Experiments on the motion of a solid sphere toward a wall: From viscous dissipation to elastohydrodynamic bouncing

In the present study, we investigate experimentally the motion of a macroscopic (non-Brownian and noncolloidal) solid sphere falling under gravity into a viscous liquid toward a solid wall. We observe the transition from a nonbouncing to a bouncing regime when increasing the Stokes number St which characterizes the particle inertia. In the bouncing regime, the recording of the particle trajectories allows us to determine the coefficient of "elastic" restitution e above the transition. We observe that e first increases with St as predicted by Davis, Serayssol, and Hinch (1986) and seems to reach a plateau at high St. (C) 1999 American Institute of Physics. [S1070-6631(99)01509-3].