In chemistry terms, resonance describes the fact that electrons are delocalized, or flow freely through the molecule, which allows multiple structures to be possible for a given molecule. Each contributing resonance structure can be visualized by drawing a Lewis structure; however, it is important to note that each of these structures cannot. Resonance Definition: Resonance is a method of describing the delocalized electrons in some molecules where the bonding cannot be.

Resonance, in acoustics: see vibration,in physics, commonly an oscillatory motion—a movement first in one direction and then back again in the opposite direction. It is exhibited, for example, by a swinging pendulum, by the prongs of a tuning fork that has been struck, or by the string of a musical. Click the link for more information.resonance, in chemistry: see chemical bond,mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as an. Click the link for more information. Resonance (acoustics and mechanics)When a mechanical or acoustical system is acted upon by an external periodic driving force whose frequency equals a natural free oscillation frequency of the system, the amplitude of oscillation becomes large and the system is said to be in a state of resonance.A knowledge of both the resonance frequency and the sharpness of resonance is essential to any discussion of driven vibrating systems.

When a vibrating system is sharply resonant, careful tuning is required to obtain the resonance condition. Mechanical standards of frequency must be sharply resonant so that their peak response can easily be determined. Farm town gifts for free. In other circumstances, resonance is undesirable. For example, in the faithful recording and reproduction of musical sounds, it is necessary either to have all vibrational resonances of the system outside the band of frequencies being reproduced or to employ heavily damped systems. See,Resonance (quantum mechanics)An enhanced coupling between quantum states with the same energy. The concept of resonance in quantum mechanics is closely related to resonances in classical physics. SeeThe matching of frequencies is central to the concept of resonance.

Seng Hock: The Butterfly Fritter: You Char Kway’s lesser known sibling! We've moved to ishootieatipost.com. By Alfred 2 comments Tuesday, April 28, 2009. Blog Archive. View My Stats: Technorati. Technorati My authority on technorati Add this blog to your faves. 2009 Ishoot Ieat Ipost Blogger Template Designed by Alfred Wong. About the Author and His Team. Dr Leslie Tay, has spent over a decade roaming around Singapore in search of the best hawker food and then publishing his mouth watering pictures and stories on his award winning food blog, ieatishootipost.sg. Dr Tay is recognized as an authority on local food lore and has delivered talks on Singapore’s Hawker Cuisine to international as well as local audiences. Ieatishootipost tampines. Singapore's best hawker and restaurant food reviews, recommendations and local food recipes. Never waste calories on yucky food!

An example is provided by waves, acoustic or electromagnetic, of a spectrum of frequencies propagating down a tube or waveguide. If a closed side tube is attached, its characteristic natural frequencies will couple and resonate with waves of those same frequencies propagating down the main tube. This simple illustration provides a description of all resonances, including those in quantum mechanics. The propagation of all quantum entities, whether electrons, nucleons, or other elementary particles, is represented through wave functions and thus is subject to resonant effects. See,An important allied element of quantum mechanics lies in its correspondence between frequency and energy.

Instead of frequencies, differences between allowed energy levels of a system are considered. In the presence of degeneracy, that is, of different states of the system with the same energy, even the slightest influence results in the system resonating back and forth between the degenerate states. These states may differ in their internal motions or in divisions of the system into subsystems.

The above example of wave flow suggests the terminology of channels, each channel being a family of energy levels similar in other respects. These energies are discretely distributed for a closed channel, whereas a continuum of energy levels occurs in open channels whose subsystems can separate to infinity.

If all channels are closed, that is, within the realm of bound states, resonance between degenerate states leads to a theme of central importance to quantum chemistry, namely, stabilization by resonance and the resulting formation of resonant bonds. See,Resonances occur in scattering when at least one channel is closed and one open. Typically, a system is divided into two parts: projectile + target, such as electron + atom or nucleon + nucleus.

One channel consists of continuum states with their two parts separated to infinity. The other, closed channel consists of bound states. In the atomic example, a bound state of the full system would be a state of the negative ion and, in the nuclear example, a state of the larger nucleus formed by incorporating one extra nucleon in the target nucleus.

See, resonance A condition prevailing in a system when the frequency of some external stimulus coincides with a natural frequency of the system, and producing a selective or maximum response in the system. Resonance is responsible, for example, for orbits, the in the asteroid belt, and divisions in. The phenomenon of a marked increase in the amplitude of forced oscillations, occurring in an oscillatory system when the frequency of an external periodic force approaches certain values that are determined by the inherent properties of the system.

In the simplest cases, resonance occurs when the frequency of the external force approaches one of the frequencies at which natural oscillations occur as a result of an initial impulse. The nature of the resonance phenomenon is essentially dependent on the properties of the oscillatory system. The simplest resonance occurs in a system subjected to a periodic force when the system’s parameters are not a function of the state of the system itself (a linear system).

Mechanical oscillatory systemThe characteristic features of resonance can be seen in the case of a harmonic force acting on a system having one degree of freedom, such as a mass m suspended on a spring and subjected to a harmonic force F = F 0 cos ωt (Figure 1) or an electrical network composed of an inductance L connected in series with a capacitance C, a resistance R, and a source of an electromotive force E that varies harmonically (Figure 2). Although the following remarks refer specifically to the first of these models, the explanation can be extended to apply to the second model as well.We will assume that the spring obeys Hooke’s law (this assumption is necessary if the system is to be linear); that is, the force acting from the spring side on the mass m is equal to kx, where x is the displacement of the mass from its equilibrium position and k is the modulus of elasticity. For the sake of simplicity, the force of gravity is not taken into consideration. Furthermore, assume that when the mass is in motion, it experiences a resistance from the surrounding medium that is proportional to. Electrical oscillatory system with capacitance C and inductance L connected in seriesthe velocity ẋ of the mass and to the coefficient of friction b; that is, the resistance is equal to bẋ. This is necessary so that the system will remain linear. Then the equation of motion for the mass m when an external harmonic force F is present has the form(1) mẍ + bẋ + kx = f 0cos wtwhere F 0 is the amplitude of the oscillations, ω is the angular frequency, equal to 2 π / T, T is the period of the external force, and ẍ is the acceleration of the mass m.The solution of the equation can be represented as the sum of two solutions.

The first solution corresponds to the natural oscillations of the system that occur as a result of the action of an initial impulse, and the second solution corresponds to the forced vibrations. As a result of the presence of friction and the resistance of the medium, the natural oscillations are always damped; therefore, over a sufficiently long period of time (the less the damping of the natural oscillations, the longer the time) only certain forced oscillations will continue in the system.

The solution corresponding to the forced oscillations has the formHere,Thus, the forced oscillations are harmonic oscillations having a frequency equal to that of the external force. The amplitude and phase of the forced oscillations depend on the relationship between the frequency of the external force and the system’s parameters.The dependence of the displacement amplitude of the forced oscillations on the relationship between the values of the mass m and the elasticity k can best be seen if one assumes that m and k remain constant while the frequency of the external force is varied. When the frequency is very low (ω → 0), the displacement amplitude x 0 ≈ F 0/ k. As the frequency ω is increased, the amplitude x 0 increases because the denominator in equation (2) becomes smaller. When ω approaches the value (that is, the value of the natural oscillation frequency with low damping), the amplitude of the forced oscillations reaches the maximum, and resonance occurs. With a further increase in ω, the amplitude of the oscillations decreases monotonically, and when ω — ∞, the amplitude approaches zero.The amplitude of the oscillations at resonance can be determined approximately by assuming that.

Then, x 0 = F 0/ b ω; that is, the lower the damping b in the system, the. Displacement amplitudes as a function of the frequency of an external force for various values of b ( b 6. Example of two coupled electrical circuitswork feeding the circuit is sharply reduced. In electrical engineering, this phenomenon is called current resonance or parallel resonance. It is attributable to the fact that when the frequency of an external force is close to the natural frequency of the circuit, the reactances of both parallel branches (capacitive and inductive) become identical in magnitude so that the currents in both branches are of approximately the same amplitude but almost opposite in phase. As a result, the amplitude of the current in the external network, which is the algebraic sum of the currents in the individual branches, proves to be much lower than the current amplitudes in the individual branches, which reach their highest values with parallel resonance. As is the case with a series resonance, a parallel resonance increases with a decrease in the active resistance in the branches of the resonant circuit.

Series and parallel resonances are known as voltage and current resonances, respectively.In a linear system having two degrees of freedom, particularly in the case of two coupled systems (for example, in the two coupled electrical circuits in Figure 5), the phenomenon of resonance retains the basic features indicated above. However, because the natural oscillations in a system having two degrees of freedom may occur at two different frequencies (the normal frequencies), resonance occurs when the frequency of a harmonic external force coincides with either one of the system’s normal frequencies.

Therefore, if the system’s normal frequencies are not very close to one another, two maxima will be observed in the amplitude of the forced oscillations (Figure 6) as the frequency of the external force is continuously varied. However, if the system’s normal frequencies are close to each other and the system’s damping is sufficiently high so that the resonance at each of the normal frequencies is attenuated, the two maxima may coincide. In this case, the resonance curve for a system having two degrees of freedom loses its “double-humped” character and differs little in appearance from the resonance curve of a linear circuit having one degree of freedom. Thus, the shape of the resonance curve for a system with two degrees of freedom not only depends on the circuit’s damping, as is the case of a system with one degree of freedom, but also on the degree of coupling between the circuits. Resonance curve with two maximaCoupled systems also exhibit a phenomenon that is to a certain extent analogous to the phenomenon of antiresonance in a system with one degree of freedom.

In the case of two coupled oscillatory circuits having different natural frequencies, if the secondary circuit L 2 C 2 is tuned to the frequency of an external emf connected to the primary circuit L 1 C 1 (Figure 5), then the current magnitude in the primary circuit will decrease sharply; the lower the damping in the circuits, the sharper the decrease. The reason for this phenomenon is as follows; when the secondary circuit is tuned to the frequency of the external emf, only enough current appears in the circuit to induce an emf in the primary circuit approximately equal to the external emf in amplitude and opposite in phase.In linear systems having many degrees of freedom and in continuous systems, resonance retains the same basic features as in a system having two degrees of freedom. However, unlike systems having one degree of freedom, in this case the distribution of the external force with respect to the individual coordinates plays an important role. It is possible to have special instances of distribution of the external force in which resonance does not occur, even though the frequency of an external force coincides with one of the normal frequencies of the system. In terms of energy, this can be explained by certain phase relationships established between the external force and the forced oscillations, such that the power entering the system from the exciting source in one coordinate is equal to the power delivered by the system to the source in another coordinate.

An example of this is the excitation of forced oscillations in a string when the external force, which coincides in frequency with one of the normal frequencies of the string, is applied at a point corresponding to a velocity node for the particular normal oscillation (for example, a force that matches the fundamental tone of the string is applied to the very end of the string). Under these conditions, because the external force is applied to a fixed point of the string, the force does not perform work, power does not enter the system from the source of the external force, and there is no appreciable excitation of string oscillations; that is, no resonance is seen.In oscillatory systems, whose parameters are functions of the state of the system, resonance has a more complicated character in nonlinear systems than in linear systems. The resonance curves in nonlinear systems may be markedly nonsymmetrical, and the phenomenon of resonance can occur for various relationships between the exciting frequencies and the frequencies of small natural oscillations in the system at fractional, multiple, and combined frequencies. The energetic vibration of a body produced by application of a periodic force of nearly the same frequency as that of the free vibration of the affected body. It is the condition of two bodies adjusted to have the same frequency of vibration.

There are two types of resonance: sympathetic and ground. Is a harmonic beat that develops when the natural vibration frequency of one mechanism is in phase with another mechanism's vibrational frequency. Is a self-excited vibration that develops when the landing gear of a rotorcraft repeatedly strikes the ground or deck of a ship, thus unseating the center of mass of the main rotor system. The pounding effect of the landing gear is prone to occur during start-up, ground taxi, rolling takeoff and landing, engine shutdown, and operation from the deck of a rolling or pitching ship.

When a helicopter begins to bounce from one wheel to the other in rapid succession, a pendular oscillation of the fuselage sets in. The succession of shocks is transmitted to the main rotor system, causing the main rotor blades to change their angular relationship with each other. This unbalances the main rotor system, which in turn transmits the shock back to the landing gear.

This condition, if allowed to continue, can lead to the complete destruction of the helicopter.