Rubber Band Lab

BIG Question!

How does the force it takes to stretch a rubber band depend on the AMOUNT by which you stretch it?

Lab Time

In this lab, we wrapped a rubber band over prongs then we pulled it to different lengths (such as 1 cm, 2cm, 3cm, etc)with the electronic force probe. The first time we pulled the rubber band to the different lengths it was just a single-looped rubberband but then the second time, there were two loops. We did this to see if there would be any drastic changes to our data. The data we got from our single looped rubber band looked a little like this: 

1 cm = 0.38 N

2 cm = 1 N

3 cm = 1.9 N

4 cm = 2.7 N

5 cm = 3.5 N

While our double looped rubber band looked like this:

1 cm = 3.1 N

2 cm = 5.3 N

3cm = 8.4 N

4 cm = 11 N

5cm = 12.6 N

We noticed that by double looping the rubber band that there was an increase in force even though we didn't change how far we pulled the rubber band.

Next, we had to create an equation relating the rubber band, the distance we stretched it, and the force need to stretch it. We found an equation by graphing our data and coming up with a best fit line on a graph where the x-axis is the distance in meters and the y-axis is the force in newtons. 

After all this we came up with the equation Fs=kx.

Fs=Force need to stretch the rubberband

K=Elastic constant of the rubber band

X=the distance stretched

Lastly, we wanted to find the energy/work used in this lab. Just like in our simple machines lab we wanted to find the area of the graph which is also the energy but in this lab the area would be different. The area for this lab is in the shape of a triangle so we had to use the forumla to find a triangle which is Area=1/2(Base)(Height)[A=1/2BH] . We used this forumla and just substituted in our first equation Fs=kx. Our area would be equivalent to Us(elastic potential energy, our base equal to "x" and our height equal to "Fs."We later found out that we couldn't use Fs in our new equation so we changed it to "kx." Afterwards we came to the conclusion that the equation to find the elastic potential energy is Us=1/2(k)(xsquared).

Finally we are done with the lab and now know that force is directly proportional to distance, which is the answer to our big question.

Real World Connection

I think bungie jumping is a great example for this lab. When you bungie jump you are stretching a rope "x" amount of distance depending on how much you weigh which is also the force need to stretch the rope.  The more you weigh the farther you will go down meaning that is directly proportional just like our rubber band lab. This is why when you bungie jump they need to know how much you weigh so that they can increase or decrease the amount of rope your using because if they use a long piece of rope and you stretch the rope too much then you might hit the ground leading to serious injury.