# Capillary and liquid tension problem

• greyy
In summary, The person is seeking help to understand a problem involving a capillary system with a short and thinner tube connected to a larger and taller tube. At equilibrium, the thinner tube is full of liquid while there is a meniscus on the larger tube. When a drop is added to the top of the thinner tube, the system re-equilibrates by flowing to the right, increasing the height in the right tube. The person is unsure why this is happening and is wondering about the relationship between surface tension and capillary forces in this system. They also mention the Young-Laplace equation and questions about the equilibrium state and the direction of flow when a drop is added. They believe that a delta pressure is needed for liquid movement
greyy
Dear all,
I have a problem to solve but i am not very familiar with physics.
See attached image.
Data:
1)I have a capillary system with a short an thinner tube on one end and larger taller tube communicating.
2) at the equilibrium, the thinner capillary is full of liquid, while there is a meniscus on the larger one.
3) when a drop is added on the top of thinner tube, system re-equilibrates flowing on the right, increasing the height in the right tube.

I assume total pressure on the left is higher than the pressure on the right.
But why is all happening?
surface tension on the left vs capillary forces on the right? (in a communicatin vessel system, nomally, the larger tube has lower liquid height, but here the thinner tube has no more walls.)..
Thanks in advance for any help!

Urla

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Dear haw, no. honestly. I've just given a read to the link, I am not getting.
Could you give me an explanation on the graphical example I provided?

Question 1, why at the equilibrium the larger tube has a taller liquid column compared to the thinner capillary (on left of the image)? I understand the thinner capillary is already full .

Question 2, when I perturb the equilibrium by puttin a drop on the top of the thinner capillary the liquid flows to the right. I understand that the drop has no real walls and it is just surface tension.. why is flowing to the right towards the larger capillary?

From my very limited physics knowledge, I remember that in order to have a movement of a liquid I need a delta Pressure. In this case P(@drop) > P(@larger capillary). At the equilibrium P (@thin capillary ) = P(@larger capillary)

Last edited by a moderator:
larger tube has smaller curvature, so capillary pressure is smaller. And add a drop, neglect gravity of this drop, you still add a capillary pressure downward

## 1. What is the capillary and liquid tension problem?

The capillary and liquid tension problem refers to the phenomenon where liquids, such as water, tend to rise up in narrow tubes or capillaries. This is due to the cohesive forces between the liquid molecules and the adhesive forces between the liquid and the tube's surface.

## 2. How is capillary action related to the liquid tension problem?

Capillary action is the result of the liquid tension problem. When a liquid is placed in a narrow tube or capillary, the adhesive forces between the liquid and the tube's surface are stronger than the cohesive forces between the liquid molecules. This causes the liquid to rise up in the tube, against the force of gravity.

## 3. What factors affect the height of liquid rise in a capillary tube?

The height of liquid rise in a capillary tube is affected by several factors, including the diameter of the tube, the surface tension of the liquid, and the angle of contact between the liquid and the tube's surface. Other factors such as temperature, gravity, and the presence of impurities can also play a role.

## 4. What real-life applications use the principles of capillary and liquid tension?

Capillary action and liquid tension are utilized in various everyday applications, such as in paper towels, which use capillary action to absorb water and other liquids. They are also used in wicking fabrics, ink pens, and medical devices such as microfluidic chips. Plants also rely on capillary action to transport water from their roots to their leaves.

## 5. How do scientists study and measure the capillary and liquid tension problem?

Scientists use various methods to study and measure the capillary and liquid tension problem, including capillary rise experiments, contact angle measurements, and mathematical models. These methods allow for a better understanding of the physical forces involved and their effects on different liquids and surfaces.

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