# To investigate the effects of a parachutes shape and surface area, on it time of decent.

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Introduction

SAC 1A: Investigation:

Speed of decent in a Parachute

By Andrew Cooke

Date of Practical: 05/April/2006

Aim:

To investigate the effects of a parachutes shape and surface area, on it time of decent.

Theory:

A parachute works by increasing the surface area of a free falling object; this creates more drag which results in the decrease of the speed of the object. The drag opposes the downward force of gravity.(figure 1) The force of gravity is not totally eliminated but reduced enough to allow the object to land safely. There are two equations that can be used to determine.

Figure 1

An equation can be used to work out the surface area of a parachute for a given weight

Where:

g = the acceleration due to gravity, 9.81 m/s2 at sea level

m = the mass of the rocket (propellant consumed)

ρ = the density of air at sea level (1225 g/m3)

Cd = the coefficient of drag of the parachute – estimated to be 0.75 for a round canopy

V = the descent velocity of the rocket, 11 to 14 ft/s (3.35 m/s to 4.26 m/s) being considered a safe descent speed.

Apparatus:

Two regular plastic Shopping bags

2.5m A ladder

Stop Watch

Three Washers (10+-1g)

36 pieces of 40cm Cotton Twine

Scissors

Compass

Black Permanent Maker

Glue tack

30cm Ruler

Variables:

- Controlled Variables: The height form which the parachutes where drop – (3m)

Middle

Experiment 2 – Different Surface Area

- Get the other plastic bag and cut the bottom of it and down one of the sides so that it is now one sheet of plastic, also cut of the handles. You may need to bags for this depending on your spacing between each.
- Draw out three circles using a compass, the first one having a radius of 5cm, the second one 10cm and the last one 15cm.
- Cut each of these circles out.
- Know work out the Circumference of each circle (2∏R) and the divide it by six, then
- Now make a small whole at each of these points and tie a piece of string on to each
- Measure each piece out to 30cm and cut of the end
- Group the ends of the string of each parachute together and wrap a piece of sticky tape around the end.
- Now get a bit of glue tack and stick it on the end of the sting and then to the washer.
- Now go back to the where you dropped your parachutes for the first half of this experiment, and drop this set.

Conclusion

Conclusion:

I have proved that the lager the surface area of the parachute the slower the decent of the fall, this is caused because the parachute collides with more air particles on the way down slowing the decent. Also the shape of the parachute is very important, if the parachute dose not have the ability to create a large amount of drag then there is not going to be a major decrease in the rate of decent.

Evaluation:

If I was to do this test again, I would make all my parachutes have a larger surface area, because during the drops of parachute one in experiment 2, the parachute didn’t seem to affect the rate of decent at all. I would also drop the weight without any parachute attached so that i could really see the affects the parachute had on the rate of decent. Lastly I would try and relate the practical more to real life drops, by using comely used shapes of parachutes instead of just basic shapes.

Bibliography:

Http://www.aeroyn.org/Annexes/World/parachute.html

http://www.physlink.com/education/AskExperts/ae536.cfm

http://celtickane.com/rocketry/projecti/math.php

Appendices:

Refer to back pages

This student written piece of work is one of many that can be found in our GCSE Fencing Problem section.

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