Physics Problem?

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Mecnic
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Physics Problem?

Post by Mecnic » Tue Aug 16, 2011 1:10 pm

I am under the impression that most impact forces, anchors etc are rated on 80kg (Represents average climber with gear, we all know this is not a good representation)

My question is if the climber weighs more than 80 kg is the energy he generates during his fall greater and therefore a greater impact force is created by the fall? Reversely if the climber is lighter is the force created then less?

If anchors are tested with 80kg should there be a weight limit placed on indoor walls, where the anchors have been tested with an 80kg dead drop?

I am no physicist so anyone out there who can help work out this issue or am I completely off the plot and all impact force are the same?

Will be nice to hear the views.
It was a good idea at the time

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Nic Le Maitre
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Re: Physics Problem?

Post by Nic Le Maitre » Tue Aug 16, 2011 5:01 pm

Hi
Mecnic wrote:I am under the impression that most impact forces, anchors etc are rated on 80kg (Represents average climber with gear, we all know this is not a good representation)
Anchors are not rated with 80kg loads. Ropes are tested with 80kg loads. Anchors are fastened to some immovable object and then pulled until they fail while the force is measured using a load cell. Anchors will exceed their maximum rated strength by various degrees.
Mecnic wrote:My question is if the climber weighs more than 80 kg is the energy he generates during his fall greater and therefore a greater impact force is created by the fall? Reversely if the climber is lighter is the force created then less?
Yes, the force generated is directly proportional to the climbers mass (weight), heavier climber = more impact force. The converse is true as well. Force = mass * acceleration

If you are interested read this post, it explains it all the forces and and how they work (and how to calculate them): http://www.climb.co.za/forum/viewtopic.php?f=12&t=5189

Basically do not worry about it. Anchors and the gear we use is incredibly strong. If you are heavy enough and falling fast enough to generate even half as much force as is needed to break an anchor, then you have far greater problems, like the fact that your harness will cut through your body and your kidneys will come out your nose.
Happy climbing
Nic

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Justin
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Re: Physics Problem?

Post by Justin » Tue Aug 16, 2011 5:05 pm

Nic Le Maitre wrote:... like the fact that your harness will cut through your body and your kidneys will come out your nose.
:safe:
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Mecnic
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Re: Physics Problem?

Post by Mecnic » Tue Aug 16, 2011 6:17 pm

Nic Le Maitre wrote:Basically do not worry about it. Anchors and the gear we use is incredibly strong. If you are heavy enough and falling fast enough to generate even half as much force as is needed to break an anchor, then you have far greater problems, like the fact that your harness will cut through your body and your kidneys will come out your nose.
Now that is the best reply I have read in ages. :thumleft: :lol:

Thanks for the reply
It was a good idea at the time

Chris F
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Re: Physics Problem?

Post by Chris F » Wed Aug 17, 2011 9:41 am

Nic Le Maitre wrote:your kidneys will come out your nose.
:lol: Or shit will come out of your mouth. I've met a few people with this problem.

WarthogARJ
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Re: Physics Problem?

Post by WarthogARJ » Sun Mar 11, 2012 11:06 pm

The 80kg test load is a solid mass.
And that's correct that it's used to test/rate ropes in the UIAA ad CEN standards.
It doesn't mean however that the rope is only rated for that mass, you need to specify a certain mass tho.

However a solid mass behaves much differently from a human, especially one wearing a harness with a knot.
The body is not rigid and will deform: absorbing energy.
The harness will also.
As will the knot.

So roughly speaking, an 80kg solid mass is about like a 100kg human, in terms of the g's that your body sees.

Alan Jarvis

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Re: Physics Problem?

Post by mokganjetsi » Mon Mar 12, 2012 7:59 am

slightly different issue but worth knowing: when i bought my first rope it was rated for 14 falls. i was dead scared to take a fall because i thought i would have to chuck my rope after about 10 falls. not so :) the test for single ropes is:
a direct, dead drop (i.e. no points of friction & no dynamic elements except the rope itself)
of an 80 kg weight
at a factor of near 2
onto a rope on exactly the same spot.

this scenario is near impossible in real life since:
there will almost always be friction points (quickdraws; knot; rock features)
and additional dynamic elements (belayer moving; harness & knot)
rarely, if ever, will you take a fall of factor 2
and on the off chance will you fall on a rope at exactly the same spot for a great number of times.

hence the rope breakage testing allows for a scenarios that will just not happen in real life. no dynamic rope breakages has ever occured except for ropes that cut over sharp edges or being exposed to harmful substances. ropes are retired because they lose their dynamic properties; or become too stretchy; or the sheath is worn through; or (most of the time), the climber wants a nice, shiny new rope :thumleft:

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lelikegogga
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Re: Physics Problem?

Post by lelikegogga » Mon Mar 12, 2012 9:11 am

funny-puns-fight-him-back-with-an-equal-reaction.jpg
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Warren G
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Re: Physics Problem?

Post by Warren G » Mon Mar 12, 2012 11:40 am

if you ever get bored and want to do some research take look at the stats on hangers, and their "24kn" breaking force.

but yes, i agree that gear got safe about 20 years ago, and the only time gear fails is through incorrect use- i have broken 3 Karabiner this summer using them on my slackline. On the topic of slacklines, use steel karabiners! specially for linelockers, or better still use rings
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jellybelly
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Re: Physics Problem?

Post by jellybelly » Mon Mar 12, 2012 9:45 pm

what do you use between your harness and the carabiner clipped to the slackline? a sling?

mark

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Nic Le Maitre
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Re: Physics Problem?

Post by Nic Le Maitre » Tue Mar 13, 2012 8:49 am

Even if they do, it won't be a problem in terms of the force experienced by your body because the slackline is very absorbent. It might make it difficult to de-rig your anchor especially if you used nuts.
Happy climbing
Nic

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Not
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Re: Physics Problem?

Post by Not » Tue Mar 13, 2012 9:44 am

Jelly:

I think Warren is referring to carabiners used in the rigging of the actual line - as anchor points and locking parts in a self ratchetting system. Using 'biners like this puts them into bending across the spine - the position they are weakest in. (Interestingly the gate on a 'biner carries almost no force in normal use - its there to stop the biner bending open which would cause bending on the spine which would then lead to failure at that point).

Everything I've read on highlining suggests that your tether SHOULD be dynamic - this making one out of an off-cut of a lead rope sounds good to me.
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Warren G
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Re: Physics Problem?

Post by Warren G » Tue Mar 13, 2012 10:48 am

@Not- exactly

So long as you use gear as it is indended there should be no problems. Linelockers are to be treated with respect, and after breaking biners like that I will never use alloy biners in that configuration again, they just break too easily.

Regarding the forces on the slackline: The leash should be dynamic, but that will only make the slightest difference to the over all forces, as most of it is obsorbed in the slackline stretching. The bigger risk (other than that line locker at each end of the line) is the attachement for the leash to the line: Until about a year ago there were no fatalities in slacklining, then an inexperienced German crowd rigged a line between two buildings and clipped into the line with an autolocking biner. When the slackliner fell the gate was on the line, rolled forward-unlocking the gate- then rolled to one side as the weight was placed on the biner. This caused the line to slip thru the gate, and the slackliner fell to his death. a safer way of connecting the leash to the line is to use either a steel ring, or a figure 8. The 8 can take 30kn in this application, and I doubt a highline fall would but even 2kn on it.

To fill in those who don't know why anyone would use a linelocker: there is no twists in a line locker, meaning a uniform force across the "knot", vastly increasing the strength of the "knot", compared to say a figure 8 knot, or bowline. It is the best "knot", but requires care
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pierre.joubert
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Re: Physics Problem?

Post by pierre.joubert » Tue Mar 13, 2012 11:13 am

and it also presents the line perfectly horizontally

Warren G
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Re: Physics Problem?

Post by Warren G » Tue Mar 13, 2012 11:24 am

@Pierre: but that is a bonus (not the real purpose) which is affected more by the anchor construction.

Again, if you ever get bored go run some pull tests on different knots on webbing and rope. cheap and very scary.
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Nic Le Maitre
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Re: Physics Problem?

Post by Nic Le Maitre » Tue Mar 13, 2012 12:29 pm



How to set up a linelocker
Happy climbing
Nic

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