thermal conductors and insulators
Conduction is the transfer of thermal energy between particles of matter that are touching. Thermal conduction occurs when particles of warmer matter bump into particles of cooler matter and transfer some of their thermal energy to the cooler particles. Conduction is usually faster in certain solids and liquids than in gases. Materials that are good conductors of thermal energy are called thermal conductors. Metals are especially good thermal conductors because they have freely moving electrons that can transfer thermal energy quickly and easily. Besides the heating element inside a toaster, another example of a thermal conductor is a metal radiator, like the one in the Figure 1.1. When hot water flows through the coils of the radiator, the metal quickly heats up by conduction and then radiates thermal energy into the surrounding air. Q: Thermal conductors have many uses, but sometimes its important to prevent the transfer of thermal energy. Can you think of an example? A: One example is staying warm on a cold day. You will stay warmer if you can prevent the transfer of your own thermal energy to the outside air.
One way to retain your own thermal energy on a cold day is to wear clothes that trap air. Thats because air, like other gases, is a poor conductor of thermal energy. The particles of gases are relatively far apart, so they dont bump into each other or into other things as often as the more closely spaced particles of liquids or solids. Therefore, particles of gases have fewer opportunities to transfer thermal energy. Materials that are poor thermal conductors are called thermal insulators. Down-filled snowsuits, like those in the Figure 1.2, are good thermal insulators because their feather filling traps a lot of air. Another example of a thermal insulator is pictured in the Figure 1.3. The picture shows fluffy pink insulation inside the attic of a home. Like the down filling in a snowsuit, the insulation traps a lot of air. The insulation helps to prevent the transfer of thermal energy into the house on hot days and out of the house on cold days. Other materials that are thermal insulators include plastic and wood. Thats why pot handles and cooking utensils are often made of these materials. Notice that the outside of the toaster pictured in the opening image is made of plastic. The plastic casing helps prevent the transfer of thermal energy from the heating element inside to the outer surface of the toaster where it could cause burns. Q: Thermal insulators have many practical uses besides the uses mentioned above. Can you think of others? A: Thermal insulators are often used to keep food or drinks hot or cold. For example, Styrofoam coolers and thermos containers are used for these purposes.
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thermal conduction occurs more quickly in certain solids and liquids than in gases.
--> a. true b. false
good thermal conductors include
--> a) aluminum. b) plastic. c) wood. d) two of the above
when you wear a down jacket, it prevents the transfer of cold from the outside air to your body.
a. true --> b. false
good thermal insulators include
a) air. b) styrofoam. c) iron. --> d) two of the above
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