Simple Harmonic Motion:

Simple Harmonic Motion may be defined as a straight line motion of a particle whose acceleration is proportional to the displacement from a fixed point termed as origin and is always directed towards the origin.

Let us assume a particle moving with constant speed along a circular path. The motion of the projection of this moving particle on the diameter of the circle may be considered as Simple Harmonic Motion.

Assume a circle of radius r. A particle is moving along the circumference of this circle with constant angular velocity ω in the anticlockwise direction. A particle begins its motion from the initial position A as illustrated in Figure.

Figure

Since the particle moves along the circumference of the circle, its projection oscillates along the diameter and carries out simple harmonic motion.