A home for our web original content and tons of other sweet stuff from the Interwebs.Although always awesome, our posts do not necessarily constitute endorsement by PBS or its member stations. Posts by Danielle.
The Earth spins on its axis, completing a full revolution every day. By why does it do this? One of the most common misconceptions in physics is the belief that constant motion requires a constant force. So many people believe there must be some force in the Earth (e.g. gravity, centrifugal force) that keeps it spinning. In truth, no force is required because a fundamental property of mass is that it maintains its state of motion in the absence of external forces. This property is called inertia.