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bigga
May 27, 2004, 5:52 AM
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I just had a look at the ratings on small cams...
It looks like all the smaller cams have a rating of 7 or 8 KN. Under 10 anyway...
How could that be considered bomber if a factor 2 fall is rated at 25 KN?
I have a feeling I've missed something somewhere...
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curt
May 27, 2004, 5:58 AM
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In reply to: I just had a look at the ratings on small cams... It looks like all the smaller cams have a rating of 7 or 8 KN. Under 10 anyway... How could that be considered bomber if a factor 2 fall is rated at 25 KN? I have a feeling I've missed something somewhere...
Did you ever look at a rope's maximum impact force?
Curt
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hugepedro
May 27, 2004, 6:02 AM
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^^^ What he said. Plus, if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing.
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areyoumydude
May 27, 2004, 6:06 AM
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The impact force on most ropes range from 8.5 kn to 9.5 kn.
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bigga
May 27, 2004, 6:15 AM
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I see...
After you said that I had to retake falling 101 again. Had forgoten totally the different forces at different points in the climb and had somehow gotten the idea that a factor 2 fall is 25KN anywhere. Thanks for pushing me to the refreshers course...
although my mistake has given me a pretty big buffer in my calculations:)
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alpnclmbr1
May 27, 2004, 6:32 AM
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In reply to: The impact force on most ropes range from 8.5 kn to 9.5 kn.
This is the force felt by the falling climber. In a turnaround situation such as falling on a piece of gear can approach 16kn (1.6x Force)
As far as gear strengths. A 10kn piece will very very rarely fail in normal use.
Small cams are still not considered bomber.
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bigga
May 27, 2004, 6:39 AM
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Although it still doesn't make sence to me...
First of all the impact force given on the rope is not the maximum force it can withstand but rather the force the climber will feel in a 1.78 factor fall according to Ron Bessems at http://toad.stack.nl/~stilgar/calc.php
But as far as the the cam is concerned I still can't get it all strait. A factor 2 fall produces 12 KN of force on the rope. At any point where you thread the rope through protection the force is almost doubled since the rope is pulling on both sides of the biner which is why the UIAA requires Carabiners to hold 25KN.
So if on a 1.9 factor fall the rope feels 9KN, the protection you are falling on would feel about 15KN according to http://flash.lakeheadu.ca/~lurock/factor2.html.
Now I could be wrong here, but it looks to me that in this situation, you're rope is bomber, your biner is bomber, harness, sling... all bomber... but your cam is still not bomber..
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alpnclmbr1
May 27, 2004, 6:58 AM
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They could make cams twice as strong and they still would not be bomber and they would weigh twice as much.
The limiting factor is the placement, then the rock, then the cam itself. Cam do not break in normal use. I have never heard of an undamaged cam breaking in a fall situation.
Also, for the most part, you do not get a close to factor two fall in a turnaround scenario.
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bigga
May 27, 2004, 7:02 AM
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When you say placement, do you mean the quality of the crack you are placing the protection in? ie angle, tapering etc?
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alpnclmbr1
May 27, 2004, 7:04 AM
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The quality of where in the crack you put the cam, and what cam you used.
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crshbrn84
May 27, 2004, 7:04 AM
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even though i havent been climbing long, would the use of a screamer, be good when using a micro cam to help obsorb some of the shock from the initial fall?
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squish
May 27, 2004, 7:08 AM
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In reply to: even though i havent been climbing long, would the use of a screamer, be good when using a micro cam to help obsorb some of the shock from the initial fall?
Yes. This applies regardless of how long you've been climbing.
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hugepedro
May 27, 2004, 7:09 AM
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In reply to: Now I could be wrong here, but it looks to me that in this situation, you're rope is bomber, your biner is bomber, harness, sling... all bomber... but your cam is still not bomber..
Yeah, which is why I said:
"if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing."
Why would you ever take a fall approaching factor 2 on a single micro cam?
P.S. check out the kn rating on a #3 wired nut. 5kn.
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solo
May 27, 2004, 7:13 AM
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In reply to: It looks like all the smaller cams have a rating of 7 or 8 KN. Under 10 anyway... How could that be considered bomber if a factor 2 fall is rated at 25 KN?
In reply to: .... if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing.
Think of that once more. The only situation where factor 2 fall can occur is when you fall directly on the anchor. There's no way you can produce a factor 2 fall higher on the pitch after you placed some pro. So if you are facing f2 fall on a micro cam, you are either an A6 climber or have suicidal intentions. :wink:
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elron
May 27, 2004, 10:12 AM
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I feel rather stupid asking this question, since its probably something I should know... but... is the fall factor the only thing that influences the force produced in the fall? I mean to say, does a factor 2 fall of 4 feet produce the same impact force as a factor 2 fall of 25 feet? I can't see how this is possible, but whenever falls are discussed, the only contributing factor seems to be the fall factor. I was always under the impression that the fall factor was combined with other variables such as distance fallen and amount of energy absorbed by the rope to figure how much force is felt by the falling climber.
Kevin
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taualum23
May 27, 2004, 12:33 PM
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Kevin,
Of course you are right, that the physics of falling are much more complex than any number (fall factor, for example) can make up for. Fall factor, velocity of climber, mass of climber, the impact forces of the rope, and how much rope is out all have to do with how much ACUAL force is put on the pro. If this poster, for example, is taking a factor 2 onto a micro-cam, his anchor is a micro-cam. I try not to do this.
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overzealous
May 27, 2004, 12:44 PM
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In reply to: I feel rather stupid asking this question, since its probably something I should know... but... is the fall factor the only thing that influences the force produced in the fall? I mean to say, does a factor 2 fall of 4 feet produce the same impact force as a factor 2 fall of 25 feet? I can't see how this is possible, but whenever falls are discussed, the only contributing factor seems to be the fall factor. I was always under the impression that the fall factor was combined with other variables such as distance fallen and amount of energy absorbed by the rope to figure how much force is felt by the falling climber.
Yes and no. (Someone more experienced correct me if I'm mistaken). The fall factor is an approximation of the force felt in a fall. All other factors being equal a 10 foot factor 2 fall generates the same impact force as a 50 foot factor 2. In the real world, all things are almost never equal :)
Things besides the fall factor that will effect the impact force felt include:
- friction in the system
- energy absorbed by settling of the protection, knot tightening, beley slippage, etc...
- Use your imagination... I'm sure you can think of plenty more "others"
This leads me to a question... at what point do "other factors" become more of a consideration than the fall factor. If I take a hypothetical factor two on 2 feet of rope (say a slip at the belay) should the two feet of rope be cut and discarded, or is there simply not enough force generated over this drop distance to be an issue?
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peroxide
May 27, 2004, 12:57 PM
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Fall factor etc explained.
Kevin. You are not alone.
First some definitions:
Fall Factor: Length of Fall / Lenght of Rope to Last anchor
Max Impact Force: max force felt by climber through rope
A fall factor of 2 means a fall onto belay. 20 foot fall, 10 feet of rope to belay, that is factor 2 and sucks.
The cool thing about climbing ropes though is that they are dynamic so they absorb this energy. To understand as simply as possible, they absorb energy per foot of rope.
So a fall of 10 feet above the belay or 30 feet are both factor 2 falls (20 ft fall/ 10 feet rope = 2 = (60 ft fall / 30 feet rop)) but the longer fall also has 3 times the amount of rope out to absorb the fall. So in essence the climber will feel physically similar forces on their body (yes there is accelaration etc but these details arent important at this level).
So to sum up...more rope...more energy absorption.
Now the energy back to the biner is a different story.
You take max impact force (set for each and every rope made) X fall factor X 0.84 (some energy is lost to friction around the biner) to get a decent estimate on the biner.
So assume a rope has a max impact of 10 kN. The following chart shows what the pro feels. Try it at home.
Fall factor * 0.84 * Max Impact Force of Rope = Force on biner
Rope out****distance from last piece*****fall factor******kN on pro
30___________5___________0.33___________2.8
30___________10___________0.67___________5.6
30___________20___________1.33___________11.2
30___________30___________2.00___________16.8
Manufacturers most likely build into the rating at least 20% for error (in other words a 10 kN rated nut probably is probably safe upto 12 kN of force if not higher).
In a bomber placement (good rock, cam contact, etc) cams rarely fail. The only examples are very tiny micro cams that people have daisy chain falled (factor 2) onto which means no dynamic anything...
Rock on
P :!:
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cantbuymefriends
May 27, 2004, 1:00 PM
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In reply to: This leads me to a question... at what point do "other factors" become more of a consideration than the fall factor. If I take a hypothetical factor two on 2 feet of rope (say a slip at the belay) should the two feet of rope be cut and discarded, or is there simply not enough force generated over this drop distance to be an issue?
Beal has a pretty good info page about "other factors" (ropedrag etc.), at http://www.impact-force.info/anglais/impact.html . Check especially p.2 "The theoretical fall factor" and p.3 "The actual fall factor".
Interesting to see that a lot of ropedrag will give you a higher actual fall factor. I thought it was the other way around...
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elron
May 27, 2004, 1:37 PM
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peroxide, etc... thanks for all the info. however... i'm still having trouble understanding how a 4 foot factor 2 fall can generate the same force as a 50 foot factor 2 fall. kN = force. F=ma. "m" is constant in the two cases. "a" (the acceleration from highest speed to 0) is dependent on several factors, the two biggest being initial velocity (before deceleration) and amount of time from start of deceleration to point of zero velocity. Maybe I'll grab a pen and paper later on and do some sample calculations to convince myself that this works. just seems a bit counter-intuitive. on a static rope the fall factor wouldn't even matter, i assume, since the rope doesn't stretch. so, what amount of rope stretch (elasticity) is required to go from the static rope scenario to the "fall-factor" scenario. at what point does rope stretch replace velocity as the key factor in determining the force felt by the climber?
Kevin
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fitzontherocks
May 27, 2004, 2:05 PM
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I was curious about just what cam ratings actually meant. I found this on the Metolius site. Maybe it will shed some light.
Strength ratings are derived by holding a camming unit in a steel testing fixture and pulling on it until it breaks. This is the strength rating you see printed in the company literature or stamped on the cam. If a company wants a higher strength rating, they can simply use a beefier axle or stem(or whatever part failed in the test). However, in the real world, cams rarely fail by breaking. They almost always pull out. Having the strongest axle, stem or sling is totally irrelevant if that is not the point of failure in a real-world application. If a cam pulls out at 1000 lbf because the cams slipped or because the rock pulverized, what good is an axle with a 10,000 lbf breaking strength going to do? That is the difference between designing cams to work in a testing jig versus designing cams to work in the real world. Strength is the cam©ˆs ability to hold up to a particular standard in a controlled test. Holding power is a cam©ˆs ability to maintain its placement under a load (i.e. hold a fall) in a real-world placement.
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bigga
May 27, 2004, 2:10 PM
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Solo... excellent point.... :lol:
"Think of that for a minute" Gotta admit, the obvious never even crossed my mind.....
Still, even at less than factor 2, an 8KN , 9KN Cam is still pretty well below the outer limits of popping out on a serious fall which is fine if the people using it realise this. But since I've started asking around on this subject, quite a few people (and I'm not knocking them cause I'll put money that they are more experienced climbers than I am) have told me that the small cams are absolutely bomber, when even according to the specs engraved in them by the manufacturers, they are definitely not. Someone even told me he took a factor 2 on a small cam. Now as solo pointed out, he must iether be mistaken, or should be thanking G-d almighty for saving his as* after applying close to 24KN of force on his last piece of pro which was only designed to take about 8. At least according to the specs of the cam, it seems that all of you guys who have taken these serious falls on small cams and have had the cam hold, its not because its supposed, but probably because you placed the piece unbeleavably well, in the perfect shape and quality of rock, to allow your piece to perform ABOVE its specifications. I know that to most of you guys climbing traditional, this fact is probably not news to you, it caught me back abit since its news to me (and I dont trad), but if there is someone out there who doesn't know, be aware of the amount of protection you are placing... it could be dangerous to have a false sense of security about a piece.
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bigga
May 27, 2004, 2:23 PM
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And another thing... and correct me if I'm wrong.
People are saying that a factor 2 generates about 12KN on the rope which is correct. Now assume you are falling with a tension of 12KN in the rope. The biner feels almost TWICE that force.... since the rope is pulling on the biner both on the side of the climber and on the side of the belayer, and both sides pull with the force of the tension in the rope which is as we've said 12KN... In effect its not doubled but multiplied by 1.66 for reasons that I'm not 100% percent sure of. apparantly friction between the biner and the rope as was explained to me on another web site. Iether way a factor 2 fall places about 20KN of force on the anchor... not 12.... that is why there is such a huge difference in safety requerements between carabiners...Which are required to take 25KN if I'm not mistaken since they carry double the force.... and things like your rope and harness, all required to take 15 and less. So, nope, I still don't see how a small cam is bomber...
(I'm no expert, just trying to work it out with the numbers)
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dingus
May 27, 2004, 2:29 PM
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Fuck sake man, put a screamer on it and climb!
DMT
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tedc
May 27, 2004, 2:56 PM
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In reply to: peroxide, etc... thanks for all the info. however... i'm still having trouble understanding how a 4 foot factor 2 fall can generate the same force as a 50 foot factor 2 fall. Kevin
Your confusion is understandable. And you hit upon the key to your puzzlement with the word time. While the FF does essentially determine the max force felt by the system, a longer fall with an equal FF will apply force to the system for a longer time than a shorter fall. For a given FF, the forces will max out (at about the same value) as the climber comes to a stop at the bottom of the rope stretch but the whole time the rope is stretching the force will be building and the rope stretches for a longer period in a longer fall.
It an ideal case this time is not to important because if a cam will hold 10KN for .001 sec it should hold 10KN for .1 sec right? Maybe?
Other issues like how far does the belayer get pulled up are MUCH more dependant on the amount of time a certain force is applied.
How about a FF2 onto a poorly equalized (i.e. cordalette) 3 piece anchor. Forces applied for .001sec. (maybe a 3' FF2) may only be enough to rip the first crappy piece :shock: ; where forces applied for .1sec (maybe a 15' FF2) may be long enough to POP, POP, POP all three crappy pieces. Bye,Bye :cry:
So, are all Factor X? falls the same? NO.
But then again, didn't Sharma say "Climbing isn't about MATH." :?
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peroxide
May 27, 2004, 4:18 PM
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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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bandycoot
May 27, 2004, 4:30 PM
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In reply to: So, nope, I still don't see how a small cam is bomber...
They aren't, but they hold many falls. If you want to be perfectly safe, take up synchonized swimming. There is no fall potential there and probably lifeguards so save you if you start to drown. What do you want to hear, it COULD fail? There, you heard it. That is why we as climbers typically try to incorporate a SYSTEM of protection that consists of an anchor that is redundant and equalized, and more than on piece of protection while on lead. Have you ever heard the quote, "You're soloing until you have a second piece in." If you doubt the ability of one piece to hold a fall, put in more while you're on lead. Equalize them if that makes you feel better.
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paulraphael
May 27, 2004, 4:39 PM
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Nice physics lesson, Peroxide.
I want to emphasize one point:
The fall ENERGY absorbed by the rope does increase with fall distance, even if the fall factor stays the same. This is because kinetic energy increases with a square of the distance fallen, while energy absorbing rope length increases linearly. This does not translate into higher forces because the rope's stretch increases the DURATION of deceleration. However, each unit length of rope has to absorb more total energy in a long fall than in a short one, even if the fall factor is the same.
So what? It's important to know because a long fall is harder on your rope. Long falls should edge you towards retiring the rope sooner than short falls.
A 5 foot factor 1 fall will put about the same force on your body, your pro, and your anchor as a 10 foot factor 1 fall (all else being equal, bla bla bla) but the 10 foot factor 1 fall will be much harder on the rope. Each unit of length of that rope will have absorbed roughly twice as much energy in the longer fall (four times as much fall energy absorbed by only two times as much rope).
Just keep this in mind when evaluating your ropes, deciding how much time to let the rope recover, etc. etc..
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tedc
May 27, 2004, 4:50 PM
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In reply to: ....Super long physics lesson (removed)... .....In the end we are splitting hairs if we worry about this slight time discrepancy.
You think the difference between one piece and the whole anchor blowing is splitting hiars???..... You think the difference between the belayer feeling a hard tug and being pulled up 3' (and lifting all the nuts out of an anchor) is splitting hairs???
These are only two examples of where duration of force IS relevant.
In reply to: No one I know calculates fall factors as they are climbing…
Then how do you/they decide where to place pro?
I would suggest that if you don't, in some way, calculate fall factor as you lead then you are not ready to lead trad.
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peroxide
May 27, 2004, 6:18 PM
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Ted C...
I dont quite understand how my post advocates whippers and failing belays. My post was a pragmatic approach to the science.
The question posed was related to the physics of the situation. The time spans are irrevelant outside of theory...the effect on the rope life is serious (as mentioned in the above post...thanks for expanding on the lesson)
Obviously blowing the anchor is not the gameplan.
The basic gameplan should always be the following:
1) SRENE anchor with the most bomber gear you can place. Also it needs to be multidirectional.
2) Place the first piece as soon as possible (like immediately after the belay)
3) Early in the pitch the pieces should be more closely spaced than later in the pitch.
4) Rinse lather repeat
In reality this is the common practice of scared trad climbers in general. Being a little scared is good. I do not sit there and calculate fall factors...I think 98% of us are like this. We place to be comfortable which often accomplishes the concerns above.
This was not a lesson in trad leading and SRENE belay setups (covered correctly and incorrectly in other posts and forums). Just the physics. So don't get all flustered... and if you feel that a part of the message implies negligence (and is setting a gumby up for a death trap) then I can add a note on technique to clarify.
cheers
Peroxide
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hugepedro
May 27, 2004, 8:26 PM
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Bigga,
Trust me, trad climbers know the limitations of our gear. Small cams are bomber when they are used correctly. Bomber does not mean they will never fail under any circumstance. If you ever take anything approaching a factor 2 fall on a small cam, you were not using it correctly. High fall factors are unusual. To me, anything above .5 is high, so I set and rig pro to avoid that situation, and if I have to use small cams, nuts, whatever, in a high fall factor situation, I place more than 1 piece and equalize. See? Never relying on a single micro cam where the fall factor could be high (well, except for those situations where I’m running it out with confidence). As long as you do this your main concern will be the quality of your placements, not the physical limitations of your gear.
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dredsovrn
May 27, 2004, 8:33 PM
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In reply to: The impact force on most ropes range from 8.5 kn to 9.5 kn.
Thats what I love about Bluewater Excellence ropes (well, one of the many things). 5.9kn impact force. Took my first fall on a Metolius #1 TCU (8kn).
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bigga
May 27, 2004, 9:03 PM
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Hoowaa,
who woulda thaught it would have gotten this far. This is getting a bit funny.... anyone sensing alot of tension in this room?
Just to set a few things straight...
Bandycoot... I'm not looking for answers of "yes its safe" so I can feel better. If you haven't been reading all the posts this hasn't been about that. I haven't yet graduated up to trad level, I've only been climbing for three years, and I'm not right now considering it... so as far as my own personal piece of mind is concered... the answer does nothing for me.
The reason I've been driving everyone crazy with all these question is because it seems I may have figured out a design for a new piece for small cracks that is absolutely bomber. And I mean seriously bomber (if it works the way the mathematics involved in it say it should) by far outdoing any cam (not bragging here, I haven't tested it yet so can't even tell you for sure if the thing works) and I wanted to know if such a thing is of any use to trad climbers or if they are secure with there cams as is.
That, my friend, is all. nothing more. I realise the questions by now must be getting quite tidious and irritating to people, and I've tried to keep my questions as much as possible to private messaging to Engineers etc. on the site who have been nice enough to help. But sometimes what I need is the opinion of a larger group and rockclimbing.com seems to be full of people who are both knowledgable and willing to help and I can't pass that up.
Alrighty then.thats me... Wow, three pages of posts on this subject .....
enjoy folks
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gds
May 27, 2004, 9:23 PM
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Perhaps I'm missing something.
I find the physic all very interesting but not really on point.
I don't know about some folks but when I'm leading I always try to place the biggest piece I can (considring such issues as need for future gear, anchors, etc)
So when I'm putting in a small cam or brass nut it is because I can't find anything better. Of course a RP isn't as bomber as a #5 Camalot! But somethimes it is all you can get.
And if my memory is correct much of the smaller gear transitioned to free climbing from aid. So theoriginal idea was to hold body weight rather than a fall. Free climbers adopeted these pieces becasue, while not perfect, they were better than what there was.
The physics is interesting and improtant in the theoretical sense but when actually leading I think the first instinct is/should be to get in the best piece possible in the situation.
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tedc
May 27, 2004, 9:28 PM
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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.
I'm not flustered. I'm just calling BS.
I already gave two examples of how time IS relevant in REALITY.
Need another.
You are climbing and plugging cams on an Indian Creek splitter. You get up 10' and take a little (FF0.5) fall (Foot slipped right :wink: ). Batman up and check your piece. It barely moved. You think "Sweet, bomber gear". You keep climbing and putting in cams, lets say 80 more feet. Now you take another fall (must be a little over your limit, dude :? ). It's another FF0.5. This time your cam trenches a 3" grove in the crack. Unfortunately, it was only placed 2.9" deep and you are off for a big ride.
What the hell happened?
Same force...looooonger time.
Now apologize to all the nice noobs for trying to get them killed.
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tedc
May 27, 2004, 9:31 PM
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In reply to: Perhaps I'm missing something. I find the physic all very interesting but not really on point.
You aren't missing anything. We are just "off-topic".
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alpnclmbr1
May 27, 2004, 10:07 PM
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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.
In reply to: You are climbing and plugging cams on an Indian Creek splitter. You get up 10' and take a little (FF0.5) fall (Foot slipped right :wink: ). Batman up and check your piece. It barely moved. You think "Sweet, bomber gear". You keep climbing and putting in cams, lets say 80 more feet. Now you take another fall (must be a little over your limit, dude :? ). It's another FF0.5. This time your cam trenches a 3" grove in the crack. Unfortunately, it was only placed 2.9" deep and you are off for a big ride. What the hell happened? Same force...looooonger time.
This is so unlikely as to be useless. Running it out 20 feet and whipping for 45 feet on soft sandstone.
A .5ff near the ground is common, to get a .5ff 90 feet up a route you have to do something stupid.
Most gear placements fail relatively instantaneously. They can either hold the force applied or they can't. The time of the load is irrelevant in this respect. The time span of the load is mainly a factor of the elasticity of the rope. A longer lasting impact force is just a matter of the rope needing more time to absorb the force it is capable of absorbing.
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gds
May 27, 2004, 10:17 PM
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In reply to: most gear placements fail instantaneously
I guess you don't watchclimbing movies :)
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tedc
May 28, 2004, 3:03 PM
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In reply to: A .5ff near the ground is common, to get a .5ff 90 feet up a route you have to do something stupid.
Right. now explain why a .5ff 90 feet up a sandstone crack is stupid while the same ff near the ground is OK, and you will have proved my point.
ff.5=ff.5. Or does it??
(And don't tell me the fall is dangerous because there isn't a much cleaner fall than a vertical featurless face.)
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bandycoot
May 28, 2004, 3:24 PM
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Bigga: You do know that most gear will hold more than it advertises right? They just low ball it for liability and other reasons. If you have invented something that is the shit, cool! I have a friend who has started a climbing gear company before and I could probably get you in touch with him if you're interested in manufacturing and producing this thing, he could possibly help. He loves widgets and gadgets that are new and related to climbing. He's up on Mt. Denali playing until July though.
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jt512
May 28, 2004, 3:31 PM
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If we ever get a FAQ, this post needs to go in it.
-Jay
In reply to: 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 (we are talking about very very small time spans here). In the end we are splitting hairs if we worry about this slight time discrepancy. No one I know calculates fall factors as they are climbing…. Its been a while since I have played with physics 101 so all corrections or suggestions for edits are welcome.. Cheers, Peroxide |
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taualum23
May 28, 2004, 3:34 PM
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[quote="bigga"]I may have figured out a design for a new piece for small cracks that is absolutely bomber. And I mean seriously bomber (if it works the way the mathematics involved in it say it should) by far outdoing any cam (not bragging here, I haven't tested it yet so can't even tell you for sure if the thing works) and I wanted to know if such a thing is of any use to trad climbers or if they are secure with there cams as is.[/quote]
OK, a piece for small cracks that is absolutely bomber, and you want to know id such a thing is of any use to traddies?
Well, if it works, and has benefits above what is out there, then yes, and I'll take a set. If you need help real world testing, let me know, I love to play with gear.
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gunkiemike
May 28, 2004, 3:35 PM
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In reply to: Bigga, Trust me, trad climbers know the limitations of our gear. Small cams are bomber when they are used correctly. Bomber does not mean they will never fail under any circumstance.
A friend of mine broke a nearly new gold WC Zero cam by falling a few feet on it right off the ground. A visit to Petzl's fall force calculator site indicated a peak force that - surprise - exceeded the piece's rating. And it wasn't the placement that failed (the rock was undamaged and the crack was solid) it was the axle bending that let the cam lobes blow. A Screamer would probably have made the difference. As would choosing a higher rated piece e.g. an Alien for that particular size range.
So small cams are NOT necessarily bomber, and it doesn't take a huge whip to cause them to fail. Ditto your small wired pieces, which as someone noted in this thread, are rated for less than 10 kN. Hell, even 10 kN is weak by my standards, which is why I have so much slung passive gear on my rack.
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peroxide
May 28, 2004, 3:37 PM
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alpnclmbr1 wrote:
A .5ff near the ground is common, to get a .5ff 90 feet up a route you have to do something stupid.
tedC
Right. now explain why a .5ff 90 feet up a sandstone crack is stupid while the same ff near the ground is OK, and you will have proved my point.
ff.5=ff.5. Or does it??
***********
Lets take two different ff falls of 0.5
Fall 1: 20 feet off the ground
This translates to a fall 5 feet above your last piece.
In my opinion and alpclimber..very common.
Fall 2: 90 feet off the ground
This translates to fall from 22 feet above your last piece.
Why is fall 2 more "stupid" than fall 1?
22 feet above your last piece is getting bold.
45 feet of fall gives you lots of distance to hit stuff and if you swing/push away from the rock get ready to hit the wall hard.
Normally, (just look at how people sew a crack up) this just doesnt happen unless you are blasting for the belay and pitch off or a poorly placed piece pulls. Both can be interpreted as pilot error.
This would be what I think alpclimber is getting at.
Nonetheless, falling sucks.
peroxide
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jt512
May 28, 2004, 3:48 PM
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In reply to: The reason I've been driving everyone crazy with all these question is because it seems I may have figured out a design for a new piece for small cracks that is absolutely bomber. And I mean seriously bomber (if it works the way the mathematics involved in it say it should) by far outdoing any...
A page-and-a-half ago you couldn't even calculate impact force. Something tells me this new invention of yours isn't going to live up to your "mathematics."
-Jay
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peroxide
May 28, 2004, 4:26 PM
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Are all posters to this thread liable both in terms of future royalties or lawsuits???
Now where is that edit button again....and lets see if my lawyer is free to chat...
Peroxide
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curt
May 28, 2004, 4:42 PM
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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.
Ted is right--so there. HaHa.
Curt
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thomaskeefer
May 28, 2004, 4:55 PM
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One other thing to muddy the water..
Above, people were talking about pulling pieces instantly.. well that just does not happen even though it seems instant.
This can be dangerous..
A piece that is going to pull does so when the force it is capable of holding is met and then pops just after if the load continues to increase (as in a fall and the rope ceasing to continue stretching).
Now what you have is a situation where a good deal of the stretch (aka ability to absorb force and keep it from the gear and climber) in the rope is gone. Now when you hit that next piece there is a much harsher impact on the gear because the rope is behaving closer to a static line than it had before... something to think about when placing psychological pieces...
Flame on..
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tedc
May 28, 2004, 5:43 PM
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In reply to: If we ever get a FAQ, this post needs to go in it. -Jay In reply to: Reasonably good physics lesson excluded..... (we are talking about very very small time spans here). In the end we are splitting hairs if we worry about this slight time discrepancy. Cheers, Peroxide
Only if FAQ stands for: Frickin Asinine Quote
Sorry, the rest IS good but if you get the answer WRONG you get no credit for your work. This isn't physics class. It's climbing; way up off the ground. Partial credit is like being partially dead.
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tedc
May 28, 2004, 5:45 PM
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peroxide & alpnclmbr,
It hurts my brain to discuss this with you when you can't stick to the subject. Is the duration of the loading in a long fall relevant to the safety of your protection system?
In the previous example I specifically said that you ain't going to hit anything in a 45 foot ff.5 at I.C. Is this fall still dangerous??? Why??
In reply to: Above, people were talking about pulling pieces instantly.. well that just does not happen even though it seems instant. This can be dangerous..
I feel a little better knowing that at least someone else understands this.
In reply to: 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. Ted is right--so there. HaHa. Curt
Wheeew. I was waiting for that.
I knew I was. :D
peroxide and alpnclmbr can go climbing and let Newton do the teaching.
Unless there is someone out there still listening who doesn't understand this subject I am done hammering on these two hard heads.
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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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alpnclmbr1
May 31, 2004, 11:48 PM
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In reply to: 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. Ted is right--so there. HaHa. Curt
I think and you seem to have agreed, that in the practical sense, there is nothing you can do about this factor. That seems to be a reasonable definition of "irrelevent outside of theory."
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curt
Jun 1, 2004, 12:12 AM
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In reply to: In reply to: 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. Ted is right--so there. HaHa. Curt I think and you seem to have agreed, that in the practical sense, there is nothing you can do about this factor. That seems to be a reasonable definition of "irrelevent outside of theory."
When you are climbing, there is nothing you can do to mitigate this factor--as far as I know. I think it is important beyond theory though, in the sense that you should keep in mind that not all falls with the same fall factor are equal, with respect to the potential effects on your gear. Many people seem to think that they are.
Curt
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alpnclmbr1
Jun 1, 2004, 12:21 AM
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In reply to: I think it is important beyond theory though, in the sense that you should keep in mind that not all falls with the same fall factor are equal, with respect to the potential effects on your gear. Many people seem to think that they are. Curt
All right, lets turn this hijack in another direction.
I think that the significant (and actually measured) factor in varying forces for a given theoretical fall factor calculation is the intermediate points of friction in the belay chain.
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papounet
Jun 1, 2004, 10:09 AM
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dear
I suggest you read the tests of The Italian Commission for Material and Techniques (CMT) of the Italian Alpine Club (CAI)
http://www.caimateriali.org/Eventi/Torino/computermodel.html
and the documents of the UIAA (hint , check out the archive of 2000/3 magazine http://journal.uiaa.ch/download/20003.pdf
http://www.uiaa.ch/article.aspx?c=185&a=76)
you'll find a summary at
http://www.alpineclubofcanada.ca/services/safety/Notes%20on%20Belaying.doc.
Several points to note:
1. the notion of bomber is not scientific
many reports describe instances of gear that was though bomber and failed, as many describe manky gear that held.
"bomber" is a qualifier that is totally subjective
2. the actual force on a piece of protection is influenced by many variables, such as the type of belay, the proficiency of the belayer, the number of biners or the zig-zag of the rope,...
=> there could be so much friction in the system that the is a braking effect which does not happen at the uppermost piece
=> The actual fall factor is not a true measure of the forces involved, if there is the friction in the system.
I'll let you enjoy the mathematical model developped by the CMT
http://www.caimateriali.org/...puter_model/img5.jpg
http://www.caimateriali.org/...puter_model/img8.jpg
3. unless I am mistaken , the resistance of a piece of gear is not its holding power. A tiny cam may "friction" enough with the rock to "in theory" hold the force, but the small stem will break. A tiny nut may hold just to see the tiny cable break (check manufacturer site for the specs of the cable).
4. gear with low number such as 2kn for micro-nuts were never intended for free climbing, but as progression point for aid. A stopper guaranteed at 8kn may not be enough "in theory", but it may well be enough.
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tedc
Jun 1, 2004, 6:32 PM
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In reply to: 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
Based on your demonstrated lack of ability to reason logically, I don't find it hard to believe that you could draw such a conclusion from my scenario. Sorry. To anyone else who is having the same difficulty as alpnclmbr1 let me just state simply that the above conclusion is incorrect.
It would be correct to conclude,however,that while a placement may hold a 5' FF .5 fall (low on a pitch (obviously :wink: )). That same placement may NOT hold a 20' FF .5 fall higher in the pitch. This is the essence of my "IC scenario"; and while it is not entirely the essence of my argument, it clearly demonstrates the influence of duration of force in a common climbing scenario.
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tedc
Jun 1, 2004, 6:34 PM
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alpnclmbr1 is right :shock: . There is nothing we can do to change the physics involved with a particular fall. His suggestion then is that is must be irrelevant. There is nothing we can do to change gravity either. Does that make it irrelevant. NO, If fact it is the things that we cannot change that we must understand so that we can design a protection system that actually protects us against such "givens". If you don't understand it or you consider it irrelevant than you are at it's mercy.
In reply to: All right, lets turn this hijack in another direction.
Translation: Sound the retreat.
It would be much more honorable (and informative to the rc.com population) if you would just say. "I was wrong. It is improtant to consider the extra energy (duration of force) in a longer fall."
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bigga
Jun 1, 2004, 6:53 PM
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Methinks you guys all agree with each other and just want the other to see your point. Your difference of opinion here is so subtle this could go on for ever...
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madmax
Jun 1, 2004, 8:19 PM
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This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull. (3) Pulling a piece is bad.
Bottom line is that running it out is the culprit when it comes to generating enough kinetic energy to pull a piece, regardless of the fall factor?
Seems like something most trad climbers intuitively know, but perhaps can't articulate.
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alpnclmbr1
Jun 1, 2004, 8:34 PM
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In reply to: In reply to: All right, lets turn this hijack in another direction. Translation: Sound the retreat.
Actually the translation was: lets not try to embarrass Ted to much.
In reply to: It would be much more honorable (and informative to the rc.com population) if you would just say. "I was wrong. It is improtant to consider the extra energy (duration of force) in a longer fall."
Which is more honorable? Being open to new ideas and rational discussion, or being so stuck with being right that you bury your head in the sand?
Duration is effectively a meaningless concept because there are no steps that you can take that will affect it in any way.
For the last time, technically, Peroxide was right and you were wrong and if you do not believe me, ask Curt.
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alpnclmbr1
Jun 1, 2004, 8:37 PM
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In reply to: This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull.
In most instances, this is completely wrong. Thanks ted.
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madmax
Jun 1, 2004, 8:41 PM
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In reply to: In reply to: This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull. In most instances, this is completely wrong. Thanks ted.
Okay, alpnclimbr1, and why...?
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bigga
Jun 1, 2004, 9:08 PM
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I may have missed some points in your discussion over there so my input may be way off...
If you guys are discussing the pros and cons of the length of time of impact then I'll add my two cents. correct me if I'm wrong.
A longer period of impact force would put the pro under strain for a longer period of time But... As the saying goes, its not the fall that kills you...its the sudden stop at the end that does it. The amount of force felt by any body arrested in its movement is entirely dependant on the amount of time it decelorates from its current velocity to zero. Force (felt when the rope arrests your fall) = Mass * Acceloration and acceloration is equal to the change in velocity over time (from the moment the rope began to slow you down till the moment you stopped) (this is just an average of force since deceloration is not constant). i.e the shorter the period of time you decelorate the larger the force you (and all your gear) feel. Even on a molecular level, an atom hitting a train going the other way would go through a slowing down period even before it made contact, but if it wouldn't and the deceloration period would be zero the force felt (by the train or the atom, you pick) would be infinite and so a fly could be able to break the train. ( Just an anology to show ho much period of impact influences the force felt)
So while a longer sustained force puts pressure on your gear for a longer period of time, wouldn't that be prefferable if it reduced the maximum force a piece felt, assumung a placed piece can hold up to a certain amount of force?
(I have a feeling I'm saying stuff you guys already know, if so, apologies)
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alpnclmbr1
Jun 1, 2004, 9:32 PM
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In reply to: In reply to: In reply to: This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull. In most instances, this is completely wrong. Thanks ted. Okay, alpnclimbr1, and why...?
Bigga pretty much covered it.
As far as (1) running it out increases the amount of energy in a fall. The main variable in the duration of that impact force is the elasticity of your rope. The main point is that duration and energy are not interchangable terms.
As far as (2) In most cases increasing the duration of an impact force is equivalent to lowering the force felt by a given piece of pro or anchor. This is why you use a dynamic rope instead of a static one. This is also how a dynamic belay works.
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vicum
Jun 1, 2004, 9:51 PM
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May I try to summarize?
Suppose in situation A, 10kn acts down on a piece for .001sec. In situation B, 10kn acts down on a piece for .01 sec.
Curt and Tedc think that situation has B greater chance for the piece to pull than situation A.
Alpnclmbr thinks each should hold equally well.
Is that it?
Can any of you give a good qualitative explanation WHY either conclusion should be true? Personally, I cannot see why the force acting for a longer time should affect wheather the piece pulls, unless we are talking about the mere probability of random failure.
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alpnclmbr1
Jun 1, 2004, 10:25 PM
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In reply to: May I try to summarize? Suppose in situation A, 10kn acts down on a piece for .001sec. In situation B, 10kn acts down on a piece for .01 sec. Curt and Tedc think that situation has B greater chance for the piece to pull than situation A.
This is a fact.
Read the thread because you are not even close.
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paulraphael
Jun 1, 2004, 10:28 PM
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There's a whole lot of chest thumping going on here over nothing more than conjecture. If you can't produce some EVIDENCE that shows that duration of an equal force matters (or doesn't matter) then you shouldn't be shouting at each other--you should be asking questions, nicely.
My observations:
1) I have never encountered test results that correlate load duration with likelyhood of placement failure, so I don't know the answer.
2) My training in physics leads me to believe that load duration would not be a factor most of the time (or if it were a factor, it would be a minor one compared with the others)--but again, I don't know the answer with certainty.
3) The tests performed by the industry ignore the question, because they are static. By slowly pull testing pieces, they subject them to high forces for much longer durations than any fall.
4) However, static pull tests show breaking strengths very much in line with breaking strengths during drop tests. This suggests little significant difference based on duration. However, the nature of rock is an important variable that is not taken into account here. I have not seen static tests or drop tests performed on actual rock placements. Rock is so variable that scientifically useful results would be VERY hard to produce. They still might be interesting, though.
Until we see some real evidence, there's no need to be screaming at each other about assumptions and guesses. Life is too short. Climb something.
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jt512
Jun 1, 2004, 10:45 PM
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My intuition has been telling me that increasing the duration of the force increases the probablility of failure, but I hadn't been able to figure out why until paulraphael posted this:
In reply to: 4) However, static pull tests show breaking strengths very much in line with breaking strengths during drop tests. This suggests little significant difference based on duration. However, the nature of rock is an important variable that is not taken into account here.
Then the light bulb (dim as it may be) went off: Failure is not instantaneous. This is especially true (I would think) for the rock. Subjecting the rock to a given force can cause it to start to fail, but if the duration of the force is short enough, it may not fail completely.
Hopefully, I didn't just state something completely obvious and banal.
-Jay
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curt
Jun 1, 2004, 11:15 PM
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Jay,
I was also trying to make that same point a few pages back.
In reply to: 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.
Curt
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tedc
Jun 1, 2004, 11:31 PM
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Since most of the people replying have obviously not read the whole thread and thus not understanding what is being "discussed".
Here is my first comment; to which peroxide replied "bunch of physics....then... time (duration) is irrelevant." then alpnclmbr1 jumped in and agreed with peroxide.
In reply to: In reply to: peroxide, etc... thanks for all the info. however... i'm still having trouble understanding how a 4 foot factor 2 fall can generate the same force as a 50 foot factor 2 fall. Kevin Your confusion is understandable. And you hit upon the key to your puzzlement with the word time. While the FF does essentially determine the max force felt by the system, a longer fall with an equal FF will apply force to the system for a longer time than a shorter fall. For a given FF, the forces will max out (at about the same value) as the climber comes to a stop at the bottom of the rope stretch but the whole time the rope is stretching the force will be building and the rope stretches for a longer period in a longer fall. It an ideal case this time is not to important because if a cam will hold 10KN for .001 sec it should hold 10KN for .1 sec right? Maybe? Other issues like how far does the belayer get pulled up are MUCH more dependant on the amount of time a certain force is applied. How about a FF2 onto a poorly equalized (i.e. cordalette) 3 piece anchor. Forces applied for .001sec. (maybe a 3' FF2) may only be enough to rip the first crappy piece :shock: ; where forces applied for .1sec (maybe a 15' FF2) may be long enough to POP, POP, POP all three crappy pieces. Bye,Bye :cry: So, are all Factor X? falls the same? NO. But then again, didn't Sharma say "Climbing isn't about MATH." :?
I think this is pretty clear, and two EXAMPLES were given. When I still didn't get my point across I gave the third example of the cam sliding in the sandstone crack. This example was not intended to imply that any gear or placement is more likely to fail in a longer "same FF" fall. A piece (and placement) that will hold 10KN will not fail no matter how long you apply 8KN.
The cam in IC example was a special example (given because I have seen it). It shows that if a cam has about 5KN of holding power in the placement and you fall generating about 5KN it will pull if you apply the 5KN force long enough; and, it will slip (cut grooves) and stop if you apply the 5KN for a short enough period of time. I have seen this. I have personally left the grooves in the rock. I have fortunately never had the grooves be longer that the placement was deep.
Some who have not read the entire thread assumed that the discussion was entirely about whether duration has an effect on a piece pulling. That is not entirely true. Duration does have an effect on the performance of some placements.
The first two examples are also relevant and and indicate the relevance of time in more common (for folks who don't climb sandstone cracks) climbing situations.
Anyone ever held a short (5') FF 1.5 off a hanging bealy? Pretty good jolt but not a lot of movement right?
Anyone ever held the same FF1.5 but now 15'. SERIOUS. Belayer gets jerked up several feet. (Possibly loading the anchor in the upwards direction.
If you were belaying off nuts and didn't use a lower piece then I think you might have just found deadly evidence that the difference in duration of force caused by the longer fall IS relevant.
The three piece anchor example is left as an exercise for the reader (My fingers are getting tired and I have to climb tonight.)
Oh. one more thing. Ask mtngeo if duration of force can lead to anchor failure. If he had removed the load after KB #1 or #2 pulled he wouldn't have cratered. Longer timeframe (granted) but I'm sure you all can do the necessary interpolation to apply this to your own anchors and your own falls(loads).
So yes I was yelling; because I gave the evidence and no one read or listened or understood. And I would have given up a long time ago if so many new people weren't interested enough to keep posting. I don't care about convincing a couple people that I'm right, but if lots of folks are reading they deserve to hear the WHOLE story.
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jt512
Jun 1, 2004, 11:33 PM
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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. So... wheres the booboo in my reasoning? Something a little more helpfull than "you're lost" would be nice.
Not every fall generates the maximum impact force. Most falls generate a small fraction of that. Climbers don't rely on a single small cam when the potential impact force would exceed the strength of the cam in that placement. When the possibility of a factor-2 fall exists, the minimum anchor is three equalized pieces. If the pieces are marginal, then more.
-Jay
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alpnclmbr1
Jun 1, 2004, 11:43 PM
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In reply to: My intuition has been telling me that increasing the duration of the force increases the probablility of failure, but I hadn't been able to figure out why until paulraphael posted this:
Not you to.
If the above were true nobody would use a dynamic belay. Also when placing sketchy gear you would be better off belaying with a grigri instead of an atc.
In reply to: In reply to: 4) However, static pull tests show breaking strengths very much in line with breaking strengths during drop tests. This suggests little significant difference based on duration. However, the nature of rock is an important variable that is not taken into account here. Then the light bulb (dim as it may be) went off: Failure is not instantaneous. This is especially true (I would think) for the rock. Subjecting the rock to a given force can cause it to start to fail, but if the duration of the force is short enough, it may not fail completely.
Once again there is no way to affect the balance between the duration and the force except by using a higher impact rope.
Are you guys seriously suggesting that we start using higher impact force ropes in order to address this issue.
Petition the uiaa, I am sure they would be very interested in addressing this new important issue. This has already been covered and current theory hold that exchanging a longer duration for a lower impact force is the way to go.
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alpnclmbr1
Jun 1, 2004, 11:48 PM
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Rgold your input on this would be helpful.
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jt512
Jun 2, 2004, 12:13 AM
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In reply to: In reply to: My intuition has been telling me that increasing the duration of the force increases the probablility of failure, but I hadn't been able to figure out why until paulraphael posted this: Not you to. If the above were true nobody would use a dynamic belay. Also when placing sketchy gear you would be better off belaying with a grigri instead of an atc.
Hardly. We use a dynamic belay to increase the duration of the force in order to reduce the maximum impact force. Obviously, this is a favorable trade-off. But the question at issue is: for a given maximum impact force (ie, fall factor), does the duration of force (ie, length of fall) increase the probability of failure.
-Jay
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alpnclmbr1
Jun 2, 2004, 12:19 AM
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In reply to: But the question at issue is: for a given maximum impact force (ie, fall factor), does the duration of force (ie, length of fall) increase the probability of failure.
Is that really a question? Of course it does.
Now what are you going to do with that information?
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curt
Jun 2, 2004, 12:29 AM
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In reply to: In reply to: But the question at issue is: for a given maximum impact force (ie, fall factor), does the duration of force (ie, length of fall) increase the probability of failure. Is that really a question? Of course it does. Now what are you going to do with that information?
Hopefully, when evaluating whether a gear placement is adequate or not, you are going to take into account more than just the fall factor alone. That, I think, is the lesson to be learned here.
Curt
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alpnclmbr1
Jun 2, 2004, 12:36 AM
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In reply to: Hopefully, when evaluating whether a gear placement is adequate or not, you are going to take into account more than just the fall factor alone. That, I think, is the lesson to be learned here. Curt
Sounds good to me.
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p_grandbois
Jun 2, 2004, 12:46 AM
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I think in the end Bigga would like to make the product he is making with a rating for the max force for a factor 2 fall, like a lot of pro. I am glad for one that he is doing this large amount of research, and asking questions about the KN's. Climbing may not be about math but gear production is(for a large part) It has to be able to hold up to the math to get certified. He has a great drive, and is taking the neccessary precautions.
Like I said from the start, make it as bomber as the math tells you too, then work your way down for specifics. Don't focus on the naysayers that just want to put their ethics into making gear. Math is needed for this, might as well make it right.
p.s I am majoring in Athletic Management, not math
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alpnclmbr1
Jun 2, 2004, 12:58 AM
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In reply to: Since most of the people replying have obviously not read the whole thread and thus not understanding what is being "discussed". Here is my first comment; to which peroxide replied "bunch of physics....then... time (duration) is irrelevant." then alpnclmbr1 jumped in and agreed with peroxide. In reply to: In reply to: peroxide, etc... thanks for all the info. however... i'm still having trouble understanding how a 4 foot factor 2 fall can generate the same force as a 50 foot factor 2 fall. Kevin Your confusion is understandable. And you hit upon the key to your puzzlement with the word time. While the FF does essentially determine the max force felt by the system, a longer fall with an equal FF will apply force to the system for a longer time than a shorter fall. For a given FF, the forces will max out (at about the same value) as the climber comes to a stop at the bottom of the rope stretch but the whole time the rope is stretching the force will be building and the rope stretches for a longer period in a longer fall. It an ideal case this time is not to important because if a cam will hold 10KN for .001 sec it should hold 10KN for .1 sec right? Maybe? Other issues like how far does the belayer get pulled up are MUCH more dependant on the amount of time a certain force is applied. How about a FF2 onto a poorly equalized (i.e. cordalette) 3 piece anchor. Forces applied for .001sec. (maybe a 3' FF2) may only be enough to rip the first crappy piece :shock: ; where forces applied for .1sec (maybe a 15' FF2) may be long enough to POP, POP, POP all three crappy pieces. Bye,Bye :cry: So, are all Factor X? falls the same? NO. But then again, didn't Sharma say "Climbing isn't about MATH." :? I think this is pretty clear, and two EXAMPLES were given. When I still didn't get my point across I gave the third example of the cam sliding in the sandstone crack. This example was not intended to imply that any gear or placement is more likely to fail in a longer "same FF" fall. A piece (and placement) that will hold 10KN will not fail no matter how long you apply 8KN. The cam in IC example was a special example (given because I have seen it). It shows that if a cam has about 5KN of holding power in the placement and you fall generating about 5KN it will pull if you apply the 5KN force long enough; and, it will slip (cut grooves) and stop if you apply the 5KN for a short enough period of time. I have seen this. I have personally left the grooves in the rock. I have fortunately never had the grooves be longer that the placement was deep. Some who have not read the entire thread assumed that the discussion was entirely about whether duration has an effect on a piece pulling. That is not entirely true. Duration does have an effect on the performance of some placements. The first two examples are also relevant and and indicate the relevance of time in more common (for folks who don't climb sandstone cracks) climbing situations. Anyone ever held a short (5') FF 1.5 off a hanging bealy? Pretty good jolt but not a lot of movement right? Anyone ever held the same FF1.5 but now 15'. SERIOUS. Belayer gets jerked up several feet. (Possibly loading the anchor in the upwards direction. If you were belaying off nuts and didn't use a lower piece then I think you might have just found deadly evidence that the difference in duration of force caused by the longer fall IS relevant. The three piece anchor example is left as an exercise for the reader (My fingers are getting tired and I have to climb tonight.) Oh. one more thing. Ask mtngeo if duration of force can lead to anchor failure. If he had removed the load after KB #1 or #2 pulled he wouldn't have cratered. Longer timeframe (granted) but I'm sure you all can do the necessary interpolation to apply this to your own anchors and your own falls(loads). So yes I was yelling; because I gave the evidence and no one read or listened or understood. And I would have given up a long time ago if so many new people weren't interested enough to keep posting. I don't care about convincing a couple people that I'm right, but if lots of folks are reading they deserve to hear the WHOLE story.
You are offering problems but not any solutions. This is what happens when you offer theories that are "irrevelant outside of theory"
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rtc
Jun 2, 2004, 1:05 AM
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o.k. .........I'll take the pink one. :?
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jt512
Jun 2, 2004, 1:09 AM
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In reply to: In reply to: But the question at issue is: for a given maximum impact force (ie, fall factor), does the duration of force (ie, length of fall) increase the probability of failure. Is that really a question? Of course it does. Now what are you going to do with that information?
I don't know. Not much, I suppose. Maybe it's a reason not to skip a gear placement high on a pitch.
-Jay
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bigga
Jun 2, 2004, 2:22 AM
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Philly, thanks for the good word...
This thread left my original question a few pages ago, though:)
Its been an interesting discussion all the same.
How goes the wires?
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vicum
Jun 2, 2004, 3:55 AM
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In reply to: In reply to: May I try to summarize? Suppose in situation A, 10kn acts down on a piece for .001sec. In situation B, 10kn acts down on a piece for .01 sec. Curt and Tedc think that situation has B greater chance for the piece to pull than situation A. This is a fact. Read the thread because you are not even close.
Really????? I DID read the thread.
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alpnclmbr1
Jun 2, 2004, 4:17 AM
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In reply to: Really????? I DID read the thread.
oops
Then it is a case of my being unclear. I try.
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hugepedro
Jun 2, 2004, 4:32 AM
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The only thing I've learned from this thread is that I will never buy a piece of gear designed by bigga.
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ic2d
Jun 2, 2004, 5:17 AM
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Bigga,
Seems to me your cam loading estimate is a little high, which seemed to be an important part of your original question. As has been stated, a factor 2 fall should produce about a 12 kN force on the climbers end of the rope. By your reasoning, the load felt on the biner is then closer to 25 kN as that force must be applied on both sides of the rope. Methinks this isn't entirely accurate...after all, we're not talking about a statically loaded pully system (is statically even a real word?). Anyway, since the belay end of the rope is not falling, your belayer would have to weigh somewhere in the neighborhood of 2700 pounds (for a split second) to create an equal force on the other end of the rope. The more likely scenario is that the 12 kN force created by a falling climber lasts just long enough to pull the climber upwards (and quite far on a fall like this), without an equal balancing force on the opposite end of the rope, until the fall force is damped out by rope stretch and friction. If the forces were equal on both sides, the belayer wouldn't move...right? Assuming my understanding of what's going on is correct, the belayer side of the rope never pulls more than 1 kN (making a 13 kN total load on the biner) - for your average adult male climber, that is. Now if your belayer decides to bungee jump on his end of the rope while you're falling, then thats an entirely different story.
On a side note, I'm hoping no one else has made this same statement. I suppose its possible that I may have missed it somewhere in the last 8 pages of this thread (although I rarely, if ever, make mistakes).
Where'd everyone go?
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curt
Jun 2, 2004, 6:28 AM
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In reply to: Bigga, Seems to me your cam loading estimate is a little high, which seemed to be an important part of your original question. As has been stated, a factor 2 fall should produce about a 12 kN force on the climbers end of the rope.
No it won't. In fact, it will not exceed 9 kN for any rope I know of.
Curt
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alpnclmbr1
Jun 2, 2004, 7:13 AM
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Curt,
The range for current ropes on the market is 9.2 kn to 10.5 kn. This is for a uiaa 1.78 Fall factor.
This can translate to apx. 12kn for a full factor 2.
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curt
Jun 2, 2004, 7:19 AM
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In reply to: Curt, The range for current ropes on the market is 9.2 kn to 10.5 kn. This is for a uiaa 1.78 Fall factor. This can translate to apx. 12kn for a full factor 2.
I prefer to believe this, from another thread.
In reply to: ........... Since climbing ropes develop a maximum tension of 9 kN or less, girth-hitched spectra should be adequate for any protection situation.
Thanks though.
Curt
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beesty511
Jun 2, 2004, 7:26 AM
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In reply to: No it won't. In fact, it will not exceed 9 kN for any rope I know of.
lol. I see you quote that 9kN figure in post after post whether its on the climber, the gear, or the anchor. Is that some sort of gravitational constant you worship? You don't know of any ropes where a climber will feel more than 9kn in a fall? I could provide you links to quite a few. And, that 9kN is the max for every climber for every fall? I guess the climber's weight isn't a factor on planet curt nor the fall factor. Of course, in all the fall factor threads you post to you show your ignorance of that concept too. And, the effective fall factor can be higher than the theoretical fall factor. And....
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curt
Jun 2, 2004, 7:39 AM
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In reply to: In reply to: No it won't. In fact, it will not exceed 9 kN for any rope I know of. lol. I see you quote that 9kN figure in post after post whether its on the climber, the gear, or the anchor. Is that some sort of gravitational constant you worship? You don't know of any ropes where a climber will feel more than 9kn in a fall? I could provide you links to quite a few. And, you aren't aware of any climbers that will feel more than 9kN on your magic rope? I guess the climber's weight isn't a factor on planet curt nor the fall factor. Of course, in all the fall factor threads you post to you show your ignorance of that concept too. And, the effective fall factor can be higher than the theoretical fall factor. And....
Ah, Betsy. How nice of you to chime in to spray inaccuracies once again. I have never claimed the 9kN to be the maximum force felt by the gear--only by the falling climber. And, this is also the figure cited by rgold, as you can clearly see from my post above. Why? Because as rgold states, that is the maximum tension that will be developed in a modern climbing rope. But I am sure you know far more about these things than we do dear Betsy.
Do not pass Go and do not collect $200. Instead, go directly to Jail for being an idiot.
Curt
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papounet
Jun 2, 2004, 10:01 AM
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In reply to: Curt, The range for current ropes on the market is 9.2 kn to 10.5 kn. This is for a uiaa 1.78 Fall factor. This can translate to apx. 12kn for a full factor 2.
How do you "translate it" ?
The 9.2 kn to 10.5 kn is the force felt by the climber for the first fall. subsequent falls inflict progressively more and more force. The rope (in part, because of the 5mn interval between tests) does not recover all of its elasticity.
Please note that the UIAA test measure the force on the first drop. it then only test the rope till failure and reports the maximum number of falls.
I believe it is possible to extrapolate the maximum force inflicted to the dummy for a ff 2.0 either from the modulus of the rope given by the static elongation or from the modulus given by the test at ff1.78.
The issue: we get 2 different values,
Nonetheless, using the second formula, a rope that inflict 10 kn in a ff 1.78 can be predicted to inflict 10.5 kn in ff 2.0
(of course, a rope that has been used inflict harsher falls as demonstrated in various experiments, and then the maximum force could reach 12 kn)
I am here nit picking on this 12 kn value which is often quoted as a "magical golden number".
It has been said that the setup of the UIAA test is actually a bit harsher than the 1.78 factor woul suggest.
Some practitionners such as http://www.usmga.net/resourcesaskarchivedetails.cfm?RecordID=86 say
"The UIAA test is considered more severe than reality because it removes variables like belay devices, belayer's body, friction between the climber and the rock, etc. It is therefore hard to pinpoint exactly how much force will go onto the climber. "
In fact it doesn't take also into acount the deformation of the body of the climber which does absorb energy.
read also
http://www.usmga.net/guidelines/guidelinesropes.htm
this would make me think that in most case, the actual force seen by the climber is much lower than the value reported by the UIAA test
The UIAA tests are applied by several labs. A few years ago, there was some serious isues with the consistency of the measurments, in other wors, some labs were "nicer" than others and gave lower imapct force measures. The UIAA has, I believe, engaged in a re-certification of the labs and has tightened the standards fot the testing process.
RESEARCH at Padova and by rope makers, as well as the statistical evidence that NO well maintained rope has broken in the last 20 years would make me think that in most case, the actual ff seen by the hardware is much lower than the theoritical value
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papounet
Jun 2, 2004, 10:21 AM
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In reply to: Bigga, Seems to me your cam loading estimate is a little high, which seemed to be an important part of your original question. As has been stated, a factor 2 fall should produce about a 12 kN force on the climbers end of the rope. By your reasoning, the load felt on the biner is then closer to 25 kN as that force must be applied on both sides of the rope. .... ... Assuming my understanding of what's going on is correct, the belayer side of the rope never pulls more than 1 kN (making a 13 kN total load on the biner) - ... On a side note, I'm hoping no one else has made this same statement. I suppose its possible that I may have missed it somewhere in the last 8 pages of this thread (although I rarely, if ever, make mistakes). Where'd everyone go?
Missed several points:
1. a fall with ff 2.0 will not generate 12 kn , rather 10 kn with a modern rope in (very) good condition. the 12 kn is the maximum limit stated by the UIAA standard.
2. if you do not have any carabiner acting as a pulley in your system, the anchor onto which you have affixed the belay system will see the total force of the fall 10kn.
3. if you have setup a draw on the anchor, by virtue of the friction on the biner, the force seen by the belayer side is ~= 60%, the force seen by the anchor is ( 100% +60% ) the force felt by the climber = 16 kn
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papounet
Jun 2, 2004, 10:52 AM
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In perfect rock, the duration of the force doesn't matter.
The cam holding power comes from the friction betwen the cam material and the rock. This is commanded by the angle of the cam.
To quote from the Wild Country cam book
"To go back to the friction test again, the same result would be obtained if
a block of alloy the size of a sugar cube or a block weighing two tons
were used. The angle at which the block will start to slip is independent
of the load applied. What this means in practice is that if you place a
Friend in a flare and pull on it, and it does not come out, (and so long as
you do not disturb the placement), the Friend will hold up to the limit of
the unit or the rock. "
placements fail when:
- irregularities in the rock prevent the piece from redistributing the force to the rock
- the stem is not aligned with the force (or the stopper is not aligned wiht the force)
- the rock fractures or crumbles
- the piece, due to above reason, moves out or extend beyond its range
- the cable breaks
A cam in standstone will leave groove as the rock "fails". As this failure is progressive, the shorter the duration the better (for a given force)
A cam in granite may flex a "spinter" one time too many.
Who knows the compression resistance for sandstone and granite ????
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rgold
Jun 2, 2004, 7:50 PM
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The most contentious issue in this thread has to do with the significance of the duration of forces during the arresting of a fall. Here are my opinions for the bonfire.
A number of posters have advanced the idea that the peak force acts for a longer time when there is more rope out but the fall factor is the same. This is not true; the peak force is an instantaneous event. The longer time spent arresting a longer fall (with same fall factor) means that it takes longer for the rope tension to build to the peak force, not that the peak force acts longer.
I think time variations are more properly viewed as a consequence of other processes rather than as the determining factor in fall arresting. As has been said and reiterated, the total potential energy of the leader's fall must somehow be "absorbed" by various kinds of work. The primary source of work is the work done in stretching the rope, but there is also the work done against frictional forces (which can be highly significant in the case of a dynamic belay), perhaps work done in elongating a screamer, and in the case of soft rock, the work done in dragging a piece through a yielding medium. The fall stops when the work done by the faller on various parts of the belay system adds up to the total potential energy, and time has no role in this summation.
This statement says nothing about the forces felt by faller and system, however. Assuming a successful catch, those forces are a result of the maximum tension developed in the rope, and this tension is proportional to the percentage elongation of the rope. It is this dependence on percentage elongation that ultimately accounts for the role of the H/L ratio as determining the maximum rope tension for a fall. Two falls with the same H/L ratio will stretch the rope by the same percentage and so will produce the same level of tension in the rope.
There were comments about bigger falls involving more potential energy. This is true, but longer lengths of rope allow the falling leader to do more work, because the work done depends on the actual elongation and not just the percentage elongation. This means that the bigger actual elongation corresponding to the same percentage stretch for a longer piece of rope allows the peak force to be the same, even though the fall is bigger, because more work can be done in stretching the rope.
Time variations correlate with but are not the determining factor in the peak tension achieved. The longer arresting times correspond to the fact that more distance is involved when a longer rope undergoes the same percentage elongation. However, if you stretch a rope by, say, 20%, the tension will be the same regardless of whether the stretching happened in a second or an hour.
As for gear failures in soft rock involving tracking, I don't think that the longer time involved in bigger falls with the same fall factor is an issue, because my understanding of the tracking phenomena is different, and I do know that, as mentioned, there is no peak force acting longer.
Here's what I think happens with tracking. There is a tracking threshold for the placement, i.e. the force at which tracking begins. I am going to assume for simplicity that this force remains approximately constant once tracking has begun. So what happens in a tracking failure is that the rope elongates until the tension creates a force on the piece equal to the tracking threshold. Once tracking begins, there is no further rope elongation; the rope tension remains at the level needed to initiate tracking. Energy absorbtion changes from rope elongation to the work needed to track the cam through the rock, a straight (force) X (distance) calculation if the tracking threshold is really constant. What you have, in effect, is a screamer, with tracking resistance replacing stitch ripping. Whether or not the piece fails depends on whether or not the work done in dragging it to the lip of the crack, when added to the energy absorbed by rope stretching up to the tracking threshold elongation, equals the potential energy of the fall.
Although I don't find validity in the time argument, I do agree, from the perspective of the analysis just given, that a big fall with a given fall factor is more likely to cause a tracking failure than a small fall with the same fall factor. This is because rope elongation up to the tracking threshold plus work done in tracking represents a fixed quantity of energy absorbed, whereas the bigger fall (with same fall factor) does have more potential energy to be absorbed. (The fact that there is more rope to absorb this additional energy does not intervene here because energy absorbtion has been switched to the tracking mechanism before the rope could do its job.) Thus the fall does not end with the tracking inside the crack and the piece blows. Note that the longer elongation time for the rope occurs before tracking begins and so has nothing to do with the ultimate failure of the piece.
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rgold
Jun 2, 2004, 8:22 PM
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The original question has to do with whether small cams are bombproof. Various replies suggest that there are a lot of definitions of "bombproof" in use. Some of these boil down to "it didn't fail when I/my friend/this guy I heard about fell on it." The fact that the same size cam did fail in similar falls doesn't seem to be part of this definition.
I propose that "bombproof" ought to mean "highly unlikely to fail under any conditions achievable in normal climbing circumstances."
I don't think this is an unreasonable definition, but it has as a consequence that bombproof placements are uncommon and
No small cam is bombproof.
Get used to it. This is life (and possibly death) in the real world. Climb accordingly.
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lambone
Jun 2, 2004, 8:27 PM
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In reply to: In reply to: Now I could be wrong here, but it looks to me that in this situation, you're rope is bomber, your biner is bomber, harness, sling... all bomber... but your cam is still not bomber.. Yeah, which is why I said: "if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing." Why would you ever take a fall approaching factor 2 on a single micro cam? P.S. check out the kn rating on a #3 wired nut. 5kn.
It is very possible. For instance, lets say you are aid climbing on some C3 pitch, and you take a daisy fall onto the tiny cam below you. Thiscould easily happen if you are not super carefull, and even if you are super carefull.
I think most of those very small pieces with low ratings are intended to be used primarily for bodyweight aid climbing placements. And many come with warnings that say something to that effect.
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alpnclmbr1
Jun 2, 2004, 8:31 PM
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Thanks Richard, a most informative post, as usual.
You have a talent for speaking of complex issues in laymans terms.
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tedc
Jun 2, 2004, 8:40 PM
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In reply to: Thanks Richard, a most informative post, as usual. You have a talent for speaking of complex issues in laymans terms.
Agreed.
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tedc
Jun 2, 2004, 9:05 PM
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In reply to: The most contentious issue in this thread has to do with the significance of the duration of forces during the arresting of a fall. Here are my opinions for the bonfire. A number of posters have advanced the idea that the peak force acts for a longer time when there is more rope out but the fall factor is the same. This is not true; the peak force is an instantaneous event.
Clarification: I don't think anyone, especially myself said that the "peak" force acts for a longer time. This is trivial but to say that would indicate a gross misunderstanding of the behavior of the forces in a fall. What was actually "advanced" was that the force will stay above an arbitraty threshold for a longer amount of time in a longer fall. i.e. if the max impact force for a ff 1 fall is 5KN then the force will be between 4 and 5KN for a longer amount of time in a longer fall. (same FF). I am not sure there was any confusion on this detail but just making sure.
rgold. I'll buy the explaination of the tracking cam acting just like a screamer.
Could you please apply your analysis to the case where the belayer is "peter pan'ed" higher off the belay due to a longer fall of same FF.
Also, how would you say a longer fall applies to the sequencial ripping of pieces in a 3 (or more) piece semi-equalized (cordalette) anchor. (Or does it?)
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curt
Jun 2, 2004, 9:35 PM
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In reply to: Clarification: I don't think anyone, especially myself said that the "peak" force acts for a longer time. This is trivial but to say that would indicate a gross misunderstanding of the behavior of the forces in a fall. What was actually "advanced" was that the force will stay above an arbitraty threshold for a longer amount of time in a longer fall. i.e. if the max impact force for a ff 1 fall is 5KN then the force will be between 4 and 5KN for a longer amount of time in a longer fall. (same FF). I am not sure there was any confusion on this detail but just making sure.
Ted, I did actually use the term "peak force" acting over a longer period of time several pages back, but I intended this to mean the same thing you are saying, as I thought would have been clear by my examples of potential failures that could occur in such scenarios. I guess I'll have to be a bit more careful with my choice of words. :wink:
Curt
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beesty511
Jun 3, 2004, 1:26 AM
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:roll:
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hugepedro
Jun 3, 2004, 6:06 AM
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In reply to: In reply to: In reply to: Now I could be wrong here, but it looks to me that in this situation, you're rope is bomber, your biner is bomber, harness, sling... all bomber... but your cam is still not bomber.. Yeah, which is why I said: "if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing." Why would you ever take a fall approaching factor 2 on a single micro cam? P.S. check out the kn rating on a #3 wired nut. 5kn. It is very possible. For instance, lets say you are aid climbing on some C3 pitch, and you take a daisy fall onto the tiny cam below you. Thiscould easily happen if you are not super carefull, and even if you are super carefull. I think most of those very small pieces with low ratings are intended to be used primarily for bodyweight aid climbing placements. And many come with warnings that say something to that effect.
lambone,
We are in agreement. Nobody with any sort of brain expects tiny gear to hold FF2 falls, which is what I tried to get across to bigga in 3 posts - unsuccessfully. I don't trust that stuff in .5 FF falls. Nobody expects it to hold high FF, so we don't put ourselves in that situation - we understand the limitations of our gear and we make placements and rig our system accordingly. I have complete confidence when I place micro gear because I place it in appropriate situations (low FF), or I place multiple and equalize, or I accept the risk and move on. If you put yourself in a situation where you're falling on a daisy, you realize the risk, right? And you either accept it or you do something to change it. (Falling on a daisy can cause a lot of things to fail, probably including you.)
The hilarity of this thread (aside from the fall duration argument, which was entertaining), is that this character bigga claims to be designing gear that will be better than small cams. This from someone who obviously doesn't know a thing about placing gear.
In reply to: When you say placement, do you mean the quality of the crack you are placing the protection in? ie angle, tapering etc? In reply to: (and I dont trad)
This is either the best troll ever or someone's elevator doesn't quite reach the top floor.
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papounet
Jun 3, 2004, 9:36 AM
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In reply to: As for gear failures in soft rock involving tracking, I don't think that the longer time involved in bigger falls with the same fall factor is an issue, because my understanding of the tracking phenomena is different, and I do know that, as mentioned, there is no peak force acting longer. Here's what I think happens with tracking. There is a tracking threshold for the placement, i.e. the force at which tracking begins. I am going to assume for simplicity that this force remains approximately constant once tracking has begun. So what happens in a tracking failure is that the rope elongates until the tension creates a force on the piece equal to the tracking threshold. Once tracking begins, there is no further rope elongation; the rope tension remains at the level needed to initiate tracking. Energy absorbtion changes from rope elongation to the work needed to track the cam through the rock, a straight (force) X (distance) calculation if the tracking threshold is really constant. What you have, in effect, is a screamer, with tracking resistance replacing stitch ripping. Whether or not the piece fails depends on whether or not the work done in dragging it to the lip of the crack, when added to the energy absorbed by rope stretching up to the tracking threshold elongation, equals the potential energy of the fall. Although I don't find validity in the time argument, I do agree, from the perspective of the analysis just given, that a big fall with a given fall factor is more likely to cause a tracking failure than a small fall with the same fall factor. This is because rope elongation up to the tracking threshold plus work done in tracking represents a fixed quantity of energy absorbed, whereas the bigger fall (with same fall factor) does have more potential energy to be absorbed. (The fact that there is more rope to absorb this additional energy does not intervene here because energy absorbtion has been switched to the tracking mechanism before the rope could do its job.) Thus the fall does not end with the tracking inside the crack and the piece blows. Note that the longer elongation time for the rope occurs before tracking begins and so has nothing to do with the ultimate failure of the piece.
Nice explanation. 2 remarks though:
a/ Depending on the rock characteristics and inertia of the whole system, once the tracking has begun, it may not be necessary to have the same
force applied to continue grooving. Although it is plausible ot postulate that the failure occurs during the ramp up toward peak force.
b/ as soon as the piece starts grooving (yeah, baby, yeah), the energy absorption is done in parallel by the grooving and the rope; the rope continues to do its job but has less to do.
to adress tedc question
In reply to: Also, how would you say a longer fall applies to the sequencial ripping of pieces in a 3 (or more) piece semi-equalized (cordalette) anchor. (Or does it?)
there has been long debates and some formulae requarding the effect of psychological protection blown during a fall
http://groups.google.com/...alum.mit.edu&rnum=26
my take-out of Tom Moyer's explanation is that:
if the piece #0 pulls without having dissipated any energy, the only energy absorbed will have been absorded by the streching of the rope, if the other placements are nearby (semi-equalized anchor), the rope will load the other piece without having had the time to retract and recover some ability to absord energy, so the second piece will see the same force
my interpretation is that
if the piece #0 pulls after having dissipated some energy (by deforming metal, destroying rock or ripping stiches), the next piece will be shockloaded with the instant tension of the rope, but will in the end see a lower maximum force as the rope will have to dissipate less energy.
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papounet
Jun 3, 2004, 9:51 AM
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In reply to: Could you please apply your analysis to the case where the belayer is "peter pan'ed" higher off the belay due to a longer fall of same FF.
I like the image of a "peter pan'ed" belayer.
Dear Ted,
Have a second look at the 2 graphs posted earlier from the CMT research at Padova and read the reports. You'll see that the phenomenons are complex, noticeably because of inertia.
In short, contrary to some beliefs, a jumping belay doesn't diminish hte force on the the top piece but slipping ropes in a device does !!!
It could be that the belayer is lifted higher with a longer fall of same FF., but is doesn't matter for helping a piece stay.
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alpnclmbr1
Jun 3, 2004, 2:43 PM
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Papounet,
Why do I disagree with you so much? Why are so many of the conclusions you come to and data that you offer to support them, completely contrary to the bulk of information I have read? Strange, as you seem to be reasonably intelligent.
I don't have time right now to go issue by issue, maybe later.
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tedc
Jun 3, 2004, 3:11 PM
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In reply to: to adress tedc question In reply to: Also, how would you say a longer fall applies to the sequencial ripping of pieces in a 3 (or more) piece semi-equalized (cordalette) anchor. (Or does it?)
If you say you are going to address my question then address it. Your text does not refer to the differing effects of a long and short fall and that is the (hijacked) subject of this thread.
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rgold
Jun 3, 2004, 4:00 PM
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In reply to: Could you please apply your analysis to the case where the belayer is "peter pan'ed" higher off the belay due to a longer fall of same FF.
The analysis is essentially the same as for a screamer or tracking, so I'm going to try to speak in general terms about such things.
Consider the following generic situation: during a fall, the rope stretches until some threshold tension is reached, after which the energy absorbtion mechanism switches to one that involves working against a constant resistance for some distance. When this happens, rope tension does not change, remaining at the constant resistance value for as long as the second mechanism is in effect.
In the case of a screamer, the threshold tension is whatever is needed (after considering the pulley effect) to activate the screamer. In the case of gear tracking in soft rock, the threshold tension is what is needed to overcome the tracking threshold I made up in my previous post. In the case of an (involuntary) dynamic belay, the threshold tension is the tension that initiates rope slippage in the belay device. In the case of belayer Peter Pannage, the threshold tension (at the belayer's end of the rope) is equal to the belayer's weight.
In the case of belayer flight, the combination of belayer weight and friction in the system must provide more resistance than the weight of the faller, otherwise there will be no net reduction in the faller's potential energy. This is one case when friction in the system really matters. (Frequently, there is so much friction that the belayer can't be lifted unless he or she jumps.) The amount of the faller's potential energy that is absorbed by lifting the belayer is, of course, (leader's end lifting force) X (belayer flight distance). Lifting begins when rope stretch develops the lifting force at the leader's end.
My previous statement about the role of the rope in absorbing fall energy up to the threshold value should be worded more accurately: The way in which the elasticity - H/L ratio principles work is that, in stretching up to the level need to produce the threshold tension, the rope will always absorb the same proportion of the total energy required for the rope alone to completely stop the fall. So, for example, if the rope absorbs 90% of the fall energy before the belayer is lifted for a given fall, it will absorb 90% of the fall energy for any other fall with the same H/L ratio. This leaves the remaining 10% to be absorbed by the constant resistance mechanism. But the constant resistance mechanism isn't "scalable," if the fall is twice as long (with twice as much rope out), then the remaining 10% of the fall energy is twice as much (10% of 2E is 2 X 10%E) and the belayer will have to be lifted twice as high in order to do the appropriate amount of work.
In reply to: Also, how would you say a longer fall applies to the sequencial ripping of pieces in a 3 (or more) piece semi-equalized (cordalette) anchor. (Or does it?)
Well, if there is a tracking phenomenon, e. g. an anchor in soft rock, then a long fall onto a distributed (cordalette style) anchor might extract pieces that wouldn't be extracted by a shorter fall with the same fall factor. Without a significant tracking effect(*), I don't offhand see any difference between long and short falls with the same fall factor. The fact that extracting pieces contributes (usually in a disappointingly minor way) to a reduction in the ultimate load on the remaining pieces does not seem to me to be altered by the size of the fall and in some sense is not even influenced by the fall factor.
(*) I'm waffling here and assuming an instantaneous failure during which no significant work, other than that done in stretching the rope to produce the extraction threshold tension occurs. This seems reasonable to me, but I have no idea whether it is, in fact, accurate.
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paulraphael
Jun 3, 2004, 4:23 PM
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<<(*) I'm waffling here and assuming an instantaneous failure during which no significant work, other than that done in stretching the rope to produce the extraction threshold tension occurs. This seems reasonable to me, but I have no idea whether it is, in fact, accurate.>>
since we obviously need something new to chat about, has anyone seen data on how much energy is absorbed by the (near) instantaneous failure of a piece? the assumption always seems to be that it's close to zero, but intuitively this seems strange. there must be a measureable (and i'd think significant) amount of energy used up in snapping a cable rated to 10kn--just like a bullet blasting through a wall loses a lot of energy.
thoughts? flames?
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alpnclmbr1
Jun 3, 2004, 5:16 PM
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Here are two question that have been indirectly reference in a few of the posts.
1)
What are the relative mechanisms and pro and cons of using a jumping(or getting lifted) dynamic belay versus purposely letting rope slide through the belay device?
2)
How does the theoretical fall factor force compare to the real world fall factor force for any given fall?
edit to add
How significant of a difference is there between a ff 1.78 and a ff2?
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tradklime
Jun 3, 2004, 5:38 PM
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In reply to: Missed several points: 1. a fall with ff 2.0 will not generate 12 kn , rather 10 kn with a modern rope in (very) good condition. the 12 kn is the maximum limit stated by the UIAA standard. 2. if you do not have any carabiner acting as a pulley in your system, the anchor onto which you have affixed the belay system will see the total force of the fall 10kn. 3. if you have setup a draw on the anchor, by virtue of the friction on the biner, the force seen by the belayer side is ~= 60%, the force seen by the anchor is ( 100% +60% ) the force felt by the climber = 16 kn
This then would imply that redirecting the belay is much less safe, ie. when a climber is close to the anchor it is better to catch them directly than to redirect the rope through the anchor.
If the rope is redirected, wouldn't the fall factor be less than 2?
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alpnclmbr1
Jun 3, 2004, 5:57 PM
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In reply to: Missed several points: 1. a fall with ff 2.0 will not generate 12 kn , rather 10 kn with a modern rope in (very) good condition. the 12 kn is the maximum limit stated by the UIAA standard. 2. if you do not have any carabiner acting as a pulley in your system, the anchor onto which you have affixed the belay system will see the total force of the fall 10kn. 3. if you have setup a draw on the anchor, by virtue of the friction on the biner, the force seen by the belayer side is ~= 60%, the force seen by the anchor is ( 100% +60% ) the force felt by the climber = 16 kn
1. This assumes that there is no difference between a 1.78 and a 2. Also the 12kn limit applies to a 1.78 fall. this means it could go higher in a ff2 and still pass the test
2. only if the rope is tied directly to the anchor
3.edit
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paulraphael
Jun 3, 2004, 9:13 PM
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<>
Makes a lot of sense.
Another broad question that I don't remember seeing covered here:
How much energy is likely to be absorbed by the dynamics (rope slip) of a belay device?
There's obviously no simple answer, since the amount is dependent on the variables of the rest of the system, as well as the nature of the particular device/rope/belayer. A couple of years ago Chris Harmston emailed me some results of internal tests of the ATC--basically showed how much braking force the atc exerted on different rope diameters (with a fixed amount of force on the brake hand end of the rope).
I don't have the list anymore (and Black Diamond never published it out of fear that people would draw overly simplistic conclusions. Who, us??) but it was surprising how low the forces were. In the range of 300 to 600lbs. Which would suggest a LOT of rope slip (and therefore a lot of energy dissipation, and possibly a lot of rope burn) on any kind of fall capable of generating multi-kilonewton forces at the anchor. It also makes it hard to understand how, without a truly static belay, it's even possible to generate huge forces.
This may be part of the reason real world forces tend to stay low--Harmston also said that he's never seen a piece of pro rated at 10kn or more that had failed.
Any thoughts?
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papounet
Jun 4, 2004, 8:34 AM
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In reply to: In reply to: Missed several points: 1. a fall with ff 2.0 will not generate 12 kn , rather 10 kn with a modern rope in (very) good condition. the 12 kn is the maximum limit stated by the UIAA standard. 2. if you do not have any carabiner acting as a pulley in your system, the anchor onto which you have affixed the belay system will see the total force of the fall 10kn. 3. if you have setup a draw on the anchor, by virtue of the friction on the biner, the force seen by the belayer side is ~= 60%, the force seen by the anchor is ( 100% +60% ) the force felt by the climber = 16 kn 1. This assumes that there is no difference between a 1.78 and a 2. Also the 12kn limit applies to a 1.78 fall. this means it could go higher in a ff2 and still pass the test 2. only if the rope is tied directly to the anchor 3.edit
dear alpnclmbr1
I believe I now see where we do not agree
on point 1. I based my statements on my earlier post (bad form ?)
In reply to: I believe it is possible to extrapolate the maximum force inflicted to the dummy for a ff 2.0 either from the modulus of the rope given by the static elongation or from the modulus given by the test at ff1.78. The issue: we get 2 different values, Nonetheless, using the second formula, a rope that inflict 10 kn in a ff 1.78 can be predicted to inflict 10.5 kn in ff 2.0
I found that the modulus of a rope that deliver 10kn at ff 1.78 to be ~= 30
applying to to ff2.0 is straightfoward and gives 10.5. kn.
A barely standard rope that delivers 12kn at ff 1.78 has a modulus ~= 45 would deliver 12.5 kn at ff 2.
on point 2. indeed, and it makes me scratch my head everytime.
edit: here is one of my source http://www.losalamos.org/climb/xRopes.pdf
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papounet
Jun 4, 2004, 9:25 AM
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In reply to: If you say you are going to address my question then address it. Your text does not refer to the differing effects of a long and short fall and that is the (hijacked) subject of this thread.
It seems that I have misunderstood your question .
My initial understanding of your question is "does the sequential ripping of piece in a muli-piece semi-equalized anchor IMPACT ON the duration of the fall or the force felt by the surviving piece(s) ?" (emphasis mine)
whereas your question more inline with the (hijacked) subject could rather be like "does a longer fall with same ff has more chance of ripping sequentialy the pieces of a pseudo-equalized anchor ?"
If so, please accept my apologies.
(if still wrong , please help me by clarifying your question).
If it is indeed your question, Rgold said it very well
In reply to: The primary source of work is the work done in stretching the rope, but there is also the work done against frictional forces (which can be highly significant in the case of a dynamic belay), perhaps work done in elongating a screamer, and in the case of soft rock, the work done in dragging a piece through a yielding medium.
If the potential energy of the fall is dissipated by the destruction of the rock and/or gear instead of the elongation of the rope, a longer fall will destroy more of rock and/or gear, thus having more chance of failure, and shockloading the remaining piece with the current tension of the rope.
The sequential ripping of pieces may protect the final pieces if it bleeds energy from the system through work. If they pop out, nothing happens.
This begs the question: does the strength rating of a piece of gear (such as RP= 4kn) has anything to do with the energy it would substract from the system by blowing (acting as a fuse) ?.
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papounet
Jun 4, 2004, 10:58 AM
Post #141 of 147
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In reply to: Here are two question that have been indirectly reference in a few of the posts. 1) What are the relative mechanisms and pro and cons of using a jumping(or getting lifted) dynamic belay versus purposely letting rope slide through the belay device? 2) How does the theoretical fall factor force compare to the real world fall factor force for any given fall? edit to add How significant of a difference is there between a ff 1.78 and a ff2?
dear alpnclbr1
thanks to your very good idea of collecting rgold contribution in http://www.rockclimbing.com/...iewtopic.php?t=62477, I found that before I could write up anything remotely clear, rgold did it
In reply to: I'll take a shot at it. In principle, the load on the top piece depends on the famous H/L ratio; H=total length of fall (before rope stretch) and L= amount of rope from leader to belayer. However extensive research and mathematical modelling by the Italian Alpine Club suggest what a lot of people suspected---the total length of rope involved is, in practice, less than the amount from leader to belayer because friction against carabiners and against the rock prevents the full length of available rope from responding to the forces at the top biner. This means that with the real-life L smaller, the ratio H/L is bigger and the tension developed in the rope at the top biner is higher than one would expect from the classical H/L calculation.
The italian report, he pointed at is the one I indicated (page 6 of this thread) from the CMT relating their test at Padova.
http://www.caimateriali.org/...o/computermodel.html
My take is that one one hand, the friction developped in the various biners limits the amount of rope available for streching (=> higher ff), and the other hand the same friction is energy bleed from the system.
regarding lifting, the CMT said
"It can be noted that the belayer’s lift at the maximum safety load instant (roughly 0.2 sec) is very little: this is somewhere in contrast with the current believing of the climbing world.
In fact it is a common belief that the belayer’s lifting reduces the safety chain loads.
Actually it is the low braking force generated by the belayer the true origin of the low load of the harness belaying technique also according to the tests: the low inertial force is due to the small mass involved in the braking action typical of this type of braking."
my Italian is far too bad to attempt to read the article on belaying techniques.
http://www.caimateriali.org/...odiAssicurazione.PDF
but I gather you would find a lot in it
Due to the risks of belayers jumping into the face in order to "soften" the fall", I prefer to stay firmly planted and attempt to let a few cm of rope slip
edited to add URL tags
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jt512
Jun 4, 2004, 4:04 PM
Post #142 of 147
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In reply to: regarding lifting, the CMT said "It can be noted that the belayer's lift at the maximum safety load instant (roughly 0.2 sec) is very little: this is somewhere in contrast with the current believing of the climbing world. In fact it is a common belief that the belayer's lifting reduces the safety chain loads. Actually it is the low braking force generated by the belayer the true origin of the low load of the harness belaying technique also according to the tests: the low inertial force is due to the small mass involved in the braking action typical of this type of braking."
I think you are misinterpreting this. In the experiment, as far as I can tell, the belayers did not intentionally jump, but were passively lifted. An intentional, well-timed jump increases the time over which the energy of the fall is absorbed and therefore decreases the impact force on the climber and the anchor.
In reply to: Due to the risks of belayers jumping into the face in order to "soften" the fall", I prefer to stay firmly planted and attempt to let a few cm of rope slip
Nobody jumps into the face. You are speaking from ignorance.
-Jay
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alpnclmbr1
Jun 4, 2004, 4:29 PM
Post #143 of 147
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In reply to: In reply to: Here are two question that have been indirectly reference in a few of the posts. 1) What are the relative mechanisms and pro and cons of using a jumping(or getting lifted) dynamic belay versus purposely letting rope slide through the belay device? 2) How does the theoretical fall factor force compare to the real world fall factor force for any given fall? edit to add How significant of a difference is there between a ff 1.78 and a ff2? dear alpnclbr1 thanks to your very good idea of collecting rgold contribution in http://www.rockclimbing.com/...iewtopic.php?t=62477, I found that before I could write up anything remotely clear, rgold did it
Actually, those questions were derived from problems I had with your posts. Writing the questions directed towards rgold inspired me to see if he already answered them. He had and the end result was the rgold collection. So in a sense, you get credit for that.
=-=-=-=-=
I actually haven't completely read the torino link, I will, thanks.
Here are some sites I use for reference.(all of them have problems of one sort or another)
Impact force from beal/torino
http://www.impact-force.info/anglais/impact.html
REI belay device tests
http://www.somat.com/...ons/articles/rei.htm
Forces on the Falling Climber Depending on Different Belaying Techniques
http://www.leeds.ac.uk/...mb99/wnachbauer1.htm
Rope System Analysis
http://www.wsystem.com.br/.../Download/xRopes.pdf
forces in a lead fall
http://www.uoregon.edu/...orcesinleadfalls.pdf
An Elastic Model of the Holding Power of
Spring Loaded Camming Devices
Used as Rock Climbing Anchors
http://www.mit.edu/.../cams/cams.body.html
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bigga
Jun 6, 2004, 6:18 AM
Post #144 of 147
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Registered: May 25, 2002
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Hoowa,
I went to the army for a week, come back and find the thread has born 3 more pages. took me a while to read everything up to date.
1 at a time.
Hugepedro : Don't use it. What do I care. Here's the thing see... I've done a ( pretty rugged I'll admit but still a) test and the thing works, has a range starting much lower and going much higher than todays little cams, and can hold (whatever the arguments have been on this thread) a much higher force. But if you insist, if I or someone else ever manage to get this out, I'll put some sign on it so that you'll know to avoid it :lol:
ic2d : Thanks for the info. Actualy, I was portraying the force as being double to make the physics of it a bit more obvious, but you are right that it is not double. It is actually *1.66. At least according to the information I've read so far, . Even if ropes have come a long way in past few years (which was, by the way a good point, whoever made it) and my info may be a few years old, it only means I'm looking at larger forces than I should which is fine by me. I'd rather err on the side of safety anyway, and so have been using 25kN as a model regardless.
Anyway, I'm going back into the army again soon for a bit and then exams... so I just wanted to thank all you guys for your help and input. For all you boykies who seem a bit sour... this is just fun... if it works and gets to climbers then great for everyone ( I would think), if not, so what? I (at least) learned quite a bit, had some fun, did somegood excersises for my degree and lost nothing. So Relax and lighten up.
Thanks again
Allon
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papounet
Jun 7, 2004, 12:39 PM
Post #145 of 147
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In reply to: In reply to: regarding lifting, the CMT said "It can be noted that the belayer's lift at the maximum safety load instant (roughly 0.2 sec) is very little: this is somewhere in contrast with the current believing of the climbing world. In fact it is a common belief that the belayer's lifting reduces the safety chain loads. Actually it is the low braking force generated by the belayer the true origin of the low load of the harness belaying technique also according to the tests: the low inertial force is due to the small mass involved in the braking action typical of this type of braking." I think you are misinterpreting this. In the experiment, as far as I can tell, the belayers did not intentionally jump, but were passively lifted. An intentional, well-timed jump increases the time over which the energy of the fall is absorbed and therefore decreases the impact force on the climber and the anchor. In reply to: Due to the risks of belayers jumping into the face in order to "soften" the fall", I prefer to stay firmly planted and attempt to let a few cm of rope slip Nobody jumps into the face. You are speaking from ignorance. -Jay
I may have "over-interpreted" from the CMT article (rereading myself, I would like to have it written in a different fashion).
Your point "An intentional, well-timed jump increases the time over which the energy of the fall is absorbed and therefore decreases the impact force on the climber and the anchor. "
doesn't make physics sense to me.
I would on the other hand agree on
An intentional, well-timed jump decreases the inertia of the complete braking system, decreases momentarily the friction on the top biner, thus allowing the lifting of the counterweight to occur, increases the amount of rope sliding against friction in all intermediate biners. The additional mechanical work and additional transformation into heat bleeds the fall energy. This combined with the additionnal lenght of rope involved in absorbing the fall thus decreases the impact force on the climber and the anchor.
The interplay of several mechanisms instead of just the rope streching means that the fall last longer, but it is not the increased duration that decreases the impact force.
Ps: No one I know volontarily jump into the rockface, but I have seen quite a few time a tiny gf fly up to the first bolt when belaying a (heavy) friend of mine. Oh dear, I wrote about bolts, now I will be called a sport wannabee.... :roll:
Dynamic "jump" belay seems much more practical for good stances on the ground.
In a multiple pitch hanging belay or in snow/ice, I do not see myself attempting to soften a fall by jumping; letting ropes slip seems more practical.
The data at "Forces on the Falling Climber Depending on Different Belaying Techniques were computed for low ff =0.375 and with limited runs.
http://www.leeds.ac.uk/...mb99/wnachbauer1.htm they always seem strange as the force with dynamic belay and HMS are reported higher than dynamic belay with grigri. As far as I recollect, the HMS should give a lower force than a grigri when handled without jump. Could it be that the jump cause the belayer to forego letting the rope slip and thus cancel the benefit of the HMS ?
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papounet
Jun 7, 2004, 1:11 PM
Post #146 of 147
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In reply to: So in a sense, you get credit for that.
thanks,...
I didn't know about the REI and I had forgottent about a few of the others..
The petzl simulator
http://www.petzl.com/...5&SousFamille=&News=
is actually quite complete. It includes the strength of the belay computation a well as takes into account the device used for belaying.
(PS: to use it with running belay, start with entering first the running belay 3 closest to the belay , then running belay 2 , then running belay 1, closest to the climber).
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jt512
Jun 7, 2004, 5:43 PM
Post #147 of 147
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In reply to: Your point "An intentional, well-timed jump increases the time over which the energy of the fall is absorbed and therefore decreases the impact force on the climber and the anchor. " doesn't make physics sense to me. I would on the other hand agree on An intentional, well-timed jump decreases the inertia of the complete braking system, decreases momentarily the friction on the top biner, thus allowing the lifting of the counterweight to occur, increases the amount of rope sliding against friction in all intermediate biners. The additional mechanical work and additional transformation into heat bleeds the fall energy. This combined with the additionnal lenght of rope involved in absorbing the fall thus decreases the impact force on the climber and the anchor. The interplay of several mechanisms instead of just the rope streching means that the fall last longer, but it is not the increased duration that decreases the impact force.
WTF?
F = ma
F = m(dv/dt)
The method of belaying doesn't change m or dv, so as dt increases, F decreases.
In reply to: Ps: No one I know volontarily jump into the rockface, but I have seen quite a few time a tiny gf fly up to the first bolt when belaying a (heavy) friend of mine.
A competent belayer would know not to jump if she was substantially outweighed by her partner.
In reply to: Dynamic "jump" belay seems much more practical for good stances on the ground. In a multiple pitch hanging belay or in snow/ice, I do not see myself attempting to soften a fall by jumping; letting ropes slip seems more practical.
No argument here.
In reply to: The data at "Forces on the Falling Climber Depending on Different Belaying Techniques were computed for low ff =0.375 and with limited runs. http://www.leeds.ac.uk/sports_science/abstracts/climb99/wnachbauer1.htm they always seem strange as the force with dynamic belay and HMS are reported higher than dynamic belay with grigri....Could it be that the jump cause the belayer to forego letting the rope slip and thus cancel the benefit of the HMS ?
I doubt it. The report compares a "jump" belay with a grigri to a "dynamic" belay with an HMS carabiner. This wording suggests that the dynamic belay with the HMS carabiner was effected by allowing rope to slip, not by jumping. The most straightforward interpretation is that jumping with a grigri reduces the impact forces by a significantly greater amount than does letting rope slip through a Munter hitch.
-Jay
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