9 - Heat, work, and putting heat to work

Summary

A man hath sapiences thre Memorie, engin and intellect also

Chaucer

Engines are, etymologically and in fact, ingenious things. By the end of this chapter we shall understand heat-engines, which are devices that convert ‘heat’ – an intuitive idea to be made precise here – into pushes or pulls or turns. First, however, we need to systematize some of the things we have already learnt about energy and entropy, and thereby extract the science of Thermodynamics from the statistical viewpoint of the last chapter.

Thermodynamics is a theory based on two ‘Laws,’ which are not basic laws of nature in the sense mentioned in Chapter 1, but commonsense rules concerning the flow of energy between macroscopic systems. From the point of view we are taking here, these axioms follow from an understanding of the random motion of the microscopic constituents of matter. It is a tribute to the genius of the scientists – particularly Carnot, Clausius, and Kelvin – who formulated thermodynamics as a macroscopic science, that their scheme is in no way undermined by the microscopic view, which does, however, offer a broader perspective and open up avenues for more detailed calculations. (For example, effusion – discussed at the end of the last chapter – lies beyond the scope of thermodynamics.)

Work, heat, and the First Law of Thermodynamics

The First Law of Thermodynamics is about the conservation of energy.