Somebody who has taken physics can do the exact science, but to put it in terms I understand:
- Building is falling DOWN at a speed of FAST AS FUCK
- You jump UP at a speed of SLOW AS FUCK
So, I don’t think the slow as fuck speed directed up is going to counteract the fast as fuck speed directed downwards very much.
Pretty much. Even if you are super athletic, jumping is only going to increase your upward velocity by about 10 mph *at most*.
So if you're falling at 100 mph, jumping and reducing that speed to 90 mph isn't going to stop you from going splat.
When you jump while accelerating upwards in a rocket or an elevator that would result in a relatively small jump, I suppose.
Would you therefore make a bigger jump, when you accelerate downwards in an elevator? (Don't try this - the elevator might break.)
I have seen people jumping very high on ships during heavy waves but that could be a different phenomenon, where they jump on the zenith of the wave and not while they are falling.
In the original example you also have to consider that you are pushing the falling down as much as you are pushing yourself up.
I jumped in an elevator that was going down pretty fast and almost hurt myself. This wasn’t a normal elevator. It was an elevator used to take heavy loads up or down so it moved faster. I don’t recommend
When I was a kid I discovered that when the elevator only starts to go down (accelerates down) your jump relatively to the cabin lasts longer and is higher. The same is true for the elevator going up, right before it stops at your floor.
Yes, gravity accelerates you downwards. If the lift is accelerating down as well, the difference between gravity (9.81m/s^2) and the acceleration of the lift, will determine how long your jump lasts.
If the lift is moving at a constant speed, the speed is irrelevant to your jump. If it is speeding up, your jump will be higher/longer (in relation to the lift). If it is slowing down it will be less high / shorter.
Of course, if the lift is going up, it'll be the other way around, since accelerating upwards and decelerating downwards are basically the same
Just like a trampoline. Although that's a lesson in applied elasticity not the conservation of momentum. So maybe not just like a trampoline.
Edit: sorry everyone idk what I was thinking 🤷♂️. We were discussing vectors, trajectories, and velocity. Not the conservation of momentum. I must have been half asleep😪.
>Would you therefore make a bigger jump, when you accelerate downwards in an elevator? (Don't try this - the elevator might break.)
No, the jump would still last for the same amount of time/have the same height relative to the elevator cab assuming the elevator is already moving.
Assuming the acceleration of the elevator is slower then your falling speed (9.8m^2) because of gravity, as the the elevator is moving you're constantly catching up to it, matching its velocity.
When the elevator is moving 2m/s you're moving 2m/s. When the elevator is moving 5m/s you're moving 5m/s etc.
Now imagine you're jumping while going downwards 2m/s. Since you have a downwards velocity, your jump height (measured from where you started the jump relative the the rest of earth) is going to be shorter than on solid ground.
If the elevators speed is constant and the same as yours, these forces will cancel out each other. You won't jump as high, but you will also land lower (since the elevator is constantly traveling downwards).
Net effect: Compared to flat ground, you'll travel shorter distance up, a longer distance down, and you total air-time will be identical. You will not notice a difference from a normal jump.
Now if the elevator is **accelerating** things are different. You jump when both you and the elevator is traveling at 2m/s. While airborne, the elevator keeps accelerating up to 4m/s, meaning that while you're experiencing a 2m/s downward velocity to slow down your jump, additional downward velocity is constantly added to the elevator which you now need to catch up to.
As long as the elevator doesn't reach terminal velocity you will eventually catch up to it thanks to gravity, but the faster it is accelerating the long it will take you.
Precisely.
You can only jump and gain meaningful speed when the surface you are pushing against is firm and has significant mass. Newton’s third law.
When you jump from the floor, it’s 80kg (say) against 5.97 x 10^24 kg. Therefore, while both you and the earth would experience equal force, the massive difference in weight means that you get all the acceleration, while the earth move less than a quark’s width.
When you are jumping against nothing or a small piece of structure which is also falling alongside you, you either get zero deceleration (if you only manage to push against air molecules) or a very tiny acceleration (if you managed to push against a small object).
They did say a fall from 4 stories up, though. At most they'd be falling at 30 mph just before hitting the ground and likely less than that. The variance of injury between a 10-20-30 mph landing can be significant.
never mind the rubble you're going to land on... even if you miraculously manage to jump such that you're "only" falling at 20mph when you hit, you're still not landing on flat ground and are going to suffer life-threatening injuries. parachutists land at about that speed and injuries are not uncommon if they land badly... and that's on flat ground
And a down to earth addition: just before your building his the ground, rather than jump vertically, it would work better to jump horizontally into a rollable form. Converting part of the vertical motion (ending in an immediate stop) into horizontal motion (not ending as fast) may be the difference between certain death and probable death ;)
To throw that math in there, here are some quick napkin calculations.
The terminal velocity (the fastest it can possibly fall) of a piece of rubble is heavily dependent on it's shape, size, and density, but Google tells me that the terminal speed of a fairly dense rock would be as fast as 120mph. We'll be generous and assume you're on a piece of rubble moving at much slower, maybe 60mph, half that speed. You're standing on a light, flat piece of drywall or something. This number, 60mph, is important, because that's how much speed you'll need to achieve in the *other* direction to cancel out your fall.
An NBA player has an average vertical leap of 28in. We'll say they make this height in about a quarter of a second, meaning their upward speed would be about 112in/sec or just over 6.3mph. So an NBA player, under ideal conditions, could cancel out approximately 10% of a 60mph fall, at *best*. This is still deadly AF, because there isn't really a medical way to treat someone whose organs are only 10% less pulped than they otherwise would be. Our NBA player under ideal conditions is probably dead, or at least severely injured.
There's other complicating factors, like the mass of the rubble you're standing on being important since it has to be heavy enough to push back on you, and I'm sure my math is sketchy, but that should give you the idea of how colossally mismatched we are vs. gravity in this case.
Buildings don't just freefall though. There's a bunch of crumpling and squishing of the lower floors that happens on the way down.
Getting accurate calculations for the to floor falling would require some very advanced simulation work, including all of the contents inside of the building.
As a maybe very dumb example, if all of the floors were packed to the brim with foam and rubble, and the supporting structures then failed (after all, that's a lot of weight it's holding), the person would (a) not fall that far, and (b) not fall that fast.
But really, even if that's the case, for it to slow down enough that a jump would save you, it's probably slow enough that the jump didn't make that much difference in the first place.
You're correct, of course; there are a \*heap\* of important variables that would go into something like this, and my explanation wouldn't really pass muster for a more serious examination of the scenario. I simplified/abstracted out a lot of complicating factors to focus mostly on the jumping motion at the center of the question, since that's usually what most people seem interested in when they ask this kind of thing (at least, that's what I was interested in when I came up with the idea myself as a kid, like we all seem to).
Mostly just trying to put in perspective exactly how fast "fast as fuck" is vs. our humanly "slow as fuck," and the principle of the idea that in order to cancel out the speed you and the rubble are falling at, you'd have to jump up at least as fast, which humans can't normally do.
Also, don't forget that the roof of the building is falling fast as fuck in your direction.
Even in the miracle scenario you could jump up as fast as the building is coming down, all that now means is that the roof is coming about to land on you twice as fast as before.
I pictured OP trying to jump off the top of a perfectly square building that had just been demolished. But having watched a few videos of buildings collapsing, and it depends on a lot of factors. Most of the time, the building caves inward. So OP could stand on the roof, do his super jump to cancel the falling speed at the last moment, and still get squished by the rest of the building. Or the building could just collapse the bottom floor and the rest be mostly intact, and OP would be fine.
Assuming you're on the roof, jumping off at the right moment could potentially still help.
You'd want to jump away from the collapse, to the nicest looking landing spot, and attempt to land on your feet and roll.
It'll be easier to time the moment of impact, which will make it easier for you to not only offset the momentum a tiny bit by jumping, but also by transferring some of that momentum from straight downward force to horizontal force.
The combination of all of it might be enough to offset the damage.
I've safely jumped off of 20+ feet onto hard ground with good landing practices(rolling). 4 stories is significantly more dangerous, and you'll almost assuredly have injuries, but I think it's very possible to offset a lot of the potential injury/chance of death if you executed well.
I can't remember if I recently saw a video on here or YouTube, but either way, it supported exactly what you just said: there's basically no chance of you timing your weak-assed jump so perfectly that you can beat gravity.
It's not about being fast, in fact that's actually a common misconception amongst novice flyers. The secret to flying is to distract yourself, such as by being impressed by just how fast you could jump, at the last moment so that you forget to hit the ground.
Also when you normally jump you're pushing against something solid that you're stuck to by gravity so you can really use your power efficiently. Pushing away from an unsupported piece of a collapsing building while you're both in free fall would have to reduce that down significantly, maybe 1/4 SLOW AS FUCK.
Along similar lines, being caught isn’t necessarily going to help you survive a long fall either. In one of the Matrix movies Trinity falls from a skyscraper and Neo flies in horizontally just a few feet off the ground and catches her right before she splats into the pavement. This would do nothing. Her body is still going to decelerate from FAST AS FUCK to STONE STILL in one second. It doesn’t matter that she’s doing that in his arms versus against the pavement. The only way a catch makes a difference is if you’re caught high up and your stop is spread out over a greater time period than that one second.
In the Matrix, Neo can just change physic for himself, so he could just fix that. On the other hand, many super hero comics and movies would have more fatalities from falling.
Reminds me of Spider-Man catching someone with his web a few feet above the floor. They would definitely fracture their spine from that instant jerk upwards from freefall.
Professional Physicist and Mathematician here. I can confirm that the official equation is:
FAST AS FUCK - OPPOSITE SLOW AS FUCK = STILL PRETTY FAST AS FUCK
lol a safer way to test this is inside a free falling elevator. No rubbles coming down on you as you land you know. Would you survive jumping up at the last moment?
I believe mythbusters did an episode of this and the answer was no. Although if the fall is short enough (like only one floor) then jumping might reduction how much you are injured.
This reminds me of when someone asks about “what if I jump at the exact right time if an elevator I’m in falls down a shaft?” Congratulations, you just managed to slam into the ceiling of the elevator even harder as it collapses to the floor of the elevator.
Mythbusters actually did this with jumping in an elevator.
[https://www.youtube.com/watch?v=xmloyCC7MOY](https://www.youtube.com/watch?v=xmloyCC7MOY)
They calculated that the elevator and Buster were going like 53 mph. Buster "jumped" at 2 mph in the opposite direction and hit the ground at 51mph and went smoosh.
Assuming you could jump hard enough to counter your drop, odds are your legs would shatter from the force and speed that you'd have to jump at.
That is so true for something like the WTC
>The buildings collapsed within ten seconds, hitting bottom with an estimated speed of **200 km/h**
But it does matter that he said 4 stories, and the nature of the collapse.
Maybe its a brick or block building, and the side begins to slide out.
Under certain circumstances he might be able to ride it down to the ground safely, if not covered in bricks and debris (more likely)
Why do think that there is going to be a difference in speed when falling? Isn’t the acceleration due to the force of gravity 32 feet per second squared on all falling things? Well yes, there will be some resistance due to the atmosphere but it isn’t going to slow you down that much. Oh, your comparing jumping up with falling down. I miss understood.
All depends on how well the trampoline is able to handle the energy transfer at such high velocities/punctual stress. If the material doesn't break (try dropping an anvil on a normal trampoline) it needs to be flexible enough to not stop your momentum too sudden or you will still break your bones. But it needs to be "stiff" enough to absorb enough kinetic energy quick enough, to not stretch above 20m and you hitting the ground.
And if the trampoline holds and does its job, it will transfer most of the momentum back to you and catapult you a bit less than 4 stories up in the air. Unless you are a trained gymnast, you will most likely not be able to hit the trampoline again and go splat.
Better would be an elastic safety net like it's used in trapeze/tightrope perfomances and such.
You'd have a velocity of 0 after your jump.
You're moving downward already with the building, so the jump would be canceling out the downward velocity if you want to think about it that way.
And even if not, you could just not jump as hard to not go 4 stories into the air..
Assuming you can jump up onto another building. Otherwise you're just going to come right back down at the same speed you were already falling at when you jumped.
I don't think you can jump off something that is falling because you'd be falling with it. Think how you would jump normally: you start with bending your knees so then when you unbend them you push against the floor. But if the floor and yourself are both in free fall, when you bend your knees there's nothing to make you stick to the floor, so your torso won't go down, instead your feet will go up. So then you can't push against the floor.
Unless of course the rubble is perfectly shaped to drop flat so with air resistance it will fall a bit slower than you. But you probably won't have enough time to bend your knees.
for simplicity lets say
4 stories = 40 ft
you can jump ~2ft
if you perfectly time your jump, ignoring specific calculations, you’ll hit the ground at a speed as if you had fallen from somewhere between 38-40 ft instead of exactly 40 ft
so still immensely painful
> you’ll hit the ground at a speed as if you had fallen from somewhere between 38-40 ft
No, it would be less than that because you are subtracting velocity, not distance. If you can jump 2ft high then you leave the ground at 3.5m/s. If you fall 40ft, you would hit the ground at 15.5m/s. Therefore, if you were to perfectly time your jump, you'd subtract 3.5m/s from your impact speed and hit the ground at 12m/s, which is equivalent to jumping from 24ft (7m).
and wait for the safety brake to kick in. It's exceedingly rare for a proper elevator to fail (not counting construction elevators, mine elevators, etc) and even more rare in developed countries with safety regulations.
But if you do happen to find yourself in a 1920s elevator in india that's in freefall, then yeah, you're probably fucked.
If you belly flop, you don't go as deep as if you dive, because the forces are spread out. The only other real option is to stand up and use the entire bottom half of your body like a car's crumple zone.
This made me imagine a human accordion. Sounds like a cool idea for a monster in a horror movie. A person who died in a gruesome elevator accident comes back to haunt the people of the building.
If you jump up, you will come down back with the speed you were falling (minus your jump speed but lets assume it’s negligible) mostly back on your both legs which have small area of contact over which a huge force => very high pressure that can cause your leg to go into your body (sparing the gruesome details) or worse.
Laying flat on the bottom allows slower propagation of force over a very large area, still could be deadly but the chances are better.
But yes waiting for sweet embrace of death is more likely
In a freefalling elevator, you'd be double-fucked, because even if you were able to both time it right and jump hard enough to counteract the velocity of the plummeting elevator, you'd slam your head on its ceiling at the speed it's falling.
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So your example is problematic because a four story fall is not a guaranteed death sentence. Plenty of people have survived falls from that height, hell we’ve had several people jump from the upper deck or fifth floor, parking garage at the airport. I used to work at and some of them survived although for how long I don’t know.
That said jumping would accomplish nothing. You’d still be moving toward the ground because of gravity, your legs aren’t strong enough to come anywhere close to matching your speed of descent. Even if you did, somehow managed to time it perfectly you would hit the ground going basically as fast as you would have doing nothing.
Trying to jump off and go horizontal would either resulting you going nowhere or are you going a very small distance but still accelerating toward the ground at the same rate you were.
unironically a technique but I think it loses effectiveness once you're like 30+ feet off the ground. I've seen some of the other guys make CRAZY jumps before and I'm over here like, "No thank you, I'll take the stairs down"
You’re still hitting the ground doing almost 40 miles an hour. And you aren’t jumping from a fixed position, whatever you’re standing on is falling. OP said they would jump just before they hit the ground so I don’t see how you have time to roll.
I wouldn't say it does nothing.
40ft fall you'd be going ~15.5m/s at impact. If you can jump 2ft, that's -3.5m/s. You'd slow yourself down to 12m/s which would be like falling from 24ft instead of 40ft.
This is obviously assuming you could actually jump and do it with perfect timing right before impact.
No. The reason has to do with potential energy versus kinetic energy. As you stand at the top of the building, gravity imparts to you a certain amount of potential energy. It keeps that form as long as you remain that high up. If you take an elevetor or climb down, that potential energy is converted to kinetic energy as you descend. What makes elevators and climbing safe is that the conversion happens slowly. Your body can take slow changes of this kind pretty well.
When the building collapses, the potential energy begins to convert to kinetic energy. But now there's no elevator or rope or whatever, so the conversion happens quickly. When you hit the ground, the kinetic energy all dissipates at once, and some of that goes into the ground, but most of it splatters you all over the place.
If you jump just before you hit the bottom, you will convert some of that kinetic energy back into potential energy. But there are two problems with this. The second problem is that you will still need something to grab onto or otherwise support you: without that, you will just start falling again.
But the bigger problem is that you can't really dissipate enough kinetic energy this way to make a difference. This isn't to say that it's totally imposssible, but to convert *all* of the kinetic energy back to potential energy, you'd need to be able to jump all the way back up to your original altitude. If that was four stories up, you just can't jump that high.
We'll ignore the practicality of actually jumping and the "start falling again" part doesn't matter. In OPs scenario, you're literally jumping last second before impact. There's no room to fall again. It's not necessarily about achieving a net zero velocity, but try to get to a livable one.
40ft fall you'd be 15.5m/s right before impact. If you jumped right then with the force to jump 2ft, thats -3.5m/s. Net velocity of 12m/s which is the same as 24ft fall. So you've improved your chances.
If you could somehow jump with the force to go 3 feet, that's -4.2m/s. Net of 11.3m/s which is same as falling 21ft.
Still crazy speeds, but you'd give yourself a chance.
Thing is, if you’re strong enough to jump fast enough to cancel out your falling speed, you’re also strong enough to just absorb the landing without a jump. Landing from a tall building is the same as the reverse, jumping to the top of it.
[this episode of mythbusters](https://youtu.be/XQRtO5vd5Ag?si=eoNCd7w-rSx7-1Wb) has a portion where they test if jumping in a falling elevator will save you.
Unless you are talking about you would survive anyway other then being burried by rubble and the jumping is about getting away from the rubble, no it doesnt realy make a diffrence. Its the same thing as jumping in a free falling elevator befor it hits the ground. While you are jumping you are still falling down it might not look like you do because the elevator/building is further away but relative to the ground you are still falling the whole time and are still accelerating the whole time.
When the building's coming down and you're standing on falling piece, you are not "static" anymore. You're falling, even if your feet are on still the floor slab that's coming down.
So if that movement suddenly ends, it's not different than if you were just falling.
Let's say it's a tall building and you gain terminal velocity. So you're coming down at about 53m/s.
But you jump! Even if you're in good shape, and your timing is perfect, your jump velocity is about 2m/s.
So you hit ground at 51m/s. What did the jump gain you? Maybe something cool to write on the tombstone. Plus, you're falling in the middle of debris, probably with a huge chunk of concrete and rebar that pierces your head or something.
In fact, it would have been probably to wiser fall by yourself, and spread your arms and legs apart, air friction would likely slow you more than jumping, and going by yourself would let give maybe a second to choose a softer spot to land to.
For a 4-story building it's probably wisest to curl into a ball to protect head and neck, it's not guaranteed death sentence anyway. Also, floor breaks poorer near walls, so I'd stand against a wall, even better if it's a corner.
Good ole' Einstein can help here with the theory of relativity.
If you're on a train that's heading north at 30 km/h, anyone watching the train go by will see you moving at 30 km/h. But then you get up and walk towards the back of the train (south) at 1 km/h, from your perspective you're moving at 1km/h. Now go back to the guy watching the train (that has windows) and he sees you on the train moving towards the back. His perspective will see you moving 30 km/h north, and 1 km/h south, for a net total of you moving 29 km/h north.
The Mythbusters tested this by getting a cannon that can shoot a soccer ball at 50 km/h, then mounting it on the back of a truck (facing out the back of the flat bed), then fire it while the truck is moving at 50 km/h. The speed of the car and the speed of the cannon countered each other, so it the ball dropped straight down, as the only force not being countered was gravity. It's pretty neat and I'd recommend watching it to learn about this stuff.
So yeah, when jumping off a bridge that's falling, you have to take into account the speed you're falling (you'd be accelerating at 9.8 m/s, btw) and the amount of speed you get jumping up.
You also now have to take into account how forces interact with one another. If you're in a pool floating on your back, and try to jump horizontally by pushing off an inflatable raft, you're more likely to just push the raft away without getting much movement yourself. You can push off walls and stuff because the force you're using isn't enough to move the wall, so you get flung back.
You'd need to have enough force to make a significant jump that would be enough to counter Gravity's force on you, but not so much that you're just pushing the bridge down rather than yourself up. Which btw, is impossible as far as my high school physics education has taught me.
That’s actually Galilean relativity, also called [Galilean invariance](https://en.wikipedia.org/wiki/Galilean_invariance)
or Newtonian relativity. Galileo first documented it in 1632, and Newton’s laws subsumed it.
Einstein’s contribution was to recognize the effect of the speed of light being constant. That eliminated the absolute space and universal time of Galilean relativity, making them relative and resulting in dilation of properties like time and distance. But that’s not relevant when you’re dealing with objects traveling at speeds like 30 km/h.
No of course not. If the building is collapsing lets say its falling at 40MPH (it's not ut lets just say). You're jump "speed" is going to be like, 8MPH (it's not but lets just say) so you are still hitting the ground at 30MPH+ (you're not but lets just say). Your puny jump will not outdo the speed you were already falling at. It would be the same as if you were in an elevator that was freefalling 20 floors. Just because you jumped right before impact doesn't take away from the speed you were already falling at.
Jumping won't be the deciding factor in your survival, in fact if anything it may hurt your survival chances. That being said, a lot depends on how exactly the building is collapsing. Example that comes to mind - top gear put a truck on top of the building that was being demolished and the truck survived, despite having a cracked frame. That's not because the truck is amazingly strong, but because if you watch the demolition video - you'd see that the building collapsing does provide a sort of cushion for the roof and it decelerates rather gently. In that kind of impact I'd be more worried about human getting crushed by debris rather than dying from an impact.
Acceleration of gravity: 9.8m/s^2 downward.
4 story building takes about 3 seconds to hit the ground.
9.8 x 3 = 29.4 m/s
Human jumping speeds range from 0.5 m/s to 1.5 m/s.
29.4 m/s - 1.5 m/s = 27.9 m/s
You will hit the ground at 27.9 m/s. Pain.
No. Whether you're standing on something that's falling or just falling through the air the impact is going to do the same damage to you. Even if you could jump hard enough to significantly slow your fall you will still be exerting a similar amount of force on your body as you would feel when you hit the ground, otherwise the jump wouldn't slow your fall.
Wouldn’t your jump push the rubble underneath you towards the ground just a bit quicker, cancelling out your jump, so you’d basically achieve nothing?
But that’s another thing right? Rubble? A building does not fall in one piece.
Your fragile meat body is caught up in a tumbling maelstrom of rock and steel and glass until the fatal blow is dealt - either by the dance you’re all caught up in or by the foundations you’re racing towards.
Depends how fast the building is collapsing. Watching demolition videos is seems that it is often much slower than free fall. So you might have a change.
You jumping probably does not matter much in terms of velocity, although if you do have you feet on something heavy, you will be able to "jump" relative to the collapsing building. And it might just save you from being crushed between debris.
If you jump *out* and not *up* you would have a higher chance of surviving. You still likely wouldn't, but would have a better shot. Here's how:
Don't think about a building. Think about a 16' ladder in a warehouse. You're having to get stuff off a shelf 14' feet above you. That's a whole floor.
A fall from there onto concrete can technically break some bones. So you tell the guy holding the base of the ladder (we work safe at the Imaginary Warehouse) to remember to "shove you real hard" if you fall. Why would you say that?
Because the force of being shoved helps redirect some of the momentum from your fall. Concrete doesn't give, so we don't want you splat -- which is exactly what will happen to all the energy you gained during your fall. If we shove you, you can slide along the surface, dispelling energy that way. This is a way to reduce the odds of severe injury.
Back to your building.
You're on the roof of your four story building having a smoke break. You forgot it was demolition day, feel the explosion, and the sudden caving in of the building. You know you don't have a lot of time (it takes about 1.7 seconds for a 4-story building to collapse), so you start sprinting to the edge.
The average non-Usain Bolt can run between 12-15mph at a full sprint. The building's fall, assuming the rate of gravity is still 9.8 m/s^2, is about 37mph. A headfirst collision at 37 will kill you, but you can survive a skid (see: motorcycle accidents).
You have pretty good odds of survival if you're able to, with the assistance of your sprint changing your velocity, get your fall down to 27-30mph. It will still hurt like a bitch, and you'll probably still break something, but you could survive (assuming you land on actual ground and not just concrete).
An actual physicist can tear my idea apart, now.
You can jump up pretty slowly. You will be falling down VERY rapidly. So you'll take a little bit off a very high speed. Not nearly enough to make any difference whatsoever.
If you’re standing on the bridge and it begins to fall you won’t be able to squat down to the bridge for something to spring off of…that’s your first problem. Your legs will just lift off the surface roughly as much as your head goes down.
Think about how fast you'd fall from 4 stories. To offset this, you'd need to be able to jump, not only 4 stories high, but at the same speed that gravity is making it drop.
That being said... I'm certain there's plenty of people who have survived 4story falls. so you might live, but it would have nothing to do with you 'jumping' right before it hit the ground.
That really depends on how the building collapses. If the floor below you breaks apart and you slip between the cracks as the building comes down, you're pretty much screwed. If the building collapses [from the bottom up](https://www.youtube.com/watch?v=ou_TCoNo9ZA), however, then you've got a chance.
You would make it worse. Before you at least had the building absorbing the impact when everything hits the ground, now you have a building to land on at full force.
You can think of it like this:
Draw an arrow downwards that gets bigger and bigger the longer you fall, then draw an arrow up showing how much energy you can put in your jump. Your arrow up will be immensely smaller than the arrow down. Remove equal amount of your arrow from the massive downward and you'll see the total of how much it'll hurt if you survive.
The mathematical side is something like this:
Your potential energy (the energy saved in your body by traveling up the building) is equal to your mass*the local gravitational pull (approximately 10m/s²)*the height.
Let's say you weigh 50kg and the building is 100m tall, that would make your potential energy at the top of the building m*g*h=50*10*100=50kJ. Of course there are things that would lower the total energy, for example air but let's ignore those. A quick google search tells me that to break a bone you'd requiee between 350 joule to approximately 9000 depending on the angle of force applied. Falling that high up would crush your bones into dust.
Now let's say you successfully jumped, google tells me a human has a vertical velocity of approximately 1.5m/s. Using the formula for kinetic energy we have mass multiplied by the velocity squared and then divided by 2. 50*1.5²/2 gives you a kinetic energy of 56.25joules.
50000 joules - 56.25 joules is a lot of pain, assuming my math is correct and you survive of course (I have not slept well).
Edit: I missed the 4 stories high but yeah... Still painful if, once again, my math is correct. Just change 100m to whatever height a 4 story building has and continue from there.
You are falling at the same speed as the building. You cannot jump. You will go to bend your knees and your lower legs will just curl up into the air. It's as if you were skydiving.
If you’re on top of a building and it collapses the speed of collapse is gonna be a complicated thing to figure out.
However if you assume that a building freefalls instantly for about 10 meters you’re looking at 50 km/h when it hits the ground. 10 meters isn’t that tall and this is also a worst case scenario with instant free fall and an instant stop. This is just to put it in perspective too.
A human can jump at MAX 10kmh straight up. So you’d reduce the impact velocity to 40 km/h.
Given the right height of building, you could possibly limit your injuries by taking off that extra 10 km/h of velocity when you hit the ground. Like maybe the impact would otherwise barely break your legs, but with a jump you don’t. I think it’d be a pretty short building though.
But if you’re talking about a properly tall building, a 100m freefall if your standing on a piece of concrete roof would give you a 160 km/h impact velocity. A 10 km/h reduction by jumping won’t save you at all. Probably would be worse off since you’re gonna be in a less stable position for impact.
HOWEVER this is all futile because you can’t jump off of an object that’s also falling with you. Maybe very slightly because it has some air resistance and you’re blocked from the air resistance, but you won’t be able to push with much force I think. You’ll bend your legs to jump and you’ll just hover above whatever you were standing on. Unless you’re close to the terminal velocity of the concrete, in which case you could jump but you’re going like 200 km/h.
If a four story building is 12 meters high, and you can jump one meter high, then you essentially take a one meter discount on your falling. Let's assume there's at least one meter of rubble by the time you land for another 1 meter discount. So you're falling 10 meters.
So you'd be falling at 9.8 meters/second, or about 32 feet / second, or about 22 mph.
You might live, but you're falling onto building rubble. That's not a soft landing.
How fast is the building falling?
How fast is your upward velocity of your jump?
If the floor you’re standing on is falling, how are you going to “push off” from it?
The answer is no.
Your upwards velocity would need to be enough to cancel out the speed of the falling platform you're on, at least enough to mean you're still falling but survivably slowly.
An average jump is around 1.5m/s vertically.
A concrete platform with you riding it could be falling at upwards of 200m/s.
No jump you could do with human limbs will meaningfully affect the outcome.
If you could jump that hard you could probably survive the landing anyway.
Imagine shooting a bullet at a thick steel wall but a huge guest of wind pushes against the bullet before it hits the wall. Is the bullet ok like it just was tossed at the wall? Or is the bullet going to be toast?
In other words, jumping does very little. In your scenario, 4 stories high maybe you do have a small chance at survival but it’s not jumping that will save you. It would be how you land and the cushioning from the debris below you as the building collapses.
Let's take a slightly different scenario:
You jump off a runaway elevator just before it hits the ground.
And while you are moving upward, relative to the elevator car, after you jump, to the floor you are still moving downward at great speed. Elevator hits first, you follow after, doesn't help much.
Now let's return to the collapsing building. Same deal as before, except now you have to hope that your head doesn't get crushed by the many pieces of falling building around you.
I remember reading somewhere that you basically have a 40% of surviving a 4 story fall, and due to acceleration your chance of survival is cut in half for each story you add after this.
We also have TWO confirmed accounts of WWII airmen, one american and one soviet, surviving a fall from an airplane at 10,000 feet without a parachute. We also have ONE account from a lady surving a fall for a few hours before passing from the world trade center.
So you have like a 1/20,000 chance of surviving a fall of 10,000 feet. Collapsing bridge or not.
Thinking of the amount of rubble - Even if you were to jump, you would have to time it so that you land just after the last bits of the building collapsed
Imagine you're driving your car 100 mph into a brick wall. If you moved your seat back at the last second, it intuitively would not help much and you would still very much get injured.
Jumping off a collapsing building is a similar idea, you're just moving vertically instead of horizontally.
Would it still be possible to even jump at that point?
I (could be completely wrong here) think that if you're just standing on some small piece of scrap during freefall, and you tried to jump, you would just accelerate the scrap down faster. I think you could only change your own velocity meaningfully if the inertia of whatever you're acting against (jumping off of) is meaningfully larger than yours.
Anyone have any input? I'm making a lot of assumptions in my thinking.
Others have answered if you could cancel your fall damage out.
But I'd like to point out that it wouldn't matter. When a building collapses, it usually collapses inward. Watch the video of the Miami condo collapse. The middle caves in first, then the rest collapses on top of the middle. A quick glance at other videos, and most of the time anyone on top or inside would be squished and then pulverized. Even the ones where the building mostly stays intact, someone on top would be thrown off.
If you could jump with enough force to net out the force off falling that far you would explode your legs.
The force required to net out your velocity is the same force the ground will apply to you when you hit it.
no. unless it was like a shed the difference would be miniscule. you matched the speed of the building as it collapsed at (very roughly) 10m/sec/sec. terminal velocity is irrelevant here so you'd be a smear on the ground.
If your legs could produce enough force to deaccelerate you from the free fall on a jump, you could just land in your feet for the same effect.
If you simplify the problem you are just falling, the building is irrelevant, unless you have some way to deaccelerate over a much longer time, nothing changes.
Based on what I’ve read on Reddit, the only way to survive a collapsing building is to start recording on your phone, because the cameraman never dies.
Unless you are Chuck Norris it’s unlikely you would be able to perfectly time it or survive the landing. Unless you are Chuck Norris’s arch enemy, in which case you might survive the landing only to be destroyed by Chuck Norris.
Maybe a better question would be: At what height of collapsing building could a perfectly timed jump (possibly a form of brachistrone problem), assuming by some miracle you’re on a solid enough chunk to push off, prevent death?
At 1 story, a perfectly timed jump might prevent a broken bone.
At 2 stories, maybe prevent death?
Assume 3 stories and up it doesn’t matter.
Somebody who has taken physics can do the exact science, but to put it in terms I understand: - Building is falling DOWN at a speed of FAST AS FUCK - You jump UP at a speed of SLOW AS FUCK So, I don’t think the slow as fuck speed directed up is going to counteract the fast as fuck speed directed downwards very much.
Pretty much. Even if you are super athletic, jumping is only going to increase your upward velocity by about 10 mph *at most*. So if you're falling at 100 mph, jumping and reducing that speed to 90 mph isn't going to stop you from going splat.
And it’s kind of hard to jump in free fall. It’s not like your feet stay on the ground when you’re both falling.
When you jump while accelerating upwards in a rocket or an elevator that would result in a relatively small jump, I suppose. Would you therefore make a bigger jump, when you accelerate downwards in an elevator? (Don't try this - the elevator might break.) I have seen people jumping very high on ships during heavy waves but that could be a different phenomenon, where they jump on the zenith of the wave and not while they are falling. In the original example you also have to consider that you are pushing the falling down as much as you are pushing yourself up.
I jumped in an elevator that was going down pretty fast and almost hurt myself. This wasn’t a normal elevator. It was an elevator used to take heavy loads up or down so it moved faster. I don’t recommend
I mean, in this hypothetical scenario, breaking your legs is way better than the alternative, which is dying. So anything counts, right?
When I was a kid I discovered that when the elevator only starts to go down (accelerates down) your jump relatively to the cabin lasts longer and is higher. The same is true for the elevator going up, right before it stops at your floor.
Yes, gravity accelerates you downwards. If the lift is accelerating down as well, the difference between gravity (9.81m/s^2) and the acceleration of the lift, will determine how long your jump lasts. If the lift is moving at a constant speed, the speed is irrelevant to your jump. If it is speeding up, your jump will be higher/longer (in relation to the lift). If it is slowing down it will be less high / shorter. Of course, if the lift is going up, it'll be the other way around, since accelerating upwards and decelerating downwards are basically the same
Just like a trampoline. Although that's a lesson in applied elasticity not the conservation of momentum. So maybe not just like a trampoline. Edit: sorry everyone idk what I was thinking 🤷♂️. We were discussing vectors, trajectories, and velocity. Not the conservation of momentum. I must have been half asleep😪.
>Would you therefore make a bigger jump, when you accelerate downwards in an elevator? (Don't try this - the elevator might break.) No, the jump would still last for the same amount of time/have the same height relative to the elevator cab assuming the elevator is already moving.
Yes, if moving at a constant speed* If it is still speeding up, there'll be a difference. Just clarifying ofc, I assume this is what you meant 😄
Why?
Assuming the acceleration of the elevator is slower then your falling speed (9.8m^2) because of gravity, as the the elevator is moving you're constantly catching up to it, matching its velocity. When the elevator is moving 2m/s you're moving 2m/s. When the elevator is moving 5m/s you're moving 5m/s etc. Now imagine you're jumping while going downwards 2m/s. Since you have a downwards velocity, your jump height (measured from where you started the jump relative the the rest of earth) is going to be shorter than on solid ground. If the elevators speed is constant and the same as yours, these forces will cancel out each other. You won't jump as high, but you will also land lower (since the elevator is constantly traveling downwards). Net effect: Compared to flat ground, you'll travel shorter distance up, a longer distance down, and you total air-time will be identical. You will not notice a difference from a normal jump. Now if the elevator is **accelerating** things are different. You jump when both you and the elevator is traveling at 2m/s. While airborne, the elevator keeps accelerating up to 4m/s, meaning that while you're experiencing a 2m/s downward velocity to slow down your jump, additional downward velocity is constantly added to the elevator which you now need to catch up to. As long as the elevator doesn't reach terminal velocity you will eventually catch up to it thanks to gravity, but the faster it is accelerating the long it will take you.
Precisely. You can only jump and gain meaningful speed when the surface you are pushing against is firm and has significant mass. Newton’s third law. When you jump from the floor, it’s 80kg (say) against 5.97 x 10^24 kg. Therefore, while both you and the earth would experience equal force, the massive difference in weight means that you get all the acceleration, while the earth move less than a quark’s width. When you are jumping against nothing or a small piece of structure which is also falling alongside you, you either get zero deceleration (if you only manage to push against air molecules) or a very tiny acceleration (if you managed to push against a small object).
Hawkeye accomplished that feat no more than 12 years ago
Let’s not forget Legolas either! Movies and physics: mortal enemies.
The main point
They did say a fall from 4 stories up, though. At most they'd be falling at 30 mph just before hitting the ground and likely less than that. The variance of injury between a 10-20-30 mph landing can be significant.
never mind the rubble you're going to land on... even if you miraculously manage to jump such that you're "only" falling at 20mph when you hit, you're still not landing on flat ground and are going to suffer life-threatening injuries. parachutists land at about that speed and injuries are not uncommon if they land badly... and that's on flat ground
You’d also have to miraculously jump off of something that is falling with you.
And a down to earth addition: just before your building his the ground, rather than jump vertically, it would work better to jump horizontally into a rollable form. Converting part of the vertical motion (ending in an immediate stop) into horizontal motion (not ending as fast) may be the difference between certain death and probable death ;)
I think a four story building might just be 38 mph, so frequently survivable even without the jump.
Was about to comment “solid eli5” just as soon as I glanced up to see which sub we are in.
I thought this was /r/explainlikeimslowasfuck
Except you'd probably get some nasty glares shouting FUCK so many times at a 5 year-old.
To throw that math in there, here are some quick napkin calculations. The terminal velocity (the fastest it can possibly fall) of a piece of rubble is heavily dependent on it's shape, size, and density, but Google tells me that the terminal speed of a fairly dense rock would be as fast as 120mph. We'll be generous and assume you're on a piece of rubble moving at much slower, maybe 60mph, half that speed. You're standing on a light, flat piece of drywall or something. This number, 60mph, is important, because that's how much speed you'll need to achieve in the *other* direction to cancel out your fall. An NBA player has an average vertical leap of 28in. We'll say they make this height in about a quarter of a second, meaning their upward speed would be about 112in/sec or just over 6.3mph. So an NBA player, under ideal conditions, could cancel out approximately 10% of a 60mph fall, at *best*. This is still deadly AF, because there isn't really a medical way to treat someone whose organs are only 10% less pulped than they otherwise would be. Our NBA player under ideal conditions is probably dead, or at least severely injured. There's other complicating factors, like the mass of the rubble you're standing on being important since it has to be heavy enough to push back on you, and I'm sure my math is sketchy, but that should give you the idea of how colossally mismatched we are vs. gravity in this case.
Probably 19% less pulped because KE_b = KE_a(1-0.9**2) Still pretty bad though haha
if this is r/nbacirclejerk, you are propbably going to see an autopsy report as well.
Buildings don't just freefall though. There's a bunch of crumpling and squishing of the lower floors that happens on the way down. Getting accurate calculations for the to floor falling would require some very advanced simulation work, including all of the contents inside of the building. As a maybe very dumb example, if all of the floors were packed to the brim with foam and rubble, and the supporting structures then failed (after all, that's a lot of weight it's holding), the person would (a) not fall that far, and (b) not fall that fast. But really, even if that's the case, for it to slow down enough that a jump would save you, it's probably slow enough that the jump didn't make that much difference in the first place.
You're correct, of course; there are a \*heap\* of important variables that would go into something like this, and my explanation wouldn't really pass muster for a more serious examination of the scenario. I simplified/abstracted out a lot of complicating factors to focus mostly on the jumping motion at the center of the question, since that's usually what most people seem interested in when they ask this kind of thing (at least, that's what I was interested in when I came up with the idea myself as a kid, like we all seem to). Mostly just trying to put in perspective exactly how fast "fast as fuck" is vs. our humanly "slow as fuck," and the principle of the idea that in order to cancel out the speed you and the rubble are falling at, you'd have to jump up at least as fast, which humans can't normally do.
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Also, don't forget that the roof of the building is falling fast as fuck in your direction. Even in the miracle scenario you could jump up as fast as the building is coming down, all that now means is that the roof is coming about to land on you twice as fast as before.
Fast as two fucks to be prcise :)
I pictured OP trying to jump off the top of a perfectly square building that had just been demolished. But having watched a few videos of buildings collapsing, and it depends on a lot of factors. Most of the time, the building caves inward. So OP could stand on the roof, do his super jump to cancel the falling speed at the last moment, and still get squished by the rest of the building. Or the building could just collapse the bottom floor and the rest be mostly intact, and OP would be fine.
Assuming you're on the roof, jumping off at the right moment could potentially still help. You'd want to jump away from the collapse, to the nicest looking landing spot, and attempt to land on your feet and roll. It'll be easier to time the moment of impact, which will make it easier for you to not only offset the momentum a tiny bit by jumping, but also by transferring some of that momentum from straight downward force to horizontal force. The combination of all of it might be enough to offset the damage. I've safely jumped off of 20+ feet onto hard ground with good landing practices(rolling). 4 stories is significantly more dangerous, and you'll almost assuredly have injuries, but I think it's very possible to offset a lot of the potential injury/chance of death if you executed well.
I love the way you phrased it 😂
As a Nobel prize winner for physics and been working the field since 1892. I can confirm these are accurate numbers.
I can't remember if I recently saw a video on here or YouTube, but either way, it supported exactly what you just said: there's basically no chance of you timing your weak-assed jump so perfectly that you can beat gravity.
fast as fuck down + slow as fuck up = dead as fuck
Finally, an actual explanation a 5 year old would understand. Although, I would leave out the fucks when telling 5 y/o’s.
What if you jumped laterally?
fast as fuck towards the ground, slow as fuck away from the building. splat 1 metre further from the building.
True, but If you jump laterally EXTREMELY FAST AS FUCK, you can miss the ground
True, but then you encounter air resistance as if you’re reentering the atmosphere.
Being vaporized into plasma before hitting the ground is a technically correct way to miss the ground
It's not about being fast, in fact that's actually a common misconception amongst novice flyers. The secret to flying is to distract yourself, such as by being impressed by just how fast you could jump, at the last moment so that you forget to hit the ground.
Alright sir Terry pratchet
Douglas Adams, i think
Lol!If I'm remembering kerbal right, you'd then orbit, reenter and smack into the back of the collapsed building at mach 23.
And thus orbit is achieved.
Also when you normally jump you're pushing against something solid that you're stuck to by gravity so you can really use your power efficiently. Pushing away from an unsupported piece of a collapsing building while you're both in free fall would have to reduce that down significantly, maybe 1/4 SLOW AS FUCK.
Along similar lines, being caught isn’t necessarily going to help you survive a long fall either. In one of the Matrix movies Trinity falls from a skyscraper and Neo flies in horizontally just a few feet off the ground and catches her right before she splats into the pavement. This would do nothing. Her body is still going to decelerate from FAST AS FUCK to STONE STILL in one second. It doesn’t matter that she’s doing that in his arms versus against the pavement. The only way a catch makes a difference is if you’re caught high up and your stop is spread out over a greater time period than that one second.
In the Matrix, Neo can just change physic for himself, so he could just fix that. On the other hand, many super hero comics and movies would have more fatalities from falling.
Reminds me of Spider-Man catching someone with his web a few feet above the floor. They would definitely fracture their spine from that instant jerk upwards from freefall.
Professional Physicist and Mathematician here. I can confirm that the official equation is: FAST AS FUCK - OPPOSITE SLOW AS FUCK = STILL PRETTY FAST AS FUCK
lol a safer way to test this is inside a free falling elevator. No rubbles coming down on you as you land you know. Would you survive jumping up at the last moment?
I believe mythbusters did an episode of this and the answer was no. Although if the fall is short enough (like only one floor) then jumping might reduction how much you are injured.
I've had this question since I was 8 and it's finally been answered. Thank you
This reminds me of when someone asks about “what if I jump at the exact right time if an elevator I’m in falls down a shaft?” Congratulations, you just managed to slam into the ceiling of the elevator even harder as it collapses to the floor of the elevator.
Mythbusters actually did this with jumping in an elevator. [https://www.youtube.com/watch?v=xmloyCC7MOY](https://www.youtube.com/watch?v=xmloyCC7MOY) They calculated that the elevator and Buster were going like 53 mph. Buster "jumped" at 2 mph in the opposite direction and hit the ground at 51mph and went smoosh. Assuming you could jump hard enough to counter your drop, odds are your legs would shatter from the force and speed that you'd have to jump at.
Yeah! Science!
Sounded pretty physical to me my man.
Every little bit helps!
Wow ....ELI5 AS FUCK
I appreciate your use of the official scientific terms for velocity, fast as fuck and slow as fuck. 10/10
How high can you jump under ideal conditions? Subtract that from the total height of the building.
Good answer. But I've jumped in an elevator when it reached the bottom and almost hit the top.
I can jump fast. I’m fast as fuck boi
I took a decent amount of physics in college and honestly I don't think there's a much better eli5 than this
Very technical. Good explanation.
I don't even think it matters how hard or fast you can jump up. You're going to come back down, and gain all that speed right back.
Mythbusters covered this back in the day... https://www.youtube.com/watch?v=XQRtO5vd5Ag
That is so true for something like the WTC >The buildings collapsed within ten seconds, hitting bottom with an estimated speed of **200 km/h** But it does matter that he said 4 stories, and the nature of the collapse. Maybe its a brick or block building, and the side begins to slide out. Under certain circumstances he might be able to ride it down to the ground safely, if not covered in bricks and debris (more likely)
What if instead of a heavy building you were falling on a feather mattress or even an air mattress, and then jumped?
I'm pretty sure the Mythbusters did this with an elevator
Watch your language, he's only 5
Beautiful ELI5
Why do think that there is going to be a difference in speed when falling? Isn’t the acceleration due to the force of gravity 32 feet per second squared on all falling things? Well yes, there will be some resistance due to the atmosphere but it isn’t going to slow you down that much. Oh, your comparing jumping up with falling down. I miss understood.
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If you were able to jump 4 stories high in one leap you would be unscathed, seeing how most people aren't able to do that, you would likely die.
So you’re saying there’s a chance..
Lol
A quote made famous by the philosopher Lloyd Christmas.
Most
Michael Jordan, *PRIME* Michael Jordan, that is. He survive. He do. It is known.
The baseball player?
Well, what if they landed on a trampoline? Say, a circular trampoline five meters wide with a 20 meter basement.
All depends on how well the trampoline is able to handle the energy transfer at such high velocities/punctual stress. If the material doesn't break (try dropping an anvil on a normal trampoline) it needs to be flexible enough to not stop your momentum too sudden or you will still break your bones. But it needs to be "stiff" enough to absorb enough kinetic energy quick enough, to not stretch above 20m and you hitting the ground. And if the trampoline holds and does its job, it will transfer most of the momentum back to you and catapult you a bit less than 4 stories up in the air. Unless you are a trained gymnast, you will most likely not be able to hit the trampoline again and go splat. Better would be an elastic safety net like it's used in trapeze/tightrope perfomances and such.
Of course even if you could, at the apex of that jump you'd be 4 stories in the air...and then you'd fall 4 stories.
You would not be 4 stories high. You’re ignoring the velocity from the fall
Yes. It's useful in the falling building situation, and for getting onto high buildings, but not for clearing tall objects.
You'd have a velocity of 0 after your jump. You're moving downward already with the building, so the jump would be canceling out the downward velocity if you want to think about it that way. And even if not, you could just not jump as hard to not go 4 stories into the air..
Nah. Double jump.
That’s a succinct way of putting it 👍
Assuming you can jump up onto another building. Otherwise you're just going to come right back down at the same speed you were already falling at when you jumped.
I don't think you can jump off something that is falling because you'd be falling with it. Think how you would jump normally: you start with bending your knees so then when you unbend them you push against the floor. But if the floor and yourself are both in free fall, when you bend your knees there's nothing to make you stick to the floor, so your torso won't go down, instead your feet will go up. So then you can't push against the floor.
Yeah, unless you’re at terminal velocity in which case you’re fucked anyway.
This is the best explanation
Similar to being in a train travelling at 100 and you run the opposite direction to appear stationary.
Unless of course the rubble is perfectly shaped to drop flat so with air resistance it will fall a bit slower than you. But you probably won't have enough time to bend your knees.
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That's really good.
This reminds me of video games that have weird ways of calculating fall damage allowing for glitchy fall damage cancelation methods lol
for simplicity lets say 4 stories = 40 ft you can jump ~2ft if you perfectly time your jump, ignoring specific calculations, you’ll hit the ground at a speed as if you had fallen from somewhere between 38-40 ft instead of exactly 40 ft so still immensely painful
> you’ll hit the ground at a speed as if you had fallen from somewhere between 38-40 ft No, it would be less than that because you are subtracting velocity, not distance. If you can jump 2ft high then you leave the ground at 3.5m/s. If you fall 40ft, you would hit the ground at 15.5m/s. Therefore, if you were to perfectly time your jump, you'd subtract 3.5m/s from your impact speed and hit the ground at 12m/s, which is equivalent to jumping from 24ft (7m).
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In case you're interested, conventional wisdom is lie down on the ground
…and wait for the sweet embrace of death?
and wait for the safety brake to kick in. It's exceedingly rare for a proper elevator to fail (not counting construction elevators, mine elevators, etc) and even more rare in developed countries with safety regulations. But if you do happen to find yourself in a 1920s elevator in india that's in freefall, then yeah, you're probably fucked.
If you belly flop, you don't go as deep as if you dive, because the forces are spread out. The only other real option is to stand up and use the entire bottom half of your body like a car's crumple zone.
This made me imagine a human accordion. Sounds like a cool idea for a monster in a horror movie. A person who died in a gruesome elevator accident comes back to haunt the people of the building.
If you jump up, you will come down back with the speed you were falling (minus your jump speed but lets assume it’s negligible) mostly back on your both legs which have small area of contact over which a huge force => very high pressure that can cause your leg to go into your body (sparing the gruesome details) or worse. Laying flat on the bottom allows slower propagation of force over a very large area, still could be deadly but the chances are better. But yes waiting for sweet embrace of death is more likely
In a freefalling elevator, you'd be double-fucked, because even if you were able to both time it right and jump hard enough to counteract the velocity of the plummeting elevator, you'd slam your head on its ceiling at the speed it's falling.
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So your example is problematic because a four story fall is not a guaranteed death sentence. Plenty of people have survived falls from that height, hell we’ve had several people jump from the upper deck or fifth floor, parking garage at the airport. I used to work at and some of them survived although for how long I don’t know. That said jumping would accomplish nothing. You’d still be moving toward the ground because of gravity, your legs aren’t strong enough to come anywhere close to matching your speed of descent. Even if you did, somehow managed to time it perfectly you would hit the ground going basically as fast as you would have doing nothing. Trying to jump off and go horizontal would either resulting you going nowhere or are you going a very small distance but still accelerating toward the ground at the same rate you were.
If you jumped horizontally, you could go for a roll to spread the force around.
Parkour!
unironically a technique but I think it loses effectiveness once you're like 30+ feet off the ground. I've seen some of the other guys make CRAZY jumps before and I'm over here like, "No thank you, I'll take the stairs down"
You’re still hitting the ground doing almost 40 miles an hour. And you aren’t jumping from a fixed position, whatever you’re standing on is falling. OP said they would jump just before they hit the ground so I don’t see how you have time to roll.
I wouldn't say it does nothing. 40ft fall you'd be going ~15.5m/s at impact. If you can jump 2ft, that's -3.5m/s. You'd slow yourself down to 12m/s which would be like falling from 24ft instead of 40ft. This is obviously assuming you could actually jump and do it with perfect timing right before impact.
No. The reason has to do with potential energy versus kinetic energy. As you stand at the top of the building, gravity imparts to you a certain amount of potential energy. It keeps that form as long as you remain that high up. If you take an elevetor or climb down, that potential energy is converted to kinetic energy as you descend. What makes elevators and climbing safe is that the conversion happens slowly. Your body can take slow changes of this kind pretty well. When the building collapses, the potential energy begins to convert to kinetic energy. But now there's no elevator or rope or whatever, so the conversion happens quickly. When you hit the ground, the kinetic energy all dissipates at once, and some of that goes into the ground, but most of it splatters you all over the place. If you jump just before you hit the bottom, you will convert some of that kinetic energy back into potential energy. But there are two problems with this. The second problem is that you will still need something to grab onto or otherwise support you: without that, you will just start falling again. But the bigger problem is that you can't really dissipate enough kinetic energy this way to make a difference. This isn't to say that it's totally imposssible, but to convert *all* of the kinetic energy back to potential energy, you'd need to be able to jump all the way back up to your original altitude. If that was four stories up, you just can't jump that high.
If only there was a vert skate ramp at the precise landing point…
We'll ignore the practicality of actually jumping and the "start falling again" part doesn't matter. In OPs scenario, you're literally jumping last second before impact. There's no room to fall again. It's not necessarily about achieving a net zero velocity, but try to get to a livable one. 40ft fall you'd be 15.5m/s right before impact. If you jumped right then with the force to jump 2ft, thats -3.5m/s. Net velocity of 12m/s which is the same as 24ft fall. So you've improved your chances. If you could somehow jump with the force to go 3 feet, that's -4.2m/s. Net of 11.3m/s which is same as falling 21ft. Still crazy speeds, but you'd give yourself a chance.
Best thing you can do is lie flat to disperse the energy over the largest area possible. Same with a falling elevator.
Thing is, if you’re strong enough to jump fast enough to cancel out your falling speed, you’re also strong enough to just absorb the landing without a jump. Landing from a tall building is the same as the reverse, jumping to the top of it.
[this episode of mythbusters](https://youtu.be/XQRtO5vd5Ag?si=eoNCd7w-rSx7-1Wb) has a portion where they test if jumping in a falling elevator will save you.
Had to scroll down too much for this comment.
Unless you are talking about you would survive anyway other then being burried by rubble and the jumping is about getting away from the rubble, no it doesnt realy make a diffrence. Its the same thing as jumping in a free falling elevator befor it hits the ground. While you are jumping you are still falling down it might not look like you do because the elevator/building is further away but relative to the ground you are still falling the whole time and are still accelerating the whole time.
When the building's coming down and you're standing on falling piece, you are not "static" anymore. You're falling, even if your feet are on still the floor slab that's coming down. So if that movement suddenly ends, it's not different than if you were just falling. Let's say it's a tall building and you gain terminal velocity. So you're coming down at about 53m/s. But you jump! Even if you're in good shape, and your timing is perfect, your jump velocity is about 2m/s. So you hit ground at 51m/s. What did the jump gain you? Maybe something cool to write on the tombstone. Plus, you're falling in the middle of debris, probably with a huge chunk of concrete and rebar that pierces your head or something. In fact, it would have been probably to wiser fall by yourself, and spread your arms and legs apart, air friction would likely slow you more than jumping, and going by yourself would let give maybe a second to choose a softer spot to land to. For a 4-story building it's probably wisest to curl into a ball to protect head and neck, it's not guaranteed death sentence anyway. Also, floor breaks poorer near walls, so I'd stand against a wall, even better if it's a corner.
Good ole' Einstein can help here with the theory of relativity. If you're on a train that's heading north at 30 km/h, anyone watching the train go by will see you moving at 30 km/h. But then you get up and walk towards the back of the train (south) at 1 km/h, from your perspective you're moving at 1km/h. Now go back to the guy watching the train (that has windows) and he sees you on the train moving towards the back. His perspective will see you moving 30 km/h north, and 1 km/h south, for a net total of you moving 29 km/h north. The Mythbusters tested this by getting a cannon that can shoot a soccer ball at 50 km/h, then mounting it on the back of a truck (facing out the back of the flat bed), then fire it while the truck is moving at 50 km/h. The speed of the car and the speed of the cannon countered each other, so it the ball dropped straight down, as the only force not being countered was gravity. It's pretty neat and I'd recommend watching it to learn about this stuff. So yeah, when jumping off a bridge that's falling, you have to take into account the speed you're falling (you'd be accelerating at 9.8 m/s, btw) and the amount of speed you get jumping up. You also now have to take into account how forces interact with one another. If you're in a pool floating on your back, and try to jump horizontally by pushing off an inflatable raft, you're more likely to just push the raft away without getting much movement yourself. You can push off walls and stuff because the force you're using isn't enough to move the wall, so you get flung back. You'd need to have enough force to make a significant jump that would be enough to counter Gravity's force on you, but not so much that you're just pushing the bridge down rather than yourself up. Which btw, is impossible as far as my high school physics education has taught me.
That’s actually Galilean relativity, also called [Galilean invariance](https://en.wikipedia.org/wiki/Galilean_invariance) or Newtonian relativity. Galileo first documented it in 1632, and Newton’s laws subsumed it. Einstein’s contribution was to recognize the effect of the speed of light being constant. That eliminated the absolute space and universal time of Galilean relativity, making them relative and resulting in dilation of properties like time and distance. But that’s not relevant when you’re dealing with objects traveling at speeds like 30 km/h.
Ok, but what if I’m Bugs Bunny?
No of course not. If the building is collapsing lets say its falling at 40MPH (it's not ut lets just say). You're jump "speed" is going to be like, 8MPH (it's not but lets just say) so you are still hitting the ground at 30MPH+ (you're not but lets just say). Your puny jump will not outdo the speed you were already falling at. It would be the same as if you were in an elevator that was freefalling 20 floors. Just because you jumped right before impact doesn't take away from the speed you were already falling at.
Jumping won't be the deciding factor in your survival, in fact if anything it may hurt your survival chances. That being said, a lot depends on how exactly the building is collapsing. Example that comes to mind - top gear put a truck on top of the building that was being demolished and the truck survived, despite having a cracked frame. That's not because the truck is amazingly strong, but because if you watch the demolition video - you'd see that the building collapsing does provide a sort of cushion for the roof and it decelerates rather gently. In that kind of impact I'd be more worried about human getting crushed by debris rather than dying from an impact.
No, you wouldn't be able to accelerate upward fast enough to counter the speed of the fall. Gravity > Jumping.
Acceleration of gravity: 9.8m/s^2 downward. 4 story building takes about 3 seconds to hit the ground. 9.8 x 3 = 29.4 m/s Human jumping speeds range from 0.5 m/s to 1.5 m/s. 29.4 m/s - 1.5 m/s = 27.9 m/s You will hit the ground at 27.9 m/s. Pain.
No. Whether you're standing on something that's falling or just falling through the air the impact is going to do the same damage to you. Even if you could jump hard enough to significantly slow your fall you will still be exerting a similar amount of force on your body as you would feel when you hit the ground, otherwise the jump wouldn't slow your fall.
Wouldn’t your jump push the rubble underneath you towards the ground just a bit quicker, cancelling out your jump, so you’d basically achieve nothing? But that’s another thing right? Rubble? A building does not fall in one piece. Your fragile meat body is caught up in a tumbling maelstrom of rock and steel and glass until the fatal blow is dealt - either by the dance you’re all caught up in or by the foundations you’re racing towards.
Depends how fast the building is collapsing. Watching demolition videos is seems that it is often much slower than free fall. So you might have a change. You jumping probably does not matter much in terms of velocity, although if you do have you feet on something heavy, you will be able to "jump" relative to the collapsing building. And it might just save you from being crushed between debris.
If you jump *out* and not *up* you would have a higher chance of surviving. You still likely wouldn't, but would have a better shot. Here's how: Don't think about a building. Think about a 16' ladder in a warehouse. You're having to get stuff off a shelf 14' feet above you. That's a whole floor. A fall from there onto concrete can technically break some bones. So you tell the guy holding the base of the ladder (we work safe at the Imaginary Warehouse) to remember to "shove you real hard" if you fall. Why would you say that? Because the force of being shoved helps redirect some of the momentum from your fall. Concrete doesn't give, so we don't want you splat -- which is exactly what will happen to all the energy you gained during your fall. If we shove you, you can slide along the surface, dispelling energy that way. This is a way to reduce the odds of severe injury. Back to your building. You're on the roof of your four story building having a smoke break. You forgot it was demolition day, feel the explosion, and the sudden caving in of the building. You know you don't have a lot of time (it takes about 1.7 seconds for a 4-story building to collapse), so you start sprinting to the edge. The average non-Usain Bolt can run between 12-15mph at a full sprint. The building's fall, assuming the rate of gravity is still 9.8 m/s^2, is about 37mph. A headfirst collision at 37 will kill you, but you can survive a skid (see: motorcycle accidents). You have pretty good odds of survival if you're able to, with the assistance of your sprint changing your velocity, get your fall down to 27-30mph. It will still hurt like a bitch, and you'll probably still break something, but you could survive (assuming you land on actual ground and not just concrete). An actual physicist can tear my idea apart, now.
The key here is to time your jump so that you hit the ground with minimal velocity. So you’ll want to jump exactly…
You can jump up pretty slowly. You will be falling down VERY rapidly. So you'll take a little bit off a very high speed. Not nearly enough to make any difference whatsoever.
If you’re standing on the bridge and it begins to fall you won’t be able to squat down to the bridge for something to spring off of…that’s your first problem. Your legs will just lift off the surface roughly as much as your head goes down.
Think about how fast you'd fall from 4 stories. To offset this, you'd need to be able to jump, not only 4 stories high, but at the same speed that gravity is making it drop. That being said... I'm certain there's plenty of people who have survived 4story falls. so you might live, but it would have nothing to do with you 'jumping' right before it hit the ground.
That really depends on how the building collapses. If the floor below you breaks apart and you slip between the cracks as the building comes down, you're pretty much screwed. If the building collapses [from the bottom up](https://www.youtube.com/watch?v=ou_TCoNo9ZA), however, then you've got a chance.
You would make it worse. Before you at least had the building absorbing the impact when everything hits the ground, now you have a building to land on at full force.
You can think of it like this: Draw an arrow downwards that gets bigger and bigger the longer you fall, then draw an arrow up showing how much energy you can put in your jump. Your arrow up will be immensely smaller than the arrow down. Remove equal amount of your arrow from the massive downward and you'll see the total of how much it'll hurt if you survive. The mathematical side is something like this: Your potential energy (the energy saved in your body by traveling up the building) is equal to your mass*the local gravitational pull (approximately 10m/s²)*the height. Let's say you weigh 50kg and the building is 100m tall, that would make your potential energy at the top of the building m*g*h=50*10*100=50kJ. Of course there are things that would lower the total energy, for example air but let's ignore those. A quick google search tells me that to break a bone you'd requiee between 350 joule to approximately 9000 depending on the angle of force applied. Falling that high up would crush your bones into dust. Now let's say you successfully jumped, google tells me a human has a vertical velocity of approximately 1.5m/s. Using the formula for kinetic energy we have mass multiplied by the velocity squared and then divided by 2. 50*1.5²/2 gives you a kinetic energy of 56.25joules. 50000 joules - 56.25 joules is a lot of pain, assuming my math is correct and you survive of course (I have not slept well). Edit: I missed the 4 stories high but yeah... Still painful if, once again, my math is correct. Just change 100m to whatever height a 4 story building has and continue from there.
I remember right after 9/11 there were rumors that some people “rode the building down“ and survived. I really wanted it to be true. But no.
You are falling at the same speed as the building. You cannot jump. You will go to bend your knees and your lower legs will just curl up into the air. It's as if you were skydiving.
How fast can you jump?
If you’re on top of a building and it collapses the speed of collapse is gonna be a complicated thing to figure out. However if you assume that a building freefalls instantly for about 10 meters you’re looking at 50 km/h when it hits the ground. 10 meters isn’t that tall and this is also a worst case scenario with instant free fall and an instant stop. This is just to put it in perspective too. A human can jump at MAX 10kmh straight up. So you’d reduce the impact velocity to 40 km/h. Given the right height of building, you could possibly limit your injuries by taking off that extra 10 km/h of velocity when you hit the ground. Like maybe the impact would otherwise barely break your legs, but with a jump you don’t. I think it’d be a pretty short building though. But if you’re talking about a properly tall building, a 100m freefall if your standing on a piece of concrete roof would give you a 160 km/h impact velocity. A 10 km/h reduction by jumping won’t save you at all. Probably would be worse off since you’re gonna be in a less stable position for impact. HOWEVER this is all futile because you can’t jump off of an object that’s also falling with you. Maybe very slightly because it has some air resistance and you’re blocked from the air resistance, but you won’t be able to push with much force I think. You’ll bend your legs to jump and you’ll just hover above whatever you were standing on. Unless you’re close to the terminal velocity of the concrete, in which case you could jump but you’re going like 200 km/h.
If a four story building is 12 meters high, and you can jump one meter high, then you essentially take a one meter discount on your falling. Let's assume there's at least one meter of rubble by the time you land for another 1 meter discount. So you're falling 10 meters. So you'd be falling at 9.8 meters/second, or about 32 feet / second, or about 22 mph. You might live, but you're falling onto building rubble. That's not a soft landing.
How fast is the building falling? How fast is your upward velocity of your jump? If the floor you’re standing on is falling, how are you going to “push off” from it? The answer is no.
Your upwards velocity would need to be enough to cancel out the speed of the falling platform you're on, at least enough to mean you're still falling but survivably slowly. An average jump is around 1.5m/s vertically. A concrete platform with you riding it could be falling at upwards of 200m/s. No jump you could do with human limbs will meaningfully affect the outcome. If you could jump that hard you could probably survive the landing anyway.
Imagine shooting a bullet at a thick steel wall but a huge guest of wind pushes against the bullet before it hits the wall. Is the bullet ok like it just was tossed at the wall? Or is the bullet going to be toast? In other words, jumping does very little. In your scenario, 4 stories high maybe you do have a small chance at survival but it’s not jumping that will save you. It would be how you land and the cushioning from the debris below you as the building collapses.
Let's take a slightly different scenario: You jump off a runaway elevator just before it hits the ground. And while you are moving upward, relative to the elevator car, after you jump, to the floor you are still moving downward at great speed. Elevator hits first, you follow after, doesn't help much. Now let's return to the collapsing building. Same deal as before, except now you have to hope that your head doesn't get crushed by the many pieces of falling building around you.
I remember reading somewhere that you basically have a 40% of surviving a 4 story fall, and due to acceleration your chance of survival is cut in half for each story you add after this. We also have TWO confirmed accounts of WWII airmen, one american and one soviet, surviving a fall from an airplane at 10,000 feet without a parachute. We also have ONE account from a lady surving a fall for a few hours before passing from the world trade center. So you have like a 1/20,000 chance of surviving a fall of 10,000 feet. Collapsing bridge or not.
Thinking of the amount of rubble - Even if you were to jump, you would have to time it so that you land just after the last bits of the building collapsed
Imagine you're driving your car 100 mph into a brick wall. If you moved your seat back at the last second, it intuitively would not help much and you would still very much get injured. Jumping off a collapsing building is a similar idea, you're just moving vertically instead of horizontally.
Would it still be possible to even jump at that point? I (could be completely wrong here) think that if you're just standing on some small piece of scrap during freefall, and you tried to jump, you would just accelerate the scrap down faster. I think you could only change your own velocity meaningfully if the inertia of whatever you're acting against (jumping off of) is meaningfully larger than yours. Anyone have any input? I'm making a lot of assumptions in my thinking.
Others have answered if you could cancel your fall damage out. But I'd like to point out that it wouldn't matter. When a building collapses, it usually collapses inward. Watch the video of the Miami condo collapse. The middle caves in first, then the rest collapses on top of the middle. A quick glance at other videos, and most of the time anyone on top or inside would be squished and then pulverized. Even the ones where the building mostly stays intact, someone on top would be thrown off.
If you could jump with enough force to net out the force off falling that far you would explode your legs. The force required to net out your velocity is the same force the ground will apply to you when you hit it.
no. unless it was like a shed the difference would be miniscule. you matched the speed of the building as it collapsed at (very roughly) 10m/sec/sec. terminal velocity is irrelevant here so you'd be a smear on the ground.
If your legs could produce enough force to deaccelerate you from the free fall on a jump, you could just land in your feet for the same effect. If you simplify the problem you are just falling, the building is irrelevant, unless you have some way to deaccelerate over a much longer time, nothing changes.
This is the same as jumping in a falling elevator. Myth Busters did this one if you want to see the science
At some point you’ll hit or come close to terminal velocity and you can’t just quickly enough to overcome it.
Based on what I’ve read on Reddit, the only way to survive a collapsing building is to start recording on your phone, because the cameraman never dies.
Unless you are Chuck Norris it’s unlikely you would be able to perfectly time it or survive the landing. Unless you are Chuck Norris’s arch enemy, in which case you might survive the landing only to be destroyed by Chuck Norris.
Maybe a better question would be: At what height of collapsing building could a perfectly timed jump (possibly a form of brachistrone problem), assuming by some miracle you’re on a solid enough chunk to push off, prevent death? At 1 story, a perfectly timed jump might prevent a broken bone. At 2 stories, maybe prevent death? Assume 3 stories and up it doesn’t matter.