The apparatus we have been discussing will have been more or less familiar to you. We want now to draw attention to some of the issues which we raised in the Presentation, and others which are very important for an undertsanding of the nature of thermal physics. We can do this by way of a series of questions. We will also indicate where the questions are to be studied.
(i) The calorimetric unit of heat assumes that we already have a valid scheme of temperature measurement. But how is this scheme constructed? In particular, why do we place reliance on the different thermometers we have, and expect their readings to agree with each other? These questions are examined in Study Unit 4, where we have to use three Laws of Thermodynamics.
(ii) Another question studied in the Study Unit 4, on temperature measurement, is why we associate heat flow with two bodies at different temperatures placed in thermal contact with each other. In Study Unit 4, we begin with the Zeroth Law of Thermodynamics which is related to this question.
(iii) At various points we made the assumption that we could use electrical means of heat production, and measure this heat production in terms of mechanical units of energy such as ergs or joules. But what is the link between the calorimetric unit of heat and mechanical units of energy? This question is discussed in Study Unit 2 where we introduce the First Law of Thermodynamics, which defines how heat and work (mechanical energy transfer) can be related together by means of the concept of the internal energy of a system.
(iv) In considering changes of phase, we had situations where heat input produced no increase in the temperature of the system. But something must change in the system because of the energy entering it in the form of heat. This something is known as entropy and is introduced in Study Unit 3, where we shall encounter the Second Law of Thermodynamics.
(v) At no point did we stop to ask about changes in temperature of energy of a system in terms of its internal structure. What goes on "inside" bodies which depends on temperature, entropy or internal energy? This question is pursued in Study Units 5, 6, 7, and 8. In these Units, we shall also encounter what is known as the Third Law of Thermodynamics. It appears, when one is studying what is known as "heat", that thermal physics is something completely separate from mechanics and "modern physics". Thermodynamics is the science that connects the thermal and the mechanical. In our studies of thermal physics we explore what lies beyond the calorimetric unit of heat.