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danielb
Dec 5, 2002, 3:01 PM
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I've been playing around with Petzl's Fall Simulator am thinking of writing my own simulator for a laugh.
I am wondering if anyone here knows of any good sites or books on the physics involved when climbers fall? Ie calculating the loads on the pro, rope, climbers, harness's etc...
DanielB
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boardcrazzy
Dec 5, 2002, 3:14 PM
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Any first year university physics text should give you some answers. You should be able to do it by calculating a speed for the height fallen from. Then by using the stretch in the rope, you should be able to calculate a deceleration distance, which should also get you a deceleration rate. Then it is just mass times acceleration to give you a force, which is also the tension in the rope. This force is what is on your harness. Twice the force is what is on your last piece of pro (cause the rope is doubled over).
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ksfrogman
Dec 5, 2002, 3:14 PM
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You might want to dig out your old physics books, and Newton's three laws of motion.
FYI,
Force = mass x acceleration.
y = -gt^2/2 + (Vo)(t) + Ho
where g = gravity or -32 ft/sec
Vo = initial velocity
Ho = initial height
You can play around with this formula where y is the distance travelled to calculate all sorts of things. You can use vector physics to predict forces on objects as well. Just don't remind me I was once a high school nerd incognito.
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petsfed
Dec 5, 2002, 3:46 PM
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And a rope acts like a very stiff spring so with Hooke's law
f(x)=kx
you can calculate the stretch as it absorbs force and in turn figure out (as mentioned above) the deceleration distance. And from that you can figure out the total force on the climber, the belayer and the top most anchor, assuming all of your pro is in a straight line. If not you need to factor in the friction provided by each carabiner, and the total energy dispersed through the system.
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one900johnnyk
Dec 5, 2002, 4:17 PM
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it's not all that simple though. when you fall and your rope goes straight up through the biner and down to the belayer friction will make the climber's length have a greater percent stretch than the length leading to the belayer. also you ahve to keep in mind that the uiaa % stretch is for a fixed weight (i think 176 pounds..) but i guess you can get an approximation by ignoring some of these finer points... let me know if you actually do it
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one900johnnyk
Dec 5, 2002, 4:19 PM
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also, boardcrazzy is wrong
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mountainmonkey
Dec 5, 2002, 5:13 PM
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petzl has all their equations at the bottom of the fall simulator page
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burz
Dec 5, 2002, 6:24 PM
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It is not just about force, it is about energy discipation. Kinetic energy = 1/2mv^2 this where the velocity of the falling climber (and his mass)gets calculated in.
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alexinmilton
Dec 5, 2002, 6:43 PM
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That simulater is great. Why would you want to create another one when someone already made a simulator as complete as that one? As someone else stated it gives you all of the reasoning and relations that were used.
Now, i bet everyone else did exactly what i did: A 30m fall onto a single nut with static line. Ow!
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petsfed
Dec 5, 2002, 7:10 PM
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The simulator also lacks some things, and since it is on the internet, it may not be accessible all the time. The simulator only provides for certain generic ropes, and we all know that a Mammut 10.2 rope has different characteristics from a Maxim 10.2 rope. It limits itself to the average micronuts. It assumes the strength of an ice screw. It assumes all bolts are bomb proof. It doesn't deal with the difference of putting a peice of pro 2 feet off a plumb line to the top anchor, versus 8 feet off a plumb line. Its a very general purpose fall simulator.
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quickclips
Dec 5, 2002, 7:23 PM
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one900johnnyk, has the right idea, but... the biners act as pulleys and therefore, the tension throughout the rope is the same at any moment. So the entire rope goes through the same elongation. Check into you're dymanics books for more info. If you have any questions you can PM me, and hopefully I can help you out.
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boardcrazzy
Dec 5, 2002, 10:12 PM
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one900johnnyk, I'm actually a Mechanical Engineer, so to just say I'm wrong really doesn't say much. My grasp of physics goes quite a bit beyond the high school level. You may want to get into a little more detail before you randomly spray.
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flying_dutchman
Dec 5, 2002, 10:23 PM
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biners will not act like pulleys and decrease any force unless there are more then one. when u fall, the top piece of pro and the biner attached absorb the shock; provided they dont fail. A single pulley system simple changes the direction of force.
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ksfrogman
Dec 6, 2002, 3:18 PM
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Are we talking about a European or an African swallow?
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missedyno
Dec 6, 2002, 3:23 PM
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LOL ... what... is your favourite colour??
just have to say that everytime i see this thread on the front page, i get "the politics of dancing" in my head, only of course it's the "physics of falling..."
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quickclips
Dec 10, 2002, 2:10 AM
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I wasn't saying that the biners would lessen the fall. I know the top one takes the load, I'm just saying the tension is the same throughout the rope. Therefore the strech happens pretty much evenly from the atc to climber.
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curt
Dec 10, 2002, 3:08 AM
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flying_dutchman,
The top biner(s) do indeed lessen the force of the fall in an amount equal to the friction generated by the rope passing over the biner. If there was a true frictionless "pulley" as your highest (fallen on) piece rather than a regular biner, you would be correct.
Curt
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ronamick
Dec 20, 2002, 12:43 AM
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Contact the engineering dept. at Black Diamond. They already have all of the figured out.
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metoliusmunchkin
Dec 20, 2002, 3:06 AM
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This is great! One of the dudes I climb with is in fourth year physics here at Laurentian University. His name is Felix and he's a climber originally from Berlin - I'm sure he'll have a good laugh with this one!
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