A ratchet is a mechanical device that allows continuous linear or rotary motion in only one direction while preventing motion in the opposite direction. A ratchet may be on a drive shaft and the ratchet is there to stop the shaft from reversing by the action of the ratchet pawl falling into the gap between 2 ratchet teeth when the drive motion ceases. Conversely, the ratchet can be driven by the ratchet pawl if it is oscillating back and forth. The ratchet pawl will have to move at least 1 circumferential pitch of the ratchet wheel for this action to take place.