Simple Harmonic Motion Pendulum

Simple Harmonic Motion Pendulum

When an object oscillates with constant time period even if the amplitude varies, we say it is moving with simple harmonic motion (SHM). The regular oscillation of a pendulum through a small angle are approximately simple harmonic.

The motion of the pendulum has explained here, when the bob is slightly moved to one side (say right), to extreme position A (above figure) and left free, it dose not stay there. It moves towards mean position O with increasing speed. Its speed become maximum at mean position. Due to inertia the bob dose not stay at O but over shot to the other side (left) and continues moving ahead with decreasing speed. The speed become zero at extreme position B, where the bob comes to rest momentarily. From B, the bob return back to O and continues moving towards right extreme A.

From A, the motion is repeated as before. In this way, the bob continues to and fro between A and B with O as mean position. The motion of the bob become an oscillatory motion. We say that the simple pendulum is oscillating.

Due to friction at rigid support and air resistance for the motion of the bob, the extreme points shift inwardly and the oscillation seem to die out and finally the bob comes to rest at mean position O.

• Displacement : At any moment, the distance of bob from mean position, is called displacement. It is a vector quantity.
• Amplitude : Maximum displacement on either side of the mean position, is called amplitude. In the above figure OA and OB measure amplitude.
• Vibration : Motion from the mean position to one extreme, then to other extreme and then back to mean position, is called one vibration.
• Oscillation : Motion from one extreme to other extreme, is called one oscillation. Thus, one oscillation is half vibration.