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Common KNs in real world falls
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loyota


May 12, 2009, 2:51 PM
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Common KNs in real world falls
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Since we know that most, if any falls don't produce the kind of KN force generated by the x2 lab drop test, and 10KN+ gear isn't exaclty breaking left and right... etc etc

Are there any studies or data out there regarding what range of KNs are typically generated in more real world falls (not necessarily factor 2).

John Long cites scientist Craig Connally in his book who throws out a 5.5-8.5 KN max figure. JL also mentions that in an eight year period QA at Black Diamond hadn't seen any stopper over 10KN fail and only a few 10KN carabiners fail in closed gate mode.

I guess if some yates screamers kick in at 2KN, we know we can get into that range probably without trying too hard :-D

I can't recall of hearing of any 5KN type gear breaking, I hear of Micros breaking but I don't know how low they were rated.

Anyway, just curious, be nice to know what's a little more based in the real world when you're forced / choose to start placing pro that's dropping into the lower KNs


hafilax


May 12, 2009, 3:41 PM
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Micros are typically rated at around 2-5kN.


rocknice2


May 12, 2009, 5:24 PM
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Worst real world fall???
Not counting FF2.

I'm starting P2 and it's hard right off the bat. I climb up a bit [feet level with belay device] and plug a cam and clip it. Now the cam is 7ft above belay device and 10ft above ledge.
I struggle up until the cam is at my feet and plug a nut. I'm so pumped fiddling with the nut and can't stabilize for the clip. I bitch, scream and cry in that order. Finally I peel off.
I take a 6 footer on 10 feet of rope = 6kn
Even more realistic the belayer worries I might deck and manages to take in an arm length of rope in.
A 6 footer on 8 feet of rope = 7.5kn


Partner angry


May 12, 2009, 5:32 PM
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I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.


majid_sabet


May 12, 2009, 5:46 PM
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rocknice2 wrote:
Worst real world fall???
Not counting FF2.

I'm starting P2 and it's hard right off the bat. I climb up a bit [feet level with belay device] and plug a cam and clip it. Now the cam is 7ft above belay device and 10ft above ledge.
I struggle up until the cam is at my feet and plug a nut. I'm so pumped fiddling with the nut and can't stabilize for the clip. I bitch, scream and cry in that order. Finally I peel off.
I take a 6 footer on 10 feet of rope = 6kn
Even more realistic the belayer worries I might deck and manages to take in an arm length of rope in.
A 6 footer on 8 feet of rope = 7.5kn

there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.


majid_sabet


May 12, 2009, 5:49 PM
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angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs


shockabuku


May 12, 2009, 5:54 PM
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majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Dumbass.

1 KN = 1000 N = 1000 kg m/s^2

divide 1000 kg m/s^2 by 9.8 m/s^2 to get an equivalent mass = 102.04 kg = 224.49 lbs.


curt


May 12, 2009, 5:54 PM
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majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Isn't your thumb healed yet? for God's sake back off on the meds.

Curt


rocknice2


May 12, 2009, 6:00 PM
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Sorry
Your right I mixed it up a bit.
Corrected below for 175lbs climber

rocknice2 wrote:
Worst real world fall???
Not counting FF2.

I'm starting P2 and it's hard right off the bat. I climb up a bit [feet level with belay device] and plug a cam and clip it. Now the cam is 7ft above belay device and 10ft above ledge.
I struggle up until the cam is at my feet and plug a nut. I'm so pumped fiddling with the nut and can't stabilize for the clip. I bitch, scream and cry in that order. Finally I peel off.
I take a 6 footer on 10 feet of rope = FF0.6 = 5.8kn
Even more realistic the belayer worries I might deck and manages to take in an arm length of rope in.
A 6 footer on 8 feet of rope = FF0.75 = 6.2kn

20ft fall on 10ft of rope = FF2 = 8.9kn
http://www.myoan.net/...t/climbforcecal.html
Ignore the FF on the calculator


colatownkid


May 12, 2009, 6:28 PM
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Re: [loyota] Common KNs in real world falls [In reply to]
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loyota wrote:
Since we know that most, if any falls don't produce the kind of KN force generated by the x2 lab drop test, and 10KN+ gear isn't exaclty breaking left and right... etc etc

Are there any studies or data out there regarding what range of KNs are typically generated in more real world falls (not necessarily factor 2).

John Long cites scientist Craig Connally in his book who throws out a 5.5-8.5 KN max figure. JL also mentions that in an eight year period QA at Black Diamond hadn't seen any stopper over 10KN fail and only a few 10KN carabiners fail in closed gate mode.

I guess if some yates screamers kick in at 2KN, we know we can get into that range probably without trying too hard :-D

I can't recall of hearing of any 5KN type gear breaking, I hear of Micros breaking but I don't know how low they were rated.

Anyway, just curious, be nice to know what's a little more based in the real world when you're forced / choose to start placing pro that's dropping into the lower KNs

Real world the greatest force is not necessarily a factor-2 fall. this situation actually produces a greater force:

hanging belay on a multipitch climb, the leader clips the top piece of the anchor or places a piece shortly after the anchor. the leader then continues for some distance without placing any gear and then falls. this results in a high-factor fall (though not factor 2). however, the pulley effect on the top piece results in a greater total force than a simple factor-2 fall. depending on how far the leader climbed, this force could be theoretically massive.

the max force from a factor-2 is somewhere around 9kN by my calculations. this assumes the belay is static, the belayer is about 1 meter from the anchor, and the leader is the standard 80kg climber. i don't remember the rope impact force i used in the calculations, but it was a decent median of single ropes currently on the market. these calculations were largely based on a paper rgold put together a while ago that i can't find the link to right now.

of course, assuming a static belay is not entirely realistic as the belayer will move and rope may slip, so forces could conceivably be even lower.

hope that helps.

edited to add: as fishclimb pointed out, this calculation also assumes the rope is an ideal spring and is not critically dampened (as it is in real life).


(This post was edited by colatownkid on May 12, 2009, 7:19 PM)


adatesman


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spikeddem


May 12, 2009, 6:49 PM
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adatesman wrote:
In case there's any willing guinea pigs at the NRR this weekend, I just put all the test equipment needed to test this into the car.... All we need is someone willing to take a couple FF1.5+ falls and we can finally put this to rest. If you're interested I'll most likely be in the NRAC tent and fairly easy to find.... Not too many people showing up with a pull tester.

Oh, and we're not using my rope. Angelic

-aric.

The volunteer can borrow my static rope. Laugh


fishclimb


May 12, 2009, 6:52 PM
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The key factor in calculating the Falling Force is the time it takes to decelerate. F=ma. Shorter deceleration times increase the force in a fall. But I don't know the elongation rate of the rope for certain distances as this is the key to determining the time in deceleration.

But I've heard or read the numbers 3-5 kn.


bill413


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adatesman wrote:
In case there's any willing guinea pigs at the NRR this weekend, I just put all the test equipment needed to test this into the car.... All we need is someone willing to take a couple FF1.5+ falls and we can finally put this to rest. If you're interested I'll most likely be in the NRAC tent and fairly easy to find.... Not too many people showing up with a pull tester.

Oh, and we're not using my rope. Angelic

-aric.
Oh, well, in that case count me out!

(Not that I'd make the event anyway, much as I'd like.)


taydude


May 12, 2009, 8:07 PM
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shockabuku wrote:
majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Dumbass.

1 KN = 1000 N = 1000 kg m/s^2

divide 1000 kg m/s^2 by 9.8 m/s^2 to get an equivalent mass = 102.04 kg = 224.49 lbs.

Owned by Physics!


theguy


May 12, 2009, 8:08 PM
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majid_sabet wrote:
there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.

Wong again, wabbit: UIAA Article: Beware of Quickdraws for Self-Belay

For a useful answer to the OP's question see the UIAA Technical Committee Note: How strong does your climbing gear need to be?


Partner angry


May 12, 2009, 8:11 PM
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shockabuku wrote:
majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Dumbass.

1 KN = 1000 N = 1000 kg m/s^2

divide 1000 kg m/s^2 by 9.8 m/s^2 to get an equivalent mass = 102.04 kg = 224.49 lbs.

That's got to sting!!


jt512


May 12, 2009, 8:18 PM
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majid_sabet wrote:
rocknice2 wrote:
Worst real world fall???
Not counting FF2.

I'm starting P2 and it's hard right off the bat. I climb up a bit [feet level with belay device] and plug a cam and clip it. Now the cam is 7ft above belay device and 10ft above ledge.
I struggle up until the cam is at my feet and plug a nut. I'm so pumped fiddling with the nut and can't stabilize for the clip. I bitch, scream and cry in that order. Finally I peel off.
I take a 6 footer on 10 feet of rope = 6kn
Even more realistic the belayer worries I might deck and manages to take in an arm length of rope in.
A 6 footer on 8 feet of rope = 7.5kn

there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.


*bzzzzt* Thanks for playing!


pfwein


May 12, 2009, 8:21 PM
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loyota wrote:
. . . and only a few 10KN carabiners fail in closed gate mode.
What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that.
And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor


adatesman


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Partner angry


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No battle today, just more misinformation. It wasn't as bad as normal, he was only off by a factor of 10.


adatesman


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Terry2124


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adatesman wrote:
angry wrote:
No battle today, just more misinformation. It wasn't as bad as normal, he was only off by a factor of 10.

Frown

Your looking for some excitement.

None here Frown


Partner angry


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Terry2124 wrote:
adatesman wrote:
angry wrote:
No battle today, just more misinformation. It wasn't as bad as normal, he was only off by a factor of 10.

Frown

Your looking for some excitement.

None here Frown

You're


jt512


May 12, 2009, 9:10 PM
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angry wrote:
Terry2124 wrote:
adatesman wrote:
angry wrote:
No battle today, just more misinformation. It wasn't as bad as normal, he was only off by a factor of 10.

Frown

Your looking for some excitement.

None here Frown

You're

Angry, 5 stars.

Terry, I've actually killfiled your proflile pic.

Jay


Terry2124


May 12, 2009, 9:31 PM
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angry wrote:
Terry2124 wrote:
adatesman wrote:
angry wrote:
No battle today, just more misinformation. It wasn't as bad as normal, he was only off by a factor of 10.

Frown

Your looking for some excitement.

None here Frown

You're

Can I blame it on the Red Wings game? They are losing to the Ducks.


Terry2124


May 12, 2009, 9:32 PM
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jt512 wrote:
angry wrote:
Terry2124 wrote:
adatesman wrote:
angry wrote:
No battle today, just more misinformation. It wasn't as bad as normal, he was only off by a factor of 10.

Frown

Your looking for some excitement.

None here Frown

You're

Angry, 5 stars.

Terry, I've actually killfiled your proflile pic.

Jay

Killfiled?


proflile ?????


jt512


May 12, 2009, 9:56 PM
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Terry2124 wrote:
jt512 wrote:
angry wrote:
Terry2124 wrote:
adatesman wrote:
angry wrote:
No battle today, just more misinformation. It wasn't as bad as normal, he was only off by a factor of 10.

Frown

Your looking for some excitement.

None here Frown

You're

Angry, 5 stars.

Terry, I've actually killfiled your proflile pic.

Jay

Killfiled?


proflile ?????

In plain English, I no longer have to look at that annoying, and vaguely creepy, little picture underneath your username next to your posts.

Jay


majid_sabet


May 12, 2009, 10:02 PM
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shockabuku wrote:
majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Dumbass.

1 KN = 1000 N = 1000 kg m/s^2

divide 1000 kg m/s^2 by 9.8 m/s^2 to get an equivalent mass = 102.04 kg = 224.49 lbs.

right after I post it I wanted to go back add the 9.8 meter whatever but then I said fuc* it, someone will catch it later.


shockabuku


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majid_sabet wrote:
shockabuku wrote:
majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Dumbass.

1 KN = 1000 N = 1000 kg m/s^2

divide 1000 kg m/s^2 by 9.8 m/s^2 to get an equivalent mass = 102.04 kg = 224.49 lbs.

right after I post it I wanted to go back add the 9.8 meter whatever but then I said fuc* it, someone will catch it later.

We all gotta contribute where we can.


majid_sabet


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theguy wrote:
majid_sabet wrote:
there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.

Wong again, wabbit: UIAA Article: Beware of Quickdraws for Self-Belay

For a useful answer to the OP's question see the UIAA Technical Committee Note: How strong does your climbing gear need to be?

Do not argue with wabitt cause wabitt wins

read the bottom of page 4

http://www.cwu.edu/...rints/cmj135-140.pdf


jt512


May 12, 2009, 10:19 PM
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Re: [rocknice2] Common KNs in real world falls [In reply to]
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rocknice2 wrote:
I take a 6 footer on 10 feet of rope = 6kn

[...]

A 6 footer on 8 feet of rope = 7.5kn

Do you actually think that the definition of a kilonewton is fall factor times 10?

Jay


USnavy


May 12, 2009, 11:18 PM
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Re: [loyota] Common KNs in real world falls [In reply to]
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loyota wrote:
Since we know that most, if any falls don't produce the kind of KN force generated by the x2 lab drop test, and 10KN+ gear isn't exaclty breaking left and right... etc etc

Are there any studies or data out there regarding what range of KNs are typically generated in more real world falls (not necessarily factor 2).

John Long cites scientist Craig Connally in his book who throws out a 5.5-8.5 KN max figure. JL also mentions that in an eight year period QA at Black Diamond hadn't seen any stopper over 10KN fail and only a few 10KN carabiners fail in closed gate mode.

I guess if some yates screamers kick in at 2KN, we know we can get into that range probably without trying too hard :-D

I can't recall of hearing of any 5KN type gear breaking, I hear of Micros breaking but I don't know how low they were rated.

Anyway, just curious, be nice to know what's a little more based in the real world when you're forced / choose to start placing pro that's dropping into the lower KNs

On my off time I put a lot of effort into trying to calculate how much force random lead falls actually generate. In my (field) tests I have found that the max impact force of a typical sport lead fall ranging from a .2 - .85 FF fall with a fall distance of 5 Ė 15 feet will produce 3 Ė 8 kN on the top anchor. I tested those falls with everything from a soft catch with an ATC to the hardest possible catch with a GriGri using everything from my half-ropes to my low impact force trad rope to my sport ropes to my old project ropes. But I only weigh 165 lbs with gear. With additional weight, that value will increase dramatically.

So it is possible for a biner to break on a single pitch lead fall if the gate is open well the biner is loaded. Itís unlikely it will happen way up high but during the first few bolts well the potential fall factor is high, exceeding the 7 kN UIAA open gate minimum for class D carabineers is possible.

However in a multi-pitch environment those values will increase quite a lot. A 25 foot factor 1.95 fall (quickdraw attached to belay station) with a person that weighs 200 lbs. and a belayer with an auto locking belay device could produce 15 kN or more on the top anchor in before the belay device slips.


(This post was edited by USnavy on May 13, 2009, 12:08 AM)


USnavy


May 13, 2009, 12:12 AM
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Re: [majid_sabet] Common KNs in real world falls [In reply to]
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majid_sabet wrote:
theguy wrote:
majid_sabet wrote:
there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.

Wong again, wabbit: UIAA Article: Beware of Quickdraws for Self-Belay

For a useful answer to the OP's question see the UIAA Technical Committee Note: How strong does your climbing gear need to be?

Do not argue with wabitt cause wabitt wins

read the bottom of page 4

http://www.cwu.edu/...rints/cmj135-140.pdf

If youíre going to reference a document to argue your point, it would be strongly favorable if you understood what the document said. Clearly you donít. The physics behind calculating the impact force of a lead fall is so astronomically beyond you itís unfathomable.


(This post was edited by USnavy on May 13, 2009, 12:13 AM)


majid_sabet


May 13, 2009, 12:29 AM
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Re: [USnavy] Common KNs in real world falls [In reply to]
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USnavy wrote:
majid_sabet wrote:
theguy wrote:
majid_sabet wrote:
there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.

Wong again, wabbit: UIAA Article: Beware of Quickdraws for Self-Belay

For a useful answer to the OP's question see the UIAA Technical Committee Note: How strong does your climbing gear need to be?

Do not argue with wabitt cause wabitt wins

read the bottom of page 4

http://www.cwu.edu/...rints/cmj135-140.pdf

If youíre going to reference a document to argue your point, it would be strongly favorable if you understood what the document said. Clearly you donít. The physics behind calculating the impact force of a lead fall is so astronomically beyond you itís unfathomable.

go learn how to rappel and place some anchors first then come back and talk.

and do not talk big. I crush big talkers round here left and right JR.

move it
move it move it


USnavy


May 13, 2009, 12:35 AM
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Re: [majid_sabet] Common KNs in real world falls [In reply to]
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majid_sabet wrote:
USnavy wrote:
majid_sabet wrote:
theguy wrote:
majid_sabet wrote:
there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.

Wong again, wabbit: UIAA Article: Beware of Quickdraws for Self-Belay

For a useful answer to the OP's question see the UIAA Technical Committee Note: How strong does your climbing gear need to be?

Do not argue with wabitt cause wabitt wins

read the bottom of page 4

http://www.cwu.edu/...rints/cmj135-140.pdf

If youíre going to reference a document to argue your point, it would be strongly favorable if you understood what the document said. Clearly you donít. The physics behind calculating the impact force of a lead fall is so astronomically beyond you itís unfathomable.

go learn how to rappel and place some anchors first then come back and talk.

and do not talk big. I crush big talkers round here left and right JR.

move it
move it move it
Please... LaughLaugh


(This post was edited by USnavy on May 13, 2009, 12:43 AM)


colatownkid


May 13, 2009, 4:42 AM
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Re: [adatesman] Common KNs in real world falls [In reply to]
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adatesman wrote:
angry wrote:
shockabuku wrote:
majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Dumbass.

1 KN = 1000 N = 1000 kg m/s^2

divide 1000 kg m/s^2 by 9.8 m/s^2 to get an equivalent mass = 102.04 kg = 224.49 lbs.

That's got to sting!!

If Angry and MS are going to get back together I'm going to have to find some better snack food. At the moment the only things handy are sauerkraut and a homemade apple-vinegar-based coleslaw, neither of which are very good for the knock-down drag out lovefests they're A&M are known for. If only I had popcorn!

EDIT- I thought about moving this to The Lab, but the first couple posts made me thing otherwise.

BTW, I'm totally serious about finding a guinea pig at the NRR... This is one of those things that annoys me because there's lots of speculation and no hard data. If we could find someone willing to take the fall it would be easy enough to prove/disprove a good deal of the spray that's been going around. Hell, we'll even use my rope. Its due for retirement anyway.

BTWx2- Not to say there's anything wrong with my rope; I've just been looking for an excuse to replace it since its got fuzz issues.

if you're seriously looking to do some real-world testing (which i think would be awesome!), what's stopping you from using an 80kg bag of rocks? sure, it's a little harder to move around than a person, but i'm guessing the rocks would be much more willing volunteers.


colatownkid


May 13, 2009, 5:02 AM
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Re: [pfwein] Common KNs in real world falls [In reply to]
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pfwein wrote:
loyota wrote:
. . . and only a few 10KN carabiners fail in closed gate mode.
What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that.
And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor

the "pulley effect" occurs when a load on one side of a pulley is counteracted by an equal load on the opposite side.

suppose a climber has come to a stop after having fallen. the carabiner on uppermost piece of gear is effectively acting as pulley--the climber is hanging on one side, the belayer is hanging on the other side. simply hanging there, the climber's weight must exert some force downward (we'll call it x). in order for the climber to be stationary, the belayer must be exerting an equal force down (also x). therefore, that top piece of gear must be supporting both the full weight of the climber and the belayer or 2x. hence, the total force is double what the climber would place on the piece by himself.

the same principle applies in a moving system where the climber is falling, but we know that in reality the belayer will get pulled into the air, so the doubling is only an approximation.

this is significant in the scenario i described earlier because there is no pulley effect in a factor-2 fall. the climber simply falls directly onto the belayer's belay device. when the system has come to rest (hopefully it does so before both people have hit the ground) the anchor is supporting the weight of the fallen climber directly, not through a pulley. in the high-factor scenario where the anchor has been clipped, the anchor is supporting the weight of the falling climber through a pulley, meaning it has to hold double the force.

let's suppose the factor-2 fall resulted in a force of 8 kN and the high-factor fall resulted in a force of 6kN (totally arbitrary numbers for the sake of example). 2 x 6 = 12, so the high-factor fall actually results in a higher force (12kN) than the factor-2 fall (8kN) thanks to the pulley effect.

the real issue though is that it's extraordinarily difficult to catch factor-2 falls (no personal experience here, so somebody feel free to refute me). this is exacerbated by the fact that when catching a factor-2 fall directly, the belayer's ATC will invert, meaning that the locked position is pulling the rope up, not down, making a catch even more awkward and difficult.

because of this, it might be a good idea to clip the anchor despite the higher potential force simply so it is easier for the belayer to catch the fall.


adatesman


May 13, 2009, 6:00 AM
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krusher4


May 13, 2009, 6:32 AM
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Re: [shockabuku] Common KNs in real world falls [In reply to]
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shockabuku wrote:
majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

Dumbass.

1 KN = 1000 N = 1000 kg m/s^2

divide 1000 kg m/s^2 by 9.8 m/s^2 to get an equivalent mass = 102.04 kg = 224.49 lbs.


damn everyone knows this already geezzz...


fresh


May 13, 2009, 6:40 AM
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Re: [loyota] Common KNs in real world falls [In reply to]
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in an attempt to answer the original question...

kolin powick writes this in his QC blog:

In reply to:
sport falls are typically 2-5kN
http://www.blackdiamondequipment.com/...p_archive.php#122805

I'm assuming that is the actual force on the anchor, which is of course twice the force the climber feels. I've heard that range mentioned a few other times but can't find any other sources. it's funny because this is quite a relevant question for anyone climbing trad, and there isn't much data on it.

does anyone know where the petzl fall simulator went?


marde


May 13, 2009, 6:58 AM
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according to the german alpine club (DAV)
who did meassured forces on real falls:
3 to 6kN with a tube style device or munter hitch
and 7 to 9kN with a grigri on a bolt
on the pieces.

and not more than 6kN on the belay;
they put the belay devices right on the belay and did not use a dummy runner so there is not twice the force on it.
So on a factor 2 fall it basically comes down to the braking force of the device/ hitch which is used.


jrathfon


May 13, 2009, 8:46 AM
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Re: [colatownkid] Common KNs in real world falls [In reply to]
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colatownkid wrote:
pfwein wrote:
loyota wrote:
. . . and only a few 10KN carabiners fail in closed gate mode.
What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that.
And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor

the "pulley effect" occurs when a load on one side of a pulley is counteracted by an equal load on the opposite side.

suppose a climber has come to a stop after having fallen. the carabiner on uppermost piece of gear is effectively acting as pulley--the climber is hanging on one side, the belayer is hanging on the other side. simply hanging there, the climber's weight must exert some force downward (we'll call it x). in order for the climber to be stationary, the belayer must be exerting an equal force down (also x). therefore, that top piece of gear must be supporting both the full weight of the climber and the belayer or 2x. hence, the total force is double what the climber would place on the piece by himself.

the same principle applies in a moving system where the climber is falling, but we know that in reality the belayer will get pulled into the air, so the doubling is only an approximation.

this is significant in the scenario i described earlier because there is no pulley effect in a factor-2 fall. the climber simply falls directly onto the belayer's belay device. when the system has come to rest (hopefully it does so before both people have hit the ground) the anchor is supporting the weight of the fallen climber directly, not through a pulley. in the high-factor scenario where the anchor has been clipped, the anchor is supporting the weight of the falling climber through a pulley, meaning it has to hold double the force.

let's suppose the factor-2 fall resulted in a force of 8 kN and the high-factor fall resulted in a force of 6kN (totally arbitrary numbers for the sake of example). 2 x 6 = 12, so the high-factor fall actually results in a higher force (12kN) than the factor-2 fall (8kN) thanks to the pulley effect.

the real issue though is that it's extraordinarily difficult to catch factor-2 falls (no personal experience here, so somebody feel free to refute me). this is exacerbated by the fact that when catching a factor-2 fall directly, the belayer's ATC will invert, meaning that the locked position is pulling the rope up, not down, making a catch even more awkward and difficult.

because of this, it might be a good idea to clip the anchor despite the higher potential force simply so it is easier for the belayer to catch the fall.

wow, something useful in this nonsensical thread! i think i learned this a few years ago, but had forgotten it. this does generate some interesting questions about that FF2 preventer bolt clip or first jesus piece. another thing you can do is have your belayer lowered out a bit (like 6 or 7 ft) from the hanging belay, that way there is more rpe in the system. we used this a lot on prince of darkness as the climbing was a touch stiff up to the first bolt sometimes. oh, and roan way at j-tree, course you could jsut skip this belay...

but lets say you fall 5 ft above your 2 bolt anchor, where you clipped one anchor bolt as your FF2 directional. in one case (A), the belayer is hanging off the anchor with 2 standard shoulder length slings (2ft). in the other case (B) you have your belayer out 6ft. i typically achieve this by having the climbing line extended 4ft via a clove hitch from a knot limited sliding-x master point made from a double shoulder length sling (the 4 ft of climbing line can be backed up by another 2Xshoulder sling if you feel your climbing line isn't safe enough...).

in (A) you have a 10ft fall with 7ft or rope or FF1.43 with the pulley effect on your directional biner.

in (B) you have a 10ft fall with 11ft of rope or FF0.91 with the pulley effect on your directional biner.

in both cases you can have a softer catch by picking up your belayer, however in (A) you belayer can only move 2ft as the ATC smacks into the directional biner. in (B) you get 6ft, a much softer catch.

i just went to calculate the forces in this hypothetical fall, but that linked calculator is bunk! it'd be interesting to see how adding this bit of rope into the system dissipates forces on da' jebus directional.

to those who think you couldn't monopolize that full 6ft of picking up your belayer: on POD, on ~ the 3rd pitch, the height related 10bish crux moves, I was out about 8 or 9 bolts (~90ft) from the double bolt anchor, where my belayer had already removed the "oh shit FF2 directional thank jebus biner" and was tied in via the rope into the limited sliding-x master point with about 3ft of line. i was nearing the next clip (so ~10ft above my last clip) and unexpectedly whipped. the fall generated enough force to pull her up (she weighs 25lbs less than me 160 vs 135) almost taught between her tether and the climbing line, i.e. 10ft! with stretch and that give the fall turned into a 30fter! so really it was a 20ft fall on ~90ft of line or a FF0.22, not much!

p.s. majidiot, i stand by what i said last year. you're an idiot.

"chingon"? = 1 KILO means 1000 mexican badasses?

"right after I post it I wanted to go back add the 9.8 meter whatever but then I said fuc* it, someone will catch it later. "

yup, 9.8 meter whatever, you clearly have a grasp on this subject. because adding 9.8 meter whatever to:

"wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs"

would have made this statement clearer and more accurate...

for the record, he was a factor of 10^3 off, not just a factor of 10. close only counts in horshoes and handgrenades.

"go learn how to rappel and place some anchors first then come back and talk."

typically i find rappellers are the biggest idiots you can run across at a climbing area.

"and do not talk big. I crush big talkers round here left and right JR."

is this a reference to when you kept saying sexually suggestive threats to angry in a long argument?


majid_sabet


May 13, 2009, 10:19 AM
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colatownkid wrote:
pfwein wrote:
loyota wrote:
. . . and only a few 10KN carabiners fail in closed gate mode.
What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that.
And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor

the "pulley effect" occurs when a load on one side of a pulley is counteracted by an equal load on the opposite side.

suppose a climber has come to a stop after having fallen. the carabiner on uppermost piece of gear is effectively acting as pulley--the climber is hanging on one side, the belayer is hanging on the other side. simply hanging there, the climber's weight must exert some force downward (we'll call it x). in order for the climber to be stationary, the belayer must be exerting an equal force down (also x). therefore, that top piece of gear must be supporting both the full weight of the climber and the belayer or 2x. hence, the total force is double what the climber would place on the piece by himself.

the same principle applies in a moving system where the climber is falling, but we know that in reality the belayer will get pulled into the air, so the doubling is only an approximation.

this is significant in the scenario i described earlier because there is no pulley effect in a factor-2 fall. the climber simply falls directly onto the belayer's belay device. when the system has come to rest (hopefully it does so before both people have hit the ground) the anchor is supporting the weight of the fallen climber directly, not through a pulley. in the high-factor scenario where the anchor has been clipped, the anchor is supporting the weight of the falling climber through a pulley, meaning it has to hold double the force.

let's suppose the factor-2 fall resulted in a force of 8 kN and the high-factor fall resulted in a force of 6kN (totally arbitrary numbers for the sake of example). 2 x 6 = 12, so the high-factor fall actually results in a higher force (12kN) than the factor-2 fall (8kN) thanks to the pulley effect.

the real issue though is that it's extraordinarily difficult to catch factor-2 falls (no personal experience here, so somebody feel free to refute me). this is exacerbated by the fact that when catching a factor-2 fall directly, the belayer's ATC will invert, meaning that the locked position is pulling the rope up, not down, making a catch even more awkward and difficult.

because of this, it might be a good idea to clip the anchor despite the higher potential force simply so it is easier for the belayer to catch the fall.

note, The carabiner does not act as pulley device in FF but a friction device therefore it reduces the fall factor by small amont as mentioned in the PDF I provided above . During a leader fall, we are not getting a true FF2 but some thing like FF 1.75 +- .

I think the only way we could get a true FF2 is to attach a climber to solid steel cable and drop him above an anchor and without any protection in between.

Hey Angry. you want to try this for me?

come on, I buy a candy


jrathfon


May 13, 2009, 10:35 AM
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majid_sabet wrote:
colatownkid wrote:
pfwein wrote:
loyota wrote:
. . . and only a few 10KN carabiners fail in closed gate mode.
What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that.
And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor

the "pulley effect" occurs when a load on one side of a pulley is counteracted by an equal load on the opposite side.

suppose a climber has come to a stop after having fallen. the carabiner on uppermost piece of gear is effectively acting as pulley--the climber is hanging on one side, the belayer is hanging on the other side. simply hanging there, the climber's weight must exert some force downward (we'll call it x). in order for the climber to be stationary, the belayer must be exerting an equal force down (also x). therefore, that top piece of gear must be supporting both the full weight of the climber and the belayer or 2x. hence, the total force is double what the climber would place on the piece by himself.

the same principle applies in a moving system where the climber is falling, but we know that in reality the belayer will get pulled into the air, so the doubling is only an approximation.

this is significant in the scenario i described earlier because there is no pulley effect in a factor-2 fall. the climber simply falls directly onto the belayer's belay device. when the system has come to rest (hopefully it does so before both people have hit the ground) the anchor is supporting the weight of the fallen climber directly, not through a pulley. in the high-factor scenario where the anchor has been clipped, the anchor is supporting the weight of the falling climber through a pulley, meaning it has to hold double the force.

let's suppose the factor-2 fall resulted in a force of 8 kN and the high-factor fall resulted in a force of 6kN (totally arbitrary numbers for the sake of example). 2 x 6 = 12, so the high-factor fall actually results in a higher force (12kN) than the factor-2 fall (8kN) thanks to the pulley effect.

the real issue though is that it's extraordinarily difficult to catch factor-2 falls (no personal experience here, so somebody feel free to refute me). this is exacerbated by the fact that when catching a factor-2 fall directly, the belayer's ATC will invert, meaning that the locked position is pulling the rope up, not down, making a catch even more awkward and difficult.

because of this, it might be a good idea to clip the anchor despite the higher potential force simply so it is easier for the belayer to catch the fall.

note, The carabiner does not act as pulley device in FF but a friction device therefore it reduces the fall factor by small amont as mentioned in the PDF I provided above . During a leader fall, we are not getting a true FF2 but some thing like FF 1.75 +- .

I think the only way we could get a true FF2 is to attach a climber to solid steel cable and drop him above an anchor and without any protection in between.

Hey Angry. you want to try this for me?

come on, I buy a candy

majidiot, the FF does not depend on the rope used. as per YOUR reference, FF = the total distance fallen / rope out. if you want to calculate peak force, you must factor in the elasticity of the rope. using a steel cable will increase this max force, but NOT the FF.

b) THEGUY provided the references explaining the friction factor of the pulley effect decreasing force in the system, NOT FF. you did NOT provide this information.

again, you're an idiot. or perhaps i should translate this into rc.com vernacular: "your' an idiot's."


majid_sabet


May 13, 2009, 11:07 AM
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jrathfon wrote:
majid_sabet wrote:
colatownkid wrote:
pfwein wrote:
loyota wrote:
. . . and only a few 10KN carabiners fail in closed gate mode.
What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that.
And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor

the "pulley effect" occurs when a load on one side of a pulley is counteracted by an equal load on the opposite side.

suppose a climber has come to a stop after having fallen. the carabiner on uppermost piece of gear is effectively acting as pulley--the climber is hanging on one side, the belayer is hanging on the other side. simply hanging there, the climber's weight must exert some force downward (we'll call it x). in order for the climber to be stationary, the belayer must be exerting an equal force down (also x). therefore, that top piece of gear must be supporting both the full weight of the climber and the belayer or 2x. hence, the total force is double what the climber would place on the piece by himself.

the same principle applies in a moving system where the climber is falling, but we know that in reality the belayer will get pulled into the air, so the doubling is only an approximation.

this is significant in the scenario i described earlier because there is no pulley effect in a factor-2 fall. the climber simply falls directly onto the belayer's belay device. when the system has come to rest (hopefully it does so before both people have hit the ground) the anchor is supporting the weight of the fallen climber directly, not through a pulley. in the high-factor scenario where the anchor has been clipped, the anchor is supporting the weight of the falling climber through a pulley, meaning it has to hold double the force.

let's suppose the factor-2 fall resulted in a force of 8 kN and the high-factor fall resulted in a force of 6kN (totally arbitrary numbers for the sake of example). 2 x 6 = 12, so the high-factor fall actually results in a higher force (12kN) than the factor-2 fall (8kN) thanks to the pulley effect.

the real issue though is that it's extraordinarily difficult to catch factor-2 falls (no personal experience here, so somebody feel free to refute me). this is exacerbated by the fact that when catching a factor-2 fall directly, the belayer's ATC will invert, meaning that the locked position is pulling the rope up, not down, making a catch even more awkward and difficult.

because of this, it might be a good idea to clip the anchor despite the higher potential force simply so it is easier for the belayer to catch the fall.

note, The carabiner does not act as pulley device in FF but a friction device therefore it reduces the fall factor by small amont as mentioned in the PDF I provided above . During a leader fall, we are not getting a true FF2 but some thing like FF 1.75 +- .

I think the only way we could get a true FF2 is to attach a climber to solid steel cable and drop him above an anchor and without any protection in between.

Hey Angry. you want to try this for me?

come on, I buy a candy

majidiot, the FF does not depend on the rope used. as per YOUR reference, FF = the total distance fallen / rope out. if you want to calculate peak force, you must factor in the elasticity of the rope. using a steel cable will increase this max force, but NOT the FF.
b) THEGUY provided the references explaining the friction factor of the pulley effect decreasing force in the system, NOT FF. you did NOT provide this information.

again, you're an idiot. or perhaps i should translate this into rc.com vernacular: "your' an idiot's."

First off, try to learn how to communicate with people instead of using the word idiot or whatever. 7 years old kids call each other idiot. You are a college grad and I thought at least they teach you how to talk to people.


Rudmin


May 13, 2009, 11:08 AM
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majid_sabet wrote:
I think the only way we could get a true FF2 is to attach a climber to solid steel cable and drop him above an anchor and without any protection in between.

Hey Angry. you want to try this for me?

come on, I buy a candy

That would be a theoretical fall factor approaching infinity: a fall of some distance with 0 rope out. If nothing in the system is dynamic, then it produces an infinite force. Of course, even steel cable is elastic to a degree, but you still would get extremely high forces.

If you replaced your steel cable with a dynamic rope, then it would be a theoretical fall factor of 2. But of course real falls aren't one dimensional, and humans aren't the same as iron weights, that's why it would be nice to have actual data.

The point of a fall factor, is that it models a number that scales linearly with the forces acting on the falling climber. So in general, you can say that the higher the fall factor, the higher the forces the climber (and thus the rest of the system) experience.


hafilax


May 13, 2009, 11:08 AM
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Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.


pfwein


May 13, 2009, 11:28 AM
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Thanks to all of you who addressed my Q re: pulley effect.
One thing I don't think I've seen addressed: at a hanging belay, the anchor is also holding the weight of the belayer, so when the fallen climber comes to rest, the anchor will be holding both the weight of the belayer and the climber, regardless of whether the climber clipped the anchor, right?
And before the climber comes to rest, it seems that the rope will just be elongating based on the climber's weight, the length of the fall, and amount of rope between the climber and the belay device, which again doesn't depend on whether the anchor is clipped,except the fall will be slightly shorter when the anchor is clipped (maybe I'm wrong on this point??).
I'm just having a hard time visualizing why clipping the anchor increases the force on the anchor when the only thing it seems to do is redirect the direction of the force and slightly decrease the length of the fall (both definitely good things), but thanks again to you who attempt to explain it.


jrathfon


May 13, 2009, 11:34 AM
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hafilax wrote:
Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.

Yes, Majidiot sucks at explaining things, he also sucks at understanding the fundamental concepts in the first place.

I understand the concepts of fall factor and how it is an approximation to represent forces in a complex dynamic situation. You bring up lots of the intracacies involved in the dissipation of forces in a real world fall. It's definitely an interesting problem. The UIAA paper that "theguy" presented actually has some values for frictional dissipation of forces in the system.

Rudman: according to the paper majidiot replied with force scales to the square root of FF.

Majidiot: i think i can communicate quite effectively, i would hope others in this forum agree upon this point. you however, DO NOT communicate effectively, and in fact it is quite enraging to have to sift through your absolute crap that you would call posts. in fact it's usually so enraging i feel obligated to chime in and state the obvious, that a) you never said anything you claim you said, rather you just take credit for other people's additions to the discussion and b) you have NO idea of what you are talking about.

and "idiot" is actually the perfect word to describe you:
Idiot is a word derived from the Greek ἰδιώτης, idiōtēs ("person lacking professional skill," "a private citizen," "individual"), from ἴδιος, idios ("private," "one's own").[1] In Latin the word idiota ("ordinary person, layman") preceded the Late Latin meaning "uneducated or ignorant person."[2] Its modern meaning and form dates back to Middle English around the year 1300, from the Old French idiote ("uneducated or ignorant person").

"Idiot" was originally created to refer to "layman, person lacking professional skill", "person so mentally deficient as to be incapable of ordinary reasoning".[6][7] Declining to take part in public life, such as democratic government of the polis (city state), such as the Athenian democracy, was considered dishonorable. "Idiots" were seen as having bad judgment in public and political matters. Over time, the term "idiot" shifted away from its original connotation of selfishness and came to refer to individuals with overall bad judgmentĖindividuals who are "stupid". In modern English usage, the terms "idiot" and "idiocy" describe an extreme folly or stupidity, and its symptoms (foolish or stupid utterance or deed). In psychology, it is a historical term for the state or condition now called profound mental retardation.[8]

so, i am leary to use this as then i wouldn't be able to counteract majidiots BS, but does anyone have that rc.com fix where i can ignore his posts?

also, majidiot, why do you harass people for not answering your questions, but always dodge everyone else's queries?


hafilax


May 13, 2009, 11:37 AM
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pfwein wrote:
Thanks to all of you who addressed my Q re: pulley effect.
One thing I don't think I've seen addressed: at a hanging belay, the anchor is also holding the weight of the belayer, so when the fallen climber comes to rest, the anchor will be holding both the weight of the belayer and the climber, regardless of whether the climber clipped the anchor, right?
And before the climber comes to rest, it seems that the rope will just be elongating based on the climber's weight, the length of the fall, and amount of rope between the climber and the belay device, which again doesn't depend on whether the anchor is clipped,except the fall will be slightly shorter when the anchor is clipped (maybe I'm wrong on this point??).
I'm just having a hard time visualizing why clipping the anchor increases the force on the anchor when the only thing it seems to do is redirect the direction of the force and slightly decrease the length of the fall (both definitely good things), but thanks again to you who attempt to explain it.
If you clip the anchor as the first piece the anchor feels the force of the end of the rope going to the faller and the end of the rope held by the belayer. The force on the belayer's end with be about 75% of that of the faller. The force on the anchor will be about 1.75 times the force felt by the faller.

If you belay directly off the anchor or harness with no slack to the anchor, the force on the anchor will be equal to the force felt by the faller. The belayer will have to hold the full force of the fall whereas by running the rope over a biner attached to the anchor he will only have to hold 75% of the force of the fall but the force on the anchor will be greater. Pick your poison.


hafilax


May 13, 2009, 11:41 AM
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jrathfon wrote:
so, i am leary to use this as then i wouldn't be able to counteract majidiots BS, but does anyone have that rc.com fix where i can ignore his posts?
You could be mature and read Majid's posts with an open mind and ignore his trolling or you could search for 'killfile'. I don't see why people feel the need to digitally block people out. It's quite easy to do in analog and occasionally even an idiot has something interesting to say.


jrathfon


May 13, 2009, 11:43 AM
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at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all).

there are 2 cases in your question:

(A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying)

(B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck.


jrathfon


May 13, 2009, 11:51 AM
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hafilax wrote:
jrathfon wrote:
so, i am leary to use this as then i wouldn't be able to counteract majidiots BS, but does anyone have that rc.com fix where i can ignore his posts?
You could be mature and read Majid's posts with an open mind and ignore his trolling or you could search for 'killfile'. I don't see why people feel the need to digitally block people out. It's quite easy to do in analog and occasionally even an idiot has something interesting to say.

you beat me to that explanation, but i was basically going to add, "damned if you do, damned if you don't" aka "pick your poison".

i was more joking about using the killfile, because though i don't think majidiot has anything useful to say, he can be entertaining.

i don't think having a predetermined opinion that all of what majidiot says is BS is immature, maybe narrow-minded, but i'll be right about 99.9% of the time, so i'm happy with that. i'm happy to be open-minded and have discussions with everyone on this site, with the obvious one exception.


colatownkid


May 13, 2009, 11:57 AM
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majid_sabet wrote:
jrathfon wrote:
majid_sabet wrote:
colatownkid wrote:
pfwein wrote:
loyota wrote:
. . . and only a few 10KN carabiners fail in closed gate mode.
What kind of a carabiner is only good to 10kN?--all I've seen are good to over twice that.
And please excuse my ignorance , but can someone explain the pulley effect mentioned in this thread. In something like a FF2 situation, (i.e., at hanging belay, climber goes up and then falls without any other pro, except clipping the anchor), why would clipping the anchor cause more force? Isn't it just a function of how much rope is out, and it's slightly better to clip the anchor cuz slightly lower fall factor

the "pulley effect" occurs when a load on one side of a pulley is counteracted by an equal load on the opposite side.

suppose a climber has come to a stop after having fallen. the carabiner on uppermost piece of gear is effectively acting as pulley--the climber is hanging on one side, the belayer is hanging on the other side. simply hanging there, the climber's weight must exert some force downward (we'll call it x). in order for the climber to be stationary, the belayer must be exerting an equal force down (also x). therefore, that top piece of gear must be supporting both the full weight of the climber and the belayer or 2x. hence, the total force is double what the climber would place on the piece by himself.

the same principle applies in a moving system where the climber is falling, but we know that in reality the belayer will get pulled into the air, so the doubling is only an approximation.

this is significant in the scenario i described earlier because there is no pulley effect in a factor-2 fall. the climber simply falls directly onto the belayer's belay device. when the system has come to rest (hopefully it does so before both people have hit the ground) the anchor is supporting the weight of the fallen climber directly, not through a pulley. in the high-factor scenario where the anchor has been clipped, the anchor is supporting the weight of the falling climber through a pulley, meaning it has to hold double the force.

let's suppose the factor-2 fall resulted in a force of 8 kN and the high-factor fall resulted in a force of 6kN (totally arbitrary numbers for the sake of example). 2 x 6 = 12, so the high-factor fall actually results in a higher force (12kN) than the factor-2 fall (8kN) thanks to the pulley effect.

the real issue though is that it's extraordinarily difficult to catch factor-2 falls (no personal experience here, so somebody feel free to refute me). this is exacerbated by the fact that when catching a factor-2 fall directly, the belayer's ATC will invert, meaning that the locked position is pulling the rope up, not down, making a catch even more awkward and difficult.

because of this, it might be a good idea to clip the anchor despite the higher potential force simply so it is easier for the belayer to catch the fall.

note, The carabiner does not act as pulley device in FF but a friction device therefore it reduces the fall factor by small amont as mentioned in the PDF I provided above . During a leader fall, we are not getting a true FF2 but some thing like FF 1.75 +- .

I think the only way we could get a true FF2 is to attach a climber to solid steel cable and drop him above an anchor and without any protection in between.

Hey Angry. you want to try this for me?

come on, I buy a candy

majidiot, the FF does not depend on the rope used. as per YOUR reference, FF = the total distance fallen / rope out. if you want to calculate peak force, you must factor in the elasticity of the rope. using a steel cable will increase this max force, but NOT the FF.
b) THEGUY provided the references explaining the friction factor of the pulley effect decreasing force in the system, NOT FF. you did NOT provide this information.

again, you're an idiot. or perhaps i should translate this into rc.com vernacular: "your' an idiot's."

First off, try to learn how to communicate with people instead of using the word idiot or whatever. 7 years old kids call each other idiot. You are a college grad and I thought at least they teach you how to talk to people.

it seems that some of us are confused as to what exactly a "fall factor" is. the fall factor is defined as the distance fallen divided by the total amount of rope in the system between the belay and the falling climber.

the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force. it just so happens that the more rope is available, the more energy can be absorbed.

if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

since rope is dynamic and not static, the force in the fall is more complicated. as the length of the fall increases, the force also increases. however, since the rope is dynamic, a longer fall results in more energy-dissipating rope stretch since more rope must necessarily be out for a longer fall to happen.

therefore, as a rough measure of force, it is more accurate to examine the fall factor, or the ratio of energy-dissipating rope stretch and the energy-creating fall. (note: to all physicists, i understand energy cannot be created. i just feel that this is a decent explanation in "plain english.")

what a fall factor DOES NOT do, is tell us anything specific about a definite peak load. the importance of the fall factor is that it allows us to compare the relative magnitude of various falls, ALL OTHER THINGS BEING EQUAL. this means that if the knot cinches the same amount, the belayer moves the same amount, the climber falls on the same piece with the same friction on the same carabiner, the belayer hasn't lost any weight due to sweat, etc. than a greater fall factor will result in a greater peak force on the fallen piece.

however, these other things are never equal. for this reason the fall factor is, necessarily, an approximation. it is possible that due to various factors (some of which are listed above) a factor 1.2 fall might actually result in a lower force than a factor 1.1 fall. in general, however, these factors will be similar in many climbing situations, and since we're approximating anyway, are assumed to be equal.

the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

as far as the carabiner not being a pulley is concerned...

a pulley simply redirects force. a carabiner is certainly not an idealized, frictionless pulley, but it's function is the same.

majid is correct in stating that the friction over the carabiner does reduce some of the force. (his explanation involving fall factors is not correct, though.) the classic number used in climbing calculations is that the pulley will reduce the friction on one side by one-third, so the total force on the top-piece carabiner is five-thirds times the force of the falling climber ((5/3) * Force_Climber).

the idea that the factor-2 fall does not exist is ridiculous at best in my opinion. consider the leader who is 10 feet above the belay and has not clipped any gear (that is, the only thing between him and the long ride is a belay device). if he falls, he will fall 20 feet with 10 feet of rope in the system. BY DEFINITION, 20 / 10 = 2.

(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

i think what majid is trying to say is that the theoretical peak force in a very rough approximation that does not include friction will likely be higher than the theoretical peak force in a slightly-less-than-very-rough approximation that does include friction.


hafilax


May 13, 2009, 12:04 PM
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You will never measure the force calculated from a unmodified fall factor 2 calculation in a climbing situation.


colatownkid


May 13, 2009, 12:07 PM
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jrathfon wrote:
at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all).

there are 2 cases in your question:

(A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying)

(B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck.

quoted for correctness!

yep, so that is the dilemma: if there's no pro to be had in the start of the next pitch, do you clip the anchor or not?

one last thing to consider:

a lower fall factor does result in a lower force on the top piece. assuming the leader falls shortly after having clipped the anchor (or jesus nut, etc.), there is a point at which even the doubled force (well, 1.6 times or something like that) is still less than the force of a factor-2. in other words, if you clip the anchor as a directional, there is some amount of rope that can be out above the directional and the peak force will still be less than a factor-2. it's a win-win!

unfortunately, that distance is somewhere around 1 meter (depending on how you approximate and what conditions you use), so the point is pretty moot.


colatownkid


May 13, 2009, 12:09 PM
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hafilax wrote:
You will never measure the force calculated from a unmodified fall factor 2 calculation in a climbing situation.

not arguing with you there; just thought it might be instructive to explain the point of talking about fall factors in the first place.


jrathfon


May 13, 2009, 12:13 PM
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colatownkid wrote:
jrathfon wrote:
at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all).

there are 2 cases in your question:

(A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying)

(B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck.

quoted for correctness!

yep, so that is the dilemma: if there's no pro to be had in the start of the next pitch, do you clip the anchor or not?

one last thing to consider:

a lower fall factor does result in a lower force on the top piece. assuming the leader falls shortly after having clipped the anchor (or jesus nut, etc.), there is a point at which even the doubled force (well, 1.6 times or something like that) is still less than the force of a factor-2. in other words, if you clip the anchor as a directional, there is some amount of rope that can be out above the directional and the peak force will still be less than a factor-2. it's a win-win!

unfortunately, that distance is somewhere around 1 meter (depending on how you approximate and what conditions you use), so the point is pretty moot.

unless your belayer is lowered out a bit from the anchor...

that's why a VERY truck piece above the anchor is better than a leg of the anchor itself, it's higher in the system, thus the fall is shorter.

the force on that jebus piece also exemplifies why using one leg of a trad anchor as this piece may not be the best idea.


jrathfon


May 13, 2009, 12:18 PM
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just for the ease of the catch, i always clip that directional on the bolt if the climbing is hard, and i make sure i'm either solid, or getting gear in fast off the belay. i don't want my belayer to have to catch a non-directionalized fall, and although i'm fat, i think that fatty 3/8" stainless steel bolt in granite will hold me falling the 10ft with 8ish feet of rope. see? no FF2! [sarcasm]it doesn't exist![/sarcasm]


clews


May 13, 2009, 12:31 PM
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you're definitely more right than the previous post.
you definitely can't calculate impact force just by your fall factor


colatownkid


May 13, 2009, 12:54 PM
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jrathfon wrote:
colatownkid wrote:
jrathfon wrote:
at a hanging belay, if any piece of gear is clipped (anchor bolt or jebus piece), that piece will be holding the weight of both climbers (if the belayer is picked up at all).

there are 2 cases in your question:

(A) the climber has no gear in and FF2's onto the belayer's belay device directly, which is a high load, and is hard to catch due to the belayer getting wrenched around, and the belayer must now brake in the opposite position (holding the rope up to brake, not down as originally lead belaying)

(B) a piece (anywhere) or bolt on the anchor is clipped, this reduces the fall factor by reducing the length of fall with the same amount of rope out. however, with the pulley effect (with no friction, not the case) the force on the clipped piece will be doubled (the falling climbers force has to be counter-acted by another equal force), thus resulting in a significantly high force on that piece, even though you have reduced the fall factor. this fall however is easier to catch for the belayer as the rope is directed upwards in the normal orientation, the belayer also has some cushioning effect on these forces. the force experienced by the fallen climber in this scenario is less, but you better make damn sure that first piece is truck.

quoted for correctness!

yep, so that is the dilemma: if there's no pro to be had in the start of the next pitch, do you clip the anchor or not?

one last thing to consider:

a lower fall factor does result in a lower force on the top piece. assuming the leader falls shortly after having clipped the anchor (or jesus nut, etc.), there is a point at which even the doubled force (well, 1.6 times or something like that) is still less than the force of a factor-2. in other words, if you clip the anchor as a directional, there is some amount of rope that can be out above the directional and the peak force will still be less than a factor-2. it's a win-win!

unfortunately, that distance is somewhere around 1 meter (depending on how you approximate and what conditions you use), so the point is pretty moot.

unless your belayer is lowered out a bit from the anchor...

that's why a VERY truck piece above the anchor is better than a leg of the anchor itself, it's higher in the system, thus the fall is shorter.

the force on that jebus piece also exemplifies why using one leg of a trad anchor as this piece may not be the best idea.

in that case it's hardly a dilemma.


majid_sabet


May 13, 2009, 1:13 PM
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hafilax wrote:
Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.

That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening.

When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2?

What happened to the piece in the middle that actually slowed his fall?

Why canít we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?


jrathfon


May 13, 2009, 1:13 PM
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lookin' for tools to solve a problem. but sans piece above the anchor, lengthening your belayer's stance could help. screamer on said piece/anchor leg as well?

anyways i think there is now a lot of data for the OP's question:

as per BD, 2-5 kN in a "typical" spurt-climbing fall

as per UIAA you want your gear rated better than 7 kN

a 2 kN micronut with a yates screamer (3-4 kN reduction) gives you a piece which could hold the "typical" mid-pitch fall of 2-5 kN. not sayin' I'd be happy 2 body lengths above that.

UIAA also makes a point that if loaded equally a cluster of tiny pieces could get the job done, neglecting whether or not the rock holds...

i've fallen on a #1 BD stopper at the top of a pitch and it held, course i couldn't remove it afterwords...


desertwanderer81


May 13, 2009, 1:19 PM
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majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

You fail at math.


desertwanderer81


May 13, 2009, 1:20 PM
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majid_sabet wrote:
rocknice2 wrote:
Worst real world fall???
Not counting FF2.

I'm starting P2 and it's hard right off the bat. I climb up a bit [feet level with belay device] and plug a cam and clip it. Now the cam is 7ft above belay device and 10ft above ledge.
I struggle up until the cam is at my feet and plug a nut. I'm so pumped fiddling with the nut and can't stabilize for the clip. I bitch, scream and cry in that order. Finally I peel off.
I take a 6 footer on 10 feet of rope = 6kn
Even more realistic the belayer worries I might deck and manages to take in an arm length of rope in.
A 6 footer on 8 feet of rope = 7.5kn

there is no such thing as FF2 in climbing. the best you may get is like FF1.75 or so.

And what would you call it if someone is being belayed on a pitch and falls without placing any pro???........


jrathfon


May 13, 2009, 1:20 PM
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majid_sabet wrote:
hafilax wrote:
Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.

That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening.

When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2?

What happened to the piece in the middle that actually slowed his fall?

Why canít we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?

So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible.

As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out.


jrathfon


May 13, 2009, 1:23 PM
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desertwanderer81 wrote:
majid_sabet wrote:
angry wrote:
I'm not sure that's how it works.

I could be wrong but I've never heard of being able to calculate fall forces in KN based on the distance of the fall vs. the amount of rope out. Maybe it's some sort of approximation based on fall factors.

1KN = 224 lbs or so. It's a real weight applied to your gear, not a fall factor applied to your rope.

Please correct me if I'm wrong, but I think you've got to be mistaken.

wrong girl

1 KILO mean 1000 chingon

you sould say 1N =100 kg or @ 224 lbs

You fail at math.

and physics.

Though I have a question for you majidiot: what's with the crafty use of bold text which typically does not illustrate your point?


majid_sabet


May 13, 2009, 1:24 PM
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jrathfon wrote:
majid_sabet wrote:
hafilax wrote:
Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.

That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening.

When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2?

What happened to the piece in the middle that actually slowed his fall?

Why canít we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?

So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible.

As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out.
no I was not refering to you as the college boy but the other guy


(This post was edited by majid_sabet on May 13, 2009, 1:24 PM)


shockabuku


May 13, 2009, 1:24 PM
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hafilax wrote:
You will never measure the force calculated from a unmodified fall factor 2 calculation in a climbing situation.

That's a rough sentence.


jrathfon


May 13, 2009, 1:28 PM
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majid_sabet wrote:
jrathfon wrote:
majid_sabet wrote:
hafilax wrote:
Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.

That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening.

When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2?

What happened to the piece in the middle that actually slowed his fall?

Why canít we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?

So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible.

As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out.
no I was not refering to you as the college boy but the other guy

then why'd you quote a post that was in direct response to me? eh?


hafilax


May 13, 2009, 1:34 PM
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I don't really know what happens when a piece pulls. I think it depends on how much the rope is able to recover before being stretched again since the damping in the rope is the primary energy dissipation mechanism (AFAIK).

If the rope doesn't recover at all then that piece pulls then the force applied to the next piece won't be reduced by very much. It would be as if that first piece wasn't there.

My intuition says that there is some recovery of the rope and that pulling a piece does lower the impact on the rest of the system but I have no idea by how much. I think would depend on how quickly the pieces are sequentially loaded, on how much the rope was stretched to begin with, etc.

The last time this subject came up I started reading papers discussing this but didn't find anything that satisfied my curiosity. There was a drop test experiment where an upper piece was designed to break at a certain peak force and subsequently caught by another. I can't remember the conclusion of that paper. I do remember thinking that the current physical model of dampers and springs for a rope doesn't describe the dynamics all that well, especially in the recovery after being stretched. The rope measurements showed more hysteresis than the model and I remember them adding a fudge factor in there to improve the fit.

There are folks here who have looked into this far more than I have so maybe they can chime in. adatesman has links to some of the rope dynamics papers somewhere in the Needless Destruction Theater.


majid_sabet


May 13, 2009, 1:36 PM
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jrathfon wrote:
majid_sabet wrote:
jrathfon wrote:
majid_sabet wrote:
hafilax wrote:
Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.

That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening.

When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2?

What happened to the piece in the middle that actually slowed his fall?

Why canít we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?

So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible.

As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out.
no I was not refering to you as the college boy but the other guy

then why'd you quote a post that was in direct response to me? eh?

I was only saying in bold that I do get an enjoyment out of messing with other people who disrespect me and I was not referring to you at any shape or forml . I also wanted to ask you about the falling climber while loading the piece below and you kind of answered my question.that is all


desertwanderer81


May 13, 2009, 1:41 PM
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majid_sabet wrote:
jrathfon wrote:
majid_sabet wrote:
jrathfon wrote:
majid_sabet wrote:
hafilax wrote:
Majid just sucks at explaining things and I think he gets some enjoyment out of stringing the tongue wagging dogs along. He's hinting at other factors like the cinching of the knot that effectively lowers the fall factor.

The fall factor calculation that everybody loves so much is an approximation and often a very poor one. It doesn't take into account friction (around the biner, rope drag etc), knot cinching, the movement of the belayer, rope slipping through the belay device, the climber dragging down the wall and a host of other significant energy dissipating mechanisms.

A modest approximation for the efficiency of a biner as a pulley is around 75% I believe. This is where Majid's factor of 1.75 for the force from the pulley effect is coming from. That's not even including the cinching of the figure 8 which can effectively add a couple of meters of rope to the system.

It's an amusing academic exercise to try to calculate real world forces but there is an infinite number of results even for one given fall factor depending on the actual boundary conditions of the setup. There are some rules of thumb but you will never be certain that climbing another meter will end up with a fall that will snap the RP you're nervously climbing away from.

That is true, I love to blow fuses on people with low tolerance specially those in RC and that includes the newly college boy who think he knows it all. Anyway back to FF whatever; I got few questions and may be you could explain what is happening.

When a climber falls, lets say 10 feet above an anchor, the first piece that was some 5 feet below the climber takes some of the forces .now what happens when the climber pops that piece out and continue to fall passing the anchor. Can we truly say that our climber fell 20 feet? I mean 10 feet above an anchor and 10 feet below the anchor aka FF2?

What happened to the piece in the middle that actually slowed his fall?

Why canít we say that he fell 15 feet (from that piece) or 17.5 feet or whatever?

So it turns out you do actually receive an education in college. I'd hardly call myself a college boy as you are projecting a 20 year old "idiot" frat dude. Majidiot, do you actually know my educational background, or how old I am? I believe the answer is no, so you can stop posturing. I would bet though that I have more pitches under my belt and have a better grasp on this subject than you do, though I don't really care how I measure up to you, more that the information given on the thread is as accurate or helpful as possible.

As for your question, that piece ripping will absorb some of the overall force in the system (think like a screamer), reducing the eventual peak force, though thinking about it in terms of fall factor won't really help you out.
no I was not refering to you as the college boy but the other guy

then why'd you quote a post that was in direct response to me? eh?

I was only saying in bold that I do get an enjoyment out of messing with other people who disrespect me and I was not referring to you at any shape or forml . I also wanted to ask you about the falling climber while loading the piece below and you kind of answered my question.that is all

That's the thing though! The only way you EVER mess with people is by filling thread after thread with disinformation. Your understanding of math, physics, and even climbing is limitted to the point that you should never, ever comment on anything as almost without fail, it will be wrong!


hafilax


May 13, 2009, 1:47 PM
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Maybe it comes from years of marking 1st year physics labs, but I don't find Majid to be as 'wrong' as the haters make him out to be. You just have to filter out the trolling.


jrathfon


May 13, 2009, 1:48 PM
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desertwanderer81 wrote:
majid_sabet wrote:
I was only saying in bold that I do get an enjoyment out of messing with other people who disrespect me and I was not referring to you at any shape or forml . I also wanted to ask you about the falling climber while loading the piece below and you kind of answered my question.that is all

That's the thing though! The only way you EVER mess with people is by filling thread after thread with disinformation. Your understanding of math, physics, and even climbing is limitted to the point that you should never, ever comment on anything as almost without fail, it will be wrong!

AMEN!!! But somehow, I don't think he'll get the message...

edit: quotes and PTFTW!!!!111one!elevens!!!


(This post was edited by jrathfon on May 13, 2009, 1:49 PM)


ptlong


May 13, 2009, 1:50 PM
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shockabuku wrote:
hafilax wrote:
You will never measure the force calculated from a unmodified fall factor 2 calculation in a climbing situation.

That's a rough sentence.

What does it mean?

Is halifax saying it's impossible to get 10kN tension in a rope in a climbing situation? Or what??


desertwanderer81


May 13, 2009, 1:53 PM
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hafilax wrote:
Maybe it comes from years of marking 1st year physics labs, but I don't find Majid to be as 'wrong' as the haters make him out to be. You just have to filter out the trolling.

What?? How? These are pretty basic concepts that he's butchering.

If I had an engineer working for me who had his understanding of the world, I'd fire his ass in a heartbeat.


hafilax


May 13, 2009, 1:53 PM
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Try 2:

Real world forces will never approach the value calculated with the fall factor formula.


majid_sabet


May 13, 2009, 1:54 PM
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I am not giving any wrong info. I am providing related info to the topic and whatever I have said so far, it was related to topic. If this information is wrong then people should bring it up so everyone can learn (that includes me) from it as true educational discussion. I will not tolerate against people who continue calling me names or take their personal problems and use these forums to become even with me over some unknown old business. If those sort of people want to use that sort of techniques or behavior to prove their points then I grantee you, I would the worse as*hole you guys ever wanted to deal with.

peace and lets get back on topic


(This post was edited by majid_sabet on May 13, 2009, 2:11 PM)


ptlong


May 13, 2009, 1:55 PM
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hafilax wrote:
Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

Why not?


jt512


May 13, 2009, 1:56 PM
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colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay


desertwanderer81


May 13, 2009, 2:03 PM
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majid_sabet wrote:
That's the thing though! The only way you EVER mess with people is by filling thread after thread with disinformation. Your understanding of math, physics, and even climbing is limitted to the point that you should never, ever comment on anything as almost without fail, it will be wrong!

I am not giving any wrong info. I am providing related info to the topic and whatever I have said so far, it was related to topic. If this information is wrong then people should bring it up so everyone can learn (that includes me) from it as true educational discussion. I will not tolerate against people who continue calling me names or take their personal problems and use these forums to become even with me over some unknown old business. If those sort of people want to use that sort of techniques or behavior to prove their points then I grantee you, I would the worse as*hole you guys ever wanted to deal with.

peace and lets get back on topic
That's the thing though! Your "related info" is not correct! You made the statement that 1kN is not equal to 224 lbs! 1kN IS however equal to 224lbs.

Another instance of you providing misinformation is your complete lack of understanding of what a factor of safety is! You were saying that a person who weighs (say 224lbs) and falls on a rope that is rated for 10kN would have a factor of safety of 10! That statement is so far from reality that it is absurd!!


majid_sabet


May 13, 2009, 2:04 PM
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jt512 wrote:
colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay


Jay

Lets say we use two cheap biner and both are rated to snap at 6 kn. we place one on the fig8 and attached to leader and another one to belayer's gri gri.

based on your remark, the chances of leader's biner breaking is by greater than belayer's biner ?

Right


(This post was edited by majid_sabet on May 13, 2009, 2:05 PM)


jt512


May 13, 2009, 2:06 PM
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hafilax wrote:
Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

I doubt that is true. With sufficient rope drag, the actual force should exceed the calculated force.

Jay


jrathfon


May 13, 2009, 2:07 PM
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On that last point, and something I thought was a touch iffy, in the paper majidiot actually provided, they define fall factor as Dt, the total distance fallen by the climber after stretch, divided by the length of rope, pre-stretch. I've always seen it defined as the way you just stated, fall pre stretch/rope pre stretch.


desertwanderer81


May 13, 2009, 2:09 PM
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In reply to:
Jay

Lets say we use two cheap biner and both are rated to snap at 6 kn. we place one on the fig8 and attached to leader and another one to belayer's gri gri.

based on your remark, the chances of leader's biner breaking is by greater than belayer's biner ?

Right

The force on leader's end is higher than the belayers end. The amount is based upon the amount of friction in the system.


hafilax


May 13, 2009, 2:10 PM
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jt512 wrote:
hafilax wrote:
Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

I doubt that is true. With sufficient rope drag, the actual force should exceed the calculated force.

Jay
Damnit. I was thinking of the fall factor 2 case and got too general. I give up. Blush

My attempted point was that the fall factor force calculation is a poor model for climbing situations.


jt512


May 13, 2009, 2:10 PM
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majid_sabet wrote:
jt512 wrote:
colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay


Jay

Lets say we use two cheap biner and both are rated to snap at 6 kn. we place one on the fig8 and attached to leader and another one to belayer's gri gri.

based on your remark, the chances of leader's biner breaking is by greater than belayer's biner ?

Right

Yes, assuming that the rope is clipped through one or more anchors.

Jay


desertwanderer81


May 13, 2009, 2:13 PM
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jt512 wrote:
hafilax wrote:
Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

I doubt that is true. With sufficient rope drag, the actual force should exceed the calculated force.

Jay


I was thinking the same thing when I saw that statement earlier.

Ultimately the forces which are calculated will be fairly similiar to the actual forces in the field.


jt512


May 13, 2009, 2:15 PM
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jrathfon wrote:
On that last point, and something I thought was a touch iffy, in the paper majidiot actually provided, they define fall factor as Dt, the total distance fallen by the climber after stretch, divided by the length of rope, pre-stretch. I've always seen it defined as the way you just stated, fall pre stretch/rope pre stretch.

I haven't looked at the paper Majid referenced. I suppose that in principle you could define fall factor either way, but I would think that defining it in terms of maximum stretch would complicate the derivation of the equation for maximum impact force from Hooke's Law.

Edit: Glancing at that paper, the author's expression for the maximum impact force, based on the total distance fallen (including maximum rope stretch) is actually simpler than the one based on the "free fall" distance.

Jay


(This post was edited by jt512 on May 13, 2009, 2:24 PM)


ptlong


May 13, 2009, 2:20 PM
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hafilax wrote:
jt512 wrote:
hafilax wrote:
Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

I doubt that is true. With sufficient rope drag, the actual force should exceed the calculated force.

Jay
Damnit. I was thinking of the fall factor 2 case and got too general. I give up. Blush

My attempted point was that the fall factor force calculation is a poor model for climbing situations.

Attaway came to the same conclusion as Jay:

http://www.jrre.org/ropes_101.pdf

But there are factor 2 falls that might approach the simple theoretical values as well. Think of a rope soloist run way out. Or someone belaying and the rope gets snagged in such a way as to provide a nearly static belay. The further out the leader the less important are mitigating factors like knot tightening and harness stretching.


ptlong


May 13, 2009, 2:24 PM
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hafilax wrote:
I don't really know what happens when a piece pulls. I think it depends on how much the rope is able to recover before being stretched again since the damping in the rope is the primary energy dissipation mechanism (AFAIK)....

Beverly and Attaway did drop tests to measure this. Their conclusion was that the rope recovered.

http://www.mra.org/...equential_Falls2.pdf

(edited to fix URL)


(This post was edited by ptlong on May 13, 2009, 2:35 PM)


hafilax


May 13, 2009, 2:32 PM
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http://www.mra.org/...equential_Falls2.pdf

You added a p somehow.


colatownkid


May 13, 2009, 5:45 PM
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jt512 wrote:
colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay

i stand corrected.

as for this part:

jt512 wrote:
]
In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

the only reason i mentioned this is that there seemed to be some implication that a specific fall factor could be equated with some specific impact force (across independent scenarios).


curt


May 13, 2009, 5:55 PM
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colatownkid wrote:
jt512 wrote:
colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay

i stand corrected.

as for this part:

jt512 wrote:
]
In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

the only reason i mentioned this is that there seemed to be some implication that a specific fall factor could be equated with some specific impact force (across independent scenarios).

It can if the only variable is the length of the fall.

Curt


colatownkid


May 13, 2009, 5:58 PM
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curt wrote:
colatownkid wrote:
jt512 wrote:
colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay

i stand corrected.

as for this part:

jt512 wrote:
]
In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

the only reason i mentioned this is that there seemed to be some implication that a specific fall factor could be equated with some specific impact force (across independent scenarios).

It can if the only variable is the length of the fall.

Curt

yes, but not on two different climbs at two different anchors, etc.


curt


May 13, 2009, 6:02 PM
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colatownkid wrote:
curt wrote:
colatownkid wrote:
jt512 wrote:
colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay

i stand corrected.

as for this part:

jt512 wrote:
]
In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

the only reason i mentioned this is that there seemed to be some implication that a specific fall factor could be equated with some specific impact force (across independent scenarios).

It can if the only variable is the length of the fall.

Curt

yes, but not on two different climbs at two different anchors, etc.

Yes, then too--so long as the rope has the same maximum impact force, the climber weighs the same, etc.

Curt


antiqued


May 13, 2009, 6:45 PM
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jt512 wrote:
hafilax wrote:
Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

I doubt that is true. With sufficient rope drag, the actual force should exceed the calculated force.

Jay

Both of these statements can be useful, but under different conditions. [Jay's is truer, never say never!]

The fall factor data is measured in a high FF, with real friction over the top biner, belay end knotted to a steel fixture, and a steel block. Real falls typically have a belay device with slip, attached to a belayer of finite weight, not rigidly tied in on the one end, and a soft, floppy body on the other end.
For low friction falls (zero or minimal rope drag up to the top biner), the impact force will be lower than that calculated from the UIAA test data because of auxiliary energy absorption mechanisms, usually quite a bit lower. In any serious fall the rope will slip and the belayer float, reducing impact force.

For low to modest FF falls with a convoluted rope path, the effective FF can easily be much higher than the belayer-climber calculation, because a good portion of the rope doesn't see much force, and therefore can't be absorbing much of the fall energy.
We know this because many of us weighing less than a kN catch decent size falls without leaving the ground. For example, a 20' fall on 50' of rope would be a 0.4FF, with a ~3.8kN force on the climber, and after friction, ~2.6kN (=0.7*3.8) on the belayer. That should yank people up and away, and indeed you can see it happen in gyms around the country, with their arrrow straight rope paths. But out on trad routes, many (not all, of course) such falls are trivially caught. So we know that the effective length of the rope has been reduced, and the impact force must be higher.

What about hard falls? The UIAA test is so aggressive, it is almost impossible to exceed the measured impact force. Only 12% of the rope is between the tie-off and the protection in that test. In order to duplicate it, one might clip the 'Jesus nut' 4 feet from the belay, run it out 28 more feet and then take a 56 footer with the belay tied off.

The only likely way is to misroute the rope, so that it is jammed in a crack, bends sharply under a roof, or gets pinned by the falling end of the rope (below). This can lead to real FF~2 falls if the jam or pin is very close to the top piece.



colatownkid


May 13, 2009, 6:51 PM
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curt wrote:
colatownkid wrote:
curt wrote:
colatownkid wrote:
jt512 wrote:
colatownkid wrote:
the significance of the fall factor becomes evident when one realizes that the stretch in dynamic rope serves to dissipate energy in the system and absorb some of the force.

The stretch in the rope reduces the impact force (relative to a less stretchy rope). It does not "absorb" the force. This is not a pedantic distinction, as you'll see presently.

In reply to:
if rope were totally static, the force of a fall would simply be a matter of distance fallen. the greater the distance fallen the greater the gain in velocity overtime, and the greater total force.

That is false. If the rope were truly completely static, then the force of any fall would be infinite, and completely independent of the distance fallen. The longer the fall, the greater the (kinetic) energy, not the impact force. You seem to be implying that force builds up in a fall. It doesn't. The only force acting on a falling climber is gravity.

In reply to:
what a fall factor DOES NOT do, is tell us anything specific about a definite peak load.

No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

In reply to:
majid is correct in stating that the friction over the carabiner does reduce some of the force.

Majid's statement was confusing, and possibly outright wrong. Many climbers misunderstand the effect of friction in the belay system. All friction in the system is a braking force. It increases the impact force on the climber, and decreases the impact force on the belayer. Some people speak of friction increasing the "effective" fall factor, because friction reduces the stretch in the rope, much as if there were less rope out in the first place.

In reply to:
(one final note: the fall factor is inherently an approximation since we all know from experience that rope stretch makes for a longer fall than 20 feet when 10 feet of rope is out.)

No. The fall factor is defined as the distance the climber falls with no stretch in the rope divided by the amount of unstretched rope out.

Jay

i stand corrected.

as for this part:

jt512 wrote:
]
In reply to:
the one thing the fall factor does not tell us is any value in kilonewtons that describes the max force in the system.

Right, but it's easy enough to calculate, given the assumptions above.

the only reason i mentioned this is that there seemed to be some implication that a specific fall factor could be equated with some specific impact force (across independent scenarios).

It can if the only variable is the length of the fall.

Curt

yes, but not on two different climbs at two different anchors, etc.

Yes, then too--so long as the rope has the same maximum impact force, the climber weighs the same, etc.

Curt

i give up.


Rudmin


May 13, 2009, 7:43 PM
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jt512 wrote:
No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

You mention some of the assumptions. But all these things that these ideal calculations ignore are what make real data more important:
-swinging at the bottom of a fall
-hitting the cliff on a fall rather than a perfect straight down overhang every time
-the movements and dampening of a real human body versus an ideal point mass (centre of gravity isn't right at the tie in point either)
-belayer's catch
-belayer's movements
-nylon stretch

In theory, if you take a 1 inch fall on a dyneema sling you will rip all of your anchors out or tear down the rock face, but we all know that isn't true. That's because theory assumes that the rope is line, the anchor is a single point, and the climber is a singularity at the end of that line and the whole setup exists in a vacuum.


USnavy


May 13, 2009, 8:45 PM
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adatesman wrote:
USnavy wrote:
In my (field) tests I have found that the max impact force of a typical sport lead fall ranging from a .2 - .85 FF fall with a fall distance of 5 Ė 15 feet will produce 3 Ė 8 kN on the top anchor.

If I remember right you use a retasked digital crane scale to get your force measurements? Not to be picky, but those won't work for measuring peak force during a fall and your results are most likely well under the true peak force.

Crane scales simply don't have a high enough scan rate on the force measurement (often only 10 samples/second) for this sort of thing and to do it properly you need something with a scan rate several orders of magnitude higher or an analog peak capture channel.

-aric.

EDIT- if you keep an eye on Ebay you can usually pick up a used Daytronic 4077 strain gage indicator for $250 or so and they're perfect for this sort of thing since they have a digital scan rate of 1000 samples/sec and an analog peak capture channel. Plus it will most likely work with the load cell you already have from the crane scale. They're a bit of work to get programmed for this kind of thing, but its not too bad once you read the manual a couple times. Heck, depending on what you want it to do I could just send a copy of my config that you could load onto it.

Nope. I got myself a nice strain gauge to replace the crane scale. But surprisingly the crane scale was not that far off. It seems the 15 or so samples per second got the reading somewhat close. Did you ever figure out how to modify yours so it can run on DC power?


(This post was edited by USnavy on May 13, 2009, 8:48 PM)


shockabuku


May 13, 2009, 8:46 PM
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hafilax wrote:
Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

Thank you. That's much better.


adatesman


May 13, 2009, 8:59 PM
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adatesman


May 13, 2009, 9:12 PM
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majid_sabet


May 13, 2009, 9:30 PM
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adatesman wrote:
Majid, you are the true master. I'm sorry for spoiling it, but 5 pages and counting... damn.

I'd call you out as a troll, but you seem to have a knack for picking topics that everyone thinks are common knowledge and then all hell breaks loose when people realize that not everyone thinks as they do. I'm still not 100% sure anyone actually benefits from the resulting arguments, but they sure are entertaining. And if you look past the arguments, quite informative.

I won't go so far as to tell people to back off as was requested by another user in S&F since you seem to bring a lot of this on yourself, but I will gladly sit back and enjoy the aftermath. Laugh

-a.

Aric

This is unfair that I am always the black sheep in RC.Not my fault that a single page n00bee question turns in to full blast scientific hell but to add a little heat in to this stew, I am adding few photos.




















majid_sabet


May 13, 2009, 9:50 PM
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jt512 wrote:
jrathfon wrote:
On that last point, and something I thought was a touch iffy, in the paper majidiot actually provided, they define fall factor as Dt, the total distance fallen by the climber after stretch, divided by the length of rope, pre-stretch. I've always seen it defined as the way you just stated, fall pre stretch/rope pre stretch.

I haven't looked at the paper Majid referenced. I suppose that in principle you could define fall factor either way, but I would think that defining it in terms of maximum stretch would complicate the derivation of the equation for maximum impact force from Hooke's Law.

Edit: Glancing at that paper, the author's expression for the maximum impact force, based on the total distance fallen (including maximum rope stretch) is actually simpler than the one based on the "free fall" distance.

Jay

So Jay, you are saying if this climber who was linked with a biner that was rated to lets say 5 KN and then his belayer was also was tied in to a fix anchor with 5 KN biner, the leader's biner has a higher chances of failure than belayer biner.

Now is this because the draw(B) is taking some of the load therefore, the bottom half of rope(belayer C) does not get the forces as equal as the other half ( leader side A)?




spikeddem


May 13, 2009, 10:17 PM
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majid_sabet wrote:
adatesman wrote:
Majid, you are the true master. I'm sorry for spoiling it, but 5 pages and counting... damn.

I'd call you out as a troll, but you seem to have a knack for picking topics that everyone thinks are common knowledge and then all hell breaks loose when people realize that not everyone thinks as they do. I'm still not 100% sure anyone actually benefits from the resulting arguments, but they sure are entertaining. And if you look past the arguments, quite informative.

I won't go so far as to tell people to back off as was requested by another user in S&F since you seem to bring a lot of this on yourself, but I will gladly sit back and enjoy the aftermath. Laugh

-a.

Aric

This is unfair that I am always the black sheep in RC.Not my fault that a single page n00bee question turns in to full blast scientific hell but to add a little heat in to this stew, I am adding few photos.

[IMG]http://img254.imageshack.us/img254/6869/scan0002gfn.jpg[/IMG]

[IMG]http://img26.imageshack.us/img26/4138/scan0003y.jpg[/IMG]

[IMG]http://img26.imageshack.us/img26/4991/scan00041.jpg[/IMG]

[IMG]http://img21.imageshack.us/img21/295/scan00051.jpg[/IMG]


[IMG]http://img21.imageshack.us/img21/8718/scan00061.jpg[/IMG]


[IMG]http://img8.imageshack.us/img8/1286/scan0007c.jpg[/IMG]

[IMG]http://img8.imageshack.us/img8/8462/scan00081m.jpg[/IMG]

[IMG]http://img22.imageshack.us/img22/415/scan00091.jpg[/IMG]

For efficiency, I won't remove the dots. However, I encourage everyone to hit "page down" or "page up" while looking at those photos. It's fun.


desertwanderer81


May 13, 2009, 10:26 PM
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adatesman wrote:
Majid, you are the true master. I'm sorry for spoiling it, but 5 pages and counting... damn.

I'd call you out as a troll, but you seem to have a knack for picking topics that everyone thinks are common knowledge and then all hell breaks loose when people realize that not everyone thinks as they do. I'm still not 100% sure anyone actually benefits from the resulting arguments, but they sure are entertaining. And if you look past the arguments, quite informative.

I won't go so far as to tell people to back off as was requested by another user in S&F since you seem to bring a lot of this on yourself, but I will gladly sit back and enjoy the aftermath. Laugh

-a.

If there is anything that is even remotely informative, it is in people rebuking majid. He simply comes up with things that just aren't true because he just doesn't understand what he's talking about.


USnavy


May 13, 2009, 10:43 PM
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adatesman wrote:
USnavy wrote:
adatesman wrote:
USnavy wrote:
In my (field) tests I have found that the max impact force of a typical sport lead fall ranging from a .2 - .85 FF fall with a fall distance of 5 Ė 15 feet will produce 3 Ė 8 kN on the top anchor.

If I remember right you use a retasked digital crane scale to get your force measurements? Not to be picky, but those won't work for measuring peak force during a fall and your results are most likely well under the true peak force.

Crane scales simply don't have a high enough scan rate on the force measurement (often only 10 samples/second) for this sort of thing and to do it properly you need something with a scan rate several orders of magnitude higher or an analog peak capture channel.

-aric.

EDIT- if you keep an eye on Ebay you can usually pick up a used Daytronic 4077 strain gage indicator for $250 or so and they're perfect for this sort of thing since they have a digital scan rate of 1000 samples/sec and an analog peak capture channel. Plus it will most likely work with the load cell you already have from the crane scale. They're a bit of work to get programmed for this kind of thing, but its not too bad once you read the manual a couple times. Heck, depending on what you want it to do I could just send a copy of my config that you could load onto it.

Nope. I got myself a nice strain gauge to replace the crane scale. But surprisingly the crane scale was not that far off. It seems the 15 or so samples per second got the reading somewhat close. Did you ever figure out how to modify yours so it can run on DC power?

Not all strain gage indicators are made equal... some are intended for static loads and have low scan rates, which could explain the lack of discrepancy with the crane scale.

I'm going to be offline for the next couple days, but it boils down to the fact that reading an analog peak with digital equipment is suspect unless you get into extremely fast (expensive) scan rates. I don't know what gear you're using, but frankly I'm not happy with the 1000 samples/sec I get with my Daytronic gear and if you're less than that I don't have much faith in your results. Analog is where its at as far as this is concerned and without data proving digital is good enough I'm not convinced. Fortunately (for me) my gear gives both, hence the lack of faith in the digital.

-a.

Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?


curt


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majid_sabet wrote:
jt512 wrote:
jrathfon wrote:
On that last point, and something I thought was a touch iffy, in the paper majidiot actually provided, they define fall factor as Dt, the total distance fallen by the climber after stretch, divided by the length of rope, pre-stretch. I've always seen it defined as the way you just stated, fall pre stretch/rope pre stretch.

I haven't looked at the paper Majid referenced. I suppose that in principle you could define fall factor either way, but I would think that defining it in terms of maximum stretch would complicate the derivation of the equation for maximum impact force from Hooke's Law.

Edit: Glancing at that paper, the author's expression for the maximum impact force, based on the total distance fallen (including maximum rope stretch) is actually simpler than the one based on the "free fall" distance.

Jay

So Jay, you are saying if this climber who was linked with a biner that was rated to lets say 5 KN and then his belayer was also was tied in to a fix anchor with 5 KN biner, the leader's biner has a higher chances of failure than belayer biner.

Now is this because the draw(B) is taking some of the load therefore, the bottom half of rope(belayer C) does not get the forces as equal as the other half ( leader side A)?


Yes. Because if the maximum force on the climber's carabiner is "x" the maximum force on the belayer's carabiner is something like .75x - due to friction over the top carabiner.

Curt


bill413


May 14, 2009, 5:32 AM
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spikeddem wrote:
For efficiency, I won't remove the dots. However, I encourage everyone to hit "page down" or "page up" while looking at those photos. It's fun.
Now that was fun! Thanks.


bill413


May 14, 2009, 5:34 AM
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USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?


adatesman


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jrathfon


May 14, 2009, 7:43 AM
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adatesman wrote:
majid_sabet wrote:
adatesman wrote:
Majid, you are the true master. I'm sorry for spoiling it, but 5 pages and counting... damn.

I'd call you out as a troll, but you seem to have a knack for picking topics that everyone thinks are common knowledge and then all hell breaks loose when people realize that not everyone thinks as they do. I'm still not 100% sure anyone actually benefits from the resulting arguments, but they sure are entertaining. And if you look past the arguments, quite informative.

I won't go so far as to tell people to back off as was requested by another user in S&F since you seem to bring a lot of this on yourself, but I will gladly sit back and enjoy the aftermath. Laugh

-a.

Aric

This is unfair that I am always the black sheep in RC.Not my fault that a single page n00bee question turns in to full blast scientific hell but to add a little heat in to this stew, I am adding few photos.

I may have been unclear Majid... I don't think you're a troll, rather that I suspect that you know far, far more than you let on and make your posts intentionally vague and confusing to get the discussion going about the point you're trying to make. I've been following your threads for years now and I'm convinced of this.

You take far more heat here on RC than you deserve and I'm hoping that everyone else finally figures out what's going on and backs off. (HINT HINT)

-a.

nevaarrrrrrrrrrr!!

and i think i believe the exact opposite. he repeats almost verbatim what he picks up from other users, except usually misses one keep point to make any of what he says a fallacy. couple on top of that, no understanding of simple physics or engineering and you have disastrously poor imformation being spewed.

i think it was last year that i snapped in a thread, and since then will never read his posts with anything but disdain. (maybe a little harsh) but i sure as hell won't be open-minded (making me immature).


jt512


May 14, 2009, 9:00 AM
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bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay


chalked4dyno


May 14, 2009, 9:58 AM
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A couple of years ago, I designed a loadcell for taking such measurements. I made a ring-type loadcell by bonding strain guages to a stainless rapel ring. The ring had dogbone slings sewn onto it (thanks to SterlingJim!) and I had a little battery powered amplifier attached to it. The not-so-convenient part is getting the 0-5v signal back to a DAQ. But it worked well! Got me to the national finals for an IEEE design competition... For liability reasons, the university made me aggree to not do any field testing during the course of the project. Since then I've been too busy to pull it out and do some real testing... Perhaps it's time to dust it off.


bill413


May 14, 2009, 2:33 PM
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jt512 wrote:
bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay
So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.


hafilax


May 14, 2009, 3:42 PM
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Even with finite measuring rate I'm sure it must be possible to extrapolate a peak value from a digital log. The curves approaching from + and - are usually pretty smooth aren't they?


jt512


May 14, 2009, 5:35 PM
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bill413 wrote:
jt512 wrote:
bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay
So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.

If the peak force is instantaneous (and I think it is), then you can't capture it. But if readings are taken 1000 times per second, then you can measure the force within 1/2000 of a second of the peak force, which, hopefully, is good enough.

Jay


bill413


May 14, 2009, 5:42 PM
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jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay
So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.

If the peak force is instantaneous (and I think it is), then you can't capture it. But if readings are taken 1000 times per second, then you can measure the force within 1/2000 of a second of the peak force, which, hopefully, is good enough.

Jay
Umm, within 1/500 th of a second.


jt512


May 14, 2009, 6:05 PM
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bill413 wrote:
jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay
So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.

If the peak force is instantaneous (and I think it is), then you can't capture it. But if readings are taken 1000 times per second, then you can measure the force within 1/2000 of a second of the peak force, which, hopefully, is good enough.

Jay
Umm, within 1/500 th of a second.

No. If the time at which the maximum force occurs t is in the interval [0, .001s], then

max(min{t, .001sĖt}) = .0005s.

That's 1/2000 of a second.

Jay


(This post was edited by jt512 on May 14, 2009, 6:06 PM)


Partner angry


May 14, 2009, 7:39 PM
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jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay
So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.

If the peak force is instantaneous (and I think it is), then you can't capture it. But if readings are taken 1000 times per second, then you can measure the force within 1/2000 of a second of the peak force, which, hopefully, is good enough.

Jay
Umm, within 1/500 th of a second.

No. If the time at which the maximum force occurs t is in the interval [0, .001s], then

max(min{t, .001sĖt}) = .0005s.

That's 1/2000 of a second.

Jay

It's on like Donkey Kong!!!


bill413


May 14, 2009, 7:54 PM
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angry wrote:
jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay
So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.

If the peak force is instantaneous (and I think it is), then you can't capture it. But if readings are taken 1000 times per second, then you can measure the force within 1/2000 of a second of the peak force, which, hopefully, is good enough.

Jay
Umm, within 1/500 th of a second.

No. If the time at which the maximum force occurs t is in the interval [0, .001s], then

max(min{t, .001sĖt}) = .0005s.

That's 1/2000 of a second.

Jay

It's on like Donkey Kong!!!
Smile

Jay, I think that your expression is the time during which the transient is invisible to the sampler.

That is, if at time t0 we measure a value, and at time t1 we measure a value, anything that happens within the space t1-t0 is invisble to the sampling. All we know are the endpoints.
Bill


k.l.k


May 14, 2009, 7:57 PM
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jt512 wrote:
If the peak force is instantaneous (and I think it is), then you can't capture it.

This is pretty fun. But let's just Kevork it. Why don't you just tell the poor fucker that "peak load" is an abstraction from empirical data and be done with it? The armchair engineers would need weeks just to assimilate that claim. Hell, the ME majors at my University would need a few days and probably some minor recreational drug use.

This thread is a lovely example of everything that is stupid about this site.


majid_sabet


May 14, 2009, 8:11 PM
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In reply to:
nevaarrrrrrrrrrr!!

and i think i believe the exact opposite.
he repeats almost verbatim what he picks up from other users, except usually misses one keep point to make any of what he says a fallacy. couple on top of that, no understanding of simple physics or engineering and you have disastrously poor imformation being spewed.

i think it was last year that i snapped in a thread, and since then will never read his posts with anything but disdain. (maybe a little harsh) but i sure as hell won't be open-minded (making me immature).

Actually, I want and prefer people like you to judge exactly based on what you see of me in RC and nothing more.

keep it going


(This post was edited by majid_sabet on May 14, 2009, 8:12 PM)


jt512


May 14, 2009, 8:24 PM
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bill413 wrote:
angry wrote:
jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
jt512 wrote:
bill413 wrote:
USnavy wrote:
Well the one I have says it scans at 1000 cycles a second and the manufacturer said itís an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay
So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.

If the peak force is instantaneous (and I think it is), then you can't capture it. But if readings are taken 1000 times per second, then you can measure the force within 1/2000 of a second of the peak force, which, hopefully, is good enough.

Jay
Umm, within 1/500 th of a second.

No. If the time at which the maximum force occurs t is in the interval [0, .001s], then

max(min{t, .001sĖt}) = .0005s.

That's 1/2000 of a second.

Jay

It's on like Donkey Kong!!!
Smile

Jay, I think that your expression is the time during which the transient is invisible to the sampler.

That is, if at time t0 we measure a value, and at time t1 we measure a value, anything that happens within the space t1-t0 is invisble to the sampling. All we know are the endpoints.

That's fine. The times at which some consecutive pair of samples were taken will be the endpoints of an interval containing the maximum force. Thus, if the length of that interval is 1/1000 of a second, at least one sample will have been taken within 1/2000 of a second of the maximum force.

Jay


Rudmin


May 14, 2009, 8:31 PM
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But Bill, that would still make Jay correct. A sample is taken every 0.001 seconds. The peak force will lie somewhere between two samples taken 0.001 seconds apart. The furthest time the peak force can be from one of those two measured samples before it starts getting closer to the other one is 0.0005 seconds.


jrathfon


May 14, 2009, 8:50 PM
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k.l.k wrote:
jt512 wrote:
If the peak force is instantaneous (and I think it is), then you can't capture it.

This is pretty fun. But let's just Kevork it. Why don't you just tell the poor fucker that "peak load" is an abstraction from empirical data and be done with it? The armchair engineers would need weeks just to assimilate that claim. Hell, the ME majors at my University would need a few days and probably some minor recreational drug use.

This thread is a lovely example of everything that is stupid about this site.

word.


jt512


May 14, 2009, 8:53 PM
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k.l.k wrote:
jt512 wrote:
If the peak force is instantaneous (and I think it is), then you can't capture it.

Why don't you just tell the poor fucker that "peak load" is an abstraction from empirical data and be done with it?

Because it's not an abstraction from empirical data. Clearly, there is a peak force. It's just that if it's instantaneous, then the engineers are hopelessly consigned to underestimating it when they try to measure it.

Jay


k.l.k


May 14, 2009, 9:13 PM
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jt512 wrote:
It's not an abstraction from empirical data.

Of course it is. Although, in the context of this conversation, that may be a banal philosophical point.

If you think of "peak load" as a "concept," then it's not an abstraction from empirical data-- until you want a number. If you want "peak load" to be "instantaneous," then you're inviting the engineers to respond with hopeless attempts to measure "duration" or "event" or any number of other ultimately theological concepts.

In a purely theoretical sense any system can have a measurable "peak load." But then we are fudging in a number of ways.

This is a philosophical issue that is not really relevant to the underlying impulse of the OP, which is why it is a perfect way to Kevork this thread. Or spin it out into an endless series of exercises in amateur metaphysics, which is the same thing. But the lurkers needn't worry: if we add in some fart and sex jokes, and some bad computer graphics of high school physics, we can build the paradigmatic rc thread.


patto


May 14, 2009, 9:50 PM
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jt512 wrote:
k.l.k wrote:
jt512 wrote:
If the peak force is instantaneous (and I think it is), then you can't capture it.

Why don't you just tell the poor fucker that "peak load" is an abstraction from empirical data and be done with it?

Because it's not an abstraction from empirical data. Clearly, there is a peak force. It's just that if it's instantaneous, then the engineers are hopelessly consigned to underestimating it when they try to measure it.

Jay

Not if the engineers interpolate between the two points properly. But all that is irrelevant because if the force peaked at 2000kN for 0.0005s then you still would unlikely to be breaking something. You need a non negligable amount of time at high force to break stuff.

There isn't much macro physical phenomenon that has real sharp edge behaviour. Even 'shock loads' have a ramp up if you get the time scale small enough.

I don't see why 1000samples per second would not be enough in this case. Any significant discrepency between the analogue and digital is likely to be blamed on the equipment.

In contrast if I dropped a steel ballbearing onto a steel surface then I would probably would need much greater resolution than 1000samples a second to measure the impact.


jt512


May 14, 2009, 10:11 PM
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curt


May 14, 2009, 10:28 PM
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jt512 wrote:
patto wrote:
jt512 wrote:
k.l.k wrote:
jt512 wrote:
If the peak force is instantaneous (and I think it is), then you can't capture it.

Why don't you just tell the poor fucker that "peak load" is an abstraction from empirical data and be done with it?

Because it's not an abstraction from empirical data. Clearly, there is a peak force. It's just that if it's instantaneous, then the engineers are hopelessly consigned to underestimating it when they try to measure it.

Jay

Not if the engineers interpolate between the two points properly.

How can you interpolate between two values to obtain a value that is greater than both of them?

Probably by using polynomial interpolation--or a similar best fit to the data.

http://en.wikipedia.org/wiki/Interpolation

jt512 wrote:
In reply to:
But all that is irrelevant because if the force peaked at 2000kN for 0.0005s then you still would unlikely to be breaking something.

But the duration of the peak force is 0. Does that mean that it would be impossible to break anything (How am I doing, Kerwin?).

Jay

The duration of the peak force may be zero, but since we are modeling the climbing rope as a highly damped spring (by application of Hooke's Law) the first derivative of acceleration near the peak becomes quite small--i.e. the peak tension in the rope basically follows a sine function and does not change rapidly near the peak. For that reason, I would think (for the case of a climbing rope at least) that 1000 sampling points/second would have relatively little error in the measurement of peak force, even without interpolation.

Curt


jt512


May 14, 2009, 10:48 PM
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curt wrote:
jt512 wrote:
patto wrote:
jt512 wrote:
k.l.k wrote:
jt512 wrote:
If the peak force is instantaneous (and I think it is), then you can't capture it.

Why don't you just tell the poor fucker that "peak load" is an abstraction from empirical data and be done with it?

Because it's not an abstraction from empirical data. Clearly, there is a peak force. It's just that if it's instantaneous, then the engineers are hopelessly consigned to underestimating it when they try to measure it.

Jay

Not if the engineers interpolate between the two points properly.

How can you interpolate between two values to obtain a value that is greater than both of them?

Probably by using polynomial interpolation--or a similar best fit to the data.

Yes, you're right. I looked up the definition of "interpolate" after I posted my message, and found that it included methods that would permit estimating values outside the range defined by the endpoints. I was going to amend my post, but you replied to it while I was editing it.

Jay


Partner rgold


May 14, 2009, 10:54 PM
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Some random comments.

1. Rocknice2 refers to the fall force calculator at
http://www.myoan.net/...t/climbforcecal.html

I've posted all over the place that this calculator is completely bogus, but it is hard to get the word out. (Some later posters noticed this.) Oddly, rocknice2 exhorts us to "ignore the FF on the calculator." The calculator's inability to get the FF right is the thing that provides the clue that it is worthless. For example, try calculating the "Shock (in kilo-Newtons)" for a fall in which the distance to the last anchor is zero, namely a FF 0 fall.

2. Fishclimb wrote, "The key factor in calculating the Falling Force is the time it takes to decelerate. F=ma. Shorter deceleration times increase the force in a fall." It isn't clear what "falling force" means, but the question is, in general, about the peak load to the anchor. If shorter deceleration times were the determining factor, then tiny falls (think one inch, say) would result in the highest peak loads.

3. Majid writes that there is no such thing as a fall factor 2 in climbing. This is incorrect; any time a leader falls onto the belay without intermediate gear it is FF 2.

4. In support of this, Majid cites the article by Dan Curtis in the College Mathematics Journal. http://www.cwu.edu/...rints/cmj135-140.pdf This article is a stunning example of perfectly good mathematics that is utterly rotten engineering. Curtis, for some strange reason, uses a non-standard definition of fall factor, in which the rope stretch is included in the distance fallen. He then shows (assuming the spring model), that the maximum force depends only on this fall factor.

Mathematically speaking, Curtis' approach and the standard approach are equivalent; the equations for one can be transformed to those for the other. But Curtis' equations are useless for engineering, because you have to know the rope stretch to use them. The absurdity of this approach becomes clear when you realize that knowing the rope stretch is equivalent to knowing the maximum tension in the rope for the spring model, meaning that in order to use Curtis's equations, you already have to be in posession of the answer you are interested in.

I might add that Curtis fails any reasonable test of scholarship, since his analysis has been done over and over again, and correctly, and he fails to reference any of the available accounts that predate his. (As far as I know, the original calculations were done by Arnold Wexler and Dick Leonard and were published in the Sierra Club Journal in 1947.)

5. Colatownkid speaks repeatedly of the fall factor as an approximation. I think this way of speaking confounds two different things. On the one hand is a mathematical model, based on viewing the rope, at least during extension, as an ideal spring. In this mathematical model, the fall factor determines the peak tension in the rope and so the peak load to the top piece. No approximations are involved. The model is, however, just that---a model, meaning that it includes some but not all of the features of reality. The results of the model are thus approximations to the real situation.

6. The ideal spring model is the simplest model and actually seems to be fairly good at predicting loads. But it is certainly possible to create more complicated models that include features of reality that aren't part of the spring model's assumptions. Most of the more complicated models include viscous damping in either simple or complicated ways. One of the problems with these models is that there does not seem to be an accompanying explanation of why a rope would be subject to viscous damping. The damped models can be fitted to experimental data, and one can hope that they provide predictive value for situations analogous to the ones in which the data was collected, but one also has to wonder whether such models can predict rope behavior when the situation is not analogous to the one used for the trials. (A good example: by how much will a screamer reduce peak load?)

7. Halifax keeps saying that the fall factor calculation is a poor model. I guess this would need some kind of quantification, and then an agreement about what kinds of answers one wants from a model. If the spring model regularly overstates the peak load in a consistent way that is not "too far off," (definition required), then it has some value in providing a useful upper bound.

8. Attaway, in the paper mentioned by ptlong, has an interesting take on the modeling process. He speaks of "system stiffness," and some of his experimental data show that fairly complicated systems with friction and damping exhibit "system stiffness," meaning that the whole kit and kaboodle together behaves (during dynamic extension) remarkably like an ideal spring. The problem, of course, is determining a priori what the spring constant for the system is.

9. I had the impression from Attaway that the system behavior for dynamic ropes was far more spring-like (which is to say that Hooke's law applies) for dynamic loading as opposed to slow loading. If this is true, it would suggest that models employing viscous damping are really not right, since by definition the effects of viscous damping are more pronounced at higher velocities.

10. As for measuring peak load, since the rate of change of tension with respect to time is near zero as the rope tension approaches its maximum value, the tension isn't going to change all that much in one of those tiny intervals near or containing the maximum value.


k.l.k


May 14, 2009, 10:58 PM
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Re: [rgold] Common KNs in real world falls [In reply to]
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rgold wrote:
Some random comments.

1. Rocknice2 refers to the fall force calculator at
http://www.myoan.net/...t/climbforcecal.html

I've posted all over the place that this calculator is completely bogus, but it is hard to get the word out. (Some later posters noticed this.) Oddly, rocknice2 exhorts us to "ignore the FF on the calculator." The calculator's inability to get the FF right is the thing that provides the clue that it is worthless. For example, try calculating the "Shock (in kilo-Newtons)" for a fall in which the distance to the last anchor is zero, namely a FF 0 fall.

2. Fishclimb wrote, "The key factor in calculating the Falling Force is the time it takes to decelerate. F=ma. Shorter deceleration times increase the force in a fall." It isn't clear what "falling force" means, but the question is, in general, about the peak load to the anchor. If shorter deceleration times were the determining factor, then tiny falls (think one inch, say) would result in the highest peak loads.

3. Majid writes that there is no such thing as a fall factor 2 in climbing. This is incorrect; any time a leader falls onto the belay without intermediate gear it is FF 2.

4. In support of this, Majid cites the article by Dan Curtis in the College Mathematics Journal. http://www.cwu.edu/...rints/cmj135-140.pdf This article is a stunning example of perfectly good mathematics that is utterly rotten engineering. Curtis, for some strange reason, uses a non-standard definition of fall factor, in which the rope stretch is included in the distance fallen. He then shows (assuming the spring model), that the maximum force depends only on this fall factor.

Mathematically speaking, Curtis' approach and the standard approach are equivalent; the equations for one can be transformed to those for the other. But Curtis' equations are useless for engineering, because you have to know the rope stretch to use them. The absurdity of this approach becomes clear when you realize that knowing the rope stretch is equivalent to knowing the maximum tension in the rope for the spring model, meaning that in order to use Curtis's equations, you already have to be in posession of the answer you are interested in.

I might add that Curtis fails any reasonable test of scholarship, since his analysis has been done over and over again, and correctly, and he fails to reference any of the available accounts that predate his. (As far as I know, the original calculations were done by Arnold Wexler and Dick Leonard and were published in the Sierra Club Journal in 1947.)

5. Colatownkid speaks repeatedly of the fall factor as an approximation. I think this way of speaking confounds two different things. On the one hand is a mathematical model, based on viewing the rope, at least during extension, as an ideal spring. In this mathematical model, the fall factor determines the peak tension in the rope and so the peak load to the top piece. No approximations are involved. The model is, however, just that---a model, meaning that it includes some but not all of the features of reality. The results of the model are thus approximations to the real situation.

6. The ideal spring model is the simplest model and actually seems to be fairly good at predicting loads. But it is certainly possible to create more complicated models that include features of reality that aren't part of the spring model's assumptions. Most of the more complicated models include viscous damping in either simple or complicated ways. One of the problems with these models is that there does not seem to be an accompanying explanation of why a rope would be subject to viscous damping. The damped models can be fitted to experimental data, and one can hope that they provide predictive value for situations analogous to the ones in which the data was collected, but one also has to wonder whether such models can predict rope behavior when the situation is not analogous to the one used for the trials. (A good example: by how much will a screamer reduce peak load?)

7. Halifax keeps saying that the fall factor calculation is a poor model. I guess this would need some kind of quantification, and then an agreement about what kinds of answers one wants from a model. If the spring model regularly overstates the peak load in a consistent way that is not "too far off," (definition required), then it has some value in providing a useful upper bound.

8. Attaway, in the paper mentioned by ptlong, has an interesting take on the modeling process. He speaks of "system stiffness," and some of his experimental data show that fairly complicated systems with friction and damping exhibit "system stiffness," meaning that the whole kit and kaboodle together behaves (during dynamic extension) remarkably like an ideal spring. The problem, of course, is determining a priori what the spring constant for the system is.

9. I had the impression from Attaway that the system behavior for dynamic ropes was far more spring-like (which is to say that Hooke's law applies) for dynamic loading as opposed to slow loading. If this is true, it would suggest that models employing viscous damping are really not right, since by definition the effects of viscous damping are more pronounced at higher velocities.

10. As for measuring peak load, since the rate of change of tension with respect to time is near zero as the rope tension approaches its maximum value, the tension isn't going to change all that much in one of those tiny intervals near or containing the maximum value.

Dude, it's almost 11 on the West Coast. That's like, what, next week, East Coast Time?

Kudos for the epic post. That was some serious early morning labor. Grading finals?


k.l.k


May 14, 2009, 11:01 PM
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Re: [jt512] Common KNs in real world falls [In reply to]
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jt512 wrote:
[Yes, you're right. . . . I was going to amend my post, but you replied to it while I was editing it.

Jay

Whoa, stop the presses!

God on ya, JT!

Good work here tonight, folks. We'll see you next week. Stop off at the receptionist on your way out, and schedule your next appointment.


jt512


May 14, 2009, 11:01 PM
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Re: [rgold] Common KNs in real world falls [In reply to]
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rgold wrote:
10. As for measuring peak load, since the rate of change of tension with respect to time is near zero as the rope tension approaches its maximum value, the tension isn't going to change all that much in one of those tiny intervals near or containing the maximum value.

Stop being practical. You're a mathematician. The expected value of the maximum of a series of measurements of impact force is less than the true maximum impact force, no matter how trivial the difference, dammit.

Jay


curt


May 14, 2009, 11:02 PM
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Rich is well known to be a night-owl. I suspect rc.com is his usual treatment for insomnia.

Curt


jt512


May 14, 2009, 11:14 PM
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curt wrote:
Rich is well known to be a night-owl. I suspect rc.com is his usual treatment for insomnia.

Curt

Curt, when we make consecutive posts to a thread, the juxtaposition of our profile pics seems kinda' gay. Would you mind changing your profile pic? It's not like that problem has any historical significance, or anything.

Jay