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What effects the period of a pendulum?

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Alun Roberts

Physics Practical

What effects the period of a pendulum?


My aim is to investigate what effects the period of a pendulum.


The variables in this experiment are:

  1. The length of the pendulum.
  2. The size of the pendulum’s swing or displacement.
  3. The mass of the pendulum.
  4. The shape and air resistance of the pendulum.

Scientific Explanation

As the pendulum swings from its fixed point it contains energy and as it swings it goes through energy transfers. At the top of its swing the pendulum is for a moment still or stationary, at that point it has its maximum gravitational potential energy and has no kinetic energy. When the pendulum falls from the top of its swing its speed increases and is at it’s most at the bottom of the swing. Here it has its most kinetic energy and its least potential energy, as the pendulum rises to the top of its swing the speed decreases until it is stationary at the top again. Here it has no kinetic energy but has its most gravitational potential energy again. As the pendulum

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  1. Changing the length of the pendulum.
  1. Changing the size of the swing [displacement]

Length [cm]

Mass [g]

Displacement [cm]

Time for 20 swings [s]









  1. Changing the air resistance of the pendulum.

This does have a small effect on the pendulum’s time per swing, however this would be very hard to study without using very large pendulums and very accurate timing equipment. Therefore I will not be testing air resistance in this


After studying my results from the pre-test I have decided to test the length of the pendulum and not the mass or the size of the swing. I have chosen to do this as this has the greatest affect on the pendulum’s period. In my main experiment to keep the test fair I will be keeping the

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        To improve my experiment I feel that it would prove worthwhile to find a method to make the pendulum perfectly round to a correct size so that its diameter and radius can be found. This would make the measuring more accurate as we would know exactly where the centre of the pendulum is. Also the string can stretch under the weight of the pendulum slightly so I feel to improve this we could use a more rigid type of string that doesn’t stretch at all.

        To extend the investigation I could test the air resistance to prove that this does have an effect on the time per swing. To do this I would have to use much longer string and very big pendulums to easily notice a variation in the results.

 Another way of extending the investigation would be instead of having the pendulum swinging I could have it attached to an elastic cord so that it would spring up and down vertically. I would test how the length of the cord and the distance the cord is stretched before release affects the amount of time it takes for the pendulum to rise and fall above the arm it is attached to.  

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