Water as unyielding as concrete

What people think is a safe position doesn't always work.
Landing feet first isn't a generally good idea, since people tend have their feet flat against the water - this can "tip you over" so that you end up prone or supine for the main impact.

 

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My choice would be feet first, hoping like hell my feet would stay together. Doing the splits after impacting the water would be very bad indeed.

 

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Like I said: feet first can be a bad idea. One (distant) colleague on my college diving/ swimming team did so after jumping off a 10 metre board.
He split the back of his head open when the impact tipped him over. Only the skin split (as opposed to his skull) but, as with most scalp wounds, it was a very bloody mess.

On the other hand the results of tipping over can be hilarious. Or at least I thought so the time my brother ended up going in face-first.

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Oh well. One can break the backbone simply by doing a poor head-jump from the brink of the water.

 

F = ma

a = F/m

The mass of a cone, m, is proportional to it's volume, which is proportional to the square of its base, b (the cone's height held constant).

The force acting on the cone is proportional to the cross-sectional area of the cone, which is proportional to the square of its base.

So, a ~ b²/b², so the b² cancel, making the acceleration (deceleration) independent of the base. Unless I'm missing something here, they would decelerate at the same rate.

 

Um, wouldn't a larger area in contact with the water cause a larger force/ reaction?

I dunno about Lilalena's cylinder vs. cone because the cone has a rapidly increasing area (which also ends up FAR larger than that of the cylinder). So maybe at the instant of initial impact it would fare better and then get rapidly worse. Maybe too rapidly, given the rate of divergence from point to 2 metre circle.

 

You're right, Dywyddyr. I misread Lilalena's comparison, and I thought they were both cones.

 

I do believe the entire answer to this question will be clear when friction is brought into the mix.

Friction is roughly proportional to the SQUARE of the velocity, so it really takes off quickly as velocity increases.

The unyieldingness of water stems from the friction forces that resist penetration of the water.

The crucial variable here is velocity and how much friction increases with it.

 

How much friction is there on the surface during impact? Where does the friction arise?

Already discussed - it's unlikely to be friction.

Friction increases with velocity?
Data please.

 

How about water cannons -

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What does the use of water cannons - and the damage that can be done with them - say about water? About matter in general?

We can imagine water being static and an object entering it at a certain velocity.
We can also imagine a "piece of" water moving at a certain velocity toward an object, or an object also moving toward a moving "piece of water".


Just trying to think outside of the box.

 

It's the same thing (as you knew).
The problem I have is the phrase "entering it at high velocity" (as I noted in my previous post).
The damage/ break-up occurs on impact i.e. pre-"entry".

 

Such as when hit by a rock.

We can also imagine being hit by a substance that seems harder than water - such as dough, for instance.
Dough seems soft enough, but if someone throws a piece at you, it's not unlike being hit by a stone.


Apparently, we are mislead by the usual image we have of water - namely, that it is a malleable substance.

When in fact it might be more useful to consider these things in terms of velocity and specific weight - as opposed to "water" and "rock", or "dough".

 

Um...

Both my post #20.

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Actually, I waxed all philosophical and attempted to reconceptualize the whole matter from the usual atomistic thinking into a more holistic one, in order to circumvent the usual concepts we have of matter.

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If you tried to do a dive with one hand clenched in a fist entering first (instead of pointed) would your fist skid along the water / hardly enter it?

 

But, but, but... that's more or less what I said (although slightly more, er, numerically).

E.g. "When in fact it might be more useful to consider these things in terms of velocity and specific weight"

 

Depends.
Post #26

I've done dives (English Header as it was [possibly] erroneously called*) with my hands behind my back** and had no problems...

* The one where you stand at the side of the pool/ edge of the board and "bounce" straight upwards, then twist before coming down vertically (care must be taken to not the dry bit of the "pool" - aim for the water

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- effectively nearly scraping the edge with your chest).
That would have given me ~ 2 metres (from poolside, obviously more if from a board).

** It was fun doing this into 1 foot of water, especially when others tried to emulate me.

 

Yes. I tried a different wording.

Terms like "water" or "rock" can be very misleading.

Ice is still water, and lava is still rock - but ice and lava are not what we would usually think of at "water" and "rock".

 

Water is not to be toyed with. I almost drowned once.

 

Do you think an ocean of jello or dough would act like concrete too or ... maybe it would be different because there are more air bubbles in them, also they can crumble or break...

I've recently been getting disappointed a lot by Google also - even when searching for things that I wouldn't have considered to be obscure at all.

It makes me think they're preparing us for the day only the page 2 onwards results are free. Page 1 you have to pay for.