Why Does Water Rise Differently in a Capillary Tube Compared to a Wider Pipe?

[Creativity]

Hello,
recently i was thinking of a capillair and what would be the pressure on the top of the liquid in the capillair.I was predicting something like this to happen:
-capillair will rise water to the height x above the water surface in the glass of water
-if i will apply some underpressure(under atmospheric) at the top of the capillair, then the water will rise additional height y above the x(so total water level in capillair x+y above the surface in glass of water).
-if the same underpressure would be applied to noncapillair tube, it would also rise water to height y.

My thought was that water inside of the capillair is in stational conditions(all forces are adding to zero,so water does not move anymore in any direction).However I got surprised when i made following experiment:
I placed a capillair and parallel to it a much wider pipe to compare the height of risen water.Both pipes were connected with a t-junction.Initially i let the water to rise in the capillair.Water in the wider pipe have not risen.Then i sucked some air out of the pipe system to create underpressure,but water in capillair has not rised any higher than in wider tube!
I got perplexed..if water in the glass is in equilibrum and if water in the capillair too...then why is equally applied underpressure not rising water to the same relative height(relative to the original level be it capillair water surface top or glass of water sufrace).


Any help would be much appreciated :) and no,it is not homework or any assignment :D just a part of my design for a capillair pump.

 

[Valerie Park]

The reason why the water in the capillary did not rise higher is because of the surface tension of the liquid. Surface tension is a property of liquids that causes them to resist an external force. When you applied the underpressure, it caused the liquid in the capillary to be pushed down, but the surface tension of the liquid prevented it from going down any further. This means that the amount of pressure needed to push the liquid further down is greater than the pressure you applied. Therefore, the liquid in the capillary did not rise any higher.

 

[sir-pinski]

First of all, it is important to understand the forces at play in a capillary. The main force responsible for the rise of water in a capillary is surface tension. This is the cohesive force between molecules on the surface of the liquid, which pulls them together and creates a kind of "skin" on the surface of the water. This force is stronger in smaller tubes, which is why water rises higher in a capillary than in a wider pipe.

In your experiment, you are correct in assuming that the water in the capillary and the wider pipe are in equilibrium, meaning that the forces acting on the water are balanced. However, the key difference between the two is the surface area. In a capillary, the surface area is much smaller, so the surface tension force is able to lift the water higher. In the wider pipe, the surface area is larger, so the force is spread out and not as strong.

In addition, when you apply underpressure at the top of the capillary, you are essentially decreasing the atmospheric pressure on the surface of the water. This allows the surface tension force to pull the water up even higher, as there is less resistance from the surrounding air pressure.

In the wider pipe, the underpressure may not have as much of an effect because the surface area is larger and the surface tension force is not as strong. This is why you may not see the same relative height of water rise in the wider pipe as in the capillary.

I hope this explanation helps to clarify the forces at play in a capillary and why the water may not rise to the same relative height in the wider pipe. Good luck with your capillary pump design!