My aim is to try and find out whether there is any connection between the way rubber bands and springs stretch once weights have been added.
Factors that may affect the experiment are:
In this experiment I will use the number of weights as my variable. Therefore, so that this is the only factor that affects my experiment, I will use the same elastic band each time to ensure that the thickness and length of the band will remain the same throughout my experiments.
I will make sure that the room temperature is the same each time I do an experiment my using a thermometer to check the temperature. This should not be too much of a problem however, as I will be using the same room each time I repeat the experiment and the outside temperature will not have changed to the extreme that it will drastically affect the room temperature.
I think that as the weights are added to the elastic band, the extension will not be proportional to the load. This is because I already know that this applies to springs (Hooke’s Law) and I know that springs act in a different way to elastic bands because of the composition of their atoms. Elastic bands’ atoms are all tangled up and very random whereas springs’ atoms are more regular and coiled.
I think that this is an important factor as it shows a quite noticeable difference between the two and it gives me more reason to believe that the band will stretch in a different way to the spring. Thus being the elastic band will untangle and the spring will uncoil. The following diagram shows the comparison:
I think that once the elastic band has been stretched, because of the atom formation shown above, it will not retain its original shape as well as the spring. This is because as the spring is stretched, up to it’s elastic limit, it uncoils and is strong enough, as Hooke’s law states, to return to its original form. The band however, I think will be weaker as once the particles have been unravelled from the weight of the load, they will find it hard to restore their original shape. This is because the bonds will be weakened as the band is stretched. As the spring is metal, the bonds holding together the atoms are stronger and will not as easily snap.
Before I start I will take the temperature of the room so that when I repeat the experiment I can check that the room is of a similar temperature. I have decided to measure this in Celsius, as it is a more modern and accurate way of reading the temperature.
I will clamp the stand securely to the table to make sure that any movement is minimal and therefore helping the results be as accurate as possible. The band will be suspended from the top of the stand. I’ll measure the band before any weights are added so that it is possible to calculate the extension. To begin with 1 Newton will be added to the spring. The new length of the spring is obtained using a 30cm ruler that is clamped tightly to a stand to improve accuracy. I will use a smaller ruler 15cm long as a ‘pin-pointer’ between the ruler and the band to help measure the length and again improve accuracy. This will be recorded and the original length of the band subtracted from the extended band length to find the extension. This process will be repeated for weights 2N, 3N, 4N, 5N, 6N and 7N. I chose these weights because it gives me a good range to work from and will enable me to do a direct comparison with the spring as these same weight values were used in that experiment also. If I was to go too much higher with the weights, the band is likely to snap and I will have to start again from scratch with another band to ensure that factors such as band length and width are not altered throughout the experiment.
As I have already stated, I will measure the temperature of the room in Celsius and the weights in Newton’s. I will also have to measure the length of the spring and I have decided to measure this in centimetres correct to the nearest 10th of a centimetre as I feel that this gives a sensible yet still accurate reading. I will record the extension in a table and then later the results will be presented on a graph.
As well as the points I have previously mentioned there are a few other things that need to be done to ensure that the experiment is safe and fair. I will need to wear goggles to protect my eyes from any bands that may happen to snap and shoot into my eye. I will stand during the experiment with my stool under the desk so that if the clamp stand for any reason is not properly secured and falls, I can move out of the way quick enough to prevent it from falling onto my feet. Each time I add weights I will expect the band to oscillate. I will make sure I wait until the band is still before I take my readings to ensure that they are exact. I will also make sure I measure from the same place each time. I will repeat the experiment so that I can take an average of the results and obtain a more accurate result.
My graph, shown on the next page, shows that the extension does not go up in proportion to the load for the band. For example, with the spring, when the load was doubled, the extension doubled as well. However, with the band, this did not happen. For example, at 3N the band extension was 5.7cm. Therefore, at 6N the bands extension should be 11.4cm, but it’s not-it’s 17.55cm! This shows very clearly that the extension is not proportional to the load. Because of this, the spring is a straight line and the band is curved.
The results fit well with my prediction. They show that the extension is not proportional to the load as I predicted and that the band unravels unevenly and randomly. I know that a spring uncoils but a band unravels. I now know that elasticity is a result of the forces of attraction and repulsion between the molecules of the material. Maybe the elastic band was not as strong as its molecules were further apart and so the forces weren’t so severe.
My experiment went very well. There was very little difference between the results each time I did the experiment that shows that it must have been accurate. Nothing went wrong during the experiment that shows that it was well planned out. I think that the units I chose were sensible and practical and that I worked very safely taking as many safety precautions as necessary. I made sure that all factors that needed to stay the same did so.
To improve my experiment I would do another one so that I had three sets of results instead of two. This would make it more accurate. I would also try doing the experiment again but using a completely new elastic band to see if this affected the experiment as it may be stronger.
My results seem pretty accurate as when I compare the results from both experiments, the largest difference between them is on 0.3cm.
My evidence is strong enough to confirm my prediction because it clearly shows that the extension does not go up in proportion to the load and this is what I predicted. It shows a comparison between springs and elastic bands which shows what my results would be if the extension was going up in proportion to the load. Also, as my results were accurate, I think it is safe to say that my evidence is strong enough to confirm my prediction.
If I were to do any further experiments I would try springs/bands in parallel and two springs/bands in series and see how these affected my results.