Reciprocating motion
Encyclopedia
Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth 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 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 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 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.
Reciprocating motion is clearly visible in early steam engine
s, particularly horizontal stationary engines
and outside-cylindered steam locomotives, as the crank and connecting-rod usually are not enclosed.
Mathematically, reciprocating motion is approximately sinusoidal
simple harmonic motion
. Technically, however, the reciprocating motion produced by a rotating crank
departs slightly from simple harmonic motion due to the changing angle of the connecting rod during the cycle.
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
. It is found in a wide range of mechanisms, including reciprocating engine
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...
s and pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s. The two opposite motions that comprise a single reciprocation cycle are called strokes.
A crank
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...
can be used to convert circular motion
Circular motion
In physics, circular motion is rotation along a circular path or a circular orbit. It can be uniform, that is, with constant angular rate of rotation , or non-uniform, that is, with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of...
into reciprocating motion, or conversely turn reciprocating motion into circular motion.
For example, inside an internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
(a type of reciprocating engine), the expansion of burning fuel in the cylinder
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...
s periodically pushes the piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
down, which, through the connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....
, turns the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
. 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.
Reciprocating motion is clearly visible in early steam engine
Steam engine
A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
s, particularly horizontal stationary engines
Stationary steam engine
Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars , agricultural engines used for ploughing or...
and outside-cylindered steam locomotives, as the crank and connecting-rod usually are not enclosed.
Mathematically, reciprocating motion is approximately sinusoidal
Sine wave
The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields...
simple harmonic motion
Simple harmonic motion
Simple harmonic motion can serve as a mathematical model of a variety of motions, such as the oscillation of a spring. Additionally, other phenomena can be approximated by simple harmonic motion, including the motion of a simple pendulum and molecular vibration....
. Technically, however, the reciprocating motion produced by a rotating crank
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...
departs slightly from simple harmonic motion due to the changing angle of the connecting rod during the cycle.
See also
- OscillationOscillationOscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
- Rotary reciprocationRotary reciprocationThe action in which a body's displacement returns to its starting location in a given time repeatedly in a rotary axis but without traversing a full rotation, i.e. back and forth not round and round. The velocity over which the displacement occurs with each repetition not necessarily being constant...
- Reciprocating sawReciprocating sawA reciprocating saw is a type of saw in which the cutting action is achieved through a push and pull reciprocating motion of the blade.The term reciprocating saw is commonly assigned to a type of saw used in construction and demolition work...
- Rotary reciprocating saw
- Agitation