Development of the concept Of energy
Heat and internal energy
In chapter 7 we talked about energy in general and noticed that heat is involved as a step in practically all the various energy transfers which lead to the production of that most useful of all forms of energy, namely electricity.
Our present concept of energy and its measurement arose out of a search for an understanding of what it was that made things hot. As this quest took more than two and a half centuries, it is well that we should spare a little time in this chapter saying something about the scientists who were responsible for it. On page 78 we explained that, in physics, the word heat is the name given to energy in the process of transfer from one body to another as the result of a temperature difference between them. Once heat has been transferred to a body or substance, it ceases to be heat and instead becomes internal molecular energy. In the past, and this must be remembered when reading older textbooks, the word heat has been used to mean the same thing as internal energy. Indeed, the early scientists who themselves were responsible for the development of the idea of energy used the word heat in the same way.