Thermodynamics is that branch of physics which seeks to derive relationships between properties of matter, especially those which are affected by temperature, and a description of the conversion of energy from one form to another. Mechanical engineering systems are primarily about energy exchanges. All mechanical engineers must therefore be well grounded in the relationships which describe those exchanges. They must also be skilled in analysing machinery and systems in which the energy exchanges occur. Thermodynamics is therefore an essential and most important part of any mechanical engineering course of study.