{{short description|Repetitive back-and-forth linear motion}} {{onesource|date=May 2022}} [[Image:Steam engine in action.gif|thumb|Double-acting [[stationary steam engine]] demonstrating conversion of reciprocating motion to rotary motion. The [[piston]] is on the left, and the [[Crank (mechanism)|crank]] is mounted on the flywheel axle on the right]] [[File: Rotary to Reciprocating Motion.gif|thumb|Machine demonstrating the conversion of rotary motion to reciprocating motion using gears. The bottom pair of gears drives the mechanism]]
'''Reciprocating motion''', also called '''reciprocation''', is a repetitive up-and-down or back-and-forth linear [[motion (physics)|motion]]. It is found in a wide range of mechanisms, including [[reciprocating engine]]s and [[pump]]s. The two opposite motions that comprise a single reciprocation cycle are called [[stroke (engine)|stroke]]s.{{Citation needed|date=September 2010}}
A [[Crank (mechanism)|crank]] can be used to convert into reciprocating motion, or conversely turn reciprocating motion into circular motion.{{citation needed|date=May 2022}}<ref>{{Cite book |last=Mobley |first=Keith R |title=Plant Engineer's Handbook |publisher=Butterworth-Heinemann |year=2001 |isbn=0 7506 7328 1 |location=USA |pages=723-755}}</ref>
For example, inside an [[internal combustion engine]] (a type of reciprocating engine), the expansion of burning fuel in the [[cylinder (engine)|cylinder]]s 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 the circular motion of the crankshaft, which ultimately propels the vehicle or does other useful work. {{Citation needed|date=May 2022}}
The reciprocating motion of a pump piston is close to but different from, [[sine wave|sinusoidal]] [[simple harmonic motion]]. Assuming the wheel is driven at a perfect constant rotational velocity, the point on the crankshaft which connects to the connecting rod rotates smoothly at a constant velocity in a circle. Thus, the 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 slightly from sinusoidal. Additionally, if the wheel is not spinning with perfect constant rotational velocity, such as in a steam locomotive starting up from a stop, the motion will be even less sinusoidal. {{Citation needed|date=May 2022}}
==See also== *{{annotated link|Oscillation}} *{{annotated link|Stroboscope}} *{{annotated link|Reciprocating saw}} *{{annotated link|Reciprocating engine}} *{{annotated link|Rotary saw|Rotary reciprocating saw}} *{{annotated link|Agitator (device)|Agitation}} *{{annotated link|Scotch yoke}} *{{annotated link|Crank (mechanism)|Crank}} *{{annotated link|Crankshaft}} *{{annotated link|Swashplate}} *{{annotated link|Trip hammer}} *{{annotated link|Slider-crank linkage}} *{{annotated link|Straight line mechanism}} *{{annotated link|Reciprocating compressor}} *{{annotated link|Sun and planet gear}}
==References==
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[[Category:Mechanical engineering]]
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