Natural Resonance Quality

Objects will vibrate at one or more natural frequencies when struck, plucked, hammered or otherwise disturbed. The frequency of the natural vibration depends on the physical properties of the object. But there is another physical property, the natural frequency quality, which affects the amplitude of the vibrations.

Some objects are very resonant at particular frequencies, like the strings of a piano, while other objects are barely resonant. The difference is known as the Q or quality of the resonance.

An example of an object with a high Q is a bell. It will have a distinct frequency at which will it resonate. When it is struck, it will resonate at that frequency loudly and for a long time. You would not, however, be very successful at getting the bell to ring at any other frequency.

An example a low Q object is Jell-O. Jell-O is responsive to a wide range of input frequencies but it is not as responsive to any particular frequency.

Dampening

Dampening is the process of lowering the Q value of resonance by making it more difficult or impossible for the object to vibrate uncontrollably.

A good example of dampening in everyday life is the shock absorbers on a car. These shock absorbers dampen the car springs' natural tendency to "bounce" down the road. In one example, a very heavy boat was literally flying down the freeway because of the small cracks in the concrete slabs. As it turned out, by going the exact wrong speed, the next crack would hit just after the boat had returned to the ground. Soon the boat was spending more time flying than driving until the speed was reduced to leave the high Q tendencies of the boat trailer springs.

Another great example is the foot petals of a piano. The foot petals, when depressed, will bring a soft cushion in contact with the piano strings to absorb the vibrational energy, essentially quenching the vibrations.