Making sense of data - For my Physics coursework I was given the results of an experiment.
Physics coursework –
Making sense of data
For my Physics coursework I was given the results of an experiment, which involved rolling two differently sized balls (initially 3 however one was marble and did not work with the light gate because it gave 2 readings as it reflected light) one small, silver, with a diameter of 0.006 m and weighing 0.00708 kg and one large, slightly rusty, with a diameter of 0.011 m and weighing 0.01672 kg, down a ramp from different heights and measuring the velocity they travelled at using a light gate, connected to a computer which worked out how long the light beam was broken for. The diagram bellow shows how the experiment was set up:
I then had to decided what I was going to use these results for, I decided that I would use them to see if the height the ball is dropped from effects the amount of energy change by working out the difference of potential energy and kinetic energy of the ball. This would mean I would have the amount of energy at the start from calculating potential energy, then the amount of energy at the end of rolling it down the ramp by calculating kinetic energy. I could then find the amount of energy change by subtracting kinetic energy from potential energy. I will calculate the potential and kinetic energy from the mean of 3 tests per experiment.
To calculate potential energy I will use the formula:
PE = mass (kg) x gravity (N) (using 9.8) x height (m)
This is a preview of the whole essay
To calculate kinetic energy I will use the formula:
KE= 0.5 X mass (kg) x velocity2 (ms-1)
In theory I should predict that the kinetic energy would stay the same as the potential energy is however when rolling down the ramp energy will be lost through moving air out the way, in sound energy of the ball rolling, and in friction causing heat energy. This means I predict that as the ball is dropped from a higher height there will be more energy lost, as there is more distance for it to loose the energy. I also predict that the second, large ball will lose more energy than the small one because it is rusty and therefore will create more force making the loss greater. It will also loose more as if it is bigger it will lose more pushing air out of the way and more through noise. These are what I predict the graph will look like for in general for both ball 1 and 2.
Here are the results for my experiment:
Graphs for potential and kinetic energy difference and for the velocity are attached.
I have one odd result for the small ball at height 0.22 m on test 3. I have left this out of the mean result. This anomaly could of occurred from not being exact when measuring the height the ball was dropped from, or from putting a force on it when rolling it down the ramp.
My results show that my prediction was correct. My graphs show that as the height dropped from gets higher the more energy is lost. My graphs also match my predicted graphs with a straight line and the larger ball having higher values than the smaller ball. I think this is because as the ball has more distance to roll it has more time to lose energy in the forms of heat sound and moving air out of the way which makes the velocity slower. This makes the kinetic energy change as velocity is used in the equation for this. The bigger ball also lost more energy than the small ball, this could have been due to the rust on the large ball, which would of caused more friction. However the larger ball only sat on the edges of the ramp as it rolled down as pictured bellow:
Where as the small ball actually sits in the ramp as pictured:
This should of meant the small ball lost more energy in this as more of it would be touching meaning there would be more friction therefore more energy lost. However I think the other energy losses of the large ball weighed out the energy losses of the small ball, therefore overall it lost more energy.
I had one result, which I thought was an abnormality, which is marked on the larger ball graph. I think this could of occurred from putting a force on the ball when rolling it. To improve this I could try and form a devise where you would open a gate to let the ball out and roll down without a human having to release the ball. This would ensure that there was no force being put on any of the balls. It could also of been caused by something interrupting the light gate such as more light occurring in the room for some reason.
In conclusion I have found out that the higher a ball is dropped from the more energy there will be lost from it. I can see that the loss of energy would of either been down to the balls size so there is more energy to be lost or down to the rust on the surface of the ball. However I can see that:
PE=KE and the equations for these are:
M X G X H = 1/2 X M X V2
And as mass is on either side of the equations they can both be taken away making no difference showing mass does not affect energy loss. This means that the loss was down to the surface of the balls.
I think overall my experiment was conducted quite well. I had one problem at the start when the third ball I wanted to use reflected light so it could not be used in the light gate as it gave two readings, so I could only use 2 balls. I also had problems using the spreadsheets, as I had not done many calculations before, however I soon got the hang of them and could use them to work out the calculations for potential energy and kinetic energy. I also had the problem that the experiment may not be accurate because as the ball is dropped it may have had force exerted onto it altering the results. Using some kind of gate to let the balls drop down the ramp themselves, making sure no force was exerted on them, could combat this.
I could improve the experiment I did by making sure the third ball I used was suitable with the light gate by making sure its surface did not reflect light. I would additionally improve it by using a gate of some sort to let the balls run out so that it would not be possible to put any extra force on them as I state above, this would also make sure that the ball was dropped from the right height. I would also try and make sure that nothing else would interrupt the light gate maybe by making sure that the light in the room was at a constant level by closing blinds. This would reduce the errors in my results.