10. Repeat points 3-9 for two, three and four springs in parallel
Variables
To make the results fair I will have to control some of the variables and keep them the same. I will have to keep the metre ruler the same at every measurement in case the scale is different, on a different ruler. Also I will need to use the same hanger on each of the sets of parallel springs. I need four springs at one point, but to keep it a fair test all four of these springs will have to be of the same type. To test this I will measure them to see if they are all the same length, and also weight them to see if their weights are the same.
Some variable will need to be changed. As I am measuring springs in parallel I will need to change how many springs will be bearing the weights. Also the amount of weight on the hanger will have to be changed each time (1-5N). With the metre ruler I will measure the extension of the spring once a particular weight is added.
Results Tables
1 Spring
2 Springs
3 Springs
4 Springs
Interpretation and Evaluation
From my evidence I can clearly see that the less springs in parallel the greater the extension of the springs.
From my graph (on the next page) I can see that all four of the lines are straight and accending upwards. This shows that the springs I used where obeying Hookes Law, as the extension for each is proportional to the load. When the first weight (1N) was added to two springs in parallel and three springs in parallel the results seemed anomalous. In both cases the extension is lower that the other four results.
Gradient Table
I predicted that if a spring has a load of 1N it would have a certain extension (x). Two springs in parallel will share the 1N load and each will feel 0.5N. The extension for each one of them will be half the extension for one spring on its own (x/2). Three springs would be x/3 and four x/4. From my gradient table (above) I can see that the gradient for one spring is 4.24 cm/N. this means that x/2 should have been 2.12 cm/N. The gradient I recorded was 1.98 cm/N. This was slightly low but relatively close. X/3, according to Hookes Law should have been 1.41 and I got 1.4. This was almost exactly what it should have been making this result very accurate. From my results x/4 was 0.83 cm/N, but again this is quite low, as it should have been 1.06 cm/N. As the results for two, three and four springs in parallel are slightly low, compared to one spring on its own. This may not be because the last three results are inaccurate but that my result for one spring is wrong. It may be too high causing the rest of my results to seem too high.
One reason for these results being inaccurate may be because of the method that I used to carry out the experiment. Overall I feel that the method I used was quite good but one point which I would add if doing it again would be to attach an optical pin to the bottom of the hanger so when you are reading from the ruler it points exactly to a particular point. This increases the accuracy of my results. Another point which I could have added to the method was, when measuring springs in parallel it is wise to put a piece of paper in between each of the springs. This would have to be done because when I was measuring the extension the spring’s coils would merge together. This meant that the springs didn’t extend to their full potential and so the results weren’t very accurate.
Another reason I can think for my gradients being slightly off. When carrying out this experiment I chose two new springs, which were very similar. These were used for two and four springs in parallel. The other two springs were slightly older and had been used many times before. They were used for 1 spring and 3 springs in parallel. Due to this these two older springs extended more than the new ones. This is because they had been used before and so they were easier to stretch and the weights pulled them down much more efficiently that the two new ones. The new ones had never been used before and so the weights found it harder to stretch these springs. This all made the results for the new springs slightly higher compared with the old springs. This can be seen in my gradient table.
In conclusion, from my evidence I feel that my results were quite good. All of the springs used Hookes Law, as each one of the extensions was directly proportional to the load. Also the prediction that I made was accurate because like I said the more springs that are in parallel the less the extension will be as they share the load. My results proved my prediction although some of them were slightly low. Due to this my evidence is less reliable because of a number of these anomalies within my results.
