Apparatus:
String, Thin Plastic, Tape, Plastic Film Case, 2p Coins, Scales, Meter Stick/s, Stop Watch. (see Diagram 1)
Method:
First of all we will set up our investigation by holding a parachute in the air and dropping it. We will measure the speed at which the parachute reaches the ground by timing the parachute and measuring the distance, in cm, at which it is dropped from (see Diagram 1). We will then calculate the speed at which the parachute fell. We will vary the weight/mass of the parachute by adding coins to the parachute each time we do the investigation. First we will do the investigation with no coins, then we will add 1 coin, then 2, then 3 and so on until we reach 6 coins. We will measure the weight of the coins in grams. To keep the test fair, we will keep the surface area of the parachute and the height at which it is dropped the same each time we do the investigation. To calculate the speed of the parachute we will use the equation:
Speed = Distance
Time
We will make our results more accurate by doing each investigation at least 3 times. We will try to be as accurate as possible at starting and stopping the timer at the correct moment. We can make sure our results are reliable by doing the investigation more than once. By doing so, we can obtain more consistent results making the investigation reliable. To drop the parachute from a higher place we will have to stand on a table or a chair, we will have to make sure that we do not fall off!
For our preliminary work we established what height we should drop the parachute from. We tried dropping the parachute from the height of the table top and found that the time it took to fall to the ground was too short to be accurate. We then tried dropping the parachute from the height of the ceiling, this was much better so we measured how high it was and used this height as our fixed height. This helped our experiment because it made the timing much easier to do accurately.
Analysis of Results
There is a minor pattern in the results (see Table 1) we found. For the second to fourth results the difference between the results increases at a constant rate (see Table 2). This, and the rest of the results, is plotted on Graph 1 where the line of best fit is a smooth curve. The curve on Graph 1 corroborates the results on table 2 proving that the results have an increasing decrease. This means that the decrease in Average time for every result got less each time. From Graph 1 I conclude that mass does affect the speed at which a parachute falls. The heavier parachutes fall faster than the lighter ones. This conclusion fits most of the results. It does not, however, fit the average time of the parachute with an added mass of 0g and the parachute with an added mass of 42g.
The reason for the result we found is that the Net Downward Force is equal to the Downward Force (or mass) minus the Upward Force (or air resistance). The air resistance is affected by surface area; bigger surface areas create more air resistance. We did not alter the surface area so the air resistance stayed the same. We changed the mass, or downwards force, in so doing we increased the Net Downwards Force. If the Net Force (or overall force) increases then the parachute will fall faster, therefore making the time it takes to reach the ground less. My results support this conclusion because each time the mass of the parachute was increased it reached the ground quicker (excluding the first and the last results). On Graph 1 the points (except for the first and last) were all very close to the line of best fit. My conclusion also supports my prediction. In my prediction I thought that increasing the mass would make the parachute fall faster, this is also what I concluded. Assuming that there is a constant gravitational pull, my conclusion would be correct under any circumstances.
Evaluation of Investigation
I think that the planning of the experiment went well as did the preliminary work and the prediction. The planning was well done and this resulted in an organized experiment. The preliminary work went well because it meant that we knew what height to drop the parachute from as our original idea would have made accurate timing difficult. My prediction also went well basically because it was right! We managed to reduce errors in our work to produce accurate results simply by being careful to start and stop the timer at the correct time. One method we used to reduce timing errors was to count to three out loud before dropping the parachute. We did this to make sure that both the person dropping the parachute and the person timing knew when the parachute was going to start falling.
We had two anomalous results, the first result (the parachute with no added mass) and the second result (the parachute with 42g added mass). They were anomalous because the difference between them and the result next to them (Table 2) was a minus number, meaning that they had fallen slower with greater mass when they should’ve fallen faster. At first, I thought that the second result (the parachute with 7g added mass) was an anomaly instead of the first result, I had decided this using Graph 1. From Graph 1, I can see that the first anomaly is either the first or the second result, but upon comparing these findings with Table 2, I found that, in fact, the first result was the anomaly. I think that the anomalous results were because of human error in the timing. I think our results (except the anomalies) were very reliable, we did the experiment three times and then found the averages, and we then used the average times for all graphs, tables and conclusions. If we needed to improve the reliability of the experiment we could repeat it more times but I think this would be unnecessary. I think that our chosen procedure for carrying-out the experiment was quite suitable, the only thing I would change is where the tests took place. If I was to do this again I would do it in a more open space so that there would be less re-tests because of the parachute hitting something whilst it was falling, but I wouldn’t do it outside since air movement would affect the results also. If I was to do any further work to provide additional relevant evidence I would repeat the test with a larger parachute or drop the parachute from a different height or change the mass intervals to see if the same conclusion was met, I would then use this to back-up my conclusion or to extend the experiment.
Catherine Baty 10JM