Consider the Whitworth Quick-Return Mechanism illustrated, which is driven by the crank ("driving link") AP. The slider at P is free to slide along the "driven link" OC.

Assume that, at time t = 0, the crank and driven link are in the vertical position (so that θ= 0, φ= 0) and thereafter the crank AP rotates in a clockwise direction at 20 revolutions per minute about A.