- Be careful with the callipers as they could be dangerous as they have lots of pointy parts made from metal which could be dangerous if not treated with enough care.
- Make sure that the sand does not go in anyone’s eyes otherwise it would cause them discomfort especially if they wore contact lenses.
- Make sure that there is no one underneath the path of the ball before I drop it to avoid injuring anyone.
Preliminary results:
From the readings recorded I have decided to use the ball size of 18mm as I think this will produce good results as the crater produced was neither too big nor to small to take readings from.
(Graph on attached page)
From these readings I have decided to take readings at 10cm intervals and I will record readings from balls being dropped up to the height of 60cm as I think going any higher will not help me to find a conclusion from my data.
Prediction:
I predict that the distance from one side of the crater will increase as the height the ball is released from increases:
The reason for this is because when the ball is dropped from a higher height each time it will have more gravitational potential energy and therefore will create a bigger crater. Sending a shock through the sand and pushing the sand out around the hole produced. This creates a mound around the hole. The mound produced will be bigger as the height increases.
Method: the method will stay the same from the preliminary experiment. I will repeat each height three times to give an accurate range of results.
Results:
(graph on attached page)
Analysis:
My graph does link in with my prediction in certain ways, but it is not exactly identical. I thought that if a graph of distance across the crater against height the ball was dropped from would produce a graph with a straight line meaning that they were proportional. To predict this I had to assume that width across the crater was proportional to depth because if a graph of depth versus height dropped from was plotted a straight line should have been produced. The reason they were proportional is because the deeper the crater produced the wider it must be and therefore they should be reasonably proportional. The graph produced was not straight however and had a number of different details to its shape:
- The graph produced did not go through the origin. This was because when the ball was placed on the surface of the sand it creates a small crater as its weight compacted the sand.
- The line then started to rise in a proportional manner. This was because the ball was creating a crater in the loose surface sand which was easily moved outwards when the ball hit the surface.
- The graph then began to level off. This was because as it had more potential energy it penetrated deeper and deeper into the sand throwing out more sand; however the deeper the ball went into the sand the more compacted the sand became. This is due to the pressure of the sand above it. Eventually when the ball had been dropped from a high enough height it would have penetrated deep enough into the sand to reach the bottom. After this if the ball had been dropped from a higher height it would have no longer produced a bigger crater because there would be no sand left to push outwards. This shows me that potential energy is not quite equal to work done in this experiment. This is because the force by the sand would have to be a constant. This is not the case as the sand becomes deeper it becomes more compacted and therefore it provides a larger force. Therefore I cannot prove with this experiment that gravitational potential energy is equal to work done because the force is different.
For the first few points the graph shows a gradient of y=x but then it begins to level off.
Evaluation:
I think my plan and method were both well constructed and if these were followed properly then the results produced would have been accurate enough. However there were errors in my experiment:
- The sand was of varying density as the sand became deeper, as mentioned in the analysis. Therefore I could have instead of simply levelling the sand after every experiment I could have emptied it out and then replaced it in the tray meaning that it would not have been compressed by the balls previously dropped on the sand.
- The ball was not dropped into the middle of the sand container every time. This may have meant that the full extent of the crater was not shown. This could have been counteracted by dropping the ball down a pipe which was clamped above the centre of the tray of sand.
- When the ball was removed from the crater some sand fell into the hole and the crater became smaller. I should have just left it in the crater and measured around it. As I was not measuring the depth of the crater.
- Not enough readings were taken in the lower end of heights. I should have taken readings from 0cm up to 20cm in 5cm intervals and I should have also taken more readings maybe up to as high as 1 meter. Thus giving me a more accurate picture of what was occurring.
I think that my results were reasonably reliable and accurate. I have not found any anomalous readings and this shows that the results collected were accurate enough. However there was a scope for improvement. To make the experiment more accurate with the same apparatus I could have emptied the sand container as previously mentioned. This would have made sure that the sand was roughly the same density throughout. If I was to repeat the experiment with different apparatus I would use digital callipers to obtain more accurate readings as the callipers I used were not accurate enough as the small numbers were hard to read. I would also use a better system to measure where I was dropping the ball in the box of sand as mentioned above, for example dropping the ball down a tube.
Further work: I would do an experiment measuring the depth of the crater. This would allow me to show that distance across the crater is proportional to depth. To do this and obtain a high quality of results I would have to use new sand every time and pour water into the sand to make it denser. This would allow me to remove the ball with the magnet and thus measure the depth of the crater. But this would mean using new sand every time as I would not be sure as to how much water remained in the sand after each experiment due to evaporation etc.
