# Investigating factors affecting the stopping distance of a tub catapulted along a surface.

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Introduction

Kelly Ide 10G18.03.2003

## Investigating factors affecting the stopping distance of a tub catapulted along a surface

## Introduction

The stopping distance of an object is how far it travels before it stops. It stops because, as it slows down there is less pushing force, so the friction is greater. They are unbalanced so it stops. All the kinetic energy is transferred to heat energy.

Stopping distance can be affected by many factors-

- Elastic Potential Energy of the elastic band – If the band has more elastic potential energy this will be transferred to kinetic energy. If the tub has more kinetic energy it will move further.
- Mass of tub – If the tub is heavier the tub’s stopping distance will be less. Kinetic energy is found by ½mv2. If the mass increases, the speed would have to decrease in order to keep the kinetic energy constant. If the launch speed is lower, the stopping distance will be less.
- Slope of surface – If the tub is going down a slope it would go further because there would be more gravitational potential energy due to the height, and this would be converted to more kinetic energy. If it was going up a slope because it would need more kinetic energy to convert back to gravitational potential energy.
- Friction between the surfaces – If there were more friction (e.g. Carpet) the forces would not be balanced, so the car would stop quicker. Also more kinetic energy would be transferred to heat energy, so it would run out of kinetic energy quicker.
- Air resistance/shape of tub – Air resistance slows movement because it acts with friction. If the tub has a larger force of air resistance acting on it, it will move slower, lessening its stopping distance.

Middle

G.P.E = mgh = ½mv2

The mass is kept constant, and gravity does not change so we find the relationship h ∝ v2

From our graph of stopping distance against height we found that

sd ∝ h as the graph is a straight line.

So we have the three relationships –

m ∝ 1/v2

h ∝ v2

sd ∝ h

We then can find that m ∝1/h and from this we get the relationship m ∝1/sd. When plotting mass against stopping distance I would get a negative curve, because as mass increases the stopping distance decreases. As 1/sd is the inverse the graph will have a positive gradient. The graph would look like this –

#### Method

A tub will be collected and the mass weighed. The two elastic bands will be knotted together and fixed onto two chair legs. The margarine tub will then be pulled back 10cm and released. The distance will be measured from the point of release. It will then be repeated twice and then repeated for the next mass. To attach the weights blue tack will be used, so to keep the test fair it will also be stuck in the pot when there are no weights in it. The surface, air resistance and elastic potential energy of the band will be kept the same to ensure it is a fair test. The stopping distance will be measured using a meter rule, as we will be measuring to the centimetre.

Conclusion

One problem with our experiment was that the tub did not always travel straight forward, and we measured straight ahead to keep it fair. Another problem was that the tub did not always release the same. Sometimes it caught on the elastic band and a few times it hit the wall. To improve this experiment we would need to do it in an open space to prevent it hitting the walls. Another way to improve it would be to fit a holder onto the elastic band (see below)

Then the elastic band would be pulled back, the tub slotted in the holder and then released. The tub would move forward and would not catch on the band. This would improve the accuracy of the results.

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

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