How will changing the distance an elastic band is stretched effect the distance a plastic tub travels down a runway?

David Pasque

How will changing the distance an elastic band is stretched effect

the distance a plastic tub travels down a runway?

Aim

The aim of this experiment is to see how changing the distance an elastic band is stretched will effect how far a tub is catapulted down a runway.

Plan

In our experiment we plan to test how far we can catapult a plastic tub across a runway using an elastic band. We are going to get a runway and place it on a flat surface; at one end we will place a piece of wood horizontally across the width of the underside of the runway. The wood will have two nails in it on which the elastic band will be stretched around, this will come over the top of the runway to allow the elastic band to be pulled back and catapult a plastic tub along the runway. The equipment we will be using is:

Runway,

Plastic Tub,

Length of wood with a nail in either end,

Elastic band,

Ruler,

Pencil

This is how we will lay out our experiment:

The results we are going to collect are the distance the plastic tub travels. The variable we are going to alter in this experiment is the distance the elastic band is stretched backwards. This will change the force of the elastic band. We are going to change the distance of the elastic band being stretched 10 times, starting at 3cm, and finishing at 30cm, therefore a 3cm gap in between each. We will repeat this experiment 3 times, and work out the averages to eliminate any inaccurate results and to ensure all our results are accurate. To keep this experiment a fair test we will take a few precautions to ensure there is no foul play. We will use the same plastic tub, runway, elastic band, and the same direction in which the plastic tub is fired. We are going to use the same plastic beaker because if we use different tubs for each experiment, the shapes may be different, or the weight may be different and this will affect the distance the tub will travel. We are going to keep the runway the same as this could also affect the distance the tubs travels, due to the friction of the runway or length of the runway. We will also make sure that the runway is on a flat surface at all times, and in the same place and this could affect the results due to gravity. If the runway is sloping downwards the gravity will pull down on the tub and cause it to move further. We will make sure that the wood with the nails will be kept secure with no movement. We will use the same elastic band because if we change elastic bands they may have different forces in which they fire at, they may be different lengths or thickness and also they may have different tensions. This may cause the results to be inaccurate. Lastly we will make sure that we catapult the tub in the same direction as if we change direction this may affect the results due to air resistance. The wind may be blowing in a different way, which will cause inaccurate results.

Prediction

I think that as the distance the elastic band is stretched back increases, so will the distance the tub travels. I think this because of the following equation:

Work Done = Force x Distance

The force, in this case being friction, will stay the same because the weight inside the tub is staying constant and we are using the same surface throughout the experiment, these are not changing so the force will also stay constant and not change. According to my prediction, as the work done (energy given to the tub ...

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Prediction

I think that as the distance the elastic band is stretched back increases, so will the distance the tub travels. I think this because of the following equation:

Work Done = Force x Distance

The force, in this case being friction, will stay the same because the weight inside the tub is staying constant and we are using the same surface throughout the experiment, these are not changing so the force will also stay constant and not change. According to my prediction, as the work done (energy given to the tub by the elastic band) increases, so will the distance the tub travels.

Method

The way we carried out our experiment was how we planned it apart from two things that we added to ensure a more accurate experiment. When we were measuring how far we pulled back the elastic band, we actually marked on the runway each distance to ensure that it was the exact distance that it needed to be so when we repeated the experiment it would be in exactly the same place. This kept the test fairer and I think gave us more accurate results.

The second thing we altered is we put weights in the tub. When we were carrying out test runs we soon found out that the tub would fly way past the end of the runway and usually end up on the floor. To overcome this problem we put 500grams of weights in the tub. This made the tub catapult only onto the runway; as a result our results were easier to measure and so more accurate.

Results

This is our table of results that we collected from our experiment.

From looking at this table of results I can see that as I increase the distance the elastic band is stretched, the distance travelled increases, but I cannot see a pattern in the rate of increase, I will have to draw out a graph to make this clearer.

(Graph attached)

I have drawn a line of best fit onto my graph to try and see any patterns but I still can’t find any, to find a pattern I will have to draw out a table to work out the percentage increase.

By looking at my table I can see that there is a fairly obvious pattern. Each time there is an increase I can see that each increase is about 40% or 50%. This pattern shows me that the distance travelled is increasing at a steady and similar amount each time.

Conclusions

My results show that as I increased the distance that the elastic band is stretched; the distance the tub travels also increases. This matches up with my prediction and so my prediction was right. I can tell that my prediction was right from the graphs because my line of best fit is curving up, starting at 0. This tells me the distance the tub travelled increases as the distance the band is stretched increases. If the line has been curving down, this would tell me that as the distance the elastic band is stretched increased, the distance the tub travelled would decrease.

I know that the results didn’t increase proportionally because if the had done then the line would be a diagonal line, starting at 0 and going directly through the centre of the graph. As this matches up with my prediction, this means that the equation in which I associated this experiment was also correct. The equation was

Work Done = Force x Distance.

Evaluation/Criticism

If I were given opportunity to do this experiment again I would change a few things about how I carried it out. Firstly I would have put more measures in place to make sure my methods were fairer, one of then being make sure it is the same person who pulled the elastic band back each time and also have a longer runway so as the tub didn’t crash into the end. I would also make sure that my results were more accurate by marking all the measurements on at once, and also repeating my experiment 5 times to ensure better and more accurate results. I would improve the whole thing by using a much thicker rubber band, as the ones we were given were very thin and could snap easily.

In my table of percentage increase I can see that there is one result that does not fit the pattern. I think this is because it is just a duff result and if I were to do this experiment again I would ensure that this didn’t happen by repeating the experiment 5 times.

If I were to do another experiment to find more about my aim I would probably do an experiment to test how increasing the amount of elastic bands affects the distance a plastic tub will catapult.