Measurements of the collision properties of small spheres

TLDR

Collisions of small spheres are modeled using three coefficients: normal restitution, friction, and tangential restitution for non‑sliding impacts. The study aims to measure collision properties of small spheres against each other and against a flat wall. The experiment releases spheres in free fall without spin and determines the coefficients from stroboscopic photographs of their trajectories near impact. The measurements confirm that the collision model accurately describes the impact dynamics.

Abstract

An experiment to measure the properties of the collisions between two small spheres or between a small sphere and a semi-infinite flat wall are described. The apparatus releases the particles in a free-fall without initial spin. The impacts are modeled in terms of three coefficients. The first is the coefficient of normal restitution. The second represents the frictional properties of the contact surfaces. The last characterizes the restitution of the tangential components of the velocity of the contact point for impacts that do not involve sliding. The coefficients are calculated from stroboscopic photographs of the ballistics of the particles near the collision. The results establish that the collision model provides an accurate description of the dynamics of the impacts.