Experiment 1, change of angle
Diagram
Set up the retort stand with clamp near
top. Tie weight at bottom of string and
secure string into place with cork.
Place angle measurer at point of pivot,
change angle of string by pulling weight up
to required angle. Take protractor away and
let weight swing, time for 10 swings, record
in table. Divide time by 10 to get time for 1
swing, repeat for all other angles. Do
experiment 3 times, and work out an average.
Experiment 2, change of weight
Diagram
Set up the retort stand with clamp near
top. Tie 1st weight at bottom of string,
secure string into place with cork.
Let weight swing and time for 10 swings,
record in table. Divide time by 10 to get
time for 1 swing. Repeat for all weights.
Do experiment 3 times, and work out an
average.
Experiment 3, change in length of string
Diagram
Set up the retort stand with clamp near
top. Tie weight at bottom of string,
secure string into place with cork, at 10cm
length, using a ruler to measure from middle
of weight up to pivot. Let weight swing and
time for 10 swings, record in table.
Divide time by 10 to get time for 1 swing,
repeat for 20cm, 30cm, 40 etc. Do experiment
3 times, and work out an average.
Preliminary results
Analysis
The preliminary work helped us to determine that the only factor, which affects the time of a pendulum swings, is changing the length of string.
Main experiment
Plan
In this experiment I plan to investigate into how changing the length of a string on a pendulum affects how long it takes to swing. I will be carrying out an experiment to collect valid evidence to prove my prediction.
Apparatus needed Diagram
- Retort stand
- String
- Timer
- Weight
- Ruler
- Clamp
- Cork
The only thing that will be changed, in this experiment, is the length of string. Everything else in the experiment must be kept the same, in order to produce precise and reliable results. The weight will be kept the same, although the preliminary work proved this to have no affect, air resistance could affect the results. The type of string will also be kept the same because there is friction at the point of pivot, and certain types of string could produce more friction than others, causing the pendulum to stop quicker. The person timing will be the same throughout the experiment because of reaction times.
The following experiment will be used in the experiment:
- The retort stand is placed on a solid surface and the clamp is fixed into place near the top.
- The cork is clamped into place, it and its position should remain the same throughout the experiment
- The string is threaded through the cork. This ensures that the pendant swings from a single fixed point.
- The length of string is measured to 10cm, from the pivot to the middle of the weight. The remaining string coming out the top of the cork should be tied into place to stop the string slipping and changing length.
- The weight is pulled to an angle of around 45 degrees and 10 swings are timed, this is done 3 times and an average worked out.
- The lengths go up in intervals of 10cm, starting at 10cm and ending at 100cm. Each length is timed for 10 swings 3 times and an average worked out.
- Record your results in a table.
Prediction
I predict that when the length of string is shortened the time for one complete swing will be faster. The only two variables in this experiment are time and length therefore I believe they will have some relationship and an equation will show this.
Obtaining Evidence
Results table
Graphs
Analysing
Conclusion
The experiment determined that the shorter the length of string the faster the pendulum swung. The equation for the time of swing is: T= 2Π√l/g, in this equation the only two variables are time and length, everything else remains constant, the force of gravity acting on the pendulum remains the same no matter where the pendulum is.
My prediction was correct, when the length of string is shortened the time for one complete swing is faster, this is because time is proportional to the square root of the length
Time is not directly proportional to L, this is shown by graph 1, which shows a curved line of best fit, telling us that as the length of string increases so does the time, but there is no direct link between them. There is a direct link to time and square root of the length, graph 2 shows us this because there is a straight line of best fit. This straight line would carry on if longer lengths of string were used.
Evaluating
Evaluation
I found that the method I used produced reasonably consistent results and any anomalous points I did have were not very large. The results we collected were sufficient enough to support the conclusion. The only problem was the anomalous results, I think that if the experiment was repeated, for the anomalous results, then they would fit in with the line of best fit on the graphs.
A difficult part of the experiment was measuring the length of string as we had to measure from the centre of the weight. This wasn’t marked on and we had to guess. If I did this experiment again I’d use a weight with the centre of mass marked on, to make it easier to measure.
Another problem was in reaction times while timing, the results produced wouldn’t of been perfectly accurate. However the same person timed throughout the experiment and I think lateness on timing the different lengths would have cancelled each other out. A way to improve this would be to have a light gate which would use infra-red lights to tell when the pendulum had completed its swing, this would have produced more accurate results and I think this method wouldn’t produce any anomalous results.