A mirror,
A long thin rubber band,
100g Masses.’ (1 Newton weights)
The variables in this experiment are the thickness and length of the rubber band and the load, which is added to the rubber band, also there is temperature as it may effect the rubber and the metal Newton weights.
‘I predict that the extension will double if the force doubles and the extension will treble if the force trebles. I also predict that the rubber band will not return to its normal length once it has reached its elastic limit as it will be plastic, and I support my prediction with Hook’s Law.
To make this a fair test I will add and remove the same weight each time.
To make my measurements as accurate as possible I will take the reading by placing a mirror behind the meter ruler and placing the pin through the bottom of the rubber band. I will then taking the reading from eye level by looking in the mirror until the pin and the image overlap to become one.
To make my experiment as safe as possible I will fix the clamp stand to the table with a g-clamp. I will also make sure the rubber band is fixed to the clamp securely by tightening the clamp onto the rubber band.
Diagram:
Method:
First of all I setup the apparatus and made sure it was all safe and secure, I then took a measured the length of the rubber band while it didn’t have any extra mass on. I then started to add on a mass of 100g I took the reading using my pin, mirror and ruler and recorded it in a table. I kept adding 100g onto the rubber band and recording it using my pin, mirror and ruler until I reached a mass of 1500g. From my results I then worked out the extension of the rubber band and recorded it in the table. I then packed the apparatus away, and plotted a graph of my results.
Results:
Conclusion:
These results partially agree with my prediction because I was wrong about the extension doubling if the force doubled, and the reason for this is that the extension is not directly proportional. But I was right about the rubber band not returning to its original length once it has reached its elastic limit because it has become plastic, and my prediction and conclusion are supported by Hook’s law.
Evaluation:
I think that my results are reasonably accurate if you take into to account the fact that I was not in a high sophisticated laboratory with precision recording equipment. There was one result, which didn’t fit into the pattern of results because it was anomalous. I included the measurement in my table of results and also plotted it on my graph but missed it out when I drew the line of best fit. The experiment could be improved by measuring the length of the rubber band when removing the mass.
