To investigate and observe how the amplitude (angle of release), affects the time period of one oscillation of a pendulum.

Variables:

Independent variable - I am changing the amplitude (angle of release.)

Dependent variable – I will be recording the time taken for 10 oscillations.

Control – Length of string (50cm), mass of bob (34.7g), gravitational constant (Earths gravitational pull) and type of string.

Apparatus:

• Cork.
• Stopwatch.
• Bob.
• String.
• Scissors.
• Clamp stand.
• Protractor.
• Metre ruler.
• Top pan balance.

Method:

1. Use the ruler to measure approximately 50cm of string. Leave a few centimetres extra, as you are required to tie it, this will compensate for the extra string need to tie a knot.
2. Cut the string at the selected measurement.
3. Set up the clamp stand.
4. Tie the bob to the string.
5. Use the scissors to slit the cork half way from the edge to the centre.
6. Fit the protractor inside the slit, so that it is secure firmly.
7. Place the cork onto the clamp making sure everything is intact.
8. Tie the other end of the string to the clamp.
9. Ensure that you line up the string on the 0° point on the protractor.
10. Take hold of the bob and extent the string it to its full length firmly.
11. Raise the bob to the side aligning it to the 10° point on the protractor.
12. Let go of the bob, as soon as you do this start the stopwatch.
13. Allow 10 oscillations to complete, at this moment stop the stopwatch and record your findings. (An oscillation is when the bob fully returned to its stating point once you have let it go.) The reason that 10 oscillations are chosen is that it is a sound amount to use to enable you to gain accurate and reliable results.
14. Perform this experiment again twice so that the average time period may be taken from the three trials. This makes your results even more accurate and reliable because more readings have been taken, so that an average can be obtained.
15. Repeat these steps again. Except increase the amplitude of the string each time by 10° until 70°. E.g. 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°, 100°.
16. Once the results have been collected and recorded. You will be able to calculate the time period for one oscillation from the average time period. This can be done by dividing the average time period by 10.

Results:

Analysis:

After this experiment I can say that amplitude does have an affect on the time period of one oscillation. From these results a pattern has been made clear by a minute amount, this pattern is that as the amplitude increases so does the time period for one oscillation. My graph shows a very smooth curve that is almost a straight line. The reason for this can be seen in my results, as the time period only increased by such a minute amount each time. The reason for this can be that the different ranges used were not big enough. It also means that amplitude is a small factor which affects the time period of a pendulum. Although my results turned out like this, I took three readings which made the results as accurate as possible. I have come to the conclusion that amplitude only affects the time period of one oscillation by a small amount and only until another factor starts to affect the time period, otherwise the affect the amplitude has will go unnoticed. I received no anomalous results in my experiment.

In my prediction I stated that as I increase the amplitude of the pendulum string the time period for one oscillation increases. This is backed up on the scientific theory that if the pendulum is raised at a greater angle it will have to cover a greater distance. Also as it is raised higher it will have more gravitational potential energy than kinetic energy. The higher the angle is the greater the gravitational potential energy. Since there is more gravitational potential energy, it means that there will be less kinetic energy as less of the gravitational potential energy will be converted to kinetic energy, and that there is more distance to cover. The pendulum will encounter more air resistance, as the bob and the pendulum string causes friction with the air it gradually creates heat energy which is low grade and no use can come of it.

Evaluation:

The evidence obtained was reliable and the procedure used to obtain this evidence was accurate. The entire accuracy of both experiments was fairly good. Both experiments used aid of a human and a human made all the measurements which were vital for the success of the experiment. For the length factor my percentage error was very low which illustrated to me that the experiment was conducted accurately. The experiment in which amplitude was a factor was quite different as my results led me to believe something else. As I have said before my percentage error was very low this signifies that my results are able to support a firm conclusion. The reliability of my evidence is fairly good. In the experiment in which amplitude was a factor, the results were also reliable and I repeated my readings three times so that I could obtain and average. I did the same in the other experiment as well.

For further improvements to the investigation I would experiment in the mass of the bob and if it affects the time period of one oscillation. I would also be interested in calculating the speed at which the bob travels and how factors can affect this as well.