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| {{about| mechanical resonance in [[physics]] and [[engineering]]|a general description of resonance| resonance|mechanical resonance of sound including musical instruments|acoustic resonance|the music album by American rock band [[Tesla (band)|Tesla]]|Mechanical Resonance}}
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| [[Image:Resonance.PNG|thumb|right|Graph showing mechanical [[resonance]] in a mechanical oscillatory system]]
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| '''Mechanical resonance''' is the tendency of a [[mechanics|mechanical system]] to respond at greater amplitude when the [[frequency]] of its oscillations matches the system's natural frequency of [[vibration]] (its ''[[resonance frequency]]'' or ''resonant frequency'') than it does at other frequencies. It may cause violent swaying motions and even catastrophic failure in improperly constructed structures including bridges, buildings and airplanes—a phenomenon known as resonance disaster.
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| Avoiding resonance disasters is a major concern in every building, tower and bridge [[construction]] project. The [[Taipei 101]] building relies on a 660-ton [[pendulum]] — a [[tuned mass damper]] — to modify the response at resonance. Furthermore, the structure is designed to resonate at a frequency which 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.
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| Many resonant objects have more than one resonance frequency. It will vibrate easily at those frequencies, and less so at other frequencies. Many [[clock]]s keep time by mechanical resonance in a [[balance wheel]], [[pendulum]], or [[Quartz clock|quartz crystal]].
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| ==Description==
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| The natural frequency of a simple mechanical system consisting of a weight suspended by a spring is:
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| :<math>f = {1\over 2 \pi} \sqrt {k\over m} </math>
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| where ''m'' is the [[mass]] and ''k'' is the [[spring constant]].
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| A [[swing set]] is a simple example of a resonant system with which most people have practical experience. It is a form of pendulum. If the system is excited (pushed) with a period between pushes equal to the inverse of the pendulum's natural frequency, the swing will swing higher and higher, but if excited at a different frequency, it will be difficult to move. The resonance frequency of a pendulum, the only frequency at which it will vibrate, is given approximately, for small displacements, by the equation:<ref>[http://www.physics.rutgers.edu/~jackph/2005s/PS02.pdf Mechanical resonance]</ref>
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| :<math>f = {1\over 2 \pi} \sqrt {g\over L} </math> | |
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| where ''g'' is the [[standard gravity|acceleration due to gravity]] (about 9.8 m/s<sup>2</sup> near the surface of [[Earth]]), and ''L'' is the length from the pivot point to the center of mass.(An [[elliptic integral]] yields a description for any displacement). Note that, in this approximation, the frequency does not depend on [[mass]].
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| Mechanical resonators work by transferring energy repeatedly from [[kinetic energy|kinetic]] to [[potential energy|potential]] form and back again. In the pendulum, for example, all the energy is stored as [[gravity|gravitational]] energy (a form of potential energy) when the bob is instantaneously motionless at the top of its swing. This energy is proportional to both the mass of the [[Bob (physics)|bob]] and its height above the lowest point. As the bob descends and picks up speed, its potential energy is gradually converted to kinetic energy (energy of movement), which is proportional to the bob's mass and to the square of its speed. When the bob is at the bottom of its travel, it has maximum kinetic energy and minimum potential energy. The same process then happens in reverse as the bob climbs towards the top of its swing.
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| Some resonant objects have more than one resonance frequency, particularly at harmonics (multiples) of the strongest resonance. It will vibrate easily at those frequencies, and less so at other frequencies. It will "pick out" its resonance frequency from a complex excitation, such as an impulse or a wideband noise excitation. In effect, it is filtering out all frequencies other than its resonance. In the example above, the swing cannot easily be excited by harmonic frequencies, but can be excited by [[subharmonic]]s.
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| ==Examples==
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| Various examples of mechanical resonance include:
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| *[[musical instruments]] ([[acoustic resonance]]).
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| *Most [[clock]]s keep time by mechanical resonance in a [[balance wheel]], [[pendulum]], or [[Quartz clock|quartz crystal]].
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| *[[tidal resonance]] of the [[Bay of Fundy]].
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| *[[Orbital resonance]] as in some [[natural satellite|moon]]s of the [[solar system]]'s [[gas giants]].
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| *The resonance of the [[basilar membrane]] in the [[ear]].
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| *Making a child's [[Swing (seat)|swing]] swing higher by pushing it at each swing.
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| *A wineglass breaking when someone sings a loud note at exactly the right pitch.
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| [[Image:Display 01.jpg|thumbnail|right|''Resonance Rings'' exhibit at [[California Science Center]]]]
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| Resonance may cause violent swaying motions in improperly constructed structures, such as bridges and buildings. The [[London Millennium Footbridge]] (nicknamed the ''Wobbly Bridge'') exhibited this problem. A faulty bridge can even be destroyed by its resonance (see "[[Angers Bridge]]"); that is why soldiers are trained not to march in [[lockstep marching|lockstep]] across a bridge, although it is suspected to be a myth, see e.g., [[MythBusters (2004 season)#Breakstep Bridge|MythBusters' 'Breakstep Bridge']]. Mechanical systems store potential energy in different forms. For example, a [[spring (device)|spring]]/mass system stores energy as tension in the spring, which is ultimately stored as the energy of bonds between [[atom]]s.
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| ==Resonance disaster==
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| In mechanics and construction a '''resonance disaster''' describes the destruction of a building or a technical mechanism by induced vibrations at a system's [[resonance]] frequency, which causes it to [[oscillate]]. Periodic excitation optimally transfers to the [[system]] the [[energy]] of the vibration and stores it there. Because of this repeated storage and additional energy input the system swings ever more strongly, until its load limit is exceeded.
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| ===Failure of the original Tacoma Narrows Bridge===
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| {{main|Tacoma Narrows Bridge (1940)}}
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| The dramatic, rhythmic twisting that resulted in the 1940 collapse of "Galloping Gertie", the original [[Tacoma Narrows Bridge (1940)|Tacoma Narrows Bridge]], is sometimes characterized in physics textbooks as a classic example of resonance; however, this description is misleading. The catastrophic vibrations that destroyed the bridge were not due to simple mechanical resonance, but to a more complicated oscillation caused by interactions between the bridge and the winds passing through its structure — a phenomenon known as [[aeroelasticity#Flutter|aeroelastic flutter]]. [[Robert H. Scanlan]], father of the field of bridge aerodynamics, wrote an article about this misunderstanding.<ref>K. Billah and R. Scanlan (1991), ''Resonance, Tacoma Narrows Bridge Failure, and Undergraduate Physics Textbooks'', [[American Journal of Physics]], 59(2), 118--124 [http://www.ketchum.org/billah/Billah-Scanlan.pdf (PDF)]</ref>
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| ===Other Examples===
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| * Collapse of [[Broughton Suspension Bridge]] (due to soldiers walking in step)
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| * Collapse of [[Angers Bridge]]
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| * Collapse of [[Königs Wusterhausen Central Tower]]
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| * Resonance of the [[Millennium Bridge (London)#Resonance|Millennium Bridge]]
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| * [[The_Power_(Snap!_song)#Tremors_at_Techno-Mart|Evacuation of the 39-story TechnoMart]] commercial-residential high-rise in Korea in 2011 due to a class performing [[Tae Bo]] exercises to the song "The Power".
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| ==Applications==
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| Various method of inducing mechanical resonance in a medium exist. Mechanical waves can be generated in a medium by subjecting an electromechanical element to an alternating electric field having a frequency which induces mechanical resonance and is below any electrical resonance frequency.<ref>Allensworth, et al., United States Patent 4,524,295. June 18, 1985</ref> Such devices can apply mechanical energy from an external source to an element to mechanically stress the element or apply mechanical energy produced by the element to an external load.
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| The [[United States Patent Office]] classifies devices that tests mechanical resonance under subclass 579, [[resonance]], [[frequency]], or [[amplitude]] study, of Class 73, [[Measuring]] and [[Experiment|test]]ing. This subclass is itself indented under subclass 570, Vibration.<ref>USPTO, [http://www.uspto.gov/go/classification/uspc073/defs073.htm Class 73, Measuring and testing]</ref> Such devices test an article or [[mechanism (technology)|mechanism]] by subjecting it to a vibratory force for determining qualities, characteristics, or conditions thereof, or sensing, studying or making analysis of the vibrations otherwise generated in or existing in the article or mechanism. Devices include methods to cause vibrations at a natural mechanical resonance and measure the [[frequency]] and/or [[amplitude]] the resonance made. Various devices study the amplitude response over a [[frequency range]] is made. This includes [[nodal point]]s, [[wave length]]s, and [[standing wave]] characteristics measured under predetermined vibration conditions.
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| == See also ==
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| * [[Resonator]]
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| * [[Reed switch]]
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| * [[Transducer]]
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| * [[Electrical resonance]]
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| * [[Laser applications]]
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| * [[Dunkerley's Method]]
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| * [[String resonance]]
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| == Notes ==
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| {{reflist}}
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| == Further reading ==
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| * S Spinner, WE Tefft, ''A method for determining mechanical resonance frequencies and for calculating elastic moduli from these frequencies''. American Society for testing and materials.
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| * CC Jones, ''A mechanical resonance apparatus for undergraduate laboratories''. American Journal of Physics, 1995.
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| == Patents ==
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| * {{US patent|1414077}} Method and apparatus for inspecting materials
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| * {{US patent|1517911}} Apparatus for testing textiles
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| * {{US patent|1598141}} Apparatus for testing textiles and like materials
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| * {{US patent|1930267}} Testing and adjusting device
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| * {{US patent|1990085}} Method and apparatus for testing materials
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| * {{US patent|2352880}} Article testing machine
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| * {{US patent|2539954}} Apparatus for determining the behavior of suspended cables
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| * {{US patent|2729972}} Mechanical resonance detection systems
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| * {{US patent|2918589}} Vibrating-blade relays with electro-mechanical resonance
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| * {{US patent|2948861}} Quantum mechanical resonance devices
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| * {{US patent|3044290}} Mechanical resonance indicator
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| * {{US patent|3141100}} Piezoelectric resonance device
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| * {{US patent|3990039}} Tuned ground motion detector utilizing principles of mechanical resonance
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| * {{US patent|4524295}} Apparatus and method for generating mechanical waves
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| * {{US patent|4958113}} Method of controlling mechanical resonance hand
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| * {{US patent|7027897}} Apparatus and method for suppressing mechanical resonance in a mass transit vehicle
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| [[Category:Mechanical vibrations]]
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| [[Category:Earthquake engineering]]
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Irwin Butts is what my wife loves to contact me although I don't truly like becoming called like that. I am a meter reader. North Dakota is our birth place. What I adore doing is performing ceramics but I haven't made a dime with it.
Also visit my site :: at home std test (pop over to this site)