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What affects the speed of a trolley down a ramp?
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What affects the speed of a trolley down a ramp? Skill Area P: Planning experimental procedures Introduction A trolley is pushed to the top of a ramp, the summit being 20cm from the ground, and then is released. It rolls all the way down the ramp, of 1 metre, before it come in contact with a carpet at the bottom. A couple of keen scientists thought it would be interesting to record the time taken for the trolley to reach the bottom and then calculate its average speed. They let the trolley fall down the ramp three times after that, just to make their results more accurate. They also wanted to investigate if the height of the summit made any difference to the average speed, so they raised the ramp to 30 and pushed the trolley down the ramp again and recorded the time. Basically I have been asked to act as the two enthusiastic experts and test, as a primary objective, to see if the height of the summit affects the average speed at which the trolley travels down the ramp. Based on my existing scientific knowledge, I know that this experiment depends on a certain type of energy being converted into another type. When the trolley is raised to the top of the ramp, it gains a certain amount of potential energy – this is converted into kinetic (movement) energy as the trolley travels down the ramp. Too see what factors may affect the way the experiment turns out, it may be useful to look at the formula that is used to calculate potential energy: P.E = mhg (where m=mass, h=height and g=gravity) Obviously, The more potential energy initially means the greater the kinetic energy at the bottom of the ramp. If it has more kinetic energy it will be travelling faster, so its stopping distance will be greater. The only factors left are the variables I will be experimenting with in this investigation Primary Experiment 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. Secondary Experiment I will be investigating if the average speed changes by adding extra mass to the trolley. There will always be smaller forces that could slightly affect the result, such as friction between the ramp and the trolley’s wheels, and air resistance. There is no way I can control any of these factors, but they shouldn’t affect the results so much as to give completely inconsistent readings for each experiment. Planning When planning my experiment, I will need to take into consideration the following points: Safety Fair testing Equipment How many results I will take What range of variables I will experiment with Safety With this straightforward experiment there is not much that needs to be taken into consideration. No harmful substances are being used, neither are flames, solvents, so all-in-all a relatively safe experiment. Obviously we will need to take precautions when increasing the mass of the trolley and make sure that all the weights are securely fixed to it by using sellotape, string etc. Especially when the trolley reaches high speeds, the likelihood of weights falling off is increased and this could be potentially harmful to a spectator. Also at the bottom of the ramp some sort of barrier will need to be placed to prevent damage to the trolley as it hurtles off the edge of the carpet, the rest is all common sense. Fair Testing 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 changing 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. As with height, this will be varied but only in the second experiment. With the primary experiment we should limit 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 convert 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.
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