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guanoboy
Apr 28, 2006, 8:09 PM
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let me start by saying that i don't really slackline, but I'd like to hear from the physicists out there about the forces generated on anchors and the slack line. After all the discussion about anchors on rc.com it reminded me about keeping the angles between the power point and anchor points much less than 60 degrees. It seems slacklining would generate some terrific forces on the anchor and the slack line. How does the line absorb the force of a fall?
thanks
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guanoboy
Apr 29, 2006, 12:30 AM
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ok this guy figured it all out...
http://www.wanderingphotographer.com/other_int/slack_pages/slackline_analysis/static_analysis_2.htm
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coldclimb
Apr 29, 2006, 1:13 AM
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Yeah that's a good link, but that assumes a static line, which most lines, or rather specifically what we climbers refer to as "slacklines" are not. The nylon we use is dynamic, which makes the forces more difficult to calculate, and I'm not sure if I've heard of anyone figuring out an accurate formula. That site will give you an idea though.
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patto
Apr 29, 2006, 10:10 AM
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In reply to: Yeah that's a good link, but that assumes a static line, which most lines, or rather specifically what we climbers refer to as "slacklines" are not. The nylon we use is dynamic, which makes the forces more difficult to calculate, and I'm not sure if I've heard of anyone figuring out an accurate formula. That site will give you an idea though.
Actually treating the line as static is NOT a problem. As is said on the linked website. :
"The line is static. This assumption actually does not affect the final force on the anchors when the person is standing still, because in this situation the line has effectively become a static system."
Treating the line as dynamic make no difference to force calculations. Of course a dynamic LOAD (ie the person) is not calculated and cannot be calculated as then the person's legs themselves become part of the calculation.
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tagaustatoppen
Apr 29, 2006, 3:10 PM
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In reply to: coldclimb guanoboy wrote: ok this guy figured it all out... http://www.wanderingphotographer.com/other_int/slack_pages/slackline_a nalysis/static_analysis_2.htm Yeah that's a good link, but that assumes a static line, which most lines, or rather specifically what we climbers refer to as "slacklines" are not. The nylon we use is dynamic, which makes the forces more difficult to calculate, and I'm not sure if I've heard of anyone figuring out an accurate formula. That site will give you an idea though.
I have never slacklined before and i have idea so i am kind of interested to know is there enough rope length that it would have enough dynamics to make a lot of difference?
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gunkiemike
Apr 29, 2006, 9:16 PM
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Using a dynamic rope - which really begs a separate discussion, since webbing is the standard material for 'lining, and webbing is typically considered, in a climbing setting at least, to be static - allows for some stretch. Which creates additional deformation (sag) in the line. Which reduces the force exerted on the anchor.
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mitguy
Apr 30, 2006, 12:38 AM
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Approximating the line as static is probably an acceptable assumption as the force created on a static line will be higher than for a dynamic line. The additional step of working out what the forces on the anchor are when the person is at any point of the line is just a simple step further, and involves setting up a simple system of equations and some basic trig. The effects of bouncing can be taken into account by using the concept of impulse (a force over time) and an approximation of how long it takes for the line to reverse the person's direction to calculate how much force the line must generate on the climber (and hence on the anchors from Newton's 3rd). I'm not really interested in carrying out the calculations, but it should be pretty easy by looking up the equations online and some simple math. If you want to take into account the dynamice properties of the rope, check out a text book on mechanical engineering.
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cliffhanger9
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Apr 30, 2006, 1:49 PM
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In reply to: yeah forces are weird and wild-- thats why overcompensation 'aka being bomber' is a good thing... afraid of your knot breaking or not comforatable with using only one line--- shackles can help.. http://i5.photobucket.com/...slacker/IMG_2670.jpg
not to get off topic here but...i cant say i ve seen a setup like that before - care to explain? or shoew more pics? i cant see whats going on with that shackle there..thanks!
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gymslackerclimber
May 1, 2006, 4:41 AM
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ive never seen one like it either..
the webbing is just a bit wrapped around the shackle, then binered, the wrap pintched the line or creates the friction that locks the line in..
the green webbinig is wrapped the same way.. the only reason there is two lines is for a highline.. but the only reason for the shackle, also, is for a highline.. its just that its all clean and neat and knotless,
but i would love to know the results of if there is any slippage in this hitch (or what ever its called).. but this system is WAY bomber- if it can hold tension with lines over 200ft- it will probably hold for most anything
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mrbumguy
May 24, 2006, 6:13 AM
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The few one time I slacklined, the rope oscillated side to side like crazy under my feet. Not sure how this actually affects the forces at the anchor, but something tells that it raises them. Or maybe it's not significant. Or maybe I'm wrong. Worth thinking about though.
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