Preliminary Results
These results helped me with my prediction because the gave me an early sign of how the air brakes worked and they showed me that as the number of blades went up the time it took for the weight to fall was slower. Near the end it also showed me that after time the number of blades did not seem to make as much as a difference on the air resistance as it had done earlier.
Apparatus
Method
In the method we used goggles and a shield as safety measures, we used the goggles because if any of the blades flew out of the cork our eyes would be protected and we used the shield as an extra safety measure to make sure the blades did not fly out dangerously. We used the number of blades as a variable because the number of blades will give us many different results and it is quick enough for us to get many results. Also by doing the number of blades it could also help us give a more scientific explanation for our results because we would be talking about air resistance. We kept the weight the same because if we had two variables we would not get time for enough results and we would end up with only a few. The weight also had to be kept the same because if we did do variables for the weight we could only add 20g on either side which would not show us that much change, this was because if it was anymore than 20g on either side it would either be too slow or too fast to time.
Repetition was important in the experiment because it helped us get reliable results and it stopped us from getting bogus results because even if we did we would get an average of all the results anyway. Repetition also helped us to do the experiment quicker because after we kept on repeating the experiment we could do it a lot faster which meant we could gain many more results. To make our results reliable, after every time we had got one result we always checked that the blades were still in the same place and they were still spaced out evenly. We also looked after all our results and if we had seen a result out of place we would do it again to make sure that our data was consistent. We drew a line on the bar to show which was the right height to drop the string from and we taped the end of the string to make sure it was exactly one metre in length to make sure that there was going to be no difference about the dropping height. To make this a fair test I have to make sure I drop the weight from the same height and I have to make sure that the blades were evenly spaced.
Obtaining
We obtained our results and we wrote them in a table, we also gave an average to make sure that we did not get any bad results.
I have also done results in comparison to the area of the blades to show how the area can change the speed at which the mass drops.
I think the results we have gained here are very consistent because any results we think that were wrong we have done again to make sure that they are right and we made sure with every result we have got that we had done the experiment properly.
Analysis
Our results show that as the number of blades increases the difference in times between the blades lowers and near the end the increasing numbers of blades seem to make no difference at all. The graph also shows this because as the graph gradually nears the end the steepness of it reduces and it actually starts to level off. The area of blades shows that as the area increases the speed that the mass drops at will also be faster but after time the area does not seem to matter anymore and the mass will start to drop at around the same time from 240cm in area through to 300 cm.
The mass does not drop any faster after that certain number of blades because if the number of blades increases the space which is in between the blades for air to pass through reduces which means air resistance has been reduced which means the air brake will not work as well. Because when we used only 2 or 3 blades there was a large space for air to pass in between the blades which meant there was a lot of air resistance and the air brake could work with great effect and slow the mass down considerably more each time a blade was added. But as the number of blades increased so did the gap in between each of the blades and the air resistance was dramatically reduced because the air had no space to expand in between the blades to slow down the weight.
But I have also learned that as the number of blades increased so did the actual mass of the cork and blades which meant that the weight would fall down slower because it had a larger mass to spin around. That is why the smaller number of blades is faster than the larger number of blades because the mass of the smaller number of blades was smaller which meant that the mass could fall down a bit faster. Then when it to the larger number of blades the mass was heavier and air resistance was still there but not as much which meant that the mass would fall slower. But near the end the extra blades seemed to make no difference on how the weight dropped, this shows that air resistance had dropped and I think that if I had a few more blades I think that the times would drop because there was less air resistance after every time even though there was more mass.
My results do agree with my prediction because I predicted as the number of blades increased so would the time it took for the mass to drop. Then I also predicted that the increase in blades would soon close the gaps in between the blades for the air to enter and resistance would drop which meant times would start to go faster. But I actually got it wrong because I predicted the mass would drop faster but it dropped a bit slower but near the end times started to be the same which could have meant that the blades may soon drop down faster. My results agree with my prediction because you could see that as the number of blades increase the time it takes for the mass to drop will be slower. But you could also see that near the end the increase in blades made no difference because air resistance was not going to increase anymore and it actually started to reduce and I think if I added additional blades the times would actually start to drop.
I have also compared falling times between blades to show if all my results agreed with each other.
I have done the percentage difference compared to the time of one blade. It shows that as the number of blades increases the differences in the time also increases as each blade is added, it shows that in the beginning the percentage difference is very dramatic but as more blades are added the difference gradually becomes less. Then near the end percentage difference only changes 1% in the last 3 values which shows the increase in blades is making no difference and it is getting harder for air to get inside the blades to slow them down. These percentage differences agree with all my results because it shows a steady increase in the length of time it takes for the mass to drop, then it agrees that near the end of the experiment the blades seem to make no difference at all to the speed at which the mass falls down. I did not use 1 blade as the example for the percentage differences because I found that I got quite a wide range of results for 1 blade and I did not find it very consistent. I found that for 2 blades I gained more consistent results and I could use it as a good comparison for all the other blades.
I then drew a graph to show my results in a different way.
At the early stages of the graph you can see a steep increase which shows the difference of having no blades or having 1 or 2 blades. The graph shows that just 1 or 2 blades can make a drastic difference in the speed at which the blades fall and it shows the blades do pick up a lot of air resistance in its early stages. From then on the graph increases in a steady rate but you can tell that in the earlier part of the experiment where it was only at 3 blades the steepness of the graph shows that an extra one blade slowed down the speed at which the mass dropped dramatically. This showed that in the earlier stages it was easier to increase the air resistance because it was easier for the air to enter into the blades and the effectiveness of the air brake was a lot greater.
Then nearer the end of the graph the steepness starts to decline which shows the speed at which the mass is dropping is not changing as much as before. This shows that the air resistance is increasing in only small amounts and the air is finding it harder to fit in the gaps between each of the blades. Then at the end of the experiment it shows that the increase in time as the blades are added has stopped and this is shown by the graph levelling off and the increase has stopped. This gives an indication that the air resistance cannot be increased anymore because there is no more space for the air to enter and I think if the graph went onto a few more blades it would soon start to decline. This is what the graph has shown me in this experiment.
Evaluation
In this experiment we have used a very simple procedure of gaining three results for each blade and working out an average from those 3 results. But I think this procedure wasn’t as good as I think it could be because we could have used better equipment and I think that we could have gained more results. We gained a few anomalous results in this experiment; I think we have gained a very odd result for 6 blades because this resulted in an odd plot in my graph. I think the reasons for gaining this was result were that we simply did not space out the blades correctly or we went wrong with the timing at while we were doing that number of blades.
We could have improved the experiment by using more reliable timing which could have been done by light gates which would have gave us more precision. We could have also used a string that was exactly 1cm in length rather than shortening the string by using tape because that might have started a problem in making sure that we had the right the right string length. Also instead of doing the experiment off a stand we could have attached the air brake to a wall which could have stopped the air brake bending or the stand leaning over at times. Instead of using cotton string we could have used a strong rubber string which would have gave us a smoother dropping of the weight and it will be easier to wind the string back up. Instead of using a cork I would use a rubber cork which would make sure that the blades did not fall out of the cork. I have shown this new set of apparatus in a plan I have made.
I don’t think my data is enough to make a concrete conclusion because I don’t think I had used the right method, the method was not right because I think that hand method timing is not that precise nor had the right materials to make precise enough results to make a concrete conclusion about the experiment. If I were to make a concrete conclusion to the experiment I would have to take down a lot more results and I would try and make all of my results very consistent.
If I was going to make a concrete conclusion I would have to make sure the spacing of the blades was extremely accurate, I could do this by using a tape measure and I would have to use light gates for timing. To make a concrete solution I would also have to justify my conclusion to the point at which it would never go wrong and I could not do that with my results because I have not done enough blades to finish my conclusion. This is because if I had added more blades it would help me finish my conclusion instead I just presumed what would happen which means that I did not get enough results to justify my conclusion. So I don’t think my own data is enough to make a concrete conclusion for this experiment.
By Nathan Ranamagar 4s
