Potential energy in an elastic band that is transformed into kinetic energy and the distance the band flies when fired

Physics Coursework

Aim: I aim to find a link in the relationship between the amount of potential energy in an elastic band that is transformed into kinetic energy (when the band is fired) and the distance the band flies when fired.

Prediction

I think that the higher the potential energy of the elastic band, the higher the kinetic energy will be meaning that the band will fly further and the work done will be higher. I also think that as I pull the elastic band further back (thus increasing the work done and the potential energy) and fire it, it will have a longer braking distance because it will have a higher velocity.

Method

Measure the distance each band stretches when it is pulled with each amount of force. You need to use forces from 1N to 6N with increments of 1N. Measure the length of each band when stretched in cm.
Stretch the band over the edge of the ruler and pull it back to the length recorded.
Fire the elastic band and record its distance and its approximate braking distance.
Repeat each test 3 times to ensure a fair test.
Record your results and find an average for each set of three.

Equipment needed

Stand
Tape measure
Spirit level
Elastic bands
Ruler

Results of preliminary test

In the preliminary test I measured the length of each elastic band when each amount of force was applied. I then fired different types of elastic band to see how far they would fly.

Work done = Force x Distance

1 = 11.66J

2 = 44.6J

3 = 69.6J

4 = 197.72J

5 = 268J

6 = 388.2J

We must consider that friction is working on the band when it hits the floor.

This is a preview of the whole essay

Work done = Force x Distance

1 = 11.66J

2 = 44.6J

3 = 69.6J

4 = 197.72J

5 = 268J

6 = 388.2J

We must consider that friction is working on the band when it hits the floor.

Friction can tell us the kinetic energy that the band has because if we can measure the braking distance of the band we can work out the Kinetic energy by taking friction and braking distance into account. I will be able to work out the friction acting on the elastic band by this because I will already know the kinetic energy of the elastic band because the potential energy is going to be more or less the same as the kinetic energy as only very little energy will be lost to sound and heat energy when the elastic band is fired.

I can work out the friction acting on the bands in this way:

K.E = P.E =

11.66J divided by braking distance (1.5) = 7.77N
44.60J divided by braking distance (2.53) = 17.63N
69.60J divided by braking distance (3.27) = 21.3N
197.72J divided by braking distance (5.93) = 33.34N
268J divided by braking distance (8.07) = 33.21N
388.20J divided by braking distance (7.5) = 51.76N

Plan

My preliminary results are very varied and therefore unreliable. I don’t think they helped me to decide on a plan other than showing me what to look for in the real experiment. I think that in my main experiment I will have to use the same rubber band so that my results represent a fair test. This will be one of my controlled variables. The others will be:

The height that the band is launched from
That the elastic band is fired from a level surface that is parallel to the floor

My independent variable (the one that I will change) will be:

The amount of force that is applied to the elastic band

I will do this by applying the following increments of force:

I will use a Newton meter to measure on a ruler how long the elastic will be when that amount of force is applied. This is so that in my experiment I can just pull the band back to the desired length and it will mean that that many Newtons is being applied to it.

My dependant variables (the outcomes) will be the length each band flies and the braking distance of each band.

Main experiment

Analysis

Results

I used a medium/medium-sized elastic band for the experiment as I decided that because it was an all-rounder it would give a fairer representation of the physics involved here.

Work done = Force x Distance

13.11J
31.00J
91.89J
212.68J
319.35J
430.20J

Work done = Potential Energy = Kinetic Energy

Friction = Kinetic Energy divided by Braking Distance

13.11J divided by 1.57 = 8.35N
31.00J divided by 2.53 = 12.25N
91.89J divided by 3.87 = 23.74N
212.68J divided by 5.97 = 35.62N
319.35J divided by 13.63 = 23.43N
430.20J divided by 10.50 = 40.97N

We can see from this that the higher the work done, the higher the kinetic energy because this is directly proportional to work done and the higher the kinetic energy, the higher the braking force and thus the higher the friction. This is because when something has a higher kinetic energy it needs a stronger force to slow it down. This increases the braking distance as well because friction is not high enough to stop it instantly.

Conclusion

My results show that the higher the force exerted on the elastic band before it is fired, the further the elastic band will fly and the higher its braking distance will be. When the braking distance increases in length, it increases the amount of friction exerted on the band to slow it down. This friction needs to increase as the kinetic energy of the band increases because otherwise the band would keep on sliding along the floor forever.

This conclusion supports my prediction and proves that the higher the work done, the higher kinetic energy will be when the potential energy is released.

Evaluation

There are a few odd values in my results but this is because this experiment was a very hard experiment to keep under full control. I tried to make it as fair a test as possible by firing each elastic band at each desired force 3 times so that I would get an average result but there were some extreme values cropping up on my result. I think that this is something that most experiments suffer from but thankfully I don’t think it has affected my overall results too badly.

If I did this experiment again I would make sure it was in a far more controlled environment than the classroom because people can get in your way or distract you from your work. I would also take extra care when using the levelling equipment to make sure that my elastic band was exactly parallel to the ground every time it was fired.

I have found out from this experiment that there is a direct relationship between work done, potential energy and kinetic energy and that these can be used in combination with braking distance to give a result for the amount of friction exerted on contact with the floor. However I don’t think that friction can stay constantly at that value because as the band slows down there will be no need for friction to be so high, so I think that friction must be directly proportional to velocity.