How do you add up an anchors KN?

Bounce test forces:

supertopo.com/climbing/thre…

johnnyrig wrote:Bounce test forces: supertopo.com/climbing/thre…

Thanks for the link. I remember reading that when it came out, and being skeptical of the results.

I suppose one plausible explanation for the discrepancy between his results and mine is that in measuring peak force on a load cell you are measuring only force, while when bouncing on a screamer, that force needs to be active long enough to break the stitch. In other words, "work" (in the physics sense of force times displacement) is the relevant factor.

Now in practical terms, which is more relevant - pure force numbers, or a measure of work? As Jim Titt elucidated, it might depend on what type of gear you're talking about - a nut might require much more energy to drag through a placement. But in all cases, a very low-energy bounce that generates a moderate force that can do a low amount of work, IMO, tells you only part of the story, and it may not be enough of the story to know if your piece was any good.

GO

The reason for the brittle/ductile energy absorbtion difference is, at heart, that work = force X distance. You don't get much (or anything) in the way of energy absorbtion until the load in question acts over a distance. For the most part, the deformation of climbing gear that has failed is measured in millimeters, so just extracting it is not going to absorb much if any detectable fall energy.

As Jim mentions, if you somehow manage to drag a nut down a crack, that process could absorb a detectable level of fall energy, although I don't think this happens very much. Something that does happen in soft rock is that cams can track out, leaving a trail of grooves behind. Even here though, you get at best a couple of inches of action, so not much in the way of energy absorbtion.

Perhaps one of the guiding misconceptions underlying some of these discussions is that forces can be "absorbed." They can't. A force either is or isn't. Energy, on the other hand, can be absorbed if your system can perform work.

Just to review, this came up because I said that I thought the cascade failure of a three point anchor would not be accompanied by much if any energy absorbtion stemming from the failure or extraction of the pieces, making it possible that the three-point set-up is no stronger than a single piece.

rgold wrote:Perhaps one of the guiding misconceptions underlying some of these discussions is that forces can be "absorbed." They can't. A force either is or isn't. Energy, on the other hand, can be absorbed if your system can perform work.

This is one of the most persistent misconception in climbing. It is frequently repeated by many experienced climbers.

So what?

Nobody is climbing with cables.

Not so much a misperception as it is an overly-analyzed problem that really isn't one.