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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).
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.
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.
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. 😂
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.
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
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
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
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!
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.
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.
I'm so happy you called them "cows tails!" That's what we called them when I first started climbing. All the people I climb with now have never heard that term, I started wondering if it was in my head. 😂😂😂
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 :)
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).
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.
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.
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
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.
Man John really is a spelling bee rap god! Next I wanna see him spell out as quickly as he can: "Cow's tail! Cows' tails! Cow's tail? Cows' tails?" three times in a row. Keep nerding out guys! Awesome stuff as always!
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.
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.
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
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
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.
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.
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.
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.
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.
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.
It's a good case for keeping your tethers short, so if you do fall on it it's not as bad. I just use alpine draws, but still wouldn't want to fall on them.
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.
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.
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.
There will be a cross over on rope length for the force of a factor 2 fall. Below a certain length, you will not reach terminal velocity, reducing the speed that you are catching. Until you reach terminal velocity, the potential energy will increase. The elongation of the rope - time that the force will spread out - will increase with the length of rope, though I imagine there is another point at which this also drops off.
Have you got any data on how many km of a nylon rope vs an aramid rope vs an aramid-coated rope it takes to wear through belay devices to their safety limit marker? be interesting to see how toothed devices (including ASAP style devices) fair up against different ropes too. Replacement/repairability of devices? just a thought!
While this seems neat, I can tell you from caving that ropes utterly glazed in mud wear out ascender teeth after a few miles of rope climbing. No aboveground scenario comes close to that level of abuse, sans maybe slopeside stabilization. I reckon it would take a machine running rope in an infinite loop, and going constantly for months, to wear out teeth using clean ropes.... All that said: I hope that ropes are being chosen first and foremost for their physics based on the rigging, rather than paying any mind to how they affect a consumable item like an ascender. 🤷
@@rachelhasbruises 20 years in industrial rope access... kevlar seems to chew metal quite badly. geotechnical is the testing ground for robust kit. If you can't jump on it, it shouldn't be there
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 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.
I think that the ratio between his much rope is in the system and how tall is the fall is not the main factor. The tablet the fall the more speed that you'll get, if we go back to a newton bein Kg*m/s^2 we can see that if we take your weigh multiply by your speed and divide it by how fast you come to full stop will give us a really close number how how many Newtons will be in that change of speed. The rope here is basically a spring that had the capacity of elongate and slow you down a little while doing so, that's what happens when rope "dissipates" force. But any additional speed will translate into force when we come to full stop. Summarizing a 10m rope can "dissipate" so much energy, all the remaining energy will it is when we come to full stop. Adding 1 meter of rope will increase how much energy it can dissipate. Falling 1 extra meter will allow us to gain more speed during the fall, If we keep a ratio of 2m if rope by meter of fall the final KN will keep getting higher. If we keep doing it indefinitely we'll eventually have to reach terminal velocity, so if we keep getting higher with a longer rope, we eventually should be able to gently slow down the fall.
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.
What happens if you add an actual shock absorber to the line? Shocks made for motorcycles might provide the right amount of damping force, and shouldn't be too expensive. Obviously it is extra kit that you don't want to carry on a climb; but if it can provide 3kn or 4kn deceleration over a few inches, rather than a sharp peak of 7kn+, that makes a big difference.
A Yates Screamer is a (single use) shock absorber designed for climbing and also used by some rescue teams (albeit in different ways). Most models activate at 2kN, while the Scream Aid activates lower and I’ve seen other models that are made to activate at 2.5kN. Different Screamer types will reduce the force by different amounts by design.
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"
More than a couple times in my life I've set up a toprope or rappel on hangars a foot or more down an edge by laying down on the edge and clipping to the hangars with a dyneema sling "for safety". I'm 205ish lbs. I'd heard that you're not supposed to get above the anchor with a static line, and some of those edges were a bit sketchy and I feared I'd actually fall on my sling, but it seemed like a three-foot drop couldn't possibly be that bad. I'm definitely switching to a dynamic tether after this. Thanks for possibly saving my life here. Also, if anyone has suggestions on how to more safely rig those types of setups, I'd love to hear them.
The key to being safer setting things like that up is to have another rope, usually another piece 50 feet long will do it. You find something to attach it to back from that edge and belay yourself with it to get to the top-rope anchor.
Bobby has a video for setting up toprope anchors from above on his own channel. Recommends belaying yourself on a static rope anchored to a rock or tree at the level where you're setting up.
You could pre-rig (& backup) your rappel on the rope, then clip the middle of your rope as your tether. A sling on the bolt makes a handy step down into the rappel position.
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).
I would really love to see via ferrata sets on the fall tower! See this video for inspiration: ua-cam.com/video/A5w9Kkd-f2w/v-deo.html Your episode is a clear proof why you should never ever use a rope on a via ferrata. On via ferrata it may happen, that you have a fall factor way higher than 2:1. Imagine you have 1meter rope on your harnest and you have a distance between the anchors of you steel rope of 2m, you may fall 4m with only 1m rope in your system. 😮 There are two things that i would like to see: A) how does the via ferrata set compare to a short rope like you have in this video with a person of ~ 80 kg and a fall of 4m. Would you survive with a via ferrata set? B) how is the load on a via ferrata set with a fall of 2m until the set reaches the anchor with different weights. (Maybe you can reproduce this with an attached static rope?! These sets do only work greater that 40kg . They are told to be deadly for lighter kids i.e. 25kg. But what is the difference if you weight 60, 80 or 120 kg?
I'm wondering why people still drop static weights (metal, stones, similar). It has nothing to do with the actual physics on the rock (or in the cave). If you drop your metal weight into a bomber metal chain setup that is lengthening nearly zero, you will end up with nearly infinite forces (according to math), even if your drop is just a few inches. If you do the same factor 2 drop with your own body, nothing will happen. Your body can easily deform enough to absorb a 2-inch fall in no matter how static material. But this ability of our body in this calculation is a constant, while the energy is linear to the length of the fall. So, if you fall 5 meters, you can already nearly neglect the deformation factor, as the deformation from 5m drop into static stuff will definitely kill you. But it will not at 2 inches, no matter how static the material, just because the movement in your body will make sure the forces are tiny. Your center of gravity will decelerate very slowly, e.g. by limbs moving down. That's why some mountaineering associations are experimenting with more useful setups, like dropping lorry tires made of rubber or similar things that behave more like humans. At least I typically go climbing with humans, not so much steal weights ;) On the other hand static loading IS interesting when it comes to fancy accidents like having a heavy flake with a bolt in it come loose and falling down, with that bolt happening to be one of your main anchoring points. Stuff like that happened.
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!!!!" 😅
13.31 kN / 9.8m/s² = 1360 kg. Not sure what rope that is, but I found a Sterling 9mm polyester static rope that says it's 62 g/m. So 1360kg / 62g/m = 21935m. Roughly twice the max cruising altitude of commercial airlines.
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.
The photo that introduces the video: That’s real life. While doing what he is doing in that photo may not be wise. It’s absolutely nothing like the drop-tests. If he fell in the position of the photo. He would basically lean back, the rubber from his shoes would take most of his weight and he would barely generate any force on the anchor. Typically- (hopefulluy) the way we use lanyards/personal anchors are a means to prevent catastrophic slipping from generally safe stances. We don’t use them to catch factor 1 or 2 lead falls. Because of the nature of the stances where we typically use lanyards - They just don’t have an opportunity to receive enormous forces. The Petzl product would be used for jugging (lot’s of rope out). It wouldn’t be used for say via-ferrata. Petzl has products for via-Ferrata that have built in shock absorbers.
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.
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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.
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).
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
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.
Plenty of cow tail jokes, but this video left me wanting some cow tales too.
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.
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.
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
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.
Gotta love the "perfect descent" bit. Hilarious.
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.
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
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.
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!
really enjoyed the format!
you keep on improving with each episode!
Great episode!!!
2:27 buy new mattress. I recommend sandwich construction with multiple hardness/softness levels and definitely with one or 2 layers of memory foam.
Wow, that is very educational. I'd not been aware of these extreme force risks. Thank you
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.
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.
Thanks for the grammar/spelling lesson Jon, you legit had my five year old absolutely riveted!
I'm so happy you called them "cows tails!" That's what we called them when I first started climbing. All the people I climb with now have never heard that term, I started wondering if it was in my head. 😂😂😂
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 :)
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).
The unstitching feature of the spelegyca was in the petzl product description (even if its not a good enough absorber)
The cow jokes made this video amazing!
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.
One of the most important videos for any climber to watch
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.
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
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.
Same knot gives you a bigger percentage of total rope stretch in the smaller system therefore affecting the overall result in said system.
Man John really is a spelling bee rap god!
Next I wanna see him spell out as quickly as he can:
"Cow's tail! Cows' tails! Cow's tail? Cows' tails?" three times in a row.
Keep nerding out guys! Awesome stuff as always!
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 🤣❤️
I love this channel.
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.
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
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
Very good video, thank you for all. I translate your video for via ferrata people how climb with cow-tails so with out absorber choc 🤙
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.
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.
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.
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.
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.
This shid is super interesting, thanks Jenksie
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.
You got to do more arborist gear stuff
Be interesting to see this done with the ever popular caving barrel knot instead of fig 8s.
It's a good case for keeping your tethers short, so if you do fall on it it's not as bad. I just use alpine draws, but still wouldn't want to fall on them.
"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.
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.
so glad you are using the term 'caving' / 'cavers' etc. and not the dumb 'spelunking' word!
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.
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.
There will be a cross over on rope length for the force of a factor 2 fall. Below a certain length, you will not reach terminal velocity, reducing the speed that you are catching. Until you reach terminal velocity, the potential energy will increase. The elongation of the rope - time that the force will spread out - will increase with the length of rope, though I imagine there is another point at which this also drops off.
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.
that grey hair coming out now looks really good on you imho. gives you even more authority:)
Also ghe knots are the same for the long/short tails, so on gje long tail ghe knot is proportionally less impactfull
Have you got any data on how many km of a nylon rope vs an aramid rope vs an aramid-coated rope it takes to wear through belay devices to their safety limit marker? be interesting to see how toothed devices (including ASAP style devices) fair up against different ropes too. Replacement/repairability of devices? just a thought!
While this seems neat, I can tell you from caving that ropes utterly glazed in mud wear out ascender teeth after a few miles of rope climbing. No aboveground scenario comes close to that level of abuse, sans maybe slopeside stabilization. I reckon it would take a machine running rope in an infinite loop, and going constantly for months, to wear out teeth using clean ropes....
All that said: I hope that ropes are being chosen first and foremost for their physics based on the rigging, rather than paying any mind to how they affect a consumable item like an ascender. 🤷
@@rachelhasbruises 20 years in industrial rope access... kevlar seems to chew metal quite badly. geotechnical is the testing ground for robust kit. If you can't jump on it, it shouldn't be there
Thx!
2:25 🤣 i can totaly relate to you ;D
Try sleeping in a Yucatán hammock fixed my back. I sleep like a rock now.
That whole video made me hurt just WATCHING it.
commented too soon. Good to see Ryan getting a perfect descent line back in.
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?
Super nice enought Video!!!
When knots start to soften your fall, you know something's wrong, or about to be very wrong.
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.
I think that the ratio between his much rope is in the system and how tall is the fall is not the main factor.
The tablet the fall the more speed that you'll get, if we go back to a newton bein Kg*m/s^2 we can see that if we take your weigh multiply by your speed and divide it by how fast you come to full stop will give us a really close number how how many Newtons will be in that change of speed.
The rope here is basically a spring that had the capacity of elongate and slow you down a little while doing so, that's what happens when rope "dissipates" force. But any additional speed will translate into force when we come to full stop.
Summarizing a 10m rope can "dissipate" so much energy, all the remaining energy will it is when we come to full stop.
Adding 1 meter of rope will increase how much energy it can dissipate.
Falling 1 extra meter will allow us to gain more speed during the fall,
If we keep a ratio of 2m if rope by meter of fall the final KN will keep getting higher.
If we keep doing it indefinitely we'll eventually have to reach terminal velocity, so if we keep getting higher with a longer rope, we eventually should be able to gently slow down the fall.
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.
What happens if you add an actual shock absorber to the line? Shocks made for motorcycles might provide the right amount of damping force, and shouldn't be too expensive.
Obviously it is extra kit that you don't want to carry on a climb; but if it can provide 3kn or 4kn deceleration over a few inches, rather than a sharp peak of 7kn+, that makes a big difference.
A Yates Screamer is a (single use) shock absorber designed for climbing and also used by some rescue teams (albeit in different ways). Most models activate at 2kN, while the Scream Aid activates lower and I’ve seen other models that are made to activate at 2.5kN. Different Screamer types will reduce the force by different amounts by design.
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"
I've always called them chicken slings...
I use the petal as my cowtail. But when I use it there is never any slack. So there is no fall factor
More than a couple times in my life I've set up a toprope or rappel on hangars a foot or more down an edge by laying down on the edge and clipping to the hangars with a dyneema sling "for safety". I'm 205ish lbs. I'd heard that you're not supposed to get above the anchor with a static line, and some of those edges were a bit sketchy and I feared I'd actually fall on my sling, but it seemed like a three-foot drop couldn't possibly be that bad. I'm definitely switching to a dynamic tether after this. Thanks for possibly saving my life here.
Also, if anyone has suggestions on how to more safely rig those types of setups, I'd love to hear them.
The key to being safer setting things like that up is to have another rope, usually another piece 50 feet long will do it. You find something to attach it to back from that edge and belay yourself with it to get to the top-rope anchor.
Bobby has a video for setting up toprope anchors from above on his own channel. Recommends belaying yourself on a static rope anchored to a rock or tree at the level where you're setting up.
You could pre-rig (& backup) your rappel on the rope, then clip the middle of your rope as your tether. A sling on the bolt makes a handy step down into the rappel position.
Can you test a factor 2 on a semi-static traverse line?
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)
Also, why do you use a webbing for personal anchor instead of rounded rope?
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).
The knots have a bigger impact on short links
Can you strength test the petzl zigzag and compare it to prussic
Greenscreen at 4:10? Or does the blurred background just look weird?
Did you guys ever tested the Petzl adjust?
Any plans to do a cowstail test like this with a 200lb load?
U need to test cowstails with shocks absorber in the system
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.
hey did u try the beal jocker 8.5?
I would really love to see via ferrata sets on the fall tower! See this video for inspiration: ua-cam.com/video/A5w9Kkd-f2w/v-deo.html
Your episode is a clear proof why you should never ever use a rope on a via ferrata.
On via ferrata it may happen, that you have a fall factor way higher than 2:1.
Imagine you have 1meter rope on your harnest and you have a distance between the anchors of you steel rope of 2m, you may fall 4m with only 1m rope in your system. 😮
There are two things that i would like to see:
A) how does the via ferrata set compare to a short rope like you have in this video with a person of ~ 80 kg and a fall of 4m. Would you survive with a via ferrata set?
B) how is the load on a via ferrata set with a fall of 2m until the set reaches the anchor with different weights. (Maybe you can reproduce this with an attached static rope?!
These sets do only work greater that 40kg . They are told to be deadly for lighter kids i.e. 25kg.
But what is the difference if you weight 60, 80 or 120 kg?
BREAKTEST THE AUSTRIALPIN COBRA BELT BUCKLE!!!
I'm wondering why people still drop static weights (metal, stones, similar). It has nothing to do with the actual physics on the rock (or in the cave).
If you drop your metal weight into a bomber metal chain setup that is lengthening nearly zero, you will end up with nearly infinite forces (according to math), even if your drop is just a few inches. If you do the same factor 2 drop with your own body, nothing will happen. Your body can easily deform enough to absorb a 2-inch fall in no matter how static material. But this ability of our body in this calculation is a constant, while the energy is linear to the length of the fall. So, if you fall 5 meters, you can already nearly neglect the deformation factor, as the deformation from 5m drop into static stuff will definitely kill you. But it will not at 2 inches, no matter how static the material, just because the movement in your body will make sure the forces are tiny. Your center of gravity will decelerate very slowly, e.g. by limbs moving down.
That's why some mountaineering associations are experimenting with more useful setups, like dropping lorry tires made of rubber or similar things that behave more like humans.
At least I typically go climbing with humans, not so much steal weights ;)
On the other hand static loading IS interesting when it comes to fancy accidents like having a heavy flake with a bolt in it come loose and falling down, with that bolt happening to be one of your main anchoring points. Stuff like that happened.
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!!!!" 😅
What about factor 1?
oh here’s a question for thought how long would that green static rope have to be before it would break under its own weight.
13.31 kN / 9.8m/s² = 1360 kg. Not sure what rope that is, but I found a Sterling 9mm polyester static rope that says it's 62 g/m. So 1360kg / 62g/m = 21935m. Roughly twice the max cruising altitude of commercial airlines.
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.
I want to come out to California just so I can have you drop a live human a little bit
hi can you test the cowtail rope by using petzl shunt and s.tec duck and test it on the semi statics rope
ua-cam.com/video/M2a1zdpScPo/v-deo.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
The photo that introduces the video: That’s real life. While doing what he is doing in that photo may not be wise. It’s absolutely nothing like the drop-tests. If he fell in the position of the photo. He would basically lean back, the rubber from his shoes would take most of his weight and he would barely generate any force on the anchor. Typically- (hopefulluy) the way we use lanyards/personal anchors are a means to prevent catastrophic slipping from generally safe stances. We don’t use them to catch factor 1 or 2 lead falls. Because of the nature of the stances where we typically use lanyards - They just don’t have an opportunity to receive enormous forces. The Petzl product would be used for jugging (lot’s of rope out). It wouldn’t be used for say via-ferrata. Petzl has products for via-Ferrata that have built in shock absorbers.
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.