Shock loads

In case you don’t know, a rope that can handle shock loads well and stretch a good bit is good when climbing because if you had a rigid rope that only stretched 5% before snapping, you would be much more likely to snap the rope for any given fall, and much more likely to get injured yourself.

When we’re talking about deceleration, a very important factor is how long it takes to slow down. It doesn’t take all that much force to seriously hurt the human body; it’s easy to break a limb from even ten feet up. The reason landing on a rigid surface like concrete is a lot worse than landing on a soft surface like dirt is because with the minimal deformation of the concrete, your deceleration happens a lot faster.

Imagine you’re climbing and you fall ten feet before taking up the slack in your rope. Let’s assume you were on an overhang and fell cleanly without scraping the wall to mess with the acceleration. You’re falling for ~0.8 seconds and you hit a top speed of ~25 feet per second. Rope #1, a rigid rope, allows you a stopping distance of, hell I dunno, six inches. That’s a stopping force of about 3400 pounds for a 180 pound person, almost 19g. Ouch. Rope #2, a stretchy rope, allows you a stopping distance of two feet. That’s a stopping force of about 850 pounds, under 5g.

Pretty big difference. Yes, there’s lots of rounding above. Deal.