What causes liquid to rise in a capillary tube?

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Liquid rises in a capillary tube primarily due to surface tension, which allows the liquid to climb against gravity. Air pressure may play a role, but it is not the main factor unless the tube is closed. The contact angle between the liquid and the solid surface determines whether the liquid will rise or fall; a contact angle greater than 90° indicates a hydrophobic surface, causing the liquid to descend. Understanding these principles is crucial for applications like damp-proofing, where hydrophobic treatments are used to manage liquid movement in materials. Capillary action is a fundamental concept in fluid dynamics and has various practical implications.
AudioFlux
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This question struck me when i was watching a liquid rise in a capillary tube. I'm curious to know from where the energy gets transferred to the liquid to rise above the surface. Well, one possible explanation that i can think of is air pressure. Though, it can be a possible reason only if the other end is closed (i don't remember if it was open or closed). So am i on the right track?
 
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Hi AudioFlux! :smile:
AudioFlux said:
I'm curious to know from where the energy gets transferred to the liquid to rise above the surface. Well, one possible explanation that i can think of is air pressure.

No, it's surface tension, see …

http://en.wikipedia.org/wiki/Capillary_action#Height_of_a_meniscus
http://en.wikipedia.org/wiki/Wetting
http://en.wikipedia.org/wiki/Contact_angle :wink:

(if the contact angle is greater than 90°, the solid surface is hydrophobic, and the liquid will fall …

this is how those damp-proofing injections work, they line the capillaries in the bricks with a hydrophobic lining)
 
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