· 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.
· Mass of toy car - 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, which will not happen as gravity is a constant and cannot be changed.
· 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 energy as the toy car moves down the ramp. The friction between the wheels 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 car, 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.
· 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 toy car
Equipment:
Before we begin, we will need a list of equipment for the experiment to ensure it all runs smoothly:
- Toy car
- Ramp
- Metre Stick
- Stop clock
- Books (to position the height of the ramp)
Using this equipment, we can easily obtain results with a high degree of accuracy. The usage of books means we can increase the height by any amount because some books are thicker than others are. We can get the height of the ramp at the start line almost exactly on the said measurement.
Preliminary Results:
Weight of Toy Car = 48g
My preliminary results turned out well, in my real experiment I have decided to use a distance of 89 and a car weight of 46.5 also my range of height will go from 10 (cm) to 50 (cm) in 5 cm) steps.
Why?
From this experiment I expect to find out what factors affect the speed of a body when no manual force is applied to them (i.e. pushing them). This experiment is being conducted to prove the potential and kinetic energy formulae, which, once completed, can be used to calculate exactly the results of any situation using these theories. For example, the planning of a roller coaster - if we prove the formulae, they can be applied to find the exact speed of the train at the bottom of a raised track x metres in height.
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.
Diagram:
Length of ramp
Height Toy Car
Books Ramp
1. Set out equipment as shown in the diagram
2. Ensure the height at the start line is 5cm using the metre stick
3. Ensure there is no extra weight is attached to the car
4. Hold the car with its back wheel touching the start line
5. Simultaneously start the stop clock and release the car (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 5cm. Use the metre stick to check
12. Repeat from step 4 until you have obtained results for height from 10cm through to 50cm
Predictions:
Primary Experiment
As I mentioned in the Introduction, the experiment is based on the potential energy at the top of the ramp being converted into kinetic energy at the bottom.
MxGxH= 0.5xMxV
Height is directly proportional to velocity.
√H V
Using this theory, we can say:
Potential Energy (at the top) = Kinetic Energy (at the bottom)
The formula for kinetic energy is:
K.E = ½ x mass x velocity squared
K.E = ½mv2
Knowing this we can write:
P.E = K.E
mgh = ½mv2
The formula can be simplified
20h = v2
SQRT(20h) = v
This formula will give us the average velocity for the trolley going down a ramp of h metres high. Once we have found this we can use the equation for average speed to find out how long it will take the car to reach the finish line and actually produce a theoretical result prior to conducting the experiment. Obviously, this won't be necessary for a simple prediction, but it shows that the higher the ramp is raised, the higher the velocity of the trolley will be resulting in a quicker time to reach the finish line. I can also predict from this formula, the shape of the graph v against h. As h increases uniformly, by lets say 5cm each time, v will increase too - but not in proportion. This is due to the square root in the formula that we have to use to find v. The higher the height goes, the fewer gaps there will be between the velocity of the present and previous heights.
Therefore, I predict
Increase in height of ramp = Increase in velocity of trolley
Conclusion:
My prediction was proved correct as the graph clearly shows that the speed does indeed increase when the ramp is raised higher. This is due to the fact that more potential energy is given to the trolley as it is raised higher - height is part of the formula that makes up P.E:
P.E = mgh
P.E = mass x gravity x height
So the higher an object goes, the more gravitational potential energy it gains. When it falls, it's potential energy is converted into kinetic energy and; since energy can neither be created or destroyed, only converted; it will move at a faster speed. If we were to conduct this experiment in a place with no air resistance and no friction, we would see that the speed of the trolley stayed perfectly constant as mass plays no part in the equation of potential energy being converted into kinetic.
P.E = K.E
Mgh = ½mv2
Mass x gravity x height = ½ x mass x velocity2
Gravity x height = ½ x velocity2
Mass is cancelled out and theoretically has no impact on the speed of which an object travels when it is given gravitational potential energy.
So, to sum up, as you lift an object to a height, the chemical energy stored in you (which comes from the food you eat) is converted into gravitational potential energy. Obviously, the higher you lift the object, the more energy you are using and therefore the more potential energy the object is gaining. Potential energy is converted into kinetic energy completely so the object when released will move at a faster rate depending on how high it is lifted.
Height does significantly affect the speed at which a trolley travels down a ramp.
Evaluation:
The experiments went very well and ran efficiently, thanks to the plan we had drawn out beforehand. This extra equipment made us sure that our results were accurate and could be counted on. We had arranged to collect a sensible amount of results, although they may be subject to slight human error, which gave us enough information to draw a conclusion from. I would not choose to change the amounts if I conducted the experiment again because we managed to achieve maximum outcome in the time allowed.
If I were to do this experiment again, I would experiment with different surfaces of ramp. Also I would use a car, or try to calculate a solution in which it travelled in a straight line. The main problem we found in our experiment was that the car kept swaying to the sides, creating a longer journey and most of the time falling of the edge. This wasted a lot of time, as we had to conduct the result again. This also could have been due to uneven surface, so a spirit level may come in handy.
To take the potential/kinetic energy element even further, we could look into elastic potential energy and see if it works on the same principle as gravitational potential energy. A simple experiment, such as pulling a toy car back against an elastic band and letting go to see how far it travels or at what speed it reaches would be of interest. And we could also look into what parameters affect the outcome, such as distance elastic is pulled, weight of car, type of surface etc.
All these things would help further our progress in this area of physics and help our understanding of the subject
