Rigid-body dynamics of a football

Abstract

The motion of a spinning football provides interesting illustrations of some of the principles of rigid-body motion. The familiar ‘‘wobbly spiral’’ is an example of torque-free precession; it is shown that the ‘‘wobble-to-spin’’ ratio depends only on the principal moments of inertia of the football. The angular momentum of a spinning football is not always conserved in flight. The response of a football to aerodynamic forces can best be understood by comparing its motion to that of a spinning top or gyroscope.