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brenta wrote:Initially, when the rope has just come taut and the tensions are low, static friction prevents the rope from moving across the biner and the climber with less rope is decelerated more violently. However, the tension in the rope on his/her side increases until the difference in tension between the two sides cannot be compensated by friction. Then the rope moves.

Right, didn't think of that. Would be great to have some simulation to see how everything actually plays together.

So Brenta, pre-determined spacing of Pro and rope slack between the two individuals when planned simul technique at "old skool" grades at or above 5.8 through 5.10 has no bearing on the rope tension/slack issue?

Of course Brenta and Fortmental, the two of you are elite experts at this simul- climbing gig even though neither you two have actually participated in it at grades at or above 5.8. And lets not even think about the rope diameter 8.9 -11mm (all having a completely different stretch characteristic of their own) or whether one uses a Single or Doubles, potential rope drag factor that may occurred as well that was not addressed. Factors of their own that totally and most assuredly insert a whole new mechanical twist on the rope slack and stretch issue.

But please, do carry on with your hypothetical science of this situ.

I think it's interesting to get the theory straight first and then think about real life deviations and how they would affect the scenario.

95% or better chances that Reality will throw in variants that completely chuck the Theory deal right out the window.

The latest DMM Sling test results prove that and quite frankly, are very mind boggling. Another factor to be thrown into the equation that will end in totally different dynamic rope results between a standard 24" X 11/16" sewn runner, an 8mm x 24" Dyneema Sling or some different length Draws etc attached to the Pro etc.

Something else to remember, most slings and biners are rated a good 8-12 KN's greater than most Pro they are attached to. As the latest DMM tests show, the Dyneema Slings exert upwards of 22KNs of "static energy" before they blow. Thus, the Pro may indeed blow if one is directly attached to the Dyneema sling due to the force exerted on it from a simple 230cm fall directly onto the slackened Dyneema Sling. Read about the tests & Watchthe video and see for yourselves. Of course a dynamic rope will indeed incorporate a whole different set of factors. But, still a variable to be considered in this entire hypothetical equation.

Let's start from the end...

The Chief wrote:But please, do carry on with your hypothetical science of this situ.

...and remove a bit of confusion. There are two sub-threads to this discussion.

1. Analysis of Tom and Bill's accident. This is what you focused on in your initial comment, saying that you would have rather soloed. I disagreed, and still do, but there was nothing that one would identify with science in that sub-thread. So, your exhortation to "carry on" must refer to the other sub-thread, namely,

2. Analysis of a second's fall that pulls the first off the rock. No one involved in the discussion so far has direct experience of that situation. The issue is whether anything meaningful may be said through reasoning. You obviously claim it cannot. Let's review your argument.

The Chief wrote:So Brenta, pre-determined spacing of Pro and rope slack between the two individuals when planned simul technique at "old skool" grades at or above 5.8 through 5.10 has no bearing on the rope tension/slack issue?

Spacing of pro, be it pre-determined or accidental, and rope slack obviously affect rope tension at all kinds of grades. Even my neighbors' dog would know it if they had one.

Note that Tom fell on a section of Redguard that is significantly easier than 5.8. We are talking about 5.4-5.5 depending on exact position and guidebook. On the other hand, once the falling second has pulled the first off a vertical face, does it matter whether it was 5.4 or 5.12?

How did you come up with the 5.8 threshold? You didn't read carefully or maybe it wasn't just curiosity that made you ask those questions...

The Chief wrote:Of course Brenta and Fortmental, the two of you are elite experts at this simul- climbing gig even though neither you two have actually participated in it at grades at or above 5.8.

In fact, here comes the textbook example of ad hominem. More predictable than a Swiss train and as logically flawed as these things get.

The question is: When the leader is pulled into the top biner by the falling follower, does (s)he stop right there, or does the rope start moving through the biner?

What is your argument? Do you have one? Are you suggesting that since you have no way to tell, nobody does?

The Chief wrote:And lets not even think about the rope diameter 8.9 -11mm (all having a completely different stretch characteristic of their own)

It is well documented that the "stretch characteristics" of ropes correlate much better with rope brand than with diameter.

The Chief wrote: or whether one uses a Single or Doubles,

...or one strand of half rope, for that matter.

The Chief wrote: potential rope drag factor that may occurred as well that was not addressed.

Your syntax is getting a little garbled here; hence, it's not entirely clear whether you are referring to Tom and Bill's specific accident or talking of a second's fall. I'll stick to the latter. Of course, rope drag may have an impact, which goes from helping the first resist the pull from the falling second (positive) to increasing the effective fall factor for the first (negative).

The Chief wrote: Factors of their own that totally and most assuredly insert a whole new mechanical twist on the rope slack and stretch issue.

If you are just trying to say that real-life falls involve all sorts of factors that a simplified model leaves out, then, yes, of course, that's another of those things even my neighbors' dog would know if they had one.

If you are implying that consequently simplified models have nothing to tell us, then you are wrong, as thirty years of involvement in scientific and technological research would no doubt teach you.

Instead of taking advantage of others' experience in fields in which you have none, you always try to put them down as if you felt belittled. I know it's part of your Internet persona, which I kind of like (well, most of the time) and I'm not much irked by it. But, don't you ever suspect it would be easy for me to put you down? On the contrary, I spent time sanitizing my reply of unnecessary sarcasm so that this discussion may be constructive.

So, now I await your answers to my questions.

The Chief wrote:The latest DMM Sling test results prove that and quite frankly, are very mind boggling.

Actually, those results were mostly old news and well in agreement with the theory. The discussions they have stirred have been primarily on how realistic it is to use a rigid mass in place of a human body.

The Chief wrote:As the latest DMM tests show, the Dyneema Slings exert upwards of 22KNs of "static energy" before they blow.

The kN is a unit of force, not energy.

brenta wrote: The discussions they have stirred have been primarily on how realistic it is to use a rigid mass in place of a human body.

My initial point exactly.

This particular test clearly shows the difference between types of slings, their dynamic (or lack of) impact within the systems and the addition of many more variables within your hypothetical equation.

Anyone taking falls on a regular basis would understand the factors in which this test shows and how this difference of material alone, can make a bigass difference on the final impact of a fall throughout the system.

"The question is: When the leader is pulled into the top biner by the falling follower, does (s)he stop right there, or does the rope start moving through the biner?

What is your argument? Do you have one? Are you suggesting that since you have no way to tell, nobody does?"


There is no solid answer as there are many variables that can be thrown into this equation. First being the difference of weight between the two individuals(obvious if the leader weighs more or less than the follower). The second being the amount of rope slack between the two. The third being what type of (Single or Double Rope System) Rope and Diameter etc. The fourth being if the Pro fails and if so, how many pieces within the system do thus elongating the fall etc. The fifth being rope drag as I mentioned. The sixth being how much rope is out. The seventh is the amount of "Air Time" versus frequent impacts during the actual fall. Etc etc etc.

Anyone that takes falls on a regular basis would clearly understand the "Insanity" I speak of. Far too many variables in the Real World of falling to allow for any set conclusion. Just can't be done.

Example: I took a 25 footer just last week on a slab route with the rope being out over 90' and I 10' above my last piece/bolt. My partner felt a very slight tug when it all came to an end. The week prior a 20 footer with almost the same results and the fall was on an overhanging crux with 100' of rope out clipped through 14 bolts.

Point: One can paint a picture on a canvass. But when the reality of it all comes true, that real picture becomes something that looks absolutely nothing like that which was originally painted.

5.8 was just a generic number that I threw into this equation as it is a conservative rating that I see most folks these days are climbing at out in the "real world" of trad.

The Chief wrote:[b]
[i]"The question is: When the leader is pulled into the top biner by the falling follower, does (s)he stop right there, or does the rope start moving through the biner?


There is no solid answer as there are many variables that can be thrown into this equation.

There is no solid answer as long as you ignore high school level physics. For the lead climber to stop and stay right at the biner, there would be infinite force applied to the leader, the rope, and the anchor. Figuring this out takes no knowledge of climbing. All the variables you mention would affect how far the leader fell past the biner, but not if.

mconnell wrote:"The question is: When the leader is pulled into the top biner by the falling follower, does (s)he stop right there, or does the rope start moving through the biner?"

The Chief wrote:

There is no solid answer as there are many variables that can be thrown into this equation.

There is no solid answer as long as you ignore high school level physics. For the lead climber to stop and stay right at the biner, there would be infinite force applied to the leader, the rope, and the anchor. Figuring this out takes no knowledge of climbing. All the variables you mention would affect how far the leader fell past the biner, but not if.

First of all, that is not relevant to the question posted.

If the Leader in a similar case relevant to the original question, weighs 200 or so pounds and the follower weighs 70-80 lbs less than that, the rope distance is 40-50 meters between them, lets say 10-15 pieces of solid placed pro, the Leader is 3-5' above the last placed piece, with substantial rope drag due to improperly placed runners, or lack of, this situ makes no impact on your high school level physics text book answer?

OooooKay!

brenta: 1 The Chief: 0

It's like watching a SNL skit between an astrophysicist and the captain of the football team.

Who gives a tish about all of the universalburificationtochaosasafunctionofnonlineartemporaldisplacements here. Bottom line, you embrace a certain level of risk when a team chooses to simul pitches- this freedom of choice is what makes the hobby/sport/way-of-life appealing to many an adventurer worldwide. No one gives a flying sh*t that you would rather solo 5.8+, go to supertopo to spray. No one wants to read deep into the X^2 = fCx^3 if X-.000000323=q crap. I want to see the accident report. I want to see what can be done to prevent this. I want to spread the word to my partners. Give me something palatable, digestible and easy to sh*t out. This thread should have been tamed a page ago.

Keep It Simple Stupid

knoback wrote:"Life is short. The Art is long. Experience is difficult." Hippocrates said that about medicine, but it's true of climbing, too. The basic physics does matter, and if you don't understand it, you are going to f-up. You just have to avoid applying it too broadly. That seems to be Chief's basic point. Anecdotal evidence alone is just bullshit. "Fall on Rock/Ice, Failed to Place Adequate Protection" - this kind of discussion is way more useful than those sorts of insights from ANAM. Thanks for the analysis y'all.

Pheeeeeeeeeeeew.... thanks Knoback. Thought maybe any sorts out there with any experiential climbing and real good falling time may have actually gone astray.

It's not a matter of being right or wrong nor keeping score.

It's a matter or sharing real time experiences with all the variables for me. Not what is put down on paper, tested in the control enviro of a lab then written in "the text book".

Bottomline, each and every situ and scenario is completely different. As are each and every individual that ties into a rope and gets on the rock. Current time variables play a big factor in every incident in the end and none are the same as the other, none. Nor can a text book formula mathematical analysis answer be applied to them all. Impossible.

But some just don't get that side of the story I guess. They would rather pat one another on the back in agreement and not be the one to stand up and throw in the proverbial wrench named reality. Nope. That doesn't go well when shoulder to shoulder within the tribe.

If they did, they'd be banished to the corner or even tossed out the door and deemed a lunatic.....oh well.

As for the OP, remember, nothing is always what some or all may perceive it to be. Appears the latest reality of variables is a broken hold that may be the match which initiated this particular conflag.

I'm all for not making broad, far-reaching claims based on a controlled lab test or just a few observations. But both of the following two claims are ridiculous:

1. There is still disagreement on the physical reality of a simul-climbing fall, and because it is so complicated with so many potential variables, it is impossible to know what will happen and we should give up trying.

2. We're not 100% sure a simul-climbing fall will be safe and work in the way some think it will, so you should always just climb unroped instead.

Yes, it's complicated. No, I don't understand the physics. And even physicists may disagree on what would happen here. But the bottom line is that one of these guys is alive because they were tied together, so the system "worked" in my view. I'd prefer to get fucked up in a bad simul-climbing fall caused by my partner falling then watch him careen down a wall because we thought it safer to climb unroped. It's all situational, but this particularly incident has not made me any less likely to choose simulclimbing as a viable option in the mountains.

Time to wrap up and move on. Chief, I'll make one last attempt to explain why mconnell got the right answer and gave the right reason. I'm making this non-insignificant effort for you. Please, read carefully.

We'll start from the ideal case and then, once we understand that, we'll move on to include the "real world disturbances" that trouble you so much.

We need two important laws of Physics:

1. Newton's second law of motion says that the acceleration of a body is proportional to the force applied to it. If you want to stop a falling body in a short distance, you need to apply a large force. If you want to go from 0 to 60 in 5 seconds in a big truck you need more torque than in a bike.

2. Hooke's law of elasticity says that the force exerted by a spring is proportional to its stretch. This proportionality law applies to ideal springs, but we'll see that we can use it for non-ideal real ropes too. The reason is that we only need to assume that the force grows with stretch, not that it is exactly proportional, and that is true of real ropes for not too large stretches, which is all we need. The other important observation is that a long rope is a weaker spring than a short rope. Any climber is aware of that.

Our ideal case has no friction and two identical climbers taking completely clean falls at the same non-zero speed. There is only one piece of pro. There is no slack in the rope and the mass of the rope is negligible compared to the mass of the climbers. We ignore air drag and make other reasonable assumptions of that nature. Once again, we review the ideal case because it provides a baseline for the analysis of real falls.

As the climbers fall, the rope goes through the biner connected to the only piece of pro until the leader hits the biner. At this point both climbers start decelerating. Why? Because the rope is "caught" in the biner and opposes their fall. The rope stretches and in so doing applies a force to the climbers.

Suppose for a moment that the rope were locked off at the biner as soon as the leader reaches it. Then, effectively, the leader and the follower would be falling on two separate ropes: one very long, and the other very short. The long rope would give the follower a very soft catch, but the very short rope would produce forces so high that something would probably break.

However, the rope is not magically locked off at the biner. Therefore, in the absence of friction, it stretches uniformly. This means that its tension is uniform, which means that the two identical climbers are decelerated at the same rate. Since their initial speeds are equal, they remain equal. This can only be achieved by rope moving through the biner from the second's side to the first's side, because initially there is no rope of the leader's side.

All right, we made it through the ideal case. We didn't write any equations. Rather, we did a little bit of what in some circles is called Qualitative Physics. We concluded that in the ideal case, the leader is not stopped abruptly, but decelerates at the same rate as the follower. The middle point of the rope does not move. Each half of the rope arrests one climber. Since the rope that arrests the leader is half the rope between the leader and the second, it is as if the fall factor had been doubled. On the other hand, if the leader had fallen from 10 feet above the last pro in pitched climbing, the rope would have come taut after a 20 feet fall, whereas here it comes taut after just 10 feet because the second is "taking in slack."

Let's not get caught in these details, though, because we still have our main task to undertake.

Let us first assume that everything is like before, but there is friction between rope and biner. The effect of friction is that the tension in the rope is no longer the same on the two sides of the biner. However, it cannot be arbitrarily different. Friction can only do so much. Initially, friction is strong enough to prevent slippage of the rope, but as the very strong spring on the leader's side tries to stop him/her in a very short distance, its tension grows very quickly, which creates a large imbalance until the rope slips.

Something must be noted here. We have not made precise assumptions about the forces. Once again, we have resorted to a qualitative argument. The reason why this works is that the rope on the leader's side is initially so short (in fact, we are assuming zero length) that if no rope slipped through the biner, the imbalance would grow enough to exceed friction. Friction is a complex phenomenon, but once again, we don't need the exact value of the friction force.

We have taken care of friction at the top anchor. Let us now look at weight imbalance between the two climbers. With little or no friction at the biner, we know that eventually the heavier climber will pull up the lighter climber all the way to the biner. Suppose the follower is heavier. Does that prevent the lighter leader from falling lower than the biner? No, because the tension on the follower side is now higher, but the tension on the leader side will grow indefinitely unless there is some slippage. Once it has grown large enough, slippage will occur. Eventually, the leader will bounce up, but that's not our current concern.

We account for more than one piece of pro in the same way. Additional pro adds friction. Friction makes it harder for the leader to pull rope to his/her side. However, if no rope slips, tension grows indefinitely. Hence, at some point, some rope will slip. Less rope than in the absence of friction, but still some.

Once we understand the basic argument, we see how to apply it to other factors. For instance, do we need to assume that the two climbers have the same initial speed? Of course not. Hence, the fact that they didn't have clean falls does not trouble us (though it's likely to trouble them).

Did we ever concern ourselves with the specs of the rope (diameter, impact force rating,...)? No, because from the beginning we stipulated to work only with a qualitative version of Hooke's law that makes no distinction between a Mammut Tusk and a Beal Stinger. In sum, our conclusion for the ideal case continues to hold in the real world.

brenta wrote:"Did we ever concern ourselves with the specs of the rope (diameter, impact force rating,...)? No, because from the beginning we stipulated to work only with a qualitative version of Hooke's law that makes no distinction between a Mammut Tusk and a Beal Stinger. In sum, our conclusion for the ideal case continues to hold in the real world."

There most certainly is distinction between 8.5 Doubles and an 11mm Single especially in the clipping of placed pro within the two distinctive rope techniques and if the pro blows on either system.

I am not concerned with impact force ratings here. Rather, I am concerned with elongation % between the two at 1st drop as both different systems certainly have a clear distinction between the two in a real world fall scenario. Especially if the first piece below the leader blows and there is slack in the the 2nd Double line or twice the amount of drag etc.

Whole different enchilada Brenta. And you would certainly know that had you ever taken substantially lengthy (25+ feet) falls on both systems. Because one will exert a greater initial force on the follower than the other due to their elongation % properties or lack there of.

This is a solid reason Aid (Simul or Belayed) Climbers will never use a Double Rope system.

Diameter of Rope & Rope Type used has much to do with Hooke's Law in this exact scenario and the initial load exerted on the follower.

And how bout them "Twins" for a 25-50 footer..... not!


Your original proposed question was regarding the leader getting sucked up into the first biner after the follower falls. And I say that if a large margin of weight exists between the two with the leader being heavier, the leader will have far less chances of this occurring if they are in fact heavier than the lighter falling follower.

"The question is: When the leader is pulled into the top biner by the falling follower, does (s)he stop right there, or does the rope start moving through the biner?"

Now, unless you do not take lengthy falls on a regular basis, I do not expect anyone here to even begin to understand this reality.

brenta wrote:"Once we understand the basic argument, we see how to apply it to other factors. For instance, do we need to assume that the two climbers have the same initial speed? Of course not. Hence, the fact that they didn't have clean falls does not trouble us (though it's likely to trouble them)."

Odd, as leader speed increase (distance) or decreases, you are saying that it doesn't play a major factor in the initial Impact Forces on both the elongation properties of the rope and the initial force exerted on the follower? Nor the distance of rope out between climbers either?

The conclusion I came to continues to hold even if we contrast a Tusk and an Ice Line. Your bringing up the single vs. double issue shows that you didn't understand what I wrote at all. Same with the comment about the "large margin of weight."

The Chief wrote:Odd, as leader speed increase (distance) or decreases, you are saying that it doesn't play a major factor in the initial Impact Forces on both the elongation properties of the rope and the initial force exerted on the follower? Nor the distance of rope out between climbers either?

I have said none of that. If you think I did, you should really work on your reading comprehension. Take it easy, one sentence at a time, figure out what it means--which is not whatever hogwash you'd like me to say so that you could prove it wrong--until the big picture emerges.

You are on your own, though. I said it was my last attempt. I'm done with this thread.