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Comment by riffraff | Hacker News Reader

I remember reading about someone jumping from a big height and purposefully going in feet first to break his legs and not his back, but I've always wondered how deep you would actually go if you hit the water hard enough to break your ankles.

I mean, it's already a slightly terrifying experience to jump from a tall trampoline and go a few meters deep, if you're not used to it.

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Not that deep, water is massively higher density than air (imagine the Column of air above you when you stand outside that goes up for miles and miles, you only need to go 10m under water to equal that weight, i.e. 10m ~ 1atm).

There is footage of people firing guns into water and you can see the bullets deceleration.

>There is footage of people firing guns into water and you can see the bullets deceleration.

Mythbusters did an episode on this one. Bullets shot out of high-powered rifles simply shatter on contact with the water, turning into a bunch of shrapnel.

https://www.youtube.com/watch?v=yvSTuLIjRm8

Mythbusters also did an episode where they compared dropping (dead) pigs onto concrete and dropping pigs on to water, from a height where they reached terminal velocity comparable to a humans. Both pigs were Very Dead. IIRC, the pig dropped into water was slightly less Very Dead, but it was still Very Dead. They weren't actively guiding themselves to land feet first but I wouldn't expect much out of that.

Water could be a component of a survival plan (e.g., "my partially deployed parachute is slowing me down enough to make this the equivalent of a high dive"), but "just land in water" is not a survival plan on its on from terminal velocity.

How you land in the water is key. In the Navy they teach us to point our toes, cross our arms, and basically make ourselves hit as little of the surface as possible when jumping from the top of a tall ship.

This is also why you should not try and land in water at terminal velocity.

Darn it, I guess I'll have to change my plans for Sunday if that's the case....

So let's say I'm falling at terminal velocity and I'm falling to a point roughly at the shore of a deep body of water. I have just enough control to deviate so I'm landing completely on (hard, dry) land, or completely in water that is over 20 feet deep.

You're saying I shouldn't try to land in the water?

(Let's assume there is no beach of sand. This is at a dam or something)

If those are your options, then you should go head first into the dam. You're not going to survive, so you want to die quickly, not suffering in pain for a few minutes.

Related, I wonder how high the risk of drowning is in a situation like that. I expect I would impulsively gasp from the shock/pain and inhale a lot of water.

We had a nearby case where two special forces dudes drowned in parachute training exercise because due to wind changes they landed on a major river. Water landing is not safe even if you're an experienced skydiver, you may have to swim quite far to get to the shore while not really prepared for long-distance swimming, with all your clothing, boots, parachute and all that.

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