Bungee jumping is an activity that involves jumping from a tall structure while connected to a large elastic cord. The tall structure is usually a fixed object, such as a building, bridge or crane, but it is also possible to jump from a movable object, such as a hot-air-balloon or helicopter, that has the ability to hover above the ground. The thrill comes from the free-falling and the rebound. When the person jumps, the cord stretches and the jumper flies upwards again as the cord recoils, and continues to oscillate up and down until all the kinetic energy is dissipated.
The elastic rope first used in bungee jumping, and still used by many commercial operators, is factory-produced braided shock cord. This special bungee cord consists of many latex strands enclosed in a tough outer cover. The outer cover may be applied when the latex is pre-stressed, so that the cord's resistance to extension is already significant at the cord's natural length. This gives a harder, sharper bounce. Accidents where participants became detached led many commercial operators to use a body harness, if only as a backup for an ankle attachment. Body harnesses generally derive from climbing equipment rather than parachute equipment.