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# Efficiency of energy transfer on a rolling object

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Introduction

Holly O’Nione 11HO

Aim: To investigate the efficiency of energy transfer on a rolling object.

To do this I will investigate the input variable which is the factor we’re changing. I shall change the height of the slope, which therefore means the input variable is the gravitational potential energy (G.P.E) as the height moved affects it.

Prediction

I predict that the transfer of energy will be more efficient the steeper the slope gets. This is because as the slope gets steeper, the marble will rotate less and less (so less rotational energy) and make less and less contact , and when the slope has a gradient of 100%, the marble will not rotate at all, but just fall straight down. The marble’s energy changes from G.P.E, as it falls vertically, to kinetic energy. However, as it comes down the slope it rotates. Some energy is lost as rotational energy.

G.P.E = K.E + Rotational Energy

Therefore I will need to measure the velocity at the bottom as there is no Kinetic Energy (K.E) or rotational energy is at the top.

I will need to find out the efficiency of the energy transfer from G.P.E to K.E. The formula is:

Efficiency = Useful energy transferred (KE) x 100

Total energy supplied (GPE)

To work this out I need to know the G.P.E the marble has at the top (therefore the maximum G.P.E)

Middle

th of a second and the time I will repeat the timing five times for each height and use the average of these five results. This will make the investigation reliable as it will reduce the effect of anomalous results.

When I record the time it will be made to two decimal places as the stopwatch limits me by only showing this amount of accuracy.  For length and height it will be measured in metres to the nearest millimetre (three decimal places) because this is quite easy to see on the ruler. This is as accurate as the ruler will allow.

Before I do my actual investigation, I shall carry out a preliminary experiment in order to see if I need to make changes to my plan.  The preliminary procedure will include three heights:

0.200m, 0.400m and 0.600m

I shall do 5 repeats for each and work out an average and the efficiency which should not exceed 100%.

Results for Preliminary Procedure

 Height (m) Time 1 (s) Time 2 (s) Time 3 (s) Time 4 (s) Time 5 (s) Avg Time (s) Efficiency (%) 0.200 2.50 2.60 2.44 2.50 2.40 2.488 64.52 0.400 1.75 1.69 1.79 1.72 1.66 1.722 67.60 0.600 1.40 1.38 1.47 1.40 1.34 1.398 68.22

This shows what I expected as the efficiency increased each time. Therefore I should keep the same amount of repeats. However, I should do more measurements with a greater range (8 measurements) and smaller interval (0.100m). In my actual investigation I shall use the following heights:

0.100m

0.200m

0.300m

0.400m

0.

Conclusion

This is probably because I was more alert at the beginning of the experiment and so my reaction time was shorter. Apart from this I cannot see any reason why the first readings I took were anomalous.

However, I do think that my evidence is valid because I kept all factors which could affect the experiment constant apart from the input variable of the height.

I do not think that I have collected enough evidence to fully support my conclusion.  In order to do this, I must do the experiment again. Next time I shall use a larger range of heights so I can see if the trend continues.  Also, if there is a larger range, an anomaly will not show up as obviously on the graph.  I would not repeat the experiment any more than I did this time as more repeats wouldn’t affect the average much more.

I did not have many difficulties in this experiment except with the timing. If I were to do this experiment again, I would use light, motion or pressure sensors which are connected to a computer to record the times. I would do this because a computer’s reaction time is very accurate.

To obtain more evidence to support my conclusion, I would use a greater range of heights. Another way to do this is to shorten the intervals. The experiment would still have a range of heights from 0.100m to 0.800, but it is conducted every centimetre instead of every ten centimetres.  This would make the trend much clearer. Therefore, this would make the trend and therefore my conclusion clearer.

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

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