The  periodic motion is defined as any motion that repeats itself at regular time intervals, such as exhibited by the guitar string or by a child swinging on a swing. A very common type periodic motion is simple harmonic oscillation and object which exhibit this property is called simple harmonic oscillator. In simple harmonic motion, the acceleration of the system, and therefore the net force, is proportional to the displacement and acts in the opposite direction of the displacement. Example of this motion is movement of an object attached to a string on a frictionless surface.