THE COEFFICIENT OF RESTITUTION OF ICE PARTICLES IN GLANCING COLLISIONS - EXPERIMENTAL RESULTS FOR UNFROSTED SURFACES

Both Saturn's rings and planetesimal disks are made up of particles in Keplerian orbits. Inelastic collisions between these particles regula te their dynamical evolution and possible aggregation. We present an e xperiment to simulate glancing collisions in Saturn's rings and in pla netesimal disks and thus measure contributions to the energy loss for both normal and tangential velocity components. In this experiment, a spherical iceball mounted on a long-period, two dimensional pendulum i s made to impact a flat ice surface in a low-temperature environment. This paper describes the experimental apparatus in detail and presents results for smooth unfrosted surfaces. The energy loss for tangential motion is surprisingly low, indicating that very little friction is p resent at low impact speeds for relatively smooth ice surfaces and tem peratures near 100 K. We have also investigated room-temperature colli sions of a rubber ball on a rough surface to understand the energy los s in situations where the tangential friction force is not small. In t his analogous case, the energy loss is maximum for impact angles in th e range 45 degrees-60 degrees. (C) 1995 Academic Press, Inc.