Factors Affecting the Time Period of a Pendulum

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Factors affecting the time period of a pendulum

Aim: To investigate the factors affecting the time period of a pendulum.

The time period of a pendulum is the time taken for the pendulum to swing from the first position, A, through positions B and C and back to position A again.


Many factors can affect the time period of the pendulum. These factors are: length of string, angle from which the pendulum is dropped, the air resistance and the weight of the pendulum. In this experiment I will be changing the length of the string and seeing how it affects the time period of the pendulum.

I predict that as the string gets longer, the time period will increase. I think this will happen because the bigger the string, the greater the distance the pendulum needs to travel and so the more time it will take. This will occur because the string is like the radius of the circle and so changing the length of string will change the circumference of the circle, so the longer the piece of string; the bigger the circle, and the bigger the distance that the pendulum will travel.

Equipment List:
- string (180 cm) – to be tied to the weight to make the pendulum - small weight (50g) – to be the bob for the pendulum
- clamp and stand- to hold the pendulum so the experiment is more accurate - protractor – to measure always the same angle for the pendulum to be released - stop watch- to time the pendulum

- 50 cm ruler- to measure the string
- scissors – to cut the string


Fair Test:
So that the experiment is fair, I will keep the weight of the pendulum always the same. It will always be 50g. I will also make sure the pendulum is dropped from the same angle (30º), I will use a protractor to make sure the angle from which the pendulum is dropped is always the same. I will also try to keep the air resistance the same. To keep the air resistance the same I will carry out all trials in the same place, a closed classroom with no open doors or windows. I will only change the length of the string each time, I will start with 10 cm, then I will try the experiment with 20 cm and finally with 30 cm. The type and material of the string will also be kept the same.


1) Set up the equipment as shown in the diagram.
2) The length of the string is 10cm.
3) Use a protractor to measure 30º, pull the pendulum so that it is at 30º


4) Let the pendulum go and let it swing
5) Start the stopwatch immediately
6) Count each time the pendulum returns to that position
7) Once you get to 5 stop the stopwatch
8) Record your results
9) Repeat steps 3-8 3 times
10) Now change the length of the string to 20cm
10) Repeat steps 3-8 3 times.
11) Change the length of the string to 30 cm.
12) Repeat steps 3-8 3 times

This experiment has very few hazards. The only way to make this experiment dangerous would be for pupils to abuse the equipment by swinging the pendulums around.

Results Table:

|Length of String (cm) |Time taken to complete 5 oscillations (s)|Time Period (for 1 oscillation) (s) | |20 |05.21 |1.042  | |20 |05.21 |1.042 | |20 |05.22 |1.044 | |30 |05.26 |1.052 | |30 |05.15 |1.029 | |*30 |04.98 |0.996 | |30 |05.99...
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