Fair Testing and Accuracy:
I will make the test fair by only changing the two variables that need to be changed to determine the experiment, so I will only change the length of the pendulum and the mass of the bob, all other variables will be kept the same. This includes angle at which the pendulum is released and air friction. These variables must be kept the same if the test is considered to be a fair one. I will make the test fair so that my results are accurate. I will try to make my results more accurate by repeating the experiment at least once. This means that I can take an average from the two results which is more accurate than just taking one. By taking an average I also hope to get rid of any anomalous results, however these results may not be in trend with the others due to the fact that if one set of results had an anomaly and the other didn’t then the average would create a result that may be higher or lower than the trend.
Safety: I will make sure the test is safe by making sure nobody is around the pendulum when it is swinging as it might hit somebody in the face etc.
Apparatus:
For the experiment I will use the following apparatus;
- Stand
- Boss
- Clamp
- String
- Plasticine
- Stopwatch
- Ruler
Diagram:
Method:
Set up the apparatus as shown above. Measure the length of the string until it is 10cm and measure a mass of 40g which is done by using plasticine. Then hold the pendulum by the bob and by keeping the string taught bring the pendulum to 90 degrees, so that it is horizontal. Then making sure the string is still taught release the pendulum, do not exert any force onto the pendulum as this will make the test unfair. As you release the pendulum use a stop watch and start timing and as the pendulum completes one full oscillation stop the timer. So you stop the timer when the pendulum reaches the point where it started. Repeat this experiment for all different masses and lengths. I am going to do a length range from 10cm to 35cm and a mass range from 40g to 65g. I did not choose these ranges based on preliminary experiments, but I felt the ranges were suitable for the experiment. Each mass will be done for each length and visa versa. Record the results in a table.
Obtaining Evidence
I obtained the following results from the experiment which I repeated once and then I took an average of the two results.
First set of results:
Second set of results:
Average of the two sets:
Analysing
I have put the collected average set of results onto a graph which is separate on a piece of graph paper. Both the graph and the average table results show that the length of time the pendulum takes to do one complete period is affected by the time. As seen in the table, but more easily seen on the graph the time the pendulum takes to do one complete period increases as the length of the pendulum increases. On the graph each colour represents a different length of string and the lines of best fit are in blue. The lines of best fit go up in time for each length, clearly showing that the pendulum takes longer to complete a full period when the length of the pendulum is longer. This is also shown in the table. If you look down a column then the time increases as the length of the string increases. However the graph and the set of results in the tables show that mass does not affect the time it takes for a pendulum to complete a full oscillation. Although the lines of best fit go up in time for each length they are all almost completely horizontal. So as mass is on the x axis it shows that no matter what the mass the time it takes for the pendulum to complete a full period nearly always stays the same, as long as the length is the same. This can also be seen in the table. If you look across each row then the time stays roughly the same all the way across. This means that mass does not affect the pendulum. This only works for one row at a time as each row has a length attached to it as well.
Conclusion:
From the results I conclude that length does affect the time it takes for a pendulum to complete one full period, but mass does not. This is proved by all the results I have collected and how explained above. This conclusion supports the prediction in one way, but not another. I predicted that length will affect the pendulum and it did, an increase in length meant it increased the time it took the pendulum to do one complete oscillation. However I also predicted that mass would affect the pendulum, but it did not. I will prove why length does affect the pendulum and why mass does not in the scientific knowledge below.
Scientific Knowledge backing my conclusion:
The following explains why length affects the time taken for a pendulum to complete one full period and what the affect is. A pendulum is able to work when the bob (weight at the end of a pendulum) is raised to an angle larger than the point at which is vertically suspended at rest. By raising the bob, the pendulum gains Gravitation Potential Energy or GPE, as in being raised, it is held above this point of natural suspension and so therefore is acting against the natural gravitational force. Once the bob is released, this gravitational force is able to act on it, thus moving it downwards towards its original hanging point. We can say therefore, that as it is released, the GPE is converted into Kinetic Energy (KE) needed for the pendulum to swing. Once the bob returns to its original point of suspension, the GPE has been totally converted into KE, causing the bob to continue moving past its pivot point and up to a height equidistant from its pivot as its starting point. By returning to its original angle of release the pendulum has created an arc shaped swing, in which the pendulum then travels again and again. So the longer the length of the string the larger the arc in which the pendulum travels is and so it will take the pendulum longer to complete a period as it has further to travel. The following explains why mass does not affect the time it takes for a pendulum to complete one full period. When the bob is raised to an angle larger than the point at which it is vertically suspended at rest it is being acted upon by a force greater than the pull of gravity. So when the pendulum is let go from this angle gravity pulls the pendulum back down towards this vertical position causing it to swing. The acceleration of the pendulum as it reaches this vertical point of rest is equal to the deceleration of the pendulum as it goes past this vertical point of rest. So it is acceleration due to gravity which is the same to any body no matter what its size or mass. So mass will never affect the time it takes for a pendulum to complete one full period.
Evaluation
I think that the experiment I designed did do what it was meant to do as it proved which factors did or did not affect the rate at which the pendulum did one complete period. I think that the evidence I obtained was quite accurate and did support my conclusion and some of my prediction, where I was right. You can tell how accurate the experiment is by measuring the distance, on the graph, from the results to the line of best fit. In my experiment most of my points where very close to the line of best fit and so I think the experiment was quite accurate. However the experiment did produce some anomalous results, easily seen on the graph, which means somewhere a mistake was made. The anomalous was probably due to human error, for example the starting and the stopping of the stopwatch may have caused time delays which resulted in these anomalies. I could have improved the experiment and made it more accurate by repeating the experiment even more times, say five, and then taking an average from all of these results. This probably would have got rid of any anomalous results and in general made the results more accurate and reliable. I could have also increased the range of the variables, for example instead of using 10cm to 35cm for length of the pendulum, I could have used ranges from 10cm to 100cm. This would make sure that the results were even more accurate and I could make even surer that length did affect the pendulum. I could also increase the mass variable range to make certain that mass does not affect a pendulum. I could have determined these ranges if I had done preliminary tests, which would show suitable ranges and maybe even suitable variables to use. To also improve the accuracy by counting how long it took the pendulum to do ten complete periods, thereby meaning the stopwatch did not have to be started and stopped so quickly and so reducing human error. If time permitted I would have also done the experiment in a slightly different way. Instead of timing how long it took for the pendulum to do one complete period for each mass and length, I would have set the pendulum off and counted how many complete periods the pendulum did before it stopped. By counting and not timing it reduces human error again and so making the results more accurate and reliable. However I still think the experiment is accurate and reliable enough to support my conclusion despite any anomalies I might have found. To extend the experiment and find additional relevant evidence I could choose any of the other variables, which I thought might affect the pendulum, listed in the plan, and see if any of these do prove to affect a pendulum. For example do exactly the same experiment that I have just done, but keep the mass and length the same and change the angle at which the pendulum is released. Then you could time how long it took for the pendulum to complete one full period and do this for different angles. By recording the results you would be able to see if the angle at which the pendulum is released does affect the time taken to do one complete period. Another variable you could change would be air friction, so you could keep the mass and length the same, but change the air friction. To do this you could do the experiment both inside and outside. Again by recording the results you could see if this variable does affect the pendulum.
