Elementary preamble to a theory of granular gases

Granular materials partake almost dramatically at times of the properties of solids and, under different circumstances, of some properties of gases. Here, within the mechanics of mass points, an elementary analysis, involving predominantly velocities rather than places, is shown to lead to a global equation concerning the shuffling motions (in addition to continuity and Cauchy's equations); it involves a stirring tensor and rules the evolution of a Reynolds' tensor.