Granular Gas — Inelastic Collisions

Particles lose kinetic energy on collision (coefficient of restitution e < 1), leading to cooling, clustering, and inelastic collapse.

Granular gases (Haff 1983): inelastic collisions cause Haff's cooling law T ~ (1+t/t0)^{-2}. Below e_c(phi), clustering instability develops (van Noije-Ernst). At e→0, inelastic collapse: infinite collisions in finite time. This simulation uses event-driven MD.