Dogbones

If you are worried about fall factors while sport climbing, chances are you have done something very, very wrong.

William Kramer wrote: Get that, no factor 2 with the rope in the system, and also back to wires on a nut will fail before the sling, the knot test in the video link posted just got me wondering. What other ways do you do an alpine draw?

Eh, close, but not quite. A fall factor is defined as the vertical distance of the fall divided by length of rope (or sling, or whatever) out from the belay from the fixed and of the rope (usually the belay) to the climber.

In the normal use of the phrase, a factor 2 fall is one in which the climber climbs above the belay (say, 10 feet), has no pro, and falls all the way underneath the belay (20 foot fall). 20ft/10ft = 2. The rope is clearly in the system, as the factor 2 is onto the rope, onto the belay, but it's still a factor 2 fall.

If the climber places a piece 10 feet up (ignoring extension length), climbs up another 10 feet, and falls, there is 20 feet of rope out, and a fall of 20 feet. 20ft/20ft = fall factor of 1. If the piece was slung 2 feet out (so that the rope met the bottom of the sling 8 feet from the belay and took a fall from the same height (20 feet from the belay), the fall would be 24 feet long with 20 feet of rope out. 24ft/20ft=fall factor of 1.2.

The analogous situation with a 2 foot sling is if a person has a sling attached directly from the harness to the piece (bolt, gear, whatever), climbs up 2 feet, and falls. A factor 1 is if he/she falls with his/her waist at the piece. Don't ever let this happen.

All things equal, taking a factor whatever fall onto a rope is MUCH better with a dynamic rope than a relatively static nylon sling, which is in turn substantially better than doing the same on a very static dyneema sling.

shoo wrote:If you are worried about fall factors while sport climbing, chances are you have done something very, very wrong. Eh, close, but not quite. A fall factor is defined as the vertical distance of the fall divided by length of rope (or sling, or whatever) out from the belay from the fixed and of the rope (usually the belay) to the climber. In the normal use of the phrase, a factor 2 fall is one in which the climber climbs above the belay (say, 10 feet), has no pro, and falls all the way underneath the belay (20 foot fall). 20ft/10ft = 2. The rope is clearly in the system, as the factor 2 is onto the rope, onto the belay, but it's still a factor 2 fall. If the climber places a piece 10 feet up (ignoring extension length), climbs up another 10 feet, and falls, there is 20 feet of rope out, and a fall of 20 feet. 20ft/20ft = fall factor of 1. If the piece was slung 2 feet out (so that the rope met the bottom of the sling 8 feet from the belay and took a fall from the same height (20 feet from the belay), the fall would be 24 feet long with 20 feet of rope out. 24ft/20ft=fall factor of 1.2. The analogous situation with a 2 foot sling is if a person has a sling attached directly from the harness to the piece (bolt, gear, whatever), climbs up 2 feet, and falls. A factor 1 is if he/she falls with his/her waist at the piece. Don't ever let this happen. All things equal, taking a factor whatever fall onto a rope is MUCH better with a dynamic rope than a relatively static nylon sling, which is in turn substantially better than doing the same on a very static dyneema sling.

Thanks, nice explanation. Thus the importance of that first anchor after belay. I do all the things suppose to do, just trying to understand why. Had good idea why, but wasn't 100% on it (still not, but closer), and most forums on the subject are pissing matches, so thanks for the lesson, do appreciate it

This is a bit of a derail, sorry, but I'm really curious about using the math of fall factors for static materials.

The original theory stems from the fact that by happy accident the distance fallen can be ignored, but I thought that was due to the elasticity of the rope. So long falls required lots of rope, which means more rope to absorb the higher energy of long falls. Short falls have less energy, but less rope. By cosmic coincidence these factors can eliminate a lot of complicated physics in estimating the force of a fall. So we can compare relative magnitude of falls without concerning ourselves with distance fallen.

That's my memory of the blurb from Mountaineering: Freedom of the Hills when it described fall factors.

Does the math really work out the same with static or semi-static materials? I wouldn't be too surprised if it was still close. I've always been leery of assuming falls onto Dyneema or other static materials can be adequately described with only the fall factor.

An imaginary and completely inelastic substance would seem to make the fall factor math false, at least. Meaning, distance fallen and attached mass has to come back into play to determine force. Meaning each fall is back into needing a case-by-case analysis to understand.

I'd be willing to bet that the most falls on static slings directly tied to bolts, happen on sport routes, and involve someone wearing a PAS..

teece303 wrote:This is a bit of a derail, sorry, but I'm really curious about using the math of fall factors for static materials. . .

The FALL FACTOR is the same, regardless of materials. The FORCE caused by a given fall factor is NOT the same. The primary driver of why the force is different given a fall factor is the elasticity of the materials. Thus, a more elastic material (nylon rope) will result in lower forces (on the anchor, person, and sling/rope) than a less elastic material (static slings).

If you are really interested in the physics, one thing to keep in mind is that this is a vastly simplified model. In reality, ropes and other materials don't perfectly behave like ideal springs, but they come fairly close. The fall factor math takes into account that ropes are close enough to ideal springs to simplify the math of estimating fall forces. Furthermore, things like the friction over carabiners, the malleability of falling objects (people fall), dynamic elements in the system (like belayers) make substantial impact on actual forces exerted during a fall.

Another thing to keep in mind is that I am not a physicist.

Indeed, the fall factor is the same either way. But it may or may not be useful for anything, is my curiosity.

Fall factor tells us nothing if the arresting material is completely inelastic. It is a very useful simplification for elastic climbing ropes.

But what about still elastic, but much less so, materials like Dyneema? Is the fall factor worth knowing with that material? I dunno.

I'm not a physicist, either, but math and physics are my friends. Perhaps a project for a rainy weekend...

teece303 wrote:Indeed, the fall factor is the same either way. But it may or may not be useful for anything, is my curiosity. Fall factor tells us nothing if the arresting material is completely inelastic. It is a very useful simplification for elastic climbing ropes. But what about still elastic, but much less so, materials like Dyneema? Is the fall factor worth knowing with that material?

Yes, fall factor still tells you something. Even a steel cable can be modeled as a spring. It's just a really, really stiff spring. If you look at the formula for impact force, such as en.wikipedia.org/wiki/Fall_… the spring constant or modulus of elasticity is multiplied by the fall factor.

A small fall factor still means lower force, but it has to be several times smaller on static than it would be with dynamic rope. This is why people can top-rope on static rope and not die, while a factor 1 fall on static rope, dogbones etc would be bad.