2d Granular Gas in Knudsen Regime and in Microgravity Excited by Vibration: Velocity and Position Distributions

Dynamics of quasi-2d dissipative granular gas is studied in microgravity condition (of the order of l0(-4)g) in the limit of Knudsen regime. The gas, made of 4 spheres, is confined in a square cell enforced to follow linear sinusoidal vibration in ten different vibration modes. The trajectory of one of the particles is tracked and reconstructed from the 2-hour video data. From statistical analysis, we find that (i) loss due to wall friction is small, (ii) trajectory looks ergodic in space, and (iii) distribution p(v) of speed follows an exponential distribution, i.e. p(v)almost equal to exp(-v/ v(xo, yo) ), with v(xo, yo) being a characteristic velocity along a direction parallel (y) or perpendicular (x) to vibration direction. This law deviates strongly from the Boltzmann distribution of speed in molecular gas. Comparisons of this result with previous measurements in earth environment, and what was found in 3d cell [1] performed in 10(-2)g environment are given.