Simple Pendulum

You must have seen childrens enjoying swing. See the structure of swing carefully, you will notice that, children sitting on a rope/metal chain which is suspended from a fix support performs to and fro motion about same path again and again. Kids enjoys this motion, which is nothing but oscillatory motion. Those kids itself acts as a pendulum, called as simple pendulum. So what exactly is the simple pendulum? Where it is used?

Simple pendulum is a simple arrangement made with a point object like a metal ball with hook and light weight string whose one end is tied to fix and rigid support and other end is attached to the hook of metal ball(the metal ball oftenly called as BOB).

Initially after suspending the bob from rigid support it remains at rest at the position called as ‘mean position’. Then it is slightly pulled away from mean position and released, so that it performs oscillatory motion between two points A and B repeatadly. The positions A and B are termed as extreme positions. Refere figure shown below.

Such motion is called as oscillatory motion. When bob displaced from point O (mean position) goes to extreme position A then towards B and finally reaches to mean position O, is said to completed one oscillation. Path traced from position A to A (or B to B) is also termed as one complete oscillation.

The time required to complete one such oscillation is called as period or periodic time. The method to find the periodic time for simple pendulum is given below.

  • Take a string of length 100 cm
  • Fix its one end on rigid support
  • Attach a bob of certain mass to other end
  • Allow pendulum to settle at rest.
  • Now displace it slightly and softly so that it can performs oscillatory motion.
  • Using stop watch, wrist watch or timer in mobile measure time require to complete 20 oscillations
  • Keep record of the time in note book.
  • Repeat the above procedure for two more time for accuracy. Record time in notebook as below,

Time for 20 oscillation

1)    10 second 2)    10 second

3)    10 second


  • Now perform the simple calculation as follows

Using above procedure one can find time period for simple pendulum.

In practice period of simple pendulum depends upon some factors like length of string, gravity at that point. This information about simple pendulum is very useful in studying the time and its measurement at different locations as well as on the surface of other planets also. The pendulum clock is one of the best example in our routine which explain its importance.

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