The role of surface tension in capillarity

AI Thread Summary
Surface tension plays a crucial role in capillarity by exerting an upward force on water in a tube until it balances with gravity. This upward force is attributed to both surface tension and adhesive forces between the water and the container material. The meniscus behavior varies depending on the liquid; for water in glass, it rises due to adhesion, while for mercury, it descends. The discussion highlights a debate over whether surface tension or adhesive forces are more responsible for the observed capillary action. Ultimately, both perspectives contribute to understanding the mechanics of fluid movement in narrow spaces.
Shackleford
Messages
1,649
Reaction score
2
From what I've read, the surface tension pulls upward on the given volume of water and when this surface tension force equals the force of gravity (weight), there is no more vertical movement up the tube.

Why is it said that the surface tension pulls upward on the mass of water when surface tension refers to the increased horizontal intermolecular attraction of the top surface layer? Why do you not say that the upward force on the volume of water is the adhesive forces from the container material?
 
Physics news on Phys.org
Hi Shackleford! :smile:

I think both views are correct …

a) Surface tension is a force parallel to the liquid surface and pointing towards the solid surface.

So when the meniscus goes up (as with water in a glass tube), the force is up, but when it goes down (as with mercury in a glass tube), the force is down.

In other words …
Shackleford said:
… the surface tension pulls upward on the given volume of water and when this surface tension force equals the force of gravity (weight), there is no more vertical movement up the tube.
b) But the reason why the meniscus is up for water on glass is that water adheres to glass

and so …
Shackleford said:
the upward force on the volume of water is the adhesive forces from the container material.

(And see also http://en.wikipedia.org/wiki/Surface_tension#Liquid_in_a_vertical_tube" for a third argument about minimising the surface area of the water. :wink:)
 
Last edited by a moderator:
Shackleford said:
From what I've read, the surface tension pulls upward on the given volume of water and when this surface tension force equals the force of gravity (weight), there is no more vertical movement up the tube.

Why is it said that the surface tension pulls upward on the mass of water when surface tension refers to the increased horizontal intermolecular attraction of the top surface layer? Why do you not say that the upward force on the volume of water is the adhesive forces from the container material?

I understand the molecular interpretation of surface tension is commonly taught that way, but I'm not convinced it provides any real insight. It's much simpler to see the result in terms of continnum mechanics:

http://www.agron.iastate.edu/soilphysics/a577cap.html
 
Last edited by a moderator:

Thread '1:1 versus 2:1 Mechanical Advantage debate'

The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
View full post »

Thread 'Newton's first law?'

Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
View full post »
Thread 'Beam on an inclined plane'

Thread 'Beam on an inclined plane'

Hello! I have a question regarding a beam on an inclined plane. I was considering a beam resting on two supports attached to an inclined plane. I was almost sure that the lower support must be more loaded. My imagination about this problem is shown in the picture below. Here is how I wrote the condition of equilibrium forces: $$ \begin{cases} F_{g\parallel}=F_{t1}+F_{t2}, \\ F_{g\perp}=F_{r1}+F_{r2} \end{cases}. $$ On the other hand...
View full post »

Similar threads

Surface Tension and Capillary Rise
Replies
1
Views
1K
Surface Tension - Using hot soapy water to wash clothes
Replies
1
Views
2K
How Does Increased Surface Tension Affect Liquid Surface Area and Volume?
Replies
2
Views
2K
Surface Tension and force required to pull a thin ring
Replies
4
Views
4K
Confusion regarding surface tension direction and force balance
Replies
39
Views
2K
Surface Tension: Plate-Water Interface
Replies
4
Views
2K
Impacted on a Surface wave of a tension-ed Anchor cable
Replies
9
Views
2K
Why is low surface energy important for water droplets on hydrophobic surfaces?
Replies
3
Views
2K
I How Does Surface Tension Balance Small Objects on Water Surface?
Replies
5
Views
1K
What Drives Surface Tension in Liquids?
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top