Prediction
Terminal velocity is reached when the force of air resistance acting on the parachute is equal to the weight on it.
From this, I predict that the heavier the weight on the parachute, the greater the terminal velocity will be. This is because it takes longer for the air resistance to match the parachute’s weight if it is heavier.
Obtaining the Evidence
The aim of this investigation was to find out how weight affects the terminal velocity of a parachute.
We carried out our experiment indoors so no draft could disfigure the results. We controlled the variables, which we needed to keep the same throughout the experiment such as the area of the parachute, and the height it was dropped from. The weight of the parachute was varied as it was increased in steady amounts in 10g weights. We used these types of weights because they were manageable and easy to measure. We ended up with ten sets of results and did not go beyond, as the parachute tended to tangle up and fell too fast for us to measure accurately. For each different result, we repeated it at least three times so we could compare them until we were satisfied that they were constant and so reliable by eliminating the anomalous results. We then calculated an average for each one. Before this we carried out some preliminary work which included velocity and air resistance.
Results in seconds
Average does not include anomalous results
☹ = Anomalous result
2.6=height parachute falls from
Analysing the evidence
Looking at the graph, I can see that the line of best fit could be linear. It moves upwards in a steep gradient so the velocity relates to the time in a positive way. It is not directly proportional, as the line does not go straight through the origin. It looks as though the trend may move in a curve, although the line seems to move astray which could be a sign of the increased weight leading the trend astray so the line could be different. Although it still means that as the weight gets heavier, the terminal velocity goes up so my prediction was correct. See Prediction on page 1.
Evaluating the evidence
I have some confidence in my results as each one was consistent. Although the graph could have been more accurate to make it more reliable as the line of best fit is not definite. The evidence is still good enough to maintain a firm conclusion, as any inaccuracies would be too small to cause any prominent differences.
Anomalous results could have been a consequence of many factors such as the time the parachute was dropped to the time the stopwatch was pressed may not have been in co-ordination. Or there may have been a slight draught which could have delayed the landing.
I could have improved the evidence of the investigation by allowing a larger height for the parachute so the landing would last longer and the accuracy would improve when measuring. Also height could be added for the initial acceleration so it would not be included in the time, possibly 0.5m extra. We could have tried to extend the results to be more confident about the trend
