# Periodic Motion

Motion which repeats itself after a fixed interval of time is known as periodic motion. A pendulum is an example of periodic motion. The periodic motion in which a body moves back and forth continuously is called as vibratory motion.

## A Simple Pendulum

A simple pendulum consists of a massive object hung by a string from a fixed support. A simple pendulum completes every swing in exactly the same time, provided its length is kept constant. Whether the amplitude of ocscillations of a pendulum is large or small, the time taken for one complete oscillation remains the same.

## Why Pendulum Keeps Oscillating

When we pull the pendulum bob to one side and release it, the restoring force applied by gravity and the tension in the thread which makes it to bring the bob back to its mean position and keps it oscillating. Basic terms used in pendulum are:

1. Length of Pendulum: The length of thread from the point of suspendion to the centre of bob is called length of the pendulum.

2. Oscillations: One complete to-and-fro movement of the pendulum bob is called oscillation.

3. Time Period: The time taken by the pendulum bob to make one complete oscillation is called time-period of the pendulum. The formula of time perioad of simple pandulum is: T=2π√(1/g).
4. The time period of a simple pendulum depends on,
1. Length of the pendulum
2. Acceleration due to gravity
The time-period of a simple pendulum does not depends on,
1. Mass of the bob
2. Nature of the material of the bob
3. Amplitude of oscillations

5. Amplitude: When a pendulum swings the maximum height it get form the center on the either side is known as its displacement.

6. Frequency of Oscillations: The number of complete oscillations made by a simple pendulum in one second is called its frequency. The SI unit of frequency is 'hertz'.