Bungee jumping
Bungee jumping is an activity in which a person jumps off from a high place (generally of several hundred feet/meters) with one end of an elastic cord attached to his/her body or ankles and the other end tied to the jumping-off point. When the person jumps, the cord will stretch to take up the energy of the fall, then the jumper will fly upwards as the cord snaps back. The jumper oscillates up and down until the initial energy of the jump is dissipated.
In the 1950s David Attenborough and a BBC film crew had brought back footage of the "land divers" of Pentecost Island in Vanuatu, young men who jumped from tall wooden platforms with vines tied to their ankles as a test of courage. This film inspired Chris Baker of Bristol, England to use elastic rope in a kind of urban vine jumping. The first modern bungee jump was made on 1 April, 1979 from the 250ft Clifton Suspension Bridge in Bristol, and was made by four members of the Dangerous Sports Club. The jumpers, led by David Kirke, were arrested shortly after, but continued with jumps in the US from the Golden Gate and Royal Gorge bridges, spreading the concept worldwide. By 1982 they were jumping from mobile cranes and hot air balloons, and putting on commercial displays.
The first operator of a commercial bungee jumping concern was New Zealander, A.J.Hackett, who made his first jump from Auckland's Greenhithe Bridge in 1986. During the following years Hackett performed a number of jumps from bridges and other structures (including the Eiffel Tower), building public interest in the sport. Hackett remains one of the largest commercial operators, with concerns in several countries.
Despite the inherent danger of jumping from a great height, several million successful jumps have taken place since 1980. This is attributable to bungee operators rigorously conforming to standards and guidelines governing jumps, such as double checking calculations and fittings for every jump. Unfortunately accidents in this sport tend to be of the spectacular, bizarre, and terminal variety. A relatively common mistake is to use too long a cord. The cord should be substantially shorter than the height of the bridge to allow it room to stretch. To illustrate how easy it is to overestimate the permissible length of cord, consider the following question:
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When the cord reaches its normal length, does one:
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The answer, perhaps surprisingly, is (c). One does not even start to slow until the cord has already stretched somewhat, because the cord's resistance to distortion is zero at the natural length, and increases only gradually after, taking some time to even equal the jumper's weight. See also Potential energy for a discussion of the spring constant, and the force required to distort bungee cords and other spring-like objects.
Equipment
The elastic rope first used in bungee jumping, and still used by many commercial operators, is factory-produced braided shock cord. This is comprised of many latex strands enclosed in a tough outer cover. The outer cover may be applied when the latex is prestressed, so that the cord's resistance to extension is already significant at the cord's natural length. This gives a harder, sharper bounce. The braided cover also provides significant durability benefits. Other operators, including A J Hackett and most southern-hemisphere operators, use unbraided cords in which the latex strands are exposed. These give a softer, longer bounce, and can be home-produced.
Although there is a certain elegance in using only a simple ankle attachment, the many accidents in which participants have become detached lead many commercial operators to use a body harness, if only as a backup for an ankle attachment. Body harnesses are generally derived from climbing equipment rather than parachute equipment.
Retrieval methods vary according to the site used. Mobile cranes provide the greatest recovery speed and flexibility, the jumper being lowered rapidly to ground level and detached. Many other mechanisms have been devised according to the nature of the jump platform and the need for a rapid turn-around.
Competition
For the many participants who make jumps as a one-off thrill, the idea of competing is irrelevant, but regular jumpers have gone to great lengths to devise criteria for competition, mostly based on acrobatics. Bungee jumping was featured in the early days of the ESPN Extreme Games (X Games) but the lack of an objective measure of skill detracted from the event compared to other extreme sports.
Bungee jumping in the movies
Several major movies have featured bungee jumps, most famously the opening sequence of the 1995 James Bond film "Goldeneye" in which Bond makes a jump over the edge of a dam (in reality the dam is on the Swiss-Italian border, and the jump was genuine, not an animated special effect).
Variations
In "Catapult" (Reverse Bungee or Bungee Rocket) one starts on the ground. While one is attached to the ground the cord is stretched upward; then one is released from the ground and one shoots up into the air.
"Twin Tower" is similar with two oblique cords.