"To return to the ground, they (people enjoy dangling and dancing from the tree trunk) rappel - the most dangerous aspect of the sport - by hooking to a rack, which supplies friction to the rope, slowing the trip down."
I wonders how can rack supply friction to the rope? I looked up two words, rack and hook, but had hard time in understanding those description. Please help me out!
ANSWER:
Okay, I don't know too much about mountaineering or climbing equipment, however, I understand a little. "Rack" in general means the set of equipment carried up a climb. However, in this case, it is referring to attachments on the harness that the climber gets into, probably a sit harness (waist belt and two leg loops ). Attached to this harness are special devices called descenders or belay devices that help to control the descent on a rope and creates friction by putting bends in the rope.These devices are usually made of aluminum or steel. Specifically, they are called carbiners (from a German word meaning hook) which are metal loops or rings used as connectors (when you hook something, you connect or attach it). They apparently connect to the harness and the rope goes through them. This secures the rope and catches it by holding it and controls the slide downward.
Friction refers to the ever-present resistance to motion that occurs whenever two materials are in contact with each other. It is characterized as the force of friction. In some situations , we want friction to increase, thus increasing the resistance to motion (such as in rappelling). So, you have two solid surfaces (which are microscopically rough) rubbing against each other or sliding against each other. But,you don't want them so rough that there is a "plowing effect" when they make contact or else one or the other would wear out (a sort of erosion) quickly and simply break. This kind of friction is called sliding friction or kinetic friction. So, your body weight is a force that increases the force of friction and it is the combined forces that slows your fall (acceleration) downward. In physics there is the coefficient of kinetic friction (sliding friction) which has been determined for different surface contacts, the lower this number or value is, the better is the sliding (slipping on ice). So, obviously, you want two things in contact when you are rappelling that that have this as a higher number or value. Companies that make the special climbing rope and the aluminum and steel racks have researched and experimented with different materials to get the best combination of lasting durability and safety.
The sport of rappelling , like any sport, has its special equipment or gear, and terminology and jargon AND its followers who probably can explain this with much more preciseness and clarity. ANYWAY, I hope this helps a little. "Ambiguous Bill"
