Damped and Driven Harmonic Motion

Real oscillators do not continue to move forever. They gradually decrease their motion.

This may be good or bad. You may want the sound caused by a piano or a guitar to continue for a while. But you may want the oscillation of your car to stop immediately after going over a bump. That is the purpose of shock absorbers.

If you give only little pushes to an oscillator -- but ensure that those pushes come at just the right time -- you can  still give the oscillator a very large amplitude. A fine example of this is pushing someone on a playground swing. If you give just a small push, but give it at the right time, your friend can still end up swinging very high. This is an example of resonance of a driven harmonic oscillator.

Another example of resonance are these carefully matched chime boxes. The the motion of the air caused by the sound from one will cause the other one to vibrate.

Physical Pendulum

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(c) 2005, Doug Davis; all rights reserved