Thermodynamics is the science that deals with work and heat, and the transformation of one into the other. It is a macroscopic theory, dealing with matter in bulk, disregarding the molecular nature of materials. The corresponding microscopic theory, based on the fact that materials are made up of a vast number of molecules, is called statistical mechanics.

Benjamin Thompson, Count von Rumford (1753-1814) recognized from observing the boring of cannon that the work (or mechanical energy) involved in the boring process was being converted to heat by friction, causing the temperature of the cannon to rise. With the experiments of James Joule (1818-1889), it was recognized that heat is a form of energy that is transferred from one object to another, and that work can be converted to heat without limit. However, the opposite is found not to be true: that is, there are limiting factors in the...