MEASUREMENTS OF THE COLLISION PROPERTIES OF SMALL SPHERES

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 wit hout initial spin. The impacts are modeled in terms of three coefficie nts. The first is the coefficient of normal restitution. The second re presents the frictional properties of the contact surfaces. The last c haracterizes the restitution of the tangential components of the veloc ity of the contact point for impacts that do not involve sliding. The coefficients are calculated from stroboscopic photographs of the balli stics of the particles near the collision. The results establish that the collision model provides an accurate description of the dynamics o f the impacts.