Examples of reciprocating motion include a rack and pinion mechanism, a Scotch yoke mechanism and a traversing head shaper. These examples define this repetitive, up-and-down or back-and-forth linear motion.
The reciprocation cycle is comprised of two opposite movements called strokes. A crank on a mechanism is used to turn circular motion into reciprocating motion.
In rack and pinion mechanisms, a table is moved up and down the central pillar of a drill as a crank is turned. This makes it easy to move a table with minimal effort.
In Scotch yoke mechanisms, linear motion is converted into rotational motion. The piston, or other reciprocating part, is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part.
A traversing head shaper mechanism works by moving a hardened cutting tool backwards and forwards across a work surface. On the return stroke, the tool is lifting clear of the work surface, reducing the cutting action to one direction.
Reciprocating motion is also found in engines and pumps. Internal combustion engines utilize reciprocating motion when the expansion of burning fuel in cylinders periodically pushes the piston down; through the connecting rod, this turns the crankshaft. The continuing rotation of the crankshaft drives the piston back up for the next cycle. The piston moves in a reciprocating motion and initiates the circular motion of the crankshaft, which propels the vehicle or does other useful work.