8. What is an equation of state?

           Anything observed in the universe is the result of the action of many basic particles (billions, billions, and billions of particles). To describe observables we thus must consider large numbers of particles. What we do is take a large number of particles in a given volume of space and determine properties which describe the behavior of the group in a small local volume of space. The equation describing the properties of this group is called an equation of state.  The most common equation of state and the one from which practically every observable in the universe can be derived is the “ideal gas” equation of state. The equation is very simple

What this equation represents is as follows:

1.      Consider a volume of space.
2.      The volume contains many perfectly elastic, hard, spherical, smooth particles all with the same diameter and mass making up a rare gas.
3.      The particles are all moving at constant speed in a straight path (except when they collide) at a root mean square velocity .
4.      The density is the number of particles per unit volume times the mass of each.
5.      The pressure p is the force per unit area required to contain the gas in the volume.

           It is believed that this equation represents everything in the universe except at the very core of the elementary particles of physics and transiently when a gas is moving in a curved path.

            The eight conservation laws along with equations of state are the tools (and the only tools) we have to explain all the observed physical phenomena which occur in the universe.