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An investigation into factors that effect the braking distance of a trolley

Extracts from this document...

Introduction

An investigation into factors that effect the braking distance of a trolley.

(1) Skill Area P: Planning Experimental Procedures

Aim:

To investigate factors, which determine the stopping distance of a trolley accelerating down a ramp.

When a car is situated at the top of ramp, we say it has gravitational potential energy. When the car travels down the ramp, the gravitational potential energy is transferred to kinetic energy, so therefore

KE= ½mv²  

(Kinetic Energy = ½ x mass x velocity²)

At the bottom of the ramp work has to be done in order to stop the car; so therefore

Work Done = Braking Force x Braking Distance

Also, this must be equivalent to the original energy of the car, which was gravitational potential. So, assuming no other loss of energy:

Potential Energy = Kinetic Energy = Work Done

Background Information:

When a mass is raised and there are no opposing forces acting upon it, the potential energy gained will be converted to kinetic energy as it falls back to earth due to the gravitational pull. The potential energy gained must therefore be equal to the kinetic energy it produces due to the theory of energy conservation - energy cannot be created or destroyed. This is shown in the formula: -

PE = mgh

From this formula we can assume that the height of the trolley will have a direct correlation to its stopping distance. It is logical to predict that if the height of the trolley (h) is increased the potential energy it gains will be larger and consequently the kinetic energy it is converted to will be greater. Therefore it is logical to predict that the greater the height of the trolley the greater the stopping distance will be.

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Middle

Independent Variables:

  • Mass / weight of trolley – Mass is present in the formulas for acceleration, force, potential energy and kinetic energy. Therefore any change in the mass of the trolley will affect the outcomes of these equations.
  • Gradient of the slope – This depends on the height of the ramp. This is the factor that I will be investigating to see how its effects affect the braking distance.
  • Length of slope – The longer a trolley has to roll down the runway, the quicker is the possibility of reaching its peak speed.
  • Different surfaces (friction) – The friction between the wheels of the trolley and the surface of the runway will use up some of the energy from the trolley that it is being converted to kinetic energy.
  • The point on the wooden plank where the trolley is released – The trolley has to be released from the same point on the wooden plank to keep the experiment a fair test.
  • The units of measurement used – If different measurements are used for each experiment then the overall conclusion will be biased.
  • Gravity – This factor is hard to change unless you go to a different planet, but it is still an independent variable because it is used in the equations for potential energy, acceleration and weight. Therefore, any change in gravity will affect the values for these equations.
  • Air Resistance – Again this is hard to change and its results are virtually insignificant anyway. The main way to avoid changing this would be to use the same trolley.

Factors affecting the experiment:

  • The wheels of the trolley used will produce friction reducing the trolley's kinetic energy
  • The material used for the ramp will play a role in friction produced
  • The shape of the trolley will produce air resistance when it is moving
  • The position the trolley is released from will have to be the same for each experiment

Measurements:

The ranges of measurements I plan to use for the heights of the ramp are:

  • 05 cm
  • 10 cm
  • 15 cm
  • 20 cm
  • 25 cm
  • 30 cm
  • 35 cm
  • 40 cm
  • 45 cm

The reason for this is because that they are reasonable heights to use. The numbers of measurements I will do are 3 for each height. This is a logical amount of measurements for the time of which the experiment has to take place within.

Repetitions:

The repetition of results is crucial to gain the best and most accurate results. The experiment will be repeated 3 times, for each of the heights, and an average will be taken, so that if any anomalous results occur then it will not affect the outcome as much as if only 2 recordings were taken for example.

Apparatus:

  • 1 metre wooden runway
  • 9 ramps
  • Trolley
  • Marker pen
  • Metre stick

Method:

  • 1. Set the height of the ramp (Ranging from 5 – 45 cm)
  • 2. Place the wooden runway on the appropriate ramp.
  • 3. Roll the trolley down the ramp 3 times for each height.
  • 4. Mark where the trolley stops
  • 5. Measure the distance form the end of the runway to the stopping point of the trolley to          indicate stopping distance.
  • 6. Record the results produce a table and draw a graph to identify trends.

Safety

As with all experiments, safety is an important issue to make sure that nobody is hurt and nothing is damaged.

  • Basic lab rules will be followed at all times throughout the experiment such as not running.
  • The most important safety issue to note is that the runway should be stable so that it doesn’t collapse and injure anybody or damage equipment.
  • Someone will ensure there is no possibility of the trolley going off in inappropriate directions.
  • Most importantly is common sense. If the experiment is carried out responsibly, there will be no problems, but if there isfoolish behaviour in the lab, there could be accidents.

Reliable Evidence:

To collect reliable evidence we will:

  • Take three readings of each height. This is so that any data that seems to be anomalous can be retaken. E.g. if the highest reading differs to the lowest reading by more than 10%, we will collect more data so that the data is reliable.
  • Collect data from many heights so that when we come to draw graphs, they can be drawn accurately.
  • Not push the trolley or exert any force on it when it is released from the starting point.
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Conclusion

Accuracy of Results

The results were measured very carefully and to the best of human judgement. I would estimate the results were measured to within the nearest centimetre. This is easily accurate enough to show a clear distance between heights, accurate enough that the repeated results didn't differ so much as a consequence of this correlation it proved my theory.

Also, the graphs are fairly accurate due to the precision of the results, and you can see that there is a fairly accurate straight line. All in all, I am satisfied with the reliability of the results, as they have enabled me to analyse and do what I need with them. However, as with any experiment there are the occasional anomalous results, which I got, but this did not hinder any of my work, and can be explained.

Strong evidence:

My evidence was reliable and strong enough to support my conclusion, in graph this was clearly exploited.

What Improvements Would Be Made If Redone?

1. Reduce the friction of the system.

2. Make the trolley more aerodynamic.

3. Electronically measure the stopping point for more accuracy with results.

4. Do the experiment more times.

5. I could use a real car but that would be very expensive and it would take a long time to get a lot of   results, also biased results may occur.

If we did any of these proposals I'm sure we would get a fairer test with more accurate results.

Anomalous results:

As far as I can tell, no anomalous results were present, (An anomalous result being a result that does not agree with the general trend of the other readings).

Overview

Overall, I think that the experiment was conducted systematically, and produced enough results with reasonable precision, which allowed me to show my prediction to be true. It correlated well with the theory and there were not too many unexpected results.

GCSE Science Coursework

...read more.

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