Inelastic kinetic theory: The granular gas

A brief introduction to the physics of granular materials, with strong emphasis on granular gases, is presented. A Boltzmann equation for granular gases, composed of monodisperse smooth inelastic spherical particles is presented, and an extension of the ChapmanEnskog expansion is used to derive constitutive relations for these gases. A further extension to the case of weakly frictional granular gases is presented as well. Much stress is put on distinguishing between the specific properties of materials whose "elementary constituents" are macroscopic grains (which experience dissipative interactions), and "regular" or molecular matter. In particular, the lack of scale separation in granular materials is demonstrated, and some of its consequences are explained.