We are reporting an experimental study performed on a granular gas enclosed into a 2D cell submitted to controlled external vibrations. Experiments are performed in microgravity during parabolic flights. High‐speed optical tracking allows to obtain the kinematics of the particles and the determination of all inelastic parameters as well as the translational and rotational velocity distributions. The energy into the medium is injected by submitting the experimental cell to an external and controlled vibration. Two model gases are studied beads and disks; the latter being used to study the rotational part of the particle’s dynamics. We report that the free cooling of a granular medium can be predicted if we consider the velocity dependence of the normal restitution coefficient and that the experimental ratio of translational versus rotational temperature decreases with the density of the medium but increases with the driving velocity of the cell. These experimental results are compared with existing theories. We also introduce a model that fairly predicts the equilibrium temperatures along the direction of vibration.
Part of the book: Granular Materials