I will use 100g weights because anything smaller would take too long to do and anything bigger would be too heavy and the spring would reach its LOP (limit of proportionality) too quickly.
Apparatus
1 X Lump of plasticine
1 X Mass holder
1 X Meter ruler
1 X Clamp
1 X Boss
1 X Spiral spring
1 X Retort stand
1X Paper clip
1 X Large weight
And a collection of 100g discs.
Method
I set up my apparatus as shown in fig 1. I then started to add the small weights 100g at a time. After adding each weight I left the spring to settle, then when the paper clip stopped on a point on the ruler I noted down the reading and added another weight.
I did the experiment 4 times, and each time the springs reached the limit of proportionality at different points so instead of having results stopping at different points I stopped at 1300g as this was the point where weakest spring reached it’s limit of proportionality.
(fig. 1)
Safety
This is a potentially dangerous experiment as there are heavy weights and extended springs being used. Here are some ways to make it safer:
- You could wear goggles when placing more weights onto the mass holder.
- Place the weights on at arms length.
- Place the weights on the mass holder gently do not drop them on it.
- Make sure the large weight holding the clamp on the table is secure and will not fall off.
- When placing weights on the mass holder don’t let anyone stand in a 2m radius of the experiment.
- When the spring looks like it will break abort the experiment.
Fair test
Ways of making it a fair test are:
- Trying to get springs that are the same strength.
- Always using the same weight intervals. (100g)
- Always try and read the ruler from the same point.
- I will do the experiment 4 times because you then have a smaller chance of having errors and if you have a bad reading you can compare it with the rest.
- To make it a fair test whenever I start the experiment I will always finish it, and if for some reason I can’t, when I come back to it I will start it again.
Results
Analysis
If I add up all the sound results I have (all up to 900g, after this they start to change) I get 29.75, if I divide this by 9 I get the average increment which is:
-
= 3.72
9
So I have found 100g mass gives the average extension of 3.35cm.
My +/- error range is =
+ = Average ext. – Biggest = 3.72 – 3.95 = -0.23
- = Average ext. – Smallest = 3.72 – 3.375 = 0.35
From this I can see my largest error to be only 0.35cm. I can extend this to say my experimental error is +/- 0.35cm per 100g extension.
Because this figure is small it shows I have executed the experiment reliably.
Evaluation
The results that are in red I have ignored because they do not follow my pattern and are anomalous results. A reason for them being like this could be due to the error of parallax. This is shown below:
If I were to repeat the experiment I would try to minimise the magnitude of errors by using a more accurate method of measuring the extension. At the moment I am just using a ball of plastercine and a paper clip, there are many ways of decreasing the margin of error for example using lasers but this is prohibitively expensive and add an added danger. For the amount of reduction in error this would be pointless as there is always going to be a slight error.
Conclusion
I have found that the extension is proportional to the load and therefore I have satisfied my original prediction.
