Talk:Newtonian fluid

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This article doesn't work at all for me, anymore. I keep getting errors, i.e.: "

A simple equation to describe Newtonian fluid behaviour is

   Failed to parse (Can't write to or create math output directory): \tau=\mu\frac{dv}{dx}

where

   Failed to parse (Can't write to or create math output directory): \tau

" Sim 03:15, 1 September 2006 (UTC)

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The article is well and good for those who have done uni-level maths, but makes little sense at all to those who don't... compare non-Newtonian_fluid, which is very clear as to what's going on. --User:Firien § 11:55, 3 February 2006 (UTC)

• How about now? Should I be removing the template? Sim 01:21, 6 February 2006 (UTC)
  • A colleague and I have done some looking into the subject (ok, a lot of looking into the subject :) and expanded further as just added to the article page. I'm happy to have the template removed, if you think what's down now is good? --User:Firien § 12:02, 6 February 2006 (UTC)

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What's with the removal of the delta factor? Here - while I can't parse it completely, I think the component is the shear perpendicular to a given face (i=j) by grad velocity, which looks like a flow factor, which the shear should depend on; flagging it also because it's the only edit by that IP, and I'd like to get it verified before letting it go! --User:Firien § 18:46, 8 February 2006 (UTC)

The current form is fine for $i\neq j$, but that does need to be noted or replaced with $\tau _{ij}=\mu \left({\frac {\partial v_{i}}{\partial x_{j}}}+{\frac {\partial v_{j}}{\partial x_{i}}}\right)-\left(p_{m}+{\frac {2}{3}}\mu \nabla \cdot {\overline {v}}\right)\delta _{ij}$ —kotepho 2006-03-19 22:54Z

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The article currently starts with: "A Newtonian fluid (named for Isaac Newton) is a fluid that flows like water". I find this confusing because: 1. it's not clear in what way it's supposed to flow like water, and: 2. water is not a newtonian fluid - for large stress it reacts like a solid (i.e. when an asteroid hits water, it shatters as the hydrogen bonds have no time to realign), and for small stresses there are miniscus forces (so a jesus lizard can walk on water) so the stress/rate of strain curve is not linear and doesn't go through the origin.

Also, it's not clear to me if the 'rate of strain', and the velocity gradiant that appears in the equation are the same thing.

I hope someone who considers himself qualified will rewrite the definition. 88.153.104.131 20:27, 22 July 2007 (UTC)

This section needs rewording?

For a Newtonian fluid, the viscosity, by definition, depends only on temperature and pressure (and also the chemical composition of the fluid if the fluid is not a pure substance), not on the forces acting upon it.

Suggested rewrite:

By definition the viscosity of a Newtonian fluid does not depend on the forces acting upon it. For a given pure chemical substances the viscosity depends only on pressure and temperature. For a mixture the viscosity also depends on the chemical composition. —Preceding unsigned comment added by 130.86.76.10 (talk) 21:46, 26 May 2009 (UTC)

Lead section is incomprehensible to non-physicists

I have added the {{technical}} template here on the talk page because I find the introductory section too short to relay any comprehensible meaning to a lay person. __meco (talk) 09:29, 15 August 2009 (UTC)

Doesn't it just! It reads like an exercise in making something everyday seem impenetrably difficult. How about this:

When a liquid feels no more hard nor runny when it is compressed, e.g. by stirring, then it is Newtonian.  Ketchup becomes more liquid as you stir it then thickens again when you stop stirring; a corn flour and water mix seems to become a solid when you try to stir it then it relaxes back to a liquid when you stop stirring; these two are non-Newtonian liquids.

SandJ-on-WP (talk) 12:06, 15 September 2019 (UTC)

Term is often incorrectly used

When I was in elementary school my science teacher mentioned "Newtonian fluids" to the class, claiming that they had both solid and liquid characteristics and holding up Silly Putty as an example. Now that I'm all grown up I realized that she was actually referring to non-Newtonian fluids. Stonemason89 (talk) 16:58, 17 June 2010 (UTC)

Merger of viscous stress tensor

Viscous stress tensor has largely the same material as in this article and in Navier–Stokes equations#Stresses. And originally the material now in Viscous stress tensor was in viscosity. How to deal with this? To me, inclusion/merger here seems the most logical place, since the modelling of the viscous stress tensor is essential the modelling of a Newtonian fluid. -- Crowsnest (talk) 14:09, 3 October 2012 (UTC)

I want this material to be covered in as much depth as possible, so I would prefer it to remain a separate article - even if it is intrinsically linked to several other concepts. It seems to be quite an important topic in its own right. --عبد المؤمن (talk) 16:41, 5 January 2013 (UTC)

I would oppose the merge, too. Wikipedia is not a textbook, but a reference work: most readers come here looking for specific information. Lumping articles is generally bad for them, as they have to look through pages and pages to find the information they want. Moreover, when following a wikilink (say, on stress tensor) they will either have to search again for the right section on a large article (say, Newtonian fluid), or they will be directed to a section of that article that cannot be understood without reading several previous sections.
Lumping does not seem to help editors, either: the presumed convenience of having all related topics in one file is negated by the need to think about all those topics at the same time, and the irresistible urge to cast them in a common notation and logical order --- a goal that Wikipedia cannot ever achieve, and and therefore should not waste effort in trying to.
Indeed, cleaning up a large article is many days' work, so it is very unlikely that one of the few (and dwindling) experienced editors will dare to do it.
Keeping separable articles separate is good for readers, attracts more editors, allows them to concentrate on one small topic at a time, encourages them to do general article cleanup, and makes it easier to create wikilinks to correct, self-contained explanations of related topics.
--Jorge Stolfi (talk) 11:57, 16 January 2013 (UTC)

PS: On the other hand I agree that the viscous stress tensor article actually has lots of material that does not quite belong there; and some of that stuff should perhaps be moved to this article.-- Jorge Stolfi (talk • contribs) 03:23, 17 January 2013

The merge tag has been inserted again in the article but there seems to be no new argument here. Again, I am opposed to the merge. "Viscosity tensor" is one concept, "Newtonian fluid" is another quite distinct concept. The tensor is used (or may be used) also in many other articles such as viscoelasticity. The use of concept A in the definition of concept B is not reason enough to merge "A" and "B". --Jorge Stolfi (talk) 01:06, 13 March 2013 (UTC)

OK, I closed the merge tags out as no consensus. When there is no consensus to merge, simply remove the templates from the article pages—don't move them to the talk pages. Discussion of changes to the merge process, which may eventually result in implementation of talk page merge tags, is at Wikipedia talk:WikiProject Merge. – Wbm1058 (talk) 03:25, 13 March 2013 (UTC)

Contradictory statement

The statement "Water and air are examples of (practically) Newtonian fluids, which include , and exhibit the Weissenberg effect" is contradictory because the Weissenberg effect is exhibited by non-Newtonian fluids. It should be removed.Skater00 (talk) 21:35, 6 March 2013 (UTC)

Indeed, that was probably an editing accident, sorry. Someone already fixed it. --Jorge Stolfi (talk) 05:45, 13 March 2013 (UTC)

Minus?

My professors and books always explained me that the strain of a newtonian fluid is defined as follows:

$\tau =-\mu {\frac {du}{dy}}$

Shouldn't we add a minus to this formula? — Preceding unsigned comment added by 145.94.226.124 (talk) 10:06, 14 December 2016 (UTC)