From snodawg@aol.com Fri Mar  3 13:53:39 EDT 1995
Article: 29473 of rec.climbing
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From: snodawg@aol.com (Sno Dawg)
Newsgroups: rec.climbing
Subject: Re: What's a Kill-O-Newton?
Date: 21 Feb 1995 22:10:20 -0500
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Although kN's might be the proper way to express a piece of gears
strength, I always convert kN's into lbs (224.8 lbs = 1 kN) and then think
of it in terms of how much a car weighs.  For example, 10kN equals about
2,248 lbs, which is about half the weight of a compact car.  25 kN is
about  5,620 lbs, which is about the weight of a BMW.  

I've seen a few attempts at mathematically trying to quantify the forces
involved in a climbing fall, but they required such sweeping generalities
that they didn't correlate to reality at all.  Some of the factors that
effect the fall force are:

- Amount of rope out
- Elongation of the rope
- Tightness of the knot
- The number of pieces placed and the friction that they cause
- The type of belay device
- The forces absorbed by the human body
- How tightly the belayer is anchored

The best demonstration of fall forces I've ever seen was one done by the
head tester at REI, where he substituted a load cell in place of a
quickdraw on an overhanging indoor climbing wall.  He then had the climber
take a few falls and a computer plotted the forces.  The fall scenarios
were almost identical, but the results varied quite a bit depending on the
factors mentioned above.  In the worst case scenario, the belayer was
firmly anchored, using a fairly static belay device, the knot was tight
and the rope had been fallen on recently.  The climber took a typical
sport climbing fall, about 5 feet above the last bolt and fell a total of
about 10-12 feet.  The load peaked out at about 1,900 lbs (8.5 kN), which
is getting into the open gate breaking strength of some lightweight
biners, small stoppers and aid placements.

Andrew