TABLE OF CONTENTS Who...is not familiar with Maxwell s memoir on his dynamical theory of gases? ...from one side enter the equations of state; from the other side, the equations of motion in a central field. Ever higher soars the chaos of formulae. Suddenly we hear, as from kettle drums, the four beats put n=5. The evil spirit v vanishes; and...that which had seemed insuperable has been overcome as if by a stroke of magic... One result after another follows in quick succession till at last.... we arrive at the conditions for thermal equilibrium together with expressions for the transport coefficients.
Ludwig Boltzmann
The perfect gas is an idealization of reality. As we have seen, this idealization gives rather accurate results for equilibrium properties of most gases, but there are some properties of these gases on which it can shed no light. In particular, if we are to understand transport processes such as diffusion and conduction in real gases, collisions must be taken into account (the photon gas is an exception; photons in a vacuum do not interact with each other). A gas which is ideal in its thermodynamic properties, but in which the molecules undergo collisions, is called quasi-ideal. We confine our attention to elastic collisions; that is, encounters between two particles in which the total kinetic energy is conserved but the direction of motion of one or both particles is altered. Such a process is called scattering.
The simplest system...
