Regensburg 2007 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 31: Granular matter / contact dynamics II
DY 31.6: Talk
Friday, March 30, 2007, 11:30–11:45, H2
The hopping ball: a common measurement method for the coefficient of restitution revisited — •Thomas Schwager1, Christof Krülle2, and Thorsten Pöschel1 — 1Charite, Augustenburger Platz 1, 13353 Berlin — 2Experimentalphysik V, Universität Bayreuth, D-95440 Bayreuth
The coefficient of restitution is the central characteristics of the damping properties of granular material. One common way to measure this coefficient is to let a sphere fall on a rigid plate and measure the time interval between successive collisions. These measurements, however, are afflicted with intense stochastic fluctuations which drastically increase towards lower impact velocities -- rendering the results problematic for the most interesting case of slow impact. As an added puzzle the distribution of the variations is non-Gaussian. These experimental results put the use of a deterministic coefficient of restitution in question. We present here a theoretical model of the particles which is in quantitative agreement with the experiment and which allows to shed light on the mechanism causing the stochastic variations. This in turn allows to extract useful information for the case of slow impact. Based on this model we will present a damping model which incorporates the observed statistical properties of the particle collisions. The consequences of this model for the theory of granular gases is discussed.