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# This project involves testing a catapult by using a rubber band to catapult a mass using various forces. Our aim is to choose and investigate variables of our choice and its effects using a simple catapult.

Extracts from this document...

Introduction

Catapult investigations

Planning:

Aim - This project involves testing a catapult by using a rubber band to catapult a mass using various forces. Our aim is to choose and investigate variables of our choice and its effects using a simple catapult.

Preliminary method -

1. Using a tripod, a rubber band and a long sheet of paper set a catapult.
2. Test it and observe which variables you will keep constant and which you will change.
3. Record the preliminary results into a table.
4. Write up your predicted outcomes.

Diagram for the preliminary experiment - Bird’s eye view of the experiment

Preliminary work results -

 Extension (cm) Distance travelled (cm) 1 0 2 1.2 3 3.5 4 6.5 5 11.9 6 19.5 7 28.2 8 40.9 9 64.8 10 71.6 11 80 12 103.2 13 122.1 14 139.9

Preliminary graph -

Commenting on my preliminary work -

From the preliminary results and the graph I can already see a pattern forming. The pattern is that the more force I apply the rubber band (therefore moving back more on the scale), the length that the mass travels also increases. This means that the force is proportional to the distance that the mass travels after being catapulted. During this experiment I kept everything constant and only changed the force (pulling back from various distances).

I only got one set of results and therefore I wasn’t able to get very reliable evidence as there was no mean I could calculate from more than one set of results but hopefully this preliminary work I carried out will help me in the real experiment.

Middle

Predictions - After carrying out preliminary experiments, I am able to make my predictions for what will happen in my results for the real experiment. I predict that as extension increases, so will the distance that the mass travels. This is because as extension increases, the force increases as they are proportional to each other according to Hooke’s Law. Hooke’s Law states that if you stretch something with a steadily increasing force, then the length/distance will become steadily greater too. In this case the more force you apply to the spring, the further the mass will travel. However there is also the elastic limit that stops the elastic band behaving normally and so once it gets stretched too much, the line of the graph will go straight horizontally.

The way I will expect my graph to be will be a slightly ‘S’ shape. I predict that at the start of the graph, the line will be slightly increasing and when the extension of the rubber band gets to about 6 or 7, the distance that the mass travels will be a lot greater but when

Conclusion

As for the suitability of my method the only thing I could improve is to extend the scale further to a maximum of 18cm extension. This is because I would see what happens when I do use an even greater force than I already have and therefore I could extend my investigation of my chosen variables by getting even more results. I would also repeat each set of experiments five times in total which would mean that I would get even more reliable evidence than I already do and I would conduct the whole experiment on a very long board or make sure I have much more space to conduct my experiment so that I could finish getting the results for the last two sets of experiments and even go back further to see what happens when catapulting the mass back from 15, 16, 17, or 18cm.

Another factor worth thinking about in order to extend the whole investigation is to investigate other variables and if they have anything in common with those which I have already investigated (whether their effects are similar to my chosen variables).

I don’t think that I got a firm conclusion because I did not fully finish the experiment except for the first set of results which matched my prediction. The factors which I could improve in order to get a firm conclusion are stated on the previous page.

This student written piece of work is one of many that can be found in our GCSE Forces and Motion section.

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