Talk:Hydrostatic equilibrium

Pressure gradient force?
The term pressure gradient force relates to horizontal gradients, not the vertical. The atmosphere resists gravity not because of the pressure gradient force, but because of its expansive internal energy, i.e. heat. Tmangray 02:22, 1 April 2007 (UTC)
 * Wherever pressure differs with location, there's a pressure gradient force. Horizontal, vertical, oblique, doesn't matter.  It's just that we normally only consider the horizontal components, because the vertical component achieves hydrostatic equilibrium almost instantaneously and doesn't tell us anything interesting about the hydrodynamics. --Dan Wylie-Sears 2 (talk) 02:25, 1 November 2019 (UTC)

Terms describing conditions outside Hydrostatic equilibrium ??
From my observations, my surrounding atmosphere is rarely in equilibrium, so I am assuming the conditions either side could be defined, hopefully with names, any ideas?

I'd then like to be able to describe Hydrostatic equilibrium in context, something like "Xair gains energy as it approaches equilibrium, but due to mixing and cooling it often becomes Yair" any suggestions ? Teeteetee 15:26, 22 January 2007 (UTC)

Merge
I've suggested a merge for Hydrostatic equilibrium and Hydrostatic balance. Both describe (I think) the same thing. Anyone for or against this merge? --H2g2bob 16:30, 23 May 2006 (UTC)

I agree. The difference is just grammatical. -- Red icarus 12:31, 25 May 2006 (UTC)

I've merged the two. --H2g2bob 19:27, 2 June 2006 (UTC)

Suggested Change
A body in hydrostatic equilibrium is not necessarily an oblate spheroid. It could also be  a triaxial ellipsoid, as was shown by Jacobi. This is discussed in great detail in Chandrasekhar's book Ellipsoidal Figures of Equilibrium. An expert should correct this article accordingly. -- OinkOink 19:31, 16 September 2006 (UTC)

For that matter, a body in hydrostatic equilibrium need not even be an ellipsoid. For example, Poincaré studied pear-shaped bodies of equilibrium. --OinkOink 16:25, 22 January 2007 (UTC)

Astrophysics
The astrophysics section is currently just embarrassing. No, a star is not like a balloon! And what's that nonsense about an "isotropic gravitational field"? OinkOink 00:15, 17 December 2006 (UTC)

I agree with "OinkOink" - especially the part about "centrifugal force"! —Preceding unsigned comment added by MlssStaun (talk • contribs) 06:46, 9 October 2007 (UTC) MlssStaun 07:02, 9 October 2007 (UTC)
 * While speaking from a position of relative ignorance,I came in here specifically to say that I found that section delightful in its clear plain language and description--— Tumadoireacht Talk/Stalk 06:41, 15 January 2011 (UTC)

Article seems weird
The definition given in the head, besides being vague, seems wrong. Doesn't hydrostatic equilibrium require isotropic stress (i.e. stress is only the hydrostatic pressure)? Note that the velocity field may be constant over time (in the Lagrangian view) but the fluid may be accelerating (in the Eulerian view). Presumably one shoudl say that the flow velocity is small enough for the inertia to be negligible? I thought I had some idea of what hydrostatic equilibrium was, but this article managed to destroy that little knowledge giving nothing in return... --Jorge Stolfi (talk) 20:00, 24 February 2013 (UTC)
 * I believe you're correct. That's how I understand it from physics classes way back when, and that's what the reasoning in the "mathematical consideration" section implies.  I'm changing the lead to say "for each parcel of fluid" instead of "at each point". --Dan Wylie-Sears 2 (talk) 02:33, 1 November 2019 (UTC)

Article too focused on astrophysics
The concept of hydrostatic equilibrium is important in every context where there is fluid standing still. (It is what prevents the tea from squirting out of a teapot's spout, for example). However this article makes it seem that it is an abstruse topic of interest only to astrophysicists and (a little) to meteorlogists. Besides (as others pointed out above) celestial bodies and atmosphere are hardly good examples of fluids in hydrostatic equilibrium, except in the most crude approximations. --Jorge Stolfi (talk) 20:04, 24 February 2013 (UTC)

Hydrostatic fluid merged (invisibly for now) here
The article hydrostatic fluid has been merged into this one, since a "hydrostatic fliud" is (or should be) nothing else than a fluid in hydrostatic equilibrium. However, that text has been left as a HTML comment in the head section for now, pending clarification of the questions above (namely, if the definition of "hidrostatic equilibrium" given here is correct and general enough.) --Jorge Stolfi (talk) 20:08, 24 February 2013 (UTC)

Hydrostatic equilibrium of solids
The article introduces hydrostatic equilibrium for fluids. Later, it talks about planets being in hydrostatic equilibrium. It's not clear why that makes sense:


 * must planets be internally liquid? Seems not.
 * does solid rock at high pressure behave like a liquid anyway?
 * does solid rock at high pressure fracture so that, even though it's not a liquid, it can rearrange anyway, a bit like in landslides? If so, hydrostatic equilibrium is not restricted to fluids, and the article should IMHO clarify this.

The article later says that (dwarf) planets "have sufficient gravity to overcome their own rigidity", which leaves the above questions open. That's maybe on purpose, but one could just list possibilities. I've browsed a bit some Wikipedia articles (on fluids, solids, etc.) without being able to figure it out. (I got physics in high school, but we did not remotely cover such topics). Could someone revise the article to clarify this point for the layman?

--Blaisorblade (talk) 21:14, 17 June 2015 (UTC)

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Astrophysics
I want to know which are another seven objects in hydrostatic equilibrium. Ayush pushpkar (talk) 05:19, 29 May 2019 (UTC)

And a related question, is it still the case the Juno is the largest non-equilibrium object? According to the page on Vesta, observations from Dawn have shown that it is not in hydrostatic equilibrium and it's much larger than Juno. Dbenford (talk) 00:34, 29 January 2021 (UTC)


 * can u please point the links for juno and vesta to precise articles??? Yashpalgoyal1304 (talk) 07:08, 1 April 2021 (UTC)

The Moon
Afaik the Earth's Moon isn't considered to be in hydrostatic equilibrium either. This would make it the largest object that isn't in hydrostatic equilibrium, not Iapetus. Haumea per its equatorial equator would also be larger than Iapetus and doesn't have a spherical shape but the shape of a rugby ball. Iapetus on the other hand does look spherical, unlike the section phrase describes it. The phrase has been changed but someone changed it back without elaboration. 213.142.96.15 (talk) 13:01, 15 June 2021 (UTC)