Heat has been closely associated with the comfort and support of people
throughout history. You can imagine the appreciation when your earliest ancestors
first discovered fire and learned to keep themselves warm and cook their food.
You can also imagine the wonder and excitement about 3000 b.c., when people
put certain earthlike substances on the hot, glowing coals of a fire and later
found metallic copper, lead, or iron. The use of these metals for simple tools
followed soon afterwards. Today, metals are used to produce complicated engines
that use heat for transportation and that do the work of moving soil and rock,
construction, and agriculture. Devices made of heat-extracted metals are also
used to control the temperature of structures, heating or cooling the air as
necessary. Thus, the production and control of heat gradually built the basis
of civilization today (Figure 5.1). The sources of heat are the energy forms that you learned about in chapter
4. The fossil fuels are chemical sources of heat. Heat is released when oxygen
is combined with these fuels. Heat also results when mechanical energy does
work against friction, such as in the brakes of a car coming to a stop. Heat
also appears when radiant energy is absorbed. This is apparent when solar energy
heats water in a solar collector or when sunlight melts snow. The transformation
of electrical energy to heat is apparent in toasters, heaters, and ranges. Nuclear
energy provides the heat to make steam in a nuclear power plant. Thus, all energy
forms can be converted to heat. The relationship between energy forms and heat appears to give an order
to nature, revealing patterns that you will want to understand. All that you
need is some kind of explanation for the relationships--a model or theory that
helps make sense of it all. This chapter is concerned with heat and temperature
and their relationship to energy. It begins with a simple theory about the structure
of matter, and then uses the theory to explain the concepts of heat, energy,
and temperature changes. |
2002 McGraw-Hill Higher Education