Rolling a Car down a ramp.

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Rolling a Car down a ramp

PLANNING

When planning my experiment, I will need to take into consideration the following points:

  • Fair testing
  • Equipment
  • How many results I will take
  • What range of variables I will experiment with

I will be investigating, by varying the height the summit of the ramp is raised off the ground, if the average speed increases or decreases.

Method

I have decided to produce a step-by-step guide for each experiment just to ensure that when we actually come to conducting the practical work, it runs flawlessly. This will also help us conduct fairer tests, as we will be following the same set of steps each time we collect a result.

1. Set out equipment as shown in the diagram

2. Ensure the height at the start line (the summit of the ramp) is 10cm using the metre stick

3. Ensure there are no extra weights attached to the trolley

4. Hold the trolley with its front touching the start line

5. Simultaneously start the stop clock and release the trolley (be careful not to push it or exert any extra force on it)

6. Stop the clock when the front of the trolley reaches the finish line

7. Record the time taken for the trolley to reach the finish, next to the relevant height, in a table

8. Repeat from step 4 twice more so you end up with three results for the same height then continue onto step 9

9. Add all these results together and divide the answer by three to obtain the average.

10. Record this average in the table

11. By placing more books underneath the raised end of the ramp, increase the height at the summit by 10cm. Use the metre stick to check

12. Repeat from step 4 until you have obtained results for height from 10cm through to 25cm

Fair Test

As with all scientific experiments, only one variable must be altered at one time. All the rest must remain constant to ensure good sensible results. By using present knowledge, I know that the following factors can affect the outcome and must be controlled:

  • Height of ramp - as this is included in the formula for potential energy, the height of the ramp should affect the speed of the trolley in some way. I will be modulating this variable in the primary experiment, but it should be constrained to a single height in the secondary experiment.
  • Mass of trolley - mass is also included in the formula for potential energy and so could affect the speed of the trolley one-way or the other. As with height, this will be varied but only in the second experiment. With the primary experiment we should constrain it simply by not adding any weights to the trolley and always using the same trolley to collect each result.
  • Gravity - the last portion of the formula for potential energy is gravity, which will affect the outcome if it is increased or decreased. The way to maintain this factor is to simply stay on the same planet.
  • Friction - I mentioned that the only factors that should affect the outcome of the experiment would be mass, height and gravity - because they make up the formula for the potential energy. But other factors may use some of this energy when it is being converted into kinetic (movement) energy as the trolley moves down the ramp. The friction between the wheels of the trolley and the surface of the ramp can 'steal' some of the energy used to move the trolley and convert it to heat instead. This can slow down the trolley, but only very slightly. To maintain the same friction for all the results we should use the same material for the surface of the ramp, and the same material for the wheel of the trolley. No grease should be added to lubricate any equipment.
  • Air resistance - there is very little we can do to control this factor, and its effects would be so insignificant it may not matter. Basically, we just need to make sure we have the same trolley and we'll have to mind we don't accidentally attach a parachute to its back end.
  • Water resistance - just to point out the obvious, it wouldn't be recommended to conduct one experiment in air and one in water...water is far denser than air and will create a stronger atomic 'barrier' which will drastically slow down the trolley.
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With these points in mind it is essential that we must keep the same trolley, use the same ramp and keep the mass constant in the experiment. We will also have to keep the length of the runway the same, just so the trolley has enough time to accelerate.

I am keeping these the same because you are only allowed one thing to change for it to be a fair test and if I didn’t keep these the same it wouldn’t be a fair test.

And there was only one thing that I changed each time, which ...

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