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bigwallgumbie
Apr 6, 2004, 5:55 AM
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No akclimber, I don't think there are ANY smart people posting in this thread. None.
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ryanhos
Apr 6, 2004, 6:06 AM
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In reply to: No. You are confused. The "weight" you are dropping weighs 225 lb, or 1 kN, regardless of how high it is dropped from.
In reply to: However, all else equal, the force exerted as a result of dropping an object of a given weight will depend on the height from which it is dropped. |
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andypro
Apr 6, 2004, 6:13 AM
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In reply to: total weight on the anchor is 2(climbers + gear) + 1 rope. (multiply by gravity to get force...) Friction does not apply here.
actually...weight is already a multiplication of gravity. This si a case of either/or, not both.
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jason1
Apr 6, 2004, 6:55 AM
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In reply to: In reply to: Force(N)= Mass(Kg)xAcceleration(M/s2) or F=ma N=kg(m/s2) In other words, the length of the fall is irrelevant, correct? To use the original example, a 74.8 kg climber falling ANY distance generates 74.8 kg X 9.8 m/s2 = 733 newtons
Correct... so the force applied to the top piece is going to be around twice that if you don't account for friction... if you do the common factor is around 1/3... i think petzel uses 2/5 but there again you'd have to figure how much rope is actually running to determine how much friction is really a factor... in a factor 2 fall the amount of force reduction caused by friction is nil.... probally only slightly better in cases of short (16-20') falls or in falls which the dynamic properties of the rope is limited to such a lenght...
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reedcrr
Apr 6, 2004, 8:21 AM
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Wow so many bright young indiviuals in this post...
Let me see where do I begin....
Let's just sum this up....
At 28 Kn it is going to take 6295 pounds of force (Lbf. (either pushing or pulling) to possibly cause a failure in the Williams locking carabiner. Want an easier way to see this visually? Take a 1/2 x 4 stainless steel rawl bolt commonly used to set up anchors...drill a hole into solid rock and place the bolt properly. Once tightened and in place it will take the combined weight of 41 men of average weight (150 lbs.), and one small child, to break the bolt in to two pieces or at the very least bend it to the point of breaking. No this does not count jumping on the bolt to add more force!
At 7 Kn it will only take 10 men and a golden retriever.... but get this the bolt will hold! However the Williams locking carabiner will not! Bottom line don't cross-load the carabiner or leave the gate unlocked where it can open on it's own!
As stated in a previous post.... 1Kn = 225 Lbf (although you incorrectly stated pounds...not pounds of force!) or my little brother Jim sitting on my chest trying to get me to say uncle! Both Jim and gravity are keeping him on my chest and the amount of force I would need to get him off of me would have to equal his weight, provided that he did not move!...unless of course he just gives up! :)
Hope that clears the intent of my post up clearly...if not go cry in your beer and go back to school and take more tests!
Peace to all the Elvi out there!
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davidgduval
Apr 6, 2004, 9:49 AM
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In reply to: Well our climber coming to a stop after falling 21 Feet is going to generate around 1230 Dekanewtons (DaN) of force.
Could you please post the equation which you used to arrive at this figure?
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djjackson
Apr 6, 2004, 2:40 PM
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Does the group have any one who can take the original problem and attempt an explanation, to include type of rope fall factor, gravity ( force= mass x acceleration, if I recall basic physics)? Current issue of Rock and Ice has a fairly good article regarding dynamic and static belays, which touches on the problem in the thread. Also see website Rescue Dynamics for good articles regarding physics and actual trials of rope, carabiners,etc.
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rgold
Apr 6, 2004, 4:00 PM
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In reply to: This means that in this senario this 165 Lb. climber, falling 21 Feet (again remember 8.25 ft. above the protection to 12.25 ft. below the protection) is placing 12.29 Kn of force on the belayers locking carabiner.
A number of people have mentioned this makes no sense without specifying a fall factor. To that observation I'd add that these numbers are not very realistic in any case. I think it is pretty rare nowadays to find a dynamic rope with a UIAA impact force much more than 9 kN. Mammut, whose ropes tend to be the stiffest, makes an 11mm rope, (The Flex) with an impact rating of 9.2 kN. Bluewater's 11mm rope (the Enduro) is rated at 8.8 kN. These ratings are very close to the maximum rope tension obtainable, since they are obtained from a factor 1.78 fall. The post was describing a missed clip on a sport climb, and sport climbs are usually one pitch. This means that the fall factor will have to be less than 1 (or else the climber hits the ground, thereby sparing the cross-loaded carabiner). The impact rating are done for an 80 kg climber, whereas reedcrr uses a 75 kg climber, which would reduce the forces a little more. Now to this add the fact that after the climber's rope has passed through the top biner, the tension on the other side, because of rope friction on the biner, will be about 2/3 of the tension on the leader's side, so the belayer's locker will experience no more than 2/3 of the leader's impact. In reality, friction through other carabiners could reduce the load on the belayer much more.
Put all this together and you get a load on the belayer that is going to be way less than 12 kN, which is, by the way, the threshold set by the UIAA for bodily injury.
This doesn't alter any of the cautions about the weakness of cross-loaded biners. Those warnings could, however, have been made with numbers a little more relevant to climbing.
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mtnjunkie
Apr 6, 2004, 4:50 PM
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The only illustrative point made in this thread is the absolute need for the physics of climbing to be abstracted into fall factors.
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robmcc
Apr 6, 2004, 4:58 PM
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In reply to: The only illustrative point made in this thread is the absolute need for the physics of climbing to be abstracted into fall factors.
This may be the most insightful comment yet.
Rob
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robmcc
Apr 6, 2004, 5:07 PM
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In reply to: In reply to: Force(N)= Mass(Kg)xAcceleration(M/s2) or F=ma N=kg(m/s2) In other words, the length of the fall is irrelevant, correct? To use the original example, a 74.8 kg climber falling ANY distance generates 74.8 kg X 9.8 m/s2 = 733 newtons
Nope, absolutely wrong. 733 newtons is the force that climber places on the rope while hanging. Gravity is providing a downward acceleration of 9.8 m/s2 which is opposed precisely by the tension in the rope applying an upward acceleration of 9.8 m/s2. I'm hand waving a bit, but won't bother to explain unless someone feels like caling me on it. :)
As a fall is arrested, that upward acceleration is much higher. I remember in my biggest fall, which at around 35' wasn't that big, how strong the pull on the rope was. Say you decelerate at 5 gs or so, your equation becomes
74.8 kg X 49 m/s2 = 3665 newtons, or 3.7 kN
If instead you hit the ground and various parts of your body decelerate at an unhappy 50gs, you get a nice 37 kN impact force, hard parts break, soft parts tear, and you don't survive. Same fall, faster stop, radically different outcome. Soft catch or fatal impact, it all depends on how fast you stop. Anyone attempting to calculate this stuf without taking that into account is just plain wrong. Defend your erroneous calcs, original poster, or give it up.
Rob
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jason1
Apr 6, 2004, 8:45 PM
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i think you're confusing velocity and acceleration....
the acceleration due to gravity is constant...
velocity increases with time....
9.81m/s2(5s)= 49.05 m/s
9.81m/s2(6s)= 58.86 m/s
9.81m/s2(7s)= 68.67 m/s
you're right about crunching the math... it only gives guidelines... each fall is a case by case assessment and at best an estimate...
i wish we could hear what dr. kodos has to say on the subject... FREE KODOS!!!!!!
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robmcc
Apr 6, 2004, 8:50 PM
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In reply to: i think you're confusing velocity and acceleration.... the acceleration due to gravity is constant....
The key words there are "due to gravity". Gravity is not the only force acting on the climber. The rope exerts a force on the climber as well. Unlike gravity, that force is not constant.
Rob
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jason1
Apr 6, 2004, 9:05 PM
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you're absolutly right, i'm not arguing that gravity is the only force in this situation...
I am saying that the acceleration dosn't go up as you fall down... velocity dose...
acceleration would go down gradually as the friction of the system and the dynamic properties of the rope kick in... then if you have any screamers on the pieces count them in too... and any friction due to the rock...
if you want to find the acceleration it's the second derivitve of a position/time graph...
ROCK ME DR. KODOS!!!!! dr. kodos, dr. kodos
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robmcc
Apr 6, 2004, 9:21 PM
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In reply to: I am saying that the acceleration dosn't go up as you fall down... velocity dose...
If you read anywhere in anything that I've written that I think gravitational acceleration is not constant, you've misread. This thread started out with a completely incorrect description of the forces in a fall. Correcting those errors seemed worthwhile. Correcting your misreading of my posts doesn't.
Rob
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drunkencabanaboy
Apr 6, 2004, 9:22 PM
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In reply to: i think you're confusing velocity and acceleration.... the acceleration due to gravity is constant... velocity increases with time.... 9.81m/s2(5s)= 49.05 m/s 9.81m/s2(6s)= 58.86 m/s 9.81m/s2(7s)= 68.67 m/s you're right about crunching the math... it only gives guidelines... each fall is a case by case assessment and at best an estimate... i wish we could hear what dr. kodos has to say on the subject... FREE KODOS!!!!!!
Oh yah - but what about Terminal Velocity!?
ROFL ROFL
how friggin ridiculous is all of this? No one is getting any safer. LOL
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jason1
Apr 6, 2004, 9:40 PM
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74.8 kg X 49 m/s2 = 3665 newtons, or 3.7 kN
sorry if i misread...
terminal velocity is irrelavant when dealing in terms of acceleration...
like i said guys it's an estimate... the goal of putting up newton's 2nd law was to explain what a KN is, and give a general sense of how it is derived...
and as i said before... free kodos
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jason1
Apr 6, 2004, 9:51 PM
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If you read anywhere in anything that I've written that I think gravitational acceleration is not constant, you've misread. This thread started out with a completely incorrect description of the forces in a fall. Correcting those errors seemed worthwhile. Correcting your misreading of my posts doesn't.
Rob
jeeze, dood... ain't no need to go all kodos on me and $H1T... i'm just putting it out there...
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robmcc
Apr 6, 2004, 9:52 PM
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49 m/s2 is a sample acceleration imposed on the climber AWAY from the earth by the tension in the rope. As I said, gravity is only one of the forces acting on the climber.
Rob
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bigwallgumbie
Apr 6, 2004, 9:53 PM
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In reply to: In reply to: Oh yah - but what about Terminal Velocity!? terminal velocity is irrelavant when dealing in terms of acceleration...
Score 5 points for drunkencabanaboy....
This is quickly becoming my alltime favorite thread on rc.com
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jason1
Apr 6, 2004, 9:56 PM
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i'm sorry, i don't understand...
can you explain how you came up with 49m/s2?
mea culpa, mea culpa, mea moxie, mea culpa...
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drunkencabanaboy
Apr 6, 2004, 10:34 PM
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In reply to: terminal velocity is irrelavant when dealing in terms of acceleration...
au contraire!
http://hypertextbook.com/facts/JianHuang.shtml
:lol:
This thread is about as useless as the guy with the really loud and obnoxious leaf blower outside. He's prob getting paid $20/hr to blow around dust... psh. My rent money at work.
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ipsofacto
Apr 6, 2004, 11:13 PM
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23456789
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jason1
Apr 7, 2004, 3:03 AM
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ok,you're right about terminal velocity being another factor that we have to account for with rope stretch and friction of every molecule that we brush up against and whats lost for heat and sound and did i hear a butterfly flapping its wings...
and you gotta admit that's a long fall if you're playing with terminal velocity....
write your congressman, FREE KODOS!!!
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drunkencabanaboy
Apr 7, 2004, 2:38 PM
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In reply to: ok,you're right about terminal velocity being another factor that we have to account for with rope stretch and friction of every molecule that we brush up against and whats lost for heat and sound and did i hear a butterfly flapping its wings... and you gotta admit that's a long fall if you're playing with terminal velocity.... write your congressman, FREE KODOS!!!
NOW we are getting to the important stuff! :lol:
LOL
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