Effect of number density on velocity distributions in a driven quasi-two-dimensional granular gas

The motion of mono-disperse spherical steel particles in a vibration driven quasi-two-dimensional (2D) square cell is studied. The cell is horizontally vibrated to eliminate the effect of gravity compaction. The velocity distributions at different particle number densities are studied and found to obey the form \exp-\beta(|v_y|/\sigma_y)^\alpha, in which v_y and \sigma_y are velocity and its variance in the transverse direction, and \alpha and \beta are fitting parameters. The value of \alpha is found to decrease with the number density of particles increasing. To investigate the effect of the bottom plate, the molecular dynamics simulation without considering any bottom friction is performed. The accordance between the simulation result and the experimental result shows that the influence of bottom plate friction force on the high energy tail of the velocity distribution can be neglected.