Impact of a double sphere dropped vertically onto a horizontal surface

Abstract

A simple experiment is described concerning the vertical bounce of a nonspherical object. The object consisted of two golf balls joined together. The balls were dropped onto a heavy, rigid horizontal surface and were filmed with a video camera to measure the coefficient of restitution (COR). For spherical objects, the COR is usually defined in terms of the vertical speed of the centre of mass and can vary between zero and unity depending on the elastic properties of the object and the surface on which it bounces. For nonspherical objects, the COR is best defined in terms of the vertical speed of the contact point. For the two golf balls, the centre of mass COR was found to vary between −4 and +2 depending on the incident spin and the angle of inclination of the long axis. The contact point COR was found to be 0.8 ± 0.2, regardless of the incident spin and angle of inclination.