A pendulum should be timed over multiple swings.

How many swings to record each time?

15 is a usual number for a simple pendulum bob.

However, if the period is very short or very long, a different number of swings may be used. As a guide we would want to have the total time be 20-30 seconds. This will allow you to take

Do I need to have the same number of oscillations for each reading?

No.  But you would then need to record the number of swings in your table of data.

 

Example
Try for yourself using the following video: pendulum swinging (a) Time the time for 10 complete oscillations. (b) State the period of the pendulum. (a) t = 11.6 s (accept 11.4 s – 11.8 s)        Remember that a stopwatch should be read to 0.1 s. (b) Period = 11.6 ÷ 10 = 1.16 s        11.6 is 3 sig. fig. so final answer is also to 3 sig. fig. precision Show Answer

 

Practical Skills