CONTENTS About This Book iv Science and Measurements 1 1.1 What is Science? 2 1.2 Science Laboratory 7 1.3 Measurements 14 1.4 Measuring Tools 17 Recall 32 Put on your Thinking Cap 33 Project 34 Matter 35 2.1 States of Matter 36 2.2 Physical and Chemical Changes 54 2.3 Density 58 Recall 63 Put on your Thinking Cap 64 Project 65 Temperature and Heat 66 3.1 Temperature and Scale 67 3.2 Thermometers 68 3.3 Expansion and Contraction of Matter 71 3.4 Heat Capacity 79 3.5 Heat Transfer 84 3.6 Heat Conductors and Heat Insulators 89 3.7 How Types of Surfaces Affect Heat Absorption and Emission 92 3.8 Body Temperature Regulation 97 Recall 100 Put on your Thinking Cap 101 Project 102 Motion and Force 103 4.1 Motion 104 4.2 Force and Motion 116 Recall 125 Put on your Thinking Cap 126 Project 127 CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 ii
Living Things 128 5.1 Biodiversity 129 5.2 Living and Non-living Things 133 5.3 Classification of Living Things 136 Recall 151 Put on your Thinking Cap 152 Project 153 Interactions Among Organisms and the Environment 154 6.1 Biotic and Abiotic Components 155 6.2 Food Chains and Food Webs 160 6.3 Nutrient Cycles in an Ecosystem 163 6.4 Interactions between Organisms 165 6.5 Factors that Affect the Organisms and Environment 168 Recall 178 Put on your Thinking Cap 179 Project 180 Earth and the Solar System 181 7.1 The Solar System 182 7.2 Earth and Its Satellite 189 7.3 The Sun 197 Recall 200 Put on your Thinking Cap 201 Project 202 CHAPTER 5 CHAPTER 6 CHAPTER 7 iii
ABOUT THIS BOOK Focus-on Science is a pedagogy-driven series developed to provide a clear and effective learning trajectory for Grade 7 to Grade 9 students. The inquiry approach used in the Textbook assists students in acquiring scientific knowledge and science process skills through a variety of activities, experiments and projects. To make learning more engaging, photographs, infographics, diagrams and examples are used to present the content. In addition, animations, videos, simulations and Augmented Reality (AR) models are included to help bring science to life. Chapter Opener A short write-up with trigger questions based on a photo, as in the chapter introduction, to pique students’ interest. Experiment Engages and helps students to develop science process skills, manipulative skills and an inquisitive attitude through welldesigned laboratory experiences. Sudi fastens his seat belt before he starts to drive. What happens to Sudi when the brake is applied suddenly upon seeing a cat crossing in front his moving car? Why is it necessary to use the seat belt? Motion and Force CHAPTER 4 What will you learn? Describe motion in terms of distance, displacement, speed, velocity and acceleration Measure speed Understand the relation between force and motion Understand Newton’s Laws of Motion and their applications in daily life Demonstrate Newton’s Law of Motion The temperature of a matter increases when it is heated and decreases when it is cooled. However, the temperature remains constant during a change of state, that is during melting (solid to liquid), boiling (liquid to gas), freezing (liquid to solid) and condensation (gas to liquid). During melting and boiling, the kinetic energy gained by the particles is used to overcome the forces of attraction between the particles. The temperature of the solid or liquid remains the same. On the other hand, during condensation and freezing, the particles release energy to the surroundings, thus enabling them to be pulled closer together. The temperature of the liquid or gas remains the same. Temperature (°C) Boiling point Melting point Ice Water Ice + Water Steam Time (min) Water + C Steam B D A Problem statement Does temperature remain constant during the changes of state? A Temperature during the melting of ice Hypothesis The temperature of ice remains constant during the melting process. Manipulated variable Responding variable Constant variable Quantity of ice cubes Materials and apparatus glass rod and wire gauze Ice cubes, thermometer, beaker, Bunsen burner, tripod stand, Procedure 1 Set up the apparatus as shown in the diagram below. Ice cube Thermometer Glass rod Wire gauze Bunsen burner 2 Experiment Temperature remains constant during changes of state At point A to B, the temperature of the mix of ice and water remains the same, at the melting point. At point C to D, the temperature of the mix of water and steam remains the same, at the boiling point. The change of temperature during the heating of ice 48 What will you learn? The chapter’s learning outcomes which provide an idea of what students will learn. iv
Science Facts Provides additional information related to the topic taught in order to stimulate students’ interest in learning science. Activity Provides students with a total learning experience through learning by doing, encouraging them to reflect on the experience and think critically. The blue whale is the world’s largest animal, reaching a length of 30 metres or more and weighs as much as 24 elephants. Some species of whales can live for more than 200 years. Science Facts What is the best tool for measuring the circumference of an infant’s head? Why? Think About It Measuring Length Length is the distance between two points. The SI unit for length is metre (m). Short lengths are measured in centimetres (cm) or millimetres (mm). Long distances are measured in kilometres (km). A ruler such as the metre rule can be used to measure the length of short straight lines or objects. The metre rule gives an accuracy of 0.1 cm. The correct reading is obtained only when the eyes are vertically above the mark on the ruler. Parallax error happens when the measurement reading is more or less than the actual reading. This occurs when the mark on the ruler is viewed from the wrong position. 0 1 2 3 cm 4 5 6 7 8 9 10 11 12 13 14 15 Correct One end of the object is at the ‘0’ mark. Wrong Wrong 18 The correct eye position when taking a reading Activity 2 Aim: To measure average and instantaneous speed of a toy car on the runway Materials and apparatus: Photogate (timing gate) system and electronic timer, toy car and runway Procedure: A Measuring average speed 1 Set up the apparatus as shown in the diagram. Distance between two timing gates Black strip to break infrared beam Transparent card First timing gate linked to the timer Second timing gate linked Toy car to the timer Runway Electronic timer 15 cm 2 Adjust the distance between two timing gates to 50 cm. 3 Release the toy car from the high end of the runway. 4 Catch the toy car once it passes the second timing gate. Record the time taken. B Measuring instantaneous speed 1 Set up the apparatus as shown. Transparent card Length of black strip that breaks the infrared beam Timing gate linked to the timer Toy car Runway Electronic timer 15 cm 2 Release the toy car from the high end of the runway. 3 Catch the toy car once it passes the timing gate. 4 Record the time taken. Results: Activity A Calculate the average speed of the toy car in m/s by dividing the distance between the timing gates by the time taken. Activity B Calculate the instantaneous speed of the toy car in m/s by dividing the length of the black strip by the time taken. Discussion: Why is it advisable not to place the timing gate too high on the runway or too close to the bottom of the runway? Measuring speed Caution • Do not place the timing gates too high on the runway. • Do not place the timing gates too close to the bottom of the runway. After a hot shower, it is likely that Chapter 4 Motion and Force 109 you would not be able to see your reflection in the mirror. You have to wipe off the moisture from the mirror’s surface first. This is because condensation occurs when warm water vapour comes into contact with the cooler mirror surface. Have you ever wondered why we can see someone’s breath when he is out in very cold weather? Water exists on Earth in all three states of matter: solid, liquid and gas. Liquid water can be found in the oceans, rivers, lakes and streams, as well as in the soil and underground. Glaciers and snow all contain solid ice. The Earth’s atmosphere contains water vapour which is a gas. Let’s study how water exists in different states in the water cycle. When the warm and moist vapour of his breath comes into contact with the cold and humid air, it condenses into tiny water droplets. We can see these droplets take on a cloud-like appearance. Water cycle Resource 53 Chapter 2 Matter Think About It Provides questions that encourage students to find the answers to support constructivist learning. Resource Helps students make learning more enjoyable and in a more engaging way via scanning QR codes to access fascinating videos, animations, simulations, AR models, etc. Resource v
THINKING CAP Put on your 1 Have you noticed that an electric fan continues to revolve for some time even after the current is switched off? How do you explain this? 2 How does swimming relate to Newton’s Third Law of Motion? Explain. 3 Why does a bird flap its wings shortly before it takes-off? 126 1 The systematic study of nature and how it affects us and our environment is known as . The application of scientific knowledge for the use of mankind is called . 2 We use to carry out experiments and make accurate measurements or observations in the laboratory. 3 Students must follow rules and precautions in the laboratory in order to prevent accidents when they carry out the experiments. 4 Students must be able to recognise the hazard warning that are placed on labels of bottles or containers of hazardous substances in order to handle the substances properly. 5 A investigation is a series of steps done systematically to study a problem or an event that involves the use of one or more science process skills. 6 The process of utilising numbers to define physical quantities is known as . 7 A quantity is a quantity that can be measured and has value. 8 Length, mass, time, temperature and electric current are quantities. 9 Area, volume, density and velocity are obtained by multiplying or dividing two or more basic quantities. They are known as quantities. 10 Unit is the process of converting one unit of measurement to another for the same quantity by multiplying or dividing by conversion factors. 11 Length is the distance between two points and its SI unit is . 12 Micrometer screw gauges are used to measure the and diameters of small objects while vernier calipers are used to measure short lengths, the internal and external , and the of objects. 13 An area is the extent of a surface or a plane figure. The SI unit for area is . 14 The of a liquid can be measured using a measuring cylinder, beaker, pipette or burette. 15 The volume of regular-shaped and irregular-shaped solids can be measured by using the water method. 16 The of an object is the quantity of matter contained in the object while the of an object is the pull of the Earth on the object. 17 A is the standard instrument used to measure time intervals in the laboratory. The SI unit of time is . 18 The measurement of how hot or cold an object is its . Its SI unit is and it is measured using a . 19 The density of a substance is defined as its mass per unit volume and its SI unit is . RECALL Fill in the missing words. 32 Project Activity objective: Introduce Newton’s First Law of Motion Problem statement: Newton’s first law of motion states that an object remains at its original state, whether it is at rest or moving at uniform velocity in a straight line, unless acted upon by an external force. Also known as the law of inertia, it has important applications in our daily life and this project will demonstrate the first part of the law: An object at rest stays at rest. Concept applied: Newton’s First Law of Motion Procedure: 1 Work in a group of five students. Each group is to build a tower of at least 60 cm tall. 2 Brainstorm the design of the tower and the role of each member in the group. 3 Determine the material to build the tower. The material used must be stackable and it is a set of identical material. For different testing, materials of different mass will be used to build the towers. 4 Build the tower. 5 Prepare notecards by punching a hole on one end and tying a string through the hole. Place the cards in the tower as shown in the picture. 6 Starting at the top, pull the first notecard quickly from the tower. Observe and record your result. 7 Continue to pull one or two more cards from top to bottom and observe what happens. 8 What improvements need to be done if the test is not successful? 9 If this was done successfully, get everyone in the group to pull the cards out at the same time. Would the result be the same as in steps 6 and 7? 10 What improvements need to be done if the test is not successful in step 9? 11 Now try to build a tower of the same height by using materials that has less mass. 12 Repeat steps 6 to 10 and record your result. 13 Alternatively, you can try another test where the cards are without the holes and string. Would this make the pull easier? Would this affect the result? Presentation: You may present your findings with a video or any method that is suitable. Share with the groups the improvements you had done for successful testing. Submit a report. Inertia Tower Chapter 4 Motion and Force 127 Put on your Thinking Cap Challenges students with questions that promote higher-order thinking skills. Recall Assists students in recalling concepts learned and serves as a summary of key points. Project Appears at the end of each chapter that helps students develop problem-solving and critical thinking skills, and to connect what students have learned to the real world. vi
We are used to seeing steam coming from a hot drink. In the picture on the right, is the steam coming from the hot coffee, or from the air above it condensing due to heat from the coffee? If the hot coffee is replaced with hot chocolate, how do you turn the hot chocolate, liquid form to solid form? Matter CHAPTER 2 What will you learn? Describe the arrangement and movement of particles in solid, liquid and gas, and their properties Explain what happens in changes of state using the particle theory Describe the physical and chemical changes Define density and calculate the density of a material Explain why some objects float and some objects sink in water
Solid Solid 2.1 States of Matter Matter is anything that has mass and volume. According to the particle theory of matter, matter is made up of very small particles that cannot be seen with a light microscope. These tiny particles are discrete. This means that the particles are completely separate from one another and there are spaces between them. The particles of matter are in constant motion. Solid The particles in a solid are packed closely together in a fixed and regular pattern. They are held together in fixed positions by very strong forces of attraction. The spaces between particles are very small. Thus, they cannot move around and can only vibrate in their fixed position. With an increase in temperature, the particles gain kinetic energy and vibrate faster and more strongly. Solids cannot be compressed because the particles are close together and have very little space to move into. Thus, they have a fixed shape and volume. As a result, solids do not flow. Due to the limited spaces among the particles, solids diffuse the slowest compared to liquids and gases. In general, solids have the highest density because the particles are closely packed and have a large number of particles per unit volume. Particles of copper Copper Wire Solid, Liquid and Gas Matter can exist in three states which depend on how the particles are arranged. The three states of matter are solid, liquid and gas. Water is an example of a matter that exists in all three states. (a) Water is liquid at room temperature. (b) Ice is water in solid state. (c) Steam and water vapour are water in gaseous state. The arrangement and movement of particles are different in different physical states of matter. Hence, each state of matter has different physical properties. 36
Liquid The particles in a liquid are quite close together but are arranged randomly without a fixed pattern. They are held together by strong forces of attraction but not as strong as in solids. The spaces between particles are moderate. Thus, they are able to move freely and collide with one another. When a liquid is heated, its particles gain kinetic energy, resulting in an increased collision rate. Liquids cannot be compressed to any extent because the particles are still arranged quite closely and have little space to move into. Thus, they have a fixed volume. Since the particles can move, liquid can flow and take the shape of its container. They have moderate density because the particles are arranged randomly without a fixed pattern and has slightly smaller number of particles per unit volume compared to solids. They diffuse slowly. For example, when a perfume is sprayed at a corner in a room, the smell of the perfume can be detected a few metres away. Gas The particles of gas are far apart from one another. They have little or no forces of attraction between them. The spaces between particles are large. Thus, they are able to move freely and randomly in all directions at high speeds. When a gas is heated, collisions occur more frequently among the particles as they gain more kinetic energy and move faster in all directions. Gases can be easily compressed because the particles are far apart and have large spaces to move into. Thus, they have no fixed volume. They flow much more easily than a liquid because the particles move randomly in all directions and spread out as far as they can, occupying the entire space of the container quickly. They take the shape of their container. Gases have very low density because the particles are arranged far apart and has a smaller number of particles per unit volume compared to solids and liquids. They diffuse rapidly. For example, bromine gas in a gas jar diffuses and spreads evenly throughout another gas jar filled with air within a few minutes. Liquid Gas Chapter 2 Matter 37
Activity 1 Aim: To show that matters have mass and occupy space Materials and apparatus: Balloons, needle, thread, cellophane tape, metre rule, green beans, retort stand and clamp, measuring cylinder and lever balance Procedure: Activity A 1 Set up the apparatus as shown below. Balloons Needle Cellophane tape Metre rule P Q Thread 2 Balance two balloons on a metre rule. 3 Use a needle to prick balloon Q through the cellophane tape. Then, record your observation. Activity B 1 Weigh an empty measuring cylinder with a lever balance and record its mass. Lever balance Empty measuring cylinder 2 Place a random amount of green beans into the measuring cylinder. Weigh the measuring cylinder and record its mass. Lever balance Measuring cylinder containing green beans Matter has mass and occupies space 38
Observations: Activity A The air in balloon Q escapes and the metre rule tilts to the . Activity B (a) Mass of empty measuring cylinder = g (b) Mass of measuring cylinder and green beans = g Discussion: 1 What is meant by matter? 2 Give inferences for your observation in (a) activity A (b) activity B 3 Give four examples of objects around you that have mass and occupy space. 4 Rizal found that his flat bicycle tyre inflates after being pumped. Why does this happen? 5 Which of the following substances are matter? (a) Water (b) Sound (c) Soil (d) Time (e) Heat (f) Sunlight 6 Why is the mass of air not measured using the lever balance? Conclusion: Write down your conclusion. Chapter 2 Matter 39
Activity 2 Aim: To make a simulation about the arrangement and movement of particles in solid, liquid and gas Materials and apparatus: A plastic container with partitions, and marbles Procedure: 1 Put marbles in each of the sections A, B and C in the plastic container as shown in the diagram below. A B C Marble Plastic container 2 Move the plastic container back and forth repeatedly. 3 Observe the arrangement and movement of the marbles in each section. Observation: Label section A, section B and section C in the tree map below. Draw the arrangement of the particles, and complete the characteristics of each matter (solid, liquid and gas) with the words given. loose solid orderly very loose high moderate low liquid vibrate randomly quickly gas Arrangement and movement of particles in solids, liquids and gases Matter Section A Section B Section C • Compact and • about a fixed position • kinetic energy • and not in order • Move and sometimes collide • kinetic energy • and in disorder • Move at random and often collide • kinetic energy 40
Discussion: 1 (a) What is represented by the marbles? (b) What is matter made up of? 2 The diagrams below show two syringes, one filled with air and another filled with water. Both syringes are pressed down. Air Water (a) Which syringe is easier to be compressed? The syringe filled with air or the syringe with water? (b) Explain why it is easier to compress that syringe. 3 Based on the diagram below, label solid, liquid or gas for (a) to (d). Conclusion: Particles in solid, liquid and gaseous states have different and . d a c b Chapter 2 Matter 41
Diffusion Rate in Three States of Matter When a freshener is sprayed at a corner in a room, the smell of the freshener can be detected a few metres away. The spread of this freshener’s smell is due to the diffusion of freshener particles from a high concentration area (region A) to a low concentration area (other regions). What do you know about diffusion? Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration. It can occur in solids, liquids and gases because there are spaces between the particles of solids, liquids and gases. A few factors influence the diffusion process, altering the rate and extent of diffusion. These factors are: • Temperature • The particle’s size • Area of interaction A room freshener will be diffused into the air allowing us to detect the scent. Let’s look at this example. People sitting in the living room may smell the freshly made food in the kitchen. This is due to air diffusion. Chemical compounds from the food reaches us as aroma. Since the escaping compounds travel more quickly when food is hot due to an increase in kinetic energy, we can smell the food from a distance away. In contrast, the kinetic energy of the aroma emitting from cold food is insufficient to go a wide distance, therefore we can only detect it from a close distance. Region A 42
When a tea bag is submerged in hot water, the process of diffusion begins. The highly concentrated tea particles travel through the beg into the lower concentration of particles in the water. This affects the colour of the water. The particles of tea move through the spaces between the particles of water quickly. Thus, the colourless water turns brown. You can find this substance in the laboratory. When you place this crystal in water, the water will turn purple. What is it? What is its medical use? Think About It When we light the incense stick, the smoke diffuses into the air and spreads throughout the room. It spreads because the particles move in all direction at the same time. As a result, its scent quickly spreads throughout its surroundings. Chapter 2 Matter 43
Problem statement What is the difference between the rate of diffusion in solids, liquids and gases? Hypothesis The rate of diffusion increases from to to . Manipulated variable Responding variable Constant variables Temperature and pressure Materials and apparatus Copper(II) sulphate crystals, agar, cork, distilled water, smoke, gas jars, lid, test tube and test tube rack Procedure A Diffusion in solids 1 Pour hot agar (5%) into a test tube until it is almost full. 2 Let the agar cool and solidify. 3 Place a piece of copper(II) sulphate crystal on top of the agar. Close the test tube with a cork and turn the test tube upside down. Agar Copper(II) sulphate crystal 4 Leave the test tube for two days and record your observation. B Diffusion in liquids 1 Fill a test tube with distilled water. 2 Then add copper(II) sulphate crystal into the test tube. Distilled water Copper(II) sulphate crystal 3 Leave the test tube for one hour and record your observation. C Diffusion of gases 1 Fill a gas jar with smoke. Then place a lid on it. 2 Invert another gas jar over it. Smoke Lid Gas jars 3 Remove the lid and observe the changes Experiment 1 Rate of diffusion in solids, liquids and gases 44
Observation Activity Observations A The entire agar turns as the particles of the copper(II) sulphate crystal diffuse into the agar. B The whole test tube of water turns as the particles of the copper(II) sulphate crystal diffuse into the water. C The smoke particles diffuse into the air in the inverted gas jar. Discussion 1 Explain your observation using space-time relationship. (a) Activity A: The rate of diffusion of copper(II) sulphate crystal in solids is because the spaces between the particles in solids are . (b) Activity B: The rate of diffusion of copper(II) sulphate crystal in liquids is because the spaces between the particles in liquids are . (c) Activity C: The rate of diffusion of smoke in gases is because the spaces between the particles in gases are . 2 What is diffusion? 3 (a) Predict the rate of diffusion of copper(II) sulphate crystals in hot water compared to water at room temperature. Does it decrease, increase or remain the same? (b) Give a reason for your answer in 3(a). Conclusion Is the hypothesis accepted? Write down your conclusion. Chapter 2 Matter 45
Changes of State Matter can change from one state to another when it is heated or cooled, that is with a change in temperature. Heat energy is absorbed or released by its particles causing a change in the energy of the particles. As a result, a change in the state of matter occurs. Melting When a solid is heated, heat energy is absorbed by its particles. The heat energy is then converted to kinetic energy and the particles begin to vibrate faster. At the melting point (the temperature when a solid turns into liquid), the particles gain enough energy to overcome the forces of attraction between them and break away from their fixed positions. The particles now move freely and randomly. Hence, the solid turns into a liquid. Freezing When a liquid is cooled, heat energy is released by its particles. The particles lose kinetic energy and begin to move slowly and come closer together. When the particles no longer have enough energy to move freely, the forces of attraction between the particles will pull the particles together to settle in a fixed position. At the freezing point (the temperature when a liquid solidified into solid), the particles can only vibrate about their fixed positions and a solid is formed. Sublimation When solids such as ammonium chloride, iodine crystals, solid carbon dioxide (dry ice) are heated, the particles at the surface of the solid gain enough energy to break away and escape as a gas. When these solids change directly to its gaseous state without going through the liquid state / melting process, the process of sublimation has occurred. Solid 46
Condensation When a gas cools down, heat energy is released by its particles. The particles lose kinetic energy and begin to move more slowly. The forces of attraction between the particles will pull the particles closer to each other. At the condensation point (the temperature when a gas liquefied into liquid), the gas will turn into a liquid. Boiling When a liquid is heated, heat energy is absorbed by its particles. The particles gain heat energy and begin to move faster as the temperature rises. The collisions also occur more frequently. At the boiling point (the temperature when a liquid boils and turns into a gas), the particles gain enough kinetic energy to overcome the forces of attraction between them. The particles now spread apart and move about rapidly in all directions. Hence, the liquid turns into a gas. Evaporation A liquid can also change to a gas through evaporation. When a liquid absorbs heat at any temperature below its boiling point, it changes into gas. It occurs slowly and continuously only on the surface of the liquid where the particles have gained enough kinetic energy to overcome the forces of attraction to escape from the surface of the liquid. Liquid Gas Deposition When a gas is cooled, heat energy is released by its particles. The particles lose kinetic energy and begin to move more slowly. The forces of attraction between the particles will pull the particles closer to each other. In deposition, a substance changes directly from a gas to a solid phase without going through the liquid state. Some examples of this process are the formation of snow from water vapour and the making of dry ice using carbon dioxide. Chapter 2 Matter 47
The temperature of a matter increases when it is heated and decreases when it is cooled. However, the temperature remains constant during a change of state, that is during melting (solid to liquid), boiling (liquid to gas), freezing (liquid to solid) and condensation (gas to liquid). During melting and boiling, the kinetic energy gained by the particles is used to overcome the forces of attraction between the particles. The temperature of the solid or liquid remains the same. On the other hand, during condensation and freezing, the particles release energy to the surroundings, thus enabling them to be pulled closer together. The temperature of the liquid or gas remains the same. Temperature (°C) Boiling point Melting point Ice Water Ice + Water Steam Time (min) Water + C Steam B D A Problem statement Does temperature remain constant during the changes of state? A Temperature during the melting of ice Hypothesis The temperature of ice remains constant during the melting process. Manipulated variable Responding variable Constant variable Quantity of ice cubes Materials and apparatus Ice cubes, thermometer, beaker, Bunsen burner, tripod stand, glass rod and wire gauze Procedure 1 Set up the apparatus as shown in the diagram below. Ice cube Thermometer Glass rod Wire gauze Bunsen burner Experiment 2 Temperature remains constant during changes of state At point A to B, the temperature of the mix of ice and water remains the same, at the melting point. At point C to D, the temperature of the mix of water and steam remains the same, at the boiling point. The change of temperature during the heating of ice 48
2 Record the initial temperature of the ice cubes. 3 Heat the beaker slowly and stir the ice cubes using the glass rod. 4 Observe and record the temperature every three minutes until the temperature remains constant. B Temperature during the boiling of water Hypothesis The temperature of water remains constant during the boiling process. Manipulated variable Responding variable Constant variable Volume of water Materials and apparatus Distilled water, thermometer, flat-bottomed flask, Bunsen burner, tripod stand, glass tube, rubber stopper, retort stand and wire gauze Procedure 1 Measure 100 ml of distilled water and pour it into a flat-bottomed flask. 2 Set up the apparatus as shown in the diagram. Thermometer 100 ml distilled water Bunsen burner Glass tube Flat-bottomed flask 3 Heat the distilled water until its temperature reaches 60°C. Then, record the temperature every three minutes until the temperature remains constant. Result Time (minutes) Temperature (°C) Activity A Activity B Beginning of experiment 3 6 9 12 15 Chapter 2 Matter 49
Discussion 1 (a) Plot a graph of temperature against time for activity A. (b) What happens to the ice cubes as the temperature remained constant? (c) What is the melting point of ice? 2 (a) Plot a graph of temperature against time for activity B. (b) What happens to the water as the temperature remained constant? (c) What is the boiling point of water? 3 Why does the temperature remain constant during the change of state of matter? 4 Draw the changes in the arrangement of water particles before and after reaching the boiling point. Conclusion Is the hypothesis accepted? Write down your conclusion. During the changes of state, only the arrangement and movement of the particles in a matter will change, while the quantity of the particles in a matter remains unchanged. In this case, the mass of a matter remains constant during the changes of state. This is called conservation of mass. Problem statement Does the mass of the matter remain constant during a change of state? A Melting of ice Hypothesis Mass remains constant during the melting of ice. Manipulated variable Responding variable Constant variable Temperature Materials and apparatus Beaker, lever balance and ice cubes Procedure 1 Place the ice cubes in an empty beaker. 2 Weigh and record the initial mass of the beaker filled with ice cubes. Lever balance Ice cube Beaker 3 Allow all the ice to melt into water. Weigh and record the final mass of the beaker with water. Experiment 3 Mass remains constant during changes of state 50
B Dissolution of sugar in water Hypothesis The mass of the sugar remains constant after dissolving in water. Manipulated variable Responding variable Constant variable Temperature / Volume of water Materials and apparatus Distilled water, sugar, beaker, glass rod and lever balance Procedure 1 Prepare a beaker filled with 200 ml of distilled water. 2 Add three spatulas of sugar into the beaker and record the mass. Lever balance 200 ml of water + 3 spatulas of sugar Beaker Scale 3 Stir the solution until the sugar is completely dissolved and record the mass. C Expansion by heat Hypothesis The mass of the metal ball remains constant when heated. Manipulated variable Responding variable Constant variable Heating time Materials and apparatus Metal ball, ring, Bunsen burner, triple beam balance and tongs Procedure 1 Weigh and record the initial mass of the metal ball with its ring. 2 Set up the apparatus as shown in the diagram and heat the metal ball for three minutes. Bunsen burner Metal ball Ring 3 Weigh the metal ball with its ring when it is still hot and record its final mass. Chapter 2 Matter 51
Result Record your result. Activity Mass (g) Beginning of experiment End of experiment A B C Discussion 1 (a) What happened to the mass at the beginning and the end of the experiment in activity A, B and C? Has the mass decreased, increased or remained the same? (b) Give a reason for your answer in 1(a). 2 Which of the following substances will have the same mass after going through changes? Why? (a) A piece of paper is crumpled up (b A potato is diced up (c) Burning of iron powder Conclusion Is the hypothesis accepted? Write down your conclusion. Dew is formed through condensation of water vapour in the air. (Gas ➔ liquid) Wet clothes dry under the sun when water evaporates to become water vapour. (Liquid ➔ gas) Ice cream melts quickly on a hot day. (Solid ➔ liquid) You may or may not be aware that you have observed examples of state changes in your daily life. Consider some of the following examples. 52
After a hot shower, it is likely that you would not be able to see your reflection in the mirror. You have to wipe off the moisture from the mirror’s surface first. This is because condensation occurs when warm water vapour comes into contact with the cooler mirror surface. Have you ever wondered why we can see someone’s breath when he is out in very cold weather? Water exists on Earth in all three states of matter: solid, liquid and gas. Liquid water can be found in the oceans, rivers, lakes and streams, as well as in the soil and underground. Glaciers and snow all contain solid ice. The Earth’s atmosphere contains water vapour which is a gas. Let’s study how water exists in different states in the water cycle. When the warm and moist vapour of his breath comes into contact with the cold and humid air, it condenses into tiny water droplets. We can see these droplets take on a cloud-like appearance. Water cycle Resource Chapter 2 Matter 53
Snow melts into water as a result of the Sun’s heat. This water flows into oceans, lakes and rivers. Water from melting snow and ice also enters the soil, providing water for plants and turning into the groundwater we drink. How does water enter the atmosphere? The Sun’s heat causes water to evaporate from oceans, lakes and rivers. Evaporation occurs when liquid water on Earth’s surface turns into water vapour in our atmosphere. Warm water vapour rises through the atmosphere of the Earth. As it rises higher and higher in the atmosphere, the cool air of the atmosphere causes the water vapour to turn back into liquid water, resulting in clouds. This is known as condensation. When a cloud becomes occupied with liquid water, it falls to the ground as rain or snow. Rain and snow then fill lakes and rivers, and the cycle begins again. 2.2 Physical and Chemical Changes Each substance has unique physical and chemical characteristics. Physical characteristics such as melting point, boiling point, mass, density, solubility and heat conductivity are characteristics that can be observed. Our five senses and scientific instruments have the capacity to detect them. Chemical characteristics such as flammability and rusting are characteristics that change the chemical nature of a substance. This can be observed when a substance combines with other substances or changes into a new substance during a chemical reaction. In the changes of the states of matter that you have learned, no new substance is formed. The particles are of the same kind even though the arrangement and movement of the particles have changed. Therefore, the changes of state affect the physical characteristics of matter, while the chemical characteristics are unaffected. Ice remains as water even after it freezes to a solid state. No new substance is created and the particles are the same before and after the process. Similarly, the melting of a candle as the candle burns does not result in the formation of new products. The materials that make up the candle remain the same. These are examples of physical changes. This means a substance’s composition is unaffected by changes to its physical characteristics. The melting of a candle is a physical change but the burning of a candle is a chemical change. Why? Think About It 54
Chemical changes involve chemical reactions and the creation of new products. It is an irreversible change. How do we know if a chemical change has happened? If you notice a substance change its colour or its temperature, produce bubbles, or a new product is formed, then chemical changes have happened. When wood is burning, the wood reacts with oxygen in the air to transform into carbon dioxide, water vapour and ash. Wood burning is a chemical change, it is not reversible. Rust is a coating that occurs on the surface of iron (e.g. a padlock). Rust and iron are not the same. Rusting on the padlock is a chemical change because a new substance called ‘iron oxide’ is formed during this process. Is it considered physical change if we mix different types of nuts together? Remember that a substance’s physical change is a change in its physical appearance, but its chemical identity remains unchanged. Crushing a can merely alters the shape of the can. The chemical identity remains unchanged. Cutting a tomato into smaller pieces only changes the size of the tomato, not its composition Chapter 2 Matter 55
Burning fireworks results in a chemical change. Fireworks release sound, heat and light energy as they explode. As a result, energy changes are involved in chemical changes. What are the other examples of physical and chemical changes of matter in your daily life? Think About It When you dissolve a vitamin C effervescent tablet in water, gas bubbles form and the water turns orange, indicating that a chemical change has occurred. Activity 3 Aim: To differentiate between the physical and chemical changes in matter Materials and apparatus: Distilled water, sodium chloride powder, iron nail, test tube, beaker, glass rod and spatula Procedure: Activity A 1 Add one spatula of sodium chloride powder to 50 ml of water and stir with a glass rod. Spatula Water Stir Sodium chloride powder 2 Record your observation. Physical and chemical changes in matter 56
Activity B 1 Clean the iron nail with sandpaper and put it into a test tube. Distilled water Iron nail 2 Add 10 ml of distilled water in the test tube as shown in the diagram. 3 Record your observation after seven days. Observations: Activity Observation Type of changes A The sodium chloride powder in water. B The iron nail . Discussion: 1 Give inferences for your observations in Activity A and B. 2 How does iron rust? Iron rusts when it is exposed to and . 3 Complete the table below by identifying the changes in the situations listed. Situation Physical change / Chemical change (a) Bromine exists as liquid at room temperature (b) Wood rots when exposed to rain (c) Iron(III) oxide reacts with strong acids (d) Water boils at 100°C (e) Nickel sticks to a magnet (f) Salts dissolve in water (g) Paper burns when it is lit Conclusion: What is the difference between physical and chemical change? Chapter 2 Matter 57
2.3 Density You are given a Styrofoam cup and a ceramic cup of the same size, which cup is more dense? How do you determine their densities? The density of a material is the amount of mass that fits into a given volume. Study the diagram below, we have two materials of the same volume. Which diagram shows the material tightly packed? Two materials of the same volume with different mass We say that the tightly-packed material has a higher mass and a higher density. We can compare the densities of different objects which have the same volume by comparing their masses. Density of a substance is the mass per unit volume of the substance. The SI unit for density is kilogram per cubic metre (kg/m3 or kg m–3). Another unit that is often used is gram per cubic centimetre (g/cm3 or g cm–3). In Chapter 1, you have learned the measuring tools for mass and volume, this means that if we know the mass and volume of a substance, we can calculate its density by using the formula: A pure substance has the same density when measured under the same condition. For example, pure gold has the density of 19.3 g cm-3. Any gold with the density of higher or lower than this value is impure. Using this idea, Archimedes proved that the crown of King Hiero II was not made of pure gold. Science Facts Density (g cm–3) = Mass (g) Volume (cm3 ) Example 1 A block of lead measuring 10 cm of length, 5 cm of width and 2 cm of height has a mass of 1130 g. What is the density of the lead block? Solution: Density of lead block = 1130 g 10 cm 3 5 cm 3 2 cm = 11.3 g cm-3 58
Activity 4 1 A list of materials is given as below. Air, petrol, rubber, glass, diamond, gold, aluminium, seawater, ice, water, platinum, iron 2 Find out the density of each of the materials from books or the Internet. 3 Based on the information obtained, arrange the density of the materials in increasing order. 4 Identify each of the materials as solid, liquid or gas. 5 Which state of matter has the lowest density? 6 Which state of matter has the highest density in general? Densities of different materials Relationship between Density and Floating or Sinking Take a look at the diagram below. Do you notice that the material with the highest density is positioned at the lowest part of the measuring cylinder? Petrol (0.8 g cm-3) Cork (0.24 g cm-3) Wood (0.9 g cm-3) Glass (2.5 g cm-3) Water (1.0 g cm-3) Mercury (13.6 g cm-3) Arrangement of materials with different densities in a measuring cylinder A material that is less dense than a liquid will float on the liquid while a material that is denser than a liquid will sink in the liquid. This is how the concept of density explains why some materials float, while others sink. Whether a material floats or sinks in a liquid is determined by its density. Let’s explore some examples on how this concept is applied. You may be wondering why, when oil and water mix, they do not dissolve in one another. Oil always floats on top of the water. This is because oil is less dense than water. Oil floats on top of the water. Chapter 2 Matter 59
Activity 5 1 Prepare two raw eggs of similar size and weight, two glasses, water and salt. 2 Fill one glass about ¾ full of water. Predict whether the egg will sink or float in the water. 3 Place an egg carefully in water. Does it sink or float in water? Why? 4 Fill another glass with the same amount of water. Then add 2 tablespoons of salt and stir until it has completely dissolved. 5 Predict whether the egg will sink or float in the salt water. 6 Place the other egg in the salt water. Does it sink or float? Why? Sink or float The density of the water in the Dead Sea is so high that we can easily float on it. Do you know why? Think About It You might believe that all heavy objects sink in water. Is this true? No! All ships would sink into the ocean if this was the case. Density is defined as mass per unit volume, so a bigger volume and smaller mass will result in lesser density. A ship is designed and constructed to be large with a large volume of air in it, and built with different materials so that it has a lower average density. A density lower than water will allow the ship to float on water. An upward force known as upthrust is exerted on an object, when it is partially or completely submerged in a liquid, and pushes it upward. The object floats on the liquid if this force is equal to its weight. When a ship is overloaded with lots of containers, its weight exceeds the upthrust and causes it to sink. Science Facts 60
Activity 6 Aim: To study the relationship between the mass and density of various solids that have the same volume Materials and apparatus: Cubes of copper, iron, glass, cork, lead and digital balance Procedure: 1 Prepare five types of cubes which have the same volumes as the diagram below. Copper Iron Glass Cork Lead 2 Weigh each cube and calculate its density by using the following formula: Density = Mass Volume Note: Volume = length 3 width 3 height 3 Record the results in the table. Result: Cube Volume (cm3) Mass (g) Density (g cm–3) Copper Iron Glass Cork Lead Discussion: 1 Define density. 2 What is the relationship between mass and density if the volume is the same? 3 Arrange the solids above based on their densities in an ascending order. 4 A marble has a density of 2.3 g cm-3 and a volume of 8 cm3 . Calculate the mass of the marble. 5 Complete the statements below to explain the application of the concepts of density in a submarine. Sea water is pumped into the ballast tank causing the submarine to be denser and in the water. Sea water is pumped out from the ballast tank causing the submarine to be less dense and on the surface of sea water. Conclusion: Density when the mass increases for various types of solid materials that have the same . Relationship between mass and density of various solids that have the same volume Chapter 2 Matter 61
Activity 7 Aim: To determine the density of solids using the water displacement method Materials and apparatus: A stone, iron cube, thread, water, digital balance and measuring cylinder Procedure: 1 Weigh a stone using a digital balance and record its mass. 2 Pour 50 ml of water into a measuring cylinder. Record the initial volume of water. 3 Tie the stone with a thread and lower it into the water as shown in the diagram. Record the final volume of water. Stone Thread Water 4 Determine the volume of the stone. Then, calculate the density of the stone. 5 Repeat steps 1 to 4 with an iron cube. Result: Mass of object (g) Initial volume of water (cm3) Final volume of water (cm3) Volume of object (cm3) Density (g cm-3) Stone Iron cube Discussion: 1 What is the formula of density? 2 Water displacement method is a method that is used to measure the volume of an object. Conclusion: Write down your conclusion. Determine the density of solids using water displacement method 62
1 Matter is anything that has and volume. It is made up of tiny and particles that are completely separate from one another with spaces between them. 2 The three states of matter are solid, and gas. 3 The particles in solids are packed closely together in a fixed and pattern. They cannot move around and can only in their fixed position. Solids be compressed because the particles are close together and have very little space to move into. They cannot flow because the particles are closely packed, thus they have a fixed . 4 The particles in liquids are still quite close together but are arranged without a fixed pattern. They are able to move and collide with one another. Liquids be compressed to any extent because the particles are still arranged quite closely and have little space to move into. They flow because the particles are free to move around, thus they take the shape of their container. 5 The particles in gases are from one another. They are able to move freely and randomly in all at high speeds. Gases can be compressed because the particles are far apart and have large spaces to move into. They flow much more than a liquid because the particles move randomly in all directions and spread out as far as they can to occupy the entire space of the container quickly. Thus, they take the shape of their container. 6 Matter can change from one state to another when heat energy is absorbed or by its particles. 7 Melting, freezing, , boiling, , condensation and deposition are processes involved in the changes of state. 8 When a substance’s composition is unaffected by changes to its physical characteristics, it is called changes while changes involve chemical reactions and the creation of new products. 9 The mass per unit volume of a substance is called . Its SI unit is per cubic metre. 10 A material that is less dense than a liquid will on the liquid while a material that is denser than a liquid will in the liquid. RECALL Fill in the missing words. Chapter 2 Matter 63
THINKING CAP Put on your 1 The following table shows the melting points of four substances. Substance Melting point (°C) Nitrogen –210 Mercury –38.8 Iron 1538 Magnesium 650 Which substance has the highest melting point? Explain how the melting point is related to its force of attraction. 2 73.6 cm3 of water freezes into ice with a density of 0.92 g cm-3. What is the volume of the ice? (Note: The mass of ice remains the same when changing state from solid to liquid and vice versa.) 3 How is it possible to say that a fruit’s ripening causes a chemical change? 64
Project Activity objective: Understand the concept of density that allows objects to float or sink in water Problem statement: The object’s ability to float or sink depends on their density. This can be demonstrated by using a submarine model. Concept applied: Density and water displacement method Action plan: 1 Identify various objects that can float or sink in water. 2 Test the ability of objects to float or sink in water. 3 Determine the materials to be used and calculate the total cost of the material. Procedure: 1 Divide the class into groups of four. 2 Each group will brainstorm the concept of density and water displacement method. Search information on materials that float and sink, and on the design of a submarine model from the Internet and books. 3 Identify various objects that can float and sink in water. 4 Test the abilities of objects to float and sink in water. 5 Design a submarine model using the objects identified and tested. 6 Build the submarine model. Discuss how you can make it float and sink. Test it. 7 Redesign and rebuild the model, if necessary. Presentation: 1 Demonstrate to the class how the submarine model can float and sink. Share with the class your experience of designing and building the model. 2 Submit a report that include steps 2 to 7 in the procedure. Build a Submarine Model Chapter 2 Matter 65
When the iron is turned on, the temperature increases gradually until it reaches the point where it may be used to iron clothes. We can feel the warmth of the clothes when we iron them. How does the iron’s heat get transferred to the clothing? Are there any safety measures that can automatically switch off the electricity to the iron if we keep it on for a long time? Temperature and Heat CHAPTER 3 What will you learn? State different temperature scales Describe the various types of thermometers Explain how expansion and contraction of matter can be applied in daily life Define heat capacity, specific heat capacity and specific latent heat of fusion and vaporisation Perform calculation involving heat capacity, specific heat capacity and specific latent heat of a substance Explain the ways of heat transfer Differentiate between heat conductors and heat insulators Explain how living organisms regulate their body temperature
3.1 Temperature and Scale Temperature is a measurement of how hot or cold an object is. The thermometer is the tool used to measure temperature. Temperature is measured in Celsius, Fahrenheit, Kelvin or less commonly Réaumur. Temperature Scales We must have a scale with numbers on a thermometer before using it. The temperature scale must be defined. A temperature scale is a way to measure temperature relative to a beginning point (zero) and a unit of measurement. The temperature scale is usually obtained by choosing two temperatures known as fixed points. There are four types of scales which are the Fahrenheit scale, Réaumur scale, Celsius scale and Kelvin scale. TEMPERATURE SCALE TIMELINE The Fahrenheit Scale Daniel Gabriel Fahrenheit, a German physicist and engineer, developed the Fahrenheit scale as a method for measuring temperature. The melting point of ice, which is 32°F, and the boiling point of water, which is 212°F, are used as standards on the Fahrenheit temperature scale. The interval between these two temperatures (212°F and 32°F) is divided into 180 parts, known as degrees Fahrenheit. The Réaumur Scale This is a temperature scale named after René Antoine Ferchault de Réaumur for which the freezing and boiling points of water are defined as 0°R and 80°R respectively. The Celsius Scale In the Celsius scale, the two fixed points are melting point (0°C) of ice and boiling point (100°C) of water. Both temperatures are determined at atmospheric pressure. The Celsius scale was proposed by the Swedish astronomer Anders Celsius. The interval between these freezing and boiling points is divided into 100 equal parts, called degrees Celsius. The Kelvin Scale Kelvin is the base unit of temperature in the International System of Units (SI) and has the unit symbol K. By convention, –273.15°C is used to represent absolute zero on the Kelvin scale. This is the lowest possible temperature at which there is no movement between the particles that make up matter. On the Kelvin scale, the melting point of ice (273.15 K) and the boiling point of water (373.15 K) are used as references. The Kelvin scale divides the range between these two temperatures (273.15 K and 373.15 K) into 100 equal parts. It should be noted that one Kelvin is equivalent to one degree Celsius. 1724 1730 1743 1848 Chapter 3 Temperature and Heat 67
The Fahrenheit, Réaumur, Celsius and Kelvin scales Based on the four scales, their units can be converted from one to another. The following conversion is used to find the temperature in 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 3.2 Thermometers There are several types of thermometers that have their respective functions. In general, thermometers must be affordable, simple to use, safe, sensitive and able to measure a wide range of temperatures in order to be effective. The most common thermometer for measuring temperature is the liquid-inglass thermometer. Liquid-in-glass Thermometers The liquid-in-glass thermometer works using the principle of expansion and contraction of liquid when the temperature increases and decreases. Liquid expansion and contraction occur in the capillary tube. The bulb holds a liquid such as alcohol or mercury. When there is an increase in heat, the liquid inside the bulb expands, pushing up into the tube. The temperature can be read from the scale marked on the tube. Mercury Thermometers In a mercury thermometer, the capillary tube is filled with mercury, and the tube is labelled with a standard temperature scale. The mercury expands and contracts as the temperature changes, allowing the temperature to be read from the scale. The temperatures of the body, liquid and vapour can Capillary tube Bulb 212°F 32°F –40°F Boiling point of water Freezing point of water 180 Fahrenheit degrees Fahrenheit 100°C 0°C –40°C 100 Celsius degrees Celsius 373.15 K 273.15 K 233.15 K 100 Kelvins Kelvin 80°R 0°R –32°R 80 Réaumur degrees Réaumur Mercury thermometer 68
all be determined with mercury thermometers. Mercury is used in thermometers because it conducts heat well, is easy to see because it is reflective and this allows the thermometer reading to be determined more easily. Alcohol Thermometers Due to mercury’s toxicity, it has been replaced by alcohol. Alcohol thermometers have functions similar to mercury thermometers. The most popular option is made of ethanol since it is inexpensive and presents a relatively low risk of leakage. Since it is transparent, the liquid is made more visible by the addition of dye. Types of Thermometers Various sizes and shapes of thermometers are available depending on the requirements of the user. Thermometers are divided into two categories based on their functions, clinical thermometers and laboratory thermometers. People use clinical thermometers to check their body temperatures. Digital thermometers, electronic ear thermometers and forehead thermometers are a few examples. In laboratories and during the testing of some samples, laboratory thermometers are used to gauge the temperatures of objects as well as their boiling and freezing points. In addition, maximum-minimum thermometers let meteorologists determine the highest and lowest temperatures at any given location. Examples of laboratory thermometers are pyrometer thermometer and probe thermometer. Digital Thermometers Traditional thermometers have been replaced by more modern thermometers called digital thermometers. These thermometers are regarded as the most accurate when used properly. Digital thermometers provide temperature readings on a display screen and through an electronic circuit. Readings can be obtained from the rectum, under the tongue or under the armpit. Additionally, they are inexpensive, widely accessible and easy to use. Electronic Ear Thermometers Electronic ear thermometers measure body temperature from inside the ear canal using infrared technology. They gauge temperature using the tympanic membrane in the ear. Children benefit greatly from this kind of thermometer as these thermometers can immediately record body temperatures. However, they are pricey and might not be able to detect the body temperature precisely if the thermometer is not inserted correctly. Digital thermometer Electronic ear thermometer Chapter 3 Temperature and Heat 69
Forehead Thermometers Forehead thermometers read temperature using infrared technology. The superficial temporal artery, a branch of the carotid artery, is monitored using infrared sensors. There is no physical contact when taking temperature readings with a forehead thermometer. However, they are not as precise as standard digital thermometers. Pyrometer Thermometers Pyrometer thermometers are remote-sensing tools that allow distance temperature measurement. Typically, the thermal radiation emitted by these thermometers is used to determine the object’s temperature. The fact that these thermometers do not even require you to touch anything is one of their main advantages. Therefore, pyrometers are perfect for keeping track of the temperatures of moving objects or surfaces. They can also be used to measure the temperatures of objects that are too hot to touch or have complex structures. They are employed to gauge temperatures greater than 2000°C. These modern thermometers are widely used to check people’s temperatures in offices, malls, train stations and other public places, particularly during the Covid-19 pandemic. A technician uses a pyrometer thermometer to check the heat of a condensing unit. 70
Probe Thermometers The probe thermometer is one of the most popular types of thermometers. These thermometers are ideal for conducting cleanliness tests in food sector retail stores and laboratories due to their rapid temperature readings. Typically, probe thermometers have a pointed tip that facilitates immersion and penetration. The two types of probes that are available are fixed probe and wired probe thermometers. 3.3 Expansion and Contraction of Matter Most matter expands when heated and contracts when cooled. An example of the effect of heat is thin glass cracking when hot water is poured onto it. The increase in the size of objects when they are hot is called expansion. The decrease in their sizes when they are cooled is called contraction. Expansion and Contraction of Solids The atoms or molecules in a solid vibrate at all temperatures. As its temperature increases, the atoms vibrate more vigorously and these vibrations push the atoms further apart. The volume of the solid increases and the solid expands. When the solid is cooled, the atoms vibrate less vigorously and they become closer together. The volume of the solid decreases and the solid contracts. We can apply the principle of expansion and contraction of matter in making instruments that are useful in our daily life. Bimetallic Strip in a Fire Alarm An automatic fire alarm uses a bimetallic strip to switch on the electric bell when there is a fire. The heat from the fire causes the bimetallic strip to bend towards the contact point. Arrangement of particles in a solid Heated Cooled Cold Hot A probe thermometer is generally used to instantly measure the temperature of food and liquid samples. Chapter 3 Temperature and Heat 71
When the bending strip touches the contact point to complete the circuit, the fire alarm rings. Bimetallic Strip as a Thermostat The bimetallic strip is also used as a thermostat in an electric iron for controlling and maintaining temperature. As temperature rises, the bimetallic strip bends away from the contact point and cuts off the current. When the bimetallic strip cools down, contact is made again and current flows to heat up the iron. The bimetallic strip is made by combining two different metals with different expansion and contraction rates. Science Facts Iron and copper are joined together and fixed side by side. The bimetallic strip will bend when heated, with iron within and copper outside. This shows that at the same temperature, copper expands more than iron. The bimetallic strip bends with copper inside and iron outside when cooled to room temperature. This shows that copper contracts more than iron does. An automatic fire alarm Bimetallic strip Brass Iron Batteries Contact point Electric bell Thermostat in an electric iron Bimetallic strip Temperature control Heating coil Contact point To power supply The bimetallic strip bends upwards Contact point Copper Copper Copper heated cooled Iron Iron Iron Resource 72
Electric Cables Electric transmission cable and the cables of cable cars sag on a hot day and tighten during a cold night. Therefore, allowances have to be made for the expansion and contraction of the cables. Electric cables sag in hot weather and tighten during a cold night. Bridges and railroad tracks have expansion joints to allow them to freely expand and contract with the temperature changes. Concrete Road Bridges are typically made of concrete and steel. These components expand with higher temperatures and contract at lower temperatures. Thus, expansion joints are needed to provide gaps in the bridges. Expansion joints are basically gaps in the bridge that allow the bridge to expand and contract. Without these gaps, the concrete road surfaces may crack due to the forces that build up when the concrete expands during the hot weather. Railroad Tracks When laying railroad tracks, gaps have to be left between successive lengths of rail to allow for expansion on hot days. Without the gaps, the track buckles and this affects the safety of the trains. Expansion joint Chapter 3 Temperature and Heat 73
Expansion and Contraction of Liquids When a liquid is heated, the molecules of the liquid gain more energy and move more vigorously. This allows them to have greater freedom to move. Thus, the liquid expands. Arrangement of particles in a liquid At lower temperatures, the molecules of the liquid have less energy and move closer to each other. This causes the volume of the liquid to decrease and the liquid contracts. This principle is applied in the thermometer we use. Mercury in a Thermometer Mercury is a liquid metal that can expand and contract when there is a change in temperature. This makes it suitable for temperature measurement and it is used in a thermometer. How does the thermometer show the reading of temperature when the bulb of the thermometer comes in contact with a hot object? Explain in terms of expansion and contraction of liquid how this happens. Think About It Heated Cooled Cold Hot (a) Mercury in a laboratory thermometer (b) Mercury in a clinical thermometer -10 0 10 20 30 40 50 60 70 80 90 100 110 120 Mercury Bulb Constriction Capillary tube Linear scale -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Mercury Linear scale Capillary tube Bulb (a) (b) 74
Steam or hot water vapour rise in the air because it expands and becomes less dense than the surrounding air. Expansion and Contraction of Gases The molecules of a gas are farther apart compared with the molecules in a solid and liquid. Gas molecules move at high speeds in all directions. If a gas is confined in an expandable container, the volume of the gas will increase with increasing temperature. The volume will decrease as the temperature drops. Arrangement of particles in a gas When the gas is heated, the molecules become more energetic, move faster and are farther apart. This causes the volume of the gas to increase and expansion is said to have occurred. At a lower temperature, the molecules move very much slower due to less energy. They are closer together, causing the volume to decrease and contraction occurs. Let us take a look at the examples below. What will happen if you leave an inflated balloon in the sun for a while? As the air inside absorbs heat from the surroundings, the balloon will enlarge in size. What will happen if a bottle with an inflated balloon tied to the mouth of the bottle is submerged in ice-cold water? As the bottle cools, the air inside the bottle and balloon contracts, causing the balloon to shrink in size. These are the most visible examples of the expansion and contraction of air due to the change of temperatures. Hot-air Balloons Heat causes air to expand, which makes it less dense than the air around it. This causes the heated air to rise, causing steam and smoke to rise, hot air balloons to float, and other phenomena. Heated Cooled Cold Hot Chapter 3 Temperature and Heat 75
Activity 1 Aim: To study the effect of heat towards the expansion and contraction of solids, liquids and gases A Expansion and contraction of solids Materials and apparatus: Metal ball, metal ring, Bunsen burner, iron bar and gauge (i) Procedure: 1 Drop a metal ball through a ring as shown in the diagram. Ring Holder Metal ball 2 Take out the ball through the ring and heat the ball over a Bunsen flame for a few minutes. Then, drop it through the ring again. What do you observe? 3 Allow the ball to cool down to room temperature and drop it through the ring again. What do you observe? Observation: Write down what you observe. Discussion: 1 Why can’t the metal ball pass through the ring after it is heated? 2 Why can the metal ball pass through the ring after it is cooled down? (ii) Procedure: 1 Place the iron bar in the gauge. Does the iron bar fit in the gauge? Gauge Iron bar 2 Heat the iron bar for a few minutes. Then stop the heating and repeat step 1. 3 When the iron bar is cooled, repeat step 1. Observation: (a) Before heating, the iron bar in the gauge. After heating, it in the gauge. Inference: This is because the iron bar when hot. (b) When cooled, the iron bar in the gauge. Inference: This is because it has to its initial length. Conclusion: Write down your conclusion. Expansion and contraction of solids, liquids and gases 76
B Expansion and contraction of liquids Materials and apparatus: Thermometer, beakers, ice, cold water and hot water (i) Procedure: 1 Rub both of your palms together until your feel the warmth of your palms. 2 Hold a thermometer bulb with both palms and observe the mercury level in the thermometer. Laboratory thermometer 3 Then, place the thermometer in a beaker filled with ice and observe the mercury level in the thermometer. Ice Laboratory thermometer Observation: (a) When both palms hold the thermometer bulb after rubbing, the mercury level in the thermometer . Inference: This is because heat from the palms after rubbing, causes the mercury to . (b) When the thermometer is placed in a beaker filled with ice, the mercury level in the thermometer . Inference: This is because the mercury when it is cooled. (ii) Procedure: 1 Place a thermometer in a beaker of hot water as shown in the diagram. Observe the movement of the mercury column. Chapter 3 Temperature and Heat 77