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So my guess as to why a longer fall with the same factor produced a higher force is the knots. They absorb a fixed amount of energy, independent of rope length, while the rope will absorb energy proportional to it's length. Hence in a longer rope the knots tightening up, and absorbing energy is proportionally a smaller factor of all the energy absorbed.
Pretty much this. The knot tightens up - this gives some rope and takes out some energy. And while more force will also tighten the knot more this almost certainly not linear but a rather steep increasing curve so applying 10x as much force only makes the knot give a tiny bit more rope.
This was exactly my thought as well. Tightening knots flatten the force curve through inner friction, hence take a lot of energy per cm lengthening, more than the streight (dyn.) rope. Would be an interesting comparison to make a cow tail of a slightly longer piece of rope, bind another knot (fig. 8?) right in the middle in order to end up with the same overall length and then compare results (force curves -> amount of energy is surface of force curve over distanc; and peak forces).
No references given "Tests carried out by American and French military have shown that even young,fit, trained parachutists can only withstand impact forces up to 12kN" - British Standard 8437 "Code of practice for selection, use and maintenance of personal fall protection systems and equipment for use in the workplace" , also states falls should be limited to 6kN, energy absorbing lanyards should resist forces of 2kN without deploying , full body harnesses for fall arrest systems
I would love to see a kong slyde or petzl adjust drop tested. It just seem to me like they would start to slip at some point and absorb most of that energy into the breaking device. Or maybe there is just too little rope to make any difference.
Thanks for doing this one. Dynamic cows tails are standard in rope access and I frequently see guys putting way too much faith in them. By the IRATA rules you should never expose yourself to anything more than factor one at a max fall of 600mm. In the real world this gets broken all the time. I've recently upgraded to the new Edelrid absorber sling. Highly recommend and you can hang full weight on it too 👍
Short system has less resulting force than long per inch of rope between the knots, because the short system has the same rope length in the knots. So short systems have more rope to fall so a lower effective fall. Falling 4m in a properly fitted harness might hurt in a factor 2 fall, but it won’t kill you any more than stepping off a 4 meter roof onto concrete will (unless you carefully do a header).
Just a heads up, you can order rope by the meter, including arborist type rope. That includes the really stretch 50% stretch climbing rope. Definitely a good be for cows tails
Did you ever do tests on gear with shock absorbers aso you mentioned it in the video? I would be super interested to know it as i have been gettin into this sort of climbing besides rope climbing :)
I've heard of people breaking their belay loop on a factor 2 PAS fall. I connect my percell prusik personal anchor to my harness with a DMM accessory carabiner that intentionally breaks at 4kn. I never use my PAS as a life supporting device, I am always tied into my climbing rope and only use the PAS for cleaning an anchor or switching to belay.
in some parts of europe they use a knot called a trilonge on their cowstails which is specifically designed to shock absorb. It's like a double overhand with one loop pulled out and folded into itself. Would be so curious if it works / if type of knot makes a significant impact in force of falls.
Fall factor has the great advantage that you can estimate it while leading, other than that it is not all that good to think about. The difference due to the amount of rope in the system will be vary from one rope to the next, and it seems like it is not linear at all. Rope stretch is a really complicated thing. For any given cowstail set-up, there would be some distance that it is safe to fall on it. With a longer attachment the safe fall distance would increase some amount, depending on the material, but probably the safe fall distance will increase far less than the additional length of material.
The swing might the main case, But another difference between the long vs short fall factor two is the fraction absorbed by the knots. The knot is going to absorb roughly the same energy in both situations, but there is twice as much energy in the longer fall. So the knot is absorbing a lower fraction of the total energy, putting more into the load cell.
It is so bizarre that these fatal falls look so undramatic and don’t to someone who doesn’t climb look like they should be lethal (I know logically that they are).
Great stuff. I’m a caver who uses Dynamic cows’ tails. I’ve had to tied some out of static for friends when I’ve taken them out caving and felt guilty about it at the time. But after watching this we’re screwed no matter what type of rope is used. 😅😅 More gear respect ✊
Erhmm... You're definitely way more screwed using static... ...and even moreso if you're the type of caver who was taught to clip a hand ascender to everything as a "safety"
Hi, I love your channel, awesome work! I’d like to ask you a question: what’s the theoretical force applied to a static rope during a fall? For example, let’s say we have a mass of 100kg that takes a fall during 1s, which means the rope will stop the fall after 5m with a final speed of 10 m/s (rounding g to 10 m/s2). Generating a momentum of 1000 kg.m/s. Assuming an actual static rope, meaning 0% elongation, does that mean the force is infinite? And for an more realistic scenario, let’s consider 3% elongation.
7:29 Ryan ".... then with the knots rock hard 17.04Kn, that would kill you!" Me "GOOD!!! At that force I definitely wouldn't want to be alive after that fall!!!!" 😅
So nearly equally dangerous, wonder if guys out there can feel the difference when climbing on them as really isn't the very static made for most efficient assending the rope.
My hunch is that in most caving situations the caver would be sliding down rock or swinging out and back in rather than completely free falling. As you say in the video it would be hard to factor that in but I'd be very interested to know what difference it makes if the weight is running down a concrete slab at 85 degrees rather than falling freely.
A couple thoughts: Why the longer cow tail had more force: perhaps the knot acts as a constant energy absorption; if you added intermediate knots, maybe that would reduce the energy for the bigger one I’m curious if you’ve thought about measuring energy instead of force? Specifically as the integral of force over distance. I think that might be more meaningful for breaking than peak force (the energy dissipation provided by a system)
The fall factor is the sole determining the force (given that rope elasticity, fall mass, and gravity are consistent) - F ∝ √(fall factor) HOWEVER!!! The duration of the force is determined also by velocity - it takes more time to decelerate mass that moves quicker if you have a constant force, and surely the damages on your body are greater the longer you experience the force. For instance, jet fighter pilots can stand short bursts of 7Gs, but if you were to live a day in 7Gs you'd die for sure. So just because a 100 meter factor 2 whipper and a 0.5 meter factor 2 fall generate the same force, they are not equally dangerous.
Can you please explain why choose 300lbs/136Kgs as the load, when most tests are based on 80kgs? Not so many cavers or canyoners tip the scales at this load, none that I have met anyway :-)
There's something delightful about how normal people can wear a flannel in a California winter, whereas Jenks is standing there in a his arctic parka... 😂
@@NippyKindLangur234 no, silly. Jenks freezes when it's colder than 65°F outside and I'm teasing him about it. It's just an endearing quirk about him. Go fight for something important if you're looking to start arguments. 😂
Just wondering the design methodology of using 300lbs for this test. It seems you are using the numbers to warn us against taking these falls but shouldn’t you use a lighter load? For example, I’m roughly 200 lbs, since people are also dynamic, generally we absorb/spread the impact around, such that using a 100 lb weight would more accurately display the forces I feel here. As such, wouldn’t I expect then to experience forces about 3x lower than the ones you have here? 19 => 6.33 not great but more livable? Just asking on why 300 lb was used
Really enjoy these expts and vids , top notch stuff! Thank you so much, we use them in class :) Agree that the knots could have some effect in slowing a falling person to a stop, but would think the time you are falling and therefore the time you are speeding up during the fall , is a bigger factor. Bit like jumping off a table, both in terms of height of table affecting the time speeding up in the drop and time required to bring you to an injury free stop . People bend their knees to slow down as they hit the floor when jumping off a table (see parachutist tuck and roll technique)and you don't keep knees straight and rigid unless looking for a serious injury and shock (same principal with crumple zones and air bags in cars). The longer it takes a person to slow down, the smaller the forces required and also like jumping off a table if it's a very small table (height wise) you don't build up a lot of velocity before coming into contact with the ground . Some figures: If you free fall for 2 seconds your velocity at that point is appox 20m/s (or 44 mph)downwards. If you fall for 1 second your velocity is approx 10 m/s (22mph) downwards . If fall for .5 sec approx 5 m/s (11 mph). There is more force required to bring you to a stop, the faster you are going. I think the longer rope allows the person falling to get to a bigger velocity before starting to slow them to a stop, and the extra length/stretch of the longer rope (and knots) doesn't have enough stretchiness to ease the person to stop with a small/gentle enough slowing down force. So the longer rope had much higher shock loading , sometimes greater than the breaking strength of the rope (or a person's back). High speed camera could be used to give a more accurate measurement of the timings here (slow mo guys collaboration maybe ?) Just my 2 cents.
First, I do think that, with some of the techniques we use in France, there would be something else breaking in the system long before you could reach this high of a force. That is why if I am clipped in with my personal anchor to a hangar I have a golden rule of always be in tension in something, wether it is the rope or my personal anchor or something else. There Is only a few cases where it is not possible and then it is for a few seconds and with just enough slack to unclip it. That makes that, in my experience, even a factor 1 fall is extremely rare in caving.
This still counts as a worst case scenario, but I think it's overselling the danger of short falls, because it's not accounting the energy absorbtion of human body and the harness waist belt tightening around the body. In a long enough fall, the amount of energy that the human body and harness can absorb is insignificant, so the fall factor is probably the only thing that matters in a long fall. But small falls just don't have enough impulse to overcome the human body absorbtion. A 10 inch fall on a 5 inch rope may generate 10kn with a steel weight, human body would never come close to those numbers. Imagine decking from 10 inches onto a flat concrete, butt first, which is pretty much as static as a fall can get. It may make a good bruise, but I think it would be quite unlikely to truly injure you, and it definitely won't put 10kn into the concrete. Add the harness which will distribute the force even more evenly, and I don't think it would be a big issue. In the extreme case, imagine 2mm of fall on 1mm of steel wire. There just isn't enough kinetic energy in that kind of fall to do you any harm, and yet the same fall may break the biners if you replace the human with a theoretically absolutely static weight. While the static rope and harness may stop your skin around your waist statically, your arms, legs, chest, head, your bones and plenty of internal organs won't all deccelerate at the same time, thus they won't all be pulling on the rope at the same time, reducing the peak force and prolonging it. But ofcourse, the longer the factor-2, the more insignificant the body absorbtion is. So, I think fall factor is the only thing that matters, except for very short falls.
Notes from around 4:30 in. The maths behind the force being the same for the same fall factor (ff) independent of the fall distance uses an important assumption. The assumption is that the dynamic rope absorbs all of the energy. This means that the knot tightening and the extra rope length hidden in the knot is not accounted for. My guess is that in the small falls these factors are none negligible. If you did this test with many different length ropes then for extremely small falls the forces will be low but as the fall distance grows this should asymptotically go to a constant value as the knot tightening and extra rope in the knot becomes negligible. FF is all that matters in the limit of long falls, off an infinitely strong anchor, with a perfectly ridged weight, and no swinging. Basically when nothing else absorbs the energy. Would be interesting to plot max force vs fall distance to see if it does asymptotically become flat or if there are some more assumptions (rope only experiencing elastic deformation and following hooks law) that need to be thought about. If it’s of interest I might run some basic calculations to play a bit although I am not a rope expert
I feel like testing with rigid weight vs human body inflates max forces but I have no idea by how much Could you do some safe falls of factor 0.1, 0.2, 0.3 etc with human and with weight to compare the difference? It would be really interesting to see if the difference is 5% or 100% etc
If you could do this at factor 1 that would have been great to compare the impact. Which is probably more reprasentative. They are also usually non vertical falls with some swing in them. But this put me straight on my suspission climbers belyaching about factor 2 falls being death :P which I formely didn't think applied to such short lengths of rope and falls. Also its been said a lot that knots take up alot of the fall, but wow thats a lot of impact. Great data. I wonder how much was also rope first time stretch due to its non-recovering distortion. Retying drop tested rope with new knots would seperate fix these two factors. Big caving love.
Would be intresting to see the diference in forces on the drop tower testing between solid mass drop (like these metal weight or something that you used) and manequine or pig corpse. I wonder how all tissues flexibility will affect the force generation. Also the test will allow to asses spine injuries.
You can treat "cow's tail" as one unit and pluralize it to "(cow's tail)s". As a rule of thumb, if a bunch of native language speakers are saying something, it isn't wrong.
Did you lose/destroy your dummy? dropping weights like that over short distances doesn't really tell you much of anything IMO. I've fallen on ± a meter of dynamic rope before and it's uncomfortable but nothing close to what an actual 6-7kn fall would feel like. Totally agree that you should respect fall factors a whole bunch more when you're clipped through a static line. That's gotta hurt.
The dummy was only 90lbs / 40kg. It wasn't heavy enough to get anything helpful. Even the dummy isn't as helpful as it's not flesh. I might have to go do human testing :)
Yeah, rigid masses are a really poor model of a human body. There's a reason you don't use a rubber mallet to drive a nail. I once took a FF2 onto a spectra daisy while aid climbing, felt no worse than getting thrown in wrestling or Judo (which can definitely injure someone if they don't fall right).
If we're saying the knot tightening makes the difference between 6-10 on the short one, i feel like the "extra length" isn't getting you double the elasticity for double the height.
These are the types of exposides that are interesting and educational even for long-time climbers. You do not get this type of data and then knowledge without testing. Thanks for making this film!
Biggest learning for me is how much energy the knots take. Accordingly, it would make sense after a rough catch of my teather to untie the knots and do fresh ones.
people jump from higher heights. They dont absorb 13kN or 1,3 tons. Absorbing it with your legs would IMO equal to explosively lifting a 2600 pound barbell. It doesnt make perfect sense. I've seen tests with a climber absorbing a short and a long fall and they reached like 3 kN max. *It has to be the inneria and a sudden stop. Like a boxer measuring his punching force at 700 pounds while he couldnt ever lift that. Extreme example would be a bullet delivering 1000 joules without the gun moving much not to mention ripping your arm.
i think the only difference you would find when you keep the same fall factor on dynamic rope with different lengths is in what things outside of the rope absorb. at same fall factor, as you increase the length you increase the speed, thus force of impact, and proportionally increase the length of rope, thus it's impact absorption capacity too. however, other parts of the chain have some capacity to absorb energy. as you've shown the knots absorb a lot, but 2 knots can only absorb so much, be it on a 50cm or a 5m length of rope, so they proportionally absorb less on longer falls with longer ropes. slack in your harness, padding from your clothes, body flexibility, all of those have a fixed capacity to absorb the impact too. and there's the fact that you rarely fall perfectly straight down into a hang, you always have some swinging motion, and the swinging angle will always be smaller (thus dissipate less energy) with longer falls/rope. and i think that's why despite fall factor leading to the same measured impact force regardless of length, we are in practice mostly fine taking a drop on 50cm of static rope from above our anchor point, but get injured if we take a factor 2 on 5m of dynamic rope.
Hi Rayan, as usual very informative content! Thank you, just one question about a doubt that came with my friend: I have an opinion and my friend another.. If we test two cow’s tail: one with fresh knot with 30cm (for example) lenght and ono otherone with rock solid knots on it, both with the same intitial lenght (knot to knot), wich one will have the higher KN number? For me the one with fresh knot will produce less KN due of the tighting of the knots. For my friend the added lenght that the rope will gain from the tightinig of the knots ends up producing more force on the anchor. Thank you so much for your reply to our questions.
About long and short factor 2 falls, a simple reasoning from a engineer. There question is really which increases the fastest, the rope stretch of the fall force. With 2 falls, one longer than the other. The stretch of the rope increases linearly to the length of the rope. But the force of falling, is N = mass * velocity, but velocity is not linear to the length of the fall, but to the time of the fall, since acceleration is constant at these speeds. The time of fall is an integral of the acceleration over distance.. With simple physics, constant acceleration. If you fall 5 meters (2.5m rope) you'll fall for 1 second and have 10m/s final velocity. If you fall for 20 meters (10m rope) you'll fall for 2 seconds and have a final velocity of 20m/s. So four times more rope and twice the velocity and force. Rope stretch increasing faster than the fall force. This implies that a shorter fall will at _some_ sweet spot create the biggest _force_. Since a really short fall is a very little force, especially with stretch of knots and so on.
I think that fornthe factor 2 falling, the difference in hight will change the forces depending on how elastic the rope will be. Because with more falling distance you have a longer acceleration so a bigger speed, if the rope it’s super static, like a dyneema rope it won’t strech so all the force made to stop your velocity will be in a very short time, so the pick force will be way higher than with a smaller fall in factor 2. Can’t wait to see if you make a video about this, because it’s very interesting
4:53 "I think the moral of the story so far is try not to factor 2 fall." No shit Sherlock. Assuming that the rope is perfectly linearly elastic, is the only elastic thing in the system and there's no aerodynamic drag, the maximum force is only dependent on the fall factor and not on the length of the fall. I unfortunately don't know about the nonlinearities and dampening behaviour of a rope, but with constant FF and different lengths, you should be getting forces in the same ballpark.
This is gonna sound weird, but use castration bands on your rope/webbing to help keep stuff in position. Unfortunately it might make people think it would change the results, but can't make everyone happy.
I've seen some people install vertical ladders in caves with a vertical static rope next to it to clip into, I dont think that clipping into that rope does much.
Curious regarding the fifi - would it make sense to use those on a tether that would break particularly low so that if it was the shorter link in the system you'd break it and fall onto the actual belay?
4:00 sudely the difference is because the longer rope has the same size knot as the short one. And that knot absorbs a lot of the force. So what im saying is the short one isnt really as much of a fall factor 2 as the long one.
There has been a lot of discussion on this topic since DMM did a similar video. The question is... does the fact that the load in both video cases (weights) increase the shock loads to a higher extent than if a test dummy/real human might? The arms and legs beginning able to carry on falling before hitting the arrested main part load. Does this decrease the total peak loads or just increase the duration of a lower total peak? The spine flexibility effectively acting like a shock absorber?🤔
This exactly the response that was given from the DAV tech team and the reason why testing gear is not done with weights like this... There is simply no accident reporting that this is a real problem. And yes, there is a good system in place in Europe to keep track on this.
Our data is at www.hownot2.com/post/cow-tails and you can sign up for the newsletter at www.hownot2.com/sign-up
Check out our new store! hownot2.store/ where we sell Swift Dry Protect dynamic rope by the foot for cow tails. hownot2.store/products/swift-protect-pro-dry-rope-8-9mm
So my guess as to why a longer fall with the same factor produced a higher force is the knots. They absorb a fixed amount of energy, independent of rope length, while the rope will absorb energy proportional to it's length. Hence in a longer rope the knots tightening up, and absorbing energy is proportionally a smaller factor of all the energy absorbed.
I agree.
Same with the energy that a human body absorbs.
Pretty much this.
The knot tightens up - this gives some rope and takes out some energy. And while more force will also tighten the knot more this almost certainly not linear but a rather steep increasing curve so applying 10x as much force only makes the knot give a tiny bit more rope.
This was exactly my thought as well. Tightening knots flatten the force curve through inner friction, hence take a lot of energy per cm lengthening, more than the streight (dyn.) rope. Would be an interesting comparison to make a cow tail of a slightly longer piece of rope, bind another knot (fig. 8?) right in the middle in order to end up with the same overall length and then compare results (force curves -> amount of energy is surface of force curve over distanc; and peak forces).
No references given "Tests carried out by American and French military have shown that even young,fit, trained parachutists can only withstand impact forces up to 12kN" - British Standard 8437 "Code of practice for selection, use and maintenance of personal fall protection systems and equipment for use in the workplace" , also states falls should be limited to 6kN, energy absorbing lanyards should resist forces of 2kN without deploying , full body harnesses for fall arrest systems
okay so 12 kN is the limit gotcha
seriously being the guy to find out for those "tests" must have sucked hard
That's with a parachute harness, very different to what climbers use.
I would love to see a kong slyde or petzl adjust drop tested. It just seem to me like they would start to slip at some point and absorb most of that energy into the breaking device. Or maybe there is just too little rope to make any difference.
Yes please :)
Me too. Something like that seems to be a good idea instead of something like cows tail.
Count me in for the kong slyde and kong kisa
Screamer too plz!!
I'm also on team slyde
How do Personal Anchor Systems like the Beal Dynaclip or Petzl Connect Adjust compare? Probably very similar to the dynamic rope cow’s tail?
Probably also depends on how wet and muddy the tails are... I imagine those would have some amount of slippage in true cave conditions.
2:27 buy new mattress. I recommend sandwich construction with multiple hardness/softness levels and definitely with one or 2 layers of memory foam.
Thanks for doing this one. Dynamic cows tails are standard in rope access and I frequently see guys putting way too much faith in them. By the IRATA rules you should never expose yourself to anything more than factor one at a max fall of 600mm. In the real world this gets broken all the time.
I've recently upgraded to the new Edelrid absorber sling. Highly recommend and you can hang full weight on it too 👍
Short system has less resulting force than long per inch of rope between the knots, because the short system has the same rope length in the knots. So short systems have more rope to fall so a lower effective fall.
Falling 4m in a properly fitted harness might hurt in a factor 2 fall, but it won’t kill you any more than stepping off a 4 meter roof onto concrete will (unless you carefully do a header).
Thanks for the grammar/spelling lesson Jon, you legit had my five year old absolutely riveted!
Wow, that is very educational. I'd not been aware of these extreme force risks. Thank you
Just a heads up, you can order rope by the meter, including arborist type rope. That includes the really stretch 50% stretch climbing rope. Definitely a good be for cows tails
Did you ever do tests on gear with shock absorbers aso you mentioned it in the video? I would be super interested to know it as i have been gettin into this sort of climbing besides rope climbing :)
I've heard of people breaking their belay loop on a factor 2 PAS fall. I connect my percell prusik personal anchor to my harness with a DMM accessory carabiner that intentionally breaks at 4kn. I never use my PAS as a life supporting device, I am always tied into my climbing rope and only use the PAS for cleaning an anchor or switching to belay.
One of the most important videos for any climber to watch
in some parts of europe they use a knot called a trilonge on their cowstails which is specifically designed to shock absorb. It's like a double overhand with one loop pulled out and folded into itself. Would be so curious if it works / if type of knot makes a significant impact in force of falls.
Fall factor has the great advantage that you can estimate it while leading, other than that it is not all that good to think about. The difference due to the amount of rope in the system will be vary from one rope to the next, and it seems like it is not linear at all. Rope stretch is a really complicated thing.
For any given cowstail set-up, there would be some distance that it is safe to fall on it. With a longer attachment the safe fall distance would increase some amount, depending on the material, but probably the safe fall distance will increase far less than the additional length of material.
The swing might the main case, But another difference between the long vs short fall factor two is the fraction absorbed by the knots. The knot is going to absorb roughly the same energy in both situations, but there is twice as much energy in the longer fall. So the knot is absorbing a lower fraction of the total energy, putting more into the load cell.
It is so bizarre that these fatal falls look so undramatic and don’t to someone who doesn’t climb look like they should be lethal (I know logically that they are).
Great stuff. I’m a caver who uses Dynamic cows’ tails. I’ve had to tied some out of static for friends when I’ve taken them out caving and felt guilty about it at the time. But after watching this we’re screwed no matter what type of rope is used. 😅😅
More gear respect ✊
Erhmm... You're definitely way more screwed using static...
...and even moreso if you're the type of caver who was taught to clip a hand ascender to everything as a "safety"
The knots have a bigger impact on short links
Can you test a factor 2 on a semi-static traverse line?
Also, why do you use a webbing for personal anchor instead of rounded rope?
This shid is super interesting, thanks Jenksie
Any way to test how much energy your harness is going to absorb? That 300 lb weight is completely unforgiving. Thanks for the great content.
I once belayed a 60kg dummy made out of concrete. The fall felt super hard, like a >80kg person. (I’m 66kg myself)
commented too soon. Good to see Ryan getting a perfect descent line back in.
Did you guys ever tested the Petzl adjust?
Hi, I love your channel, awesome work!
I’d like to ask you a question: what’s the theoretical force applied to a static rope during a fall?
For example, let’s say we have a mass of 100kg that takes a fall during 1s, which means the rope will stop the fall after 5m with a final speed of 10 m/s (rounding g to 10 m/s2). Generating a momentum of 1000 kg.m/s.
Assuming an actual static rope, meaning 0% elongation, does that mean the force is infinite?
And for an more realistic scenario, let’s consider 3% elongation.
“Metric inches”, haha, I see what you did there. . . 😀
7:29 Ryan ".... then with the knots rock hard 17.04Kn, that would kill you!"
Me "GOOD!!! At that force I definitely wouldn't want to be alive after that fall!!!!" 😅
The tale of cow's tails by testing cows' tails while being watched by cattle with their tail's? 🤔 🤯
So nearly equally dangerous, wonder if guys out there can feel the difference when climbing on them as really isn't the very static made for most efficient assending the rope.
hi can you test the cowtail rope by using petzl shunt and s.tec duck and test it on the semi statics rope
th-cam.com/video/M2a1zdpScPo/w-d-xo.html
You can see the link I shared for example. I really hope you can do it. Because I really to see it
Thank you
metric inches‽
As someone who is 300 lb with gear this is not confidence inspiring.😅
My hunch is that in most caving situations the caver would be sliding down rock or swinging out and back in rather than completely free falling. As you say in the video it would be hard to factor that in but I'd be very interested to know what difference it makes if the weight is running down a concrete slab at 85 degrees rather than falling freely.
A couple thoughts:
Why the longer cow tail had more force: perhaps the knot acts as a constant energy absorption; if you added intermediate knots, maybe that would reduce the energy for the bigger one
I’m curious if you’ve thought about measuring energy instead of force? Specifically as the integral of force over distance. I think that might be more meaningful for breaking than peak force (the energy dissipation provided by a system)
How would you measure the energy?
Isn't mgh easier ?
Yeah but I don't weigh 300lbs.
That Petzl cow's tail isn't "completely static". The stitching is designed to tear with a fall.
The fall factor is the sole determining the force (given that rope elasticity, fall mass, and gravity are consistent) - F ∝ √(fall factor)
HOWEVER!!! The duration of the force is determined also by velocity - it takes more time to decelerate mass that moves quicker if you have a constant force, and surely the damages on your body are greater the longer you experience the force. For instance, jet fighter pilots can stand short bursts of 7Gs, but if you were to live a day in 7Gs you'd die for sure. So just because a 100 meter factor 2 whipper and a 0.5 meter factor 2 fall generate the same force, they are not equally dangerous.
"100 meter factor 2 whipper" 😱
@@drew5334 you're telling me you don't take 100m 2.0 whippers on a daily basis? Are you even climbing bro?!
Square root of the fall factor
@@serges5681 aha! Okay! Thanks for the correction! I'll edit my original comment to avoid misinforming!
@@serges5681 did I get it right? My intuition says it's the other way around
(F ∝ (fall factor)²)
Can you please explain why choose 300lbs/136Kgs as the load, when most tests are based on 80kgs? Not so many cavers or canyoners tip the scales at this load, none that I have met anyway :-)
Ryan! Stop chewing your nails man we need you!!!!
There's something delightful about how normal people can wear a flannel in a California winter, whereas Jenks is standing there in a his arctic parka... 😂
We gatekeeping cold weather now?
@@NippyKindLangur234 no, silly. Jenks freezes when it's colder than 65°F outside and I'm teasing him about it. It's just an endearing quirk about him.
Go fight for something important if you're looking to start arguments. 😂
As a Californian... I resemble this remark
It's very funny, I can't wear a puffer unless it's below 0c having grown up in the not extreme but often miserable England.
Just wondering the design methodology of using 300lbs for this test. It seems you are using the numbers to warn us against taking these falls but shouldn’t you use a lighter load?
For example, I’m roughly 200 lbs, since people are also dynamic, generally we absorb/spread the impact around, such that using a 100 lb weight would more accurately display the forces I feel here.
As such, wouldn’t I expect then to experience forces about 3x lower than the ones you have here? 19 => 6.33 not great but more livable?
Just asking on why 300 lb was used
I think the forces with the shorter cowtail were lower because the knots absorbed most of the force in that scenario, not the rope itself.
The elongation from knots tightening is much higher as a factor of fall length on a short cows tail, effectively reducing the fall factor.
Really enjoy these expts and vids , top notch stuff! Thank you so much, we use them in class :)
Agree that the knots could have some effect in slowing a falling person to a stop, but would think the time you are falling and therefore the time you are speeding up during the fall , is a bigger factor. Bit like jumping off a table, both in terms of height of table affecting the time speeding up in the drop and time required to bring you to an injury free stop . People bend their knees to slow down as they hit the floor when jumping off a table (see parachutist tuck and roll technique)and you don't keep knees straight and rigid unless looking for a serious injury and shock (same principal with crumple zones and air bags in cars). The longer it takes a person to slow down, the smaller the forces required and also like jumping off a table if it's a very small table (height wise) you don't build up a lot of velocity before coming into contact with the ground .
Some figures: If you free fall for 2 seconds your velocity at that point is appox 20m/s (or 44 mph)downwards. If you fall for 1 second your velocity is approx 10 m/s (22mph) downwards . If fall for .5 sec approx 5 m/s (11 mph). There is more force required to bring you to a stop, the faster you are going.
I think the longer rope allows the person falling to get to a bigger velocity before starting to slow them to a stop, and the extra length/stretch of the longer rope (and knots) doesn't have enough stretchiness to ease the person to stop with a small/gentle enough slowing down force. So the longer rope had much higher shock loading , sometimes greater than the breaking strength of the rope (or a person's back). High speed camera could be used to give a more accurate measurement of the timings here (slow mo guys collaboration maybe ?) Just my 2 cents.
Hey Ryan, can you do some more testing on fresh versus previously loaded knots? Really curious in a climbing context.
That was a huge difference.
First, I do think that, with some of the techniques we use in France, there would be something else breaking in the system long before you could reach this high of a force. That is why if I am clipped in with my personal anchor to a hangar I have a golden rule of always be in tension in something, wether it is the rope or my personal anchor or something else. There Is only a few cases where it is not possible and then it is for a few seconds and with just enough slack to unclip it. That makes that, in my experience, even a factor 1 fall is extremely rare in caving.
The unstitching feature of the spelegyca was in the petzl product description (even if its not a good enough absorber)
This still counts as a worst case scenario, but I think it's overselling the danger of short falls, because it's not accounting the energy absorbtion of human body and the harness waist belt tightening around the body. In a long enough fall, the amount of energy that the human body and harness can absorb is insignificant, so the fall factor is probably the only thing that matters in a long fall. But small falls just don't have enough impulse to overcome the human body absorbtion. A 10 inch fall on a 5 inch rope may generate 10kn with a steel weight, human body would never come close to those numbers.
Imagine decking from 10 inches onto a flat concrete, butt first, which is pretty much as static as a fall can get.
It may make a good bruise, but I think it would be quite unlikely to truly injure you, and it definitely won't put 10kn into the concrete. Add the harness which will distribute the force even more evenly, and I don't think it would be a big issue.
In the extreme case, imagine 2mm of fall on 1mm of steel wire. There just isn't enough kinetic energy in that kind of fall to do you any harm, and yet the same fall may break the biners if you replace the human with a theoretically absolutely static weight.
While the static rope and harness may stop your skin around your waist statically, your arms, legs, chest, head, your bones and plenty of internal organs won't all deccelerate at the same time, thus they won't all be pulling on the rope at the same time, reducing the peak force and prolonging it.
But ofcourse, the longer the factor-2, the more insignificant the body absorbtion is. So, I think fall factor is the only thing that matters, except for very short falls.
Notes from around 4:30 in. The maths behind the force being the same for the same fall factor (ff) independent of the fall distance uses an important assumption. The assumption is that the dynamic rope absorbs all of the energy. This means that the knot tightening and the extra rope length hidden in the knot is not accounted for. My guess is that in the small falls these factors are none negligible. If you did this test with many different length ropes then for extremely small falls the forces will be low but as the fall distance grows this should asymptotically go to a constant value as the knot tightening and extra rope in the knot becomes negligible. FF is all that matters in the limit of long falls, off an infinitely strong anchor, with a perfectly ridged weight, and no swinging. Basically when nothing else absorbs the energy. Would be interesting to plot max force vs fall distance to see if it does asymptotically become flat or if there are some more assumptions (rope only experiencing elastic deformation and following hooks law) that need to be thought about. If it’s of interest I might run some basic calculations to play a bit although I am not a rope expert
I feel like testing with rigid weight vs human body inflates max forces but I have no idea by how much
Could you do some safe falls of factor 0.1, 0.2, 0.3 etc with human and with weight to compare the difference?
It would be really interesting to see if the difference is 5% or 100% etc
If you could do this at factor 1 that would have been great to compare the impact. Which is probably more reprasentative. They are also usually non vertical falls with some swing in them.
But this put me straight on my suspission climbers belyaching about factor 2 falls being death :P which I formely didn't think applied to such short lengths of rope and falls.
Also its been said a lot that knots take up alot of the fall, but wow thats a lot of impact. Great data. I wonder how much was also rope first time stretch due to its non-recovering distortion. Retying drop tested rope with new knots would seperate fix these two factors.
Big caving love.
Would be intresting to see the diference in forces on the drop tower testing between solid mass drop (like these metal weight or something that you used) and manequine or pig corpse. I wonder how all tissues flexibility will affect the force generation. Also the test will allow to asses spine injuries.
I'd pay to watch Jenks try to wrangle a pig corpse into a climbing harness 🤣❤️
"for more shits and giggles we dropped a fresh long one". 😏
the "fresh long one" was an accident but worked so well!
You can treat "cow's tail" as one unit and pluralize it to "(cow's tail)s".
As a rule of thumb, if a bunch of native language speakers are saying something, it isn't wrong.
Did you lose/destroy your dummy? dropping weights like that over short distances doesn't really tell you much of anything IMO. I've fallen on ± a meter of dynamic rope before and it's uncomfortable but nothing close to what an actual 6-7kn fall would feel like.
Totally agree that you should respect fall factors a whole bunch more when you're clipped through a static line. That's gotta hurt.
The dummy was only 90lbs / 40kg. It wasn't heavy enough to get anything helpful. Even the dummy isn't as helpful as it's not flesh. I might have to go do human testing :)
Yeah, rigid masses are a really poor model of a human body. There's a reason you don't use a rubber mallet to drive a nail.
I once took a FF2 onto a spectra daisy while aid climbing, felt no worse than getting thrown in wrestling or Judo (which can definitely injure someone if they don't fall right).
BREAKTEST THE AUSTRIALPIN COBRA BELT BUCKLE!!!
Plenty of cow tail jokes, but this video left me wanting some cow tales too.
Gotta love the "perfect descent" bit. Hilarious.
You got to do more arborist gear stuff
If we're saying the knot tightening makes the difference between 6-10 on the short one, i feel like the "extra length" isn't getting you double the elasticity for double the height.
Great episode!!!
really enjoyed the format!
you keep on improving with each episode!
These are the types of exposides that are interesting and educational even for long-time climbers. You do not get this type of data and then knowledge without testing. Thanks for making this film!
Biggest learning for me is how much energy the knots take. Accordingly, it would make sense after a rough catch of my teather to untie the knots and do fresh ones.
spelegyca*
Edit: I absolutely love this episode!
Same knot gives you a bigger percentage of total rope stretch in the smaller system therefore affecting the overall result in said system.
people jump from higher heights. They dont absorb 13kN or 1,3 tons. Absorbing it with your legs would IMO equal to explosively lifting a 2600 pound barbell. It doesnt make perfect sense. I've seen tests with a climber absorbing a short and a long fall and they reached like 3 kN max.
*It has to be the inneria and a sudden stop. Like a boxer measuring his punching force at 700 pounds while he couldnt ever lift that. Extreme example would be a bullet delivering 1000 joules without the gun moving much not to mention ripping your arm.
i think the only difference you would find when you keep the same fall factor on dynamic rope with different lengths is in what things outside of the rope absorb.
at same fall factor, as you increase the length you increase the speed, thus force of impact, and proportionally increase the length of rope, thus it's impact absorption capacity too. however, other parts of the chain have some capacity to absorb energy. as you've shown the knots absorb a lot, but 2 knots can only absorb so much, be it on a 50cm or a 5m length of rope, so they proportionally absorb less on longer falls with longer ropes. slack in your harness, padding from your clothes, body flexibility, all of those have a fixed capacity to absorb the impact too. and there's the fact that you rarely fall perfectly straight down into a hang, you always have some swinging motion, and the swinging angle will always be smaller (thus dissipate less energy) with longer falls/rope.
and i think that's why despite fall factor leading to the same measured impact force regardless of length, we are in practice mostly fine taking a drop on 50cm of static rope from above our anchor point, but get injured if we take a factor 2 on 5m of dynamic rope.
Hi Rayan, as usual very informative content! Thank you, just one question about a doubt that came with my friend:
I have an opinion and my friend another..
If we test two cow’s tail: one with fresh knot with 30cm (for example) lenght and ono otherone with rock solid knots on it, both with the same intitial lenght (knot to knot), wich one will have the higher KN number?
For me the one with fresh knot will produce less KN due of the tighting of the knots.
For my friend the added lenght that the rope will gain from the tightinig of the knots ends up producing more force on the anchor.
Thank you so much for your reply to our questions.
I think the drop tower needs an improvement. Dropping the weight near the beams may be counterproductive over time as the beam gets hit over and over.
The cow jokes made this video amazing!
About long and short factor 2 falls, a simple reasoning from a engineer.
There question is really which increases the fastest, the rope stretch of the fall force.
With 2 falls, one longer than the other.
The stretch of the rope increases linearly to the length of the rope.
But the force of falling, is N = mass * velocity, but velocity is not linear to the length of the fall, but to the time of the fall, since acceleration is constant at these speeds. The time of fall is an integral of the acceleration over distance..
With simple physics, constant acceleration.
If you fall 5 meters (2.5m rope) you'll fall for 1 second and have 10m/s final velocity. If you fall for 20 meters (10m rope) you'll fall for 2 seconds and have a final velocity of 20m/s. So four times more rope and twice the velocity and force. Rope stretch increasing faster than the fall force.
This implies that a shorter fall will at _some_ sweet spot create the biggest _force_. Since a really short fall is a very little force, especially with stretch of knots and so on.
I think that fornthe factor 2 falling, the difference in hight will change the forces depending on how elastic the rope will be. Because with more falling distance you have a longer acceleration so a bigger speed, if the rope it’s super static, like a dyneema rope it won’t strech so all the force made to stop your velocity will be in a very short time, so the pick force will be way higher than with a smaller fall in factor 2.
Can’t wait to see if you make a video about this, because it’s very interesting
4:53 "I think the moral of the story so far is try not to factor 2 fall."
No shit Sherlock.
Assuming that the rope is perfectly linearly elastic, is the only elastic thing in the system and there's no aerodynamic drag, the maximum force is only dependent on the fall factor and not on the length of the fall. I unfortunately don't know about the nonlinearities and dampening behaviour of a rope, but with constant FF and different lengths, you should be getting forces in the same ballpark.
This is gonna sound weird, but use castration bands on your rope/webbing to help keep stuff in position. Unfortunately it might make people think it would change the results, but can't make everyone happy.
I drop a fresh long one also 👍🏼🤠🇨🇦
so glad you are using the term 'caving' / 'cavers' etc. and not the dumb 'spelunking' word!
That whole video made me hurt just WATCHING it.
I've seen some people install vertical ladders in caves with a vertical static rope next to it to clip into, I dont think that clipping into that rope does much.
Can that cow tail get you out when you go headfirst down a vertical hole and get stuck.
Caving…that’s a big nope for me.
ok.. why did the rope break at 5:08??? Was it was used to many times under load? I am confused by that part of the test.
Also ghe knots are the same for the long/short tails, so on gje long tail ghe knot is proportionally less impactfull
Greenscreen at 4:10? Or does the blurred background just look weird?
Curious regarding the fifi - would it make sense to use those on a tether that would break particularly low so that if it was the shorter link in the system you'd break it and fall onto the actual belay?
I've always called them chicken slings...
Try sleeping in a Yucatán hammock fixed my back. I sleep like a rock now.
Moo-ving video. Utterly shocking. Cows" tail tipped past the breaking point
What about factor 1?
4:00 sudely the difference is because the longer rope has the same size knot as the short one. And that knot absorbs a lot of the force. So what im saying is the short one isnt really as much of a fall factor 2 as the long one.
U need to test cowstails with shocks absorber in the system
I use the petal as my cowtail. But when I use it there is never any slack. So there is no fall factor
Can you strength test the petzl zigzag and compare it to prussic
Ryan why are you always in a puffy, dont you live in california? 😅🥵
I want to come out to California just so I can have you drop a live human a little bit
I wonder if Joe Rogan is ever going to go back to Fall Factor
lol … bed time back pain …. oh the stuggle is real
There has been a lot of discussion on this topic since DMM did a similar video. The question is... does the fact that the load in both video cases (weights) increase the shock loads to a higher extent than if a test dummy/real human might? The arms and legs beginning able to carry on falling before hitting the arrested main part load. Does this decrease the total peak loads or just increase the duration of a lower total peak? The spine flexibility effectively acting like a shock absorber?🤔
This exactly the response that was given from the DAV tech team and the reason why testing gear is not done with weights like this...
There is simply no accident reporting that this is a real problem. And yes, there is a good system in place in Europe to keep track on this.
hey did u try the beal jocker 8.5?
That is react the rope
2:25 🤣 i can totaly relate to you ;D