Elasticity

Hello dear scientists,

I am posting the results that we got for the second experiment that we carried out, calculating the elasticity constant of different kelps and seeing how much force was required to break it. I have the raw data and I have processed it but I cannot upload a word document. I have sent you an e-mail with it. Here I am writing the results. First I am going to explain how I processed the data: we hanged the bull kelps (three of them with different diameters) and we hanged weights. The force applied was calculated with Newton's second law: by multiplying the mass by g=10 m/s^2 (rounded Earth's gravitational field strength). We measured the distance that the bull kelps were stretched. From there I drew the graph force against displacement and I calculated the elastic constant (by Hooke's Law: F=k·x). Then knowing the elastic constant and the displacement at which the bull kelps were broken I calculated the force that was applied (in order to break it we stretched the bull kelps with our hands, this is an important point to taki into consideration as an evaluation of the experiment, since there is likely to be an error in the displacement that we measured). Here are the results:

For the first bull kelp (diameter at the base: 4 mm; diameter of the bulb: 19 mm):
The elastic constant was 27.8 N/m and it broke when a force of 9 N was applied.

For the second bulb kelp (diameter at the base: 7 mm; diameter of the bulb: 47 mm):
The elastic constant was 42.6 N/m and it broke when a force of 13.2 N was applied.

For the third bull kelp (diameter at the base: 17 mm; diamter of the bulb: 55 mm):
The elastic constant was 921 N/m and it broke when a force of 197 N was applied.

I think that we should look at the diameter of the base to realize that the greater the diameter the greater the force that was required to break it. I do not think though that we could draw a relation between the diameter and the elastic constant with only three trials.
With the information that was given by Alex (the rate of growth of the Nereocystis is very rapid-sometimes as fast as 17 cm per day- being able to grow up to 36 m long) we can conclude that if the bull kelps grow so quickly and therefore the diameter increases and the strength also increases, the force that is needed to break it is very large (we have seen that for a bull kelp with diameter 17 mm at the base it was needed a force of 197 N; we have to consider that the bull kelp was about 50 cm long, so when it grows more, the force will be much greater). I have also found that the storms and waves can drag them (which means pull them out the soil but not break them, althought we could think that it is needed a great force to do it since the elastic constant of the bull kelps, as we have also seen, can be quite large).

Well, this is the physics of the bull kelps dear fellow scientists,

Horacio