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.

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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 -


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. To solve this I have to repeat the same experiment in order to get the mean which would provide much more accurate and reliable results. Sometimes the mass left the surface or ended up rolling. If this were to happen, I would discard that result and repeat it again. Also when I pulled back the rubber band back 13 or 14cm, the tripod moved slightly. To solve this problem, I stick blue-tack to the tripod and the surface in order to keep the tripod in place. When I was pulling back the mass, the elastic band moved up and down the legs of the tripod. This would probably affect the results slightly so to prevent this from happening I will make sure the elastic band always starts and stays in the same position.

     There was another problem with the elastic band when it starts twisting which would mean more force applied to the mass than there should be when catapulting it and when catapulting the mass, it sometimes travelled to the left or the right so I would have to always pull back the mass from the centre of the elastic band and I will draw a straight line down the track from where the mass is catapulted and only accept the results of which the mass finished travelling in that straight line. These are all of the problems I will solve in the real experiment and make it a fair test.

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Variables - There are a number of different variables which can be investigated in the experiment. They include:

  1. no. of rubber bands used
  2. different masses used (100g masses stuck together)
  3. the lengths of how far back you pull back the rubber band(s) (different forces applied)
  4. carrying out the experiment on different surfaces
  5. different temperatures of rubber bands (this wouldn’t be a very good variable to investigate because it has very little effect and it would be very hard to investigate this variable)

I am going to investigate variable no. 1 (no. of ...

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