Prediction
I predict that as I extend the length of the string, the time for one period will increase.
I am going to investigate the length of the string because I think this is the factor that will affect the period of a pendulum the most. If the string is longer the bob will have more of a distance to travel than if the string was shorter. To keep the investigation fair I must keep all the other variables the same.
I am going to use 6 different lengths of string. These 6 lengths are 0.8m, 0.7m, 0.6m, 0.5m, 0.4 m and 0.3m. I will measure the string from the centre of the bob and lay the string flat to measure it.
I am going to repeat this experiment 3 times to make it a fair test. I am going to pull the strings back 50° from the fiducial mark for each length. This is so the investigation will be fair as I am keeping the angle of drop the same for each length of string. I will also be suing the same bob, so there will be no weight change.
Apparatus
Stand
Clamp
2 Wooden blocks
String
Stopwatch
Protractor
Blue tack
1 Metre ruler
A Bob
Method
1 – Set up apparatus as shown in diagrams (see fig 1 and fig 2)
2 – Make a fiducial mark.
3 – Measure out the length of string 0.8 and mark it.
4 – Make marks at 0.7m, 0.6m, 0.5m, 0.4m and 0.3m intervals.
5 – Put string in-between blocks as shown in fig 2.
6 – Pull string back, at an angle of 50° using the protractor.
7 – Let go of string.
8 – Start the stopwatch and start counting at 0, when the string passes the fiducial mark. Count 10 periods.
9 – Record results.
10 – Do the same, using each different length of string.
11- Repeat the whole experiment 3 times to make it a fair test, remembering to record results.
Analysis
My results table shows the length (in metres) of the string that I used, the time taken for 10 cycles, the average for ten cycles and the average time for one period. To find the average time I added column 1, 2 and 3 then divided by 3. To find the time of 1 period I divided the average time by the number of swings. Also in my results table are my predicted results for 1 period for each length of string. I worked out my predicted results by using a formula:
T = 2Π √ L/g
My graph shows my results and my predicted results. In the graph, the lines begin to curve. This shows that as the length increases the time for 1 period also increase but because the graph curves, it shows that the time taken for 1 period is gradually evening out.
My results are not perfect. My line is slightly off the predicted line. This is because of human error.
Even though my results are not that accurate they still prove my prediction. As I extended the length of the string the time taken for 1 period did increase.
From my results I can conclude that my results did prove my prediction, but if I wanted to do the experiment accurately would to use laser beams so that you can see exactly when the string passes the fiducial mark.
Evaluation
My results were not spot on. My line was slightly off compared to the predicted results line. This is because of human error. When using the stopwatch it is difficult to exactly start it and stop it when the bob passes the fiducial mark. The angle of drop could also have been slightly off. At 0.4m this result doesn’t really fit in with the pattern. This is an anomalous result. I think that this is slightly out because of human error as I have mentioned before.
My method was quite reliable. I don’t think that I would change any of it as I understood it well while I was doing my experiment.
