A question about water and wood.

[Gara]

Okay so this morning I picked up a very brand new copy of the Discworld book, "Going Postal".

http://homepage.ntlworld.com/ak_gara/Lookie.jpg

Here is a little snippit from the first page.

It runs: the sea is, after all, in many respects only a wetter form of air. And it is known that air is denser the lower you go and lighter the higher you fly. As a storm-tossed ship founders and sinks, therefore, it must reach a depth where the water below is just viscous enough to stop it's fall.

My question is, is this even possible, if yes, why, if no, why?

I'm guessing it's just being used for the story and is not true.

[NateTG]

There are a couple of problems with that:

The description of water as wetter form of air is a bit bizarre in this context.

The passage indicates viscous rather than dense. Viscosity is something different than density, it has to do with the amount of friction the boat has with the water, and doesn't appreciably increase with water pressure.

Moreover, the compressibility of water is limited. Just because the density of water increases as pressure increases, does not mean that the density of water ever reaches 2.

[Gara]

Well that's that asnwered :) thanks.

Question acually seems rather silly now that I think about it.

Anyway to lock this topic?

[russ_watters]

No need to lock the topic, its an interesting one and a perfectly reasonable question. I just took up scuba diving and buoyancy is a bit counterintuitive: your buoyancy decreases the lower you go due to your body and buoyancy compensator (an inflatable life vest, essentially) being compressed. So you actually sink faster the lower you go.

[pervect]

I'm guessing it's just being used for the story and is not true.

Yes - water is not very compressible, unlike air, so water doesn't get appreciably denser as you go deeper. Air, on the other hand, is compressible, so air does get denser as one changes altitude.

Of course that's how it works in our world (reality), Discworld is a bit different, being supported on the backs of four elephants on a giant turtle and all :-)

Going back to the real world, viscosity doesn't have much to do with the issue - viscosity would affect how fast one sunk (think of it like friction), but would not change the point at which one stopped sinking. One would only stop sinking at neutral buoyancy, which would be a function of the density of the water and not its viscosity.