Talk:Fluid

Solids which behave like fluids
How does one categorize materials such as sugar or grain, which in bulk have very fluid-like behaviors? A very large number of plastic beads or metal ball-bearings would behave exactly like a fluid. D e nni &#9775;  23:22, 27 June 2006 (UTC)
 * They are solids. When modelling them, the word used is "granular flow". The distinction is not the the solids behave like fluids but that small abjects together exhibit fluid-like behaviours. And by the way, they do not behave like fluids in many cases.CyrilleDunant 09:08, 29 June 2006 (UTC)
 * I don't see how a large container of, say, BBs, would behave any differently from a fluid, except for the property of wetting, and the presence of surface tension. D e nni &#9775;  01:27, 30 June 2006 (UTC)

Definition of a fluid
A fluid is defined as a substance that continually deforms (flows) under an applied shear stress. All liquids and all gases are fluids.

^^ This does not apply to some classes of non-newtonian fluids. (i.e. Bingham plastics).

Removed: notion of deformation under a shear stress regardless of how small the applied stress is. This is 100% untrue.

More generally, the stress is a function of the rate of change of deformation, rather than a function of the deformation itself. Removed 'no matter how small' from the article as a start, as mentioned above, fluids (i.e. Bingham) may have a yield stress. — Preceding unsigned comment added by Oddbodbloke (talk • contribs) 11:21, 26 November 2011 (UTC)

Confusion
This article needs a rewrite as several parts of it are rather confusing. Please refer to the Rheology article, in which the definitions are much clearer. LouisBB (talk) 14:45, 4 November 2008 (UTC)

There are other, different Fluids.
There is another fluid. An art piece by Allan Kaprow called Fluids, done in 1967 in Los Angeles. There ought to be a page about that. —Preceding unsigned comment added by 24.184.156.70 (talk) 04:00, 23 March 2010 (UTC)

Gases are fluids too!
There are glaring mistakes in the introduction:

'Fluids are a subset of the phases of matter and include only liquids' This is not true. Fluids include both liquids and gases.

'Although the term "fluid" includes in common usage, "fluid" is often used as a synonym for "liquid", with no implication that gas could also be present.' This sentence is lacking the word "gases" after the word "includes". — Preceding unsigned comment added by 164.143.244.33 (talk) 18:21, 5 February 2013 (UTC)

What substance "fluid" refers to
Which substances are included in "fluid" (and what is not) greatly differ among scientific domains. But it seems there is one thing in common: "fluid" is a term of generalisation in each domain, when an older term does not fit to some objects of interest. --Wotheina (talk) 07:25, 23 June 2021 (UTC)
 * Dynamics: liquid + gas
 * Rheology: classic fluid + plastics
 * Particle physics: classic fluid + plasma + electron fluid + ...
 * Physiology: blood + lymph + liquids inside cells + ...
 * Hydraulics (including break fluids): oil + non-oil
 * Machining: oil + non-oil liquid + mist + ...