Practical - Stress-Strain graph of an elastic band

[JanineSamson]

Homework Statement

Hi,

I have a practical to do soon, it's only a basic thing because we've only been doing physics for just over a month - plotting a stress-strain graph for an elastic band...


2. The attempt at a solution

Now, I was just going to measure the original length of the band & add weights each time measuring the extension so the Force being the independant variable and the extension being the independant one.

Problem is, when it comes to working out the stress what do I use for the cross-sectional area? As it's stretching the cross-sectional area on a rubber band would probably change quite a lot, how do you deal with this? Or would you just mention that in the write up as a "source of error" and use the initial area before you started stretching it?

Any help would be greatly appreciated, this is my first practical so I'm not really sure what to do.

Thanks in advance.

 

[LowlyPion]

Here is a link that touches a bit on your concerns:
http://en.wikipedia.org/wiki/Poisson's_ratio#Volumetric_change

Since you mention an elastic band, then I would say that you can determine observationally the change in width between extremes and model that as a linear change in cross-sectional area across the range of applied forces. If it exhibits only small change over the range then you can surely ignore it.

 

[thomate1]

I would suggest using the initial cross-sectional area of the elastic band before any stretching occurs as the cross-sectional area for calculating stress. This is because the cross-sectional area of the band will indeed change as it is stretched, making it difficult to accurately measure and calculate. However, it is important to mention this as a potential source of error in your write-up. Additionally, it would be beneficial to take multiple measurements and calculate an average cross-sectional area to improve the accuracy of your results. Overall, the most important thing is to carefully document your methods and any potential sources of error in your experimental design. Good luck with your first practical!