PILOT TEST: Before the actual investigation we did a pilot test to see our estimate results. ‘Apparatus:
stand & clamp
Newton meter
Spring
elastic band
‘Method: In the pilot test I used the above apparatus. First I clamped the Newton meter on, then suspended the spring on. I measured at what point the spring was at without weights on, with a ruler. Then put on 1N of weights and see how low its gone, then repeat the same things 6 times. In the end I found out that the average elastics limit for both was 12N. Then do the same with the elastic band. After getting all the results, plot it down on a graph.
spring (all measurements in mm)
band (all measurements in mm)
Graphs:
PREDICTION: I predict the greater the force applied to the spring or elastic band, the further it will stretch. This is because extension is proportional to load and so if load increases so does extension and so stretching distance. I will also work out the extension which is done by taking away the extended length from the original length. In order to see if my prediction was correct, I will use Hooke’s Law. (-Robert Hooke (1635-1703), English scientist, best known for his study of elasticity. Hooke also made original contributions to many other fields of science.) He said that extension is proportional to the downward force acting on the band, and there will be a elastic limit where the band and the spring can’t take no more and will constantly drop and with the band it will actually break.
Detailed Method: My method of experimentation will be to use a clamp stand and boss clamp to suspend a spring from. A second boss clamp will hold in place a metre rule starting from the bottom of the spring to measure extension in mm. I will then add weights to the spring and measure extension.
Before deciding on the range of experimentation I carried out a pilot test to find the elastic limit of the springs we had. To do this I added weights to the spring until it did not return to its original shape. This occurred at 12N and so I set a limit of weight to 10N for my experiments. The reason why 11N was not used is that 10 experiments is a more standard number and also that the limit of proportionality is slightly less than the elastic limit of the spring, therefore using 10N ensure I do not exceed the proportional or elastic limit of the spring. I also hope to carry out the experiment 3 times and also take an average to increase the reliability of my results.
Due to the pilot test no strict safety precautions need to be used, as the only potential danger would be if the spring snapped, however this will not happen if there is no more than the maximum load on the spring of 6N at any one time. This will also remove the problem of the stand on which the experiment is taking place from falling over. The weights available are 1N masses and so I will take 6 extension measurements starting at 1N up to 6N of force on the spring and band.
Results Table
spring (all measurements in mm)
band (all measurements in mm)
These results are also plotted on a graph below.
The principle of Hooke’s Law can be seen in a graph of spring extension.
1. At this point the limit of proportionality has been reached this is where Hooke’s law is no longer accurate.
2. This point is the spring’s elastic limit if the force is removed from the spring it will no longer return to its original shape.
Beyond this point the atoms in the spring material begin to break their bonds until eventually the spring yields and breaks.
This shows that Hookes Law does have a limit as a spring does and does have limitations and if kept within these boundaries will provide reliable accurate results.
