Rotation of a ring around a horizontal rod

Abstract

A simple experiment is described where a metal ring was rotated by hand on a horizontal rod. The ring rotated about 100 times before coming to a stop, so the friction force on the ring remained very small. However, measurements of the rotation frequencies of the ring around the rod and around its centre of mass indicated that the ring was sliding rather than rolling, with an unusually low coefficient of sliding friction. The results can be explained if any given contact point on the ring slides to a stop when it first contacts the rod.