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General Climbing Discussion

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Half Ropes 17-Jun-2006 At 11:54:07 AM Nick Kaz

Message

On 16/06/2006 JamesMc wrote:
>Actually Nick, I reckon there's heaps of friction between a krab and a
>rope if there is a lot of contact pressure. Take your abseil example.
> All the energy from the abseiler's loss of height goes into heat. Some
>in the abseil device, some into the rope, and a bit into the air. I don't
>know the proportions.

Think of how hot your hand gets compaired to the belay device. The crab is a better radiator of heat, thats why heatsinks are made of aluminium rather than hands and ropes... well that and other reasons... Just like your hand there is massive friction between the two ropes which can't be quickly radiated quickly so it melts the rope.

>Also imagine belaying a lead fall where the rope goes through a pulley
>with zero friction. The belayer would feel a harder pull than if the rope
>just went through a krab.

This is true because no energy is lost to rope drag. the reason a belayer fells a small force is due to rope drag and elongation.

> The difference is due to the friction in the krab. The harder pull would mean less heat going into the rope at the pulley, and more at the belay device.

yes.

>However the rope is rigged, the energy loss from a falling climber loosing
>altitude turns into heat. The way to minimise the heat in the rope would
>be to increase the size of the karabiners and belay device, in order to
>get a greater heat sink effect. Using 2 krabs would help make a better
>heat sink. Ten krabs would be better still. I couldn't be bothered with
>the weight as I think the heat issue is too small to matter.

There is no heat issue between the crab and the rope, it is between the two ropes.

>James Mc
>
>(PS I don't know the answer, I just a skeptic thinking out loud)

PS my brain is fried, exams are driving me nuts and I havent looked at this stuff in about 3.5 years.

If your realy intrested in finding out everything you ever wanted to know about it get a hold of a first year physics book. I recomend "physics for scientists and engineers" by D. C. Giancoli. Its one of the best phyiscs texts I own, I got it for first year and I still use it alot in third.