8000 = ½ x 80 x v²
v² = 8000/40 = 200
From the above calculation, we can say that v² = 200 m/s. So my theory that there is a link between GPE and KE is proven. For the equation of GPE, mass and gravitational field strength remains constant; and in the equation for KE, ½ m also stays constant. If you change the height on one side, the squared speed will change on the other side. The information above can be drawn together to aid my prediction. I predict that as the height is increased, the speed of the trolley will be increased. My reasons are shown above and below.
There are five variables that will affect the speed of a trolley.
- Height of Ramp – the higher the ramp, the greater the vertical height. As we know from scientific knowledge, the greater the height, the more potential energy the trolley gains and therefore the faster it will travel.
- Surface of Ramp – this is largely to do with friction. If for example, we used carpet as our ramp, there would be more friction and the trolley would travel slower; if however, we used plastic, there would be less friction and the trolley would travel quicker.
- Bearings on Wheels – if there are no bearings on the wheels of a trolley, then the wheels will not turn as easily as if there were bearings.
- Mass of Trolley – the heavier the trolley, the more GPE it has at the top of the ramp, therefore the greater the kinetic energy at the end.
- Length of Runway – this allows the trolley to build up more speed if on a long runway.
I did some preliminary work, to try and find out which variable to use for my Coursework. I already had some idea that I was going to change the height of the slope. This is because I calculated that the height is the only variable that directly affects the speed of a trolley. My reasons are shown below.
In my preliminary work, I tested the use of light gates for my experiment. Light gates are connected to a power supply and have a short beam of light that passes across a small gap. When the beam of light is cut, the light gate turns on a clock that records the amount of time that the light gate is inactive. In one way, light gates are more accurate than ticker tape. Ticker tape measures to an accuracy of 1/50 of a second, but a light gate will measure to 1/100 of a second. The only problem with the use of light gates is that at a high gradient, it will not record a time. In the preliminary tests that I did, I found that the time for a height of greater than 0.45m will not be recorded by the light gate. I also found out that a 10cm card was not often recognised, even at lower heights. Based on the facts that I have mentioned above, I feel that the variable that I will change, should be directly linked with the equation: mgh = ½ mv². After removing the constants from both sides, I am left with: h=v². I have decided to
change the height of the ramp in my experiment. I could not change the speed because I am trying to find a factor that will affect the speed.
To carry out the experiment I am going to need the following:
- Trolley
- Ramp
- Retort Stand
- Light Gate
- Connecting wires
- Power Supply
- Clock that is started by light gate
- Ruler
Below is a diagram showing how my apparatus will be set up.
Method
1. Set out equipment as shown in the diagram.
2. Measure the height at the top of the ramp; our first height will be 0.05m.
3. Make sure that there are no extra weights attached to the trolley.
4. Hold the trolley with its front touching the start line, and aimed towards the light gate.
5. Let go of the trolley, being careful not to help it on its way by giving it a little push.
6. Ensure that the trolley passes through the light gate.
7. When the trolley has passed through the light gate, we will record the time taken for the 20cm card to pass the distance.
8. Repeat from stage 4 twice more so we will end up with three results for the same height then continue onto stage 9.
9. Add all these results together and divide the answer by three to obtain the average.
10. Record all results and the average in a table.
11. Raise the height again with the retort stand to the second height
12. Repeat from step 4 until we have obtained results for heights from 0.05m through to 0.45mm