What is the difference between dynamical clustering and cooling ? This question is often debated. Cooling is the mechanism in which successive inelastic collisions dissipate the energy of the granular gas, leading to large scale inhomogeneities called clusters. The latter being observed in different parts the experimental cell. In order to avoid cooling, continuous injection of energy through moving walls can be envisaged. Depending on the number of particles, the balance between dissipation and energy injection leads to a cluster in the middle of the cell. This is called dynamical clustering.

Both physical phenomena are related to energy dissipation but they are . In order to visualize that difference, the following video is proposed : at the beginning a dynamical clustering is shown before wall motion stops, leading to cooling.

UPDATE : New movies have been also added in WP sections : energy injection and dissipation (WP1), asymmetric driving (WP3) and Maxwell’s demon (WP4).