Patty Magnuson, age 13, of Lynn, Mass., for her question:
WHEN WAS THE FIRST PARACHUTE JUMP MADE?
In 1783, more than 200 yars ago, a French physicist named Sebastian Lenormad made the first successful parachute jump. He made his jump from the top of a tower. Then in 1797 a Frenchman named Andre Garnerin made the first parachute jump from a balloon.
People had been thinking about parachutes long before the first successful jump. The great Italian painter Leonardo da Vinci put the idea of a parachute down on paper in 1495.
The operation of the parachute is based on simple principles. There are two forces that act on any falling object: air resistance and gravity.
Gravity pulls the object quickly toward the earth. But air resists the object's movement. Because the pull of gravity is much stronger than the resistance of the air, the air can only slow down the speed of the falling object.
Large, flat surfaces offer a greater area of resistance to the air than do thin, sharp surfaces. Therefore, an object shaped like a saucer falls more slowly than one shaped like a needle. This is the principle of the parachute.
Today parachutes are used to deliver cargo, and they are also used for emergency jumps from aircrafts. Special military uses of the parachute were developed during the 1930s. Both the Allies and the Germans used paratroops, or the parachute troops, during World War II.
Today, some jet planes use parachutes as brakes in landing. Parachutes are also used on the space shuttle and for recovering experimental guided missiles and radio controlled targets.
For many years, parachutes were made of silk. ,But generally nylon is used today because it is cheaper and stronger.
Parachutes designed for human use are about 24 to 28 feet across when extended. Parachutes used for cargo are sometimes 100 feet across.
The most commonly worn parachute today is the seat pack. Others attach to the wearer's chest or back.
Parachutes descend at the rate of about 15 feet per second or slightly faster, depending on the weight of the parachutist. Parachute jumps from less than 500 feet above the ground are dangerous because this height does not allow enough distance for the parachute to open completely.
Parachutists land with such force that they can sprain their ankles or break some bones. This is particularly true if they land on rough ground.
Wind also creates a hazard because it adds sideways to the speed of the fall.
Parachute jumping has become a sport that has gained many followers in Europe, Canada and the United States. The parachutist has found it necessary to learn to judge wind speed, altitude and direction.
Manufacturers have developed a parachute called the vortex ring. It has four cloth sections that rotate during descent. The rotating sections function much like the rotating wings of a helicopter and allow better control of the parachute.