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Parachutes

What are parachutes for?

A safe landing making the speed at which you hit the ground smaller.
Parachuting animals
Parachuting supplies
Parachuting parts of a re-usable rocket back to earth
Para sailing being pulled behind a speed boat!
Returning space capsules to earth (the Apollo flights)
To slow down the landing speed of a plane

A brief history of parachutes


The first parachute was designed in 1514 by Leonardo da Vinci in Italy, but it was never used. The first man to make and use one was the Frenchman Andre Garnerin who jumped from a balloon over Paris in 1797. In 1838 John Hampden, an Englishman, made a parachute jump from 2800 m using an umbrella-like parachute made of canvas and bamboo. The name parachute actually comes from two words, one Italian "para" meaning prevent and the French word "chute" meaning fall.

How do they work?

A parachute is like a large umbrella. If you tie a small brick to the handle of an opened umbrella and then drop it out of a window it will float downwards (make sure that the brick is tied in firmly and check that there is no one underneath!)

When you jump out of a plane your speed increases. As it does so the friction between you and the air also increases this is called drag. When your drag and your weight are equal you are falling at a steady speed known as your terminal velocity. This can be over 80 m/s if you fall head down!

It's pretty obvious that if your hit the ground at this speed you would never get up again so a parachute is designed to slow you down by increasing the drag on you so that your terminal velocity is much less just a few metres per second.

In fact paratroops' parachutes slow them down so that they land at around 6 m/s about the same as if they had jumped off a 1.8 m wall. Still quite fast and the paras have to learn to land properly by bending their knees and rolling on impact.

The bigger the area of the parachute the more air friction (drag) there is.

Some parachutes are really big: a paratrooper has a parachute 10 m in diameter but to drop heavy equipment like a vehicle parachutes with a diameter of over 30 m are used. For anything heavier a number of parachutes are fixed together.

Parachutes can be guided by letting some of the air spill out of the front or back of the parachute. There is also a hole in the middle to allow the parachute to fall vertically.

Parachutes can be circular, the traditional shape, or rectangular the shape used for some military and stunt use.

For a simple but effective experiment to investigate the behaviour of parachutes please see:
Parachute experiment
 
 
 
© Keith Gibbs 2013