Simple harmonic motion

In physics, simple harmonic motion (SHM) is a periodic motion that is neither driven nor damped. An object in simple harmonic motion experiences a net force which obeys Hooke's law; that is, the force is directly proportional to the displacement from the equilibriliium position and acts in the opposite direction of the displacement.
A simple harmonic oscilattor is a system which undergoes simple harmonic motion. The oscillator oscillates about an equilibrium position (or mean position) between two extreme positions of maximum displacement in a periodic manner. In fact, the motion of the oscillator can be described by means of a sinusoidal function. Mathematically, the displacement from the equilibrium position x is given by

where

A is the amplitude which is the maximum distance from the equilibrium position (in SI units m);

ω is the angular frequency which is a multiple of frequency f, and ω = 2πf (in SI unit: s^-1);

φ is the phasewhich is the elapsed fraction of wave cycle.

http://en.wikipedia.org/wiki/Simple_harmonic_motion