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The rate of heat flow is proportional to the difference in temperature. Thermal equilibrium occurs when temperatures are equal. Heat flow stops in thermal equilibrium. The rate of heat transfer between a warmer and a colder body slows down as the temperature difference between them gets smaller. Heat conduction is the transfer of heat through or between materials by direct contact. Thermal conductivity describes the rate at which heat is conducted through a substance. Convection is the transfer of heat by the motion of liquids and gases, such as hot air rising above a candle flame. Free convection occurs when the fluid moves on its own owing to differences in density. Forced convection occurs when fluid flow is driven by wind, pumps, fans, or other means. Thermal radiation is the transfer of heat energy through electromagnetic waves, including light. Radiation can travel through space without the presence of matter whereas both conduction and convection occur only through matter. All three mechanisms of heat transfer (conduction, convection, and radiation) usually act at the same time, but not all are equally effective at any given temperature or in any given situation. 
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thermal equilibrium, Newton’s law of cooling, heat transfer, thermal conductivity, convection
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Review problems and questions |
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- Describe a situation you experienced in the last 24 hours in which heat flows through
- conduction.
- convection.
- radiation.
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Answers will vary. Some examples are as follows:- I touched a metal utensil in a pot of hot water and got burned.
- I warmed and dried my hands using hot air from a hand dryer.
- I felt the Sun warm up my skin.
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- Some people place mirrored reflectors in their car windows on hot, sunny days to reduce the heat gain by
- conduction.
- convection.
- radiation.
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c. radiation
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- If you drop some confetti above a warm radiator, the flakes of paper will rise as warmed air above the radiator rises. This is a good example of heat transfer through
- conduction.
- convection.
- radiation.
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b. convection
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- The end of a silver spoon gets warm a few moments after the bowl of the spoon is immersed in hot soup. The end of the spoon gets warm mainly because of
- conduction.
- convection.
- radiation.
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a. conduction
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