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hafilax
May 13, 2009, 6:37 PM
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pfwein wrote: Thanks to all of you who addressed my Q re: pulley effect. One thing I don't think I've seen addressed: at a hanging belay, the anchor is also holding the weight of the belayer, so when the fallen climber comes to rest, the anchor will be holding both the weight of the belayer and the climber, regardless of whether the climber clipped the anchor, right? And before the climber comes to rest, it seems that the rope will just be elongating based on the climber's weight, the length of the fall, and amount of rope between the climber and the belay device, which again doesn't depend on whether the anchor is clipped,except the fall will be slightly shorter when the anchor is clipped (maybe I'm wrong on this point??). I'm just having a hard time visualizing why clipping the anchor increases the force on the anchor when the only thing it seems to do is redirect the direction of the force and slightly decrease the length of the fall (both definitely good things), but thanks again to you who attempt to explain it.
If you belay directly off the anchor or harness with no slack to the anchor, the force on the anchor will be equal to the force felt by the faller. The belayer will have to hold the full force of the fall whereas by running the rope over a biner attached to the anchor he will only have to hold 75% of the force of the fall but the force on the anchor will be greater. Pick your poison.
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hafilax
May 13, 2009, 6:41 PM
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jrathfon wrote: so, i am leary to use this as then i wouldn't be able to counteract majidiots BS, but does anyone have that rc.com fix where i can ignore his posts?
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jrathfon
May 13, 2009, 6:43 PM
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at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all).
there are 2 cases in your question:
(A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying)
(B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck.
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jrathfon
May 13, 2009, 6:51 PM
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hafilax wrote: jrathfon wrote: so, i am leary to use this as then i wouldn't be able to counteract majidiots BS, but does anyone have that rc.com fix where i can ignore his posts? You could be mature and read Majid's posts with an open mind and ignore his trolling or you could search for 'killfile'. I don't see why people feel the need to digitally block people out. It's quite easy to do in analog and occasionally even an idiot has something interesting to say.
you beat me to that explanation, but i was basically going to add, "damned if you do, damned if you don't" aka "pick your poison".
i was more joking about using the killfile, because though i don't think majidiot has anything useful to say, he can be entertaining.
i don't think having a predetermined opinion that all of what majidiot says is BS is immature, maybe narrow-minded, but i'll be right about 99.9% of the time, so i'm happy with that. i'm happy to be open-minded and have discussions with everyone on this site, with the obvious one exception.
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colatownkid
May 13, 2009, 6:57 PM
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majid_sabet wrote: jrathfon wrote: majid_sabet wrote: colatownkid wrote: pfwein wrote: loyota wrote: . . . and only a few 10KN carabiners fail in closed gate mode. What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that. And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor the "pulley effect" occurs when a load on one side of a pulley is counteracted by an equal load on the opposite side. suppose a climber has come to a stop after having fallen. the carabiner on uppermost piece of gear is effectively acting as pulley--the climber is hanging on one side, the belayer is hanging on the other side. simply hanging there, the climber's weight must exert some force downward (we'll call it x). in order for the climber to be stationary, the belayer must be exerting an equal force down (also x). therefore, that top piece of gear must be supporting both the full weight of the climber and the belayer or 2x. hence, the total force is double what the climber would place on the piece by himself. the same principle applies in a moving system where the climber is falling, but we know that in reality the belayer will get pulled into the air, so the doubling is only an approximation. this is significant in the scenario i described earlier because there is no pulley effect in a factor-2 fall. the climber simply falls directly onto the belayer's belay device. when the system has come to rest (hopefully it does so before both people have hit the ground) the anchor is supporting the weight of the fallen climber directly, not through a pulley. in the high-factor scenario where the anchor has been clipped, the anchor is supporting the weight of the falling climber through a pulley, meaning it has to hold double the force. let's suppose the factor-2 fall resulted in a force of 8 kN and the high-factor fall resulted in a force of 6kN (totally arbitrary numbers for the sake of example). 2 x 6 = 12, so the high-factor fall actually results in a higher force (12kN) than the factor-2 fall (8kN) thanks to the pulley effect. the real issue though is that it's extraordinarily difficult to catch factor-2 falls (no personal experience here, so somebody feel free to refute me). this is exacerbated by the fact that when catching a factor-2 fall directly, the belayer's ATC will invert, meaning that the locked position is pulling the rope up, not down, making a catch even more awkward and difficult. because of this, it might be a good idea to clip the anchor despite the higher potential force simply so it is easier for the belayer to catch the fall. note, The carabiner does not act as pulley device in FF but a friction device therefore it reduces the fall factor by small amont as mentioned in the PDF I provided above . During a leader fall, we are not getting a true FF2 but some thing like FF 1.75 +- . I think the only way we could get a true FF2 is to attach a climber to solid steel cable and drop him above an anchor and without any protection in between. Hey Angry. you want to try this for me? come on, I buy a candy majidiot, the FF does not depend on the rope used. as per YOUR reference, FF = the total distance fallen / rope out. if you want to calculate peak force, you must factor in the elasticity of the rope. using a steel cable will increase this max force, but NOT the FF. b) THEGUY provided the references explaining the friction factor of the pulley effect decreasing force in the system, NOT FF. you did NOT provide this information. again, you're an idiot. or perhaps i should translate this into rc.com vernacular: "your' an idiot's." First off, try to learn how to communicate with people instead of using the word idiot or whatever. 7 years old kids call each other idiot. You are a college grad and I thought at least they teach you how to talk to people.
it seems that some of us are confused as to what exactly a "fall factor" is. the fall factor is defined as the distance fallen divided by the total amount of rope in the system between the belay and the falling climber.
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force. it just so happens that the more rope is available, the more energy can be absorbed.
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.
since rope is dynamic and not static, the force in the fall is more complicated. as the length of the fall increases, the force also increases. however, since the rope is dynamic, a longer fall results in more energy-dissipating rope stretch since more rope must necessarily be out for a longer fall to happen.
therefore, as a rough measure of force, it is more accurate to examine the fall factor, or the ratio of energy-dissipating rope stretch and the energy-creating fall. (note: to all physicists, i understand energy cannot be created. i just feel that this is a decent explanation in "plain english.")
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load. the importance of the fall factor is that it allows us to compare the relative magnitude of various falls, ALL OTHER THINGS BEING EQUAL. this means that if the knot cinches the same amount, the belayer moves the same amount, the climber falls on the same piece with the same friction on the same carabiner, the belayer hasn't lost any weight due to sweat, etc. than a greater fall factor will result in a greater peak force on the fallen piece.
however, these other things are never equal. for this reason the fall factor is, necessarily, an approximation. it is possible that due to various factors (some of which are listed above) a factor 1.2 fall might actually result in a lower force than a factor 1.1 fall. in general, however, these factors will be similar in many climbing situations, and since we're approximating anyway, are assumed to be equal.
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.
as far as the carabiner not being a pulley is concerned...
a pulley simply redirects force. a carabiner is certainly not an idealized, frictionless pulley, but it's function is the same.
majid is correct in stating that the friction over the carabiner does reduce some of the force. (his explanation involving fall factors is not correct, though.) the classic number used in climbing calculations is that the pulley will reduce the friction on one side by one-third, so the total force on the top-piece carabiner is five-thirds times the force of the falling climber ((5/3) * Force_Climber).
the idea that the factor-2 fall does not exist is ridiculous at best in my opinion. consider the leader who is 10 feet above the belay and has not clipped any gear (that is, the only thing between him and the long ride is a belay device). if he falls, he will fall 20 feet with 10 feet of rope in the system. BY DEFINITION, 20 / 10 = 2.
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)
i think what majid is trying to say is that the theoretical peak force in a very rough approximation that does not include friction will likely be higher than the theoretical peak force in a slightly-less-than-very-rough approximation that does include friction.
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hafilax
May 13, 2009, 7:04 PM
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You will never measure the force calculated from a unmodified fall factor 2 calculation in a climbing situation.
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colatownkid
May 13, 2009, 7:07 PM
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jrathfon wrote: at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all). there are 2 cases in your question: (A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying) (B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck.
quoted for correctness!
yep, so that is the dilemma: if there's no pro to be had in the start of the next pitch, do you clip the anchor or not?
one last thing to consider:
a lower fall factor does result in a lower force on the top piece. assuming the leader falls shortly after having clipped the anchor (or jesus nut, etc.), there is a point at which even the doubled force (well, 1.6 times or something like that) is still less than the force of a factor-2. in other words, if you clip the anchor as a directional, there is some amount of rope that can be out above the directional and the peak force will still be less than a factor-2. it's a win-win!
unfortunately, that distance is somewhere around 1 meter (depending on how you approximate and what conditions you use), so the point is pretty moot.
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colatownkid
May 13, 2009, 7:09 PM
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hafilax wrote: You will never measure the force calculated from a unmodified fall factor 2 calculation in a climbing situation.
not arguing with you there; just thought it might be instructive to explain the point of talking about fall factors in the first place.
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jrathfon
May 13, 2009, 7:13 PM
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colatownkid wrote: jrathfon wrote: at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all). there are 2 cases in your question: (A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying) (B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck. quoted for correctness! yep, so that is the dilemma: if there's no pro to be had in the start of the next pitch, do you clip the anchor or not? one last thing to consider: a lower fall factor does result in a lower force on the top piece. assuming the leader falls shortly after having clipped the anchor (or jesus nut, etc.), there is a point at which even the doubled force (well, 1.6 times or something like that) is still less than the force of a factor-2. in other words, if you clip the anchor as a directional, there is some amount of rope that can be out above the directional and the peak force will still be less than a factor-2. it's a win-win! unfortunately, that distance is somewhere around 1 meter (depending on how you approximate and what conditions you use), so the point is pretty moot.
unless your belayer is lowered out a bit from the anchor...
that's why a VERY truck piece above the anchor is better than a leg of the anchor itself, it's higher in the system, thus the fall is shorter.
the force on that jebus piece also exemplifies why using one leg of a trad anchor as this piece may not be the best idea.
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jrathfon
May 13, 2009, 7:18 PM
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just for the ease of the catch, i always clip that directional on the bolt if the climbing is hard, and i make sure i'm either solid, or getting gear in fast off the belay. i don't want my belayer to have to catch a non-directionalized fall, and although i'm fat, i think that fatty 3/8" stainless steel bolt in granite will hold me falling the 10ft with 8ish feet of rope. see? no FF2! [sarcasm]it doesn't exist![/sarcasm]
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clews
May 13, 2009, 7:31 PM
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you're definitely more right than the previous post.
you definitely can't calculate impact force just by your fall factor
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colatownkid
May 13, 2009, 7:54 PM
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jrathfon wrote: colatownkid wrote: jrathfon wrote: at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all). there are 2 cases in your question: (A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying) (B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck. quoted for correctness! yep, so that is the dilemma: if there's no pro to be had in the start of the next pitch, do you clip the anchor or not? one last thing to consider: a lower fall factor does result in a lower force on the top piece. assuming the leader falls shortly after having clipped the anchor (or jesus nut, etc.), there is a point at which even the doubled force (well, 1.6 times or something like that) is still less than the force of a factor-2. in other words, if you clip the anchor as a directional, there is some amount of rope that can be out above the directional and the peak force will still be less than a factor-2. it's a win-win! unfortunately, that distance is somewhere around 1 meter (depending on how you approximate and what conditions you use), so the point is pretty moot. from the anchor... that's why a VERY truck piece above the anchor is better than a leg of the anchor itself, it's higher in the system, thus the fall is shorter. the force on that jebus piece also exemplifies why using one leg of a trad anchor as this piece may not be the best idea.
in that case it's hardly a dilemma.
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majid_sabet
May 13, 2009, 8:13 PM
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hafilax wrote: Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor. The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms. A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system. It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.
That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening.
When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2?
What happened to the piece in the middle that actually slowed his fall?
Why can’t we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?
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jrathfon
May 13, 2009, 8:13 PM
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lookin' for tools to solve a problem. but sans piece above the anchor, lengthening your belayer's stance could help. screamer on said piece/anchor leg as well?
anyways i think there is now a lot of data for the OP's question:
as per BD, 2-5 kN in a "typical" spurt-climbing fall
as per UIAA you want your gear rated better than 7 kN
a 2 kN micronut with a yates screamer (3-4 kN reduction) gives you a piece which could hold the "typical" mid-pitch fall of 2-5 kN. not sayin' I'd be happy 2 body lengths above that.
UIAA also makes a point that if loaded equally a cluster of tiny pieces could get the job done, neglecting whether or not the rock holds...
i've fallen on a #1 BD stopper at the top of a pitch and it held, course i couldn't remove it afterwords...
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desertwanderer81
May 13, 2009, 8:19 PM
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majid_sabet wrote: angry wrote: I'm not sure that's how it works. I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors. 1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope. Please correct me if I'm wrong, but I think you've got to be mistaken. wrong girl 1 KILO mean 1000 chingon you sould say 1N =100 kg or @ 224 lbs
You fail at math.
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desertwanderer81
May 13, 2009, 8:20 PM
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majid_sabet wrote: rocknice2 wrote: Worst real world fall??? Not counting FF2. I'm starting P2 and it's hard right off the bat. I climb up a bit [feet level with belay device] and plug a cam and clip it. Now the cam is 7ft above belay device and 10ft above ledge. I struggle up until the cam is at my feet and plug a nut. I'm so pumped fiddling with the nut and can't stabilize for the clip. I bitch, scream and cry in that order. Finally I peel off. I take a 6 footer on 10 feet of rope = 6kn Even more realistic the belayer worries I might deck and manages to take in an arm length of rope in. A 6 footer on 8 feet of rope = 7.5kn there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.
And what would you call it if someone is being belayed on a pitch and falls without placing any pro???........
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jrathfon
May 13, 2009, 8:20 PM
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majid_sabet wrote: hafilax wrote: Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor. The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms. A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system. It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from. That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening. When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2? What happened to the piece in the middle that actually slowed his fall? Why can’t we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?
So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible.
As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out.
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jrathfon
May 13, 2009, 8:23 PM
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desertwanderer81 wrote: majid_sabet wrote: angry wrote: I'm not sure that's how it works. I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors. 1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope. Please correct me if I'm wrong, but I think you've got to be mistaken. wrong girl 1 KILO mean 1000 chingon you sould say 1N =100 kg or @ 224 lbs You fail at math.
and physics.
Though I have a question for you majidiot: what's with the crafty use of bold text which typically does not illustrate your point?
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majid_sabet
May 13, 2009, 8:24 PM
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jrathfon wrote: majid_sabet wrote: hafilax wrote: Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor. The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms. A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system. It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from. That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening. When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2? What happened to the piece in the middle that actually slowed his fall? Why can’t we say that he fell 15 feet (from that piece) or 17.5 feet or whatever? So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible. As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out.
(This post was edited by majid_sabet on May 13, 2009, 8:24 PM)
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shockabuku
May 13, 2009, 8:24 PM
Post #70 of 211
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hafilax wrote: You will never measure the force calculated from a unmodified fall factor 2 calculation in a climbing situation.
That's a rough sentence.
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jrathfon
May 13, 2009, 8:28 PM
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majid_sabet wrote: jrathfon wrote: majid_sabet wrote: hafilax wrote: Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor. The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms. A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system. It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from. That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening. When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2? What happened to the piece in the middle that actually slowed his fall? Why can’t we say that he fell 15 feet (from that piece) or 17.5 feet or whatever? So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible. As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out. no I was not refering to you as the college boy but the other guy
then why'd you quote a post that was in direct response to me? eh?
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hafilax
May 13, 2009, 8:34 PM
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I don't really know what happens when a piece pulls. I think it depends on how much the rope is able to recover before being stretched again since the damping in the rope is the primary energy dissipation mechanism (AFAIK).
If the rope doesn't recover at all then that piece pulls then the force applied to the next piece won't be reduced by very much. It would be as if that first piece wasn't there.
My intuition says that there is some recovery of the rope and that pulling a piece does lower the impact on the rest of the system but I have no idea by how much. I think would depend on how quickly the pieces are sequentially loaded, on how much the rope was stretched to begin with, etc.
The last time this subject came up I started reading papers discussing this but didn't find anything that satisfied my curiosity. There was a drop test experiment where an upper piece was designed to break at a certain peak force and subsequently caught by another. I can't remember the conclusion of that paper. I do remember thinking that the current physical model of dampers and springs for a rope doesn't describe the dynamics all that well, especially in the recovery after being stretched. The rope measurements showed more hysteresis than the model and I remember them adding a fudge factor in there to improve the fit.
There are folks here who have looked into this far more than I have so maybe they can chime in. adatesman has links to some of the rope dynamics papers somewhere in the Needless Destruction Theater.
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majid_sabet
May 13, 2009, 8:36 PM
Post #73 of 211
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jrathfon wrote: majid_sabet wrote: jrathfon wrote: majid_sabet wrote: hafilax wrote: Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor. The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms. A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system. It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from. That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening. When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2? What happened to the piece in the middle that actually slowed his fall? Why can’t we say that he fell 15 feet (from that piece) or 17.5 feet or whatever? So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible. As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out. no I was not refering to you as the college boy but the other guy then why'd you quote a post that was in direct response to me? eh?
I was only saying in bold that I do get an enjoyment out of messing with other people who disrespect me and I was not referring to you at any shape or forml . I also wanted to ask you about the falling climber while loading the piece below and you kind of answered my question.that is all
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desertwanderer81
May 13, 2009, 8:41 PM
Post #74 of 211
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majid_sabet wrote: jrathfon wrote: majid_sabet wrote: jrathfon wrote: majid_sabet wrote: hafilax wrote: Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor. The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms. A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system. It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from. That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening. When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2? What happened to the piece in the middle that actually slowed his fall? Why can’t we say that he fell 15 feet (from that piece) or 17.5 feet or whatever? So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible. As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out. no I was not refering to you as the college boy but the other guy then why'd you quote a post that was in direct response to me? eh? I was only saying in bold that I do get an enjoyment out of messing with other people who disrespect me and I was not referring to you at any shape or forml . I also wanted to ask you about the falling climber while loading the piece below and you kind of answered my question.that is all
That's the thing though! The only way you EVER mess with people is by filling thread after thread with disinformation. Your understanding of math, physics, and even climbing is limitted to the point that you should never, ever comment on anything as almost without fail, it will be wrong!
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hafilax
May 13, 2009, 8:47 PM
Post #75 of 211
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Maybe it comes from years of marking 1st year physics labs, but I don't find Majid to be as 'wrong' as the haters make him out to be. You just have to filter out the trolling.
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