A wooden ball is attached to the rim of a spinning wheel. The ball is held in place by a string. When the string is cut, the ball flies in a straight tangent to the wheel.
Demonstration Instructions: Overview:
When the ball is attached to the string, it experiences an inward centripetal acceleration which forces it to move in a circular path. When the string is cut there is no net force on the ball and the ball follows a straight path, tangential to the position where it was cut. Within the ball's non-inertial reference frame, it experiences a fictitious centrifugal force. It feels as if it is being pulled outward. The ball, however, does not fly straight outward when released, but tangent to the wheel. Centrifugal force is just an artifact of the ball's non-inertial reference frame.
See page 158, University Physics, for information regarding centripetal vs. centrifugal force.
Young, Hugh D., Roger A. Freedman, and A. Lewis Ford. Sears and Zemansky's University Physics: With Modern Physics, 12th ed. San Francisco: Pearson Addison-Wesley, 2008.