Temperature

Defining temperature in thermodynamics is particularly troublesome, even though it seems obvious to all of you about what it is. The Zeroth law is mechanism for defining temperature and it says, ``if two objects are in thermal equilibrium with a specified object, then the two objects would be in thermal equilibrium with each other--and in fact they have the same temperature.'' That specific object in the previous sentence is a thermometer.

It is very important to learn the difference between temperature, heat capacity and heat. Many people get confused by this. Heat is the work-less transfer of energy from one entity to another. Temperature is that which is equal when heat is no longer conducted between bodies in thermal contact. Heat capacity is how much the temperature changes as you add heat to a body that remains in the same state.

Note that the sentences in the above paragraph start growing lots of clauses (e.g., `` $\ldots$body that remains in the same state.''). This happens in thermodynamics because the exceptions to the rule have to be removed so that the logic can proceed from true statements. Unfortunately, it increases the effort that one must exert in reading (rigorous) thermodynamics books.