FOCUS-ON WORKBOOK SCIENCE 7 for effective reflection and assessment of mastery Assessment papers for Topical reinforcement exercises and engaging practices Contextual-based higher-order thinking questions evaluating performance Consulting author Giam Kah How
CONTENTS Science and Measurements 1 1.1 What is Science? 1 1.2 Science Laboratory 3 1.3 Measurements 6 1.4 Measuring Tools 7 Objective Questions 13 Concept Map 15 HOTS Daily Application 16 Online Quick Quiz 16 Matter 17 2.1 States of Matter 17 2.2 Physical and Chemical Changes 24 2.3 Density 26 Objective Questions 29 Concept Map 31 HOTS Daily Application 32 Online Quick Quiz 32 Temperature and Heat 33 3.1 Temperature and Scale 33 3.2 Thermometers 34 3.3 Expansion and Contraction of Matter 36 3.4 Heat Capacity 39 3.5 Heat Transfer 42 3.6 Heat Conductors and Heat Insulators 44 3.7 How Types of Surfaces Affect Heat Absorption and Emission 47 3.8 Body Temperature Regulation 47 Objective Questions 49 Concept Map 51 HOTS Daily Application 52 Online Quick Quiz 52 Motion and Force 53 4.1 Motion 53 4.2 Force and Motion 60 Objective Questions 66 Concept Map 68 CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 HOTS Daily Application 69 Online Quick Quiz 69 Assessment 1 70 Living Things 80 5.1 Biodiversity 80 5.2 Living and Non-living Things 82 5.3 Classification of Living Things 84 Objective Questions 93 Concept Map 95 HOTS Daily Application 96 Online Quick Quiz 96 Interactions Among Organisms and the Environment 97 6.1 Biotic and Abiotic Components 97 6.2 Food Chains and Food Webs 99 6.3 Nutrient Cycles in an Ecosystem 104 6.4 Interactions between Organisms 106 6.5 Factors that Affect the Organisms and Environment 108 Objective Questions 110 Concept Map 112 HOTS Daily Application 113 Online Quick Quiz 113 Earth and the Solar System 114 7.1 The Solar System 114 7.2 Earth and Its Satellite 121 7.3 The Sun 126 Objective Questions 128 Concept Map 130 HOTS Daily Application 131 Online Quick Quiz 131 Assessment 2 132 CHAPTER 5 CHAPTER 6 CHAPTER 7 ii
Science and Measurements CHAPTER 1 1.1 What is Science? 1. Technology is the application of scientific knowledge in our daily life. Fill in the blanks with the following words. communication transportation medicine agriculture construction home (a) Technology such as satellites, computers, the Internet, televisions and phones have helped make global communication easier and faster. (b) Machines have been used in agriculture to carry out heavy and difficult tasks such as ploughing and harvesting. (c) Trains, ships and aeroplanes are examples of modes of transportation that enable us to transport people and goods. (d) Powerful machines such as cranes and tractors are used in construction . (e) Due to the discoveries of new drugs, vaccines, antibiotics, and surgical methods and equipment, medicine can now treat more diseases than before. (f) At home , useful home appliances such as washing machines, dishwashers and robot vacuums make housework easier and faster. 2. Tick (✓) the uses of artificial intelligence (AI). (a) Serve as a smart assistant ✓ (b) Facial detection and recognition ✓ (c) Develop new mathematical theorems (d) Self-driving cars ✓ (e) Maps and navigation ✓ (f) Use common sense to make decisions in real-time (g) Grammar checker ✓ (h) Care for others (i) Manufacturing robots ✓ (j) Invent new scientific tools (k) Marketing chatbots ✓ Extra Info Artificial intelligence (AI) i Chapter 1 Science and Measurements 1
3. Complete the following table. Name the described fields of science. State two examples of jobs related to each of the fields of science. Description Field in science Examples of jobs (a) Study of the moon, stars, planets, the sun and other objects in space Astronomy Astronomer, aerospace engineer (b) Study of the properties of matter and its reactions Chemistry Chemist, pharmacist (f) Study of matter and energy and how they interact with each other Physics Engineer, architect (c) Study of weather and climate change Meteorology Meteorologist, broadcaster meteorologist (d) Study of rocks, soils and minerals Geology Geologist, geochemist (e) Study of living things Biology Medical doctor, nurse 4. Match each of the scientists to his contributions. Scientist Contributions Benjamin Franklin Thomas Edison Orville Wright and Wilbur Wright Albert Einstein • Invented the electric bulb. • Developed telegraph devices, phonograph, carbon transmitter and direct current generator. • Discovered the theory of relativity, which revolutionised our understanding of space, time, gravity and the universe. • Discovered the photoelectric effect. • Invented the lightning rod. • Developed the glass armonica and urinary catheters. • Designed, built and flew the first controlled, powered airplane. 2
1.2 Science Laboratory 1. The following shows some of the apparatus commonly used in a science laboratory. Match each apparatus with its function. A B C D E F G H Apparatus Function of apparatus Apparatus Function of apparatus H To measure the volume of a liquid C To separate insoluble solids from mixtures when used with filter paper B To measure the volume of a liquid accurately G To contain a small amount of chemicals or to mix solutions A To supply flame for heating E To contain chemicals when uniform heating is required F To collect filtrates D To contain, mix and heat a large amount of chemicals and liquids 2. Answer the following questions. (a) Give three examples of apparatus that can be used for filling liquid chemicals. Test tube, boiling tube, beaker, conical flask, flat-bottomed flask (any three) (b) A student wants to heat 30 m of ethanol. What is the warning symbol that can be seen on the bottle’s label? State the apparatus that can be used for heating the ethanol. Warning symbol: Flammable Apparatus used: Boiling tube, tripod stand, beaker, Bunsen burner, wire gauze (Ethanol is flammable, it is heated using a water bath.) (c) The figure shows an apparatus. Is this apparatus suitable to be used to heat liquids and semi-solids to high temperatures? Explain your answer. The apparatus is a crucible. It is not suitable for heating liquids and semi-solids. It is used to heat solids to high temperatures. Chapter 1 Science and Measurements 3
3. Match the hazard symbols to their danger and examples correctly. Danger of substance Substances with hazard symbol Examples of hazardous materials (a) Easily catches fire and burns. Alcohol, acetone (b) Easily explodes when mixed with other substances. Bromine, sulphur dioxide (c) Causes damage to the skin or eyes upon contact. Concentrated sulphuric acid, concentrated potassium hydroxide (d) Causes death or harm if absorbed through the skin, swallowed or inhaled. Mercury, cyanide (e) Gives out radiation that can cause cancer or destroy body tissues. Uranium, plutonium (f) Irritates (causes itchiness and rashes) skin, eyes and the respiratory system. Hydrogen gas, butane gas 4
4. Determine whether each of the following statements about the safety rules is true or false. Statement True/False Pour back any unused chemical into its original bottle. False Turn the Bunsen burner off when not in use. True Wash and return all apparatus to their proper place after use. True Throw solid wastes into the sink. False Always read the label on a reagent bottle before using its content. True Taste or smell chemicals in the laboratory. False 5. Arrange the following steps in a scientific investigation in the correct order. Number the steps from 1 to 8. Step Order Step Order (a) Analysing and interpreting data 6 (e) Forming a hypothesis 2 (b) Planning an experiment 3 (f) Carrying out the experiment 4 (c) Identifying the problem 1 (g) Writing a report 8 (d) Making a conclusion 7 (h) Collecting data 5 6. Fatin conducted an experiment to determine the boiling points of distilled water and a salt solution. The recorded results are shown in the table below. Solution Boiling point (°C) Distilled water 100 Salt solution 104 (a) What is the scientific attitude that we should practise when recording the results of an experiment? Honest and accurate in recording data (b) Tick (✓) on the noble values obtained from this experiment. (i) Practising a clean lifestyle (ii) Realising that science is a means of understanding the natural world ✓ Chapter 1 Science and Measurements 5
1.3 Measurements 1. Complete the table below to show the SI units, symbols and measuring instruments for some quantities. Base quantity and its symbol SI unit Symbol of unit Measuring instrument Time (t) second s Stopwatch Mass (m) kilogram kg Lever/beam balance Electric current (I) Ampere A Ammeter Temperature (T) Kelvin K Thermometer Length (I) metre m Metre rule 2. The following table shows the symbols, values and standard forms of prefixes. Complete the table. Prefix Symbol Numerical value Standard form centi c 0.01 × 10–2 kilo k 1000 × 103 deci d 0.1 × 10–1 mega M 1 000 000 × 106 nano n 0.000 000 001 × 10–9 milli m 0.001 × 10–3 micro μ 0.000 001 × 10–6 giga G 1 000 000 000 × 109 3. Rewrite each quantity in the stated unit. (a) 7.35 kg = 7350 g (h) 4290 m = 4 290 000 mm (b) 6700 cm = 67 m (i) 51 000 cm = 0.51 km (c) 209 g = 0.209 kg (j) 126 000 mg = 0.126 kg (d) 763 kg = 763 000 g (k) 12 m2 = 120 000 cm2 (e) 4 kg = 4 000 000 mg (l) 69 000 cm2 = 6.9 m2 (f) 870 km = 870 000 m (m) 8 m2 = 8 000 000 mm2 (g) 25 km = 2 500 000 cm (n) 3 000 000 cm2 = 0.0003 km2 6
1.4 Measuring Tools 1. The figure shows the results of four shooters, P, Q, R and S, in a shooting competition. Each shooter shot five times. P Q R S (a) The results are recorded in the following table. Tick (✓) the corresponding results. Shooter Consistency Accuracy P ✓ Q ✓ ✓ R ✓ S (b) Which shooter has the most accurate and consistent shots? Shooter Q (c) Which shooter has shots that are not accurate and not consistent? Shooter S 2. Sam used four types of measuring tools: a metre rule, a pair of Vernier calipers, an opisometer and a micrometer screw gauge to measure a few quantities. The following shows the readings obtained by Sam. 145.0 cm 6.25 mm 18.0 cm 6.34 cm Complete the table by writing the measuring tools used and the readings taken. Quantity Measuring tool Reading Height of a girl Metre rule 145.0 cm A curved line Opisometer 18.0 cm Diameter of a copper rod Micrometer screw gauge 6.25 mm Diameter of a 250 m beaker Vernier calipers 6.34 cm Chapter 1 Science and Measurements 7
3. The figures show some measuring tools with their readings. Write the correct reading for each measuring tool. (a) (b) (c) (d) (e) 4. A student faced some problems while taking readings using the measuring tools as shown in the figures. As a result, it affected the accuracy of the measurement. 0 cm 1 2 3 4 5 6 7 0 cm 0 cm 1 0 5 10 1 0 5 10 X Y 0 5 mm 20 25 30 35 Length = 6.78 mm 25 5 20 10 15 30 Time = 20 s Plasticine 80 90 100 70 60 50 40 30 20 10 Scale 35 37 39 41 Mass = 30 g Temperature = 37.5° Diameter = 3.23 cm 0 1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10 8
(a) The error in a measurement is the difference between the measured value and the actual value. State the type of errors shown in the figures above. X: Parallax error Y: Zero error (b) What causes error X to occur? The error occurs due to the wrong position of the eyes while taking a reading. (c) How can we reduce both types of errors, X and Y? Underline the correct answer. Error X can be reduced by taking measurements (once / several times) and getting the (average / minimum) value. When taking the reading, the observer’s eyes should be (parallel / perpendicular) to the scale of a measuring tool. Error Y can be corrected by subtracting the zero correction from the (actual / highest) reading. The error can also be reduced by taking the reading using (same / different) measuring tool(s). Choose a measuring tool that gives (accurate / sensitive) reading value. 5. The figure shows two regions X and Y on grid paper. X Y 1 cm 1 cm (a) Based on the figure above, estimate the respective areas of regions X and Y. X: 72 cm2 Y: About 41 cm2 (b) Is the area of region Y determined accurately? No, only an approximate area can be found. (c) Do you think the area of region Y obtained in (a) is more or less than its actual area? Explain your answer. Less than its actual area because only grid squares that are fully covered, half-covered, and more than half-covered are counted. Grid squares that are less than half-covered are not counted. Chapter 1 Science and Measurements 9
(d) If the grid of the graph paper is changed to 1 m × 1 m, what would happen to the estimated area? The estimated area of the region will be less accurate. 6. The figures display the readings of the liquid and mercury volumes in measuring cylinders, observed from three different eye positions. Tick (✓) the correct method of taking the reading. 50 60 70 Liquid 20 ✓ 10 Mercury (a) What is the volume of the liquid in the measuring cylinder? 57 m (b) What is the volume of the mercury in the measuring cylinder? 15 m 7. The figure shows a method used to measure the volume of irregular-shaped solids. 48 ml 50 ml 35 ml Water Thread Cork Stone (a) What method is used above? Water displacement method (b) Find the volume of the stone and cork. The volume of the stone is 13 m. The volume of the cork is 2 m. (c) What is the difference in volume between the stone and the cork? 11 m 10
8. The table shows the differences between mass and weight. Fill in the blanks correctly. Mass Difference Weight The quantity of matter contained in an object Definition The gravitational pull of the Earth acting on the object kilogram (kg) SI unit Newton (N) Lever balance, beam balance or electronic balance Measuring tools Spring balance or compression balance Constant and not affected by gravitational pull Accuracy Changes with the gravitational pull at a place 9. A student carried out an activity to estimate the length of a toothbrush. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 (a) Given that the length of a paper clip is 2 cm, what is the estimated length of the toothbrush? 12 cm (b) What is the actual length of the toothbrush? 14.5 cm (c) Percentage error is the difference between the actual value and the estimated value compared to the actual value and is expressed as a percentage. Calculate the percentage error in the measurement. 17.24% 10. Ahmad weighed 100 pieces of A4 paper on a balance and the results were recorded in the table. Calculate the average reading and estimate the mass of one piece of A4 paper. Mass of 100 pieces of A4 paper (g) Mass of one piece of A4 paper (g) First reading Second reading Third reading Average 500.0 499.5 500.5 500.0 5.0 (a) Based on the results above, predict the mass of 15 pieces of A4 paper. 75.0 g (b) A student wants to determine a more accurate estimated mass of one piece of A4 paper. Would you recommend the student to use 50 or 500 pieces of A4 paper? Explain your recommendation. 500 pieces of A4 paper. A more accurate measurement can be obtained by using more pieces of paper. Chapter 1 Science and Measurements 11
11. A teacher gave a quiz to three students. The time taken by Ann, Ben and Calvin to solve the quiz is shown below. (a) Write the time taken by each of them. Ann 25 5 20 10 15 30 03:50 Ben 25 5 20 10 15 30 04:15 Calvin 25 5 20 10 15 30 03:30 (b) Who finished the quiz the fastest? Calvin 12. (a) The table shows the densities of water, substance P and substance Q. Substance Water P Q Density (g cm–3) 1.0 0.9 1.4 Predict whether substances P and Q will sink or float. Substance P will float on the surface of the water. Substance Q will sink in the water. (b) Complete the table using the following formula. Arrange the densities of the substances in ascending order. Density = Mass Volume Substance Mass (g) Volume (cm3 ) Density (g cm–3) Order Wooden block 16 8 2.00 3 Stone 12.4 4 3.10 4 Zinc 198.8 28 7.10 5 Alcohol 11.9 15 0.79 2 Cork 6 25 0.24 1 (c) Why does a hot air balloon float in the air? The air inside the hot air balloon is less dense than the air surrounding it. 12
Objective Questions A B C D Choose the best answer. 1. Jane is carrying out an investigation to determine how the length of the pendulum affects the time for one complete swing. Which two measuring tools should she include in her investigation? A Stopwatch and measuring cylinder B Stopwatch and metre rule C Test tube and metre rule D Retort stand and crucible 2. Which skill is being discussed when someone is describing changes in parameters such as location, direction, shape, size, volume and mass with time? A Communicating B Observing C Interpreting data D Using space-time relationship 3. Fatim uses two different measuring tools to measure the volume of a liquid. The results he recorded are shown below. The volume of the liquid is 5 m when measuring tool X is used. The volume of the liquid is 5.05 m when measuring tool Y is used. The actual volume of the liquid is 5.05 m. What conclusion can he make based on his results? A Measuring tool Y is more sensitive than measuring tool X. B Measuring tool Y is less sensitive than measuring tool X. C 5 m is more accurate than 5.05 m. D Both readings obtained in the experiment are consistent. 4. The figure shows the reading of a micrometer screw gauge when used to measure the diameter of object X. 15 20 40 35 30 25 What is the diameter of object X? A 20.33 mm B 20.35 mm C 22.33 mm D 22.53 mm 5. James wants to measure the thickness of a piece of wire. He coils the wire around a pencil tightly. Metre rule 10 11 12 cm Pencil 25 turns Wire What is the thickness of the wire? A 0.084 cm C 2.1 cm B 0.9 cm D 12.1 cm 6. Simon followed the steps below when conducting an experiment in his science laboratory. • He filled a beaker partially with water. • He weighed a stone with a spring balance and it weighs 0.65 N. • He dipped the stone into the water in the beaker and weighed it with a spring balance. Chapter 1 Science and Measurements 13
Spring balance Beaker Stone What will happen to the weight of the stone dipped in water? A It will remain as 0.65 N. B It will be more than 0.65 N. C It will be less than 0.65 N. D It will have no weight. 7. The figure shows the eye positions to take the reading of a liquid in the measuring cylinder. 30 P Q R S 25 20 15 10 5 ml Where are the positions of the eye when a parallax error occurs? What is the correct reading? Eye position when parallax error occurs Correct reading A R 21 m B Q, S 22 m C P, Q, S 20 m D P, Q, S 21 m 8 The figure shows a footprint found on a wet floor. 1 cm 1 cm What is the estimated area of the footprint? A 8 cm3 C 17 cm3 B 14 cm3 D 22 cm3 9. The boiling point of water varies at different altitudes, ranging from 80°C to 100°C. Which of the following Celsius thermometers would give the most accurate reading of the boiling point at different altitudes? A 80° C 0° 100° 0° B 95° D 75° 150° 50° 10. What is the advantage of using standard units? A Everything can be purchased at the same price. B Scientists from one country can communicate in the languages of those in other countries. C All measurements can be taken using the same instruments. D Measurements are understood globally. 14
Concept Map Complete the concept map below about science and measurements. Fields and careers in science Scientific investigation Science laboratory Technology Measuring tools Artificial intelligence Science process skills Apparatus and their uses • Identifying a problem • Forming a hypothesis • Planning an experiment • Carrying out the experiment • Collecting data • Analysing and interpreting data • Making a conclusion Scientific attitudes and values Accuracy, sensitivity and consistency Measuring length, volume, mass, time , temperature, density Rules and safety precautions in the laboratory Hazardous substances and hazard warning symbols application of scientific knowledge scientists work at steps Science Measurements Physical quantities and units measured by Chapter 1 Science and Measurements 15
HOTS Daily Application Online Quick Quiz The information below shows two recipes used by Mandy and Kim separately. Vanilla Cake Recipe by Mandy 1 Mix 64 g of butter and 128 g of sugar well. 2 Beat 2 eggs and add to the mixture above. 3 Add in (192 g of all-purpose flour + 7.35 g of baking powder) and (64 g of milk + 8.4 g of vanilla extract) alternately. 4 Pour the mixture into a greased pan. 5 Bake for 20–25 minutes at 180°C in a preheated oven. Vanilla Cake Recipe by Kim 1 Mix ½ cup of butter and 1 cup of sugar well. 2 Beat 2 eggs and add to the mixture above. 3 Add in (1½ cups of all-purpose flour + 1¾ teaspoons of baking powder) and (½ cup of milk + 2 teaspoons of vanilla extract) alternately. 4 Pour the mixture into a greased pan. 5 Bake for 20–25 minutes at 180°C in a preheated oven. The Mandy baked is fluffy but the cake made by Kim is not. Cake baked by Mandy Cake baked by Kim In your opinion, why are there differences in the cakes baked by Mandy and Kim? Suggest the measuring tools they used. Explain your answer. Although the recipes used are quite similar, Mandy and Kim might have used different types of measuring tools when making the cake. Mandy used an electronic balance to measure the masses of the ingredients. Kim might have used different sizes of cups and spoons for measuring. The electronic balance uses standard units while cups and spoons are in non-standard units. Thus, the measurements made by Mandy are more accurate than Kim’s. 16
Matter CHAPTER 2 Properties: • The particles cannot move freely. • The spaces between the particles are very small . • The particles are packed very closely together. Properties: • The particles move freely but slowly . • The spaces between the particles are small . • The particles are packed quite closely . Properties: • The particles move freely and fast . • The spaces between the particles are very big . • The particles are not arranged in order . Examples: Salt Wood Examples: Wine Milk Examples: Hydrogen Cooking gas 2.1 States of Matter 1. Tick (✓) the characteristics of the different states of matter. Characteristic State of matter Solid Liquid Gas Can be weighed ✓ ✓ ✓ Occupies space ✓ ✓ ✓ Has a fixed shape ✓ Has a fixed volume ✓ ✓ 2. Draw the arrangement of the particles in a solid, a liquid and a gas. Complete the tree diagram below by giving two examples for each state and fill in the blanks to differentiate their properties. Solid Liquid Gas Matter Chapter 2 Matter 17
3. Differentiate the particle movements between a solid and a gas. The particles in a solid can only vibrate at fixed positions, whereas the particles in a gas move around freely at random and at very high speeds. 4. The figure shows two examples of matter, X and Y, in two different containers. X X Y Y (a) Based on the figure above, state one physical property of each X and Y. X: Does not have a fixed shape Y: Has a fixed shape (b) Identify the state of matter of X and Y. X: Liquid Y: Solid (c) Which of the following figures represents the arrangement of particles in X and Y respectively? Y X 5. Tom hung several balloons for his sister’s birthday celebration. Tom noticed that the balloons had deflated the next day. After 1 day (a) Explain what happened to the balloons after a day. The balloons deflated because the air in them diffused out. (b) What conclusion can you make from this situation? Air is a matter that consists of tiny and discrete particles. 18
6. Fatin carried out an activity by placing a crystal of copper(II) sulphate at the bottom of a boiling tube containing water, as shown in the figure. (a) Explain what happens to the copper(II) sulphate crystal and the water in the boiling tube after two hours. The copper(II) sulphate crystal dissolves in water. The diffusion of copper(II) sulphateparticles into the water causes the water to turn blue. (b) Draw on the diagram below to support your answer in (a). (c) Fatin carried out another two activities to show the rate of diffusion in matter. Bromine liquid Bromine gas Air After 2 minutes After 1 day Jelly Copper(II) sulphate crystal Y Z (i) Based on her observations in activities X, Y and Z, compare the rate of diffusion in the solid, liquid and gas. The rate of diffusion is the fastest in the gas (Y), medium in the liquid (X) and the slowest in the solid (Z). (ii) Give an inference for each of her observations in activities X, Y and Z. X: All of the water turns blue because the spaces between liquid particles are larger than solid particles. Y: Bromine gas diffuses very fast in the air because the spaces between air particles are the largest. Z: Only part of the jelly turns blue because the spaces between solid particles are the smallest. Water Copper(II) sulphate crystal X Chapter 2 Matter 19
(iii) Arrange the rate of diffusion of different types of matter in descending order. Y, X, Z (iv) State two factors that affect the rate of diffusion in matter. Mass, size, charge, pressure, temperature, concentration, solubility and state of matter (any two) (v) If the copper(II) sulphate crystal in activity X is replaced with a concentrated copper(II) sulphate solution, will there be a difference in the rate of diffusion in the water? Explain your answer. Yes, diffusion happens faster as the liquid particles are able to move freely. 7. The figure shows the changes in the states of water. Ice cubes Water Water vapour Q T U S P R (a) Based on the figure above, name processes P, Q, R, S, T and U. P: Melting R: Freezing T: Deposition Q: Boiling S: Condensation U: Sublimation (b) What is sublimation? Give an example of a substance that sublimes. Sublimation is the process by which a substance changes from the solid state directly to the gaseous state without passing through the liquid state. For example, dry ice is the solid state of carbon dioxide. When it is left at room temperature, it sublimes into a gas without turning into a liquid. (c) Read the following statements and underline the correct answers. (i) Process Q involves (heat release / heat absorption). (ii) During process P, the particles (gain / lose) energy and start to vibrate (faster / slower). (iii) During process T, the particles (gain / lose) energy and move (faster / slower). This causes the forces between the particles to become stronger. (d) State the difference in the movement of particles during processes P and R. The particles vibrate faster during process P but move slower during process R. 20
(e) State a natural phenomenon that involves processes P and S, respectively. P: Melting of snow S: Formation of dew/formation of clouds 8. The graph below was drawn by Jane after carrying out an activity to show the changes in temperature when some ice cubes were heated. Temperature (°C) Ice 0 100 Water Gas Time (min) K L M N O (a) Based on the graph, (i) which part represents the boiling point of water? What is the boiling point of water? NO; 100°C (ii) what is the melting point of water? How do you determine it? 0°C. The melting point of water is determined by the horizontal line on the curve between the solid state and the liquid state. The temperature remains constant during the change of state, which is melting. (iii) identify the states of matter that are present in • LM: Solid and liquid • NO: Liquid and gas (iv) why does the water temperature remain unchanged at LM and NO? Because the heat energy absorbed is used to overcome the forces of attraction between the particles. (b) Explain the difference in the movement of ice particles before and after heating. Before heating, the particles vibrate in fixed positions. After heating, the particles move freely, faster and collide with each other. (c) Jane heated the ice, which has a mass of 120 g. Predict the mass of water produced from the heating of the ice. Explain your answer. 120 g. When there is a physical change, the mass of matter remains the same. Chapter 2 Matter 21
9. Ben took some ice cubes from the freezer and placed them in a beaker. Then he began heating the ice cubes in the beaker. After some time, he stopped heating the beaker and put it on a table. Temperature (°C) 80 70 60 50 40 30 20 10 0 –10 1 A B C D E F 2 3 4 5 6 7 8 9 10 Time (min) (a) Which part of the graph shows the melting of the ice? BC (b) What is the temperature of the freezer? –10°C (c) What happens to the temperature of the water at segment CD? At point C, all the ice cubes have melted to become liquid water and the temperature of the water increases during segment CD. (d) Can you determine the boiling point of water from the graph above? Explain your answer. No. The water was only heated to 70°C and did not reach its boiling point. (e) Describe what happens at segment DE. The cooling of the water occurred and its temperature dropped. (f) Draw the arrangement of water particles at segment CD. Large space Particle 22
10. (a) Nova carried out an activity to determine the mass of a metal ball before and after heating. She recorded the results in a table as shown below. Initial mass of the metal ball 1 kg Final mass of the metal ball after heating 1 kg (i) What happened to the final mass of the metal ball after being heated? The mass of the metal ball remains the same as its initial mass. (ii) Explain your answer in (a)(i). During the expansion of the metal ball, the quantity of matter in the metal ball remains unchanged. The mass of the metal ball remains the same as there are no changes in its state. (b) Nova carried out another activity to determine the mass of sugar before and after dissolving it in water. She recorded the results in a table. Initial mass of 250 m of water + 3 tablespoons of sugar 287.5 g Final mass of 250 m of water + 3 tablespoons of sugar after it completely dissolves in water 287.5 g (i) What happened to the mass of sugar before and after it is dissolved in water? Its mass remains the same. (ii) What conclusion can you make about this activity? The mass of the sugar remains the same after it dissolves in water. 11. The figure shows how water exists in different states in the water cycle. Surface runoff Rivers and streams Lake Groundwater Rain Clouds Sun Oceans Process Y Process X Extra Info Water cycle i Chapter 2 Matter 23
(a) Name processes X and Y that occur in the water cycle. X: Evaporation Y: Condensation (b) What process occurs when liquid water changes into water vapour? Evaporation (c) How are clouds formed from water vapour? The water vapour condenses into tiny water droplets that gather to form clouds. (d) What happens when clouds get too heavy to hold water in the water cycle? Water falls as rain to the ground. (e) Where can liquid water and solid ice be found on Earth? (i) Liquid water: Oceans, rivers, lakes, streams, in the soil and underground (ii) Solid ice: Glaciers and snow (f) What is the main source of energy for the water cycle? The sun (g) State the importance of the water cycle. It ensures the availability of water for all organisms, including plants, animals and humans, in order for them to survive. 2.2 Physical and Chemical Changes 1. Fill in the blanks. (a) When a new substance is formed with different properties than the original substance, this change is called a chemical change. (b) If the chemical properties of a substance remain unchanged but the appearance or the shape of a substance changes, it is said that the substance undergoes a physical change. (c) A physical change is reversible while a chemical change cannot be reversed. (d) Whether a substance undergoes a physical change or chemical change, its mass always remains the same. (e) A chemical change occurs when a substance changes colour or temperature, produces bubbles or forms a new product. Extra Info Physical and chemical changes i 24
2. A student carried out an activity to differentiate between the physical and chemical changes in matter. Iron nail Distilled water Sodium chloride powder Spatula Water Stir X Y (a) What will happen to the iron nail in activity X and the sodium chloride powder in activity Y? X: The iron nail rusts. Y: The sodium chloride powder dissolves in water. (b) What types of changes occur in activities X and Y? Explain your answer. X: Chemical change, because the iron is changed into rust, which is a new substance. Y: Physical change, because no chemical reaction occurs and there is no new substance produced. (c) Give one example each for the types of changes mentioned in (b). Chemical change: Burning of paper Physical change: Melting of an ice cube (d) (i) What process is involved in activity X? How does it occur? Rusting. The iron nail reacts with the dissolved oxygen and water to produce rust. (ii) State one method to prevent the process in (d)(i) from occurring. Ensure the iron nail does not come into contact with either oxygen or water. / Applying paint or grease. (e) What inference can you make from activities X and Y? The rusting of iron is a chemical change as a new substance is formed. Dissolving sodium chloride powder in water is a physical change as no new product is formed. Chapter 2 Matter 25
3. The table below shows the properties of three different substances. Substance Properties Colour Able to dissolve in water Able to rust Sugar Colourless ✓ ✗ Vinegar Colourless ✓ ✗ Steel Silver ✗ ✓ (a) State one physical property and one chemical property of any two substances in the table above. Sugar: Can dissolve in water and does not rust Steel: Does not dissolve in water and able to rust (Accept other suitable answers) (b) Choose one of the substances in the table above. Then state two of its physical properties which are not stated in the table. Vinegar: Tastes sour and has an odour (Accept other suitable answers) 2.3 Density 1. (a) What is meant by density? The density of a substance is the amount of mass that fits into a unit volume of the substance. (b) The table below shows the mass and volume of objects K, L and M. Object Mass (g) Volume (cm3 ) K 12 4 L 13.5 5 M 21 6 (i) Calculate the density of each of the objects. Density of K Density of L Density of M = 12 4 = 13.5 5 = 21 6 = 3 g/cm3 = 2.7 g/cm3 = 3.5 g/cm3 (ii) Which object has the lowest density? Object L (iii) Which object is denser than object K? Object M 26
(iv) Given that object N has a density of 4.2 g/cm3 , arrange objects K, L, M and N in order of decreasing density. N, M, K, L 2. The densities of two liquids, Y and Z, are 0.95 g/cm3 and 1.24 g/cm3 respectively. Both liquids are poured into a beaker. Which liquid will float on top of the other? Explain your answer. Liquid Y will float on top of liquid Z because liquid Y has a lower density than liquid Z. 3. (a) The figure shows the position of object X when it is placed in 400 cm3 of water, liquid P and liquid Q respectively. Water Liquid P Liquid Q Object X Object X (i) State an inference based on the position of object X in water. Object X floats in water, so it is less dense than water. (ii) Compare the density of liquid P with that of liquid Q. Liquid P is denser than liquid Q. (iii) Arrange water, liquid P and liquid Q in ascending order of their density. Liquid Q, liquid P, water (b) The figure shows an activity conducted to determine the density of liquid P. 160 180 200 140 120 100 80 60 40 20 Empty beaker Lever balance 60 g 160 180 200 140 120 100 80 60 40 20 200 cm3 liquid P 120 g (i) Based on the figure, calculate the density of liquid P. Density of liquid P = 120 g – 60 g 200 cm3 = 0.3 g/cm3 Chapter 2 Matter 27
(ii) Based on the figure in (a) and the density of liquid P, predict the density of object X. 0.3 g/cm3 (iii) Draw and label the positions of object X, water, liquid P and liquid Q if they are placed in a measuring cylinder. 4. Underline the correct answer. (a) A raft is used to carry people on a river because it is (less dense / denser) than water. (b) Plastic balls are tied on fishing nets to keep the nets afloat in the sea because it is (less dense / denser) than water. 5. When Azmin puts an egg into a beaker containing water, it sinks in the water, as shown in the figure below. Beaker Water Egg (a) Why does the egg sink in water? The egg has a greater density than the water. (b) Suggest one way to make the egg float on the water. Dissolve some salt in the water until the salt solution formed is denser than the egg. 28
Objective Questions A B C D Choose the best answer. 1. Which of the physical states of water has particles with the highest kinetic energy? A Water B Ice C Melting ice D Steam 2. When a solid is melting, why do its particles move farther apart? A The particles move slower. B The particles start to lose their shape. C The particles repel each other more strongly. D The particles have higher kinetic energy and collide with one another more often. 3. The figure shows the arrangement of particles in substance X at room temperature. Substance X is most probably A nitrogen gas B vinegar C iron rod D carbon 4. Why does diffusion occur faster in a gas than in a liquid? I Gas particles move faster. II Gas particles are packed closely together. III The spaces between gas particles are larger. A I and II only B I and III only C II and III only D I, II and III 5. An experiment is carried out by filling two jars with carbon dioxide and hydrogen, as shown in the figure below. Gas jar X filled with hydrogen Gas jar Y filled with carbon dioxide Lid If the lid separating the two jars is removed, what will the components in gas jar X be after a few minutes? A Carbon dioxide only B Hydrogen only C Mixture of carbon dioxide and hydrogen D Carbon monoxide and water 6. A drop of red ink is placed at the bottom of a glass filled with water. After a few minutes, the water turns red because the ink particles A have vibrated in their positions B have combined with the water particles C have filled the spaces between the water particles D are smaller than the water particles Chapter 2 Matter 29
7. Some ice cubes are placed in an empty glass and left for some time. Which of the following shows the change of state for the ice cubes after an hour? A Liquid → gas B Liquid → solid C Gas → liquid D Solid → liquid 8. Which of the following pairs is matched correctly? Process Example A Melting Solidifying of melted candle wax B Deposition Formation of iodine crystal from iodine vapour C Condensation Formation of snow D Evaporation Dew forming on grass 9. There are two objects with the same volume but different masses. Which object will be denser? A The object with more mass B The object with less mass C The object with a larger size D The object with a smaller size 10. The figure shows a metal block with a mass of 540 g. 5 cm 8 cm 3 cm What is the density of the metal block? A 0.22 g/cm3 B 2.25 g/cm3 C 4.5 g/cm3 D 9 g/cm3 11. The table below shows the densities of three substances X, Y and Z. Substance Density (g/cm3 ) X 0.5 Y 0.9 Z 2.3 Which substances can float on water if the density of water is 1.0 g/cm3 ? A X, Y and Z B X and Y only C Z only D None 12. The article below is about the hot air balloon. The Hot Air Balloon Festival returns for the third time on 8 and 9 April 2023! This festival allows visitors the opportunity to float up into the sky in a hot air balloon. Which statement explains why a hot air balloon can float up into the sky? A The wind blows the balloon upwards. B There is no gravity acting on the balloon. C The balloon rises due to air resistance. D The air inside the hot air balloon is less dense than the air surrounding it. 30
Concept Map Complete the concept map below about matter. Properties of matter Physical and chemical properties Mass per unit volume of a substance Changes in states of matter • Diffusion is the fastest in gases and the slowest in solids . • Diffusion in liquids is slower in gases but faster in solids. Physical and chemical changes definition compare definition Anything that has mass and occupies space Solid Gas Matter Diffusion rate in three states of matter Liquid Three states of matter Density Melting Solid Liquid Gas Deposition Freezing Condensation Boiling / Evaporation Sublimation Chapter 2 Matter 31
HOTS Daily Application Online Quick Quiz Ahmad creates a model of a submarine using a plastic bottle, two straws and a container, as shown in the figure below. Plastic bottle Straw Container Water Why does the model of a submarine float on water? What will happen to the submarine when it is filled with water, or the water is sucked out? Explain how the concept of density can be used in a submarine. The model of a submarine is less dense than the water. When the submarine is filled with water, it will sink into the water. When the water in the submarine is sucked out, it will float in the water. To make a submarine float, water is pumped out of the ballast tank. This makes it less dense than seawater. To make a submarine sink, water is pumped into the ballast tank. This makes it denser than seawater. 32
Temperature and Heat CHAPTER 3 3.1 Temperature and Scale 1. Answer the questions below. (a) What is temperature? Temperature is a measurement of how hot or cold an object is. (b) What is the tool used to measure temperature? Thermometer (c) State the three units of temperature. Celsius, Fahrenheit, Kelvin 2. Thermometers are used to measure temperature according to well-defined scales of measurement. (a) What is a temperature scale? A temperature scale is a range of numbers used to measure temperature relative to a starting point (zero) and a unit of measurement. (b) Four types of scales are shown in the table below. Complete the table. What type of scale is used? Who developed/ proposed the scale? What is the freezing point of water on this scale? What is the boiling point of water on this scale? What is the interval between the freezing and boiling points called? Fahrenheit scale Daniel Gabriel Fahrenheit 32°F 212°F Degrees Fahrenheit Réaumur scale René Antoine Ferchault de Réaumur 0°R 80°R Degrees Réaumur Celsius scale Anders Celsius 0°C 100°C Degrees Celsius Kelvin scale Lord Kelvin 273.15 K 373.15 K Kelvins 3. The following formulas are used to convert temperatures to different units. Temperature from Celsius to Kelvin: K = °C + 273.15 Temperature from Celsius to Fahrenheit: °F = 9 5 °C + 32 Temperature from Celsius to Réaumur: °R = 4 5 °C Chapter 3 Temperature and Heat 33
Based on the formulas given, calculate the following. (a) Convert 80°C to Kelvin = 80°C + 273.15 = 353.15 K (b) Convert 373.15 K to Celsius = 373.15 K – 273.15 = 100°C (c) Convert 25°C to Fahrenheit = 9 5 25°C + 32 = 77°F (d) Convert 50°C to Réaumur = 4 5 50°C = 40°R 3.2 Thermometers 1. The figure shows two types of liquid-in-glass thermometers X and Y. P and Q are two liquids that are commonly used in such thermometers. Silver liquid P Capillary tube Thermometer X Bulb Red liquid Q Thermometer Y (a) Name the liquids P and Q. Liquid P: mercury Liquid Q: alcohol (b) Why is liquid P used in thermometer X? Give one reason. It is a good conductor of heat. It is opaque and shiny and hence clearly visible. (Any suitable answer) (c) Why is liquid Q preferred for use in liquid-in-glass thermometers over liquid P? Liquid Q is less toxic and inexpensive compared to liquid P. (d) State one use of thermometer X. Used to measure body temperature Extra Info Thermometers i 34
(e) How does the liquid-in-glass thermometer work? A liquid-in-glass thermometer works based on the principle of expansion and contraction of liquid. The liquid in the capillary tube expands when the temperature increases and contracts when the temperature decreases. 2. Thermometers come in a variety of sizes and shapes to meet the requirements of the users. Some types of thermometers are shown below. P Q R (a) Name thermometers P, Q and R. P: Digital thermometer Q: Probe thermometer R: Electronic ear thermometer (b) Classify the thermometers above based on the following two categories. Clinical thermometer: P (Digital thermometer), R (Electronic ear thermometer) Laboratory thermometer: Q (Probe thermometer) (c) State one use of each of the following thermometers. (i) Thermometer P: Used to measure body temperature (ii) Thermometer Q: Used to instantly measure the temperature of food and liquid samples (d) Which type of thermometer uses infrared technology in reading temperature? R (electronic ear thermometer) (e) Where can thermometer P be placed when taking the temperature of the human body? In the rectum, under the tongue or under the armpit (f) Which of the three thermometers above is the most commonly used? Justify your answer. P (Digital thermometer). It is inexpensive, widely accessible and easy to use. Chapter 3 Temperature and Heat 35
3.3 Expansion and Contraction of Matter 1. Draw the arrangement of the particles when they are heated. Briefly describe the arrangement. Arrangement of particles Description (a) Solid heated The particles vibrate more vigorously. (b) Liquid heated The particles move further away from each other. (c) Gas heated The particles move faster and further apart compared to liquid. 2. An activity is carried out to study the effect of heat on a metal ball. Metal ball Ring Holder Metal ball Ring Holder After the metal ball is heated After the metal ball has cooled down (a) What can be observed after the metal ball is heated? The metal ball cannot pass through the ring when it is heated. (b) What can be observed after the metal ball is cooled to room temperature? The metal ball can pass through the ring when it is cooled. (c) What conclusion can be made from this activity? When heated, the metal ball expands, increases in size and cannot pass through the ring. 36
(d) Explain your answer in (c). When the metal ball is heated, the heat causes the atoms in the metal to vibrate more rapidly, which increases the space between the atoms. As the space between the atoms increases, the metal ball expands in size. 3. The figure shows a vessel with an open glass tube on one end and a closed glass sphere on the other. The vessel is filled with water, with air trapped inside the sphere. The water level in the sphere and the tube is at level X. Air Water X Open glass tube Glass sphere The air in the glass sphere is then heated by a hairdryer. (a) Circle P, Q or R to show the water level in the open glass tube after the glass sphere is heated. At X X P Below X X Q Above X X R (b) Explain your answer in (a). When the glass is heated, the air expands and pushes the water up the tube. 4. Complete the passage below about the fire alarm with the correct words. Electric bell Batteries Contact point Iron Brass An automatic fire alarm uses a bimetallic strip of brass and iron to switch on the electric bell when there is a fire. When a fire occurs, the strip is heated. The strip then expands and bends towards the contact point to complete the circuit. As a result, the fire alarm rings loudly. Chapter 3 Temperature and Heat 37
5. Fatima is having difficulty removing the cap of a bottle of chilli sauce. Suggest one method for her to unscrew the bottle cap. Explain your answer. Dip the bottle cap in hot water. The cap will expand when it is heated. 6. The figure shows two situations that we encounter in our daily lives. Gap Railway track Expansion joints Railway track Bridge (a) Why are gaps left in between successive rails when laying a railway track? The gap is to allow for expansion on hot days. When the rails get hot, they expand. This prevents the tracks from buckling. (b) Why are expansion joints used in bridges? Bridges are made of steel, which expands and contracts with temperature. Expansion joints are usually used to allow for the expansion and contraction of the bridge deck. This prevents the bridges from cracking. 7. The figure shows two sections of phone cables. Phone cables Pole P Q (a) How do the phone cables in sections P and Q differ from one another? The phone cables in section P are slack but the phone cables in section Q are taut. (b) What happens to the phone cables during a cold night? (i) P: The phone cables will contract and become shorter. (ii) Q: The phone cables will contract and snap. 38
(c) What principle is shown by the phone cables during the day and at night? The principle of expansion and contraction of matter (d) A thermostat also uses the same principle. Which component in the thermostat functions in the same way? A bimetallic strip 3.4 Heat Capacity 1. What is the specific heat capacity of a substance? The amount of heat required to increase the temperature of 1 kg of the substance by 1°C. 2. The specific heat capacity of metal Y is 390 J kg–1 °C–1. How much heat is needed to raise the temperature of 6 kg of metal Y from 15°C to 50°C? Q = mcθ = 6 × 390 × (50 – 15) = 81 900 J 3. The initial temperature of water is 72°C. What is its final temperature if 75 600 J of heat is removed from 5 kg of water? [Specific heat capacity of water = 4200 J kg–1 °C–1] Q = mcθ θ = Q mc = 75 600 5 × 4200 = 3.6°C Final temperature = 72 – 3.6 = 68.4°C 4. Calculate the change in temperature of 3.0 kg of water at room temperature if 189.0 kJ of heat is added. [Specific heat capacity of water = 4200 J kg-1 °C-1] Q = mcθ θ = Q mc = 189 000 3 × 4200 = 15°C Extra Info Specific heat capacity i Chapter 3 Temperature and Heat 39
5. (a) What is the specific latent heat of vaporisation of a substance? The amount of heat needed to change 1 kg of the substance from the liquid to the gaseous state without any change in temperature. (b) What is the specific latent heat of fusion of a substance? The amount of heat needed to change 1 kg of the substance from the solid to the liquid state without any change in temperature. 6. How much heat is required to change 1.5 kg of water at 100°C to steam at 100°C? [Specific latent heat of vaporisation of water = 2.26 × 106 J kg–1] Q = mL = 1.5 × 2.26 × 106 = 3.39 × 106 J 7. A mass of steam at 100°C releases 9.04 × 106 J of heat energy to produce water at 100°C. What is the mass of water produced? [Specific latent heat of vaporisation of water = 2.26 × 106 J kg–1] Q = mL m = Q L = 9.04 × 106 2.26 × 106 = 4 kg 8. How much heat energy is needed to change 5 kg of ice at 0°C into water at 30°C? [Specific latent heat of fusion of water = 3.36 × 105 J kg–1; specific heat capacity of water = 4200 J kg–1 °C–1] Energy needed to melt 5 kg of ice Q1 = mL = 5 × 3.36 × 105 = 1.68 × 106 J Energy needed to change the temperature from 0°C to 30°C Q2 = mcθ = 5 × 4200 × (30 – 0) = 6.3 × 105 J Total energy needed = Q1 + Q2 = 1.68 × 106 + 6.3 × 105 = 1.68 × 106 + 0.63 ×106 = 2.31 × 106 J 40
9. A solid substance with a mass of 500 g is heated by a heater that gives out heat at the rate of 80 J per second. The initial temperature of the substance is 20°C. The heating curve of the substance is shown below. Temperature (˚C) Time (min) 20 40 60 80 100 0 2 4 6 8 10 90 67 X Y Z W (a) What is the melting point of the substance? 67°C (b) Explain why the temperature in stage YZ remains constant although the heater is working. The heat absorbed is used to overcome the attractive forces between the particles. (c) Calculate the specific heat capacity of the substance in the solid state. Heat supplied = mcθ 80 × 60 × 2 = 0.5 × c × (67 – 20) c = 9600 23.5 = 408.5 J kg–1 °C–1 (d) Calculate the specific heat capacity of the substance in the liquid state. Heat supplied = mcθ 80 × 60 × (10 – 8) = 0.5 × c × (90 – 67) c = 9600 11.5 = 834.8 J kg–1 °C–1 (e) Calculate the specific latent heat of fusion of the substance. Heat supplied = mL 80 × 60 × (8 – 2) = 0.5 × L L = 28 800 0.5 = 5.76 × 104 J kg–1 Chapter 3 Temperature and Heat 41
3.5 Heat Transfer 1. The figure shows an activity where a metal ball with an initial temperature of 25°C is placed into a beaker of boiling water. Boiling water Metal ball (a) Underline the correct words to complete the following statements. (i) The temperature of the metal ball will (increase / decrease). (ii) The temperature of the water will (increase / decrease). (b) The set-up is left for a day. Tick (✓) the correct information about what happens at the end of the activity. (i) The rate of heat flow from the boiling water = The rate of heat flow into the metal ball ✓ (ii) The rate of heat flow from the boiling water The rate of heat flow into the metal ball (iii) The temperature of the metal ball The temperature of the water (iv) The temperature of the metal ball = The temperature of the water ✓ (c) How is heat transferred from the water to the metal ball? Through conduction 2. Fill in the blanks with suitable words to explain heat transfer. Method Property Conduction Convection Radiation Medium of heat transfer Takes place in solids Takes place in fluids Takes place in vacuum How heat is transferred Heat is transferred through the vibrating particles that are in contact Heat is transferred by the movement of the convection current Heat transfers in the form of electromagnetic waves Rate of heat transfer The rate of heat transfer is slow The rate is slower compared to conduction The transfer of heat is at the speed of light 42
3. Fill in the blanks with the information about heat flow in natural phenomena. Sea Land Cold air Hot air Hot air Cold air Sea Land The land heats up faster than the sea. The land cools faster than the sea. The hot air on the land is less dense and it rises. The hot air on the sea is less dense and it rises. Cool air from the sea moves to the land to fill the empty space left by the hot air. Cool air from the land moves to the sea to fill the empty space left by the hot air. The movement of cool air from the sea to the land is called a sea breeze . The movement of cool air from the land to the sea is called a land breeze . This phenomenon involves heat flow through convection . This phenomenon involves heat flow through convection . 4. The sun is the main source of heat energy for the earth. (a) By which method is heat transferred from the sun to the earth? Radiation (b) Explain your answer in (a). Heat can be transmitted through space or a vacuum by radiation. 5. A recreational group organises a jungle survival programme in Bali’s tropical rainforest. The figure shows an activity conducted during the programme. Chapter 3 Temperature and Heat 43
(a) Zul goes to a stream to obtain some water and boils it in a cooking pot placed over the campfire. (i) State the principle involved in transferring the heat from the cooking pot to the water. Convection (ii) Zul pours the boiling water into a cup. When he holds the cup of water, it feels hot. How is heat transferred from the boiling water to the cup? Through conduction (b) Zul trips while carrying a bucket of water, causing the water spills onto his shoes. Describe how Zul can dry his shoes faster. Zul can place his shoes near the campfire. The higher the surrounding temperature, the faster the water from the wet shoes evaporates. (c) Zul sets up a tent in the shade of trees. He notices that the air inside this tent is cooler than the air inside the tent set up in an open area. Describe how this condition occurred. The leaves of trees absorb and filter solar radiation. The process of transpiration through leaves lowers the surrounding temperature. 3.6 Heat Conductors and Heat Insulators 1. (a) What is a heat conductor? A substance that allows heat to flow through it easily. (b) What is a heat insulator? A substance that prevents or slows down heat from flowing through it. 2. In the figures below, identify each part of the object that is a heat conductor or a heat insulator. Label the parts as ‘Conductor’ or ‘Insulator’. Conductor Insulator Insulator Insulator Conductor Conductor Insulator Conductor 44
3. Match the heat insulators to their uses. Heat insulator Use Wool blanket or cloth Used as a base for hot cooking utensils Fibreglass or polystyrene Used as a handle in utensils to protect the hand from the heat while holding it Cork, asbestos, tiles Used for warming the body by trapping a layer of air Wood or plastic Used as an insulator in the wall of a refrigerator or an ice box to maintain the cold temperature 4. An activity is conducted to analyse the heat conductivity of four materials P, Q, R and S and determine which material is the best heat insulator. Wax was used to stick the thumbtacks to the ends of the four rods. Heat P Q R S The time taken for the thumbtacks to fall off from the rods is recorded in the table. Rod P Q R S Time taken for the thumbtack to fall off (seconds) 40 75 38 24 (a) Which material is the best conductor? Explain. S. Its thumbtack fell off first as the heat travelled the fastest along the rod. (b) Which material is the best insulator? Explain. Q. Its thumbtack fell off last as the heat travelled the slowest along the rod. (c) Arrange the materials in decreasing order of heat conductivity. S, R, P, Q Chapter 3 Temperature and Heat 45
(d) Based on the activity, which material is most suitable for making the handle of a frying pan? Why? Q. It does not allow heat to flow through it easily. This can prevent our hands from getting burned due to the heat flowing from the pan. 5. An activity is carried out to study if different materials have different abilities as heat insulators. A B C D Thermometer Cotton wool Paper Aluminium foil Hot water Hot water The results are recorded in the table. Flat-bottomed flask Temperature (°C) A B C D Initial temperature 90 90 90 90 Final temperature (after 5 min) 78 75 65 70 Difference in temperature 12 15 25 20 (a) Complete the table by calculating the difference in temperature. (b) (i) Which material acts as the best heat insulator? Give your reason. Cotton wool. It prevents the most heat loss as the temperature of water in its flask was the highest after 5 minutes. (ii) What conclusion can be made from this activity? Different materials have different abilities as heat insulators. (c) You want to bring some hot food in a container to a beach. (i) From the figure, which material will you choose to wrap the container? Why? Cotton wool. It acts as a heat insulator that helps slow down the loss of heat from the warm container to the surroundings, keeping the food warm. (ii) Besides choosing the right material as a heat insulator, give another suggestion to improve thermal insulation. Use a few layers of insulators. For example, wrap the food in aluminium foil, then wrap it with cotton wool. 46
3.7 How Types of Surfaces Affect Heat Absorption and Emission 1. An activity is carried out to investigate the absorption of heat by a dark, dull tin and a white, shiny tin. Black and dull tin White and shiny tin Burner wrapped with wire gauze Thermometer The results are recorded in the table below. Characteristics of tin Temperature of the air (°C) Change in temperature (°C) Initial reading Final reading (after 15 min) Black and dull 22 26 4 White and shiny 22 23 1 (a) Complete the table above by calculating the change in temperature for both tins. (b) Which object absorbs heat faster? Black and dull tin (c) State the characteristics of an object which is a better heat absorber. An object with a black and dull surface (d) What is the purpose of using the wire gauze in the experiment? To ensure that the heat from the Bunsen burner is equally distributed on all sides. 2. State two daily life applications that use the principle of heat absorption and emission. Justify your answers. The outer surface of an oil tank is shiny so that it reflects heat and prevents the oil from heating up. The surface of a solar panel is painted black so that it absorbs heat well. 3.8 Body Temperature Regulation 1. The animals that live in a particular habitat are listed below. snake, dog, owl, rabbit, bee, fish, lizard, toad, goat, bat (a) Classify the animals above into homeothermic and poikilothermic. Chapter 3 Temperature and Heat 47
(i) Homeothermic animals: dog, owl, rabbit, goat, bat (ii) Poikilothermic animals: snake, bee, fish, lizard, toad (b) Why are the animals in (a)(i) considered to be homeothermic? They maintain a constant body temperature regardless of the outside temperature. (c) A dog that runs around in the sun can quickly overheat. Give one way by which the dog regulates its body temperature. The dog pants, allowing the water in its mouth to evaporate, keeping it cool. (d) Some animals use different methods to regulate their body temperatures. Underline the correct answers for the following examples. (i) (Desert lizards / Rats) bask in the hot sun before retreating to the cold shade and burrowing. (ii) (Penguins / Polar bears) have thick layers of hair, skin and oil that help them in maintaining body temperature in cold environments. (iii) (Butterflies / Birds) can sunbathe and adjust their posture in the sun to absorb heat. 2. The underlined words are incorrect. Replace them with the correct words. (a) The capacity of organisms to maintain their body temperature within specified ranges despite a change in the surrounding temperature is called osmoregulation. thermoregulation (b) The cerebrum is a part of the brain that regulates body temperature. hypothalamus (c) Humans maintain a flexible body temperature regardless of changes in the surrounding temperature. constant (d) When our brain senses changes in body temperature, it will carry out the changes through receptors such as muscles, sweat glands and hair. effectors (e) Sweat glands secrete sweat that helps the body to control its temperature by promoting heat loss through respiration. evaporation (f) When our body temperature is low, thyroid hormone is released to decrease metabolism. increase (g) When we feel cold, the muscles in the body will contract and relax rapidly to generate heat, resulting in shaking. shivering 48