A tabletop demonstration of distributed friction: the spinning wine glass

Abstract

When a wine glass is dragged on a table along a circular path, a spontaneous rotation about its vertical axis can develop even if the applied hand force does not directly introduce a yaw torque. This document provides a structured formal derivation of the governing equations that are responsible for this behavior. The analysis shows that the mechanism responsible for this effect is the redistribution of pressure onto the table when applying the force with your hand. This causes an uneven frictional force distribution which exerts a torque on the glass, causing it to spin.