# I Capillary and liquid tension problem

1. Aug 13, 2017

### 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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2. Aug 13, 2017

### haw

3. Aug 14, 2017

### greyy

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: Aug 14, 2017
4. Aug 14, 2017

### haw

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