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Bumping Along Even though conduction is a transfer ofkinetic energy from particle to particle, in a solid, the particlesinvolved don’t travel from one place to another. As shown inFigure 17, they simply move back and forth in place, bumpinginto each other and transferring energy from faster-moving particlesto slower-moving ones. Conduction usually occurs in solids.How is energy transferred by conduction?Conductors It’s dinnertime and the hamburgers are frozensolid. This is one time when you want to transfer heat rapidly. Youcould put a frozen hamburger on a metal tray to speed up thethawing process. Materials through which it is easy to transferenergy are thermal conductors. Most metals are good conductorsof heat. Metals such as gold, silver, and copper are the best thermalconductors. Copper is widely available and less expensivethan gold or silver. Some cooking pans are made of steel but havecopper bottoms. A copper bottom conducts heat more evenly. Ithelps spread heat across the bottom surface of the pan to preventhot spots from forming. This allows food to cook evenly.Insulators Some materials are poor conductors of heat.These materials can be used as thermal insulators. When you arecold, for example, you can put on a sweater or a jacket or addanother blanket to your bed. You are keeping yourself warm byadding insulation. The clothes and the blanket are poor conductorsof heat. In fact, they make it more difficult for heat to escapefrom your body. By trapping your body heat around you, youfeel warmer.Blankets and clothes help keep you warmbecause they are made of materials that containmany air spaces, as shown in Figure 18.Air is a good insulator, so materials that containair are also good insulators. For example,building insulation is made from materialsthat contain air spaces. Materials made ofplastics also are often good insulators. If youput a plastic spoon in boiling water, it takes along time for it to get hot. Many cookingpans have plastic handles that won’t meltinstead of metal ones. These handles remainat a comfortable temperature while the pansare used for cooking. Other examples ofinsulators include wood, rubber, and ceramicmaterials such as tiles.Figure 17 In a solid, particlescollide with each other as theyvibrate back and forth.Figure 18 Under high magnification,this insulating material isseen to contain many air spaces.Explain how increasing the numberof air spaces in a materialaffects the movement of heat.SECTION 2 Temperature 175Thinsulate is a trademark of 3M. Photo courtesy 3M
Figure 19 The furnace’s fanhelps circulate hot air through yourhome. Warmer air particles moveupward while cooler air particlesmove downward.Explain why the hot air ducts areplaced near the floor.Hot airCold airExhaustAir ductFurnaceFanComparing EnergyContentProcedure1. Pour equal amounts ofhot, cold, and roomtemperaturewater intoeach of three transparent,labeled containers.2. Measure and record thetemperature of the waterin each container.3. Use a dropper to gentlyput a drop of food coloringin the center of eachcontainer.4. After 2 min, observe eachcontainer.Analysis1. Based on the speed atwhich the food coloringspreads through the water,rank the containers fromfastest to slowest.2. Infer how water temperatureaffected the movementof the food coloring.3. In which container do thewater particles have themost kinetic energy?Feeling the Heat Think about getting into a car that hasbeen closed up on a sunny day. Do you prefer a car that hasfabric-covered or vinyl-covered seats? Even though the massesof the seats are similar and the temperatures of the surroundingsare the same, the vinyl material feels hotter on your skinthan the fabric does. How hot something feels also is affected byhow fast heat flows, as well as the actual temperature. Vinyl is abetter conductor than fabric, so heat flows to your skin morerapidly from the vinyl than from the fabric. As a result, the vinylfeels hotter than the fabric does.Convection Heat also can be transferred by particles that donot stay in one place but rather move from one place to another.Convection (kun VEK shun) transfers heat when particles movebetween objects or areas that differ in temperature. This type oftransfer is most common in gases and liquids. As temperatureincreases, particles move around more quickly, and the distancebetween particles increases. This causes density to decrease astemperature increases. Cooler, denser material then forces thewarmer, less dense material to move upward.Some homes are heated by convection. Look at Figure 19.Air is warmed in the furnace. The warm, less dense air is thenforced up through the air duct by the furnace fan. The warm airgets pushed up through the room by the cooler air around it. Asthe warm air cools, it becomes more dense. Cool, dense air sinksand is then pulled into the return air duct by the furnace fan tobe warmed again and recirculated.176 CHAPTER 6 Energy
Page 1 and 2: Energysections1 Energy Changes2 Tem
Page 3 and 4: ■ Explain what energy is.■ Desc
Page 5: Food Is ChemicalEnergy You transfor
Page 8 and 9: Increasing Potential Energy When yo
Page 10 and 11: Kineticenergy istransferredto grass
Page 12 and 13: Figure 12 Temperaturedepends on the
Page 14 and 15: The Celsius Scale Another temperatu
Page 18 and 19: Examples of Convection Eagles and h
Page 20 and 21: Hydrogengas moleculeHydrogenatomOxy
Page 22 and 23: Energy-Releasing Reactions Endother
Page 24 and 25: Imagine standing at the top of a mo
Page 26 and 27: 4. Pour 100 mL of room-temperature
Page 28 and 29: Energy Changes1. Energy is the abil
Page 30 and 31: 18. Concept Map Below is a concept
Page 32: Record your answers on the answer s

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