Is the pressure at points P1 and P2 the same in surface tension controversy?

  • Thread starter i_island0
  • Start date
  • Tags
    Surface
In summary, the conversation discusses the relationship between capillary rise and the shape of the meniscus. The speaker mentions two points, P1 and P2, where the pressure is indicated and two other points, 1' and 2', where the pressure is atmospheric. They question whether P1 and P2 are the same or different, and if different, how can the meniscus be hemispherical. The conversation also touches on the role of surface tension and proposes using a different equation to calculate pressure. However, the speaker is still unsure and seeks clarification from others.
  • #1
i_island0
123
0
We know about capillary rise. And we say that meniscus is hemispherical in shape.
Now please see this picture.
http://www.flickr.com/photos/63184961@N00/3030969897/

There i am mentioning two points where the pressure is indicated as P1 and P2.
I am also mentioning two other points 1' and 2'. the pressure there is atmospheric (Po).
Are these pressure P1 and P2 same or different.
If same, then pressure P1' and p2' will be different owing to different heights h1 and h2. But we know that P1' = Po and P2' = Po.
If different, then how can the shape of meniscus be hemispherical. It must be flat then.
Where am i going wrong??
 
Physics news on Phys.org
  • #2
i_island0 said:
Are these pressure P1 and P2 same or different.
If same, then pressure P1' and p2' will be different owing to different heights h1 and h2.

The flaw in your reasoning lies here. I suspect you are calculating P1' and P2' by using an equation that neglects surface tension? If so, you're ignoring the effect that you want to study.
 
  • #3
Mapes said:
The flaw in your reasoning lies here. I suspect you are calculating P1' and P2' by using an equation that neglects surface tension? If so, you're ignoring the effect that you want to study.

Surface tension is a surface phenomenon. So when i am inside the liquid, surface tension has no role to play.
I am using P = Po + dgh (d: density of liquid) to find the pressure. So where is the flaw?
 
  • #4
i_island0 said:
So when i am inside the liquid, surface tension has no role to play.

Sure it does. Any portion of the liquid will move to reduce the total energy of the system; this is the meaning of equilibrium. Surface energy affects the entire system.

Your equation for pressure only includes potential energy changes related to gravity, not surface tension, so it predicts a flow from 2' to 1' because of a pressure difference. It neglects the fact that this flow would rearrange the surface profile to be flatter, which would result in a net energy penalty.
 
  • #5
Mapes said:
Your equation for pressure only includes potential energy changes related to gravity, not surface tension, so it predicts a flow from 2' to 1' because of a pressure difference. It neglects the fact that this flow would rearrange the surface profile to be flatter, which would result in a net energy penalty.

So can you please tell me what should be the correct equation then. As i m really confused about all this.
 
  • #6
Analytically, the meniscus shape looks like a problem for variation calculus: find the curve that minimizes total system energy. There may be some literature out there on this problem, but I don't know. You could also solve it numerically through simulation. Hopefully someone with more fluids experience can weigh in.
 
  • #7
thx.. i wish some one can reply on this. AS far as i understand, the curvature of meniscus should not be hemispherical.
 

1. What is surface tension?

Surface tension is a physical property of liquids that causes the surface of the liquid to behave like a thin elastic skin. It is caused by the cohesive forces between the liquid molecules, which pull the molecules at the surface inward, creating a net force that minimizes the surface area of the liquid.

2. Is surface tension controversial?

Yes, there is still ongoing debate and controversy surrounding the exact mechanisms and theories behind surface tension. Some aspects of surface tension, such as its relationship with temperature and pressure, are well-established and widely accepted. However, there are still disagreements and differing theories about other aspects, such as the role of intermolecular forces and the exact behavior of the molecules at the surface.

3. What are some applications of surface tension?

Surface tension has many practical applications in our daily lives, such as its role in capillary action (the movement of liquids through narrow spaces), the formation of bubbles and foams, and the ability of insects to walk on water. It also has important industrial and scientific uses, such as in the production of emulsions, the measurement of surface tension in materials, and the creation of self-assembling structures.

4. How do scientists study surface tension?

There are various experimental techniques used to study surface tension, such as the drop weight method, the capillary rise method, and the Wilhelmy plate method. These methods involve measuring the forces acting on a liquid surface and using mathematical equations to calculate the surface tension. Computer simulations and theoretical models are also commonly used to study surface tension and its behavior at the molecular level.

5. Can surface tension be altered or controlled?

Yes, surface tension can be altered or controlled by changing factors such as temperature, pressure, and the presence of surfactants (substances that lower the surface tension of a liquid). This is why surface tension plays a crucial role in many industrial and technological processes, such as the production of detergents and the operation of inkjet printers.

Similar threads

Bernoulli's Equation Applied to Two Free Surfaces
    • Mechanics
Replies
34
Views
6K
B Confusion when considering pV=nRT in Two Balloon experiment
    • Classical Physics
Replies
7
Views
819
I Irreversible adiabatic processes & entropy change (clarification needed)
    • Thermodynamics
Replies
22
Views
2K
Pressure Calculations at Points A and B using Pascal's Paradox
    • Engineering and Comp Sci Homework Help
Replies
2
Views
2K
Problem regarding a Normal Shock Wave and Blunt Nosed Object
    • Engineering and Comp Sci Homework Help
Replies
1
Views
2K
Pressure variation across streamlines in a free jet
    • Mechanics
Replies
25
Views
6K
Measuring Height of Meniscus in Capillary Action
    • Introductory Physics Homework Help
Replies
1
Views
3K
Why are liquid surfaces at constant pressure?
    • Mechanics
Replies
2
Views
1K
Question about Fluid Mechanics, pumping
    • Engineering and Comp Sci Homework Help
Replies
6
Views
2K
Calculating Pressure Difference in an Equilibrium Hydrostatics System
    • Introductory Physics Homework Help
Replies
2
Views
1K

Hot Threads

Recent Insights

Back
Top