Thermometer Beaker Hot water 2 Take out the thermometer and place cold water in a beaker. Then place the thermometer again in the beaker. Observe the movement of the mercury column again. Observation: Write down what you observe. Discussion: How does the rise or fall of the mercury column relate to its volume? Conclusion: Write down your conclusion. C Expansion and contraction of gases Materials and apparatus: Basin, conical flask, balloon, hot water, ice, glass tube and coloured liquid droplet (i) Procedure: 1 Set up the apparatus as shown in the diagram. Glass tube Coloured liquid droplet Hot water 2 Pour hot water into the basin and leave the apparatus for 5 minutes. Observe what happens to the coloured liquid droplet. 3 Replace the hot water with ice. What happens to the coloured liquid droplet? Observation: (a) The coloured liquid droplet moves when the flask is placed in hot water. Inference: This is because the air in the flask when heated. (b) The coloured liquid droplet moves when the flask is placed in ice. Inference: This is because the air in the flask when it is cooled. Resource 78
(ii) Procedure: 1 Set up the apparatus as shown in the diagram. Balloon Hot water 2 Pour hot water into the basin and leave the apparatus for 5 minutes. Observe what happens. 3 Then, replace the hot water with ice and leave the apparatus for 5 minutes. Observe what happens. Observation: Write down what you observe. Discussion: 1 Based on your observation, why does the balloon’s size change when the apparatus is placed in hot water? 2 Based on your observation, why does the balloon’s size change when the apparatus is placed in ice? Conclusion: Write down your conclusion. 3.4 Heat Capacity Heat is a form of energy. An object becomes hot when it absorbs heat. Heat is measured in joules (J) and it is transferred from a hot area to a cold area. The heat capacity, C of a substance is defined as the quantity of heat required to raise the temperature of the substance by 1°C or 1 K. The unit for heat capacity is J °C-1 or J K-1. It is expressed using the following equation: C = ( Q ) Q = C or where Q is the heat absorbed or released in joules (J) and is the temperature change in °C or K. Specific Heat Capacity Do you know why the body of a cooking pot is usually made of stainless steel? The specific heat capacity of steel is low. It heats up quickly when only a little heat is applied. When cooking food, this can save energy and time. The specific heat capacity, c of a substance is the amount of heat required to increase the temperature of 1 kg of the substance by 1°C. Different substances have different specific heat capacities. Its unit is J kg–1 °C–1. Take a look at the substances given in the table. Chapter 3 Temperature and Heat 79
Substance Specific heat capacity (J kg–1 °C–1) Substance Specific heat capacity (J kg–1 °C–1) Water 4200 Mercury 139 Copper 387 Gold 129 Glass 840 Iron 452 Water has a specific heat capacity of 4200 J kg–1 °C–1. In order to increase the temperature of 1 kg of water by 1°C, 4200 J of heat is needed. 25°C 1 kg water 4200 J heat 26°C 1 kg water 25°C 1 kg copper 387 J heat 26°C 1 kg copper Copper has a specific heat capacity of 387 J kg–1 °C–1. In order to increase the temperature of 1 kg of copper by 1°C, 387 J of heat is needed. Therefore, water needs almost 10 times more heat than copper of the same mass. Remember that heating substances with high specific heat capacities need a lot of heat energy and a longer time to heat up. They also need a longer time to cool down. For example, land heats up quicker than the sea. This is because the specific heat capacity of seawater is greater than that of land. More heat energy is needed to heat seawater up to reach the same temperature increment as land and so it takes longer. Seawater also takes a longer time to cool down. The quantity of heat gained or lost by an object is given as Q = mc where, Q = heat gained or lost in joules, J m = mass of the object in kg c = specific heat capacity in J kg–1 °C–1 θ = change in temperature in °C Example 1 How much energy must be provided to raise the temperature of 2 kg of water from 25ºC to 35ºC? Solution: Mass, m = 2 kg Specific heat capacity of water, c = 4200 J kg–1 ºC–1 Change in temperature, θ = 35 – 25 = 10ºC Q = mcθ = 2 3 4200 3 10 = 84 000 J 80
Example 2 1 kg of water with a temperature of 15ºC is placed in a refrigerator. What is its temperature after 29 400 J of heat has been removed from it? Solution: Mass, m = 1 kg Specific heat capacity of water, c = 4200 J kg–1 ºC–1 Heat removed, Q = 29 400 J Q = mcθ θ = 29 400 1 3 4200 = 7°C Final temperature = 15 – 7 = 8°C Specific Latent Heat When heat is continuously supplied to an object, the temperature of the object will increase. The temperature will increase to a point where it will remain constant. At this point, the object changes its state of matter. When we boil water, the temperature of the water will increase. When it reaches its boiling point of 100°C, the temperature will remain constant. The water changes into steam. The melting point of ice is 0°C. At this point, the ice is melting, turning into water. The temperature remains constant until all the ice has turned into water. The graph below illustrates the temperature changes of when ice is heated against time. Temperature Time 100°C Solid and liquid Liquid and gas Solid Liquid Gas Heat is absorbed by ice (solid) to raise its temperature Heat is absorded by the melting solid without a temperature change Heat is absorbed by the liquid to raise its temperature Heat is absorbed by the boiling liquid without any changes 0°C in temperature. Chapter 3 Temperature and Heat 81
When 1 kg of a substance is melting and boiling, it absorbs heat without an increase in the temperature. The heat absorbed is known as specific latent heat. Therefore, the specific latent heat of a substance is the amount of heat required to change the state of matter of 1 kg of the substance at a constant temperature. Its unit is J kg–1. During melting or boiling, the temperature of the substance does not change even though the heat is being absorbed by the substance. This is because the heat absorbed does not increase the kinetic energy of the particles but is used to overcome the force of attraction between the particles in order to change its state. The quantity of heat gained or lost when a substance changes its states is given by: Q = mL where, Q = heat gained or lost in joules, J m = mass of the object in kg L = specific latent heat in J kg–1 The specific latent heat of vaporisation of a substance is the amount of heat needed to change 1 kg of the substance from the liquid to the gaseous state without any change in temperature. Take a look at the diagram below. The specific latent heat of fusion of a substance is the amount of heat needed to change 1 kg of the substance from the solid to the liquid state without any change in temperature. Boiling at 100ºC Condensation at 100ºC Freezing at 0ºC Releases latent heat of vaporisation Releases latent heat of fusion Absorbs latent heat of vaporisation Melting at 0ºC Steam Water Ice Absorbs latent heat of fusion 82
The table below shows the specific latent heat of some substances. Substance Melting point (°C) Specific latent heat of fusion (J kg–1) Boiling point (°C) Specific latent heat of vaporisation (J kg–1) Water 0 3.36 3 105 100 2.26 3 106 Mercury –39 1.14 3 104 357 2.96 3 105 Gold 1063 6.28 3 104 2808 1.72 3 106 Copper 1083 2.07 3 105 2566 4.73 3 106 In general, the specific latent heat of vaporisation of a substance is greater than its specific latent heat of fusion because: • more energy is required to break the forces of attraction between liquid molecules in order to change into gaseous state. • extra energy is required to overcome the atmospheric pressure. • energy is used to overcome the surface tension of a liquid when its molecules change into the gaseous state. Example 3 How much energy is required to change 0.65 kg of ice into water at 0ºC? Solution: Mass, m = 0.65 kg Specific latent heat of fusion of water, L = 3.36 3 105 J kg-1 Heat needed, Q = mL = 0.65 3 3.36 3 105 = 2.18 3 105 J Example 4 6.78 3 106 J of heat energy is released from a mass of steam at 100°C to produce water at 100°C. What is the mass of water produced? Solution: Specific latent heat of vaporisation of water, L = 2.26 3 106 J kg-1 Heat released, Q = 6.78 3 106 J Q = mL m = Q L = 6.78 3 106 2.26 3 106 = 3 kg Chapter 3 Temperature and Heat 83
3.5 Heat Transfer Heat transfer, whether in the form of heating a kettle of water or in a natural phenomenon such as a thunderstorm, usually involves the transfer of energy from one location to another. Heat flows from a hotter object or place to a cooler object or place. Heat is transferred by three methods: (a) conduction through solids (b) convection by movement of the liquids and gases (c) radiation by emitting electromagnetic wave directly from a source The heat is transferred from the metallic pan to the food through conduction Conduction Conduction is the process of heat transfer from a hotter region to a colder region through solids, such as metals, when in contact. When a metallic pan is heated, the particles at the bottom part of the pan that received direct heat will vibrate more actively. These particles collide with their neighbouring particles and heat transfer takes place to the whole pan and then from the pan to the food in the pan. Most metals are good conductors of heat. Materials that cannot conduct heat such as glass and wood are insulators. Activity 2 Aim: To study how heat is transferred through solids by conduction Materials and apparatus: Iron rod, thumbtacks, Bunsen burner, wax and retort stand Procedure: 1 Stick a few thumbtacks to an iron rod using melted wax at fixed intervals. 2 Heat the rod with the Bunsen burner at position X. Bunsen burner Wooden block Thumbtack Wax Iron rod Retort stand X 3 Observe the thumbtacks to see the order in which they fall off. Observation: Write down what you observe. Discussion: Why is the wooden block used in this activity? Conclusion: Write down your conclusion. Heat transfer by conduction 84
The circulating movement of fluids that rises and falls continuously is known as the convection current. Activity 3 Aim: To study how heat is transferred by convection in liquid Materials and apparatus: 100 ml beaker, Bunsen burner, tripod stand, wire gauze and a small piece of potassium permanganate(VII) Procedure: 1 Fill a large beaker with water almost to the brim. 2 Using a glass rod, place a small piece of potassium permanganate(VII) crystal into the beaker. 3 Heat the water in the beaker slowly and record the direction of the flow of water. Observation: Draw what you observe. Discussion: Explain what happens when the water is heated. Conclusion: Write down your conclusion. Heat transfer by convection Warm air rises Cool air sinks Convection Convection is the process of heat transfer from a hotter region to a colder region by movement of a heated fluid, such as liquid or gas. When a fluid is heated, the hotter fluid expands, becomes less dense and rises whereas the colder fluid becomes denser and goes down replacing the empty space left by the hot fluid. Sea and land breezes develop as a result of convection. Land warms up more quickly than the sea during the day. The air above the land warms up, expands, becomes less dense and rises. The heated air rising above the land is subsequently replaced by cooler air from the sea. Sea breeze is created when cool air from the sea blows inland. At night, when the land loses heat more quickly than the sea, a land breeze develops. Can you describe the formation of a land breeze? Bunsen burner Beaker Water Potassium permanganate(VII) crystal Hot fluids will rise Cool fluids will go down Sea breeze during the day Chapter 3 Temperature and Heat 85
Radiation Radiation is the transfer of heat in the form of electromagnetic waves directly from a hot object. Why do you feel warm after standing in the sun for some time? How do you receive heat from the sun? Heat transfers from the Sun to the Earth by radiation in the form of electromagnetic waves, even though there is empty space (vacuum) in between the Sun and the Earth. Radiation does not require any medium to transfer heat, and this is different from convection or conduction which requires the movement of a medium from one place to another, or the collisions of particles in a medium. Activity 4 Aim: To study how heat can travel through a vacuum by radiation Materials and apparatus: Bell jar, bulb and vacuum pump Procedure: 1 Fix an electric bulb inside a bell jar as shown. 2 Remove the air in the bell jar using a vacuum pump. Then, switch on the bulb. 3 Feel the side of the bell jar by touching it with both hands. 4 Record your observation. Observation: Write down what you observe. Discussion: Why is it necessary to remove the air from the bell jar? Conclusion: Write down your conclusion. Heat transfer by radiation To switch Bell jar Bulb To vacuum pump Heat radiation travels in all directions. Shiny and bright surfaces emit relatively less heat radiation compared to that of dark, dull surfaces. Surfaces that efficiently emit heat radiation also efficiently absorb heat radiation. Science Facts 86
Alternatively, you can carry out the following activity using different materials from Activities 2 to 4. Activity 5 Aim: To show how heat is transferred Materials and apparatus: Copper / Metal rod, cardboard, candle, paper spiral, rice, metal spoon, toothpick, water, thread, stick, Bunsen burner, 250 ml beaker, tripod stand, wire gauze, retort stand with clamp Procedure: Activity A 1 Set up the apparatus as shown in the diagram. Toothpick Wax Retort stand Copper rod Cardboard A B C D E F Bunsen burner 2 Heat the copper rod for a few minutes. What happens to the toothpicks? 3 Record your observations. Activity B 1 Fill a beaker with water until it is nearly full. 2 Put some rice into the water. 3 Heat the water in the beaker by placing a burning Bunsen burner under the beaker in the middle position as shown in the diagram. Rice Hot water Wire gauze Tripod stand 4 Observe the movement of the rice when the water becomes hot. 5 Describe the movement of the rice. Methods of heat transfer Chapter 3 Temperature and Heat 87
Activity C 1 Set up the apparatus as shown in the diagram. Stick Candle Paper spiral Thread 2 Observe what happens to the paper spiral and record it. Activity D 1 Take a metal spoon and expose it to direct sunlight for 15 minutes. 2 Touch the spoon after 15 minutes. What do you feel? Observation: (a) Activity A: The wax and the toothpick one by one starting with toothpick and finally . Inference: Heat is transferred along the copper rod from the heated end to the end. (b) Activity B: The rice moves to the surface and then moves . The movement repeats forming a convection current. Inference: The hot water below becomes dense and rises to the . water on the surface which is denser moves downwards to replace the space left by the hot water. (c) The paper spiral . Inference: The less dense hot air moves and the dense cold air moves to replace the space left by the hot air. (d) The hand feels . Inference: The spoon becomes after receiving from the sun. Discussion: 1 Identify the method of heat transfer that occurs in each of the activities A to D. 2 State the medium where each method takes place. 3 Compare the rate of heat transfer in each method. Conclusion: Write down your conclusion. 88
3.6 Heat Conductors and Heat Insulators Have you ever tried using a metal spoon to stir a pot of boiling soup? You probably know how rapidly heat energy moves from the hot soup through the spoon and into your hand if you have tried it. This is because the metal spoon is a good conductor of heat. A heat conductor is a substance that allows heat to flow through it easily. Metals like silver, mercury, aluminium, lead, cuprum, iron and zinc are good conductors of heat. Good heat conductors become hot easily when heated and become cold easily when cooled. On the other hand, a heat insulator is a substance that prevents or slows down the rate of heat flowing through it. Back to the example given, you will know how much simpler it is to stir hot soup when using a wooden or plastic-handle spoon. This is because neither wood nor plastic conducts heat easily. Non-metal substances like wood, plastic, asbestos, cork, water, air and polystyrene are good insulators of heat. Good heat insulators are substances that take time to become hot when heated and are slow to cool down when cooled. The bottom of an electric iron is made of metal (iron and steel) that can conduct heat to clothes to remove wrinkles. The handle is made of plastic which is a heat insulator, allowing us to hold the iron. Cooking utensils such as pots are usually made from aluminium or steel. They are good conductors of heat so that the heat can be transferred to the food quickly. However, the handle of utensils is made of plastics so that our hands do not get burnt while holding it. Cork mat is a heat insulator that reduces heat loss from the pot to the table by conduction. Chapter 3 Temperature and Heat 89
Activity A Problem statement Which material is the best insulator of heat? Hypothesis Among insulating materials such as glass, plastic and wood, wood is the best insulator of heat. Manipulated variable Type of insulators Responding variable Time taken for cobalt chloride paper to change color Constant variable Size of materials Materials and apparatus Glass rod, wooden rod, plastic rod, cork, cobalt chloride paper and metal trough Procedure 1 Set up the apparatus as shown in the diagram below. Wooden rod Glass rod Plastic rod Hot water Metal trough Cork Cobalt chloride paper Hot water Metal trough Cobalt chloride paper Plastic rod Glass rod Wooden rod (a) Experimental set-up (b) Top view 2 Insert the rods of different insulators (wood, glass and plastic) through corks at the side of the metal trough. Make sure the length of all the rods inside the trough is the same. 3 Place a piece of moist cobalt chloride paper at the end of each rod. 4 Pour boiling water into the trough so that the end of each of the rods is heated at the same temperature. 5 Record the time taken for the pink cobalt chloride paper at the end of each rod to turn blue. Result Type of insulator Time taken for cobalt chloride paper to change colour Wood Plastic Glass Discussion Which material is the best insulator of heat? Why? Conclusion Is the hypothesis accepted? Write down your conclusion. Experiment 1 Investigating different materials as heat insulators 90
Activity B Problem statement Do different materials act as different heat insulators? Hypothesis Different materials act as different heat insulators. Manipulated variable Responding variable Constant variables Materials and apparatus Cotton wool, paper, aluminium foil, hot water, flat-bottomed flasks, hollow rubber stopper, thermometer, retort stand and clamp, and stopwatch Procedure 1 Take four flat-bottomed flasks. Label them as A, B, C and D. Wrap flask A with cotton, flask B with paper, flask C with aluminium foil and flask D without any wrapping. 2 Fill the flasks with hot water to the top. 3 Close flask A with a rubber stopper inserted with a thermometer as shown. Repeat the same for flask B, C and D. 4 Record the initial temperature of water in each flask. Hot water A B C D Thermometer Cotton wool Paper Aluminium foil Hot water 5 Leave the flasks for 10 minutes. Record the final temperature for each of the flatbottomed flasks. Result Temperature (ºC) Flat-bottomed flask A B C D Initial temperature Final temperature Difference in temperature Discussion 1 Why is flat-bottomed flask D left unwrapped? 2 Arrange the three materials in ascending order based on the ability to release heat. 3 Does cotton act as the best heat insulator compared to paper and aluminium? Give your reason. 4 Based on the activity, which material is suitable to make winter coats? Why? 5 A chick gets protection under the hen's wings which are fluffy. Explain how. Conclusion Is the hypothesis accepted? Write down your conclusion. Chapter 3 Temperature and Heat 91
3.7 How Types of Surfaces Affect Heat Absorption and Emission Have you ever wondered why you feel cooler wearing a white shirt on a hot day? This is because brighter-coloured clothes are poor heat absorbers. People choose to wear brightercoloured clothes in hot weather over dark-coloured clothes. Every object absorbs and emits heat. Its ability to absorb and emit heat is determined by the surface type and colour, as well as the surrounding temperature. Let’s carry out experiments to explore this concept. Activity A Problem statement Which surface absorbs heat better? Hypothesis A dark and dull object absorbs heat better than a white and shiny object. Manipulated variable Responding variable Constant variable Materials and apparatus Dark and dull tin, white and shiny tin, laboratory thermometer, Bunsen burner, wooden block and stopwatch Procedure 1 Set up the apparatus as shown in the diagram. Thermometer Black and dull tin White and shiny tin Wooden block 2 Put the two tins at a distance of 10 cm away from the Bunsen burner. 3 Record the initial temperature of air in each tin. 4 Turn on the Bunsen burner. 5 Record the final temperature after 15 minutes. Result Surface of the tin Temperature of air (ºC) Initial reading Final reading Black and dull White and shiny Discussion Based on the result, which tin absorbs heat better? Why? Experiment 2 Investigating heat absorption and heat emission 92
Activity B Problem statement Which surface emits heat better? Hypothesis A dark and dull object emits heat better than a white and shiny object. Manipulated variable Responding variable Constant variable Materials and apparatus Dark and dull tin, white and shiny tin, hot water, laboratory thermometer, wooden block and stopwatch Procedure 1 Set up the apparatus as shown in the diagram. Thermometer Black and dull tin White and shiny tin Wooden block Hot water at 80°C 2 Fill 250 ml of hot water into both tins. 3 Record the initial temperature of water in each tin. 4 Record the final temperature after 15 minutes. Result Surface of the tin Temperature of water (ºC) Initial reading Final reading Black and dull White and shiny Discussion 1 Based on the result, which tin emits heat better? 2 State the characteristics of the object which is a better heat absorber and heat emitter. Conclusion Is the hypothesis accepted? Write down your conclusion for both Activities A and B. Rough surfaces absorb and emit heat more effectively than smooth surfaces. This is because a polished surface is a good reflector and a poor absorber—it has a low emissivity. Science Facts Chapter 3 Temperature and Heat 93
Application of Heat Absorption and Emission Are you aware that the concept of heat absorption and emission is used in our daily lives? Consider some of the examples provided below. Petrol is highly flammable. Thus the petrol tank of a petrol tanker is painted silver and shiny because a bright surface does not absorb much heat and this can keep the petrol at a lower temperature. The car mechanic holding the manometer is filling gas in the car's air conditioning compressor. Heat radiators in cars, machines and air conditioners are painted black to provide a cooling effect by radiating most of the heat. The compressor at the back of the refrigerator is usually black to allow for rapid heat emission into the surrounding environment. Wearing light-coloured clothes during outdoor activities especially during hot weather can keep us cool because they are good reflectors of heat. Generally, the base of cooking utensils is black. The black surface absorbs heat well, and this can speed up the cooking process. 94
Green building technology incorporates heat concepts into buildings to reduce the impact of rapid development on the environment and human health. It involves designing a building with features like low energy consumption, excellent design flexibility and minimal maintenance costs. Green building technology incorporates some of the following features. The walls are painted with bright colours because bright surfaces are poor heat absorber. Windows are designed for maximum air circulation in the house. The roof surfaces are applied with a heat reflecting coating to keep the house cool and reduce electricity usage. More trees are planted in the surroundings to provide shade. Modern business buildings are fitted with glazed windows to cool the building. Chapter 3 Temperature and Heat 95
Green building technology also emphasises the importance of installing energy-efficient and self-sufficient home appliances. Refrigerators, washing machines, dishwashers and microwave ovens are examples of such technologies. These technologies are aimed at creating zero-energy homes and commercial buildings. Water conservation is another aspect of green building. Green buildings are environmentally friendly structures that conserve water. Thus, all water fixtures, such as faucets, toilets and shower heads are water efficient. Science Facts The use of glass in the roof or ceiling allows natural light to enter the house, which saves energy. A rainwater collection tank collects water that can be used to water plants or wash cars. The home has solar panels installed on the roof that absorb energy from the Sun and convert it into electrical energy. The solar water heater is a cost-effective way to generate hot water at home without the use of electricity. 96
3.8 Body Temperature Regulation The capacity of organisms to maintain their body temperature within specified ranges despite a change in the surrounding temperature is known as thermoregulation. Humans maintain a consistent body temperature regardless of changes in the outside temperature. Through metabolic processes, they produce heat. The hypothalamus in our body controls how warm or cold the body is. It senses changes in body temperature and carry out the changes through effectors like muscles, sweat glands, hair, and so on. Controlling heat production and heat loss from the body allows for the maintenance of a constant body temperature. When the body temperature is high The hypothalamus starts heat-releasing processes to increase body heat loss as below. • The widening of superficial arteries allow body heat to escape into the atmosphere via the skin. • The sweat gland produces sweat that evaporates on the skin, cooling down the body. • Controlling the release of thyroid hormones that lowers internal metabolism. When the body temperature is low The hypothalamus activates heat-generating processes to boost body heat generation as below. • The tightening of superficial arteries reduces heat lost from the body. • The smooth muscles shiver to produce heat. • Thyroid hormone is released to increase metabolism. When we are hot, we sweat to release our body heat to maintain our body temperature. Chapter 3 Temperature and Heat 97
Most animals must keep their internal body temperatures within a specific range. Some animals often produce heat from within to keep their bodies at a constant temperature. No matter what the situation, their body temperature remains constant. On the other hand, certain animals rely on outside heat sources, and the environment affects how hot or cold their bodies are. Therefore, we can classify animals into two groups: homeothermic and poikilothermic, based on how stable their deepbody temperature is. Animals that keep a relatively constant body temperature regardless of the outside temperature are said to be homeothermic. Birds and mammals make up the majority of homeothermic animals. Some animals, such as dogs and lions, are unable to sweat. Instead, they pant to allow the water in their mouths to evaporate, keeping them cool. Birds do not have sweat glands to lower their body temperature. They release heat through conduction (the contact with items that are colder than the skin), the radiation of heat through the surface of the skin, and the convection, or irradiation of heat in the surrounding air. Canaries should always be kept in well-ventilated areas because of this. Penguins live in colder climates than any other birds. However, they are able to keep a steady body temperature because of their plumage, which has a higher density of feathers and forms many layers on their skin. The average body temperature of polar bears is 37°C. Thick layers of hair, skin and oil allow them to keep their internal temperature isolated from the outside environment. 98
The green iguana regulates its body temperature by transferring heat from its head to its body or from its mouth, nose and eyes—areas where warm or cold blood is delivered—during the process of heat exchange between its head and body. Poikilothermic animals control their body temperature based on the surrounding environment. This occurs because they lack of the ability to control their body temperature by producing heat—which is why these kinds of animals are commonly referred to as cold-blooded animals. Take a look at the examples below. Desert lizards interact with their surroundings to regulate their body temperature. In order to maintain a constant body temperature, the lizards bask in the hot sun before retreating to the cold shade and burrows. A grasshopper that is long and thin increases its body heat by exposing its sides to the sun while a grasshopper with a broad, flat back would face the sun perpendicularly. While extending the legs cools it by raising it off a heated surface and allowing air to circulate around its body, crouching allows heat absorption from a warm surface into the abdomen. What happens to lizards in the cold? Think About It Butterflies can sunbathe and position themselves differently in the sun to absorb the most heat. Chapter 3 Temperature and Heat 99
1 A measurement of how hot or cold an object is using a thermometer is known as its . 2 In the Celsius scale, the two fixed points which are usually chosen are the point of ice and the point of water. 3 Mercury and alcohol thermometers using capillary tubes are known as thermometers. These thermometers work using the principle of expansion and contraction of liquid when the temperature changes. 4 Most matter when heated and when cooled. 5 When temperature increases, the atoms of a solid vibrate more vigorously to increase its , so the solid expands. 6 Mercury is used in a thermometer because it is a metal that can expand and contract when there is a change in temperature. 7 Heat causes air to expand, which makes it less than the air around it and causes the heated air to rise. 8 Heat is a form of that is measured in joules (J) and it is transferred from a hot area to a cold area. 9 The specific heat capacity, c, of a substance is the amount of heat required to increase the of 1 kg of the substance by 1°C. 10 The specific latent heat of vaporisation of a substance is the amount of heat needed to change 1 kg of the substance from the to the state without any change in temperature. 11 The specific latent heat of fusion of a substance is the amount of heat needed to change 1 kg of the substance from the to the state without any change in temperature. 12 Heat is transferred by conduction through , by movements of liquids and gases, and radiation that can transfer heat through . 13 Sea and land breezes are natural phenomena as a result of . 14 We can feel the warmth of the sunlight because it reaches us through . 15 A heat is a substance that allows heat to flow through it easily. A heat is a substance that prevents or slows down the rate of heat flow through it. 16 A and object is a better heat absorber and heat emitter than a white and shiny object. 17 is the capacity of organisms to maintain their body temperature within specified ranges despite a change in the surrounding temperature. 18 Humans regulate body temperature through the in their body to control how warm or cold the body is. RECALL Fill in the missing words. 100
THINKING CAP Put on your 1 Ms Annisa pours hot coffee into two porcelain cups. Porcelain cup X has an iron spoon in it and porcelain cup Y has a wooden spoon in it. After a while, the coffee in cup X is colder compared to that in cup Y. Explain why. 2 As compared to wearing a thick jacket in the winter, why do people who live in cold regions choose to dress in layers? 3 Explain why an air conditioner is usually fixed near to the ceiling of a room. Chapter 3 Temperature and Heat 101
Project Activity objective: Design and build a solar oven to heat up 100 ml of water in a cup. Problem statement: The heat energy from the Sun makes our Earth habitable for humans and other living things. Heat transfers better in the atmosphere by convection. There are a variety of ways we can harness the heat energy from the Sun to meet our needs. Concept applied: Conduction, convection and radiation Procedure: 1 Work in a group of five students. Appoint a leader in each group. Other members are the researcher, designer, builder and recorder. 2 Brainstorm on how to build a solar oven to heat up 100 ml of water in a cup using the Sun as the only source of energy. The temperature of water in the oven must increase by 10°C in 15 minutes. 3 Design a prototype of the solar oven. List the materials needed. 4 Build the oven and test it. 5 Record the initial temperature of the water and the final temperature of the water (after 15 minutes). 6 Improve your oven, if necessary. Suggested materials: A plain box, a box with a black bottom, a black-bottomed box coated with aluminium foil, a cup, plastic wrap Presentation: Present your design, the solar oven built and the recorded temperatures in a creative way. You can take pictures for your presentation. During your presentation, you may reflect on your solution design. Then, submit a complete report. A Solar Oven 102
The Sun is visible during the day, while the moon is typically visible at night. However, occasionally we can also observe the Moon during the day. Why? What other celestial bodies are there in our Solar System other than the Earth, the Moon and the Sun? Earth and the Solar System What will you learn? Describe the characteristics of the eight planets and the Sun Describe some other objects in the Solar System Describe why we experience days, nights and seasons Explain why the Moon’s shape changes over the period of a month Explain how lunar and solar eclipses happen Explain how the Moon influences the tides Explain the use of space technology CHAPTER 7
7.1 The Solar System The Solar System is made up of the Sun and eight planets that orbit it. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The Sun is the central focus of the Solar System. Other objects in our Solar System include dwarf planets, meteors, asteroids and comets. While orbiting the Sun, the planets rotate on their own axis and their distance to the Sun varies depending where they are in their orbit. Mercury • The planet closest to the Sun. • The smallest planet in the Solar System. • Mercury’s diameter is 40% smaller than that of the Earth. • Mercury’s sky is always dark because it lacks a layer of atmosphere to scatter sunlight. • Due to the lack of an atmosphere to burn up meteoroids, Mercury’s surface is pockmarked with craters and rocks from countless impacts, much like the Moon. • During the day, the temperature on its surface is extreme. It is approximately 480°C during the day, and at night, approximately –170°C. Earth • The third planet in the Solar System. • The fifth largest planet in the Solar System. • Earth is the only planet in the universe that is home to life. • Earth is surrounded by a layer of atmosphere made up of nitrogen gas, oxygen, carbon dioxide, argon and water vapour. • Water covers 71% of the Earth’s surface, while land covers the remaining 29%. Venus • The second planet closest to the Sun. • Venus has a layer of atmosphere with a high carbon dioxide content. Due to the high carbon dioxide content, the temperature on its surface is around 460°C. • Unlike the Earth, this planet rotates from east to west. This means that the Sun rises west. • According to astronomers, Venus is the “Earth’s twin” because it has about the same age, mass and volume as the Earth. Mars • The fourth planet from the Sun. • It is also known as the Red Planet. • It has two moons which are Phobos and Deimos. • Its surface is covered in reddish sand dust, craters, volcanoes and canyons. • It has a thin atmosphere and an extremely high carbon dioxide content (96%). 182
Planets in the Solar System A planet is a massive sphere-shaped body that revolves around the Sun. The planet is an opaque object, thus it can reflect light rather than illuminate it like the stars. Let’s take a look at the eight planets in the Solar System. The four planets that are closest to the Sun, namely Mercury, Venus, Earth and Mars are made up of solid rocks. They are terrestrial planets. The four planets further away from the Sun, namely Jupiter, Saturn, Uranus and Neptune are much larger. They are made up of swirling layers of cold gases like hydrogen or helium and super-cold liquids like ammonia. Saturn • The sixth planet from the Sun. • After Jupiter, it is the second largest planet. • It is made up of gases and is classified as a gas giant planet. • Saturn has a density that is 30% less dense than water. • Saturn has at least 82 moons, the largest of which is Titan. • It has a ring system made up of ice with small amounts of rocky material and dust. Neptune • The eighth planet from the Solar System. • Neptune is blue because of methane. • It takes the longest time to orbit the Sun, 165 years (Earth time). • It is the most distant planet in the Solar System, thus the temperature on its surface is extremely cold, about –201°C. Jupiter • The fifth planet from the Sun. • It is the largest planet in the Solar System, with a diameter 11 times that of Earth and a mass 320 times that of Earth. • It has at least 79 moons orbiting it and the largest moon is Ganymede. • Jupiter has a massive gravitational pull that is nearly 2.53 times that of Earth. Uranus • The seventh planet from the Sun. • It is the third largest planet in the Solar System. • It is made up of ice and rocks. It has a ring like Saturn, but thinner and darker. • Its axis of rotation is tilted, almost parallel to its orbit around the Sun. • It has 27 moons orbiting the planet. Chapter 7 Earth and the Solar System 183
Characteristics Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Average distance from the Sun (million km) 57.9 108.2 149.6 227.9 778.3 1427 2871 4497 Relative mass (× earth) 0.055 0.815 1 0.107 317.8 95.159 14.536 17.147 Diameter (km) 4879 12 104 12 756 6 794 139 822 116 460 51 118 49 528 Density (g/cm3) 5.4 5.2 5.5 3.9 1.3 0.7 1.27 1.6 Gravitational pull (m/s2) 3.7 8.87 9.8 3.71 24.79 10.44 8.87 11.15 Surface temperature (°C) 430 462 15 –63 –108 –139 –197.2 –201 Time taken to orbit the Sun (time on Earth) 88 days 224.7 days 365 days 687 days 11.9 years 29.5 years 84 years 164.8 years Time taken for one complete rotation on its axis (time on Earth) 59 days 243 days 24 hours 25 hours 10 hours 11 hours 17 hours 16 hours Velocity of rotation on axis (km/h) 10.89 6.52 1 674.4 868.2 45 300 35 500 24 800 23 500 Number of natural satellites or moons 0 0 1 2 at least 79 at least 82 27 14 Main atmospheric contents No atmosphere 96.5% carbon dioxide, 3.4% nitrogen, 0.1% argon, helium, neon, sulphur dioxide, water vapour 78% nitrogen, 21% oxygen, 1% argon, carbon dioxide, water vapour 96% carbon dioxide, 1.9% nitrogen, 1.9% argon, 0.2% oxygen, carbon monoxide 89.6% hydrogen, 10.1% helium, 0.3% methane, ammonia, ethane, water 96% hydrogen, 3% helium, 0.4% methane, ammonia, ethane, water 83.3% hydrogen, 15.5% helium, 2.4% methane 80% hydrogen, 19% helium, 0.1% methane, ethane Condition of planet’s surface No colour, craters covered in fine dust, has plains, mountains and valleys. Orange in colour, sandy and rocky, with big plains, volcanoes and huge craters. Water on 71% of the surface, with plains, mountains and volcanoes Red, sandy and rocky, with big plains, volcanoes and wide craters. Does not have a hard surface. Covered only in gas. Gas changes to liquid and solid as it approaches the core of the planet. General characteristics of planets in the Solar System 184
Activity 1 1 Working in groups of four, use the data from the table of ‘general characteristics of planets in the Solar System’ and look for the sizes of the eight planets. 2 Find out the size of the Sun in this chapter or via the Internet. 3 Using modelling clay and sports balls or any other things that you think are suitable to make a set of planets including the Sun. 4 Use a suitable scale to size down the size of the planets and the Sun, and the distance of the planets from the Sun. 5 Add important notes for each of the planets. 6 Use your creativity to design and display the planets around the Sun. Write down the scales in your display. Model of Solar System Other Objects in the Solar System In our Solar System, there are many celestial objects with the Sun is at the centre. The eight planets in our Solar System all orbit the Sun in elliptical orbits. Other than the eight planets, there are many other objects in the Solar System. Let us look at a few of these objects. Satellites Satellites are celestial bodies that orbit other celestial bodies with a higher mass. The moon is an example of a satellite. It is the only naturally occurring satellite of the Earth. Mercury and Venus do not have natural satellites, while Mars has two, Phobos and Deimos. There is a vast network of natural satellites orbiting the big planets like Saturn and Uranus. With at least 79 moons, Jupiter has the greatest number of naturally occurring satellites. The four largest moons of Jupiter are Io, Europa, Ganymede and Callisto. Besides the naturally occurring satellites, there are artificial satellites that are man-made and launched from Earth. Jupiter and its moons. Chapter 7 Earth and the Solar System 185
Dwarf Planets Dwarf planets, like the eight major planets, are round in shape and orbit the Sun. Unlike planets, they do not have a clear path around the Sun. The path of a dwarf planet around the Sun is scattered with other objects such as comets and asteroids. A dwarf planet is significantly smaller than any of the eight major planets. Ceres, Pluto, Eris, Makemake and Haumea are the first five recognised dwarf planets. Pluto is located in the Kuiper Belt, a donut-shaped region of icy objects beyond the orbit of Neptune. It was long considered to be the ninth planet in our Solar System. However, the International Astronomical Union (IAU) confirmed in 2006 that Pluto shares its orbital neighbourhood with other icy Kuiper Belt objects. Pluto was thus reclassified as a dwarf planet. Eris is located in the Kuiper Belt. It is similar in size as Pluto, but it is three times farther away from the Sun. Given that Eris’s surface is extremely cold, it appears unlikely that life could exist there. Makemake is located in the Kuiper Belt. Slightly smaller than Pluto, it is the second brightest object in the Kuiper Belt as seen from Earth. Haumea is a dwarf planet located in the Kuiper Belt that orbits the Sun much further out than Neptune. It is roughly the size of Pluto and has two moons. Its rapid rotation on its axis is one of its outstanding features. Ceres is the largest object in the asteroid belt between Mars and Jupiter, and it is the only dwarf planet in the inner Solar System. It was the first object in the asteroid belt to be found in 1801. Ceres became the first dwarf planet to host a probe when NASA’s Dawn arrived there in 2015. 186
Comets Comets are rocky objects that orbit the Sun and are composed of a mixture of gas, ice and frozen dust. Most of the comets originate from the Kuiper Belt and Oort Cloud. The structure of the comet is divided into two parts: the head and the tail. The head part can reach a length of 250 thousand kilometres, while the tail part can reach a length of 150 million kilometres. They have their own elliptical orbits around the Sun. Their average speed ranges between 10 and 70 km/s depending on their distance from the Sun, and they can be either periodic or non-periodic. Asteroids Asteroids are large rocky and metal objects that orbit the Sun in the Solar System. Larger asteroids are also known as planetoids. The size of asteroids vary significantly, ranging from 1 m to 1000 km in diameter. The average temperature on the asteroid’s surface is –73°C and the average speed is 25 km/s. Asteroids are mostly found in the asteroid belt between Mars and Jupiter. Ceres, Pallas, Juno, and Vesta are the four largest asteroids. Collisions can happen between asteroids and the Earth if the asteroids and the Earth are at an intersection point at the same time or are located extremely close to each other. Comet Asteroid Kuiper Belt Asteroid belt Halley’s Comet was last seen across the Earth in 1986 and is expected to be seen again in 2061. Science Facts The asteroid belt and Kuiper Belt are two distinct regions in the Solar System. Chapter 7 Earth and the Solar System 187
Meteoroids, Meteors, Meteorites Meteoroids are rock and metal fragments formed by the debris of asteroids or comets that orbit the Sun. Its size ranges from as fine as sand to a maximum of one metre. Its surface temperature in space is close to 0°C. Meteoroids are free to move in space and are influenced by the gravity of the planets and moons that surround them. Meteoroids enter the Earth’s atmosphere at very high speeds, ranging from 11 km/s to 72 km/s, depending on their size and trajectory. When a meteoroid enters the Earth’s atmosphere, the meteoroid is known as a meteor. Molecular friction between the air and the meteor produces heat until it burns, resulting in a streak of light. The meteor usually burns up completely in the atmosphere. When many meteors enter the Earth at a time, they are known as meteor showers or meteor rain. The meteor that does not completely burn up in the atmosphere and falls to the surface of the Earth is known as the meteorite. Craters form as a result of being hit by these meteorites. 188
7.2 Earth and Its Satellite Our home planet, Earth, is the third planet from the Sun and the only planet where living things can be found. It has one natural satellite that we know as the Moon. It is the only planet in our Solar System with liquid water covering 71% of its surface. Earth’s atmosphere is mostly nitrogen with plenty of oxygen. Earth’s atmosphere protects us from ultraviolet radiation from the Sun as well as incoming meteoroids. It also regulates global temperatures, allowing life to grow and thrive. Movement of Earth in the Solar System There are two major ways the Earth moves in our Solar System. The Earth rotates on its axis, making a full rotation each day, and the Earth orbits around the Sun once each year (revolution). Day and Night We have seen the Sun’s daily path across the sky when it rises in the morning and sets at night. Do you realise that it is the Earth’s rotation on its axis that causes these things to happen? The axis of the Earth is the imaginary line passing through its centre with the North Pole and South Pole located at either end of the axis. As the Earth rotates on its axis and revolves around the Sun, it is slightly tilted at an angle of 23.5 degrees. Since it rotates slowly, smoothly and consistently at the same speed, we are not conscious of this movement. The Earth takes 24 hours to make a complete rotation on its axis, and this results in day and night. Half of the Earth faces the Sun as it rotates, and the other half faces away. Can the day and night have different duration? As the Earth rotates, different regions on the Earth face the Sun and receive sunlight at different times. This can occur in different regions of the same country. There are three time zones in Indonesia, one for each of West Indonesia, Central Indonesia and East Indonesia. Which region experiences sunshine first? Sunlight Sunrise Axis The South pole is the point on Earth’s surface that is furthest south. The North pole is the point on Earth’s surface that is furthest north. Day Night Chapter 7 Earth and the Solar System 189
Calendar Year The Earth makes one complete revolution around the Sun. The common year on the Gregorian calendar, often known as the modern calendar, has 365 days, whereas a leap year has 366 days. This is because the Earth rotates on its own axis and takes 365¼ days to complete one revolution around the Sun. If it is a leap year, it takes the Earth 366 days to complete one revolution. Every four years, there is a leap year. The diagram below shows the rotation and revolution of Earth on its own axis. Seasons The tilt of the Earth on its axis and the movement of the Earth around the Sun are two key factors that determine the climate of the Northern and Southern Hemispheres. While the Earth orbits the Sun, its axis is tilted at an angle of about 23.5 degrees relative to its orbital plane. This tilt causes the Earth’s axis to precess, which leads to a gradual change in the direction in which it points over time. As a result, the angle at which sunlight strikes various locations of the Earth changes throughout the year. Locations that are struck perpendicular by direct sunlight receive more heat energy and are hotter, whereas the indirect sunlight locations receive less energy from the Sun, and they are cooler. The variations in temperature produce the four seasons in Earth: spring, summer, autumn and winter. 365 1 4 days 24 hours Moon Sun Earth How does the Gregorian calendar differ from Julian calendar in terms of leap year calculation? Think About It The Gregorian calendar, which is the most widely used calendar in the world today, was introduced by Pope Gregory XIII in 1582. It replaced the Julian calendar, which had been in use since ancient Rome. Science Facts 190
The diagram below shows the occurrence of four seasons. Summer occurs in the Northern Hemisphere in June because the northern section of the Earth is tilted towards the Sun, whereas winter occurs in the Southern Hemisphere because these parts are tilted away from the Sun. After three months, the Northern Hemisphere will transition to autumn, while the Southern Hemisphere will transition to spring. Six months later, the Northern Hemisphere of the Earth begins to tilt away from the Sun. As a result, winter will be experienced in the Northern Hemisphere, while summer will be experienced in the Southern Hemisphere. In the fourth quarter of the year, the Northern Hemisphere will transition to spring, while the Southern Hemisphere will transition to autumn. Countries such as Indonesia, Malaysia and the Philippines are positioned near the equator and receive almost the same amount of sunlight throughout the year. These countries do not have four seasons, although they have rainy and dry seasons. Summer Winter Winter Summer September 22 Spring Autumn June 21 December 22 March 21 Spring Autumn In polar regions such as Finland, Greenland and Alaska, the Sun remains visible in the sky for 24 hours around summer solstice. This phenomenon is known as the midnight Sun, and they also experience polar night when the night lasts for 24 hours. This occurs around winter solstice. Science Facts Chapter 7 Earth and the Solar System 191
Moon as Earth’s Satellite The Moon is about 363 300 km away from Earth. The Moon rotates in the same way that the Earth does. However, the Moon takes approximately 27 days to complete one rotation on its axis. The Moon also revolves around the Earth in its orbit and it takes an approximate time of 27 days as well. As a result, the same surface of the Moon always faces towards the Earth at all times. As the Moon continues to revolve, we can see a greater portion of its bright face. Currently, the Moon appears as a semicircle, which is known as the First Quarter Moon. As time passes, the First Quarter Moon transitions into the Waxing Gibbous Moon, with over half of the Moon’s visible side illuminated by the Sun. At this stage, the Moon is entirely visible to us as its illuminated portion faces the Earth directly, which is referred to as the Full Moon phase. The Earth is positioned between the Sun and the Moon, forming a straight line, allowing us to see the Moon as a complete circle. As the Moon continues to revolve, a lesser portion of its illuminated side is facing the Earth, which is known as the Waning Gibbous Moon phase. As time progresses, we are only able to view half of the illuminated portion of the Moon, which is referred to as the Third Quarter Moon phase. Phase 3 Phase 4 Phase 5 Phase 6 Phase 7 Earth Resource 192
The final phase is the Waning Crescent Moon, during which we can only observe a small section of the illuminated side of the Moon. The whole cycle starts with a New Moon, where the Moon is between the Sun and the Earth. The dark side of the Moon is facing us, making the Moon ‘invisible’ in the night sky. This is why we do not see the Moon at night during this phase. As the Moon orbits around the Earth, a small part of it that is illuminated by the Sun can be seen from the Earth. We see the illuminated part of the Moon as a crescent. This phase is known as the Waxing Crescent Moon. Phase 8 Phase 1 Phase 2 Sun Moon Day 1 Day 14 to 16 Day 28 Day 30 New Moon Full Moon Waning Crescent Moon Phases of the Moon at different times in a month Phases of Moon The Moon does not emit its own light, but rather appears visible to us on Earth because it reflects sunlight. However, the Moon appears to change shape as we observe it each day due to different portions of its surface being illuminated during its orbit around the Earth. These alterations in appearance are known as the phases of the Moon. The lunar cycle, which repeats itself, takes approximately 29.5 days for the Moon to reach the same visual phase. Movement of the Moon around the Earth Chapter 7 Earth and the Solar System 193
Total lunar eclipse Activity 2 1 Carry out this activity in pairs. 2 On a piece of durable, black poster board, make a hole in the centre. Make sure the size of the hole can let your head poke through. 3 Colour eight ping pong balls using a blue marker pen so that they are half blue and half white. 4 On the board, mark the direction that the sun is coming from. 5 Apply hot glue to attach all the ping pong balls to the board all around the circle as shown. Let the white side of the balls face the sun. 6 To view the moon phases, two of you will alternately poke your heads through the hole and turn the board counterclockwise. Making a Moon model to observe the phases of the moon Lunar Eclipse When the Sun, Earth and Moon align in a straight line, the Earth blocks the Sun’s light and creates a shadow. This phenomenon is known as a lunar eclipse, or an eclipse of the Moon, which occurs when the Moon moves into the Earth’s shadow. A lunar eclipse can be observed from any region of the Earth where it is night-time. The shadow cast by the Earth during a lunar eclipse is comprised of two parts, the umbra and the penumbra. A total lunar eclipse occurs when the Moon passes completely through the umbra. The sequence below depicts the changing appearance of the Moon during a lunar eclipse. Partial eclipse (penumbra) Partial eclipse (penumbra) Moon Moon’s orbit Sun Earth Total eclipse (umbra) After passing through the umbra, the Moon gradually exits the shadow, and we begin to see a section of the illuminated Moon. Over time, it progresses back into the Full Moon phase again. 194
Tides Have you ever wondered what causes tides to occur? Why do tides change in height and intensity throughout the month? Tides are the rhythmic rise and fall of the ocean water level that occurs twice in a day. They are primarily caused by the gravitational force of the Moon. This force attracts the ocean water to bulge out towards the Moon. Another bulge occurs at the opposite side. This creates high tides at the bulges. Moon A B D C High tides High tides Earth Occurence of tides Look at the diagram above. A and C experience high tides. B and D experience low tides. As the Earth rotates faster than the Moon revolution, every place on the Earth experiences two high tides and two low tides each day. The ocean is constantly moving from high tide to low tide, and then back to high tide. When it is New Moon or Full Moon, the gravitational forces of the Moon and Sun are combined. The high tides are very high and the low tides are very low. These are known as spring tides. They occur when the Earth, Moon and Sun are in a line. Sun Earth Moon Spring tide during New Moon Sun Earth Moon Spring tide during Full Moon Chapter 7 Earth and the Solar System 195
When it is First Quarter Moon or Third Quarter Moon, the effects of the gravitational forces of the Sun and Moon cancel each other. This results in a smaller difference in the high tide and low tide. This is known as neap tides. Sun Earth Moon Neap tides Tides are important as they create tidal streams that circulate the ocean, bringing fresh food and water to other areas. Tides also create a great ecology at the beaches as different living things adapt to the high tides and low tides daily. Knowledge of tides is important for navigation of ships through coastal waterways, fishing and also a variety of water-related sport activities. The Use of Space Technology Much of the technology we use today depends heavily on space technology, with one of the most widely used technologies being the Global Navigation Satellite System (GNSS). It comprises a network of satellites that transmit positioning and timing data to GNSS receivers. These receivers use the data to determine precise locations. GNSS receivers are now integrated into smartphones to support mapping and route planning applications. This system is also used in transportation to accurately determine locations, reduce delays, accidents and operating cost, as well as enhance efficiency and safety. Global Navigation Satellite System (GNSS) 196
Earth-observation satellites (EOS) are used to observe the Earth from space, allowing for various applications such as predicting weather patterns, improving agricultural practices, detecting forest fires and oil spills, measuring ocean waves, assessing gas emissions, monitoring climate change and reducing disaster risks. Communication satellites are also used to relay voice, video and data signals to and from multiple locations worldwide. The International Space Station (ISS) is a large spacecraft orbiting the Earth where astronauts can temporarily live and work to gain knowledge about living and working in space. The ISS’s laboratories provide the crew members with the ability to conduct research that is impossible to carry out on Earth. International Space Station Based on the 2016–2020 space chart, Indonesia’s space development has made significant progress in recent years. During the 2016–2020 period, the country achieved several noteworthy milestones in space science. For instance, it established a regional space weather information and prediction system, as well as an early warning information system for extreme atmospheres. In addition, Indonesia made significant strides in remote sensing, with the National Remote Sensing Data Bank becoming operational. Science Facts 7.3 The Sun The Sun is composed of a massive ball of gases, primarily hydrogen (76%) and helium (22%), with the remaining 2% made up of other elements. As the only star in our Solar System, the Sun is also the closest one to Earth. Its characteristics are shown in the table below. Characteristic Measurement Rotation on its axis at the equator 25.38 Earth days Mass 1.99 3 1030 kg Density 1.41 g cm–3 Surface gravity of the Sun 27.9 3 surface gravity of Earth Diameter 109 3 diameter of Earth Distance from Earth 149.6 million km Temperature of the surface 5500°C Temperature of the core 15 million°C Time taken for its light to reach the Earth 8 minutes What would happen if the Sun is further away from Earth? Think About It Characteristics of the Sun Chapter 7 Earth and the Solar System 197
The Sun is made up of two main layers, which are the inner layers (core, radiation zone, convection zone) and the Sun’s atmospheric layers (photosphere, chromosphere, corona). Besides being the source of light and heat, there are other phenomena that occur on the surface of the Sun that affect the lives on Earth. The phenomena are solar prominence, solar flares, sunspots and solar wind. Solar prominences are large, bright features that extend out from the Sun’s surface in a ring shape, and can contain plasma, hydrogen and helium gases. They typically last for several days or months. Solar flares are explosions of hot gas that occur in the chromosphere layer. During a flare, charged particles such as electrons, protons and gamma rays are released. Flares usually occur near sunspots and last for a few minutes or hours. Sunspots are dark regions on the photosphere. They appear darker than their surroundings because they are cooler and emit less light. They typically last for a few weeks and are associated with strong magnetic fields. While sunspots do not cause droughts on Earth directly, they are sometimes associated with changes in the Sun’s activity that can affect our planet’s climate. Solar wind is a stream of charged particles, including electrons, protons and alpha particles, that flows outward from the Sun and fills the Solar System. The solar wind can reach speeds of hundreds of kilometres per second and interacts with the Earth’s magnetic field to create a protective bubble called the magnetosphere. When the solar wind is particularly strong, it can cause the aurora borealis and aurora australis. While sunspots and solar flares can affect the strength of the solar wind, they do not directly cause the aurora. Instead, they can produce energetic particles that can interact with the Earth’s magnetic field and trigger auroras. Prominence Sunspot Solar flare Chromosphere Photosphere Convection zone Radiation zone Core Corona The structure of the Sun 198
Solar Eclipse A solar eclipse occurs when the Moon passes between the Sun and the Earth in a straight line, causing the Moon to block some of the Sun’s light and casting a shadow on the Earth. Solar eclipses can only be seen by those in the part of the Earth experiencing daytime at the time of the eclipse. Penumbra Umbra Total eclipse Partial eclipse Moon’s orbit Sun Moon Earth Resource When the Moon blocks the Sun, it produces a shadow with two regions, the umbra and the penumbra. The part of the Earth that is in the umbra region experiences a total eclipse. The sky in that area will gradually turn dark and the people will experience total darkness for a few minutes even though it is daytime. The people in the penumbra region will not be able to see a part of the Sun and will experience a partial eclipse. The shape of the Sun during a solar eclipse is shown in the sequence below. Total solar eclipse Chapter 7 Earth and the Solar System 199
1 The eight planets in the Solar System are Mercury, , Earth, Mars, , Saturn, Uranus and Neptune. 2 Each planet rotates on its axis and orbits around the Sun. While orbiting, the planets do not have a fixed from the Sun. 3 The terrestrial planets are made up of while the four planets farther away from the Sun are made up of swirling layers of . 4 Saturn is the only planet that has a system made up of ice, rocky material and dust. 5 Celestial bodies that orbit other celestial bodies with higher mass are known as . 6 The difference between dwarf planets and planets is the orbital path of a dwarf planet is scattered with other objects such as and asteroids. 7 Comets are objects most of which originate from the Kuiper Belt and Oort Cloud. 8 Asteroids are rocky and metal objects that are found in asteroid belts between and . 9 Meteoroids are fragments of rock from asteroids, but they are known as when they enter the Earth’s atmosphere. 10 The Earth on its axis and around the Sun, causing day and night, and the seasons to occur. 11 We observe the Moon changing because it reflects light from the Sun when it orbits around the Earth. 12 A eclipse occurs when the Sun, Earth and Moon are in a straight line and the Moon moves into the Earth’s shadow. 13 Tides are the alternate rising and falling of the ocean water level in a day caused by the force of the Moon. 14 GNSS receivers are integrated into smartphones to support applications that show maps and which are useful in transportation to determine their precise locations. 15 The Sun is in the centre of the Solar System that is made up of core, radiation zone, convection zone, photosphere, and corona. 16 The examples of phenomena that occur on the surface of the Sun are solar prominence, solar flare, and solar wind. 17 When the Moon is in a straight line between the Sun and the Earth, it blocks some light from the Sun from reaching the Earth, forming a eclipse. RECALL Fill in the missing words. 200
THINKING CAP Put on your 1 Why aren’t meteors visible during the day? 2 Do you think that the Moon would still have phases if it emitted its own light? Explain your opinion. 3 How does the classification of the Sun as a star relate to its physical properties and behaviour? Chapter 7 Earth and the Solar System 201
Project Activity objective: Brainstorm the characteristics that make Earth a planet for living things and how an individual can contribute to save the Earth. Problem statement: Scientists believe the Earth can support life due to its characteristics such as mineral richness, surface temperature and atmospheric content. However, human activities for decades had resulted in the destruction of the natural environment, depletion of natural resources and changing of climate. It is the responsibility of every individual to save the Earth as it is the only planet that can support living things. Procedure: 1 Split the class into groups. Each group is to identify the following facts: (a) The reason why the Earth is the most suitable planet for living things. (b) Can other planets support life if Earth’s resources run out? 2 Students in each group discuss, then search information on the Internet and books. List down all the references. Concept applied: The Earth as a planet for living things Action plan: 1 Carry out a forum which consists of five students in each group. 2 Appoint a leader in each of the groups. 3 Do a brainstorming on the topic given. 4 Other group members record the outcomes of the brainstorming session. Solution: The brainstorming must include at least the following aspects. You are encouraged to add more: (a) Characteristics of the Earth that makes it a planet suitable for life, such as water content, oxygen content and sunlight (b) The role of every individual in saving the Earth, such as the use of energysaving devices and practicing 5R (refuse, reduce, reuse, repurpose, recycle). Presentation: Present the findings using Microsoft Powerpoint. Then, submit a complete report. The Earth as a Planet for Living Things 202