In this chapter we consider briefly some of the basic concepts of heat and temperature. The treatment is simple and restricted to those aspects which will be of use in later parts of the book.

Temperature

The concept of temperature

The concept of temperature originally arose from a sensory feeling of hot or cold. Probably all physical concepts arise in a similar way; the next step is to turn the idea into something more general and, in particular, more objective. One such approach is as follows. It is found that a given mass of gas is completely specified by its volume V and its pressure P. Suppose we start with 1 kg of a gas and subject it to any changes we wish, whether by compressing it, cooling it, allowing it to expand, heating it; we then take another 1 kg specimen of the same gas and carry out a completely different series of operations. If we end up with the same values of V and P for the two samples, the final states will be found identical in every way – colour, warmth, viscosity, and every objective and subjective test to which we can subject the sample.

If we end up with different P, V values there is something different about the samples and if they are placed in contact changes take place until they reach identical P, V values (see section 2.1.3 below).