Introduction

In order to have a good understanding of the laws of thermodynamics, it would be helpful to have a deep appreciation of the meaning of the words law and thermodynamics. So let's take a moment to think about words before launching into a detailed discussion of the First Law. We are aided in this by the nature of science itself, which unlike ordinary prose and poetry aims to give words a more or less precise meaning.

We are familiar with the concept of law from our everyday experience. Laws are rules that we are not supposed to break; they exist to protect someone's interests, possibly our own, and there may be a penalty to pay if the one who breaks a law gets caught. Such are civil and criminal laws. Physical laws are similar but different. They are similar in that they regulate something, namely how matter behaves under given circumstances. They are different in that violations are not known to have occurred and they describe what is considered to be a basic property of nature. If a violation of a physical law should ever seem to occur, one would think first that the experiment had gone wrong at some stage, and only second that maybe the ‘law’ wasn't a law after all. For instance, Galileo, like Copernicus, believed that the orbits of the planets were circles, for the circle is a perfect shape and perfection is of the heavens.