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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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Introduction

WenXi Chen

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.image09.pngimage00.pngimage01.png

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.
  • Place a margarine tub at the centre of it.
  • Place 2 metre rulers in a row from the position of the margarine tub.
  • Hook a newton metre on to the centre of the rubber band and pull it back in accordance with the required force.
  • Release newton metre.
  • Measure and record the distance travelled by the tub.
  • Repeat for the other forces.

image13.png

Diagramimage14.png

image20.pngimage18.pngimage19.pngimage16.pngimage17.pngimage02.pngimage15.png

Fig.1 Front view of apparatus.

image21.png

Fig.2 Side view of apparatus

Fair test

We made sure that it was a fair test by the following conditions:

  • All tests were carried out on the same surface to minimise variations in friction, etc.
  • All tests were carried out with the same rubber band; elasticity, energy storage potential, etc, may be different in various rubber bands.
  • Use the same margarine tub for all tests or the mass, size and shape may vary.
  • Always place the tub in the same position at the start of each experiment.
  • Make sure that the newton meter is always hooked at the centre of the rubber band to avoid directional change of the tub after catapulting.
  • Always newton meter around the same amount of rubber, eg, if the rubber band is looped around the stool, hook it around both lengths:
...read more.

Middle

image04.pngimage07.pngimage06.png

Fig.3 Correct method of latching

Results

(Anomalous results are highlighted)

Distance travelled by margarine tub in cm

Force in newtons

Experiment 1

Experiment 2

Experiment 3

Average

1

7

8

7

7.3

2

18

21

18

19

3

39

40

41

40

4

52

40

54

48.6

5

76

71

62

69.6

6

102

102

90

98

7

110

115

127

117.3

8

116

117

140

124.3

9

144

153

158

151.6

10

192

183

160

178.3

Table.1 Table of complete results

Analysis

Average distance travelled

7.3

19

40

48.6

69.6

98

117.3

124.3

151.6

178.3


image08.png

Increase in distance from previous distance.

Table.2 Table to show increase in distances

From the average points, the graph shows a generally straight line of increase. As the force exerted increases, so does the distance which the margarine tub travels.

On average, the increase from each previous (i.e. one less newton)

...read more.

Conclusion

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.

image11.pngimage23.png

image12.png

Fig.4 Measuring extension

...read more.

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