How to properly fall into water from great height

[[wcip]Angel]

Hi all

I had a drunken disagreement with one of my flat mates last night. (Well I was drunk and he was sober.) We were discussing the proper way to adjust your body should you happen to fall into the ocean from, say, an airplane. Let's say that parachute never opened!

He said it was impossible to survive any way, rendering the discussion pointless. My argument was that I had heard of people surviving those kinds of falls. Sure, they broke a good deal of bones in their body, but they survived the impact with water. In response, he then said that you should probably land with your legs first, shaping your body into a nail landing feet-first into water. I was pretty adamant that doing so would push your legs all the way up to your shoulders, thus crushing your entire body. I believe that in order to survive an impact like that, you need to break the water surface with your hands first as divers do, thus reducing the level of impact on the rest of your body. Your hands and arms will most likely break, but the damage to your head and the rest of the body is survivable.

What do you think, fellow lurkers?

[Chesspiece_face]

Anything that would allow you to survive a fall such as this would be entirely out of your control. The best way for you to shape your body to hit the water would be to cross your fingers.

The terminal velocity of the average human body free falling with limbs splayed is above 120 mph. Bringing those limbs close to the body would increase falling speed up to around 200 mph. Head first pointing to the ground can increase your rate of falling to up to nearly 600 mph. Human reaction time or accuracy falling at these speeds would limit any ability to control your impact position in much of a meaningful way.

[LochnarITB]

I thought Mythbusters had done something like this.

Google search on "mythbusters fall into water"

[Zingydex]

Scientifically, hitting the watter at terminal velocity is essentially the same as hitting solid rock. It's not necessarily the skeleton-smashing impact that kills you - there's also the dozens of G's from the sudden deceleration rupturing all your internal organs to contend with.

[kandrathe]

I believe, as with arguing, facing death is much better done while intoxicated.

But, here are some principles I would employ. 1) slow down as much as possible using your clothing or jacket as a small parachute, 2) treat the landing as if you were landing on hard ground, 3) probably semi-fetal with feet first in a spring position would be best to protect the head and vital organs, 4) attempt to convert your velocity into horizontal force which would allow you to transfer some of the energy into tumbling to slow down. 5) don't put yourself into the position of being at a great height over water without a helmet, life preserver, and parachute.

[DeeBye]

CANNONBALL!!!!

[Nystul]

1. Hit the button hanging around your neck.
2. Yell "Help! I've fallen, and I can't get up!"
3. Hope they bring a parachute with them.

Edit:
1b. seta gravity = 0
2b. Bind g "+grapple"
3b. gggggggg
4b. GOD
5b. .... This server sux!1111
6b. Rocket jump? If I can time it just right...

[Jester]

Angel' date='Nov 1 2009, 04:30 AM' post='174263']
What do you think, fellow lurkers?

I'm debating soundtrack. Should it be Tom Petty - "Free Falling" - or maybe Afro Celt Sound System feat. Peter Gabriel - "When You're Falling"? Or maybe some Dylan - "Blowin' in the Wind"? Tough not to go with REM, though - it really is the end of the world as you know it, and it's just so darn cheerful.

Decisions decisions. Probably you want to do a quick back-of-the-envelope calculation about how much time you have before you hit the ground. Wouldn't want the song to end too quicky, or after you're paste on the ground.

On a more physical note, are there actually reports of people surviving terminal velocity falls into open water? Soft ground, maybe. If you get just the right point of impact, it might help break your fall. A snowy incline would be ideal. But water? That's like hitting solid pavement. Not to mention the fact that your rescuers would have to be within feet of you, because you're sure not going to swim to shore.

-Jester

Afterthought: This page has all sorts of neat facts. Apparently, falling into water without assistance at terminal velocity is pretty much fatal. From a couple hundred feet, you'd want to be legs-first if you didn't know what you were doing, or maybe in a dive position if you were an expert. From 35,000 feet, you'd want to be someone else, somewhere else.

[--Pete]

Hi,

What do you think, fellow lurkers?

Use the same method recommended for nuclear attack: bend over, put your head between your legs, and kiss your ass good-bye. :w00t:

You are not going to survive. You can distract yourself during those last few moments by figuring out how to minimize your death. Throughout most of the fall, you can minimize your velocity by getting into a starfish position, maximizing your cross section. At some carefully selected time, you want to get into the ideal position for hitting the water. While hitting hands first does give you a smaller entry point, the shoulder joint isn't really designed for load bearing. My guess, both arms will be ripped off, followed very soon after by the head. Feet first does have the advantage of presenting a stronger structure. However, I fear your argument against this position is correct.

The Douglas Adams solution is, I would think, best. Simply miss the water. :lol:

--Pete

[Crusader]

Well there are cases known of people surviving jumping in water from great height without any means of deceleration. Feet-first nail is the best approach, because you will have a longer braking path going under water lessening the strains put on your body and giving the most protection to head and upper chest (the most critical parts of the body). If you land horizontal you immediately stop. You will always suffer broken bones throughout your body and severe internal injuries.

A rare few parachutists who had no chute unfold (not even partial) survived crashing into trees and bushes. Water should be even more lenient.

[Jester]

Well there are cases known of people surviving jumping in water from great height without any means of deceleration. Feet-first nail is the best approach, because you will have a longer braking path going under water lessening the strains put on your body and giving the most protection to head and upper chest (the most critical parts of the body). If you land horizontal you immediately stop. You will always suffer broken bones throughout your body and severe internal injuries.

A rare few parachutists who had no chute unfold (not even partial) survived crashing into trees and bushes. Water should be even more lenient.

As the perennial skeptic, do you have any confirmed cases of people surviving high altitude drops into open water with no mitigating factors (parachute, plane pieces, etc...)?

My understanding is that water is not more lenient than trees and bushes. Branches help break your fall, and trees are at least slightly elastic, as is the ground. Water is incompressible - upon impact with your legs, they will be forced upwards with enormous force, killing you instantly. The fact that it becomes much more forgiving a second later does not help you survive the initial impact, which I can only imagine would be as fatal as a similar impact onto solid concrete - maybe worse.

-Jester

[Delc]

You probably want to throw something out ahead of you in an attempt to break the surface tension.

[Jester]

You probably want to throw something out ahead of you in an attempt to break the surface tension.

The problem isn't surface tension. The problem is hydraulics and viscosity. Water doesn't compress - so it functions as a surface with zero elasticity. If you're lowering yourself slowly into water, there's no problem, since it will flow around you. But if you're just hitting it square on at terminal velocity, you're toast. Throwing something ahead of you would not save you.

At least, not according to Mythbusters. It might help a little bit, so you might as well do it, but at terminal velocity, it's the difference between splat and splat.

-Jester

[--Pete]

Hi,

A rare few parachutists who had no chute unfold (not even partial) survived crashing into trees and bushes. Water should be even more lenient.

Nope. We think "water = soft, wood = hard", and in many ways we are right. But what we actually need to look at is the deceleration. As the old joke goes, it's not the fall that kills you, it's the sudden stop at the bottom.

In shock dynamics, most experiments are destructive. After the test is done, there is nothing left but fragments. Occasionally, though, it is desirable to do some post test studies. For these, the sample needs to be relatively intact. There are many methods used to achieve this, but they share one common property. They all decelerate the sample over some distance. It is the reduction of the stress of a sudden stop that allows the sample to survive.

In all the stories I've seen of people surviving falls from high altitude, their speed was reduced over some distance, either by hitting an inclined surface, or by hitting some yielding surface. The people who hit trees or bushes had to be doubly lucky -- first to have hit the tree in the first place, then to have missed the big parts that would have stopped them suddenly. By absorbing the person's energy, the breaking and bending of the branches slowed the person gradually (relatively speaking).

Water will not do that. As a first approximation, you hit the water all at once. You hit it so fast that it doesn't quite have the time to get out of the way and make room for you. You decelerate from whatever velocity you hit the water at to zero in about 1ms (assuming 4 transits of the pressure wave through a 6f body at about 5000f/s -- roughly the speed of sound in our soft tissues). If we assume a terminal velocity of about 120 m/h (starfish position), we get about 5000g. If, branches, snow, or a sloped roof reduce the velocity to zero over 1/2s, then the answer comes out to about 10g -- quite survivable.

--Pete

[Klaus]

The problem isn't surface tension. The problem is hydraulics and viscosity. Water doesn't compress - so it functions as a surface with zero elasticity. If you're lowering yourself slowly into water, there's no problem, since it will flow around you. But if you're just hitting it square on at terminal velocity, you're toast. Throwing something ahead of you would not save you.

At least, not according to Mythbusters. It might help a little bit, so you might as well do it, but at terminal velocity, it's the difference between splat and splat.

-Jester

Well, it's a matter of scale, I think. If you had a sufficiently large object (say, a boulder) to fall behind, it would leave a cavitated space behind it where the water would be "softer" (since it's at least partly made up of air bubbles). A smaller object (like a hammer, which Mythbusters used) just doesn't have enough of an effect. Whether the bubble content of the water can be made high enough to help seems iffy - and of course, if the object is too large, you end up going splat into the back of the rock instead of the water. :)

So, if you have a boulder to push out in front of you, I figure it's worth a shot, but I wouldn't expect too much.

[Jester]

A smaller object (like a hammer, which Mythbusters used) just doesn't have enough of an effect. Whether the bubble content of the water can be made high enough to help seems iffy - and of course, if the object is too large, you end up going splat into the back of the rock instead of the water. :)

Jumping out of a plane with no parachute, it's not implausible that you might have something smallish that you could throw in front of you. It'd be pretty freaky if you had a boulder - where'd that come from? (Maybe you were making a connecting flight in Colorado? Nyuk nyuk...) If we're talking about something large enough to have the necessary effect, we're also talking about something well beyond the "unaided" free fall.

-Jester

[Klaus]

Jumping out of a plane with no parachute, it's not implausible that you might have something smallish that you could throw in front of you. It'd be pretty freaky if you had a boulder - where'd that come from? (Maybe you were making a connecting flight in Colorado? Nyuk nyuk...) If we're talking about something large enough to have the necessary effect, we're also talking about something well beyond the "unaided" free fall.

-Jester

Maybe you're a cartoon character and you can produce an arbitrary number of anvils on command. :)

I was just exploring the problem space, not asserting that it was reasonable or not. Of course, it's not reasonable to expect to have a boulder falling with you. A large turbofan engine from a disintegrated aircraft might be a (remote) possibility, however. Of course, you'd have little chance of surviving the breakup of such an aircraft to begin with, but still...

[Jester]

I was just exploring the problem space, not asserting that it was reasonable or not. Of course, it's not reasonable to expect to have a boulder falling with you. A large turbofan engine from a disintegrated aircraft might be a (remote) possibility, however. Of course, you'd have little chance of surviving the breakup of such an aircraft to begin with, but still...

People have survived the breakup of airplanes by riding various pieces of debris down. It's extremely unlikely, but it's not impossible. But debris it opens up a whole other set of variables that aren't accessible to someone just falling straight down, unaided. They're better off making peace with themselves and enjoying the view. :P

-Jester

[LochnarITB]

It'd be pretty freaky if you had a boulder - where'd that come from?

We'd need to establish the level of improbability - it could have been a whale!

[Klaus]

We'd need to establish the level of improbability - it could have been a whale!

True. However, the bowl of petunias probably wouldn't be very useful.