The Collaborative International Dictionary
Reciprocate \Re*cip"ro*cate\ (r[-e]*s[i^]p"r[-o]*k[=a]t), v. i. [imp. & p. p. Reciprocated (r[-e]*s[i^]p"r[-o]*k[=a]`t[e^]d); p. pr. & vb. n. Reciprocating.] [L. reciprocatus, p. p. of reciprocare. See Reciprocal.] To move forward and backward alternately; to recur in vicissitude; to act interchangeably; to alternate.
One brawny smith the puffing bellows plies,
And draws and blows reciprocating air.
--Dryden.
Reciprocating engine, a steam, air, or gas engine, etc., in which the piston moves back and forth; -- in distinction from a rotary engine, in which the piston travels continuously in one direction in a circular path.
Reciprocating motion (Mech.), motion alternately backward and forward, or up and down, as of a piston rod.
Wikipedia
Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth linear motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes.
A crank can be used to convert circular motion into reciprocating motion, or conversely turn reciprocating motion into circular motion.
For example, inside an internal combustion engine (a type of reciprocating engine), the expansion of burning fuel in the cylinders periodically pushes the piston down, which, through the connecting rod, turns the crankshaft. The continuing rotation of the crankshaft drives the piston back up, ready for the next cycle. The piston moves in a reciprocating motion, which is converted into circular motion of the crankshaft, which ultimately propels the vehicle or does other useful work. The vibrations felt when the engine is running are a side effect of the reciprocating motion of the pistons, as the crank and connecting-rod usually are not enclosed.
Reciprocating motion is close to, but different from, sinusoidal simple harmonic motion. The point on the crankshaft which connects the connecting rod, rotates smoothly at a constant velocity in a circle. Thus, the horizontal displacement, of that point, is indeed exactly sinusoidal by definition. However, during the cycle, the angle of the connecting rod changes continuously. So, the horizontal displacement of the "far" end of the connecting rod (i.e., connected to the piston) differs from sinusoidal.
Usage examples of "reciprocating motion".
Shortly before dawn an odd droning rasping sound was heard in the distance, which Aillas recognized and identified: the voice of the sawmill, where heavy steel blades ten feet in length were driven up and down in reciprocating motion by the power of a waterwheel, to cut planks from pine and cedar logs carted down from the high Teach tac Teach by timber-cutters.
To avoid it, some ingenious person suggested that a number of saws should be fixed to a frame in a mill, so contrived as to work with a reciprocating motion, upwards and downwards, or backwards and forwards, and that this frame so mounted should be yoked to the mill wheel, and the saws driven by the power of wind or water.