# Objects that don't float in water, sink to the bottom ...
**URL:** https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159
**Category:** Factual Questions
**Created:** [March 29, 2004, 8:49pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159 "2004-03-29T20:49:17Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@SettingSun](https://boards.straightdope.com/u/SettingSun)
#### Post date: [March 29, 2004, 8:49pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/1 "2004-03-29T20:49:17Z")
True “neutral buoyancy” is impossible to obtain. Consequently, an object at rest will rise to the surface or sink to the bottom. Still true?
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [March 29, 2004, 8:57pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/2 "2004-03-29T20:57:23Z")
In practical terms, I can see that it might be unattainable, but in theoretical terms, it _ought_ to be possible, or at least I don’t see why not.
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### Author:  [@Grey](https://boards.straightdope.com/u/Grey)
#### Post date: [March 29, 2004, 9:01pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/3 "2004-03-29T21:01:39Z")
> [@SettingSun](#):
>
> True “neutral buoyancy” is impossible to obtain.
Cite?
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### Author:  [@SettingSun](https://boards.straightdope.com/u/SettingSun)
#### Post date: [March 29, 2004, 9:09pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/4 "2004-03-29T21:09:03Z")
> [@Grey](#):
>
> Cite?
Archimedes (287? - 212 B.C.)
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### Author:  [@Grey](https://boards.straightdope.com/u/Grey)
#### Post date: [March 29, 2004, 9:16pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/5 "2004-03-29T21:16:05Z")
Do you mean he wasn’t neutrally buoyant before or after he was dead?
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### Author:  [@borschevsky](https://boards.straightdope.com/u/borschevsky)
#### Post date: [March 29, 2004, 10:04pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/6 "2004-03-29T22:04:13Z")
In a body of water, the deeper water should be denser due to gravity, so an object with the correct density should float at a certain depth in the water, neither sinking nor rising.
Same idea as a hot air balloon.
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### Author:  [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)
#### Post date: [March 29, 2004, 10:20pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/7 "2004-03-29T22:20:33Z")
> [@borschevsky](#):
>
> In a body of water, the deeper water should be denser due to gravity, so an object with the correct density should float at a certain depth in the water, neither sinking nor rising.
>
> Same idea as a hot air balloon.
No it shouldn’t. It will be under greater _pressure_ but it won’t become denser. Liquids, like solids, do not compress under pressure. The density of water is always 1g/ml.
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### Author:  [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)
#### Post date: [March 29, 2004, 10:24pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/8 "2004-03-29T22:24:16Z")
What about a **submarine**?
Even under no forward propulsion, the ballast could be adjusted to any depth.
And **borchevsky** water (unlike air) is not compressible and so water has a constant density despite the presure to which it is subjected. (I imagine there could be a _negligible_ increase at higher pressures but this is inconsequentail for this discussion.)
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### Author:  [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)
#### Post date: [March 29, 2004, 10:25pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/9 "2004-03-29T22:25:47Z")
Darned !
**ReallyNotThatBright** types faster than I do.
Sorry for repeating the same information.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [March 29, 2004, 10:25pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/10 "2004-03-29T22:25:56Z")
> [@Really Not All That Bright](#):
>
> No it shouldn’t. It will be under greater _pressure_ but it won’t become denser. Liquids, like solids, do not compress under pressure. The density of water is always 1g/ml.
That isn’t true; liquids don’t compress very much, to the extent that for many applications, they can be _considered_ incompressible, but they are compressible nonetheless, as are solids.
(if this were not so, sound waves would not be able to travel under water)
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### Author:  [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)
#### Post date: [March 29, 2004, 10:29pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/11 "2004-03-29T22:29:46Z")
And **SettingSun**
How abount a website link for neutral buoyancy being unattainable?
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### Author:  [@kniz](https://boards.straightdope.com/u/kniz)
#### Post date: [March 29, 2004, 11:05pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/12 "2004-03-29T23:05:19Z")
[Neutral Buoyancy at Cosmonaut Training Center](http://www.superiortravel.com/specials/adventzone/neutbuoy.htm)
> [@](#):
>
> \*\* "Neutral buoyancy is the term used to describe when something has an equal tendency to float as it does sink. Objects that are configured to be neutrally buoyant seem to “hover” underwater. This is accomplished with a combination of weights and flotation devices. Large, neutrally buoyant items can be easily manipulated much like in orbit.\*\*
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### Author:  [@SettingSun](https://boards.straightdope.com/u/SettingSun)
#### Post date: [March 29, 2004, 11:15pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/13 "2004-03-29T23:15:04Z")
> [@wolf\_meister](#):
>
> And **SettingSun**
> How abount a website link for neutral buoyancy being unattainable?
This is the best site I found on the Internet, but not really comprehensive to the OP … [Archimedes Law](http://www.geocities.com/gwmccue/Systems/Ballast_System.html)
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [March 29, 2004, 11:15pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/14 "2004-03-29T23:15:36Z")
I’m trying to work out what the objection would be; my best guess is that factors like convection currents and maybe even Brownian motion might make it a practical impossibility.
But in theory, all you should need is a body whose displacement exactly equals its own mass.
Actually, it might be quite difficult to go from the position of _sunk_ or _floating_ to a position of static neutral buoyancy, as slowing your ascent or descent would actually involve adjusting the buoyancy to _the other side_ of neutral and in an ideal model, you would only end up oscillating about a fixed point by ever-smaller amounts, never actually achieving rest.
maybe that’s what the OP means.
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### Author:  [@SettingSun](https://boards.straightdope.com/u/SettingSun)
#### Post date: [March 29, 2004, 11:23pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/15 "2004-03-29T23:23:09Z")
> [@Mangetout](#):
>
> … and in an ideal model, you would only end up oscillating about a fixed point by ever-smaller amounts, never actually achieving rest … maybe that’s what the OP means.
No, the “law” is an object at **rest** will either float to the surface or sink to the bottom …
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [March 29, 2004, 11:26pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/16 "2004-03-29T23:26:35Z")
Pardon me, but that sounds like a contradiction; could you explain a little more?
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### Author:  [@SettingSun](https://boards.straightdope.com/u/SettingSun)
#### Post date: [March 29, 2004, 11:31pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/17 "2004-03-29T23:31:34Z")
> [@Mangetout](#):
>
> Pardon me, but that sounds like a contradiction; could you explain a little more?
If you hold an object perfectly still at some depth in water and release it, it will either float to the surface or sink to the bottom.
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### Author:  [@kniz](https://boards.straightdope.com/u/kniz)
#### Post date: [March 29, 2004, 11:36pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/18 "2004-03-29T23:36:07Z")
What’s the argument about? They use it in cosmonaut training. Are they breaking the law? :rolleyes:
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [March 29, 2004, 11:39pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/19 "2004-03-29T23:39:10Z")
OK, why?
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [March 29, 2004, 11:43pm UTC](https://boards.straightdope.com/t/objects-that-dont-float-in-water-sink-to-the-bottom/237159/20 "2004-03-29T23:43:32Z")
What will happen if the object precisely of the same overall density as water - i.e. the water it displaces when fully immersed weighs exactly the same as the object?
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