Introduction To Resonance
Musical instruments demonstrate the acoustics of pitch wonderfully. Think about a xylophone with its mathematically designed bars laid out from long to short. Look at the drawing of a child's xylophone to the right. Notice the bars decrease (get smaller) from large(left) to small(right).
Any object, when energized so that it begins to vibrate, has its own frequency. This natural vibration frequency is the resonate frequency for that object.
Sound is produced by vibrations in a medium. Every medium has its own frequency of vibration, or natural frequency. For example, one object may vibrate at 250 hertz, while another object vibrates at 510 hertz. So the first object has a natural frequency of 250 hertz, and the second object has a natural frequency of 510 hertz.
An object vibrating at its natural frequency can cause a nearby object to start vibrating if that object has the same natural fequency.
The second object picks up some of the vibration energy of the first object and vibrates "in sympathy" with it.
Picture a drinking glass sitting on your desk. You are playing a guitar. The glass on your desk absorbs some of the energy of the guitar when the two frequencies are the same. The glass vibrates in sympathy with the guitar.
The ability of an object to vibrate by absorbing energy of its own natural frequency is called resonance.