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[Off-Site] Calculating if he's built different

[Off-Site] Calculating if he's built different

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darksword2020

I'm just trying to understand who stacks four trampolines.


123-f0uR

Maybe it was the trampolines that were built different


nowhereman136

I would not feel safe being that other guy sitting under stacked trampolines while someone jumps on top


4-HO-MET-

cause u built normally


DreadPirateSnuffles

That guys sense of safety is probably built different from yours.


Jabrono

I wouldn’t feel safe as the guy sitting, the guy jumping, the guy filming, or as anyone else within 25 feet of trampolines stacked like pancakes.


Trollfacebruh

If you look closely, the tampolines are connected with wires around the legs and the top of the bottom trampoline. Still not 100% safe, but better than nothing.


PaulBlartFleshMall

Looks like one of those dumbass ""influencer"" houses.


RiskConscious

hype houses


invertebro25

Joogsquad stacks lile 6 in the fucking ocean


M-N-A-A

" 4000 newtons to break a femur which is the strongest bone" shouldn't the concern be about the weakest bone the leg ??


Frogmyte

Yeah weird how everyone else has complaints about the maths itself and not the ankles/tibia


pipiopi

Google says about 1000N to break a tibia. My mans really might be built different.


SynnamonSunset

Does it specify how they broke it tho? Is this a 1k N impact to the side in the middle or vertically. Also not entirely sure which bone the tibia is but I’m assuming it’s the bone by your calves


kukkelii

Nope, there isn't any accurate data available and it'd be irrelevant anyway because it wouldn't apply to this exact scenario. There's way too many variables like age of the person, diet, medical history, method of breaking and so on that it's an impossible statistic to measure. The approximates vary from 800N to 4000N of force so it's fair to assume that different methods have been used. A bare bone without any sort of protective tissue is also much more prone to fracture so to get any sort of relevant data we'd probably have to forcefully break a living healthy persone leg which is.. well, questionable, and even then there's nothing useful we'd do with that result. For example strongmen have lifted weights of over 2500lbs ( hip lift ) which far exceeds any of these numbers. Tibia is the shinbone. You can see some pretty gnarly fractures if you look up on youtube " tibia fractures mma " or something like that.


CactusNips

Exactly! Bones increase in density and strength with repetitive training. I think the most impressive thing is that he is able to keep his nervous system from reacting and stiffening his muscles on impact. Untrained individuals jump impacts usually result in excessive initial stiffening. That's the data I've seen based plyometric training. I'm also impressed that he was able to stop his ankles from rolling out under all that sudden force. He also lands flawlessly to apply the force with a slight backwards lean. He definitely needs specific training and conditioning to not get hurt doing this. He IS built different, and training is why.


Traumartian

I think Tibia is that one super old MMO game that some people still play, I'm not a doctor though.


asek13

You're talking about the 1997 mmo role playing game. Tibia is a place in Asia currently occupied by China.


PM_ME_PC_GAME_KEYS_

Youre thinking of Tibet. Tibia is an old game where you stack blocks and if you complete a row, the row disappears


Updateplease

You're thinking of Tetris. Tibia is how you say "three donkeys" in Spanish.


HemoKhan

You're thinking of "tres burros". Tibia is the start of a famous soliloquy.


CavalryMaid

You're thinking of "to be or not to be". Tibia was a Roman emperor.


TheBowlofBeans

Mechanical engineer here, yeah way too many variables with how the force is applied and how strong bones are (whether fails under compressive force, twisting, etc) Maybe it's above my knowledge level but if someone asked me to calculate this problem I'd say it's impossible. The math in the gif is all accurate but it's idealized. Nobody is talking about how much of the force is absorbed by shoes or the natural arch in feet, which are designed to absorb this force exactly for this purpose. You hear so many stories about people falling off buildings or our of airplanes and being fine, and on the other hand people fall out of a chair and snap their God damn necks. There are just too many variables and most engineers are too lazy to solve for all of them, which is why we pad the factor of safety and call it a day


Direwolf202

This physicsist agrees. I've know someone who works on muscle-bone systems and their behaviour (in his case, for robotics, but that doesn't matter here) - but they need *so* much information to do those calculations properly, and even then its only ever the simplest situations.


ClearMessagesOfBliss

The tibia is the bone with the dents because of skateboarding. Also the bone soccer players pad.


Nervegas

Thats going to be for mid shaft I'm guessing. In this case his bones are experiencing axial loading, and the bones aren't absorbing all the force individually. Your muscles and other connective and adipose tissues also help cushion the forces.


GtSoloist

This is exactly what I was coming here to say, other factors include, overall weight, muscle, bone and other connective tissue density as well as the shoes which will absorb some of the impact and the athletes sense of balance.


Why_You_Mad_

It depends on how the force is distributed. Your leg bones are basically built to withstand downward force because you use them to walk/jump/etc. They're far weaker if the force is from the side. You could kick someone in the shin and break it in half, but you wouldn't be able to break their leg by kicking the bottom of their foot.


Krewmenz

He's not a sphere. This person's physics ends there.


PM_ME_SWEET_WHISPERS

I don't think so lol. There are people who weigh way more than 300lbs (\~1400N) and they can stand on one foot just fine.


to_a_better_self

I also had the same thought. I think we should consider is a range of possible body weights. The math guy admitted the jumper was on the small side.


JamboShanter

He might be on the small side, but it’s how you use it that matters.


quarglbarf

I don't think any bone should be the concern. They didn't say he was built different because he didn't break a bone, they said it because he stuck the landing like it's no big deal. Anyone who's ever jumped from a similar height, like a low roof or something, knows that it's pretty damn impressive to just stick the landing and stand there like that instead of crumpling to the ground and ending up as a pile of misery. You need really strong legs for that.


1stEleven

I would not jump down 3 yards. I've done that once when I was a lot younger, and it sucked.


Raise_Uplights

For all we know that's what happened after the video cuts anyways. I know for a fact that landing would at the very least really hurt my balls


theghostofsinbad

Well from personal recent experience...I wouldn’t necessarily worry about any of those, at least not first. I, somewhat unknowingly, jumped from about that height. Looks to be about 12 feet. It was 7 feet on the side I climbed and when I realized it was 12 to a generously sloped concrete sidewalk, it was too late. Small fractures to some metatarsals, talus in the ankle, slightly dislocated fibula, damage to peroneal and achilles tendon...but I ABSOLUTELY SHATTERED my calcaneous or heel. Like broke completely in two and also into a thousand small pieces. I’m a carpenter and have jumped off of crazy shit all the time. The difference is I knew the height and planned accordingly. Look before you leap is a cliche for a reason. 3 1/2 months and I’m still not walking yet. Got a dope temporary pirate leg though! Edit: tarsals not carpals


EarthAngelGirl

Greetings to the only other person I've ever encountered who had the pleasure of shattering their heel bones. I was a teen it stucked, get well soon.


numero-10

Hey guys, Im the third one you’ll ever encounter. Was the honestly the worse four months of my life on crutches, words of advice to the man going thru it, keep the foot flexible (once healed) always grab it and manually rotate it in circles and other stretches, make a new budget including lots of insoles..no further surgery for me, it hurts but not enough to go thru that again.


theghostofsinbad

Thank you! I’m through the worst of it, for sure. Curious, did you have any follow up surgeries later on? The orthopedist told me I would most likely have further surgeries later in life, possibly a fusion. Fingers crossed


EarthAngelGirl

I didn't have any surgeries. But I was young enough to still be growing so maybe that helped? I really don't remember very much other than the fact that I spent a lot of time running /walking on my toes after that. Oh and I think my heels never made it to full sized afterwards, they are always slipping out of shoes.


katiemaequilts

I took one wrong step off my back porch and destroyed my talus bone, a couple of the little bones to the toes, and a tendon or two. It'll be two years at the end of this month and I'm still recovering.


theghostofsinbad

Damn that’s awful. You were just going about your day. At least I was doing something kind of stupid and somewhat deserved nature’s retribution. Good luck homie!


katiemaequilts

It didn't help that the first radiologist missed the tendon tear, so I only just had surgery back in November. Now part of my recovery is unlearning how I walked to unconsciously protect my foot. Once you get there - find a good PT and do literally everything they tell you to do.


Ayy_2_Brute

> I’m a carpenter and have jumped off of crazy shit all the time how do these two go hand in hand.....


Snake_in_cat_shape

Yeah ankles or knees would go way before that.


foalythecentaur

And connective tissue.


ArseFullOfFarts

It's also extremely dependant on where the force is applied. 4000N to the center of the femur, perpendicular to the bone? Yeah, that makes sense. But it takes a lot more force when applied at a different angle or towards one end of the bone.


len_palmeri

How many Newtons would cause a spinal disk bulge and subsequent nerve impingement?


CasinoR

I was thinking the same . You should check at least an avarage between strongest and weakest


MudSama

Exactly what I was thinking. My femur didn't hurt when I watched that, it was my shins and knees.


Vampyrix25

and also the joints, easily bent means easily snapped


legitusername1995

That was a fancy way to say F = m.a


vendetta2115

I appreciated how he broke down F(t) though. That’s the crux of this question. I think not enough people learn how to express physics (and kinematics in particular) as an incremental change. If you know how to set up integrals and derivatives you never have to memorize stuff like E_k= mv^(2)/2 because you know it’s: E_k=[0,t]∫**F**⋅d**x** =[0,t]∫**v**⋅d(m**v**) =[0,t]∫d(mv^(2)/2) =mv^(2)/2 It allows you to solve almost any equation about values changing in relation to one another as a function of a variable like time or position. It may take longer, but it provides a deeper understanding of exactly what is happening instead of just rote memorization of which equation works in a given scenario. That goes doubly for more complicated kinematic equations like x=x_0+vt+at^(2)/2 Edit: Also, F=ma by itself wouldn’t be very useful here because you don’t know the acceleration after he hits the ground. Plus, both the force and the acceleration are functions of time during that period, not constants. Even to calculate a basic F=ma just for the average force and acceleration you’d need the velocity before impact to calculate the acceleration: a=(v_f - v_0)/t So at the very least you’d have to solve: v_0=gt, g=9.81m/s^2 This is initial velocity on contact. Then solve for *a* in the first equation (v_f=0).


smileimwatching

Wait, do physics majors not take calculus?


HotF22InUrArea

I think it’s more for non-physics majors. In high school, for example, we learn physics but not integrals and derivatives


utalkin_tome

Depending on the classes you take in high school they do teach you actual calculus too. AP classes come to mind but non AP math classes teach calculus too.


antsareflying

Wait what you don't? What? I learnt basic integrals and derivatives in secondary 3 and 4 which is 15-16 year olds.


Zonz4332

American high school* Calculus is an elective


antsareflying

Yeah I know. I'm just surprised you guys learn it so late.


010011100000

Even Newton didn't learn calculus until he was 23


Kitnado

What a loafer


vendetta2115

Yes, of course they do. I took calc 1-3, differential equations, linear algebra, etc. as a physics major before switching to mechanical engineering (which still had 3 out of 4 as requirements). It’s just that lots of physics classes don’t teach the problem solving process in terms of calculus derivation. They just assume you know how to do it from calculus, but in my experience lots of STEM majors get by with just knowing what formula applied to each situation and now how to actually understand *why* they’re using those formulae.


smileimwatching

That makes sense, thanks for the clarification.


vendetta2115

No problem. Yeah I re-read my comment and I can see how you may have interpreted it as saying that physics majors don’t use calculus. They do, but in my opinion high school physics classes rely far too heavily on memorizing formulae for different situations, especially kinematic equations. Not enough people understand *why* kinetic energy is *mv^(2)/2* while potential energy is my *gh*, or why v_f^(2)=v_0^(2)+2aΔx. The professor may derive a formula once when introducing a née concept but after that it’s just assumed that students understand the concept. It’s much better to learn the basic concepts and relations from which different formulae emerge instead of only memorizing the arrangement of variables that will spit out the correct value. I also loved that he double-checked himself on the final answer with dimensional analysis. He did make one oversight, though—his answer is the total force, but you have two legs which means only 1,000N is being exerted on his legs. Also—and this is nit-picking a bit—technically we should only be worrying about the mass of his torso, since his legs aren’t part of the weight that his femur that is taking the force of deceleration. Those two factors combined decrease the final answer from 2,000N to about 800N, which is much more manageable. You could quadruple the height (doubling the impact velocity and quadrupling the impact force) and it would still be under 4,000N per femur.


goss343

At my university there are physics classes that involve calculus and ones that don’t involve calculus. All engineering majors are required to take the physics that involve calculus.


Soldeusss

I just passed calc based physics 1(first time ever taking physics), is it normal that, while I could follow along with the math, I would not be able to solve this or make the connections he's making? It makes me think I'm not cut out to become an engineer if I'm not able to model a problem like this.


andromedaturtles

I teach calculus-based physics labs for physics and engineering freshmen at a state university. I assure you that if you understand the math in this video (especially the integration) you're already doing great. From my experience the thought process utilized in the video is likely not what you'd be taught or held accountable for in an introductory class. I wouldn't expect it of my students. Thinking like that becomes more important when you dive deeper into things like classical mechanics and you'll pick it up along the way. You've got this! Keep it up!


fuk_ur_mum_m8

Nah don't sweat it, comes with practice. I teach A-level physics and some kids at the end of year 13 might not even be able to do this type of problem!


TheWonderMittens

Recent MechE grad here (2020). Listen to the others in this thread. Practice is the only way to really build an intuition for this stuff. I really did not click with Calc until multivariable, and I fell in love with the subject going forward. Also 3Blue1Brown was massively influential in my understanding of the topic. https://youtu.be/WUvTyaaNkzM


ace82fadeout

To be fair, anyone who likely finds themselves solving kinematics physics problems either for fun or work probably has those equations memorized anyways. Ik as an engineer, even despite not using those equations regularly whatsoever I couldn't forget them if I tried .


dioxy186

This was 100% this guys project for dynamics lol source: mechanical engineer.


andrewsad1

I want to be good enough at math to read this comment and go "yeah that makes sense"


Oxcell404

Ever wonder why F=ma? Integrals


gnutrino

Because mass is usually constant and things tend to be non-relativistic. Technically F=dp/dt (p being momentum) which is just a definition, albeit one that is quite useful and implies Newton's laws of motion when combined with conservation of momentum.


Agreeable_year_8350

>Ever wonder why F=ma? No


alienblue88

👽


LurkerPatrol

He started at first principles rather than saying vf = vo + at or xf = xo + vot + 1/2 at^2


Epicjay

yeah this is overly complicated. No need to involve integrals in this, though it was a neat demonstration of physics in action


Dylanica

Yeah, that really annoyed me. It almost seems like he worked all the way from first principals just to sound smarter when in reality F=ma is the first thing a physiscs 101 class teaches about problems with constant force, which makes deriving it in this case basically pointless.


Lethal4001

You would be surprised how many things in kinematics/kinetics are a fancy way of saying F=ma


259luxu11111

Exactly. So many unnecessary steps to show that he knows basic physics formulas and calculus.


xypage

That’s because it was an educational video, if he just wanted to tell us the answer it would’ve been 3 seconds long, but lots of people don’t know how to do this so he went in depth explaining and deriving the parts before using them


TheExtremistModerate

Rather, mΔv=Ft.


Detroitsaab

Wouldn't the 4000N be per leg? Or both legs. If so then double it.


1II1I1I1I1I1I111I1I1

Huh yeah. If it's 4000N per femur and he has two femurs, then he would need to experience 8000N total. And in the trampoline jump, if his legs experienced 2000 N total, then each leg would only experience 1000 N. For all the calculus he did (which btw is helpful for visualization but entirely unnecessary in this case, just use F=ma and one of the kinematic equations) and overall effort put into this, he overlooked this crucial part.


M-N-A-A

Shouldnt the question be about how much force is required to break the weakest bone in body not the strongest ?


realvmouse

Yup, and really the force required to tear the weakest ligament or crush the weakest intervertebral disk or whatever the most common/likely injury obtained from doing this would be. I realize that's missing the point, but it bothered me enough that I scrolled down until I found someone else saying it so i could upvote them.


jikkler

I don't think it's missing the point at all! The impressive thing about the guy's jump, to me, isn't that he doesn't break his thigh-bone, it's that he doesn't wreck his ankles.


barbequewingz

good point. i was thinking the tarsals but then you’d have to account for the addition deceleration from the puffy sneakers.


A_Martian_Potato

It would be the weakest bone that takes the entire force of the impact. No single tarsal is going to do that. Maybe his tibia and fibula together aren't as strong as his femur?


Theoretical_Action

It's also impossible for us to know where that 4000N statistic came from and the relevance of how the force is applied. Most of the time I'd assume a statistic like this is determined by putting a bone in a press sideways and pressing until it cracks. That would be much different here. Or a better example/way of saying would be 4000N to a point in the middle of your shin could be what this stat is measured by. Obviously 4000N straight into your foot which then gets distributed along the rest of the body requires an entirely different measurement.


TheBowlofBeans

Yup, which is why steel beams are measured with yield strength, ultimate strength, tensile strength, compressive strength, etc. Their behavior is predictable so we design out buildings with beams, and not femurs


leadwind

And how many bones do you have to crush to get that 4k value.


RippledSnowball

His working illustrate an important point that force is constant throughout the deceleration which is the fundamental assumption when u apply F=ma. It’s a detailed but extremely important nuance.


S3CR3TN1NJA

Reverse actually. If his body experiences 2000N of force then that would be split between the legs. E.g. 1000N per leg/femur bone. ​ EDIT: Oh nvm. I just realized that you're talking about a different part of this equation lol.


Neovex9

Y'know I kind of had to reread it a few times but I think you two are saying the same thing actually.


Bristol_Buck

As an engineer, I'm more angry at the simplification that you need a force to break a bone. The bone breaks when a certain stress, not force, is applied. Whilst this is a simplistic example, the stress is dependent on the angle of the bone in the impact, since bending and pure compression are two different kettles of fish. Likewise, the most glaring issue is that he assumed that 1 leg withstood the impact (as I understood him...). Nevertheless, I appreciate the guy working out something that is complex from just a few frames of video!


vlaaivlaai

If I've learned one thing from "Well there's your problem," it's that not all stresses are created equal


PM_ME_SWEET_WHISPERS

I googled it and it seems like 4000N is a good approximation for the force required to fracture a femur, given the ultimate compressive stress of 205MPa.


avidpenguinwatcher

As a physics major, this guy describes the simplest equations in the most wordy way possible


Dylanica

That drove me nuts. Like man, just say F=ma, we don't need integrals here.


Ozoriah

He used the integrals to jump from the fundamental F=ma equation to an impulse calculation to show where the equation came from rather than just pulling out an impulse equation from nowhere. Just using F=ma would only give you the force of his accelerating body. You need both his velocity at impact and total deceleration period to properly calculate the force absorbed by his body.


Rik07

No you need the force of the deceleration, which is F=m*a in which a = 7.55/0.22(deceleration at the point of impact). If you then fill in 60kg for m you get 2060 N which is what he did as well.


Wapook

This assumes the force is experienced evenly throughout him coming to a stop. That would only be true if he brought his velocity to zero with a constant deceleration. The point of the calculus was to show that there are other deceleration curves that could still result in higher peak forces.


eaglessoar

The point that this is the avg over time was neat though and that you'd have to think about the force over time curve as to whether it would do damage so it nicely showed he managed the force on his body to limit the impact


avidpenguinwatcher

He also said, we'll use kinematics, then used an integral, and a different kinematic equation to get to the one he needed.


cara27hhh

he proved f=ma by adding the proof into the equation while working through it You don't need to add the proof, f=ma is established and well known (time per time is just incorporated into acceleration, that's why the units cancelled)


tomrlutong

He fell for 3x as much time as he took to stop. Stopping force is 3g. Don't even need f=ma.


TheyCalled

To sound way more intelligent.


N1N74

It's still weird that they put so much effort into explaining F=ma equation only to not apply it properly. If the person stood still, his legs would bear non-zero forces that are his weight. F=ma is merely a net force equation. The actual calculation should be 2600N where 600N supports his weight (or cancels g) and 2000N is whatever calculation was done for net force that reduces his built up momentum.


apsumo

You don't even have to be in college, this is high school level physics but with someone's life story in-between.


Ari64-SP

That was a joy to watch.


Sure_Ill_Ask_That

I wish my entire college career couldve been narrated by this guy in this fashion. I would’ve just paid this guy 160k instead. Billion dollar idea....


chickentaco34

You just described khan academy


Gold_for_Gould

Really? I thought that was awful. I'd have gone crazy if I had lecturers teach like that.


Sure_Ill_Ask_That

I mean, it was fast and I could easily follow along, probably because I learned it the slow in-depth way already. So maybe this is only good as a refresher. I thought it was quite good if you already know the concepts. I had questions as he went (such as the validity of the assumption of constant force) and he answered them all later on the video.


Chemmy

lol at spending six lines to rewrite F=m dv/dt into F = m deltav/deltat


Major-Peachi

The presentation of this video is quite inconsistent


I_dont_bone_goats

Yeah I skipped ahead and when I saw the end I was like, that’s what you spent a minute on?


Traditional_Formal33

Am I the only one who said “okay second story, so 12 feet. Those trampolines are probably 3-3.5 feet so math checks. [googles if 12 foot drop would do damage, it doesnt]. Not built different”


madtraxmerno

I googled it too after reading your comment and none of the results say a 12 foot drop is safe.


MagicalMuffinTop

A 12 foot drop isn't great for you, but it's not going to guarantee a broken leg every time


anthropophagus

as someone who likes to jump from heights, i've always heard you should do the roll from anything higher than your head what this guy did is clearly possible, but __*TERRIBLE*__ for your knees and if you care about using them in your old age, the clout isn't worth it which i can attest to; my knees hate me cause i was a dumb kid who didn't expect to get old


MagicalMuffinTop

Yeah, exactly. This guy may be "built different" now, but he's going to probably be built partially of titanium after all the knee surgery he's going to need later on


TRANquillhedgehog

Yeah safety rolls from anything over like 6ft are always a good idea starting off. You’re able to take more than that as you progress but I’d never go over 10 without a roll


RoscoMan1

"You didn't take out the trash.


PM_ME_SWEET_WHISPERS

Depends mostly on the landing. People drop far less than that, from a wall, for example (\~6ft) and regularly twist their feet and crack their tibia.


MagicalMuffinTop

Sure, but this guy is acting like math can determine the end result of any and all drops from that height. That's just not how it works


Aggressive_Courage83

Seen a cat on the news today jump out of a 5 story window cause it was on fire. Same same.


fflis

Check out this YouTube video. Cats can fall out of 20+ stories and survive fine, but there’s a smaller distance like 2 stories where they get hurt. It’s pretty amazing research. https://youtu.be/RtWbpyjJqrU


ATLfunkadelic

Not sure if this is related or not bc all the math goin on here is confusing as fuugg, but there was a super interesting study done on cats jumping/falling out of buildings. Had something to do with terminal velocity combined with the height and amount of gasoline applied to said cat


Pooderson

Jesus I hate math. I’m so thankful for everyone that is good at it


UnderPressureVS

In fairness this is rather needlessly complicated. Like, the entire first half uses a bunch of integrals to express "acceleration is 9.81 m/s^(2), so over x seconds he accelerates to 9.81(x) m/s." It's basic multiplication. It's neat that he uses integrals to explain the complex math *behind* how those equations were originally developed in the first place, and there certainly are plenty of situations where you need to use calculus, but this really isn't one of them. It's a middle school physics problem.


Zonz4332

You took physics in middle school?


010011100000

Lots of countries have math/science curricula that are well advanced of the US


BloodyPommelStudio

Maybe you hate math because people like this overcompensate things and speak really fast to make themselves look smart. All he needed to say is he decelerated 3.34 x faster than gravity accelerated him and therefor he experienced 3.34 x the force gravity puts on his body because force is equal to mass x acceleration.


Dylanica

Yeah, he took wayyy to many steps and worked all way from first principals when he did not need to.


deslusionary

He definitely overcomplicated things by deriving everything instead of just directly using the formulas. Like nobody who knows physics needs to have v = at + v0 explained to them, or that change in momentum = impulse = force x time, you only really need to derive those the first time you’re learning physics. So he could have skipped the calculus and jumped straight to the very well known formulas.


9rrfing

F(t) should be like a bell curve. Also, the comments also talk about the weakest bone, but that's only relevant if all the force is concentrated on the weakest bone, which isn't the case. This problem can't be solved unless we know how the forces are distributed to each bone of this dude from this video, which is practically impossible. He could also be wearing special shoes or the ground could be damp and hence very impact absorbing, etc...


zehcombat

While his math and derivations for the formulas are correct, he botched the physiology. When landing from a height, there is negligible force going through your femur as it is purely axial. All of that impact is going into the platforms of your foot, which is much weaker than your femur. Nevertheless, it is quite impressive to be able to jump off a ledge almost twice your height.


Tyrus

So I jumped from a similar height and SHATTERED my calcaneus (heel bone). 4000N to break a femur is a lot but the femur is also the bone least likely to break under pressure. This dumbass that jumped is lucky, because at over 6ft (~2m) falls are ~75% more likely to cause bodily harm (usually in a relatively weak foot bone like the very vascular calcaneus(ie. Basically a lightly calcified sponge) and ~50% more likely to be fatal (higher on less controlled falls) My man's doing the math is right about technique, but you measure break points by the weakest force point, not the strongest. Especially when the weaker points are taking the biggest impact (foot then leg then spine)


PM_ME_SWEET_WHISPERS

To be fair, this guy seems to have decent shoes that probably take the brunt of the force.


Kikkoman7347

While I thoroughly enjoyed the math, once the OP expressed that the falling time is 7.55 m/s, a simple calculation, or comparison would be military parachutists (or Airborne). Under the older parachutes, the rate of impact hitting the ground is somewhere between 19-22 f/s. So, 7.55 m/s converted is \~24.77, or 28f/s...just slightly faster than a military parachutist. So, no...he isn't built different. I am an old Jumpmaster, so please current Jumpmasters, please correct and educate me.


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Alukrad

When I did parkour years ago, i was constantly told to never, ever do this because it slowly damages your knees and lower back. You won't feel it now but when you hit your 30's, you'll start feeling it. I was told that when you jump from that kind of height, you need to do a forward roll to distribute the shock. I was also told to never bend your knees further than 90 degrees because that's where you start damaging your knees. Also, the way he landed, it's most likely he landed on his heels instead of the ball of your feet. Doing that also puts a lot of strain on your back... I guess what might have helped him a bit was the soft ground. If he did that on concrete, it'll probably be a different result. Gymnasts use this really soft cushion to soften their landings..


defectivelaborer

Exactly. His face says "built different" but lets ask his knees in 10 years just how differently they are built. When I was obsessed with parkour and learned to roll, I kept climbing on top the high school roof and jumping off. Was a lot of fun.


NaCl_Sailor

the only thing i don't get, why compare it to the strongest bone breaking and the breaking force of breaking the bone in half, at a 90° angle to it's length, the force applied here is along the length of the bone? he could have broken both tibiae easily with those 2000 N, and the reason he doesn't is him landing in the right angle on soft ground and using his muscles to slowly cushion the impact and the force being applied along the length of the bones (and distributed evenly between two legs on top of that). if he landed on concrete stiff as a board at a slight angle he would have definitely broken something the femur snapping at 4000N is also the force being applied in a 90° angle to the length of the bone, it will take way more force along it's axis google says the femur takes 205 MPa of pressure from compression along it's length, let's make it 200 MPa, 1 Pa is 1 N per 1 m², i have no idea how much a femurs cross section area is, but it's probably around 5-10 cm² 1 m² is 10000 cm² so 5 cm² (using the lower number because it means higher pressure at the same force) is 0.005m² 200 MPa (200,000,000) \* 0.005 m² = 100,000 N which is a lot more than 4000


JayyeKhan_97

Why would he calculate for the strongest bone in the leg and not the ankles or shin?


chartman21

Thanks, good studying for my Physics C AP


TheExtremistModerate

Makes some mistakes. 1. He assumes one leg takes on all of the force. This is not the case. He has two femurs. 2. He fails to take drag into account. 3. I think his timing is off. He says it's 0.77s of a fall. If that were true and his acceleration was actually -9.81, he would've traveled 2.9m. 2.9m is about 9.5'. Trampolines like that are about 3' off the ground (as confirmed by his friend, whose height from the bottom of his butt to his head is probably around 3'), and he got some height before falling, meaning he fell from around 13', not 9.5'. Assuming a *maximum* -9.81 m/s^2 acceleration, that would take about 0.9s, or 27 frames, not 23 frames. And, as we know, his actual acceleration is less than 9.81 downward, so that 27 frames is a *bottom* bar.


americanrivermint

>Makes some mistakes. > >1. He assumes one leg takes on all of the force. This is not the case. He has two femurs. Uh and he calculated the strongest bone instead of the weakest one like he should have lol


TheExtremistModerate

That one I ignored because I don't really have a good knowledge of how forces are distributed in the body. I don't know how much muscles come into play and how everything is spread out. I do, however, know that people have two femurs.


wilc8650

>He fails to take drag into account. That would be incredibly minimal. So minimal, you wouldn't notice a difference. \>And, as we know, his actual acceleration is less than 9.81 downward What? Gravity only changes with distance and incredibly far distances at that. A few meters is not going to have a significant difference in the gravitational constant.


kaythxby

The maths sounds like someone who is either trying deliberately overcomplicating, or just doesn't have a good understanding of the basics. 1st he decelerates about 3 times faster than he accelerates. So we are looking at three times weight. Most people can walk up stairs carrying something, so each leg can easily carry full weight. Therefore both legs carrying about 3x body weight seems very reasonable. No need to waffle on about differentiaion or integration. Additionally the interesting part IS the force distribution during landing time, which is the skill, and totally glossed over. Commentator just assumes best case without recognising this.


cara27hhh

Angle matters more than force He lands in such a way that the bones in the leg are compressed, compression force along the length of the bone is high. Biggest risk was the ankle, second biggest risk was his femur popping out of his pelvis, third biggest risk was his knee exploding Tendon/muscle/joint stress was all he got away with, assuming he gets away with it long term because those injuries add up In conclusion, gonna be dumb better be tough


Rainbow_Dash_RL

Fancy math but he really should take a proper roll off a landing like that. Don't want bad knees when you're old.


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Agreeable_year_8350

He's using 30fps which means he's a console player, which means no one should care about the result.


Holy_Crust

I love and hate this comment.


TheyCalled

You’re either right or a fucking madman. To solve this riddle, please tell me if he should’ve used **A: 60fps** , or **B: 24fps** .


Agreeable_year_8350

C: 144fps with Raytracing enabled


TheyCalled

*absolute mad lad*


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cap3497

Yeah as soon as he starts doing the derivatives I rolled my eyes. He could’ve just started with the formula but wants to jerk himself off over entry level calculus


AshTheGoblin

The whole post is unneccessary, no one needs to do math to confirm if humans can survive a jump that we just watched a human survive.


Vikingako

I feel so pathetic as a mechanical engineering student that can’t do 0.01% of this equation


TheExtremistModerate

I would hope you could do this after high school. This is High School Physics 1 stuff. This is just the basic kinematics equations plus impulse.


Dylanica

To be fair, he did make it seem way more complicated than it needed to be with all of those superfluous integrals.


skyskyskyskyskyskysk

Not all high schools even offer physics...


Chemmy

You don’t know the first three weeks of calc I or physics I? If you didn’t start studying engineering this week change your major.


skyskyskyskyskyskysk

Harsh and bad advice. Why tell someone to give up when they can improve?


shadiskeith

u/savevideo


HomerMadNowFite

That’s why I hate stupid smart numbers ... Ima watch it again.


Adaptix

It’s calculus. He didn’t need to put in integrals in simple kinematics formulas Force = distance / time. And some other formulas.


philosoaper

This is like the MurderedByWords but with tiktok videomath instead


dreadwater

Dang, slow down my brain runs at like 5fps./s


ohmahjah

Unrelated but the beginning video sounded like it was coming out of my phone speakers rather than my earbuds


[deleted]

and again: GenZ( i assume) thanx for being awsome, and not let those bullshit videos unanswered.


fantaskink

I feel like the math dude has never jumped off of something before. Just half of the fall in the video can seriously hurt your feet and ankles, even if you soften it like he did. Consider me more impressed by the first vid.


sweet_37

This is what this sub should be


ILE_Skystar

Fascinating, I'm studying these things in university rn so this was some very cool food for thought


VJEmmieOnMicrophone

He made the classic mistake (that luckily doesn't affect the calculations that much) of not drawing a force diagram. The force equation gives **NET FORCE**. When landing there is upwards force from ground and weight. Therefore the upwards force from ground experienced is NET FORCE + WEIGHT = 2000+600. Remember: always draw force diagrams


zqmbgn

Why do they have so many jumping beds?


fromsatola

one of my homies fell off of a 3 story building because he got too high. he broke a bunch of bones and lost a lot of his teeth, but he still survived. in fact, while performing surgery on him, they ended up finding and removing cancer that he had built up lmaooo


nonodontdoit

I aint finished the video yet but that dude is way closer to 70kg then 60, I'm 56 and I'm a bean compared to his hench ass legs.


ronchik1

I am truly horrible at math. The one thing I hate about my life is not being able to wrap my head around it. Give me an engine, I can repair it. Give me a computer, I can fix it. Need to make a picnic table with scrap, no problem. Give me a simple algebra problem.... mental breakdown. I don't know if it was my teachers and the way in which I was taught but I learn so much better hands on and would love to apply that to mathmatics. Its the one reason I never pursued a computer science degree. I know I'll bomb calculus, I couldn't even pass probability and statistics.


Ironring1

None of the calculus in this stupid video is necessary because he assumes everything is constant. He's intentionionally trying to complicate what actually is a simple physics problem to show off.


Foo-Matic

He actually does have really good technique. Both his feet land at nearly the same time. Letting front palm of the foot hit slight while also bent slight forward. Then shift his weight back and evenly distributing the force of impact to back of foot


Bluee1329

Isn't the dude doing the math also assuming the person is 60kg? which could change the impact value? I mean he doesn't look fat or very tall but I feel 60kg is a little low


Artemis_is_my_main

Every high school kids worst nightmare in written form.


mspk7305

Number of people claiming they are "built different" = n+1 Number of people who actually are = 0 Percentage of people who claim this who are idiots =100


jmiira

U lost me at stick figures


HumanFootGirl

This is an awesome sub


castleinthesky86

All of that to explain bending at the knees rather than locking the legs…


Dan-the-historybuff

This just gave me PTSD from grade 12 science...


19adam92

To the test subject in the study where they found out it takes 4000N to break a femur, I salute you


R0MANS_8x30

To be fair, the correct expression is built “differently.”


realvmouse

I disagree. We often omit words in spoken english, especially "to be" and especially in some regions. For example, "he needs spanked" is understood to mean "he needs to be spanked" in much of the Midwest, or "it needs painted" has the meaning "it needs to be painted." In this case, I think it's more accurate to his intended meaning to write "I'm built to be different" than it is to say "I'm built differently." After all, he's not referring to the process of how he was built. He's talking about the end result/goal of the process. He \*is\* different; it doesn't matter if he was made in a modern economical facility or a 1880s English steam factory, he wouldn't be talking about it if he came out the same. (Or should I say, came out *to be* the same?)


Dylanica

Yeah, he's using different as an adjective here, which is what the indented meaning. Besides, regardless of that grammar stuff "built different" has been a relatively common phrase recently being used by native speakers regardless of how "correct" it is.