
Rock climbing evolved from a necessity of traversing rocky mountain terrain to an athletic sport sometime in the late 1800s. Today, rock climbing is a popular sport, with an established set of standards and rating system for determining route difficulty.
Rock climbing is typically done in pairs, with one person climbing, and the other person belaying (protecting the climber from falling). Both the climber and the belayer attach the rope to their climbing harness with a figure eight knot. In outdoor climbing, the lead climber goes up the rock first, placing protection devices in the cracks of the rock, usually nuts or spring-loaded 'cams', every so often to limit their maximum possible fall distance. The maximum fall distance equals twice the distance from the climber to the last point of protection, plus any stretch and slack in the rope. If the lead climber falls, the belayer's job is to stops the rope from giving using a belay device, which greatly increases the friction on the rope to make it easier for the belayer to control.