How would you interpret the young modulus of a rubber band?

Hi, I'm doing some AS coursework at the moment - to find the young modulus of a rubber band. I managed to get a value of 6.59x10^5 Pa. What does this tell me? Is the young modulus just the ratio of tensile stress: tensile strain? What is the young modulus of rubber typically like???

thanks, any help is appreciated :smile:

Reply 1

Morbo

The Young modulus, E, is a measure of the stiffness of a material, and defined as tensile stress (F/A) divided by tensile strain (e/l), where F is the applied force, A is the cross-sectional area over which the force is applied, e is the extension (or compression) of the material, and l is the original length of the material at zero stress.

Wikipedia quotes a value of E for rubber between 10⁷-10⁸Pa for small strains. (Depending on specific rubber compound, obviously)

The reason it specifies "small strains" is because the Young modulus for rubber varies with strain. Rubber is a non-linear material. You notice this fact because initially, it is very easy to stretch a rubber band. However, as you stretch it further, there comes a point where it just doesn't want to stretch any more.

At this point, the cross-sectional area of the rubber has become smaller (the band is much skinnier), and you are pulling with a greater force, so the stress is very high. However, the band is not extending much, and so the strain is very low. I believe this leads to a much larger value of E at high strains.

As for why your Young modulus is lower than Wikipedia's values, I'm not sure. Perhaps Wikipedia has made a mistake, perhaps there are some rubber materials with E that low, or maybe you have made a mistake? Something to check out.