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ptlong
May 27, 2010, 2:53 PM
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I'm pretty sure Patto is correct.
NIST defines the pound as exactly 0.45359237 kg.
The kilogram, in turn, is defined by a chunk of platinum-iridium kept somewhere in France. They have made copies but when later compared to the original they tend to not match up exactly. It appears that the standard, which is over 100 years old, is slowly losing mass. The changes are quite small, yet still an issue, and a better standard for the kg is something that is being worked on.
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csproul
May 27, 2010, 3:06 PM
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ptlong wrote: I'm pretty sure Patto is correct. NIST defines the pound as exactly 0.45359237 kg. The kilogram, in turn, is defined by a chunk of platinum-iridium kept somewhere in France. They have made copies but when later compared to the original they tend to not match up exactly. It appears that the standard, which is over 100 years old, is slowly losing mass. The changes are quite small, yet still an issue, and a better standard for the kg is something that is being worked on.
(This post was edited by csproul on May 27, 2010, 3:12 PM)
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swoopee
May 27, 2010, 3:10 PM
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I thought slug was mass and pound was force.
But anyway I thought the discussion was about kilonewtons, particularly as they apply in climbing. So here is my opinion, meaning most probably wrong and therefore worthless, anytime I fall I expect the force on the tie in points of my harness to be somewhere in the neighborhood of 0.85-0.90kN assuming that the fall is not so hard as to stretch the rope to max elongation before slowing my velocity to somewhere in the vicinity of 0. So that said, I have to guess that the force at the other end of the rope is close to the same, maybe a bit lower due to friction and the force on the anchor is very close to the combined forces.
In other words, assuming that the belayer is not tied in, or at least can be pulled upward a few feet, the force on the top anchor is roughly equal to, or slightly greater than the weight of the climber + the weight of the belayer.
So, while I know this is probably all wrong and everyone is gonna try to explain why, it works for me, and I do not worry about taking "reasonable" falls because I believe that the forces on climber, belayer, and anchor are relatively small quantities relative to what the gear will hold. 
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jt512
May 27, 2010, 3:16 PM
Post #179 of 311
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swoopee wrote: I thought slug was mass and pound was force. But anyway I thought the discussion was about kilonewtons, particularly as they apply in climbing. So here is my opinion, meaning most probably wrong and therefore worthless, anytime I fall I expect the force on the tie in points of my harness to be somewhere in the neighborhood of 0.85-0.90kN assuming that the fall is not so hard as to stretch the rope to max elongation before slowing my velocity to somewhere in the vicinity of 0. So that said, I have to guess that the force at the other end of the rope is close to the same, maybe a bit lower due to friction and the force on the anchor is very close to the combined forces. In other words, assuming that the belayer is not tied in, or at least can be pulled upward a few feet, the force on the top anchor is roughly equal to, or slightly greater than the weight of the climber + the weight of the belayer. So, while I know this is probably all wrong...
Not "probably." "Completely" might describe it.
In reply to: ...it works for me...
"It" does not "work for" you. "It" is completely wrong. It just doesn't matter, because the gear you're using is strong enough to hold the actual impact forces. If, you were to design an anchor based on "it," you'd quickly discover—well, your survivors would, anyway—how well "it" "works for" you.
Jay
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hafilax
May 27, 2010, 3:32 PM
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kriso9tails wrote: raingod wrote: (Also I'm Canadian and have been raised to hate the imperial system) Ron Well, I'm willing to bet that the average Canadian doesn't know their weight in kilos off the top of their head nor their height in centimeters. Much like the Queen, it's debatable just how alive imperial measurements are in Canada, but at the very least we can be certain that they aren't quite dead yet.
I don't know my height or weight in metric... or is that mass. I'm so confused.
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ptlong
May 27, 2010, 4:13 PM
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csproul wrote: My point is that in every day use, even by people with only a rudimentary knowledge of physics, people in the US understand a pound to be a unit of weight, not a unit of mass. I think this is the point that Curt has been making too.
My impression is that the average man on the street doesn't make the distinction.
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redlude97
May 27, 2010, 4:29 PM
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ptlong wrote: csproul wrote: My point is that in every day use, even by people with only a rudimentary knowledge of physics, people in the US understand a pound to be a unit of weight, not a unit of mass. I think this is the point that Curt has been making too. My impression is that the average man on the street doesn't make the distinction.
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swoopee
May 27, 2010, 5:01 PM
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I've been climbing off and on for 35 yrs, and no one has died yet.  I am not saying build anchors to hold 2 kN, all I am saying is if you have good gear placements, don't fricking worry about it, and climb on. If you don't have good gear placements, but they're the best you can get, well either climb on, or bail, but quit worrying about the forces involved in a fall because it is simply impossible to calculate, especially while climbing. No one really has a clue so this entire thread has been pointless. Now shut up and climb. Or don't.
That said, I am total agreement with your initial response to the OP.
(This post was edited by swoopee on May 27, 2010, 5:07 PM)
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swoopee
May 27, 2010, 5:10 PM
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jt512 wrote: swoopee wrote: I thought slug was mass and pound was force. But anyway I thought the discussion was about kilonewtons, particularly as they apply in climbing. So here is my opinion, meaning most probably wrong and therefore worthless, anytime I fall I expect the force on the tie in points of my harness to be somewhere in the neighborhood of 0.85-0.90kN assuming that the fall is not so hard as to stretch the rope to max elongation before slowing my velocity to somewhere in the vicinity of 0. So that said, I have to guess that the force at the other end of the rope is close to the same, maybe a bit lower due to friction and the force on the anchor is very close to the combined forces. In other words, assuming that the belayer is not tied in, or at least can be pulled upward a few feet, the force on the top anchor is roughly equal to, or slightly greater than the weight of the climber + the weight of the belayer. So, while I know this is probably all wrong... Not "probably." "Completely" might describe it. In reply to: ...it works for me... "It" does not "work for" you. "It" is completely wrong. It just doesn't matter, because the gear you're using is strong enough to hold the actual impact forces. If, you were to design an anchor based on "it," you'd quickly discover—well, your survivors would, anyway—how well "it" "works for" you. Jay
Just reread your post, and actually that was my point. We are actually in agreement here, dang it.
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jt512
May 27, 2010, 5:43 PM
Post #185 of 311
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swoopee wrote: jt512 wrote: swoopee wrote: I thought slug was mass and pound was force. But anyway I thought the discussion was about kilonewtons, particularly as they apply in climbing. So here is my opinion, meaning most probably wrong and therefore worthless, anytime I fall I expect the force on the tie in points of my harness to be somewhere in the neighborhood of 0.85-0.90kN assuming that the fall is not so hard as to stretch the rope to max elongation before slowing my velocity to somewhere in the vicinity of 0. So that said, I have to guess that the force at the other end of the rope is close to the same, maybe a bit lower due to friction and the force on the anchor is very close to the combined forces. In other words, assuming that the belayer is not tied in, or at least can be pulled upward a few feet, the force on the top anchor is roughly equal to, or slightly greater than the weight of the climber + the weight of the belayer. So, while I know this is probably all wrong... Not "probably." "Completely" might describe it. In reply to: ...it works for me... "It" does not "work for" you. "It" is completely wrong. It just doesn't matter, because the gear you're using is strong enough to hold the actual impact forces. If, you were to design an anchor based on "it," you'd quickly discover—well, your survivors would, anyway—how well "it" "works for" you. Jay Just reread your post, and actually that was my point. We are actually in agreement here, dang it.
Although we may be in agreement that, since the gear is good enough, your underestimation of the impact forces doesn't matter, we are not in agreement about the magnitude of the impact forces. You believe that the force on the anchor in a typical lead fall is just over two times body weight. However, it can easily be shown that the force on the anchor in a top rope "fall" with no slack in the rope will be about 3-1/3 times body weight. Thus, you believe that a typical lead fall will produce less force on the anchor than the mildest possible toprope "fall."
Jay
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USnavy
May 27, 2010, 5:45 PM
Post #186 of 311
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csproul wrote: patto wrote: curt wrote: And, a "pound force," as used here, is the original and traditional definition of a "pound." The "pound mass" is a mere convenience created much later to allow weights and masses to be used interchangeably here on Earth--where the acceleration due to gravity is pretty much constant. SIGH. You can argue tradition and convenience all you want. 1000 years ago isn't really that relevent when the difference between weight and mass wasn't established. Today. In the modern world. A pound is a unit of mass primarily. A unit of force in the FPS system. Today. In the modern world. A pound force is defined by a pound mass. (which is defined in terms of a kg) Today. In the United States. In US Customary units, a pound is a unit of mass. And yet, if you were to ask 100 people what a pound is (in the US anyway), I bet almost all of them would tell you that a pound is a unit of weight, i.e force and not a unit of mass.
If you have three cards, two yellow, one orange, all flipped upside down and identical on their back side, and you flip one over revealing a yellow card what are the chances that the next one you choose will be orange?
(This post was edited by USnavy on May 27, 2010, 5:46 PM)
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jt512
May 27, 2010, 5:53 PM
Post #187 of 311
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USnavy wrote: csproul wrote: patto wrote: curt wrote: And, a "pound force," as used here, is the original and traditional definition of a "pound." The "pound mass" is a mere convenience created much later to allow weights and masses to be used interchangeably here on Earth--where the acceleration due to gravity is pretty much constant. SIGH. You can argue tradition and convenience all you want. 1000 years ago isn't really that relevent when the difference between weight and mass wasn't established. Today. In the modern world. A pound is a unit of mass primarily. A unit of force in the FPS system. Today. In the modern world. A pound force is defined by a pound mass. (which is defined in terms of a kg) Today. In the United States. In US Customary units, a pound is a unit of mass. And yet, if you were to ask 100 people what a pound is (in the US anyway), I bet almost all of them would tell you that a pound is a unit of weight, i.e force and not a unit of mass. If you have three cards, two yellow, one orange, all flipped upside down and identical on their back side, and you flip one over revealing a yellow card what are the chances that the next one you choose will be orange?
1/2, if you flipped over the first card; 1/3 if Monty flipped it over.
Jay
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edm
May 27, 2010, 5:54 PM
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As I've been reading through this thread I have found myself in agreement with Curt et. al. (the Pound is a Unit of Force camp), but I was intrigued by Patto's challenge to find a definition of the pound based on force.
After a bit of looking it appears that Patto is actually right. Here is a link to a NIST history of units of weights and measures in the US:
http://www.nist.gov/...pubs/sp447/index.cfm
I find this interesting because American schools definitely teach that a pound is a unit of force, and the classic example is that a 180 pound person on Earth will weigh 30 pounds on the moon. Apparently this is not actually the case, since Congress has defined the pound in terms of the kilogram for over 100 years at least.
Further evidence is in NIST's guide to the SI system:
http://physics.nist.gov/cuu/pdf/sp811.pdf
In the conversion tables towards the end, the term "pound" is used a unit of mass, whereas the term "pound-force" is specified for force.
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csproul
May 27, 2010, 6:00 PM
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That sounds like something Majid might post.... I'd have to ask whether you knew a prioiri that the first card flipped would be yellow.
http://en.wikipedia.org/wiki/Monty_Hall_problem
What does this have to do with anything?
edit: looks like Jay beat me to it
(This post was edited by csproul on May 27, 2010, 6:03 PM)
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redlude97
May 27, 2010, 6:07 PM
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edm wrote: As I've been reading through this thread I have found myself in agreement with Curt et. al. (the Pound is a Unit of Force camp), but I was intrigued by Patto's challenge to find a definition of the pound based on force. After a bit of looking it appears that Patto is actually right. Here is a link to a NIST history of units of weights and measures in the US: http://www.nist.gov/...pubs/sp447/index.cfm .
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edm
May 27, 2010, 6:14 PM
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There are 26 pdf documents in that link, all scanned in from a print document from 1976 and thus not searchable. You must be a damn fast reader!
Anyway, Appendix 5 "The U.S. yard and pound" discuss the definition of the pound based on the kilogram, which I don't think anyone is disputing is a measure of mass.
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bigo
May 27, 2010, 6:15 PM
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csproul wrote: That sounds like something Majid might post.... I'd have to ask whether you knew a prioiri that the first card flipped would be yellow. http://en.wikipedia.org/wiki/Monty_Hall_problem What does this have to do with anything? edit: looks like Jay beat me to it
That link just blew my mind. cool thanks.
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hafilax
May 27, 2010, 6:20 PM
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Can someone change the thread title to:
Meaningless discussion of kN
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bigo
May 27, 2010, 6:24 PM
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edm wrote: There are 26 pdf documents in that link, all scanned in from a print document from 1976 and thus not searchable. You must be a damn fast reader! Anyway, Appendix 5 "The U.S. yard and pound" discuss the definition of the pound based on the kilogram, which I don't think anyone is disputing is a measure of mass.
Sure it's a measure of mass, but people use it as a measure of weight all of the time. When have you heard anyone give you their weight in KNs?
This thread is silly. A pound is used to describe force and mass and often it doesn't matter which flavor is being used since a lb-m weighs a lb-f on earth. If it does matter you can usually figure it out in the context it is being used. If you need to know how much your truck can carry, you are probably talking about a 2000 lbs of mass that weighs 2000 lbs of force. If you want to know when a cable will break, you are talking about xxxlbs of force that could be 'generated' by suspending xxxlbs of mass from it.
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redlude97
May 27, 2010, 6:35 PM
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edm wrote: There are 26 pdf documents in that link, all scanned in from a print document from 1976 and thus not searchable. You must be a damn fast reader! Anyway, Appendix 5 "The U.S. yard and pound" discuss the definition of the pound based on the kilogram, which I don't think anyone is disputing is a measure of mass. 
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rgold
May 27, 2010, 7:37 PM
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In spite of the massive size of this thread, people keep pounding the same points over and over again. Pool old Newton would have succumbed to a headache days ago. Is there no way to force them to stop? If only we could just send out a cease-and-desist telegram!
I think that about covers it...
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kriso9tails
May 27, 2010, 7:40 PM
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I'm glad you weighed in with your opinion here.
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rgold
May 27, 2010, 7:48 PM
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Thanks. If we can't force it to end, perhaps we can at least accelerate its demise?
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chadnsc
May 27, 2010, 7:53 PM
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Yes, yes it does. Now will all you internet physicist please stop as I feel like I'm listening to a group of high school geeks arguing about which version of Star Trek is better.
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drector
May 27, 2010, 7:53 PM
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There appears to be too much friction between the users on this thread.
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