### Author Topic: Climbing Physics Puzzler  (Read 9042 times)

#### DLottmann

• Guest
##### Climbing Physics Puzzler
« on: November 05, 2013, 07:37:44 PM »
This one is right up your alley Champ!

You have a 3 piece anchor in a bomber vertical crack with the classic “pre-equalized” 7mm 6m cordelette (looped with a double fisherman though that is not too relevant).

Your lowest piece is a solid #1 BD Cam. 6 inches above that you have a .75 BD Cam, and your top piece is a bomber looking #7 nut.

You tied off the cordelette to form a master point with a figure eight on a bight. The “leg” to the #1 is 6 inches long, the “leg" to the .75 is 12 inches long, and the “leg" to the nut is 18 inches long. The angles between the arms are very minimal, less than 10 degrees from the outer arms.

The leader clips the master point before leaving the station, climbs up 5 feet, and falls. Let’s assume the fall is clean, the belay sucessfully arrests (though it is violent), and all the gear holds.

Which piece of protection withstood the most force, or did they all receive 1/3ish.

#### Pete Jackson

• NEClimbs Senior Member
• Posts: 259
• RCA guy. Want to help? PM me.
##### Re: Climbing Physics Puzzler
« Reply #1 on: November 05, 2013, 08:06:38 PM »
This one is right up your alley Champ!

You have a 3 piece anchor in a bomber vertical crack with the classic “pre-equalized” 7mm 6m cordelette (looped with a double fisherman though that is not too relevant).

Your lowest piece is a solid #1 BD Cam. 6 inches above that you have a .75 BD Cam, and your top piece is a bomber looking #7 nut.

You tied off the cordelette to form a master point with a figure eight on a bight. The “leg” to the #1 is 6 inches long, the “leg" to the .75 is 12 inches long, and the “leg" to the nut is 18 inches long. The angles between the arms are very minimal, less than 10 degrees from the outer arms.

The leader clips the master point before leaving the station, climbs up 5 feet, and falls. Let’s assume the fall is clean, the belay sucessfully arrests (though it is violent), and all the gear holds.

Which piece of protection withstood the most force, or did they all receive 1/3ish.

The #1 cam takes 55% of the impact force, the ..75 takes 27%, and the nut takes 18% of the force.

And I cannot wait to hear the arguments over this one.
We came to climb, not to whine.

#### hobbsj

• NEClimbs Full Member
• Posts: 147
##### Re: Climbing Physics Puzzler
« Reply #2 on: November 05, 2013, 08:23:16 PM »
This one is right up your alley Champ!

You have a 3 piece anchor in a bomber vertical crack with the classic “pre-equalized” 7mm 6m cordelette (looped with a double fisherman though that is not too relevant).

Your lowest piece is a solid #1 BD Cam. 6 inches above that you have a .75 BD Cam, and your top piece is a bomber looking #7 nut.

You tied off the cordelette to form a master point with a figure eight on a bight. The “leg” to the #1 is 6 inches long, the “leg" to the .75 is 12 inches long, and the “leg" to the nut is 18 inches long. The angles between the arms are very minimal, less than 10 degrees from the outer arms.

The leader clips the master point before leaving the station, climbs up 5 feet, and falls. Let’s assume the fall is clean, the belay sucessfully arrests (though it is violent), and all the gear holds.

Which piece of protection withstood the most force, or did they all receive 1/3ish.

The #1 cam takes 55% of the impact force, the ..75 takes 27%, and the nut takes 18% of the force.

And I cannot wait to hear the arguments over this one.

Care to explain?  Is it the the length of each leg?  Not seeing how you came up with those percentages.....May be the beer making my math skills fuzzy along with my vision.

#### danf

• NEClimbs Senior Member
• Posts: 364
##### Re: Climbing Physics Puzzler
« Reply #3 on: November 05, 2013, 08:48:27 PM »
The #1 cam takes 55% of the impact force, the ..75 takes 27%, and the nut takes 18% of the force.

And I cannot wait to hear the arguments over this one.
I'm not sure how to compute that, but based on my understanding, that sounds right.  It's all pretty well explained in the second edition of John Long's anchor book.  Which is part of the reason why I keep a cordellette tied and ready for a sliding X anchor system, rather than the typical one described above.  One of these days, hopefully, my wife will be ready to swap leads with me and I can (to quote Strand) "just use the F'n rope".

#### DLottmann

• Guest
##### Re: Climbing Physics Puzzler
« Reply #4 on: November 05, 2013, 08:49:40 PM »
Pete got the gist of it. Let's let lucky like explain the why.

#### strandman

• NEClimbs God
• Posts: 5829
##### Re: Climbing Physics Puzzler
« Reply #5 on: November 05, 2013, 09:22:22 PM »
The belayer gets 99% of the force because the idiot leader didn't have a piece clipped..the cordalette fails and all the gear remains as booty

#### lucky luke

• NEClimbs God
• Posts: 1762
##### Re: Climbing Physics Puzzler
« Reply #6 on: November 05, 2013, 11:04:04 PM »
The leader clips the master point before leaving the station, climbs up 5 feet, and falls. Let’s assume the fall is clean, the belay sucessfully arrests (though it is violent), and all the gear holds.

It is a fall factor 2 directly on the anchor. What I want to protect as much as I can...it is my anchor. No anchor and I am death in that situation.
The question is how I can protect my anchor? The question of the force on the pro is not important because one way to rig the anchor is to do a clove hitch on the first cam, an other on the second and an other on the third. In that way, if the first didn't hold the fall, it will take a percentage of energy, if the second don't hold, it will take an other percent of energy and the third have some chance to hold (present in john long with piton).

How I can I protect my anchor is more than an interesting question. Some study show that when load, the harnest took a part of the energy.  The energy took by the harnest and rope running true the device can be as hight as 20 %. So, if you belay directly on your harnest, instead of risking your life by using the anchor as a first pro, you have 20% more chance that it will hold.

personally, I use a sliding x on the anchor and I back up the sling with my rope on a protection. If I don't think that one of my pro will hold more than 12KN, I will double it with an other. For example, if my second and third pro was no as safe as I want, I will use a sling between them to a master point and an other sling joining the master point to the other pro. I will use a back up differently.

As usual, what is important is that the anchor hold the fall. If one pro hold 100 % and the other 0 is not more important than if each pro old 33% of the fall. It is superficial rules and that kind of challenge doesn't help to safe life of people. I think that the new generation of climber have a lack of knowledge on safety.(not apply to every climber, some are very safe and have bad advice...)

#### DGoguen

• NEClimbs Senior Member
• Posts: 347
##### Re: Climbing Physics Puzzler
« Reply #7 on: November 06, 2013, 07:43:10 AM »
This one is right up your alley Champ!
Let's let lucky like explain the why.

Dave, you're starting threads looking for arguments at this point.
Around here they come by themselves willingly, don't rush it.
Don't Climb

#### DLottmann

• Guest
##### Re: Climbing Physics Puzzler
« Reply #8 on: November 06, 2013, 10:04:35 AM »
I really wasn't trying to start any arguments... but was honestly curious if LL would answer the question simply or go off on a tangent. I won't declare what happened but for anyone (Hobbsj) who was interested in the answer...

Danf and Pete referred to it... the issue raised in Long's book is that cordelette material is somewhat dynamic. It stretches under load. Therefore it's reasonable to argue that any 3 point anchor tied off this way, the SHORTEST leg will see the most force when the master point is loaded. JL uses this as an argument for abandoning the ever popular cordelette method and adopting "Equallette's and Quads"... or as some would say, to have a reason to write a new book...

I do not subscribe to this rejection of the method, since most of the time if I use a cordelette I just try to not have one leg that is incredibly short, but if I do I make sure that that piece of gear is bomber, and as LL mentions, worry more about protecting the belay by getting a solid first piece soon after leaving the anchor.

There's a dozen different ways to build an anchor and 11 of them are totally fine, provided the individual placements are solid.

Personally my cord stays on the back of my harness 99% off the time... there are quicker ways of building solid anchors than using a 20 foot loop of cord IMO.

#### lucky luke

• NEClimbs God
• Posts: 1762
##### Re: Climbing Physics Puzzler
« Reply #9 on: November 06, 2013, 10:12:09 AM »
As usual, what is important is that the anchor hold the fall. If one pro hold 100 % and the other 0 is not more important than if each pro old 33% of the fall.

#### DLottmann

• Guest
##### Re: Climbing Physics Puzzler
« Reply #10 on: November 06, 2013, 10:21:01 AM »
As usual, what is important is that the anchor hold the fall. If one pro hold 100 % and the other 0 is not more important than if each pro old 33% of the fall.

I love how you quote yourself.

And agreed.

#### pappy

• NEClimbs Senior Member
• Posts: 392
##### Re: Climbing Physics Puzzler
« Reply #11 on: November 06, 2013, 10:25:51 AM »
The belayer gets 99% of the force because the idiot leader didn't have a piece clipped..the cordalette fails and all the gear remains as booty

As usual, Strand is the only one that got it right.

I had a cordalette once, one of my buddies gave it to me as a birthday present. First time out I lost it. It wasn't intentional, really, just Freud in action, but climbers should not carry extraneous pieces of gear.
If you're gonna be stupid, you gotta be tough.

#### JBro

• NEClimbs God
• Posts: 1354
• Doing God's work
##### Re: Climbing Physics Puzzler
« Reply #12 on: November 06, 2013, 10:37:07 AM »
I really wasn't trying to start any arguments...

Come on man you live for this shiiite!

Have a quiche, now, or maybe a tort.  You deserve it!
-bristolpipe

I like to keep things simple, even if it's faaaken painful and miserable.
-Stoney Middleton

This is grain, which any fool can eat, but for which the Lord intended a more divine means of consumption.
-Friar Tuck

#### steve weitzler

• NEClimbs God
• Posts: 525
##### Re: Climbing Physics Puzzler
« Reply #13 on: November 06, 2013, 01:03:28 PM »
Strand falls and I rescue his wife.

#### sneoh

• NEClimbs God
• Posts: 2112
##### Re: Climbing Physics Puzzler
« Reply #14 on: November 06, 2013, 02:26:33 PM »
Watch out, Strand.  And lock yourselves in.

"You have to decide to do a flag, where you can broke your vertebrae or a barn door depending of your pro" - the poster formerly known as Champ