Title: Experimental measurements of the collapse of a 2D granular gas under gravity

Author (Poster): Greg Voth, Wesleyan University

Abstract:

We experimentally measure the decay of a quasi-2D granular gas under gravity. A granular gas is created by vibro-fluidization, after which the energy input is halted, and the time dependent statistical properties of the decaying gas are measured with video particle tracking. There are two distinct cooling stages separated by a high temperature settling shock. In the final stage, the temperature of a fluid packet decreases as a power law $T \propto (t_c-t)^\alpha$ just before the system collapses to a static state. The measured value of $\alpha$ ranges from 3.3 to 6.1 depending on the height, significantly higher than the exponent of 2 found in theoretical work on this problem [Phys Rev. E 73, 61305 (2006)]. We also address the question of whether the collapse occurs simultaneously at different heights in the system.