How to measure time

1e) Describe how to measure a variety of time intervals using clocks and stopwatches.

 Here we are going to talk about the physical quantity Time. SI units seconds (s).

Measuring Instruments for time are

1) Pendulum clock
2) Clock
3) Stopwatch

( a simple stop watch )

 ( a simple stop clock)

Measuring time using stop watch and stop clock

Measuring time using stop watches and stop clocks is very easy. The only thing needed is the accuracy in pressing the start button at the right time. To avoid errors experiment can be repeated again so that an average of reading can be taken.


 Avoid Errors

Now due to introduction of digital stop watches reading of the time has become easier but still when an analogue stop watch (stop clock) is used,  parallax error should be avoided.
Repeating the experiment is important for getting an accurate reading as by taking an average of the readings, errors can be reduced. Human reaction error can also generate a difference in the time recorded and original time.
An important part of measuring time in o level course is measuring time period using a Simple pendulum. Details of it are discussed below.


A Simple Pendulum

(image above shows a simple pendulum)

A simple pendulum makes use of a swing (oscillation)  of the metallic bob to measure time period.

Note:  The oscillation refers to a swing of bob from left to right and back to the starting position.

The Time period of the pendulum is the time taken for one complete oscillation. Remember the time period is very dependent on the length of the pendulum(i.e. distance from fixed point to the bob see next image) and the gravitational force . when the length increases time period increases while when the gravitational force increases time period decreases.

One more thing that you should keep in mind is the definition of frequency. Frequency is the number of oscillations of the pendulum in one second.

How to find time period using a Simple pendulum.

  • First measure time for 20 complete oscillations using a stop watch or a stop clock (remember measuring time period of just one oscillation will not be accurate and can introduce errors)
  • Find T1 (time period 1) using formula TOTAL TIME FOR 20 OSCILLATIONS/20
  • Once you have found T1 repeat the experiment for next four times to find T2 T3 T4 T5
  • In end to get an accurate reading of time period  take average of the 5 time periods i.e. T1+T2+T3+T4+T5/5


  1. this os really usefull for my o level examinations in 2015....thankyou...!!

    1. You are welcome!
      Don't forget to share it with your friends :)

  2. You are really a helping hand. May Allah grant you with Paradise for this wonderful work. I surely will share it with my friends. I hope that if any organization could give you reward for this.
    When you will post other remaining topics! Do post them swiftly.

  3. Thank you very much. Helping a lot.

  4. I have a question in my book asking, how can you measure the time period of a pendulum more accurately.

    Please help.