Editing Resonance (section)

==Types==

===Mechanical===
{{Main|Mechanical resonance|String resonance}}
[[File:Resonating mass experiment.jpg|thumb|upright|School resonating mass experiment]]

[[Mechanical resonance]] is the tendency of a [[mechanics|mechanical system]] to absorb more energy when the [[frequency]] of its oscillations matches the system's natural frequency of [[vibration]] than it does at other frequencies. It may cause violent swaying motions and even catastrophic failure in improperly constructed structures including bridges, buildings, trains, and aircraft. When designing objects, [[engineers]]  must ensure the mechanical resonance frequencies of the component parts do not match driving vibrational frequencies of motors or other oscillating parts, a phenomenon known as [[mechanical resonance#Resonance disaster|resonance disaster]].

Avoiding resonance disasters is a major concern in every building, tower, and [[bridge]] [[construction]] project. As a countermeasure, [[shock mount]]s can be installed to absorb resonant frequencies and thus dissipate the absorbed energy. The [[Taipei 101]] building relies on a {{convert|660|t|ST|adj=mid|pendulum}}—a [[tuned mass damper]]—to cancel resonance. Furthermore, the structure is designed to resonate at a frequency that does not typically occur. Buildings in [[seismic]] zones are often constructed to take into account the oscillating frequencies of expected [[ground motion]]. In addition, [[engineer]]s designing objects having engines must ensure that the mechanical resonant frequencies of the component parts do not match driving vibrational frequencies of the motors or other strongly oscillating parts.

[[Clock]]s keep time by mechanical resonance in a [[balance wheel]], pendulum, or [[Quartz clock|quartz crystal]].

The cadence of runners has been hypothesized to be energetically favorable due to resonance between the elastic energy stored in the lower limb and the mass of the runner.{{sfn|Snyder|Farley|2011}}

====International Space Station====

The [[rocket engine]]s for the [[International Space Station]] (ISS) are controlled by an [[autopilot]]. Ordinarily, uploaded parameters for controlling the engine control system for the Zvezda module make the rocket engines boost the International Space Station to a higher orbit. The rocket engines are [[hinge]]-mounted, and ordinarily the crew does not notice the operation. On January 14, 2009, however, the uploaded parameters made the autopilot swing the rocket engines in larger and larger oscillations, at a frequency of 0.5&nbsp;Hz. These oscillations were captured on video, and lasted for 142 seconds.<ref>{{cite news |last1=Oberg |first1=James |title=Shaking on Space Station Rattles NASA |url=http://www.nbcnews.com/id/28998876/#story |archive-url=https://web.archive.org/web/20130815215631/http://www.nbcnews.com/id/28998876#story |url-status=dead |archive-date=August 15, 2013 |access-date=1 January 2021 |work=NBC News |date=4 February 2009}}</ref>

===Acoustic===
{{Main|Acoustic resonance}}
[[Acoustic resonance]] is a branch of mechanical resonance that is concerned with the mechanical vibrations across the frequency range of human hearing, in other words [[sound]]. For humans, hearing is normally limited to frequencies between about 20&nbsp;[[Hertz|Hz]] and 20,000&nbsp;Hz (20&nbsp;[[kHz]]),{{sfn|Olson|1967|pp=248&ndash;249}}  Many objects and materials act as resonators  with resonant frequencies within this range, and when struck vibrate mechanically, pushing on the surrounding air to create sound waves.  This is the source of many percussive sounds we hear.

Acoustic resonance is an important consideration for instrument builders, as most acoustic [[Musical instrument|instruments]] use [[resonator]]s, such as the [[string resonance|strings]] and body of a [[violin]], the length of tube in a [[flute]], and the shape of, and tension on, a drum membrane.

Like mechanical resonance, acoustic resonance can result in catastrophic failure of the object at resonance. The classic example of this is breaking a wine glass with sound at the precise resonant frequency of the glass, although this is difficult in practice.<ref name="UCLA">{{cite web |last1=UCLA Physics & Astronomy Department |title=50. Breaking Glass with Sound |url=http://demoweb.physics.ucla.edu/content/50-breaking-glass-sound |website=Lecture Demonstration Manual |publisher=[[University of California, Los Angeles]] |access-date=1 January 2021}}</ref>

===Electrical ===
{{Main|Electrical resonance}}
[[Image:Tuned circuit animation 3.gif|thumb|upright=1.1|Animation illustrating electrical resonance in a [[tuned circuit]], consisting of a [[capacitor]] (C) and an [[inductor]] (L) connected together. Charge flows back and forth between the capacitor plates through the inductor.  Energy oscillates back and forth between the capacitor's [[electric field]] ({{mvar|E}}) and the inductor's [[magnetic field]] ({{mvar|B}}). ]]

[[Electrical resonance]] occurs in an electric circuit at a particular ''resonant frequency'' when the [[Electrical impedance|impedance]] of the circuit is at a minimum in a series circuit or at maximum in a parallel circuit (usually when the transfer function peaks in absolute value). Resonance in circuits are used for both transmitting and receiving wireless communications such as television, cell phones and radio.

===Optical ===
{{Main|Optical cavity}}

An [[optical cavity]], also called an ''optical resonator'', is an arrangement of [[mirror]]s that forms a standing wave [[cavity resonator]] for [[light wave]]s. Optical cavities are a major component of [[laser]]s, surrounding the [[gain medium]] and providing [[feedback]] of the laser light. They are also used in [[optical parametric oscillator]]s and some [[interferometer]]s. Light confined in the cavity reflects multiple times producing standing waves for certain resonant frequencies. The standing wave patterns produced are called "modes". [[Longitudinal mode]]s differ only in frequency while [[transverse mode]]s differ for different frequencies and have different intensity patterns across the cross-section of the beam. [[Optical ring resonators|Ring resonators]] and [[Whispering gallery|whispering galleries]] are examples of optical resonators that do not form standing waves.

Different resonator types are distinguished by the focal lengths of the two mirrors and the distance between them; flat mirrors are not often used because of the difficulty of aligning them precisely. The geometry (resonator type) must be chosen so the beam remains stable, i.e., the beam size does not continue to grow with each reflection. Resonator types are also designed to meet other criteria such as minimum beam waist or having no focal point (and therefore intense light at that point) inside the cavity.

Optical cavities are designed to have a very large [[Q factor|''Q'' factor]].<ref name="q factor">{{cite web |title=''Q'' factor, quality factor, cavity, resonator, oscillator, frequency standards |url=http://www.rp-photonics.com/q_factor.html |website=Encyclopedia of Laser Physics and Technology |access-date=1 January 2021}}</ref> A beam reflects a large number of times with little [[attenuation]]—therefore the frequency [[line width]] of the beam is small compared to the frequency of the laser.

Additional optical resonances are [[guided-mode resonance]]s and [[surface plasmon resonance]], which result in anomalous reflection and high evanescent fields at resonance. In this case, the resonant modes are guided modes of a waveguide or surface plasmon modes of a dielectric-metallic interface. These modes are usually excited by a subwavelength grating.

===Orbital ===
{{Main|Orbital resonance}}

In [[celestial mechanics]], an [[orbital resonance]] occurs when two [[orbit]]ing bodies exert a regular, periodic gravitational influence on each other, usually due to their [[orbital period]]s being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of the bodies. In most cases, this results in an ''unstable'' interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. Under some circumstances, a resonant system can be stable and self-correcting, so that the bodies remain in resonance. Examples are the 1:2:4 resonance of [[Jupiter]]'s moons [[Ganymede (moon)|Ganymede]], [[Europa (moon)|Europa]], and [[Io (moon)|Io]], and the 2:3 resonance between [[Pluto]] and [[Neptune]]. Unstable resonances with [[Saturn]]'s inner moons give rise to gaps in the [[rings of Saturn]]. The special case of 1:1 resonance (between bodies with similar orbital radii) causes large Solar System bodies to [[Clearing the neighbourhood|clear the neighborhood]] around their orbits by ejecting nearly everything else around them; this effect is used in the current [[definition of planet|definition of a planet]].

=== Atomic, particle, and molecular ===
{{Main|Nuclear magnetic resonance|Resonance (particle physics)}}

[[File:HWB-NMR - 900MHz - 21.2 Tesla.jpg|thumb|upright|[[Nuclear magnetic resonance|NMR]] Magnet at HWB-NMR, Birmingham, UK. In its strong 21.2-[[Tesla (unit)|tesla]] field, the proton resonance is at 900&nbsp;MHz.]]
[[Nuclear magnetic resonance]] (NMR) is the name given to a physical resonance phenomenon involving the observation of specific [[quantum mechanics|quantum mechanical]] [[magnetism|magnetic]] properties of an [[atom]]ic [[atomic nucleus|nucleus]] in the presence of an applied, external magnetic field. Many scientific techniques exploit NMR phenomena to study [[molecular physics]], [[crystallography|crystal]]s, and non-crystalline materials through [[NMR spectroscopy]]. NMR is also routinely used in advanced medical imaging techniques, such as in [[magnetic resonance imaging]] (MRI).

All nuclei containing odd numbers of [[nucleon]]s have an [[Spin (physics)|intrinsic angular momentum]] and [[magnetic moment]]. A key feature of NMR is that the resonant frequency of a particular substance is directly proportional to the strength of the applied magnetic field. It is this feature that is exploited in imaging techniques; if a sample is placed in a non-uniform magnetic field then the resonant frequencies of the sample's nuclei depend on where in the field they are located. Therefore, the particle can be located quite precisely by its resonant frequency.

[[Electron paramagnetic resonance]], otherwise known as ''electron spin resonance'' (ESR), is a spectroscopic technique similar to NMR, but uses unpaired electrons instead. Materials for which this can be applied are much more limited since the material needs to both have an unpaired spin and be [[paramagnetic]].

The [[Mössbauer effect]] is the resonant and [[recoil]]-free emission and absorption of [[gamma ray]] photons by atoms bound in a solid form.

[[Resonance (particle physics)|Resonance in particle physics]] appears in similar circumstances to [[classical physics]] at the level of quantum mechanics and [[quantum field theory]]. Resonances can also be thought of as unstable particles, with the formula in the [[#Universal resonance curve|Universal resonance curve]] section of this article applying if ''Γ'' is the particle's [[Particle decay#Decay rate|decay rate]] and <math>\omega_0</math> is the particle's mass ''M''. In that case, the formula comes from the particle's [[Propagator (Quantum Theory)|propagator]], with its mass replaced by the complex number ''M''&nbsp;+&nbsp;''iΓ''. The formula is further related to the particle's decay rate by the [[optical theorem]].