MIT Physics Demo -- Centrifugal versus Centripetal Motion

A wooden ball is attached to the rim of a spinning wheel. The ball is held in place by a string. When the spring is cut, the ball flies in a straight tangent to the wheel.

In the camera's frame of reference, the ball constantly accelerates around in a circle due to the centripetal force pulling it inwards. When the string is cut, the acceleration stops, and the ball flies away in a straight tangential line. When the string is cut in the rotating frame of reference, a ficticious force (centrifugal force) accelerates the ball.