1.1 What is thermodynamics?Thermodynamics is the science which has evolved from the original investigationsin the 19th century into the nature of \heat." At the time, the leadingtheory of heat was that it was a type of fluid, which could flow from a hot bodyto a colder one when they were brought into contact. We now know that whatwas then called \heat" is not a fluid, but is actually a form of energy { it isthe energy associated with the continual, random motion of the atoms whichcompose macroscopic matter, which we can't see directly.