Changing the Period of a Pendulum

period of pendulum

A pendulum consists of a mass at the end of a thin cord, known as the Bob is connected at the fixed point. When the mass is drawn towards high and left, the gravitational force accelerates it back to its previous position. Changing the length of the pendulum changes its period. Long length pendulums swing with a smaller frequency and therefore have a longer period.


To change the period of a pendulum

Apparatus Required:

Apparatus for pendulum experiment

  • Weights
  • Stopwatch
  • Tape
  • Ruler
  • Thread
  • Straw
  • Table


  • Tie a weight to a thread.
  • Tie the thread to a straw and tape the straw on the table in such a way that around half of an inch hangs over the edge.
  • Tape the other end of the thread with the table in such a manner that the length from the straw’s end to the middle the weight is 4 inches.
  • Let the pendulum settle and be in constant.
  • Pull the bob about one inch and leave it gently. Make sure to make the pendulum swing in a steady arc.
  • When you let it go, start the stopwatch and note the number of times it swings from its initial point and back to original until you count at least 10 swings. Repeat this three times and take the average of the collected data of the three trials. The no of swings divided by the time taken is called the period of the pendulum.
  • Extend the length of the pendulum to 5 inches and repeat the procedure.
  • Increase the weight of the bobs and repeat the above procedure.


Only the length affects the period of a pendulum. Changing the weights and the distance pulled to swing has no effect on the time taken to finish a swing from an initial to the final position. The period of the pendulum remains same in both the cases.

Practise This Question

State true or false.
a × (b + c) = a × c + b ×