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An Experiment Investigating if Chosen Variables Have an Affect On A Simple Pendulum.

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Joseph Tilbury 11 B

18th October 2002

Physics: An Experiment Investigating if Chosen Variables Have an Affect On A Simple Pendulum.


The point of this investigation is to determine the effect of selected variables have on a simple pendulum.  A simple pendulum is a small, heavy body suspended by a light inextensible string.


At the end of this section I will make a prediction based on the following scientific knowledge.

The two factors affecting the swing of a pendulum are the forces acting upon it and energy. They affect the swing in different ways.

A complete swing (to and fro movement completed) of the pendulum is called an oscillation and the time taken for one of these oscillations is called the period. The energy of the body is continuously changing from gravitational potential energy (GPE) to kinetic energy (movement). The pendulum has gravitational potential energy as anything that is above ground and that can fall has GPE. The gravitational potential energy can be transferred into kinetic energy in a pendulum as it swings. The pendulum only has gravitational potential energy when it is at the top of its swing as it is here that the body on the end of the string has the potential to fall. It increases momentum all the time that it is moving.

...read more.


T = mg = W

where: T = tension

            m = mass

           W = weight

            G = the force of gravity on the Earth’s surface

When the pendulum is oscillating:

T = W, consequently T – W = 0 = Fres

Where: T = tension

            W = weight


Due to the fact that length has an affect on the pendulum, I predict that as the length of the pendulum increases, the length of the period of the pendulum will also increase. The mass of the suspended body will have no affect on the time it takes for the pendulum to swing as long as the angle of amplitude ( the angle between the pendulum’s rest position and highest movement) is kept at a small angle.

Using the equation t = 2π √ 1/g I will calculate how long it will take for each length to complete 30 oscillations (the amount of oscillations I am using in the results) and these are shown in my table of results, in the predicted period column.


My plan is for the investigation to test my hypothesis. The only variable I am investigating is the length of the pendulum’s string, and I will allow this to vary to the lengths I am investigating, which are (in metres):

  • 0.8m,
  • 0.9m,
  • 1m,
  • 1.1 m,
  • 1.2 m and
  • 1.3 m

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I trust that my method was successful as it provided me with accurate results, which correspond with the formula stated.

I found it hard to measure the angle of amplitude and this could be one reason why the two sets of results did not perfectly match. Other reasons for errors could include inaccurate measurements of the string and angle, and error in judgment when stopping the stopwatch. To eliminate these mistakes, a protractor could be attached to the clamp to measure the angle and more people, or perhaps a laser beam, could be used to gain a more accurate average of the time of the oscillations.

The only factors that affect the pendulum are the gravitational field of the Earth and the length of the pendulum. To extend the investigation, I could have timed each length more than 6 times and the average would have further ironed out any human errors. It may me useful to do the experiment again in a different place on Earth to see what affect the gravitational pull has on the pendulum. To investigate the work that has been started further, I could extend the prediction that I have made which would then need to include a bigger range of length variables.

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