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redlude97
May 26, 2010, 6:09 PM
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adatesman wrote: jt512 wrote: patto wrote: jt512 wrote: Most Americans don't even know what mass is, and, for purposes of understanding the strength of climbing gear, they don't need to. Thanks to gravity being a constant, you don't need to know the mass of a falling object to calculate the impact force on a piece of climbing gear. Jay  Excuse me Jay!? Mass is integral to calculating impact force. You most definately need to know the MASS. The standard equation for the maximum impact force T1 on the climber is T1 = w + sqrt(w^2 + 2krw) , where w is the climber's weight, k represents the elasticity of the rope (not a function of the climber's mass), and r is the fall factor. You'll have to help me out here: why do I "definately" need to know the climber's "MASS" to calculate the impact force? The rest of your post is sillier than I have the patience to respond to. Jay Because your assumption that the direction of fall will always lie parallel to the direction of gravity is flawed. Or don't you ever climb less than vertical slab?
(This post was edited by redlude97 on May 26, 2010, 6:11 PM)
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jt512
May 26, 2010, 6:11 PM
Post #102 of 311
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adatesman wrote: jt512 wrote: patto wrote: jt512 wrote: Most Americans don't even know what mass is, and, for purposes of understanding the strength of climbing gear, they don't need to. Thanks to gravity being a constant, you don't need to know the mass of a falling object to calculate the impact force on a piece of climbing gear. Jay Excuse me Jay!? Mass is integral to calculating impact force. You most definately need to know the MASS. The standard equation for the maximum impact force T1 on the climber is T1 = w + sqrt(w^2 + 2krw) , where w is the climber's weight, k represents the elasticity of the rope (not a function of the climber's mass), and r is the fall factor. You'll have to help me out here: why do I "definately" need to know the climber's "MASS" to calculate the impact force? The rest of your post is sillier than I have the patience to respond to. Jay Because your assumption that the direction of fall will always lie parallel to the direction of gravity is flawed.
How many times can you be wrong in one thread, Aric? Are you going for some sort of a record? And no, I won't explain why you're wrong yet again. You're just wasting my time.
Jay
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jt512
May 26, 2010, 6:17 PM
Post #103 of 311
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roadstead wrote: jt512 wrote: beau wrote: Thanks everybody for the input, but no one seems to know what kilonewton ratings mean in practical terms for the climber. . . • the impact force calculator is useless, since I don't know what Fall Factor and Friction Factor are . . . • and jt512 is right, the article could have stopped at the first line saying 1kn = 225 pounds . . . The question is, if I weigh 140 pounds, what's my 6kn nut going to do for me if I shock load it, say in a fall of 2 feet, or 10 feet, or 20 feet? The only variables for a computation equation would be 1) weight of the climber, 2) distance of fall, and 3) kn rating of the piece. Am I wrong about this? Yes, you're wrong about what the only variables are. The maximum impact force a climber feels in a fall is, in theory, a function of only the climber's weight, the elasticity of the fall, and the fall factor, defined as the distance of the fall divided by the amount of rope available to absorb the fall. Call this force T1. Then the force on the belayer is a fraction (1 – µ) of T1, where µ is the proportion of T1 that the belayer does not feel due to friction between the rope and the anchor. Call the force on the belayer T2. Then the force on the top anchor is T1 + T2. You can assume that µ, the friction factor, is 1/3. Now that you know what the fall factor is, go plug your numbers into the online calculator, and see whether the nut would be expected to hold. Jay All of this and the OP leads 5.6 outside 
Wow, that statement is even too elitist for me! If the OP is a beginning leader, then this is exactly the right time for him to learn the basics of fall factors, impact forces, and the limitations of his gear.
Jay
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kriso9tails
May 26, 2010, 6:28 PM
Post #104 of 311
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hafilax wrote: You don't fall on slab. You slide, scrape and tumble.
You just murdered my mental image of taking some sort of magical whipper on slab. How does it feel to kill someone's dreams?
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adatesman
May 26, 2010, 6:40 PM
Post #105 of 311
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kennoyce
May 26, 2010, 6:47 PM
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Sorry patto, it does look like you are a bit confused on several things.
First of all. The links you referred to suggesting that a lb is a measurement of mass are incorrectly using pound to denote pound mass. for a better view of mass in the english system see http://en.wikipedia.org/wiki/Slug_(mass), and to see a correct definition of pounds force see http://en.wikipedia.org/wiki/Pound-force
patto wrote: Actually no. Most things in industry have a safe working load figure. Eg the mass of a person on a step ladder or the weight of a truck across a small bridge. A 100kg person using a ladder will put a much greater force on the ladder than 100kg*9.8 force. Any movement of a 100kg person can cause significantly higher forces. In contrast climbing gear is rated at the MAXIMUM force (3sigma) before breaking. This is a completely different rating methodology.
Here you have some truth mingled with fiction. You are right about the industry using a safe working load (SWL) also known as a working load limit (WLL) for the ratings on their gear. Where you go wrong is the reason for this use. A SWL or WLL is still a measurement of force not mass. The reason it is below the breaking strength is not to account for dynamic loading, but to help avoid costly QC testing and lawsuits. Generally the SWL or WLL is determined by finding the breaking strength and dividing it by either 5 or 10 for the factor of safety. Once again the purpose of this is to be a maximum recommended force seen by the product, not mass. I hope that helps you understand it more clearly.
As you mentioned, in the climbing equipment industry they don't use SWL's or WLL's, but use the breaking strength of the equipment (not necessarily always to 3 sigma standards, this depends on the company). Climbing companies do this because they do generally test every single piece of equipment to much beyond what the SWL or WLL would be. This is a costly process for them, but it is necessary due to the life saving nature of the equipment they produce.
patto wrote: kennoyce wrote: A carabiner is safe up to 5000 lbs in mass as long as it is only under the acceleration due to gravity, why you may ask. because 5000 lbf and 5000 lbm exert the same force on the object as long as the only acceleration is that of the earths gravity (and we assume that g is constant everywhere on the earth which is a good enough assumption here). Um no. This would not be 'safe'. As before safe working load is a long way away from the upper limit of breaking strain.
What I said above is completely correct as long as the acceleration on the mass doesn't exceed "g" as I stated. In this case the carabiner will be completely safe because the maximum force it can withstand will not be exceeded. Of course here on earth that would mean that the mass would have to be static, but take that same carabiner to the moon, and now it can hold that mass even if it is a bit dynamic, or even a much higher static mass.
This is why force must be used and not mass. A mass can never damage or break anything unless acted upon by an acceleration.
I'm really not trying to start a pissing match like Jay and Aric are doing, but you do need to get some facts straight.
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jt512
May 26, 2010, 6:53 PM
Post #107 of 311
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adatesman wrote: jt512 wrote: You're just wasting my time. Jay I like to think of it the other way around, but there you go.
That is a completely unjustified statement. You have done nothing in this thread but nitpick every post I've made. And the nitpicking would be bad enough if you were at least technically correct, but you've been consistently wrong. In contrast, I have answered the OP's questions concisely, first by pointing out the relation between pounds and kilonewtons he was looking for (you did notice where he said that I was right, that the article could have ended after the first sentence), and then by pointing him to an online impact force calculator that I developed, and then by explaining to him the basics of the relationship between fall factor and impact force. How dare you accuse me of being the problem in this thread. Furthermore, if you hadn't been so hellbent on proving me wrong about something, anything, no matter what the cost to your own reputation on this website, you might have actually learned something.
Jay
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adatesman
May 26, 2010, 6:59 PM
Post #108 of 311
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chadnsc
May 26, 2010, 7:00 PM
Post #109 of 311
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adatesman wrote: kennoyce wrote: I'm really not trying to start a pissing match like Jay and Aric are doing, but you do need to get some facts straight. I wouldn't quite call it a pissing match... As I said several pages back I'm just poking Jay. For whatever reason I'm curious what it takes to get him to actually concede a point or admit he might be wrong about something. Unfortunately it seems he has more patience for this bologna than I do... 
I would call it a pissing match, and Adat as a mod you know that me saying you and Jay should get a room means a great deal. 
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rgold
May 26, 2010, 7:03 PM
Post #110 of 311
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Jay's statement is logically and physically correct.
There is no formula involving rope dynamics that involves m as an isolated term, as opposed to mg=w. (This would include falling on slabs, penduluming, pushing off, etc.) It follows that knowing w is sufficient for all possible calculations, and so a knowledge of m is not required if w is available.
None of the various purported "deductions" based on Jay's statement and used to attack it are logical consequences of anything he said.
Give it a rest already.
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adatesman
May 26, 2010, 7:05 PM
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jt512
May 26, 2010, 7:07 PM
Post #112 of 311
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adatesman wrote: kennoyce wrote: I'm really not trying to start a pissing match like Jay and Aric are doing, but you do need to get some facts straight. I wouldn't quite call it a pissing match... As I said several pages back I'm just poking Jay. For whatever reason I'm curious what it takes to get him to actually concede a point or admit he might be wrong about something.
Like I said. It's you wasting my time, not the other way around, as you falsely claimed in your last post. And by the way, the correct way to get someone to concede a point is to actually find something wrong that they've said, not by making idiotic statements about needing to know mass on slabs, or by misreading my posts, or by repeating someone else's fallacious conclusions.
Jay
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jt512
May 26, 2010, 7:11 PM
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adatesman wrote: Interesting selective memory, Jay. If you look back, this all started when I questioned your calling the article that was posted lame when it actually did a good job of answering the OP's question correctly.
Wrong again, Aric!
The OP himself wrote: [A]nd jt512 is right, the article could have stopped at the first line saying 1kn = 225 pounds . . .
And you're a moderator? Well, the who the hell is moderating you?
Jay
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adatesman
May 26, 2010, 7:15 PM
Post #114 of 311
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jt512
May 26, 2010, 7:20 PM
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adatesman wrote: jt512 wrote: adatesman wrote: Interesting selective memory, Jay. If you look back, this all started when I questioned your calling the article that was posted lame when it actually did a good job of answering the OP's question correctly.Wrong again, Aric! Does it not do a good job of explaining what a kilonewton is, and in simple to understand terms?
I've stated my opinion on the article at least twice in this thread. No need to do it again.
Jay
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kennoyce
May 26, 2010, 7:20 PM
Post #116 of 311
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adatesman wrote: me wrote: I'm really not trying to start a pissing match like Jay and Aric are doing, but you do need to get some facts straight. I wouldn't quite call it a pissing match... As I said several pages back I'm just poking Jay. For whatever reason I'm curious what it takes to get him to actually concede a point or admit he might be wrong about something. Unfortunately it seems he has more patience for this bologna than I do...
Sorry if I offended you by calling it a pissing match. It is certainly entertaining to read through it all. Unfortunately I am at work and don't have enough time to "poke" patto. I just really don't like people spewing mis-information.
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adatesman
May 26, 2010, 7:34 PM
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jt512
May 26, 2010, 7:41 PM
Post #118 of 311
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adatesman wrote: jt512 wrote: adatesman wrote: jt512 wrote: adatesman wrote: Interesting selective memory, Jay. If you look back, this all started when I questioned your calling the article that was posted lame when it actually did a good job of answering the OP's question correctly.Wrong again, Aric! Does it not do a good job of explaining what a kilonewton is, and in simple to understand terms? I've stated my opinion on the article at least twice in this thread. No need to do it again. Jay Very true, but I don't recall the opinion expressed being anything other than thinking the article was lame and overly long, neither of which are judging it on its technical merits. So once again, does the article do a good job of explaining what a kilonewton is, and in simple to understand terms, or not?
I'd give it a C–. It's wordy and contains too many irrelevancies.
Seriously, the answer to "What is a kilonewton?" is "It's a unit of force in the metric system that is equal to 225 lb."
Jay
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adatesman
May 26, 2010, 7:57 PM
Post #119 of 311
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jt512
May 26, 2010, 8:06 PM
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adatesman wrote: jt512 wrote: I'd give it a C–. It's wordy and contains too many irrelevancies. Seriously, the answer to "What is a kilonewton?" is "It's a unit of force in the metric system that is equal to 225 lb." Jay But is it not technically correct?
As far as I can tell, yes.
Jay
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adatesman
May 26, 2010, 8:10 PM
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jt512
May 26, 2010, 8:25 PM
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adatesman wrote: jt512 wrote: adatesman wrote: jt512 wrote: I'd give it a C–. It's wordy and contains too many irrelevancies. Seriously, the answer to "What is a kilonewton?" is "It's a unit of force in the metric system that is equal to 225 lb." Jay But is it not technically correct? As far as I can tell, yes. Jay Then why make the assumption that the full, correct answer is not actually the answer that the OP was looking for and instead provide an arguably incorrect, shorter answer that may have left him even more confused?
First of all, I've seen the question asked by climbers on the internet or in person something on the order of 50 times, and every single time all the climber needed and wanted to know was that *sigh* a kilonewton is a unit of force equal to 225 lb. Secondly, that answer is not "arguably incorrect." It's correct, period, at least to three significant figures. Third, to someone who is so scientifically ignorant that they have to ask the question in the first place, it is ridiculous to argue that that one-sentence answer would be more confusing to them than a wordy, convoluted monologue involving a constellation of irrelevant (to them) factoids about time, distance, force, weight, and mass, in two different systems of measurement.
Jay
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curt
May 26, 2010, 8:30 PM
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adatesman wrote: jt512 wrote: I'd give it a C–. It's wordy and contains too many irrelevancies. Seriously, the answer to "What is a kilonewton?" is "It's a unit of force in the metric system that is equal to 225 lb." Jay But is it not technically correct?
Because it's 224.8?
Curt
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ptlong
May 26, 2010, 8:32 PM
Post #124 of 311
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adatesman wrote: But is it not technically correct?
It has a few minor errors and reads like it was written by someone who didn't have a full grasp of the subject. Whether or not "lame" is the right adjective is a matter of opinion, but I'd agree with the C- grade.
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dugl33
May 26, 2010, 8:38 PM
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curt wrote: adatesman wrote: jt512 wrote: I'd give it a C–. It's wordy and contains too many irrelevancies. Seriously, the answer to "What is a kilonewton?" is "It's a unit of force in the metric system that is equal to 225 lb." Jay But is it not technically correct? Because it's 224.8? Curt
Well, technically 224.81...
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