Parachutes Investigation

Planning: The purpose of this investigation is to collect details about how the weight of an object can affect the speed that a parachute drops. The main aims of the investigation are to find out the way that different forces act on objects when dropped. The forces that act upon the parachute are, gravity and air resistance. Gravity pulls the weight on the parachute down, and air resistance acts against the parachute. A diagram is shown below of how the different forces act on the objects.

In this case the parachute and the weight:

The equipment I will be using to construct the parachute is as follows: 30cm x 30cm polythene sheet for the actual parachute, scissors for cutting string and polythene, string for tying weight to parachute and plasticine for the weight. First a 30cm x 30cm sheet of polythene was cut from a polythene sheet. Next, lengths of 30cm string were tied to each corner of the polythene sheet by making small holes in each corner and threading the string through and then tying it.

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The loose ends hanging down from the corners were then tied together using another piece of string, this time only 10cm long, this is also what the plasticine attached to. Finally the plasticines mass was measured using digital scales for an extra degree of accuracy. It wasn't possible to make the weight exactly right so the actual weights have been recorded. The weights were as follows: 5.01g, 10.04g, 15.06g, 20.04g, 24.98g, 30.03g, 35.04g and 40.

03g.

The equipment used for the actual test included: 1 timer (accurate to one hundredth of a second) to time how long it took for the parachute to fall, metre ruler to measure the distance from the ceiling (start) to the floor (finish), digital scales (accurate to one hundredth of a gram) for measuring how heavy the weight (plasticine) is.

Two people were needed per group, one to drop the parachute and one to time the drop. The parachute was made, as mentioned on the previous page, and the plasticine was weighed. It was then attached to parachute. The dropper then proceeded to drop the parachute from a height of 10ft. The time was recorded and then the process was repeated twice more, and then an average taken. The variable that our group changed was the mass of the plasticine. The area of the parachute remained constant throughout the tests. Also to aid in fair testing, the same person did the same job, so that they did the same thing each time, so that was another constant. The range of weights that we were to use was 5g, 10g, 15g, 20g, 25g, 30g, 35g and 40g. It was decided that these weights would be used from earlier, basic preliminary tests where it was ascertained that anything more than 40g would not allow the parachute any time for air resistance to take affect, and anything lighter than 5g would be too light. So it was concluded that the weights should a factor of 5g.

And finally, my predictions as to the results of the tests. I predict that as the mass of the plasticine increases the quicker it will fall to earth, unless it becomes so heavy that air resistance becomes greater, in which case it will slow down slightly for the heavier objects. My reasoning behind this prediction is that as the mass of the object increases the gravitational pull increases, if the mass doubles then the gravitational pull quadruples, and if the mass quadruples the gravitational pull increases by a factor of 16. Gravitational pull is basically the increase in mass squared. The parachute will also cause air resistance to take affect. If there is a very large surface area then there will be a lot of resistance but the surface area of our groups was not particularly large so not as much air resistance can take affect. Plus as the parachute gets faster due to an increase in mass of the plasticine, the less time air resistance has to come into affect. So as the mass of the object on the parachute increases the time it takes to descend decreases.

Obtaining Evidence: As outlined above the tests were undertaken and the results recorded. Three times were collected for each different mass used, and then an average calculated from them. So from

10ft. the parachute was dropped. The average time was used to collect accurate evidence, in case there were any anomalistic results. Some anomalistic results had to be checked and repeated. Often these were corrected; probably a small timing error was the cause of the anomaly. I left a couple of these anomalistic results in the results, just to demonstrate these results. It was difficult to carry out a very precise and meticulous procedure, for the reason that without very accurate timing equipment, then the timings are bound to be inaccurate. Also, without having proper dropping equipment the parachute will fall in different ways, resulting in more anomalistic results.

Analysing and Considering Evidence:

Weight (grams)

Reading 1

Reading 2

Reading 3

Average

5.01g

1.26 secs

1.36 secs

1.67 secs

1.43 secs

10.04g

1.08 secs

0.96 secs

0.90 secs

0.98 secs

15.06g

0.76 secs

0.85 secs

0.77 secs

0.79 secs

20.04g

1.36 secs

0.78 secs

0.70 secs

0.95 secs

24.98g

0.81 secs

0.68 secs

0.65 secs

0.71 secs

30.03g

0.60 secs

0.65 secs

0.61 secs

0.62 secs

35.04g

0.60 secs

0.65 secs

0.71 secs

0.65 secs

40.03g

0.65 secs

0.75 secs

0.62 secs

0.67 secs

The above graph shows all the results. Below are individual graphs of the individual results, with a small summary of each one.

Time 1 graph shows the first set of results. There is one anomalistic result, and that is on the 20.04g result. Other than that the results are pretty much as expected. And as I said as the weight increases the air resistance increases so it slows down slightly, as indicated by the 40.03g result.

Time 2 graph is exactly the results I expected. As the weight increases for the first seven results the speed at which it drops increases, and then, due to air resistance the speed decreases slightly.

Time 3 graph again shows how the results were expected to turn out.

These average times would be perfect if it were not for the anomalous result in the time 1 graph. Other than that all the results were as expected and predicted.

As I have mentioned above, the scientific understanding behind this procedure was as follows. If a parachute drops from a height with an object on the end gravity will act upon the mass of the object causing it to fall to the ground. However, when the weight becomes heavier then the air resistance increases, eventually balancing out the forces and ultimately becoming greater than the force of the gravity, resulting in the speed at which it drops slowing down.

This conclusion that I have drawn supports my prediction. In my prediction I said that as the weight increases the speed at which the object drops on the end of the parachute increases. But as the weight increases a lot, the air resistance becomes greater, and eventually unbalances the gravitational pull of the Earth, causing the object to slow down.

Evaluation: I do not think that the data that we collected was 100% reliable. The equipment and techniques that were used in the procedure weren't very effective. For instance, when dropping the parachute and object the dropper's hand would knock the parachute, causing the chute not to fully open, resulting in a loss of air resistance and a faster drop and an anomalous result. Another problem was the height at which the parachute was dropped. It was only 2.8m and this caused the chute to sometimes not open properly. The strings would also add weight to the parachute so the masses recorded on the digital scales of the plasticine, would have to have the mass of the string added. The timer had to be very accurate with his timing to obtain reliable evidence.

I feel that the evidence that was obtained supported my conclusion, however I do not feel that it was totally reliable. Some of the anomalies that were recorded are evidence of the unreliability of some of the data. There were more anomalies than were recorded in the graphs and table. They were just repeated because otherwise there would be too many anomalous results.

Further work could be carried out to obtain more reliable evidence. This may include not only researching one variable, but also systematically researching many variables and taking averages of these to obtain much more data. The variable factors that could be changed may include, height from which the parachute is dropped, preferably a lot higher than in these tests, so the chute has time enough to fully open. Another factor that can be varied may be the area of the parachute. In these tests we used a 30cm x 30cm parachute. I don't feel that this was enough, as sometimes the parachute dropped and the chute didn't open.

So in conclusion I would say that the evidence collected from the procedure that was carried out was relevant in the sense of preliminary data. The data that I collected wasn't enough to draw a firm conclusion from, but the data could be used could be used in further tests. Very basic preliminary tests were carried out before this procedure, but the data from the main experiment could be furthered by using it in further work. It could be used to change variable factors like I mentioned in the previous paragraph. So in the end this procedure would only be 100% reliable as very comprehensive preliminary work.