Bungee jumping

Bungee jumping is an activity in which a person jumps off from a very high place (generally of several hundred feet/meters) with one end of an elastic cord tied to his/her ankle 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.

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 custom had apparently been practised for centuries, but it is not clear whether it was directly responsible for inspiring the modern sport of bungee jumping.

The form of bungee most often practised today as a "sport" was first attempted by the Oxford University Dangerous Sports Club, who made an experimental jump from the 75m (245-feet) high Clifton Suspension Bridge in Bristol, England around 1970.

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. A.J Hackett is largely credited with inventing the modern sport of bungee jumping, and most other jumpers use ropes, equipment, and methods pioneered by him.

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 of 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:

When the cord reaches its normal length, does one:
  • (a) stop?
  • (b) start to slow?
  • (c) keep getting faster?

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.

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