Chapter 5: Heat and Heat Transfer PDF

U N I T B Energy Transfer Technologies What does the science of physics have to do with f ighting fires? Plenty! In order to protect themselves from the intense heat, firefighters wear special protective clothing. The clothing uses spec...

U N I T B Energy Transfer Technologies What does the science of physics have to do with f ighting fires? Plenty! In order to protect themselves from the intense heat, firefighters wear special protective clothing. The clothing uses special materials that prevent heat transfer. At the same time, firefighters use water to increase heat transfer. When water is sprayed over flames, the liquid water quickly heats and changes to water vapour. This change in state transfers heat away from the fire. Put a fire ladder against the side of a building and you have an inclined plane ready to get firefighters to the heart of the fire — or to help victims to safety. Fire axes are levers. When used to break through doors, they act as an extension of the firefighter’s arm. In this unit, you will study all of these things. You will study what heat is, how it transfers from one object to another, and how to reduce or increase heat transfer. You will also study how simple machines transfer energy. As you work on the unit, you may consider exploring related occupations — from auto mechanic to chef. 78  Chapter 5 Heat and Heat Transfer 80 Chapter 6 Controlling Heat Transfer 104 Chapter 7 Simple Machines and Energy Transfer 128 Energy Transfer Technologies MHR 79 unit S K I L L C H E C K Initiating and Planning T A Performing and Recording C Analyzing and Interpreting JE Communication and Teamwork O Detergent Dilemma R P Advertisers promote one brand of detergent over Design Criteria another. But are their claims accurate? Even if they A. Test at least three different detergents. are, how do you decide among the many options? Note: Be sure the detergent solutions are In this activity, you will use what you learned in prepared as directed on the product’s packaging. the unit to design an investigation that will help You need to test the effectiveness of each you decide which detergent works the best. product at the concentration recommended by the manufacturer. Challenge B. Use the same washing conditions for each Design an investigation that will determine how detergent. well different detergents remove stains. C. Include the following: a problem statement; a list of apparatus, materials, and safety precautions; and a detailed procedure. D. Outline the criteria you will use to determine how well each stain was cleaned. Plan and Construct 1 With your group, determine the washing conditions for your test. (a) What temperature will the water be? Include instructions for reaching this temperature. (b) How will you agitate the laundry? For example, you might use a jar that can be Safety Precautions shaken or stir the mixture in a larger container such as a pail. Contact with laundry detergents can irritate your eyes, (c) How much will you agitate the laundry? lungs, and stomach. Include instructions on: Materials how long the sample will be agitated, large jar whether it will be shaken or stirred, and variety of materials to make stains (such as ketchup, grass, mustard, raspberry juice) how vigorous the agitation will be. fabric thermometer 2 Based on your decisions in Step 1, write out the problem you will investigate. For example, variety of detergents “Which detergent removes stains best in cold water water with gentle agitation?” 76 MHR Investigating Properties of Matter 3 What type of container will you use? Add this 0 What control will you use? For example, how to the list of apparatus. will you show that it is the detergent doing the cleaning, and not just the water and agitation? 4 What type of fabric(s) will you use? You might choose a natural fabric (such as cotton) or a ! How will you rate each detergent’s ability to synthetic (such as polyester). Or, you could remove a stain? Write out the criteria for your test a variety of fabrics. Make a decision and assessment. add the item(s) to your list of materials. You might compare the performances. For example, brand C left more stain visible 5 How many detergent samples will you test? than brand B. Add these to the list of materials. Be sure to include a variety of brands and types of You could rate each detergent’s perform- detergents — some that wash in cold water, ance against a scale. For example, you some that include bleach, and so on. might use a scale such as: Level 1 — no stain visible 6 What kinds of stains will you test? Add these Level 2 — some discoloration visible on substances to the list of materials. close inspection 7 Write out a procedure for staining the fabric. Level 3 — stain clearly visible For example, will you rub in the stains or dab Level 4 — no different than the stain them on? How large will each stain be? before washing 8 How long will you leave the stains on before @ Design a table for recording your observations. washing? 9 Detergents will irritate skin, eyes, and lungs. # Have your group’s procedure approved by the What safety precautions will you follow? To teacher, and then carry out the investigation. help you decide, research the precautions on each product’s web site or MSDS. Write out $ Clean up any spills and wash your hands the safety precautions for this investigation. thoroughly after doing the activity. www.mcgrawhill.ca/links/science.connect1 Manufacturers often provide safety information for their products on their web site. Go to the above web site, then to Internet Connects, Unit A, Closer, and on to Laundry Detergent Safety. Unit A Project MHR 77  C H A P T E R 5 Heat and Heat What do car engines and human bodies have in common? Why does heat appear to flow? How does your body cool down on a hot day? A climber must always be aware of heat. Having the right clothes for the sport and paying attention to weather can be the difference between a memorable day and a helicopter ride to the closest hospital. When an object is C limbers often depend on bare hands when climbing rocks. This In addition, you will study that heat can do work, how heat transfers, heated, does its one is wearing gloves because sliding and how the transfer of heat affects weight increase? Does down the rope can cause rope burn. weather. You will see how the process the object get bigger? Excess heat can be a problem of heat energy transfer affects When a block of wood is warmed, has some- with weather, people, and machines. temperatures and climates on Earth. thing measurable been In this chapter, you will learn about By the end of the chapter, you will added? Discuss this understand why knowledge of heat the modern theory of heat. You will with a partner and write your ideas in look at how heat travels and how transfer is so important to this climber. your Science Log. heat transfer is important in various technologies. You will also study how the systems your body uses to cool down or warm up are similar to the systems used to control engine and machine temperatures. 80 MHR Energy Transfer Technologies  Transfer Starting Point Where Does Heat Come From? Rappelling down a cliff face is an exhilarating experience and a fast way to get down a mountainside. Smart climbers wear gloves to protect themselves from rope burn. How do their hands get burned? Where does the heat comes from? Safety Precaution What You Need In the past, many groups used bow drills to start fires. manual hand drill drill bit small piece of hardwood What You Y Will Learn What to Do 1. Feel the temperature of a drill bit. In this chapter you will learn: where heat comes from 2. The teacher will use the bit and drill to how heat transfers from one object to another make a hole in a piece of hardwood. the way climate is controlled by heat transfer 3. Cautiously feel the bit again. methods of heat transfer used by various technologies 4. Wash your hands thoroughly. Why It Is Important Your body must stay close to 37°C. If your body gets What Do You Think? too hot, your internal organs may be harmed or you will 1. In the above activity, where does the heat get sick. If your body is too cold, you risk hypothermia. Is this why Canadians have more kinds of clothes than come from? anyone else in the world? 2. Look at the drawing with the bow drill. Discuss what might happen to the wood in Skills You Will Use the groove on the board. In this chapter you will: 3. Think about questions 1 and 2. Why should investigate processes of thermal energy transfer motorcyclists wear leather suits, even in analyze technologies that transfer heat energy summer? compare three methods of heat transfer interpret weather and climate patterns in your area Heat and Heat Transfer MHR 81  5.1 The Nature of Heat Friction theory has been around for centuries. When two surfaces are rubbed together, the parts that touch resist movement. This resist- ance is friction. It was Count Rumford who used observations about friction to change the way scientists look at heat. In the late 1700s, Count Rumford observed that heat was created when metal cut metal. This heat results from friction. Rumford was an engineer and scientist who was hired to manufacture cannons in Munich, Germany. During this project, one worker carelessly touched a rod being used to bore a hole through a piece of metal. His hand was seriously burned. Figure 5.1 Workers boring a cannon barrel. Robert Brown and Random Movement Have you ever watched popcorn popping in an air popper? The What did Rumford notice about heat? random, dancing motion of the kernels is easy to observe. The cause of this motion is easy to explain. Would it surprise you to know that a similar type of random, dancing motion is occurring in the glass of water? www.mcgrawhill.ca/links/science.connect1 Robert Brown was a botanist studying how pollen fertilizes an egg (ovum) in a flowering plant. When observing grains of pollen under a microscope, he noticed tiny particles moving around. What was causing these particles to move? To find out, go to the above web site. Go to Internet Connects, Unit B, Chapter 5, and then to Brownian Motion. Figure 5.2 Robert Brown 82 MHR Energy Transfer Technologies  Robert Brown was the first to realize this. During the 1800s, he was using a microscope to observe pollen grains in a drop of water. He noticed that although the microscope was quite still, the pollen grains bounced around. When he increased the temperature of the water, the jiggling motion increased. This jiggling motion became known as Brownian motion. Observing the motion was simple. Explaining the cause was much more difficult. At first, Brown thought that the pollen grains were alive. Later, he reasoned that water must be composed of tiny unseen particles. These particles are in constant, vibrating motion. The motion of the pollen grains must be caused by collisions between the pollen grains and the other unseen parti- cles. Brown was unsure what the particles were. Figure 5.3 In this popcorn popper, popcorn kernels are heated and kept up by a blast of hot air. After reading this section and doing either the Internet Connect or Disc Connect, describe Brownian Motion and how it is affected by temperature. Figure 5.4 This appears to be a glass of stationary water. Brown found that the water is in constant motion. Disc If you have ever watched a lottery draw on television, you may have observed the random motion of the numbered balls before they drop into the slot. But would you watch a glass of water with the same interest? Robert Brown, a Scottish botanist, did. While observing pollen grains under a microscope, Brown noticed that the pollen grains were moving in the water. What caused this motion? What happened to this motion when the temperature increased? To answer these and other questions, load the student CD-ROM onto your computer. Launch the Brownian motion applet and follow the instructions. Figure 5.5 Robert Brown’s microscope. Heat and Heat Transfer MHR 83  S K I L L C H E C K Initiating and Planning Performing and Recording 5–A Analyzing and Interpreting Communication and Teamwork Mysterious Motion Robert Brown and the scientists who came after him had a difficult job explaining heat. The nature of heat is complex. You cannot see heat, only observe what it does. In this investigation, just like a scientist, you are going to experience things you can- not see. From your experience, you will hypothesize about what is happening. Problem Is water really still when is seems to be stationary? Safety Precaution Apparatus Materials 250 mL beaker food colouring medicine dropper hot and cold water Be cautious with glass. Handle hot water carefully. Procedure 1 Pour 200 mL of cold tap water into the beaker. 2 Place the beaker on a table. Wait until the visible motion of the water in the beaker has stopped. 3 Draw some food colouring into the medicine dropper. 4 With the medicine dropper just above the surface of the water, release one drop of food colouring into the water. Do not move or disturb the beaker. 5 Observe what happens. 6 Repeat steps 1 to 5, this time using 200 mL of hot water. 7 Clean up any spills and wash your hands thoroughly. 84 MHR Energy Transfer Technologies  Analyze 1. Describe the motion of the food colouring in each beaker of water. 2. What similarities did you observe? The unseen particles that 3. What differences did you observe? Brown said caused the jiggling motion interested Conclude and Apply other scientists too. These particles were first 4. Provide an explanation for the way the food colouring moved. called atoms. Later, they were called molecules. (a) What do you think caused this motion? (b) Why didn’t the drops of food colouring just remain on the surface of the water? 5. Compare the motion of the food colouring in the hot and the cold water. Explain any differences. Extend Your Knowledge 6. Would you expect to make the same observations if you used cooking oil or vinegar instead of water? Predict what might happen. Test your prediction. Check Your Understanding Key Terms friction 1. What did Brown guess was the smallest part of the mixture of water and Robert Brown pollen grains? Brownian motion 2. What is the name of the motion that Brown saw with pollen grains in water? Describe this type of motion. 3. As the temperature of the water increases, what happens to the motion of food colouring in water? Heat and Heat Transfer MHR 85  5.2 Heat and Temperature Heat cannot escape through a dog’s thick coat. Dogs pant to get rid of excess heat. Figure 5.6 Unseen particles in matter move and collide like these bumper cars. The modern theory of heat began with Robert Brown. He was first to suggest that the energy that came with heat — or thermal energy — was related to Two iron rods, one larger the jiggling motion of unseen particles of a substance. What are these unseen than the other, are both at particles? What causes the jiggling motion? the same temperature. How do their average In Unit A, you studied the particle theory of matter, which states: kinetic energies compare? All matter is composed of tiny, unseen particles. These unseen particles are in constant, random motion. Kinetic means movement. Kinetic art, 25 mL @ 30°C 100 mL @ 30°C ⫽ less kinetic energy ⫽ more kinetic energy such as mobiles, is art that moves. Kinetic energy is a form of energy associated with motion. Kinetic energy is a measure of the C C amount of motion particles have. We can use kinetic energy to explain the difference between heat and temperature. 38 37 35 The motion of particles can be compared to bumper cars at a fair. Like bumper cars, atoms and molecules collide with each other at different speeds. All particles have Temperature is the average Heat is the sum of all kinetic of all kinetic energies of all energies of all particles in an different kinetic energies. particles in an object. The object. The water in this beaker temperature of the water in has more heat than the water in both of these beakers is the the beaker on the left. Figure 5.7 Heat and temperature are same. related, but they are not the same. 86 MHR Energy Transfer Technologies  Key Terms Check Your Understanding heat 1. Explain the difference between heat and temperature. thermal energy kinetic energy 2. You place a frying pan on a burner to fry an egg. As the pan gets hotter, temperature how is the kinetic energy of the particles that make up the pan affected? 5.3 Transfer of Heat There have been many predictions about when Earth will end. Fear of Y2K computer problems brought excitement to New Year’s Eve 2000. As you study transfer of heat, you will learn about another proposed end to the universe. S K I L L C H E C K Find Out Initiating and Planning Performing and Recording Blending Water What to Do Analyzing and Interpreting 1. Pour 100 mL of Communication and Teamwork water into each beaker — hot in one, cold in the other. 2. Measure the temperature of the water in each beaker. 3. Pour the water together into the empty beaker. 4. Predict what the temperature will be in two minutes. Wait, then take the temperature. 5. Wipe up any spills and wash your hands Safety Precaution thoroughly. Be careful with glass. What Did You Discover? Handle hot materials with care. 1. Was the temperature of the final mixture between the two starting temperatures? What You Need 3 beakers 2. Predict what the temperature will be if you did this again with 50 mL of water in each beaker. 2 thermometers hot and cold water 3. Predict the final temperature for two different starting temperatures in each beaker. Heat and Heat Transfer MHR 87 SCIENCE Myths A little more than a hundred years ago, scientists showed that light and thermal energy travel to Earth Use a diagram to show as electromagnetic how heat energy flows waves. They knew between a hot and a that waves needed a cold object. substance to travel Figure 5.8 Heat flows from hot objects to cooler ones. In the through. Scientists Find Out Activity — Blending Water, the hot water lost heat and thought space must be the cool water gained heat until the two liquids came to the made up of some type same temperature. In this set-up, heat travels from the hot bar to the cool bar. of substance. They thought that this substance was a low- Forms of Heat Transfer density solid. They Heat flows from hot to cold. The flow continues until both objects are at the called it aether. same temperature. But what really happens? How does thermal energy transfer from one object to another? Read the descriptions below, and then identify each of the forms of heat transfer shown in Figure 5.9. Conduction In Figure 5.10, the molecules of the hot burner vibrate quickly. They have more kinetic energy than the molecules of the cooler pot. Contact between pot and burner causes the molecules of the hot burner to collide with the slower molecules of the cool pot. The collisions result in a transfer of kinetic energy. The molecules of the cooler pot start to vibrate faster, gaining kinetic energy. The molecules of the hot burner vibrate slower, losing kinetic energy. This transfer of heat by contact is called conduction. molecules of pot Figure 5.9 There are three forms of heat lecules of burner transfer shown in this diagram. After reading pages 88–89, Figure 5.10 Conduction is a method of heat transfer that identify each one. requires contact. Contact between warm molecules and colder molecules causes a transfer of kinetic energy. 88 MHR Energy Transfer Technologies  less dense air rises Convection If you hold your hand above the hot burner of a stove, you will feel a warm current of air. Why? warm, fast air cools Heat is transferred, by conduction, from the molecules hot burner to the air molecules touching the burner. These air molecules gain kinetic cool, dense energy, vibrate faster, and get farther apart. air sinks These warm molecules are farther apart than cooler ones, so the warm air is less dense than the cool air around it. This warm air rises, making the warm current that you feel. Cool, denser air rushes in to take the place of the warm air. cold, slower molecules Because of this continuous air flow, all the air replace rising in the room will become warmer. This transfer of warm air heat by movement is called convection. Figure 5.11 Convection is the movement of matter in the form of currents. Convection occurs only in liquids and gases. Radiation Look at the hand in Figure 5.12. The hand is close to the side of a burner but not above the burner. The front of the hand becomes warm while the back remains cool. The front of the hand is not being heated by conduction or Identify the three forms of convection. There is no contact with the burner and convection currents of heat transfer. Explain how warm air would rise away from the hand. heat is transferred in each. The front of the hand is heated by radiation. Radiation is produced by vibrating electrons, which are tiny particles present in all atoms. This vibration makes a wave called an electromagnetic wave or infrared radiation wave. These waves are similar to the waves your hand can create when it vibrates in calm water. Waves or ripples run away from your moving hand. molecules of hand Infrared radiation waves travel from the near burner speed up burner. They strike the hand and transfer heat energy to the molecules in the hand. This causes the molecules in the hand to vibrate faster. Hot objects warm cool ones until their temperatures are the same. Some people believe this evening out of heat will happen to the universe. According to the theory, the temperature of the entire universe will be the same eventually. When this happens, heat will no longer transfer. Without a source of energy, life will be impossible! This prediction is called the “Heat Death of the Universe.” Figure 5.12 Radiation is the transfer of heat by electromagnetic waves. Heat and Heat Transfer MHR 89  S K I L L C H E C K Initiating and Planning Performing and Recording 5–B Analyzing and Interpreting Communication and Teamwork Heat Conductivity Rate On a cold morning, objects made of copper, glass, iron, and aluminum are placed outside. After one hour, all are at the same temperature. But they do not feel equally cold to the touch. Which object feels coldest? Which feels warmest? To find out, compare the conduction rate of heat transfer through various substances. Problem What is the conduction rate of heat transfer through various substances? Prediction 1. Predict which material will conduct heat the fastest: copper, glass, iron, or aluminum. 2. List these materials in order, from the fastest rate of heat transfer to the slowest. State any reasons for your prediction. Safety Precautions Materials matches candle Clean the equipment and wash your hands thoroughly at the end of the investigation. wax beads Apparatus glass rod Bunsen burner clamp 2 clamps heat source metal rod glass rod and metal rods of equal diameter and length heat conductivity apparatus support stand 2 support stands timing device ruler Procedure Part 1: Compare the Rates of Heat Transfer of Glass and Metal 1 Light the candle. Let it burn until there is 3 Arrange the rods so that the free ends come some melted wax at the top. Tilt the candle together over the Bunsen burner flame. carefully, and place drops of wax along the metal and the glass rods, one drop every 4 cm. 4 As the rods heat, observe the melting of the wax beads. Record your observations. 2 Use clamps to attach one end of each rod to a support stand. 90 MHR Energy Transfer Technologies  Part 2: Compare the Rate of Heat Transfer of Various Metals Analyze 1 Place a drop of wax on the 1. What do your results tell you about the transfer of heat end of each metal rod of through metals and non-metals? the heat conductivity apparatus. 2. List the tested materials according to their ability to transfer heat, from fastest to slowest. 2 Secure the conductivity apparatus hub over the flame. Conclude and Apply 3 Time how long it takes for 3. Compare your results with your predictions. Can you each wax bead to melt. explain any differences? Record your observations. 4. Describe three places in your home where you want a fast wax beads transfer of heat. List three situations where you want a different slow transfer of heat. metals wooden handle heat 5. While baking a cake, you want to avoid burning the source bottom of the cake. Should you use a glass or a metal baking pan? 6. Why do some materials feel colder than others? The metals to be tested are joined at one point Key Terms Check Your Understanding conduction 1. There are three methods of heat energy transfer: conduction, convection, convection and radiation. radiation (a) Which method can occur only in liquids and gases? (b) Which method can occur only if there is contact between two surfaces? (c) Which method can occur in a vacuum or in outer space? 2. A hot object is in contact with a cooler object. (a) Does thermal energy flow from the hot object to the cooler object? (b) Explain your answer. 3. As you stand in front of a bonfire, the flames warm you. Use what you have learned about heat transfer to explain: why the part of your body facing the fire is warmer than the part facing away why the flames and smoke rise 4. A metal spoon and a wooden spoon are placed in a refrigerator for several hours. Which will feel colder when it is taken out of the refrigerator? Why? Heat and Heat Transfer MHR 91  5.4 Heat Transfer in Nature Convection causes many weather phenomena, such as winds. You will study that in this section. You will also learn how climate, or average weather conditions based on long-term records, is affected by lakes and oceans. Complete Investigation 5–C to see how liquids and gases behave. S K I L L C H E C K Initiating and Planning Performing and Recording Analyzing and Interpreting 5–C Communication and Teamwork Heat Convection in Liquids and Gases: Teacher Demonstration Problem How is heat distributed in liquids and gases? Prediction Predict the best place to put a heating duct in a basement room. Justify your prediction. Safety Precautions Materials food colouring matches If the paper towel used in Part 2 begins to burn out of control, place paper towel it in the tin tray. water When you have finished Part 2, place the smoking towel in the tin tray. Procedure Apparatus Part 1: Observe Convection in a Liquid block of wood gas convection apparatus 1 Place the glass cooking dish 2 Pour water into the baking hot plate as in the figure shown here. pan until it is about full. Put one end on the hot plate large glass cooking pan tin tray and the other end on the 3 Turn the hot plate on low. block of wood. Make sure that the baking pan is level. 4 Add a drop of food colour- ing to the water above the hot plate. 92 MHR Energy Transfer Technologies 5 Observe what happens to Analyze the colouring and record your observations. Part 1 6 Wipe up any spills and wash your hands thoroughly. 1. What happens to the food colouring over the hot plate? 2. What happens if you place the food colouring at the cold Part 2: Observe Convection end of the cooking dish? in Air 1 Your teacher will set up the Part 2 gas convection apparatus as 3. What happens to the smoke over the cold chimney? shown. 4. What happens to the smoke inside the gas convection apparatus? 5. What happens to the smoke in the hot chimney? Conclude and Apply 6. Use your knowledge of convection of thermal energy. Explain the movement of water in the glass cooking pan. 7. Use your knowledge of convection of heat. Explain the movement of air in the gas convection apparatus. 2 Observe what happens to 8. What is the most effective location for heating ducts in a the smoke in the apparatus. basement room? Does your answer confirm your initial Note your observations. prediction? Extend Your Knowledge 9. Name one situation where convection in liquids is important 10. Name one situation where convection in gases is important. 11. Brainstorm answers to questions 9 and 10 that have not been mentioned in this chapter. Convection Currents and Weather Many cottages are on the shores of lakes where convection currents keep the cottages cool in the daytime and warmer at night. In the evening, the air over the water cools more slowly than the air over the land. Warm air from over the water rises and moves toward the land, keeping it warm. This is just like the dye moving from over the hot plate to the cool end of the cooking pan. During the day, cool air from the lake moves toward the warm land in the same way that dye moved from the cold end of the cooking pan to the hot end. Turn the page to learn the name of the convection currents and how they work. Heat and Heat Transfer MHR 93  Sea and Land Breezes You have demonstrated that warm air rises and cool air sinks. The circular movement that results was identified as convection. All the winds you ever feel start with convection currents. Here is how they work. Land and sea breezes are convection currents of air that occur near a shoreline. They are both created by differences in temperature near the surface of Earth. On a sunny day, radiant heat from the Sun strikes Earth’s surface. Heat is absorbed by land and water. But land and water heat at different rates. Land heats quickly, but also cools quickly. Water heats slowly and takes longer to cool. Sea Breeze B C A D A. Sun’s rays warm land more rapidly than they warm water. B. Warm air is less dense. Warm air rises. C. Air over water is cooler. Cool air is more dense and sinks. D. Cool air flows toward land to replace the warm air that has risen. Figure 5.13A A sea breeze usually occurs on a hot summer day. If you are close to shore, you will feel a breeze blowing from sea to land. This is a sea breeze. A sea breeze is a cool wind that blows from an ocean or lake toward land. It is a cool and welcome relief on a hot day. 94 MHR Energy Transfer Technologies Land Breeze B C D A A. The sea loses heat more slowly than the land. The air over the sea is warmer. Mountain breezes affect the climate of B. Warm air over the sea rises. Calgary. At night, air near the mountains cools, sinks, and flows toward the valleys C. Air over land is cooler. Cool air is more dense and sinks. in Calgary. This mountain breeze cools D. Cool air flows toward the sea to replace the warm air that the city. has risen. Why does Grande Prairie have so many thunderstorms? The answer is in the Figure 5.13B A land breeze is a mild wind that flows from land to ocean. Land number of shallow lakes nearby. breezes usually occur in the evenings. Land breezes often serve to carry air pollutants out to sea, away from coastal cities. Land breezes are weaker than The shallow lakes quickly heat up sea breezes because there is less temperature difference between the land and during sunny days. Warm lake water sea during the evening. heats the air, causing it to rise. As the air rises, it cools and sinks back to the lake. This cycle of rising and sinking air builds convection currents. These currents often create the thunderstorms so common in the area. Place thermometers into equal-sized containers of soil and water. Leave the containers in direct sunlight for several hours. Record the temperatures. Then List or sketch the steps place the containers in the shade for that produce a sea breeze. an hour. Note the temperatures. Do soil and water heat and cool at the same rate? Heat and Heat Transfer MHR 95  S K I L L C H E C K Initiating and Planning Performing and Recording 5–D Analyzing and Interpreting Communication and Teamwork How Oceans Affect Climate Does being near a large body of water, such as an ocean or large lake, affect climate? Think about it, and predict what you will find. Analyze the climate data from several Canadian cities to see if your answer was correct. Climate Pattern Statistics for Five Canadian Cities Mean January Mean July Annual Temperature Temperature Precipitation Average Annual City (°C) (°C) (cm) Sunshine (hours) Calgary, Alberta -11 17 43.7 2208 Québec, Québec -12 19 109.9 1708 Winnipeg, Manitoba -18 20 53.5 2230 Regina, -17 19 39.8 2277 Saskatchewan Vancouver, 2 17 106.8 1931 British Columbia What to Do Analyze 1 Oceans and large lakes are able to hold large amounts of thermal energy without much 1. Compare the mean temperatures, annual change in temperature. How is the tempera- precipitation, and number of annual sun- ture of the air above the ocean affected by the shine hours in Vancouver to those in the temperature of the ocean? other cities. What effect does nearness to 2 Using a map of Canada, locate the cities given the ocean seem to have? in the table. Use a map of the world to notice 2. Why is Vancouver warmer in winter than that the cities are about the same distance Calgary? Use your knowledge of heat north of the equator. transfers to explain. 3 Use the data given to make four different bar Conclude and Apply graphs, one for each column of data. On each graph: 3. Use climate data to help you choose a Place the names of the cities on the place to live. Which city would you horizontal axis (x-axis). choose to live in if: Place the statistic you are analyzing on the vertical axis (y-axis). (a) You did not like cold temperatures? (b) You wished to grow vegetables that require a lot of sunshine and water? (c) You suffered from arthritis that causes severe joint pain when damp weather approaches? 96 MHR Energy Transfer Technologies How Oceans Help to Moderate Climates Oceans are able to store large amounts of thermal energy. This prevents the area around them from having extreme temperature changes. Oceans moderate the climate of land areas near them. This means that they prevent the area from becoming either too hot or too cold. Here is how it works: In cool weather, an ocean can release a great Figure 5.14A Vancouver is beside the ocean and at the foot of amount of heat without cooling much itself. mountains. How will this location affect its climate? Even during very hot or very cold days, and as seasons change, the temperature of oceans remains constant. As the Sun warms air above the ocean, heat flows from the air into the water, cooling the air. When the temperature of the air above the ocean cools, heat flows from ocean to air and warms the air. You could say oceans prevent land near them from getting very warm or very cold. Because of this, coastal cities like Vancouver have moderate climates. Figure 5.14B Calgary is inland and near mountains. How will this location affect its climate? Referring to a specific Canadian city, explain how oceans moderate climate. Key Terms Check Your Understanding sea breeze 1. The city of Winnipeg is located near Lake Winnipeg, a large lake. Why land breeze does Winnipeg not experience much of a drop in temperature at the end moderate of a hot day? 2. List or sketch the steps that produce a land breeze. 3. On a hot day, which place would be cooler? Explain why you think so. a beach beside a large lake 20 km away from the lake Heat and Heat Transfer MHR 97  5.5 Heat Transfer and Technologies Do dull, rough surfaces absorb heat more readily than smooth, shiny ones? Develop an investigation to find out. Figure 5.15 Tea drinkers rinse an empty teapot with hot water before adding more hot water and tea. How might this affect the tea leaves and the temperature of the finished tea? Many household technologies either transfer or prevent the transfer of heat through conduction, convection, or radiation. That is why metal cooking pots have hard plastic or wooden handles. What other techniques are used to handle hot food? Most cooks want to control how food is heated. Consider what happens when heating soup on a stove. The pot is heated by conduction through contact with the heating element. The soup at the bottom of the pot heats up first through conduction. Heated soup rises to the top because it is less dense. Colder soup near the top of the pot flows to the bottom because it is denser. A circular motion in the soup results. These convection currents in the pot heat the soup to a uniform temperature. www.mcgrawhill.ca/links/science.connect1 Your home or apartment is heated using technologies designed to transfer heat by conduction, convection, and radiation. In most cases, a non-renewable energy source is used. Can renewable sources of energy be used instead? Can designers take advantage of solar energy to heat your home or school? To answer these and other questions, go to the above web site. Go to Internet Connects, Unit B, Chapter 5, and then to Renewable Energy. 98 MHR Energy Transfer Technologies  When an oven is turned on, convection air currents move heat inside the oven. Air at the bottom of the oven is heated by burning gas or an electric element. Heated air becomes less dense and rises to the top of the oven. Cooler air sinks to the bottom. The hot air heats the oven walls. These walls then radiate heat in all directions. In this way, food in the oven is cooked by both convection and radiation. There is also conduction from the baking pan. Light-coloured surfaces reflect more heat than dark surfaces. This is why people in hot countries often wear white garments. Use a labelled sketch or diagram to show how an Figure 5.16 Metal cooking pots and utensils are used around the world. oven heats food. Firefighters train constantly to learn how to control heat transfer. Training helps them do their job and protect their own life. If you have considered becoming a fire- fighter since you enjoyed playing with your first toy fire truck, you are now closer than ever. If you are in good physical condition and are working toward a high school diploma, the big steps are behind you. The firefighter in the photo is trained to extinguish structural fires in a city. Her job is what most people think of as firefighting. But there is more. In Alberta, you can take special training to learn how to control wild- land fires. Also, Alberta has a worldwide reputation for expertise in extinguishing chemical and oil fires. Any of these firefighting opportunities promise excitement and high interest. Figure 5.17 Heat and Heat Transfer MHR 99  Getting Rid of the Heat Combustion of fuel inside an engine produces a large quantity of thermal energy. If this energy were not removed, the engine would overheat and be damaged. Here is how the engine is protected: The engine’s cooling system contains a liquid coolant. Heat is conducted from the engine to the coolant. The coolant is pumped through the engine block to the radiator. A radiator is a honeycomb made of a metal alloy. The metal alloy is a good conductor. Sketch one device that Heat from the coolant is conducted through this alloy to air. protects against heat Either a fan or the motion of the vehicle forces this air through the radiator. transfer. Explain how it Heat is transferred to the air that rushes through the radiator. works. These three techniques use conduction to protect engines from heat damage. Figure 5.18 Radiators like A. coolant input this are used to cool gas and from engine A diesel engines. B. radiator core C. coolant outlet to engine D. tube B E. veins made of metal alloy E D C Figure 5.19 An air-cooled engine has no radiator. How do the fins on this engine keep it from overheating? 100 MHR Energy Transfer Technologies Keeping It Cool When you put a little water on the back of your hand, your hand becomes cool. That is because thermal energy transfers from your hand to the water through conduction. Water absorbs heat from your hand and evaporates. Evaporation removes thermal energy as the water molecules leave the water droplets and move into the air. Your hand feels cooler. This form of cooling is usually called cooling by evaporation. Evaporation caused the cooling, but the cooling action started with conduction of heat away from your hand. Heat Transfer in a Refrigerator B A. A fluid called a coolant circulates expansion valve through the pipes. B. Heat from the food transfers to the cooler air surrounding it. Thermal A energy then transfers from the air to the coolant. C. The coolant evaporates as it gets warmer. It is pumped to the E compressor. D. When it reaches the compressor, pressure is applied to change it back into a liquid. C E. The liquid coolant is pumped to these coils. Thermal energy is released into the room. The cycle starts again. Figure 5.20 Feel the pipes on the back of a fridge. They compressor are hot. Heat from the items inside the fridge has been transferred to these pipes. The warm pipes release the thermal energy into the room. D Check Your Understanding 1. List the transfers of energy involved in boiling water in a pot. Describe each transfer. 2. Explain how three kinds of energy transfer are used in an oven when you bake bread. 3. Suppose you are given two cups of hot chocolate. One cup is made of shiny metal, and the other cup is made of a metal that has been painted black. Which cup will keep your hot chocolate warm longer? Explain. 4. Describe two ways of cooling gasoline engines. Heat and Heat Transfer MHR 101  C H A P T E R 5 Review Key Terms friction thermal energy conduction sea breeze Robert Brown kinetic energy convection land breeze Brownian motion temperature radiation moderate heat Reviewing Key Terms (k) A wind that occurs as a result of air If you need to review, the section numbers show flowing from the sea to the land is called you where these terms were introduced. a _____________. (5.3) (l) A jiggling motion of small particles in 1. In your notebook, write the correct term to water is called _____________. (5.1) complete the following sentences: (a) The sum of all the kinetic energies of an Understanding Key Ideas object is its _____________. (5.2) Section numbers are provided if you need to review. (b) The average of all the kinetic energies of an object is its _____________. (5.2) 2. What theory did Brown suggest to explain the (c) The energy due to motion of particles in nature of heat? (5.1) an object is its _____________. (5.2) 3. You take the temperature at various locations in (d) A process of heat transfer that occurs when a container of water. You find the temperature two objects are in contact with each other is the same at all locations. Are all the particles is _____________. (5.3) of water vibrating at the same speed? (5.2) (e) The process that releases heat when two objects rub together is _____________. (5.1) 4. You hold a burning candle in one hand. Which (f) The first person to observe a sign of of the three processes of heat transfer occurs in molecular motion was _____________. (5.1) each of the following situations? (5.4) (g) A process of heat transfer that involves the (a) Your other hand is held high above the circular flow of air or liquids is called burning candle and feels heat. _____________. (5.3) (b) Your other hand is held near to the side of (h) A process of heat transfer that involves the flame. The front of your hand feels heat. electromagnetic waves is called _____________. (5.3) (i) A wind that occurs as a result of air flowing from the land to the sea is called a _____________. (5.4) (j) Oceans keep land near them from having temperature extremes. We say that oceans _____________ temperatures. (5.4) (c) A drop of wax falls on your hand and you feel heat. 102 MHR Energy Transfer Technologies  5. Why do land breezes occur during the 11. You are planning a holiday to an area with a evening? (5.4) hot climate. Describe some clothes you should take with you. Explain why they will 6. Toronto, Ontario is beside Lake Ontario. The keep you cool. (5.3) temperature there does not drop much at night, after a hot day. Why is this? (5.4) 12. You open the hood of an overheated car. Draw a diagram showing where conduction, 7. Use a sketch to show why hot air registers are convection, and radiation of heat are taking placed on the floor and air conditioning out- place. (5.5) lets are placed near the ceiling. (5.4) Developing Skills Critical Thinking 13. James Prescott Joule measured water 8. A boat in a harbour on a hot sunny day has a temperature at the top and then at the flag hanging from the mast. (5.4) bottom of a waterfall. Would he have (a) In what direction will the flag blow detected a difference in temperature? at noon? Explain your answer. (5.5) (b) Which way will it blow just after sunset? 14. A vacuum has nothing in it: no air, no liquid. Problem Solving/Applying Do you think it is possible to measure the temperature of a vacuum? Explain your 9. Look at the identical objects below. In which answer. (5.3) object is the average kinetic energy of the particles greater? Explain. (5.2) 1. Take another look at the chapter opener on page 80. List some concerns about heat that a climber must consider. 20°C 40°C 2. Check your original answers to the Getting Ready questions on page 80. How has your thinking changed? How would you answer these questions now that you have investigated the topics in this chapter? 10. Look at the objects below. Do their particles have the same average kinetic energy? Which object has more heat? Explain. (5.2) 60°C 60°C Heat and Heat Transfer MHR 103