Hooke's Law Graphs Homework: Analyzing Spring & Elastic Band

[NakedNoodles]

Homework Statement

http://i568.photobucket.com/albums/ss125/NakedNoodles08/GraphsandData-1.jpg

Hello Physics Forums, i stumbled upon you guys when i stumbled within my physics work. The problem i am to put forth revolves around Hooke's law. I am conducting an experiment on Hooke's Law (although we have not learned it yet, hence there are no links to such information), the experiment revolves around the testing of a spring and elastic band for similarities between their forces versus extensions. The write up is only 600 words maximum in length, and includes a data analysis, discussion (validity, accuracy and reliability of measurements) and error analysis.

My problem revolves primarily around the graph shapes, which we are to compare. I have uploaded images of both, and as one can see the spring graph is very deformed and the elastic band graph behaved in a more than normal elastic manner? I am quite new to physics prac write ups and would be very thankful for any of your knowledgeable advices.

Homework Equations

Weight in the data was used as 9.8 for the force calculations
Extension is measured from the head to base of the spring and rubberband

The Attempt at a Solution

I have attempted to draw a line of best fit on both graphs, and i think both are quite correct. However, i cannot come to decipher the spring graph, the vast majority of the student's graphs were a straight line (however i was awarded the extremely stretchy spring - making readings difficult with the bounce). The elastic band graph is very straight, and behaved more so like a spring would.

If anyone could help me with my problems i would have a great appreciation. Really am stuck on the graphs and cannot find any possible explanation for the spring shape, two anomalies is out of the question?

 

[rl.bhat]

While doing the experiment on Hook's law, you have to take the reading for extension while loading and unloading to be sure that you are within the elastic limit. Looking your graph I feel that you have crossed the elastic limit.

 

[NakedNoodles]

Thanks rl.bhat I thought it had something to do with the elastic limit, as the spring we were awarded lacked a lot of tension. This would also explain the straight line at the start of the spring graph (the rest of the class got a flat segment to begin with), as there is very little force required to uncoil our spring? Would it be correct to say the rubber band had increased tension at the start of its stretching - as the line was greater inclined? As i have already completed the experiment my physics teacher won't let me repeat it, should i say that the spring experiment is invalid as tension was not controlled (why does tension increase within the elastic limit?). Once again, any help would be much appreciated, i am quite a novice to physics.