The variables that I will change in my experiment is the force, my range of force I will be using is from 2N to 12N of force.
Prediction
My prediction is the further you pull back the elastic band, the more distance the mass will travel across the floor. As the elastic band is stretched the elastic band has potential energy stored. As you release it the force is turned to kinetic energy on the weight.
The weight is slowed slightly by friction from the floor so the results will not be as accurate. To work out the work done as the force moves the equation that can be used is:
work done = force x distance
When you pull the elastic band back the force doubles and so does the distance. So the stored energy I predict will quadruple.
Preliminary Experiment
For our preliminary experiment we rounded up the distance (in cm) to the nearest 10. We completed 3 sets of results
From completing and looking at these preliminary results I can see that rounding up to the nearest ten is not a reliable enough number to round up to. It is not accurate enough to prove whether or not my prediction is correct. So I will round my results to 1dp instead in the main experiment.
By doing the preliminary experiment, I have decided to make some changes to my main experiment. In the main experiment I will need more sets of results, preferably 5 if I have enough time to do so, as I know at least 2 results out of 5 will be accurate enough to draw a conclusion from.
I’m keeping the range of 2-12 newtons of force for my main experiment because this is a sufficient enough range to make a decent conclusion from.
Main Experiment Results
These are the five sets of results I completed from my main experiment. As you can see some are not as constant as others. So I will draw up on a graph the two most reliable, constant sets of data. These are the 2nd and 5th results, calculated to 1dp accuracy.
The graph is shown on a separate page and shows the average of the 2nd and 5th sets of data, an anomalous result and also a curve of best fit.
After obtaining my results, I can now input the formula to work out the energy needed to catapult the weight in Joules; I will round the calculations to 1dp.
Graph Analysis and Conclusion
The first part of my hypothesis was correct that the further the elastic band is stretched the further the distance the weight travelled, this is proved by me first graph.
Another part of my hypothesis that was also correct was that the graph curved as a result of the friction from the floor.
However the second part of my hypothesis which I predicted the amount of stored energy would quadruple is not all correct.
Just from looking at the table above of the force against energy it is obvious that the energy needed more than doubles. By looking at the graph I can see that as the force is doubled from 2N to 4N, it has over quadrupled because the energy needed goes from 15J to 121J.
However the distance doubles from 4N to 8N, the distance to weight is not quadrupled. It goes up from 26cm to 66cm which means this result only doubled.
The same thing happened when the elastic band’s stretch was doubled from 6N to 12N; it went up from 42cm to 127cm, which is triple the distance travelled.
I believe the reason for this is that some energy is lost through the elastic band because the elastic band is stretched across the stool so it is strained more than it should be. Also I believe that each time I had to pull my arm back further to increase the force each time I had to use extra chemical energy from my arm that will have been transferred into the elastic band, thus sending the weight an even further distance each time.
Evaluation
I found one anomalous result on each graph that didn’t fit into the trend of the rest of the results, and that was the 10N point on both graphs. I don’t think it fitted in with the pattern because the people doing these sets of results did the results alternatively so the results weren’t all done by the same person, to the method used of releasing the elastic band may have been slightly different. If I were to repeat the experiment I would make sure that only one person did the whole experiment to ensure both accuracy and reliability.
There is no more precise position or method to release the weight that I can think of, however I could have made the experiment more accurate perhaps by drawing a straight line on the floor to indicate where the centre part of the stool is, to release the weight in the middle of the stool, instead of slightly to the side (as I probably did do during the experiment).
If I were to repeat the experiment, I would make it further more reliable and accurate. I would do this by reducing the friction from the floor as the weight travels. I could do this by getting a very large sheet of glass and using it to catapult the weight across from the elastic band, this way hardly any friction is created when it travels.
If I were to further investigate the effects of elastic bands, I would experiment with elastic bands of various thicknesses, to see if the thickness of an elastic band effects the distance the weight travels. Or I would find out what happens when an elastic band is stretched almost to breaking point – whether it would store more energy or less.