Talk:Stokes' law

Requested move

 * The following discussion is an archived debate of the . Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section. 

Do not move. —Wknight94 (talk) 00:03, 5 September 2006 (UTC) Stokes' law → Stokes's Law – Currently, the main article is at Stokes' law and Stokes's Law redirects to it. The two should be reversed, since Stokes's Law is the gramatically correct name (see Saxon genitive). Capi 23:33, 25 August 2006 (UTC)

Survey
Add "* Support" or "* Oppose" followed by an optional one-sentence explanation, then sign your opinion with ~
 * Support, I was the nominator. Capi 23:37, 25 August 2006 (UTC)
 * Oppose --Philbarker 16:26, 31 August 2006 (UTC).
 * Oppose. Good research by Phil Barker below. Andrewa 19:32, 31 August 2006 (UTC)
 * Oppose on grounds of euphony, plus "Stokes' law" is What I Was Taught. --Trovatore 00:35, 1 September 2006 (UTC)
 * Oppose, looks silly. Melchoir 23:11, 1 September 2006 (UTC)
 * Oppose, Stokes' is how most texts write this. --Polaron | Talk 03:29, 2 September 2006 (UTC)

Discussion
Add any additional comments

I'm not altogether happy about this one. Google seems to show that Stokes' law and Stokes law are more common than Stokes's law, although all three have currency. Brittanica goes with Stokes's law. Interesting. Andrewa 03:33, 31 August 2006 (UTC)

(you may have read some of this elsewhere) Are you going to put in a redirect request for Achilles' heel? Fowler's Modern English Usage ISBN 0198691157 has an article on "possive puzzles", the jist of which is that --s' used to be the norm and is still retained in poetic and reverential contexts; otherwise add the s, so Stokes' Law--it predates the 's usage, and is to some extent reverential. --Philbarker 16:24, 31 August 2006 (UTC)
 * ps, other --s' examples: Bayes' theorem, Reynolds number, War of Jenkins' Ear, St James' Park (but not St. James's Park) and Davey Jones' locker. Also see: Apostrophe. --Philbarker 17:04, 31 August 2006 (UTC) (amended 1 September 2006)


 * Good points IMO, which should be added to the policies and guidelines. In my brief career in Physics, it was always Stokes' law or Stokes' Law when being formal (textbooks papers etc) and Stokes Law on the blackboard. So I'm thinking Brittanica is wrong here. Andrewa 19:36, 31 August 2006 (UTC)


 * Quibble: "Reynolds number" is not a possessive; "Reynolds" is being used appositively, as in Gödel number (not Gödel's number). --Trovatore 01:10, 1 September 2006 (UTC)


 * you're only saying that because it's true :-) --Philbarker 08:42, 1 September 2006 (UTC)


 * The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Units
thanks for the article - very helpful Suggest the metric units are chagned to the more universal "SI", rather than as shown. Jerryjoynson 08:06, 25 June 2007 (UTC)


 * Unit is kgm/s2 — Preceding unsigned comment added by 103.228.156.52 (talk) 08:42, 11 May 2018 (UTC)


 * True but this combination is usually called N (for Newton). I have now related N and also Pa-s to kg, m and s in the article. Dirac66 (talk) 22:35, 13 May 2018 (UTC)

Symbols
Suggest that the symbol for velocity be changed to a common v... It took me a while to realise that the capital V there did not refer to volume. —Preceding unsigned comment added by 170.140.163.29 (talk) 21:14, 31 July 2008 (UTC)


 * Good idea which seems to have been only partially adopted in 2008, as the section on Terminal velocity still uses V. I will change them to v now.


 * Also the article now confuses r and R. The section Statement of the law uses r for spherical radius, but later sections use R for spherical radius and r for a cylindrical coordinate which is not the same thing. I will change the section Statement of the law to be consistent with the other sections. Dirac66 (talk) 01:19, 22 May 2017 (UTC)

A-level Physics
Stokes' law is a theme in some of the UK OCR A-level Physics coursework. This means that this article will get increased traffic for the time that students investigate it. Whilst this shouldn't be a problem, I ask that editors with knowledge of this subject please keep an eye on it to revert vandalism, misleading information and good-faith edits which contain untrue information.

I don't predict us having any troubles with this article - A-level Physics students are pretty mundane when it comes to vandalism - but I think it's worth keeping an eye on. And I thought you might appreciate the heads up! Greggers (t &bull; c) 18:03, 23 March 2009 (UTC)

Grammar
Sorry to bring this up again, but I feel that the article should read "Stokes's law", regardless of both the popularity of an incorrect spelling and the formal use in a science paper instead of an English one.

I will bring this up continuously until I feel this issue has been resolved, instead of ended using logical fallacies and the like. 69.199.23.90 (talk) 20:40, 26 June 2009 (UTC)


 * Both variants seem to be allowable, depending on which sources are used regarding style, see Apostrophe. A Google Scholar search shows that in scientific publications "Stokes' law" is far more common than "Stokes's law". -- Crowsnest (talk) 21:44, 26 June 2009 (UTC)


 * Just because something is common does not mean that it is correct. I think we ought to change it, if only to create consistency throughout the entire encyclopedia. Looking at the page, I promounce the title "Stokeses law." If we're going to pronounce the letter, shouldn't we write it also? Just so that we remain consistent with the most important rule, i.e. "Put an apostrophe ess after every single noun to makeit possessive"?67.77.198.183 (talk) 00:03, 27 June 2009 (UTC)


 * Support - You may think that it looks silly but the fact is that Stokes' is incorrect and implies that there are many Stokes to which this law belongs to. The correct grammatical name is Stokes's Law, and any text book that gets this wrong should seriously consider learning the english language. 58.169.132.27 (talk) 07:46, 29 October 2010 (UTC)


 * Support - This grammar issue is bothering me also. Why is Gauss's Law correct in Wikipedia but Stokes's Law incorrect?


 * Support - It's a ludicrous issue, and often childish and embarassing that there ever was a debate at all. :/ — Smuckola (Email) (Talk) 20:19, 11 August 2014 (UTC)


 * Support, unless... - I was taught that, for proper names, "Charles's" and "fetus's" are correct English while "Charles'" and "fetus'" are wrong. But maybe the second "s" should be omitted if the name ends in "s" because it derives from a plural noun?  That is, if the name "Stokes" derives from the plural of "stoke", then the genitive is indeed "Stokes'"? But that does not make sense, because the proper name is singular even in that case... On the other hand, if his last name was Stoke and he had a brother and the law was named after both, then it would be indeed "Stokes' law". However... OK, I guess that I should have stopped after the first sentence... --Jorge Stolfi (talk) 23:48, 5 July 2019 (UTC)


 * It seems that different educators teach different rules of grammar in this respect. Wikipedia goes with WP:COMMONNAME.   Dbfi<i style="color: #4e4;">r</i><i style="color: #4a4">s</i>  06:40, 6 July 2019 (UTC)


 * Support - "Stokes's law" is grammatically correct, and this is not a title, but a description of a physical law. I am surprised to see that this discussion has continued for years, but with no change to the entry. I only clicked on the Wikipedia page today because I was looking for an explanation for why it used the incorrect term. The fact that many people have written it incorrectly in the past has no bearing on whether it is correct now, and the problem will only be compounded by Wikipedia proudly retaining the error.

The Law
Shouldn't it be more accurately expressed by replacement of 'V' for velocity by $$-|V|.\hat{V}$$? since, as it is, it could imply that the force acts in the same direction as the velocity. At least make it clear by replacing $$F_{d}$$ with $$|F_{d}|$$.

Also, 'V' could be more generally defined by 'relative' rather than the absolute velocity defined here, since that is merely a special case when the fluid is stationary. Hai2410 (talk) 10:40, 15 January 2010 (UTC)

Possible errors
I disagree with:

"eta is the fluid's kinematic viscosity (in St m2/s)"

It appears to me that eta is the dynamic viscosity (in Pa.s kg/m/s).

Also "mu" should be "eta" in the terminal velocity expression (second equation).

I don't want to change this before asking other people's opinion first.

Terminal velocity formula: 2/9 or 1/18?
A few days ago editor 201.127.250.217 changed the formula for terminal velocity of a sphere falling in a fluid from
 * $$v = \frac{2}{9}\frac{\left(\rho_p - \rho_f\right)}{\mu} g\, R^2$$ to
 * $$v = \frac{1}{18}\frac{\left(\rho_p - \rho_f\right)}{\mu} g\, R^2$$, which was then reverted by editor Jackfork.

However the article terminal velocity writes the formula in terms of the diameter d = 2R as
 * $$V_t = \frac{g d^2}{18 \mu} \left(\rho_s - \rho \right)$$, which is equivalent to the first form above since (2/9)R2 = (1/18)d2. So it would seem that the source of the confusion is that some sources write the formula in terms of radius with a factor 2/9, and other sources write it in terms of diameter with a factor 1/18 which is equivalent. The version with 1/18 R2 is incorrect. Dirac66 (talk) 01:02, 12 November 2017 (UTC)

Reverted Move
I have changed the page title back to what it was before December 2017 in light of previous consensus. I would note that there are reasons pointing either way. Various style guides are split on the issue, but our own house style would seem to support "Stokes's". The guide for article titles does not weigh in one way or the other, however the criterion on naturalness indicates, at least for me, that even if "Stokes' Law" is nominally incorrect, its wide use by the sources cited, and in the article itself, then without a compelling reason to go against that grain, the common title should be preferred. --Ipatrol (talk) 20:14, 21 October 2018 (UTC)


 * The old discussion you are referring to is 12 years old now. Things changed, in particular MOS:POSS is nowadays fairly clear on the singular possessive. I'll spare you long reading, as well as providing references to other similar discussions. The gist is, the singular possessive almost always is written with "-'s" (there are literally just a couple allowable common-use exceptions like "Jesus'" – and even that is not a prescription, so writing "Jesus's" is totally fine and in fact is preferred since a lot of people pronounce it as "Jesusez"). So with Stokes'/Stokes's Law, the main distinction that needs to be made is whether the use of the name Stokes is attributive or possessive: if former, then the only proper way to write it is "Stokes Law" (similar to "Reynolds number"), but if the latter, then the MOS:POSS prescribes "Stokes's Law". Since the "attributive vs. possessive" is clearly resolved by common usage in this case towards the latter (considering both "Stokes' Law" and "Stokes's Law" variants encountered in many sources), the title should be "Stokes's Law". cherkash (talk) 01:07, 22 October 2018 (UTC)


 * Well running a search engine test returns about 250k for both "Stokes' law" and "Stokes law", 50k for "Stoke's law", and 18k for "Stokes's law". As for links on the wiki, they seem to be spread in an approximately uniform way among the various redirects. Trying to cut to the heart of the matter and see what other sources have said on the spelling of this specific term, yields a few results, but none of them very sure on the issue. An document from the International Geoid Service Bulletin notes that, "there is some quite considerable variation throughout the literature and it is common to see the possessive written as Stokes’", but asserts that is incorrect. Jason Rosenhouse was unsure on the subject. A book written in 2013 uses "Stokes'", and specifically notes the apostrophe. Nothing else comes up in search results. Meanwhile, it seems we had a discussion about naming theorems early in Wikipedia's history that apparently went nowhere. Digging around more generally on the subject of possessives and apostrophes reveals a sordid litany of arguments, flamewars, fights over British vs American English (and accusations of "language imperialism"), and all kinds of other nasty things I'd rather not drag in here. --Ipatrol (talk) 03:44, 22 October 2018 (UTC)
 * A principled discussion (as opposed to flamewars, etc. you mentioned) centers around two points: one, the grammar role of the noun "Stokes" (possessive form of a noun, attributive use of a noun, etc.), and two, the style of a singular possessive (if this is indeed what "Stokes" is determined to be grammatically). I think it's fairly clear from the use of "Stokes/Stokes's/Stokes' Law" in practice, that the grammatical role intended seems to be "possessive form of a noun". Then the style (Stokes' vs. Stokes's – which are the only two options debated in the case of a possessive) is determined fully by our own Wiki's MOS (Manual of Style): the reason being is that if something is regularly misspelled in the sources, this is not a good reason for us to misspell it in Wikipedia – we should mention the misspelling with "sic" if it's a direct quote, or could mention a common misspelling with "also often written as XXXX" comment in the first sentence of the lead paragraph when this is the case. Using any variation of "how is it spelled in reliable sources?" question makes not much sense beyond establishing grammatical role – mostly because the spelling is not an encyclopedic fact that needs to be established by reliable sources, but rather a stylistic choice controlled by a publication's own MOS (once the grammatical role is established). cherkash (talk) 13:31, 22 October 2018 (UTC)
 * The 18K for Stokes's is not very impressive when compared to 50k for Stoke's which I think we all agree is incorrect since it would imply that the scientist was named Stoke. As for the grammar rules, I think they also vary with source and we should follow general usage for this term. So Stokes' law is the best article title since it is the most widely used. We can mention Stokes law and Stokes's law once each in the lead. Dirac66 (talk) 23:29, 22 October 2018 (UTC)


 * I don't think you read very carefully what I wrote, . Specifically, it's not clear what your "As for the grammar rules, I think they also vary with source" really means. Do you mean that the grammatical role of "Stokes" (possessive vs. attributive) varies by source? Or do you mean the grammar rules to follow (Stokes' vs. Stokes's) vary? cherkash (talk) 02:55, 23 October 2018 (UTC)
 * I've moved it back. There was simply not enough justification for the recent move, per the discussion above. cherkash (talk) 18:02, 6 November 2018 (UTC)


 * I think you are wrong, but I won't edit war over this entry. For grammar and correct spelling, I quote the Oxford English Dictionary (Second Edition): "Stokes' law  n. (also Stokes' formula) the statement that the resisting force on a spherical particle moving through a fluid is 6πηVr ..."   <i style="color: blue;">D</i><i style="color: #0cf;">b</i><i style="color: #4fc;">f</i><i style="color: #6f6;">i</i><i style="color: #4e4;">r</i><i style="color: #4a4">s</i>  18:49, 6 November 2018 (UTC)
 * OED may be guided in their choice by their internal manual of style, or by whatever other stylistic choices they've decided to make. In this sense, their style is not authoritative for us on Wikipedia, and WP:MOS (and more specifically, MOS:POSS) is the guide for us here. cherkash (talk) 22:28, 15 November 2018 (UTC)

Removed "Heuristic Proof"
I boldly removed the Heuristic Proof section (quoted below). It was completely unsourced, unclear, not obviously correct or useful, and seems likely to be original "research". (It is also poorly formatted, but that would have been easily fixed.) Unless someone can find a source and clarify the section so it makes sense, it does not belong in the article.

The actual proof section could be improved, e.g. based on Landau and Lifshitz, and a properly sourced heuristic discussion of the contributions of pressure and friction terms to Stokes Law might be possible, but this "Heuristic Proof" is not helpful.

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Heuristic Proof
The mysterious six in Stokes' formula can be derived from adding the surface area of a sphere to the surface area of its lower hemisphere:
 * $$A = 4\pi r^2 + 2\pi r^2.$$

When each term is multiplied by v/r, the number of radial lengths per second of the ball's descent through the fluid, we obtain the rate at which oil is sliding off of the "duck's back", a meters squared per second quantity. This is also the rate of change of volume over time (the chain rule requires the v/r factor). When multiplied by the viscosity this yields a fluid force. A drop of oil moving over the surface is pushing against the viscosity: meters squared per second multiplied by a kilogram per meter-second nets out to newtons of force. The greater the fluid's speed and the greater the resistance it encounters, the greater the fluid force. For the upper hemisphere: $$ F_{drag} = 2\pi rv\mu.$$ For the lower hemisphere: $$ F_{drag} = 4\pi rv\mu.$$

The latter represents the streamlines pushing upwards on the lower half of the ball. One way of coming at this is to view the speed of the streamlines pushing up on the lower hemisphere as v-(-v) or 2v against a speed of only v for the overall descent of the ball. The lower hemisphere is like the biker in front of his passenger catching the "wind", which is just produced by the bike's motion, and shielding his passenger. The quadruple term would refer to the lower hemisphere and the double term would apply to the upper hemisphere. A more graphic example would be that a victim doesn't care which "end" of an iron ball hit him in the noggin, but the ball does care; you'd rather be the upper hemisphere of the ball. The much vaunted symmetry of the sphere has its limits. This also bears comparison to the change in momentum of a ball bouncing off a wall: mv-(-mv) = 2mv: $$ F_{drag} = 2\pi rv\mu + 4\pi rv\mu.$$.

26901785
26901785 106.79.237.12 (talk) 08:52, 20 March 2023 (UTC)

Stokes' assumptions: laminar not strong enough
In the list of assumptions for Stokes' equation for the drag force on a sphere, laminar is not a strong enough constraint. It is required, and including it in the list certainly a nice way to say that it's not applicable to fast, turbulent flows... but flow around a sphere is laminar by nearly any definition—without eddies, vortexes, or unsteadiness—to at least Re(d) ~10 (and with stable eddies to ~130), while error exceeds 10% (common engineering cuttoff) before Re=1 and a factor of 2 by somewhere around Re=15.

Since Re figures so cleanly in the cutoff, I'll be making an edit to include reference to "negligible inertial effects" or something shortly. (It'd be nice to give readers good numbers here but I don't have a good reference for that yet... Comparison to Proudman's solution (Oseen equations) would work for the 10% cutoff, in a pinch (gives Re ~0.68)), but the choice of one math model over another really should be grounded in empirical work and that's a messier literature... BoilingLeadBath (talk) 14:15, 9 November 2023 (UTC)