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Method
1. I am going to clamp the piece of string between two small blocks of wood ensuring that the blocks were level with each other so that they would not effect the pendulum swinging.
2. A mass of 200 grams is going to be attached securely to the end of the string.
3. I am going to be start swinging at 10 degrees using a protractor to measure the angle.
4. I am then going to swing the pendulum 20 times with each piece of string. The lengths of string are going to be, 20, 40, 60,80,100cm.
5. A stopwatch will be used to measure the time taken for 20 swings of the pendulum.
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Variable Table
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Preliminary Investigation
I constructed the equipment provided to begin my investigation. On swinging the pendulum the stand moved slightly because it hadn’t been secured properly. I took some readings but they were not consistent. I improved my reading by tightening the G-clamp to stop the clamp stand moving.
Preliminary Data
I investigated the effects of varying the mass used in the pendulum. I also investigated the effect of varying the angle of the pendulum and I also investigated the effect of varying the length of the pendulum. The results are shown in these tables.
1. Varying the mass by 100g had little effect on the time for twenty swings.
2. Varying the angle of swing had very little effect on the time for twenty swings.
3. Varying the length of the pendulum has a large effect on the time per twenty swings.
From preliminary work I can see that the length of the pendulum is the only variable that has a large effect on the time per swing.
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Length of simple pendulum results
The length of the pendulum has a large effect on the time for one complete swing. As the pendulum gets longer the time per swing increases.
The formula to find secondary evidence is:
T= 2 Π √ L/G
G = 10
L= level of pendulum in meters
Analysis and Evaluation
The evidence obtained from my experiment backs up my prediction that as the length of the pendulum increases, the time per swing increases.
Some of my results were not accurate because there will always be a certain amount of human error and this could not be helped because of the equipment provided.
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Improvements
Things that might have affected the accuracy
- An error in measurement of string. To improve this I could have marked off points with a pen to ensure they were accurately measured.
- An error in measurement of angle for pendulum start. To improve this I could have attached a protractor to the clamp stand so that it was in a fixed position and easy to read.
- Depending on human reaction time, slow reactions when starting the stop-clock might have affected the results.
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Extending My Investigation
To extend my investigation I would provide more results to check that my conclusions were correct. I would like to try using a much longer pendulum to gain more accurate results. To improve the timing I would like to use computer light gates, which would be more accurate than a stopwatch.
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Conclusion
This diagram shows how the blue pendulum has the most gravitational potential energy at the top of its swing because the angle is steeper. This means the kinetic energy and speed through the centre will also be greater than the red pendulum. The steeper the arc the bigger the acceleration of the pendulum will be. A bigger acceleration means a shorter time for each swing. Therefore as the string gets longer the time per swing gets longer. There would have been very little air resistance because the mass was only 200 grams. If the mass was larger there might have been an affect. The pendulum moves by the force of gravity pulling on it. If the pull of gravity were less I would expect the time for each swing to be longer.
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Graph
Using the results from the secondary evidence and the averages, I drew a graph and compared the two sets of data. The graph shows a smooth curve with a positive gradient. This indicates that as the length of the pendulum is increased the period will increase.
See graph on next page.