The coefficient of restitution of a spherical particle in contact with a flat
plate is investigated as a function of the impact velocity. As an experimental
observation we notice non-trivial (non-Gaussian) fluctuations of the measured
values. For a fixed impact velocity, the probability density of the coefficient
of restitution, p(ϵ), is formed by two exponential functions (one
increasing, one decreasing) of different slope. This behavior may be explained
by a certain roughness of the particle which leads to energy transfer between
the linear and rotational degrees of freedom.Comment: 4 pages, 4 figure