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{{otheruses|oscillator (disambiguation)}}
'''Oscillation''' is the repetitive variation, typically in [[time]], of some measure about a central value (often a point of [[equilibrium]]) or between two or more different states.  Familiar examples include a swinging [[pendulum]] and [[Alternating current|AC]] power.  The term [[vibration]] is sometimes used more narrowly to mean a mechanical oscillation but sometimes is used to be synonymous with "oscillation."  Oscillations occur not only in physical systems but also in [[ecology|biological systems]] and in human [[society]].
[[Image:Simple harmonic oscillator.gif|right|frame|An undamped [[spring-mass system]] is an oscillatory system.]]

==Simplicity==

The simplest mechanical oscillating system is a [[mass]] attached to a [[linear]] [[spring (device)|spring]], subject to no other forces; except for the point of equilibrium, this system is equivalent to the same one subject to a constant [[force]] such as [[gravity]].  Such a system may be approximated on an air table or ice surface.  The system is in an [[mechanical equilibrium|equilibrium]] state when the spring is unstretched.  If the system is displaced from the equilibrium, there is a net ''restoring force'' on the mass, tending to bring it back to equilibrium.  However, in moving the mass back to the equilibrium position, it has acquired [[momentum]] which keeps it moving beyond that position, establishing a new restoring force in the opposite sense.  The time taken for an oscillation to occur is often referred to as the oscillatory ''period''.

The specific [[dynamics (mechanics)|dynamics]] of this spring-mass system are described mathematically by the [[Harmonic oscillator#Simple harmonic oscillator|simple harmonic oscillator]] and the regular [[period (physics)|periodic]] motion is known as ''[[simple harmonic motion]]''.  In the spring-mass system, oscillations occur because, at the [[statics|static]] equilibrium displacement, the mass has [[kinetic energy]] which is converted into [[potential energy]] stored in the spring at the extremes of its path.  The spring-mass system illustrates some common features of oscillation, namely the existence of an equilibrium and the presence of a restoring force which grows stronger the further the system deviates from equilibrium.

The [[harmonic oscillator]] offers a model of many more complicated types of oscillation and can be extended by the use of [[Fourier analysis]].

==Damped, driven and self-induced oscillations==

In real-world systems, the [[second law of thermodynamics]] dictates that there is some continual and inevitable conversion of energy into the [[thermal energy]] of the environment.  Thus, ''damped'' oscillations tend to decay with time unless there is some net source of energy in the system. The simplest description of this decay process can be illustrated by the harmonic oscillator.  In addition, an oscillating system may be subject to some external force (often [[sinusoidal]]), as when an AC [[Electronic circuit|circuit]] is connected to an outside power source.  In this case the oscillation is said to be ''[[driven oscillations|driven]]''.

Some systems can be excited by energy transfer from the environment.  This transfer typically occurs where systems are embedded in some [[fluid]] flow.  For example, the phenomenon of [[flutter]] in [[aerodynamics]] occurs when an arbitrarily small displacement of an [[aircraft]] [[wing]] (from its equilibrium) results in an increase in the [[angle of attack]] of the wing on the [[Earth's atmosphere|air]] flow and a consequential increase in [[coefficient of lift|lift coefficient]], leading to a still greater displacement.  At sufficiently large displacements, the [[stiffness]] of the wing dominates to provide the restoring force that enables an oscillation.

==Coupled oscillations==

The harmonic oscillator and the systems it models have a single [[degrees of freedom (physics and chemistry)|degree of freedom]].  More complicated systems have more degrees of freedom, for example two masses and three springs (each mass being attached to fixed points and to each other).  In such cases, the behavior of each variable influences that of the others.  This leads to a ''coupling'' of the oscillations of the individual degrees of freedom.  For example, two pendulum clocks mounted on a common wall will tend to synchronise. The apparent motions of the individual oscillations typically appears very complicated but a more economic, computationally simpler and conceptually deeper description is given by resolving the motion into [[normal mode]]s.

==Continuous systems - waves==

As the number of degrees of freedom becomes arbitrarily large, a system approaches [[continuum|continuity]]; examples include a string or the surface of a body of [[water]]. Such systems have (in the [[classical limit]]) an [[infinite]] number of normal modes and their oscillations occur in the form of [[wave]]s that can characteristically propagate.

==Examples==
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See also: [[list of wave topics]]

===Mechanical===
*[[Double pendulum]]
*[[Quantum harmonic oscillator]]
*[[Foucault pendulum]]
*[[Helmholtz resonance|Helmholtz resonator]]
*[[swing (seat)|Playground swing]]
*[[String instrument]]s
*[[Tuning fork]]
*[[Vibrating string]]
*Oscillations in the Sun ([[helioseismology]]) and stars ([[asteroseismology]])

===Electrical===
*[[Alternating current]]
*[[Armstrong oscillator]] 
*[[Astable|Astable multivibrator]]
*[[Blocking oscillator]]
*[[Clapp oscillator]]
*[[Colpitts oscillator]]
*[[Delay line oscillator]]
*[[Electronic oscillator]]
*[[Hartley oscillator]]
*[[Oscillistor]]
*[[Pierce oscillator]]
*[[Relaxation oscillator]]
*[[RLC circuit]]
*[[Royer oscillator]]
*[[Vačkář oscillator]]
*[[Wien bridge oscillator]]
*[[Oscillators and Multivibrators]]
*[[Virtual Cathode Oscillator]]

===Electro-mechanical===
*[[Crystal oscillator]]
*[[Loudspeaker]]
*[[Microphone]]

===Optical===
*[[Laser]] (oscillation of [[electromagnetic field]] with frequency of order <math>10^{15}</math>Hz)
*[[Oscillator Toda]] or [[self-pulsation]]  (pulsation of output power of [[laser]] at frequencies <math>10^{4}</math>Hz -- <math>10^{6}</math>Hz in the transient regime)
*[[Quantum oscillator]] may refer to an optical [[local oscillator]], as well as to a usual model in [[quantum optics]].

===Biological===
*[[Circadian rhythm]]
*[[Lotka–Volterra equation|Prey-predator systems]]
*[[Neural oscillations]]

===Human===
*[[Electroencephalography|Brain waves]]
*[[Pilot-induced oscillation]]
*[[Voice production]]
*[[Insulin release oscillations]]

===Economic and social===
*[[Business cycle]]
*[[Generation gap]]
*[[Malthusian]] economics
*[[News cycle]]

===[[Climate]] and geophysics===
*[[Chandler wobble]]
*[[El Niño|El Niño-Southern Oscillation]]
*[[Quasi-biennial oscillation]]
*[[Tide]]s in the [[Earth]]'s [[ocean]]s

===Chemical===
* [[Belousov-Zhabotinsky reaction]]
* [[Mercury beating heart]]
</div>

==See also==
<div style="-moz-column-count:3; column-count:3;">
*[[BIBO stability]]
*[[Critical speed]]
*[[Dynamical system]]
*[[Feedback]]
*[[wikibooks:Circuit Idea/How do We Create Sinusoidal Oscillations?|How do We Create Sinusoidal Oscillations?]] from [[wikibooks:Circuit Idea|Circuit Idea]] reveals the philosophy of LC oscillations
*[[Oscillation (mathematics)]]
*[[Periodic function]]
*[[Reciprocation]]
*[[Rhythm]]
*[[Self oscillation]]
*[[Signal generator]]
*[[Strange attractor]]
*[[Structural stability]]
*[[Time period]]
*[[Tuned mass damper]]
*[[Vibration]]
*[[vibrator (mechanical)|Vibrator]]
</div>

==External links==
* [http://www.magnet.fsu.edu/education/tutorials/java/oscillator/index.html Interactive Java Tutorial on Electronic Oscillators] National High Magnetic Field Laboratory
* [http://www.lightandmatter.com/html_books/3vw/ch01/ch01.html Vibrations] - a chapter from an online textbook
* [http://workhealthsafety.blogspot.com/2007/06/vibration.html Dealing Vibration at work]

[[Category:Oscillation| ]]

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[[de:Schwingung]]
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[[el:Ταλάντωση]]
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[[ja:振動 (物理現象)]]
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