Fictitious force

An observer who is not an inertial observer must introduce additional forces, if he wants to explain the motion of the bodies around him with the help of the mechanical law “force equals mass times acceleration”. These additional forces are called fictitious forces in physics. In contrast to “real” forces such as electric, magnetic or gravitational forces, for which one can always state what body is causing the force, fictitious forces seem to come out of the blue.

The best-known example: An observer on a rotating chain carousel must introduce the centrifugal force if he wants to explain how the seats of the chain carousel are pulled outward.