Talk:Capillary action

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There are some animals that use Capillary Action, such as the M.horridus, yet I see no mention of this here. Please add this so you can complete the article. Meapyeah (talk) 16:58, 7 May 2014 (UTC)

Initial Discussions[edit]

glass to a pool of blood on the fingertip after a prick. How does it work though? That's what I came here to find out, and I had to make the entry myself! I don't know, but I wonder if it has something to do with surface tension. Maybe the water molecules are attracted to the sides of the capillary tube. Successive H20 molecules leapfrog eachother up the sides of the tube. Each higher molecule is happy to have found some tube wall it can call it's own. Then surface tension brings up the column a bit more, then another molecule finds the wall a bit higher and so on? It seems like quite a thermodynamics problem though: What is providing the power to lift the column of water? Where is that energy coming from?"

The above text was cut and pasted from the article page. So far the questions raised by the above user have not all been addressed on the article Theresa knott 14:18 May 13, 2003 (UTC)

I can't answer the question of what's happening on a molecular scale, though the article on adhesion may help. I can give some physical reasoning, though. In any case, it's likely the result of electrical attraction between two molecules. Perhaps each molecule has at any particular time a positively charged region and a negatively charged region, causing the attraction (Van der Waals forces; perhaps it's a more permanent distribution of charge like for polar molecules or ions. In any case, I think it's possible to answer the conservation of energy question by considering a positively charged particle. The total potential energy for this particle will increase if the particle is raised (because of gravity) and it will decrease if the particle is moved towards negative charges. In other words, the work needed for the positively-charged particle going up is positive because you'd have to push it, and the work needed for the particle going towards a negatively charged region is negative because opposites attract. So for a particle to be attached sideways to a surface, the electrical and gravitational potential energies must cancel out, which is certainly possible. So the short answer to the conservation of energy question is that gravitational potential energy gets transferred into the electrical potential energy in between the atoms, so energy is conserved.
Why do molecules seem to prefer the electrical energy to the gravitational energy? In this case we have to consider forces (derivatives of potential energy) rather than the potential energies themselves. Forces occur in regions where potential energy changes. Consider a thin vertical tube placed just above the surface of the water, at y=0. The gravitational force is d/dy (mgy) = mg, which is true everywhere along the tube. The electrical potential energy is constant from y=b on up at U_e=-C along the inside of the surface of the tube, but there is a sharp drop from 0 at y=0 to -C at y=a. Somewhere between y=0 and y=b the slope of the electrical potential energy will be opposite the force of gravity; we'll call this place a. (See the mean-value theorem). A single particle of water starting at y=0 under these conditions would accelerate upwards until y=a, when the forces cancel out. After y=a the gravitational force wins out, and before y=a the electrical force is stronger. Now, if we were only talking about a single particle, there'd be no drag, so you'd see a particle oscillating about y=a. However, we're talking about a fluid, so instead of a force accelerating a particle, the force pulls a fluid at a constant velocity (with the missing kinetic energy of the accelerating particle being converted into heat).
One more factor we have to consider is that when a bunch of positively charged particles congregate in an area of negative P.E., the P.E. then rises because the region has become more electrically neutral. This is called saturation. This causes the point at which the forces cancel out to rise a little bit (draw a curve of the P.E. before and after saturation at y=a to see what I mean.) Then the liquid rises to the new y=a, which then gets saturated, and so on. This can't continue forever, though. At some point y=a_f the P.E. function gets stretched out enough along y such that the only way to get a slope great enough to counter the force of gravity is to have a constant slope from y=0 to y=a. (Or you could simply run out of water.) For any height greater than y=a_f the average slope would be too small. 21:33, 4 September 2006 (UTC) John S.


Is capillary action the same thing as Capillarity? And if so, should they be merged? --liquidGhoul 06:59, 16 June 2006 (UTC)

I agree - Capillarity should become a redirect to Capillary action, as Capillary action is the more widely used term. The Capillarity page seems to add no further information. Ozhiker 11:46, 9 August 2006 (UTC)

Is gravity necessary?[edit]

I thought that capillary action occurred with or without gravity, so shouldn't the definition on the top of the page be changed? 19:55, 4 September 2006 (UTC) John S.

And even if it is to be included, the word "gravity" should be used judiciously. The first sentence seems to imply that gravity is a force, which it clearly is not. It might be nit-picking, but I had to point it out. Monkeyface13 (talk) 15:20, 20 November 2012 (UTC)


moved this tage here - because the page has been idle for ages, and this tag is ugly!....


cheers, Petesmiles 00:13, 29 December 2006 (UTC)

Moved it back because there are no references.--BirgitteSB 16:35, 30 May 2007 (UTC)


According to this site the contact angle does not matter in determining the height that the water will climb a tube.

This is confirmed on this site which also has derivation of the height formula. This comes from the formula for the adhesion force and the formula for the gravitational force. 06:17, 2 April 2007 (UTC)

Can someone please double check the formula and the values used for the equation? There is an error in there. I was able to derive the 1.4 * 10^-5 from the values provided. But, if this part is true, the height of the column of water would be about 14 cm for a 0.1 mm diameter tube and about 7 cm for a .2 mm tube. So, either one of the numbers supplied are incorrect, or the results are incorrect.

--Jlinde 17:09, 10 November 2007 (UTC)

Regarding the temperature changes of the surface tension, the article states the formula is gamma*V^2/3=k(Tc-T-6), meaning surface tension would be gamma = k(Tc-T-6)/(V^2/3). As stated: k=2.1*10^-7 J/K/mol^(2/3) Tc=374°C T=20°C thus surface tension = 1.06*10^-5 Can somebody confirm this or am I doing something wrong in the calculation? (talk) 13:47, 27 June 2010 (UTC)

Capillary Action and Plants[edit]

In response to the box at the top of the page.

"A common misconception is that water moves in xylem by capillary action—the movement of water along a small-diameter conduit (such as a capillary) as a result of surface tension in the meniscus at the leading surface of the moving water. Surface tension does play a critical role in water movement in xylem, as described above, but the relevant force acts at the surface site of evaporation within leaves, not within the xylem conduits. Water movement within the xylem conduits is driven by a pressure gradient created by such force, not by capillary action." - Transpirational pull

So I am not sure that such discussion would be applicable to this section. 06:53, 2 April 2007 (UTC)

Jurin's Law ?[edit]

Hi ,

I'm a french wikipedian humble contributor. I'm looking for a confirmation : The formula presented in the main text of this article, is the Jurin or the Laplace's law ? In my opinion, James Jurin was the first to express it like that in 1718 (if I'm right)... But I already see the term Laplace's law in scientific litterature... Laplace made this job with soap bubbles, isn't it ? Is there someone to give me an definitve answer ?

Thank's in advance, Dam s.vador 12:42, 18 June 2007 (UTC)

Not quite up to "definitve" yet but I think that what you are looking for is here [1]. He was of course building on earlier work of Francis Hauksbee in 1709. Jurin law or Jurin height do seem to be modern terms [2]. Laplace's name, in my view, applies solely in the sense of the, more general, Young-Laplace equation. Hope this helps.Cutler 15:59, 5 September 2007 (UTC)


This article does not make it sufficienty clear that the phenomenon occurs in two related but different situations:

  1. Capillary action seen in thin tubes - a static phenomenon described by the usual equation, derived from the Young-Laplace equation; and
  2. Flow in porous media - a dynamic phenomenon in which viscosity is important and described by Washburn's equation.

Read the surface tension article and realise that we are not worthy. I will try to have a go at cleanup some time.Cutler 15:28, 5 September 2007 (UTC)

No, actually you can observe both the dynamic case (at short times) and static case (by waiting long enough) in both single cylindrical capillaries and in the void space of porous media. —DIV ( (talk) 07:03, 10 September 2009 (UTC))


In the formula for height, h=2TcosØ/dgr where, t=surface tension Ø=angle of contact d=density g=grav. acceleration r=radius of capillary REFER SURFACE TENSION (talk) 18:02, 12 June 2010 (UTC)NIK

Surface Tension[edit]

The article is using surface tension in a slightly confusing way. First we are told that capillary action ".. occurs because of inter-molecular attractive forces between the liquid and solid surrounding surface ..", but then "Surface tension pulls the liquid column up ..". I get the impression that the second sentence refers to the air-liquid interface, which cannot be correct. This can be easily seen from the figures of the capillaries, the surface between the liquid and the air is exactly the same no matter how high the liquid rises, so there is no way that this can be the cause of capillary action. The formula of the capillary height is also 'misleading' in this way. The liquid-air surface tension enters as a constant, and gives the impression that the effect happens at the liquid-air interface. I guess that this constant multiplied by the cosine of the contact angle tells us something about the liquid-solid interaction, which is the important parameter. In this sense there is nothing incorrect in the article, but a non-expert will get the impression that capillary action is caused by the water(-air) surface inside the capillary. Perhaps surface tension is not a useful concept in this article? -- (talk) 19:43, 14 February 2011 (UTC)

Height of a meniscus[edit]

I made the calculation for water less approximate and tried but failed to correct the dimension from meter to the correct meter^2 I've not yet learned to use the math functions. — Preceding unsigned comment added by Zedshort (talkcontribs) 22:26, 19 January 2012 (UTC)

Dubious etymology[edit]

The following statement about the etymology of the term was unreferenced and sounds like guesswork:

This would suggest the scientific phenomenon was first observed between contiguous hairs, for example within a paint-brush. In medicine and biology, it usually refers to the smallest blood vessels. The word "capillary," in the non-anatomical sense, means narrow tube.

I have no source either, but the term "capillary" for glass tubes and for the blood vessels surely is only a Latinate way of saying "hair thin". I don't remember which one I heard first, "capillary tube" or "capillary action", but they usually go together, so it seems at least plausible that the action was named by physicists after the tube (because it is most dramatic in such tubes).
Anyway, the etymology should be backed by a reliable source. --Jorge Stolfi (talk) 04:02, 25 February 2013 (UTC)

capillary action of non-aqueous fluids?[edit]

I had been taught that soldering relies on capillary action - that the molten solder metal flows into the narrow space between the heated metal components to be joined.

If this is the case, then the mechanism cannot be based on hydrogen-bond attraction. I came to this article to try to find out about this, yet here, the only examples given are of aqueous liquids and polar solids (the mercury in the diagram is used to illustrate capillarity action _not_ happening).

So, is flow of molten metal during soldering a capillary phenomenon, or not? If it is, there should be some mention of it, and the molecular/atomic mechanism; if not, then a note to say that it's a different thing.

Thanks very much if someone can clarify this point in this article. (talk) 01:20, 3 April 2013 (UTC)

I see no mention of hydrogen bonds in this article. It only mentions that adhesion is needed for capillary effect to occur, not specifying the various bonds that can cause adhesion. The diagram illustrates how there is repulsion between mercury and glass, but if the tube was made of metal, mercury would exhibit capillary effect. I'm not sure of the extent of capillary action in soldering, but adhesion between the solder and the parts to be soldered is important part of properly wetting the surface. --Petteri Aimonen (talk) 08:55, 14 April 2013 (UTC)


This article explains "wiking" but hardly, and has many details about meniscus but nothing about pressure and area, air pressure, and why this makes a difference.

That being so, it says a long "capillary straw", placed vertically especially between areas of differing pressure, that the pumping of fluid against gravity operates purely on meniscus: and that then capillary is merely a pseudonym for meniscus. That's not what i've heard.

However my remark is: I don't know what your reading from what decade: but the definitions were not (are not thank you) the same.


in addition to the comment above. The main article states (despite contradition in MANY SOURCES) that "down" meniscus of Hg is the driving force behind thermometors. I've heard but will not cite that the expansion rage of Hg due to temperature might be involved, as is STP (pressure and temperature standards) in building one.

I'm finding allot of wiki articles with contributions deleted which maddenly describe everything except why one would likely read the article. And i think it is from competing gov workers who are making "for pay" encyclopedias and almanacs using tax money, just a guess.

And wait a minute Hg thermometer: even wikipedia Mercury-in-glass_thermometer doesn't mention meniscus. I take back my comment about "there being many sources" and cite that.

And I never was a fan of "continuum math" texts, they are "too new" for me, redefine things already defined and sometimes confusingly, and appear contrived. — Preceding unsigned comment added by (talk) 19:12, 10 September 2014 (UTC)

Cinder Blocks[edit]

I love material science and that subsection, but the absorption of moisture by cinder blocks is not necessarily completley defined as capillarly - and probably doesn't belong in the article.

Ionic attraction[edit]

Intermolecular attraction "in general" should not be used as meaning "capillary"

For example: capillar and cavity: not the same word or definition

Now as to porosity, it is possible for moisture to be attracted ionically, due to lack of moisture of the material. Hydroscopic is a topic.

This obviously arrives at: the fact of dryness (below standard moisture at STP) and porosity allowing moisture to permeate within - is not capillary necessarily - or in general. Saying so would then define all chemical reacations as capillary: which is just more and more far afield from the definition.


Capillary \Cap"il*la*ry\, n.; pl. {Capillaries}. 1. A tube or vessel, extremely fine or minute. [1913 Webster]

more: caput (head) capilla (hair), captus (capturing, taking), capis (vessel). and these were used to describe things figuratively. (of latin/greek family origins)

It's frustrating to have words re-defined so that they no longer have individual meaning: it makes it impossible for those who wish a vocabulary with differentiation. (new webster's is awful with this, giving the same definitions for many words to all mean the same - which used to be different so as to convery different ideas)

Obviously what i mean is: capillary implies tubes, not porosity. defining the two as the same simply destroys the language. saying meniscus is capillary are the same is a next intrusion of common sense.

Assessment comment[edit]

The comment(s) below were originally left at Talk:Capillary action/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Rated "top" as high school/SAT biology content and important biophysical concept, e.g. water conduction in plant cells. The article could need some expansion with biological examples and context. - tameeria 05:10, 19 February 2007 (UTC)

Last edited at 05:10, 19 February 2007 (UTC). Substituted at 10:50, 29 April 2016 (UTC)