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USnavy
Nov 9, 2007, 8:07 AM
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flint
Nov 9, 2007, 8:25 AM
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Do they not teach you math, physics or engineering in the Navy... Some days I am so ashamed of my passport.
OK to the topic. You get a factor one fall at 40m when you fall 20m. This is because you have fallen half the length of the rope you have out. So lets simplify it and say you divided 20 by 40 and you got .5
Now, if you were to jump off a bridge with a 60m rope, you would also be falling the full 60m length... Causing a factor 2 fall, or 60 divided by 60 = 1
This is completely different as I hope this simplified example has shown. No the guys at petzl are pretty sharp at what they do...
Please don't bungee on your climbing rope... Amazing how much someone can learn from the names of the items they purchase... It is a CLIMBING rope, not a climbing/bungee rope.
j-
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flint
Nov 9, 2007, 8:27 AM
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USnavy wrote: I noticed that the force calculator on Petzel's site is dependent on fall factor. The simulator basically states that the fall factor is what depicts how much stress the equipment sees, not the length of the fall. It suggests this by stating a fall of 5m from a height of 10m produces the same force as a fall of 20m from a height of 40m (both fall factor 1 falls). The simulator also states that a fall using the two examples I listed with a weight of 75kg produces a force of 10 kN on the anchor with a 10.5mm rope. Well judging by the info that simulator provided me with I could tie a dynamic rope to a bridge, jump off of it, fall the full 60m of the rope (fall factor 1) and place only 10kN of force on the rope and bridge. Well that doesn’t sound right. Is the simulator actually correct? I don’t understand how you can fall 60m and produce as much force as if you were to fall 5m with a fall factor of 1. Does anyone actually know of someone who used a dynamic rope as a bungee rope? Does it actually hold?
Had to quote you, don't like to see people save face by deleting posts.
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notapplicable
Nov 9, 2007, 12:11 PM
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flint wrote: Do they not teach you math, physics or engineering in the Navy... Some days I am so ashamed of my passport. OK to the topic. You get a factor one fall at 40m when you fall 20m. This is because you have fallen half the length of the rope you have out. So lets simplify it and say you divided 20 by 40 and you got .5 Now, if you were to jump off a bridge with a 60m rope, you would also be falling the full 60m length... Causing a factor 2 fall, or 60 divided by 60 = 1 This is completely different as I hope this simplified example has shown. No the guys at petzl are pretty sharp at what they do... Please don't bungee on your climbing rope... Amazing how much someone can learn from the names of the items they purchase... It is a CLIMBING rope, not a climbing/bungee rope. j-
The fall you described (bold is mine) only generates a FF of 1, as your math showed. Where do you get a FF of two?
To create a FF of 2 you have to fall twice the distance of the rope out. So if the guy attached the rope at street level then climbed 60 meters up the bridge supports and took a whip he would be looking at a FF of 2. 120 meter fall divided by the 60 meters of rope = 2
I think your attitude was a little harsh to have given the wrong answer to the mans question. Perhaps the low levels of oxygen up on that high horse are causing your problems in math?
Edited to add: OP, I would guess that the rope would hold atleast one of those jumps but you will quickly trash the thing. DONT DO IT, BUY A BUNGEE CORD. (Emphasis on the period)
(This post was edited by notapplicable on Nov 9, 2007, 12:14 PM)
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Carnage
Nov 9, 2007, 2:29 PM
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USnavy wrote: http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?do=markup_help; Get Markup Help Does anyone actually know of someone who used a dynamic rope as a bungee rope? Does it actually hold?
read up on dan osman, know mainly for being a free soloist, but died doing this. he did many jumps and his gear held. ive heard 2 explanations of why his gear broke on his las jump. 1) cause ropes crossed and the heat from friction melted 1 rope, 2) cause crossed ropes put an unholdable amount of stress on a knot.
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jt512
Nov 9, 2007, 2:44 PM
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USnavy wrote: I noticed that the force calculator on Petzel's site is dependent on fall factor. The simulator basically states that the fall factor is what depicts how much stress the equipment sees, not the length of the fall. It suggests this by stating a fall of 5m from a height of 10m produces the same force as a fall of 20m from a height of 40m (both fall factor 1 falls). The simulator also states that a fall using the two examples I listed with a weight of 75kg produces a force of 10 kN on the anchor with a 10.5mm rope. Well judging by the info that simulator provided me with I could tie a dynamic rope to a bridge, jump off of it, fall the full 60m of the rope (fall factor 1) and place only 10kN of force on the rope and bridge. Well that doesn’t sound right. Is the simulator actually correct? I don’t understand how you can fall 60m and produce as much force as if you were to fall 5m with a fall factor of 1. Does anyone actually know of someone who used a dynamic rope as a bungee rope? Does it actually hold?
Oddly enough, they sometimes even hold factor-2 falls.
Jay
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rgold
Nov 9, 2007, 2:46 PM
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USNavy, there are sources explaining how dynamic ropes work all over the web. If you don't want to look too far, you could jump to my post here, download the attached StandardEqn.pdf, and read up. But this is just one of many sources.
(This post was edited by rgold on Nov 9, 2007, 2:47 PM)
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zealotnoob
Nov 9, 2007, 2:56 PM
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flint wrote: Do they not teach you math, physics or engineering in the Navy... Some days I am so ashamed of my passport. OK to the topic. You get a factor one fall at 40m when you fall 20m. This is because you have fallen half the length of the rope you have out. So lets simplify it and say you divided 20 by 40 and you got .5 Now, if you were to jump off a bridge with a 60m rope, you would also be falling the full 60m length... Causing a factor 2 fall, or 60 divided by 60 = 1 This is completely different as I hope this simplified example has shown. No the guys at petzl are pretty sharp at what they do... Please don't bungee on your climbing rope... Amazing how much someone can learn from the names of the items they purchase... It is a CLIMBING rope, not a climbing/bungee rope. j-
Yeah man...this is pretty damn bad. ...wouldn't want you deleting it to save face.
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jt512
Nov 9, 2007, 3:01 PM
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zealotnoob wrote: flint wrote: Do they not teach you math, physics or engineering in the Navy... Some days I am so ashamed of my passport. OK to the topic. You get a factor one fall at 40m when you fall 20m. This is because you have fallen half the length of the rope you have out. So lets simplify it and say you divided 20 by 40 and you got .5 Now, if you were to jump off a bridge with a 60m rope, you would also be falling the full 60m length... Causing a factor 2 fall, or 60 divided by 60 = 1 This is completely different as I hope this simplified example has shown. No the guys at petzl are pretty sharp at what they do... Please don't bungee on your climbing rope... Amazing how much someone can learn from the names of the items they purchase... It is a CLIMBING rope, not a climbing/bungee rope. j- Yeah man...this is pretty damn bad. ...wouldn't want you deleting it to save face.
Thanks for quoting that, so I could see it without taking Flint out of my killfile.
Jay
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microbarn
Nov 9, 2007, 3:12 PM
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If you fall farther, then you have more rope out to absorb the force and spread out the time of the absorption.
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reg
Nov 9, 2007, 3:24 PM
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Carnage wrote: read up on dan osman, know mainly for being a free soloist, but died doing this. he did many jumps and his gear held. ive heard 2 explanations of why his gear broke on his las jump. 1) cause ropes crossed and the heat from friction melted 1 rope, 2) cause crossed ropes put an unholdable amount of stress on a knot.
dano's jump rope crossed his "anchor" rope which was melted and broke. this happened because he changed his jump position at the last minute attempting to get a longer jump distance to up his record, it was dark when he jumped aiding in the mistake. he had gone up to retrive his rig after the park service told him they would do it which ment he would lose his gear if he didn't. he was not suppose to jump anymore but instead of cleaning the rig he made a last attempt. changing his position at the last minute - under pressure - in the dark ..............
he was on the cell phone when he jumped - which he often did - with one of his close friends who was delayed getting there to help him remove the rig. the friend (just can't remember who or which book i was reading - i'll find it if needed) was telling him not to do it then listened to the jump live. sad story esp. because just days earlier he was interviewed and he said his guardian angles needed a vacation and he was headed for some couch time with his family.
to the op: FF 2 happens when the leader does not have any gear in and falls onto the belay. say she climbs away 10 feet up the rock then falls. she will fall 20+ feet - onto the belay - with only 10 feet of rope out = FF2 but if even one piece where put in - even clipping a leg of the anchor would reduce to less then FF2 - i believe John Long refered to it as the "jesus nut" - the first piece. that piece is where you measure the fall distance from - then any rope from that piece back to the belay is added to the rope lenght thus reducing the FF. the more pieces you put in at the beggining - the lower the FF.
all dynamic climbing ropes are designed by code to limit impact to 12kn max. when used correctly. if you fall 10' on 5' of rope there isn't much stretch if any. but falling a full rope lenght onto a ridgid anchor, i believe, would result in a FF2 with a impact force of not more then 12kn and a fall distance of ~260 feet depending on percent of elongation designed into the rope.
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j_ung
Nov 9, 2007, 3:26 PM
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USnavy wrote: It suggests this by stating a fall of 5m from a height of 10m produces the same force as a fall of 20m from a height of 40m (both fall factor 1 falls).
The two falls actually don't produce the same force. The farther fall generates much more force, but there's more rope to handle that force in direct proportion. When people say, "both falls generate the same force," what they actually mean is that the top piece feels the same force in both falls, because the longer length of rope "absorbs," more of it.
(This post was edited by j_ung on Nov 9, 2007, 3:27 PM)
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jt512
Nov 9, 2007, 3:28 PM
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j_ung wrote: USnavy wrote: It suggests this by stating a fall of 5m from a height of 10m produces the same force as a fall of 20m from a height of 40m (both fall factor 1 falls). The two falls actually don't produce the same force. The farther fall generates much more force, but there's more rope to handle that force in direct proportion. When people say, "both falls generate the same force," what they actually mean is that the top piece feels the same force in both falls, because the longer length of rope "absorbs," more of it.
You are confusing force with energy, and consequently your post makes no sense.
Jay
(This post was edited by jt512 on Nov 9, 2007, 3:28 PM)
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zealotnoob
Nov 9, 2007, 3:39 PM
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OT: Another quirk of the climbing system that can be surprising is the pulley effect. I.e, if you bail from a climb, off a single piece of pro, by having your partner lower you, you're applying twice the amount of force on that piece than if you rapped from it...
(This post was edited by zealotnoob on Nov 9, 2007, 3:42 PM)
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shockabuku
Nov 9, 2007, 3:42 PM
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flint wrote: Do they not teach you math, physics or engineering in the Navy...
Right, because every sailor needs to know that.
flint wrote: Some days I am so ashamed of my passport. j-
Sometimes I'm so ashamed of my countrymen.
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greenketch
Nov 9, 2007, 4:17 PM
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USNavy, You are on the right track assuming that a longer fall creates more kinetic energy. As previously stated you need to look at the entire picture not just the line item. A rope functions as the resistance that dissapaites that energy. The critical factor is not the length of fall, it is the amount of rope that is involved in the catch.
The ropes internal construction functions to limit the force excerted at any moment. So reexamineing the formula you are questioning. The weight and the distance fallen give you the force generated. The ratio of rope involved to fall distance gives you a correction factor for the time of disapation, and the type and placement of gear helps figure how that force is applied.
A larger fall caught with a a low percentage of rope is fairly soft and gradual (long period of disapation) and a small fall caught on a high percentage of rope is pretty brutal (short period of disapation).
Go back to the fall calculator and enter two falls, one that is a 50 footer caught on 150' of rope, and one that is a 15 footer caught on 8 feet of rope. Look close at the forces applied to the climber.
Now keep in mind that the time of disapation also is the time the rope is stretching. In the second example I gave the climber will deck do to rope stretch if the belayre/anchor is at the deck. The only way for this to happen is for folk who are above the ground (second pitch or higher) where it is actually possible for the faller to end below the belayer. A 10' fall on 5' of rope is brutal.
As to the rest of your question I have not taken 600' + jumps like Dan Osman. I have taken a fall that was a bit over 80'. It was near the end of a lead and was caught on 150' of rope, nice ride, one of the softest catches I ever had. Now bear in mind I think I had to clean my shorts after I stopped moving. That was a long time in the air.
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angry
Nov 9, 2007, 4:25 PM
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Guys, give flint a break. He lives in Ohio after all, he's got enough problems.
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curt
Nov 9, 2007, 10:57 PM
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These types of threads are the funniest on RC.com, for sure. Lots of people explaining the math/physics behind fall-factor and resultant force calculations--and getting it completely wrong. Do as rgold suggested above and read his article on the subject.
Curt
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j_ung
Nov 9, 2007, 11:13 PM
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jt512 wrote: j_ung wrote: USnavy wrote: It suggests this by stating a fall of 5m from a height of 10m produces the same force as a fall of 20m from a height of 40m (both fall factor 1 falls). The two falls actually don't produce the same force. The farther fall generates much more force, but there's more rope to handle that force in direct proportion. When people say, "both falls generate the same force," what they actually mean is that the top piece feels the same force in both falls, because the longer length of rope "absorbs," more of it. You are confusing force with energy, and consequently your post makes no sense. Jay
Me ... several thousand miles ... physics. Thanks for the clarification.
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trenchdigger
Nov 9, 2007, 11:20 PM
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curt wrote: These types of threads are the funniest on RC.com, for sure. Lots of people explaining the math/physics behind fall-factor and resultant force calculations--and getting it completely wrong. Do as rgold suggested above and read his article on the subject. Curt
I'll second that!
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curtis_g
Nov 9, 2007, 11:57 PM
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third. says the ME student sick of his Theoretical and Applied Mechanics homework.
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rocknice2
Nov 10, 2007, 12:30 AM
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j_ung wrote: jt512 wrote: j_ung wrote: USnavy wrote: It suggests this by stating a fall of 5m from a height of 10m produces the same force as a fall of 20m from a height of 40m (both fall factor 1 falls). The two falls actually don't produce the same force. The farther fall generates much more force, but there's more rope to handle that force in direct proportion. When people say, "both falls generate the same force," what they actually mean is that the top piece feels the same force in both falls, because the longer length of rope "absorbs," more of it. You are confusing force with energy, and consequently your post makes no sense. Jay Me ... several thousand miles ... physics. Thanks for the clarification.
j_ung
Imagine a force curve on a gragh .. Force/time .. The area under the curve is total energy expended.
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ptlong
Nov 10, 2007, 12:42 AM
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rocknice2 wrote: Imagine a force curve on a gragh .. Force/time .. The area under the curve is total energy expended.
Please refer to Curt's post above.
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