Class exercise 2 – Pendulum

Aim: To find out the effect of changing the length of a pendulum on the period of oscillation

Hypothesis: The longer the length of the pendulum, the longer the period of oscillation


  • Retort stand, split cork
  • Strings, scissors, ruler
  • Pendulum bob
  • Stopwatch



–       Base of retort stand should be facing away from pendulum

–       Excess string should not be in the way of the pendulum’s swing

Screen Shot 2013-01-21 at 8.56.35 PM

1.  Tie the pendulum bob on one end of a thread.

2. Clamp the other end firmly between two pieces of split cork to make a pendulum.

3. Measure the length of the string L between the middle of the bob and the edge of the split cork clamping the thread, for L = 80.0 cm.

4. Give the pendulum bob a slight displacement and allow it to oscillate steadily. An example of a complete oscillation is when the bob moves from A to B and back to A (see diagram 2).

  • When displacing the pendulum, make sure it is in a plane parallel to you (not swinging diagonally, orbiting etc.)
  • Place your eyes at the same level as the pendulum to reduce parallax error

5. Time N steady oscillations, t1, using a stopwatch. Repeat the measurement a second time and record it as t2. Vary N from 10 to 20 oscillations depending on L.

6. The time taken for 1 complete oscillation is called the period, T. Calculate the average time
taken < t >, period T, and the value of .

7. Repeat the experiment for various readings of L between 50.0 cm to 100.0 cm.

8. Tabulate your results in the table given.


Screen Shot 2013-01-21 at 9.01.07 PM


  1. Plot the graph of T / s against  √L/cm^1/2 , and determine the gradient of the graph. Show your working clearly.


Gradient = 0.2/0.6

= 1/3

2. Why was it necessary to measure the time taken for 20 oscillations instead of measuring the period directly?

>> To increase the accuracy of the measurement of the period by taking the average of 20 periods and thus reducing errors such as human reaction time in operating the stopwatch.

3. What were the controlled variables? How did you ensure that they did not affect the experiment?

–       Angle at which the pendulum is released: I ensured that the pendulum was released parallel to the corner of a drawer behind it in order to fix the angle at which it was released

–       Environmental factors (e.g. the wind created by the fans in the laboratory): Although I did not take this variable into account, I could have switched off the fans and closed the doors to create a controlled environment.


The longer the length of the pendulum, the longer the period of the oscillation. Therefore, my hypothesis was correct.


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