Lamar Sale, age 9, of the U.S.A.F. Academy, Colo., for his question:
WHO INVENTED THE PARACHUTE?
For many years parachutes were made of silk. Today, however, they are made of nylon since this material is stronger and cheaper. Parachutes designed for human use measure from between 24 and 28 feet across when extended. Those used for cargo are sometimes 100 feet across. The seat pack is the most common type used, although some attach to the wearer's back or chest.
Looking very much like a large umbrella, a parachute is used to slow down the fall of a person or an object from aircraft.
The parachute's operation is based on simple principles: air resistance and gravity are the two forces that act on any falling object. While gravity pulls the object quickly toward the earth, the air resists the object's movement. Large, flat surfaces offer a greater area of resistance to the air than do thin, sharp surfaces.
The first successful parachute jump was made in 1783 when a French physicist named Sebastian Lenormand floated down from a tower. In 1797 the first parachute jump from a balloon was made in France by a man named Andre Jacques Garnerin.
During the 1930s special military uses were developed for the parachute. And then during World War II, both the Allies and the Germans used parachute troops in battle.
Parachutes are worn as harnesses that consist of a series of straps that fit around the shoulders and legs. The harness gives support to the parachutist during the descent. When a cord is pulled, the parachute jumps out of the pack and the air forces it open. Special holes or slots are built into the parachute's canopy that allow some of the air to flow through, thus reducing the area of resistance and also reducing the amount of swaying during the descent.
Parachutes descend at the rate of about 15 feet per second or a little faster, depending on the weight of the parachutist. A jump is unsafe unless made more than 500 feet above the ground.
Hitting the ground after a parachute jump is much like the action you'd have by jumping from a moving car. If the ground is rough, it is possible that the jumper's ankles could be sprained or broken if special precautions are not taken. The jumper must have control over his parachute and must be able to judge wind speed, altitude and direction.
In recent years, parachute jumping has become a sport that is attracting followers in America and Europe.
Special sport parachutes are used by skydivers. When the ripcord is pulled, a pilot chute opens first and pulls out the main canopy quickly. Within just a few seconds the full parachute is open and the jumper is brought down to earth very slowly.