Physics 33.1 Surface Tension (5 of 12): What Causes Capillary Action?
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- Опубліковано 23 вер 2013
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In this video I will explain what causes capillary action.
Next video in this series can be found at:
• Physics 33.1 Surface ...
If professors at my college explain like this, I would never skip classes!
Thank you. When we were students we often did not get much out of going to class and at times were very frustrated when the lecture did not help us understand the concepts. That is when my wife suggested we make these videos. We are glad that they have been helpful.
Thanks sir Michel, The little steps the small equations everyone everyother video ignores (ex : p=m/v ... etc) makes all the difference Thank you for your dedication sir Really appreciate it 😊
This series is amazing, haven’t been able to find a good set of surface tension problems elsewhere
Glad you found our videos. 🙂
Bravo! Real good explanation. Very professional too
Outstanding teaching! Fantastic.
thanks.... this video has made me interested in physics again😃!
This professor is one in million ❤❤❤ I can't explain how much beautiful and clear you study. Wonderful 👏 👏 👏
Thank you! 😃
Great presentation(voice/pace). I have a question. Instead of having a glass tube, what about a flat plate of glass? Given the width of the flat plate = (2πr) of tube. Per the equation, the result should be the same? Maybe a little higher due to the fact that the plate has 4 sides; however, if you smear some "oil" on the other sides that would negate that effect.
Nicely done!
Nice video sir.
What is relationship between capillary pressure and saturation of water during counter current flow through porous media? They are linearly related with same direction or opposite direction?
A good explanation
Excellent!
using this to help my understanding of chromographh i’m only doing a levels but i wish u were my teacher
Glad you found our videos.
Thanks, just saved me a bunch of time :D
very nice video! everything is crystal clear.
i would just like to notify a small mistake in the last part of the derivation.The subject of the equation should be h not R.
can't thank enough for the work.
thank you so much for this video :)
Thank you sir!
Can I get the proof of F(LS)-F(SA)=-F(LA)COStheta
Thank you very much
What equipment would be use in a experiment like this?
Lucid! Clear as water!
Thank you very much for the vid. But I have a question which I am confused about
For the length 'L', why did we not have '2l' where little l would be the circumference between water and glass, making the equation 4.pi.r ? In other words, arent there 2 contact surfaces between water and glass ? (between outer glass and water tub, and between inner glass and rising water) ?
+Ali Dahroug In this case with a test tube, only the inner surface of the test tube causes the liquid to rise inside the tube. The outside surface does not have any effect on that.
very interesting topic!
Glad you think so!
I totally figured it out. Thanks.
Excellent!
Thanks for the insightful video, i have a question though.
You explain surface tension between the water and the air to counterbalance the weight of the fluid. However, is it not the attraction of the water to the glass tube that contributes to counterbalancing the weight?
+Adam Klinger The adhesive forces between the water molecules and the glass surface causes the meniscus, but it is the surface tension, (the cohesive forces between the water molecules), that drives the water up the tube.
+Michel van Biezen
Thanks for the prompt response,
ok, but as you mention early on in the video, the discrepancy between water rising and Mercury not is due to the fact that water is more adhesive to the glass, thats why i was a little confused.
Can we predict (without experimenting) that the top most part of the volume can support the rest of the volume? How do we know that the volume will not fragment into droplets?
shouldnt it be cos^2 theeta cuz u have considered only the vertical component of the surface tension?
awesome sir
Thank you.
God bless you Michel!
Thank you.
The lessons are very good and I understand very well but pls if the captions can be removed for is to see the solving properly it would be great
That is a UA-cam feature and they can be turned off by the user at any time. (Just hit the CC button).
Hello sir and thank you so much for the video.
I have two questions please,
1- The reason why the shape of the water/air interface is curved and not straight is because the adhesive forces between the glace and water are higher in the parameter than in the center? Or is there an other reason?
2- If the solid surface (in here the glace) was equally wetted by both water and air, how the rise and the shape of the interface would be?
Thank you so much
1. Yes, the water is more attracted to the glass surface and the surface takes on the shape of a hanging cable. 2. If the wetting was equal, there would be no change in the height inside compared to outside.
+Michel van Biezen thank you for your time.
for the answer 2, there would be no rise even if the interfacial tension between the two fluids was high? because the rise has a rule to balance the pressure difference between the two fluids
"no change" is reference to the original fluid height (outside the tube)
Thanks very much for the tutorial. One thing I'm not quite understanding though, you say the contact angle between water and glass is 0 zero degrees, hence the cos term goes to 1. How can it possibly be 0 degrees? I'm struggling to visualise what a zero degree contact angle would look like.
The water on the inside is pulled up along the glass edge due to the attractive forces. Think of the shape of the meniscus following the equation y = 1/x with y being along the glass edge.
I understand now with reference to that curve, thank you so much!
Thank you so much !!!!
You're welcome!
Knowledge. up move.
? 🙂
are the gamma signs can also be called Specific Weight?
So does capillary action only act vertically & not horizontally? I'm trying to work out if capillary action could take place through several courses of bricks in a wall. Would the render stop capillary action at the first course of bricks? Could moisture travel horizontally along a cement layer?
Capillary action is caused by the attactice force between the glass and the liquid. This tends to pull the liquid up to the wall of the glass.
@@MichelvanBiezen Yes, but could cappilary action happen through courses of brickwork & it's mortar (differing materials of the brick & the mortar) or would it stop at the mortar.
An glass tube is dipped into mercury.Height of the dipped part is 20cm.An person put his thumb on the top of the glass tube and get it out of the mercury.What is the height of the sucked Hg in the glass tube,Sir?Height of the glass tube is 60cm.
You describe capillary action as an effect of surface tension, but isn’t the rise attributed to the stronger adhesive forces between the liquid and water, whereas surface tension is a result of cohesive forces between water molecules. I am really struggling to understand the relationship between these two forces, could you please explain a bit more specifically? Thanks
Koray,
Yes, understanding the surface tension is tricky and confusing especially since the height of the water column in a narrow tube depends on the surface tension coefficient of the liquid-air interface. The rise of the liquid in the tube is caused by the cohesive forces between the liquid molecules and the molecules in the tube wall and also because of the lack of attraction between the liquid molecules on the surface, since the surface of the liquid was cut by the tube. (Think of the surface of the liquid (water) as a "fabric" like material that is held together by the attractive forces of the top layer molecules.) If you push a narrow tube from below the water surface upward, it would not break through the surface until the force breaks through the surface tension, that force would be equal to the surface tension that pulls a column of liquid up the inside of the tube.
your formula should be "h" not "R" ?....so what type of material will have small "R" in order to increase the "h" or height of the rise? or what do you have to do with water to increase its surface tension (S)?
You can measure the level of seriousness of a given physics professor on the size of his bow tie
you ate❤
Thank you. Glad you like our videos.
I am still struggling to understand how energy is conserved when there is extra gravitational potential energy from the liquid that has risen due to the capillary action. Is there less energy stored in the molecular bonds between water and glass than water to water molecules?
The extra potential energy comes from the adhesion forces between the glass and the liquid. W = f x d
Sir, what will happen if we take a capillary tube of insufficient height? Does the liquid overflow in that case?
That is a great question. We can best answer that with the conservation of energy. If the water overflowed, then we would have a perpetual motion machine pulling up more and more water to replace the water that overflowed. That would violate the law of conservation of energy. Thus the water would not overflow.
Thanks
You are welcome. 🙂
I think surface tension is force between two same matter & I didn-t get why the direction of the surface tension is such..
It seems the mass of the water between the meniscus and the top ring is treated as negligible?
And the water is being pulled up due to the cohesive forces and thus plays little to no role in the pressure at the bottom of the tube.
I want to ask what are the meaning of F(LS), F(SA) and F(LA) are respectively? Does it mean that F(ST) mentioned in the video is equal to F(LA)?
If you watch the video, it is explained in the video
lol@@MichelvanBiezen
Say, I have test tubes of different diameters(assume the exaggeration) and I am immersing them vertically into the liquid
Then what can u say about the height of the water column inside the tubes(small, medium, large)
Would it be same???
No, it would be higher in the smaller tubes.
@@MichelvanBiezen but my book says height of the liquid column is independent of the cross sectional area,
N it also says avoiding capillary action so I guess it's due to the vacuum that is there in the tube is holding the water column
I gave u my clue but still can't imagine the scenario where all will have same water level ( I want some mathematics in here)
You have to go to a different principle here. What you are referring to is not capillary action. Is it this concept instead? Physics - Fluid Statics (6 of 10) The Barometer
@@MichelvanBiezen yup
sir how capilary action beyond the pascal law
sir there are two vertical surface of tube one in which u showed surface tension force and other u didn't showed the resolving both force will balance downward weight so it will be 2*pi*diameter*surface tension cos(contact angle) = density* g*area*h ??? plzz explain to me sir...
The surface tension (N/m) is resolved in to vertical and horizontal components.
The horizontal forces cancel out each other being equal and opposite along the entire circumference.
whereas the vertical force which is resolved is not acting on onside of the fluid in fact it is acting along the circumference, hence it is only one component. For finding out net upward force we are multiplying with its circumference .
why surface tension is upwards ? isnt cause by the intermolecular forces so it should pointed downwards ? thanks in advandance
In the case of capillary action, with glass and water, the forces are upward. (With mercury and glass the forces are downward).
what is the height in case of pressure difference on the both sides of meniscus?
The meniscus has very little volume of fluid and is thus typically ignored
sir I didn't get why the direction of surface tension is such..
+do or die
It depends on the forces between the molecules in the fluid and the molecules in the tube. They either attract or repel.
+Michel van Biezen i got it so we are considering repulsive force acring on periphery of the maniscus
Why is force between liquid and air negative?
The molecules are more attracted to the glass surface. (opposite direction from the "air")
I don't think this is right.
If whether a liquid is more attracted to a solid than to the liquid itself determines the direction of capillary action, you would compare γ(solid-liquid) and γ(liquid). But in fact, what determines the direction of capillary action is the shape of meniscus (convex/concave) or the boundary condition of the contact angle (θ> pi/2 or θ< pi/2 ). This is solely determined by the comparison between γ(solid-liquid) and γ(solid) (refer to Young's equation). In other words, this is a tag of war between the liquid/solid interface and air/solid interface. When the air/solid interface has higher interface tension than that of the liquid/solid one, the liquid rises in the tube spontaneously. In this way, you can explain why a plastic sponge soaks water even though they are very unfriendly each other!
Shouldn't you multiply the nominator by cos of theta? The cos of theta between the water, glass and air is not zero.
The angle between glass and water is typically very close to zero degrees, and therefore cos(theta) ~ 1
What would be an application of this theory?
oil recovery
In agriculture, you need to lower the surface tension of the water used to apply, say, foliage fertilizers, because if you don't, water (with its dissolved fertilizers) won't reach all the crevices and other hard-to-reach parts of the plant. For this, you buy surfactants, additives that lower the surface tension of the water. But, how much surfactant do you need to obtain the desired effect? Am I being sold too much surfactant? Do I even need to buy a surfactant in order to reduce the surface tension of the water that I'm using? Surface tension is very important in some fields my friend :)
You did not explain the equations listed.
Did you watch the videos in the playlist from the beginning? Concepts are systematically explained in order.
way the water climbs only the inner surface of glass tube..what about the adhesion between the outer surface and water molecules
The water will climb up on the outer surface as well forming a "meniscus", but not as high as on the inside.
thank you for your time,but what is the reason beyond the water level differences between the inner and outer surface of a the tube
All good questions. On the inside the attractive forces pull on a very small column of water (because of the small radius) and thus pull the column up a to a large height. On the outside, there is much more liquid thus the water will not rise nearly as much. Remember, pressure is F/A. Thus a large area requires much more force.
That was very useful,thank you very much.
This is so simple compared to how the 200 dollar ragone thermo textbook explains this.
I don't get why surface tension is parallel to the interface here, but in video 1 it was perpendicular.
In this case the tube cuts through the surface of the water and the water molecules inside the tube instead are attracted to the glass molecules and are pulled up the tube.
all you added to me was just more confusion ... because of the first law with the three forces ... which you put on the board but didnt explain its principle or even tried to explain the force between the air and the surface , What i am trying to say is that you cant address some principle without fully explain it and just ignore it ... i dont someone who sloves mathmatical equations ... i need someone who can explain the theoritical parts of the science
Yes indeed, we didn't explain the exact reason for WHY there is capillary action. These videos are designed to help students with the homework problems in the chapter. 🙂
@@MichelvanBiezen
and thats nice .. dont get me wrong ... but the proplems solutions can sometimes be found easily .. but the case is different for finding a channel that explains theoretical parts of particular proplems or branch of science
I hope you could do a playlist that discuss theoretical parts
Thx .. and Good Luck
We have in the design stages a playlist that describes the conceptual understanding of natural phenomenon and "why" things are the way they are.