# To find out the difference in velocity it takes for a parachute to hit the ground with the same parachute model dropped at the same height but using different weights of plastacine (which represents the parachutist).

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Introduction

Rebecca Lee 10Y

Investigating the Free-Fall Velocity of a Parachute

Physics Practical Assessment: C4: Planning and Evaluating

Aim

To find out the difference in velocity it takes for a parachute to hit the ground with the same parachute model dropped at the same height but using different weights of plastacine (which represents the parachutist).

Introduction/Theory

Terminal Velocity is reached when the velocity becomes constant, so the drag is equal to the weight. The drag, which makes it fall slower, is mainly from the air resistance force trapped beneath the surface area of the parachute. A free-fall parachutist achieves terminal velocity because once dropped, the weight of the parachutist is equal to the drag force from the parachute. The diagrams below illustrate the process of reaching terminal velocity.

1. 2. 3.

The weight of the After a few seconds. After terminal velocity is

parachutist reached.

(the plastacine ball).

The possible variables that can be used are:

- The weight of the parachutist to see if it effects the acceleration.
- The area of the parachute to see if it increases the drag.
- The length of the parachute string to see if it increases/decreases the drag.
- The height of which it is dropped from to see at which height would it hit the ground the fastest at.

Fair Test

To make this experiment a fair test and to control the variables it is considered that:

- It will be dropped in a place which is not windy and made sure that it is redone if it bumps into something because it will affect the results.
- The height of which it is dropped will always be measured 2 meters.
- The same parachute will be used each time.

The changing variable is:

- The weight of the parachutist, so each time 5 grams will be added on to see how it effects the time taken to hit the ground.

Equipment

The equipment needed in this experiment is:

- A plastic garbage bag for the parachute
- String for the connecting rope
- Plastacine for the weight of the parachutist
- A metre ruler to measure the height
- Tape and scissors for construction
- A scale to measure the plasticine
- A timer to record the times

Middle

The way that I am measuring the free-fall velocity is by timing it from when it is let go and then when it first contacts the ground. Each time, the parachutist gets 5g heavier.

The readings I am going to record are done 10 times to get am average and timed using a stopwatch in seconds/milliseconds, so it is a more accurate answer.

Results Table (also see graph)

Mass (g) | Try 1 (s) | Try 2 (s) | Try 3 (s) | Try 4 (s) | Try 5 (s) | Try 6 (s) | Try 7 (s) | Try 8 (s) | Try 9 (s) | Try 10(s) | Average (s) | Velocity d/t (m/s) |

5g | 1.59s | 0.97s | 1.60s | 1.37s | 1.98s | 1.47s | 1.78s | 2.10s | 1.50s | 1.79s | 1. |

Conclusion

The different variables I could have used to extend my work were:

- To change the area size of the parachute to investigate different drag
- The height of which the parachute would be dropped from
- The length of the string to see how it effects the parachute shape

I think that using these three variables would be useful to find out how the drag, height, and shape would effect the time taken for it to hit the ground. What I would expect to find out for these are:

- Size of parachute – it would take a longer time for the parachute to hit the ground as the size increases because a bigger surface area would mean that more air is trapped beneath the parachute surface holding it up for longer
- Height – with a shorter distance, it would take less time to hit the ground, and with a longer distance, longer time.
- Shape – the longer the strings, the time taken is shorter because of the weight as well as the shape is longer, so then there is less air trapped underneath a oval shaped area.

This student written piece of work is one of many that can be found in our GCSE Forces and Motion section.

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