Synopsis

Many things are in constant motion – the wheels of a bicycle, a football in flight, the platters within a computer, and even our planet itself. All rotating objects possess inertia, a tendency to maintain their motion unless acted upon by an external force. A bicycle tire continues to turn until the brakes are applied. A football spirals through the air until it is caught. The Earth maintains its rotation around its axis, day and night, week after week. It has spun for more than four billion yea