To investigate the factors that affect the stopping distance of a catapulted margarine tub. In this experiment, I will be concentrating on the effect that varying the mass of the catapulted tub has on its stopping distance (sd.).

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Mairéad Kelly 10G

Aim:

        

To investigate the factors that affect the stopping distance of a catapulted margarine tub. In this experiment, I will be concentrating on the effect that varying the mass of the catapulted tub has on its stopping distance (sd.).

Introduction:

        

Things that move eventually have to stop. However, where they stop depends on several factors- their mass (the mass of the moving object), the speed the moving object is going at, the friction between the surfaces and the air (or water) resistance and movement around the object. The stopping distance (or sd.) of an object is how far it travels before stopping.

         

As an object moves forwards, it has kinetic energy (KE) pushing it. However, as it moves, it also creates friction. This changes the KE (kinetic energy) of the moving object into heat energy. This means that there is less KE and more friction. The forces become unbalanced as more and more of the KE is transformed into heat energy. The force pushing the object forwards is then less than the force pushing it back, so the tub stops moving. The larger the force of friction acting on the object, the faster it loses speed.

        

The type of surface that the catapulted margarine tub (or any moving object) is moving along also affects the amount of friction that acts on the object. A very smooth surface – for example, a mirror- would create much less friction than a very rough surface- for example, sandpaper. This in its turn would also affect the sd. of the tub- for a smooth surface, the stopping distance would have lengthened, and for a rough surface, the sd. would be shortened.

If a margarine tub uses a stretched elastic band to catapult it forwards, then the amount the elastic is pulled back determines how far the object travels before stopping. When the elastic band is pulled back then it has Elastic Potential Energy (EPE) which is changed to kinetic energy (KE) when the band is released. If the elastic band is pulled back further then it has a higher level of EPE to start off with, so when it is released, it will have more KE and the margarine tub will go further before stopping.

If the margarine tub was on a sloped surface, going down, then the same amount of EPE and KE would take it further than it would on a flat surface because the KE would turn into GPE (Gravitational Potential Energy) which would pull the tub down the slope and work with the KE, not against it. However, if the tub was moving up the slope, the same amount of EPE and KE would take it less of a distance up the slope because the GPE would not help pull it down and forwards, it would pull it down and backwards, and work against the KE.

Air resistance slows down the moving margarine tub (or any other object) because it acts against the object like friction. If the tub has a large force of air resistance acting against it, then it will slow down more rapidly which would lessen its stopping distance. The air resistance working against the tub is also affected by the shape of the tub. A bigger tub has a larger surface area for the air resistance to act on and therefore there is more air resistance working against the bigger margarine tubs. If an object is moving through a liquid, then instead of air resistance, it is affected by ‘drag’ or water resistance. Drag and air resistance are both frictional forces, and they both always work in a direction that opposes the direction that the object they are affecting is moving in.

The mass of the margarine tub also affects its stopping distance. This is because if the tub has a larger mass then there will be more gravity acting on it. The gravity causes more friction, which unbalances the forces (see above) and this slows down and stops the tub more quickly, which lessens the sd. (stopping distance). In this experiment, mass is the variable.

Prediction and Fair Testing:

In this experiment, I will be varying the mass of the margarine tub that I am catapulting- from 0 to 600g, moving up by one hundred grams every time. In order to ensure that the experiment is a fair test and that my results are not affected by other factors than the mass, I will keep the following factors constant:

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Surface: the margarine tub will be sliding along the same piece of floor for every experiment. This is because if I changed the surface that it moved over, it could create more or less friction (if the surface was smoother then less friction, if it was rougher, then more friction) which would affect the stopping distance of the tub and affect my results.

EPE: In order to make sure that the catapulted tub has the same amount of KE every time it is catapulted, I will pull the elastic band back the same distance (22cm) each time. This will ...

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The report shows a good level of research and detail. 1. The introduction is very well researched and shows a good understanding of the science surrounding this investigation. 2. The fair testing section also shows a good level of detail. 3. References need to be included and colour changes removed. 4. The analysis section is good. However it is also brief and does not attempt to explain the results. 5. The evaluation shows some good practice but there is a large amount of information repeated from earlier sections. **** (4 stars)