Resonant frequency is the natural frequency of a system, such as an electrical circuit, mechanical structure, or a vibrating string, at which the system tends to vibrate if it is disturbed. It is also known as the resonance frequency or natural frequency.

Mechanical resonance

This article is about resonance mechanics in physics and engineering. For a general description of resonance, see Resonance. For mechanical sound resonance, including musical instruments, see acoustic resonance. For the music album by American rock band Tesla, see Mechanical Resonance (album).
Tendency of a mechanical system

Chart showing mechanics resonance in a mechanical oscillatory system

mechanical resonance is the tendency of a mechanical system to respond with greater amplitude when the frequency of its oscillations coincides with the natural frequency of the vibration (It is resonant frequency or resonant frequency) closer than other frequencies. It can cause violent swaying motions and potentially catastrophic failures in incorrectly constructed structures, including bridges, buildings and airplanes. This is a phenomenon known as a resonance disaster.

Avoiding resonance disasters is a major concern in all buildings, towers and bridges. construction project. The Taipei 101 building relies on a 660-ton pendulum-an tuned mass damper— to modify the resonance response. Furthermore, the structure is designed to resonate at a frequency that it normally does not. buildings in seismic zones are generally constructed to take into account the oscillating frequencies of expected ground motion. Furthermore, engineers designing objects with motors must ensure that the mechanical resonance frequencies of the component parts do not coincide with the vibration frequencies of motors or other heavily oscillating parts.

Many resonant objects have more than one resonant frequency. It will easily vibrate at these frequencies and less at other frequencies. Several clocks keeping time by mechanical resonance in a rocking wheel, pendulumor quartz crystal.


The natural frequency of a simple mechanical system consisting of a weight suspended by a spring is:





\displaystyle f=1 \over 2\pi \sqrt k \over m

Where m it’s the pasta and k it’s the constant spring.

AN balance is a simple example of a resonant system that most people have hands-on experience with. It is a pendulum shape. If the system is excited (pushed) with a period between pushes equal to the inverse of the natural frequency of the pendulum, the swing will oscillate higher and higher, but if excited at a different frequency, it will be difficult to move. The resonant frequency of a pendulum, the only frequency at which it will vibrate, is given approximately, for small displacements, by the equation:





\displaystyle f=1 \over 2\pi \sqrt g \over L

Where g it’s the acceleration due to gravity (about 9.8 m/stwo close to the surface of Earth), and I is the length from the pivot point to the center of mass. (One elliptic integral produces a description for any displacement). Note that, in this approximation, the frequency does not depend on pasta.

Mechanical resonators work by repeatedly transferring energy from kinetics for potential form and come back again. In the pendulum, for example, all energy is stored as gravitational energy (a form of potential energy) when the weight is instantly immobile at the top of its swing. This energy is proportional both to the mass of the bob and its height above the lowest point. As the weight descends and gains speed, its potential energy is gradually converted into kinetic energy (energy of motion), which is proportional to the mass of the weight and the square of its velocity. When the weight is at the bottom of its stroke, it has maximum kinetic energy and minimum potential energy. The same process happens in reverse as the bob rises towards the top of its swing.

Some resonant objects have more than one resonant frequency, particularly at harmonics (multiples) of the strongest resonance. It will easily vibrate at these frequencies and less at other frequencies. It will “select” its resonant frequency from a complex excitation such as an impulse or a wideband noise excitation. It is actually filtering out all frequencies beyond its resonance. In the example above, swing cannot easily be excited by harmonic frequencies, but it can be excited by subharmonics.


resonance rings display on California Science Center

Several examples of mechanical resonance include:

Resonance can cause violent oscillating motions in constructed structures such as bridges and buildings. The London Millennium Walkway (nicknamed wobbly bridge) presented this problem. A faulty bridge can even be destroyed by its resonance (see Broughton Suspension Bridge and Bridge of Angers). Mechanical systems store potential energy in different forms. For example, one springThe /mass system stores energy as tension in the spring, which is finally stored as the energy of the bonds between atoms.

resonance disaster

Resonances excited by marching soldiers caused several bridge collapses. This sign is not Albert Bridge, London warns soldiers to break step when crossing.

In mechanics and construction resonance disaster describes the destruction of a building or a technical mechanism by vibrations induced in a system resonance frequently, which oscillate. Periodic excitation is optimally transferred to the system The energy from the vibration and stores it there. Because of this repeated storage and additional energy input, the system oscillates more and more strongly until its load limit is exceeded.

Tacoma Narrows Bridge

The dramatic and rhythmic twist that resulted in the 1940 breakdown of “Galloping Gertie”, the original Tacoma Narrows Bridge, is sometimes featured in physics textbooks as a classic example of resonance. The catastrophic vibrations that destroyed the bridge were due to an oscillation caused by the interaction between the bridge and the winds that pass through its structure – a phenomenon known as aeroelastic vibration. Robert H. Scanlanfather of the field of bridge aerodynamics, wrote an article about it.

Another examples


There are several methods of inducing mechanical resonance in a medium. Mechanical waves can be generated in a medium by subjecting an electromechanical element to an alternating electric field with a frequency that induces mechanical resonance and is below any electrical resonance frequency. 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.

The United States Patent Office classifies devices that test mechanical resonance in subclass 579, resonance, frequencyor amplitude study, class 73, measuring and testing. This subclass is indented in subclass 570, Vibration. These devices test an article or mechanism subjecting it to a vibratory force to determine its qualities, characteristics or conditions, or by sensing, studying or analyzing the vibrations generated or existing in the article or mechanism. The devices include correct methods to cause vibrations in a natural mechanical resonance and measure the frequency and/or amplitude the resonance done. Several devices study the amplitude response in a frequency range It is made. That includes nodal points, wavelengthsand standing wave characteristics measured under predetermined vibration conditions.

See too


Further reading

  • 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.
  • CC Jones, A mechanical resonance machine for undergraduate laboratories. American Journal of Physics, 1995.


Source: Mechanical resonance

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