There are also controlled variables. These variables are ones which do not want to be changed, in order to keep the experiment fair. The variables have to be controlled so that they do not make this an unfair test, hence the name controlled variables. These variables are such things as the height from which the parachutes are dropped, the weight attached to the parachute and the type of plastic used to make the parachute. These can be controlled by keeping them the same for every experiment, but variables such as the hole in the top of the parachute have to be proportional to the area of the parachute itself.
Procedure
This experiment can be conducted very safely and efficiently using the procedure suggested, and it is the procedure I would recommend. First of all, the metre ruler should be used to measure the height of the room being used. The room should be at least 2.86m high, which is the height from which the parachutes were dropped in this experiment. The height should be marked, and this will be the height from which the parachutes will be dropped. The first parachute can now be made. A circle of plastic should be cut with a diameter measured to exactly 10cm. This can be done by using a compass or a piece of spare string tied to a pen, 10 from the nib of the pen to the point where it should be held to the plastic. The plastic can then be marked on to with a near perfect circle, and then cut out with scissors. Six small holes should then be cut into the parachute. The holes should be the diameter of the string being used. The holes should also be 0.5cm in from the edge of the parachute and equally spaced 60° around the parachute. The string can then be tied around the holes and the edge of the parachute. The string should be tied so that it leaves 3mm of string after the knot has been tied. The weight can then be tied on to the strings that are attached to the parachute. The parachute can now be taken to the 2.86m height and dropped. The parachute should be timed as it falls, and the horizontal distance from the point it was dropped should also be measured. Following the first experiment, the second parachute can be made to similar proportions, but bigger. The sizes are shown below on the following table:
Results
Proportional Results
Graph
Standard Deviation of Results
Histogram of Results
Anomalous Results
In this experiment, I have found 1 set of anomalous results. These anomalous results could be put down to a number of factors including:
- Parachute made wrong size
- Hole on centre of parachute too small or too large
- Strings wrong length
- Timing on descent inaccurate
- Wind affected parachute on descent
- Holes made in wrong place
Trends
The trends of the results included the fact that the speed increased at an exponential rate, as shown on the graph. The total distance fallen averaged 2.99, but the standard deviation of those results was 0.148, which is comparatively close. The histogram shows that this a direct proportion in the histogram.
Evaluation – Accuracy and Reliability
The accuracy of my results was fairly good from my opinion. There was one anomalous result in the graph. The graph actually showed a positive result in that it was a particular shape, exponential. The results were fairly accurate, there may have been one or two anomalous results within the group that was misplaced. The reasons for this are stated in the anomalous results section. The measurement of the data was also fairly accurate according to the trends in the graph. The precise accuracy will be shown below.
Percentage Error Calculation
The best way to calculate the accuracy of one’s results is to do a calculation based on them. This is shown in steps below.
- Collect results
- Calculate the mean (average) of one set of results.
- Find the range by subtracting the largest number from the smallest number for each group of results
- Divide range by 2
- Divide the product of step 4 by the mean
- Multiply by 100
The number that is left is a percentage error. From this, how accurate the results are can be calculated
1% - The data is very accurate
5% - The data is reasonably accurate
10% - Middling error value
25% - Error value is too high, unreliable results. Retest is needed
Evaluation - Procedure
There were some fundamental problems with the fairness if the experiment, some of them I was able to overcome, some of them mattered so minutely that they did not need controlling, or I was not able to control them. I closed the windows and made as little movement as possible while conducting the experiment in order to prevent the wind from blowing the parachute. This was quite effective, as the wind could have easily blown the parachute off course or blown it up or down. I also used the same weight each time, in case the other weights were different weights, either by manufacturing fault or by usage of the weights, getting chips out of them or being otherwise damaged. This was useful because it made the test fairer, because lighter weights would make the parachute fall slower than normal, and bigger weights would make the parachute fall faster than normal. There was the problem of not have very accurate measuring instruments, that could measure to the nearest millimetre accurately. This could not easily be solved, so we had to use the only available instruments. The parachutes were made exactly circular, using a piece of string and a pen. This proved useful, as we could be sure that the parachutes were exactly circular. The plastic that was available, was not the best of materials to make parachutes from. This is for a number of reasons, the plastic was prone to being stretched and misshaped quite easily, distorting the shape of the parachute and making it descend at a different rate. The plastic was also very easy to fold and crumple, so it was not always flat, which could have changed the rate of descent again.
Evaluation
The overall experiment was fairly precise and accurate as far as I can see. The problems encountered were minor, and there was only one anomalous result. If I had more time, I would have re-done the experiment at least 10 times in order to get an accurate result from that particular parachute area. This experiment could also be expanded into more areas than just parachutes, there are also many types of parachute, such as the parafoil, where it is designed to travel both forwards and down, very efficiently. This could be compared to the results of the original parachutes or even another further type of parachute. The parachutes could also be extended, so that they were much larger or much smaller in area than the sizes used in the above experiment. There are also other areas of study with the same parachutes, so instead of changing the area of the parachute, change the weights on the bottom to 20g or 5g for example.