causes the gas to expand. The gas contracts when the gas is cooled and the particles move slower.
In a confined space, heating increases the pressure of gases. The pressure decreases when cooled.
In a confined space, heating the gas causes the particles to collide with the sides of the container more often and with greater force. Pressure depends on force and so it increases too. The pressure decreases when the gas is cooled and there are fewer and less forceful collisions.
37
The particle model
Evidence for the particle model Scientists don’t believe in a model unless repeated experiments have proven it to be accurate. Scientists should be objective at all times. This means that they should only rely on evidence collected from experiments that have been repeated many times around the world. The particle model is not just an idea. This evidence has come from repeated experiments.
Fig 2.1.5 Diffusion happens when the dividing plate is removed from between two gas jars. In this case, one jar of brown nitrous oxide gas is mixing via diffusion with a jar of colourless air.
Dissolving Although a sugar cube seems to disappear when it is dissolved in a hot cup of tea, its sugar particles are still there—you can taste them! The water particles in the tea have pulled the sugar cube apart and spread the sugar particles throughout the cup. Go to
Prac 6 p. 42
Science
Clip
Science Focus 1 Unit 3.1
That really smells! Solvent particles (e.g. water): these surround the particles in the solid, pulling them apart and then spreading them thinly throughout the liquid. The liquid is known as the solvent.
Solute particles (e.g. sugar): dissolving spreads these thinly throughout the liquid. Solute is the substance being dissolved.
Natural gas (methane, CH4) is normally odourless, making it undetectable if there is a leak or something is left on. To make natural gas extra smelly, chemicals called mercarptans are added to it. Mercaptans are the smelliest substances on Earth. The human nose is so sensitive to them that it can detect one mercaptan particle amongst several billion molecules of air.
nerve (to brain) particle dissolves in moist nasal membrane
moist nasal membrane
Fig 2.1.4 The process of dissolving can be explained by the particle model. The solid that dissolves is known as the solute. The liquid that dissolves a solute is known as the solvent.
Diffusion
nose
The smell from an open bottle of perfume will quickly reach you, even if you are on the other side of the room. The gas particles have travelled across the room via a process called diffusion. Science In the particle model, gas particles move quickly. Stench warfare Sometimes they collide The US military is currently with each other, causing developing a ‘stink bomb’ them to change directions. that would drive away hostile As a result, they make a crowds in riots. Some smells zig-zag path from the we find pleasant, others are bottle. Particles may also nasty and others naturally diffuse through solids and evoke fear. It’s these fearful smells that the bomb would liquids; for example, an ink release, sending a wave of stain may spread through panic through the protesters. paper or clothes.
Clip
38
nostril
Fig 2.1.6 Particles of onions are entering your nose whenever you smell fried onions.
Science
Clip
Penis-eating fish! In 2001, two men in Papua New Guinea had their penises bitten off by piranha-like fish. The men had been fishing, standing up to their waists in the Sepik River. They had a wee in the water and the urine diffused far and wide until the fish sensed it. The fish followed the faint urine trail and bit off its source!
Unit
Brownian motion
2.1
In 1827, a Scottish botanist named Robert Brown used a microscope to look at pollen grains suspended in water. He saw that the pollen grains were constantly moving around as if they were being jostled by something. This jiggling motion is now known as Brownian motion and can be easily explained by the particle model. The particle model explains that the water particles are vibrating and moving about, bumping into the pollen grains. pollen grain Worksheet 2.1 The particle model
Fig 2.1.7 Individual water molecules can’t be seen, but their effect on a pollen grain can be observed under the microscope. This jiggling is known as Brownian motion.
2.1
QUESTIONS
Remembering 1 List three types of models that are used in science.
Applying 12 Identify a food or drink that contains:
2 List five different examples each of a solid, a liquid and a gas.
a both solid and liquid material
3 State what is meant by the term phase of matter.
b both a liquid and a gas
Understanding 4 Describe the term matter in your own words. 5 Describe Brownian motion and how it was first discovered. 6 Some people could mistakenly classify sugar, soft plasticine and mud as liquids because they take the shape of their container. Clarify the definition of a solid so that people cannot make this mistake. 7 Describe what happens to the particles in a solid when it dissolves.
c only solid d only liquid. 13 a Identify how the fragrance of a perfume travels throughout a room. b Use a diagram to illustrate how the perfume particles make their way across the room. 14 Identify which of the following statements are objective, based solely on evidence: a If I go outside with wet hair I will catch a cold.
8 Explain why diffusion is evidence for the particle model.
b I know it is raining outside because I can see the rain.
9 When trying to prove a new scientific model, a scientist should repeat their experiments a number of times. Explain why.
c The X-rays showed that I have a broken arm. d Many people say that exercise is good for you.
10 Explain why the particle model predicts that gases can be compressed, but predicts that solids and liquids cannot. 11 Foam rubber is a solid, yet it is easily compressed. Explain how this can be.
>> 39
The particle model Analysing
Evaluating
15 Compare the properties of solids, liquids and gases by completing the table below.
16 There must be some bonds or attractions, however weak, between the particles in a liquid. Justify this statement.
Property Shape Ease of compression
Solid
Liquid
Gas
Definite
17 Propose a reason why a liquid (i.e. brake fluid) is used in brake lines to transfer pressure to a car’s brakes from the foot pedal, whereas gas is used in shock absorbers. 18 Propose what might happen to the bonds (i.e. attractions) between particles when the material they belong to is heated and changes:
Very low
Bonds between particles
Weak
Movement of particles
Medium
a from a solid to a liquid b from a liquid to a gas.
Creating 19 Construct your own version of the particle model. Draw it as three layers, with solid at the bottom, changing into liquid and, finally, gas at the top. 20 Design a device that uses foam balls and an air blower with a variable speed control (say, a vacuum cleaner on reverse) to model the motion of particles in liquids and gases.
2.1
INVESTIGATING
Investigate your available resources (e.g. dictionary, textbooks, encyclopaedias, Internet etc.) to: 1 Explain the difference between a fluid and a liquid. 2 Find out about capillary action. Design an experiment to demonstrate it. 3 Compare ‘true’ and amorphous solids, using examples of each. 4 Find out more about the viscosity of liquids. Explain how temperature affects the viscosity of honey. 5 Explain what surface tension is and how it enables some insects to walk on water.
40
e -xploring W
n eb D To find out more about the science applications esti natio below, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge. • Find out more about solids, liquids and gases, and investigate plasma, the fourth state of matter. Compile a summary of the states of matter and their properties using only labelled diagrams.
• Oooze! Find out how to make a substance that acts like a liquid and a solid.
Unit
PRACTICAL ACTIVITIES
2.1
2.1
Method
1
Particle role play
A role play is another type of model that can help explain something that is hard to see. In this role play you will experience the movement of particles.
Aim Use role play to simulate how particles move in a solid, liquid and gas.
2
1 As a class or in groups, organise a role play in which the class members act as particles in a substance. In particular, think about how you will represent the movement and bonding of the particles. 2 Use your ‘particles’ to model a solid, then a liquid and, finally, a gas.
Question Write a description of the movement of the class members to describe and contrast each state of matter.
Plasticine particle models
Aim To build a model showing the arrangement of particles in various solids.
Equipment • plasticine
Fig 2.1.8
Method 1 Use the plasticine to make 16 identical balls.
spheres arranged in a ‘body-centred cubic’ pattern
Questions
2 Investigate the different ways you can pack several of the balls together in regular patterns. One way is shown in Figure 2.1.8.
1 Specify the number of regular arrangements you were able to construct.
3 Sketch the different packing arrangements you come up with.
2 Specify which phase would be most likely to show regular packing patterns.
3
Silly putty
3 Use the spoon to mix thoroughly.
Aim
4 Use the plastic spoon again to measure out three spoonfuls of borax solution into the second cup.
To determine whether ‘silly putty’ is a solid or a liquid.
5 Add it to the water–glue mixture and stir rapidly.
Equipment
6 Remove the lump of ‘silly putty’ and rinse it under cold water.
• saturated borax solution
• food dye (optional)
• small container (e.g. film canister)
• two plastic spoons
• white PVA glue
• two small disposable paper or plastic cups
Method
Questions 1 Roll your ‘silly putty’ into a ball. Describe how the ‘silly putty’ bounces. 2 Sit a ball of ‘silly putty’ on a flat bench top. Describe what it does over five minutes.
1 Use the plastic spoon to measure out three spoonfuls of PVA glue into the cup.
3 Put your ‘silly putty’ in a small container (e.g. a film canister). Describe how the silly putty changes shape over time.
2 Add one spoon of water. One or two drops of food dye (no more) can be added at this stage.
4 Assess all your observations and decide in which state of matter ‘silly putty’ belongs.
41
The particle model
4
? Comparing viscosity
DYO
Viscosity describes how easily a liquid flows. Water flows easily and so has a low viscosity, whereas honey, which does not flow as easily, has a high viscosity.
2 Design an experiment to compare the viscosity of each liquid. 3 Present your work as an experimental report, including all the normal sections like aim, equipment, method, results, discussion (questions) and conclusion.
Questions
Aim To rank liquids according to their viscosity.
1 List the liquids from most viscous to least viscous.
Method
2 Assess your experiment and determine how you would do things better next time.
1 Collect five liquids that you can find readily around your home, such as water, honey, detergent, unwhipped cream and tomato sauce.
? 5
Compressibility
DYO
Aim To compare the compressibility of a gas with that of a liquid.
Equipment • plastic syringe (no needle attached) • water • rubber stopper
Method 1 Draw some air into the syringe.
2 Press the opening of the syringe hard against the rubber stopper, as shown in Figure 2.1.9, and try to compress the air by pushing the plunger. syringe
3 Now draw some water into the syringe and repeat step 2.
Questions 1 State which substance you were able to compress. 2 Use particle diagrams to explain what happened with both substances.
solid rubber stopper
Fig 2.1.9
Aim To investigate diffusion in liquids.
Equipment • food dye • eye dropper • test tube or beaker
Method
1 Explain why the spread of colour cannot be explained by gravity alone. 2 Explain how temperature affected your observations. 3 Explain the process of diffusion in this experiment in terms of particles.
one or two drops of food dye water
1 Almost fill a beaker or test tube with cold water.
test tube
2 Add a drop of food dye and let the mixture stand for several minutes, sketching what you observe every 30 seconds or so.
Fig 2.1.10
3 Repeat steps 1 and 2, using hot water.
42
Questions 2
Diffusion of food dye
1
6
The nature and practice of science
2.1
Prescribed focus area:
Unit
Science Focus Observation and discovery The individual particles that make up all matter are so small that you cannot see them. It is through observation and experiment that we have been able to reach our present understanding of matter. Although we cannot see the particles, there has always been evidence available for those who are observant enough to notice it, and interested enough to try and understand what they see.
Fig 2.1.12 The Scottish botanist Robert Brown was interested in understanding the world around him.
Fig 2.1.11 Robert Brown’s study of pollen led to the idea of Brownian motion, one of the major pieces of evidence that confirms the particle model.
By early in the nineteenth century, experiments on the behaviour of different states of matter had led to the kinetic theory of matter. Part of this theory stated that all the tiny particles of matter move constantly. The model of tiny particles of matter that developed was all based on deduction (making conclusions based on evidence) rather than on direct observation of the particles themselves. Having made observations, a good scientist will then investigate further, to try and understand what they have observed. The Scottish botanist Robert Brown (1773–1858) was an enthusiastic scientist whose search for an understanding of the world led to the first observation of molecules in motion. He sailed to Australia and collected vast numbers of Australian plants. When he returned to England, Brown used a microscope to study the plants. It was while using his microscope to make observations on tiny pollen grains that he made an interesting observation. Brown could see them jiggling and slowly moving about in zig-zag paths through the water.
Knowing that the tiny pollen grains were not alive, Brown wondered why they appeared to be moving about. To investigate further, he placed a tiny drop of a stain into a drop of water on a microscope slide. He was surprised to see that the tiny particles of the stain also jiggled about and moved in the drop of water. Brown was unable to provide a full explanation for his observations, but he reported his findings anyway. Regardless, his findings supported the suggestion that all tiny particles of matter move constantly. The motion of tiny non-living objects jiggling about and moving through a drop of water became known as Brownian motion. pollen grains
drop of water on microscope slide
Fig 2.1.13 Jiggling pollen grains in a drop of water. In the diagram, the blue lines represent the movement of the blue water molecules, and the wiggly red lines show the movement of the pollen grains.
43
The particle model
STUDENT ACTIVITIES 1 a Describe what is a model. b Describe an example of how the particle model can be used to predict the behaviour of each state of matter when a solid is heated. c Investigate and explain what these other scientific terms mean, and when they are used: inference, hypothesis, prediction, theory, law, observation. 2 a Outline the features of a good scientific model that can lead to it becoming accepted without anybody seeing the thing that the model suggests is there. b Discuss this in a group and create a final list of the most important features of a good scientific model. c Present your findings to the class. 3 The inference from ‘Brownian motion’ is that the water molecules moving in the water droplet, although too small to see, are observed because of the jiggling effect produced by their collisions with the pollen grains. Create a short story, or comic strip, to show how the water molecules bumping into the pollen grains produce ‘Brownian motion’. L
44
4 Brown mounted the pollen grains in water at room temperature. Another experiment that would have been useful would be to place identical pollen grains into a drop of warm water. a Explain why this experiment might have assisted Brown in understanding what he saw. b Predict the result you would expect to observe. c Use a microscope to test your prediction. 5 a Describe the features of Robert Brown’s approach that enabled him to make an important contribution to science knowledge. b Outline how technology might have helped Brown in his work.
Unit
2.2
context
Changes of state
Substances can exist in three different states—solid, liquid and gas. Heating or cooling a substance might just simply
alter its temperature. Sometimes, however, the substance might change state.
Fig 2.2.1 Liquid is one of the three states of matter. It often forms rounded droplets like these drops of mercury. Mercury is the only metal that is a liquid at normal room temperature.
Applying a model melting. A solid wax candle, for example, absorbs Ice changes state when it melts. It absorbs heat energy enough heat energy from the flame to melt and from whatever is around it (e.g. the air, a glass of change into pools of liquid wax. lemonade or the Esky it’s in) and changes from a solid to a liquid. Likewise, the solid wax of a candle is quickly turned into a liquid after the candle is lit. Some of the Melting point wax is also turned into a gas that keeps the flame burning. The temperature at which a particular solid changes Most substances change state if enough heat energy into a liquid is called the melting point. The table is added or removed from them. This process can be below shows the melting point of various substances. explained by using the particle model. Substance
Solid to liquid
Water
To change a solid (e.g. ice) to a liquid (e.g. water), heat energy must be added to make the particles vibrate more. This causes solids to expand. Adding more heat energy eventually ‘loosens’ the linking bonds between the particles and a liquid is formed. This change is called
Candle wax Sugar Table salt
Melting point (°C) 0 60 186 801
Gold
1064
Diamond
3550
45
Changes of state
Liquid to solid The reverse of melting is freezing, otherwise known as solidification. When a liquid loses energy, the vibration of particles lessens and the bonds between particles are once again strong enough to keep them in fixed positions.
Boiling point The temperature at which a liquid boils is called its boiling point. Some sample boiling points are shown in the table below. Substance
Boiling point (°C)
Water
100
Freezing point
Candle wax
400
The freezing point of a substance is the temperature at which the substance changes from being a liquid into a solid. As freezing and melting are the reverse of each other, the freezing point and the melting point of a substance occur at the same temperature.
Table salt
1465
Gold
2856
Diamond
4827
Evaporation A liquid does not have to boil for vaporisation to occur—boiling just speeds up the process. Evaporation is occurring whenever a liquid changes into a gas at a temperature below its boiling point. The warmer the liquid, the faster the rate of evaporation. A puddle of water will eventually evaporate on a dry day as particles at the surface absorb enough energy from the air to escape the liquid. It will Prac 1 p. 49 evaporate even faster on a hotter day. larger bubbles
Fig 2.2.2 Changing states of matter—solid state (ice), liquid state (water), gaseous state (steam).
Liquid to gas A liquid changes into a gas when heat completely breaks the bonds between the particles. When heat is added to a liquid, small bubbles of gas soon begin to form within the liquid. When enough heat is added, these gas bubbles become large enough to float to the surface and boiling occurs. When a liquid boils, bubbles of gas escape into the air. This is known as vaporisation.
46
Fig 2.2.3 Boiling occurs when bubbles of gas escape from the liquid.
Gas to liquid The opposite of vaporisation is condensation. Condensation occurs when gas particles lose heat energy and turn into liquid. When you breathe out on a very cold day, the water vapour in your breath (a gas) condenses to form tiny droplets of water that are suspended in air and appear fog-like. A similar thing happens when you breathe on a window. Small water droplets condense on the glass, making it difficult to see your reflection.
Unit
Sublimation is a much less common change. Sublimation occurs when a solid absorbs heat and changes directly to a gas without melting and going through the liquid phase. An example of sublimation is when dry ice (frozen carbon dioxide) sublimes to form carbon dioxide gas. Sublimation is also the word used when a gas changes directly into a solid. Substance
Sublimation point (°C)
Dry ice (carbon dioxide)
–78.5
Mothballs (naphthalene)
48.0
Graphite
2.2
Solid to gas
3825
Fig 2.2.4 When you breathe out your breath contains a lot of water vapour. Breathing onto a cold mirror causes the vapour in your breath to condense into a fine film of liquid water droplets. Worksheet 2.2 States of matter
Prac 2 p. 50
Prac 3 p. 50
Fig 2.2.5 Dry ice sublimes to form a thick white cloud that is often used on stage and in movies to produce the effect of fog.
Science
Clip
Lord Kelvin, superscientist! William Thomson was born in 1824 in Belfast, Ireland. William was one bright kid, starting university when he was 10 years old and becoming a professor at 22! He invented the absolute temperature scale (later called the Kelvin scale), a method of refrigeration, the depth sounder, an accurate marine compass and many other inventions, improvements and theories. In 1892 he became a lord (Lord Kelvin). He died in 1907.
Fig 2.2.6 Sublimation of iodine
47
Changes of state
2.2
QUESTIONS 11 Figure 2.2.8A shows the particles in a solid. Identify which of B, C or D best represents the solid after it was heated.
Remembering 1 State the scientific term used to describe when:
A
a a liquid changes into a gas b a gas changes into a liquid
12
c a solid changes directly into a gas. 2 State another term for freezing. 3 Specify which change of state is the opposite of:
B
C
D
a melting b condensation. 4 Specify the: a boiling point of water b melting point of gold c freezing point of wax Fig 2.2.8
d sublimation point of dry ice. 5 Name two substances that sublime.
Identify which of the following is likely to be closest to the melting point of steel:
Understanding 6 Describe what happens at the melting point of ice and identify at what temperature it happens.
A 0°C
7 Describe what happens to the particles when water boils.
C 100°C
8 Explain why the melting point of a substance must be the same as its freezing point.
D 1500°C
Applying 9 Identify three changes of state that commonly occur around your home. 10 Identify the correct terms for each change of state shown in Figure 2.2.7.
B 60°C
13 Identify which of the following is likely to be closest to the melting point of oxygen: A 200°C B 0°C C 20°C D 100°C 14 The temperature of liquid water cannot go higher than 100°C. The lowest temperature steam can be is 100°C. Use this information to explain why steam burns are normally worse than burns from boiling water.
gain heat
Analysing 15 Compare evaporation and boiling by listing their similarities and differences. solid
liquid
16 Analyse the following substances and determine whether they would be a solid, liquid or gas:
gas
a sugar at 200°C b table salt at 1400°C lose heat
c gold at 3000°C Fig 2.2.7
48
d mothballs (naphthalene) at 500°C.
Unit
18 Kevin notices that when his pool is heated to 27°C, the water level falls by about 10 cm each week. a Explain how this can happen when 27°C is much lower than the boiling point of water; i.e. 100°C.
2.2
b Analyse what is likely to happen if the pool was:
2.2
17 Analyse what would happen to an unlit wax candle on a 40°C day.
i not heated ii heated to a higher temperature, say 30°C.
Evaluating 19 Compare the physical properties of dry ice and water ice. Evaluate which is better for producing fog for a stage effect.
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Explore the history of the thermometer, and the three different temperature scales (Celsius, Fahrenheit, kelvin).
• the advantages of both methods over normal freezing and drying • the storage life of foods after snap freezing or freeze drying. Present your work as a brochure for shoppers. N
2 Find out about snap freezing and freeze drying. Find out: • the differences between frozen food and snap-frozen food, and dried food and freeze-dried food • what types of food are snap-frozen or freeze-dried
2.2
e -xploring To find out more about dry ice and sublimation, a list Web Destination of web destinations can be found on Science Focus 1 Second Edition Student Lounge. Produce a brochure with a set of rules for handling dry ice safely.
PRACTICAL ACTIVITIES
Ice to water to steam 1 temperature graph
3 Light the Bunsen burner and keep the airhole opening in the same position throughout the experiment. Fig 2.2.9 thermometer
Aim To investigate what happens to the temperature of water as it changes state.
Equipment • • • • •
ice cubes water Bunsen burner bench mat gauze mat
• • • •
tripod beaker (250 mL) measuring cylinder (100 mL) thermometer (0°C to 110°C) or temperature probe
Method
ice + water gauze mat tripod
Bunsen burner
1 Mix several ice cubes with 100 mL of water. 2 Place the thermometer in the ice–water mixture and record the temperature once every minute for three minutes.
bench mat
>> 49
Changes of state 4 Heat the ice–water mixture, and continue to record the temperature at one-minute intervals until the water boils. Measure the temperature for three more minutes after boiling starts, but stop boiling if the water level falls below 50 mL. 5 Record your measurements in a table.
Questions 1 Present the results in a graph, showing temperature on the vertical axis and time in minutes on the horizontal axis. N
CO2 hovercraft
2 Aim
To observe the process of sublimation.
Equipment • small pieces of dry ice • tongs
• compass • plastic film canister with lid
Safety
!
Never touch dry ice with your bare skin as it will freeze very quickly, leaving a nasty ‘burn’.
2 Explain why you had to keep the airhole opening fixed during the experiment. 3 Your graph probably did not start exactly at 0°C. Explain why. 4 Identify any level sections in your graph. Explain why level sections may occur. 5 Imagine you were able to capture the steam produced when all the water has evaporated and measure its temperature as you continued to heat it. Describe the temperature graph that would be observed.
2 Use a compass to poke several small holes in the lid of the film canister. 3 Place a small piece of dry ice in the film canister and put the lid on. 4 Put the enclosed canister on your desk so that the lid is at the bottom. 5 Try pushing the canister and record your results.
Questions 1 Describe what happens to a piece of dry ice as it sits on your desk. 2 Identify what change of state is occurring. 3 Explain your observations in terms of a particle model.
Method 1 Use the tongs to place a small piece of dry ice on your desk and record your observations.
Teacher demonstration 3
4 Describe what happens when you push the film canister across the desk and explain your observations in terms of a particle model.
Fig 2.2.10 test tube
Iodine sublimation
Watch your teacher gently heat the test tube in a fume cupboard until a small amount of purple gas is produced. Observe what happens as the iodine cools.
!
Safety
speck of iodine fume cupboard Bunsen burner
Iodine gas is poisonous—exercise caution and use a fume cupboard. Check the MSDS. Safety glasses must be used. Seal the test tube with a rubber stopper after heating and leave inside the fume cupboard.
bench mat
2 Identify whether any liquid iodine formed.
Questions 1 Describe the iodine at the start of this demonstration and any changes in state that occurred.
50
3 Describe the coating on the side of the test tube as the contents cooled. 4 Explain how you know that the purple substance produced after heating was a gas.
Unit
2.3
context
Expansion
Substances don’t always change state when heated or cooled—sometimes they expand or contract instead. Solids, liquids and gases expand when heated and contract when cooled. This property of solids, liquids and gases can be very
useful in things like thermometers, hot-air balloons and reinforced concrete. However, expansion and contraction can also be a problem, causing buildings to crack and causing powerlines to sag.
Fig 2.3.1 Pipes need to be engineered so that they don’t buckle when they expand from heating and don’t leak when they contract from cooling.
Expansion and particles
Expansion of solids
A substance may change state when heated or cooled, but this depends on how much heat is gained or lost. If a substance doesn’t change state, then its temperature will change and it will either expand (get larger) or contract (get smaller). The particle model easily explains expansion and contraction. Most solids and liquids expand when heated. This occurs because their particles vibrate more rapidly. They push each other further apart so that the substance takes up more space. In a gas, heating the particles makes them move at higher speed and push harder against anything they come in contact with. If the gas is in a balloon then the balloon would expand. If the gas is heated inside a steel cylinder then the gas particles would hit the sides of the cylinder harder and more often, creating a Prac 1 higher pressure in the cylinder. p. 55
Different solids expand at different rates. The table below shows how much a 1 metre length of different solids will expand when the temperature is increased by 1°C, 10°C or 100°C. 1 metre length expansion table Temperature
1°C
10°C
100°C
Solid
Expansion amount (in mm)
Invar (nickel–steel mixture)
0.001
0.01
0.1
Wood (oak)
0.003
0.03
0.3
Pyrex
0.003
0.03
0.3
Glass
0.009
0.09
0.9
Platinum
0.009
0.09
0.9
Steel
0.011
0.11
1.1
Concrete
0.011
0.11
1.1
Iron
0.012
0.12
1.2
Brass
0.019
0.19
1.9
Aluminium
0.025
0.25
2.5
51
Expansion
+ –
Steel and concrete expand at the same rate. This allows steel rods to be used as reinforcement for concrete with no risk of cracking. If aluminium was used instead of steel then the bars would expand twice as much as the concrete and would crack it.
battery
alarm bell
bimetallic i strip bends upwards up to complete compl the circuit and an turn bell on the alarm al concrete slab invar brass
steel reinforcing rod
Fig 2.3.2 Iron rods in reinforced concrete give the concrete more strength. Iron and concrete expand at the same rate and so the concrete will not crack when the temperature changes.
invar heat
brass
Science Fig 2.3.4 Brass
cold day
expands much more than invar when heated. The brass layer lengthens but is stuck to the invar layer. Both are forced to bend to relieve the tension between the two layers. A bimetallic strip can be used to trigger a fire alarm.
hot day
Fig 2.3.3 Power lines sag more on hot days. Heat makes the metal wires expand to become slightly longer.
Tight-fitting lids on glass jars can be released by warming the jar, perhaps by placing it in hot water. Steel expands more than glass when heated and so the lid becomes loose. Likewise, the ends of a garden hose expand slightly when heated so that they are connected more easily. When the hose ends cool, they contract and fit around the connection more tightly. Prac 2 p. 55
52
Clip
Cracking dishes and bimetallic strips A cold dish or glass may crack when it’s run under hot water due to one side trying to expand faster than the other, leaving the object no choice but to crack. Not all expansion is a nuisance. A thermostat in a heater, oven or refrigerator may use a bimetallic strip to control a switch. A bimetallic strip is made of two different metals. Because one expands more than the other when heated, the strip bends so one metal expands a greater distance than the other, just as a runner on the outside of a curved track runs further than a runner in an inside lane.
Expansion of liquids Liquids generally expand much more than solids when heated. This means space must be left for liquids to expand into when filling containers such as petrol and liquid petroleum gas (LPG) tanks. Thermometers contain a liquid (mercury or coloured alcohol) in a bulb connected to a narrow tube that makes the liquid rise noticeably when heated.
Unit
expansion chamber
radiator
Fig 2.3.5 A car radiator contains water that is used to cool the engine. This water expands when it absorbs engine heat, and may overflow into an expansion chamber.
Gases expand and contract more than solids and liquids when heated and cooled. A gas tries to expand when heated, but may be stopped by its container. If so, then heating causes the gas to exert a greater pressure on its walls. If the gas is cooled, then it exerts a lower pressure inside the container. If the walls of the container are flexible (such as in a balloon) then this increased pressure will push the walls out further, making the container expand. Likewise, the container will shrink in size if the gas is cooled.
The unusual behaviour of water At most temperatures, water acts like other substances when heated or cooled. At 4°C or above, it expands when heated, whereas below 0°C it contracts. However, between 0°C and 4°C water behaves quite strangely. As the temperature of water changes from 0°C to 4°C it contracts instead of expanding. This means that water at 4°C will always sink to the bottom because the particles in water at 4°C are packed more tightly than at any other temperature. Likewise, water expands when the temperature drops to freezing point. This gives ice the ability to float on water and also explains why bottles filled with water crack when placed in the freezer.
Worksheet 2.3 Graphing
Prac 3 p. 56
2.3
Expansion of gases
Prac 4 p. 56
ice layer 1ºC 2ºC 3ºC 4ºC
Fig 2.3.6 The fact that water is most dense at 4°C means that water in lakes and ponds at 4°C will sink to the bottom, pushing the less dense warmer water to the top, where it is cooled by the cold air and winds. Once all the water is at 4°C it freezes from the top down. This is extremely important for the survival of fish and other animal life living below. Fig 2.3.7 Hot-air balloons rise to great heights by making use of the fact that hot, expanded gas is less dense than cooler gas.
53
Expansion
2.3
QUESTIONS
Remembering 1 State what happens to the pressure as gas is heated inside a container. 2 State the temperatures at which water expands and contracts in the way that is opposite to what other substances do. 3 State whether liquids expand more or less than solids when heated. Give a reason for your answer. 4 List the following in order from least to greatest expansion when heated: concrete, pyrex, brass, platinum.
Understanding 5 Describe why particles in a substance take up more space when heated. 6 Describe what the particles in a gas are doing to cause pressure. 7 Describe what happens to the movement of the particles in a solid as it is heated.
15 An old-fashioned incandescent light globe is made of glass with a platinum filament. a Use the table on page 51 to state the expansion abilities of both glass and platinum. b Describe what you notice about their expansion abilities. c Assess why the answer to part b is important. 16 Calculate by how much these materials would expand. N a a 1 metre steel rod heated so that its temperature rises by 100°C b a 1 metre plank of wood that increases in temperature by 1°C c a 2 metre block of concrete heated so that its temperature goes up by 10°C d a 50 centimetre iron rod that increases in temperature by 100°C. 17 Assess which type of bimetallic strip would bend most when heated: one made of iron and brass, or one made of iron and aluminium?
8 Explain why it is more important to have a constriction in a clinical thermometer than in a laboratory one.
Evaluating
9 Explain why invar is often used to make accurate technical instruments that are used in hot situations.
18 Propose a reason why you think mercury or coloured alcohol is used in thermometers instead of coloured water.
10 Explain why a clinical thermometer is usually shaken after use.
Applying
19 Propose a reason why bridges have small gaps at each end. gap
gap
11 Identify two uses of expanding liquids. 12 a Identify two problems that expanding solids can cause. b Explain how each problem is overcome. 13 Draw a diagram to demonstrate how a bimetallic strip can be used in a light switch that is activated by the heat of your hand.
Analysing 14 Use the expansion table on page 51 to assess which solid or solids expand: a most when heated b least when heated c the same as steel d the same as platinum e three times more than wood f four times more than pyrex.
54
Fig 2.3.8
20 Some barbecue hotplates make sounds when they are first heated or begin to cool down. Propose what causes these sounds.
Creating 21 Construct a bar graph, comparing the expansion of different substances using the information in the table on page 51. N 22 Construct a table like the one on page 51, but for a 10-metre length of each material. N
Unit
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to find how a spiral of bimetallic strip can be used as a temperature gauge or how it is used in flashing car indicators.
2.3
e -xploring
2.3
2.3
We b Desti nation To find out more about how different types of thermometers work, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
PRACTICAL ACTIVITIES
Ball and hoop
1 Aim
To investigate the expansion of metals on heating.
!
Safety 1 DO NOT HEAT THE CHAIN. 2 After use, place the equipment onto the heat-proof mat to cool. The brass ball will remain hot for a long time. BE VERY CAREFUL. Fig 2.3.9
Equipment • ball and hoop apparatus • Bunsen burner
• tongs • bench mat
Method
3 Use the tongs to carefully place the ball on the hoop. Does it still fit through?
Questions
1 Check that the ball fits through the hoop when both are at room temperature.
1 Identify the scientific idea or concept that this activity demonstrates.
2 Heat the ball over a Bunsen burner (blue flame) for one minute or so.
2 If, using a different ball, it did not fit through the hoop at room temperature, explain what you would do to make it fit.
The bimetallic strip
2 Aim
To investigate the operation of a bimetallic strip.
Equipment • • • •
bimetallic strip tongs Bunsen burner bench mat
Method 1 Hold a bimetallic strip using the tongs and heat it in a Bunsen burner flame until you notice an effect. 2 Repeat the experiment, but this time heat the other side of the bimetallic strip.
Questions 1 Describe what would happen as more heat is applied. 2 Explain how you can tell which side of the strip is expanding the most.
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Expansion
3
Expanding air
Aim
small balloon
To investigate the expansion of air.
Equipment • • • •
500 mL beaker Bunsen burner gauze mat tripod
string
• • • • •
Method 1 Set up the apparatus as shown in Figure 2.3.10. 2 Ensure that you have just enough weight to keep the balloon at the bottom of the beaker and below the top of the water level. 3 Heat the water gently with the Bunsen burner and record your observations.
The gas thermometer
4 Aim
To show that air expands when heated and contracts when cooled.
Equipment • • • • • • •
weight
small water balloon weight string water bench mat
any flask of about 500 mL to 1 L rubber stopper (to fit flask) with glass tube insert clear plastic tubing to fit glass tube retort stand bosshead and clamp food dye ice cubes
Fig 2.3.10
Questions 1 Describe what happened to the balloon as you heated the water. 2 Use the particle model to explain your observations 3 Propose why the balloon may start to float.
Questions 1 Explain what your hands did to the air in the flask. 2 State what cooling did to the air. 3 State any evidence from this experiment that air can expand and contract. 4 Explain how this apparatus could be used as a simple thermometer. Fig 2.3.11
retort stand
clamp
Method 1 Use Figure 2.3.11 as a model to build a gas thermometer. 2 Gently place your hands around the flask. Record your observations. 3 Take your hands off. What do you see?
clear plastic tubing
flask
4 Place one or two ice cubes on the flat bottom of the flask. Record all your observations. rubber bung with glass tubing food dye/water
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bosshead
Unit
2.4
context
Density
Many people have been tricked into believing that a kilogram of lead is heavier than a kilogram of feathers. Of course they both weigh the same since they both contain one kilogram of matter.
Lead has a high density, meaning that only a little of it is needed to make up one kilogram. Feathers have such low densities that a huge pile of them is required to make up one kilogram.
Technically, density is defined as the mass of a one centimetre cube of a substance. The mass of one cubic centimetre of water is one gram, so the density of water is one gram per cubic centimetre. Different substances have different densities. Gold, for example, is very dense, having a density of 18.9 grams per cubic centimetre. The particle model explains why some substances are denser than others. Since all substances are made of different types of particles, then the density of a substance depends on how heavy these particles are and how closely they are packed together. This suggests that gold particles are much heavier and closely packed together than water particles. Fig 2.4.1 An object will float on water if it is less dense than water.
Density and the particle model The term density is used to describe how much mass is packed into each cubic centimetre of a substance.
Science
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Black holes Astronomers believe that black holes in outer space come in various sizes, some no bigger than a pinhead, but with a mass many times greater than that of our Sun, making black holes the densest objects imaginable! The gravitational attraction of black holes is so strong that not even light can escape.
air
foam rubber
wood
oil
Calculating density water
glass
steel
copper
lead
gold
iron
Most substances and objects are not in convenient one centimetre cubes, and so their densities need to be calculated instead. Two things are needed to calculate the density of an object: • the mass of the object (e.g. in grams) • its volume (e.g. in cubic centimetres, abbreviated as cm3). To find the mass of an object you can simply place it on a set of scales or on a balance. However, finding the volume can be more difficult.
Fig 2.4.2 Each of these cubes has a volume of one cubic centimetre (1 cm3); however, they all weigh a different amount because they are of different densities.
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Density Volume
So, for the lump of plasticine:
Two different ways can be used to find the volume of an object. Regular shapes If the object is a regular shape, such as a sphere, cube, cylinder or cone, then you can calculate its volume using a mathematical formula. For example, you can find the volume of a rectangular prism by multiplying length × width × height (V = L × W × H).
L = 4 cm
4.8 3
Prac 2 p. 61
= 1.6 grams per cubic centimetre = 1.6 g/cm3 Worksheet 2.4 Density
Prac 3 p. 62
Floating and sinking An object floats if its average density is less than that of the liquid it is in. Pure water has a density of 1 g/cm3. This means that the average density of an object must be less than 1 g/cm3 if it is to float. Gold has a much higher density than water and so it sinks. In contrast, oil floats because it has a density of only 0.9 g/cm3.
H = 2 cm
W = 3 cm
density =
Volume V = L x W x H =4x3x2 = 24 cm3
Fig 2.4.3 Maths can be used to calculate the volume of regular shapes. Prac 1 p. 61
Irregular shapes If an object is irregular or oddly shaped, then its volume can be found by placing it in a measuring cylinder and measuring how far the water rises. Note that 1 mL takes up the same space as 1 cm3. This method will not work, however, if the object is porous or absorbs any water. 110
110
100
100
90
90
80
80
75 mL
70
70
60
60
50
50 mL
density of egg is greater than density of liquid
40
30
30
20
20
10
10
salt water
density of egg is less than density of liquid
float in salt water than it is to float in fresh water.
Fig 2.4.4 The object in the measuring cylinder at right has a volume of 75 – 50 = 25 mL or 25 cm3.
Sample calculation A lump of plasticine has a mass of 4.8 grams and a volume of 3 cubic centimetres. Density is found by dividing the mass by its volume. Mathematically, this is shown as the formula: mass density = volume
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egg
Fig 2.4.5 Salt water is denser than fresh water, making it easier to
50
40
fresh water
Salt water is more dense than fresh water. As a result, it is easier for us to float in the ocean than in a freshwater lake or river. An egg will sink in fresh water because its average density is just greater than that of the water. Mixing some salt in the water increases the density of the liquid to just greater than that of the egg. The egg’s density is now less than that of the liquid and so the egg floats.
Science
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Get low and go, go go! Firefighters advise that if you are ever caught in a house fire you must move outside as fast and as low as you can. The reason? The smoke and intense hot air from the fire will be less dense than the air close to the floor and will rise. You could easily be overcome by this heat and smoke if you stood and ran. You would then collapse before you got outside. The air near the floor will be cooler and have less smoke and this is where you need to be. Don’t just lie there though! Crawl out as quickly as you can!
Unit
Controlling density
Go to
Science
Clip
Brewing scientifically
Science Focus 1 Unit 7.5
stronger beer
Prac 4 p. 62
I n t e r a c t i ve
2.4
hydrometer
Fish contain a swim bladder that can be used to control the fish’s average density by adding or removing air. This allows the fish to float, sink or stay suspended as it swims. Changes to the temperature or the amount of salt in the water can affect its density, so a fish may need to be able to alter its density simply to remain at the same depth. Scuba divers wear inflatable vests that use the compressed air from their tanks to do the same job. Submarines work on the same principle, using compressed air to expel water from ballast tanks, getting less dense in the process.
weaker beer
Beer brewers use a hydrometer to measure the density of beer at various stages in the brewing process. Depending on the alcoholic strength of the liquid, the hydrometer floats at different levels. A higher alcohol content causes the brew to have a higher density. The higher the density of a liquid, the higher an object will float.
Fig 2.4.6 Brewers use the term ‘specific gravity’ to refer to density. The stronger the beer, the higher the hydrometer floats.
2.4
QUESTIONS
Remembering
Applying
1 State which weighs more: a tonne of gold or a tonne of sawdust?
10 A piece of metal has a mass of 6 g and a volume of 2 cm3. Calculate the density of the metal. N
2 State what is meant by the density of a substance.
11 Calculate the volume of a block of glass of length 4 cm, width 2 cm and height 3 cm. N
3 State the density of: a water
12 Calculate the volume of the brick in Figure 2.4.7. N
b wood c copper
6 cm
d gold. 4 Name the two things we need to know to find the density of an object. 5 State the mathematical formula for:
8 cm
Fig 2.4.7
20 cm
Fig 2.4.8
a the volume of a rectangular prism b density.
Understanding
13 Calculate the volume of the stone shown in Figure 2.4.8. N
100 mL
100 mL
90
90
80
80
70
70
60
60
50
50
8 Explain why an egg will float in salt water, but not in fresh water.
40
40
30
30
20
20
9 Explain how steel-hulled ships can float when steel is more dense than water.
10
10
6 Describe two ways to find the volume of an object. 7 Describe how you could predict whether an object will float or sink in a liquid.
14 If the mass of the stone in Question 13 is 32 grams, calculate its density. N
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Density
2.4
QUESTIONS
Analysing 15 Calculate the density of each of the following: N
18 A type of garden potting mix has a density of 1.2 g/cm3. Calculate the mass of 2 litres (2000 cm3) of this potting mix. N 19 Calculate the mass of 4 cm3 of gold. N
2 cm 32 g
26.4 g
2 cm 4 cm
20 The tile shown in Figure 2.4.11 has a density of 2.5 g/cm3. Calculate how much a load of 100 of these tiles will weigh. N
4 cm
3 cm
4 cm
2 cm B
A 90 g
10 cm 5 cm
7700 kg
volume = 50 cm3 C
10 cm
5 cm
4 cm
Fig 2.4.11 D
Evaluating
Fig 2.4.9
16 Calculate the density of a type of rubber if a sample of it has mass 75 g and volume 50 cm3. N 17 Calculate the volume of the object in the measuring cylinder in Figure 2.4.10 if it contains 30 mL of liquid. N
60 mL 50 40 30 20 10
Fig 2.4.10
2.4
22 A lump of brand A concrete has the same mass as a lump of brand B concrete, but the brand B lump has less volume. State which concrete brand is the most dense and justify your answer. 23 Propose how you could find the density of an oil sample using a beaker, an electronic balance and a calculator.
Creating 24 Perspex has a higher density than a type of cooking oil, but a lower density than water. Construct an illustration to demonstrate what would happen if all three are placed in the one beaker.
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find out what Plimsoll lines on ships are used for.
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21 Two blocks of wood, one oak and the other cedar, have the same volume, but the cedar block has less mass than the oak. Evaluate the densities of oak and cedar.
2 Explain how Archimedes helped the King of Syracuse to determine whether the goldsmith who made the king’s crown used pure gold or not.
Unit
1
PRACTICAL ACTIVITIES
Density of cubes
2.4
2.4
3 Copy and complete the table below for each 2 cm cube. N Volume (cm3)
Aim
Substance
To measure and calculate the density of cubes of different substances.
Aluminium
8
Equipment
Brass
8
Mass (g)
• density kit containing 1- and 2-cm cubes of various substances • scales • ruler • calculator
Method
8
Questions
1 Find the mass of each cube using the scales. 2 Copy and complete the table below for each 1 cm cube. N Substance
Density (g/cm3)
Mass (g)
Volume (cm3)
Aluminium
1
Brass
1
Density (g/cm3)
1 Explain why 8 cm3 is given as the volume of the larger cubes when the side length of each cube is only 2 cm. N 2 Identify which of the densities you calculated were similar. Explain this result. 3 List the substances in order of density from smallest to largest.
1
2
Density of irregular objects
4 Repeat steps 2 and 3 for the other objects. 5 Copy and complete the table below. N
Aim To determine the density of various objects by displacing water.
Object
Mass (g)
Volume (cm3)
Density (g/cm3)
Equipment • measuring cylinder (100 mL) • various irregular objects that are small enough to fit in the measuring cylinder (e.g. stone, ball bearing, bolt) • plasticine • scales • water
Method 1 Find the mass of each object using the scales. 2 Pour 50 mL of water into the measuring cylinder. 3 Hold the measuring cylinder at an angle and gently slide one of the objects into the water, as shown. Note the new water level and, hence, find the volume of the object.
Questions 1 Compare your densities with those found from previous experiments or from Figure 2.4.2. 2 List the possible sources of error in this experiment.
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Density
3
Density of liquids
? DYO
Aim
1 Design your own way of finding the mass of, say, 50 mL of each liquid.
To design an experiment to determine the density of various common liquids.
2 Calculate the density of each liquid.
Equipment • measuring cylinder • scales • various liquids (e.g. water, cooking oil, salt water, honey etc.)
4
Questions 1 Explain how you found the mass of the liquid in each case. 2 Draw a diagram to demonstrate where each liquid would float if all the liquids were all placed in the one beaker and allowed to settle into layers. Hint: The most dense layer will be at the bottom.
Average density
Aim
Questions
To investigate how the shape of an object affects how it floats.
1 Explain what you did to make the plasticine float.
Equipment
2 If plasticine is more dense than water, discuss why plasticine can float when made into different shapes. Hint: Consider the term average density.
• plasticine • a tub of water
Method 1 Roll the plasticine into a ball and put it into the water. Record your results. 2 Change the shape of the plasticine to see if you can make it float. 3 Experiment with different shapes to see what shape floats best.
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Method
3 Relate your observations to metal ships. How does a metal ship float when a block of iron will sink?
CHAPTER REVIEW Remembering 1 State the three phases of matter.
17 Substance A has a melting point of 10°C. Identify its state at normal room temperature.
2 List a household example of each of the states of matter.
Analysing
3 Record the different possible changes of state in the table below.
18 Compare the bonds between particles in a solid with those in a liquid.
To solid From solid From liquid From gas
To liquid Melting
19 Assess which of the following are possible units for density. (There may be more than one answer.)
To gas
A grams B cubic centimetres C cubic centimetres per gram
4 Name a substance that sublimes.
D grams per cubic centimetre
5 State the opposite term to expansion.
E kilograms per cubic metre.
6 Specify which states of matter are compressible.
Evaluating
Understanding
20 Evaluate whether the following statements are true or false.
7 Describe two phenomena discussed in this chapter that can be explained by the particle model.
a Density is how heavy an object is.
8 Explain what is a model and why they are used in science.
c An object will float if it has a higher density than the liquid it is in.
9 Describe one piece of evidence that supports the particle model.
b Density describes the amount of mass in a certain volume.
21 Sometimes when oil spills from a ship at sea it catches alight. Propose why this is possible given that there is so much water.
10 Explain why a dish may crack when run under hot water. 11 Explain how a thermometer works. 12 Explain what causes gas to exert pressure when placed in a container.
Creating
Applying
22 Construct a diagram to demonstrate how a bimetallic strip may be used to control the heating element in an electric iron.
13 Identify at which of these temperatures water is the most dense. Give a reason for your answer.
23 Design an experiment to find the density of a piece of metal that has an irregular shape. 24 Using your knowledge of the particle model, construct diagrams to demonstrate the arrangement and motion of particles in a solid, a liquid and a gas.
A 0°C B 1°C C 3°C D 4°C
pt
a
Worksheet 2.6 Sci-words
on
Ch
14 Identify all the changes of state involved when a container of frozen soup is thawed out and boiled.
s
Worksheet 2.5 Crossword er R sti ev i ew Q u e
15 Identify a method you could use to find the volume of a brussels sprout. 16 For the block of metal shown in Figure 2.4.12, calculate its: N a volume b density.
5 cm
1100 g
Fig 2.4.12 4 cm
5 cm
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3
Mixtures and their separation
Prescribed focus area: The applications and uses of science
Key outcomes
Additional
Essentials
4.3, 4.7.5
•
Mixtures are an important part of your everyday life.
•
A solution is a type of mixture in which a solid is dissolved in a liquid. The solid is known as the solute and the liquid is known as the solvent.
•
Water is an important solvent for both living things and industry.
•
Industry uses the processes of filtration, sedimentation, sieving, distillation, chromatography, evaporation, condensation, crystallisation and magnetic attraction to separate components of a mixture.
•
Useful substances may be obtained by separating pure substances from mixtures using a variety of separation techniques.
•
Crystallisation can be used to separate a solute from a solvent.
Unit
3.1
context
Types of mixtures
Soft drinks, Vegemite, orange juice, milk, sea water, hair gel, deodorant and sunscreen are just some of the mixtures you might use every day. Even the air you breathe and the blood in your veins
are mixtures. Clearly, mixtures are an important part of your everyday life and so it is important that we understand what they are and how they behave.
Solutions Solutions are the most common type of mixture. A solution is formed when one substance (known as the solute) dissolves in another (the solvent). For example, when sugar is mixed with water, the solute is the sugar and the solvent is the water. A sugar solution has been formed. The sugar particles have dissolved and are now spread through the water particles, making them impossible to see anymore. You know it’s still there because you can taste it. It is the same with salt solutions. Although the salt seems to have disappeared, it definitely can be tasted. Sugar and salt solutions are transparent (see-through) and look just like water. This transparency is a characteristic of all solutions. A solution may be coloured (e.g. orange soft drink) but it will always allow light to pass straight through it. Solutions can also be made by dissolving a liquid in a liquid, or a gas in a liquid. If one substance can dissolve in another, the substance is said to be soluble. A substance that will not dissolve is called insoluble; for example, sand is Prac 1 insoluble in water, but sugar is soluble in water. p. 70
Fig 3.1.1 Most houses recycle their plastic, aluminium, glass and paper waste. They then need to be separated.
solvent
solute
solution
What is a mixture? A mixture contains two or more chemically Quick Quiz pure substances that can be separated easily using a physical process such as sieving or filtering. To form a mixture, two or more pure substances are mixed together. No new substances are formed. Instead, the particles of each Fig 3.1.2 A solute does not disappear when it dissolves. It is still in pure substance are spread between the particles of all the other pure substances. For example, if you mix a packet of the solution. This can be proved by weighing the solute and solvent and the solution they form. The total mass of a solution is always Smarties and a packet of M&Ms, you create a mixture of equal to the mass of the solvent plus the mass of the solute. The mass Smarties and M&Ms. You don’t create a new type of is conserved. chocolate!
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Types of mixtures
Concentration When a solvent (e.g. water) contains a large amount of solute (e.g. salt) the Prac 2 Prac 3 p. 71 p. 71 solution is said to be concentrated. The opposite of concentrated is dilute. Adding more solute makes the solution more concentrated, whereas adding more solvent will dilute a solution. If more and more solute is added to a solvent, a point is reached where no more will dissolve. When a solution reaches this point, it is said to be saturated. Caramel, for example, is made from a saturated sugar solution.
Fig 3.1.3 Soft drink is a solution of sugar, flavourings, colourings and carbon dioxide gas in water.
Common solutions Solution
Solute
Solvent
Uses
Soda water
Carbon dioxide (gas)
Water (liquid)
Preparing soft drinks
Salt water (saline solution)
Sodium chloride (solid)
Water (liquid)
Cleaning contact lenses, cooking
Two-stroke motor fuel
Oil (l)
Petrol (l)
Running a lawn mower
Lime water
Calcium hydroxide (s)
Water (l)
Testing for carbon dioxide
Methanol (l)
Pure alcohol (l)
Methylated spirits
A dilute solution has a small amount of dissolved solute.
A concentrated solution has a large quantity of dissolved solute.
Fig 3.1.4 A concentrated solution has more solute particles
Cleaning oilbased paints
dissolved in it than a dilute solution.
Science Science
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How come pizza still tastes good the next day? The tomato paste base of a pizza does more than add flavour. Water trapped in tomato fibres does not mix with fat in the cheesy toppings. This is because the base does not absorb fat from its toppings and so the pizza tastes very similar to how it did the previous day.
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Clip
Snowy solutions The freezing point of a solvent is lowered when a substance is dissolved in it. That’s why antifreeze is added to a car radiator when going to the snow. It makes it less likely that the water in the radiator will get cold enough to freeze, stopping it from cracking. Winter is bitterly cold in Europe and northern America and a salt–gravel mixture is sprinkled on roads to prevent ice forming and to give cars better grip.
Solutions are clear and transparent, allowing light to pass straight through. In contrast, colloids are ‘cloudy’ due to light being scattered (reflected) off their larger particles. The substance in which the particles are being spread is known Science as the dispersion medium. The dispersion medium can be a solid, Brown dams and rivers a liquid or a gas, as can the particles Some dams and rivers that are mixed in with it. This always appear brown and results in several possible colloid never settle out clear. Some combinations: of the brown colour is • sols suspended soil. There may • emulsions also be some colloidal clay particles present, which do • foams not settle out. • gels Prac 4 p. 72 • aerosols.
3.1
A mixture of water and sand is not a solution, but is known as a suspension. In a solution, the sizes of the solute and solvent particles are similar. In a suspension, the particles being mixed are much bigger than those in a solution. The particles start off being suspended in the liquid, making it cloudy. If left undisturbed, however, the particles will settle to the bottom of the container. The substance that settles out of a suspension is called the sediment. Sediment can be strained or filtered out of a suspension. Some medicines are suspensions, as are some types of paint—they separate into different layers and therefore need to be re-mixed before use.
Unit
Suspensions
Clip
Colloid type Sol
Fig 3.1.5 The particles in a suspension are much larger than those making up a solution and can be strained or filtered. If left long enough, the particles drop out and form a sediment on the bottom of its container.
Colloids A colloid is a mixture that is between a solution and a suspension. The particles in a colloid are bigger than those in a solution, but smaller that those of a suspension, and do not settle out as quickly.
Fig 3.1.6 Acrylic paints are colloids whereas oil paints are suspensions.
Particle type Solid
Dispersion medium
Examples
Liquid
Blood, ink, paint
Emulsion
Liquid
Liquid
Milk, mayonnaise, hand cream, vinaigrette
Foam
Gas
Liquid
Shaving foam, whipped cream
Gel
Liquid
Solid
Jelly, hair gel
Aerosol
Liquid
Gas
Fog, mist clouds
Solid aerosol
Solid
Gas
Smoke
Sols A sol is a colloid where particles of a solid are spread throughout a liquid. Blood plasma is an example of a sol in which solid blood proteins are spread throughout water. Blood is made up of blood plasma and blood cells.
Emulsions An emulsion is a colloid in which particles of a liquid are spread throughout another liquid. Milk, for example, is an emulsion of liquid fat spread throughout water.
I n t e r a c t i ve
67
Types of mixtures Normally, oil and water will not mix. Detergent, however, helps break up fat and oil drops into small particles that allow an oil–water emulsion to form. A chemical that helps fats form an emulsion is called an emulsifier. Detergent helps emulsify fats, as does bile in our intestines, making fats easier to digest. Many foods contain emulsifiers to stop fats separating into layers.
Fig 3.1.8 A gel is a colloid in which liquid particles (e.g. water) are held between the particles of a solid (e.g. gelatine). Jelly is a wellknown example of a gel. Gels melt easily when heated.
Fig 3.1.7 A foam is a colloid made up of a gas mixed with a liquid. Shaving foam and fire extinguisher foam are examples. Worksheet 3.1 Mixtures
Worksheet 3.2 Wordfind
Prac 5 p. 72
Fig 3.1.9 Aerosols have liquid or solid particles spread throughout a gas. Mists and fogs are aerosols in which water droplets are spread throughout air. Smoke is a solid aerosol formed when solid carbon is spread into air.
3.1
QUESTIONS
Remembering 1 State two examples of suspensions. 2 List two examples of substances that are: a soluble in water b insoluble in water. 3 State whether the following statements are true or false: a In a solution, the solvent is always water. b A solute is always a solid. c A substance that is insoluble must be a solid. d When a mixture is made, new substances are not formed.
Understanding 4 Define what is meant by the terms solution, solute and solvent. L
68
5 Explain why the particles in a suspension sink, whereas those in a colloid do not. 6 Explain why some medicines need to be shaken before using them. 7 Outline how a torch could be used to test for a colloid. 8 Explain how detergent changes an oil–water suspension into an emulsion.
Applying 9 Identify the correct answer. When coffee powder is mixed with hot water, the water is the: A solute B solvent C solution D colloid.
>>
Unit
A they are spread too thinly throughout the solvent
a Draw a line graph showing the relationship between the amount dissolved and the temperature of the water.
B they have been destroyed by the solvent
b Interpret the graph and predict the amount of solid that could be added to water at 35°C and 85°C.
C they have been converted to solvent particles
c State a conclusion to the investigation.
D they have been converted to a different substance.
3.1
10 Identify the correct answer. In a solution, the particles of the solute cannot be seen because:
Creating
11 Identify the substance that settles out of a suspension of:
17 Construct labelled diagrams to illustrate:
a a mixture of chalk and water
• a concentrated solution
b muddy water
• a dilute solution
c used engine oil that contains bits of worn metal.
• an emulsion • a suspension.
Analysing 12 Analyse the diagrams in Figure 3.1.10 below, and determine which represents a solution, a suspension and which represents a colloid.
18 Identify three classes of colloids and the dispersion medium of each. Give an example of each and construct a table to display your answer.
13 Compare a concentrated and a dilute solution by listing their differences and similarities.
19 Design an experiment to determine whether cordial is a suspension or a solution. In your experiment, you should:
14 Classify each of the following as either a solution or suspension: glue, saline (salt water), cream, whisky, muddy water, sunscreen.
a Outline a clear aim for the experiment.
15 Graffiti remover is used to wash paint from a wall. Classify the paint as either solvent, solute or solution.
c Suggest ways of reducing any wastes that might be made in the experiment.
Evaluating 16 To test the solubility of an unknown solid, students placed a solid into 200 mL of water. They then decided to see if solubility changed with increasing water temperature. The results are shown in the table. N Temperature (°C)
25
Amount of solid (g)
17
30
45
55
65
70
75
b Identify conditions (variables) that will change or should be kept constant.
20 Remembering that the solute is not destroyed when dissolved in a solvent, construct and complete the table below. Hint: Refer to Figure 3.1.2. N
Mass of solvent (g)
Mass of solute (g)
100
12
60 20
32
40
46
49
Mass of solution (g) 90
65
52
180
Fig 3.1.10 A
B
dispersion medium
C
solvent particles
solute particles sediment
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Types of mixtures
3.1
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find out about mixtures of metals, known as alloys. a Clarify what is an alloy. b Explain why an alloy is a mixture. c Identify some alloys that may be found around the home. d Relate the use of each alloy to its properties, such as lightness or resistance to rust.
e -xploring We b
Desti nati To find out more about the science behind the use of salt to melt ice on roads, a list of destinations can be found on Science Focus 1 Second Edition Student Lounge. Create a brochure to explain to drivers why the salt is used and how it works.
on
2 Find a method to separate the solid from the liquid in a suspension. Find out how it is done in industry. 3 Identify the components of a soft drink. Compare the ingredients of diet and regular soft drinks.
3.1
PRACTICAL ACTIVITIES
Testing solubility in water
1
Method
Aim
1 Use a spatula to place a very small amount of a substance into a test tube.
To test the solubility of various substances in water.
2 Half fill the test tube with water.
Equipment
3 Place a rubber stopper in the top of the test tube and shake it in an attempt to dissolve the substance.
• • • • • • • • • • • • •
salt sugar ground-up coloured chalk copper sulfate flour soil household and other substances, as provided by your teacher test tubes test-tube rack water rubber stopper(s) spatula(s) safety glasses
4 Return the shaken test tube to the test-tube rack and observe it. 5 Repeat steps 1 to 4 for the other substances, recording your observations.
Questions 1 Classify all the substances tested as either soluble or insoluble. 2 Explain why it was important to use a very small amount of each substance. 3 Identify which substance appeared to be: a most soluble b least soluble.
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Unit
3.1
Temperature and solubility
2 Aim
copper sulfate/water
To find out how temperature affects the solubility of two different chemicals.
Equipment • • • • • • •
test tubes test-tube rack tongs copper sulfate calcium acetate spatula safety glasses
Method
Bunsen burner
bench mat
Fig 3.1.11
Questions
1 Fill the test tubes with cold water to a depth of 5 centimetres.
1 Describe the effect (if any) of heat on solubility.
2 Use the spatula to add a tiny amount of copper sulfate to a test tube, and gently swirl the test tube to dissolve the chemical.
2 Explain the difference in solubility between copper sulfate and calcium acetate.
3 Continue adding more chemical until a small amount remains undissolved in the test tube. 4 Gently heat the solution for about 10–20 seconds. Do not boil it.
3 Calcium acetate and air have similar solubilities. Use this information to explain the bubbles that are seen as water is first heated.
5 Again, swirl the test tube and try to dissolve more chemical.
4 Describe what happens as a saturated solution cools. (You may have to leave your test tube of copper sulfate solution overnight before answering this question.)
6 Place the test tube in the rack and leave it to cool. Observe what happens as it cools.
5 Draw diagrams to show what happens to the solute and solvent particles as a saturated solution cools.
7 Repeat steps 1 to 6, using calcium acetate.
3
Surface area and solubility
4 Swirl both beakers for 10 seconds in an attempt to dissolve as much of the sugar as possible.
Aim To examine whether surface area has any effect on the rate of dissolving.
Fig 3.1.12
Equipment • two sugar cubes • two beakers water
• water
Method 1 Place an equal amount of water (e.g. to a depth of 5 centimetres) at the same temperature in each beaker. 2 Crush one of the sugar cubes into separate crystals. 3 Place the whole cube in one beaker and the crushed cube in the other.
sugar cube
sugar crystals (crushed sugar cube)
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Types of mixtures Questions 1 The crushed cube has a greater surface area (imagine it spread over the bottom of the beaker). Describe what effect increasing the surface area of a solute has on the rate of dissolving.
2 Describe why the entire crushed cube is used up rather than just some of it. 3 State reasons for keeping water level and temperature the same in both experiments.
Light transmission in mixtures
4
light source
Aim To examine the effect of light transmission in various types of solutions.
light sensor
Equipment • • • • • •
data-logging equipment with light intensity probe copper sulfate (solution) muddy water (suspension) starch in water (colloid) light source beaker
Method
Fig 3.1.13
keep these distances fixed
4 If time permits, take several measurements for both the suspension and the colloid and draw a graph of intensity versus time for each. N
Questions
1 Place some copper sulfate solution in a beaker and direct a beam of light into the beaker, as shown.
1 Compare the amount of light transmitted through each substance.
2 Use a light sensor to measure the intensity of the light that passes through the liquid.
2 Explain why it is important to keep the sensor and light source at the same distance from the beaker in each case.
3 Rinse the beaker and repeat steps 1 and 2 for both the suspension and the colloid. Keep the sensor and light source at the same distances from the beaker.
3 Identify the type of graph you used in step 4.
Forming an emulsion
5
4 State a reason for using this type of graph.
Method
Aim
1 Use a funnel to pour an equal amount of water and cooking oil into the plastic bottle.
Examine how two liquids that are insoluble in one another behave when forced to emulsify.
2 Screw on the cap tightly.
Equipment • • • •
clear plastic bottle with a screw top cap water cooking oil funnel
3 Observe the oil and water and record your observations. 4 Turn the bottle upside down several times and record your observations. 5 Shake the bottle and record your observations.
Questions 1 Describe what happens to the oil and water mixture as you start to agitate it. 2 Identify what sort of mixture you make when you shake the bottle violently.
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Unit
3.2
context
Separating insoluble substances
It is often necessary to separate mixtures into the pure substances which make them up. This is possible because the pure substances keep their own physical properties even when they are all mixed together. Different mixtures are made in different ways and so different methods
are used to separate them. Separating mixtures is important for many industrial processes, including purifying metals, removing sediment from old bottles of wine and separating the cream from milk—just to name a few.
Science
Clip
Whale of a filter
Fig 3.2.1 Surgical masks are one type of filter.
Separation processes for insoluble substances The insoluble particles in mixtures like suspensions and colloids are much larger than the soluble particles dissolved in solution. As a result, they require special processes to remove them from the dispersion medium.
Instead of teeth, the baleen whale has a filtering device composed of 300 plates of whalebone (baleen) hanging from the roof of its mouth. These baleen filter small plankton called krill from sea water. The whale then uses its huge tongue to wipe the filter clean before swallowing the krill.
The main processes used are: • decanting • sieving and filtration • gravitation separation and centrifuging • magnetic separation and electrostatic separation • froth flotation.
73
Separating insoluble substances
Decanting Decanting is a simple method of separation that can be used to separate suspensions. The suspension is left long enough for most of the sediment to collect at the bottom of a container. The liquid above the sediment is then carefully poured into another container.
Sieving is very important in industry. Crushed ore can be sieved to collect the bigger pieces that require further crushing prior to extraction of metals. Fishing nets with various-sized holes ensures that only legallysized fish are caught. Any fish that is too small goes straight back into the water. Fruit such as apples and oranges are also separated into their different sizes by throwing them onto a board with different diameter holes after picking.
Fig 3.2.3 A sieve in action in the kitchen. Fig 3.2.2 Old wines often form sediment that can be mixed back into the wine if a bottle is moved too much during pouring. To avoid this happening, wine is often decanted from the bottle into a decanter before pouring.
Sieving and filtration Both these methods use a fine mesh to trap the larger particles. The smaller particles go straight through.
Sieving Sieving is useful when there are different-sized particles in a mixture. Sieves are commonly used in the kitchen to remove lumps from flour. Likewise, a special sieve called a colander catches spaghetti while letting the hot water pass through.
74
Filtration Filtration uses a very fine sieve called a filter. One type of filter used in the laboratory is filter paper. Filter paper contains millions of tiny holes that allow particles in a solution to pass through, but not the larger particles. These get trapped in the filter paper. Filters are found in coffee plungers, tea bags, dust masks, vacuum cleaners, car fuel systems, and spa and swimming pools.
Worksheet 3.3 Filtering
Prac 1 p. 78
spinner
3.2
wet clothes
Unit
filter paper funnel residue (solid material left in the filter paper) filter stand beaker
spin
water forced out through small holes
filtrate (liquid that passes through the filter paper)
Fig 3.2.4 Filtering is used to separate solids from liquids. The insoluble particles are too large to pass through the tiny holes in the filter and get trapped in it. The liquid flows straight through.
Getting particles moving These next two methods involve getting the particles moving so that they separate.
to basin
Fig 3.2.5 A washing machine spin dries clothes using a centrifuge
Gravity separation
action. A salad spinner works the same way.
When a mixture of water and particles of different weights is stirred or shaken, the heaver particles will migrate towards the bottom of the container. This is how panning for gold works—tiny (but heavier) specks of gold sink to the bottom of the pan, where they remain Prac 2 p. 79 when the lighter gravel is washed off.
Blood is separated using a centrifuge. The centrifuge holds special test tubes at an angle so that the heavier particles in a liquid are forced to the bottom of the tubes. Milk and its cream can be separated this way too.
Centrifuging Another method involving the movement of particles is centrifuging. The spin drier in a washing machine is a type of centrifuge. When the spin cycle activates, the drum rotates rapidly, forcing the clothes and water against the drum wall. The walls contain small holes that allow water to pass through them and be pumped out, leaving the clothes ‘spun dry’.
Science
Clip
Now that’s smart! In the 1950s, scientists studying the Japanese macaque fed the monkeys grains of rice on the beach. They expected the monkeys would spend some time picking the rice from the sand. However, one smart female, named Imo, took a handful of rice and sand and threw it into the water. The rice floated while the sand fell to the bottom, allowing her to skim the rice from the surface. Soon the other monkeys learnt the same behaviour.
Fig 3.2.6 A laboratory centrifuge is used to separate blood into different layers. The heavier red blood cells have been pushed to the bottom while the lighter plasma is nearest the top.
75
Separating insoluble substances
Using magnetism and electricity These next two methods use the invisible force fields from a magnet or electricity to attract the particles that are to be removed.
charged wires
Magnetic separation Magnets attract iron and steel (an alloy of iron) but do not attract other metals, such as copper, gold or aluminium. Magnets also have no effect on plastics, glass, paper or cardboard. Therefore, magnets provide an easy way of separating iron and steel from non-magnetic materials. A bar magnet, for example, could be used to separate iron filings from sand in the laboratory. In industry, electromagnets are commonly used to separate iron and steel from plastics and other nonmagnetic metals. This is done by suspending a powerful electromagnet over a conveyer belt that is carrying scrap. When enough iron is Prac 3 collected, the electromagnet is turned off to p. 79 release its load. Go to
Science Focus 1 Unit 7.6
charged particles collect on plate
+ + +
+ + +
+
–
+
–
+
–
– – –
–
charged plate
– –
smoke
Fig 3.2.8 An electrostatic precipitator helps to keep the atmosphere free of fine dust and smoke particles by attracting them to the large, electrically charged plates. This type of filtration system is very effective because it does not stop the flow of gas up the chimney but cleans it on the way up.
Froth flotation Froth flotation is used in the processing of minerals. During copper production, rocks containing grains of copper must first be crushed and ground to a fine powder—this is called liberation. Once liberation has occurred, the powder is mixed with water and special chemicals in flotation cells. Air is then blown into the mixture to produce bubbles of froth. Chemicals in the mixture stop the bubbles bursting and help the copper stick to the bubbles. The unwanted part of the powdered rock, called gangue, falls to the bottom of the flotation cells. Copper ore, containing a high proportion of copper, may then be skimmed from the top of the flotation cells.
Fig 3.2.7 Electromagnets can be turned on and off, allowing them to separate iron and steel from scrap materials.
Electrostatic separation
76
Industrial chimneys can contain electrostatic precipitators, which remove waste products by charging particles as they move up a chimney. Once charged, the particles are attracted to charged metal plates and are prevented from being released into the atmosphere.
Fig 3.2.9 Froth flotation of copper ore. The copper ore sticks to the bubbles while the sand and rock sinks to the bottom.
Unit
QUESTIONS
Remembering 1 List four methods for separating insoluble components from a mixture. 2 State whether the following statements are true or false: a Filtration may be used to separate a solute from a solution.
Analysing 15 Complete the table below to compare all separation methods studied in this section. Add as many lines as you need. L Separation method
Brief description
Example
Decanting
Liquid gently poured from one container into another, leaving sediment at the bottom of the original container.
Wine from an old bottle poured into a carafe, leaving sediment behind.
b Filtrate is what passes through a filter.
Understanding 3 Explain how you would decant water from a sand–water mixture. 4 Give an example to explain how the sieving process works.
3.2
3.2
5 Explain what the residue is in filtration. 6 Describe how the spinning of a centrifuge causes separation. 7 Outline the process of froth flotation by placing the following terms in order from first to last: chemicals added, skimming, liberation, air blown in. 8 Define gangue and explain where it comes from. 9 Explain why salt can’t be separated from salt water using filter paper. Clarify your answer using diagrams, showing the sizes of water and salt particles.
Applying 10 A quarry produces a mixture of small and large crushed rock pieces. Identify and describe the basic method that may be used to separate the small and large pieces.
paper element
11 Identify a separation method to assist with each of these problems. a A container of small metal nuts and bolts is spilt on the grass near a workshop.
Fig 3.2.10
b An orchardist wishes to separate under-sized fruit before packing fruit for market.
Evaluating
c An industrial chimney belches unacceptable amounts of waste into the atmosphere.
16 Propose a reason why test tubes in a centrifuge are at an angle and not vertical.
d A beekeeper needs to remove honey from honeycomb before bottling.
17 Propose reasons why the paper element in an oil filter is folded, as shown in Figure 3.2.10.
12 Identify and explain two uses of filtration in your home. 13 Identify some household appliances that contain a centrifuge. 14 During a heavy downpour, rain washes only the heavier stones from a driveway into a pile at the lowest point of the driveway. Identify and explain which separation method has occurred.
Creating 18 Draw a cross-section diagram of the filtration method used in the laboratory. 19 Design a simple device to stop leaves entering stormwater pipes after being washed down the spouting of a roof. Specify which separation technique has been used.
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Separating insoluble substances
3.2
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find out about kidney dialysis, why it is needed, how often a patient needs it and possible alternatives. Create one of the following: • a pamphlet on the condition for patients L • a video that the doctors might give their patients to take home • a website for Kidney Health Australia
3.2
• an advertisement encouraging people to donate one of their kidneys. 2 Design a method to separate the aluminium, steel, glass and plastic containers that are thrown into the recycling bin. Separate these materials. Compare your method with an industrial method such as one a local recycler might use. 3 Examine the possibility of placing sugar and powdered milk into a tea bag so that a cup of tea could be made even more quickly. Design a newspaper advertisement to promote the new product. L
PRACTICAL ACTIVITIES
Filtration
1 Aim
To filter a mixture to obtain a filtrate and a residue.
Equipment • crushed (powdered) coloured chalk and copper sulfate mixture • conical flask • beaker (100 mL)
• • • •
funnel filter paper stirring rod safety glasses
Method 1 Place the powdered mixture into the beaker, and add about 50 mL of water. 2 Use the stirring rod to mix the water and powder as best you can. 3 Fold the filter paper as shown in Figure 3.2.11 and place it in the funnel. Then place the funnel in the conical flask. 4 Tip the water–powder mixture into the filter paper.
open out Fig 3.2.11 Method for correctly folding a filter paper
filter paper funnel residue
Questions 1 Contrast the size of the copper sulfate particles with that of the chalk particles. Explain your observation. 2 Produce a magnified diagram explaining how the filtrate is trapped by the filter paper. Use different symbols for the solute and solvent particles. 3 Recommend a method that might recover the copper sulfate powder from the filtrate.
78
conical flask
filtrate
Fig 3.2.12 Assembled filtering apparatus
Unit
Gravitational separation
Aim To observe how different soils separate with gravitation separation.
Equipment • three different soil samples from around the school or home • three conical flasks with stoppers • water
Method 1 Half fill the conical flasks with water. 2 Place equal amounts of the soil samples in each conical flask.
3 Insert a stopper into each flask and shake the soil–water mixture. 4 Record your observations for each soil type as the soil begins to settle.
3.2
2
5 Record how your mixtures look at the end of the period, after one day and after one week.
Questions 1 Describe what happened to each of the soil samples as they were allowed to settle. 2 What can you say about the relative sizes of the particles in each of the soil samples? Explain how. 3 Plan how you could separate the soil and water so that you can retain both the soil and the pure water.
Magnetic separation
3
plastic bag
Aim To separate a mixture using a magnet.
Equipment • • • • •
magnet
mixture of sand and iron filings sheet of newspaper magnet in a plastic bag empty container for iron filings sheet of paper
Method 1 Place the sheet of newspaper on a bench and then place a small pile of the sand–iron filings mixture on top.
paper newspaper
Fig 3.2.13
Questions
2 Spread the mixture into a flat pile and place a sheet of paper on top.
1 Explain why the sheet of paper was placed on top of the mixture.
3 Use the magnet in the plastic bag to carefully separate the mixture, placing the separated iron filings in a clean container as you go.
2 Explain why the magnet was placed in a plastic bag. 3 Propose how a similar technique could be used in industry.
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Unit
3.3
context
Separating soluble substances
The soluble particles in a solution are much smaller than the insoluble particles in a suspension or in a colloid and so cannot be separated using the same methods. Industry frequently needs to separate dissolved particles from their
solutions. The purification of water for drinking and the production of salt from sea water both rely on extracting the dissolved particles. Forensics even uses some of these techniques to work out who committed a crime.
Fig 3.3.1 The colour in this liquid indicates that there is probably something dissolved in it. Some simple methods can retrieve it.
Methods for separating soluble substances A dissolved solute might be invisible in its solution, but there are a number of simple methods for separating it from the solvent. The main processes used are: • evaporation and crystallisation • distillation • absorption • chromatography.
Evaporation and crystallisation A filter cannot separate the solute particles in a solution because the particles are far too small to be trapped by any filter. However, pure crystals of the solute (known as residue) will be left behind if the solvent is heated so that it evaporates and becomes a gas. Boiling the solution speeds up Prac 1 p. 83 the evaporation process.
Using heat The most common methods for separating soluble substances from solution are based on the fact that the solvent evaporates (turning into a gas) when the solution is heated. This leaves the solute behind as a solid. These processes include crystallisation and distillation.
Fig 3.3.2 In large-scale salt production, giant salt pans allow evaporation using the heat energy from the Sun.
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Distillation
condenser cond denseer
3.3
Distillation involves evaporation too, but collects the evaporated solvent instead of letting it escape into the atmosphere. The evaporated solvent is cooled and condensed back into a liquid, which is then collected. This liquid is known as Heat causes the distillate. As in evaporation, what solvent to remains in the original container is evaporate, turning it known as the residue. into vapour Tap water is not pure because it contains small amounts of other substances, such as dirt, fluoride and chlorine. Distillation is used to obtain pure or distilled water. Distillation is also used in the production of perfume and whisky (hence the term distillery).
Unit
Condenser is cooled by cold water flowing from the tap Vapour cools in condenser to form liquid droplets
flask solution flask lask cold water out
cold water in
distillatee
Distillate drips into flask. In ‘normal’ evaporation, this is lost to the air.
Fig 3.3.3 A laboratory distillation larger rock
larger rock
apparatus. A flask containing the solution is heated. The vapour produced then cools in the condenser to form liquid droplets of the distillate, which eventually make their way into the collection flask.
Prac 2 p. 84
Prac 3 p. 85
small rock plastic sheet
vegetation
Crude oil is made up of many different substances called fractions. Fractional distillation uses the fact that these substances boil at different temperatures. This allows them to be separated into petrol and other useful substances.
Fig 3.3.4 Life-saving distillation in the desert. This desert survival technique produces fresh water (the distillate) using a using a sheet of plastic to trap water evaporating from the ground or plants.
Fig 3.3.5 Crude oil is distilled, producing different fractions (e.g. petrol, diesel etc.) at different temperatures.
crude oil IN
0–90°C
petroleum gases aviation gasoline petrol kerosene, jet fuel
400°C heating oil diesel fuel lubricants, waxes 500+°C
PREMIUM MOTOR OIL
furnace oil, bitumen
81
Separating soluble substances
Staying dissolved Other separation methods use the fact that the solute may prefer to stick to another material rather than stay dissolved in the solute. Absorption and chromatography are examples of such processes.
Absorption Absorption occurs when a material is taken in by another. A kitchen sponge, for example, absorbs water. Special chemicals can be used to absorb particular substances from a mixture. Charcoal contains many fine pores that allow it to absorb many dangerous gases, making it useful in gas masks and breathing filters. Packages of food that must be kept free of moisture sometimes contain small sachets of silica gel, which can absorb nearly half their weight in water.
Chromatography Chromatography is a technique that can be used to separate colours in inks, food dyes and other mixtures of colours. A medium, such as blotting or filter paper, containing a spot of the mixture is placed in contact with a solvent (e.g. water). The different colours move throughout the medium at different rates and so are separated along it. Worksheet 3.4 Chromatography
Prac 4 p. 85
Fig 3.3.6 Silica gel separates water from materials by absorbing the moisture. Fig 3.3.7 Paper chromatography can be used to separate the colours in ink.
3.3
QUESTIONS
V
Remembering 1 List three substances that are soluble in water. 2 State what is meant by the term fraction in distillation 3 List three substances that are insoluble in water.
Understanding 4 Describe what is a salt pan and what it is used for. 5 Describe how distillation is different from evaporation. 6 Clarify the types of mixtures that chromatography is used to separate. 7 Explain how different colours move in chromatography.
Applying 8 Identify three examples in the home or industry for which distillation is used. 9 Identify three different fractions and their uses from Figure 3.3.5. 10 Identify an example of something that absorbs a: a liquid
b gas.
11 Identify a separation technique for each of these situations. a Joe was cooking and dropped a bag of salt into a bowl of water. He wants to get the salt back, but not the water. b Ranjana wants to recycle water from her washing machine to make drinking water.
>>
82
Unit
Separation method
Brief description
Example
Evaporating
The mixture is boiled so that the solvent evaporates. This will leave behind the solute.
Salt from sea water
d Bilal wants to breathe clean air, not paint fumes, while painting his house.
Analysing 12 Compare the separation methods in this unit by completing the table to the right. L
3.3
c The police have three pens and want to find out which one was used to write an anonymous letter.
Evaluating 13 The small silica gel packets inside various products carry a notice saying DO NOT EAT. Propose why this warning is present and what may happen if you did eat it.
Creating
14 Propose a sequence of steps for producing fresh water from sea water.
15 Construct a diagram to illustrate the process of distillation. Explain what is happening at each step.
3.3
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find out how water can be described as ‘hard’ or ‘soft’. a Explain the difference between ‘hard’ and ‘soft’ water. b Form a team and design an experiment that will test the hardness of the tap water in your home.
2 Find out how you could make a solar still to be used because you have run out of water in a desert area. Sketch the still and list the equipment that you would require. 3 Discover why air bubbles form on the inside of a beaker when it is heated.
c Determine whether the water tested is hard or soft.
3.3
PRACTICAL ACTIVITIES
V
Separation by evaporation
1
Method
Aim
1 Place a small amount of solution in the evaporating basin (half to one-third full) and place it on the gauze mat, as shown here.
To use evaporation to separate the dissolved substances from soft drink.
Fig 3.3.8
Equipment • • • • • • •
Bunsen burner salt solution or soft drink bench mat evaporating basin tripod gauze mat safety glasses
evaporating basin gauze mat
tripod
bench mat
>> 83
Separating soluble substances
2 Heat the solution, but turn off the Bunsen burner just before the last drop of water disappears. (The heat remaining in the basin will be more than enough to finish evaporating the water.) 3 Allow the crystals to cool. You may wish to stick a sample in your book under a piece of contact adhesive.
Questions 1 Describe what you saw as the water evaporated. 2 Explain why it is important to stop heating when the water is just about gone. 3 Predict where the water went.
watch-glass
A simple distillation
2 Aim
To use distillation to separate tap water so that pure water is obtained.
flask solution
Equipment • • • • • • • • • • • •
Bunsen burner gauze mat bench mat conical flask tripod watch-glass test-tube rack salt solution beaker three paperclips water safety glasses
Method Part A: The distillation 1 Assemble the apparatus as shown in Figure 3.3.9. 2 Use the watch-glass and beaker to collect distilled water. Save some of the salt solution for Part B of this activity.
beaker
Fig 3.3.9
Part B: Testing the distillate 1 Unfold the paperclips. 2 Dip one paperclip into the salt solution and then hold the dipped end of the paperclip into the blue flame of a Bunsen burner. What colour flame is produced? 3 Dip another paperclip into plain water and repeat the ‘flame test’. 4 Dip a third paperclip into your distillate and repeat the ‘flame test’.
Questions 1 Explain what the flame tests tell you about the distillate. 2 Present a reason for not using the same paperclip for all three flame tests.
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Unit
3.3
Survival distillation
3 Aim
To distill water from the leaves of various types of plants.
Equipment • plastic bags • string • access to several types of bushes and trees
Method 1 Find a bush or tree in your local area. 2 Place a plastic bag over the leaves of a branch. 3 Tie the plastic bag in place with the string so that it is fully sealed. 4 Repeat steps 1 to 3 for different types of plants in your local area. 5 Leave the bag attached for two to three days.
Fig 3.3.10
Questions 1 Identify which plant produced the most water and which produced the least. 2 Explain where the water is coming from. 3 Describe how this might be useful if you were stranded somewhere in the Australian outback.
6 Compare the water content in each bag.
Chromatography of Textas and Smarties
4
Part B: Smarties 1 Place either one or several Smarties of the same colour in the watch-glass.
Aim
2 Place a drop of water on a Smartie to extract its colour.
To use chromatography to separate the colours in Smarties and/or ink.
3 Use an eye dropper to collect some of the coloured liquid.
5 Compare results for different brands of felt-tipped pens or Smartie-type confectionery.
eye dropper/water 1
water-based Textas Smarties of various colours eye dropper water beaker filter paper watch-glass
2
• • • • • • •
4 Place a drop of dye in the centre of a piece of filter paper and repeat steps 1 to 5 of Part A. mL
Equipment
Method
filter paper
beaker
Part A: Textas 1 Using a water-based Texta pen, make a dot in the centre of a piece of filter paper. 2 Place the filter paper on top of the beaker.
Fig 3.3.11
Questions
3 Using the eye dropper, place a drop of water on the dot of ink.
1 Present a list of the colours in each Texta and Smartie you tested.
4 Repeat step 3, if necessary, to spread rings of colour from the dot. Be patient.
2 Explain why different colours spread at different rates.
5 Try different-coloured dots.
3 Assess whether this experiment could be used to decide if a lolly is a genuine Smartie.
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Unit
3.4
context
Water supply and sewage
The world’s water supplies and waste water are two mixtures that need to be treated very carefully. Removing unwanted impurities from drinking water
is important to our health. Removing impurities from waste water is important to the health of the environment.
Fig 3.4.1 Extended drought in Australia has led New South Wales, Victoria, Western Australia and Queensland to build desalination plants that will extract salt from sea water so that it is good enough for drinking. In 2008, work began on a massive desalination plant in Kurnell in Sydney, NSW. This plant will supply 15% of Sydney’s water by 2010.
Water supply Rainwater is not a pure substance but is a mixture. Rain is produced when water evaporates from oceans, lakes and other bodies of water and even from plants and soil. Because it has been in contact with substances that dissolve in it, rainwater is a dilute mixture that must be treated before being supplied to our homes. Water from domestic rainwater tanks is generally not treated, as the potential for contamination is slight.
86
Water treatment The rainwater that we normally drink has passed through an extensive water supply system. However, it must be treated to ensure it does not contain harmful levels of chemicals or bacteria.
Prac 1 p. 91
Chlorine Chlorine may be added in liquid or gas form to kill germs that can cause diseases such as gastroenteritis (‘gastro’ for short). Chlorine has a distinctive smell and taste. It is also the chemical that is added to water in swimming pools and spas in order to keep it free from bacteria and algae (but is added in much greater quantities).
Unit
3.4 Fig 3.4.2 Water is stored in reservoirs for up to five years to allow waste to settle out naturally before further treatment.
Fluoride Fluoride is added to help prevent tooth decay in consumers of the treated water. However, only about 5.7% of the world’s population drink fluoridated water. The levels of fluoride need to be monitored carefully because too much fluoride can have the opposite effect, colouring teeth with an ugly brown stain.
Sewage
Science
Clip
Dentist in a bottle Recently, some dentists have called for fluoride to be added to bottled water. Although fluoride is routinely added to public water supplies to prevent tooth decay, adding fluoride to bottled water is prohibited. Some dentists believe that this can be linked to an increase in tooth decay as more people start to drink bottled water instead of tap water.
Lime and soda ash The chemicals lime and soda ash may be used to ensure that the water is at a neutral pH, like a ‘water-balanced’ swimming pool. You will learn more about acidity and pH levels when you study acids and bases later in Science.
Electrolytes Electrolytes trap suspended particles by causing them to clump together and fall to the bottom of the tank as sediment. These clumps are called floc, and the process is called flocculation.
The terms sewage and sewerage are often confused. Sewage is the waste and water mixture that humans put down sinks, drains and toilets in their homes and in industrial processes. Sewerage is the word used to describe the network of pipes into which sewage passes. Most houses in city areas are connected to the sewerage network that leads to treatment plants and, eventually, to the ocean. However, some homes are connected to a septic tank, in which sewage is broken down by bacteria and is released into the soil, leaving a thick sludge in the tank that must be removed periodically. Because a septic tank depends on bacteria, chemicals that may kill bacteria Prac 3 should not be allowed to pass into the tank. p. 92 Worksheet 3.5 Water use
Science
Clip
Poo-burgers
Prac 2 p. 92
A Japanese scientist once promoted hamburgers made using treated sewage as an environmentally friendly food. Not surprisingly, the so-called ‘pooburgers’ never took off.
87
Water supply and sewage catchment area
storage reservoir
chlorination
fluoridation
pumping station
stand pipe
service reservoir
water mains
city houses in high areas
industry
homes water meter
schools
sewage
treatment
ocean
Fig 3.4.3 The flow of water from catchment to sewage treatment. The service reservoir is an artificial structure that stores water for use during peak demand times. The stand pipe is used to provide increased pressure to high-service areas.
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Unit
Science
Oh crap! spouting vent pipe downpipe bath
laundry sink
storm water system
kitchen
toilet gully trap
Many think that the word crap came from Thomas Crapper (1836–1910) because he invented the flushing toilet. Unfortunately, both facts seem to be wrong! Although Crapper made toilets, improved them and even installed them in Royal Palaces, he did not invent the water closet (i.e. WC). The word crap was used for poo as far back as 1846, a little too early for Crapper since he was only ten years old at the time. Instead, crap may have come from the German word krappe, meaning a vile and inedible fish!
3.4
Clip
sewerage system
Fig 3.4.4 Household connections to the sewerage system. Although sinks, toilets and baths are connected directly to the sewerage system, the downpipes are not, allowing stormwater to be run off separately. The vent pipe and gully trap release gas that might build up in the pipes. The gully trap also stops sewage from flowing back into your house if there is a blockage in the pipes.
Sewage treatment plants Blowers: pump air into aeration tank to encourage bacteria to grow
sewage in
Screen: removes larger objects
Settling tank: bacteria and other solids settle to the bottom in a thick sludge. Pebble filters: suspended solids are removed.
chemicals added
UV lamps: UV light and/or chlorine are used to disinfect sewage.
ocean
pump
Aeration tank: bacteria help break down the sewage by feeding on it. Added chemicals convert dissolved wastes into solids. These fall to the bottom of the tank.
sludge removed
Outfall: treated sewage released into the ocean. Sludge removal: sludge is removed and air dried and stored for several years. After this, some of it may be sold for use in soil and fertiliser products.
Fig 3.4.5 The activated sludge process for sewage treatment. Animati on
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Water supply and sewage
3.4
QUESTIONS
V
Remembering 1 State which chemical is added to water to: a kill germs b prevent tooth decay. 2 State the definition for the term flocculation. 3 Specify exactly what breaks down sewage in a septic tank. 4 List three items connected to the sewerage system in your house. 5 State whether rainwater is a mixture or a pure substance.
Evaluating 16 The catchment of a reservoir is the hills, creeks and rivers around the reservoir. Propose why it is important to look after the catchment of a water supply. 17 Justify why it is better to wash a car on the lawn than on the road. 18 Propose three ways that the sludge from a sewage treatment plant could be recycled or reused. 19 Each basin, sink, shower and toilet in the house has an ‘S bend’. Propose a reason why.
Understanding 6 Rainwater is evaporated water. Describe some places where this water has been evaporated from.
basin
7 Account for how rainwater picks up impurities. 8 Explain how the septic tank helps separate sewage. 9 Explain why air is blown into one of the tanks at a sewage treatment plant. 10 Explain why more chlorine is required per litre in a swimming pool than in drinking water. 11 The forest in a catchment is often said to be like a natural filter. Explain what you think this means.
Applying 12 Identify each separation technique used in the activated sludge process and describe what it removes from the sewage. 13 Identify ways in which you could save water around the home or around the school.
Analysing
90
to sewerage system
Fig 3.4.6
Creating
14 Distinguish between sewage and sewerage.
20 Design a house that would assist people in country areas to use their house roofs to collect and use rainwater.
15 Assess what could happen if sewage was not treated before being released into rivers or the ocean.
21 Why should people save water? Design and present a poster to promote reducing water waste in your home. L
Unit
INVESTIGATING
V
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Compare the amount of water used in various industrial processes (e.g. making paper, soft drinks, recycling). Present the data as both a table and a column graph. N
• how a flushing toilet works • how a toilet ‘knows’ when to stop filling the tank. Present your work in one of the following ways: • a poster
2 Find out about the history of the sewerage system and its effects on public health.
• a sales brochure from 1870 selling the new range of Crapper toilets
3 Find out about the composting toilet and produce an advertisement to sell this product. In your advertisement you must:
• an interview with Thomas Crapper for a current affairs program on TV. L
a Outline how the composting toilet works. b Discuss its advantages and benefits. 4 Find out more about Thomas Crapper and the flushing toilet. Find:
3.4
3.4
e -xploring To find out more about the history of water treatment in Australia, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
We b Desti nation
• what he invented and did • pictures of early flushing toilets
3.4 1
PRACTICAL ACTIVITIES
Water purification muddy water
Aim To purify dirty water to make it fit for drinking.
Equipment • • • • • • •
ice-cream or margarine container sand stones muddy water beakers (2 × 250 mL) tripod stirring rod
sand layer stones layer
margarine or ice-cream container
small hole in container beaker
Method 1 Prepare the container containing sand and stones as shown in Figure 3.4.7.
Fig 3.4.7
2 Pour half of your muddy water into the container, and keep half for later comparison.
Questions
3 Allow the filtrate to drain into the clean beaker long enough to collect a good sample of ‘purified water’.
1 Describe the effectiveness of the sand–stones filtration. 2 Design a method that could improve the purification (e.g. by adding stages to the basic method).
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Water supply and sewage
Testing flocculation chemicals
2
Method 1 Let the muddy water stand for a few minutes to separate out some sediment.
Aim
2 Decant some of the water into a filtering apparatus.
To identify some chemicals that cause flocculation.
3 Take the filtrate and add a few drops of one of the chemicals to be tested, stirring briefly. Note whether any flocculation occurs.
Equipment • • • • • •
250 mL beaker of muddy water filter paper conical flask funnel stirring rod some of the following: copper sulfate, iron(II) chloride, copper chloride, sodium carbonate, sodium bicarbonate, ammonium sulfate, magnesium sulfate, calcium sulfate • safety glasses
Separating artificial sewage
3
?
4 Test the other chemicals in this way.
Questions 1 Identify which chemical produced the most flocculation. 2 State which type of particles you think the chemicals that caused flocculation reacted with—those in suspension or those in solution. Explain why. 3 The ‘clumped chemicals’ are referred to as the flocculent. Explain how you could remove the flocculent.
Method DYO
Aim To separate artificial sewage.
Equipment • artificial sewage mixture provided by your teacher (containing things like bread, chopped vegetable scraps, soil, sand, detergent, oil, grass clippings, coffee, paper, plastic etc.) • other general science equipment, depending on your method
1 Design your own method of ‘treating’ your ‘sewage’ sample. There may be several stages to your process. 2 Keep a small sample of treated and untreated ‘sewage’ for comparison. 3 Clarify your process by describing the stages and their effectiveness.
CHAPTER REVIEW Remembering 1 State the difference between a solution and a suspension.
6 Explain how crude oil is separated into several types of chemicals.
2 State the correct scientific term for a:
7 Explain how rainwater can be used to pick up contamination.
a weak solution b strong solution. 3 State what is liberation in mineral extraction. 4 State why fluoride is added to our water supply.
Understanding 5 Outline the process of: a sieving b filtration.
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8 Explain why water in reservoirs is stored for several years before further treatment. 9 Explain why blowers are used in an aeration tank at a sewage treatment plant. 10 Describe how water may be disinfected in the final stages of treatment. 11 Explain what happens to a soluble solid when it dissolves in a liquid.
12 If you suspected that the contents of a bucket contained sand, clay and salt all mixed with water, explain how you would:
a Identify the solvent and solute.
a remove all impurities in one attempt
b Clarify what happens to the solubility as the temperature is increased.
b remove only the sand
c Account for your observation in part b.
c remove both the clay and the sand.
d Carefully construct a line graph to display these results.
13 Define the term floc. L
e Interpret your graph. If the volume of water was doubled, predict what would happen to the amount of solute that could dissolve at 20°C. Explain your answer.
Applying 14 Identify four mixtures found in the home.
f Draw a diagram to illustrate the experimental set-up you would use to collect the copper sulfate.
15 Paint is removed from a brush using turpentine. Identify: a the solvent
Evaluating
b the solute. 16 Identify three substances obtained from crude oil and specify two uses for each substance. 17 Identify the separation method used in gold panning.
24 Explain how a coffee filter separates coffee from the ground coffee beans. Propose a method to separate the coffee from the ground beans if you ran out of coffee filters. 25 Propose which would dissolve faster in water—one gram of cube sugar or one gram of castor sugar. Explain your answer. If you were performing an experiment to test this prediction, describe which factors must be kept constant.
18 Identify three uses for a centrifuge. 19 Identify the separation method for which charcoal is used. Describe how this technique works. 20 Define and explain chromatography. Identify how it is used in forensic science. 21 Water is a solvent for many substances. Identify suitable solvents for: a oil paint b grease
Creating 26 A mineral water company requires a scientific demonstration to show that their water contains fewer dissolved minerals than its closest competitor. Design an experiment that could be shown on television. 27 Design a method by which you could check the amount of sugar dissolved in a certain brand of cordial.
c nail polish.
Analysing
a
pt
23 Study the data presented in the table and answer the questions that follow. N
on
Ch
Worksheet 3.7 Sci-words
s
Worksheet 3.6 Crossword
22 Detergents are used when oil spills occur at sea. Discuss whether the detergent really cleans the water.
er R sti ev i ew Q u e
Volume of water used = 100 mL Temperature of water (°C)
0
20
40
60
80
100
Maximum amount of copper sulfate that would dissolve (g)
18
22
29
38
50
78
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4
Classification
Prescribed focus area: The nature and practice of science
Key outcomes
Additional
Essentials
4.2, 4.8.1, 4.8.2
•
Living things are classified according to their structural features.
•
A range of plants and animals can be identified using simple keys.
•
Animals are classified first as vertebrates and invertebrates.
•
Vertebrates are then classified as mammal, bird, reptile, amphibian or fish.
•
Invertebrates are then classified into the main groupings of arthropods, worms, molluscs or cnidarians.
•
Plants are classified first as vascular plants or bryophytes.
•
Organisms survive by producing their own food (autotrophic organisms) or by eating other organisms (heterotrophic organisms).
•
Organisms can be classified by designing simple keys.
•
Five important kingdoms are animal, plant, fungi, monera and protists.
•
Species is the most specific grouping that an organism can belong to.
•
Members of the same species are so similar that they can reproduce and produce fertile young.
Unit
4.1
context
Why classify?
Scientists need to be able to carry out many different tasks. One of the most important is classification. Classification is the organisation of different things into groups of related types. Chemists classify elements as metals, non-metals or metalloids; astronomers classify the
planets as terrestrial, gas giants or dwarfs; and geologists classify rocks as igneous, sedimentary or metamorphic. Biologists have the most difficult classification job of all— they need to be able to classify every living thing, placing every organism into groups that are similar in some way.
Classification Classification makes life a lott Quick Quiz easier for everyone, not just scientists. At the supermarket, items are organised by type or by the way they are packaged. Canned fish is in one aisle, pasta in another and sauces and bread somewhere else. Canned vegetables are in one place, the fresh ones in another and the frozen ones in the freezer. Classification in the supermarket helps you find what you want. If you need some chocolate syrup for your ice cream, then you will probably find it with the other dessert toppings. Likewise, soy sauce is likely to be found near the tomato sauce.
Fig 4.1.1 Although it may look like something from science fiction, this Hercules beetle is a very real living thing. Biologists need to be able to classify all living things, even Hercules beetles.
Libraries have their own classification system, organising their books by types, subject and author. Textbooks on the same subject are going to be in roughly the same place, novels by the same author will be grouped together, and encyclopaedias will be in their own section.
Fig 4.1.2 Goods at the supermarket are classified to make them easier to find.
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Why classify?
Keys To make their classification tasks easier, scientists use a model called a key. Keys are simple, easy-to-follow representations of classification systems. Scientists use keys because they: • are easier to use than detailed descriptions of each group • show at a glance what distinguishing characteristics each group has • make it easier to identify objects that have never been seen before • always give consistent answers, regardless of who is using them. This means that all scientists around the world will classify an object or organism in exactly the same way. A good key is clear, simple and easy to use. If a key is confusing or difficult to use then it is not a good key.
Branching keys
Dichotomous keys The most common type of branching key is a dichotomous key. Dichotomous keys have two choices at every branch. They start at the top with one large group and slowly subdivide into smaller and smaller groups until no more choices are possible.
pets
doesn’t live in water
lives in water
goldfish
doesn’t have big ears
has big ears
A branching key begins with one large group. A particular feature is then used to split the group into smaller ones. Other features are then used to split these groups further into even smaller, more defined groups of objects. Each branch in the key is a choice.
rabbit doesn’t breed quickly
breeds quickly
mixed lollies mouse
Jellybeans
chocolate coated
doesn’t bark
barks
cat
dog
other
Fig 4.1.4 This branching key can be used to classify household red
yellow
other
soft lollies
Minties
Smarties
pets. The key is dichotomous because there are only two choices at each branch.
Prac 1 p. 101
Tabular keys Maltesers
Turkish delight
Fantales
Chocolate creams
Fig 4.1.3 This branching key can be used to classify lollies into different categories.
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Tabular keys are sometimes referred to as GO TO keys. Like branching keys, the idea is to start at the top and work your way down. Tabular keys can also be dichotomous, having two choices at each level in the key.
3
4
lives in water
fish
Circular keys
doesn’t live in water
go to 2
has big ears
rabbit
doesn’t have big ears
go to 3
breeds quickly
mouse
To use a circular key, start in the middle and work your way outwards. Each ring represents another choice to be made. Eventually you arrive at the rim of the key, allowing you to identify whatever object you are investigating.
doesn’t breed quickly
go to 4
barks
dog
doesn’t bark
cat
4.1
2
Unit
1
Fig 4.1.5 This tabular key gives another way of classifying household pets. Simply follow the instructions from top to bottom. Prac 2 p. 101
lion fish Indian elephant
African elephant funnel-web spider black can house kill spider can’t kill black tarantula body mainly green
whale shark
eats le p peo
t
ea sn’t doe eople p
bony fish
us ino tilag car fish
ish
sf
es wl
elephant
ja
fish
hydra coral
tiger
sabre-toothed tiger
animals
can live on both land and water commonly found in Australia
not extinct
i
cnidarian
jellyfish
only
extinct
lives
sea fan medusa polyp
box jellyfish sea anemone
ater
multicoloured
nly
nw
mainly black
tiger shark
hairy body spider
red-back spider
large striped small fins fins
small ears
lives on lan do
flower spider
big ears
bream
not commonly found in Australia
poisonous
octopus
blue-ringed octopus
not poisonous common octopus
Indian tiger
frog
salamander
Fig 4.1.6 This circular key can be used to classify different animals. Start in the middle and work outwards.
97
Why classify?
4.1
QUESTIONS
Remembering
Analysing
1 List the advantages of classifying goods in the supermarket.
6 Use the key in Figure 4.1.8 to classify the people shown.
2 State the categories normally used to organise books in a library.
people
Understanding 3 Outline the criteria that could be used to classify:
no freckles
freckles
a the contents of your kitchen at home b the types of shops at the local mall female
c the fruit in a fruit shop d the cars in a car park e DVDs that can be rented from the local store.
no hair
hair
Eugene
Ken
Herman
no pigtails
pigtails
Louisa
Jane
4 Outline the similarities and differences between a branching key and a dichotomous key. A
Applying
male
C
B
5 Figure 4.1.7 shows six insects. Use the key to work out which is which. A
B
C
D
E
F
D
Fig 4.1.8 insects
large wings
small or no wings
butterfly shorter rear legs
very long rear legs
antennae in front of head
antennae to the rear
mosquito
grasshopper horned not horned head head rhino beetle
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Fig 4.1.7
small eyes
large eyes
termite soldier
beetle
E
Unit
cara blip
13 Choose five different types of popular salted snack foods and construct a dichotomous key to classify them.
disty
8 eyes
12 Construct a dichotomous branching key to classify a square, circle, oval and octagon.
14 Construct a tabular key to classify the people in Figure 4.1.11.
4.1
7 Use the circular key in Figure 4.1.9 to classify the alien shown. Identify the name of the alien.
2 antennae
2 eyes yista
1 eye
1 head
2 heads
n ante o nna e
xero
animals 6 legs
feep
3 heads
4 heads
yen
2 mouths
1 leg jooby
1 mouth
4 legs din
no mouth
lip
zeep
Fig 4.1.9 Ro
8 The outer ring of the circular key in Figure 4.1.9 names eleven other aliens. Draw simple sketches of what each alien might look like, being careful to contrast one from another.
Evaluating
Jacinta
Marg
Chris
Fig 4.1.11
15 Construct a circular key to classify the drinks shown in Figure 4.1.12
9 Four types of keys used in classification are: branching, dichotomous branching, tabular and circular. Assess each for ease of use and then list the keys from the one you think is easiest to use to the one you think is the most difficult.
Creating 10 Construct a question that is: a dichotomous b not dichotomous. 11 Construct a dichotomous key to classify the aliens in Figure 4.1.10. Fig 4.1.12
Fig 4.1.10
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Why classify? Fig 4.1.13
water lily
wattle bush
cactus
16 Five plants are shown in Figure 4.1.13. Construct the following keys to classify them: a a dichotomous key b a tabular key c a circular key. 17 Construct a key to classify: a all the different Rugby League jumpers b different Olympic sports. 18 Construct a key that can be used to identify the different members of your family according to their physical characteristics. tree fern
100
gum tree
Unit
1
PRACTICAL ACTIVITIES
Making a pasta key
Aim To construct a key to classify pasta.
Equipment A sample of at least five different kinds of uncooked pasta (e.g. spiral pasta, tubes, shells, bows, spaghetti etc.) in a beaker or cup.
Method
4.1
4.1
4 When you get to the point where you are at a particular type, draw the pasta or paste a sample of it in that place on your key. 5 Gather all the pasta together again and decide on a new set of characteristics by which to reclassify your pasta. Once again, construct a dichotomous key.
Questions 1 Identify the main feature of a dichotomous key.
1 Pour the contents of the beaker onto your bench. 2 As a group, decide on the characteristics (e.g. shape, size etc.) you will use to classify your sample of pasta. 3 In your workbook, construct a dichotomous key to classify your pasta.
2 Look at the keys designed by other groups. State whether they used the same characteristics that you did. 3 Evaluate the different keys you constructed. Which do you think was better? Why?
pasta
Fig 4.1.14 Start off your key like this.
2
Constructing keys
Aim
Method
To construct different types of keys to classify collected objects.
!
Safety Some plants (e.g. oleander and rhus) are known to cause allergic reactions in some people.
Equipment A collection of at least 10 of one of the following: • leaves collected from different trees and shrubs around the school • pieces of common laboratory glassware and equipment • objects from a pencil case.
1 As a group, decide on the characteristics you will use to classify your 10 objects. 2 Group the objects according to the characteristics you chose. 3 Construct a dichotomous key and a tabular key that would allow others to classify your 10 objects in exactly the same way as you did.
Questions 1 Outline some practical advantages of classifying different equipment used in the laboratory. 2 Compare the dichotomous keys you constructed with your tabular keys. Which was easiest to construct? Suggest why.
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Unit
4.2
context
Living or non-living?
Before a biologist can classify something, they must first decide whether it is living or non-living. Sometimes the task is an easy one. For example, rabbits, goldfish and blowflies are all obviously living things, whereas MP3 players, rocks and
pencil cases are all obviously non-living. Pond slime is a little more difficult to classify. Although living, it seems to be less lively than the water in a fast-flowing river. Biologists use a set of characteristics to help them decide if something is living or not.
The characteristics of life You can tell if something is living or not by looking at its characteristics. Characteristics are typical qualities. Two characteristics of kangaroos, for example, are that they eat grass and hop on their two hind legs. Some characteristics are common to all living things. All living things: • take in energy for immediate or later use • take in and use gases from the air or water in which they live • produce wastes (excretion) • respond to stimuli in their environment • have the ability to move • have the ability to reproduce • grow • are made from cells. Any individual thing that has life is referred to as an organism.
Is it living? Animals obviously meet all the characteristics of living things. Plants are living things too, although their movement and growth can be so slow that you often don’t notice it. Some non-living things possess a few of the characteristics of life but will not have them all. For something to be classified as living it must have all the characteristics of life. Fig 4.2.2 An organism is an individual thing that has life. Organisms come in all sizes— elephants and whales are massive, whereas bacteria and amoeba are microscopic.
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Fig 4.2.1 From a distance, coral reefs look much like non-living rock formations. On closer inspection, they are made up of millions of tiny living things called coral polyps. A hard skeleton is left behind when these polyps die. A typical reef has both dead coral and living polyp colonies, which are easily destroyed if touched.
Science
Clip
The living dead! Non-living things are not living now and have never lived in the past. This means that sand and a silver bracelet are non-living. Dead things have lived at some time in the past. Once upon a time, they had all the characteristics of life. This means that wood is dead (it was once part of a living tree), as is leather (it was once the skin of a living cow). Because of this, something that is dead is classified as a living thing!
Unit
4.2
Animals such as humans, dogs, cows, koalas and birds also need to eat to keep themselves warm. This is because they are endothermic, more commonly known as warm blooded. Each animal has their own ‘ideal’ operating temperature. For humans, that temperature is 37°C and roughly two-thirds of our food is used solely to keep us at this temperature. If your body temperature exceeds or falls below 37°C for more than a few minutes, then you quickly become unwell. Reptiles, such as snakes, lizards and crocodiles, don’t use the Science energy from food to keep themselves warm but, instead, Hyper and hypo gain their warmth from sunlight. This means that, despite their If your core body temperature stays higher than 37°C for too large size, crocodiles don’t need long, then you will quickly show to eat much food. Animals like symptoms of hyperthermia (too this are referred to as ectotherms much heat) or heatstroke. The or are said to be ectothermic. symptoms include reddened
Fig 4.2.3 Water displays only one of the characteristics of life (i.e. movement). It meets none of the other characteristics (e.g. it doesn’t use air, reproduce or grow). Therefore, water is classified as non-living.
Living things take in and use energy Animals and plants take in energy, using it to move, grow, reproduce and function properly.
Animals Animals are heterotrophs. This means they cannot make their own food and need to eat to survive. Food is digested and converted into glucose, a type of sugar. Glucose provides all the energy an animal needs. It does this by reacting with oxygen in a chemical reaction called cellular respiration: glucose + oxygen → carbon dioxide + water + energy
Clip
Plants Animals convert the food they eat into glucose, whereas plants make their own glucose using a chemical reaction called photosynthesis. This reaction combines carbon dioxide (taken in from the air) and water (absorbed from the soil by their roots) and is powered by energy from the Sun. Glucose and oxygen gas are produced:
skin, headaches, a high heart rate, low blood pressure, dizziness and excessive sweating (although this is likely to stop as you become dehydrated). Far more common is hypothermia (not enough heat). Symptoms are numb hands and feet, goose bumps, white or blue skin, poor logic, forgetfulness, slurred speech and intense shivering (although this is likely to stop near death).
carbon dioxide + water + energy → glucose + oxygen
Organisms that can make their own food are called producers or autotrophs. Like animals, plants then use cellular respiration to convert glucose into the energy they need: glucose + oxygen → carbon dioxide + water + energy Go to
Science Focus 2 Unit 3.2
Science
Clip
Cold-blooded? Fig 4.2.4 Animals are heterotrophs—they cannot make their own energy, so they must gain it from what they eat.
Energy is produced, as well as carbon dioxide and water vapour. Breathing provides oxygen for the reaction and gets rid of the carbon dioxide and water vapour produced by it.
Ectotherms such as lizards, snakes and crocodiles often are mistakenly thought to have cold blood. Their blood can be cold, but only on cloudy winter days or after a frosty night. This makes them very sluggish and less of a threat. During summer or after a morning sunbaking, their blood and body temperatures can be as high as any endotherm. This gives them extra energy and so they are far more active and much more dangerous!
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Living or non-living? special holes in them called stomata that allow gases to pass in and out. The lungs of animals and the insides of a plant’s leaves need to be damp so that the gases can dissolve and move into their systems. Go to
Science Focus 2 Units 3.2 & 4.4
Living things produce wastes
Fig 4.2.5 Plants absorb energy from sunlight and use it to make food via a process called photosynthesis.
There are many chemical reactions constantly going on inside organisms. Along with the useful products, these reactions also produce wastes that become poisonous if they are not removed. Humans get rid of the products of cellular respiration (carbon dioxide and water) by breathing them out. We also get rid of excess water by urinating and sweating. Plants use their leaves to get rid of the waste oxygen produced by photosynthesis, and excess carbon dioxide from respiration. The removal of waste products from an Prac 1 p. 108 organism is called excretion. Go to
Science Focus 2 Unit 4.5
Science
Clip
Carnivorous plants Carnivorous plants, such as the sundews and the Venus Flytrap, don’t get any energy from the animals they trap. Instead, they gain nitrogen, which helps plants build the materials they need to live and grow. Most carnivorous plants live in soils that are deficient in nitrogen, getting it instead from the insects and small animals they trap. One of the largest carnivorous plants in the world, a type of sundew known as Drosera gigantea, which grows to about 1 metre tall, is found in south-west Western Australia.
Fig 4.2.6 Sundews are common in New South Wales. Their sticky tentacles trap and dissolve insects. Carnivorous plants do not gain energy from the insects they trap. Instead they gain valuable nitrogen.
Living things use air
Animals take in oxygen gas and use it for respiration. Mammals (including humans) and birds use lungs to take in air and the oxygen it contains. Most amphibians, like frogs, have lungs, but they also use their skin to absorb oxygen. Fish use gills to absorb oxygen gas dissolved in the water in which they swim. Plants take in oxygen for respiration and carbon dioxide for photosynthesis. Plants use their leaves to obtain the gases they need from the air. Leaves have
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Science Fig 4.2.7 Living things produce wastes—urine and sweat are two obvious wastes that animals produce. Some animals, such as the grey wolf, use their urine to mark out their territory.
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An ice-cold glass of yeast ‘urine’! Wastes from living things are sometimes used by other living things. A type of fungus called yeast uses sugar as its energy source and produces alcohol as waste. The alcohol is then excreted into the liquid that the yeast lives in, making wine, beer, whisky, vodka etc. in the process! Drinking alcohol is equivalent to drinking yeast ‘urine’.
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In 1676, Antoni van Leeuwenhoek used a very simple microscope to look at a sample of pond water. In it he saw tiny shapes. They were moving and so he decided that they were alive. He had used one of the characteristics of life to decide that his new discovery was a living thing.
4 .2
Is it living?
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Science
Fig 4.2.8 As winter approaches, temperatures drop (the stimulus) and the leaves of many trees change colour (the response).
Living things respond to stimuli Organisms react to changes in their environment. A change like this is said to be a stimulus. It triggers a response. If you hear a loud, unexpected noise then, most likely, you will jump. The stimulus is the noise and the response is you jumping. Plants also react to change, although their responses are far less obvious than those seen in animals. Plants on a windowsill grow towards the light and sunflowers follow the Sun across the sky throughout the day. In both cases, the stimulus is sunlight. The responses are growth and movement.
Living things move
Living things reproduce All living things are capable of reproduction. This means that they can make new individuals that are very similar to themselves. Reproduction can be sexual or asexual. Sexual reproduction generally requires two parents. Asexual reproduction needs only one parent.
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Male, female or both? Many organisms have both male and female reproductive parts. They are said to be hermaphrodites. Most flowering plants are hermaphrodites, as are slugs and snails. Barramundi is a type of fish found in northern Australia. It changes from being male to being female when it reaches the age of five! This means that all barramundi under five years are male, and older ones are all female.
The ability to move by itself is a basic characteristic of life. Although the movement of an animal is usually obvious, a plant also moves whenever it grows or responds to light. Other characteristics of life, such as responding to stimuli and feeding (collecting energy), often rely on movement.
Fig 4.2.10 Living things can reproduce. Otherwise, their type will soon become extinct.
Fig 4.2.9 Living things are able to move—a composite highspeed photo of a barn owl swooping on its prey.
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Living or non-living?
Living things grow As living things become older they grow. This means they get larger, more complicated or both. Some things grow very slowly, and some grow more quickly. As humans grow they change shape and proportions. A child’s head, for example, accounts for about onequarter of their length, whereas an adult’s head accounts for about only one-tenth of their body length. Fig 4.2.11 Living things
Living things are made from cells All living things are made up from at least one cell or from materials (referred to as tissues) that are made from cells. Cells are the building blocks of life and are so small that they cannot be seen without a microscope. An organism grows because it has created more cells. Go to
Science Focus 1 Units 5.2, 5.3, 5.4
grow. Many animals, such as snakes and some insects, need to shed their old skin or outer ‘shell’ (exoskeleton) in order to grow. This dragonfly has just emerged from the skin of its larval stage so that it can grow.
Prac 2 p. 109
Fig 4.2.12 All living things are made from microscopic building blocks called cells. Onion cells are shown here.
4.2
QUESTIONS
Remembering 1 List eight characteristics of living things. 2 List five ways animals take in oxygen. 3 Name three organisms that are heterotrophs and three that are autotrophs. 4 State the correct operating temperature for humans.
8 State the term used for the removal of wastes from an organism.
Understanding 9 Explain why ectotherms are more active after a morning lazing in the Sun.
5 Name the sugar that is the source of energy for both animals and plants.
10 Plants don’t seem to move much. Describe a situation in which a plant moves under its own power.
6 Name the reaction that:
11 Describe five physical changes that happen as we get older.
a uses energy from sunlight to produce food for plants b gives plants and animals their energy.
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7 Recall the word equation for each reaction in Question 6.
Unit
4.2
12 During the Apollo 13 mission, the astronauts had a problem with the device that removed carbon dioxide from the air they were breathing. Use the equations for photosynthesis and cellular respiration to: a Explain where this carbon dioxide came from. b Explain why we don’t have similar problems on Earth.
Applying 13 Identify whether the following things are living or non-living. In each case, give a reason for your choice. a a rabbit b a pen c an apple d a human e a car f a tree g a donkey
Fig 4.2.13 Are robots alive?
h a rubbish bin. 14 Identify a single word that describes how big a living cell is. 15 Identify one non-living thing that displays a characteristic of a living thing. 16 Identify the stimulus and the response for each of the following: a Your stomach grumbles when you smell a BBQ. b Leaves drop from a tree in autumn. c You get goose bumps when it’s cold. d A shark goes into a feeding frenzy when it senses blood. e A person runs up to a seagull and it flies away. 17 Although all definitely living, the following people all fail to meet one of the characteristics of life. For each, identify the characteristic they fail to meet and explain why they can be still considered to be living. a It is unlikely that Year 7 students have had a baby of their own. b Elderly men and women often get shorter as they age. c A protester has been on a hunger strike for a week. d Some people often urinate only once a day in summer.
Evaluating 18 Some robotic toys seem to behave as if they are alive. For example, they indicate when they need ‘feeding’. a List the characteristics of life they show and those that they do not show. b Evaluate whether these toys could be alive.
Creating i 19 Imagine that you are in radio contact with an astronaut on the Moon. She has just stood in a strange, squelchy mess and thinks it may be alive. Design a procedure she could follow to find out if it is alive or not. 20 This is the story about your average person. He does the same sort of things that we all do, but there is one big difference. Aliens from another planet are watching this person! They are trying to make up their minds if he is alive. This is what they see him doing one morning. Jack wakes up when his loud alarm clock rings at 6.45 a.m. He reaches across to the bedside table and turns it off. He also turns on the bedside lamp. The bright light from the lamp makes him blink. After a short while, Jack gets out of bed and walks to the bathroom. He goes to the toilet, takes a shower and walks down the stairs. He can smell toast cooking in the kitchen and he breathes in deeply to take in the wonderful smell. After eating his breakfast, he leaves the house and walks to the tram. The cold air makes him cough as he gets on the ferry to go to work. Construct a table to summarise the things that Jack did during the morning that the aliens could use to prove he was alive. L 21 The year is 2500 and Earth has become a favourite holiday destination for aliens. Design a travel guide for these aliens so that they can identify if what they are looking at is living or non-living. All the basic Earth life forms still exist, but there are also some very life-like robots. L
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Living or non-living?
4.2
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find what NASA scientists discovered recently that suggests that there once used to be life on Mars. Explain how this evidence relates to the characteristics of life.
4.2 1
PRACTICAL ACTIVITIES
Characteristics of life
Aim To observe excretion in plants.
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2 Research why space probes are usually programmed to look for evidence of water rather than ‘little green men’ on other planets.
Safety Some plants (e.g. oleander, rhus) are known to cause allergic reactions in some people.
Part B 1 Smear a thin layer of petroleum jelly on both sides of a freshly picked leaf. Use string to suspend it from a retort stand so that air can get to both sides. 2 Do the same to an identical leaf, but this time smear only the top side of the leaf with jelly. 3 Smear the bottom side of a third leaf with jelly. 4 After a few days, record your observations of each leaf.
Equipment • • • • • • •
plastic bag string retort stand bosshead and clamp petroleum jelly access to a living plant three identical fresh leaves
Method Part A 1 Go outside and tie a plastic bag over a branch of fresh leaves. Make sure the leaves are still attached to the plant and that the bag is high enough not to be tampered with. 2 Leave it overnight and record what you observe the next day.
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Questions 1 Water was probably collected in the plastic bag set up in Part A. Identify where the water came from. 2 Identify whether cellular respiration or photosynthesis in a plant produces water. 3 Compare the three leaves in Part B. Which was the most shrivelled and which retained its shape best? 4 The petroleum jelly blocks the stomata on the leaf, stopping them from losing water. Identify which side of a leaf has the most stomata. 5 Predict what would have happened if Parts A, B and C were repeated using a rock and not a living thing.
Unit
2
1 Place about 1 centimetre of cotton wool in the bottom of each container. Moisten it with a little water.
Mustard seeds
Aim To observe the changes that occur during growth and development of a living thing.
Equipment • • • • • • •
2 Add ten mustard seeds to each cotton wool.
4.2
Method
3 Place plastic wrap over the top to stop the seeds from drying out. 4 Use the pin to make a small airhole in each piece of plastic wrap.
three small glass or plastic containers cotton wool aluminium foil sticky tape 30 mustard seeds cling wrap pin
5 Cover one of the containers completely with the aluminium foil so that no light can get in. 6 Cover another container in a similar way, but this time leave a 1 centimetre squared window in the foil near the top of the container. 7 Leave the containers in a safe place for several days.
hole cling wrap
8 Remove the foil and note any difference between the three containers of seeds.
Questions 1 Sketch your results, labelling each container. 2 Explain what this experiment has shown. container
mustard seeds
moist cotton wool
Fig 4.2.14
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Unit
4.3
context
From kingdom to species
There are an estimated 13 to 14 million different types of organisms currently living on Earth. Although every organism is unique, their similarities and differences allow them to be classified into groups. Similar organisms are
placed in the same group, with each group having its own special characteristics. The process that sorts all living things into groups is called taxonomy. A scientist who does this is a taxonomist.
Classifying living things It is usually easy to classify an organism as either a plant or an animal. However, to make sense of the huge variety of plants and animals, they need to be sorted into much smaller groups. Scientists use the way living things are ‘built’ to help split them into groups. This way, organisms that have a similar ‘body plan’ or structure will be in the same group, whereas organisms with different ‘body plans’ or structures will be in different groups. All living things are first organised into broad groupings known as kingdoms. They are then organised into smaller and more specific groupings called phylum, group, class, order, family, genus and, finally, species. Species is the smallest and most specific grouping of all.
Fig 4.3.1 Although biologists believe that there are up to 14 million different types of organisms living on Earth, only 1.7 million different species have been identified!
Kingdoms Kingdoms are the largest groups into which organisms are sorted. Animals make up one kingdom and plants make up another. But there are lots of other organisms that don’t fit neatly into the animal nor plant kingdoms. Fungi (e.g. mushrooms, toadstools and yeast) may look like plants but are very different from them. Plants use photosynthesis to produce their food (glucose), whereas fungi do not. They gain their glucose by breaking down
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living or dead matter. Hence, fungi need a kingdom all of their own. Bacteria and seaweeds need their own kingdoms too, since they also do not fit neatly into any of the other kingdoms. For this reason, all living things are classified using five kingdoms—animal, plant, fungi, protists and monera.
all life Kingdoms contain lots of different types of organisms that share only a few general features.
Organism = dog Kingdom = Animal (it is an animal) Phylum = Chordata (it has a spinal cord)
kkingdom phylum
Class = Mammalia (it is a mammal) Order = Carnivora (it’s a meat eater)
class order family genus Species are very specific. Each species contains only one type of organism.
species specie ecie
Family = Canidae (it is a dog) Genus and species = Canis familiaris (it is a tame household pet)
all living things
fungi plants e.g. mushroom e.g. rosebush animals e.g. kangaroo
Animals such as humans, echidnas, lizards and salmon have spinal cords running down their back. Others like slugs, squid and jellyfish do not. This basic structural feature is used to split the animal kingdom into vertebrates (with backbones/cords) and invertebrates (no backbones/cords). These two groupings are referred to as phyla (singular: phylum). In a similar way, some plants (e.g. grass, daisies and palm trees) have ‘transport systems’ made of special cells arranged along their trunks and stems. Other plants (e.g. mosses) do not. This feature is used to split the plant kingdom into two major groups—those with the transport systems (vascular plants) and those without (the bryophytes).
4.3
Classification starts with organisms being grouped into kingdoms. It ends with them being grouped into species.
Unit
Phyla and major groups
Fig 4.3.2
Genus As organisms are classified into more specific groupings, the number of living things in each group gets smaller. However, the organisms in each group become more and more similar in that they share more and more features. A genus is a group of organisms that share many, many features. Wolves, foxes and dingoes are all related to each other and to pet dogs—all belong to the genus Canis.
monera e.g. bacteria protists e.g. seaweed
Fig 4.3.3 All living things can be classified using five kingdoms.
Fig 4.3.4 Pet cats, tigers, lions, cheetahs and pumas are all different, but share many similarities. All belong to the genus Felis.
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From kingdom to species
Species The final, smallest and most defined group in the classification scheme is species. Although not identical, all the organisms in a species closely resemble each other. They are so similar that they can mate with each other and produce young that can also reproduce at some later stage. This is referred to as being fertile. A species is a group of similar organisms that can produce fertile young. Humans might appear different and come from different races, but we all belong to the species Homo sapiens. Despite our differences, we are similar enough to be able to reproduce; for example, a Japanese woman and a Scottish man can have a baby together because they are part of the same species. Likewise, two dogs of different breeds can produce healthy and fertile puppies because they belong to the same species, Canis familiaris. In contrast, a tiger and a frog cannot mate and produce young. Neither can a tiger and a cheetah. They all belong to different species.
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Fig 4.3.6 Each different type of organism is given a different binomial name. Organisms belonging to the same species have the same binomial name.
Cygnus atratus
Genus
Species
The ‘family’ the animal belongs to (in this case, swans)
The specific grouping within the family (in this case, black swans)
always starts with a capital letter
always spelt in lower case
New animals daily! New living species are being discovered constantly. Lost in a snowstorm in Tibet in 1995, French and British scientists found a species of wild horse that had previously been seen only in prehistoric cave paintings. Although the locals knew it existed, no-one in the outside world did! Sometimes, fossils of previously unknown extinct species are discovered. One recent discovery was a million-year-old, sabre-toothed cat skull, taking the number of known species to three.
always in italics.
always in italics.
Naming species Each species is given a unique, scientific name referred to as its binomial name. For example, many different species of gum trees are found in New South Wales. Four species are: Eucalyptus camaldulensis Eucalyptus ovata Eucalyptus pauciflora Eucalyptus maculata All gum trees belong to the same general family and so both belong to the same genus Eucalyptus. Different types of gum trees belong to different species and so each different type has its own specific name. Worksheet 4.1 Sorting
Fig 4.3.5 Despite being different species, a horse and a donkey are similar enough to be able to interbreed. Their offspring is a mule. A mule is not fertile but is sterile.
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Worksheet 4.2 Naming
(the river red gum) (the swamp gum) (the snow gum) (the spotted gum).
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The genus Homo Humans belong to the species Homo sapiens, meaning ‘intelligent man’. Other humans once belonged to the same genus as us—the now extinct Homo neanderthalensis (Neanderthal man), Homo erectus (‘upright man’) and Homo habilis (‘handy man’).
Unit
QUESTIONS
Remembering 1 State the meanings of the terms taxonomy and taxonomist.
Creating
3 State which of the groups in Question 2 has the most detailed description of the organisms in it.
14 A mnemonic is a silly sentence that helps remind you of something. You could, for example, remember the order in which organisms are classified (kingdom—phylum—class— order—family—genus—species) by, instead, remembering ‘Kind people can often find green shoes!’ Create your own mnemonic to represent the order of classification from kingdom to species.
4 Organisms are grouped into five kingdoms. List them.
15 The complete classification of a human is:
2 List these groups from the one that contains the greatest number of organisms to the group that contains the least: family, species, phylum, kingdom, genus, order, class.
5 State the structural feature that splits animals into two phyla.
Kingdom: Animal
6 State the two major groups into which plants are classified.
Phylum: Chordata (vertebrate)
Understanding
Class: Mammalia (mammal)
7 Explain how you know a terrier and a poodle belong to the same species.
Order: Primata (primates)
8 Explain how you know that a horse and a donkey are different species.
Genus and species: Homo sapiens
9 Describe how the unique scientific name for every living thing is created. 10 A subphylum represents a group smaller than a phylum but bigger than a class. Use this information to explain what you think a subclass represents.
Applying 11 The scientific name of the Tasmanian devil is Sarcophilus harrisii. Identify its:
Family: Hominidae (hominids) Use this and information from the text to construct a table that shows the similarities between a human with a dog and the differences between them. 16 You have just discovered a new species! You must now report your findings to the AS4NT (The Australian Society for Naming Things). a Outline the characteristics of your new organism. Be creative! b Construct a diagram or model of your new species.
a genus
c Classify your organism by placing it in a kingdom.
b species.
d Further classify your organism by giving it a name using the binomial naming system.
12 Identify important characteristics shared by all animals in the genus Felis (the cat family).
4.3
4.3
Analysing 13 Four native plants found in the Blue Mountains are Banksia ericifolia, Eucalytpus punctata, Acacia floribunda and Banksia marginata. Analyse this information to: a State the number of species this represents. b Name the plants that are in the same genus. c Predict if botanists could ever cross any of these plants to make new seedlings.
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Science Focus
Grouping living things
Prescribed Focus Area: The history of science On each continent, indigenous peoples established their own keys to classify the living things around them. Many early keys were based on whether the animals or plants were useful as a food source, a source of fur or natural fibres that could be woven or whether they were part of their spirituality. Animals, for example, were sometimes classified as wild or domesticated. Other classification keys were based on whether the animal lived on the land or in the sea. The term ‘fish’, for example, used to refer to anything swimming or anything that lived in the sea. Even today, creatures such as jellyfish, shellfish, crayfish and starfish include ‘fish’ in their names, despite them now being classified as creatures other than fish.
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107 Reindeers!
Likewise, shellfish and crustaceans (maypal) have at least ten categories. These are determined by how they attach to rocks, how they move about and whether they live amongst rocks or on a reef. Four distinct subgroups are: gundapuy attached to reefs or rocks warranggulpuy move over the outer surface of rocks lirrapuy move around the edges of rocks djinawapuy attached beneath rocks or inside coral.
Carl Linnaeus In 1735, the Swedish naturalist Carolus (Carl) Linnaeus (1707–1778) proposed a systematic way of grouping and naming living things. He classified all living things as either animal or plant. He then further divided all animals into six classes: Mammalia (mammals), Aves (birds), Amphibia (amphibians and reptiles), Pisces (fish), Insecta (insects) and Vermes (all the other invertebrates). In recognition of his pioneering work, Linnaeus was made a noble in 1761. From then on, he was known as Carl von Linne.
The Laps are the indigenous people of Scandinavia. Reindeer are important to them and so they have more than 107 different categories for them! Their native Saami language classifies them according to their age, condition, body shape and the shape of their antlers!
Indigenous Australian classification Aborigines traditionally classify animals according to their usefulness, where they live or how they were used. Penguins and emus, for example, are placed in the same category as kangaroos—both are ground-dwelling sources of meat and so they are grouped together. Other birds are placed in the ‘flying food source’ category. In some instances, an animal has no Aboriginal name because it was not used for anything. Some Aboriginal tribes in northern Australia name plants according to their uses or their locations, such as a swamp. In these tribes, fish (guya) are also classified according to where they live. This gives five categories: garrwarpuy living near the surface ngopuy living near the bottom mayangbuy living in rivers raypinbuy living in freshwater gundapuy living among rocks and reefs.
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Fig 4.3.7 While on a scientific expedition to the far north of Finland in 1732, Linnaeus nearly fell into an icy crevasse. He saved himself from near-death and went on to discover 100 new plant species on this expedition.
Unit
4.3
Scientists still argue over how many kingdoms there should be. Some claim that the protists should not have their own kingdom and that, instead, they should be split amongst the animal, plant and fungi kingdoms. Recent research suggests that the monera kingdom could also be split to form Science two new kingdoms. Although the argument continues, most accept that there are five basic kingdoms Weird names! (animal, plant, fungi, protists and Science Focus 1 presents monera). nine main classes of animals, Scientists also argue about how but there are other obscure many phyla and classes there are. animals with their own specialised classes. Sponges, There is no hard-and-fast definition for example, have their own for a phylum and so scientists also class (ponifera), whereas argue about its definition, too, starfish belong to another sometimes merging the idea of class class called echinoderms. and phyla together. For these Another small class is called reasons, there may be up to 89 priapulida, otherwise known as penis worms! different classes.
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Monstrous humans! Fig 4.3.8 Although there is no evidence for unicorns (white horses with single long, spiralled horns growing from their foreheads), unicorn-like horns are found on narwhals (rare arctic mammals that resemble dolphins) and some seahorses.
Linnaeus originally left room in his kingdoms for mythical animals such mermaids, satyrs, unicorns and ‘monstrous humans’. Room was left for Homo ferus (humans who walked on all fours like dogs) and Homo caudatus (humans who had a tail)!
Many students of Linnaeus went on to explore the world for new plants and animals. One, Daniel Solander, accompanied Captain James Cook on his first journey (on which he discovered the east coast of Australia in 1770). He and Joseph Banks brought back to Europe the first ever collection of Australian plants. Botany Bay (originally called Stingray Bay, then Botanist Bay) in Sydney was also named by them. Although some changes were made by the French zoologist Georges Cuvier in the early 1800s, the basic system as developed by Linnaeus is still used today.
Arguments in science Linnaeus and Cuvier proposed their kingdoms and classes based on the information they had available at the time. The development of the microscope, however, revealed characteristics of organisms that had never been seen before, particularly in plants and microorganisms such as bacteria. With this new information, new kingdoms were needed and others could be re-organised.
Fig 4.3.9 Until Linnaeus, common dandelions were known as naked ladies and a variety of other names. Using his binomial system, they became Taraxacum officinale.
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Grouping living things Naming organisms Before Linnaeus, everyone had their own names for plants and animals. Although scientists generally used Latin to name organisms, their naming was clumsy and inconsistent. Some scientists, for example, knew a common wild rose as Rosa sylvestris inodora seu canina, whereas others knew it as Rosa sylvestris alba cum rubore folio glabro.
Some scientists had even invented their own binomial naming systems, but none had ever used them consistently. Linnaeus was the first. He began to consistently name plants using his binomial system in 1753 and animals in Science 1758. Still used today, his system always gives the same name to the same Odd naming organism and related Linnaeus used his binomial names to related system to name over 13 000 organisms. The common species of plants and wild rose is now known as animals. Much of his naming was based on body parts Rosa canina.
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from the human reproductive system!
4.3
STUDENT ACTIVITIES
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find how other indigenous groups classify the living things around them. You might investigate how the Yolngu of Milingimbi (Northern Territory) classify birds or find out more about how the Laps classify their reindeer. Summarise your findings by producing a key or by listing the main points used in the key. 2 Research the lives and work of a taxonomist such as Carolus Linnaeus, Georges Cuvier, Daniel Solander, John Ray, Theophrastus, Joseph Banks, Thomas Nuttall, Caspar Wistar, Antoine Laurent de Jussieu or Colin Groves. Find: • biographical information, such as their dates and places of birth and death, their education and positions held • what they did and where they went to carry out their research • their contributions to taxonomy, zoology or botany.
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Summarise your information and produce one of the following: L • an information card • a two-minute talk to the class • a short written entry for the book Who’s Who • a short TV interview with the person.
Unit
4.4
context
Classification of animals
Animals are classified into groups according to their structural features. Structural features describe how the animals are physically made up. If animals are grouped together then it means that they have a common
structure, sharing certain features (such as wings or scales). The main structural feature used to classify animals is whether they have a backbone or not. The study of animals is known as zoology.
Vertebrates Vertebrates are animals that have a spinal cord running down their backs that carries nervous messages from their brain. This spinal cord is sometimes enclosed in a bony structure known as a spine. Because of this cord (technically known as a notochord), vertebrates are also known as chordates and are placed in the phylum chordata. There are five major classes of vertebrates/chordates— mammals, reptiles, amphibians, birds and fish. Fig 4.4.1 Humans have a very obvious spine. Humans are vertebrates. Animals without spines are known as invertebrates.
animal kingdom
vertebrates
invertebrates
backbone
no backbone
fish
birds
amphibians
mammals
cnidarians
worms
arthropods
millipedes
insects
centipedes
reptiles
Fig 4.4.2 There are five different classes of animals. The study of animals is called zoology.
molluscs
crustaceans
arachnids
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Classification of animals Mammals Most of the large animals you see every day are mammals. Your classmates and family, your pet dog or cat, the mouse in the cupboard, and the horses, cows and kangaroos in the paddock are all mammals. Mammals: • feed their young on milk from mammary glands (mamma = breast in Latin, hence the name ‘mammals’) • have hair. Sometimes this hair is not obvious (e.g. whales) or is obvious only on newborns (e.g. dolphins). In other mammals, the hair takes on another form—as wool (e.g. sheep), fur (e.g. lions) or even spikes (e.g. echidnas and porcupines) • are endotherms (i.e. warm blooded), generating their own heat using the energy from the food they eat. The mammals are split further into three orders— placental mammals, marsupials and monotremes.
Placental mammals Placental mammals give birth to developed young. Examples are humans, sheep, flying foxes, mice, dolphins and whales.
Fig 4.4.4 Most Australian mammals are marsupials.
Marsupials Marsupials give birth to tiny young that then continue to grow in a pouch. Examples are kangaroos, wallabies, koalas, wombats and possums. Monotremes Monotremes lay eggs that hatch after a few days. The young then develop in a pouch. There are only three living species of monotreme— the short-beaked echidna and platypus, which are found in Australia, and the long-beaked echidna, which is found only in Papua New Guinea. Fig 4.4.3 All mammals produce milk for their young.
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The first platypus When the first (dead) platypus was sent to England in 1799, scientists thought it was a hoax because it was so different from the animals they knew. They thought this new ‘fake’ animal had been stitched together from the body parts of other animals. The most likely were a duck (providing the bill and webbed feet), a mole or otter (the furry, streamlined body) and a beaver (its flat tail)! This first platypus still exists, being stored in the ‘Mammal Tower’ in the Natural History Museum in London. In the Aboriginal Dreaming stories, the first platypus was born after a female duck named Daroo met a male water rat named Bilargun. Daroo soon laid eggs that then hatched. The babies had Daroo’s bill and webbed feet and Bilargun’s fur and flat tail.
Fig 4.4.5 The echidna and platypus are the only types of monotreme mammals currently living on Earth.
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Reptiles Some of the most fearsome and dangerous animals are reptiles. Snakes, crocodiles and alligators are all reptiles. Australia has its fair share of killer reptiles. The estuarine crocodile (sometimes incorrectly known as the saltwater crocodile or ‘salty’) is rightly called a maneater, and snakes such as the death adder, taipan, brown snake and tiger snakes are so venomous that they can quickly kill. Other reptiles are far less feared—lizards, tortoises and turtles are all reptiles too.
4.4
Science All birds have feathers and wings. These structural features allow most birds to fly. Those Ouch! that can’t (e.g. penguins, emus, Kiwis are flightless kiwis and ostriches) have birds native to New Zealand. Although the feathers and wings that are kiwi is only about the adapted to better suit the size of a chicken, it environments in which they lays an egg weighing live. About 900 different species one-quarter of its of bird have been identified in body weight! Australia. Birds: • breathe using lungs • have scales on their legs and feet • lay hard-shelled eggs, from which their chicks will hatch • are endotherms, generating their own heat (warm blooded).
Unit
Birds
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That’s big! Fossils have been found in Australia of a species of goanna (a type of monitor lizard) that was over six metres long! The largest living monitor lizard is the Komodo dragon, which lives on Komodo Island in Indonesia and is less than half its size. Taronga Park Zoo in Sydney has Komodo dragons on display.
Fig 4.4.7 Reptiles are ectothermic, making them sluggish when cold and much more active (and dangerous) when warm.
Reptiles: have dry scales have lungs lay soft, leathery, waterproof eggs are ectotherms (with variable blood temperature). Reptiles cannot generate their own heat and must warm up by lying out in the Sun. Their body temperatures fluctuate from cold in the morning to as high as our own after some hours in the Sun. Unlike us, they cannot retain this heat and quickly cool down overnight and in cold weather. • • • •
Fig 4.4.6 All birds have wings and feathers, even if they never fly. Penguins have wings that are shaped like flippers and slicked-down oily feathers to repel the freezing water in which they swim in search for food.
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Toad ≠ frog Toads and frogs look roughly alike but are subtly different. Frogs prefer to live near water, have webbed feet, smoother skin and longer back legs that allow them to jump further than toads. Toads are usually drier, lumpier and tend to live on dry land.
Amphibians Amphibians are unique amongst the vertebrates in that they have two stages to their life—many live their early life completely underwater and the rest of their lives breathing above water. Frogs and toads are amphibians. Both start life as a tadpole with gills and slowly change into an adult frog with lungs.
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Classification of animals
Fig 4.4.8 Like all amphibians, frogs live a two-stage life. After hatching, they first live as a tadpole, slowly changing into a frog.
Amphibians: • hatch from eggs and then live a two-stage life • have a thin skin that would dry out if they did not live in a damp area • need to go back to water to reproduce because their eggs do not have a waterproof coating • are able to breathe through their skin, as well as with their lungs • are ectotherms (absorbing their heat from their surroundings).
Cartilaginous fish These fish do not have bones. Instead, their skeleton is made from firm, rubber-like cartilage (the same material that makes up the squashy part of the tip of your nose). Like bony fish, cartilaginous fish have paired fins—if there is a fin on the right side of their body, then there will be a matching fin on the left side. Sharks and stingrays are examples of cartilaginous fish.
Fish All fish have gills and are ectotherms. Most lay eggs. There are many thousands of different species of fish. They can be divided further into three groups—bony, cartilaginous and jawless fish. Bony fish These fish have a skeleton of bone. Most fish fall into this class, which includes barramundi, bream, clownfish, trout and goldfish.
Fig 4.4.10 The great white shark is a cartilaginous fish. Cartilage forms its skeleton.
Jawless fish These fish also have a skeleton of cartilage, but do not have any paired fins. There are about only 45 species of this type of fish. An example is the lamprey.
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Fig 4.4.9 Most of the fish sold in a fish shop are bony fish.
Prac 1 p. 125
vertebrates (mammals)
vertebrates (fish, birds, amphibians, reptiles)
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That’s deadly! Although the funnel-web spider is found throughout New South Wales, one of the most deadly species lives within 100 kilometres of Sydney. Females can live for 20 years, spending most of that time in their web in the ground or in stumps or tree trunks. The males are some of the most poisonous animals on Earth and have caused numerous deaths—one two-year-old child dying within 15 minutes of the bite. Luckily, there is now an effective antivenom medication.
4.4
Arachnids Spiders, scorpions, mites The great majority of animals on Earth have no backbones. and ticks are all arachnids. They tend to be small and numerous, and include insects, Most arachnids live on spiders, crabs, snails and jellyfish. Animals without land but some can live in backbones are known as invertebrates. The invertebrates the water. are then split into many different phyla. The main ones Arachnids have: are the arthropods, cnidarians, molluscs and worms. • no antennae Fig 4.4.11 There are far • only two body more invertebrates than segments vertebrates on Earth. • have four pairs of legs invertebrates (eight in total) • no jaws.
Unit
Invertebrates
Arthropods About 75 per cent of all known animals are arthropods. They form the largest animal phylum and are found everywhere—on land, in the air, and in all water systems. All have segmented bodies, paired jointed legs and an exoskeleton. An exoskeleton is a hard, outer covering that acts as an external skeleton. The arthropods form the largest of the animal phyla. The arthropods are split into five major classes—insects, arachnids, crustaceans, centipedes and millipedes.
Fig 4.4.13 When disturbed, funnel-webs attack on sight and their fangs are incredibly strong, easily piercing leather gloves. Like all spiders, funnel-webs are arachnids.
Insects There are close to one million different species of known Crustaceans insects and many more are likely to be found in the future. Crabs, prawns, shrimp, yabbies and lobsters are There are more species of insects than any other living examples of crustaceans. thing. Flies, mosquitoes, cockroaches and fleas are Crustaceans: examples of insects. • mostly live in the water Insects have: • have two pairs of antennae • one pair of antennae • breathe through gills. • bodies divided into three sections—the head, thorax and abdomen • three pairs of legs (six in total) on their thorax. abdomen head thorax
hind leg foreleg
midleg
Fig 4.4.12 All arthropods have segmented bodies. Insects have three segments.
Fig 4.4.14 A yabby is a crustacean. Its segmented body is clear in this photo.
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Classification of animals Centipedes and millipedes Centipedes and millipedes live on land, have segments along their whole body and have legs attached to each segment. Although they might look similar, some key structural features can be used to tell them apart. Centipede
Millipede
Body shape
Flattened
More rounded
Legs
One pair (two legs) per segment
Two pairs (four legs) on most segments
Antennae
One long pair
One short pair
Molluscs The molluscs make up the second largest phylum in the animal kingdom. Most molluscs live in the water (e.g. octopuses and squids), but a few types live only on land (e.g. snails and slugs). Molluscs: • have soft bodies, sometimes covered with a shell • have well-developed internal organs • have a large, muscular ‘foot’ or fleshy tentacles that are used for movement.
Fig 4.4.15 Centipedes have flattened bodies, long antennae and one pair of legs per body segment.
Fig 4.4.17 An octopus is a mollusc.
Cnidarians
Fig 4.4.16 Millipedes have two pairs of legs on each segment of their bodies. This is the African giant millipede, which can grow to lengths of over 30 centimetres.
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Cnidarians live mostly in the sea, but some are found in freshwater. All cnidarians have a bag-like body with only one opening through which they take in food and release their body wastes. This opening is surrounded by tentacles, which are covered in stinging cells that can be used to kill prey. About 10 000 different species of cnidarians have been identified so far. Cnidarians (pronounced nid-air-ee-ans) can be split further into two groups—polyps and medusas.
Worms There are three different groups of worms—roundworms, flatworms and segmented worms. Roundworms Roundworms have long cylindrical bodies that are in one piece without segments. They have a digestive tube with a mouth and anus. Some roundworms are parasitic, living off (and weakening) other living animals. Others live ‘free’ in water or damp soil. Examples of roundworms are threadworms, hookworms and the parasitic roundworms found in the intestines of humans, dogs, pigs and horses.
4.4
Fig 4.4.18 Coral polyps are living things called cnidarians.
Unit
Polyps Polyps are cnidarians that attach themselves to something like a rock. Corals and anemones are examples of polyps.
Flatworms Flatworms are similar to roundworms in that they also can be parasitic or ‘free’. They differ in that they have flat bodies instead of round ones. If they have a digestive system, it has only one opening, which acts as both mouth and anus. Flukes and tapeworms are examples of flatworms. opening acts as both mouth and anus
Medusas Medusas are cnidarians that can swim about freely. Jellyfish are medusas. Many are harmless, whereas some, like the box jellyfish, can kill. The stinging cells of others, such as bluebottles, inject a mix of chemicals that leave painful, raised red welts wherever they touch the skin.
hooks anchor the worm to the internal wall of the gut
Fig 4.4.20 An image obtained by a scanning electron microscope (SEM) of the head of a dog’s parasitic tapeworm.
Segmented worms Also known as annelids, segmented worms can be found both on land and in water. They have welldeveloped body systems and bodies with multiple segments. Examples are leeches and earthworms.
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What do I do? It is currently recommended that bluebottle stings are soaked for about 20 minutes in hot water (say under a hot shower or in a bath). The traditional vinegar solution does little since the bluebottle injects a chemical irritant that is neither acid nor base.
Fig 4.4.19 Jellyfish are medusas, a type of cnidarian.
Worksheet 4.3 Classifying
Fig 4.4.21 The segments are clear on the body of this leech. Some leeches are used in medicine to suck out blood from clots and to encourage blood flow into newly attached limbs after microsurgery.
Prac 2 p. 126
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Classification of animals
4.4
QUESTIONS
Remembering 1 State the name used for the study of animals.
c are ectotherms.
2 State the main feature biologists use to classify animals.
Analysing
3 State the phylum to which vertebrates belong.
15 Classify the following animals as vertebrates or invertebrates:
4 List the main phyla of the invertebrates.
a hamster
5 State how many species of insects are known and how many that scientists think probably exist.
b snail
6 List three characteristics of each of the following classes: a amphibians b birds c fish d mammals. 7 State: a the two types of cnidarians b the largest animal phylum c an example of a mollusc d two invertebrates that live on land and two that live in the water.
Understanding 8 Clarify what is meant by the term parasitic. 9 You have just discovered a new species of reptile. Predict what features it would have.
c mouse d dung beetle e grey nurse shark f rabbit g earthworm. 16 Contrast the following by listing their main differences: a the three types of worms b bony and cartilaginous fish c centipedes and millipedes d reptiles and amphibians e arachnids and insects f monotremes and marsupials. 17 Jimbia are animals with hair and lay eggs. Their young then develop in a pouch. Use this information to classify the jimbia.
10 Millipedes have many more legs than centipedes, despite often being about the same length. Explain why.
18 Figure 4.4.1 shows that humans are vertebrates; however, there is something wrong with this human. Carefully analyse the photo and suggest what it is.
Applying
Evaluating
11 You have discovered a new organism. It has the same classification as an animal with six legs and wings. Identify the other features you would expect the new organism to have. Explain your answer.
19 Scientists predict that there are far more types of animals and plants yet to be identified. Justify their predictions by listing reasons why different types of organisms may not yet have been found.
12 You are watching an animal and it lays an egg.
20 There are almost no fossil remains of invertebrates, particularly ones like jellyfish, flatworms and octopus. Propose a reason why.
a Identify into which groups it could be classified. b Explain what other information you would need to place it in the correct group. 13 Identify the class of animals that: a breathe through their lungs and skin b have stinging cells c feed their young milk d breathe through gills e lay soft, leathery eggs. 14 Identify three classes of vertebrates that: a lay eggs
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b have scales
Creating 21 The first European settlers in Australia were very surprised by some of the animals they found—kangaroos, koalas, wombats, Tasmanian tigers and devils, echidnas and platypus looked weird to people who had never seen them before! Imagine you are one of those first settlers. You have just seen an Australian animal for the first time. Write a letter describing the animal to someone in England who has never seen it. Note that you cannot use its real name since it has not yet been named. L
Unit
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find information about the system used to classify books in the school library. Propose what code number would be given to this textbook if it were in the library.
4.4
4.4
e -xploring We b
Desti nat To find out more about the classification of the animal kingdom (and others), a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
ion
2 Gather images of examples of animals that belong to each of the animal groups mentioned in this unit. Present your images as a poster or PowerPoint presentation, making it clear to which kingdom and phyla they belong. L
4.4 1
PRACTICAL ACTIVITIES
Fish dissection
Aim
anus
cut
To investigate the internal structure of a vertebrate.
!
Safety 1 Wear safety goggles, plastic gloves and an apron or laboratory coat. 2 Dissecting equipment (scalpels, scissors and tweezers) is extremely sharp and can cause serious cuts and eye injuries.
Start your cut at the anus. cut here to expose the internal organs
ribs dorsal fins caudal fin
3 Only pick up the scalpel when you are ready to make a cut and put it back down as soon as you are finished.
kidney
vertebral column
dder stomach air bla gonad
one perch (or similar fish; e.g. mackeral, bream) dissecting instruments dissecting board newspaper apron or laboratory coat plastic gloves safety goggles
r
live
heart anal fin
anus
Fig 4.4.22
pectoral fin intestine
bladder
Equipment • • • • • • •
gall bladder cranium
4 Wash all equipment, the board and bench according to your teacher’s instructions. 5 Wash your hands thoroughly after the prac.
oesophagus
pelvic fin
pelvic girdle
Method 1 Cover your workbench completely in newspaper and place the dissecting board on top. 2 Put your protective clothing on and get your dissecting instruments ready, placing them neatly on one side of the board.
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Classification of animals 3 Place your fish on the board and make careful observations of its exterior (e.g. How many fins does it have and where are they placed?) 4 Turn your fish over and identify the anus. As shown in Figure 4.4.22, make a shallow cut along the belly of the fish, starting at the anus and working towards the head. (You may need to scale some sections first.) Be careful not to disturb the arrangement of its inner organs. Gradually make the cut deeper.
Questions 1 Classify this fish as bony, cartilaginous or jawless. 2 The air bladder can inflate and deflate. Explain how this helps the fish. 3 Were any organs difficult to identify? 4 Describe the features of the fish that make it suited for life in the water.
5 Use Figure 4.4.22 to identify as many of the fish’s organs as possible. Leave the head until last.
2
Preserved invertebrates
Aim To examine various preserved invertebrates, noting their characteristics.
!
Safety Do not use any specimens that are preserved in formalin.
Equipment • preserved invertebrate specimens
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Method Sketch at least three specimens and list the characteristics of each organism underneath its sketch.
Questions 1 Did any of the animals you studied have an exoskeleton? List any that did. 2 Use information from this unit to identify as many invertebrates as possible. Try to identify the class and order to which each belongs (e.g. spider = arthropod, arachnid).
Unit
4.5
context
Plants and other kingdoms
Not all organisms fit into the animal kingdom. Other kingdoms are needed for plants, fungi, seaweeds and microscopic
organisms, such as bacteria. The study of plants is called botany.
Classification of plants Plants are classified according to several characteristics—their physical features and how they feed and reproduce. The animal kingdom is split into two groups—vertebrates and invertebrates. The plant kingdom is also split into two groups—vascular plants and bryophytes.
Vascular plants Vascular plants contain vascular bundles, which are cylindrical arrangements of specialised cells that transport liquids and nutrients around the plant. Most plants are vascular, the main classes being the flowering plants, conifers, cycads, ginkgos and ferns. Go to
Science Focus 2 Unit 3.1
Prac 1 p. 133
Fig 4.5.2 The study of plants is called botany.
Flowering plants
Fig 4.5.1 Most plants have well-defined transport systems to carry around water and nutrients. These plants are known as vascular plants.
The flowering plants (referred to as angiosperms) make up the largest class of vascular plants by far. The flowers of angiosperms range from large, brightly coloured blooms to small, dull ones that don’t really look like flowers at all. Seeds develop inside these flowers and, some time later, a part of the flower itself develops into fruit. Hence, fruit contain the seeds needed for an angiosperm to reproduce. Daisies, gum trees, wattles and fruit trees (such as apples and pears) are all examples of angiosperms.
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Plants and other kingdoms Male anther filament
petal
Conifers stamen
Female stigma pistil style ovary
receptacle
ovule
sepal
Fig 4.5.3 Most flowers contain reproductive organs of both the male (the stamen) and the female (pistil and ovule).
Conifers also produce seeds, but not in flowers or fruit. Instead, they produce seeds on the scales of a woody cone. Conifers generally prefer cooler climates and so only a few species occur naturally in Australia, the main species being the huon, kauri pine, bunya and hoop pines.
Cycads Unlike conifers, cycads thrive in tropical environments. Cycads produce seeds in cones. Although Australian Fig 4.5.6 Cones contain the seeds of a conifer. Their cycads look something like leaves look like needles. palm trees, they are a very different plant. Palms are not cycads but angiosperms— dates and coconuts being examples of their fruit.
Fig 4.5.4 Angiosperms are flowering plants. Seeds are held in flowers, which gradually change into fruit.
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A whopper gum tree! In 2008, a 350-year-old, 101 metre tall gum tree was discovered in the remote forests of southern Tasmania. Nicknamed ‘Centurion’, the gum tree takes the titles of world’s oldest gum tree, tallest hardwood tree and tallest flowering plant. Centurion belongs to the species Eucalyptus regnans, a name that literally means ‘King of the trees’. Regnans regularly grow to incredible heights since they are able to ‘muscle-out’ other trees for valuable soil and light.
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Fig 4.5.7 Cycads look like palm trees. Like conifers, they too produce seed-containing cones.
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Aboriginal food
Fig 4.5.5 Regnans can grow so tall that they could reach threequarters of the way to the top of the Sydney Harbour Bridge!
The Aborigines have used many poisonous substances as food after careful treatment. One example is Cycas media, a type of cycad. Its seeds are extremely poisonous but can be eaten after roasting or other treatment. The Aborigines didn’t always share their secrets with the early European settlers, many of whom were poisoned after they ate plants, fruit and seeds found in the bush.
Other kingdoms: Fungi Fungi are not plants because they are not capable of photosynthesis and so cannot make their own food. Fungi include mushrooms, toadstools and moulds. Some fungi are very useful—mushrooms can be edible, and the mould penicillium is the source of the antibiotic penicillin. Other fungi are the cause of infections, such as tinea, ringworm and thrush. Fungi are similar to animals in that they are heterotrophs; that is, they feed on other plants and animals to survive. They are similar to ferns in that they reproduce by spores.
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Ginkgo biloba is the only ginkgo known to exist and so has a class all of its own. It bears its seeds in cones but, unlike other cone-bearing plants, it sheds its leaves in winter.
Unit
Ginkgos
Fig 4.5.8 Originally a native plant of China, Ginkgo biloba is now cultivated throughout the world and sold as a natural cure for circulatory problems. Ginkgo is Japanese for maidenhair tree.
Ferns Ferns have no seeds and reproduce through spores, instead. Spore cases grow on their fronds (leaves). When ready, the cases open and release their spores.
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Fig 4.5.10 Eat a death cap mushroom and you die! For this reason, you should never eat mushrooms collected from the field or bush. Go to
Science Focus 1 Unit 5.4 Science Focus 2 Unit 5.1
Other kingdoms: Monera
Fig 4.5.9 The reproductive spores of ferns are usually easy to see under their fronds.
Bryophytes The bryophytes are small plants that do not have a well-developed vascular system or true roots. They are found in moist environments and generally prefer cooler places. Mosses and liverworts are examples of bryophytes.
Prac 2 p. 134
Poisonous mushrooms Prac 3 p. 134
The most dangerous mushroom is Amanita phalloides, commonly known as the death cap. Normally a Northern Hemisphere plant, it has been found in Australia around Canberra and Melbourne. It has a yellowish to olive-green cap and is the cause of up to 95 per cent of all fatal mushroom poisonings. It doesn’t kill straight away and there are usually no symptoms until about 10 hours after it has been eaten. Death can take up to four days.
All bacteria belong to the kingdom monera. Bacteria are microscopic organisms that are found absolutely everywhere—in the soil, on your computer keyboard and mouse, on your skin and in your intestines. Bacteria are normally associated with bad breath, pimples and infections, and diseases such as salmonella, meningitis and gonorrhoea. Yet, bacteria can be useful, too. Your intestines contain up to 1.5 kilograms of bacteria that help you digest food. Other types of ‘good’ bacteria are used to produce foods such as cheese and yoghurt.
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Plants and other kingdoms
Other kingdoms: Protists Lots of organisms don’t fit into any of the other kingdoms and so another kingdom, the protists, is needed for them. Protists live in water or inside the damp bodies of other organisms. Some protists are plant-like, using photosynthesis to make their own food. Others are animal-like, needing to feed on other organisms to survive. Protists include seaweeds, slime moulds and amoeba.
Fig 4.5.11 This infection is called impetigo. It is highly infectious and caused by the Staphylococcus bacteria.
Science
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Poo on your toothbrush! Always flush the toilet with the lid down. Studies have shown that flushing stirs up bacteria in the toilet, which then float into the room if the lid is not down. They can then stay in the air for about one hour before they settle….maybe onto your toothbrush!
Fig 4.5.12 Seaweed is a plant-like protist.
Summary: The classification of living things Kingdom
Animal
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Major group
Vertebrates (chordates)
Class
Examples
Characteristics
Mammals
Placental e.g. horses, whales
Hair, mammary glands, live young, endothermic
Mammals
Marsupials e.g. kangaroos, koalas
As above, but with pouch
Mammals
Monotremes e.g. echidna, platypus
As above, but lays eggs
Birds
Rosellas, magpies, emus
Feathers, wings, scales on legs, egg-laying, endothermic
Reptiles
Snakes, lizards, crocodiles
Scales, egg-laying, ectothermic
Amphibians
Frogs, toads
Two-stage life, egg-laying, ectothermic
Fish
Bony e.g. salmon, goldfish
Gills, bony skeleton, lay eggs, ectothermic
Fish
Cartilaginous e.g. sharks, stingrays
As above, but with skeleton made of cartilage
Fish
Jawless e.g. lampreys
As above, but jawless
Kingdom
Invertebrates
Major group
Phylum
Examples
Arthropods
Insects e.g. flies, grasshoppers
Exoskeleton, antennae, three body segments, six legs
Arthropods
Arachnids e.g. spiders, scorpions
Segmented body, no antennae, eight legs, no jaws
Arthropods
Crustaceans e.g. crabs, prawns
Segmented body, two pairs of antennae, most live in water
Arthropods
Centipedes
Long antennae, segmented body, two legs per segment
Arthropods
Millipedes
Short antennae, segmented body, four legs per segment
Molluscs
Snails, octopus
Soft bodies, large muscular ‘foot’ or tentacles
Cnidarians
Polyps e.g. coral
Hollow body, tentacles, stinging cells, are fixed
Cnidarians
Medusas e.g. jellyfish
As above, but are not fixed
Worms
Roundworms e.g. hookworms
Unsegmented cylindrical body, mouth, anus
Worms
Flatworms e.g. tapeworms
Unsegmented body, one opening
Worms
Segmented e.g. earthworms, leeches
Segmented body
Class
Examples
Characteristics
Flowering
Wattle trees, roses
Transport system, seeds in flowers, fruit or nuts
Conifers
Pine trees, firs
As above, but seeds in cones, found in cold climates
Cycads
Cycads
As above, but found in tropical climates, palm-like
Ginkgo
Ginkgo biloba
Only one species exists, seeds in cones, loses leaves
Ferns
Tree ferns, stag ferns
Transport system, spores
Mosses, liverworts
No transport system, small, live in moist environments
Mushrooms, moulds, yeast
Feed on other organisms
Bacteria
Anthrax, Streptococcus
Microscopic
Algae
Seaweed
Plant-like
Protozoa
Amoeba, paramecium
Animal-like
Vascular Plants
Bryophytes Fungi Monera
Characteristics
4.5
Animal
Major group
Unit
Kingdom
Protists
131
Plants and other kingdoms
4.5
QUESTIONS
Remembering 1 State what the study of plants is called. 2 State alternative names for: a flowering plants b monera. 3 State the type of environment in which these plants live best: a cycads
14 Angiosperms produce seeds, which are found in their flowers and fruit. Hence, all fruit have seeds. On this basis, classify the following as fruit or vegetable: a potatoes b watermelon c strawberries d tomatoes.
b conifers
Evaluating
c protists
15 Propose reasons why these following people did not inform the first European settlers about what Australian plants, seeds and fruit could and could not be eaten:
d bryophytes. 4 List four different conifers that occur naturally in Australia. 5 List three characteristics of bryophytes.
Understanding 6 Identify the part of the flower that contains the seeds in an angiosperm. 7 The ginkgo is an incredibly special plant. Explain why. 8 Explain how ferns reproduce. 9 Explain how fungi are like animals. 10 Identify two beneficial effects of bacteria and two less desirable effects. 11 Most flowering plants are both male and female, making them hermaphrodites. a Explain how this can occur. b Use this information to define the term hermaphrodite.
Analysing 12 Classify these plants as flowering, conifer, cycad, ginkgo, fern or bryophyte: a a type of palm tree that produces coconuts b my name is Japanese for maidenhair tree
a scientists back in England before the settlers began their voyage b Aborigines living nearby when the settlers arrived.
Creating 16 Using the table on page 136, construct two pie charts showing the proportions of organisms in each kingdom. One pie chart is to show the numbers of species that have been discovered. The other is to show the numbers thought to exist. Construct your pie charts using one of the two methods below. Method 1: Computer spreadsheet a Input all your information into a spreadsheet such as Excel. b Use the graph drawing function to generate the required pie charts. Method 2: Protractor N a Trace around a circular protractor. b Mark the centre of the circle and draw a straight line from it to anywhere on the perimeter. c Use the protractor to carefully measure the angles shown in the table below.
c a type of moss d a tree that has needles for leaves and cones. 13 Compare the following by listing their similarities and differences:
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Animals
Number of species discovered
Total number thought to exist
271°
268°
a ferns and fungi
Plants
56°
9°
b fungi and bacteria
Fungi
15°
40°
c cycads and conifers.
Monera
1°
27°
Protists
17°
16°
Unit
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: • Find out about common fungal infections of the body (such as tinea, thrush and ringworm).
• Find information about a rare but extremely deadly fungal infection called mucormycosis. Many fell ill with this infection after the Boxing Day tsunami that hit many Asian countries in 2004.
4.5
4.5
Summarise the information you find and display it as a pamphlet for a doctor’s surgery. L
4.5 1
PRACTICAL ACTIVITIES
Vascular plants
Aim To investigate the transport mechanisms in vascular plants.
Equipment • • • • • • •
lead pencil three test tubes test-tube rack two eyedroppers two colours of food dye collection of fresh leaves three similar fresh flowers
Method Part A Construct images of the underside of each leaf you collected by placing it upside down under a page in your workbook and using a lead pencil to shade over it. A good imprint of the leaf and its veins should be produced.
Part B 1 Nearly fill three test tubes with water and place in a test-tube rack. 2 Use an eyedropper to place three or four drops of one food dye colour into one test tube. 3 Use another eyedropper to place three or four drops of the other food dye colour into a second test tube. 4 Do not add any food colour to the third test tube. 5 Place a freshly cut flower in each test tube. 6 Record your observations the next day.
Questions 1 The presence of veins in a leaf suggests that the plant it was taken from was a vascular plant. Identify how. 2 The original colours of two of the flowers in Part B should have changed colour overnight. Explain how this shows that the flowers have a vascular system. 3 Identify the purpose of the flower in the test tube with uncoloured water.
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Plants and other kingdoms
2
Dichotomous key of plants
Aim To construct a dichotomous key for plants from the local area.
!
Safety 1 Some plants (e.g. oleander and rhus) are known to cause allergic reactions in some people. 2 The sap of some plants (e.g. agapanthus) may cause skin irritation in some people.
Method 1 Examine your plants carefully and note some of their characteristics. 2 Create a dichotomous key to identify the different plants. Include sketches of the plant specimens. If you don’t know their names, just label them A, B, C etc.
Questions 1 Give your key and samples to a classmate. Assess whether they could successfully use your key to identify the plants. 2 Evaluate your key. How could your key be improved?
Equipment Plant specimens collected from home or around the school, under supervision.
3
Growing a fungus
Aim To grow mould, a type of fungi.
Method 1 Wet each piece of food and place them all in the Petri dish so that they touch each other. 2 Place the lid on the Petri dish and seal it with sticky tape.
!
Safety
3 Place the dish in a place where it won’t be disturbed.
1 Do not eat or taste any of the bread, fruit, vegetables or cheese samples.
4 Without removing the sticky tape, record your observations over the next week.
2 Once the Petri dish is sealed with sticky tape, do not open it again.
5 At the end of the week, dispose of the Petri dish according to your teacher’s instructions.
Questions Equipment • Petri dish and lid • sticky tape • small pieces of bread, fruit, vegetables and cheese
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1 Fungus is a mould. Compare its structure with the leaves found on vascular plants such as gum trees. 2 Explain how fungi such as mould are important in recycling material in the environment.
CHAPTER REVIEW Remembering 1 List three examples of each of the following: a organisms b vertebrates c invertebrates d endotherms e ectotherms f angiosperms g conifers h fungi i protists. 2 State: a the five main classes of vertebrates b the three main orders of mammals c the four main phyla of invertebrates d the five main classes of arthropods e the five main classes of vascular plants.
Understanding 3 Explain why scientists classify things. 4 Cells were unknown before the invention of the microscope. Explain why. 5 Clarify the meanings of the following terms: a respiration b excretion c stimulus d response e taxonomy f species
8 You watch somebody run across a field being chased by a hungry lion. Identify which characteristics of life are shown by: a the person b the lion. 9 Identify whether the following pairs of animals belong to the same species: a a Lebanese man and a Chinese woman b a tiger and a gorilla c a greyhound and a poodle d a lizard and a crocodile e a donkey and a horse. 10 You are standing by a campfire, listening to the rustle of the possums in the bushes, the crackle of the fire and the laughter of your friends. Identify whether all of the things mentioned in this sentence are alive. Do any of the non-living things show any of the characteristics of life? Explain. 11 Electronic music storage systems such as iTunes classify the music they contain in a number of different ways (e.g. by artist). a Identify some of the other ways in which they classify the music. b Explain the advantages of using different keys to classify the same music. 12 Acacia gunnii and Acacia mearnsii are both wattle trees found in New South Wales. Both are very tall and have fluffy creamywhite flowers. Identify: a two characteristics that both trees share b the genus of each c the species of each.
g vertebrate
Analysing
h exoskeleton
13 Until recently, it was thought that dinosaurs were reptiles.
i heterotroph. 6 Plants and animals both use cellular respiration for energy. Explain why only plants can undergo photosynthesis.
Applying 7 Identify whether the following questions are dichotomous: a Does the animal have a backbone? b What colour is your T-shirt?
a If this was correct, list the kind of features you would expect dinosaurs to have. b Recent research has indicated that many (if not all) dinosaurs were warm blooded and that birds may have evolved from them. Use this information to classify dinosaurs, placing them in the correct animal kingdom. c Identify a feature of birds that resembles a feature of those long-extinct dinosaurs.
c Did you feed the dog? d What type of animal is that?
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14 Classify the following as angiosperm, conifer, fern or bryophyte: a pine b tree fern c apple tree d liverwort. 15 Classify these animals, stating whether they are a vertebrate or invertebrate, their class (e.g. mammal, fish) and any further group they belong to (e.g. placental mammal, bony fish):
Evaluating 16 European scientists had to change their system of classification as more and more of the world was explored during the 1700s and 1800s. Propose reasons why. 17 Although many animals, plants and other organisms have been found and named, scientists believe that there are still many more to be discovered. The table below indicates how many species in each kingdom have been named and how many are thought to exist on Earth.
a grey nurse shark b red-back spider
Kingdom
Number of species currently named
c platypus d kangaroo
Animals
e Murray cod f yabbie g sperm whale h leech i mosquito.
Estimated number of species thought to exist
1 300 000
10 000 000
Plant
270 000
320 000
Fungi
72 000
1 500 000
Monera
4 000
1 000 000
Protists
80 000
600 000
a Propose reasons why: i Almost all plants species thought to exist have already been found. ii Only a few of the monera (bacteria etc.) thought to exist have been discovered so far. b Animals are much more obvious than monera and protists, most of which need a microscope to be seen. Despite this, only 13 per cent of animals have been discovered so far. Propose which classes of animals have lots of species yet to be discovered. Justify your answer.
a
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on
Ch
pt
Worksheet 4.5 Sci-words
s
Worksheet 4.4 Crossword er R sti ev i ew Q u e
Cells
5
Prescribed focus areas: The history of science Current issues, research and developments in science
Key outcomes 4.1, 4.5, 4.8.1, 4.8.3, 4.8.4, 4.8.5
•
New scientific knowledge has changed our understanding of the world.
•
All living things are made up of microscopic building blocks called cells.
•
Cells have internal structures (organelles) such as the nucleus, chloroplasts, cytoplasm, cell membrane and wall, where each organelle has its own defined function.
•
Reactions within the cell require a constant flow of chemicals and nutrients in and out of the cell.
•
Bacteria and single-celled organisms carry out all the functions of life in one cell.
•
Larger organisms contain many different cells, where each cell is specialised to carry out a particular job.
•
Living cells need glucose and oxygen to carry out cellular respiration.
•
Diffusion and osmosis move chemicals and nutrients across the cell membrane.
Additional
The development of microscopes led to the discovery of cells and microscopic life.
Essentials
•
Unit
5.1
context
Cells and the microscope
Cells are the building blocks that make up all living things. Cells make up insects and iguanas, germs and gum trees, platypus and pond slime, daisies and dolphins. Cells are microscopic—this means that they can be seen only using a
microscope. The story of cells, therefore, is closely connected to the development of the microscope. The microscope has also allowed scientists to discover microorganisms, their structure, weaknesses and the diseases they cause.
The discovery of cells
Fig 5.1.1 Modern microscopes allow us to observe organisms and details that are impossible to see with the naked eye. This image is of a wasp’s head. It was taken with an electron microscope called an SEM (a scanning electron microscope).
Fig 5.1.2 Cork is bark from a tree. Although thicker, it resembles the paper-like bark of meleleucas often found in parks and school grounds. Hooke’s original sketch of cork cells (top) compares well with an SEM image of similar bark (right).
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Quick Quiz
Cells are so tiny that hundreds would fit on a full stop. They are far too small to be seen with the naked eye and can be seen only using a microscope. One consequence of this is that no-one knew cells existed before its invention. In 1665, the English scientist Robert Hooke used his newly invented microscope to discover cells in cork, the special bark sometimes used to stopper wine bottles. Hooke had been using his microscope to study all sorts of things, including feathers, the stinger of a bee and the foot of a fly. When Hooke placed a thin strip of cork under his microscope, he saw box-like shapes that he imagined looked like the small rooms occupied by monks of the time. These rooms were called cells and so he named the boxes cells. Hooke had found that cells were the basic blocks from which plant materials, such as bark, were built.
Unit
5.1
Science
Clip
Who discovered the microscope? Different people often invent and discover the same things at exactly the same time even though they are working in different cities or countries and have had no communication with each other. This was the case with the compound microscope. Hans Jannsen and his son Zacharias invented it somewhere between 1590 and 1607 and so did Hans Lippershey. The Jannsens and Lippershey were working in Holland but they were based in different cities and there was no contact between them. The microscopes commonly used in schools today most resemble a type of microscope invented by Robert Hooke in 1665.
Science
Fact File
People in science: Robert Hooke (1635–1703) Robert Hooke was one of the greatest experimental scientists of the seventeenth century and achieved much in the scientific fields of physics, chemistry, astronomy, as well as non-scientific fields such as architecture. Amongst his major works and discoveries, Hooke: • constructed an air pump for fellow scientist Robert Boyle (1655) • discovered the law of elasticity, which explains why balls bounce and rubber bands stretch (1660) • published the book Micrographia (meaning ‘small drawings’), in which he first used the word cell for the microscopic blocks he had seen in samples of cork (1665) • found that all matter expands when heated • found that air is made up of particles widely separated from each other • was chief assistant to the great architect Christopher Wren, helping to rebuild London after much of it was burnt down in the Great Fire of 1666. • constructed one of the first Gregorian reflecting telescopes, using it to make detailed sketches of Mars. These sketches were still being used 200 years later to help investigate its motion! • was the first to suggest that the planet Jupiter rotated on its axis like Earth did. In 1678, Hooke formulated a law that described how the planets moved. Fellow scientist Isaac Newton (1643–1727) later used Hooke’s law in a modified form. This led to a bitter and on-going feud with Newton since Hooke thought he was not being given enough credit for the law.
Fig 5.1.3 A model of Hooke’s microscope
In 1673, the Dutch amateur scientist Anton van Leeuwenhoek made amazing discoveries with simple, hand-held, single-lens microscopes. Whereas other microscopes of the time could only magnify objects so that they appeared 50 times bigger, his microscope was able to magnify objects up to 300 times. This allowed van Leeuwenhoek to observe things that had not been seen previously with earlier microscopes. He saw that muscle fibre was made of cells, that blood contained red blood cells and that animal sperm was made of individual sperm cells (which he named animalcules). Van Leeuwenhoek’s studies revealed that the animalmaterials he had studied were made up of cells, just like Hooke had with plants. One year later, van Leeuwenhoek used his microscope to become the first person ever to see single-celled organisms called protists. Then, in 1683, he discovered bacteria, which were even smaller. Van Leeuwenhoek had shown that some living things needed only a single cell, making them far too small to be seen by the naked eye (or by microscopes of lesser magnification than his).
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Cells and the microscope Science
Fact File
People in science: Anton van Leeuwenhoek (1632–1723) Anton (also known as Antoni or Antonie) van Leeuwenhoek had little formal education and even less experience in science. Despite this, he constructed microscopes with magnifications far exceeding others of his time. Whereas other microscopes took the form of Robert Hooke’s, van Leeuwenhoek’s microscope looked more like a weird magnifying glass. It was hand-held (others were on a stand) and contained only one lens (others had multiple lenses). Nevertheless, this single lens was of such high quality that it produced much clearer images than those from other microscopes in which poor-quality lenses produced blurred images that often had colour distortions. Van Leeuwenhoek studied all sorts of things, not just cells. In one investigation, he closely (too closely) investigated the properties of gunpowder, nearly blinding himself with the resultant explosion!
Science
Clip
Sperm people!
Fig 5.1.5 Scientists in the seventeenth century commonly thought that either human sperm or eggs contained tiny immature people called homunculi. Microscopes have proven this to be a fantasy.
Fig 5.1.4 Van Leeuwenhoek’s simple single-lens microscopes were able to magnify objects so that they appeared 300 times larger. Amazingly, van Leeuwenhoek made a new microscope for each new experiment!
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Inspired by van Leeuwenhoek, Nicolas Hartsoeker (1656–1725), another Dutch scientist, also used a microscope to study sperm cells. In his drawings of sperm cells, he included tiny undeveloped people that he called homunculi. Although Hartsoeker never claimed he saw homunculi, he used them to support a view, commonly held at that time, that all animals were formed from miniature sperm versions of themselves. These scientists were known as spermists. A rival camp of scientists, known as the ovists, argued instead that the homunculi existed inside the egg.
As microscopes and their magnifications improved, more discoveries were made. In 1831, for example, the Scottish botanist Robert Brown (1773–1858) used a microscope to discover a cell nucleus. He went on to find that all plant cells contained a nucleus. Likewise, Rudolph Kolliker (1817–1905), a Swiss anatomist, found in 1857 that muscle cells contained even smaller parts called mitochondria.
Robert Brown again!
The cell theory of life
Although cells had been discovered in plants, animals and microscopic protists and bacteria, no-one had yet realised that cells made up everything that is living. Then, in 1839, the German biologists Theodor Schwann and Matthias Schleiden proposed the cell theory of life. Their theory stated that: • All living things are made up of cells. • New cells are created when old cells divide in two. • All cells are similar to each other, but are not identical. It took a while for scientists to be convinced of cell theory since most thought that cells could appear spontaneously from anywhere. In 1855, however, the German physician Rudolph Virchow (1821–1902) proved once and for all that cells could only form by other cells reproducing by splitting.
Brown didn’t use his microscope to just study cells. In 1827, he found that microscopic grains of pollen continuously jiggled when in water. It was as if the grains were constantly being hit in different directions by something in the water. This erratic motion is referred to as Brownian motion.
Light microscopes
A light microscope passes light through the object or reflects light off it. A magnifying glass is an example of a simple microscope. It contains a single lens and uses light to give magnified images of small Science objects like ants. The microscopes you are likely to use at school are compound People in science: microscopes. These use two or Matthias Schleiden more lenses and come in two (1804–1881) forms: monocular and stereo. Each Matthias Schleiden practised law form has its own advantages and before developing his hobby of botany into a full-time job. He disadvantages. Monocular microscopes have used the microscope to study the structure of plants and found that only one eyepiece. They form different parts were composed of flattened, two-dimensional images cells or from material made of by focusing light that passes cells. Schleiden recognised that through a thin slice of the object. the nucleus was involved in cell Stereo microscopes have two reproduction and, along with Theodor Schwann (1810–1882), eyepieces and are generally more laid down the basics of cell theory. expensive than monocular Schleiden was one of the first microscopes. They focus German biologists to accept light that reflects off the Darwin’s theory of evolution through natural selection. specimen to form realistic Prac 1 p. 146 three-dimensional images.
Fact File
Monocular microscope
Fig 5.1.6 Microscopes have proven that all living matter is made of cells. This image shows red blood cells in a small artery.
Stereo microscope
Number of eyepieces
One
Two
Specimen type
Thin slices
Anything, no need to slice
Ideal for investigating
Inner structures of cells, bacteria and single-celled organisms
Crystal structures of rocks and crystals, fine details of insects and plants
What light does
Light passes through
Light reflects off surface
Images
Flattened, twodimensional view
Realistic, threedimensional view
Colour
Coloured images
Coloured images
The microscope A microscope is any instrument that gives magnified images of small objects. If an object can be seen only using a microscope, then it is referred to as being microscopic. Microscopes fall into two main categories: light microscopes and electron microscopes.
5.1
Clip
Unit
Science
141
Cells and the microscope Eyepiece or ocular lens.
Objective lens: each has a different magnification. Always start with the lowest magnification.
Arm Clips: hold microscope slide in place.
Stage: holds the microscope slide. Light passes through a thin slice of the specimen.
Course focusing knob: used first to bring the image into rough focus.
Diaphragm: used to control light passing through the specimen.
Fine focusing knob: used next to bring the image into clear focus.
Lamp: shines light through the specimen. Some older microscopes will have a mirror located here.
Base
Fig 5.1.7 Parts of a monocular microscope. This microscope has its own in-built lamp. Some older styles do not. They need a separate lamp, using a mirror to reflect its light up through the specimen.
D ra
The flattened image formed by a monocular microscope
g - a n d - d ro p
Specimen and image What you place under a microscope is called a specimen. What you see when you look through the eyepiece is called the image. Magnification compares the size of the image with the size of the specimen. A magnification of ×100, for example, means that the image appears one hundred times larger than the specimen. Each lens in a compound microscope has its own magnification. To obtain the total magnification, you need to multiply the magnifications of each lens used. Compound microscopes commonly magnify up to 1500 times their original size. Eyepiece magnification
Objective lens magnification
Total magnification
×10
×20
(×10) × (×20) = ×200
×20
×15
(×20) × (×15) = ×300
Prac 2 p. 147
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Prac 3 p. 148
Stereo microscopes produce more realistic 3D images
Fig 5.1.8 Each type of compound microscope produces a different kind of image. An image of human cheek cells, magnified 100 times.
A sketch of the same cells
Fig 5.1.9 The area that you see through the eyepiece is called the field of view. Only sketch a simplified drawing of what you see, without shading and concentrating only on the main lines and features.
Unit
5.1
The electron microscope Electron microscopes are more powerful than light microscopes and use tiny negatively-charged particles called electrons to form their images. There are two types of electron microscopes, which are called TEM and SEM. The transmission electron microscope (TEM) passes a beam of electrons through a thin slice of the specimen. An image is then produced and projected onto a screen for viewing. The transmission electron microscope can magnify up to a million times, making it possible for scientists to investigate the delicate internal structure of specimens such as cells. Fig 5.1.10 A transmission electron microscope (TEM) in use. Image of Giardia protozoa, magnified ×1200, as produced by a transmission electron microscope (TEM). Giardia can be found in contaminated water and can make you extremely ill.
The image is extremely detailed but flattened and two-dimensional.
The scanning electron microscope (SEM) reflects a beam of electrons off the surface of the specimen. It then constructs a black-and-white image that shows fine surface detail. Computer programs can then ‘falsecolour’ the image to make details even more obvious.
Another image of Giardia protozoa, as produced by a scanning electron microscope (SEM).
The image is realistic and appears more three-dimensional. Many of the impressive ‘super-magnified’ images seen in science magazines are obtained using an SEM.
Fig 5.1.11 Each type of electron microscope produces a different kind of image.
TEM
SEM
Specimen type
Thin slices
Anything, no need to slice
What electrons do
Electrons pass through
Electrons reflect off surface
Images
Provides view of inner structure of cells
Gives super-magnified views of specimens such as insects
Colour
Coloured images
Black and white. Can be false-coloured, using a computer.
History
First invented 1930. Commercially available from 1938 to study metals. Then used to study cells once it became obvious that electrons did not destroy them.
First invented 1942. Not commercially available until 1965 due to problems with the electron beam.
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Cells and the microscope
5.1
QUESTIONS
Remembering 1 State who:
Applying 12 Identify the parts labelled A to H in Figure 5.1.12.
a are thought to have invented the first microscope (multiple names are needed) b invented the form of microscope most similar to the ones used today
A
c developed the cell theory of life d proved that cells reproduced and didn’t just appear from nowhere. 2 State who saw the first: F
a cells B
b animal cells c bacteria
C
d cell nucleus
G
e cell mitochondria. H
D
3 List the three main points of cell theory. 4 State another name for the eyepiece. 5 State what TEM and SEM stand for.
Understanding
E
6 Explain why cells were not known about before the invention of the microscope. 7 Explain why Hooke named the ‘boxes’ he saw in cork ‘cells’. 8 Define the following terms: L a microscopic b specimen c image d field of view. 9 Use one word to clarify how big a cell is. 10 Explain what a magnification of ×10 means in terms of specimen and image. 11 The objective lens should never be moved downwards while looking through the eyepiece. Propose a reason why.
Fig 5.1.12
13 Copy the table below and calculate the missing values. N Eyepiece magnification
Objective lens magnification
×10
×10
×5
×100
×20
×40 ×100
×30
Total magnification
×300 ×600
14 A specimen is 0.2 mm long. Calculate the length of its image if it is magnified by 1000 times. N
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Unit
15 The image shown in Figure 5.1.13 is of a specimen obtained using a magnification of ×50.
19 Analyse the important details of the images shown in Figure 5.1.15 and sketch them simply and clearly. Do not shade or colour them or include too many details.
a Measure its length and width.
5.1
Analysing
b Calculate how long it would appear if viewed with a magnification of ×200. c Accurately draw what it would look like under this new magnification. N
×50
Fig 5.1.13
16 Classify the following as either a simple microscope or a compound microscope: a reading glasses b magnifying glass c monocular microscope d stereo microscope. 17 Compare the following types of microscopes by listing their similarities and differences: a a monocular microscope and a stereo microscope b a TEM and an SEM c a monocular microscope and a TEM. 18 Deduce whether the image in Figure 5.1.14 was produced by a magnifying glass, TEM, SEM or a monocular or a stereo microscope. Give reasons for your choice.
Fig 5.1.15
Evaluating 20 Bubbles are a nuisance when looking through a microscope. Propose a reason why. 21 Assess whether a monocular or a stereo microscope is most similar to an SEM.
Creating 22 Create a mini-poster, PowerPoint presentation, video, podcast or vodcast that shows how to use the microscope. L
Fig 5.1.14
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Cells and the microscope
5.1
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find the dates of key discoveries relating to the microscope and cells. Include those covered in this chapter and others that you research. Construct a scaled time line, using this information. N
3 Find out what is a micrometer. Describe how it is used. 4 Specify the units that are used when measuring small lengths. Identify their symbols. 5 Find out how an electron microscope (either a TEM or SEM) works. Summarise your information as a poster.
2 Find information on key people involved in the use and development of early microscopes. Summarise the information you find and prepare a brief presentation about their lives and achievements. Choose from the following people: Galileo Galilei, Antoni van Leeuwenhoek, Giovanni Amici, Robert Brown, Matthias Schleiden and Theodor Schwann.
5.1 1
PRACTICAL ACTIVITIES
Constructing a simple microscope
7 Slide the outer part of the matchbox to focus and produce an image of the object. 8 Experiment with different sizes of water drops.
Aim To construct a simple single-lens microscope using junk materials. drop of water
Equipment • • • • • • •
empty matchbox piece of thin plastic (e.g. cut from an overhead transparency) toothpick sticky tape scissors petroleum jelly eyedropper
plastic
ring of petroleum jelly
sticky tape
object matchbox sleeve
Method 1 Cut a window in one end and one large face of the matchbox, as shown in Figure 5.1.16. 2 Tape a piece of clear plastic over the window in the end. 3 Assemble the matchbox as shown. 4 Use the toothpick to construct a ring of petroleum jelly to hold a drop of water. 5 Use the eyedropper to place a drop of water inside the ring of petroleum jelly. 6 Place a small object (such as an insect) onto the matchbox tray.
matchbox tray
Fig 5.1.16
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>>
Unit
Questions a lens
Fact File
b stage
Using a microscope
c focus adjustment.
1 Place the prepared slide on the stage and secure it using the clip.
2 Describe any problems you encountered.
5.1
Science
1 Identify which part of your apparatus acts as the:
2 Adjust the mirror or diaphragm to maximise the light passing through the slide.
3 Explain why this microscope is a simple microscope and not a compound microscope. 4 Explain why raindrops on spectacles cause problems for the wearer.
3 Choose the objective lens with the lowest magnification and rotate it into place. 4 While looking at the microscope from its side (not through the eyepiece), adjust the coarse focusing knob to bring the stage and objective lens as close as possible to each other.
Science
Fact File
Preparing a wet mount 2 Use an eyedropper to place a drop of water or stain onto the specimen.
5 While viewing through the eyepiece, turn the coarse focusing knob so that the stage and objective lens move further apart. Keep doing this until the specimen is roughly in focus.
3 Gently lower a thin glass cover slip onto it, as shown in Figure 5.1.17.
6 Adjust the fine focusing knob to bring the specimen further into focus.
4 Soak up any excess water or stain with a piece of filter paper or tissue.
7 Adjust the mirror or diaphragm to change the amount of light so that the clearest image is produced.
1 Place the specimen on a glass microscope slide.
sample
drop of water
Fig 5.1.17 Preparing a wet mount
Method
2
Focus on the news
Aim To make a wet mount and view it using a light microscope.
Equipment • • • • • •
monocular microscope lamp, if not fitted section of newspaper containing small print eyedropper glass microscope slide cover slip
1 Tear out a small scrap of newspaper filled with small print. 2 Prepare a wet mount of the small scrap of newspaper. 3 Obtain a focused image of the newsprint. 4 Sketch the image formed. Count how many letters fit into the field of view. 5 Slowly move the slide containing the newsprint to the left, noting which way the image appears to move. 6 Determine how the image moves when the slide is moved right, away from and towards you. 7 Now obtain images using higher magnifications.
Questions 1 State how many letters fitted into the field of view at each magnification. 2 Compare the movement of the image with that of the actual specimen.
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Cells and the microscope
3
Observing everyday objects
Aim To observe common objects at various magnifications.
Equipment • • • • • •
access to monocular microscope and a stereo microscope lamps, if not fitted glass microscope slides cover slips eyedropper small samples suitable for viewing under a microscope (e.g. a sugar crystal, salt, copper sulfate, hair, clothing fibres, leaves, flowers, insects, a sample of writing etc.)
Method 1 Observe each specimen under both the monocular microscope and the stereo microscope. A wet mount may need to be prepared for some specimens. 2 If a stereo microscope is not available, shine a lamp onto the specimen from above and view it as usual using the monocular microscope. 3 Construct a table, with one column describing the images formed by the monocular microscope and another column for those formed by the stereo microscope.
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Questions 1 Compare the images formed by the monocular and the stereo microscopes. 2 Classify the specimens into those that were viewed best using a monocular microscope and those that were viewed best using a stereo microscope.
Unit
5.2
context
Plant cells
The first ever cells to be seen were plant cells, specifically the cells making up the bark called cork. Cells are the building blocks that make up every part of a plant, regardless of whether the plant is a tiny and insignificant moss or a towering gum
tree. Like all living things, plants use energy and gases, grow and reproduce. They draw water from the soil, release valuable oxygen gas and produce seeds or spores for reproduction. Each of these tasks needs a specific type of cell.
Fig 5.2.1 Cells are the building blocks that make up all plants.
Structure of a plant cell Like all living things, plants are made up of microscopic structures called cells. However, not all cells are the same. Cells are specialised to carry out different tasks in the plant. Despite their variety, all plant cells share many features. Cytoplasm: this jelly-like liquid is where energy is released and new substances are made. The cytoplasm can be thought of as the chemical factory of the cell. Cell wall: this must be rigid enough to support the plant. It contains a tough fibrous material called cellulose.
Chloroplasts: these contain a green chemical called chlorophyll. Chlorophyll traps the light energy needed for photosynthesis.
Vacuole: In plants, vacuoles are large and filled with sap. They contain air, water, wastes and food particles.
Cell nucleus: this controls all chemical reactions in a cell and how the cell develops and reproduces. The nucleus is the ‘control room’ of the cell.
Fig 5.2.2 Plant cells are made up of parts called organelles. Each organelle does a specific job inside the cell.
Cell membrane: this controls what goes in and out of the cell. It lines the inner cell wall.
A mitochondrion: mitochondria are energy capsules that contain glucose (a plant’s food) and oxygen. Mitochondria are so small they cannot usually be seen using a light microscope.
Prac 1 p. 153
D ra
g - a n d - d ro p
149
Plant cells
Food for plants
Diffusion and osmosis
Animals get their energy from the food they eat. Plants don’t eat and instead make their own food in a process known as photosynthesis. Photosynthesis is a chemical reaction that uses energy from sunlight to combine carbon dioxide with water. A sugar called glucose is produced, as is oxygen gas. The photosynthesis reaction is best shown as the equation:
Once a plant has made its food in the form of glucose, it then needs to use it. This happens within the plant’s cells. Cells need energy to carry out their required functions, such as reproduction. They obtain this energy by ‘burning’ the glucose in a chemical reaction known as cellular respiration. Respiration requires glucose and a supply of oxygen gas. The glucose is formed by photosynthesis and the oxygen is drawn into the leaves. Carbon dioxide, water and energy are its products. This reaction is best shown as:
carbon dioxide + water + sunlight → glucose + oxygen
A plant obtains its carbon dioxide by drawing it in from the air through specialised cells, which are located mainly under its leaves. Water is drawn from the soil using different specialised cells in the plant’s roots. The glucose a plant produces is used directly as food or stored for later use. The oxygen a plant produces is released back into the air. Specialised cells are needed to draw in the different materials that photosynthesis requires. Other specialised cells will transport these materials to where they are needed, and other cells will actually carry out the photosynthesis reaction. Go to
Science Focus 2 Unit 3.2
Fig 5.2.3 The box-like structure of pondweed cells is obvious when they are viewed under a microscope. The green dots are the chlorophyll-filled chloroplasts.
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glucose + oxygen → carbon dioxide + water + energy
For this reaction to occur, glucose and oxygen must flow into the cells (along with some other nutrients and minerals) and carbon dioxide and water flow out of them (along with some other wastes). The cell membrane is therefore not a solid wall but a porous ‘screen’ that allows some chemicals through while blocking others. Chemicals move across the cell membrane in two different ways: • diffusion (where oxygen, carbon dioxide and water move from a region of high concentration to a region of lower concentration) • osmosis (where water moves to dilute the concentrations of larger chemicals and nutrients).
Unit
5.2
Specialised plant cells There are millions of cells in a plant and different types of cells perform different jobs. Each cell type has its own specialised structure and is located in a position on the plant that maximises its performance.
Photosynthetic cells: These make up a layer near the top surface of a leaf. They have many chlorophyll-filled chloroplasts which make the leaf green. Most photosynthesis happens here.
chloroplasts nucleus
underside of leaf
Conducting cells: These are found in the stems and branches of the plant. They form tubes that transport water and nutrients to all parts of the plant. water-conducting tube
guard cells stoma in open position
cell magnified wilted leaf sieve food-conducting tube
straight guard cells closed stoma
cell magnified Root hair cells: Photosynthesis needs water, which is absorbed through the roots of the plant. Root hairs increase water absorption by increasing the total surface area of the root. root hair
Stomata: small openings, mostly on the underside of leaves. The plant takes in carbon dioxide and gives out oxygen though these openings. Guard cells open and close to reduce the amount of water lost through the stomata.
cell in root
nucleus soil
Prac 2 p. 154
Fig 5.2.4 Plant cells are specialised so that they can perform their specific job. Go to
Science Focus 2 Unit 3.1
151
Plant cells
5.2
QUESTIONS 7 Photosynthesis is how green plants make their own food. Identify:
Remembering 1 State the type of specialised plant cell that:
a the chemicals (reactants) the plant needs to carry out the reaction
a carries out photosynthesis b transports water and nutrients
b the chemicals (products) the reaction produces
c absorbs water from the soil d controls the opening and shutting of the holes, called stomata.
d from where the reaction gets its energy.
Evaluating
Understanding
8 Propose what would happen to a plant without:
2 Define the term organelle. L
a guard cells
3 Describe the function in the cell of:
b cellulose
a its nucleus
c chlorophyll.
b cell wall
9 Propose a likely reason for each of the following:
c chloroplasts.
a Most plants are green.
4 Explain the purpose of chlorophyll in a plant.
b Plant cells have thicker walls than animal cells.
Applying
c Photosynthetic cells are usually found only on the upper surface of a leaf.
5 Identify which type of specialised plant cell is: a ‘hairy’
d There are two different types of conducting cells forming two different pathways in the plant.
b the ‘gatekeeper’ c a ‘transporter’. 6 From the clues given, identify these substances found in a plant. Explain the function of each.
10 There are far more types of animal cells than plant cells. Propose a reason why.
a I’m green.
11 Propose a reason why animals do not need to be able to carry out photosynthesis like plants do.
b I’m found in the cell wall.
Creating
c I’m found in the vacuole.
12 Construct a 2D or 3D edible model of a plant or animal cell using biscuits, icing sugar and/or assorted lollies.
5.2
INVESTIGATING INVESTIGATING
e -xploring W
The confocal microscope is currently being developed eb Destination by an Australian company. Investigate this new type of microscope and how it may be used to observe skin cells without the removal of skin from the body. To find out more, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
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c the name of the sugar that is used by plants as food
Unit
PRACTICAL ACTIVITIES
Onion, rhubarb and banana cells
1
5.2
5.2
Questions 1 Explain why stain was recommended when viewing banana cells, but not for onion or rhubarb cells.
Aim
2 Identify which cells were easier to observe.
To observe and draw plant cells.
3 Compare the cells of the onion, rhubarb and banana by listing some of their similarities and differences.
!
Safety 1 Do not eat any of the plant or fruit samples.
Science
2 Onion and rhubarb juice may irritate the skin or eyes.
Preparing a wet mount
Fact File
1 Place the specimen on a glass microscope slide.
Equipment • • • • • • • • •
monocular microscope lamp, if not fitted potassium iodide stain filter paper glass microscope slide eyedropper cover slip samples of onion skin rhubarb stems and banana
2 Use an eyedropper to place a drop of water or stain onto the specimen. 3 Gently lower a thin glass cover slip onto it, as shown in Figure 5.2.5. 4 Soak up any excess water or stain with a piece of filter paper or tissue.
sample
Method 1 Peel a thin layer, one cell thick, of skin from an onion.
drop of water
Fig 5.2.5 Preparing a wet mount
2 Prepare a wet mount of the onion skin. 3 Obtain a clear image with the microscope and sketch the shape and main feature of onion cells you see. 4 Observe the specimen with two higher magnifications. 5 Peel some of the outer layer from a piece of rhubarb stem. 6 Prepare a wet mount and observe the rhubarb cells under the microscope. Once again, repeat with two higher magnifications. 7 Sketch the images produced. 8 Smear a thin layer of banana onto a clean glass microscope slide. 9 Stain the banana by placing a drop of iodine stain on the specimen. 10 Carefully place a cover slip on top of the banana specimen. 11 Obtain a clear image using the microscope and draw what you see.
Science
Fact File
Using a microscope 1 Place the prepared slide on the stage and secure it using the clip. 2 Adjust the mirror or diaphragm to maximise the light passing through the slide. 3 Choose the objective lens with the lowest magnification and rotate it into place. 4 While looking at the microscope from its side (not through the eyepiece), adjust the coarse focusing knob to bring the stage and objective lens as close as possible to each other. 5 While viewing through the eyepiece, turn the coarse focusing knob so that the stage and objective lens move further apart. Keep doing this until the specimen is roughly in focus. 6 Adjust the fine focusing knob to bring the specimen further into focus. 7 Adjust the mirror or diaphragm to change the amount of light so that the clearest image is produced.
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Plant cells
2
Searching for stomata
Aim To produce an image of stomata and observe them under the microscope.
!
Safety 1 Vapours from nail polish may cause an asthmatic reaction or some other reaction. 2 Ensure there is plenty of ventilation when using nail polish.
Equipment • • • • • •
monocular microscope microscope lamp, if needed fresh green leaves (agapanthus are ideal) clear nail polish clear sticky tape glass microscope slide
Method 1 Paint a thin layer of clear nail polish in a strip about one centimetre wide on the underside of a leaf. 2 Repeat on the top of the same leaf or a leaf from the same type of plant. 3 When the nail polish is dry or nearly dry, gently press a strip of sticky tape onto each strip of nail polish. If the layer of nail polish is thick, press harder. 4 Gently rub the top of each piece of sticky tape. 5 Carefully peel the sticky tape from the leaf. Much of the nail polish should peel off with it. An image of the stomata should be imprinted in the nail polish. 6 Place the sticky tape onto a microscope slide and use the microscope to look carefully for evidence of stomata.
Questions 1 Describe any stomata you see. 2 Explain the purpose of stomata. 3 Compare the number of stomata stripped from the top of the leaf to its underside. Explain why one side would have more stomata than the other.
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Unit
5.3
context
Animal cells
Like plants, animals are living things made up of cells. Animals are far more complex than plants, however, and so
many more different types of cells are found in animals than are found in plants.
Animal cells All animal cells, whether they are brain, blood or muscle cells or from a human, pig or frog, have several common features. Some of these features (called organelles) are also found in plant cells.
Fig 5.3.2 Cells are the basic building blocks of all animals, including this orangutan.
A mitochondrion: Mitochondria are energy capsules that contain glucose (from the digestion of food) and oxygen. Mitochondria are so small they cannot usually be seen using a light microscope.
Fig 5.3.1 Animal cells are not like the ‘boxes’ normally found in plants. These cells are human cheek cells. Cell membrane: This thin outer layer holds the cell together and controls what goes in and out. Animals are supported by their skeletons and do not need the thickk cell walls of plants.
Vacuole: These storage areas contain air, water, wastes and food particles. Animal cells often contain several small vacuoles.
Fig 5.3.3 Animal cells are made up of parts called organelles. Each organelle does a separate job inside the cell.
Cell nucleus: controls all chemical reactions in a cell and how the cell develops and reproduces. The nucleus is the ‘control room’ of the cell.
Cytoplasm: This jelly-like liquid is where energy is released and new substances are made. The cytoplasm can be thought of as the chemical factory of the cell.
Worksheet 5.1 Cell diagrams D ra
g - a n d - d ro p
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Animal cells
Specialised animal cells Animals are complex organisms and different cells are needed to carry out the different functions that allow them to live, move about and Science reproduce. Specialised heart cells make up the heart, liver cells make up the liver, skin cells make up skin You look dead! and so on. Blood cells carry food and All your visible skin cells are oxygen around the body; nerve cells dead! Luckily, however, the dead cells are constantly send messages from the brain to the flaking off and being muscles; bone cells help support the replaced by new skin cells body and protect the internal organs; forming underneath. At any fat cells insulate the body and store time, your dead skin energy; and sperm and eggs cells can accounts for up to two kilograms of your mass! combine to produce a new animal.
Clip
Cells are constantly dying but most are being replaced by new ones being made at roughly the same rate. Remove enough of one type of cell, however, and death is likely to occur since the body cannot rebuild them quickly enough. Serious burns, for example, destroy most of the skin cells required to keep water in the body and infection out of it. After a few days, many serious burns victims die due to dehydration (water loss) and infection. The larger the animal, the more cells, and more types of cells, it contains. The human body, for example, is made up of over one hundred million million cells, of which there are about Prac 1 two hundred different, specialised types. p. 157
Nerve cells: send messages from the brain to the muscles and back from nerve receptors to the brain.
Involuntary muscle cells: make the heart muscle beat and the diaphragm move.
Bone cells: help support the body and protect its internal organs.
White blood cell: helps the body fight off infection from bacteria and viruses. Red blood cells: carry oxygen around the body. Fat cells: insulate the body and store energy.
Fig 5.3.4 Every animal cell has its own specific job. These are just a few types of specialised animal cells.
5.3
QUESTIONS
Remembering
4 State the type of human cells that:
1 Specify how many cells our bodies are thought to contain.
a help keep out infection
2 State approximately how many different types of specialised cells there are in the human body.
b send messages from the brain to muscle
3 State an example in which a loss of one type of cells can quickly lead to death.
d assist with movement
c carry oxygen e help fight bacteria and viruses f store energy and help insulate the body.
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11 Identify the part of an animal cell that could be called: a the ‘control room’
6 Muscle cells contain large numbers of mitochondria. Discuss why this might be.
b the ‘chemical factory’
7 Predict what would happen to a human if they were not producing enough:
d the ‘powerhouse’
a red blood cells b white blood cells.
c the ‘gatekeeper’ e the ‘walls’.
Evaluating
8 Multiple sclerosis is a disease that attacks nerve cells. Predict the likely symptoms of this disease.
12 Humans produce some cells only after they reach puberty. Propose what type of cells they are.
9 Stroke restricts the amount of blood being fed to the brain. As a result, brain cells die. The more the restriction, the more brain cells that die. Predict the likely symptoms of a stroke.
13 The digestive systems of sheep, cows and rabbits contain special bacteria that help break down a substance found in the cell walls of grass. Humans, however, are unable to break it down. Propose what this substance might be.
10 Predict what humans would look like if they contained chloroplasts full of green chlorophyll in their skin cells.
5.3 1
PRACTICAL ACTIVITY
Viewing prepared slides
Aim To observe prepared slides of different specialised plant and animal cells.
!
5.3
5 Plant cells need strong cellulose-filled walls, whereas animal cells do not. Explain why.
Applying
Unit
Understanding
Safety Only use commercially prepared slides of animal products to minimise the risk of blood-borne diseases.
Equipment • monocular microscope • microscope lamp, if needed • selection of prepared slides of different animal cells
Method 1 Obtain a focused image for each of the prepared slides. 2 Sketch each image, labelling what it is, the magnification used and whether the cell is a plant or animal cell.
Questions 1 Compare the cells you observed, listing any differences and similarities.
2 Students were once allowed to prepare their own slides using a sample of their own blood. Propose a reason why this is not allowed now. 3 Propose other advantages of students using prepared slides instead of obtaining their own specimens.
Science
Fact File
Using a microscope 1 Place the prepared slide on the stage and secure it using the clip. 2 Adjust the mirror or diaphragm to maximise the light passing through the slide. 3 Choose the objective lens with the lowest magnification and rotate it into place. 4 While looking at the microscope from its side (not through the eyepiece), adjust the coarse focusing knob to bring the stage and objective lens as close as possible to each other. 5 While viewing through the eyepiece, turn the coarse focusing knob so that the stage and objective lens move further apart. Keep doing this until the specimen is roughly in focus. 6 Adjust the fine focusing knob to bring the specimen further into focus. 7 Adjust the mirror or diaphragm to change the amount of light so that the clearest image is produced.
157
Unit
5.4
context
Single cells, groups of cells
The first living things on Earth had only one cell. Bacteria are the simplest cells found on Earth today and still only have one cell. That single cell does everything needed to keep the organism alive. In
more complicated organisms, cells are grouped together in specialised colonies, according to their type. Each colony of cells does their own particular job—a job that could not be done by single cells living alone.
Protists
Fig 5.4.1 Single-celled organisms are often called germs and are the cause of many infections and diseases. This finger is so badly infected with bacteria that it has developed gangrene. The black on the finger is dead tissue and will need to be amputated. Smoking increases your risk of gangrene.
Single-celled organisms Sometimes organisms are so small and simple that they need only a single cell to carry out all of their required functions such as movement, reproduction and taking in food. These single-celled organisms are unicellular, meaning they are ‘one celled’. Unicellular organisms can be seen only using a microscope. For this reason, they are also known as microorganisms or microbes.
Other unicellular organisms, known as protists, are found living in most samples of water. You are likely to see them if you view a drop of pond water under a microscope. Protists are given their own kingdom since they do not fit neatly into either the animal or plant kingdoms—some protists are animal-like in that they feed on other organisms, whereas others are plant-like, having chloroplasts that contain the green pigment chlorophyll. There are four different types of protists: flagellates, ciliates, amoebas and sporozoans. Sporozoans are the only protist that do not move about on their own. Instead, they live in other cells, getting carried around with them. The potentially deadly disease malaria is caused by a sporozoan that lives in the blood cells of infected people. The disease can be transferred when a mosquito passes on malaria-infected blood. Although many of the protists cause disease, many others are important parts of the food chain. Go to
Science Focus 2 Unit 5.1
Bacteria Bacteria are unicellular organisms and are the simplest type of cell. Bacteria are everywhere—they are found in their millions in the soil, in the air, in your gut and on your skin. Some types of bacteria are said to be ‘good’ since they help the gut digest food. Others are used in the production of foods such as yoghurt and cheese. Bacteria also break down dead plants, animals and faeces, returning their nutrients to the soil. Other bacteria (commonly called germs) are less nice. They cause bad breath, body odour, pimples and infections. Greenish-yellow pus is a sign of a bacterial infection.
158
Fig 5.4.2 Each of these golden spheres is a bacterium cell called Staphylococcus aureus. They cause the pus in a pimple.
nucleus flagellum cell wall
Euglena
Fig 5.4.3 An SEM image of euglena. Euglena is an example of a flagellate protist. Flagellates have one, maybe two, long whip-like tails (called flagellum) that help them move. Flagellates most resemble plants since they contain chloroplasts filled with green chlorophyll.
cilia
cytoplasm
5.4
chloroplast
Unit
Multi-celled organisms
gullet eye spot
Although microorganisms only have one cell, plants and animals need many more since they are much larger and much more complex. They require a range of specialised cells, each type carrying out a specific task, such as carrying oxygen in the blood or carrying electrical messages from the brain to the muscles. These different specialised cells are then arranged into groups that help them work more effectively. It’s a bit like people working on a big project. One person working alone needs to cover all the required tasks, whereas a group can split the project according to what each member is best at. In a café, for example, some people will be the cooks, some will be cleaners, some will be waiters and others will make up the bills and deal with money. In this way, a group can perform more complex tasks than one person alone or a group with everyone trying to do everything. Cells Science are organised in a similar way— colonies of specialised cells do Please boil the water particular jobs that could not be For two months in 1998, the done by single cells living alone residents of Sydney were or by identical cells trying to do required to boil all their everything the organism needs. drinking water. Large quantities Having different types of cells of two types of microscopic makes doing these jobs more single-celled organisms, efficient, as cells can focus on one Cryptosporidium and Giardia, had been found in the water main thing at a time. Animals supply. These flagellate protists and plants that are made up of cause severe gastro-intestinal lots of cells working together are problems if taken in and boiling said to be multicellular, meaning is one way of killing them. ‘many cells’.
Clip
oral groove
nucleus Paramecium
Fig 5.4.4 Paramecium is an example of a ciliate protist. Ciliates have tiny hairs arranged around them. These beat in ‘waves’, allowing the organism to move about. Ciliates most resemble animals since they ‘feed’ on other microorganisms.
pseudopodium cytoplasm
nucleus Amoeba
Fig 5.4.5 Amoebas have the ability to change their shapes and move by ‘flowing’. Amoebas are animal-like in that they surround other microorganisms and consume them.
Worksheet 5.2 Protists
Prac 1 p. 162
Fig 5.4.6 Although small, this mouse is huge compared to a bacterium or a protist. Mice are examples of multicellular organisms, as are humans and gum trees. Even microscopic bed lice are multicellular.
159
Single cells, groups of cells Cells, tissues and organs Groups of similar cells make up tissue. Skin tissue, for example, is made from skin cells, liver tissue is made from liver cells and brain tissue is made from brain cells. Tissues can then group together to form organs. Liver tissue makes up the liver, kidney tissue makes up kidneys; and skin tissue makes up the skin.
heart muscle cells
heart tissue
heart (organ)
Fig 5.4.7 Cells make up tissue and tissue makes up organs.
Systems A group of organs that work together is called a system. An organism is formed when several systems work together. In animals, for example, groups of muscles form the muscular system. Human body systems We humans are relatively large and complex organisms and so have numerous body systems to allow us to function. Some of these systems are the: • digestive system, which allows the processing of food, releasing its energy into the body • circulatory system, which pumps blood around the body, carrying vital oxygen and nutrients to the cells and carbon dioxide and wastes away from them • respiratory system, which draws vital oxygen into the bloodstream and expels carbon dioxide from it • skeletal system (the skeleton), which protects the organs and allows the body to move • excretory system, which rids the body of wastes, particularly urine. Go to
Endocrine system
Nervous system
Fig 5.4.8 Three of the many human body systems
Plant systems The cells in plants also group together to form tissue, organs and systems. Leaf cells, for example, group to form an organ called a leaf. Several leaves then form the plant’s foodmaking system. Fig 5.4.9 Compared to animals, plants are relatively simple and so have fewer systems.
Flower: a plant’s reproductive system.
Stem and trunk: a food and water transport system consisting of a network of veins.
Leaves: use photosynthesis to produce food (glucose) for the plant.
Science Focus 2 Unit 4.1
Roots: secure the plant in the ground and draw water and nutrients from the soil.
Go to
160
Lymph system
Science Focus 2 Unit 3.1
Bulb: a food storage system in the form of a bulb.
Unit
QUESTIONS
Remembering 1 State which type of cell is the simplest. 2 List: a some benefits that bacteria bring b some bad effects that bacteria cause. 3 State the correct term for a single-celled organism. 4 List four types of single-celled organisms. 5 Name a disease caused by a unicellular organism. 6 Name four different organs.
Understanding
Evaluating 16 There are benefits and disadvantages of having specialised cells doing different jobs. a List some advantages and disadvantages of having specialised cells. b List some advantages and disadvantages of having one cell doing all jobs in a living thing. c Evaluate whether it is better to be a single-celled organism or to be made up of lots of specialised cells. 17 If a cell is represented by a circle (shown in diagram A), select the diagram (from B, C, D or E) that best represents:
7 Describe the four different methods that single-celled organisms use to get around.
a tissue
8 In complex organisms, cells are specialised to carry out a specific task. Explain the advantages of this arrangement.
c a body system.
9 Describe what components make up the following:
5.4
5.4
b an organ
A
B
C
a tissue b organ c body system. 10 Predict which human body system could be referred to as the ‘locomotion system’.
D
E
Applying 11 a Identify which single-celled organisms are plant-like and which are animal-like. b Identify how each type displays their plant- or animal-like characteristics. 12 Identify which body system is the main one involved in each of the following situations: a Your face goes red after you run for one kilometre. b Your leg moves up after you are tapped on the knee. c You need to go to the toilet. d You feel ‘full’ after a meal. e You gasp for air after swimming under water.
Analysing 13 Compare the following by ordering from smallest to largest: organ, cell, tissue, system.
Fig 5.4.10
18 When bushwalking, water from flowing creeks will be relatively safe to drink. In contrast, still water (referred to as stagnant) may make you ill. a Predict the type of organisms in this water that will make you ill. b Propose a way of ‘cleansing’ stagnant water, making it safe to drink. c Propose a reason why flowing water is safer than stagnant water. 19 Select which system best matches the body parts stated below.
14 Compare flagellates, ciliates and amoebas by listing their similarities and differences.
flower
transport system
stems
food storage system
15 Cells contain organelles, whereas human body systems contain organs. Compare an organelle in a cell with an organ in the human body by listing their similarities and differences.
leaves
water absorption system
roots
food-making system
bulb
reproductive system.
161
Single cells, groups of cells
5.4
INVESTIGATING
e -xploring W
n eb D esti natio To find out more about body systems, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge. Choose a body system and examine in more detail how it works. Produce a PowerPoint presentation or poster to show your findings. L
5.4
PRACTICAL ACTIVITY Questions
1
Life in a drop of water
Aim To observe any single-celled organisms that might be in pond water and draw them.
!
Safety Do not squirt or drink pond water, as it contains live organisms that may cause infection.
Equipment • sample of pond water or other water containing single-celled organisms (e.g. a hay infusion) • monocular microscope • lamp, if needed • glass microscope slide • cover slip • eyedropper
Method 1 Place a drop of pond water onto the glass microscope slide and cover it with a cover slip. 2 Use the microscope to view any life within the drop of water. 3 Sketch as many different organisms as you can.
162
1 Describe the size and shape of the different organisms you saw. 2 Explain how they appeared to move (i.e. by whip-like tails, beating hairs or flowing). 3 If possible, identify each as either a flagellate, ciliate or amoeba.
Science
Fact File
Using a microscope 1 Place the prepared slide on the stage and secure it using the clip. 2 Adjust the mirror or diaphragm to maximise the light passing through the slide. 3 Choose the objective lens with the lowest magnification and rotate it into place. 4 While looking at the microscope from its side (not through the eyepiece), adjust the coarse focusing knob to bring the stage and objective lens as close as possible to each other. 5 While viewing through the eyepiece, turn the coarse focusing knob so that the stage and objective lens move further apart. Keep doing this until the specimen is roughly in focus. 6 Adjust the fine focusing knob to bring the specimen further into focus. 7 Adjust the mirror or diaphragm to change the amount of light so that the clearest image is produced.
Prescribed Focus Area: Current issues in research and development Many scientists are researching special types of cells called stem cells. Stem cells offer a way of treating many diseases and conditions that currently have no cure. Stem cells can come from two sources—adults and embryos (the earliest form of life). Although some success has come from adult stem cell research, more success has come from research involving embryonic stem cells. Extracting the stem cells, however, destroys the embryo and so a potential human life is lost. It is little wonder, then, that there is much heated debate over the issue of stem cell research.
Adult stem cells The number of stem cells in our bodies decreases rapidly after we are born. Adults are left with some stem cells, but these only grow into a specific type of cell. These adult stem cells allow the body to repair minor injuries such as bruises, cuts and broken bones. Since the body has finished growing, these adult stem cells cannot develop into new nerve or brain cells. This means that the body cannot repair any injury to the nerves, brain or spinal cord. This leaves many stroke and accident victims permanently paralysed with limited brain function. It also means that the scarring associated with degenerative nervous conditions such as Multiple sclerosis (MS), motor neuron disease and Parkinson’s disease cannot be stopped or repaired, nor can the loss of function be reversed.
5.4
Stem cells
Unit
Science Focus
Embryonic stem cells We all start as a single cell called a zygote, formed when a single sperm cell (from a male) fertilises a single egg or ovum (from a female). This zygote cell then divides to form two identical new cells. These then divide again to form four cells, which then divide to become eight, then 16, 32 and so on. All these cells are identical and are known as embryonic stem cells. After about three weeks, however, the stem cells start to develop into the two hundred types of specialised cells needed for the human body to live and function. Each cell soon becomes so specialised that it can carry out only the specific task within the body it has been assigned. Some become the cells that make up heart tissue. Others develop into brain cells, skin cells, red blood cells, nerve cells or some other specialised cell that the body needs. This process of specialisation is referred to as differentiation.
Fig 5.4.12 Christopher Reeve (1952–2004) played the hero in four Superman movies. He became a quadriplegic after a horse-riding accident and became a strong supporter of embryonic stem cell research.
Embryonic stem cell research Embryonic stem cells contain in their nucleus all the information on how to build the two hundred or so different types of specialised cells that a human needs. This fact has encouraged researchers to harvest embryonic stem cells and develop methods that direct them to change into the cell types needed for a specific medical purpose.
Fig 5.4.11 The stem cells in this eight-week-old foetus have clearly begun to differentiate into skin cells, brain cells, retina cells and blood cells.
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Stem cells
Fig 5.4.13 Embryonic stem cells have the ability to form any other type of cell.
The case for Scientists working on mice have already shown that a cut spinal cord can be repaired by injecting embryonic stem cells into the broken ends of the spinal cord. This gives hope, for example, to anyone who has severed or crushed their spinal cord in a diving, bike or car accident. A damaged spinal cord can result in paraplegia or quadriplegia (more properly known as tetraplegia). Paraplegia is the loss of use of the legs, whereas quadriplegia is the loss of use of legs and arms. There are currently no successful treatments for these
injuries. Embryonic stem cells could potentially be cultivated to form new nerve cells. These might then replace the broken ones in the victim’s spinal cord, hopefully allowing them to walk again. Researchers in 2008 successfully cultivated pancreatic cells from human embryonic stem cells. Diabetics have a faulty pancreas that does not produce sufficient insulin. Therefore, they need to supplement their insulin with regular injections. This research will potentially lead to a permanent cure for diabetes. In the future, embryonic stem cells may also be cultivated to develop into: • growing new organs for someone who needs a transplant • growing new body parts to replace those lost in an accident • repairing damage to the brain from conditions such as stroke and accidents • repairing damage to the brain and nervous system caused by MS or Parkinson’s disease • repairing damaged heart muscle after a heart attack, allowing patients to once again take up physical activity • growing new skin for burns victims, stopping dehydration and infection and allowing relatively scar-free recovery.
Foetus: The stem cells in the blastocyst naturally start to differentiate into all the different cells a human body needs for its tissues, organs and systems.
Zygote: the first cell of the new human being.
human
The cells continue to divide.
sperm muscle cells
nerve cells
egg Blastocyst: the first cell has divided and divided into a ball of identical cells.
Inner cells can be collected from the blastocyst.
Fig 5.4.14 Stem cells in the blastocyst will develop into all the cells required to make up a new human. In embryonic stem cell research, the blastocyst is ‘harvested’ to remove their stem cells.
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Stem cells are placed in a growth medium.
Worksheet 5.3 Cloning
skin cells
Unit
Adult stem cell research The stem cells that adults retain cannot repair damage to nerves or the brain. Some researchers have, however, successfully changed these stem cells into other cells. This gives hope that they might be able to be cultivated into whatever cells are required to repair damage. The big advantage of using adult stem cells is that no human embryo needs to be destroyed. There are, therefore, no moral objections to their use. Adult stem cells, however, seem less likely to provide a potential cure than embryonic stem cells.
STUDENT S TUDENT A ACTIVITIES CTIVITIES 1 a Use the Internet and newspapers to gather reports on some experiments being carried out with stem cells. b Use the information collected to outline what is being studied. 2 Create a poster or cartoon strip to explain to people what embryonic stem cell research is about. L 3 To find out more about the stem cell debate, a list of web destinations can be found on We n Science Focus 1 Second Edition Student Lounge. b Destinatio Use the available websites and any other material to answer the following questions: a List the advantages and disadvantages of stem cell research. b Investigate why some in the community are concerned about stem cell research. c Produce a survey to analyse public opinion about stem cell research. Test your survey on your classmates, parents
5.4
The case against Healthy Embryonic stem cells are removed from a form of the Adult stem cells taken normal embryo called a blastocyst. This occurs within six to Patient cell taken eight days of fertilisation. Although the blastocyst Stem cells cannot survive on its own and bears no resemblance DNA of cell placed in Cell types transferred culture to a human, it is the start of a new human life. Many injected into an egg argue that it is immoral to destroy human life, regardless into patient of its age or stage of development. For this reason, many argue against embryonic stem cell research. Specific cell One potential source of embryos are those ‘left over’ types grown Embryo grown from IVF (in vitro fertilisation). Although these frozen into blastocyst embryos are unlikely ever to be implanted to form a baby, Stem cells placed in culture they are still the first stages of life. For this reason, many believe they, too, are too precious for scientific research. Fig 5.4.15 How adult stem cells might be used to repair tissue. There is no risk of rejection in the use of adult stem cells since the cells come from the patient themselves.
What’s your opinion? There are reasons for and against embryonic stem cell research and, until recently, it was forbidden in Australia. In 2007, the New South Wales government passed legislation allowing embryonic stem cell research in the State. As a future voter, you will need to decide on scientific and moral issues such as this one. What do you think should happen?
Science
Clip
Belly button stem cells! The umbilical cord connects the baby to its mother for the nine months of pregnancy and a little blood remains in it immediately after birth. Some researchers are now collecting this umbilical blood and are attempting to remove any stem cells it may contain. Isolation and growth of these cells, however, has proven to be extremely difficult.
or the community, and write a brief summary of your results. d Evaluate the information you have collected and make a decision. Do you support embryonic stem cell research? Give reasons for your answer. 4 Although adults have some remaining stem cells that can be used for research, there is strong support amongst scientists for using embryonic stem cells instead. a Investigate and list the advantages of using embryonic stem cells over adult stem cells. b It might be better for a person who has a particular medical problem to use their own stem cells rather than embryonic stem cells. Do some research to explain this idea. 5 Hold a class debate on the topic: Research into embryonic stem cells can provide enormous benefits and should continue.
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CHAPTER REVIEW Remembering
12 Identify whether tissue, organs or body systems contain:
1 State the type of material Robert Hooke was looking at when he discovered cells.
a the most cells b the least cells.
2 Sketch a plant cell and label its parts (organelles). Specify what each organelle does.
Analysing
3 Name three types of plant cells and three of animal cells. State the job of each cell.
13 Compare plant and animal cells by constructing a table like that below to show their features.
4 Name two specific protists, and state which type of protist each one is.
Feature
Plant cell
Animal cell
5 State whether a protist is a multicellular or unicellular organism.
Understanding 6 Copy and complete the following table to summarise the history of cells. Include as many scientists as you can find throughout this chapter. L Date 1609
Scientist Hans Janssen and his son
Discovery Invented the compound microscope
14 Compare simple microscopes, compound microscopes and electron microscopes by listing their similarities and differences.
Evaluating 15 Propose reasons why different types of microscopes are needed. a List the advantages and disadvantages of an organism being multicellular. b List the advantages and disadvantages of an organism being unicellular. c Evaluate whether unicellular or multicellular organisms have a greater advantage in terms of survival. d Identify whether humans are unicellular or multicellular. Explain your answer.
b Animal cells need more mitochondria than plant cells. 8 Explain what a specialised cell is and the advantages specialised cells bring to an organism.
16 Assess the value of van Leeuwenhoek’s discoveries to society and science. Give reasons to support your answer. Worksheet 5.4 Crossword Ch
Applying
10 Identify the contents of a vacuole if it is in: a a plant cell b an animal cell. 11 Identify the type of protist shown in Figure 5.5.1.
Fig 5.5.1
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pt
a
9 Calculate the overall magnification for a microscope with a ×20 eyepiece and a ×50 objective lens. N
Worksheet 5.5 Sci-words
s
a There are more types of animal cells than plant cells.
on
7 Explain why:
er R sti ev i ew Q u e
Heat, light and sound
6
Prescribed focus area:
The applications and uses of science
Key outcomes 4.3, 4.6.1, 4.6.4, 4.6.5, 4.6.6, 4.12
•
Energy cannot be destroyed—it can be changed only from one form into another.
•
Heat is a form of energy that can be transmitted by conduction, convection or radiation.
•
Light is a form of energy that can travel through a vacuum.
•
Sound needs a material to travel through.
•
A variety of energy transformations occur in everyday devices.
•
The gain and loss of heat can be controlled using insulation, of which air is an excellent example.
Potential energies store energy, whereas kinetic energy is the energy of movement.
Additional
Energy exists in many different forms.
Essentials
• •
Unit
6.1
context
Energy
Energy is one of the topics you hear a lot about in the media. Headlines about rising petrol prices, green energy and global warming are common in newspapers, on TV and on news websites. The world’s energy demand is increasing dramatically and an energy crisis seems just around the corner. For
this reason, scientists and engineers are searching for alternative energy sources. Many difficult decisions will need to be made soon about energy. As a future voter, you will need to help make those decisions. Therefore, an understanding of energy, what it is and what it does is vital for any citizen of our world.
Energy is a very difficult thing to define as there are many different ways of describing it. Different scientists describe energy in different ways, depending on the area of science they work in. This is because energy comes in many different forms. All scientists would agree on one thing, though—energy is what makes things happen.
Forms of energy Two important types of energy are kinetic energy and potential energy.
Kinetic energy Kinetic energy is the energy of movement. All moving things have kinetic energy. You have kinetic energy every time you play handball, train for netball or you walk to class.
Kinetic energy is the energy that an object has when it is moving. The faster the object moves, the more kinetic energy it has.
Fig 6.1.1 Heat and light are two different forms of energy.
What is energy? Quick Quiz Without energy, there would be no life, no movement, no light, no heat and no sound. Everything that happens on Earth is powered by energy. It lights and warms the Earth and it powers the chemical reactions that happen in the body and in test tubes. It powers photosynthesis in plants and it powers the TV and the car. It can be stored and it can be wasted.
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Fig 6.1.2 Kinetic energy is the energy of motion.
Unit
Other forms of energy
Potential energy is stored energy. It is energy that has the potential to do something. When released, it turns into other forms of energy, such as heat, sound, light or the energy of movement, which is known as kinetic energy. Food, petrol, a battery and a stretched rubber band all store potential energy in some form within their materials. Anything that is held above the ground has potential energy because gravity is trying to pull it down. Potential energy can take many different forms.
Although potential and kinetic energies are important, there are other forms of energy.
Chemical energy is stored energy that is waiting to be released. Petrol and LPG store chemical energy and release it so quickly that it may explode. Food releases its energy more slowly.
Heat energy can come from a flame, the Sun, chemical reactions, electricity and nuclear explosions. It can burn, boil water, melt plastic, dry clothes and increase the temperature.
Electrical energy can come from a battery, power point or thunderbolt. It can power an iPod, TV, Wii or a PlayStation. It can kill if handled carelessly.
Nuclear energy is energy stored in the nucleus of the atom. It can be released in radioactive decay or in a nuclear explosion. Nuclear explosions are continually happening in the Sun and in the stars and are the source of the light, heat and radiation they emit.
Elastic potential energy is the energy stored in a stretched spring or elastic band. Compressed springs store elastic potential energy too.
Gravitational potential energy is the energy that an object has when it is at a height above the ground. The higher an object is, the more gravitational potential energy the object has.
6.1
Potential energy
Sound energy can come from a radio, guitar, drum or an explosion. It can vibrate speakers, the floor and eardrums.
Work is energy. Work is done whenever a force moves an object. A crumpled car has had work done on its panels: sheets of steel have been forced to shift into new positions.
Light energy can come from a light bulb, glow-worm or a fire. Solar energy is simply light energy from the Sun.
Fig 6.1.3 Potential energy is stored energy. When released it converts into other forms of energy.
Fig 6.1.4 Other forms of energy.
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Energy
Energy and its units All forms of energy are measured with the same units. Scientists use a unit called joule (abbreviated as J) to measure energy. Another unit, kilojoule (kJ) is commonly seen on food packaging. One kilojoule is the same as 1000 joules (1 kJ = 1000 J). Another older unit for energy is calorie (1 calorie = 4.2 kilojoules).
Energy conversions Energy can be changed or converted from one kind of energy into another. All machines and appliances operate because they are able to change energy into another type, and then use this energy to make something happen. When a match is struck it is moving and so it has kinetic energy. This kinetic energy is turned into heat as the match head scrapes across the box. This heat energy releases the chemical energy stored in the match head and wood. It has been converted into light and heat energy. Food stores chemical energy, too. That’s why animals, including humans, eat it. Humans use this store of energy to do things. It allows our bodies to keep functioning and allows us to dance, ride bikes and run the 100 metre sprint. In these cases, chemical energy has been converted into the kinetic energy of movement. Climbing to the top of a diving board or the top of a mountain converts chemical energy into gravitational potential energy. A light bulb converts electrical energy into useful light energy and not-so-useful heat energy. Some of the electrical energy has been ‘wasted’.
Energy conservation
Science
Energy can never be created or destroyed. It can be changed only from one form to another. This is the law of conservation of energy. Sometimes it appears that energy is lost, but when you look closer you find that the energy has just been converted into lessuseful forms, such as sound, heat or light.
People in science: James Joule (1818–1889)
Poor conversions
Fact File
James Joule was a British physicist who found that, rather than energy being lost or destroyed (which was the common belief at that time), various forms of energy are changed from one form to another. This is the law of conservation of energy. In 1838 he began experimenting in a laboratory equipped at his own expense at his family brewery. In 1843 he determined the amount of work required to produce one unit of heat, now known as the joule.
Efficient things waste very little energy, converting its energy into useful forms, generally making them cheaper to run. Most things are inefficient, converting a lot of energy into useless forms (usually heat and sound). Cars, for example, are very inefficient—only 25 per cent of the chemical energy in petrol actually goes into movement. The rest is ‘wasted’ as heat and sound. There is so much waste heat that a car can quickly overheat. That’s why cars need radiators. Likewise, a cyclist wastes about 85 per cent of their energy. Only 15 per cent of their energy goes into moving the bike. The rest is just making them hot and bothered. This is why they sweat. chemical energy (petrol) heat/sound 75%
Prac 1 p. 174
kinetic 25%
chemical energy (food) heat/sound 85%
kinetic 15%
Fig 6.1.5 Most everyday actions involve energy converting from one form into another.
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Fig 6.1.6 Most energy conversions are inefficient, with a lot of energy being ‘wasted’.
Prac 2 p. 174
Prac 3 p. 175
Unit
6.1
The source of energy Energy from the Sun Most of the energy we use on Earth originally came from the Sun. Plants use photosynthesis to capture the Sun’s energy to make their own food—a type of sugar called glucose. Glucose is a store of chemical energy for the plant to be converted whenever the plant needs it. Animals cannot make their own energy and so must eat plants or other animals to gain the energy they need for keeping warm, moving about and reproducing. Herbivores eat the plants directly and carnivores gain their energy by eating herbivores or other carnivores.
Fig 6.1.8 Fossil fuels are the remains of prehistoric plants and animals that died millions of years ago. It is very likely that little bits of dinosaur are in the petrol pumped into every car!
Sunlight is also absorbed by non-living objects, such as rocks, and later released as heat. Of course, without the Sun’s light energy we would always be in the dark. Solar cells turn the Sun’s light energy directly into electricity.
Prac 4 p. 175
Energy from the nucleus
Fig 6.1.7 The Sun is the source of most of our energy on Earth.
The energy absorbed by plants sometimes ends up in the fossil fuels (e.g. petrol, oil and diesel) we use for transport and in the wood we use for making paper. This energy is then released once more when these materials are burnt in a car engine or a fire.
The Sun gets its energy from nuclear explosions on its surface. The first nuclear explosion on Earth happened in 1945, releasing a huge amount of energy as heat, light and sound. Since that first detonation, many similar explosions have happened on Earth. Whereas bombs and the Sun release their energy in an uncontrolled manner, nuclear reactors can control the release of nuclear energy. The ‘tamed’ nuclear energy can then be used for other purposes, such as the production of radioactive medicines and the generation of electricity. Worksheet 6.1 Energy
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Energy
6.1
QUESTIONS
Remembering
13 Clarify what is really meant when we say that energy is ‘lost’.
1 Although there are many different descriptions of energy, all scientists agree on one description. State what that is. 2 State what types of energy could be called potential energies. Give an example of each.
14 Describe the energy transformations that take place in the situations given below. Remember: The energy may be transformed more than once, and to more than one type or form of energy.
3 State what sorts of things have kinetic energy.
a toaster
4 List all the forms of energy shown in Figure 6.1.9.
b light globe c DVD player d car engine.
Applying 15 Identify the energy transformations that take place when an atomic bomb explodes.
Fig 6.1.9
16 Solar panels capture the Sun’s energy and turn it into electricity. Demonstrate how solar panels are similar to plants.
Analysing 17 For each of the energy transformations listed in the table, match the situation to which it belongs. 5 Energy has to come from somewhere. State the two main sources of energy on Earth.
Situation
A Chemical potential → heat and light
Jack in the box
B Light → heat
Torch
C Chemical potential → electrical + light and heat
Cup falling off the bench
D Chemical potential → kinetic and heat
Car braking
E Gravitational potential → kinetic + sound (and heat)
Person running
F Chemical potential → kinetic + gravitational potential
Solar hot-water heater
10 Explain what is meant by the law of conservation of energy.
G Elastic potential → kinetic
11 A herbivorous animal eats only plants. Give an example of a herbivorous animal and explain how it gets energy from the Sun through its food.
Crane lifting steel girders
H Kinetic → heat and sound
Burning wood in a fire
6 State how humans use the Sun’s energy: a directly b indirectly. 7 Petrol is burnt in a car engine to get the car moving. A lot of energy, however, is wasted. Specify two forms of energy into which this ‘lost’ energy is converted.
Understanding 8 Lifting something up gives it potential energy. a Explain how. b State what type of potential energy it has. 9 Clarify what is meant by the term energy transformation.
12 Carnivorous animals only eat other animals or insects and do not eat plants directly. Give an example of a carnivorous animal and explain how their energy also can be traced back to the Sun.
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Energy transformation
Unit
Water stored in dam high up in mountains (gravitational potential)
↓ Water falls down pipes (kinetic)
↓ Water turns turbine (kinetic)
↓ Turbine produces electricity (electrical) a Not all the energy that is stored in the water at the start is turned into electricity at the end. Some people could say that energy is ‘lost’ at each stage of making electricity. Explain where this lost energy may go at each stage of the process above.
b Identify a better term to replace the word ‘lost’. c Describe the energy changes that could occur as a person at home turns on the television and uses the electrical energy.
6.1
18 The energy transformations below occur in a hydro power station. Analyse each stage of the process and answer the questions that follow.
Evaluating 19 Energy-efficient light bulbs are more expensive than normal incandescent light bulbs. Justify, then, why we should all use energy efficient bulbs despite their cost.
Creating 20 Construct a flow chart to summarise the energy changes in each of the following situations: a a match is lit b a person parachuting out of a plane c a person doing a bungee jump d a student riding a bicycle, starting from rest.
6.1
INVESTIGATING
Investigate your local resources (e.g. textbooks, encyclopaedias, Internet etc.) to find out how the following produce energy: L • hydro, coal, tidal or nuclear power stations used to generate electricity • mini-electrical generators, such as dynamos on a bike • batteries—their different types and the chemicals used in them • ways of using the Sun to generate electricity • natural gas—how it was made originally and how it is tapped for use
e -xploring We b Desti nation
To find out about renewable and non-renewable energy sources,a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge. a Construct a table to show the advantages and disadvantages of each energy source. b Evaluate each energy source and decide whether it is suitable to use in the future. Give reasons to support your decisions. L
• LPG—its production and uses • petrol—where it comes from and how it is refined. Present your work in one of the following ways: • a flow chart showing the main steps in producing the energy • a cartoon strip showing the main stages • a set of instructions of how to make the energy • a pamphlet for tourists to a plant where that energy is produced • a set of photos showing the main stages.
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Energy
6.1
PRACTICAL ACTIVITIES Method
Relighting candles
1
When a candle burns, the wax vaporises and catches alight, releasing heat energy and light energy. If it is blown out, the vapour does not burn but appears as smoke. It also can be used to relight the candle!
1 Light a candle, then gently blow it out. 2 Lower a lit match towards the candle, following the smoke trail. 3 The candle should relight. 4 Estimate how far the flame jumps.
Questions
Aim To investigate how energy changes the state of wax.
Equipment • candle • matches
1 Identify the energies that are being emitted by the burning candle. 2 Explain where these energies came from.
Fig 6.1.10
3 Heat the saucepan slowly, constantly moving it in the flame.
Popcorn
2 Aim
To use heat energy to change the stored energy in corn into sound and motion.
4 Continue heating and, without lifting the lid, note any changes that have occurred. 5 Place the hot saucepan on the bench mat and remove the lid. Observe any changes.
Equipment • • • • •
popping corn small saucepan with lid Bunsen burner cooking oil bench mat
saucepan
Method
Bunsen burner
1 Place a small amount of cooking oil in the saucepan. 2 Cover the bottom of the pan with popping corn. Fig 6.1.11
174
>>
a was being provided to the popcorn b you heard
3 Compare the unpopped corn with the popped corn and suggest what happened to the grains.
c was in the popcorn as it was flying about the inside of the saucepan.
3 Chemical energy Aim To release chemical energy and change it into other forms.
Equipment • • • • • • •
test tubes test-tube rack two 50 mL beakers measuring cylinder sodium hydrogen carbonate (i.e. bicarb soda) hydrochloric acid (1 M) acetic acid (i.e. vinegar) (1M)
Method
3 Use a measuring cylinder to measure 10 mL of the acetic acid (i.e. vinegar) in a beaker. 4 Carefully pour the acid into the test tube. 5 Observe any energy released during the reaction. There may be more than one type of energy released, so use your senses of sight and hearing to examine the reaction carefully. 6 Repeat steps 1 to 5 using the hydrochloric acid.
Questions 1 Describe the energy transformations that took place in this reaction. 2 Describe any difference in the amount of bubbles formed by each acid. 3 Identify which acid:
1 Place a spatula of sodium hydrogen carbonate (i.e. bicarb soda) into a test tube.
a released energy the fastest. Explain how you could tell.
2 Place the test tube in a test-tube rack.
c had more chemical potential energy stored in it.
4
6.1
1 Identify what form of energy:
2 List the energy changes that occurred during the heating of the corn.
Unit
Questions
b released the most energy. Explain how you could tell.
Light energy
Aim To perform an energy transformation.
Equipment • source of light • radiometer or light sensor
Method 1 Place the radiometer or light sensor in a dark room. Observe any energy changes. 2 Place the radiometer or light sensor in the light. Observe any energy changes.
Questions 1 Describe the energy transformation that took place. 2 Draw a flow chart to identify the energy changes. 3 Predict what would happen if the light source was brighter. Fig 6.1.12 A radiometer measures light intensity.
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Unit
6.2
context
Heat
In summer you can feel the warming heat of the Sun. You sweat and fan yourself and need to take off layers of clothing to stay cool. In winter you put on extra
clothing to stop you from cooling down too much. Heat warms, dries, cooks, melts and burns. Heat is a form of energy that affects us every day.
Fig 6.2.1 Heat is a form of energy that can cook and warm us. It can also destroy.
Heat and temperature Heat something and the extra energy will raise its temperature or change its state. Temperature depends on heat but is very different to it—heat is a form of energy, but temperature is not. To understand the difference, consider two Bunsen burners set on a blue flame. One heats a beaker halffilled with water and the other heats a beaker filled with water. After one minute, both beakers have been supplied the same amount of heat energy, but the full beaker will be at a lower temperature. When an object gets hotter, its particles vibrate more rapidly. Cool it and the particles vibrate slower. Temperature measures how much these particles are vibrating.
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beaker A The smaller amount of water increases its temperature the most.
800 400
The same amount of heat has to be spread over more particles. Each particle gets less heat energy and so the temperature is less.
beaker B
Both beakers receive the same amount of heat energy.
Fig 6.2.2 Heat is not the same as temperature.
800 400
Symbol
degrees Celsius
°C
degrees Fahrenheit
kelvin
Inventor
Water freezes at
Water boils at
Commonly used by
100°C
• Most countries for weather
Anders Celsius (1742)
0°C
°F
Gabriel Fahrenheit (1717)
32°F
212°F
• USA for weather
K
William Thomson (later known as Lord Kelvin) (1848)
273 K
373 K
• Scientists only
Prac 1 p. 183
Worksheet 6.2 Temperature
Science
Fact File
• Scientists
6.2
Temperature scale
Unit
Temperature is commonly measured in degrees Celsius (°C). As shown in the table, other temperature scales are also used in different parts of the world and by different people. Heat moves from one area to any other area that is at a lower temperature. Heat can move in three ways—by conduction, convection or radiation.
Conduction occurs when the particles in one part are heated, causing them to vibrate more. These vibrations are then passed on from particle to particle through the object. The particles do not actually move along the length of the object—they just pass along the more increased vibrations.
People in science: Anders Celsius (1701–1744) Anders Celsius was born in Uppsala, Sweden, in 1701 into a family of scientists. One grandfather was a mathematician and the other an astronomer, as was his father. Anders himself became a professor of astronomy at the age of 29. He went on several geographical expeditions, including some to polar regions and the equator to compare the length of a degree along a line of longitude in both places. His measurements confirmed Isaac Newton’s opinion that the Earth was slightly flattened at the Poles compared to a perfect sphere. This expedition helped make Celsius famous, and enabled him to raise funds to build the Uppsala Observatory, where he became director. Celsius is most famous for inventing the Celsius temperature scale, in which he made the boiling point of water zero degrees, and freezing point 100 degrees (the opposite of today’s scale). In 1745 Carolus Linnaeus reversed this to the scale we use today. Celsius contributed to astronomy by making many observations, including measuring the brightness of 300 stars. To do this, he tested how many glass plates were needed to stop light from each star getting through. It took 25 glass plates to stop light from the brightest star in the sky, Sirius, from getting through.
Conduction You may have experienced conduction if you have touched a metal tap that has had hot water running from it, or felt the handle of a metal spoon that has been left in a cup of hot water.
heat conducted in this direction
Fig 6.2.3 Conduction—vibrations pass along from particle to particle away from the heat source.
Conductors Different substances conduct heat at different rates. Metals are good conductors of heat, whereas non-metals like paper, wood and plastics are not. Among the metals, copper and gold are particularly good conductors. Solids are better conductors than liquids, which are better conductors than gases. The particles in a solid are packed closer together and so any increased vibration causes a particle to bump into its neighbours. The particles in liquids are a little more spread out than the particles in a solid, so any bump is less likely to be passed on. Gases are very poor conductors because their particles are spread out even more. Gases are less efficient conductors than liquids, as the particles in a gas are spread out much more.
177
Heat
Science
When you walk barefoot across a tiled floor, it feels colder than one that is carpeted, even though they are both at roughly the same temperature as the rest of the room. Meanwhile, the rest of your body doesn’t feel cold. The reason is that the tiled floor is a better conductor than carpet and the air surrounding the rest of your body. The tiles conduct heat away from your feet, leaving the particles in them vibrating less and feeling cold. In contrast, the carpet and air keep the heat where it should be, in your feet and skin, keeping them warm.
Science
Clip
metal rod
good conductor
Fig 6.2.4 Firewalkers do not get burnt because the coals are porous and do not hold much heat. Prac 2 p. 184
Esky
H2O
poor conductors
gas
very poor conductor
Fig 6.2.5 Different substances, different conducting abilities.
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Clip
Cool pools Poor conductors are known as When you jump into a insulators. Insulators are swimming pool, the particularly useful in the water gives you a chill, kitchen, being used for even if it is at the same saucepan handles, oven mitts temperature as the and pot stands to prevent surrounding air. burns to people or surfaces. Water is a much better conductor of heat The reason many than air, so although substances are insulators is you may be comfortable that they contain trapped air. in air at 20°C, water at Air is a gas and is an the same temperature extremely poor conductor of conducts heat away from your body more rapidly, heat. Anything that traps air leaving you feeling colder is likely to provide good for a while. insulation from the heat and cold. • Many animals make use of the poor conducting Science ability of air by having thick fur coats or feathers Insulation can mean that trap air and insulate life or death them against harsh, cold The lower surface of the conditions. Birds ‘fluff up’ space shuttle is protected on cold days to trap more by tiles made of an air under their feathers insulating material that and some animals grow a stops the incredible heat thicker ‘winter coat’. of re-entry from getting inside the shuttle and • Jumpers and blankets are melting it. In 2003, the made from fluffy fibres, space shuttle Columbia like wool or Polartec, broke up on re-entry, which trap air and killing all seven astronauts insulate against the cold. on board. When Columbia was launched a week • Sleeping bags, ski-parkas earlier, a small piece of and doonas have fluffy foam had broken off and padding wedged between punched a hole in those two layers of smooth life-saving tiles! fabric. Doonas become less effective as they are crushed and occasionally need to be fluffed up again to trap more air. • Normally, windows only have one sheet of glass. Double-glazed windows have two layers of glass with an insulating layer of air trapped in between them. This limits the heat entering a building on hot days and exiting on a cold one. • Walls and ceilings often contain fibreglass insulation batts that trap air within fibreglass fibres. They stop heat from flowing in or out of a building, keeping it Prac 3 p. 184 cooler in summer and warmer in winter.
Clip
Firewalking Firewalking is not magic. Only a thin outer layer of the charcoal is on fire and only a small amount of heat needs to be conducted out of the burning coals into the foot for the coal to stop burning. Pure charcoal coals are porous, containing many small holes. The coal would need to be in contact for about a second to harm the foot. At normal walking pace each foot is in ground contact for only half a second, so there is plenty of time for a firewalker to cross a few metres of hot coals.
Insulators
Unit
6.2
Fig 6.2.6 Fur and feathers provide good insulation by trapping air. oven mitt
insulated handle
Convection
saucepan
pot stand
More heat is transferred in liquids and gases by convection than by conduction. Whereas the particles in a solid have fixed positions and can only vibrate, the particles in liquids and gases can move about. They can easily carry their heat energy with them, spreading the heat to other parts of the substance. The spread of heat due to the movement of particles in liquids and gases is called convection.
Fig 6.2.7 In the kitchen, burns would happen without insulation.
R ratings Insulation batts are often given ‘R’ ratings. The R stands for resistance to heat flow. Material
R rating (for a 2.5 cm thickness of the material)
Polystyrene foam
4.5
Insulation batt
4.0
Wood
2.3
Chipboard
2.0
Window (double glazing)
1.6
Window (single glazing)
0.9
Prac 4 p. 185
Hot air rises Hot air rises because its particles are spread out more than in cold air. This makes hot air less dense than cold air and so it will rise to get on top of it. The same happens to liquids—hot liquids rise because they are less dense than cold liquids. As they rise, the hot gases and liquids take their heat energy with them, spreading it throughout the container. Convection explains why: • Hot-air balloons rise. • Smoke rises from a fire. • It is hotter near the ceiling than near the floor. • Central heating vents are usually fitted in the floor, allowing hot air to rise from them. • Hot-water systems have their heating elements or flames at the bottom of the tank so that the heated water will rise and mix with the cold water in the tank.
Fig 6.2.8 Insulation batts can be used to insulate roofs, floors and walls.
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Heat
radiation from sun
to hot water taps
cold water
warmed water rises
roof
Fig 6.2.11 A solar hot-water system also makes use of convection. Fig 6.2.9 Gliders and hang-gliders use convection currents in the air to stay aloft much longer than would be possible otherwise.
to hot taps hot water rises convection current
cold water
cold water sinks
Winds Hot air rises and cold air drops. This results in convection currents. In the atmosphere, these currents are felt as wind. Wind is caused by hot air in one region rising and its place being taken by colder air coming in from another region. For example, air at the equator is hotter than air at the Poles, causing global winds. A sea breeze occurs during the day because the land warms up more quickly than the sea. As warm air rises above land, cooler air moves in from just above the sea to replace it. The opposite occurs at night, when the land loses heat more quickly than the sea. warm air rises
boiler
air cools and drops cool air rushes in to fill space left by warm air
Fig 6.2.10 A hot-water system showing the movement of water by convection.
Cold air drops Cold air drops because its particles are packed together more tightly than in hot air. The same happens in liquids. Cold liquids are denser than hot liquids and so will drop to the bottom of their container. This is why: • Air conditioning vents are often in the ceiling. • There is a flow of cold air onto your feet when you open an upright freezer’s door. • ‘Tub’ type supermarket freezers do not need a lid since the cold air cannot escape easily. • If caught in a fire, the safest place to be is close to the floor.
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cooler sea
warmer land A sea breeze during the day
air cools and drops
warm air rises
cool air rushes in to fill space left by warm air
cooler land
warmer sea
A land breeze at night
Fig 6.2.12 Land and sea breezes are convection currents at work.
Absorption, reflection and transmission
6.2
When you step outside into bright sunlight, you feel the warmth of the Sun on your skin. Heat from the Sun cannot reach you by conduction or convection because space is a vacuum. There are no particles between the Sun and Earth to pass along vibrations or move in convection currents. The heat transfer from the Sun to the Earth is called radiation. Radiation is the transfer of heat energy by invisible waves that do not need a material to travel through. Heat radiation is sometimes referred to as infra-red radiation. Infra-red radiation travels at the speed of light and is a type of electromagnetic wave. Visible light, X-rays and the waves that send signals to radios and the TV are other types of electromagnetic waves.
Unit
Radiation
When infra-red radiation hits something, it can be: • absorbed into the object, warming it up or changing its state • reflected off the object Science • transmitted through the object. Usually a combination of all three Killer heat happens, although the amounts depend In bushfires, it is often on each object. radiant heat that is Black and dark colours are good deadly—it can kill well absorbers of radiation, whereas white, before flames actually silver and light colours are good at reach the victims. reflecting it. This is the reason why: • The plastic coils commonly placed on the roof to heat swimming pools are black. • Black cars tend to heat up more than lightercoloured ones. • Light-coloured clothing stays cooler than dark colours.
Clip
Dark colours absorb radiated heat
absorption Light colours reflect radiated heat
Clear materials, such as glass, transmit radiated heat
Fig 6.2.13 A radiator and red-hot coals emit a great deal of radiation.
All objects give out heat radiation—the hotter the object, the more heat it radiates. Dark objects tend to radiate more heat than shiny or light-coloured ones at the same temperature. The red-hot coals of an open fire radiate a great deal of heat. If someone stands between you and the glowing embers, you notice the loss of radiated heat immediately! An electric Prac 5 p. 185 radiator gives the same effect.
reflection
transmission
Fig 6.2.14 Heat radiation can be absorbed, reflected or transmitted.
I n t e r a c t i ve
Prac 6 p. 186
Prac 7 p. 187
181
Heat The thermos flask The thermos flask is constructed to minimise all three possible ways of losing heat.
stopper polythene vacuum The walls of the flask are made of two thin layers of glass with a vacuum between to prevent heat loss due to conduction and convection
can
hot liquid
Shiny silvered coating to reduce emitted radiation
Fig 6.2.15 A vacuum flask reduces heat loss by conduction, convection and radiation.
6.2
QUESTIONS
Remembering 1 List three sources of heat. 2 List the following in order from best to worst conductor of heat: water, air, copper, outer space. 3 State another name for a poor conductor. Give an example. 4 List the three ways that heat can move from one place to another.
Understanding 5 Explain the difference between temperature and heat. 6 Explain conduction in terms of what is happening to the particles involved.
Applying 15 Draw a particle diagram to demonstrate conduction in a metal rod. 16 Draw a diagram to demonstrate convection currents in a beaker of water being heated from underneath by a Bunsen burner. 17 Draw a diagram to demonstrate how a sea breeze works. 18 Identify the type of heat transfer that applies in each case below. a No material is required. b Particles vibrate. c Particles move through a material.
7 For heat to conduct from one solid to another, two things must happen. Explain what are these two requirements.
19 Identify a household device that gives out both light and radiated heat.
8 Explain how a fur coat insulates the person who wears it.
20 Identify the correct statement and copy it into your workbook.
9 Describe what double glazing is and when it is used. 10 There are many differences between convection and conduction. Explain some of these. 11 Explain why cloudy nights are usually not as cold as nights when the sky is clear. 12 Explain how some supermarket freezers can be open at the top without losing too much cold air. 13 Some central-heating systems release hot air into a house through vents near the ceiling. Explain why this is a poor design. 14 Explain why heat cannot reach the Earth from the Sun by conduction or convection.
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polythene
A Black objects are better emitters but poorer absorbers of heat than white objects. B Black objects are better emitters and better absorbers of heat than white objects. C Black objects are worse emitters and better absorbers of heat than white objects. D Black objects are worse emitters and worse absorbers of heat than white objects. E The colour of an object does not affect how it emits or absorbs heat.
>>
25 Some hairdos keep the head warmer than others. Propose:
22 A saucepan full of water is heated on an electric hotplate. Analyse the situation and explain the different types of heat transfer happening. 23 Enclosed wood heaters are better heaters than open fires. Discuss this statement, listing the good and bad points of each.
a which would be the warmest b which would be coolest. 26 Propose the best colour for the things below (and explain each choice you have made). a solar heating panels b the outside of a house in a hot country c a car radiator, where heat is required to be lost d a fire-fighting uniform.
Evaluating
Creating
24 Propose a reason why you often feel a draft when someone leaves a door open on a cold night.
27 Construct a column graph to display the R values for the table on page 179. N
6.2
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to find out: • how radiation is involved in the enhanced greenhouse effect and global warming
6.2 1
6.2
21 Analyse how a thermos keeps food hot. Outline its main features and explain how these reduce all three types of heat loss.
Unit
Analysing
• how dinosaurs, such as the dimetrodon, were able to absorb and emit heat. Are there animals today that use similar methods to absorb and emit heat?
PRACTICAL ACTIVITIES
Feeling the heat
Aim To find out if our senses can detect temperature accurately.
Equipment • three large beakers or tubs • hot (not scalding) water • ice
800
800
800
400
400
400
Method 1 Fill three beakers or tubs with water—one with hot (not scalding) water, one with lukewarm water and one with icycold water. 2 Place one hand in the hot water (beaker 1) and the other hand in icy-cold water (beaker 3) for one minute. 3 Now place both hands in the lukewarm water. Record any differences you feel.
hot water
lukewarm water
cold water
Fig 6.2.16
Questions 1 State what each hand feels when placed in lukewarm water. 2 Explain what happened in terms of movement of heat to each hand.
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Heat
2
blob of wax
Conduction in metal rods
Aim To compare the heat conductivity of different metals.
Equipment • • • • • •
three rods made of different metals (e.g. iron, copper, brass) candle or wax drops tripod Bunsen burner bench mat timer
Method 1 Assemble the apparatus as shown in Figure 6.2.17. Melt a piece of candle wax or place wax drops at regular intervals along each rod. (Alternatively, use a temperature probe to monitor the temperature at the end of each rod for a given time.)
tripod
Bunsen burner
Fig 6.2.17
bench mat
Questions 1 List the rods in order from best to worst conductor. 2 Present your results as a graph. N
2 Begin heating the non-waxed ends of each rod, and time how long it takes each blob of wax to melt. 3 Stop heating after five minutes, if not before.
3
Insulators
3 Place a thermometer or temperature probe in the cans and record the temperature every minute for 10 minutes.
Aim To compare the insulating properties of different materials.
Equipment • two soft drink cans or small metal containers • insulating materials (e.g. cloth, cotton wool, foam, rubber, newspaper, carpet scraps, fibreglass insulation) • thermometer or temperature probe • hot water • measuring cylinder • timer
Method 1 Surround one can or container with a layer of one of the insulating materials. Leave the other can uncovered. This can is referred to as the control. 2 Use a measuring cylinder to measure a certain amount (e.g. 100 mL) of hot water into each can. (Note: You will need hot water of the same temperature later in this experiment.)
184
thermometer
4 Repeat steps 1 to 3 for each of the other insulating materials, making sure the hot water is at the same temperature as that used previously.
Extension 5 Try different thicknesses (number of layers) of a particular material. 6 Repeat the experiment but, instead of using hot water, use cold water, and attempt to heat the containers using sunlight or other suitable heating sources.
Questions 1 Present your results in a table.
insulating material
2 Construct a line graph for each container on the same set of axes. Put time along the horizontal or x-axis. Label each graph. N 3 Identify which material is the: a best insulator b worst insulator.
Fig 6.2.18
4 Explain why one container was left uncovered.
Unit
6.2
4
Convection currents
Aim beaker
To observe convection currents in water.
water
Equipment • • • • • •
large beaker (e.g. 500 mL or 1 L) dried beans (e.g. borlotti beans or chickpeas) Bunsen burner tripod gauze mat bench mat
gauze mat
beans
tripod
place Bunsen burner off-centre
bench mat
Method 1 Assemble the apparatus as shown in Figure 6.2.19. 2 Add enough dried beans to cover the base of the beaker. Most should sink to the bottom.
Fig 6.2.19
3 Heat the beaker and carefully observe what happens.
Questions 1 Sketch the pattern formed by the moving beans. 2 Explain why the particles moved in the path they did. 3 Identify where you would find similar convection currents in the home or industry.
5
Radiation emission
thermometer
thermometer
Aim To find what colour best radiates heat energy.
Equipment • • • • • •
two cans (one black and one silver or white) measuring cylinder or beaker two thermometers or temperature probes hot water beaker timer
Method
Fig 6.2.20
Questions
1 Fill each can with an equal amount of hot water at the same temperature.
1 Construct a line graph for each container on the one set of axes. N
2 Place a thermometer (or a temperature probe) in each container and record the temperature every minute for 20 minutes.
2 Identify which material is the:
3 Record your results in a table.
a better emitter of heat b worse emitter of heat. 3 It was important that the water in each can was at the same temperature at the start. Explain why.
185
Heat
6
Radiation absorption
Aim To find what colour best absorbs radiated heat energy.
Equipment • • • • • •
two thermometers or temperature probes black card white card two retort stands with clamps 100 W light globe bench mat
Method 1 Attach the black card to the bulb of one thermometer and the white card to the other, as shown. (Alternatively, use a temperature probe and study one surface at a time.) Ensure the cards are the same size. 2 Clamp the thermometers and place them on either side of the light globe. 3 Measure and record the distance between the globe and the card. Ensure the globe is placed at an equal distance between the two thermometers. 4 Connect the light globe to a power point and switch on.
Fig 6.2.21
Questions 1 Identify which colour card absorbed radiation the best. 2 In this experiment, the light globe must not be closer to one thermometer than the other. Explain why. 3 Explain why the same-sized card should be used on each thermometer. 4 State what happened to the temperature when the cards were twice the distance away. Propose a reason for this observation.
5 Record the temperature on each thermometer in a table like the one below. Time (minutes)
1
2
3
Temperature (°C) (black) Temperature (°C) (white)
6 Repeat steps 3 to 5, but with the cards placed twice the distance from the light globe.
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4
5
6
7
8
9
10
Unit
thread
Heat machines
Aim To construct a heat motor, candle snuffer or chimney machine.
Equipment
6.2
7
aluminium, not paper or cardboard
stand
• Materials to construct the machines shown in Figure 6.2.22.
Method Construct either of the three heat machines, as shown in Figure 6.2.22. Note that the spiral must be made from aluminium—not paper or cardboard.
? DYO
flame from match or Bunsen burner
match (lit)
coil of copper wire
smoke
candle
Fig 6.2.22
187
Unit
6.3
context
Light
The world would be a very dark place without light since the sense of sight depends on light entering your eye. Light is a form of energy. The energy it carries
warms the Earth, fades fabric and powers photosynthesis, the process by which plants make their food.
Science
Clip
Moonshine At night, the Moon and stars shine down brightly. Their light is very obvious. Stars produce their own light (and heat) in the same way as the Sun-nuclear explosions. Stars and the Sun are both luminous and incandescent. The Moon, however, is just rock. It produces no light or heat of its own. Instead, it acts like a giant mirror in the sky, reflecting sunlight onto Earth. The Moon is nonluminous. So are the other moons and planets in the solar system.
Fig 6.3.1 Crisp images form when light is reflected off smooth surfaces, such as mirrors and still water.
Luminous and non-luminous Sight depends on light entering the eyes to form images on their retinas. The energy carried by the light then triggers electrical impulses that travel along the optic nerve to the brain, which interprets what is being seen. This light comes directly from luminous objects or via reflection off non-luminous objects. Luminous objects, such as the Sun and light globes, make their own light and are easy to see. Non-luminous objects do not make their own light but can still be seen because they reflect the light coming from something else. Most objects that you see are non-luminous.
188
Fig 6.3.2 Non-luminous objects do not make their own light. They can be seen only because they reflect the light from other sources. If there is no light, they can’t be seen.
Unit
Angler fish, glow-worms and fireflies are luminous, generating and emitting their own light to attract prey. No heat is generated. Animals that do this are termed bioluminescent.
6.3
Many luminous objects also give out heat. These objects can be further classified as incandescent.
One of three things can happen when light falls on a substance: • If the light travels through the substance, then the substance is termed transparent. Glass, Perspex, diamond, water and air are all transparent substances. • If the light is scattered as it passes through, then the substance is considered to be translucent. Tissue paper, milk and the frosted glass you find in bathrooms are all translucent materials. • If the light is blocked by the substance and cannot get through it, then the substance is considered to be opaque. Wood, bricks and rock are all opaque materials.
Fig 6.3.3 Luminous objects make their own light.
Speed of light Light travels faster than anything else on Earth or in the universe. Light is also the fastest known way of transmitting energy. It travels at roughly 300 000 kilometres per second and does not need a material to travel through. This means that it can travel through the vacuum of space. At this speed, light takes only about 8.5 minutes to travel the 150 million kilometres from the Prac 1 p. 193 Sun to the Earth.
Transparent materials let light pass straight through.
Opaque materials block and reflect light.
How light travels Light can be thought of as travelling in thin beams or rays. A source of light sends out rays in all directions in straight lines. A light source appears brighter when you are close to it because there the rays are spaced closely together. As you move away, the light from the source seems to become less bright because the rays Fig 6.3.4 Light spreads out Prac 2 as it travels from a candle. are spread out more. p. 193
Fig 6.3.5 Light does different things when it hits different substances.
Translucent materials scatter light as it passes through it. Prac 3 p. 194
189
Light
Shadows Shadows are formed when an object blocks the light aimed at a surface. You can predict the position and type of shadow (sharp or fuzzy) using the fact that light travels in a straight line. The term umbra is used to describe a dark, full, sharp shadow. When a larger light source is used, two types of shadow are formed. In the centre will be a small, dark, full shadow (umbra). Around it will a much larger and fainter partial shadow called a penumbra.
small light source
rough surfaces, such as concrete or rough wood. Sometimes you can get both regular and diffuse reflections off the one surface. On a still morning the flat surface of a lake produces clear crisp images— regular reflection is happening. Wind will cause the surface to get choppy and all images are lost. The waves are causing diffuse reflection to happen. Regular reflection occurs from very smooth surfaces, such as mirrors, the surface of a lake on a still morning or from highly polished wood or metal. Regular reflection forms clear, sharp images.
A small light source (often called a point source) produces a sharp, dark shadow called an umbra.
object
Fig 6.3.8 Regular reflection Diffuse reflection occurs from rough surfaces. Reflection occurs but no clear image is formed. Many surfaces appear to be smooth but are rough compared to a mirror. screen
Fig 6.3.6 Small light sources tend to form crisp, dark shadows. A larger light source produces a fuzzier, partial shadow called a penumbra. larger light source
Fig 6.3.9 Diffuse reflection
The law of reflection Reflection changes the direction of light. The angle a light ray makes is the same before and after reflection. This is best summarised by the law of reflection, which states that:
object
Angle of the incoming ray = Angle of the reflected ray i=r
These angles are measured from an imaginary line called the normal, which is drawn at right angles to the surface of the mirror.
full shadow (umbra) screen
incident ray
Fig 6.3.7 Larger light sources tend to form both a crisp, dark shadow (umbra) and a fuzzier, partial shadow (penumbra).
Reflection
190
angle of incidence i angle of reflection r
I n t e r a c t i ve
Reflection happens when a light ray bounces off a surface. Reflection can be classified as either regular or diffuse. Regular reflections occur off smooth surfaces, such as a mirror or a highly polished table, and can form crisp images of whatever is nearby. Diffuse reflections do not form an image since the light is being bounced off in all directions. Diffuse reflections occur when light falls onto
mirror
normal
reflected ray
Fig 6.3.10 Reflection off a flat mirror.
Prac 4 p. 195
Uses of plane mirrors Plane mirrors do not distort the image in any way, making them very useful in bathrooms, bedrooms and in clothes shops. The image is always the same distance from a plane mirror as the object. This allows drivers to accurately predict the distances of cars behind them.
mirror
6.3
Flat mirrors (more properly called plane mirrors) form images that are almost identical to whatever is in front of the mirror—the image appears to be the same size and to be in exactly the same position as the object facing it. The image is not exactly the same, however. When you write on a piece of paper and hold it up to a mirror, the image of writing will appear to be the wrong way around. This effect is known as lateral inversion. Lateral inversion turns left into right and right into left.
Unit
Plane mirrors
1m
2m
1m
Fig 6.3.12 You do not need a mirror the same size as yourself to see your whole body. If placed correctly, the mirror needs to be only half your height. Worksheet 6.3 Laser light I n t e r a c t i ve
Fig 6.3.11 Emergency vehicles, such as ambulances and fire engines, often have their names written back-to-front so that they are easily read in rear-view mirrors.
6.3
QUESTIONS
Remembering 1 Recall the difference between a luminous and a non-luminous object. 2 List three incandescent objects. 3 Name a bioluminescent creature. 4 List four uses of plane mirrors.
Understanding
7 Explain how a shadow is formed. 8 Describe how a shadow changes when an object moves towards a screen. Assume that the light source is small. 9 The Sun is a very large and wide source of light. If, instead, it was a tiny but bright point source of light, describe how the shadows on Earth would be different.
5 Describe the evidence that suggests that light does not need a material through which to travel. 6 Explain how you can see a basketball even though it does not produce its own light.
>> 191
Light
B
D
A
E C
Fig 6.3.13
Applying
18 Calculate the angles x, y and z in Figure 6.3.14. N
10 Identify five examples that have not been mentioned in the text of: a luminous objects
z
b non-luminous objects.
y
x
11 Identify two translucent materials.
al
norm
60°
12 Calculate how far light could travel in: N a 2 seconds b 60 seconds c 1 hour. 13 Use your knowledge of reflection in a plane mirror to write the words EMERGENCY VEHICLE so that they would appear correctly when viewed in the mirror. 14 In a clothes shop, a plane mirror is needed that allows people up to 180 cm tall to see themselves in it from head to foot. Calculate what length the mirror should be. N 15 Identify which of the labels (A, B, C, D and E) in Figure 6.3.13 represent the: a normal b angle of reflection c angle of incidence d incident ray e reflected ray.
Analysing 16 Compare: a an umbra and a penumbra b a transparent and an opaque substance. 17 Classify the following substances as transparent, translucent or opaque: plastic cling wrap, baking paper, glass, cardboard, freezer bags, frosted glass, muddy water, smoggy air.
192
Fig 6.3.14
Evaluating 19 a Identify four devices that use light to perform a task. b Evaluate the importance of each device to society.
Creating 20 Design a new device that uses a plane mirror(s) to help solve a problem or make a job easier. a Describe the problem you are trying to solve. b Describe how your device will overcome the problem. c Draw a labelled diagram of your device. Include rays to demonstrate where the light will be reflected. d Design an advertisement to sell your device to the public. L
Unit
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to:
6.3
6.3
1 Find out what is meant by both a solar and a lunar eclipse. Draw diagrams to explain the differences. 2 Research how a kaleidoscope works.
6.3
PRACTICAL ACTIVITIES
Teacher Demonstration Light energy
1 Aim
light sensor
air removed
To investigate if light travels in a vacuum.
Equipment • small torch • bell jar • vacuum pump
Method
Fig 6.3.15
vacuum pump
Questions
1 Turn on the torch and place it in the bell jar.
1 Outline what happens to the light as the air is removed.
2 Attach the vacuum pump to the bell jar and remove the air.
2 Light does not require a medium to travel through. Clarify this statement.
3 Observe the intensity of the torch as the air is removed.
2
The pinhole camera
Aim
3 Make a small hole in the centre of the foil using a compass point or similar small point. 4 Place a lit candle about 30 cm in front of the pinhole/foil end of the box.
To show that light travels in a straight line. tape to join sections
Equipment • • • • • •
small cardboard box (e.g. a shoebox) aluminium foil tracing paper masking tape a candle scissors
foil
Method 1 Remove one end of the box and replace it with foil. Cut a 2 cm viewing hole in the other end of the box. 2 Cut the box in half and cover the cut end with tracing paper. Seal all gaps with masking tape.
candle pinhole
screen (tracing paper)
Fig 6.3.16 Pinhole camera
viewing hole
>> 193
Light 5 Make sure the room is as dark as possible. Observe the image formed at the tracing paper end of the box. 6 Investigate the effect of moving the candle different distances from the pinhole. 7 Investigate the effect of increasing the size of the pinhole.
Questions
candle
pinhole
1 Compare the pinhole camera with an old-fashioned film-loaded camera. What section represents the film? 2 Copy and complete Figure 6.3.17. State which way up the image is.
tracing paper
Fig 6.3.17 Formation of the image
3 Explain what happens to the image when: a the candle is moved further away from the camera b the hole is made larger.
3 Copy and complete the table below.
3
Transmission of light
Transparent
Translucent
Opaque
Aim To investigate the transmission of light through different substances.
Equipment • • • • • • • •
aluminium foil greaseproof paper glass acetate sheet baking paper brown paper bag tissue paper candle or light globe
Method 1 Light the candle or switch on the light globe. 2 Look at the light source through each of the substances and record your observations.
eye
test substance
light source
Fig 6.3.18
Questions 1 State which substances are transparent. 2 Describe how light behaves when it strikes various objects. 3 Compare the images produced by a transparent and a translucent substance.
194
Unit
Law of reflection
Aim
to power supply (12 V)
mark reflecting surface mirror
To investigate the law of reflection, i = r.
!
Safety The bulb of the light box can get very hot, so allow it to cool before packing it away.
normal mark each ray with two dots
Equipment • • • • •
6.3
4
light box and power supply ruler mirror protractor or Mathomat plain paper
Method
Fig 6.3.19
Questions
1 Assemble the equipment as shown in Figure 6.3.19, marking the position of the back of the mirror and the normal.
1 Propose a reason why the back of the mirror marked and not the front. (Hint: Check where the mirror foil is.)
2 Mark the position of the incident and reflected rays.
2 Write a conclusion about the angles of the incoming and reflected rays. N
3 Measure the angle of incidence and angle of reflection and record your results in a table.
3 List any similar examples of reflection in real life.
4 Repeat steps 1 to 3 for several different angles of incidence.
195
Unit
6.4
context
Sound
Sound, like light and heat, is a form of energy. Sound is used to communicate in medical and industrial applications and for entertainment. Sound can be the annoying scream of an emergency siren
or can be your favourite music tracks downloaded onto your iPod. Unlike light, sound needs something to travel through. It cannot travel through a vacuum and so cannot travel through outer space.
Science
Clip
In space, no-one hears you scream! Sound is caused by vibrations, and so there needs to be something to vibrate. Since space is a vacuum, there is nothing to vibrate. There is no air and no particles, and so any sound in space stops at its source. A bell jar can be used to show that sound cannot travel through a vacuum.
Fig 6.4.1 Sound starts as a series of vibrations that eventually end up in your ear.
Making sound
air in jar
no air in jar (vaccuum)
196
sound detected
no sound detected
Fig 6.4.2 Sound needs something to travel through. If the air is removed from the bell jar, then no sound is detected.
Sound is produced whenever an object vibrates and passes these vibrations into whatever material is surrounding the object. Usually, the material is air, but it can be water or a solid like the wood that makes up the body of a guitar. These vibrations could come from your vocal cords when you speak or your nose and throat when snoring. Musical instruments use vibrations to make their music. Vibrations could come from the strings of a guitar, violin or piano when plucked or struck; the reed of a clarinet or oboe when air is blown over it; or the skin of a drum that is hit. Speakers and headphones use vibrations to send out their sounds. Often, you can see the vibrations on the stings of a guitar or in the prongs of a tuning fork. Sometimes you can even feel the vibrations, especially when you are standing in front of speakers and the music is really loud! The sounds then need to get to your ear. In air, layers of air particles vibrate in turn, passing the sound energy through the air in a series of rarefactions and compressions that are known as a sound wave.
Unit
Science
Fact File
air particles
Thunder and lightning
compression
rarefaction
speaker producing a rarefaction
Fig 6.4.3 Sounds transmit as a series of compressions and rarefactions. push then pull repeatedly
Lightning is produced by a build-up of static electricity. It superheats the surrounding air, causing it to expand at a tremendous rate. This expansion produces shock waves in the air that we hear as the sound we call thunder. You can calculate how far away a storm is by: • counting the number of seconds after a lightning flash before you hear the thunder • multiplying the number of seconds by 300. (Sound travels at about 300 metres per second in air.) The result tells you how many metres away the storm is. For example, if you hear thunder 5 seconds after seeing lightning, the storm is about 5 × 300 = 1500 metres or 1.5 kilometres away.
6.4
vibrating speaker producing a compression
Science compressions
Clip
rarefactions
Sneaky birds
coil movements
wave direction
Fig 6.4.4 Sound waves transmit as longitudinal waves through air, water and other materials. These types of waves can be modelled using a slinky by scrunching up some of the spring and letting it go. The particles vibrate in the same direction as that of the sound.
Some birds will hop around on the ground, trying to create vibrations in the ground that are similar to those produced by rain. Worms under the ground are tricked into coming to the surface to escape being drowned.
wave direction coil movement
Fig 6.4.5 Another type of wave is a transverse wave. These can be modelled in a slinky by shaking the slinky sideways. The particles vibrate at right angles to the direction of the wave. Water waves transmit as transverse waves.
The speed of sound Sound travels at about 340 metres per second (i.e. 1224 kilometres per hour) in air at 20°C. This is much, much slower than the speed of light, which travels at roughly 300 000 000 kilometres per second! This dramatic difference in speeds often causes you to see something before you hear it. This is the case with thunder and lightening, and is often noticed when watching sport. For example, you will see a cricketer hit a ball before you hear the accompanying sound. If you
were sitting 340 metres from the action, then the sound would take one second to reach your ears and the light would take about ten-millionths of a second to reach your eyes! A wave travels faster in a slinky made of a stiffer spring. Likewise, sound travels more quickly in solids and liquids than in air. This is because the particles are packed together more closely. The table on page 198 shows the approximate Prac 1 p. 202 speed of sound in some different materials.
197
Sound Approximate speed of sound in the material (metres per second)
Material Air at 0°C
330
Air at 20°C
340
Air at 30°C
350
Water
1400
Wood
4500
Steel
5000
Once the speed of sound is known it can be used to calculate distance or depth. For example, the speed of sound in water is 1400 metres per second. If it takes one second for a sound vibration to return to a ship after bouncing off a shoal of fish, then the sound has travelled 1400 metres. Therefore, the distance to the fish is 700 metres. This technique of finding distances and depth is known as echolocation. Ships and fishing use a system of echolocation known as sonar. Sonar uses ultrasonic sound waves—waves that are vibrating faster than humans can hear.
Science
Clip
Sonic boom On 14 October 1947, Chuck Yeager piggybacked his X-1 jet aircraft on a B-29 bomber. He separated from the B-29 at 12 000 metres and then broke the so-called ‘sound barrier’ at that altitude by taking his X-1 to a speed of 1065 kilometres per hour. Nowadays, fighter jets commonly achieve supersonic flight. Before it was decommissioned, the Concorde passenger jet travelled faster than the speed of sound on regular services between Europe and New York. A loud ‘sonic boom’ was heard as the jet caught up with and passed sound waves emitted by its engines. This phenomenon is similar to a boat travelling faster than the water waves it creates in its wake.
Prac 2 p. 202
Fig 6.4.7 A fishing boat using echolocation to locate a shoal of fish.
Echoes Sound striking a hard wall will reflect back, or echo, towards its source. Echoes can be used to calculate the speed of sound.
Fig 6.4.8 Some animals like bats and dolphins use echolocation to avoid obstacles, detect food or locate objects.
Echo is heard one second after clap.
170 m
198
Fig 6.4.6 If the echo of a loud clap takes one second to get back, then it travels roughly 340 metres in one second. This gives the speed of sound as 340 metres per second.
Radar is a similar process to sonar, except that radio waves are used instead of ultrasound to locate, direct and track various objects, such as aircraft, over long distances.
Unit
6.4
Science
Clip
Ultrasound
Fig 6.4.9 Ultrasound is often used to monitor pregnancy.
Reverberation If you yell out in an empty hall, the echo time is too short for you to detect a distinct second Prac 3 sound. p. 203 The echo partly overlaps with the original sound, producing a sound that lasts longer. This effect is known as reverberation, and it may take some time to die out as echoes become weaker and weaker. Soft materials, such as carpet and curtains, absorb the sound energy and stop the sounds echoing and reverberating. Worksheet 6.4 Sound generator
Sound graphs
Pregnant women can have an ultrasound to check the development of their unborn baby. This procedure uses an ultrasound scanner to send sound waves into the woman’s body. They are then reflected off different surfaces, such as bone and soft tissue. The echoes are then converted into images on a monitor. Using this method, the patient avoids potentially harmful X-rays or invasive surgical procedures.
Sound waves can be detected by a microphone and displayed on a cathode ray oscilloscope (CRO). A CRO converts the pressure variations in a sound wave into electrical impulses, which are then displayed as a wave on its screen. The number of compressions that pass a point (e.g. the microphone) each second is called the frequency of the sound. A high frequency produces a high-pitched sound, whereas low frequencies are deep and rumbling bass sounds.
microphone cathode ray oscilloscope (CRO)
Fig 6.4.11 A CRO produces Fig 6.4.10 Concert halls often use special sound-absorbing panels to
tuning fork
a ‘graph’ of a sound, showing pressure at different times.
reduce reverberation.
199
Sound
The sound of music
reference sound
louder
higher frequency
Fig 6.4.12 Louder sounds produce taller sound graphs. Higherfrequency sounds produce graphs that are more scrunched and tight.
guitar
oboe
piano
noise
Fig 6.4.13 Musical instruments produce smooth, repetitive, rhythmic patterns on the CRO. Noise produces a messy, irregular pattern. Voice recognition software converts spoken words into text on a computer by recognising the patterns that each different letter and word produce.
Different musical instruments produce their notes in different ways. Stringed instruments like guitars and violins use vibrating strings to make a basic set of notes whereas wind instruments like clarinets and trombones use a column of vibrating air. A string or air column Fig 6.4.14 Wind instruments use has a natural frequency valves or holes to alter the length of that depends on its the vibrating column of air. Different notes are the result. length. The string or column is said to resonate at this frequency. Resonance can cause another object nearby to vibrate at the same rate. The thin wood of a guitar, for example, resonates in response to its vibrating strings. Likewise, the body of the clarinet resonates at the same frequency as the air inside it. Other frequencies and notes can be produced on a guitar by altering the length of the string (by holding the strings at different points) or by tightening or loosening the strings. A clarinet has keys that open or close holes in the column. This changes the length of the air column Prac 4 Prac 5 p. 203 p. 203 and the resulting notes. Worksheet 6.5 Sound
Worksheet 6.6 Morse code
6.4
QUESTIONS
Remembering 1 List five sources of sound and state what is vibrating in each. 2 State the speed of sound in air at 20°C. 3 State whether the following are true or false: a CRO is short for ‘cathode ray oscilloscope’. b A CRO shows what sound waves would actually look like if air was visible. c A CRO can display a graph of pressure at different times as a sound wave passes. 4 Name two animals that use echolocation.
200
Understanding 5 Describe a test to prove that sound cannot travel through a vacuum. 6 Clarify the following terms by providing a definition for each: L a compression b rarefaction. 7 Calculate how far sound would travel (in air at 20°C) in 3 seconds. N 8 Explain an advantage of ultrasound.
Unit
9 Explain what is meant by the following terms:
18 A CRO displays the graph shown in Figure 6.4.15.
6.4
a frequency b resonance c reverberation. 10 Explain how the frequency of the sound from a guitar string can be changed. 11 Explain why empty rooms echo more than furnished ones.
Applying 12 Sketch a longitudinal wave that demonstrates its compressions and rarefactions. 13 A sound is transmitted from person X to person Y. Identify which of the following is happening: A Air particles are travelling from person X to person Y. B Air particles are passing vibrations from person X to person Y. C Infra-red waves are being transmitted from person X to person Y in the same way as radiated heat. D Heated air particles are transmitting heat by conduction from person X to person Y. E None of the above. 14 Calculate the speed of sound if it travels: N
Fig 6.4.15
Identify which of these sounds produced the display above. A a tuning fork B a guitar C a piano D noise. 19 A student stands at the end of a road and yells towards a house some distance away. If she hears an echo 2 seconds later, calculate how far she is from the house. N 20 Identify which of the displays (left, centre or right) in Figure 6.4.16 was caused by the loudest sound.
a 9000 metres in 30 seconds b 800 metres in 4 seconds. 15 From the following list, identify the substance in which sound travels the fastest: air at 30°C, water or steel. 16 Identify an example of a useful and a not-so-useful echo. 17 Identify what makes the sound when each of the following instruments is being played: a a violin
Fig 6.4.16
Analysing 21 Calculate how many seconds it would take sound (in air at 20°C) to travel 1 kilometre. N
b a flute c a drum.
6.4
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: • Find out how vocal cords work. • Find out more about the sound barrier and a sonic boom.
e -xploring We b
ion
Desti nat To construct models of instruments called the chook and the punji, web destinations can be found on Science Focus 1 Second Edition Student Lounge.
201
Sound
6.4
PRACTICAL ACTIVITIES flame
1
A sound cannon
Aim To make a sound cannon that will blow out a candle.
Equipment • • • •
cardboard tube (e.g. a poster tube) self-adhesive contact or plastic cling wrap masking tape or rubber bands a match
Method
small hole (1–2 mm)
contact or cling wrap
Fig 6.4.17
Questions
1 Place the contact/cling wrap over each end of the tube, stretch it taut and hold it tight with tape or rubber bands.
1 Explain what happened to the flame when you tapped the end of the tube.
2 Make a small hole in one end, using a pin or compass end.
2 Explain why it is important to seal both ends of the tube, and for the contact/cling wrap to be tight.
3 Hold a lit match a few centimetres in front of the hole and sharply tap the other end.
2
3 Explain why the small hole was necessary.
The speed of sound
Aim To compare the speeds of sound and light.
Equipment • teacher with a starting pistol (or two garbage bin lids) • long tape measure or trundle wheel for measuring 100–300 metres • stopwatch
Method 1 Measure a straight distance of between 100 and 300 metres with a clear view from the start to the finish. 2 Your teacher should stand at the start with the starting pistol or garbage bin lids. 3 Several students should stand at the finish with stopwatches. 4 The teacher fires the starting pistol or bangs the lids together. The students start their watches when they see a wisp of smoke rise from the starting pistol or the movement of the lids, and stop them when they hear the sound of the pistol. (Alternatively, use a sound detector to determine the time taken for the sound to reach you.) 5 Calculate an average of the times recorded.
202
measure distance
Fig 6.4.18
Questions 1 The people with stopwatches started timing when light reflecting from the smoke reached their eyes. Explain whether the time this takes is a significant factor. 2 Explain the advantage of calculating an average. 3 Use your average to calculate the speed of sound. To do this, divide the distance (in metres) by the time (in seconds). N
Unit
Aim
Method
To determine the reflecting or absorbing capacity of different materials.
Design your own experiment to test and compare the reflecting and absorbing qualities of various materials (e.g. cardboard, glass, wood, plasterboard, curtains).
Equipment • a sound level meter or sound probe/data-logging system • various materials to test as reflectors and absorbers of sound
4
6.4
3
Reflection and absorption of sound
? DYO
Measuring cylinder resonance
Aim To examine resonance in a measuring cylinder.
Equipment • 250 mL measuring cylinder • tuning fork
Method 1 Strike a tuning fork and hold it at the top of the measuring cylinder. (If a sound detector is available, you may wish to use one to measure the intensity of the sound produced.) 2 Add a small amount of water to change the length of the air column in the measuring cylinder, and repeat step 1. Note whether the sound produced is louder or not. 3 Keep adding water and testing the sound produced when a struck tuning fork is held at the top of the cylinder.
Construct a musical instrument
Fig 6.4.19
Questions 1 Determine the length of air column that has a resonant frequency equal to that of the tuning fork. 2 Explain why water is added in small amounts.
Method
Aim
1 Design and build your own musical instrument that uses only recycled materials. Your instrument must be able to play the song Twinkle, Twinkle Little Star.
To construct a musical instrument.
2 Demonstrate your instrument to the class.
5
? DYO
CHAPTER REVIEW Remembering 1 List all the types of energy that you can. 2 List the three ways that heat can flow from one region to another. 3 State which coloured objects best: a absorb heat b emit heat.
4 Sound waves transmit as a wave. State whether they are longitudinal or transverse waves. 5 State whether the following are true or false: a Sound needs a material to travel through. b Light needs a material to travel through.
203
Understanding
19 Identify which diagram below best represents an actual sound wave.
6 Using examples, explain the following terms: a conservation of energy b energy transformation.
A
7 Choose two appliances used in the home and describe the energy transformations that happen when they are used. 8 Outline how a sea breeze works.
B
9 Explain why not all shadows are sharp. 10 Write a definition to clarify the term umbra. 11 Explain the difference between an echo and a reverberation.
C
Applying 12 Identify the type of heat transfer that does not require a medium.
D
Fig 6.5.2
13 Identify an example of radiated heat.
Analysing
14 a Explain the difference between a luminous object and an incandescent one.
20 Classify the following as either heat insulators or heat conductors:
b Identify an example of each.
nail, foam Esky, wooden table, plastic cup, barbecue grill, frypan handle, woollen jumper, metal oven tray.
15 a Explain what is a lateral inversion. b Demonstrate your understanding of this by writing your name in capital letters, laterally inverted.
21 a Compare water with air as conductors of heat. Which one is best?
16 A person standing 160 metres from a wall hears an echo from it 1 second after calling out. Calculate the speed of sound based on this information. N
b Explain your choice.
17 A vibrating tuning fork placed on a tabletop causes the tabletop to vibrate at the same frequency. Identify what this effect is called. 18 Three sounds are displayed on a cathode ray oscilloscope, as shown in Figure 6.5.1.
22 a Many applications and uses of science in everyday life were introduced in this chapter. Copy and complete the table below to summarise some of these applications. L b Identify two more technologies not listed in the table below and add them to your summary. 23 A boat is using echolocation to find fish. The signal is sent down into the water and returns to the boat after 1 second. The speed of sound in water is 1400 metres per second.
a Identify which sound is the highest in pitch. b Identify which sound is the loudest.
a Calculate the depth of the fish. b If the sound returned in 0.5 seconds, calculate what would be the depth of the fish. N
C
a
pt
Worksheet 6.8 Sci-words
Fig 6.5.1 Technology
Ultrasound
204
Thermos Fish finder (echolocation) Guitar Solar hot-water system Insulation batt
Use of technology
Viewing unborn babies
on
B
Ch
A
s
Worksheet 6.7 Crossword er R sti ev i ew Q u e
Type of energy (heat, light, sound)
How it works
Sound
Sound waves are sent into the body and reflected back from bones, tissue etc. The reflected sound is changed into an image on a screen.
7
Forces
Prescribed focus area: The applications and uses of science
Key outcomes 4.3, 4.6.2, 4.6.7, 4.6.9, 4.6.10 Forces cause acceleration, deceleration, a change in direction or a change in shape.
• •
Forces can act at a distance through a field.
• •
Mass is the amount of matter in an object.
•
All objects exert a force of gravity on all other objects.
• • •
Magnets are used in a variety of situations.
•
Forces have a size and a direction and are shown as arrows in a diagram.
•
Sir Isaac Newton developed laws of gravitation and motion.
Friction is a contact force that slows down objects. Weight is the pulling force caused by gravity.
Essentials
•
Like poles of magnets repel each other. Unlike poles of magnets attract each other.
Additional
Unit
7.1
context
What are forces?
Forces in body contact sports, such as rugby or AFL, are very obvious—players are thrown about, pushed or pulled to the ground or stopped in their tracks by another player. When a horse falls at the
racetrack, the jockey is dragged to the ground by the force of gravity. Impact with the ground provides another force and may be enough to break the jockey’s bones.
Fig 7.1.1 The weight of a falling horse is a force that all jockeys try to avoid!
206
Push, pull or twist
What forces do
Forces are best described as a push, a pull or Quick Quiz a twist. Most forces actually touch the object they are pushing or pulling around. Forces such as friction, air resistance and buoyancy are impossible to see but still touch the object that they are affecting. These forces are called contact forces because they touch the object. Other forces act through an invisible force field and don’t actually touch the object that they are pushing or pulling around. Instead, the field does the pushing and pulling. These forces are known as non-contact forces. The forces caused by gravity, magnetism and electricity are non-contact forces.
A force causes an object to change the way it is moving or to change its shape in some way. If an object has sped up (accelerated), slowed down or stopped (decelerated) or changed direction, then a force caused the change. Likewise, if an object (or even part of an object) has changed shape, then a force caused the change. Sometimes this change is permanent, but often the object bounces back to its original shape. If this happens, the object is said to be elastic.
Unit Forces are needed to decelerate or slow something down. The force may even stop it.
7.1
Forces are needed to accelerate something, or get it going faster.
Forces are needed to twist, break or change the shape of something.
Forces are needed to change the direction that something is travelling in.
Fig 7.1.2 A force is anything that changes motion.
Acceleration An object is accelerating whenever it changes speed. When an object increases its speed, its acceleration is said to be positive. This means that speed is being added so that it goes faster and faster. If the object slows, then it is said to be decelerating. This deceleration is also called negative acceleration because speed is being subtracted, making it go slower and slower.
Science
Clip
That’s fast! A massive particle accelerator called the synchrotron was opened in Victoria in 2007. This tube uses a combination of different magnets to accelerate electrons to speeds approaching the speed of light. The synchrotron will be used as an incredibly sensitive microscope that will allow scientists to study the structures of diseases and the drugs that might provide cures for them.
Fig 7.1.3 A bike gets faster as it accelerates. It slows when it decelerates.
207
What are forces?
How to draw forces
Measuring forces
Usually, there are a number of different forces acting on an object all at the same time. Each force is often pushing or pulling in different directions and, often, this needs to be made clear in a diagram. Scientists draw forces using special arrows called vectors. The direction of the arrow shows the direction of the force and its length represents how big the push or pull is—big forces are shown as long arrows, whereas short arrows indicate small forces.
A spring gets shorter when it is squashed and longer when a pull force stretches it. The bigger the force, the more the spring is squashed or stretched. These facts give us a way of measuring forces. If a pointer is attached to the spring then any change in the length of the spring can be measured. The bigger the change, the bigger the force. Spring balances and most kitchen and bathroom scales use this method to weigh things. All forces are measured in newtons, named after the English scientist Sir Isaac Newton (1642–1727). The unit newton is Prac 1 Prac 2 p. 210 p. 211 abbreviated as N.
the ground pushes up
Worksheet 7.1 Forces in flight
force of pushing pedal
air (wind) resistance
NEWTONS 0 10
50
20
40 30
40
50
kg
60
GRAMS 0 50 100
weight force 150
Fig 7.1.4 Forces are drawn as arrows. The longer the arrow, the bigger the force. Fig 7.1.5 Forces cause springs to get longer or get shorter. This I n t e r a c t i ve
7.1
QUESTIONS
Remembering 1 A force is applied to an object. List four things that might happen to it.
Understanding 6 Copy the statements below and modify any incorrect statements so that they become true.
2 State what must be inside an instrument that can measure the force applied to an object.
a Force is needed to change the direction of an object.
3 State the unit used to measure forces, its symbol and who it was named after.
c A force is required to change the shape of an object.
4 State other words or phrases that could be used instead of acceleration and deceleration. 5 Specify how forces are shown in diagrams.
208
gives a way of measuring the force. All scales and weighing devices have a spring that gets longer or shorter because of the weight.
b Things slow down naturally. No force is involved. d Objects speed up when they fall because there is a force involved. e Twisting is caused by a force.
>>
12 Identify which of the situations in Figure 7.1.7 are showing: a push forces
8 Identify three examples of non-contact forces.
b pull forces
9 Identify three examples of situations in which the following forces are acting:
c twist forces.
7.1
7 Identify five examples of contact forces.
Unit
Applying
a push forces b pull forces
A
B
C
c twist forces. 10 Identify three examples of situations in which an object: a speeds up b slows down c changes direction d changes shape permanently e changes shape for a short time but then bounces back to its original shape f stops.
E D
11 Identify which of the situations in Figure 7.1.6 show: a acceleration b deceleration c change in shape d change in direction. A
B
F
G
Fig 7.1.7
Analysing
C
13 Elastic means that the material will bounce back to its original shape after the force is removed. Inelastic materials might bounce back a little but never regain their original shape or size. D
Classify the following materials as either elastic or inelastic: a an elastic band b a crumpled piece of paper c plasticine d a car wreckage
Fig 7.1.6
e wet mud f a diving board g a drinking glass.
>> 209
What are forces?
Creating
14 Compare the forces shown in Figure 7.1.8. a Which is the biggest force?
16 Construct small, simple sketches of the following situations:
b Which forces are the same size?
• a weightlifter lifting a weight
c Which forces are in the same direction?
• a spanner tightening a nut • a nail being hammered
B
• a small child pulling along a toy
A C
• a strong wind pushing your hair backwards
E D
• a sliding door opening • a football falling to the ground after it has been kicked. a On each of your sketches, draw arrows to show the directions of the main forces. Indicate the size of the forces using arrows of different lengths.
Fig 7.1.8
15 Compare the size of a force needed to stop a truck to that of stopping a car.
7.1
b Under each diagram, write words to describe the forces as either a push or a pull, and contact or non-contact.
INVESTIGATING
e -xploring We
b Desti natio To explore more about forces, a list of web desitinations can be found on Science Focus 1 Second Edition Student Lounge.
7.1 1
PRACTICAL ACTIVITIES
Measuring forces
Aim To measure the force required to perform some common activities.
Equipment • spring balance • various objects on which to test (e.g. door, sticky tape, pencil case)
Method 1 Use a spring balance to measure the forces listed below. a Open and close different types of doors. b Pull off sticky tape stuck to a bench. c Pull your science textbook off the bench. d Lift or unzip your pencil case.
210
n
2 Some of the forces may change as you measure them. If so, record the smallest and largest measurements you take. We call this the range of measurements. 3 Note that some of the forces may be too large or too small for you to be able to measure.
Questions 1 Look carefully at your results. Explain what factors made some measurements very large. 2 List the forces in order from smallest to largest. (If you cannot measure the force, predict the order and give reasons to justify your answer.)
Unit
2
7.1
Build your own force-measuring device
Aim To build a simple force-measuring device using everyday materials.
Equipment bosshead and clamp
Materials as shown in Figure 7.1.9.
cardboard
Method
0
1 Build one of the three designs shown in Figure 7.1.9.
hacksaw blade or plastic ruler
2 Place a mark on the scale with no masses. Mark it as zero (no force). 3 Progressively add masses of 50 grams, marking the scale each time.
50 g masses
retort stand
4 Since the scale is going to measure force, you will need to label the scale in newtons, not in grams. Use the table below to help you. This is called calibration of the scale. 5 Use the force-measuring device to re-measure the weight of some objects around you (e.g. your pencil case, keys etc.). Mass added (g)
wooden dowel
Equivalent weight force (N)
0
0.0
50
0.5
100
1.0
150
1.5
plastic graduated cylinder or measuring cylinder
Questions 1 Clarify the meaning of the term calibration. Explain why calibration is important.
markings on dowel
2 Explain what happens to your device when heavier objects are placed on it. 3 Identify what part of your device limits the weight that can be measured.
metal washers
rubber band
coil spring
Fig 7.1.9 Build one of these designs.
211
Unit
7.2
context
Friction
You use friction every day but probably don’t think about it. Imagine trying to walk if there was no grip or friction between your shoes and the floor. Imagine how fast you could go on your
bike if there was no friction with the air or ground. There could also be problems if there was no friction between your brake pads and the wheel rim—the brakes wouldn’t work!
Science
Clip
What a drag! When something moves through air, it needs to push the air out of the way and then around it. The air passing over the surface has its own friction force, called air resistance or drag. Cars and commercial aircraft are designed to minimise the drag to save on fuel consumption, and jet fighters, rockets, missiles and arrows are designed to travel as fast as possible. An object is called streamlined if it cuts through the air with little air resistance or drag.
Fig 7.2.1 The tread on a tyre gives it traction in wet weather. Friction also wears the tread down, eventually making it bald.
What is friction? Friction is a force that happens whenever an object slides or rolls over something. Friction always acts opposite to the direction that the object is moving and acts to slow it down. A bike, for example, will gradually come to a stop if it’s not pedalled. Pedalling provides a push force that overcomes the friction between the bike’s tyres and the road and so it keeps the bike moving. This push force stops when you stop pedalling—the only force left is friction and that slows you down. The same thing happens if the school bus driver turns the engine off while driving. The engine provides enough push to overcome friction. When the engine is turned off, the friction is able to slow down the bus until it Prac 1 p. 216 eventually comes to a stop.
212
Friction (opposite direction)
Motion (the direction in which the jet ski is facing/moving)
Fig 7.2.2 Friction always opposes motion, slowing you down.
Unit
Reducing friction
Friction is caused by the roughness of the surfaces that try and slide or roll over each other. Friction always acts in the opposite direction to the object’s movement. Rough surfaces have a lot of friction. If you try to slide one rough surface over another rough surface, then the bumps and hollows on one will catch on the bumps and hollows of the other, slowing down the movement. Smooth surfaces have bumps and hollows, too, although their ‘roughness’ often can be seen only under a microscope. Even smooth Prac 2 surfaces will slow down if pushed or pulled p. 217 across another surface.
If you could reduce the friction between the moving parts of a machine then the machines would be more efficient, using less energy, and you would travel further and faster. There are a few easy ways of reducing friction. • Lubricating the surfaces with oil or grease fills the hollows that cause friction. This makes the surfaces smoother and easier to slide over each other. • Polishing and waxing makes the surfaces smoother by removing some of the bumps and filling up some of roughness that catches and causes friction. • Wheels, rollers or ball bearings reduce friction by allowing the surfaces to roll instead of slide. This is most obvious if you need to push a car. It is much easier to push a car if the handbrake is off since this allows the wheels to roll. If the handbrake is on, then the wheels need to slide over the road surface. This is a nearly impossible task! Ball bearings allow the axles of your skateboard or inline skates to roll more freely by reducing the friction, allowing you to go as fast as possible.
7. 2
What causes friction?
Fig 7.2.3 Even smooth surfaces have bumps and hollows—an electron microscope image of the ‘smooth’ surface of a polished wooden table.
Going bald and getting hotter Friction slows down objects sliding and rolling over each other. It also wears them down by breaking off some of the bumps and making them smoother. Friction causes tyres to become bald and it can cause grazes to the skin when rugby players slide across the paddock when taking a try. Friction can also be a problem in machines. Engines, gearboxes and wheels all have parts moving across other parts. These parts gradually lose their sharp edges, become smaller or thinner and, eventually, are not able to do the job they were designed to do. Friction also causes heat to be generated. Rubbing hands on cold mornings generates heat through friction. In a car, this happens throughout its engine. The heat needs to be released through the radiator, otherwise the car would quickly overheat.
blades and ball bearings
Fig 7.2.4 There is less friction if wheels spin on bearings. That means you can go faster!
• The most effective way of reducing friction is to stop the surfaces touching each other at all. A hovercraft does this by squeezing a blanket of air underneath it so that the craft loses contact with the ground. In this way, the hovercraft can travel over extremely rough surfaces (ground or water) without slowing down because of friction.
213
Friction grab the wheel rim directly or slide against other discs or pads attached to its axles. Friction between the two surfaces slows the spinning wheel and brings the bike, car, train or aircraft to a stop. Friction also generates heat and this is why brake pads get very hot after a lot of braking, such as when you are travelling down a long hill. On your bike, you need to make sure the brakes are in good condition so that the friction of the brake pads against the rim is high. Fig 7.2.5 A hovercraft uses a blanket of air to reduce friction.
The ground pushes back on the skateboard and moves it forward
You push the ground backwards
Fig 7.2.7 You need friction to move forward.
Friction also allows things to move forward. To move forward, the wheels of a bike or a car must first push backwards. Likewise, walking first needs the foot to push backwards. If the surface is rough then friction pushes back, getting you moving. Traction is lost if the surface is smooth. There is no ‘grip’, there is nothing to ‘push off’ and you slide and skid all over the place! Once moving, friction is needed to give control so that you can turn and come to a skid-free stop. To maximise traction, racing cars use ‘slicks’ (wide tyres with no tread) in dry weather. If the track is wet, then tyres with a deep tread are needed to ‘pump’ water from the road surface. Bikes and ‘normal’ cars need to cope with all conditions and so have Prac 3 p. 217 tread on their tyres also.
Fig 7.2.6 Wind tunnel tests of drag—smoke is blown over the object to see how the object cuts through the air.
Useful friction So far, friction seems to be a problem force. But friction works for us too in two very important ways. Brakes rely on friction to slow down bikes, cars, trains and aircraft when they land. Discs or pads either
214
Fig 7.2.8 Mountain bikes use a wide, blocked tread to give them even more grip on rough and loose ground.
Unit
QUESTIONS
Remembering
d your doona or blankets through the night
1 State five examples of objects that naturally slow down (or stop) because of friction.
e your shoelaces
2 List the disadvantages of friction as a force.
g the way you stop.
f the way you move across a room
3 State five examples of surfaces that have very little friction between them.
Applying
4 Friction allows us to do many things. List at least 10 situations in order from greatest frictional force to least.
13 a Explain why surfboarders wax their boards.
5 List three machines or devices that would benefit from using bearings in their wheels.
Understanding
7. 2
7.2
12 Identify a device that needs friction to work. b Identify other sports that use wax.
Evaluating 14 Propose a reason why:
6 Copy the following and modify any incorrect statements so that they become true:
a A snowboarder hates friction but a cyclist is happy it’s there.
a Friction is caused by bumps and hollows of the surfaces catching on each other.
b Weightlifters put chalk on their hands when attempting a heavy lift.
b Smooth surfaces have no bumps or hollows.
c Cars put on chains over their tyres when travelling in the snow.
c Friction causes a moving object to speed up. d Friction is a non-contact force.
Creating
e Drag slows a moving object.
15 Construct a table to summarise the different ways that friction can be reduced. L
f ‘Streamlined’ is a word used to describe shapes that cut through the air easily. 7 Define the term traction. 8 Friction makes hinges on a door squeak, allows us to write with a pencil and to file our nails. Explain each of these situations in terms of friction. 9 Predict the order from most to least friction for the blocks in Figure 7.2.9.
16 How did the slaves of ancient Egypt move the massive blocks of stone across the desert to build the pyramids and temples? Use the contents of your pencil case to construct a model demonstrating how these large blocks may have been shifted over the sand. 17 Overnight scientists have discovered that friction has disappeared! What can we expect today in this new, frictionless world? Create a short piece of writing on friction. You must explain:
B
C
long round dowels
oil
A
1 what friction is 2 how you intend to move about and stop 3 what will happen to structures—will nails hold and screws stay in? Write your piece as:
Fig 7.2.9
• a diary page about your exploits after getting out of bed
10 The tread on tyres gives a car more grip in the wet but less grip in the dry. Explain why tread is only important in the wet.
• a newspaper front page explaining what is happening in the world
11 In a world without friction, predict what would happen to:
• a pamphlet from the government explaining to residents how to cope in this strange new world. L
a objects that you hold on to b pieces of wood nailed together c pieces of wood screwed together
215
Friction
7.2
INVESTIGATING
Investigate your available resources (e.g. textbook, encyclopaedias, Internet etc.) to find out how disc and drum brakes work. List the advantages that disc brakes have over drum brakes.
7.2 1
e -xploring To explore the forces involved in skateboarding, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
We b Desti nation
PRACTICAL ACTIVITIES
Measuring friction
Aim To observe and measure the friction of objects on different surfaces.
3 Thread a piece of string through one end of your elastic band chain. Tie this string around one of the shoes. Straighten out the chain and put the ‘0 mm’ of your ruler at the end like you did before. 4 Construct a table to record your results. Shoe
Equipment • a selection of shoes (gumboots, runners, slippers, walking shoes, sandals) • thick rubber bands to make a chain • 25 or 50 gram masses • spring balance • string • different surfaces (e.g. classroom floor, playground, carpet)
Extension (cm)
Runner Sandal Gumboot Walking shoe Slipper
5 Pull on the elastic band chain and make a note in your table of how much the elastic bands have stretched at the moment when the shoe starts to move. Repeat with each shoe, remembering to ensure that they each have the same mass. 6 Sort out the shoes in order of how much they ‘grip’ the floor. Remember that the shoes with the most friction are the ones with the most stretch on the elastic band chain. Compare your prediction with the observed result. 7 Repeat steps 1 to 6 with a different surface, until all surfaces have been tested.
Questions Fig 7.2.10
Method 1 Inspect the soles of the shoes and try to predict which shoe will provide the most friction. Write down your predictions. 2 To make the test fair, all the shoes must have the same mass. Use the balance to determine the mass of each shoe. Record each value. To make sure each shoe has the same mass, place masses inside each shoe, as required.
216
1 Identify the purpose of making all the shoes have the same mass before the measurements are taken. 2 State what this variable is called. 3 State whether the shoes stay in the same order of gripping ability on a different floor surface. 4 Write a statement to describe friction (using your results as a guide).
Unit
Comparing friction
Method 1 Construct a table in your workbook with the headings ‘Material’ and ‘Angle’.
Aim To compare the friction of different materials on a surface.
2 Predict which material would have the least friction and which would have the most. Arrange them in order in the table.
Equipment
3 Place a wooden block on the wooden ramp.
• protractor • wooden blocks • a selection of different materials (e.g. unvarnished wood, carpet, various grades of sandpaper, rubber grip material) • a wooden ramp • lubricant, such as detergent
wooden block
7. 2
2
4 Slowly lift one end of the wooden ramp until the block is just about to slide. 5 Measure the angle between the ramp and the desk, using a protractor. Record the angle. 6 Place one of the selected materials on the ramp and repeat the experiment. 7 Repeat with all the other materials.
ramp
8 Repeat the experiment, but this time lubricate the surface instead of making it rougher.
material to be tested protractor
Questions
90
1 Describe what happened to the angle as you changed the roughness of the surface.
benchtop
2 Explain your answer in terms of friction. Figure 7.2.11
3
Constructing roller ball
Aim To build a model that will demonstrate different forces.
Equipment • A range of junk materials
? DYO
Your task is to design and build your own structure that will allow a normal-sized marble to drop a vertical height of 70 centimetres in as close to 20 seconds as possible. • Your structure must stand by itself and cannot be higher or longer than 70 centimetres. • The materials you can use are things that are readily available at home (e.g. cardboard boxes, tubing, plastic containers, glue, tape etc.) • The marble must pass across/through a minimum of four different materials/structures. • You must label all forces that are involved in the trip (i.e. label every push and pull).
217
Unit
7.3
context
Gravity
You’re on your bike, travelling along at high speed, when you unexpectedly hit a rock. You lose control and the bike flies
out from under you. There is only one way to go—down!
What is gravity? Gravitational force is a non-contact force that attracts objects to each other. You are constantly attracted to the planet immediately underneath you. This attraction gives us our feeling of weight and means that we cannot simply jump up and fly away. When you fall from your bike, it is the force of gravity that attracts you and pulls you to the ground. Gravity makes things fall down. Of course, ‘down’ depends on where you are on Earth! Although, normally, it is a very small force, gravity becomes significant when you are near a large object, such as a planet like Earth, a moon or a star like the Sun. Fig 7.3.1 Gravity makes things fall down, including this snowboarder.
Prac 1 p. 222
Fig 7.3.2 Astronauts do not change when they go into space. Although their mass is exactly the same as back on Earth, they feel weightless in space.
Science
Clip
I find you attractive! Building on the earlier work of Galileo and Johannes Kepler, the English scientist Sir Isaac Newton (1642–1727) developed the law of gravitation in 1687. This law suggests that all things with matter are attracted to all other things with matter. This means that you are currently being pulled towards the desk in front of you…and the person sitting next to you…and the ceiling…and everything else in the room! It sounds like some sort of nightmare until you realise that the gravitational force is actually extremely small—so small that most things do not affect us.
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Worksheet 7.2 Pressure
Weight Weight is the term given to the force of gravity pulling on a mass. Weight is a non-contact force. Although gravity physically doesn’t touch you, you know it is there because your body is constantly stopping you from collapsing or from falling over. Sometimes, this gives people a sore back. You also know it’s there because you find it difficult to lift heavy objects and you can’t just go floating around the room! Weight is a force and so is measured like all other forces—weight is measured in newtons (N).
The effect of mass and gravity
The effect of distance Gravity lessens as you get further away from Earth. This is because gravity depends on distance. This may seem strange since your weight doesn’t seem to get any smaller if you climb a mountain. This is because you have to go much further away than that for the decrease in gravity to be noticeable. A 70 kilogram person normally has a weight of about 700 newtons (exactly 686 newtons) at sea level. The table below shows what happens to the person’s weight as they travel to the Moon. Distance from Earth’s surface
What is normally found at this height
Mass (kg)
Weight (N)
0
Sea level
70
686.0
305 m
Top of Centrepoint tower
70
685.8
2228 m
Top of Mt Kosciusko
70
685.5
10 km
Normal height of commercial airliners
70
683.8
395 km
Height of space station
70
608.3
595 km
Hubble space telescope
70
573.9
35 900 km
AUSSAT-2 communications satellite
70
15.4
190 000 km
Half-way to the Moon
70
0.8
7. 3
Mass is the amount of matter in an object. Unless you break up the object or add things to it, the mass of an object never changes. Astronauts, for example, can be ‘weightless’ in space even though their body mass is exactly the same as back on Earth. Mass is normally measured in kilograms (kg), but is sometimes measured in grams (g) for smaller things or tonnes (t) for very large objects. Often, we use the terms ‘mass’ and ‘weight’ interchangeably in everyday speech. They are, however, different things.
Unit
Mass
Weight depends on mass since the more massive something is, the heavier it will be. This means that elephants and whales have greater weight than a mosquito or ant. The gravity on each planet and moon is different, and so your weight also depends on which planet or moon you happen to be on. The Moon, for example, is much smaller than Earth and has a gravitational pull about one-sixth that of Earth’s. This also means that your weight on the Moon is only one-sixth your weight on Earth, allowing you to jump about six times higher than on Earth! You are, of course, exactly the same person and so your mass has not changed. Of all the solar system, Jupiter has the highest gravity (about 2.5 times that on Earth). Mercury has only one-third the gravity of Earth’s, whereas Venus, Saturn, Uranus and Neptune have gravities roughly the same as that on Earth.
Fig 7.3.3 You are a little lighter at the top of Centrepoint than at its base.
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Gravity AUSSAT-2 communications satellite 36 000 km
Space station 400 km
70 kg 574 N
70 kg 0.8 N
70 kg 15 N
Commercial aircraft 10 km 70 kg 608 N
70 kg 686 N 70 kg 683.3 N
Hubble Space Telescope 600 km
2 km 70 kg 685.5 N
Fig 7.3.4 Gravity and the weight of an astronaut get less as the astronaut travels further away from Earth.
Measuring mass and weight
Falling down
Mass can be measured only by using a balance. If the two sides of the balance are the same, then the mass on both sides is equal. This would be the case whichever planet you were on, whether it was Earth, the Moon or Mars. Weight is the force due to gravity and so you must use gravity to measure it. You allow gravity to stretch or squash a spring to give you a measurement.
The weight of an object causes it to accelerate as it falls. The Moon has no atmosphere and so all things fall at exactly the same rate on its surface, regardless of how big or heavy they are. This is because there is no air to push back on the objects to slow their fall. On Earth, there is an atmosphere and so things do tend to fall at different rates. The air gives almost no resistance to streamlined, heavy objects that are falling, whereas light, bulky objects tend to flutter side-to-side as theyy fall. Feathers and sheets of paper are catching so much air that they can’t fall straight. The upward force that slows an object’s fall Prac 3 p. 223 is called air resistance.
0
100
200
300
400
500
600
0
10
20
30
40
50
60
70
80
90
100
1
2
3
4
5
6
7
8
9
10
0
Prac 2 p. 223
50 40 20 10 0
Fig 7.3.5 A beam balance (top) measures mass, whereas a spring balance (bottom) measures weight.
220
Fig 7.3.6 A hammer and feather fall at exactly the same rate on the Moon due to the lack of air slowing them down. I n t e r a c t i ve
Unit
QUESTIONS
Remembering 1 State units that are commonly used to measure: a mass
b weight.
2 State whether weight is: a a push force or a pull force b a contact or non-contact force. 3 List three things on which gravity depends.
Understanding 4 Copy the following and modify any incorrect statements so that they become true: a Weight is measured in grams. b Kilogram is a unit for mass. c Weight is a force. d There is no gravity on the Moon. 5 The gravity on Mercury is only one-third the gravity of that on Earth. Explain what this suggests about the mass and size of Mercury. 6 In space, does an astronaut have less mass or less weight? Explain.
7. 3
7.3
Analysing 13 Contrast mass and weight by stating their key differences. 14 An astronaut in a space suit is very heavy. If the mass on Earth of an astronaut and their suit was 140 kilograms, then calculate what their mass and weight in the suit would be: a b c d
if they visited your school on top of a 2000 metre high mountain while repairing the Hubble Space telescope half-way to the Moon.
15 Three balls, a tennis ball, a cricket ball and a shotput, were dropped at the same time. The experiment was photographed on the way down but, unfortunately, only the tennis ball was recorded on film. Copy the diagram into your workbook and predict where each of the other objects would be at the same time as the tennis ball if you were: a on the Moon b on Earth. tennis ball
cricket ball
shotput
Applying 7 Identify where on Earth you think gravity would be the greatest and where it would be the least. 8 Identify three activities you could do on the Moon that would be extremely difficult to do on Earth. 9 Identify the direction in which weight force is pointing. (Be careful…there may be trick!) 10 The following comment was overheard in a Year 7 class recently: “Of course 1 kg of lead is heavier than 1 kg of feathers! It’s lead, isn’t it?” Identify what the student has got wrong and how they may have come to have this opinion. 11 All things fall at the same rate due to gravity. a Identify the evidence that supports this statement. b Identify the evidence that does not support this statement. 12 You are travelling the solar system. Identify on which planets you will have: N • • • •
the same mass roughly the same weight about one-third your weight on Earth about 2.5 times your weight on Earth.
Fig 7.3.7 Draw in where the cricket ball and shotput will be.
Evaluating 16 Propose a reason why the atmosphere doesn’t escape into space. 17 You are slightly taller when you get up in the morning than when you go to bed. Propose a reason why. 18 Astronauts who return to Earth after a long time in space notice that they are a little taller and much weaker. Propose a reason why.
>> 221
Gravity
Creating 19 Imagine a world without gravity. Nothing would fall down. Create a piece of writing about a world without gravity. You can produce:
• a set of rules for going to bed without gravity and a design for the bed
• a pamphlet for umpires explaining the rules of a sport invented for a world without gravity
• a poster of exercises to keep astronauts fit and to stop their muscles getting weaker while on long space missions. L
7.3
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find and record the masses, in kilograms, of: a an average adult man and woman c an average family car. 2 Find and record the world records for: a the largest mass that a man and a woman have lifted b the heaviest thing living at this moment
7.3
c the smallest living thing d the heaviest of the dinosaurs e the heaviest ship ever built. 3 Investigate how gravity keeps planets, such as Earth, revolving around the Sun and keeps the Moon revolving around the Earth.
b an average newborn baby
4 Find out how NASA changes the direction of its deep space missions by having the spacecraft ‘caught’ in the gravitational field of a planet.
PRACTICAL ACTIVITIES
Falling objects
Aim
4 Repeat with all the objects, until you have compared every object with the drop of the 50 gram mass. Make sure you drop the different objects from the same height as in step 3.
To see if all objects fall at the same speed.
5 Arrange the objects in the table below.
1
Equipment • 50 gram mass • a range of different objects that will not break or cause damage when they fall • a soft landing place for the objects (e.g. carpet, cushion or sponge)
A lot faster than the 50 gram mass
Method 1 Collect a range of objects of different masses and different shapes and sizes. 2 Drop the 50 gram mass and one of the other objects at the same time from the same height. Ensure that the objects fall onto something soft so as to reduce any damage. 3 Drop the objects from a measured height.
222
• a diagram or model of a gravity-free home, bathroom or toilet
About the same as the 50 gram mass
A lot slower than the 50 gram mass
Objects that flutter instead of drop
6 Now drop the 50 gram mass and a single sheet of A4 paper at the same time and from the same height. 7 Add these results to the table. 8 Now crumple the paper into a loose ball. 9 Drop the 50 gram mass and the paper ball and record your results again.
>>
Unit
Questions 1 Identify the column in which you placed most of the objects. 2 Identify the type of objects that fluttered on the way down. Explain your answer. 3 Identify whether any masses fell faster than the 50 gram mass. If so, explain why. 4 Explain why it is necessary for the objects to be dropped from the same height each time.
2
5 Using your results as a guide, complete the following sentence: Most objects fall at the same rate as/faster than/slower than a 50 gram mass. 6 Describe the difference between the sheet of paper, the loosely crumpled ball and the tight ball. 7 Identify which object dropped the slowest. Explain your answer. 8 Draw a conclusion by completing these sentences: Objects that catch the air fall ______ than objects that do not. Objects that do not catch air fall ______.
Measuring mass and weight Object
Aim
7. 3
10 Crumple the paper into a very tight ball and repeat the experiment.
Mass measured from beam balance (g)
Weight measured from spring balance (N)
To accurately use a beam balance and spring balance to find the mass and weight of different objects.
Equipment • beam balance • spring balance • a variety of objects of different masses and sizes
Method 1 Use the beam balance to measure the mass of each of the objects. 2 Now use the spring balance to measure the weight of each object. 3 Record all your measurements in a table like the one shown.
3
Testing strength
? DYO
Aim To find the stretch and strength of one of the following objects: • a plastic supermarket bag • sticky tape
Questions 1 State the maximum mass that could be recorded using the beam balance. 2 State the maximum weight that could be recorded using the spring balance. 3 Using your results as a guide, copy and complete the following sentence: N The weight of an object was about _________ times the mass of the object.
Method 1 Design your own experiment that measures how far a plastic supermarket bag, sticky tape, nylon fishing line or an elastic band stretches as masses are added. 2 Keep adding masses until it breaks.
• a nylon fishing line
3 Draw a line graph of the stretch obtained as each mass is added.
• an elastic band.
4 Mark clearly the mass required to break the object.
Equipment • various masses • either a plastic supermarket bag, sticky tape, a nylon fishing line or an elastic band
223
Unit
7.4
context
Balanced and unbalanced forces
There are usually a number of different forces acting on an object at the same time. Sometimes these forces are balanced. They cancel and nothing
happens. At other times, the forces are unbalanced. It is only then that the object accelerates, decelerates, changes direction or changes shape.
Fig 7.4.1 In a tug of war, forces are pulling in different directions. What happens depends on whether the forces are balanced or not.
Balanced but not moving There are at least two forces acting on you right now as you are sitting down reading this textbook. There is the downward pull of gravity or weight. Your weight is pulling you into the chair. You know this force exists because if the chair broke then gravity would cause you to fall down to the floor. You are not falling, however, because gravity is not the only force acting on you. The chair is also pushing you … upwards. You can feel its push through the pressure on your backside, flattening your buttocks a little more than normal. It also compresses your spine a little. There are two forces acting on you right now and they balance. This means that they are equal in size but opposite in direction. The downward and upward forces are playing a tug of war and neither of them is winning—there is no overall force on you. You are not moving because the forces are balanced. The forces are balanced on any object that is not moving. The room in which you are currently in is not 224
moving and so you know that all the forces on it are balanced. Likewise, all the forces on the cars in the teacher’s car park and the bikes in the bike shed are balanced since they are not moving either. chair pushes back with the same size force as the weight force
weight force
Fig 7.4.2 Forces are balanced if they are equal in size but acting in opposite directions.
Prac 1 p. 228
Unit
Balanced but moving
7. 4
Most cars on a freeway travel at a constant speed. They are not speeding up or slowing down. Once again, there is no overall force on the car because all of the forces are balanced. Friction with the road and the drag of the air balances the forward push from the wheels. An easy way of telling whether the forces on an object are balanced is to look at what the object is doing. The forces on an object must be balanced if it: • is not moving • is not speeding up • is not slowing down • is not changing direction • is not changing shape.
lift
thrust
drag
weight
Fig 7.4.4 The main forces on an aircraft
Unbalanced forces If one force is bigger than all of the others put together, then it will win the tug of war on an object. The forces then are unbalanced and so the object will: • speed up • slow down or stop • change direction • change shape. car accelerates
car travels at constant speed
Forces on an aircraft An aircraft flies because of a balancing act between the four main forces that act on it. These forces are its weight, lift, thrust and drag. • Weight is the force that causes everything, including an aircraft, to fall. • Lift is an upward force that allows an aircraft to stay in the air. The wings provide lift because they have a special shape called an air foil or aerofoil. The top surface of the wing is longer than the bottom surface. The air passing over the top of the wing has further to go and moves faster than the air travelling the shorter distance under the wing. High-speed air has lower pressure than air that is slow or not moving. This causes the wing to be ‘sucked’ upwards, taking the aircraft with it. Science • Thrust is the push force that gets an aircraft moving and is provided by jet engines or No air? No aircraft! propellers that push it forward. Aircraft would not be able to The upwards-lift force also take off on the Moon. The lack of any atmosphere means no needs thrust to get the air lift force is possible, so moving at high speed over the aircraft would always stay on wing. the ground regardless of how • Drag is friction caused by air fast they travelled. Helicopters sliding around the aircraft. Drag would also be grounded. Rockets are the only craft that slows down an aircraft. have the ability to take off Aeroplanes have streamlined when there is no air. shapes to minimise drag.
Clip
car slows down
Fig 7.4.3 What a car does depends on which force is the winner in the tug of war.
Prac 2 p. 229
Prac 3 p. 229
225
Balanced and unbalanced forces
Flight: The ultimate balancing act All the forces on an aircraft are balanced when it is sitting stationary on the ground. wing
Prac 4 p. 230
cross-section
As an aircraft picks up speed on the runway, the lift force builds until it is greater than the aircraft’s weight. This is when it takes off. The forces are unbalanced— there is an overall push upwards, lifting the aircraft into the air. At cruising altitude, the lift is the same as the weight—the aircraft stays at the same height and speed because the forces are balanced. As the aircraft approaches an airport, it slows down. The lift decreases, making the forces unbalanced once more. Its weight is greater than its lift and it starts to descend.
Science
Clip
lift
air must travel further over the top
Early attempts at flight
air moves faster and has less pressure
air is slower and has higher pressure
weight
Humans have always wished they could fly and have the freedom of movement of birds. Most early attempts tried to imitate how birds flew. The first recorded ‘flight’ was made by Bladud, the ninth King of Britain, in 843 BCE. Unfortunately, King Bladud had simply strapped wings made out of feathers onto his arms, so his flight was very short, very vertical and had a very messy landing! The Renaissance artist/scientist Leonardo da Vinci (1452–1519) drew some of the earliest sketches of flying machines. One design flapped its wings. Another was an aerial screw, a primitive ancestor of the helicopter.
airflow direction of travel
Fig 7.4.5 An air foil generates the lift that keeps an aircraft flying.
take-off
landing
Fig 7.4.6 Balanced and unbalanced forces on an aircraft
7.4
QUESTIONS
Remembering
Understanding
1 List the signs to look for if the forces on an object are: a balanced
b unbalanced.
2 A car is travelling along the freeway. State what will happen to the car when all forces acting on it are: a balanced
b unbalanced.
3 Specify the two forces acting on you as you sit and read this question.
226
Prac 5 p. 230
cruising
4 Two forces act on an object. Explain how they can be balanced. 5 Copy the following and modify any incorrect statements so that they become true: a Forces are balanced when there is no overall force. b Forces are normally balanced when the forces are the same size and acting in the same direction. c If I am sitting on a chair, the only force on me is my weight force.
Unit
e A balanced force is needed if an object is going to accelerate.
b Three students against four students. c Ten students versus another ten students of equal strength. d Two students versus ten students. 16 The class tug of war continues. Analyse each of the games shown in Figure 7.4.7 and predict who will probably win. a
6 A bike is slowing down to a stop. Explain why the forces on it must be unbalanced.
c 3 people
7 Tom is trying to push a broken-down car and cannot get it moving. He is pushing with a force of 500 newtons. Predict the size of the force that must be resisting his push and in which direction it will be operating.
b
3 people
2 people
2 people 6 people
8 Outline the four forces that are important in the flight of an aircraft. 9 Outline what is special about the shape of an air foil and explain how this allows the air foil to create lift.
7. 4
d A car travels at constant speed when the force from the driving wheels balances the push backwards of the air (we call this air resistance) as well as the friction between the road and the wheels.
3 people
d
3 people
3 people
10 people
10 Copy the following and modify any incorrect statements so that they become true:
10 people 5 people
a Air moving over an air foil causes thrust. b The top part of a wing is longer than the bottom. c Fast-moving air has higher pressure than slow-moving air.
e 3 people
d An aircraft will take off only if the lift is greater than the weight. e There is no overall force on an aircraft when it is at cruising altitude.
3 people
3 people
Fig 7.4.7
11 There is no lift and no drag on an aircraft that is not moving. Explain why.
Evaluating
Analysing
17 Propose reasons why:
12 A helicopter also creates lift, but with its rotor blades. Analyse what shape a rotor blade must have for it to provide lift for the helicopter. 13 Draw a diagram showing: a the likely cross-section of a helicopter rotor blade b where you would expect the air to be moving fastest
a Aircraft need to pick up speed on a runway before they can take off. b Aircraft always try to take off by heading into the wind. c Heavy aircraft need longer runways to take off. d Aircraft need longer and faster run-ups on hot days than on cold days.
c where the pressure would be least
Creating
d the direction of the lift force that is produced by the rotor.
18 Construct simple sketches of the situations below and add arrows to show the balanced forces involved.
14 When a helicopter is stationary, the spinning blades on both sides of the rotor give the same lift. When the helicopter is moving, however, the blades provide more lift on one half of their spin than on the other half. Use your knowledge of air movement and lift to explain why. 15 Analyse the following games of tug of war and predict who will win. a A team of three students goes against another team of three students of equal strength.
a A student leans against the wall. b A person is standing. c A hang-glider floats in the air. d A skateboarder is cruising at constant speed along a footpath.
>> 227
Balanced and unbalanced forces 19 Construct simple sketches of the situations below and add arrows to show the unbalanced forces involved. (Note that the length of one arrow will need to be bigger than the length of the other arrow.) a A student sits back on only two legs of a chair. b A parachutist jumps from a plane but hasn’t yet opened their chute. c A stone is dropped. d A passenger, not wearing a seatbelt, is involved in a car accident. e A parachutist is landing on the ground.
7.4
20 Construct simple diagrams to show aircraft in the given situations. Include arrows to demonstrate the forces involved. Assess whether the aircraft is taking off, landing, cruising, at the departure gates or in trouble. a Lift is zero, thrust is zero and drag is zero. b Lift equals weight and thrust equals drag. c Lift is greater than weight and thrust is greater than drag. d Lift is less than weight and thrust is less than drag. e Lift is less than weight, thrust is zero and drag is high.
INVESTIGATING
Investigate your available resources (e.g textbook, encyclopaedias, Internet etc.) to: 1 Construct a timeline of the major developments in human flight. N 2 Find out more about helicopters. Research:
e -xploring W
n eb D To explore information about forces on an aircraft, esti natio a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
a why they have a small rotor on their tail b how they get their thrust to move forward c why they don’t tip over because of unequal lift from the two sides of the rotor. Present your findings to the class in group presentations. Use a form of presentation media, such as PowerPoint.
7.4 1
PRACTICAL ACTIVITIES
Tug of war #1
Aim To examine balanced and unbalanced forces.
Equipment • long thick rope • thick gloves • large area to play tug of war (e.g. grass oval)
Method 1 Have the same number of students of roughly the same size on either end of the rope. 2 Have the students pull the rope on either end. Observe and record the results.
228
3 Decrease the number of students on one end of the rope and increase the number of students on the other end and repeat. 4 Attach another rope and have a three-way tug of war. Try out the combinations shown in Figure 7.4.7.
Questions 1 Explain why no-one will probably win when equal numbers of students are pulling at each end. 2 Explain why unequal numbers are needed for any team to win. 3 In a three-way contest, such as that shown in Figure 7.4.8, the lone person on the stem of the T will probably win, despite having 20 people to struggle against. Explain why. 10 people
10 people 1 person
Fig 7.4.8
Unit
Tug of war #2
2
pulley
Aim
7. 4
string washer
clamp benchtop
To examine balanced and unbalanced forces.
Equipment • • • •
three pulleys and clamps string or heavy cotton thread metal washer or ring 50 gram masses
mass
mass 3 masses
3 masses
1 Set up the apparatus as shown in Figure 7.4.9.
3 masses
4 masses
2 Attach the masses as shown in the first diagram and support them until they are all attached.
4 masses
3 masses
Method
3 masses
3 masses
3 Let go all of the masses at the same time. 4 Take note of any movement of the washer.
3 masses
3 masses
5 Repeat for each combination of masses illustrated.
Questions
3 masses
1 Identify the situations in which the washer did not move. 2 Explain what this suggests about the forces on the washer. 3 State the situations in which the washer did move.
3 masses
3 masses
2 masses
4 Explain why this suggests that the forces were not balanced. 3 masses
3
Wonky tower
?
Method DYO
Aim To construct as tall a structure as you can, using no more than 20 drinking straws.
Equipment • 20 drinking straws • 50 gram masses • glue and/or pins
Fig 7.4.9
You are to design and construct as tall a structure as you can by using no more than 20 drinking straws. The structure must be able to stand without any other support and must be able to hold a 50 gram mass at its very top. You can cut straws and can use pins or glue to join the straws, but you are not allowed any other materials.
Questions 1 Identify whether the forces on each joint in the structure are balanced. Explain your answer. 2 Identify the very important non-contact force that is acting and is trying to topple the tower.
229
Balanced and unbalanced forces
4
fine line
Creating lift folded paper
blow air through straw
Aim To create lift.
ping pong balls
straw
Equipment • • • • • •
one sheet of paper two ping-pong balls fine cotton thread or fishing line retort stand, bossheads and clamps sticky tape drinking straw
straw
blow air through straw
Fig 7.4.10
Questions
Method 1 Set up the two experiments shown in Figure 7.4.10. Support the ping-pong balls with the retort stand, bosshead and clamp. 2 Blow air strongly through the straw, in the directions shown. 3 Record all observations.
1 In these experiments, movement has been created by passing air quickly over a surface. Construct a diagram of each situation, and identify where the air is moving the fastest, where the air has the lowest air pressure, and the direction of any movement. 2 Copy and complete the following sentence: An air foil is pulled into an area of ___________-speed air or ____________________ pressure. 3 Has lift been created in this experiment? Explain.
5
paper
Making an air foil
Aim To construct and test an air foil.
Equipment • a selection of light cardboard or polystyrene • paper or plastic cling wrap • sticky tape or glue • cotton thread • small weights (e.g. paperclip) • fan with safety grille
Method 1 Use the diagrams to construct an air foil and attach it to the fan as shown in Figure 7.4.11.
paper
card
paper
wing shape paper
cotton threads to adjust the angle wing shape
Fig 7.4.11
2 Set the fan on different speeds and observe how well the air foil ‘flies’. Is the wing ‘stable’ or does it flick about? 3 Attach small weights. Observe whether the wing is now more or less stable. 4 Test to see how many paperclips the wing can hold. 5 Change the angle of the wing by shortening the lower strings, and once again test fan speed, stability and how many paperclips the wing can hold.
230
paperclips
Questions 1 Assess whether fast or slow fan speeds would be expected to give the most lift. 2 State what was observed when fan speed was increased. 3 Specify the maximum number of paperclips your air foil could hold in ‘flight’. 4 Specify the angle at which the wing was most stable. 5 Specify the angle at which the air foil held the most paperclips. 6 Propose reasons why the air foil was sometimes unstable.
Unit
7.5
context
Forces in water
Two special forces are involved when objects are placed in water. Buoyancy allows you to sit on your surfboard and float while waiting to catch a wave.
Surface tension allows you fill a glass above the rim without it spilling and it enables small insects to walk across the surface of water without sinking.
buoyancy
weight
Fig 7.5.2 Buoyancy equals weight force and the ship stays afloat.
buoyancy
Fig 7.5.1 Surface tension allows a bubble to form, and buoyancy allows a bubble to float and form froth on top of water. weight
Buoyancy A lump of steel sinks if it is placed in water, yet a ship made from steel doesn’t. It floats instead. The ship’s weight is balanced by the water pushing upwards on its hull. The force that keeps the ship from sinking is called buoyancy.
Prac 1 p. 233
Prac 2 p. 234
buoyancy
weight
Fig 7.5.3 Weight is greater than buoyancy and the ship sinks.
231
Forces in water A ship would definitely sink if it was solid steel— steel sinks because it is much denser than water. However, the ship’s hull is hollow and contains air, making the average density of the ship less dense than the water on which it floats. Water gives the ship its upward buoyancy force, which then balances the downward weight force of the ship. As the ship is loaded, it gets lower and lower in the water. The ship will sink if it is loaded too much, or if the hull is holed and fills with water. The buoyancy force is now not enough to balance the weight of the ship, and so it will sink. Go to
Science Focus 1 Unit 2.4
Science
Prac 3 p. 234
Worksheet 7.4 Forces in water
Clip
Dead man’s float If you want to float in a pool, then breathe in and fill your lungs with air. Get rid of all the air and you will generally sink—the buoyancy is now not enough to keep you afloat. It is easier to float in the sea than in a pool because salt water is denser than fresh water, meaning that it gives you more buoyancy.
7.5
Surface tension Water often creates a ‘film’ or ‘skin’ on its surface. This skin can be strong enough to keep afloat objects that would normally sink. It also makes water take on shapes that are quite unexpected.
All water particles have a force of attraction, called cohesion, between them that holds the particles together. Cohesion at the surface is called surface tension and is sometimes strong enough to form a ‘skin’. Surface tension also accounts for why drops of water can hang from a tap without falling and why glasses can be filled with water to above their brims.
Prac 4 p. 235
Prac 5 p. 235
QUESTIONS
Remembering 1 State what happens to a ship if: a its weight equals its buoyancy b its weight is greater than its buoyancy. 2 State what cohesion at a surface is called and what it forms on the surface.
Understanding 3 Copy the following, modifying any incorrect statements so that they become true: a Gravity is the force that keeps a ship afloat. b An iceberg stays afloat because its buoyancy balances its weight force. c A ship will sink if its weight is greater than its buoyancy. d Small objects often float because they are very dense. 4 Explain how density and buoyancy are related.
232
Figure 7.5.4 This steel paperclip should sink but is held afloat by the cohesive ‘skin’ on top of water in a brimming glass. Its weight makes an indent in the water but is not enough to break the ‘skin’. Some small insects are so light that they don’t break the ‘skin’ either, allowing them to walk across its surface. Other animals are far too heavy and would fall straight through.
5 Describe what happens to the water level on a ship as it is loaded. Explain why it happens using the terms weight and buoyancy. 6 Explain in terms of density and buoyancy why ships sink when they have a hole in them. 7 Use buoyancy to explain how a steel submarine floats on top of the water while it is in harbour. 8 When out at sea, the submarine ‘dives’. Describe what the crew must do to allow it to dive.
Applying 9 Identify whether the following are examples of buoyancy or surface tension at work: a b c d e
a duck floats on water a mosquito walks across water droplets of water form on a freshly washed and waxed car a diver straps on a weight belt to stay below the surface a drop of water hangs from a tap.
Unit
Analysing 11 Classify these objects as either those that float on water or those that sink: a a small pebble
7. 5
10 Plimsoll lines are lines painted on the hull of a ship to show where the waterline should be under different conditions. Figure 7.5.5 shows a partly loaded ship with the waterline level with the lines labelled L and R. Use the codes shown to identify which Plimsoll line the waterline would be level with if:
b a house key
a the ship is empty
c a paperclip
b the ship is fully loaded c the ship is loaded and is expecting heavy and dangerous seas.
d a cork e a drop of car oil and a drop of cooking oil f a cricket ball
Fig 7.5.5
g a book and a sheet of paper h an ice cube i a leaf j an inflated balloon and a deflated balloon.
Evaluating LT LS LW LWNA
7.5
LTF TF LF F L
R
12 When a piece of newspaper is dropped in water, it will probably float, but after a while it will sink. Propose a reason why. T S W W
INVESTIGATING
Investigate your available resources (e.g. textbook, encyclopaedias, Internet etc.) to find why it is impossible for a person to sink in the Dead Sea, which is located on the Israeli– Jordanian–Palestinian border. It is also recommended that people
7.5
13 Icebergs do not sink even though they are often kilometres across and contain thousands of tonnes of ice. Propose two reasons why.
with small cuts or open wounds do not swim there because it would be very painful for them. Find out what is strange about the Dead Sea that could account for these two facts.
PRACTICAL ACTIVITIES
1 Paper boats
? DYO
Aim To construct a paper boat and determine how much mass it can hold.
Equipment • sheet of A4 paper or aluminium foil of the same size • access to a tub or sink of water
Method 1 Design and build your own boat that will hold a pile of paperclips. 2 Run a competition between groups to see which boat can contain the greatest number of paperclips.
Questions 1 Identify whether the boat floats due to buoyancy or surface tension. 2 The boat sinks if too many paperclip are added. Use the terms introduced in this unit to explain why this happens.
233
Forces in water
2 How do ships float?
spring balance 50 40 20 10 0
Aim To determine what happens to the total force on a ‘ship’ as it is loaded.
elastic band/string water
Equipment • 100 mL conical flask • large container of water (e.g. plastic ice-cream container or bucket) • spring balance • elastic band or string • cork or rubber stopper
Method 1 Copy the table shown below. Observations as flask is lowered into water
Reading on spring balance as flask is lowered into water (N)
Empty flask Quarter-full
stopper flask ice-cream container filled with water
Fig 7.5.6
6 Record observations on what is happening to both the flask and the reading on the spring balance. 7 Repeat steps 4 to 6 for a flask quarter-full and half-full with water.
Questions 1 State the weight of the empty flask in air. 2 In this experiment, the spring balance gave the total force on the sealed flask. What did you notice about this reading as it was lowered into the container of water? Explain why it altered. 3 Draw a diagram showing the weight and buoyancy forces on the flask as it was lowered into the container of water.
Half-full
2 Start with an empty flask and seal it with the stopper. 3 Tie a loop of string or place an elastic band tightly around the neck of the conical flask. Use it to attach the flask to the hook of the spring balance. 4 Weigh the sealed conical flask. 5 Lower the conical flask into the large container of water.
4 When the flask just sank, roughly assess what fraction of it was filled with water.
A special case of floating
5 Carefully rest a pin on the edge of the beaker and see if it is possible to get the other end to float on top of the water.
3 Aim
To determine if a steel pin can float.
Equipment • two fine pins
• 250 mL beaker
Method 1 Fill the 250 mL beaker with water until it is nearly full.
5 Explain why the buoyancy force is sometimes insufficient to keep objects afloat.
6 If unable to make it float, then carefully use another pin to push it into the centre of the beaker. 7 It may take some time to be successful—keep trying if it fails. 8 Record all observations of the water around the pin.
250 mL
2 Place a pin on the surface of the water, recording carefully what happens. 3 Now add more water very slowly and carefully. 4 Place your eye level with the surface of the beaker and draw what is seen.
234
Fig 7.5.7
>>
3 If pushed too hard, the pin sinks once again. Explain what has happened to the surface tension now.
2 With care, the pin floats. Use the idea of surface tension to explain why.
4 Sugar lumps and milk swirls
Part B 1 Pour milk into the Petri dish until it is nearly full.
Aim
2 Wait until the milk stops moving.
To investigate how the surface tension of water can be altered.
Equipment • • • •
7. 5
1 A pin normally drops to the bottom of a beaker of water. Explain why.
Unit
Questions
eyedropper matchsticks milk detergent
• • • •
sugar cube or cotton cloth food dye of different colours large beaker large Petri dish or saucer
Method Part A 1 Fill a beaker with water and place a few matchsticks on top of the water to form a circle. 2 Slowly dip the sugar cube or cotton cloth into the centre of the matchsticks. 3 Observe the behaviour of the matchsticks. Record your observations.
3 Carefully place a drop of food dye on the milk. Do not stir. 4 Add drops of different colours elsewhere on the milk. 5 Place a single drop of dishwashing detergent anywhere on the milk.
Questions 1 Identify what the sugar cube or cotton cloth is doing to the surface tension. 2 Use this to explain why the matchsticks move in and come closer together. 3 The detergent attaches itself to the fat in the milk and reduces the surface tension of the water. Explain how the detergent gets the food dye to move. 4 Predict what would happen if low-fat milk was used instead.
5 Five cents worth of water Aim
2 mL
To observe how many drops of water can fit on the top of a five cent piece before it spills over.
1
Equipment • five cent piece • eyedropper
• access to tap water • warm water and chilled water
Method
Fig 7.5.8
1 Place the five cent piece on a flat surface.
5 Repeat the experiment, but this time use warm water and then cold water. Keep everything else the same.
2 Using the eyedropper, carefully place one drop at a time onto the centre of the coin.
6 Once again, record your results in the table.
3 Count the number of drops of water that land on the five cent coin without it spilling over. 4 Record your results in a table similar to the one below. Type of water Tap water Warm water Cold water
Number of drops Attempt 1 Attempt 2
Questions 1 Describe the shape of the water on the five cent piece. Use terms introduced in this unit to describe why this shape occurs. 2 Was there a difference between the number of drops that you counted for the different temperatures of the water that you used? If so, propose a reason why it may have happened. 3 Predict whether a different liquid (e.g. soft drink or milk) would show similar results. Explain your answer.
235
Unit
7.6
context
Magnetic forces
Magnets exert an invisible force on other magnets and on objects that contain iron,
nickel or cobalt. This force is called a magnetic force.
Fig 7.6.1 Iron filings make the force-field visible around a magnet.
236
What magnets do
Attraction and repulsion
Although magnets are strongest when touching, most have the ability to push and pull from some distance away. Magnetic forces are non-contact forces. This is what makes them useful as door latches. Magnets can also operate through paper and many other materials, allowing them to hold photos and notes on the fridge. Magnets can: • attract metals containing iron, nickel or cobalt. Steel is an alloy of iron, containing a high percentage of it. Therefore, magnets also attract steel. • at times, attract and pull the ends of other magnets towards them, or repel and push the other ends of those same magnets away • point to the North and South Poles of the Earth • make other iron-containing objects magnetic.
The magnetic force fields are particularly strong at the ends of a magnet. The ends are called poles—the north pole and the south pole. What a magnet does depends on its poles. • Poles that are the same (called like poles) push away or repel each other. • Poles that are different (opposite/unlike) pull together or attract each other.
Science
Clip
Which direction do we go? It is thought that birds, turtles and even bees may use the magnetic field of the Earth to navigate while travelling over long distances.
Prac 1 p. 239
Prac 2 p. 240
Magnetic fields
Fig 7.6.3 Unlike poles (north–south) attract and pull together.
Non-contact forces must have a method of moving other objects without touching them. This happens because there is a force field around the magnet. This magnetic field is the area around a magnet where a magnetic force is felt. Magnetic field lines show the direction an iron filing or a compass needle would point in the field. Scientists show the direction of the field with arrows that point away from the North Pole and towards the South Pole.
7. 6
Fig 7.6.2 Like poles (north–north or south–south) repel and push away from each other.
Unit
If magnets are dropped, hit or heated, the domains can be knocked out of alignment and the magnetism lost. Magnets made out of soft iron or mild steel tend to lose their magnetism very quickly. Permanent magnets are made from harder steel or cast iron in which the domains are more resistant to being knocked about.
Prac 3 p. 240
Making and destroying magnets The first magnets were simply lumps of rock that were naturally magnetic. These rocks contained a lot of iron and were called magnetite or lodestone. Magnets, iron and steel are all thought to have inside them mini-magnetic particles called domains. In unmagnetised iron, these domains are pointing in different directions. The forces from these mini-magnets cancel out each other and give no overall magnetism. If another magnet is used to push these domains around, they can become aligned and the piece of iron will become magnetic. S
N
N
S
S
S
N N
N
S
N
S N
S
N S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
S
S
N
N
N
S
N
S
N
S
Fig 7.6.4 Iron becomes magnetic if its domains align.
This can be done by: • stroking the piece of iron or steel repeatedly, in the same direction, with another magnet • lining up a piece of iron with the North and South Poles of the Earth and gently tapping it • leaving the iron in the core of an electromagnet.
Fig 7.6.5 Compasses and iron filings clearly show the direction and strength of a magnetic field.
237
Magnetic forces These lines never cross and come straight out of any surface. Lines that are close together show strong fields. Weak fields have their lines widely spaced. Magnetic fields are strongest at the magnet’s poles and get weaker as we move further away from them.
geographic axis
N
S
true North Pole
Earth’s magnetic north pole
Magnetic Earth The ancient Chinese, Romans and Greeks all used lodestone as a primitive compass to help them in their navigation. Although used much less now than in the past, compasses are still used in navigation. Compasses are small magnets that are allowed to move. The compass needle aligns itself with the Earth’s field lines and Science can be used to find north or south. This suggests that the interior of Watch it! the Earth is actually a magnet, with The fine inner workings of a its own magnetic field flowing from watch can be easily the South Pole to the North Pole.
S
N
Clip
destroyed if a strong magnet comes nearby. The backs of watches are always made from stainless steel to shield the mechanism from magnetic fields.
Earth’s magnetic south pole
Fig 7.6.6 Bar magnets and the Earth have similar magnetic fields.
Worksheet 7.5 Magnets Prac 4 p. 241
7.6
QUESTIONS
Remembering 1 State whether magnetic forces are classified as contact or non-contact forces. 2 List three metals that can be attracted to magnets. 3 Specify what steel contains that makes it attracted by magnets. 4 List the rules for attraction and repulsion of magnetic poles. 5 Recall the magnetic fields around a bar magnet and a horseshoe magnet by sketching their fields.
Understanding 6 Copy the following and modify any incorrect statements so that they become true: a b c d
238
The north pole of a magnet will attract other north poles. Compasses are actually small magnets. The area around a magnet is called its poles. The ends of a magnet are called its magnetic field.
e Domains must be aligned for a piece of iron to be a magnet. f The Earth does not have any magnetic field. 7 Outline what happens to the domains in a piece of iron when it becomes magnetised. 8 Explain what a magnetic pole is. 9 Explain how a compass works. 10 Describe how a material that contains iron can be made magnetic. 11 Predict what the Earth’s core is made up of, given that the Earth has a magnetic field.
Applying 12 Identify where the magnetic field on a magnet is strongest and where it is weakest. 13 Compasses are not as important as they once were. GPS is taking their place. Identify what GPS stands for.
>>
Unit
7. 6
14 The aurora australis is an amazing show of lights in the night Evaluating sky that happens only at the South Pole. It happens when 15 Propose a meaning for the term ferromagnetic. (Hint: Use particles from space follow the magnetic field of Earth until they the periodic table to find the chemical symbol for iron.) enter the Earth’s atmosphere. a Draw the magnetic field of Earth, identifying where the field is strongest. b Identify where the field lines actually touch Earth, and predict where on the Earth you would expect to see an aurora.
7.6
INVESTIGATING
Investigate your available resources (e.g. dictionary, textbooks, encyclopaedia, Internet etc.) to: 1 Find out about Alnico, the material that most permanent magnets are made from. a Use a periodic table to identify the meanings of the chemical symbols Al, Ni and Co. b Name the three elements that the alloy Alnico contains. c Propose a reason why each one might be included. 2 Find out what electromagnets are used for, particularly in simple electrical devices such as doorbells and telephones. Produce a report to explain how these electromagnetic devices work. 3 Explain why screwdrivers and screws are often accidentally magnetised when an electrical device such as a power drill has been operating nearby. Investigate how an electric motor works and how it could affect a screwdriver.
7.6 1
4 Describe the differences between Earth’s geographic and magnetic north poles. 5 Investigate how magnetism records sound and images on computer hard disks. Draw a series of diagrams to show how these devices record information. 6 Research why you should never store magnets (even fridge magnets) next to USB flash drives or computers.
e -xploring To find out more about compasses and making your own, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
We b Desti nation
PRACTICAL ACTIVITIES
Attracted to magnets?
Aim To determine what materials are attracted to magnets.
Equipment • bar or horseshoe magnet • watch-glass • a selection of different metals (e.g. aluminium, zinc, magnesium, tin, copper) • a selection of different objects (e.g. nails, paperclip, rubber, plastic, cotton wool)
Method 1 Place a material or object on top of an upturned watch-glass so that it can spin if attracted by the magnet. 2 Hold the magnet close to the object and record what happens in a table like the one shown. 3 Repeat with the rest of the materials and objects, making sure that you keep the magnet the same distance away from the object each time.
>> 239
Magnetic forces
Object/material
Magnetic? (Y/N)
Questions 1 Name the objects that are magnetic.
Zinc Aluminium Tin Copper Magnesium Paperclip Nail Rubber Cotton wool Plastic
2 Name the objects that are not magnetic. 3 Explain the relationship between the objects that are magnetic. 4 Predict what other materials may be magnetic.
Attracting and repelling
2 Aim
To investigate the two poles of a bar magnet. S
N
N
Equipment • watch-glass • two bar magnets
Method 1 Balance a magnet on the back of a watch-glass. 2 Hold another magnet near the poles, as shown in Figure 7.6.7, and record your results in the table below. North pole
South pole
Questions
North pole
1 Propose a rule for the attraction and repulsion of magnetic poles.
South pole
2 Explain the term poles.
Magnetic fields
3 Aim
To observe magnetic fields.
Equipment • • • • •
wooden board or bench mat sheet of A4 paper bar or horseshoe magnet fine iron filings (preferably in a shaker) can of hairspray
Method 1 Place a magnet on the board or bench mat and lay the sheet of paper over the magnet.
240
Fig 7.6.7
2 Sprinkle a small amount of the iron filings onto the sheet, gently tapping the sheet to spread them out around the magnet. 3 After a pattern is established, spray hair spray over the sheet to fix the filings in their positions. 4 You now have a permanent record of the magnetic field of the magnet. Paste it into your workbook.
Questions 1 Identify where the magnetic field was the strongest. 2 Identify and describe any positions on the magnet where no (or very few) filings were attracted. 3 Describe what you noticed about the strength of the field further away from the magnet.
Unit
Aim
Method
To determine what blocks or shields a magnetic field.
Part A 1 Set up the apparatus as shown in Figure 7.6.8.
Equipment • • • • • • •
7. 6
Shielding
4
paperclip fine cotton thread or fishing line sticky tape or plasticine or Blu-Tack 50 gram mass two bar magnets retort stand, bosshead and clamp sheets of various materials (e.g. paper, aluminium foil, iron, steel, lead, plastic, wood, tin, cardboard)
2 Now place another magnet near the paperclip. Try different combinations of poles (e.g. north with north, north with south, south with south). 3 Record the direction that the paperclip moves in each case. Part B 4 Find the maximum distance that could be left between the paperclip and the magnet before the clip would drop. Part C 5 One by one, insert the different sheets between the paperclip and the magnet.
N bar magnet S
bosshead and clamp
paper clip
Questions 1 State what happened to the paperclip when other magnets were brought near it. 2 Propose a reason why the paperclip was more likely to drop when further away from the magnet.
retort stand cotton thread
3 List the materials that caused the paperclip to drop. 4 Propose what happened to the magnetic field when the paperclip dropped.
sticky tape or plasticine or Blu-Tack 50 g mass
Fig 7.6.8
241
CHAPTER REVIEW Remembering 6 Complete the table below to summarise how forces are important in our everyday lives. Give two examples for each type of force.
1 State three words that summarise what is a force. 2 List what a force does to an object to which it is being applied.
7 Reducing friction would make machines more efficient. Explain what is meant by this statement.
3 List three ways in which friction may be reduced. 4 State whether each of the following statements is true or false: a Gravity depends on the planet we are on.
8 When we swallow food, there is a lot of friction from our throat. Explain what makes swallowing food easier.
b The mass of an object depends on where we are in the universe.
9 Describe three ways in which a magnet can be made. 10 Use the idea of domains to explain how magnets can lose their magnetism.
c There is no gravity on the Moon. d The gravity on the Moon is less than on Earth.
11 Describe three situations in which it is important to be able to reduce friction.
e Weight is measured in kilograms. f All objects have their own gravity and pull all other objects towards them. g A ship floats because its buoyancy balances its weight.
Applying 12 For each of the diagrams in Figure 7.7.1, identify whether it shows:
h Buoyancy is a downward force.
magnetic force
i Drag always makes objects go faster.
push
Understanding
pull surface tension
5 Match the words with their correct meanings. L force
caused by rough surfaces sliding
lift
spring balance
a unit of mass
weight
friction
reduces friction
friction
newton
forces that add up to zero
buoyancy
lubricant
push or pull
drag.
heat
causes large friction
sandpaper
produced by friction
kilogram
a unit of force
balanced forces
measures mass
balance
measures weight Type of force
Push Pull Friction Gravity Magnetic Buoyancy
242
Where used Skateboarding
How it works Skateboarder pushes ground with foot to move forward
b a
c
e
d
Fig 7.7.1
13 Identify an example of where each of the following forces can be seen in action: a a contact push force
Analysing 15 Classify the examples below according to whether friction can be seen as an advantage or a disadvantage:
b a non-contact push force
a stopping in a hurry
c a contact pull force
b pushing a fridge across the floor
d nuisance friction
c running a car engine
e useful friction
d parachuting from a plane
f drag
e turning quickly on your bike.
g gravity
16 An astronaut has a mass of 140 kilograms on Earth.
h buoyancy
a Use Figure 7.3.4 on page 220 to calculate their weight.
i surface tension
b The astronaut goes into space on a mission. What would be their mass in space?
j magnetic force. 14 The weight of a small rocket on Earth is 6000 N. Identify where in the solar system its weight would be: N
c What would be their weight in deep space where gravity is zero? N
a 1000 N
Creating
b 2000 N
17 Construct small, simple sketches of the situations below. For each, draw all the forces that are acting in the sketch. a A kite is flying. b A basketball is being thrown towards the hoop. c A magnet is affecting a compass. d A fish is hauled in on a line. Worksheet 7.6 Crossword Ch
a
pt
Worksheet 7.7 Sci-words
s
d 15 000 N
on
c 6000 N
er R sti ev i ew Q u e
243
8
Earth in space
Prescribed focus area: The history of science
Additional
Essentials
Key outcomes 4.1, 4.9.1, 4.9.2, 4.9.5
•
The solar system is made up of many different objects, including Earth, its Moon, other planets and the Sun.
•
The planets and their Moons in the solar system move around the Sun in an ellipitical orbit.
•
We experience night and day because the Earth spins on its axis.
•
As the Earth orbits the Sun, the tilt of its axis causes different parts of the Earth to experience different seasons.
•
Tides are caused by the gravitational pull of the Sun and Moon.
•
Our ideas about the working of the solar system have changed over the centuries.
•
Different cultures see the constellations in different ways.
•
The planets and moons in the solar system have very different physical features.
Unit
8.1
context
Earth’s movement in space
The Earth moves around the Sun while spinning on its own axis. This movement
in space gives us day and night, the year and the seasons.
Science
Clip
Using the Sun and Moon as a calendar The ancient civilisations measured the days, seasons, months and years by following the movements of the Sun and Moon. Chinese, Babylonians, Mayans, Indigenous Australians and many other cultures developed complex ways to predict seasonal changes. This way, they knew when to plant crops or move to a new location in search of seasonal foods. Survival depended on this ancient scientific knowledge of the Earth’s movement in space.
Fig 8.1.1 Earth’s movement in space determines the seasons and the length of the day and year.
Day and night The Earth has an imaginary line joining the Quick Quiz North and South poles. This line is called its axis and the Earth spins around it once every 24 hours. It is because of the Earth’s spin that we experience day and night. The part of the Earth receiving light directly from the Sun is experiencing day. Meanwhile the other side of Earth experiences night because no direct sunlight is falling on it. The direction of this spin is from west to east. This is why people in eastern Australia (such as those living in Sydney, Wollongong and Newcastle) start and end each day before those in the west (e.g. Perth). The direction of the spin makes the Sun, the Moon and stars appear as if they move from east to west.
The Earth’s axis is tilted, meaning that days and nights are of different lengths at most places around the globe. Only at the equator are day and night roughly of equal length. Science
Sunrise and sunset The terms sunrise and sunset seem to suggest that the Sun is moving and causes them. Sunrise is, however, caused by the Earth spinning towards the Sun. Sunset is caused by the Earth spinning away from the Sun.
Clip
Let’s go for a quick spin The Earth is spinning and so we are always moving. If you are standing at either the North or South Pole, then you don’t move at all…you just turn on the spot over 24 hours. At the equator you are travelling at an amazing 1600 kilometres per hour!
245
Earth’s movement in space
The year N
night
The Earth travels around the Sun once per year. The path the Earth takes is called its orbit. This means that the Earth takes one year to complete one orbit of the Sun. The Earth spins on its axis as it orbits the Sun, just as a spinning top moves in a circular path while it spins.
axis day
light from the Sun 1 year
S axis
23.5° tilt
Sun 1 day N
Fig 8.1.2 The Earth spins on its axis, causing alternating day and night.
Earth
area about to experience sunset
Fig 8.1.5 The Earth spins on its axis once per day and takes one year to orbit the Sun. As the Earth orbits the Sun, stars appear in different parts of the night sky and the length of day and night changes.
Sun Earth
area about to experience sunrise
Fig 8.1.3 Earth rotation from west to east makes the Sun appear to move from east to west. This causes sunrise and sunset.
N
light from the Sun
Science
equator equal length day and night longer nights
longer days
Northern Hemisphere
S
Southern Hemisphere
Fig 8.1.4 Everywhere on Earth experiences a 24-hour long day. These 24 hours are split into night and daylight hours. The split is equal only at the equator. If the Northern Hemisphere points towards the Sun, then its daylight hours will be longer than its night. Meanwhile in the Southern Hemisphere, the night will be longer.
246
An Earth year is 365¼ or 365.25 days. For convenience, a calendar year needs to have an exact number of days. A calendar year has exactly 365 days with an extra day being added every four years to catch up on the quarter days that must be accounted for. This longer calendar year is known as a leap year and the extra day is added to February (making it February 29). Generally, a leap year occurs every four years and is divisible by 4. However, years ending in 00 (e.g. 1900, 2100, 2200 etc.) are not leap years unless they are divisible by 400.
Clip
Time zones Most countries are small enough to have all their cities and towns working on exactly the same time. Larger countries are generally split into different time zones to account for the Earth’s spin and to keep the hours of dawn and sunset roughly consistent across them. To do this, USA and Canada have six time zones and Russia has twelve! Australia has three basic time zones. As a result, Adelaide’s times are half an hour behind Sydney’s, and Perth is two hours behind. During summer there are five time zones because Queensland and Northern Territory do not change their clocks for ‘daylight savings’. Despite being such a huge country, China has only one time zone!
North Pole
8.1
sunlight
sunlight
Unit
North Pole
equator equator
Earth’s axis of rotation South Pole
South Pole
Fig 8.1.6 Different amounts of light and heat from the Sun produce the seasons.
Seasons The Earth experiences seasons as it orbits the Sun. This is because the Earth’s tilt exposes some parts of the planet more to the Sun than others. This means that some regions will get more heat than others. southern autumn equinox 21 March
southern winter solstice 21 June
Clip
Sun
southern spring equinox 21 September
In summer, the Sun’s energy is concentrated over a smaller area, producing a greater heating effect. This results in higher temperatures. In winter, the same amount of energy is spread over a larger area and so that area does not heat up as much. The Earth is thought of as being made of two half spheres, known as hemispheres. When it is summer in the Southern Hemisphere (which contains Australia), it is winter in the Northern Hemisphere. Conversely, when it is winter here, it is summer there. The longest day each year Science is called the summer solstice. The shortest day occurs at the winter solstice. Day and night Collision course are of equal length twice each The Earth’s orbit around the Sun occurs largely through empty space, year. This occurs at the two filled with a little space dust and the equinoxes.
southern summer solstice 21 December
Animati on
Fig 8.1.7 Seasons depend on where Earth is in its orbit. These are the seasons experienced by the Southern Hemisphere.
Prac 1 p. 249
occasional asteroid that crosses it. Space dust is so fine that it poses no risk to us, despite the fact that the Earth sweeps up about 30 000 tonnes of it per year. Asteroids are lumps of rock ranging from one metre to many hundreds of kilometres across. Collision with them would cause extreme damage and possible extinction of life! This is a worrying thought since it is estimated that over 100 million asteroids will cross our orbit at some time!
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Earth’s movement in space
8.1
QUESTIONS
Remembering 1 State what is meant by the Earth’s axis. 2 State the angle of the Earth’s tilt. 3 Specify how long it takes the Earth to: a rotate once on its axis
12 a Identify the location on Earth where it could be dark for more than 24 hours at a time. b Explain why this is possible. 13 For the area marked A on Earth in Figure 8.1.8, identify whether day or night is longer.
b travel once around the Sun. A
4 State whether the statements below are true or false. a A leap year is one that the number 4 divides into without any remainder. b The year 2000 was a leap year.
Sun
c The year 2100 will be a leap year. 5 List the seasons of the year and the months that they (roughly) span in the Southern Hemisphere. Next to this list, write the seasons that the Northern Hemisphere would experience at the same time.
Understanding
Fig 8.1.8
6 Describe the feature of the Earth that is responsible for the seasons.
Analysing
7 Define the following terms:
14 Contrast an equinox from a solstice.
a hemisphere
Evaluating
b solstice
15 Propose why the stars appear to move from east to west. (Hint: Think about the direction of the Earth’s rotation.)
c equinox. 8 If the Earth’s axis was not tilted, explain whether there would be: a seasons b day and night. 9 If the Earth tilted even more, explain how the seasons would be affected. 10 It is hot at the equator all year. Explain why.
Applying 11 Identify the location on Earth where day and night are always the same length.
248
Earth
Creating 16 Construct a diagram to show how a season occurs. 17 Construct a model to demonstrate how seasons, day and night and a year occur. 18 Scientists have just announced that the Earth is about to stop spinning on its axis! What may be the consequences? How will the weather and climate be affected? Will plants grow? Is this the end, or will life be possible in some areas? Write an account that synthesises what life would be like on Earth, using the answers to the questions.
Unit
8.1
8.1
INVESTIGATING
Investigate your available resources (e.g. dictionary, newspapers, Internet etc.) to: 1 Find out and record sunrise and sunset times for two weeks. Describe any changes in the length of day and night. 2 Explain the meaning of aphelion and perihelion.
3 List the five climatic zones on Earth. Produce a poster to display your information, with examples of what these zones commonly are like. 4 Find the speed at which the Earth: N a spins on its axis b moves around the Sun.
8.1
PRACTICAL ACTIVITY
A model Earth
1
mark where you live (approximately!)
Aim To model night, day and the seasons.
Equipment • • • • •
sphere (e.g. a ping-pong ball or foam ball) skewer or fine rod wedge lamp piece of string of length 60 centimetres
Method 1 Assemble the apparatus as shown in Figure 8.1.9, and place a mark on the Earth model to represent where you live. 2 Rotate the Earth model on its axis to simulate day and night. 3 Keeping the axis at the same angle, move the model around the lamp (the Sun) while a partner keeps it spinning on its axis to simulate day and night.
sphere (Earth)
rod string lamp (Sun)
wedge
Fig 8.1.9
Questions 1 Explain the purpose of the piece of string. 2 Describe what you notice about the length of day and night as you move around the ‘Sun’ in step 3 above. 3 Draw and clearly label a diagram to demonstrate your model in four positions, representing each season.
249
Unit
8.2
context
The Moon
The Moon is the closest celestial body to Earth and is the only one that orbits us. The Moon is the second brightest object in the sky after the Sun. It doesn’t make
Fig 8.2.1 The Moon is our closest neighbour in space.
its own light but, instead, acts like a giant mirror-ball, reflecting sunlight onto us. The Moon is the only celestial body that has ever been visited by humans in person.
Lunar statistics The Moon is our immediate neighbour in space, being between 380 000 and 410 000 kilometres from us. It orbits the Earth, just as Earth orbits the Sun, taking about a month to do so. Like Earth, the Moon is roughly spherical and has gravity. It is much smaller than Earth, however, having a diameter about the same as the distance from Sydney to Perth. This smaller size (and mass) makes its gravity about only one-sixth that of Earth’s gravity.
Science
Fact File
The Moon Mass
0.012 times that of Earth
Diameter
3476 km (about ¼ or 0.27 × Earth’s diameter)
Gravity
About one-sixth (0.16) that on Earth
Atmosphere
None
Surface temperature
–230°C to 123°C
Period of rotation (day)
27.3 days
Time to orbit Earth
29.5 days
Tilt of axis
5°
Science
Clip
Mysterious Moon The Moon has inspired more stories, myths, prayers and rituals than just about anything else. In its surface markings, different cultures see a man, a woman weaving or even a rabbit! Many once believed that a full moon made people go mad. This belief took the name from the Roman goddess Luna, and so those who went mad were known as lunatics. Many religious festivals are based on the cycles of the Moon. The Christian festival of Easter, for example, falls on the first Sunday after the first full Moon after 21 March. Ramadan, the Islamic month of worship and fasting, starts and ends with the first sightings of a thin crescent Moon.
250
Missions to the Moon The Moon is our closest neighbour in space and so it makes sense that it was the first celestial body that humans visited. Many unmanned scientific missions have been sent to the Moon looking for the presence of life and water, and to determine the composition of the rocks that make it up. The first manned landing occurred in 1969 when the US space agency NASA landed Apollo 11 on the Sea of Tranquility. The lunar module that landed (code-named Eagle) was piloted by astronaut Buzz Aldrin.
Fact File
Moon missions French author, Jules Verne, wrote From the Earth to the Moon, a novel about an imaginary visit to the Moon 1959 First Russian unmanned mission 1961 US first unmanned hard landing probe 1961–1969 US-manned Apollo missions, testing different aspects of a manned landing 20 July 1969 Eagle lunar module from Apollo 11 lands on surface, and Armstrong and Aldrin become the first humans to walk on anything other than Earth 1969–1972 Apollo 12, 14, 15, 16 and 17 land two men each on the Moon. Apollo 13 aborts due to explosion and multiple system failures 14 December 1972 Challenger lunar module from Apollo 17 blasts off from Moon’s surface. No humans have visited the Moon since 1970–1973 Soviet-unmanned probes 1990–1993 Japanese orbital and hard landing probes 2003 European lunar orbiter 2007 Japanese lunar orbiter 2008 Indian-manned lunar orbiter
8.2
1865
Its commander, Neil Armstrong, was first to set foot on the lunar surface. While Eagle landed on the surface, a third astronaut, Michael Collins, stayed in orbit around the Moon in the command module (code-named Columbia). The Moon differs from Earth in two very important aspects. • It has no atmosphere and, therefore, no air to provide oxygen to breathe. This is why astronauts must wear space suits with breathing apparatus. • Its gravity is far less than that on Earth, meaning that astronauts weigh only one-sixth of their Earth weight. The astronaut’s mass (e.g. the amount of bone, muscle and skin) remains exactly the same as on Earth. After an extended time, this lack of gravity leads to a loss of muscle strength and bone density.
Unit
Science
The lunar landscape Before 1609, most scientists thought that the surface of the Moon was smooth. In that year, however, Galileo Galilei (1564–1642) used a telescope to view details of the Moon’s surface. The two main types of lunar landscape he observed were highlands and vast plains known as maria (singular = mare). Scientists believe that about 4 billion years ago the Moon was a hot, fluid mass that eventually cooled enough to form a crust. This crust was bombarded by meteorites to create the highlands and craters. Some of the depressions caused by meteorite impacts were then filled with lava from lunar volcanoes. The lava then became solid to form large, smooth areas or maria.
Fig 8.2.2 Buzz Aldrin was the second man to step onto the Moon. Neil Armstrong was the first.
Fig 8.2.4 A full moon showing dark areas of lava-filled impact basins. Space probes have found very few maria on the other side not seen from Earth (known as the ‘dark side’).
Fig 8.2.3 Moon buggies like this one were used in the last Apollo missions to the Moon. They were left there.
Apollo missions in 1971 and 1972 found that the interior of the Moon is still hot. In 1998, the Lunar Prospector found evidence of water in the form of ice mixed with lunar dirt at the Moon’s poles.
Prac 1 p. 255
251
The Moon Science
Clip
The dark side
Science
The time taken for the Moon to orbit Earth is nearly the same time as it takes to spin once on its axis. This results in us only ever seeing the one side of the Moon from Earth. The other side is often called the ‘dark side of the Moon’ since it had never been seen until the early Apollo missions.
Phases of the Moon The Moon takes about the same time to orbit Earth as it does to complete one spin, and so we always see the same face of it. How much of the Moon’s face we see depends on where it is in its orbit around the Earth. These different views are known as phases. There are eight main phases of the Moon.
Clip
Once in a blue moon There is a saying once in a blue moon, which means not very likely. A ‘blue moon’ is the name given to the second full moon in the same month. Since the time between two full moons is 29.5 days and a month is about 30.5 days, a blue moon is rare, occurring only once every two and a half years.
Science
a
Clip
Bugs on the Moon! Some early astronomers thought that the dark patches on the Moon were caused by huge migrating swarms of insects! Later on, in 1651, the Italian astronomer Giovanni Riccioli (1598– 1671) suggested that the dark areas on the Moon were seas. Although the Moon has no surface water, his method of naming has become a tradition and continues today, with names such as ‘Sea of Tranquility’ and ‘Sea of Serenity’.
Prac 2 p. 256
Fig 8.2.5 a Half the Moon is always in sunlight, but we on Earth do not always see the full half. This produces the phases of the Moon. b The eight phases of the Moon.
b
new moon
A
waxing crescent
first quarter
gibbous
full moon
gibbous
third quarter
waning crescent
B
C
D
E
F
G
H
views of the Moon from point on Earth
252
?
Unit
Lunar eclipse
The ancient Chinese recognised a connection between tides and the Moon’s cycle. About twice a day the sea level rises to a high tide and falls to a low tide—the average time between two high tides is 12 hours 25 minutes. In 1687, the English scientist Sir Isaac Newton (1642–1727) proposed his theory of gravity. He used his theory to explain that tides happened because of the Moon’s gravitational pull on the Earth. The gravitational force between two objects is noticeable only when one or both objects are very large, as is the case with the Moon and the Earth. The Moon attracts the oceans towards it, enough to cause a bulge in the oceans facing the Moon. This bulge causes water to be drawn from other areas on Earth, giving a low tide. If this was the only effect, there would be one high tide and one low tide a day—not two. The Earth’s rotation, however, causes a similar bulge on the other side of the Earth.
Lunar eclipses occur when the Moon passes into the shadow of the Earth, making it completely or partially ‘disappear’. They occur up to three times a year.
8.2
Tides
low tide
water pulled by Moon’s gravity
Earth N
Moon high tide water not as strongly attracted by Moon’s gravity is ‘left behind’, causing another high tide
Fig 8.2.6 Tides are caused by the gravitational pull of the Moon.
G penumbra F E Sun
D
Earth
umbra
C B A
penumbra
Moon’s orbit
Fig 8.2.7 A lunar eclipse occurs when the Moon passes into the shadow of the Earth.
Animati on
253
The Moon
8.2
QUESTIONS
Remembering 1 a State the year in which the first person walked on the Moon. b Name who was the first.
sunlight
c Name the second person to walk on the Moon. 2 State whether the Moon has:
Moon
a an atmosphere b gravity. 3 State how far the Moon is from the Earth, rounding to the nearest 100 000 kilometres. 4 State how long it takes for the Moon to orbit the Earth.
Fig 8.2.8
20 The tidal bulges are missing from Figure 8.2.9. Use a copy of the diagram and include them.
5 State the number of tides that occur per day.
Moon
6 State who used a telescope to view the Moon in 1609. 7 Specify where water may exist on the Moon.
Understanding 8 Describe what the Apollo missions discovered about the core of the Moon. 9 Explain why we always see the same side of the Moon. Earth
10 Explain what a ‘phase’ of the Moon means. 11 Describe how a lunar eclipse occurs. 12 Predict how the tides would be affected if the Moon was: a larger
Analysing
b further from the Earth.
21 Contrast a waxing crescent from a waning crescent.
13 Describe what is meant by ‘the dark side of the Moon’.
Evaluating
14 Use Figure 8.2.7 to describe how the duration of a lunar eclipse would be different if the Earth was smaller.
22 More meteorites reach the surface of the Moon than the surface of the Earth. Propose a reason why.
Applying
23 There are more extreme temperatures on the Moon than on the Earth. Propose a reason why.
15 Identify the two main types of lunar landscape, and describe them briefly.
Creating
16 Identify what causes the tides on Earth.
24 Construct a drawing of each of the following:
17 Calculate (approximately) the number of Moons it would take to equal the mass of the Earth. 18 Use Figure 8.2.7 to explain what happens during: a a penumbral lunar eclipse b a partial lunar eclipse. 19 Copy and modify Figure 8.2.8 to show where the Earth would be placed if a ‘quarter moon’ is to be seen.
254
Fig 8.2.9
a a gibbous moon b a crescent moon. 25 Construct a diagram to demonstrate how the tides are created. 26 Design a colony that meets the requirements people will have on the Moon. Anticipate some of the difficulties of life on the Moon. Consider factors such as food, temperature, oxygen and the possibility of meteorite strikes.
Unit
INVESTIGATING
Investigate your available resources (e.g. dictionary, textbooks, encyclopaedias, Internet etc) to: 1 Produce a poster of the Moon, showing the names of the maria and highlands. 2 Find out what are ‘neap’ and ‘solar’ tides.
8.2
8.2
e -xploring We b Desti nation To construct a model of the Lunar Prospector that discovered ice on the Moon, a list if web destinations can be found on Science Focus 1 Second Edition Student Lounge.
3 Obtain a tides chart and produce a key to explain how to use it. 4 Find the NASA website and its video clips of Moon missions.
8.2
PRACTICAL ACTIVITIES
Crater formation
1 Aim
To investigate how craters get their shape.
Equipment • • • • • •
flour chocolate icing sugar shallow tray (e.g. foil tray) three rocks (ranging about 1 cm to 7 cm in size) newspaper metre rule
Method 1 Spread the newspaper under the shallow tray. 2 Place a fairly thick layer of flour in the tray, and smooth it. 3 Cover this with an even, thin layer of chocolate icing sugar to represent an outer layer of rock. 4 Drop the rocks onto the flour from a height of one metre. Remove them after each drop. 5 Increase the height to two metres and repeat. 6 Record the diameter of each crater and its shape for the three rocks.
chocolate icing sugar
flour
Fig 8.2.10
Questions 1 Make a list of the factors that affected the type of crater formed. 2 Did the same rock make the same size crater every time? Explain your answer. 3 The experiment assumes that all objects hit planets or moons vertically. Design an experiment to see the effect of an impact at an angle.
255
The Moon
2
Phases of the Moon
Aim To construct a flip book to show the main phases of the Moon.
Method 1 Record the phases of the Moon every third night for one month, using copies of a record box like the one in Figure 8.2.11. 2 If the sky is cloudy, you will have to guess what the Moon may look like. 3 Paste the diagrams onto stiff cardboard.
Date
4 Place the pages in order from a new moon and secure them to make a small booklet.
Time
5 Flip the pages with your thumb to see the Moon’s phases.
256
Fig 8.2.11 Moon view record box
Unit
8.3
context
The Sun
Our Earth depends on the Sun to supply the energy that life on this planet needs to flourish. With care, scientists can observe features on the Sun’s surface,
particularly during solar eclipses. Although these occur every year, each eclipse can be observed only from certain parts of Earth.
Our nearest star The Sun (also known in astronomy as Sol) is our nearest star. Being about 4.5 billion years old, the Sun is currently in ‘middle age’, with another 4.5 billion years or so of ‘life’ left. Astronomers believe that the Sun is a secondgeneration star. This means that it formed after a previous star collapsed. Its debris then combined with interstellar gas to form the Sun.
Vital for life The Sun is our source of heat and light energy. Plants use light energy from the Sun to carry out photosynthesis, a process during which they make the food they need for growth and reproduction. One of the by-products of this process is oxygen. Animals rely on plants since they breathe in the oxygen that plants produce. Many animals also feed on plants. Other animals feed on those animals. Ultimately, the Sun is essential to the continuation of life on Earth. The Sun is vital for life in many other ways, too. • We release the Sun’s energy whenever we burn fossil fuels, such as oil, coal, gas and petrol. The bodies of dead plants and animals in the Earth’s crust have been converted over millions of years into these fossil fuels.
Fig 8.3.2 A simple food chain shows that all life on Earth ultimately depends on the Sun.
Fig 8.3.1 The Sun is the closest star to planet Earth. This image shows a spectacular solar flare extending 588 000 kilometres from the Sun’s surface.
O2
CO2
257
The Sun
Fig 8.3.4 Since late 2008, solar collectors have provided all 100 residents of the small Queensland town of Windorah with all the electricity they need.
Fig 8.3.3 Fossil fuels, such as petrol, store in their chemicals energy that came from the Sun many millions of years ago.
• Heat from the Sun is felt directly in the warmth you feel when you are outside in the sunlight. • The Earth itself is warmed by this radiation. Different parts of the Earth heat up by different amounts, creating pressure differences in the atmosphere. These in turn create winds that increase evaporation, leading to rainfall. • Some of the sunlight falling on Earth is reflected back and would escape into space if not for the Earth’s atmosphere. Greenhouse gases in the atmosphere trap some of this heat and so the atmosphere and Earth’s surface is kept warm enough for life. The atmosphere and Earth’s magnetic field also protect the planet from other, more harmful radiation from the Sun, such as ultraviolet (UV) radiation. • The Sun provides the massive gravitational force necessary to keep the Earth and other planets in orbit around it.
Solar technology Solar energy has long been used to dry clothes and warm houses. Simple technologies, such as clothes lines and north-facing windows, have allowed us to use this free and limitless source of energy. More recently, energy from the Sun has been used as an alternative to using fossil fuels. Swimming pools are often warmed by placing coils of black tubes on nearby roofs, and some houses are now using solar panels to warm water for use inside. Others are using solar power to generate their own electricity, and some towns are using solar collectors for their power.
258
Energy production in the Sun Like all stars, the Sun produces energy due to nuclear reactions in its core. The intense temperature and pressure at the core causes the nuclei of hydrogen atoms to fuse, joining together to form helium. This reaction releases a huge amount of energy and is called nuclear fusion. Go to
Science Focus 2 Unit 6.4
Solar statistics The Sun is a star, but because it is much closer than other stars, it appears much larger and brighter.
Science
Fact File
The Sun Mass
333 400 times the mass of the Earth
Diameter
1 392 000 km ( = 109 × Earth’s diameter)
Gravity
28 times that on Earth
Surface temperature
4500 to 2 000 000°C (average 6000°C)
Core temperature
15 000 000°C in the core
Period of rotation (day)
Equator 26 days Poles 37 days
Tilt of axis
122°
Scale model Diameter
300 mm
Unit
Features of the Sun
Sun
Fig 8.3.5 A total of 109 Earths would fit in a line across the Sun’s diameter. A total of 1.3 million Earths would fill its interior!
The Sun itself orbits around the centre of the Milky Way, the galaxy in which we live. It takes 225 million years for the Sun to complete its orbit and so scientists have agreed that the Sun is ‘stationary’ for all practical purposes.
Missions to the Sun There have been over 30 missions to the Sun and many more are planned to take place by 2014. Missions to the Sun (known as heliophysics missions) aim to understand the effects of the Sun on Earth. A typical mission was the Ulysses space probe launched in 1990. Ulysses passed by the Sun’s south pole in 1994 and again in 2000. It passed the Sun’s north pole in 1995 and again in October 2001.
!
Safety Although you can see the features of the Sun from Earth, you should never look directly at it. Its intense brightness can permanently damage your eyes, leading to blindness.
Several features of the Sun may be observed from the Earth using special solar telescopes. • Sunspots and solar flares were first observed on the Sun’s surface by Galileo in 1611. Sunspots are depressions on the Sun’s surface that appear darker because they are several thousand degrees cooler than the surrounding gas. The number of observable sunspots follows an 11-year cycle, and varies from zero to about 200 in a year. • Solar flares come from sunspots and can reach a height of hundreds of thousands of kilometres above the Sun’s surface. Solar flares can cause interference with mobile phone, radio and television reception on Earth. • Prominences are a larger type of solar eruption and consist of a streamer of glowing gas. They can be observed from Earth during a total solar eclipse. • Solar winds are formed by streams of particles being constantly emitted by the Sun into space. They travel at speeds of about 500 kilometres per second.
8.3
Earth
Corona: a faint halo extending out a great distance from the Sun (1 000 000–2 000 000°C). The corona includes clouds of gas called prominences. Chromosphere: a thin ring around the edge (4500–1 000 000°C) Photosphere: the visible surface of the Sun (5000°C)
Sun
Fig 8.3.6 The Sun’s atmosphere has three main layers— photosphere, chromosphere and corona.
Science Science
Clip
Passengers on aircraft zapped! A typical solar flare releases energy that is equivalent to one billion hydrogen bombs and throws 100 billion tonnes of dangerous particles into space. The magnetic field of Earth normally protects us from all this. Due to a solar flare, aircraft passengers can receive radiation equivalent to that of one medical X-ray.
Clip
Rotation rates Different parts of the Sun rotate at different rates. The solar equator rotates once every 26 days, whereas the Sun’s polar regions rotate once every 37 days.
Prac 1 p. 261
259
The Sun a
Fig 8.3.7 a Solar winds send particles towards the Earth’s North Pole and South Pole regions, where they interact with gas particles in the atmosphere to cause a spectacular light display called an aurora. b Aurora australis is often called the southern lights. g
solar wind aaurora au uro ur ror ora ra b
day
nnight ight ht atmosphere aaurora au aur uro ro ror orraa ora
Solar eclipses
total solar eclipse
Sun is behind Moon
Moon
partial solar eclipse
solar corona now visible
annular solar eclipse
Moon Sun
Moon Sun
Fig 8.3.8 There are three types of solar eclipse. Solar eclipses can
There are three types of solar eclipse: • A total solar eclipse is when the Sun is covered by the Moon. • A partial solar eclipse is when the Moon covers only part of the Sun. • An annular solar eclipse occurs when the Moon is at its greatest distance from Science the Earth. All solar eclipses occur when the Moon comes between the Earth The Sun has and the Sun and the Moon’s abandoned me! shadow falls on the Earth.
Clip
Worksheet 8.3 Sunrise, sunset
occur up to twice a year, but do not all happen in the same place.
8.3
QUESTIONS
Remembering
260
The word eclipse comes from the Greek word for abandonment—the eclipse was seen as the Sun abandoning the Earth!
Understanding
1 List the following in order from closest to most distant from the centre of the Sun: chromosphere, photosphere, corona.
6 Plants and animals both depend on the Sun for food. Explain how.
2 State a harmful type of radiation from the Sun. 3 Name two types of energy provided by the Sun.
7 Explain why there would also be no oil deposits inside the Earth if there was no Sun.
4 Name Earth’s nearest star and its distance from Earth.
8 Explain what each word means in the term nuclear fusion.
5 State the maximum temperature that is thought to be reached within the Sun.
9 Describe three features of the Sun. 10 Explain how the Sun affects: a rainfall b wind.
>>
c minute
Applying
d hour.
15 Specify how many kilometres a light year is equivalent to.
12 Identify the region of the Sun that is:
16 Calculate how many minutes it would take light to travel from the Sun to Earth.
a hottest b ‘coolest’ c its visible surface.
Evaluating
13 If the Earth is drawn as a circle of diameter 1 mm, calculate how large the Sun would need to be if drawn to the same scale.
17 Imagine the Sun has just ‘died’. Propose what would happen to Earth and life on it over the next few: a hours b days c years.
Analysing
Creating
The distances in space are so huge that kilometres are not used to measure them. Instead, distances are measured in light years. A light year is the distance a beam of light will travel in one year, or 365 Earth days. Light travels at a speed of 300 000 kilometres per second (km/s).
18 Construct a drawing to demonstrate the view from Earth during: a a partial solar eclipse b an annular solar eclipse.
8.3
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find out where an aurora other than aurora australis occurs. What is it called?
3 Find out when the next solar eclipse will occur that can be seen from your local area. Produce an advertisement to get people out to watch the eclipse, but make sure you inform them about how they can view the event safely without damaging their eyes. L
2 Find out more about the Ulysses probe. Construct a labelled diagram of its structure to show what it can do.
8.3
PRACTICAL ACTIVITY
The sunspot cycle
1
Method 1 The approximate numbers of sunspots recorded over a 14-year period are given below. Use these data to construct a sunspot line graph. Place the years on the horizontal axis. Place the number of sunspots on the vertical axis. N
Aim Use existing data to predict the number of sunspots up to the year 2013.
2 If the graph follows a similar cycle for the next 11 years, sketch the predicted number of sunspots up to the year 2013.
Equipment •
8.3
14 Use this information to calculate how far light travels in one: a day b year
Unit
11 The Sun is less dense than Earth. Explain how this can be when the Sun is much bigger and has a much larger mass.
graph paper
3 How many sunspots do you predict for the year 2013? If possible, check your prediction using the Internet. Year
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Sunspots
157
142
146
94
54
30
18
9
22
64
93
120
111
104
261
Unit
8.4
context
The solar system
Look up into the sky on a clear night and you will see many of the planets that the ancient astronomers saw. You might also see an assortment of space junk and satellites that move across the night sky like slowly moving stars. Modern astronomers make closer observations of the planets and the stars beyond using
telescopes. Space probes have been sent to many of the planets in the solar system to collect even more information about them. This new knowledge has given us a much greater understanding than before of Earth and the seven other planets of our solar system.
Science
Clip
Pluto: The non-planet
Fig 8.4.1 The relative sizes of the planets are shown. The rings of the gas giants are not shown. Until recently, there were nine planets in the solar system. In 2006, Pluto was re-classified as a dwarf planet, meaning that there are eight official planets in the solar system.
Eight planets of the solar system The term solar system takes its name from Sol (the Greek word meaning Sun), the star at its centre. The planets of our solar system orbit around the Sun. At the same time, each planet rotates on its own axis. The time taken for a planet to spin once on its axis is called its day. The time taken for a planet to orbit the Sun once is called its year. All the planets have days and years of different lengths. The four innermost planets (i.e. Mercury, Venus, Earth and Mars) are termed terrestrial planets, meaning
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Until 2006, Pluto was considered to be the ninth planet of the solar system. In that year however, the members of the International Astronomical Union (IAU) agreed to create a new class of ‘dwarf planets’. Dwarf planets are like other planets in that they have enough gravity to pull them into roughly spherical shapes. They differ, however, from ‘normal’ planets in how they affect small masses in their paths. ‘Normal’ planets have enough gravity to sweep their orbits clear of debris, whereas the gravitational pull of dwarf planets is insufficient to do so. Pluto has been classified as a dwarf planet, along with the asteroid Ceres and Eris (formerly known as 2003UB313), which orbits the Sun three times further out than Pluto. The dwarf planet list will keep growing as new celestial bodies are found that fit into this category.
that they are ‘Earth-like’. All the terrestrial planets move around the Sun in the same plane (a large imaginary flat surface) in almost circular orbits. The larger outer planets (i.e. Jupiter, Saturn, Uranus and Neptune) are known as the gas giants because of their outer layers, which are composed of gases such as hydrogen and helium. The gas giants move in elliptical or oval orbits. They, too, move in the same plane as all the other planets.
Unit
8.4
Sun Mars Earth Venus
Jupiter
Saturn
Uranus
Neptune
Mercury
Fig 8.4.2 The distances in this diagram are to scale, but the sizes of the planets are not.
1 AU 1 AU Sun Sun
Fig 8.4.3 An astronomical unit (AU) is the distance from Earth to the Sun.
The terrestrial planets
Earth Earth
Science
Each planet is given a symbol by modern astronomers. These symbols were invented by the Greeks who imagined each planet to be a god.
Science
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Fact File
Hey you, AU! The average distance from the Earth to the Sun is called an astronomical unit (AU) and equals 149 600 000 kilometres. If you travelled at 100 kilometres per hour, then it would take about 170 years rs to get from the Earth to the Sun!
Mercury, Venus, Earth and Mars all can be seen without a telescope. For this reason they were known to most ancient civilisations. The terrestrial planets could be easily referred to as the ‘ancient’ planets.
Diameter measurements are made at the equator for each planet. For comparison, the diameter of the Sun is 1 392 000 km.
Mercury Mass
0.056 times that of Earth
Moons
None
Di Diameter
4878 km ( = 0.38 × Earth’s diameter)
Su Surface
Similar to Earth’s Moon, with craters, lava-flooded plains and smooth mountains
At Atmosphere
Mainly helium, which blows past Mercury from the Sun
Gr Gravity
0.38 times that on Earth
Su Surface te temperature
Drops to –170°C at night and rises to 430°C in the day
Pe Period of rotation (d (day)
59 Earth days
Tilt of axis
0°
Distance from Sun
0.39 AU (58 million km)
Time to orbit Sun (year)
88 Earth days
Scale model (Sun = 300 mm) Diameter
1 mm
Distance from Sun
12.5 m
Mercury
Fig 8.4.4 Mercury shows its heavily cratered surface.
Mercury was known in ancient Sumer (now Iraq) some 5000 years ago. This planet moves very quickly across the sky. It was named after the Roman god, Mercury, who was the swift messenger of the gods.
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The solar system Mercury is the closest planet to the Sun, so close that it is often difficult to observe. One time that it is very visible is in the dark of the morning or evening. For this reason it appears as a morning and evening star. Despite its proximity to the Sun, Mercury is not the hottest planet in the solar system. Mercury is the smallest planet of the solar system, being about the size of Earth’s Moon. Like the Moon, it has a very old surface containing craters and plains. Much of our knowledge of Mercury comes from the American spacecraft Mariner 1. In the 1970s it flew past Mercury three times, photographing and mapping roughly half the planet’s surface. In 2004, the Messenger spacecraft was launched to investigate the geology, atmosphere and magnetic field of the planet Mercury. It took three and a half years for Messenger to get to Mercury, flying within 200 kilometres of its surface. In 2008, it pulled itself onto a path that will lead it to back to orbit Mercury in 2011. It takes ten minutes for Messenger’s radio signals to reach Earth and its flight controllers at NASA.
Science
Fact File Venus
Mass
0.815 times that of Earth
Moons
None
Diameter
12 103 km ( = 0.95 × Earth’s diameter)
Surface
Extensive cratering, volcanic activity, mountain ranges, a 1500 km trench.
Atmosphere
80 km thick layer of carbon dioxide with some water vapour. Clouds contain concentrated sulfuric acid droplets.
Atmospheric pressure
90 times that on Earth (enough to crush early Space probes)
Gravity
0.9 times that on Earth
Surface temperature
460°C
Period of rotation (day)
243 Earth days
Tilt of axis
30°
Distance from Sun
0.72 AU (108 million km)
Time to orbit Sun (year)
225 Earth days
Venus Venus was recorded by the Babylonians in approximately 3000 BCE and it is also mentioned in the astronomical records of the ancient civilisations of China, Central America, Egypt and Greece.
Scale model (Sun = 300 mm)
Fig 8.4.5 A radar image of Venus sent from the Magellan mission.
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Diameter
2.6 mm
Distance from Sun
23.3 m
Venus is the hottest planet in the solar system and is the planet closest in size to Earth. Venus has an acidic and crushing atmosphere that would make it impossible for life to exist on it. When visible, Venus is the third brightest object in the sky after the Sun and Moon. It is so bright that it is known as the morning and evening star. Venus spins from east to west, a direction opposite to the spin of Earth and the other planets. This opposite spin is called retrograde movement. Venus also revolves very slowly. A day is longer than its year. Scientists are curious about why Venus developed so differently from Earth and the other planets. One thought is that a comet or asteroid may have crashed into Venus in the distant past and that this collision slowed its rotation and reversed its spin.
Fact File Earth
Mass
1.0 times that of Earth (5 980 000 000 000 000 000 000 000 kg)
Moons
One (known as ‘the Moon’)
Diameter
12 756 km
Surface
Two-thirds water, one-third land
Atmosphere
78% nitrogen, 21% oxygen, 1% carbon dioxide, argon and water vapour and other gases
Gravity
1.0 times that on Earth
Surface temperature
Average 22°C
Period of rotation (day)
1 day
Tilt of axis
23.5°
Distance from Sun
1 AU (150 million kilometres)
Time to orbit Sun (year)
365.25 days
Earth Earth is the third planet from the Sun. Seventy per cent of Earth’s surface is covered by water and so the planet is also known as the blue or water planet. Earth is the only planet currently known to support life. It has a molten core, upon which float the massive rocky tectonic plates that make up its surface. Earth is orbited by its Moon and many artificial communication satellites.
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The surface of Venus cannot be observed directly using telescopes because of its thick, acidic cloud layer. Most of our knowledge of Venus comes from the Magellan mapping probe that left Earth in 1989 and fell into orbit around Venus in 1990. The images it sent back showed sharp-edged craters and massive volcanoes, and were used to map 98 per cent of the planet’s surface. The Venus Express, which was launched by the European Space Agency in 2005, continues to send back scientific data about the planet.
Unit
Science
Scale model (Sun = 300 mm) Diameter
2.7 mm
Distance from Sun
32.2 m
Mars
Fig 8.4.6 Earth showing Australia and snow-covered Antarctica.
Mars is named after the Roman god of war. Mars is known as the ‘red planet’ and has been the subject of many science fiction movies and books. Mars would be accurately called ‘the rusty planet’, as its red appearance is due to rust (iron oxide) in its surface soil and rocks. There are some similarities between Earth and Mars—a Martian day is only 30 minutes longer than an Earth day and its 25.2° tilt causes seasons similar to Earth’s (only twice as long). Many space probes have been sent to Mars to collect data on its rocks and weather, and to see if there is any evidence of past or microscopic life. Some of the most important missions were Viking 1 and 2, Pathfinder, the Mars Global Surveyor (which found that water once existed on Mars) and Odyssey (which discovered ice under its surface). These were space probes that collected data about the rocks, weather and any evidence of microscopic life. In 2007, the Phoenix Mars Mission was launched as a ‘budget’ Mars Exploration Program. This mission was designed to determine the existence of water and the habitability and potential biology on the planet.
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The solar system Science
Fact File Mars
Fig 8.4.7 Mars showing red earth and polar caps.
Mass
0.107 times that of Earth
Moons
Two (Phobos—diameter 23 km, Deimos—diameter 10 km)
Diameter
6794 km ( = 0.53 × Earth’s diameter)
Surface
Soft red soil containing iron oxide (rust), giving the planet its red appearance. Cratered regions, large volcanoes, a large canyon and possible dried-up water channels. Polar caps of frozen carbon dioxide and water.
Atmosphere
Very thin, mainly carbon dioxide
Gravity
0.376 times that on Earth
Surface temperature
–120°C to 25°C
Period of rotation (day)
1.03 Earth days
Tilt of axis
25.2°
Distance from Sun
1.52 AU (228 million km)
Time to orbit Sun (year)
687 Earth days
Scale model (Sun = 300 mm)
Fig 8.4.8 The Mars Phoenix mission. The landing system on Phoenix allows the spacecraft to touch down within 10 kilometres of its targeted landing area.
The asteroid belt The asteroid belt is made up of thousands of small rocky metallic bodies and dust in orbit around the Sun. The largest asteroid is Ceres, having a diameter of about 1000 kilometres. Researchers have found several nearEarth asteroids, but none are predicted to crash into Earth in the near or distant future. Fig 8.4.9 Thousands of asteroids lie in a belt between Mars and Jupiter. One is Ida, an asteroid big enough to have a gravitational field that has trapped its own orbiting moon, Dactyl.
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Diameter
1.4 mm
Distance from Sun
49.1 m
Unit
The gas giants
Science
Jupiter is the largest planet in the solar system with a diameter more than 11 times that of Earth. Ancient astronomers named the planet Jupiter, after the ruler of the gods in the Roman state.
Hooked on astronomy Robert Hooke (1635–1703) was the English scientist who discovered cells. He was also one of the first men to build a reflecting telescope. He used this telescope to discover a previously unknown star in the constellation of Orion. His observations with his telescope led him to suggest in 1664 that Jupiter rotated on its axis just like Earth. His detailed sketches of Mars were used two hundred years later to determine how fast it spun.
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Jupiter
Science
Fact File Jupiter
The Great Red Spot is a giant hurricane about three times the size of the Earth.
Mass
318 times that of Earth
Moons
Over 60 moons and four rings, including the four largest moons: Io, Ganymede, Europa and Callisto. These are known as the ‘Galilean’ moons.
Diameter
142 984 km ( = 11.21 × Earth’s diameter)
Surface
Liquid hydrogen
Atmosphere
Hydrogen (84%) and helium (15%). Upper layer contains white clouds, probably composed of solid ammonia.
Gravity
2.525 times that on Earth
Surface temperature
Cloud top –150°C
Period of rotation (day)
9 h 55 min
Tilt of axis
3.1°
Distance from Sun
5.2 AU (778 million kilometres)
Time to orbit Sun (year)
11.8 Earth years
Fig 8.4.10 Jupiter showing alternating east and west wind belts.
In March 1979, Voyager 1 flew by Jupiter and detected a faint series of rings around the planet, measuring 29 kilometres thick and 6400 kilometres wide. The first active volcano outside Earth was also observed on Io, one of Jupiter’s sixty or so moons. In July 1994, the Hubble space telescope photographed the collision of the comet ShoemakerLevy 9 with Jupiter.
Science
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Shoemaker puts the boot in The Shoemaker-Levy 9 comet that struck Jupiter in 1994 was actually a series of 21 comets! The explosions caused by the impacts had the equivalent power of an atomic bomb going off every second for five or six years. Some of the resulting dust clouds were bigger than Earth.
Scale model (Sun = 300 mm) Diameter
30 mm
Distance from Sun
168 m
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The solar system
Fig 8.4.11 Saturn showing the cloudy atmosphere and the separation between the two bright rings (called the Cassini Division). Worksheet 8.1 Saturn’s rings
Saturn
Uranus
Saturn is the second-largest planet in the solar system. It was named after the Roman god of agriculture and is most easily recognised by its impressive ring system. This system was discovered by Galileo in 1610. The space probe Voyager 2 detected over 100 000 rings when it flew by Saturn in 1981. The rings are only tens of metres thick, spread out to a diameter of 270 000 kilometres and are thought to be composed of particles of ice and ice-covered rock, ranging from tiny particles to large rocks. Like Jupiter, Saturn is a world of gas—a planet so light that it would float on water.
The English astronomer William Herschel accidentally discovered Uranus in 1781. Uranus was named after the Greek god of the heavens. Uranus is a strange planet because its axis is tilted at an angle of 98°—an angle that makes it virtually lie on its side as it orbits the Sun.
Science
Fact File Saturn Mass
95.184 times that of Earth
Moons
At least 30 moons and rings in seven bands
Diameter
120 536 km (= 9.45 × Earth’s diameter)
Surface
Liquid hydrogen. Winds up to 1800 km/h
Atmosphere
Very thick layer of hydrogen and helium
Gravity
1.064 times that on Earth
Surface temperature
–180°C
Period of rotation (day)
10 h 39 min
Tilt of axis
26.7°
Distance from Sun
9.6 AU (1400 million km)
Ancient and modern planets
Time to orbit Sun (year)
29.5 Earth years
Although the other planets of the solar system were known to ancient civilisations, Uranus and Neptune were discovered only relatively recently. This is because they can be seen only by using a telescope. Neither of these planets appear in any of the textbooks printed before Captain Cook landed at Botany Bay in 1770. These books show only six planets—the ancient planets.
Scale model (Sun = 300 mm) Diameter
25 mm
Distance from Sun
307 m
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Fig 8.4.12 Uranus, showing the vertical rings and moons (white spots) orbiting the planet.
Science
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Science
Planet George When William Herschel discovered Uranus in 1781, he first thought it was a comet. When he then found it was a planet, he wanted to name it George, after the British King George III.
Neptune was identified by German astronomer Johann Galle in 1846 after it was noticed that Uranus had strayed from its orbit. The cause was the gravitational attraction of ‘nearby’ Neptune. Neptune is sometimes referred to as the twin of Uranus and is named after the Roman god of the sea. Voyager 2 flew past Neptune in 1989, examining its rings. These are the least known and understood of all the ring systems.
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Neptune
Unit
This tilt gives Uranus the strangest seasons of all the planets, with each season lasting 21 years! Like Saturn, Uranus has a large number of moons, and a ring system that is quite faint in comparison. Voyager 2 discovered additional moons and rings when it flew by in 1986.
Science
Fact File Uranus
Mass
14.54 times that of Earth
Moons
At least 21 moons and 11 rings
Diameter
51 200 km (= 4.01 × Earth’s diameter)
Surface
Likely to be frozen hydrogen and helium
The Great Dark Spot is a huge cyclonic storm with winds up to 2400 km/h.
Hydrogen, helium and very
<
>
Atmosphere Gravity
0.903 times that on Earth
Surface temperature
–220°C
Period of rotation (day)
17 h 14 min
Tilt of axis
98°
Distance from Sun
19.2 AU (2875 million km)
Time to orbit Sun (year)
84 Earth years
Scale model (Sun = 300 mm) Diameter
10.1 mm
Distance from Sun
618 m
Fig 8.4.13 Neptune, showing its blue-green atmosphere. The Great Dark Spot seen at the centre is about 13 000 kilometres by 6600 kilometres in size.
Science
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Extrasolar planets
Science
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Zombie bums Author Andy Griffiths’ description of Uranus in his novel Zombie Bums from Uranus is partly accurate. It does have an explosive methane atmosphere (with added hydrogen for extra bang!), but its surface is definitely not sticky and poo-like!
Since July 2003, about 117 planets have been located revolving around other stars outside our solar system. Several of these are in what are called ‘habitable zones’ around their parent stars, where the temperature would permit water to remain in a liquid state. Perhaps life exists on one of these planets.
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The solar system Science
Science
Fact File
Clip
Planet X Neptune Mass
17.15 times that of Earth
Moons
Eight moons and five rings
Diameter
49 528 km ( = 3.88 × Earth’s diameter)
Surface
Frozen hydrogen and helium
Atmosphere
Mainly hydrogen, helium. Very high winds of over 600 km/h
Gravity
1.135 times that on Earth
Surface temperature
–220°C
Period of rotation (day)
16 h 7 min
Tilt of axis
29.3°
Distance from Sun
30.1 AU (4500 million km)
Time to orbit Sun (year)
165 Earth years
For several years, many scientists believed there was an undiscovered planet, ‘Planet X’, beyond Pluto that was responsible for unexplained deviations in the orbits of Uranus and Neptune. When Voyager 2 provided more accurate information about the masses of Uranus and Neptune, it was discovered that both planets were heavier than first thought. New calculations using these more accurate masses were then able to explain the deviations in orbit, ending any support for the existence of Planet X.
Scale model (Sun = 300 mm) Diameter
9.7 mm
Distance from Sun
968 m
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Prac 1 p. 273
Prac 2 p. 273
Prac 3 p. 274
QUESTIONS
Remembering 1 List the planets in order from: a largest to smallest b closest to most distant from the Sun c lowest to highest gravity. 2 Name the planets known as the gas giants. 3 Name three spacecraft, and at least one planet visited by each.
Understanding 4 a Name the body in the solar system that lost its status as a planet in 2006. b Explain why it is now regarded as a dwarf planet. c Name two other dwarf planets. 5 Clarify what is meant by a terrestrial planet. 6 Explain why there is less information available about the outer planets than the inner ones.
Applying 7 Identify the following planets by unscrambling their names: a PETENUN b SUNEV c ARMS d RATUNS e ITUPREJ f SUNRAU g TEHAR h RECYRUM 8 Identify which planets could be called: a ancient planets b modern planets. 9 Identify which planet: a is the hottest b is the coldest c has a giant hurricane raging that is larger than the Earth
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Unit
e Saturn: Divide your age by 29.5.
e spins the opposite way to all the others
f Uranus: Divide your age by 84.
f has a day length similar to that of Earth’s
g Neptune: Divide your age by 165.
g spins on its side as it orbits the Sun
Analysing
h has a crushing atmosphere
12 Calculate the range of surface temperature on Mercury. N
i has a rusty surface j is covered by a thick yellow layer composed mainly of carbon dioxide k is two-thirds under water l has the most impressive ring system m was discovered because it was noticed that a neighbouring planet strayed from its orbit n has a day that is longer than its year o has the strongest gravity p is known as the morning and evening star q is the most dense. 10 Identify which planets have:
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d has an atmosphere that blows past it from the Sun
Evaluating 13 Propose a reason why it is unlikely that life exists or has existed on planets other than Earth. 14 Discuss the evidence that early astronomers used to support the idea that life may exist on Mars. Is this evidence still relevant? Justify your answer.
Creating 15 The year is 3000 and you are on holiday at a resort on another planet in the solar system. Construct a postcard with a stamp and write a letter describing your holiday to someone back home on Earth. 16 Construct a scale diagram of the solar system showing:
a atmospheres
a the relative sizes of the planets
b a moon or moons
b the relative distances from the Sun to the planets. N
c ring systems
Your diagram must fit neatly onto poster paper, so you will need to scale down the planet sizes and distances to make them fit. Explain why it is not convenient to have the same scale in a diagram of the solar system for both size and distance.
d methane in their atmosphere. 11 Calculate your age on the following planets: N a Mercury: Multiply your age by 365 then divide by 87.97. b Venus: Multiply your age by 365 then divide by 225. c Mars: Multiply your age by 365 then divide 687.
17 Choose any three planets. Construct a table like the one below and enter the data for each planet.
d Jupiter: Divide your age by 12.
Planet name
__________________
__________________
__________________
Mass Diameter Surface Atmosphere Gravity Surface temperature Moons Period of rotation Distance from Sun Time to orbit Sun
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The solar system 18 Much of the information we know about the outer planets came from the Voyager 1 and 2 missions. Use the information in the table to construct a scaled timeline for each mission. N Date
Mission
20 August 1977
Voyager 2
Launches
5 September 1977
Voyager 1
Launches
5 March 1979
Voyager 1
Flies by Jupiter
9 July 1979
Voyager 2
Flies by Jupiter
12 November 1980
Voyager 1
Flies by Saturn
25 August 1981
Voyager 2
Flies by Saturn
24 January 1986
Voyager 2
Flies by Uranus
25 August 1989
Voyager 2
Flies by Neptune
1998
Voyager 1
Most distant human-made object
2002 and beyond
Voyager 1 & 2
Exploring past Pluto
8.4
INVESTIGATING INVESTIGATING
Investigate your available resources (e.g. textbook, encyclopaedias, Internet etc.) to: 1 Find out what or who each planet was named after. Construct a booklet that summarises this information, including pictures of each planet and the person or object the planet was named after. L 2 Find out what the given statement means. Money spent on space exploration would be better spent on things like medical research and aid programs. Organise a class debate on this issue. L
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What happened?
e -xploring We To find out more about the solar system, a list of b Desti nation web destinations can be found on Science Focus 1 Second Edition Student Lounge. There, you will also find a link to a website that allows you to construct a model of a space probe, such as the Cassini spacecraft that was sent to explore Saturn.
Unit
PRACTICAL P RACTICAL A ACTIVITIES CTIVITIES
Construct a model solar system
1
8.4
8.4 Aim
To represent the relative sizes and distances of the planets.
5 Go outside and place the Sun in position.
Equipment
6 The inner planets should be placed in position from the Sun within the school grounds. Measure the distance for each planet using a trundle wheel.
• • • • • •
modelling clay play dough or plasticine scale model information from Unit 8.4 a basketball to represent the Sun photocopy of street map of the local school area trundle wheel
Method 1 Get into small groups of students. 2 Copy the ‘scale model’ information from the ‘fact file’ for each planet into one table. 3 Using clay, play dough or plasticine, make a model of each planet according to the size in the scale model. 4 Obtain a street map of the local school area. Decide where the Sun will be located and use the scale of the map to find the position of the outer five planets. N
7 Ask your teacher whether your group may place the outer planet models in position outside the school grounds. Measure the distance for each planet using a trundle wheel and check your street map to see if this is correct. Otherwise, mark on the street map where the other planets should be located.
Questions 1 For the outer planets, did the distance measured by the trundle wheel agree with the position marked on your street map? 2 Compare the spacing of the inner planets to that of the outer planets.
Classify the planets
2 Aim
Questions
To classify the planets using different criteria.
1 Explain why Pluto is no longer classified as a planet.
Method
2 Name the classification now given to Pluto.
1 Classify the planets according to the following rules: a Size: Small planets have diameters less than 13 000 kilometres, and large planets greater than 13 000 kilometres. b Composition: Rocky or terrestrial planets, and gas planets. c Distance from the Sun: The inner planets and the outer planets. The asteroid belt is the separating boundary. 2 Write a key for identifying the planets from their descriptions. 3 Use someone else’s key to identify the planets and evaluate whether their key is effective.
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The solar system
3
Jumping on other planets
7 To calculate your average jump: N • Add: Jump 1 + Jump 2 + Jump 3
Aim
• Divide by 3.
To observe what a change in gravity does to your jump.
8 To calculate the height that you could jump on other planets: N
Equipment • metre ruler or tape measure • calculator
• Divide: Your average jump ÷ Gravity.
Questions
Method
1 Identify the planet where you could jump:
1 Select a safe, clear space, perhaps outside. 2 One of your laboratory partners needs to hold the metre ruler vertically, with the ‘zero end’ touching the ground. 3 Another partner needs to be crouched down, with their eyes level with the ruler. 4 Stand next to the ruler and jump as high as you can.
a the highest b the lowest c about the same as on Earth. 2 Explain why would jumping on the Moon be easier than on Earth?
5 Your lab partner must read off the height that your feet reach in the jump. 6 Repeat three times and record your information in the table below. Jump 1 (cm)
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Jump 2 (cm)
Jump 3 (cm)
Average jump (cm)
Planet
Gravity compared to Earth’s
Mercury
0.38
Venus
0.9
Earth
1.0
The Moon
0.16
Mars
0.376
Jupiter
2.525
Saturn
1.064
Uranus
0.903
Neptune
1.135
Height you could jump on this planet (cm) (column 4 ÷ column 6)
Unit
Early astronomy
Prescribed Focus Area: The history of science People in the city do not see many stars when they look into the sky on a clear night. There is no light pollution in the bush and outback Australia, and that is where you can obtain true darkness. It is only then that you can get an awe-inspiring, clear view of the stars and planets. It is easy to understand, then, why ancient peoples were fascinated by the stars and planets.
8.4
Science Focus
Astronomy and Indigenous Australians The Australian Aboriginals were keen observers of the movement of the Sun, Moon and stars. Like the Inca people in South America, some Indigenous tribes saw the Milky Way as a pathway to the ancestors and the Dreaming spirits. The Aboriginal tribes used the motion of the stars across the night sky to predict the seasons and the time when certain food sources would become available. The constellations of the Southern Cross (Crux) and the seven sisters (Pleiades) are known to be of special significance to the Aboriginals. Each tribe often had different names and Dreaming for them.
Fig 8.4.14 The Milky Way is very clear and bright when there are no city lights.
Astronomy is the study of the motion of the stars and planets. For thousands of years, ancient astronomers had seen points of light that appeared to move amongst the stars—they called these ‘planets’, meaning ‘wanderers’. Nearly all early cultures had their own ideas on the stars and planets. Most studied the way they moved across the night sky, and many planets were worshipped or named after their gods (the names of Greek and Roman gods are still used in naming those planets known in ancient times). Other cultures used their observations of the motion to make predictions about events such as the seasons. Astronomy seems to have begun around 3000 BCE when the Mesopotamians, Egyptians and Chinese grouped stars together into collections known as constellations. Large structures like the pyramids of Egypt and Stonehenge in Great Britain (both constructed about 2500 BCE), show how important the motion of the Sun and other objects in the night sky was to these ancient peoples.
Fig 8.4.15 The seven sisters, known as Pleiades, as seen by the Aboriginals.
The Pitjantjatjara tribe originally inhabited the Western Desert area. To them, the first appearance of Pleiades in the east just before dawn was a signal that the dingoes would be having pups. The people would then know that newly born pups could be found if they searched the dingo lairs. For the Aboriginal tribes in the south-east of Australia, their Dreaming story for the Pleiades had the stars as seven young women. They believed that the young women had shown a lot of courage by insisting on doing all the tribal initiation rites that the men had to do. In honour of their bravery, they were placed into the heavens together after their life on Earth. There they acted as a role model for others.
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Early astronomy
Theories of the solar system The geocentric model Pythagoras (575–495 BCE) was a Greek scientist and mathematician. Although he is best known for his important and useful rule for right-angled triangles, Pythagoras proposed a theory we now know to be wrong. He suggested that the Earth was the centre of the universe. Aristotle (384–322 BCE), Hipparchus (190–120 BCE) and Claudius Ptolemy (83–168 CE) proposed more detailed models in which Earth was placed at the centre of the solar system. This type of model is known as a geocentric model (geo is a Greek word meaning Earth). Ptolemy developed his geocentric model of the solar system using star measurements taken by Hipparchus. In his book, titled Almagest, produced in Babylon in about 150 CE, Ptolemy provided the first reasonably accurate way to predict how various bodies moved across the sky. Those who used the information in the Almagest were able to predict, within about a hand span, where a star or planet would be in the night sky at any date and time. Ptolemy’s model was based on Aristotle’s idea that the objects of the heavens were ‘all perfect’, and moved in perfect circular orbits around the Earth. This is not totally correct and so Ptolemy needed to make changes to enable his model to predict the motions more accurately.
C
ls stia ele
containing all the phere s
tar
Fig 8.4.17 The Ptolemy model predicted that Antares, a red star in the constellation of Scorpio, should be in the position where the thumb tip is. Ptolemy’s model was accurate enough to predict that Antares would be found somewhere within the circle that is formed when the hand is rotated around the thumb.
The influence of culture and religion During the fifteenth century, the growing Christian church adopted the geocentric model as religious truth, and believed it to be in line with biblical teachings. The issue of having Earth at the centre the universe, however, was to prove very difficult.
s
Mars Venus Moon Jupiter
Earth
Mercury
Sun
Saturn Ptolemy model
Fig 8.4.16 The geocentric model by Ptolomy.
276
Fig 8.4.18 Ptolemy with Urania, the goddess of astronomy. Ptolemy is holding a quadrant used for measuring the altitude of stars. In the bottom left corner is an astrolabe for measuring the altitude and position of stars and planets.
Unit
Another ancient Greek, Aristarchus (310–230 BCE) questioned the geocentric model and proposed instead a model in which the Earth and other planets revolved around the Sun. This is known as a heliocentric model (helio is the Greek word meaning Sun). Aristarchus also thought that the Moon went around the Earth.
banned in 1616 and placed on the Church’s official ‘Index of forbidden books’, where it remained until 1835.
8.4
The heliocentric model
Saturn Saturn Jupiter Jupiter Mars Moon
Earth Earth Venus Venus Mercury Mercury
Fig 8.4.20 Pages from the book published by Copernicus in 1543, which described the heliocentric model of the solar system.
Sun
Copernicus model
Fig 8.4.19 The heliocentric model of Copernicus.
The geocentric model continued to be favoured by scientists and philosophers until the end of the fifteenth century. People who opposed this model were often in danger of being imprisoned or put to death by the religious authorities, who thought that humankind and Earth had to be the centre of everything. In the 1530s, Polish astronomer Nicolas Copernicus (1473–1543) began to examine all the available astronomical data and Ptolemy’s model. Copernicus thought that Ptolemy’s model needed too many modifications to make it accurate. He suggested that this model was too complex and could not truly reflect a perfect design from God. In 1514, Copernicus produced instead that the Sun was at the centre of the solar system—the heliocentric model. The ideas of Copernicus were frowned upon and viewed by many as heresy (against the teachings of the Church). Copernicus continued to work on his heliocentric theory, completing a book on it in 1530, which took another 13 years to get published because of Church opposition. Copernicus saw a printed copy of the book only on the day he died. The book was eventually
Slow to change The Italian mathematics professor Galileo Galilei (1564–1642), known simply as Galileo, was a strong supporter of Copernicus’ ideas. Despite the banning of Copernicus’ book, copies of it were available and Galileo was able to get a copy. Galileo thought that its heliocentric model made sense and he became a strong supporter of it. In 1609, Galileo constructed a telescope and used it to examine the Moon and Jupiter. He proved that there were mountains and craters on the Moon and that there were moons orbiting around Jupiter. His observations exposed mistakes in the geocentric model and contradicted what the Church was teaching. Galileo was condemned by the Church and forced to publicly declare that he was wrong in his support of the heliocentric model. He was also forced to state that he made up the images others had seen through his telescope. He was kept under house arrest for the rest of his life. The Pope officially reversed the Church’s stand against Galileo in 1983.
>> Fig 8.4.21 Galileo demonstrating his telescope in 1609.
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Early astronomy About the same time, the Danish astronomer Tycho Brahe (1546–1601) took many detailed measurements of the positions of stars and planets in an attempt to improve the geocentric model and disprove the heliocentric model. Ironically, the German astronomer Johannes Kepler (1571–1630) used Tycho Brahe’s data to finally show that Copernicus’s idea of a heliocentric model was correct after all! Worksheet 8.2 Space exploration timeline
Fig 8.4.22 Jupiter and the two Galilean moons, named after Galileo. He was the first person to view them through a homemade telescope.
STUDENT ACTIVITIES 1 We know only a few of the ideas and stories that Aboriginal people had regarding the stars and planets. a Propose reasons why this is so. b Compare your ideas with those of your classmates. c To find out more information about Aboriginals and astronomy, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
We b Desti nation
2 The Milky Way is spectacular when seen from a very dark location. a Investigate the Milky Way. Explain what it is and why it lights up the night sky so brightly. b Find a story that involves the Milky Way and retell it by writing a picture story book or drawing a series of cartoons. 3 Galileo used a poem to describe his ideas about the motion of the planets and stars. Unfortunately, this got him into even more trouble with the Catholic Church. Imagine you are Galileo and first see the Moon with a telescope. Using the image of the Moon, write a short poem to try to describe it. L
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4 a Describe three reasons why most ancient peoples, and church officials, could not believe that the Earth was in orbit around the Sun. b Design and perform an experiment or measurement to prove that the Earth is moving around the Sun and not the Sun around the Earth. 5 One of the brightest stars in the night sky is Alpha Centauri. This star is one of the Pointers that point towards the Southern Cross. Use the Internet to investigate Alpha Centauri. List some reasons why it might be considered ‘special’.
CHAPTER REVIEW Remembering
a tides
1 List the planets in order, starting with the one closest to the Sun.
b seasons
2 State the things that make it possible for us to survive on Earth.
d year
3 State the scientific definitions of the terms ‘day’ and ‘year’.
f solar wind.
4 Specify the term for when day and night are of equal length. 5 Specify the word starting with the letter ‘l’ that is used to describe aspects of the Moon. 6 Name the astronomer who first used a telescope to find errors in the geocentric model. 7 Use the ‘fact files’ in this chapter to answer the questions below.
c day/night e lunar eclipse 19 Describe how cultures depend on the Sun and Moon for survival. 20 State which planet would be easiest to move to if we had to leave the Earth? Explain why.
Applying 21 Calculate whether the year 2500 will be a leap year.
a Name the planets with more than 15 moons.
22 Draw a diagram to demonstrate an annular eclipse.
b List the terrestrial planets.
Analysing
c Name the planets that have methane in their atmosphere.
23 The geocentric model was accepted before the heliocentric model. Compare these two models of the solar system.
d Name the planet that is most similar to Earth and explain your reasons for choosing this planet. e State how long a day and a year is on Mars. f Name the planet that looks red and explain why this is the case. 8 Name two space probes and state which planet(s) they explored. 9 Name the planet that has an orbit which overlaps that of another.
Understanding 10 Describe one aspect or fact about each planet. 11 Outline three examples of our dependence on the Sun. 12 Define the term nuclear fusion. L
24 Classify the following as supporters or opponents of the heliocentric solar system model: Aristotle, Copernicus, Ptolemy, Brahe, Kepler.
Evaluating 25 Could any other planets in the solar system support life? Propose reasons why. 26 Propose why scientists did not support the heliocentric model for a long time when they knew it to be a better model than the geocentric model. 27 Of the eight planets and the Sun, identify which is the most important body in the solar system. Give reasons for your answer.
13 Explain why sunspots appear dark when they are obviously very hot.
Creating
14 Clarify how long it takes the Moon to orbit the Earth.
29 Construct a table that shows the distance from the Sun, the day length and the year length for each planet.
pt
a
18 Explain the following phenomena. Include a description of what each phenomenon is and what are its cause and effect. Give examples where appropriate.
Ch
17 Use a diagram to describe what causes an aurora.
Worksheet 8.4 Crossword
Worksheet 8.5 Revising the facts
s
16 Explain the differences between a prominence and a solar flare.
on
15 Describe gravity on the Moon.
28 Construct a drawing of the eight main phases of the Moon.
er R sti ev i ew Q u e
Worksheet 8.6 Sci-words
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9
Our planet Earth
Prescribed focus areas: The implications of science for society and the environment Current issues, research and developments in science
Key outcomes
Additional
Essentials
4.4, 4.5, 4.9.3, 4.9.4, 4.9.5, 4.9.6
•
The Earth has an inner structure of core, mantle, crust and lithosphere.
•
The main gases that make up the air are nitrogen, oxygen and carbon dioxide.
•
Greenhouse gases keep Earth warm enough for life to exist on Earth.
• •
Rocks are composed of minerals.
•
Igneous rocks are volcanic in origin; sedimentary are layers packed into a whole; and metamorphic rocks are igneous or sedimentary rocks changed into another form.
•
There are a broad range of careers in geology.
•
Changes in the atmosphere can be detected using different methods.
•
Evidence suggests that climate change is related to an increase in CO2 in the atmosphere.
•
Sedimentary rocks are layers of sediment being laid down, pressed together and bound by chemical processes.
Rocks can be weathered by physical and chemical changes.
Unit
9.1
context
Our Earth
The structure of our planet Earth is something that scientists are still trying to understand. Most of the evidence they
have comes from measuring the vibrations caused by earthquakes and making inferences about what might be inside our planet.
Structure of the Earth The crust
Quick Quiz
The crust is the layer of Earth upon which all living things live. It contains the land and seas. The first thing encountered when digging into the crust is a thin layer of soil and sand. Underneath this is a layer composed mostly of solid rock. Just like the shell of an egg, the crust is brittle and can crack or break easily. Since its formation roughly 4.5 billion years ago, the crust has cracked to form twelve major ‘pieces’ or tectonic plates. The crust is thickest under the continents (about 70 kilometres thick) and thinnest under the oceans (about 11 kilometres thick). Diagrams showing Earth’s inner structure are never to scale since the crust would be invisible if they were. In reality, the crust is extremely thin when compared to the diameter of the Earth—like a postage stamp stuck on a basketball. The temperature of the crust increases from an average of 20°C at the Earth’s surface, to about 500°C at its maximum depth. Prac 1 p. 285
Fig 9.1.1 The lava that explodes from a volcano is one piece of evidence that suggests that the inside of Earth is made of molten rock.
Science
crust (8–64 km thick) mantle (2800 km thick) outer core (2300 km thick) inner core (1400 km radius)
Clip
Journey to the centre of the Earth
Fig 9.1.3 The stories told in A
Fig 9.1.2 The inner structure of the Earth (not to scale).
Journey to the Centre of the Earth and The Core could not happen due to the intense heat and pressures experienced there.
In 1872, French author Jules Verne wrote a world-wide bestselling novel called A Journey to the Centre of the Earth, in which dinosaurs fought to the death deep inside a hollow Earth. In 2008, a 3D movie was released, starring Brendan Fraser and loosely based on Verne’s original book. A similar far-fetched film about a journey to the centre of the Earth was The Core, released in 2003.
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Our Earth The mantle
The core
Conditions of extreme heat and pressure mean that humans have never travelled deeper than the crust. The deepest mines are still in the crust and no hole has ever been drilled as far as the next layer, known as the mantle. This layer is about 2800 kilometres thick, with temperatures of 500°C near the crust and 3000°C nearer the core. The mantle has three layers: • The upper mantle is solid, very much like the crust. The upper mantle and the crust together form a rigid layer of rock called the lithosphere. • Below the lithosphere is a narrow layer of semimolten (soft or liquid) rock called the asthenosphere. • Below this is the lower mantle, which is solid due to the extreme pressure from the material above.
At the centre of the Earth is the core. The core itself is made up of two parts: a liquid outer core measuring 2300 kilometres thick, and a solid inner core that is 2800 kilometres thick. • The outer core is made of continually moving, molten metal. Although solid at normal temperatures, the iron and nickel found in the outer core has melted from intense heat inside the planet to become a sludgy liquid. The movement of this metal gives the Earth its North and South Poles and its magnetic field. This field acts as a ‘cosmic shield’ for the Earth, protecting us by deflecting large doses of cosmic rays from the Sun. The temperature of the outer core varies from 4000 to 6000°C. • The remaining 1400 kilometres to the centre of the Earth is made up of the inner core, where temperatures range from 4000 to 7000°C. At these temperatures the iron and nickel that make up the inner core should be liquid, but these metals are kept solid by the extremely high pressures from the weight of all the layers above.
Worksheet 9.1 Our Earth
Shifting plates
Fig 9.1.4 Even the deepest of mines only ever scratch the crust. They never get near the mantle. You can, however, feel a little of its heat when you descend deep down in a mine.
282
The crust of the Earth looks as if it could never move, but bits of it are moving all the time. The lithosphere is broken into huge slabs of rock called tectonic plates. These plates ‘float’ on the semi-molten rock of the asthenosphere below them. Currents in the asthenosphere slowly move the semi-molten rock and also carry the plates along with it—the plates are continually moving. The idea that the Earth’s lithosphere is made up of shifting plates was first introduced in 1969 and is known as the theory of plate tectonics. The plates move until they eventually crash into one another, break away from each other or slip along or under each other. This sliding is not smooth—rocks stick and jam. Pressure builds until the rocks can take no more. Then the layers suddenly slip past each other, explosively releasing the stored energy. An earthquake happens, and the most severe damage occurs at the edges of the plate. When two surfaces rub over each other, the friction between them generates heat. Sometimes, the friction between the rocks causes some of them to melt. Sometimes this molten rock will emerge as a volcano. For this reason, volcanic activity and earthquakes tend to both happen along the edges of the tectonic plates.
Unit
Shifting continents
9.1
Shifting plates also suggest that the continents must be moving slowly. When Alfred Wegener, a German meteorologist, suggested in 1912 that continents could shift, the idea sounded so ridiculous that it was not believed at first. There are clues, however, that the continents were once stuck together as super-continents and that they have slowly shifted to their current positions. These clues include the shapes of the continents and the types of rocks and plant life found on them, as well as stripes of magnetic material on the ocean floor.
Science
Clip
A changing Earth The map of the world will look very different in the distant future. The continents are on shifting plates, so they are travelling slowly across the surface of the Earth. Australia is drifting north by about 5 centimetres each year. The Mediterranean Sea is slowly being squeezed shut, the Atlantic Ocean is getting wider and the Himalayan Mountains are getting higher. Mt Everest is now about 50 centimetres higher than when Tenzing Norgay and Edmund Hillary climbed it in 1953.
Fig 9.1.5 The edge of a tectonic plate. The San Andreas fault causes up to five tremors a day through California, USA.
Eurasian plate
North American plate Caribbean plate
African plate Pacific plate
Cocos plate Nazca plate
Indian– Australian plate Earthquake site Volcano
South American plate
Antarctic plate
Fig 9.1.6 Earth’s plates move in different directions as they split, bang and scrape together. Volcanoes and earthquakes occur much more often near plate boundaries.
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Our Earth
9.1
QUESTIONS
Remembering 1 List the layers of the Earth from inside to outside, specifying the thickness of each layer.
Understanding
11 Use the information in the table to accurately plot a line graph showing how temperature changes as we dig into the crust. Depth (km)
0
2
4
6
8
Temperature (°C)
20
87
153
220
286
2 Clarify what is meant by ‘the crust of the Earth’. 3 Outline what causes an earthquake and where they are most likely to occur. 4 Copy the following and modify any incorrect statements so that they become true.
a 1 km b 5 km
a The inner core of the Earth is solid.
c 10 km
b The iron and nickel in the crust give the Earth its magnetic field.
d 20 km.
c The crust is very thick compared to the total volume of the Earth. d Mines are often deep enough to go into the mantle. 5 Describe how life on Earth would be affected if there was no magnetic field.
Applying 6 Identify where the crust is: a thickest b thinnest. 7 Identify which of the layers of the Earth is: a the thickest b the hottest c mainly made of iron and nickel
13 Use the graph to roughly determine the depth at these temperatures: N a 50°C b 100°C c 200°C d 300°C.
Creating 14 Imagine you have invented a machine that will dig 100 kilometres towards the centre of the Earth every hour. The journey will take a little over two and a half days. Create a series of four diary entries for the time of day when you enter each new layer of the Earth. Calculate how long it will take to get through each layer and describe the conditions found in each. 15 Construct and label a diagram of the inner structure of planet Earth which outlines the positions of:
d liquid
a the Poles
e solid.
b the equator
8 Identify two events that are caused by the plates of the Earth crashing into each other or moving apart.
Analysing 9 Australia is drifting northwards at 5 centimetres each year. This means that, eventually, Sydney will be where Newcastle is now! Calculate how long this will take if the distance between Newcastle and Sydney is 100 kilometres. N
Evaluating 10 Scientists want to explore the Earth’s structure by digging a hole through the crust into the mantle. Assess the advantages and disadvantages of choosing central Australia for the dig.
284
12 Use your graph from Question 11 to estimate the temperature at these depths: N
c the direction it spins d the crust e the outer and inner core f the outer and inner mantle g the lithosphere and asthenosphere.
Unit
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find the position on Earth where a hole would emerge if you dug from where you live, straight through Earth to the other side. 2 Investigate the seven continents of the world and identify the highest mountain on each.
4 Use an atlas to find the spot on Earth where you would expect the crust to be:
9.1
9.1
a thickest b thinnest c thinnest while you are still standing on land. Explain why you chose these three sites.
3 a Investigate and write a short report on how the journeys of these sailors assisted us in thinking the Earth was not flat but spherical. i Christopher Columbus in 1492 ii Magellan and his ship Victoria in 1519. b Compare what they found to the work done by Eratosthenes of Cyrene in about 250 BCE.
9.1 1
PRACTICAL ACTIVITY
The crust is like an eggshell
Aim To observe first-hand a model of the Earth’s plates.
Questions 1 Describe what happens to the cracks in the shell. 2 Record your observations. 3 Explain how this cracked egg is similar to the Earth.
Equipment • a fresh hard-boiled egg
Method 1 Tap the egg firmly so that the shell cracks, but do not peel off the shell. 2 Squeeze the egg gently but not enough to destroy the egg. 3 Try to slide one piece over another.
Fig 9.1.7 The cracks are in the egg’s shell only.
4 If an ant was standing on one of the cracks while you were performing the experiment, describe what it would experience.
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Unit
9.2
context
Rocks and minerals
Geology is the study of the Earth, including its rocks and minerals. Rocks are made from various kinds of minerals, combined in various ways, and are
important for mining, construction and other industries—as well as supporting all living things on the Earth’s surface.
Minerals Minerals are natural substances in which the particles are arranged in patterns. Sometimes the patterns form beautiful shapes known as crystals. Metals, gems and industrial materials of many kinds are made from minerals. Just eight chemical elements make up 98% of all minerals—oxygen (element symbol O), silicon (Si), aluminium (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K) and magnesium (Mg). The two most common elements that make up the Earth are oxygen and silicon, so it is not surprising that these elements are also common in minerals. Quartz, for example, is made up of silicon and oxygen. Native metals are minerals made up of only one metal element, such as gold, silver or platinum.
Fig 9.2.1 Geologists study the Earth, its rocks, ore and minerals. Seismologists are geologists that study earthquakes, and vulcanologists study volcanoes. quartz
mica
Fig 9.2.3 Native silver is a mineral that consists of only one element, silver (Ag).
feldspar
Fig 9.2.2 Minerals are made of various chemical elements, and have their particles arranged in regular patterns.
286
Unit
Properties of minerals
9.2
Several different properties are used to classify minerals into families. Science
Crystals Many minerals have a distinctive crystal structure and colour, and so different minerals will usually reflect light differently. Lustre is a term that refers to the way a mineral reflects light.
Science
Clip
Cool as crystal The word crystal comes from the Greek word kyros, meaning icy cold. In ancient times, it was believed that quartz crystals were composed of water that had frozen so solid that it could never melt.
Clip
Piezoelectricity When two brothers, Pierre and Jacques Curie, sandwiched a thin slice of quartz between two layers of tin and applied pressure to it in 1880, they detected a short pulse of electricity. This so-called ‘piezoelectricity’ can be generated using tiny quartz crystals, and is used to keep time in watches and clocks. The sparks in many barbecue lighters are also caused by piezoelectricity.
Prac 1 p. 291
monoclinic (augite)
cubic (diamond)
triclinic (plagioclase)
hexagonal (emerald)
orthorhombic (olivine)
tetragonal (zircon)
cleavage plane Fig 9.2.6 Several cleavage planes can be seen in these calcite crystals.
Colour and streak
Science
Fact File
Cleavage planes Some crystals have an internal structure that causes them to break apart more easily in particular directions. These are called cleavage planes.
Some minerals have a very distinctive colour. Malachite, for example, has a deep green colour. Nevertheless, colour is not reliable enough to use as a way of identifying the mineral. A better method is to crush the mineral into a powder. The colour of a powdered mineral is called its streak and often can be seen by rubbing a mineral on an unglazed white tile. Some minerals do not produce a streak, whereas other powdered minerals have a differentcoloured streak than the mineral itself.
Fig 9.2.4 Crystals often have distinctive shapes that allow them to be identified. Shown are the most common shapes found in crystals.
Fig 9.2.5 The distinctive flat crystals of wulfenite.
Fig 9.2.7 This azurite (a copper compound) sample contains a bright blue pigment.
287
Rocks and minerals Minerals used by Aboriginal artists
Hardness
Powdered minerals are used by various native tribes around the world as decorations and paint materials. The Australian Aboriginals collected their minerals as weathered (broken Science down) rocks. These minerals are called ochres and are crushed to a Colours of the body powder by the artists, using The colours used by the a grindstone. Aboriginals often had special Charcoal, for example, meanings. For some, the is commonly mixed with ochres represented the colours of the body. White is kaolin to make grey. The the colour of bones, brown powders are also mixed is the colour of skin, red is with egg, juice or blood to the colour of blood (a sacred make a paste that can be colour) and yellow is the then painted onto rocks or colour of body fat. the body.
Clip
One property that can be used to identify a mineral is its hardness. A mineral is harder than another if it can scratch it, without getting scratched itself. Frederic Mohs (1773–1839) invented a scale of hardness from 1 to 10, 10 being the hardest and 1 being the softest. A mineral can scratch another only if it is higher on Mohs’ scale. Mohs’ scale of hardness ess coin 3.5
steel knife 6.5
1 2 3 4 5 6 7 8 9
Ochres (minerals) used in Australia 10
Where ochre is collected
Name of ochre
Colour of streak
Haematite
Red
Found as pebbles
Kaolin
White
In creek beds
Limonite
Yellow (or brown)
Water-worn pebbles in creek beds
Charcoal
Black
Produced in fires
Talc Gypsum Calcite Fluorite Apatite Orthoclase se Quartz Topaz Ruby, sapphire (corundum) m) Diamond
fingernail 2.5
iron nail 5.5
emery board 9.5
Fig 9.2.9
Different colours in minerals are caused by the different chemicals in them. The red colour of haematite, for example, is caused by iron oxide (more commonly known as rust). These ochres are often mixed to make other colours.
Fig 9.2.10 A dentist’s drill has diamond pieces on its surface. Diamond is the hardest substance on Mohs’ scale, with a hardness of 10. Tooth enamel has a hardness of about 5.
Science
Clip
Conflict-free diamonds These are diamonds guaranteed not to have been obtained through the use of violence, human rights abuse, child labour or environmental destruction, from the initial stage of mining right through to cutting and polishing. Today, only two diamond mines in the world, both in Canada, produce certified conflict-free diamonds.
Fig 9.2.8 Aboriginal rock art that was painted using powdered ochre.
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Uses
Common salt
Food preservative, source of sodium and chlorine
Graphite
‘Lead’ in pencils, ‘brushes’ in electric motors
Phosphate
Matches, fertilisers
Tungsten
Light bulb filaments, saw blades and drill bits
Sulfur
Used to make sulfuric acid, fertiliser
Rocks Petrology is the study of rocks. A petrologist collects rock samples, looks at their properties and works out which minerals they contain. Granite, for example, is a rock made from three minerals (quartz, mica and feldspar), whereas limestone is another type of rock and contains just one mineral (calcium carbonate). Clay and sand are also types of rock but have been broken into much smaller pieces than most other rocks.
Petrologists study the minerals in rocks and work out whether it is worthwhile getting them out of the Earth. Ores are rocks or minerals that contain elements that can be extracted profitably. For example, iron is extracted from an ore called haematite, and aluminium from the ore bauxite. Australia has large mines for extracting aluminium, iron, uranium and many other elements from rocks. Ore
9.2
Mineral
Unit
Ores
Common uses of minerals
Element that may be extracted
Azurite
Copper
Bauxite
Aluminium
Carnotite
Uranium
Cassiterite
Tin
Chalcopyrite
Copper
Galena
Lead
Haematite
Iron
Fig 9.2.11 Granite is made up of the minerals quartz, mica and feldspar.
Prac 2 p. 291
Fig 9.2.12 Haematite (iron ore) occurs in several forms, including this so-called kidney ore.
289
Rocks and minerals
9.2
QUESTIONS
Remembering 1 List: a four examples of minerals b four characteristics of minerals c three examples of rocks. 2 List the following minerals in order from softest to hardest: apatite, calcite, talc, quartz, diamond.
Understanding 3 Describe: a what a geologist does b what a petrologist does. 4 Clarify the following terms and give an example of each: a minerals b rock c ore. 5 Explain what Mohs’ hardness scale is used for. 6 Explain how a native mineral is different from most other minerals. 7 Describe what ochre is and what it has been used for. 8 Explain how ochre is prepared before being used for painting. 9 The following statements are incorrect. Modify each so that it becomes true. a A mineral is any substance found in the ground. b The two most common elements that make up the Earth are oxygen and aluminium. c Gold and silver are metals, not minerals. d Mineralogy is the study of minerals.
Applying 10 Gneiss contains feldspar, quartz, mica and hornblende. Identify which of these: a are minerals b is a rock.
9.2
13 Use Figure 9.2.9 on page 288 to predict whether: a orthoclase would scratch gypsum b quartz would scratch topaz c calcite would scratch your fingernail d diamond would scratch glass. 14 Gold has a hardness of 2.5 on Mohs’ scale of hardness. Use this information and Figure 9.2.9 on page 288 to identify materials that would scratch: a the band of a gold ring b the sapphire in a gold ring.
Analysing 15 Discuss whether an ore is a rock or a mineral. Could it be both?
Evaluating 16 Propose a reason why kitchen cleaning pastes (e.g. Jiff) should not be used to clean a silver ring.
Creating 17 a Construct a line representing Mohs’ scale of hardness from 1 to 10. b Predict where each of the following would go on the line and mark them on it: i glass (rated 6 on Mohs’ scale ) ii tungsten carbide, a type of abrasive (8.5) iii gold (2.5) 18 Write a short, short story—it can be a mystery, spy story, science fiction story or any other genre you like—in which the hardness of two different materials (e.g. tooth enamel and diamond or steel and glass) is the key point in how the story is resolved.
INVESTIGATING INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 Find information about different types of gemstones, their characteristics and where they are found. 2 Research the location of Australia’s major known mineral deposits. Draw a poster-sized map showing the location of these. Include pictures of different minerals, ores and mines in Australia. 3 Present information in a chart showing how an ore is processed to produce a pure metal.
290
11 Identify the ore that contains: a iron b aluminium. 12 Identify two ore types that contain the same element. Name the element.
e -xploring We
b Desti natio To learn more about the uses of minerals in Australia, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
n
PRACTICAL ACTIVITIES
Making a crystal Aim
To grow a crystal and observe its structure.
Equipment • • • • • • • •
copper sulfate 250 mL beaker icy pole stick Petri dish Bunsen burner tripod gauze mat bench mat
9.2
1
Unit
9.2
4 Carefully decant some of the solution into a shallow layer in a Petri dish and allow this to cool overnight. Keep the rest of the solution in the beaker. Part B: Growing a large crystal 1 Obtain a small ‘seed’ crystal from the Petri dish (or ask another group for one if yours did not produce any). 2 Tie it to a length of cotton thread and suspend it in your cooled copper sulfate solution. 3 Observe the crystal every few days for a week or so.
Questions 1 Your initial solution was saturated. Explain what this means. 2 Sketch the fully grown crystal.
Method Part A: Obtaining a seed crystal
icy pole stick
1 One-third fill a 250 mL beaker with water and dissolve as much copper sulfate in it as possible. 2 Heat the solution and add more copper sulfate in small amounts until no more will dissolve.
seed crystal
3 Remove the solution from heat and allow it to settle and cool for about 5 to 10 minutes. copper sulfate solution
Fig 9.2.13
3 Identify whether copper sulfate crystals have obvious cleavage planes.
2
Observing rocks
Method
To examine the characteristics of various rocks and minerals.
Construct a table of results and comment on as many of the following characteristics as you can for the rock samples: colour, streak, lustre, crystal structure, hardness, density.
Equipment
Questions
Aim
• • • •
a selection of rock and minerals copper coin steel nail unglazed white tile
1 Of the substances you examined, identify those that had a streak that was a different colour from the mineral itself. 2 Calculate what percentage of your samples was harder than steel. (Divide the number of samples that scratched steel by the total number of samples, and then multiply the answer by 100.)
291
Unit
9.3
context
Types of rocks
Classification is one of the important skills that scientists use when studying the world around us. Geologists have found it hard to classify all the different rocks that are found on Earth based on their crystal
shape, colour or hardness and so, instead, they classify rocks according to how they were formed. This classification system results in three main classes of rocks: igneous, sedimentary and metamorphic.
Igneous rocks Igneous rocks are formed when molten material from within the Earth cools and becomes solid. Molten material is called magma when it is below the Earth’s surface, and lava when it is above the Earth’s surface. Magma reaches the Earth’s surface when volcanoes erupt. When magma cools slowly below the Earth’s surface, intrusive igneous rocks containing large interlocking crystals are formed. Intrusive means ‘forced in’, and is a good description of underground igneous rocks that have squeezed between other rock layers. Granite is an example of a slow-cooling igneous rock in which crystals are easy to see.
Fig 9.3.1 Rocks are classified as either igneous, sedimentary or metamorphic.
volcano lava extrusive igneous rock
dyke
Fig 9.3.3 Lava solidifying to form extrusive igneous rock
sill intrusive igneous rock
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magma
Fig 9.3.2 Extrusive igneous rocks are formed above the surface when lava from volcanoes cools quickly. Intrusive igneous rocks form beneath the Earth’s surface when liquid magma forces its way into gaps in solid rock and then cools slowly.
Uses of granite
Uses of basalt
Bridges
Bridges
Buildings
Buildings
Kitchen bench tops
Crushed and placed under railway sleepers
Gravestones
Crushed and covered with tar to make bitumen roads
Sedimentary rocks are made from sediment—small, broken-down bits of other rocks or the remains of animals and plants. This material is compressed and stuck together in a process known as lithification. There are two main stages in lithification: • sediment builds up in a layer (e.g. at the bottom of a riverbed or the sea). The pressure of material above it squeezes the sediment at the bottom of the layer. This pressure reduces the air gaps and the particles interlock • water seeping through the compressed sediment carries with it minerals that cement the sediment particles together even more strongly.
9.3
Uses of igneous rocks
Sedimentary rocks
Unit
Lava cools more quickly than underground magma because it is above the Earth’s surface. This causes the crystals formed to be smaller or non-existent. Extrusive means ‘pushed out’. Basalt is an example of an extrusive igneous rock containing tiny crystals and is the main rock Prac 1 p. 299 forming the ocean floor crust.
Ancient tools Aboriginal people have a very rich and deep understanding of the rocks in the regions in which they live. In the past, this was important when making tools and weapons. This knowledge is still used in making the different coloured ochres used as paints. Different rocks are identified for different purposes, depending on their hardness, ability to flake and form sharp edges, ability to be ground or worn down, and their colours. Very hard igneous rocks were suitable for making tools such as axe-heads. At Mount William in Victoria, volcanic greenstone was mined for axes. It had the hardness, toughness and fine grain needed to make heavy-duty axes with a sharpened edge. Greenstone from such quarries was traded with many other tribes around Australia. Axes made from igneous rocks have also been found in ancient Aboriginal quarries near volcanic outcrops in Kakadu National Park, Northern Territory. These axes have been dated using scientific methods and found to be over 20 000 years old.
Fig 9.3.4 Aboriginal axe-heads made from igneous rock.
Fig 9.3.5 Horizontal sedimentary rock layers are obvious in the cliffs of the Blue Mountains.
293
Types of rocks Science
Substances that form sedimentary rocks Sedimentary rock
Clip
Made from
Sandstone
Sand
Mudstone
Mud
Conglomerate
Particles of different sizes
Limestone
Remains of sea organisms (e.g. fish, corals)
Chalk
Skeletons of tiny sea animals
Coal
Compressed plant material
Uses of sedimentary rocks Sedimentary rocks are easy to split because of their layered structure. Sandstone comes in a variety of colours, and blocks of it are used to make bridges and buildings. Limestone may be Science ground to make cement, which in turn is a key ingredient in concrete, one Tourist-attracting rocks of the most important Kata Tjuta (the Olgas) is a building materials of all. group of thirty or so huge Coal is a form of rock rocks in Central Australia that made from ancient plant are the weathered remains of sedimentary rocks. They material that has been consist of both sandstone heated and compressed and conglomerate rock. The under the ground until it is largest of these rocks solid. It is burnt to provide reaches 546 metres above power for electricity the surrounding ground level. generation and heating.
Oyster mortar
Fig 9.3.6 Conglomerate rock found in the Bungle Bungle Ranges, Western Australia.
The first white settlers of Sydney had no limestone from which to grind lime for mortar used in bricklaying. Instead they collected oysters, which were abundant around Sydney Harbour, and burned and crushed them to produce the lime needed.
Facts
Prac 2 p. 300
Fig 9.3.7 Stalactites and stalagmites are formed when slightly acidic rainwater dissolves calcium carbonate (lime) out of sedimentary rock. This lime solution may then drip from the roof of a limestone cave, leaving deposits on the ceiling (stalactites) and floor (stalagmites) when the water evaporates.
Fig 9.3.8 Kata Tjuta, meaning ‘many heads’ in the local Anangu language, is a series of domes made of sedimentary rock.
Fig 9.3.9 Sydney has many buildings made of sandstone, a type of sedimentary rock.
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Unit
9.3
Metamorphic rocks Sedimentary and igneous rocks may be changed by heat, pressure or a combination of both within the Earth to form metamorphic rocks. A rock made this way is stronger than the original material because its particles are fused together. This is similar to the process of squeezing a snowball to make it stronger. Metamorphic rocks can also undergo further changes due to heat and pressure. Types of metamorphic rocks Original rock
Original rock type
Limestone
Sedimentary
Heat
Granite
Igneous
Heat, pressure Gneiss
Shale
Sedimentary
Pressure
Slate
Metamorphic
Heat, pressure Schist
Schist
Metamorphic
Heat, pressure Gneiss
Changed by
Metamorphic rock Marble Slate
Science
Clip
In the barrel of a gun In the late 1700s, geologists Sir James Hall and James Hutton set out to prove that heat and pressure could change limestone to marble. They sealed some limestone in a gun barrel and roasted it over a fire. When they examined the contents later, the limestone had, indeed, turned to marble.
Fig 9.3.10 Gneiss (pronounced ‘nice’) is a metamorphic rock that frequently contains bands of different minerals. Bends in the bands indicate where enormous pressure has folded the rock.
Uses of metamorphic rocks Marble is a popular material for paving, table tops, statues and ornaments because of its beautiful patterns and dense composition. Slate is used for roofing tiles, floor tiles and billiard table tops.
Fig 9.3.11 The Taj Mahal in India is made of white marble. It was built by the Mughal emperor Shah Jahan as a tomb for his beloved wife, Mumtaz.
The rock cycle It seems logical that if sedimentary and igneous rocks are being converted into metamorphic rocks, there should be more and more metamorphic rocks and less of the other kinds over long time periods. This does not happen because processes such as weathering or melting also break down rocks. Melted rocks become new igneous rocks, and rocks that have been broken down into small particles by weathering settle into layers of sediment and form new sedimentary rocks. Together, these processes are known as the rock cycle. For example, metamorphic rocks that are forced deep below the Earth’s surface may be melted when they come in contact with magma, whereas part of the same metamorphic rock that remains on the surface may be weathered down to sand. Worksheet 9.2 Rocks
295
Types of rocks
Heat
Fig 9.3.12 The rock cycle involves a set of processes by which rocks are formed, sometimes changed (undergo metamorphosis), broken down and then formed again.
Career Profile
Geologist
Geologists study the composition and structure of the Earth. This allows them to locate materials and minerals. Geologists work in laboratories and in the field, usually as part of a team. Fieldwork can involve spending time in remote deserts, or in tropical or Antarctic areas. Geologists can be involved in: • advising on suitable locations for tunnels and bridges • examining rock samples using electron microscopes • studying the nature and effects of natural events like weathering, erosion, earthquakes and volcanoes • taking rock samples for analysis • finding the age of rocks and fossils. A good geologist will be able to: • work as a team member or alone • keep accurate records and prepare reports • work safely in a number of different environments.
296
Fig 9.3.15 Geologists studying sedimentary rock layers in the field.
Unit
9.3
sediments fall to the bottom of rivers and oceans
weathering breaks down rocks, erosion occurs
ocean crust mantle
continental crust igneous rocks formed from molten rock
heat and/or pressure form new, metamorphic rocks
sediments build up and compact to form layers of sedimentary rock
sediments pulled deeper by movement of tectonic plates
Fig 9.3.13 This diagram shows a variety of paths that rocks can take through the rock cycle, depending on their environment and where they are.
Career Profile
Palaeontologist
A palaeontologist examines, classifies and describes animal and plant fossils found in sedimentary rocks. This helps us understand the history of life on Earth.
Palaeontologists can be involved in: • locating sites where fossils may be found • carefully digging fossils out of the rocks in which they are found • preparing fossils for display or storage • dating fossils to work out their age • using information about fossils to study other things, such as oil exploration or the history of life on the Earth. A good palaeontologist will: • be able to work safely as a team member or alone • be able to work very carefully and patiently, as it can take years to remove fossils from rocks • have a good eye for detail • love fossils.
Fig 9.3.14 One of the jobs of a palaeontologist is to inspect fossils and ancient skeletons, such as this fossilised dinosaur skull.
297
Types of rocks
9.3
QUESTIONS
Remembering 1 List the three basic types of rocks and briefly state how each is formed. 2 Specify what type of rock you would use for: a a kitchen bench top c replacing the roof on an old home. 3 State the age of some of the ancient Aboriginal axe-heads found in Kakadu National Park.
Analysing 12 Compare the following terms: a magma and lava
Understanding 4 The particles in a sedimentary rock have to stick together. Explain two ways in which this can occur. 5 Copy and complete Figure 9.3.16, which is a schematic diagram summarising the rock cycle. igneous rocks
sio n
heat/pressure
b intrusive and extrusive rocks. 13 Classify the following types of rocks as igneous, sedimentary or metamorphic and attempt to name each rock. a Commonly known as bluestone, this rock has small crystals and is found where volcanoes used to be in New South Wales. b Used for tiling floors, this rock breaks easily into layers.
er o
g
me ltin co oli n
10 The rate of cooling of molten rock affects crystal formation. Explain how this occurs and identify whether fast or slow cooling forms the biggest crystals. 11 Identify two things that may cause rocks to change in the Earth’s crust.
b mortar to cement bricks together
g
c two types of metamorphic rocks, and name their ‘parent’ rocks.
c This rock is white and made up of the remains of millions of sea creatures. d Formed inside the Earth by heat and pressure, this rock has layers of minerals that are visible.
melting
e This rock forms where muddy rivers flow into lakes.
su re
s ero
es
lt me
ing
ion
f This rock has large, easily seen crystals and forms inside volcanoes.
pr at/ he
Fig 9.3.16
6 Granite is formed underground and yet, often, granite boulders are seen above ground in many areas of Australia. Explain how this could happen.
14 Compare the work of a geologist with that of a paleontologist by listing the similarities and differences in what they do.
Evaluating 15 Stalactites and stalagmites often occur in pairs. Propose a reason why this occurs.
7 Draw a sketch to explain the difference between a stalactite and a stalagmite.
16 Although coal is made from plant material, a lump of coal burns much longer than a similar-sized piece of plant material. Propose a reason why this might happen.
8 Clarify the meaning of these terms:
Creating
a sediment b lithification.
Applying 9 Identify: a two types of igneous rocks
298
g This rock was mined by Aboriginal people and used for axeheads.
b two types of sedimentary rocks and describe what they are made from
17 Imagine you are a piece of magma in a volcano. Write and draw a short graphic novel that describes what happens to you as you erupt from the Earth and form a rock. Follow your life through the rock cycle as you become different types of rock.
Unit
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 a Research from what type of rock Uluru (formerly known as Ayers Rock) is made. b Draw a diagram to demonstrate how Uluru was formed. c Describe the cultural history of Uluru and its mythology to the Australian Aboriginals. d Discuss with your teacher how to present your findings. 2 Investigate in more detail how coal is formed, and explain the difference (besides colour) between brown and black coal. Present your information as a poster that includes the key stages in coal mining.
9.3 1
3 Investigate the properties of artificial sedimentary rocks made from various combinations of sand, dry clay, small stones, plaster mix and water.
9.3
9.3
e -xploring To explore animations of how the main types of rock are created, and learn more about the rock cycle, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
We b Desti nation
PRACTICAL ACTIVITIES
Crystals and cooling rates
Aim
6 Allow each to stand overnight and pour off any excess solution from the 100 mL beakers. 7 Observe any crystals formed.
To observe the effect of cooling rates on crystal size.
Equipment • • • • •
copper sulfate two 100 mL beakers two 500 mL beakers 250 mL beaker stirring rod
• • • • •
Bunsen burner tripod gauze mat bench mat safety glasses
Method 1 One-quarter fill the 250 mL beaker with cold water, and dissolve as much copper sulfate in it as possible. 2 Heat the solution and add more copper sulfate in small amounts until no more will dissolve. You now have a saturated copper sulfate solution. 3 Carefully place half of the solution in each of the 100 mL beakers. 4 Place one 100 mL beaker inside a 500 mL beaker with some cold water, as shown in Figure 9.3.17. 5 Place the other 100 mL beaker inside an empty 500 mL beaker.
cold water
saturated copper sulfate solution
air only
Fig 9.3.17
Questions 1 Describe and sketch any crystals formed in the small beakers. 2 Compare the contents of the beakers to see if there are any key differences between them. If so, describe them. 3 Explain what caused larger crystals to form.
299
Types of rocks
2
Concrete evidence
Concrete is made from a combination of two or more of the following: cement, sand, crushed rock and water. Cement is made from limestone, baked at high temperature. Concrete has many properties in common with sedimentary rocks.
Aim To make various types of concrete.
Equipment • • • • • •
cement (dry, powdered) sand finely crushed rock plastic teaspoon paper or plastic cups water
Method 1 In one cup, place three teaspoons of sand and three teaspoons of cement. Label this cup 3S, 3C. 2 In another cup, place four teaspoons of sand and two teaspoons of cement. Label this cup 4S, 2C. 3 In another cup, place two teaspoons of sand and four teaspoons of cement. Label this cup 2S, 4C. 4 In another cup, place three teaspoons of finely crushed rock, two teaspoons of sand and one teaspoon of cement. Label this cup 3R, 2S, 1C. 5 Now gradually add a small amount of water to the first cup and mix until you get a thick, even paste. Repeat for the other cups. 6 Leave each cup to dry overnight. 7 Design your own test for the strength of each concrete sample.
Questions 1 Explain why it was important to have the same total amount of ingredients in each case. 2 Identify which sample was strongest. 3 Identify whether you think concrete setting is a physical or chemical change. Explain why.
300
?
DYO
Unit
9.4
context
Weathering and erosion
Soil, sand, pebbles and boulders are simply rocks that have been broken down into smaller particles. The natural processes of rocks breaking down are caused by wind, water, temperature and
other factors. Humans also can speed up these changes through their actions, some of which can have negative effects on the environment.
Break it down The process of breaking down rocks into smaller pieces is called weathering. Once weathered, any material that is loose can be moved away by the wind; water from rain, creeks and rivers; and the ice of glaciers. This movement is called erosion. The material that is washed away is called sediment and is the first step in making sedimentary rocks. Rocks seem tough but can be broken down in a variety of ways.
Fig 9.4.2 Surf is constantly pounding away at the rocks making up the coast. This is physical weathering in action.
The small particles of soil and sand that are carried away by wind and water have an abrasive action, which can act like sandpaper on other rocks that they scrape across. Farming and drought loosen the soil and can speed up erosion by the wind.
Chemical weathering Fig 9.4.1 Extreme erosion—wind dumped 140 000 tonnes of soil from farmland on Melbourne in 1983.
Physical weathering Physical weathering (sometimes called mechanical weathering) is when rocks break into smaller pieces. Waves crashing on rocky shores break down our coasts. Dramatic changes in temperature break rock into small flakes—water expands when it freezes and can split rocks if it freezes in cracks on frosty nights.
Prac 1 p. 305
Chemical reactions can also happen to rocks, changing their composition and properties, and even dissolving them. Such reactions are known as chemical weathering. Burning fossil fuels and other industrial activity adds harmful pollutants to the air. Some of these pollutants are acidic and can dissolve in rainwater to form acid rain. Acid rain is a product of pollution that can speed up the process of chemical weathering. It can also have many effects on the environment, including:
301
Weathering and erosion Gases dissolve in water vapour and form sulfuric acid Wet deposition (acid rain) can cause die-back of new growth, leaf fall, and root damage to trees and crops. It increases soil acidity and releases poisonous chemicals into soils, lakes and rivers
Smoke and fumes from power stations and factories Sulfur dioxide (SO2)
Lakes acidified
Dry deposition— smoke and soot blacken buildings. Sulfur dioxide corrodes metal and stone and damages plants
Fig 9.4.3 Industrial waste gases pollute the water cycle, forming acid rain.
• dissolving statues and buildings made of certain rocks, such as marble • killing fish and animals in rivers and lakes • killing forests, leading to erosion • making soils too acidic for plants and crops Prac 2 p. 305 to grow.
Biological weathering Other weathering can be caused by animals scratching and breaking apart rocks with their tracks, as they look for food and when they build burrows. Seeds can settle and grow in small cracks in rocks, and tree roots can search out cracks for a better grip. As these plants grow, so do their roots, forcing the crack wider until eventually the rock splits. Any weathering due to living things is called biological weathering.
Earth with roads, houses and cities. Exhaust gases from cars and factories have added destructive gases to the air. These can slowly chemically weather away rock on mountainsides and the rock used for city buildings. Building houses, roads and their cuttings, breakwaters and piers in the sea, and ploughing on farms all change how water and wind flow. Without careful planning, these changes can increase the amount of soil and sand that is washed away. Plant cover and the roots of trees help to keep soil bound together and make it less likely to be eroded. Drought, overgrazing and forest clearing can remove grass and plant cover, allowing the wind and water to remove the soil.
Worksheet 9.3 Weathering
People and erosion Science has produced many inventions. These need to be built and fuelled, often from materials found in the Earth’s crust. Humans have changed the surface of the Earth dramatically, particularly in the past 200 years since the Industrial Revolution. We have physically broken down rocks by mining them, sometimes using explosives, and by landscaping the
302
Fig 9.4.4 An example of biological weathering—the growing roots of this tree will soon split open the rock.
Career Profile
Fig 9.4.6 Kangaroos have soft feet that cause less weathering and erosion of dry, fragile Australian soils than the hard hooves of cattle.
9.4
Human activities, including scientific and technological activities, have played a role in increasing erosion and in causing other kinds of environmental damage. Science and technology can also play an important role in protecting the environment and developing solutions to environmental problems. Contour ploughing (where furrows run around a hill and not down it) on farms, gutters and the sealing of roads are all used to direct water in order to minimise erosion. Livestock numbers are monitored, particularly in times of drought, to minimise overgrazing. Wind speed can be reduced by windbreaks and stands of trees. Models of buildings, piers and breakwaters can be used to simulate erosion and plans can be changed to minimise problems before building starts. Choosing to walk or ride instead of driving a car can mean that you are producing less harmful gases that will form acid rain and contribute to climate change. Modern car exhaust systems must have catalytic converters that reduce the amount of pollutants pumped into the air. New hybrid petrol/electric cars are available that produce less than half the pollution of normal cars. Industrial chimneys can have ‘scrubbers’ attached to remove some of the dangerous chemicals discharged from them, and industrial processes can be changed to release less harmful pollutants. There are things we can all do to help. Think about it!
Unit
What can we do?
Science
Clip
Roo steaks and burgers Animals such as sheep and cattle are well adapted for moist climates like England because they have hard hooves, but their hooves can break down the soil in Australia’s drier climate and contribute to weathering and erosion. Kangaroos are well adapted to living in Australia and have softer feet that don’t damage the soil. Many people are realising that, as well as being tasty and nutritious, kangaroo meat can also be a better environmental choice than beef or lamb.
Environmental scientist
Science has had a large impact on our society and especially on the environment. Environmental scientists have the important job of measuring, recording and finding methods to control the harmful effects of human activity on our environment. Environmental scientists can be involved in: • investigating the effects of chemical spills and accidents on the environment • assisting farmers, industry and others in methods to reduce their negative effect on the environment • testing pollution in water, soil and air • assessing the environmental impact of new housing estates and industrial developments • upholding anti-pollution laws. A good environmental scientist will be able to: • work as part of a large team • communicate by writing clear, accurate reports • apply the scientific method to an investigation • be passionate about environmental issues.
Fig 9.4.5 Environmental scientists often research and gather data about wildlife populations.
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Weathering and erosion
9.4
QUESTIONS
Remembering
12 In your own words, summarise what an environmental scientist does.
1 List three different kinds of weathering, stating what each one involves.
Applying
2 State what type of weathering is involved in:
13 Identify three causes of:
a mechanical weathering
a mechanical weathering
b decomposition.
b biological weathering.
3 List four ways in which weathered material can be moved.
Understanding 4 Clarify the meanings of the following terms: L a soil b decomposition c weathering d sediment. 5 Explain the difference between erosion and weathering.
14 Identify the chemical released into the air that speeds up chemical weathering. Explain how this chemical gets into the air. 15 Identify two things that you can do that will help stop or slow weathering and erosion.
Analysing 16 Compare the similarities and differences between sand and boulders.
6 Describe what happens to water when it freezes.
Evaluating
7 It is dangerous to leave a filled glass bottle in the freezer. Explain why.
17 Propose who should take responsibility of stopping the weathering caused by humans.
8 Explain two ways in which humans and science have accelerated weathering.
18 Develop an argument and justify your position as to why you think humans have or have not sped up erosion and weathering.
9 Describe how acid rain speeds up chemical weathering. 10 Many ancient statues in cities have changed shape in the past 50 years. Propose a reason why. Identify which parts of a statue are most likely to be weathered and explain why. 11 Chemical weathering is more likely in the city than the country. Explain why.
9.4
Creating 19 The Environment Protection Authority (EPA) has responsibility for protecting the environment. An environmental scientist employed by the EPA gets up and watches a morning news report that there has been an oil spill in Sydney Harbour. Write a diary describing their day, starting from when they hear the news.
INVESTIGATING
Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: 1 a Research ways of minimising erosion in one of the following situations: • in rivers • on beaches
b Use this information to go out and find examples of these methods. Take some photographs of them. c Produce a poster with your photos to show how these methods work. L 2 Describe what these geographical features are and how they form:
• on farms
a river deltas
• around building or road construction sites.
b sandbanks and sandbars in rivers. 3 Produce a crossword about weathering and erosion. L
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Unit
1
PRACTICAL ACTIVITIES
You’re cracking me up!
Aim
4 After about a minute, carefully drop the hot rock into the water.
To investigate the effect of changing temperature on rocks.
5 Carefully observe what happens.
Equipment
6 Once cool, repeat two to three times with the same rock, recording your observations.
• • • • • • •
9.4
9.4
large tin Bunsen burner bench mat matches safety glasses tongs sample(s) of rock (e.g. granite, sandstone or shale)
Questions 1 Identify the type of weathering you are simulating. 2 Draw a conclusion about the effect of changing temperatures on rock. 3 Explain other ways that temperature changes can crack rock.
Method 1 Put on your safety glasses. 2 Three-quarters fill the tin with cold water. 3 Hold a small piece of rock in a blue Bunsen burner flame with tongs.
2
Acid rain
Aim To simulate the effect of acid rain on various rocks.
Equipment • • • • •
safety glasses watch-glass eyedropper dilute sulfuric acid samples of rock (e.g. limestone, marble, sandstone, shale, granite, basalt) • three 100 mL beakers • hammer
Part 2 1 Measure out three identical samples of limestone or marble chips. 2 Use a hammer to make the particle sizes in one pile large, another medium and the last small. 3 Place each pile in a 100 mL beaker. 4 Add the same volume of dilute sulfuric acid to each. 5 Record the time required to dissolve the limestone completely.
Questions 1 Identify the type of weathering you are simulating.
Method
2 Draw a conclusion about the effect of acid on rock.
Part 1
3 Draw a conclusion about how the size of a rock affects the rate at which it is damaged.
1 Place the rock sample on the watch-glass. 2 Place two to three drops of acid on the surface of the rock. 3 Record your observations.
305
Unit
9.5
context
The atmosphere
We live in a thick layer of gases that surrounds the Earth. This mixture of gases is known as air and the layer itself is known as the atmosphere. The atmosphere moves and swirls about us, often quite violently, with winds, storms,
cyclones and tornadoes. It stretches several hundred kilometres upwards from the Earth’s surface, providing us with oxygen to breathe and clean water to drink. It also protects us from harmful radiation from the Sun and from stray meteorites.
Fig 9.5.1 Cyclones are extreme weather, causing the atmosphere to swirl violently around an eye in its centre. This is a satellite image of a cyclone off the coast of North Queensland.
Layer upon layer Although the atmosphere can be considered to be about 800 kilometres high, it is very thin at the top and much more dense down where we live at the Earth’s surface.
306
Ninety-nine per cent of all the air in the atmosphere is found in the first 80 kilometres from the surface, with little left for the remaining 700 kilometres or so.
Unit
The final layer is the exosphere, which begins at about 600 km and extends out into space.
9.5
exosphere re 120
110
100
thermosphere e
At the outer limits of the atmosphere we find the largest of the layers, the thermosphere. This is a region of increasing temperature and few air particles.
mesosphere re
Above the stratosphere is the mesosphere, which extends to about 80 km and where the temperature again falls to –93°C.
90
The region called the ionosphere begins near the top of the stratosphere and extends through the mesosphere and thermosphere, but is most noticeable at altitudes above about 80 km. The ionosphere is also where meteors begin to burn up and where harmful gamma rays from the Sun are screened out.
80
Altitude (km)
70
60
50 The stratosphere is the next layer and extends to 50 km high, with temperatures gradually increasing to –10 °C at the top. It is a region of very low air pressure and fast jet-stream winds. Most commercial aircraft fly here. Within the stratosphere is the all-important ozone layer. This blocks out almost all harmful solar radiation, which, if allowed through, could injure or kill most living things.
40
stratosphere e
30 ozone 20
10
Mt Everest
0 sea level –100 –80
–60 –40 –20 Temperature ( °C)
troposphere e
0
20
40
We live in the troposphere, the layer that touches the Earth’s surface. This is where three-quarters of all air is found and where the clouds and weather occur. The troposphere has a height of about 10 to 13 km, and as you climb higher the temperature drops from an average of 17 °C to –52 °C.
Fig 9.5.2 Layer upon layer—the Earth’s atmosphere. The temperature at each level is shown as the solid curve.
Science
What’s in air?
Shooting stars
The air we breathe is made up of more than ten different gases. One of the most important gases in the air is oxygen (O2). This is the gas that humans and all other animals breathe. Although it only makes up 21 per cent of the atmosphere, it is
constantly being replaced by plants. Like animals, plants also use some of the oxygen in air to produce energy. Only a tiny 0.03 per cent of the atmosphere is carbon dioxide (CO2). It is vital to plants since they use it to make their own food. Carbon dioxide
Fact File
A shooting star is actually a meteor—what you are seeing is a small rock, maybe the size of a walnut, burning up because it is travelling extremely fast in the atmosphere 100 kilometres or so above the Earth.
307
The atmosphere Australians alone add 70 million tonnes (1 tonne = 1000 kilogram) of carbon dioxide to the atmosphere each year. At 78 per cent, nitrogen (N2) is the most abundant gas in the atmosphere. Nitrogen gas is almost chemically inert—that is, it doesn’t participate easily in chemical reactions. The fact that nitrogen in the air dilutes the concentration of oxygen is vitally important to life on Earth. Pure oxygen can be poisonous to animals and plants. Too much oxygen can cause extreme fires, making almost everything flammable.
nitrogen N2 78%
oxygen O2 21%
The greenhouse effect ozone O3, carbon dioxide CO2, other gases these make up just 1% of air
Fig 9.5.3 Although carbon dioxide makes up only 0.03 per cent of the atmosphere, it keeps the planet warm through the greenhouse effect. Increase its proportions and climate change may result due to the enhanced greenhouse effect.
is also one of the gases animals breathe out. It is a natural part of our environment—in fact, it is an essential part. Living things could not exist without it since all living things get their energy from plants that make their food using carbon dioxide. Carbon dioxide in our atmosphere is increasing, changing the natural balance, as a result of: 1 Forest depletion—trees use up carbon dioxide and every tree that is cut down increases the amount of this gas in the atmosphere by reducing the amount removed from the air. 2 Fossil fuels—every time fossil fuels, such as petrol, oil, gas and coal, are burnt in car engines, factories, homes and power stations, carbon dioxide is produced. 3 Rotting garbage in tips breaking down to release carbon dioxide.
CO2 concetration (parts per million)
360 350 340
The greenhouse effect During the night, this stored heat is released slowly back into the air, keeping it warm. If all this heat escaped back to space, we would freeze at night. Clouds, water vapour and gases such as carbon dioxide and methane reduce this loss to space and keep the atmosphere warm. Carbon dioxide is very effective in trapping this heat. This greenhouse effect keeps the Earth at a temperature that can support life. It is a natural and essential phenomenon. On our neighbouring planets, Venus is extremely hot (average temperature over 460°C) because it has a much greater concentration of greenhouse gases in its atmosphere, and Mars is cold (–140°C) because it has almost no greenhouse gases.
330 320 310 300
Fig 9.5.4 Carbon dioxide has been increasing in concentration.
290 280 1850
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The Sun does not warm the atmosphere directly. If it did, the atmosphere would be hotter at the top than the bottom and snow would never be found on mountaintops. Instead, the Sun mostly warms the surface of the Earth—both land and ocean—which then warms the atmosphere. The part of sunlight that we can see (called visible light) and the part of sunlight that gives us heat (called infrared or IR radiation) mostly pass straight through all the layers of the atmosphere. The sunlight falls on the Earth’s surface and is absorbed, heating up the rocks, water and Prac 1 p. 312 buildings that it hits.
Continued burning of fossil fuels will increase its concentration even more.
1900
Year
1950
2000
Unit
9.5
Radiation passes straight through glass
Radiation passes straight through atmosphere
greenhouse
Heat cannot escape easily through carbon dioxide so atmosphere stays warm
Heat energy cannot escape through glass easily so greenhouse stays warm The greenhouse
The atmosphere
Fig 9.5.5 The greenhouse effect got its name from similarities between the way some gases in the atmosphere trap heat and the way glass or clear plastic in greenhouses traps heat.
The enhanced greenhouse effect is caused by an increase in the amount of carbon dioxide (and some other pollutant gases) in the atmosphere. The amount of carbon dioxide in the atmosphere has increased by 37 per cent since the early 1800s. Many scientists believe that this increase has led to increased energy in the Earth’s climate systems—global climate change. Glaciers have been gradually retreating (melting and getting smaller), huge icebergs are breaking off Antarctica more than ever before, and the ice has been getting thinner in Greenland. Science and technology have led to many inventions and activities that add carbon dioxide to the air. We do not yet fully understand the implications this might have for society and the environment in the future. Australian scientists predict that some of the following changes may occur: • The melting of much of the polar ice caps would raise sea levels, flooding coasts, cities and some entire island countries. • Expansion of the water in the oceans would also raise sea levels, causing further flooding. • Increases in the numbers of wild storms and cyclones. Cyclones could move further south. • More droughts and heatwaves. • More bushfires. • Less rain and snow. Ski resorts may go out of business. People will need to collect their own water with tanks. • The places animals and plants live in will change. Some may become extinct.
• Increased temperatures may cause bacteria to grow faster, causing more disease in humans and other animals. • Some plants may grow faster with higher temperatures. This would be good news for farmers. But less rain may mean that farmers can grow fewer plants and fewer varieties. • Increased heat may cause more humans to suffer from heat stroke and illness. With all these possible changes to the environment, it is clear that we must start reducing the amount of greenhouse gases Prac 2 we release into the atmosphere. p. 312 1.2 Change in average temperature (°C)
The enhanced greenhouse effect
1.0 0.8 0.6 0.4 0.2 0 1880
1900
1920
1940 Year
1960
1980
2000
Fig 9.5.6 Average global temperatures are increasing, but this does not mean that all areas will get hotter—some years and some countries may get colder. Most will experience more extreme weather events, such as cyclones and droughts.
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The atmosphere
Career Profile
Environmental engineer
Environmental engineers work to design ways to do things better, so that we reduce the impact of humans on the environment. Some environmental engineers specialise in climate change issues. They provide advice and services on energy management and greenhouse gas reduction to companies and the government, as well as advising companies on the probable impacts of climate change on their business. Environmental engineers are in one of the fastest-growing job areas as we try to find ways to live without harming the Earth. Environmental engineers can be involved in: • measuring greenhouse gas emissions • carrying out environmental audits • reviewing facilities to identify where environmental improvements can be made • finding ways for companies to reduce greenhouse gas production. A good environmental engineer will be able to: • work as part of many different teams • communicate with people from many different backgrounds
9.5
• apply the scientific method to collect and analyse data • give people clear advice on how to improve what they are doing • be passionate about environmental issues.
Fig 9.5.7 An environmental engineer completing air sample testing in the laboratory.
QUESTIONS
Remembering 1 State whether the greenhouse effect is a natural phenomenon or one caused by humans.
f The ozone layer is part of the stratosphere.
2 State what these chemical formulae stand for:
h Most of the air is in the ionosphere.
a O2 b N2 c CO2
Understanding 3 Copy the following, and modify any incorrect statements so that they become true: a Humans live in the ionosphere. b Commercial aircraft travel in the stratosphere. c Oxygen is the most common gas in the atmosphere. d Meteors burn up in the troposphere. e The ionosphere protects us from X-rays and gamma rays.
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g Weather happens in the troposphere. 4 Describe what happens to the air temperature as we go higher in the: a troposphere b stratosphere c mesosphere d ionosphere. 5 a List the main gases in the air, giving the percentage of each. b Describe a purpose for each gas you have listed in part a. 6 Describe why it is important that we have a greenhouse effect on Earth. 7 Describe two effects that the enhanced greenhouse effect may have on the Australian environment.
>>
Unit d Describe three ways in which humans are adding CO2 to the atmosphere.
9 The troposphere is the atmosphere of Earth. Explain why this statement:
e Discuss three ways in which you could reduce the amount of carbon dioxide you produce every day.
a is wrong b has some truth in it.
14 Analyse Figure 9.5.6 to determine which 20-year period showed the greatest increase in Earth’s temperature. N
Applying
Evaluating
10 Identify the layers of the atmosphere that could be considered the:
15 The atmosphere does not escape into space. Propose a reason why.
a hottest
Creating
b coldest
16 The enhanced greenhouse effect is a very serious problem. L
c thickest. 11 Identify the cause of the enhanced greenhouse effect. N 12 Use Figure 9.5.6 to find the increase in the average temperature of Earth between the years: N a 1880 and 1940 b 1940 and 2000.
Analysing 13 Sea levels are expected to rise in the future. a State a possible reason for this. b Identify where the water would come from. c Describe the possible effects of this.
9.5
9.5
8 Describe two effects that the enhanced greenhouse effect may have on Australian society.
a As a class or in large groups, organise an information display about the enhanced greenhouse effect and global warming. You should include information to teach people about: • what is the greenhouse effect • what is the enhanced greenhouse effect and its causes • the possible effects of the enhanced greenhouse effect on Australia • how they can help reduce the problem through everyday decisions. b Your display should use different ways to communicate, such as signs, posters, pictures, video, sound and activities. Make it fun! c Get your display set up in the science area or during Science Day, Open Day or even at a local shopping centre.
INVESTIGATING
1 Record in a diary the day and night temperatures reached over a week and the amount of cloud cover each night. Which days had the greatest difference between day and night temperatures? What was the cloud like on those days? Summarise your findings. L
2 Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to: a Find how sunscreens work. What does the SPF number on a sunscreen indicate? b Examine reasons why Australians are more likely to develop skin cancer, and recommend ways to minimise the risk. Produce a sign/poster for use at the beach to inform sunbathers of the skin cancer risk and solutions. L
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The atmosphere
9.5
PRACTICAL ACTIVITIES
An already wet planet
1
Questions
Aim To calculate the percentage of water on the Earth’s surface.
Equipment
1 Did you count the number of squares covered by lakes and rivers, islands and small land masses? If not, explain why. 2 About 29 per cent of the Earth’s surface is land, whereas the other 71 per cent is water (97 per cent of that is salt water and 2 per cent is stored as ice in Antarctica and Greenland). Describe any difference between the percentages that you calculated and the percentages given here.
• A4 map of the world • graph paper • calculator
Method 1 Trace or copy the main continents from a map of the world onto graph paper or paper divided into grids.
3 State three suggestions as to why your percentages may be different to those given.
2 Count the number of squares covered by the continents. 3 Do not count squares that are less than half-filled. Count squares that are more than half-filled as full squares. 4 Use subtraction to calculate the number of squares covered by water. N 5 Use a calculator to find the percentage of the Earth that is land by completing this calculation: N 100 × Earth Total no. squares 6 Calculate the percentage of water on Earth. N
2
An even wetter planet
Aim To examine what would happen if the sea level rose.
1 Identify which pieces of land have completely disappeared.
Method
2 Describe six problems that would occur in a shrunken world like this.
1 On the map from the previous activity, extend inland all the oceans, seas and bays by one graph square. 2 Reduce the lands covered in ice by two graph squares.
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Questions
3 Identify what could cause this to happen in reality.
Unit
Global climate change
Prescribed Focus Area: Implications for society and the environment Is global climate change a serious cause for concern? Scientists and governments around the world generally agree that human activities are leading to global warming, although there is a vocal minority who agree that warming is occurring but believe that it has other causes. A number of different gases, including methane, contribute to climate change, but carbon dioxide is the largest contributor.
Evidence in the ice Scientists collect ice cores from Antarctic ice by drilling down as deep as 4.7 kilometres. The deeper they drill, the older the ice is, as each year new snow falls on top. As snow builds up, tiny air bubbles are trapped in the ice. Scientists can study these trapped gases to work out the amount of carbon dioxide that was in the atmosphere more than 400 000 years ago.
9.5
Science Focus
Fossil fuels Fig 9.5.9 This piece from an ice core shows tiny bubbles of trapped air from the atmosphere.
Predicted level CO2 in 2100
650 600 550 500 450 400
Current level
CO2 Temperature CO2 (ppm)
CO2 and temperature over 420 000 years
Temperature (˚C)
The main cause of increasing carbon dioxide levels in the atmosphere is the burning of fossil fuels, such as coal and oil. Petrol, diesel and kerosene (jet fuel) are all distilled from oil, and are also fossil fuels. These substances are actually made from vegetable matter that grew on the surface of the Earth millions of years ago. It was covered by sedimentary rocks and compressed and transformed by heat in the Earth’s crust into very dense sources of energy. When fossils fuels are burned this ancient carbon is released into the atmosphere as extra carbon dioxide.
350
20
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10
250
A B
200 0 –10 400 000
150 100 300 000
200 000
100 000 now
Years before present
Predicted temperature rise by 2100
A – It is normal for the level of carbon dioxide to go up and down, but the amount of carbon dioxide in the atmosphere is now at the highest level ever. Notice that the Earth’s temperature changes in line with changes in the amount of carbon dioxide in the air. B – On the temperature line, the troughs represent the Ice Ages, during which the average temperature on Earth was up to six degrees lower than today. The peaks are when warmer periods occurred on Earth.
Fig 9.5.10 Carbon dioxide levels over the past 420 000 years. Fig 9.5.8 Fossil fuels, such as petrol and coal, release massive amounts of carbon dioxide when they are burned.
The graph shows a prediction for the year 2100 if humans keep increasing carbon dioxide levels at the current rate.
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Global climate change Evidence of surface temperatures To find out what the temperature on Earth was in the past, scientists use evidence from such sources as tree ring growth or coral cores. These sources, combined with historical records, can produce results going back only about 1000 years. That is because this is the age of the oldest living trees and corals. These measurements also confirm that the Earth’s average temperature is rising to its highest level ever. Ice cores give evidence of temperatures going back further than these records from living things because the depth and density of the ice layers allows scientists to calculate temperatures in the past.
Evidence from changing weather patterns The increase in unpredictable weather around the Earth, and the increased frequency of the el Niño/la Niña weather patterns (alternating droughts and wet periods), has caused many people around the world to consider carefully what the effect of global warming may be. Meteorology (the science of weather and climate) is one of the sciences in which it is most difficult to make precise predictions. It is difficult to make accurate predictions of exactly what will happen as the Earth warms.
One thing that is clear is that the Earth is slowly warming, and there is new and stronger evidence that most of the warming observed over the past 50 years has been caused by human activities. Go to
Science Focus 1 Unit 9.5
Evidence from coral reefs Over the past decade, there have been increasing records of coral bleaching. Corals have single-celled plants or algae living in their coral tissue which help them to survive. When ocean temperatures increase above 30°C, the algae, which are essential to the coral’s health, begin to die. This in turn kills the coral. The most recent evidence is of particular concern. Many parts of the Great Barrier Reef are beginning to be bleached. Previously, this had been observed only closer to the equator.
Fig 9.5.12 This section of the Great Barrier Reef has been bleached and is now dead. The cause was increasing ocean temperatures.
Summary of scientific information
Fig 9.5.11 There is already worldwide evidence that glaciers are receding and shrinking back up the mountains.
One prediction is that the polar ice caps on Earth will begin to melt and sea levels will begin to rise, possibly flooding many low-lying and coastal communities. This has already created great concern for communities on many small islands. These people are worried that as the oceans rise their whole islands may be lost below the water. Many models of global climate change predict that Australia will become drier as temperatures slowly increase.
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Atmospheric carbon dioxide changes: • Atmospheric carbon dioxide has increased by 31 per cent since 1750. • About three-quarters of the carbon dioxide emissions produced by humans during the past 20 years has been from the burning of fossil fuels (currently about 6 600 000 000 tonnes per year). A lot more has been caused by land clearing. • As carbon dioxide levels go up, so does the Earth’s temperature. • At present, the land and the ocean absorb about half of human carbon dioxide emissions. The rest remains in the atmosphere.
Unit
1 A lot of Australia’s electricity and transportation is now produced by the burning of fossil fuels such as coal. Australians possibly produce more greenhouse gases per person than anyone else in the world. a List the ways that you produce greenhouse gases like carbon dioxide. b List the ways that you, as an individual, can contribute to reducing greenhouse gas emissions. c Choose one of the items on your list and make an effort to do this activity. d Report back to the class about how successful you have been in reducing the amount of carbon dioxide you produce. 2 Many people think that the contribution of an individual will make no difference. But it is definitely true that many little contributions will quickly add together to ultimately make a large contribution. Discuss this topic in small groups. a Explain why some people think that an individual cannot make a difference.
c Describe why many people, such as friends and family, may find it difficult to make any changes to reduce their use of fossil fuels and electricity use.
9.5
STUDENT ACTIVITIES
d List ways that you can help others make small contributions that collectively will reduce the greenhouse emissions created by your school, your home and your community. 3 To answer the questions below, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge. Use the links available to find answers to the following questions:
We b Desti nation
a Which countries produce the most greenhouse gases? b Which countries produce the greatest amount of greenhouse gases per person? c What is the predicted rise in sea levels over the next 50 years? d Which locations and countries are most at risk from rising sea levels?
b Describe a number of examples to prove that lots of little contributions can add up to be very significant.
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Unit
9.6
context
Weather
The weather affects everyday decisions, such as what we wear, how we travel and where we go. Extreme weather causes floods, drought and often destruction.
The Earth’s equator receives a lot more concentrated heat and light energy from the Sun than do the North and South Poles, causing the air over the equator to rise and the air over the Poles to drop. Convection currents take warm air to the Poles and cooler air back to the equator. The atmosphere is also swirled around by the spin of the Earth, creating a series of winds called tradewinds.
light and heat from Sun
equator hot air rising
Fig 9.6.1 Not many people enjoy bad weather. air moving in to replace air that has risen
Wind As air is heated, it expands and becomes ‘lighter’ or less dense. Cold air is ‘heavier’ and more dense than warmer air. Because of this, hot air rises whereas cold air drops. This process is called convection and happens in our houses, the kitchen oven and in the atmosphere. Sunlight is more concentrated at the equator
Sunlight spreads further at the poles
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Fig 9.6.2 The Sun’s heat is spread over a smaller area at the equator—this makes the equator hotter than the rest of the planet.
cold air sinking
warm air moving to cooler region
Fig 9.6.3 Global movement of air.
Looking at the situation simply, this would cause winds that always blow roughly in the same direction, but winds don’t actually do this. The Sun heats different materials at different rates. Land areas heat up more quickly than lakes, oceans and the seas. Dark colours increase in temperature faster than light colours. This means that bitumen roads, car parks, newly ploughed fields and dark-coloured rocks (such as basalt) heat faster than sand and marble, fields of crops and shiny metal roofs. Convection currents and winds are created because of differences in temperatures and air pressures in local areas, as well as globally.
Unit
9.6
If the clouds cool further by being pushed upwards or over colder regions, the tiny droplets begin to join to make bigger drops that will fall as rain or, if it is cold enough, sleet or snow. Tiny specks of high floating dust often start the process. Sometimes it is cold enough for the water vapour to cool just above the ground, forming fog. Hail formation is still not fully understood. One explanation is that the supercooled raindrops freeze on the surface of dust particles or snow. These small hailstones are blown up and down inside the cloud by the storm’s wind. They gradually gather more water and increase in size until they become too heavy and fall to the ground. Another explanation is that they grow in size as they fall through the storm cloud.
clouds form
Fig 9.6.4 Wind patterns over the Earth.
water droplets fall as rain
pressure variation
water evaporates
rain water run-off high air pressure
rain water run-off sea or lake
low air pressure
Fig 9.6.6 Clouds are cooled water vapour. This is called condensation. surface wind
Fig 9.6.5 Local winds are caused by different heating rates, and differences in air pressure.
Looks like rain! Water is constantly evaporating from anything wet on Earth, whether it is a lake, the ocean or the washing on a clothesline. More water evaporates from the oceans and seas than anywhere else. This warm water vapour rises, cooling as it gets into higher and colder levels of the atmosphere. When cold enough, it condenses back into liquid water, forming clumps Prac 1 p. 321 of small droplets that we normally call clouds.
If the drops are heavy enough, they fall as rain. This flow of water from sea to clouds to rain, then run-off from land to sea, is called the ‘water cycle’.
Science
Clip
Severe thunderstorms These usually develop in the late afternoon when the atmosphere is moist and unstable. High cumulonimbus clouds rapidly develop along with lightning, thunder, severe wind gusts, heavy rain and large hail. Many thunderstorms are short-lived (about one hour) and limited in size. Thunderstorms can travel large distances and cause significant damage. A thunderstorm in Sydney in 1999 was unusual in that it lasted over five hours, with hailstones measuring up to 9 centimetres. The rain, hail and wind affected 22 000 properties, with $2 billion in insurance losses.
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Weather
Too much movement…cyclones
Cumulus clouds do not produce rain.
Altocumulus clouds produce light showers.
In the Southern Hemisphere, winds move in a clockwise direction around a low on a weather map, and anticlockwise around a high. A cyclone (known as a hurricane in the USA and a typhoon in Asia) begins as an intense low over a stretch of ocean, usually in the tropics. The warm humid air begins to spiral clockwise and upwards, cooling and condensing as it goes. Energy is released and the air is warmed again, forcing it to go even higher, reducing the air pressure at ground level even more. Air is sucked in from the seas around, bringing high-speed winds and torrential rain. The cyclone usually keeps going until it passes over land and loses its supply of water and its energy.
Science
Clip
It’s raining fish!
Stratocumulus clouds produce drizzle.
Cirrus clouds consist of ice crystals, and do not produce rain.
There have been over 20 reports of fish raining down over Australia in the past 50 years. A man on the northern coast of NSW woke up to find fish all over the roof of his house. In 1989, sardines showered down on sunny Ipswich in Queensland. Three fish storms occurred in the same month in Killarney, 320 kilometres inland from the Northern Territory coast. A cyclone can suck up water from a lake or the ocean, taking fish with it. The fish are carried into the thunderstorm clouds and fall with rain. If the storm goes high enough into the atmosphere, the fish can be carried for hundreds of kilometres in jet-stream winds. They can rain down from clear skies hundreds of kilometres from the ocean or storms. Many other animals have been reported as rain, including snails, eels, mussels, frogs, spiders and even snakes.
Fig 9.6.8 A satellite image of a low pressure weather system off Stratus clouds produce drizzle or fine rain. They may form fog at low levels.
Cumulonimbus clouds produce thunderstorms with lightning.
Nimbostratus clouds produce heavy rain or snow.
Cirrocumulus clouds do not produce rain.
Australia’s southern coast. The winds spiral clockwise and move towards low pressure.
L Fig 9.6.7 Types of clouds
winds Worksheet 9.4 Cloud types
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Unit
9.6
dry air sinking
cooled air sinking spiralling moist air
eye
rain
warm moist air sucked in
Fig 9.6.9 Tropical cyclones cause massive amounts of air to shift.
Career Profile
Meteorologist
Meteorologists forecast the weather and study the atmosphere to improve our understanding of the Earth’s climate. Meteorologists can have a major effect on both society and the environment. Their weather predictions affect our society every day, especially when the forecast is inaccurate. Their advance warnings for dangerous weather can save both lives and property. A meteorologist can be involved in: • using different scientific instruments to forecast the weather • examining satellite images of clouds for dangerous weather • preparing special reports for shipping, agriculture, fishing and flying • issuing warnings of cyclones, storms, floods, frosts, fire dangers and strong winds • reporting air pollution. A good meteorologist will be able to: • record and analyse many different types of data • be part of a team • use different instruments to gather data in the field • write accurate reports.
Fig 9.6.10 A meteorologist releasing a weather balloon to measure temperature and humidity in the atmosphere.
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Weather
9.6
QUESTIONS
Remembering
Applying
1 List the other names used for cyclones.
13 Identify the types of clouds most likely to cause rain.
2 State the name of the winds that circle the world, caused by the Earth’s rotation.
14 Identify what causes a cyclone to lose strength.
Understanding 3 Copy the following and modify any incorrect statements so that they become true: a Hot air rises and cold air drops. b The equator receives more concentrated heat energy from the Sun than the Poles do. c Hot air circulates away from the Poles to the equator. d Tradewinds are local winds.
15 Gliders often increase their height by riding ‘thermals’ (rising hot air). Identify where these might be found. 16 Draw a simplified diagram to demonstrate the water cycle.
Analysing 17 Gather weather maps from the newspaper for one week. Then analyse each map to complete the following: a Draw arrows on the maps to indicate the directions you would expect the winds to blow. b Shade areas in red where it would be warmer; shade in blue where it would be cooler.
e All rocks heat up at the same rate.
c Draw water drops or snowflakes where you would expect rain or snow.
4 Explain what is needed to cause a cloud to rain. 5 In your own words, describe what the water cycle is. 6 Describe what causes a cyclone to begin. 7 Explain why the North and South Poles would be even colder if there were no convection currents. 8 Predict whether the temperatures at the equator would be higher or lower if there were no convection currents. 9 Plants are also involved in the water cycle. Describe how you think they fit in. 10 The water in your body could once have been in the body of a great scientist. Explain how this could be possible.
d Interpret the maps and your findings to describe Australia’s weather over the week.
Evaluating 18 Deduce why it is unwise to eat snow.
Creating 19 Imagine that you are a water molecule in the Pacific Ocean. Create a first-person account (e.g. ‘I was just floating around when…’) describing your adventures in the water cycle. L
11 In your own words, summarise the role of a meteorologist. 12 Predict the direction of the winds in the areas shown in Figure 9.6.11. forest
bitumen
Fig 9.6.11
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sea
land
road
black rocks
white sand
Unit
INVESTIGATING
1 Keep a diary and record the types of clouds you see over the next week and any rainfall that occurs (i.e. none, rain, drizzle, spitting). L 2 Investigate your available resources (e.g. textbooks, encyclopaedias, Internet etc.) to find how tornadoes form and why they are rare in Australia but common in the United States. Find out how storm chasers in the United States collect information about tornadoes.
9.6
W
eb D esti natio To explore satellite photos of the weather and learn more about forecasting, a list of web destinations can be found on Science Focus 1 Second Edition Student Lounge.
n
Method 1 In the beaker, heat about 100 mL of water until boiling.
Aim To determine what conditions are needed to make clouds.
Equipment • • • • • • • • •
e -xploring
PRACTICAL ACTIVITY
Making clouds
1
9.6
9.6
3 Observe and note in your results what happens. 4 Repeat the experiment, but this time place ice cubes in the evaporating dish, as shown in Figure 9.6.12.
400 mL beaker ice cubes evaporating dish Bunsen burner bench mat tripod gauze mat matches safety glasses ice cubes
2 Turn off the gas and cover the beaker with an evaporating dish.
5 Write your observations in your results.
Questions 1 Explain what water vapour is. 2 Describe what happens to water vapour as it cools. 3 Explain how cooling water vapour could cause a cloud.
evaporating dish 400 mL beaker
Fig 9.6.12
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CHAPTER REVIEW Remembering
Understanding
1 State whether each of the following is true or false: a The radius of the Earth is approximately 12 800 kilometres.
a is the hottest
b The thickest layer of the Earth is the mantle.
b is about 20–25°C, on average
c Sedimentary rock is a type of mineral.
c is made of liquid rock
d Rocks can contain a number of different minerals.
d is where the jet-stream winds occur
e The mantle is where most volcanic and earthquake activity occurs.
e contains most of the air
f The crust is thickest under the continents.
f is made mostly of iron and nickel. 5 Use a diagram to explain why:
g The moving around of pieces of rock by wind and water is called weathering.
a the Mediterranean Sea is being slowly squeezed shut
h The layer of the atmosphere that humans and animals live in is called the stratosphere.
c the Himalayan Mountains are getting higher
i The magnetic field of the Earth comes from movements in the outer core. j Winds move in a clockwise direction around a low. k Condensation is the name given when water turns from liquid to vapour. l Hot air is more dense than cold air. m Water heats up more quickly than rock. n The Sun heats up the atmosphere. o Australians add 70 tonnes of carbon dioxide to the atmosphere each year. p At night the Earth releases heat back into the atmosphere. q Greenhouse gases trap heat in the atmosphere. r More carbon dioxide in the atmosphere traps more heat. s Clouds help trap heat in the atmosphere on cold nights. 2 Recall the different types of rocks by matching a rock type to its correct description.
b the Atlantic Ocean is getting wider 6 Describe the effects in the future if: a carbon dioxide concentrations increase further b acids are continually released into the air. 7 Describe two uses that Aboriginals had for rocks. 8 a Explain the term ochre. b Describe how ochres were prepared and used by the Aboriginals. 9 Copy and complete this table to summarise the science careers covered in this chapter. Job title
Main tasks
Skills required
Geologist Palaeontologist Environmental scientist Greenhouse engineer
Rock type
Description
sedimentary
formed from molten material
metamorphic
made from broken-down particles compressed into layers
Applying
igneous
made from other rocks changed by heat and/or pressure
10 On Mohs’ scale of hardness, a particular mineral has a hardness of 6.5. Identify a mineral it would:
3 List the layers of the Earth and atmosphere in the correct order, starting from the centre of the Earth: outer core, stratosphere, troposphere, mantle, inner core, ionosphere, mesosphere, troposphere, crust.
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4 From the list in Question 3, clarify which layer:
Meteorologist
a be able to scratch b not be able to scratch.
19 Classify each of the following as either sedimentary, igneous or metamorphic:
a the rock cycle
a shale
b the water cycle
b sandstone
c the Earth’s structure
c granite
d the greenhouse effect
d limestone
e acid rain.
e conglomerate
12 Identify the element that may be extracted from chalcopyrite.
f gneiss
13 Identify two uses for examples of each of the three major types of rock.
g basalt.
15 Make a sketch to demonstrate the air movement around a cyclone.
Analysing
Worksheet 9.5 Wordfind pt
a
17 Compare the following items:
20 What kinds of evidence are there to suggest that humans are one of the main causes of the global climate change that scientists are observing? Critically evaluate the various kinds of evidence. Which piece of evidence do you find most convincing, and why?
Ch
16 List eight types of cloud and classify them in order from those most likely to give heavy rain to those that will not bring any rain.
Evaluating
Worksheet 9.6 Sci-words
s
14 Draw a diagram to demonstrate the wind direction around a low pressure system.
on
11 Draw simplified diagrams to demonstrate any three of the following:
er R sti ev i ew Q u e
a rock and mineral b crystal and mineral c pigment and streak d rock and ore. 18 Classify in order from hardest to softest: calcite, quartz, corundum, topaz.
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Ask
Sci ci Q Bu Busters team B
Chalk talk The big Moon Hot versus cold
Chalk talk
The big Moon
Hot versus cold
Chalk talk Hi Q Busters, I was at school yesterday when there was a loud squeal coming from the chalk as the teacher wrote on the blackboard. What causes this? Can you suggest anything I can pass on to our teacher so she doesn’t do it again? It’s driving the whole class mad! Best wishes, Isabella REPLY
Cereal sounds Stormy weather
Hi Isabella,
The frequencies of the squealing chalk depend on the following things:
That’s one theory anyway. There is another, which is based on impurities in the chalk stick. These small hard bits of grit scratch against the blackboard much like your fingernails would. And what about the solution? Well, you can ask your teacher to try these: • Snap the chalk in two. This should double the frequency of the sound and therefore should not be heard.
•
where the chalk is held by the fingers
•
•
at what angle it is held
Push down heavier onto the blackboard. This should rub the grit off quickly and the lesson should be squeak free.
•
how tightly the piece of chalk is held
•
Use the whiteboard.
•
the length of the piece of chalk.
Or maybe you could experiment yourself, and then pass on the results to your teacher.
If a piece of chalk is held incorrectly, it first sticks to the blackboard and then suddenly crumbles. The chalk then slips and vibrates, causing the loud squeal. As the vibrations die down and the chalk dust falls out of the way, friction between the chalk and the board increases until the chalk sticks once again and the cycle is repeated.
For example, if the chalk is held just above the blackboard contact point and at right angles to it, the frequencies are higher than if the chalk is held at a 45° angle. In the first case, vibrations are generated along the length of the chalk. In the second case, the chalk vibrates by bending.
Happy chalking! The Q Busters Team
The big Moon Dear Q Busters, The other night when we had a full moon it looked enormous just as it rose, but then got smaller later in the night. How can this be? I thought the Moon was the same distance away from the Earth all of the time! From Rachel REPLY
Hi Rachel, Many theories have been put forward, and many experiments have been conducted. The findings suggest that it’s only an optical illusion.
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To prove this for yourself, hold a ruler at arm’s length and measure the Moon as it rises. Make a note of this measurement, and then wait awhile
until the Moon is higher in the sky. Measure it again, compare your measurements, and you’ll find it’s more or less the same size no matter where it happens to be in the sky. One theory suggests that the mind judges the size of an object based on its surroundings. With a low Moon the trees and houses near you appear smaller against the moon which, in turn, makes it appear bigger than it really is.
Pic of full moon?
Another way to prove it is to look at the low Moon though a rolled-up piece of paper. This will block out the surroundings and the illusion should vanish. Happy Moon gazing! The Q Busters Team
Hot versus cold Dear Q Busters, Someone at school said she heard on the TV that hot water freezes faster that cold water. This can’t be true, can it? Please help as I am now confused about freezing water. Regards, Alexandra REPLY
Hi Alexandra, This would seem to be completely wrong by what you have been taught so far in Science. This phenomenon, where hot water appears to freeze faster than cold water, actually has a special name. It’s called the Mpemba effect. It is named after the Tanzanian high school student, Erasto Mpemba, who, in 1963, discovered it when experimenting at school. There is still great debate out there over whether this is fact or fiction, but here are the two main theories at present.
the surface. Well, this is removing most of the dissolved gases in the water. The gases actually reduce water’s ability to conduct heat. Therefore, with less dissolved gas in the water, it can cool faster. But we still don’t know for certain. Happy freezing! The Q Busters Team
1. Evaporation. As you know, when hot water is placed in an open container it begins to cool with steam coming off. This will reduce the amount of water in the container. With less water to freeze, the process can take less time. 2. Dissolved gases. When you are boiling water, Alexandra, you know that it’s boiling because you can see the bubbles rising and popping on
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Ask
Sci cii Q Bu Busters team
Chalk talk The big Moon Hot versus cold Cereal sounds Stormy weather
Cereal sounds
Stormy weather
Cereal sounds Hi Q Busters, I’ve always been fascinated by the sound my breakfast makes when I add cold milk to it. Mum said I’m not allowed to use product names when I write to you, so I’m calling them ‘rice thingos’. They make different sounds—crispy, crunchy sounds. My obvious question is—how does this happen? Yours truly, Hamish Hi Hamish, This question relates to two separate things—how the rice was cooked and what happens as you pour in the milk. Let’s look first at how they are made. Grains of white rice are first steamed and then followed by heating in an oven, making them all crisp and crunchy. This makes the little starch granules in them expand and this gives a unique structure of tiny air-filled pockets and tunnels inside the outer shell. So, when you pour milk over your cereal, the cereal absorbs the milk. As the milk flows into the crispy outer shell of the ‘rice thingos’, it puts pressure on the air inside. The air shoves back against the walls until they shatter. This shattering makes a sound that you hear.
REPLY
If you look very carefully, you will also see tiny air bubbles coming to the surface of the milk. Once the ‘rice thingos’ are wet enough and all of the air pockets have burst, the sounds stop, letting you finish your soggy cereal. The Q Busters Team
Stormy weather Dear Q Busters, I have always been fascinated by thunder and lightning. Mum and Dad told me about the dangers of lightning when I was little so I know that standing under a tree in a lightning storm is a really bad idea, but I love watching the free fireworks show in the sky. The other day we had a big storm and the lightning was around us for about an hour. While I was watching from a safe place, it got me thinking. I hope you don’t mind two or three questions, but I need to know what’s going on up there. Here goes: • How is thunder made? One of my teachers said it was the lightning breaking the sound barrier, another said that it was clouds colliding. • How is it that some thunder is a sharp crack and others just seem to roll on for a long time? • Sometimes I can see lightning, but don’t hear it. What’s going on here? Sorry for the question overload. Thanks, Miya
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REPLY >>
Hi Miya, We love thunder and lightning, too, and there’s some really interesting science behind these phenomena. We will answer each of your questions in turn. 1 Thunder happens because lightning is really hot—about five times hotter than the Sun’s surface. It’s so hot that it causes the air very close to it to be superheated. The air rapidly expands in a fraction of a second. This rapid expansion of the air creates a compression sound wave that you hear as thunder. 2 The reason thunder rumbles is due to two things.
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The first is that lightning is really a big spark about eight kilometres in length that zig-zags all over the place. It can have many branches coming out in all different directions, which can look really cool. What happens is that the sound waves created by each lightning branch reach you at different times. The sound wave that has travelled a greater distance will be softer and arrive later than the lightning closer to you, so you hear it as rumbles that go on and on.
If you have had lightning strike very close to you the thunder sounds more like an explosion. This is because the sound waves didn’t have a chance to bounce off many things before you heard it. 3 It’s actually impossible to have lightning without thunder and it’s impossible to have thunder without lightning. If you see lightning but don’t hear thunder, it’s simply that you are too far away to hear it. Lightning is pretty bright and can be seen for many kilometres, but sound (such as thunder) is a wave and will dissipate over both distance and time. Under normal conditions you usually can’t hear thunder any more than about eight kilometres away. Phew! There you go, Miya. Three questions for the price of one! Happy storm watching! The Q Busters Team
The second thing is that the thunder (sound waves) will bounce around—off the clouds, the ground and other nearby objects. It’s the same way that your voice echoes in a large hall.
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Put these two things together and the result is that some of the noise arrives at the same time, giving the loud sound, and then they fade away, softening the sound. Then other bits arrive so the sound gets loud again, and so on. This is the rumbling that you hear.
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Got a question? Email the Sci Q Busters team at: [email protected]
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Index Page numbers in bold refer to key terms in bold type in the text
A abbreviations, measurement units see units of measurement Aboriginals see Indigenous Australians absorption 82, 181 accelerate 207 accelerated 206 acceleration 207, 225 acid rain 301–2 activated sludge process 89 adult stem cells 163–5 aerofoil 225 aerosol 68 air 104, 180, 214, 231–2, 306–10, 316– 19 air foil 225, 226 air resistance 220 aircraft, forces on 225–6 airhole (Bunsen burner) 10 amoebas 158, 159 amphibians 119–20, 130 analysis 26 angiosperms 127–8 animals 102–5, 110–12, 115, 117–23, 130–31, 155–6 annelids 123 annular solar eclipse 260 arachnids 121 Aristarchus 277 arthropods 121, 131 asexual (reproduction) 105 asking questions 3 asteroid belt 266 asthenosphere 282 astronauts 220, 250–52 astronomical unit 263 astronomy 275–8 atmosphere 306–10 attraction (magnetism) 236–7 attracts 218 aurora 260 autotrophs 103 axis 245
B bacteria 131, 139, 158 balance 220 balanced forces 224–6 ball bearings 213 bar magnets 238 beam balance 19–20, 220
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bimetallic strips 52 binomial name 112 biological weathering 302 bioluminescent 189 birds 119, 130 blastocyst 164, 165 boiling 46 boiling point 46 bonded 36 bone cells 156 bony fish 120 botany 127–31 branches 3 branching keys 96 Brown, Robert 43, 141 Brownian motion 39, 43, 141 bryophytes 111, 129, 131 Bunsen burner 10–11 Bunsen, Robert 11 buoyancy 231
C calendar year 246 calorie 170 carbon dioxide 104, 150, 307–10, 313 carnivores 171 carnivorous plants 104 cartilage 120 Cassini division 268 cathode ray oscilloscope 199 cell membrane 149, 155 cell nucleus 149, 155 cells 106, 138–43, 149 animal 155–6 plant 149–51 single and groups 158–60 stem 163–5 cell theory 141 cellular respiration 103, 150 cellulose 149 cell wall 149, 159 Celsius, Anders 177 centipedes 122, 131 centrifuge 75 centrifuging 75 changes of state 45–7 characteristics 102 characteristics of life 102–6 chemical energy 169–70 chemical weathering 301 chlorine 86 chlorophyll 149 chloroplasts 149, 150–51, 159 chordata 117
chordates 117 chromatography 82 chromosphere (Sun) 259 ciliates 158, 159 circular keys (classification) 97 circulatory system 160 classification 95–7, 102–6, 110–12, 114–23, 127–31, 292–7 list, living things 130–31 cleavage plane 287 climate change 308, 309–10 clouds 317–19 cnidarians 122, 131 cohesion 232 collar (bunsen burner) 10 colloid 67 colour (minerals) 287 common solutions 66 compass 238 compound microscope 141 compression 196–7 concentrated 66 condensation 46, 317 conducting cells 151 conduction 177 conductors 177–8 conifers 128, 131 conservation of mass 65 contact (force) 206 contract 36 contraction 51 controlled variable 30 convection 179, 316 convection currents 180 conventions 19 Copernicus, Nicolas 277 coral reefs 314 core (Earth) 282 corona (Sun) 259 corrosive 4 cosmic rays 282 ‘cosmic shield’ 282 cross-section 10 crude oil 81 crust (Earth) 281 crustaceans 121, 131 crystal structure 287 crystallisation 80 crystals 286 cycads 128, 131 cyclone 318–19 cytoplasm 149, 155, 159
day (Earth) 245–6 day (planet) 262 decanting 74 decelerate 207 decelerated 206 deduction 43 density 57–9 deoxyribonucleic acid (DNA) 165 dependent variable 30 diagrams 10–11 dichotomous (keys) 96 differentiation 163 diffuse (reflection) 190 diffusion 38, 150 digestive system 160 dilute 66 disciplines 3 discovery 43 discussion 26 dispersion medium 67 dissolving 73–6, 80–82 distance 219 distillate 81 distillation 81 distillation apparatus 81 DNA (deoxyribonucleic acid) 165 domains (magnetism) 237 drag (force) 225 drawing forces 208 dry deposition 302
E Earth 265, 281–3 and Sun 257 as magnet 238 axis 245–7 heliocentric model 277 in space 245–7 Ptolemy model 276 statistics 265 see also atmosphere; planets; solar system; weather earthquake 282 echo 198 echolocation 198 eclipse 253, 257, 260 ectothermic 103 ectotherms 103 efficient 170, 213 elastic 206 elastic potential energy 169 electrical energy 169 electricity, magnetism 76 electrolytes 87 electromagnetic waves 181 electron microscope 141, 143, 213
electrostatic precipitator 76 electrostatic separation 76 embryonic stem cells 163–5 emulsifier 68 emulsion 67 endocrine system 160 endothermic 103 energy 168–71 as work 169 chemical 169, 170 defined 168 elastic potential 169 electrical 169 gravitational potential 169 heat 168, 170, 176–82 joule 170 kinetic 168 light 169, 188–91 nuclear 169, 171 potential 168 solar 257–60 sound 169, 170 energy conservation 170 energy conversions 170 enhanced greenhouse effect 309 environmental engineer 310 environmental scientist 303 equator 246–7, 316 equinoxes 247 southern autumn 247 southern spring 247 equipment 9–11, 25, 81 erosion 296, 301–2 error 18–19, 26 instrument 18 parallax 18 reading 18 zero 19 evaporation 46, 80–81, 317 excretion 104 excretory system 160 exoskeleton 121 exosphere 307 expand 36, 45, 316 expansion 51–3 expansion chamber 53 experiments 29–30, 43 extrasolar planets 269 extrusive igneous (rock) 292
F fair tests 29–30 fat cells 156 ferns 129, 131 fertile 112 field of view 142 filter 74
filtration 74–5, 76 fish 120, 130 flagellates 158, 159 flatworms 123, 131 flight 226 floating and sinking 58–9 floating dust 317 floc 87 flocculation 87 flowering plants 127–8, 131, 160 fluoride 87 foetus 164 fog 317 food chain 257 forces 206–38 action / reaction 214, 224 magnetic 236–8 push, pull, twist 206 see also Newton fossil fuels 171, 258, 308, 313 fossils 119 fractional distillation 81 fractions 81 freezing 46 freezing point 46, 53 frequency (wave) 199–200 friction 212–14 froth 76 froth flotation 76 full moon 252 fungi 129
Index
D
G galaxy 259 Galilei, Galileo 251, 268, 277 Galle, Johann 269 gangue 76 gas giants 262 gases 35, 37–8, 47, 51–3, 65–7, 149, 306–10 gel 68 genus 111 geocentric 276 geocentric model 276 geologist 296 geology 286–9 germs 158 ginkgo 129, 131 global climate change 308, 309–10 glucose 103, 150, 171 gravitational force 218–19, 253 gravitational potential energy 169 gravity 218–20, 250, 253 gravity separation 75 greenhouse effect 308, 309–10 grouping 114–16, 117 see also classification
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H
J
hail 317 hardness 288 heat 45, 51–3, 80, 168–71, 176–82, 296 friction 212–14 Sun 257–60 see also global climate change; greenhouse effect heat energy 169, 170, 176–82 heat, conductors 177–8 heatstroke 103 heat transmission 181 heliocentric model 277 heliophysics 259 hemispheres 247 herbivores 171 hermaphrodites 105 Herschel, William 268, 269 heterotrophs 103 highlands (lunar) 251 high (pressure system) 318 history, science 114–16, 275–9 Hooke, Robert 138–40, 267 hovercraft 213 hyperthermia 103 hypothermia 103 hypothesis 30
jawless fish 120 jellyfish 123 jet-stream winds 307 joule 170 Joule, James 170 Jupiter 267 heliocentric model 277 Ptolemy model 276
I ice 313 igneous rocks 292–7 image (microscope) 142 incandescent 189 incompressible 36, 37 independent variable 30 Indigenous Australian classification 114 Indigenous Australians astronomy 275 early tools 293 minerals 288 inefficient 170 infection 158 inference 17 infra-red radiation 181, 308 inner core 282 insects 121, 131 insoluble 65 insoluble substances 73–6 see also mixtures insulation 179 insulators 178 intrusive igneous (rock) 292 invertebrates 111, 121–3, 131 involuntary muscle cells 156 ionosphere 307 irregular shapes 58 IVF 165
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K Kelvin, Lord 47 Kepler, Johannes 278 keys (classification) 96 kinetic energy 168 kinetic theory of matter 43 kingdoms 110, 115, 127–31
L laboratory safety 3–4 lateral inversion 191 lava 281, 292 Moon 251 law of conservation of energy 170 law of reflection 190 leaf structure 149–51 liberation 76 life, cell theory of 141 life characteristics 102–6 lift (force) 225 light 168–71, 188–91 speed of 189 Sun 257–60 light energy 169 light microscope 141–2 lime 87 Linnaeus, Carl 114–16 liquid 35, 37–8, 45–6, 51–3, 65–7, 75 lithification 293 lithosphere 282 lodestone 237–8 longitudinal waves 197 low (pressure system) 318 lower mantle 282 lubricating 213 luminous 188 lunar eclipse 253 lunar landscape 251 lunar statistics 250 lustre 287 lymph system 160
M magma 292 magnet 76, 236–8 magnetic field 237–8, 282 magnetic force 236–8 magnetic separation 76
magnetite 237 magnification 142 major groups 111, 130 mammals 118, 130 mantle (Earth) 282 maria (lunar) 251 Mars 265–6 heliocentric model 277 Ptolemy model 276 marsupials 118 mass 19, 57, 65, 219 and weight 219 materials see equipment matter 19, 35, 218 measurements 9, 17–20, 18, 26 see also units of measurement mechanical weathering 301 medium 82 medusa 123, 131 melt 45 melting point 45 meniscus 19 Mercury 263–4 heliocentric model 277 Ptolemy model 276 mesosphere 307 metamorphic rock 295–7 meteor 307 meteorologist 319 method, experimental 25 metric system 18 microbes 158 microorganisms 158 microscope 9, 138–43, 141 microscopic 138, 141 Milky Way 259, 275 millipedes 122, 131 minerals 286–9 mirrors 190–92 mistakes 18–19, 26 mitochondria 140 mitochondrion 149, 155 mixtures 65–8, 73–6 models 35, 45 molluscs 122, 131 monera 129, 131 monocular microscope 141–2 monotremes 118 Moon 250–53, 324–5 heliocentric model 277 missions 250–51 phases 252 Ptolemy model 276 solar eclipse 260 moonshine 188 motion 168 Mpemba effect 325 multi-celled organisms 159
N naming organisms 116 naming species 112 native metals 286 negative acceleration 207 Neptune 269–70 nerve cells 156, 164 nervous system 160 new moon 252 Newton, Sir Isaac 208, 218, 253 newtons (N) 208 night 245–6 nitrogen 308 non-contact (force) 206, 218, 219 non-luminous 188 normal (imaginary line) 190 North Pole 238, 245 north pole (magnetism) 236 Northern Hemisphere 247 notochord 117 nuclear energy 169, 171 nuclear fusion 258 nucleus 140
O objective 38 observations 17–20, 26, 29–30, 43 ochres 288 opaque 189 optical illusion 324 orbit 246 Earth around Sun 247 Moon around Earth 252 ores 289 organelles 149, 155 organism/s 102, 116, 158–60 see also classification organs 160 osmosis 150 outer core 282 ovule 128 oxygen 104, 149, 307 ozone layer 307
P palaeontologist 297 panning 75 parallax error 18 parasitic 123 partial solar eclipse 260 particle model 35–9, 43, 57 particles 51, 66–7, 75–6, 177, 232 penumbra 190 petrologist 289 petrology 289
phases (matter) 35 phases (moon) 252 photosphere (Sun) 259 photosynthesis 103, 150, 171, 257 photosynthetic cells 151 phyla 111 phylum 111 physical properties 36 physical weathering 301 pistil 128 Pitjantjatjara 275 placental mammals 118 plane mirror 191 planets 262–70 see also Earth; solar system; Sun planning experiments 30 plant systems 160 plants 103–5, 115, 127–31, 149–51, 257 platypus 118 Pluto 262 point source 190 poisonous 4 poles (magnetic 236–7 polishing 213 pollution 301–2, 307–9 polyps 123, 131 potential energy 169 prediction 17 prescribed focus areas 43–4, 114–16, 163–5, 275–9 producers 103 prominences 259 protists 130, 139, 158 Ptolemy model 276 pull of gravity 224 Pythagoras 276
Q qualitative 17 quantitative 17 questions, asking 3
R radiation 181 solar 258 UV 258 rain 317–19 rainwater 86 rarefactions 196–7 rays 189 reading error 18 red blood cells 156 reflection 181, 190 regular (reflection) 190 regular shapes 58 religion 276 reporting 25–6 reproduction 105, 128–9, 163–5
reptiles 119 repulsion (magnetism) 236–7 residue 80, 81 resonance 200 respiration 104 respiratory system 160 response 105 results 26 retrograde movement 264 reverberation 199 rock cycle 295–7 rocks 286–9, 292–7 rollers 213 root hairs cells 151 R ratings 179 roundworms 123, 131
Index
multicellular 159 muscle cells 164 music 200
S safety 4, 11, 25 safety flame (Bunsen burner) 10 salt 80 sap 149 saturated 66 Saturn 268 heliocentric model 277 Ptolemy model 276 scanning electron microscope (SEM) 138, 143 Schleiden, Matthias 141 science asking questions 3 branches of 3 defined 3 history 114–16, 275–9 nature/practice of 43 scientific classification 95–7 diagrams 10 drawing 10–11 method 25 models 35 reporting 25–6 scientific report 25 seasons 245–247 sediment 67, 293, 301 sedimentary rock 293–4 segmented worms 123, 131 separating substances 73–6, 80–82 septic tank 87 sewage 86–9, 87 sewerage 87, 89 sexual (reproduction) 105 sieving 74 simple microscope 141 single-celled organisms 158 sinking/floating 58–9 skeletal system 160 skin cells 164
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sleet 317 snow 317 soda ash 87 soil degradation 302 Sol (Sun) 257, 262 sol 67 solar eclipse 257, 260 solar flares 257, 259 solar system 262–70, 275–9 solar technology 258 solar winds 259–60 solidification 46 solids 35–6, 45–7, 51–3, 65–7 solstice 247 southern summer 247 southern winter 247 soluble 65, 73–6, 80–82 soluble substances 80–82 see also mixtures solute 38, 65–6, 80 solute particles 38 solutions 65–6, 73–6, 80–82 solvent 38, 65–6 solvent particles 38 sonar 198 sonic boom 198 sound 168–71, 196–200 sound energy 169, 170 sound graphs 199–200 sound wave 196–7 South Pole 238, 245 south pole (magnetism) 236 southern autumn equinox 247 Southern Hemisphere 247 southern spring equinox 247 southern summer solstice 247 southern winter solstice 247 space 245–7 see also planets; solar system; Sun species 110–112 specimen 142 speed 207, 225 spiders 121 spinal cord 164 spine 117 spores 129 sporozoans 158 stamen 128 stars 257–60, 275–8 see also solar system state, changes of 45–7 states of matter 35 stem cells 163 stereo microscope 141–2 sterile 112 stimulus 105 stomata 104, 151 stored energy 169
stratosphere 307 streak (mineral) 287 streamlined 212 sublimation 47 Sun 171, 245–7, 252, 257–60 features 259 heliocentric model 277 missions 259 Ptolemy model 276 statistics 258 see also solar system; weather sunrise/sunset 245–6 sunspots 259 surface tension 231, 232 suspension 67 synchrotron 207 system (organs) 160
T tabular keys (classification) 96–7 taxonomist 110 taxonomy 110 tectonic plates 281, 282–3 telescopes 9, 139 temperature 176, 176–82, 314 see also global warming terrestrial planets 262–3 theory of plate tectonics 282 thermos flask 182 thermosphere 307 Thomson, William 47, 177 thrust 225 tides 253 tissue 160 total solar eclipse 260 tradewinds 316 translucent 189 transmission electron microscope (TEM) 143 transparent 65, 189 troposphere 307
U umbra 190 unbalanced forces 224–6 unicellular 158 units of measurement day (Earth) 245–6 day (planet) 262 distance 18 energy 170 force 208 heat 177 height 18 length 18 light 189 mass 18, 219, 220 sound 197–8 speed 18, 189
temperature 18 time 18 volume 18 weight 220 year (Earth) 246 year (planet) 262 upper mantle 282 Uranus 268–9
V vacuole 149, 155 van Leeuwenhoek, Anton 139–40 vaporisation 46–7 variables 29, 30 vascular bundles 127 vascular plants 111, 127–9, 131 vectors 208 Venus 264–5 heliocentric model 277 Ptolemy model 276 vertebrates 111, 117–19, 130 vibration, sound 196–7 viscosity 36 visible light 308 volume 58
W water 35, 53, 58, 81, 103 forces in 231–2 tides 253 water supply 86–9 waves longitudinal 197 sound 196 transverse 197 waxing 213 weather 314, 316–19, 326–7 weathering 295, 296, 297, 301–2 weight 219, 224, 225 and buoyancy 231 and mass 219 weightlessness 218 wet deposition 302 wheel 213 white blood cells 156 wind tunnel 214 winds 180, 316–19 work, and energy 169 working scientifically 29–30 worms 123, 131
Y year (Earth) 246 year (planet) 262
Z zero error 19 zoology 117 zygote 163, 164
