Heat and Temperature

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Every great advance in science has issued from a new audacity of imagination ~ John Dewey (1859-1952)

Thermal energy is the energy associated with heat. Although the concept of heat is not new, its formal understanding only became clear during the nineteenth century when it was shown that heat is the result of the motion of molecules—a concept that laid the foundation for the laws of thermodynamics.

In this chapter, we will give formal definitions of heat and temperature and explain how heat can be transferred as a result of a temperature difference. Then we will discuss various modes of heat transfer and the laws of thermodynamics. Finally, we will show how these laws can be used to design practical devices and more efficient machines.


Heat and Temperature

Two of the earliest words that children learn are “hot” and “cold”. They quickly learn to avoid touching hot stoves and getting too close to fires. They also learn to protect themselves with warm clothes in wintry weather and to stay in the shade on hot summer days. In spite of this common perception, precise definitions of heat and temperature are no less elusive than most abstract concepts in physics. As we shall soon learn, heat is a form of energy that flows from a hot object to a cold object as a result of a temperature difference that exists between them.


(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

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