The force you exert on pulling back a rubber band, which will in turn catapult an empty margarine tub, affect the distance which the margarine tub will travel.
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Margarine Tub Investigation Aim The target of this investigation is to find out how the force you exert on pulling back a rubber band, which will in turn catapult an empty margarine tub, affect the distance which the margarine tub will travel. We will not be changing any of the other factors of the experiment, only the force and extension of the rubber band, for that is the variable which we are investigating. Prediction I predict that the more force you exert, the further the margarine tub will travel, however, I think that the force and distance relationship will not increase evenly, instead it would first increase rapidly, then the increase will be less significant, and then rise slightly. Scientific reason for prediction Rubber is not a material which obeys Hooke's law and its extension doesn't increase uniformly. Some elastic materials are intended to absorb energy. The greater the force that is applied, more the rubber band is extended. The force in the rubber band is stored as potential energy which is reverted into kinetic energy once I have let go of it, this energy is transferred into the margarine tub as kinetic energy and therefore it moves. A stretched or compressed elastic band is capable of doing work when released. As the rubber band is released, the force that it exerts diminishes with distance. Equipment * Rubber band * Chair/stool * Rulers * An empty margarine tub * A newton meter that goes up to 10N Procedure * Loop the rubber band around the front legs of a chair.
On average, the increase from each previous (i.e. one less newton) experiment is 18.77cm although there is a rather large difference in the range between experiments. The range of the largest increase and the smallest is 21.4cm; the smallest increase being 7N to 8N, which was only 7cm and the largest was from 5N to 6N; which was 28.4cm. However, ignoring any anomalies, you can see that the increase in differences between distances are normally larger in the second half of the experiments with the larger forces, than the in the first half with the smaller forces. One thing I noticed was the relationship between the distance travelled and the force exerted, there seemed to be a strong pattern forming; the distance of a certain force multiplied by 3 is more or less equal to the distanced travelled by the margarine tub at a force that is twice the size of the primary force. See Table 3. Force (N) Distance (cm) 1 7 8 7 1 x 3 21 24 21 2 18 21 18 2 x 3 54 63 54 4 52 40 54 Table.3 The results show a strong relationship between each other, when the force doubles, the distance trebles. I also noticed that the relationship worked very well for the first few values but not so fittingly for the later half (larger forces). This fits well with the Force/Extension law of rubber; if the pattern had occurs throughout the results then it would mean the relationship between force and extension could be plotted as a straight line, but that is not the case.
* The release mechanism; I think that the way we released the rubber band could have been improved, rather than letting the whole newton meter go, we could just have a detachable part for the device could have dragged across the floor and lengthened time of impact. * I would mark out the centre of the tub so that I got it exactly centre each time rather than just estimating. * I would mark out the centre of the rubber bad so that I got it exactly centre each time rather than just estimating. In addition to this set of experiments, I would also like to measure the speed of the retraction of the elastic band and the extension of it so that I can incorporate it into some of the other rules of physics and see if it fits with my analysis. If I had those results I could introduce momentum into the analysis as well. I could also test out some larger forces to see if the pattern mentioned in Graph 1 actually applies in this case. The results I had attained did not quite show that pattern but it could have just been a small section of a bigger whole. To measure the speed of the retraction, I would measure the distance of the extension and time the lapse between release of the rubber band and the impact with the tub and divide the distance by the time. See Fig.4. Fig.4 Measuring extension WenXi Chen
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