1. Gas is a medium in which the constituent particles, such as atoms and molecules, move freely and randomly between collisions. The collision duration in gases is many orders of magnitude shorter than the mean time of free flight between collisions. The degree of rarefaction of a medium in gas dynamics is discussed in Refs. 1-4.
2. B. Processes in a Medium
3. T Translational Processes of establishment of equilibrium or quasistation
4. R Rotational Processes ofestablishment ofequilibrium or quasistationary