 Let us now look at the way properties are classified. One way to classify properties in thermodynamics is to look at the origin of these properties. For example, some properties could be primitive properties. Primitive properties are defined elsewhere and used in thermodynamics. For example, from geometry we use volume defined in geometry, mass, velocity defined in mechanics, kinetic energy, gravitational potential energy also defined in mechanics. So these are the properties which are defined by other branches of physics and are absorbed in thermodynamics with all their characteristics as defined in other branches of physics. A very common property which we will be using is pressure, force per unit area which is defined in mechanics. Then come the most important set of properties. Let us call them basic thermodynamic properties. These are based on the laws of thermodynamics. Since we are going to study basically three laws of thermodynamics, the three laws will give us three basic thermodynamic properties. For example, the zeroth law will help us define a thermodynamic property called temperature. The first law will help us define a thermodynamic property called energy from which because energy is an idea which is common to many other branches of physics, we will extract a component which is thermal energy. And finally the second law which will help us define the third and a very important thermodynamic property called entropy. We also have a third type of property known as the derived property. Derived properties are used to short forms. These are combination of other properties. One very common combination is the following. We come across this combination u plus e is the thermal energy and pressure volume product added together. This combination turns up so often in thermodynamics that we give it a short form and another name enthalpy. The symbol often used is H, the name is enthalpy. There are other properties which we will come across later as derived properties. For example, the Gibbs function, the Helmholtz function. Another illustration of a derived property are compressibility or expansion coefficient. For example, for a fluid, this is known as an alpha and is known as the isobaric thermal expansion coefficient. And there are many