Parachutes
If something is dropped, gravity will make it fall faster and faster. If a person jumps out of an airplane, they will start to fall very fast. While falling, a person will fall at 118 miles per hour. To keep from hitting the ground so fast, the parachute was invented.
How a Parachute Works
A parachute looks a lot like a large umbrella. It is used to slow down a person’s fall – rather than going 118 miles per hour, a person may go 15 miles per hour. A parachute is very simple. It uses air resistance. Air resistance is a force that helps slow things down. If you have held your hand out of a car window while the car was moving, you have felt air resistance. Something large and flat gives more air resistance but something thin and sharp, like a knife or a needle, gives very little air resistance. Think about it – if you drop a sheet of paper and a pencil at the same time, which one will hit the ground first?
The Parachute Designers
Leonardo da Vinci (1452-1519), a great artist, designed the first parachute. He drew a parachute shaped like a pyramid with four strings holding a man. Although Leonardo designed the first parachute, the first parachute wasn’t built until two hundred and fifty years later. Inventors finally made a parachute in 1777. That year, Joseph Montgolfier dropped a sheep attached to a parachute. Later, in 1785, J.P. Blanchard dropped a dog from a balloon. Can you guess why they didn’t use their own parachute?
The First Parachute Jumps
The first person to use a parachute was L.S. Lenormand – he jumped from a tower in 1783. With Lenormand’s jump and those that followed, the parachutes were dropped. In other words, the parachutes were already open and the man was just hanging there before they let go of the parachute. Later, in 1797, the first high parachute jump was made. On October 22, 1797 André Jacques Garnerin made the first high parachute jump above Paris, France. He rode a balloon up to 3,200 feet (975 m) and then he jumped from the basket. He was definitely a daredevil. Garnerin’s design had a problem – his parachute did not have a vent at the top to let the air out, so he spun wildly as he fell. Luckily, he landed unhurt half a mile from the balloon. Garnerin was the first man to design a parachute that could slow a man's fall from a high altitude.
Parachute Design
The first parachutes were rigid. They didn’t fold into a bag. Instead, they had ribs covered with material. The ribs were usually made of a lightweight wood. The first non-rigid parachute that was used was made in the 1880s. The first parachutes were always dropped from a balloon. They were always open before being dropped. In 1908, an American, A. L. Stevens made a parachute that was carried in a pack.
For many years, parachutes were made of silk. Nowadays, silk is no longer used. However, nylon is used. Nylon is stronger and cheaper. A parachute for a person is usually 24 to 28 feet across. A parachute for cargo can be very large. Sometimes the army will drop a tank or a jeep from a plane and those are very heavy so the parachute must be very large. Sometimes a cargo parachute can be over 100 feet wide.
Modern Parachutes
Today, a parachute is kept in a pack – similar to the way people wear a backpack. A parachute is held on with a harness. A harness holds the person safely to the canopy. Between the harness and the canopy are suspension lines, or ropes. The canopy is the largest part of the parachute – this is what provides the air resistance.
Comprehension Questions:
1. Look up the word gravity in a dictionary – write the definition below. ______
2. Look up the word gravity in a bilingual dictionary – write the word gravity in your own language. ______
3. If a person jumps out of a plane, how fast will they fall? ______
4. Do not use a dictionary for this question – guess what the word invented means. ______
5. What does a parachute look like? ______
6. Can a parachute slow a person’s fall? ______
7. What does a parachute use to slow things down? ______
8. Who designed the first parachute? ______
9. The first parachute was designed in the 1400s. How many years later did someone make the first parachute? ______
10. Draw a picture of the first time a parachute was used:
11. Who was the first person to use a parachute? ______
12. Who made the first high parachute jump? ______
13. How high up was he when he jumped from the hot air balloon?______
14. Did he have a problem? If so, what was the problem? ______
15. The first parachutes were rigid. This means that they were ______.
16. When was the first parachute made that was carried in a pack? ______.
17. Who invented the parachute that could be carried in a pack? ______.
18. What are parachutes made of today? ______.
19. How wide is a parachute that is made to carry people? ______.
20. What is another way to call suspension lines? ______.
Make a Parachute
Build your own parachute using Leonardo da Vinci's design for the first ever parachute. It looks like a pyramid! Here’s how.
/ 1. Take a sheet of fairly stiff paper 30 cm long and 16cm wide.Fold it in half.
2. Open it out and draw a line 1cm from the long edge to the middle fold.
3. Cut off this section and fold back the remaining piece – it’s a tab so that you can glue your parachute together.
4. Now fold it along the diagonal - from corner to corner.
5. Open it out like a book and measure 15cm up from the centre fold. The diagram will show you exactly where to measure.
6. Now join up the points then cut out your shape.
7. Fold it into a pyramid shape and glue it into place.
8. Make a small hole near each corner at the base.
9. Now tie strings, each the same length, to each hole.
/ You’ve made the Leonardo Da Vinci parachute! Test it by attaching a weight (a piece of egg carton makes a good basket for the weight) to the strings and throwing it up into the air.
Experiment with different types of material.
Does newspaper or card or plastic carrier bag work better?
How can you measure this?
Write up a report of your investigation of different materials.
· Can you imagine you are Leonardo da Vinci?
· Find an illustration which shows you how he might have worked.
· Can you write out his thoughts as he designed his parachute?
· What did he know at that time?
· What materials were available for making his parachute?
· What tools could he use?
· Did he have scissors?
· Can you illustrate your writing and make it look “old”?
Science Projects with Toy Parachutes
By Dr. Jean Potvin
Parks College Parachute Research Group
There are many interesting scientific experiments that can be done to study the physics of parachutes. These experiments involve dropping test parachutes of different designs in order to see their effects on the payload's descent speed. Such design modifications include:
· changing the payload weight
· lengthening or shortening the length of the suspension lines
· changing the number of suspension lines
· increasing or decreasing the radius of the parachute
· cutting holes and/or slits in the parachute fabric
Some theory:
By virtue of being blunt and large, parachutes generate a lot of air resistance or "drag". When attached to a freefalling payload, the large drag generated by a parachute helps in reducing the payload's fall speed by acting against the payload's weight. In general, parachute drag will increase with the radius of the chute and thus reduce the payload's speed. Also, drag will be reduced when holes or slits are cut in the canopy fabric, i.e., the more holes, the faster the descent. Finally, adding suspension lines will reduce the effective parachute surface area; in contrast, lengthening them will increase it somewhat. In terms of fall speeds, this means that adding suspension lines will increase the descent rate while lengthening them will decrease descent rate.
The descent speed of a payload attached to a parachute is calculated by a well-known formula discussed in another page on this web site, Calculating the Descent of a Round Parachute.
How to make small parachutes for science projects:
Toy parachutes can be purchased or made by using simple materials such as strings, plastic from garbage bags or nylon fabric from old (discarded!) tents. These pictures show some of the designs we have tested, a parachute without holes and a parachute with holes.
Other sources of small parachutes:
Hobby stores that sell model rockets usually sell small rocket recovery parachutes, made from both plastic for small rockets, and from fabric for the larger rockets. A parachute supply company called Para-Gear also sells a small parachute. Item: A3333, Name:Parachute Toy. Note: Before simply purchasing a parachute, make sure your research or science project allows you to do so! An important part of your project might be to make your own, which is easy, fun, and inexpensive anyway.
How to measure descent rates:
A typical experiment would consist in dropping different parachute designs and measure the descent speed of each design. The easiest way to measure descent speed is by suspending under the payload a long weighted line called a "plumb line", and by measuring the time between the landing of the plumb line weight and the landing of the payload. The length of the plumb line should be measured before or after the drops. The descent speed is simply given by dividing the plumb line length be the landing time interval of the payload and plumb line weight. An important note: the weight at the end of the plumb line should be small relative to that of the payload so to not change the desired descent speed of a given design. The weight is used to keep the plumb line straight during the descent.
Some final remarks:
* In general, chutes that do not have holes and slits cut in the fabric tend to oscillate wildly during their descent. This is due to the fact that the excess air caught by the descending canopy spills to one side when there is too much of it in the canopy. This sideways spill in turns pushes the canopy in the opposite direction to one side of the payload, thus generating the oscillation when the spill is repeated. One way to reduce the oscillations is to cut holes and slits that let some trapped air through. There are all sorts of hole and slit patterns that can be cut as shown in an article by Dr. C. W. Peterson that was published in Physics Today, August 1993 (the magazine Physics Today can be found at university and college libraries).
* Tests chutes may be covering some horizontal distance while descending. This may be due to the presence of winds, and/or to the parachute being unevenly trimmed. Uneven trim arises whenever the suspension lines are not of the same length or when the holes/slits are not of the same size or located symmetrically with respect to the parachute's center.
In the event that the chutes go forward, a proper measurement of the descent rate should involve the extra measurement of the horizontal distance covered. This is easily done by measuring the horizontal distance between the drop point and the landing point of the payload.
Then the descent speed is given by:
travel distance
v = ------
landing time interval
where
(travel distance)^2 = (horizontal distance)^2 + (plumb line length)^2