Resonance

From HvWiki

In general, resonance is anything that involves proper timing or driving at the right frequency to get a larger output from a system.

Everything has a resonant frequency and it is dependent on the makeup of that object and the enviroment around it. A system given energy and left alone will resonate with it's resonant frequency.

A pendulum is an example of a simple resonant system. When a pendulum is pushed and then released, it will travel from one extreme to the next and back in exactly the same amount of time, no matter how much potential energy it is given. In other words, a pendulum pulled back a foot and released will return in the same amount of time as if it had been pulled back two feet. Therefore, it's frequency is always the same. The weight distribution and length of 'cord' determine the time constant. In the pendulum system, energry is periodically changed between forms; kinetic and potential. At the bottom of the swing the pendulum will have maximum kinetic and minium potential, however at either peak of the swing it will have minimum kinetic and maximum potential energy. This is analogous to an LC circuit in electronics, where energy swings between energy stored in the magnetic field of the inductor and energy stored in/around the dielectric and plates of the capacitor.

Some things resonate in the audible spectrum. You may not be able to hear the pendulum, but have you ever heard the "ring" of dropping a spoon on the floor? Bells are designed to have a certain resonant frequency. Other systems have a higher-than-audible resonant frequency. We can use these systems in radio and other similar applications.

The ability for an object to remain in resonance is it's "Q" or "quality." Q determines how long a system will stay in resonance when given energy and released. A pendulum with a light string will swing much longer than one with a rusty metal hinge at the top. The same applies to all resonant systems, generally the greatest factor that decreases "Q" is the amount of resistance in a system and thus determines the rate of energy loss.

A system with a low "Q" is generally referred to as "damped." This can extend to being critically damped, overdamped or underdamped.

The most prolific of the resonant systems is probably the LC oscillator.

Examples of Resonance

A Tesla coil relies on resonance to produce a very high voltage output from relatively low voltage input.

An singer singing the resonant note of a drinking glass can shatter it.

An antenna is designed to resonate at a certain frequency to obtain maximum reception.

A poorly designed skyscraper can be brought to rubble if it is built with a resonant frequency similar to the gusts of wind pushing it. In worst case scenarios, the wind adds a small 'push' on each gust like pushing someone on a swing, until the amount of deviation is sufficient to cause structural damage or failure of the supports and the building collapses. This effect can be made worse because the bottom end of the skyscraper is 'grounded' (anchored) the top end is free to move, the height causes a lever effect that makes the vibrations cause very large amplitude movements on the higher levels.

The principal of resonance allows a constant power input to a system to develop and store the energy over time.