Description:
<jats:p>The model of a linear Rayleigh gas is used to demonstrate some basic features of irreversible processes. The macroscopic aspects of the model provide an introduction to the conceptions of friction, relaxation, complex susceptibility, and energy dissipation. Fluctuations are discussed on the basis of a Langevin equation for the model that is derived starting from elementary collision dynamics. The relation between observable fluctuations and molecular dynamics is elucidated in terms of time correlation functions for the model and for real systems. Examples are given including the transport of matter, electricity, momentum, and energy as well as dielectric, magnetic, and chemical relaxation.</jats:p>