Physics for Cavers article

Thanks to Ted Williams for sending a link to this interesting article:

Physics for Cavers: Ropes, Loads, and Energy By William Storage & John Ganter

Everyone knows that force is what breaks a rope. But some might not realize that the force a rope experiences depends heavily on the properties of the rope itself. Few aspects of caving cause as much confusion as so-called shock loads. When cavers use this term they are usually talking about dynamic loads resulting from stopping a fall. When scientists talk about shock loads they are concerned with extremely rapid load application, such as that encountered in ballistics studies—nothing like what cavers mean. To a scientist, our loading conditions are simple physics, the stuff Newton worked on. But this “simple” Newtonian physics has important implications for rigging and vertical technique.

Dynamic loads arise from acceleration or deceleration of a mass. Weight is merely a static load, the consequence of gravity pulling on a mass. The relationship between the weight of an object and the force generated by its acceleration is more subtle. A falling body accelerates because of gravity, but this does not cause a dynamic or “shock” load. The dynamic load is caused when the body stops falling; when it is decelerated by an applied force. This force can come from a rope, or the ground. As the rope begins to store the energy of the falling climber, the load increases. It then decreases, during the rebound, down to a static load, the climber’s weight.

Unlike popular usage, engineers and scientists have specific meanings for the commonly used terms. This is not merely jargon, because it prevents some of the misunderstandings that can lead to bad conclusions—a valid concern for cavers. A force is simply a load; a push or pull on an object. It can be thought of as a muscular effort. Formally, work is the product of force and distance; the distance through which the force acts. When a 180-lb climber ascends ten feet up a rope, he does 1800 lb-ft of work against gravity.

Energy is the capacity to do work. The amount of energy something possesses is exactly equal to the amount of work it can do. These concepts are needed to understand the way a rope behaves during a fall.

the rest of the story:

http://bstorage.com/speleo/Pubs/rlenergy/Default.htm

Tom