# What affects the Motion of a Trolley on a Runway?

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Introduction

## What affects the Motion of a Trolley on a Runway?

Variables:

- Mass of trolley
- Surface the trolley is running on
- Height of the runway
- Distance the trolley travels

The variable I have decided to change is height of the runway in relation to velocity.

Prediction:

Predicted results:

Height (m) | Velocity (m/s) |

0.05 | 1.0 |

0.10 | 1.4 |

0.15 | 1.7 |

0.20 | 2.0 |

0.25 | 2.2 |

0.30 | 2.4 |

I predict that as the height increases, the velocity also increases. This is because the formula for velocity is:

v = (2gh)

(where v = velocity, g = gravity, h = height)

So if the height increases, v must also increase. Gravity on earth is always 10m/s2, therefore the formula for velocity can be simplified to:

v = (20h)

A predicted sketch graph of the results would probably be as below:

The law of conservation of energy says that potential energy (PE) at the top = kinetic energy (KE) at the bottom, therefore all the energy in potential energy at the top must be transferred into two things at the bottom, movement and heat. Any energy at the bottom which is ‘missing’ must have been transferred into heat energy, by friction. We know that if there was no friction, all the energy would be turned into velocity, and the predicted results reflect this ‘perfect’ result.

Middle

Velocity (m/s)

0.10

0.95

0.20

1.34

0.30

2.11

Method:

We set up the experiment as above with the data logger connected to the light gate so it could record the results by itself reliably and accurately. The data logger then relays this information to the computer, and the software we used was able to work out the actual velocity by itself, so there was no chance of human error. This also meant we could easily take 2 or 3 repeats of each measurement from which to take an average.

We started the measurements at 5cm, measuring from the top of the table to the top of the runway at where the trolley was starting, and we took 3 results from that point. We repeated this for the other measurements, up to 30cm and took an average.

We kept the test fair by using the same trolley each

Conclusion

Most of the results are near enough to the line to not be counted as anomalous results, but there is one anomalous result, which is indicated on the graph. This was caused by the trolley getting caught halfway through the light gate on the last reading of the first measurement, so the velocity was vastly reduced, and in turn, brought down the average.

If I had the time I would redo this experiment, using an air-track, and I would focus especially on the height between 0 and 0.1m to see what happens there – whether there is a straight line, or if there is a curve. I would also like to increase the height, but use a protractor instead to measure the degrees so I can go higher. This would show if and where the curve of the line of best fit comes almost horizontal, because the trend at the moment shows that it might become almost horizontal, at approximately 0.6m on the experimental curve, and probably fairly near that for the predicted results.

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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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