To investigate the stretching of an elastic band when it has some load on it.

Prediction: 

I predict that the results graph for extension versus load is a straight line with a curve to it at the top when it has reached the elastic limit.  This shows that extension is directly proportional to the load. This is called Hooke’s law.

Preliminary Results: 

 I have planned to put a weight of up to 880g and to start of at the elastic bands original with a load of 0g.  So as part of my preliminary work I just want to check whether 880g is too much for the elastic band, so if it snaps I will have to get another elastic band and think of the elastic limit more carefully but then again not every elastic band has the same limit.

        I am going to find out how much the band stretches as I increase the load by 40g each time. It is much easier to maintain the extension rather than the force.

Preliminary Results Table

Looking at these results I can see that it has reached its elastic limit at 760g are on the elastic band so if I put 880g that is still ok.  To measure the extension it is the     length-original length e.g. 25-14=11cm so therefore 11cm is the extension.  I will give the full results that I have obtained in my actual experiment.  These results are just a rough guide and a range of observations just to check that I do not exceed the elastic limit.

Apparatus: 

Clamp stand: - to hold everything in place.

Elastic band: - to put some load on to it to measure the elastic

limit.

Ruler (0-100cm): - to measure how much the elastic band has stretched after more loads have been added.

Weights: - to stretch the elastic band in order to find out the limit.

Ruler (0-15cm): - to help the accuracy of the experiment by helping to see clearer how much the band has stretched.

Safety: 

Make sure that the base of the clamp stand is pointing towards you, therefore if the elastic band snaps it will fall away from you.

Diagram:

Method:

1. I drew a table for my results, which looked like the one in my preliminary results.
2. I then collected all my apparatus and assembled it as shown in the diagram.
3. I measured the original length of the elastic band, which was without any load or weights and recorded the result in my table.
4. I got 40g of weights and put them on the elastic band by using a weight holder I also knocked the weight of this of the 40g so it would be a fair and accurate test. I then recorded this result in my table.
5. I repeated step 4 until I had put on all the amount of weights that were required for the experiment and this is shown in my preliminary results.
6. The experiment was then repeated using the same methods and calculations. I did this so my investigation is accurate and also to make it a fair test.
7. Now that I have completed the experiment I have to draw and plot these results into graphs.

How to keep a fair test: 

I have tried very hard to keep this experiment a fair test by:

1. Using the same elastic band.
2. Same materials
3. Same size elastic band
4. Using the same equipment
5. Keeping the style of the experiment the same.
6. And finally by using the same person reading the measurements on the ruler.

Maintaining accuracy: 

I think that the accuracy of the experiment was maintained very well and I did this by:

1. Making sure that the ruler is vertical with the elastic band.
2. Reading the measurements at eye level.
3. Taking readings more than once and then tallying up the average.
4. Not taking the elastic band beyond its limit.

Results for Experiment 1.

Results for Experiment 2.

 

Average of results 1&2

Analysis:

Well my graph for experiment 1 shows that the load is directly proportional to the weight because it goes up in a straight line and when it reaches the elastic limit it curves.

So therefore it shows that my prediction was correct because my graph has a slight curve to it at the top just before it reaches the elastic limit.

        The elastic band measures 14cm without any load and as I added 40g the elastic band measured 16cm.  When the load was 80g the length was 18cm, but when the load was120g the elastic band stretched by 3cm. This shows that towards the middle of the experiment the elastic bands extension increases as the load. This is because it is reaching its elastic limit. So therefore the graph is a lot steeper in the middle than at the beginning and end.

        In the middle when the load is 240g the length of the elastic band is 31cm and when the load is 280g the length is 42cm. When the load is 320g the length is 42cm it has stretched by 11cm. From 42cm to 52cm it has stretched by 8cm so it is a big difference between 11cm and 2cm. Then towards the end it starts to go up by 2cm and then 1 cm, this is when you know that it has almost reached its elastic limit.  When the load is 720g the length is 80cm this is the elastic limit point I know this because when I continued the experiment to 880g the length stayed the same 80cm.

 So in conclusion 80cm was the elastic limit and I think if I tried putting on some more loads it would have snapped the elastic band.

Evaluation:

By looking at my results I can see that I have quite a few anomalous results this is because of the accuracy of the experiment. The accuracy of the experiment could have been effected by:

1. The ruler not always being straight.
2. The style of the experiment could have changed.
3. The same equipment was not used.
4. The measurements were not read accurately at eye level.
5. And last of all it could have been because we didn’t finish the experiment in one lesson so we had to do it in several lessons. So during this period the equipment could have been used and moved around, this could affect the way the experiment is carried out.

                               

The accuracy in number 5 could be improved by working a lot quicker and trying to get the experiment complete in the lesson or if not perhaps labelling the equipment is a good idea so that you can use the same equipment and recognize which set of apparatus you used last time.

        If I were to change my experiment I would compare the elastic band with a spring and see the difference at the end. This would extend the investigation further because not only would I be investigating the elastic band, I would also be investigating the spring. Also with this investigation I would have to do further research on springs.

        But then again if I was to do this same investigation again I would try and improve the accuracy of the results by repeating the experiment a third time and concentrate more on making it a fair test.

        Overall I was very pleased with the out come of my investigation, but the points made above could improve it.