Could we survive a dive into water from out terminal velocity?
August 17, 2010 11:26 AM   Subscribe

Say a very light, very healthy person took a dive from some stupidly high altitude, and spread themselves out into a skydiving position so that they just reached their minimum terminal velocity. Would it be at all possible that this person could survive the drop if they landed in the sea, assuming they quickly rearranged themselves into a more streamlined diving position just before impact?
posted by insperatum to Sports, Hobbies, & Recreation (17 answers total) 6 users marked this as a favorite
You might find this interesting.
posted by HuronBob at 11:30 AM on August 17, 2010 [9 favorites]

The most pertinent bit of HuronBob's link: 'Like concrete, liquid doesn’t compress. Hitting the ocean is essentially the same as colliding with a sidewalk, Hamilton explains, except that pavement (perhaps unfortunately) won’t “open up and swallow your shattered body.” '
posted by ocherdraco at 11:35 AM on August 17, 2010 [3 favorites]

Well, people have survived falling off the Golden Gate Bridge. (One guy even went back and did it again. He didn't survive the second time.)

But that wasn't terminal velocity. Some quick Googling suggests the freefall distance to reach terminal velocity is somewhere around 1500 feet, and the Golden Gate is almost spot on half that height.

And very few people survive that. I'm going to go with no.
posted by Naberius at 11:43 AM on August 17, 2010 [1 favorite]

I recently watched an old MythBusters episode, in which an item was dropped into the water ahead of a person to break the surface tension, but the crash test dummy was literally torn up from impact.

On their forum, MythBuster fans and folk said there are ways to survive, or at least increase your chance for survival, when dropping or diving into water.
posted by filthy light thief at 11:43 AM on August 17, 2010 [1 favorite]

The most pertinent bit of HuronBob's link: 'Like concrete, liquid doesn’t compress. Hitting the ocean is essentially the same as colliding with a sidewalk, Hamilton explains, except that pavement (perhaps unfortunately) won’t “open up and swallow your shattered body.” '

If this is the case, how is it that people survive 20 and 30 foot high dives unscathed? A dive from that height onto concrete would be pretty fatal. I'm honestly curious.
posted by drjimmy11 at 11:43 AM on August 17, 2010 [1 favorite]

It depends on how high you mean by stupidly high, doesn't it? 110m (361feet, about 30stories or so) seems really stupid to me. In fact 45m does too. But people have survived accidental falls of a lot more.
posted by Some1 at 11:46 AM on August 17, 2010

At all possible? Yes. Likely? No, and would require a near-perfect entry, good physical condition, and a lot of luck.

The Straight Dope article says terminal velocity for the Golden Gate Bridge jump is about 80mph, vs. 120mph terminal velocity given elsewhere.
posted by sninctown at 11:52 AM on August 17, 2010

If this is the case, how is it that people survive 20 and 30 foot high dives unscathed?

The notion that "liquid doesn't compress" is only partially true.

Water doesn't compress well because of the shape of its molecules and how they line up (or don't line up) when under pressure. So, yes, in a way, hitting flat water is akin to hitting a flat, hard surface.

However, saying "water doesn't compress" is missing the point that the ocean is a giant, unbounded space. You can push water aside, which is how a boat floats. When you fall into the ocean (or a pool), you're not falling into a perfectly flat, compressed "brick" of water that has nowhere to go.

This is why you can survive a 30-foot belly flop but not a 300-footer. The water molecules in a pool aren't perfectly compressed and lined up, you'll displace quite a bit of it, etc.

It will hurt like a motherfucker, of course. And the sudden deceleration will rattle your noggin around. Increase the speed, and you'll quickly approach the point where the water = concrete argument is a moot point.
posted by Cool Papa Bell at 11:57 AM on August 17, 2010 [4 favorites]

In order to really answer we'd need to know what is meant by stupidly high altitude. But anything higher than the Golden Gate Bridge and it would play out kind of like this: Is it possible? Theoretically, yes - but! Two things you must consider.

One, that once the person jumps out of whatever they're jumping out of, the theoretical possibility is all they have. They can position themselves like a skydiver and try to hit the water in the most efficient way but there is absolutely no way to predict with 100% certainty what the outcome will be. Some people fall out of planes and live. Most people who fall out of planes die. What I mean is that there is no course of action a person can take which will ensure survival, or make it anything less than a very far-away statistical outlier of an outcome.

And two, that a theoretical possibility does not translate into anything more than the idea that it's not completely impossible that the person, via nothing more than dumb luck, would survive. Having said that: No, you'd die.
posted by FAMOUS MONSTER at 12:02 PM on August 17, 2010

Displacement also explains why divers try to enter the water cleanly with a sharp point. As you enter the water hands-first, you are not displacing as much water as a belly-flop -- you are only displacing water around your hands. Then as you enter, you're introducing only a little bit more of you at a time and gradually displacing the water.

Done right, you get Olympic medals for making very little splash.

Done wrong -- trying to displace a massive amount all at once -- and you win a T-shirt in the belly-flop contest.
posted by Cool Papa Bell at 12:03 PM on August 17, 2010 [1 favorite]

Naberius: "somewhere around 1500 feet, and the Golden Gate is almost spot on half that height"

That's the tower. The road is only ~270 feet above the water.
posted by alexei at 12:35 PM on August 17, 2010

The world record for the highest dive into water is held by, depending on who you ask, Dana Kunze (172 feet and walked away) or Oliver Favre (177 feet but broke his back.) Not taking air resistance into account, their velocity on impact would have been 72 or 73 miles per hour.

Some1's link to Harry Froebess' jump would appear to beat these records, though from a bit of searching it doesn't seem to be very well attested. If he did in fact do this dive, he probably would have been going around 100 miles per hour.
posted by Johnny Assay at 12:35 PM on August 17, 2010

I'm also reminded of having to jump from approx. 50 feet in the Navy (i.e. from the deck of an aircraft carrier), how you were supposed to do it, and why.

* Feet first. Don't break your arms; you'll need them for swimming.
* Heels first. You're probably wearing boots, and that's a nice thick piece of rubber.
* Ankles crossed. If your legs separate on impact, you'll break one of them. Or break your balls. Ouch.
* Arms crossed, one hand hugging an elbow, the other over your face and covering your nose. Try to make yourself skinny. Your elbows will also protect your face a bit. Don't break your nose, don't shoot water up into your nose, don't let your head snap back.
* Pray.
posted by Cool Papa Bell at 12:53 PM on August 17, 2010 [14 favorites]

In an ancient speculative discussion I had on this topic it was pointed out that although the human skeleton could potentially withstand a fall from x height at y speed, and even break surface tension, all of one's internal organs are secured only by soft tissue. Therefore, even if the body could break the water's surface in the smoothest possible motion, any rapid deceleration would have the internal organs continue to travel at a faster rate than the skeleton, and they would all rip free from their connections, nerve endings, veins, etc. and smoosh into goo inside their corresponding body cavities.
posted by No Shmoobles at 1:46 PM on August 17, 2010

Terminal velocity is the key here. When you dive 20 feet you're still crashing into the water, but the forces involved (usually) are not injurious.

You're not at terminal velocity if you dive 20 feet into concrete, either, but you'll probably die. Or wish you died. Cool Papa Bell explained it pretty well; hitting concrete is a lot worse than hitting water for a given velocity, but at sufficiently high velocities you die either way. It doesn't matter all that much that hitting the concrete had 500% of the force necessary to kill you while hitting the water only had 200% of the necessary force.
posted by Justinian at 2:54 PM on August 17, 2010

It strikes me reading this thread that there might be at least one circumstance in which a person could hit water at terminal velocity and have a reasonable chance of surviving without great harm, and that is if the water column were to be as full as possible of air bubbles.

Too big and there wouldn't be that much deceleration, too small and too much. Maybe about the size of marbles?

The only place I can think of that would seem to have much of a chance of having such a thing occur naturally is the base of a big waterfall with a very deep pool in the zone where the entrained air is coming back up.

Could that be one reason going over Niagara in a barrel was as survivable as it was (however survivable that may have been!)?
posted by jamjam at 12:14 AM on August 18, 2010

Holy crap - read the 4th entry down in filthy light thief's Mythbusters forum link. Holy crap.
posted by allkindsoftime at 12:52 AM on August 18, 2010

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