Talk:Viscosity/Archive 1

Formula Explanation

 * I'd like to see explained the formulas of dynamic viscosity η (1 Pa·s = 1 N·s/m2 = 1 kg/m·s) and kinematic viscosity ν (m2/s). I understand what viscosity is but I don't understand much about the formulas. I'd like to understand what they represent -in common language- and how viscosity can be measured or calculated.

==Bulk Viscosity Can anyone explain what bulk viscosity is? I ought to know--I work in compressible flow and shocks but a simple explanation eludes me.

Could bulk viscosity refer to the dissipation that occurs in a fluid in pure dilatation? Diogenes 20:21, 21 Aug 2004 (UTC)

Dilatational/bulk viscosity is the "kappa" term in the "complete" general expression of Newtonian flow. The rest of the Newtonian equation comes fully from momentum balance; the kappa term is (I am not certain on this point) an after-the-fact correction. It accounts for the resistance, due to molecular interaction, of the fluid particles to expand or contract. In texts I've seen, it is an order of magnitude smaller than the viscosity, difficult to measure, and generally ignored, even in compressible flow. Alchemy3083 07:25, 10 Nov 2004 (UTC)

I understand that the answer to some of the questions above is not simple but has been carefully put together, in the simplest possible terms, by S. Vogel in his "Life in Moving Fluids; the Physical Biology of Flow", 2nd. edition (1994). Princeton University Press.

Misstatement concerning inertial forces
This is incorrect. The kinematic viscosity can be thought of as the "constant of dissapative momentum" because it gives the equation τ=ν(ρv(x))/dy. But dividing viscosity by density does not tell you anything about inertial forces. Kinematic viscosity is not a viscous/inertial relationship.

The ratio of inertial to viscous forces is given by the Reynolds Number, which is determined through the constituitive momentum balance equation, such as the Navier Stokes Equations, of which Newton's law of viscosity forms a major part. Alchemy3083 07:42, 10 Nov 2004 (UTC)

Can solids have a viscosity?
The article should stress that viscosity is an equilibrium property.

It is correct that you can perform rheological experiments on a viscoelastic liquid, but in these experiments the ratio between strain rate and stress is not be constant in time. However if you wait long enough the ratio between strain rate and stress will approach a number. This number is called viscosity.

You cannot define the viscosity of a non equilibrium system. The problem is that viscousity is only defined in the long time limit, and in the long time limit the system is no longer at equilibrium.

Of course you can always define the viscousity as a parameter of a model. This may allow you to speak of the viscousity of a non-equilibrium system. However there is a difference between defining a quantity within a model and defining it as the result of a measurement.

Similarly you can describe linear perturbations of a viscoelastic system by allowing the viscousity to be a function of time. Perhaps some day in the future wikipedia will have an article on linear response, but until this happens please stress that viscousity is an equilibrium property.

Are you referring to rheids? (Sorry, I don't know much about them - I just found that page by random, which is why I got here.) I was wondering if there is a category that would fit for them in this context. Common Man 19:40, 22 May 2005 (UTC)

Viscosity and temperature
The article says:


 * Viscosity tends to fall with temperature.

Is this correct? I thought molasses was slower in January than in July. -- Dominus 10:08, 26 Sep 2004 (UTC)


 * I clarified this point by changing the above sentence to:


 * Viscosity tends to fall as temperature increases.


 * H Padleckas 18:59, 1 Oct 2004 (UTC)


 * What is the viscosity of molasses in January? (say -10 C) How about adding a table showing the viscosity of molasses vs temperature. --69.5.156.155 21:54, 24 Nov 2004 (UTC)

I would say viscosity goes down when temperature goes up is just as obvious as thinking that viscosity, in reality, is just a reversed speed measurement.--Cacumer 20:21, 18 February 2006 (UTC)

Viscosity of Liquids
I'm not sure that the value given for glycerol is correct the CRC handbook list 934 milliPascals second Where did the value on this page come from?

It is 954 mp at 25C and 1490 mp at 20C (according to handbook of chemistry and physics 69th edition)

It is not only the viscosity of glycerol, the viscosities fot methanol, ethanol are also wrong if one compares them with those in the CRC book. Whoever publishes this type of data should put a reference...


 * The value for pitch disagrees with that given at ref. http://xtronics.com/reference/viscosity.htm. Not sure which is correct. —The preceding unsigned comment was added by 128.250.204.118 (talk) 08:09, 21 March 2007 (UTC).

the flowing glass urban myth
Is in fact not an urban myth. One can clearly observe the effects on middle-age vitrals of cathedrals...

--CyrilleDunant 15:48, 18 May 2005 (UTC)


 * What one can observe on middle-age vitrals is indeed at the origin of the myth. However, the correct explanation is not flowing glass, but a consequence of the Crown glass process used to build the vitrals. Jerome.Abela 10:30, 14 August 2006 (UTC)

I agree with Cyrille, why is that called an urban myth? I've not studied dinamics of fluids, but I've heard of that. I'll try to ask someone expert in that issues, in my university there is a glass-engineering course, if I find usefull info I'll post it here. Afonso Silva 22:49, 19 May 2005 (UTC)

--

hmm... i have not yet seen any proof of that, meaning a real "measurement"; on the other hand, glass is a so-called "undercooled fluid" and one would expect it to be viscous - nontheless it break into shards which is rather a property of a crystal than a fluid. usually, viscosity in "glasses" (anything that is physically similar to glass) depends on temperature, at room temperature this would be somewhere arounf 10^13Pas. this means that if glass flows, it flows so slow that even after a few thousand years it would only result in a change of thickness comparable to the diameter of an atom (grab the formula and calculate for a plate of glass 1m x 1m and 1cm thick). the main reason that glass flow has not been observed yet is most likely that glass is also elastic to small stresses, and i would consider glass under its own weigth to be a small stress for window-sized pieces. the reason that church windows are not homogeniously thick is more likely to be found in the method of making glass back then: use a plate of metal, dip the edge into the melt and pull it out to get a sheet of glass. this will never result in a homogenious glass plate. also, soldering such a window includes heating the glass which may lower its viscosity by many orders of magnitude until it cools, especially if its a low melting point glass --Sparks25 14:46, 26 July 2005 (UTC)


 * Even the earth's mantle, with a viscosity 10^21 Pa s is often considered a viscous fluid, so why wouldn't we consider glas one? That it cannot be seen flowing in one's lifetime, doesn't have any physical meaning, we are not the measure of everything. Thijs!

The technical answer is that glass is a fluid, but I think some of the wording in the article needs to be changed so that the casual reader does not come away with the impression that glass behaves like a fluid on any scale that is observable on an every day basis. Carl 18:42, 27 February 2007 (UTC)

On 2nd reading I think the article gets the point across, just in need of some minor edits. Carl 19:23, 27 February 2007 (UTC)

Glass is an amorphous solid, not a fluid. All solids actually flow on sufficiently long time scales; what is up for debate is whether or not glass flows on "human" time scales. The answer is that it does not.

Significance
--LouisBodo 23:00, 20 July 2005 (UTC)

I would suggest the inclusion of a section just before Contents. My suggestion is the following. Significance Viscosity is an inherent property of a fluid. Knowledge of its magnitude is indispensable for calculation of rates of flow in ducts, channels, etc, calculation of energy requirements of machines conceived for moving fluids, such as pumps, mixers, etc and in lubrication. In hydrodynamic lubrication at relatively low loads and high speeds (journal bearings) the load is supported (surfaces kept apart) by viscous forces within the lubricant which depend on their viscosity. Pressure drop in ducts is a function of the Reynold's number, which depends critically on the viscosity of the flowing liquid.

Further I would like to stress the importance of the effect of temperature on the magnitude of viscosity, saying.

Spelling error on figure
Sadly, the figure describing Newton's theory has a spelling error, twice reading "boundry" where it should say "boundary". Since it is such a beautiful figure, it would be great if the original contributor could correct these small errors, which is a far easier job (if the original file still exists) than re-doing the whole thing. Is it too much to hope that (s)he may one day check back here? And is this a deficiency in the Wikipedia concept (that the original file is not available for easy editing)? 144.213.253.14 06:12, 3 October 2005 (UTC)
 * I will try to fix this problem now. H Padleckas 16:16, 3 October 2005 (UTC)
 * IAMANIDIOT, thanks H Padleckas. --Duk 17:07, 3 October 2005 (UTC)
 * You're welcome. I have fixed the diagram and uploaded the corrected file to Image:Laminar_shear.png.  The corrected file usually does not show up immediately, but only after a few days; so let's check back in a couple of days.  H Padleckas 17:17, 3 October 2005 (UTC)
 * I still don't see these changes I made to Image:Laminar_shear.png, but I will wait further. H Padleckas 00:51, 7 October 2005 (UTC)
 * Your update went through fine, I saw it right away. You probably need to purge you browser cache or do a forced reload of the page. Also try http://en.wikipedia.org/w/index.php?title=Viscosity&action=purge. This purges the wikipedia squids. --Duk 02:42, 7 October 2005 (UTC)
 * Today I checked this picture and I see the corrections finally came through. H Padleckas 00:21, 11 October 2005 (UTC)

Misleading figure
The figure showing the parallel plate setup is misleading, as it seems to indicate that the shear stress changes along the y axis. --Slashme 05:44, 8 December 2005 (UTC)


 * I agree, particularly about the second picture (Laminar_shear_flow.PNG). It looks like a graph, but it's actually a diagram. I think adding some color to the fluid and/or the plates, and maybe using short arrows that look like vectors rather than axes would help. I can't fix the pictures myself, but I hope someone can. —Mister K 18:43, 22 September 2006 (UTC)

unitconversion.com
Do we really need four links to a single website or is it a link spam? abakharev 23:25, 10 October 2005 (UTC)

flowing
I must say, to me, all this discussion is blinded looking to the wrong side.

Viscosity seems to be an attempt to measure how much something can flow.

Anything can flow, flowing doesn't depend on vicosity, it's the other way around.

Flowing is movement of one thing from A to B. There are flowing of cells, molecules, atoms. As long as it's not zero Kelvin, it is flowing, at some level.

Now, if it's hard to measure pitch flowing, and if glass do flow, how can one tell about flowing metals?

The only way will be when some easier way to measure that pops around.

--Cacumer 17:54, 18 February 2006 (UTC)

viscosity
This is also looking to the wrong side. Since viscosity comes from flowing, we should first understand flowing and then we can understand viscosity.

I believe viscosity is overlooked. There's something in there, and it does not apply just to gas or just to liquid. If it applies to solid, I think it would also not stop there. Who knows how many states of matter are possible, in fact? We just know there are 4 today, but we didn't know that yesterday. Keep in mind that plasma is a state more energetic than gas, and it's hard to understand how it works.

If it is a measure of flowing, then it can work to measure any kind of movement.

Basically I think I would call flowing as molecule speed reversed.

--Cacumer 17:54, 18 February 2006 (UTC)

Why don't you find some sources which discuss that? And while we're at it, I'm putting a weasel words tag on the "solid viscosity" section. It shouldn't be too hard to dig up some sources for those views. Tenebrous 03:40, 16 April 2006 (UTC)

Error in equations
The equation that separates velocity gradient into a trace and a traceless term is incorrect. You probably want to change the left hand side into $$\partial_i v_j + \partial_j v_i$$ and all the factors 1/3 into 2/3. According to Fluid Mechanics by Landau and Lifshitz, the equation of stress tensor should read $$\sigma_{ij}=-p \delta_{ij} + \eta \left(\partial_i v_j + \partial_j v_i - \frac{2}{3}\partial_k v_k \delta_{ij}\right) + \zeta \partial_k v_k \delta_{ij},$$ where $$\zeta$$ is called the cofficient of bulk viscosity (second viscosity in the book), and the combination of the second and third terms is called viscous stress tensor.

The update of the equations still contain errors. Note that the stress tensor is defined with a minus sign with respect to the momentum flux density tensor in Fluid Mechanics by Landau and Lifshitz.--Huaiyu Duan 19:41, 11 May 2006 (UTC)

Please show colour diagrams!

Another nearby error: The equation for ω, the curl of v, should not include the factor of 1/2

invisicd fluid
"an idealized fluid which has no resistance to shear stress is known as an ideal fluid (Symon 1971)." In the field of aerospace, we often use the word inviscid to refer to or model an ideal fluid (according to Symon). This word is not mentioned here. 21:40, 29 May 2006


 * So be bold and add it. --Slashme 05:52, 30 May 2006 (UTC)

Unclear paragraph inc typo (?)
This paragraph needs to be expanded with proper equations and more consistent variable names. (Not t for distance!)

The relationship between the shear stress and the velocity gradient can also be obtained by considering two plates closely spaced apart at a distance t. Assuming that the plates are very large, with a large area A, such that edge effects are neglected and that the lower plate is fixed, let a force F be applied to the upper plate. Incidentally, if this force causes the plate to move, the substance is concluded to be a fluid. The velocity of the moving plate and the top, the applied force is proportional to the area and velocity of the plate and inversely proportional to the distance between the plates. Combining these three relations results in the equation F = μ(AU/t). Where mu is the proportionality factor called the absolute viscosity (with units Pa-s or slugs/s-ft). The equation can be expressed in terms of shear stress; ρ = F/A = μ(U/t). U/t is the rate of angular deformation and can be written as an angular velocity, du/dy. Hence, through this method, the relation between the shear stress and the velocity gradient can be obtained.

This sentence in particular needs immediate editing:

The velocity of the moving plate and the top, the applied force is proportional to the area and velocity of the plate and inversely proportional to the distance between the plates.

I don't know what it intended to say so I can't do it myself.

Until this is fixed I'll add an "in need of expert attention" template to the top.

--cfp 10:16, 18 July 2006 (UTC)


 * I've given the paragraph a once-over. It had some bad mistakes.  It looks as if some of the copy comes from a description of cup-and-bob viscometers, because they refer to angular velocity, not shear velocity.  Let me know if you find it acceptable now. --Slashme 11:51, 19 July 2006 (UTC)


 * Great, thanks. (I've removed the "expert attention needed" template.) --cfp 12:29, 19 July 2006 (UTC)

I still think this article needs help. For one, it uses pitch as an example of a solid that flows when the experiment was done to prove that it is in fact a liquid, not a solid. Also, glass does NOT flow. Dragon of the Pants 21:46, 21 July 2006 (UTC)


 * K well feel free to sort it / to put the expert attention box back (^_^). I'm no physicist so I'm not really the best person to do it. --cfp 01:02, 22 July 2006 (UTC)

Quark viscosity
would this be a good place to put a discussion of the quark viscosity (as opposed to behaving like a gas) from the Scientific American article in July or August of this year, and also under quarks?
 * I don't see why not as long as it's a small separate section and fully cited. --cfp 16:15, 14 August 2006 (UTC)

Note about Quark Gluon Plasma--I'm 100% positive that the viscosity is very low, quite possibly near 0, so there's no reason for the massive viscosity that is listed. If someone would kindly fix that? — Preceding unsigned comment added by 130.199.3.165 (talk) 15:39, 18 July 2011 (UTC)

the viscosity of glass
since the article quotes the viscosity of glass then specifically says it needs a quote, i had a look arond the net and found:

http://www.a-m.de/englisch/lexikon/viskositaetglas.htm has a chart of glass viscosity at different temperatures and compositions - however there are a wide range of values given and none of them are close to the 10^40 quoted, although extendign the graphs you could get to about 10^30 by 0c.

http://web.mst.edu/~brow/PDF_viscosity.pdf has some detailed maths concerning viscosity of glass and mentions that the expected relaxation time for cathedral windows is about 10^32 years

http://hypertextbook.com/physics/matter/viscosity/ quotes the viscosity of glass at room temperature at 10^18-10^21

http://www.jstor.org/view/09501207/ap000455/00a00100/4?frame=noframe&userID=8266023c@uq.edu.au/01cc99333c00501ef9900&dpi=3&config=jstor shows glass having a viscosity of 10^16 at 450c agreeing with the first website - neiter of these sources extend their graphs to 0c and i have been unable to find any that do.

http://www.cmog.org/index.asp?pageId=745 (also mentions that the viscosity of lead might be around 10^11 - and glass 10^20)

This question about the myth of glass flow very decisively addressed in a paper in the Journal of Chemical Education back in 1962 (vol 39, p. 84-85), by David Dingledy.

just a few notes on the viscosity of glass - i wasn't sure how to incorperate these, as it almost seems like a diversion from actually talking about viscosity itself

i hope someone with a little more time and understanding than i can sort this mess out. ..

2c worth, Andrew

130.102.0.178 06:53, 28 September 2006 (UTC)

Can someone with more knowledge and a proper library explain the assumption made in the equations for viscosity that probably can not be made with glass? Carl 19:35, 27 February 2007 (UTC)

molecular origins
"The viscosity of a system is determined by how molecules constituting the system interact." I'm not sure "system" is the right word here. I was gonna replace it with "fluid," but then I wondered about fluids with components that weren't whole molecules, and confused myself. this section needs some work, I think. Ojcit 18:47, 2 October 2006 (UTC)

Merging Stokes (unit) and Poise
The information on the pages Stokes and Poise is very limited. Both pages are stubs. Much of the info there is repeated here. I propose to merge both pages with the page on Viscosity and have them redirect here instead. Mausy5043 07:48, 9 February 2007 (UTC)


 * Agree. Also include Pascal second for merger and delete category units of viscosity. -Myth (Talk) 14:50, 9 February 2007 (UTC)


 * Support! GGenov 12:58, 16 February 2007 (UTC)

'Tis done Mausy5043 17:06, 17 February 2007 (UTC)


 * I think that this was a dumb idea and that at least some of them should be re-created. Especially the pascal second article, which can then include more on the prefixes and the like which is only remotely relevant to this "Viscosity" article.  Gene Nygaard (talk) 16:13, 22 December 2007 (UTC)

Use of eta or mu for dynamic viscosity
The use of mu for dynamic viscosity is very common for many fields which do not use eta. Even as an engineer I was thrown off by the eta. This is a field-specific problem, and while IUPAC does govern chemistry, it does not govern engineering fields. As reference you can check most thermodynamic books, which will use $${\mu}$$.

I totally agree with this. The usage of "eta" is quite confusing. Alamsemu 11:12, 21 May 2007 (UTC)


 * I disagree. Engineers may often use $$\mu$$, but a themodynamics book would be more likely to use $$\eta$$ to avoid confusion with the chemical potential!
 * —DIV (128.250.204.118 09:00, 19 June 2007 (UTC))


 * I would prefer mu, because that's what I used to. Regardless, this article should use one or the other consistently, but not both. It's too confusing. I'm willing to make the change if no one objects. —ALittleSlow 19:35, 8 November 2007 (UTC)

Please look over for accuracy.
I was thinking about placing this near the top so there is a quick and concise explanation of what the units of viscosity mean. This is probably one of the top reason why someone would look at this page so I hope this additional text would help them find that information quickly. This is without having to read to far into the article.

Here is my 2nd try at it, I like this one better. I typed this one up after looking up viscosity in Physics 4th Edition 2nd printing, by Serway.

When looking at a value for viscosity the number that one most often sees is the coefficients of viscosity, simply put this is the ratio between the pressure exerted on the surface of a fluid, in the lateral or horizontal direction, to the change in velocity of the fluid as you move down in the fluid (this is what is referred to as a speed gradient). For example water has a viscosity of 1.0 x 10-3 Pa∙s and motor oil has a viscosity of 250 x 10-3 Pa∙s. pg 440 Physics For Scientist & Engineers 4th Edition 2nd Printing, Raymond A Serway, Saunders College Publishing 1996

Here is the first try, I include it here for compression and to make sure I got my facts right.

Viscosity for a fluid is expressed in two ways, dynamically or kinematical, dynamic is concerted about the pressure it takes to move the fluid, and kinematics is how fast an area of fluid moves. In Dynamics_%28mechanics%29 Dynamic units what is being measured is pressure times time. If the fluid in question is placed between two plates the number tells you how much pressure in the lateral direction it takes to make the top plate move an equal distance as the thickness of the fluid in some amount of time. The SI units are Pa s or Pascal seconds. In Kinematic units what is being measured is area over time. This is to say, how quickly a given area of fluid is moving. The Si units are m2/s or meters squared per second.

Pleas look over to make sure that I not saying some thing wrong before I post to the article. Thanks Carl 19:51, 1 March 2007 (UTC)

Ideal Fluid
Why does "ideal fluid" redirect to this page? 147.226.234.34 02:50, 10 April 2007 (UTC)

Reference
Do we want to use a standers style in to reference items in this article? Also this article probably needs more documentation, especially all the data tables found within.Carl 20:40, 25 April 2007 (UTC)

Please explain units for Pa.s
Please check the description of the units Pa.s. The article says "The SI physical unit of dynamic viscosity is the pascal-second (Pa·s), which identical to 1 kg·m−1·s−1"

1 Pascal = 1 N/m2 Therefore 1 Pa.s = 1 N.s/m2 Is this the same? This is repeated later in the article. Dougsgh 22:58, 23 June 2007 (UTC)


 * A Newton has units of $$\scriptstyle \frac {kg \cdot m} {sec^2}$$. So


 * $$\scriptstyle Pa \cdot s = \frac {kg \cdot m \cdot s} {s^2 \cdot m^2}$$.


 * When you take the cancellations you have the identity with kg·m−1·s−1. Karl Hahn (T) (C) 21:20, 2 July 2007 (UTC)

Viscosity Redirects
This page has too many pages redirected to it that deserve their own article. So far I have found inviscid, ideal fluid, and inviscid fluid all redirect to viscosity. This is strange to me as if I were a typical wikipedian or browser of wikipedia and I wanted to look up the properties of an inviscid fluid which is used in say, an idealized mathematical model that assumes no viscosity I would be frustrated and confused when redirected to viscosity. In my mind it would make more sence for ideal fluid to link to a disambiguation page with links to ideal gas and a link to an article about invisicid fluids. The article about inviscid fluids would have to be created. It might include statements of the non-existance of such a fluid, what common models assume inviscid fluidity in order to ease some calculation, a link to superfluids, some fluids that are nearly inviscid, and other related info. I don't think it would have to be a long article. The first sentence could just be something like: "An inviscid fluid is an idealized fluid that has no viscosity." Since the viscosity article is such an important one I will not split these pages up myself without some confirmation from other editors. My basic questions are, why should these pages redirect to viscosity, and should we create these articles instead of redirecting to viscosity. I would really like to hear some feedback on this as I am extremely hesitant to make all the above changes without some feedback. Thanks, CoolMike 16:04, 1 August 2007 (UTC)


 * CoolMike, I agree with you completely. I suggest that you either create a new Inviscid fluid article or a new section on inviscid fluids within this article. Be Bold and go at it! - mbeychok 22:53, 11 October 2007 (UTC)

Different viscosities
I agree with previous comment. In addiytion to ideal fluid etc, there are several different viscosities. I just started adding them to this page. I think that we should treat this page Viscosity as Phenomenon. On the other had, there are different viscosity coefficients, depending on the nature of the system, geometery of the stress, time dependence of the stress. Each of this viscosity coefficients deserves its own page. I have created page volume viscosity. There might be pages for other viscosity coefficients with more details on them.

User:AndreiDukhin, October 22, 10:30 AM —Preceding unsigned comment added by AndreiDukhin (talk • contribs) 14:26, 22 October 2007 (UTC)

SOFRASER
I've removed this spamming info. The SOFRASER company is spamming its product all over other wikis (it, en, es, fr, etc.), see italian article too, and other articles like viscometer).  J  alo   15:54, 13 November 2007 (UTC)

Soap water
does soap give water more viscosity??


 * Yes, adding soap or other surfactants to water generally increases its viscosity. --Slashme (talk) 09:40, 31 January 2008 (UTC)

Viscosity of solids
Since Ito et. al. have shown that granite deforms at room temperature with vanishingly small stress, should this section be reworded? Dan Watts (talk) 01:00, 23 July 2008 (UTC)

Error in formulae!

 * Per below, no consensus on change yet.--Aervanath lives in the Orphanage 17:20, 30 September 2008 (UTC)

The formulae comparing the viscosity to the mean free path is wrong I think. Looking in Physical chemistry by Atkins (7th ed) on page 830 it states that

eta = 1/3*M*lambda*c*A

where

eta is the viscosity. I would guess this is the dynamic viscosity. Although in figures in the book the unit is given as kg/m/s - hence it is the dynamic viscosity.

M is the molar mass

lambda is the mean free path

c is the average speed of the molecules

A is the molar concentration of the gas molecules

This took me a loooong time to find... if you have a source for the formula shown please give it.

Please direct any conversation about this to johan.soderstrom ATSIGNGOESHERE gmail DOTGOESHERE com

This is the original editor, I did the edit from a friends computer, all talk messages should be directed to this IP (no, I am not a contributor - just want to clarify this little thing...)

Really, no feedback... should this page really be locked if no one is looking over it?


 * $$\eta = \frac{1}{3} M \lambda c A$$ certainly seems to be correct – it is homogeneous wrt its units, at least:


 * $$\begin{align}

kg\ m^{-1}\ s^{-1} & = ( kg\ mol^{-1} )\ .\ m\ .\ ( m\ s^{-1} )\ .\ ( mol\ m^{-3} ) \\ & = kg\ m^{-1}\ s^{-1} \end{align}$$


 * However, the formulae given at Viscosity are in terms of kinematic viscosity, not dynamic viscosity. I don't think those equations are necessarily wrong if the one you've cited is right. If you can come up with a source, then I'd be happy to add the equation you've given above. haz (talk) 08:02, 27 September 2008 (UTC)


 * OK, I've found a source which gives the following version:
 * $$\mu = \frac{1}{3} \rho c \lambda$$
 * However, if it were to be added, we'd really need to have the derivation from the ideal gas laws there as well – we can't really just quote the equation. I can't find the derivation, so perhaps you could have a look for it? haz (talk) 12:47, 27 September 2008 (UTC)

Hi... This can rather easily be derived - if I have time to do it I will show you how later this week... —Preceding unsigned comment added by 195.221.0.3 (talk) 07:35, 29 September 2008 (UTC)


 * Please do so – once the derivation is made clear, it can be added to the page. haz (talk) 21:52, 30 September 2008 (UTC)

The current formula is indeed wrong, if you check reference 15, page 23-26 (cited source by the current formula), you will find that average speed u(rms) in the current formula should be s, which equals to 1/sqrt(3)*n(rms) —Preceding unsigned comment added by 72.203.156.131 (talk) 07:11, 4 September 2010 (UTC)

Sutherland's constant, ref. temperature and ref. viscosity for Air gas can be wrong.
I think that the quantities in subject might be wrong for Air. They should be:

$$C = 110.4$$ K

$$T_0 = 273.15$$ K

$$\mu_0 = 1.716 * 10^{-5}$$ Pa·s

These values are cited in the CFD-Wiki. Their usage leads also to computations consistent with the Javascript form of the Aircraft Aerodynamics and Design Group of Stanford University.

Furthermore, very similar values to those cited above can be found at pages 647-648 of Fundamentals of Aerodynamics by J.D. Anderson Jr, second edition (McGraw-Hill).

62.159.141.53 (talk) 13:55, 26 September 2008 (UTC)

also, the table with "Sutherland's constant and reference temperature for some gases" are not identically to the values shown in the source ([19])... —Preceding unsigned comment added by 92.227.197.55 (talk) 14:46, 10 October 2008 (UTC)


 * This book says dependence on pressure can be neglected for ideal gas. Materialscientist (talk) 09:17, 9 January 2011 (UTC)


 * First, the formula for (dynamic) viscosity, μ ≈ ρ CS λ ≈ m CS / σ, could be emphasized. Second, comparing with Sutherland's formula, the sound speed in the numerator CS ~ T½, implying that the collision cross-section in the denominator σ ~ 1+C/T.  With those substitutions, the general classical formula, exactly equals Sutherland's empirical formula.  Why would the collision cross-section increase, at colder temperatures?  That implies, that the particles are becoming bigger, or "stickier", at colder temperatures.  And, indeed, at colder temperatures, gas particles begin to "stick", as they approach the phase transition, to liquid and solid states.  And, indeed, the "Sutherland temperature (C)" is always near (albeit above) the condensation (and freezing) temperatures, of the gases, listed in the current table.  The Sutherland temperature constants, for gases, seemingly reflect the fact, that at cold temperatures, near to the condensation temperature, the particles begin to become increasingly "sticky", succumbing to each other's Van der Waals like electrostatic forces, without "barreling obliviously on past", as particles do, at higher temperatures, and energies of motion.66.235.38.214 (talk) 19:23, 29 November 2012 (UTC)
 * Sutherland's formula can be combined, with Maxwell's classic formulas, for viscosity & mean particle velocity, to estimate the collision cross-section:
 *  = (8kT/πm)½
 * m/4σ = μ = μ0 (1+C/T0) / (1+C/T) × (T/T0)½
 * σ = σ0 × (1+C/T0)
 * σ0 ≈ (mkT0/2π)½ ÷ μ0 (1+C/T0)
 * The resulting collision cross-sections range from ≤(10-30)Å2; and can be compared, with the Van der Waals volumes & radii.  Defining a "Van der Waals area" = ¾ Vw/Rw, the computed collision cross-sections agree almost exactly.  Thus, there is a close connection, between the correction terms, in Sutherland's empirical formula, to Maxwell's idealized formula; and the Van der Waals forces of attraction, responsible for "sticking" particles together, from gaseous states, into liquid & solid states.  (i understand there to be a "4" in the denominator, of the Maxwellian formula, because, considering two adjacent fluid parcels, only half of the particles in the one will be flowing towards the other; and, averaging over those half, having characteristic velocity , their average velocity towards the other fluid parcel, is only ½; so the average velocity, in the appropriate direction, towards the other fluid parcel, averages out to ½ × ½  = ¼ .) 66.235.38.214 (talk) 22:00, 29 November 2012 (UTC)

See also WP:MTAA and WP:JARGON
This article has... issues. Even as someone who has taken college-level physics (albeit not recently), it's extremely dense and unhelpful and reads like an engineering textbook. Some basic things to address:


 * Each of the viscosity coefficients needs to have a layman's explanation, not just a rehashing of the name of the unit. "Dynamic viscosity measures how much a liquid moves when it is pushed by an external force" or somesuch.


 * Break down the relationships between the various viscosity coefficients. What is a function of what (i.e. weight is a function of mass and gravity), and what is an independent attribute (i.e. volume of an object is not necessarily related to its mass)?


 * The article should generally progress from "less technical" to "more technical" and must define terms before it uses them: if it hasn't gotten to Newtonian vs. non-Newtonian fluids, it should not be using those terms yet.


 * Practical examples are always helpful. Moving the pictures (and captions) further up in the article would be nice, and use the captions to give practical explanations and comparisons of the technical units for everyday substances.  Honey is viscous, sure, but what is the dynamic viscosity of honey?


 * "In relation to diffusion, the kinematic viscosity provides a better understanding of the behavior of mass transport of a dilute species." What, exactly, does that mean?  "Mass transport" in this case is not likely to mean light rail, but that is what your average reader will think of.  "Species" generally defaults to the biological meaning (blame Darwin), and will confuse readers.  The jargon may make perfect sense to a rheologist, but this is an encyclopedia for general use.

Just some thoughts. SDY (talk) 21:02, 2 November 2008 (UTC)

superfluids
Can we get some extreme examples into the table of real material viscosities, such as (various isotopes of) supercooled helium? Cesiumfrog (talk) 01:50, 25 November 2008 (UTC)

typo in 'Relation to Mean Free Path of Diffusing Particles'
Shouldn't this sentence: 'From fluid mechanics, shear stress, τ, is the rate of change of velocity with distance perpendicular to the direction of movement.'

Be more like: 'From fluid mechanics, shear stress, τ, is proportional to the rate of change of velocity with distance perpendicular to the direction of movement.'

Pgj98r (talk) 11:09, 12 December 2008 (UTC)

As long as $$ \mu $$ is constant, you're right. But I agree with you that the sentence is not accurate.

Also I think the formula immediately below this sentence should be


 * $$\tau = \mu \frac{du}{dy}.$$

Since symbol u denotes velocity in x direction in this article (see section "Newton's theory"); therefore y should be the direction perpendicular to the movement.SongJie@NTU (talk) 04:17, 22 April 2009 (UTC)


 * Well, as long as $$\mu$$ is 1, the statement is right :). Thanks for fixing. Awickert (talk) 06:38, 22 April 2009 (UTC)

Animation

 * The caption on the animation has got it backwards. I have searched the text but I can't find it on the "edit this page" section, else I would fix it myself. There needs to be a search which will search the large text field. JillCoffin (talk) 02:04, 4 February 2009 (UTC)


 * Fixed it. Search worked. What browser are you using; I know that Safari doesn't search fields. Awickert (talk) 03:23, 4 February 2009 (UTC)


 * The animation (green slime) is not correct. The green fluid is viscoelastic, otherwise the majority of it would not retract back into the tube. I'm sure it took ages to make (respect), but my feeling is that it doesn't meet wikipedia standards. Anybody else for (or against) deletion?Michi zh (talk) 18:38, 26 May 2009 (UTC)


 * ✅ There is not longer any green slime animation (not sure when it was removed). David Hollman (Talk) 07:58, 4 September 2010 (UTC)

Ideal
Is a superfluid an "ideal fluid"? 75.118.170.35 (talk) 17:28, 11 July 2009 (UTC)

Added new formula, given by Sutherland's formula
Hi, I added a new formula today, or a variant of Sutherland's formula, where I have separated the constant factors from what is not constant (factors containing the temperature). I used lambda ($$\lambda$$) to substitution the constant factor, because I couldn't come up with any better symbol. If you think there is any better symbol than lambda, please go ahead and change it. --Kri (talk) 22:07, 8 October 2009 (UTC)

Viscosity of blends of liquids
The reference is dead. http://www.hpiconsultants.com/blending/index.htm —Preceding unsigned comment added by 65.216.74.168 (talk) 19:58, 1 December 2009 (UTC)


 * The website has changed structure and I don't see the document listed anymore. There was another source for the same information. I commented out the dead link. David Hollman (Talk) 07:49, 4 September 2010 (UTC)

English units
Just a quick question about the way units are covered here. Is it the wikipedia standard not to include english units as well as all the others? I'm a chemical engineer and most of the work I do unfortunately uses lb-mass and feet and it would seem that due to the prevalence of those units in some places that they would be included here. For instance: I'm looking through a few papers at the moment and all the viscosity's are defined as (lbmass / (ft*sec) ). I know the world is moving towards standardized units but english units are still alive and kicking. Thoughts? —Preceding unsigned comment added by 70.88.83.117 (talk) 19:20, 10 February 2010 (UTC)


 * Here are the Wikipedia guidelines for units. It suggests putting secondary units in parens after the main units (and gives rules for determining which would be "secondary"; IMO SI would seem to be primary since this is a worldwide topic...) So if people are interested in non-SI they could be added.... David Hollman (Talk) 07:44, 4 September 2010 (UTC)

Viscosity of castor oil
The given viscosity of castor oil in the table is at 20°C.

It is possible to check it here http://web.cecs.pdx.edu/~gerry/class/EAS361/lab/pdf/glycerinWaterViscosity_CRC_Handbook.pdf

and here http://www.engineeringtoolbox.com/absolute-viscosity-liquids-d_1259.html —Preceding unsigned comment added by 87.77.178.154 (talk) 11:29, 22 June 2010 (UTC)

Thixotropic Viscosity Type
Thixotropy is most often used in US Industrial settings (based on my 35 years as an industrial chemist at a variety of CASE companies) to mean Shear Thinning. The term Thix Index, for example, is the ratio of two viscosities at different shear rates, with time irrelevant. Obviously you can NOT have shear thinning without the passage of time, hence it is not completely incorrect to confuse a behaviour which occurs as a function of time at a constant shear rate with one which occurs with time at variable shear rate. I have never in my industrial career encountered any acknowledgement from technical personnel that using "thixotropy" to mean shear thinning is incorrect. Hence, unfortunately, this usage must be documented (IMHO) in any article about viscosity (no matter how it clashes with the academic definition). By the way, I think it likely that this is industry dependent - I've been involved with coatings, adhesives and sealants rather than (solid) eleastomers.69.40.241.198 (talk) 00:45, 25 February 2011 (UTC)

Remove QGP from viscosity listings
Quark Gluon Plasma (QGP) should be removed from the list of given viscosity's. When formed QGP has a viscosity very close to, if not equal to zero (Physics Today, May 2011). The temperatures needed to form QGP is in the area of many trillion degrees Kelvin. For this reason, it is very misleading to list the viscosity at 25 degrees Celsius when QGP can never get that cool. If anyone can give a good reason for it remaining as it is I will not remove it.

Pkast (talk) 19:11, 25 July 2011 (UTC)7/25/2011

Gas Viscosity
Theoretical explanation needs some edits. Also too colloquial. — Preceding unsigned comment added by 99.126.240.104 (talk) 07:21, 5 March 2012 (UTC)

No viscosity in static fluid
I believe that it is not appropriate to say that "fluid is being deformed". More important, viscosity does not show "resistance to deformation^(1)" by tensile^(2) stress or shear stress. Viscosity describes the internal friction of a moving fluid, not it`s resistance to deformation (it is wrong analogy with solid deformable body). You may refer to viscosity as a "macroscopic effect of microscopic exchange of kinetic energy between fluid particles".


 * (1)In fluids, stress is not connected to deformation but to speed of deformation of fluid particles - which is obvious from presented equations.


 * (2) Actually, "tensile stress" has very little to do with viscosity, with fluids as well, as fluid can not be strained. Pressure can be related to viscosity, as in moving viscous fluids exists pressure component induced by viscosity.

user: dimitrije — Preceding unsigned comment added by 147.91.1.41 (talk) 10:07, 12 December 2012 (UTC)

Viscosity of glycerol is wrong
In the section "Viscosity of various materials" the table to the right lists the Viscosity(dynamic)of glycerol at 20degC as 1.2 Pa.s and cites [25]. If you check the table in the source citation they are listing glycerol(Glycerine) at 14.9 Poise, so 1.49 Pa.s This is more in line with values found at other trustworthy sources, though I'm using a value of 1.41 Pa.S for my calculations as I verified a range of 1.40 to 1.42 from multiple other sources (all at 20degC)  — Preceding unsigned comment added by 174.59.208.241 (talk) 14:01, 28 December 2012 (UTC)

Viscosity gif
the viscosity gif isn't explaining anything, I don't understand why it was included —Preceding unsigned comment added by 188.26.49.57 (talk) 11:23, 11 April 2010 (UTC)

The animated gif? I think that it's a fantastic visual for the layperson. Leave it in! — Preceding unsigned comment added by Only1miller (talk • contribs) 15:53, 29 November 2012 (UTC)

It's a 1.7 megabytes big animated GIF. Think about users with slower or mobile connections, or slower computers. I'd say remove it. Or make it clickable. — Preceding unsigned comment added by 188.201.252.164 (talk) 10:07, 14 August 2013 (UTC)

Plot of the different calculation methods for slurry viscosities
A plot of these different methods would be great. µ_r would be on the y-axis and ɸ on the x-axis.

I'll try to add this over the weekend if time permits. I've never uploaded a new image block and image to wikipedia before; if anyone else has the urge to do this and the experience as well, I would appreciate it. — Preceding unsigned comment added by Kronn8 (talk • contribs) 12:28, 31 October 2013 (UTC)

shear viscosity VS dynamic viscosity
'''is shear viscosity the same as dynamic viscosity.. or, how are they related???'''

Kronn8: Yes, these two are the same thing. I have changed that subtitle to "Dynamic (shear) viscosity", for clarity. — Preceding unsigned comment added by Kronn8 (talk • contribs) 12:32, 31 October 2013 (UTC)

newtonian vs nonnewtonian
consider replacing the poorly worded and overly technical current with something modeled on this, which is appropriate for a genral encyclopedia http://www.research-equipment.com/viscosity%20chart.html and dont' tell me cause my speling and gramar suck i don't have right to make comments like this — Preceding unsigned comment added by 50.195.10.169 (talk) 15:39, 3 December 2013 (UTC)

Dynamic (shear) Viscosity
If there is a force exerted on the moving plate due to the stationary one, wouldn't there be some force (the same as the former, by Newton's Third Law)acting on the stationary plate due to the moving one? Just to be clear, and if so would it be worth mentioning it here? — Preceding unsigned comment added by 111.93.131.220 (talk) 13:39, 28 January 2014 (UTC)

Newton view of viscosity
This statement in the Dynamic Viscosity section is misleading

Isaac Newton expressed the viscous forces by the differential equation

\tau=\mu \frac{\partial u}{\partial y},

Newton's only discussion of a friction in fluids is one sentence in the Principia quote (translation) here:

"The resistance which arises from the lack of slipperiness of the parts of the liquid, other things being equal, is proportional to the velocity with which the parts of the liquid are separated from one another."

There is no equation and no partial differential equation. The equation in the article is better attributed to Navier, Poisson, Saint Venant or Stokes who all derived it from fundamental considerations. — Preceding unsigned comment added by 67.193.115.212 (talk) 23:55, 24 January 2015 (UTC)

UNITS
In the information box it is stated that the SI unit for viscocity is Pa·s, however ...

The table in the article gives gas viscosities under the label μPa·s

The first mention of μPa·s in the article is to state that: μ = dynamic viscosity (Pa·s or μPa·s)

The wiki article on Drag gives the viscocity of water as 10−3 Pa·s

So, this article appears to suggest that the viscocity of air is 1,000 times GREATER than that of water.

Would someone clarify the text(s) so that this is an impossible conclusion. Drag refers to dynamic vscocity but from this article on Viscocity the first use of the word "dynamic" makes the two terms interchangeable.

LookingGlass (talk) 15:10, 24 March 2015 (UTC)

They're two different μ's and both usages are standard. When μ is stuck immediately before a unit it means the unit used is a millionth of the original unit, see International System of Units. Dmcq (talk) 11:37, 25 March 2015 (UTC)

In the article it says "The dynamic viscosity of water is 8.90 × 10−4 Pa·s". Is this one order of magnitude to low? — Preceding unsigned comment added by 128.39.88.40 (talk • contribs)


 * Seems that way. By definition water should be 1 centipoise at 20oC, which is 0.001 Pa*s. That means the value reported in the article text off by a power of ten, and yet curiously the table immediately below it uses the correct units. (+)H3N-Protein\Chemist-CO2(-) 14:29, 14 April 2015 (UTC)
 * Never mind, I wasn't really paying attention there. At room temp it's 0.89 mPa*s, thus 8.9e-4 Pa*s. I think I had a temporary malfunction of the part of my brain that does math:P (+)H3N-Protein\Chemist-CO2(-) 14:37, 14 April 2015 (UTC)

Explanation of dynamic viscosity units
"If a fluid is placed between two plates with distance one meter, and one plate is pushed sideways with a shear stress of one pascal, and it moves at x meter per second, then it has viscosity of x Pascal second."

I'm pretty sure it has a viscosity of 1/x Pa*s.

Cmatteri (talk) 20:29, 6 May 2015 (UTC)

Viscosity of honey
I believe viscosity of honey as listed now (2-10 Pa*s) is way too low. How does it have smaller viscosity than ketchup? --Metamerik~enwiki (talk) 15:00, 26 May 2015 (UTC)

Y vs. u chart
I was wondering if the axes on the y vs. velocity chart are backwards. Should it be u vs. y? The derivative is showing the derivative δu/δy. Rjtepper (talk) 01:09, 27 July 2015 (UTC)

About VISCOSITY ask Sir ISAAC NEWTON!
Which is the unit of measurement for a constant of viscosity?

It's a very good question. But who knows the answer?

Our professors have no clue. So whom to ask?

If Sir Isaac Newton could read the Wikipedia, he would turning over in his grave, exactly 32 times,

as well as Jean Leonard Marie Poiseuille (catch-32).

So, Sir Newton, VISCOSITY?, FRICTION? Please!

Ah friction, the issue chasing me in heaven and on earth all the time, and I keep saying:

"When Sir ISAAC NEWTON said FRICTION, he thinks WORK"

Just convenient epitaph, a pity that it did not carved on my grave.

I thought that was enough, to leave humanity friction law:


 * $$j = \mu \frac {dv}{dr}$$

By which I have just described the flow of impulses through any point of matter.

What, you do not know what is impulse? Well, are you in school do not teach my laws?

Namely, my second law says:


 * $$G = mass, i = impuls, M = Gi = moment, F_m = \frac{dM}{dt} = force,$$


 * $$F = \frac{F_m}{G} = \frac{di}{dt} = \frac{dv}{dt}\text{ = force per unit mass.}$$

"The flow of impulses, is in fact the work per unit mass [N m/kg] at some point in the fluid."

You still do not understand? Oh, silly me, I generously gave mankind the whole law,

and perhaps it would be better if I gave you only half of it:


 * $$\frac{j}{2} = \mu \frac{dv}{dr}\qquad\text{(flow of impulses, in only one direction!)}$$

So you would immediately be clear, the meaning and dimensions of that term:


 * $$\frac{j}{2} = \mu \frac{dv}{dr}\sim \left[\frac{v^2}{2}\right]\text{(Energy of motion of a viscous fluid} \left[\frac{m^2}{s^2}\right]\text{)}$$

Some of my good students prefer to write my law in vector form:


 * $$j = -{\mu\text{ grad }v}$$

So now when you have a law, Why did not use it?

How? Just do a balance of impulses in the fluid:


 * $$Acceleration - Deceleration - Friction = 0,$$

or, in another way:


 * $$j_f = \mu_a\frac{dv}{dr} - \mu_d\frac{dv}{dr} = \mu\frac{dv}{dr}\quad\text{(loss of impulse = friction)!}$$


 * $$\mu_a = \mu_d \text{= coefficient of self-diffusion of particles of fluid.}$$


 * $$\mu \text{ = viscosity coefficient of friction in the fluid}\left[\frac{m^2}{s}\right]$$

Equation of continuity for impulse = equation of force!


 * $$\frac{di}{dt} + \text{div} j = 0 \quad F = \frac{di}{dt}.$$


 * $$F_{\mu} = -{\text{div }j_f} = \mu \text{ div grad } v = \mu \Delta v$$


 * $$F_{\mu} = \mu \Delta v \text{, (viscous force per unit mass),  } F_r = \left( \mu \frac{\partial ^2 v}{\partial r^2}\right)_r$$


 * $$\left[\frac{N}{kg}\right] = \left[\frac{kg*m}{kg*s^2}\right] = \left[\frac{m^2}{s}\right]\left[\frac{m}{m^2*s}\right] \text{, Is not that obvious?}$$

But Sir, the question was: What is the viscosity? So, did not I already gave the answer:

"VISCOSITY is the WORK done by FLUID during MOTION"!

And, what is a fluid, Sir? This question is best to set to one of my very best student Leonhard Euler. OK. Thank you!

Mr. Euler, we heard that you know what it is "fluid"? Well, of course:

"FLUID is a group of identical particles that occupy a space that we call CONTINUUM.

Continuum is a space, in which particles of fluid are interacting, and interacts

with the boundary particles surroundings continuums. Each continuum has its own STATE.

State of the continuum, and of fluid can be SOLID, LIQUID or GASEOUS.

In each continuum rules the same laws of physics.

Each continuum respects the laws of THERMODYNAMIC EQUILIBRIUM and CONSERVATION OF MASS AND ENERGY.

Continuum - fluid, is in the fields of INERTIAL and POTENTIAL FORCES that in it

induces PRESSURE TENSOR and VELOCITY VECTOR FIELD." That's all.

And, have you, Mr. Euler, heard of the viscosity?

Yes, but it just does not interest me.

And, if, maybe, you know, how to measure the viscosity?

I have no idea, and I am only a university professor, and

We Professors, more like the "ideal fluids" - let's have a beer!

By the way, I heard that some James Prescott Joule, produces excellent beer,

using a "paddle-wheel apparatus" and maybe to ask him about that.

Let's have a beer in honor of James Prescott Joule, Leonhard Euler and Sir Isaac Newton! Cheers!

(Vjekoslav Brkić, Osijek)--213.202.80.195 (talk) 11:11, 1 October 2015 (UTC).

Units
It's somewhat annoying that in the section Viscosity of selected substances, the first table has units of milli Pa-s, the second table has units of micro Pa-s, and the third table has units of centi-poise. It means you can't directly compare the tables. Geoffrey.landis (talk) 16:12, 5 February 2016 (UTC)

References for gas viscosity model constants?
I see that the discussion of Sutherland's law cites Smits & Dussauge, who in turn cite NACA TR 1135, but TR 1135 only gives values for dry air. Converting from Rankine to Kelvin, the additive, Sutherland constant is 110.3, as is listed in Smits & Dussauge, but Smits & Dussauge fail to give T0 and μ0 or λ. The value I compute for λair by converting imperial units from NACA TR 1135 into SI units is 1.087E-6 Pa sec. (The value listed in NACA TR 1135 is 2.270E-8 lb sec / ft2)

Furthermore, F.M. White's "Viscous fluid flow" 3rd edition gives a table of Sutherland coefficients on page 28 and temperature ranges for +- 2% accuracy for a number of common gasses, but these still appear to be different than the constants listed on the main page of the article. White says his source was Hilsenrath et al. (1955).

So my question is this: Where the heck are the listed Sutherland viscosity coefficients in the article coming from?!? — Preceding unsigned comment added by 50.138.192.229 (talk) 21:24, 1 April 2017 (UTC)

Unit error
Pa*s is not kg/(m*s) but kg*m/s — Preceding unsigned comment added by 138.246.2.175 (talk) 14:44, 31 January 2017 (UTC)
 * Yes it is kg/(m s). Ulflund (talk) 05:29, 22 May 2017 (UTC)

Viscosity of Solids
Shouldn't granite viscosity at STP be added to the table? I don't quite follow how to put it in myself. Dan Watts (talk) 07:44, 1 June 2017 (UTC) Never mind. I figured out how to do it. Dan Watts (talk) 08:04, 1 June 2017 (UTC)

Animation


The animation is a wonderful one, although not quite accurate, it clearly demonstrates for the novice reader the difference between the two viscosities. I appreciate the time and effort someone put into it. When I say "not quite accurate", the surface tension of the thinner fluid would play a much greater role in "drawing" the flow into a cylindrical shape, while turbulence would cause a criss-crossing effect.

My main concern, however, is that the high-viscous flow shows a non-Newtonian fluid, in particular something pseudoplastic like ketchup. A high viscosity, Newtonian fluid would be common honey (not the few thixotropic varieties), as pictured to the right. Flow is perfectly laminar and surface tension plays a very small role.

I don't recommend changing the animation, because it is very good, but maybe it would be good to point out the difference in the caption or something. Zaereth (talk) 00:39, 11 April 2018 (UTC)

Intuitive definitions
I feel like the definitions of dynamic and kinematic viscosity could provide more-intuitive explanation. Dynamic viscosity is pretty straightforward in that it's (more or less) how hard it is to slide between your fingers (Couette flow). Kinematic viscosity is trickier. The article says "The kinematic viscosity (also called "momentum diffusivity") is the ratio of the dynamic viscosity μ to the density of the fluid ρ." To me that ratio of density means it relates to inertia, but also to how it's affected by its own weight. That is, I think that kinematic viscosity says a lot about how a liquid settles if you magically had initial conditions of a hemisphere of liquid sitting on a table: For the same dynamic viscosity, a denser liquid would settle faster 'cause its own weight pushes down on it harder. For example, mercury has a dynamic viscosity of 1.55 mPa s but water is roughly 1.0 mPa s, but mercury is 13.5x the density of water, so has a very low kinematic viscosity (and hence appears very inviscid). Is that right? Are there other intuitive explanations of kinematic viscosity? —Ben FrantzDale (talk) 17:14, 1 June 2018 (UTC)


 * I think of kinematic viscosity as a measure of the ease with which the fluid can be poured. Unfortunately I don’t have a suitable source for this concept. Dolphin ( t ) 21:56, 1 June 2018 (UTC)


 * I agree with Dolphin51. I wouldn't say mercury "settles" faster. Like most metals, mercury has very high surface tension; nearly 500 mJ/m2 as I recall. Most common liquids are on the order of tens of mJ/m2, so, depending of the size of the spherical droplet, it may not settle at all. (Huge changes in a liquid's viscosity have very little effect on surface tension, right down to the glass-transition range (Tm).)


 * The way I've always learned it, dynamic (literally "under power") viscosity (or absolute viscosity) is a measure of the liquid's viscosity under force, regardless of gravity (a dynamic force pushing on the mass externally, at a fixed interface). Imagine you have a jar full of water and a jar of honey. Stir each with a spoon and you'll easily see the dynamic viscosity of honey is far greater.


 * Kinematic ("to set in motion", implying automatically) viscosity is the viscosity of a fluid when gravity is the only force acting (a fixed force at a constant ROA, acting upon the entire mass equally --from all points internally-- in a uniform direction). Take the jar of water and the jar of honey and pour them both out. Both are fairly close in density, but the honey takes far longer to empty. This seems like a trivial distinction until you start comparing it to a non-Newtonian fluid, say ... mayonnaise. Take a jar of honey and a jar of mayonnaise, and stir each with a spoon. The honey has higher dynamic viscosity. Then, turn the jars over and dump them out. The honey will pour while the mayonnaise stays put. Zaereth (talk) 21:37, 5 June 2018 (UTC)


 * Another place this comes up is with lubricants, and, especially, grease. A good grease should have the proper dynamic viscosity for the job (let's say, lubing a gear train) at both the start-up and operating temp (let's say, arctic lube), yet the kinematic viscosity to keep from flowing out of the train when not in operation, or even during when it happens to be pushed out of a dynamic interface. Zaereth (talk) 02:14, 6 June 2018 (UTC)


 * I might also add (maybe because it's something I'm working on right now) that another place this distinction comes up is with convection. The kinematic viscosity of a fluid plays an important role is how it transfers heat. A fluid with low kinematic viscosity transmits heat through momentum diffusion, causing convection to dominate. (ie: the warmer fluid expands and rises while the cooler contracts and sinks.) A high kinematic-viscosity fluid transmits by thermal diffusion (more like a solid). Heat the water on a stove and it will remain a fairly even temperature throughout. Heat the honey on a stove and it can't convect, so it burns on the bottom. Zaereth (talk) 18:34, 14 June 2018 (UTC)

Differentiate from other things which disagree with laminar flow such as drag/turbulence/chaos. -Inowen (nlfte) 05:44, 21 August 2018 (UTC)


 * Good idea, please feel free to add, including any sources you may have. Although keep in mind that things like Reynolds number, laminar and turbulent flow, and drag are factors of things like viscosity (resistance), inertia (force), and energy (work). For example, viscous forces attempt to keep a flow laminar while the inertial forces try to tear it apart, changing it to turbulent. Zaereth (talk) 06:22, 21 August 2018 (UTC)

Correction to consider
Dear WIKI Not my first contribution, but it's been a while... in the section "Definition", it is clearly stated

"Use of the Greek letter mu (μ) for the viscosity is common among mechanical and chemical engineers, as well as physicists.[4][5][6] However, the Greek letter eta (η) is also used by chemists, physicists, and the IUPAC.[7] The viscosity μ {\displaystyle \mu } \mu is sometimes also referred to as the shear viscosity. However, at least one author discourages the use of this terminology, noting that μ {\displaystyle \mu } \mu can be appear in nonshearing flows in addition to shearing flows.[8]

Yet in the next section: General definition

In fluid dynamics, it is common to work in terms of the kinematic viscosity (also called "momentum diffusivity"), defined as the ratio of the viscosity μ to the density of the fluid ρ. It is usually denoted by the Greek letter nu (ν) and has units ( l e n g t h ) 2 / t i m e And shown thus: ν = μ ρ {\displaystyle \nu ={\frac {\mu }{\rho }}} \nu ={\frac {\mu }{\rho }}. should be revised to use (η)? — Preceding unsigned comment added by 83.110.225.234 (talk) 06:43, 20 November 2018 (UTC)


 * Hello, I appreciate you taking the time to give feedback. The 'discouragement of terminology' refers to calling \mu the shear viscosity, not in using the symbol \mu itself. So using either \mu or \eta is fine, as long as the use is consistent. For the article here, \mu has been chosen. MaxwellMolecule (talk) 02:13, 21 November 2018 (UTC)

Summary of reorganization (Nov. 30, 2018)
I combined the somewhat out of place sections on mixtures, slurries, nanofluids, amorphous materials, and eddy viscosity into the 'Molecular origins' section. I think the revised organization better reflects the priority level of each subtopic. E.g. nanofluids and slurries are cool but don't need their own section: having a section on suspensions more generally should be sufficient. I am happy for nanofluids and/or slurries to be mentioned more explicitly, but this should be kept to a maximum of 2-3 sentences each. Any new content would also have to consist of more than just a list of equations, which is what was there previously. To make this reorganization cohere, some content was removed. On the other hand, some content was retained and additional content was added. Comments/criticism welcome. MaxwellMolecule (talk) 18:19, 30 November 2018 (UTC)

Why was Orders of magnitude (viscosity) deleted from the article?
The information was excellent and very informative for the reader. I would have had no idea pitch was so viscous until I read about it on wikipedia. I came back here today and noticed the article was deleted. https://en.wikipedia.org/wiki/Wikipedia:Articles_for_deletion/Orders_of_magnitude_(viscosity)

And the deletion seemed to be out of order as everyone was in favor except for one person who went ahead without consensus to delete it. Why? Can I re-add that information to this article? Xanikk999 (talk) 00:35, 11 January 2019 (UTC)


 * It's explained at the top, but to break it down: the article was put up for deletion due to suspicions of WP:Synthesis. What this means is that the original poster felt that the sources did not support the conclusions, but rather were used in such a way as to make it look like they did (hoping nobody would go check). If true, then the information you received may be incorrect. The article was deleted because all "keep" votes were basically "I like it" or "I think it's useful", but none addressed the issue of synthesis. If you would like to re-add, or even recreate the article, you are welcome to give it a shot, but please be sure to use WP:Reliable sources, carefully cite those sources, and be careful that you are not simply taking bits and pieces out of context in order to imply something which the sources don't actually say. Zaereth (talk) 00:58, 11 January 2019 (UTC)

The information was accurate though. It should have been redone rather that outright deleted. The consensus was still against deleting it. It should be restored until better sources can be found. Xanikk999 (talk) 00:55, 13 January 2019 (UTC)


 * Doesn't work that way. WP:Consensus doesn't work by way of counting votes, but rather by way of compelling arguments. If a reason to keep is not compelling (is only a matter of personal preferences, contains logical fallacies, etc...) then it's not really a reason, is it? You can think of consensus as taking all the compelling arguments from a bunch of various individuals and melding them together into a unified plan of action, while all the useless desires and rationales are discarded. Likewise, it's unlikely that the information will be restored to mainspace until someone sorts out the sourcing issue. What I recommend is for you to ask an admin to put the info into your sandbox, so you can work on making sure everything is in order, then submit it to WP:Articles for creation when you think it's ready to be moved to mainspace. Zaereth (talk) 01:13, 13 January 2019 (UTC)

Improper phrasing
In my opinion, this statement is phrased improperly: "For example, an incompressible fluid satisfies the equation, i.e., $$\nabla \cdot \mathbf{v} = 0$$. The term containing $$\kappa$$ is absent." The previous version was: "For example, incompressible liquids satisfy $$\nabla \cdot \mathbf{v} = 0$$ and so the term containing $$\kappa$$ is absent."

I reverted this a few days ago, but then it was reverted back. To avoid edit warring, I would like a third person to review this and make a decision.

MaxwellMolecule (talk) 15:58, 17 January 2019 (UTC)

-


 * Can you be more specific? What about it do you think is improper? I fully agree with your revert, because the grammar was indeed incorrect. When they reverted you, they apparently didn't understand what about it was wrong and honestly thought their grammar was correct. I, in turn, corrected their grammatical error instead of reverting, including a detailed explanation of what was wrong in my edit summary for the purposes of acknowledging their good faith (always better to attract new editors than push them away) and to show them exactly what was wrong with it. Turns out, they're Chinese; a language devoid of things like articles and prepositions.


 * Grammatically, the sentence is correct either way. Changing both the noun and verb to singular and adding an indefinite article conveys exactly the same meaning as removing the article and changing the noun and verb to an uncountable plural form. Either way it says the same thing.


 * Or does your objection have to do with the change to the word "fluid"? All liquids are fluids, even though not all fluids are liquids, so I'm not sure this changes the meaning either, but my expertise ends where the math begins. Does this equation satisfy incompressible gases, such as supersonic flow? I can't answer that. If you think "liquid" is a better word, feel free to change it back. As for pluralization, it doesn't make a difference either way. Zaereth (talk) 21:09, 17 January 2019 (UTC)


 * Ah, it makes sense to me now. I agree that the grammar in the changed version is technically correct. But it appears to be saying something different from what was said previously. "For example, an incompressible fluid satisfies the equation ..." -- which equation is that? The point is simply that for incompressible fluids the term with kappa drops out of the generalized Newton's law of viscosity. The condition $$\nabla \cdot \mathbf{v} = 0$$ isn't a prerequisite for satisfying Newton's law of viscosity or any other equation here. Maybe this would be clearer:

"For example, incompressible liquids satisfy $$\nabla \cdot \mathbf{v} = 0$$ and so the term containing $$\kappa$$ drops out."

MaxwellMolecule (talk) 13:17, 18 January 2019 (UTC)


 * Yeah, it's like "Red apples taste better than green." versus "A red apple tastes better than a green." Your recommendation sounds fine to me. English is my forte, and the sentence reads just fine. Math is a completely different language, and one I barely speak. (When it comes to physics, I have to be able to understand it from a mechanical sense, to where I can see all the inner-workings in my mind.) Thus, I'll take your word for it, because you obviously understand it better than I. You're no where near 3RR (another reason I jumped in to help), so if you think it's an improvement, go for it. From the message the other user left on my talk page, I think they understand the problem now and likely won't war about it. Zaereth (talk) 20:23, 18 January 2019 (UTC)


 * Got it! Thanks for taking the time to look at it. I think we're in basic agreement now. I didn't mean to fuss over something so small :) MaxwellMolecule (talk) 23:02, 18 January 2019 (UTC)

Semi-protected edit request on 6 August 2019
"Volume viscosity" is very closely related to shear viscosity. Still, there is no mention of its corresponding Wikipedia article in the "See also" section (Given at bottom of a Wikipedia page) of "viscosity" page. Please add link of this "volume viscosity" page in "see also" sectoion.

Link of "volume viscosity" page is this: https://en.wikipedia.org/wiki/Volume_viscosity SmartIndian64 (talk) 17:54, 6 August 2019 (UTC)

Thanks for the input, I agree with you. I will make this change shortly unless someone else does in the meantime. I might also go through and see if there are other places in the article where volume viscosity should be linked. MaxwellMolecule (talk) 18:47, 6 August 2019 (UTC)


 * "See also" sections are really for related information which are not relevant enough to the article to be discussed directly within the text. This seems like it's more relevant than that. Ideally, we should add a brief summary of the article, in a section or subsection of its own, with a "main article" link. I was thinking about doing just that, but unfortunately was not really able to parse through that article and determine exactly what it means in English terms. I took a look deeper, and searched some books, but at the moment all I've gleaned were several salient points: 1.) It has nothing to do with incompressible fluids/flow. 2.) It is related to the structure of a fluid rather than shear stress/strain. 3.) It is more related to the elasticity of a fluid (compression and relaxation to an equilibrium), which occur almost instantaneously, thus making it very hard to measure, except when it comes to sonic shockwaves at very high frequencies (well above human hearing). 4.) It's mot necessarily a fixed value, but may be dependent on some factors such as pressure while completely independent of others, such as temperature, and 5.) it's really not that well understood. It would be helpful if someone who understands this far better than I could leave a short description here.


 * That other article needs some attention as well, to both help make it more accessible to the general reader, to eliminate the second-person and allocentric perspective, provide more secondary-sources over the primary ones, and overall help make it more encyclopedic and less academic. Zaereth (talk) 19:22, 6 August 2019 (UTC)


 * OK, I mean I get your point about the "see also" section -- if there are enough links in the main text, then I agree we don't need it there. But I thought it could go there provisionally until the main article has the proper treatment of bulk viscosity. I'm partially educated on bulk viscosity, but it is indeed only partly understood even in the literature. I certainly can try to put together a dedicated subsection, but I don't have the time at the moment (maybe in a couple weeks...). MaxwellMolecule (talk) 19:42, 6 August 2019 (UTC)


 * Well, you probably know more about it than I do. It's fine to put it there until we find a better place for it, but it may take me even longer, and much research, before I would feel comfortable adding anything myself. Zaereth (talk) 19:46, 6 August 2019 (UTC)


 * All I did now was add a "see also" link to the "General definition" section of the main article. I might just leave it at that for now, and try to write a proper subsection later. I should say that I too would need to some additional research before writing a subsection. I'll have to see how that goes..! MaxwellMolecule (talk) 19:52, 6 August 2019 (UTC)




 * I've been reading up on this a little more, as I've never really heard of it before now. (My knowledge of fluid mechanics is mostly limited to practical experience from the field.) However, it does seem similar to something I've always known but never really put much thought into, having worked many years with both pneumatics and hydraulics.


 * What this seems to be describing is viscosity related to a change in the volume of a fluid (liquid, gas, or plasma). I'm no mathematician; what I know is also limited to practical use, so I need to be able to visualize this stuff in mechanical terms or "thought experiments'. Please feel free to correct me if I'm wrong.


 * Let's say someone were to launch a balloon out of an airlock into deep space. That balloon would suddenly expand explosively, rapidly accelerating outward. However, it would not expand instantly, as (assuming it survives) the balloon would put up resistance to this expansion. Now, imagine there is no membrane but just a bubble of air, magically launched out an airlock. It too would expand explosively, but not instantly, due to some internal friction within the gas. Assuming a perfectly spherical shape, there would be no internal shear within the expanding fluid, yet an internal resistance or friction would exist that limits its rate of acceleration, due to the atoms simply moving closer to or farther away from each other. (There are some hypotheses that the accelerating expansion of the universe can be explained this way, as a bubble expanding within some total vacuum that may exist outside our universe, where even physical laws such as the speed of light may not apply.)


 * It's hard to see this on any kind of normal scale because it happens so fast, unless you go to extremely large scales, but whenever a fluid is compressed or expanded there is a moment of non-equilibrium, where a pressure differential exists within the fluid, and some atoms will be in a highly excited state and others at a much lower state, before quickly snapping back to equilibrium. Perhaps the most dramatic examples of this occurs in dynamic gas-pumped lasers. It also becomes apparent at very small scales, like when the frequency of sound literally starts to outrun the acceleration of the shockwaves, the wave is reduced (attenuated).


 * So that's basically where I'm at so far in coming up with an opening sentence. Perhaps something like, "Volume viscosity is the resistance to a change in the amount of space occupied by a fluid." Or, perhaps, "...resistance to a change in the density of a fluid." (I would say volume but it's not good to define a phrase with words from that phrase.) Zaereth (talk) 00:46, 9 August 2019 (UTC)


 * I appreciate your thoughts. A major clue towards a physical interpretation is that the volume viscosity is zero for a monatomic gas, but nonzero for gases whose molecules possess internal degrees of freedom. It does indeed turn out that volume viscosity can be interpreted in terms of energy exchanges between translation and internal degrees of freedom, and in particular the fact that there is a timescale associated with conversion of translation energy into e.g. rotational and vibrational energy.


 * So here's the thought experiment I've developed. Suppose you take a gas like CO2 with rotational degrees of freedom (DOF), and compress it slowly. The PV-work will be transformed first into (primarily) translational DOF. Then, some of the translational energy will be transformed into rotational DOF, over some finite relaxational timescale, until equilibrium (equipartition) is reached among all DOF. Compared with the slow compression of the gas, these energy transformations are very fast; hence, one can assume instantaneous equilibrium (equipartition) at each instant of time.
 * Ok great. Now, imagine compressing the gas rapidly. There will not be sufficient time for equipartition to be established, so the translational DOF will carry more energy, at a given volume during the compression, than during the slow compression. This makes the gas "hotter", with larger effective pressure, and therefore more resistant to further compression. More PV-work must be performed compared with the slow compression, and one can conceptualize volume viscosity as accounting for the extra energy dissipated.


 * Free expansion into a vacuum probably needs the full Boltzmann equation for a proper treatment since local equilibrium won't be maintained everywhere in the gas. In other words, Navier-Stokes, local temperature and pressure, etc won't be valid. That doesn't mean an effective volume viscosity can't be defined, but one would have to be careful to not accidentally important principles from the hydrodynamic regime.


 * I'm thinking discussion of the finite relaxation time between translation and internal DOF is necessary for proper description of volume viscosity. Otherwise it's hard to separate it from ordinary pressure, which also resists the compression/expansion of a gas. MaxwellMolecule (talk) 22:59, 9 August 2019 (UTC)


 * Those are some good points I hadn't even considered. I'll do some more looking on my end. To make it understandable to the general reader, one question needs to be answered first, which is the one question every book seems to evade: what is volume viscosity. If it's possible to condense the answer into a simple and, preferably, short sentence, the rest is easy. It's that first sentence that is so critical, which should begin "Volume viscosity is..." (Or "Volume viscosity equals..." since all language is really one form of math or another, if it helps to think of it in those terms. How do we condense that all into one short and elegant equation, using common English terms?) Seemed like an easy task at first, but it's like trying to find a clear definition of entropy. Something's always lost in translation. I'd better go back to the idea this may take months if not longer. Zaereth (talk) 00:38, 10 August 2019 (UTC)

Semi-protected edit request on 5 September 2019
The equation given as the Lederer Roegeirs equation for the viscosity of a mixture is incorrect. The left hand side of the equation should be a logarithm. Howie vasive (talk) 18:09, 5 September 2019 (UTC)
 * Please provide the specific correction that needs to be made, along with a reference. RudolfRed (talk) 19:18, 5 September 2019 (UTC)


 * @Howie vasive looks like you're right -- it's fixed now. On a related note, it would be good to find a second source for that equation. I might try to access the original articles cited in the LubeTech paper. MaxwellMolecule (talk) 21:46, 5 September 2019 (UTC)

Trachenko-Brazhkin definition of minimum quantum viscosity
Trachenko and Brazhkin have defined a lower bound on kinematic viscosity relative to the proton-electron mass ratio and the reduced Planck constant. — Sasuke Sarutobi (push to talk) 13:21, 29 April 2020 (UTC)

Featured picture scheduled for POTD
Hello! This is to let editors know that File:Viscosities.gif, a featured picture used in this article, has been selected as the English Wikipedia's picture of the day (POTD) for August 20, 2023. A preview of the POTD is displayed below and can be edited at Template:POTD/2023-08-20. For the greater benefit of readers, any potential improvements or maintenance that could benefit the quality of this article should be done before its scheduled appearance on the Main Page. If you have any concerns, please place a message at Wikipedia talk:Picture of the day. Thank you! &mdash; Amakuru (talk) 14:46, 4 August 2023 (UTC)


 * Not a concern, except that other readers may notice this too, but the animation not only shows different viscosities, but also the left fluid (water I suppose) is Newtonian whereas the fluid on the right (McDonalds hot-mustard, maybe?) is non-Newtonian. (For an example of a viscous Newtonian-liquid, see the photo at Honey.) Of course, that might be too much detail for a Picture of the Day caption, but just thought I'd point it out in case someone feels it is worth mentioning. Zaereth (talk) 02:01, 5 August 2023 (UTC)