Simple harmonic motion is a particular kind of periodic motion and occurs for very diverse systems when they are disturbed slightly from equilibrium The restoring force which brings a simple harmonic oscillator back to equilibrium is proportional to how far it has been disturbed from equilibrium.. The amplitude of a simple harmonic oscillator is the maximum distance that it moves from equilibrium. The period or frequency of a simple harmonic oscillator is independent of its amplitude. This makes simple harmonic oscillators very important in keeping accurate time.
During simple harmonic motion, energy is transferred from one form to another throughout the cycle but the total energy remains constant. For a horizontal spring and mass, energy changes from kinetic energy to elastic potential energy and back again. A simple pendulum is another example of a simple harmonic oscillator as long as its amplitude does not get very large; energy changes from kinetic energy to gravitational potential energy and back again. The period or frequency of a mass and spring is determined by the spring constant and the mass. The period or frequency of a simple pendulum is determined by the length of the pendulum and the acceleration due to gravity.
A damped oscillator has friction present which causes its amplitude
to gradually decrease with time. An external force which is applied
with the resonant frequency of an oscillator can cause the oscillator
to have a very large amplitude.