The concept of energy without heat or work

Several recent articles in Physics Education have discussed the difficulty of teaching the concept of energy (Schmid 1982, Warren 1983 and Watts 1983). The first step is for the teacher to gain a clear understanding of the concept. This is not easy. A common definition is that energy is the capacity of a body for doing work but there are considerable problems with this notion, so much so that it would be fair to say that it is misleading, if not completely incorrect. Consider a substance that has a high temperature. It can be made to work in cooling to a lower temperature, but the maximum work that can be done is limited by the second law of thermodynamics. This is well recognised in the study of thermodynamics of heat engines. The limitations put on the doing of work by the second law of thermodynamics make this definition of energy a very poor one. Moreover, the notion of work, like that of heat, bristles with difficulties and is best avoided wherever possible, Pitzer and Brewer (1961) comment 'There are two terms heat and work that have played an important part in the development of thermodynamics but their use has often brought an element of vagueness into a science that is capable of the highest precision'. The concept of energy is developed without the use of these two terms.