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peroxide
May 29, 2004, 2:02 PM
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I AM EDITING MY ORIGINAL USEFUL POST TO AVOID CONFUSION AND ANY POOR INTERPRETATION THAT I ADVOCATE BAD FORM. I ADVOCATE LEARNING AND DISCUSSION BOTH FOR MYSELF AND OTHERS.
I answered a question about falling and load upon an anchor. As I showed with relevant examples (which seem to absent from a majority of the other posts) why there is no major difference in the quantity of force on the anchor (which is the orginal questions) due to maximum rope impact force.
Your question, which is BROADENING the topic, is whether this bigger fall is more dangerous from an anchor standpoint because of duration. Pragmatically, like I showed, most people don't TRY to get huge falls. The duration of the loading is of course longer and is only more dangerous if the placement shifts (which means you have entered a kinetic state where the coefficient of friction is less) or your protection is SOOOOOOOOOO close to the impact force limits and the piece fails do to this.
So yes that is more dangerous. Yet, since this is supposed to be pragmatic and reflect 99.99999% of reality, this would apply primarily to falling on RPs, micro cams, poorly set nuts, rope chocks, all with 25 feet of runout. Now if you are climbing like that and it is not obviously a risk...sheesh...
Trying to negate my points globally like this is just sad. Find me a person who interpreted my posts as advocating taking big whippers on marginal gear for fun... sheesh
Pride mixed with internet climbing discussions is like old eggnog.
It smells and no one wants to swallow it.
Summary (translated from flaming language to grown up talk):
Peroxide: The magnitude of impact forces are relatively uniform for a given fall factor and rope.
TedC: Duration matters.
Peroxide: Yes it does...good for you. The situations where this is important requires bad trad climbing like placing crap pro and running it out.
P
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peroxide
May 29, 2004, 2:19 PM
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VERSION 1.3
FIRST OFF
Curiosity is always an awesome trait to have…
Yes climbing is not all about math but hey…when was www.rc.com ever totally about climbing.
EXECUTIVE SUMMARY:
Force and Energy are different. Energy = Force * distance applied. So while a longer factor 2 fall will create MORE energy...you will have more distance (rope) to absorb the energy....therefore the FORCE will be essentially constant for a given fall factor.
5 MINUTE PHYSICS FOR CLIMBERS
1) Falling
As you ascend the rock, you are building energy (gravity between you and the earth and everything else). This is easily calculated through the easy to remember equation:
MAX = PE mass * acceleration of gravity * height = Potential Energy
A solo climber who pops off will achieve nearly all this potential energy upon impact (minus air resistance and little things but come on...thats being picky). Higher he is the harder he falls. Since we are discussing falls less than 60m (the length of your common rope), air resistance can be considered to be ZERO.
Since air resistance is ZERO, potential energy (the energy you can get) and the kinetic energy (the energy you get at the end of a fall) are equal. Essentially whatever you put in you get out in the end (never ever really happens in the universe…you have to always pay taxes).
Just trust me on this…
So PE = KE (potential = kinetic)
Well KE = 0.5 * m * x2 = 0.5 * mass * distance squared
So if I dust of my calculator here and say a person jumps off a ladder at heights of 2, 4 and 6 meters (about 6, 12, and 18 feet), their speed at impact will be approx.
14, 20, 24 mph.
2) Falling on a static rope
If a rope is perfectly static then falling at the predescribed heights would be the equivalent to having a rope tied around your waist, have a friend gun a car to 14-24 mph and yank that rope tight. OUCH. This is why in the old days when ropes were not known for dynamic stretching you would do a dynamic hip belay. Letting the energy of the fall be absorbed on the back of the climber through friction (I did this while lowering a couch out of an apartment…I had lashing marks on my back)
3) Falling on a dynamic rope
A dynamic rope means that even though you paid for 60m, it will stretch if weighted (just jug a dynamic line and you will see how long it takes before you leave the ground).
This stretching can be described in non friendly science terms (but as stated above, I want to keep the lingo casual) or just to say that a certain amount of force (lets say your weight) will stretch the rope this many meters.
When you fall and the rope catches you, at that instant you are going at the 14-24 mph described above. But instead of stopping instantly, the rope begins to elongate. As the rope elongates, you decelerate (great word..just rolls off the tongue), and eventually come to a stop.
For a given fall factor, this deceleration is constant.
Why you ask… well you already understand how fall factors are calculated and why you can have a fall factor of 1.4 and fall 10, 20, or any number of feet. It just matters on length of fall and rope out between you and the belayer.
So lets look at 2 cases:
you have a fall factor of 1.5 in both cases but fall 10 feet in on and 20 feet in the other.
You will get to a higher speed in the 20 feet case but will have twice the rope out. So you have twice the rope out for twice the amount of energy absorption. So in the end you feel the same impact force and have the same deceleration.
But what happens when fall factor increases??
Well this means you have less rope out to absorb the energy…which means you have to decelerate FASTER….
4) The Anchor
SOOOOOOOOO…
Going back to the anchor…all falls of the same fall factor apply the same amount of force to the anchor. But, what ted is touching on is that the DURATION of the force before coming to a stop is longer.
The importance in duration is two fold:
--THE PIECE ITSELF IS OF MARGINAL STRENGTH (RPs, micro cams, etc.): If you load near the failure limit of the piece the microseconds will be critical if the piece partially fails and then drops the strenght well below its stated strength which is less than the appliec impact force.
--THE PIECE TO PLACEMENT FRICTION (soft rock, poor contact, thin cam in sandstone, etc.): If the force applied lasts to the point which passes the static coefficient of friction, which means the piece will begin to slip since the kinetic coefficient of friction is less, then the piece will fail.
However, to get into this situation in the first place requires pilot error since you are climbing above marginal pro (which is an inherent risk that is the responsability of the leader), running it out, or placing pro poorly (like in sandstone where using a thin cam instead of a metolius fat cam is more dangerous).
CORRECTIONS AND CLARIFICATIONS:
Please post or flame (posting nicely is far more effective and gentlemanly) away and I will do my best to expand, correct, or broaden the questions and answers.
Cheers,
Peroxide
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punk
May 29, 2004, 7:53 PM
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Now let me get the pencil and paper and do the math while I am flailing in the mid air to calculate the system integrity…. :lol:
Par the original question the way of generating FF2 is by falling DIRECTLY on to the belay device to your harness
If ever something like that happen to you then go home (provided that you still alive) and get some lessons and literature about redirecting the rope through anchor and still if you anchor will consist only of marginal placements place more then a handful of them and equalize them if u cant place multiple placements then grab the ol’drill and place a bolt if still in doubt just back off the climb (that where good solid skill of down climbing and back aiding come to play….what you don’t know how to do it….then you really earn yourself he tile of “PATZ of the year” …that is if u made it back in one piece) and learn how to prepare for unknown climb and to have true assessments of your personal and teammate abilities
:wink:
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bigga
May 29, 2004, 8:58 PM
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Jay,
What are you talking about man...
The "impact force" on the rope is your error, not mine my friend. Go look up what a ropes impact force really is, and then come back to me. I already have, and I'm not going to hash out everything I read again. Enough to mention that what it ISN'T is the maximum force a rope is rated to hold.
Quote : "A page-and-a-half ago you couldn't even calculate impact force."
Read back... I never needed to, wanted to, tried to, nor give a sh*t about calculating impact force on a rope. But thanks for your personal input to this thread.
As far as my "mathematics" goes. It may be correct, it may not be. What the hell's eating you? All I know is you haven't got a clue about my level of mathematics...
What do you think hmmm? Is this an Elitist thread? lol...
By the way... nice pics...
adios
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bigga
May 29, 2004, 9:03 PM
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Peroxide...
You must have spent a while writing that all out...
It may be a good idea if you post your post as an article... so people can look it up easier when they are interested in that stuff and dont have to search through threads...
Its good stuff.
Just a suggestion
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jt512
May 30, 2004, 5:56 PM
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In reply to: J The "impact force" on the rope is your error...
Huh?
In reply to: I never needed to, wanted to, tried to, nor give a sh*t about calculating impact force on a rope.
What exaclty is "impact force on a rope," anyway?
In reply to: By the way... nice pics...
Thanks. Credit to photoagrapher Climbsomething, who shot all but one.
-Jay
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jt512
May 30, 2004, 5:57 PM
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In reply to: J The "impact force" on the rope is your error...
Huh?
In reply to: I never needed to, wanted to, tried to, nor give a sh*t about calculating impact force on a rope.
What exaclty is "impact force on a rope," anyway?
In reply to: By the way... nice pics...
Thanks. Credit to photoagrapher Climbsomething, who shot all but one.
-Jay
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bigga
May 30, 2004, 7:26 PM
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Jay,
You braught up impact force of a rope at the very begining of this thread so I thaught you knew and I didn't, so I went to look it up, assuming from your posts that it is the maximum force the rope is tested to withstand.
Turns out "the impact force" rated on your rope is the amount of force the climber will feel in a factor 1.78 fall. In other words it is giving you information about the elongation of the rope, not its streangth. Streangth wise a rope has to be able to sustain 12KN of force in a fall, the absolute max, and all your other gear (except some traditional protection) is designed around that fact.
Check out this site if you're interested. http://flash.lakeheadu.ca/~lurock/factor2.html . He describes it very well.
By the way, double checking with a calculus professor, physics professor, statics professor and chemistry professor (all at my university), to check concepts and my numbers (just incase my numbers were bad like you said). Still holding strong on all counts. It seams like you have something against it man, but the concept is sound...
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jt512
May 30, 2004, 7:45 PM
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[duplicate]
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jt512
May 30, 2004, 7:46 PM
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In reply to: Jay, You braught up impact force of a rope at the very begining of this thread so I thaught you knew and I didn't, so I went to look it up, assuming from your posts that it is the maximum force the rope is tested to withstand...
I didn't post until page 3 of this thread, and I have never used the terms "impact force of a rope" or "impact force on a rope," both of which are nonsense.
In reply to: Turns out "the impact force" rated on your rope is the amount of force the climber will feel in a factor 1.78 fall.
No kidding.
In reply to: In other words it is giving you information about the elongation of the rope, not its streangth. Streangth wise a rope has to be able to sustain 12KN of force in a fall, the absolute max, and all your other gear (except some traditional protection) is designed around that fact.
You are so lost.
-Jay
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bigga
May 30, 2004, 7:49 PM
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Ur right,
It was Kurt...
my mistake...
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curt
May 30, 2004, 8:07 PM
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In reply to: Ur right, It was Kurt... my mistake...
The impact force figure associated with a particular rope DOES indeed relate to the maximum (peak) force felt by the climber, gear and belayer. That is all I said on this topic. Nowhere did I say it was related to the ultimate strength of the rope. I hope you are not disagreeing with this.
Curt
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bigga
May 30, 2004, 8:10 PM
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You didn't,
Like I said, I assumed... thats why I went to look. That was my fault not yours.
By the way, can anyone here be more specific then jay's " you are so lost " and leaving it there. I sincerely want to what is not correct about what I said. If there is anything.
thanks again
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alpnclmbr1
May 30, 2004, 8:58 PM
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Tedc and Curt:
You both support this conjecture that seems reasonable even to me, despite the fact that it has not been studied or quantified in any climbing specific way. Any speculation on the impacts of duration on cam placements in real rock is just that, speculation. I would assume it is a hard to quantify problem with a negligible effect or someone would of studied it already.
However when you look at the bigger picture it is friggin ridiculous. The reason you use a climbing rope instead of a steel cable is because of the “longer duration.”
Many people are aware that a lower rated maximum impact force rope is better. This is the same as offering a longer duration impact force.
Tedc: based on your IC scenario the only conclusion that I can come to is that you are advising running it out near the ground and sewing it up as you get further up the route. wtf
You guys did make one good point. A 15ft FF2 is worse then a 3ft one.
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jt512
May 30, 2004, 10:04 PM
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In reply to: You didn't, Like I said, I assumed... thats why I went to look. That was my fault not yours. By the way, can anyone here be more specific then jay's " you are so lost " and leaving it there. I sincerely want to what is not correct about what I said. If there is anything. thanks again
Unfortunately, the paragraph that I responded to in that way makes so little sense that it is difficult to see where your reasoning has gone wrong.
-Jay
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bigga
May 31, 2004, 6:37 AM
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Okay,
This is all I have been saying. Tell me if I'm wrong. The maximum force generated in the rope during a factor 2 fall is about 12KN. The piece that arrests your fall feels even more than that since the tension in the rope is pulling in the same direction from both sides of the piece
0
/ \
i.e. pieces that are meant to hold your fall need to hold an even higher force which is why the UAII requires 25KN for anchors and only 15KN for your harness.
I dont see how you can have a problem with any of that. Its basic physics.
Now back to the begining... My hole question was... based on this how can a cam rated 8KN or lower be considered a bomber piece. And as most people have told me so far it isn't. Obviously the piece can peform above its specs, and hold a larger force than its intended to, but its not a given that it will. In theory a cam should hold an infinite force, but its axle has a limit (quite a high one) and so does the rock that its placed in.
So... wheres the booboo in my reasoning? Something a little more helpfull than "you're lost" would be nice.
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alpnclmbr1
May 31, 2004, 6:57 AM
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In reply to: Now back to the begining... My hole question was... based on this how can a cam rated 8KN or lower be considered a bomber piece. And as most people have told me so far it isn't. Obviously the piece can peform above its specs, and hold a larger force than its intended to, but its not a given that it will. In theory a cam should hold an infinite force, but its axle has a limit (quite a high one) and so does the rock that its placed in.
Bomber in climbing could be equated to being good enough.
I have used pieces that are only good for 2.5kn. You just have to be aware of the limitations and behave appropriately. The same can be said of any piece of climbing equipment.
As far as how strong they are. What difference does the lab setting strength rating make as long as they never break on you in normal use?
I can think of only one or two instances where a cam has broken in use. Both due to previous misuse.
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bigga
May 31, 2004, 7:08 AM
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I agree with you.
The circumstances of going over the limit forcewise to actualy break a cam are probably extremely rare. And even then. the odds are that the rock would break first and the cam would pop since the force the rock feels is so much greater.
As someone whos never used them, I've just been trying to understand there limits. Its been pretty interesting so far.
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curt
May 31, 2004, 9:44 PM
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In reply to: Tedc and Curt: You both support this conjecture that seems reasonable even to me, despite the fact that it has not been studied or quantified in any climbing specific way. Any speculation on the impacts of duration on cam placements in real rock is just that, speculation. I would assume it is a hard to quantify problem with a negligible effect or someone would of studied it already. However when you look at the bigger picture it is friggin ridiculous. The reason you use a climbing rope instead of a steel cable is because of the “longer duration.”
Dan,
While it is often convenient to use the fall-factor in looking at peak impact forces in a fall, you must keep in mind that there is more to the story, as Ted has pointed out. The total amount of kinetic energy generated by the fall (KE = 1/2mv^2) still must still be absorbed somewhere, and as Ted has also pointed out, this is accomplished by the peak force acting on the gear for a longer time period. And, as far as gear failures or placement failures go, all of that energy generated and subsequently dissipated by the rope stretching is available to do work on the gear. This is very simple physics.
I can think of other failures, besides Ted's example of a cam placement in sandstone that would be real concerns. For example, the bending of a small camming device axle or deformation of small aluminum cams would certainly be more likely by applying a high force for a longer duration of time, rather than over a very brief period of time.
In a practical sense, you may be correct and this may be a second or third order concern. Still, it does go to show that not all falls with a given fall-factor are necessarily equal.
Curt
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alpnclmbr1
May 31, 2004, 10:10 PM
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Curt,
Name one thing that you can do to alleviate that concern, that is unique to the duration concept.
ie. we know that a longer factor two fall is worse then a shorter one.
I cannot think of anything besides using a higher max impact force rated rope.
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curt
May 31, 2004, 10:32 PM
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In reply to: Curt, Name one thing that you can do to alleviate that concern, that is unique to the duration concept. ie. we know that a longer factor two fall is worse then a shorter one.
OK, I am glad you now agree. You seemed to be arguing this point before.
In reply to: In reply to: In reply to: The time spans are irrevelant outside of theory... Your physics is fine. (I guess, I didn't check.) Your conclusion was absolutely incorrect. Your statement, quoted above, is wrong and, yes, dangerous to anyone who doesn't know any better. Peroxide is right and you are way wrong.
Curt
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alpnclmbr1
May 31, 2004, 10:40 PM
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All right maybe that is not a fair question, since you stated the practical sense comment.
As far as I know there is no basis for wanting to increase the max force on an anchor in order to shorten the duration of that load.
This is the only way that you can effect the duration of the absorbtion of a given amount of fall energy.
In reply to: The total amount of kinetic energy generated by the fall (KE = 1/2mv^2) still must still be absorbed somewhere, and as Ted has also pointed out, this is accomplished by the peak force acting on the gear for a longer time period.
"peak force acting on the gear" does not absorb anything unless the cam fails and then it is a minimal amount for most placements.
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alpnclmbr1
May 31, 2004, 10:45 PM
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In reply to: In reply to: Curt, Name one thing that you can do to alleviate that concern, that is unique to the duration concept. ie. we know that a longer factor two fall is worse then a shorter one. OK, I am glad you now agree. You seemed to be arguing this point before. In reply to: In reply to: In reply to: The time spans are irrevelant outside of theory... Your physics is fine. (I guess, I didn't check.) Your conclusion was absolutely incorrect. Your statement, quoted above, is wrong and, yes, dangerous to anyone who doesn't know any better. Peroxide is right and you are way wrong. Curt
Not at all. I attribute the difference between different length fall factor 2 falls to a difference in the magnitude of the fall forces versus the ameliorating factors such as belayer movement, harness, knots, non spherical falling body factors, etc.
The load duration factor is an open question in my mind.
Is what you are taking away from this concept the idea that somehow a short factor 2 fall is alright but a longer one is not? Of course not.
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curt
May 31, 2004, 10:54 PM
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In reply to: All right maybe that is not a fair question, since you stated the practical sense comment. As far as I know there is no basis for wanting to increase the max force on an anchor in order to shorten the duration of that load. This is the only way that you can effect the duration of the absorbtion of a given amount of fall energy. In reply to: The total amount of kinetic energy generated by the fall (KE = 1/2mv^2) still must still be absorbed somewhere, and as Ted has also pointed out, this is accomplished by the peak force acting on the gear for a longer time period. "peak force acting on the gear" does not absorb anything unless the cam fails and then it is a minimal amount for most placements.
OK, you still don't get it. The total kinetic energy generated by the fall (KE= 1/2mv^2) does indeed have to be absorbed somewhere. And, there is a hell of a lot more kinetic energy generated in a long fall, than there is in a short fall even though the fall factors of the two falls are identical.
So, how can that be? The fall factor is the same in both cases--therfore the impact force on the gear is the same. How do you then absorb all the additional KE generated in the longer fall? The answer is that the rope, as it stretches more and over a longer period of time, applies the peak force to the gear and climber for a greater time period. In that case, there is more total energy applied to the climber and gear and more chance for something to fail. That's all.
It doesn't mean you should use a higher impact force rope to shorten the duration of the energy absorption because with ANY rope of ANY impact force a longer fall will impart force to the gear over a longer period of time than a short fall will.
Curt
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curt
May 31, 2004, 11:04 PM
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In reply to: Is what you are taking away from this concept the idea that somehow a short factor 2 fall is alright but a longer one is not? Of course not.
I am not saying that a short fall-factor 2 fall is OK, but I am saying that a longer fall-factor 2 fall is worse than a short one, because of the "duration of force applied" effect we are discussing here. This is true for any given fall factor, not just ff = 2. There could be a higher chance for gear failure in that scenario. I believe that was TedC's original point.
Curt
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