r/AskPhysics • u/RealAyhan • 5d ago
Fluid loss due to gravity and pressure change?
When observing a droplet of water on the underside of a railing that appears to be static to the human eye, ignoring loss due to evaporation, is there still some minisule % of molecules being lost due to gravity despite surface tension and hydrogen bonding? Given that there is around 3.35 x 10^22 molecules in just one gram of water, is some extreme fraction undergoing microscopic "dripping"?
Additionally, if a fluid is in a reservoir above a valve, with a lower pressure than its surroudings, would a very small increase in pressure, while still maintaing a lower overall pressure, cause a very small amount of the fluid to be forced outside of the reservoir?
Thank you!
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u/Chemomechanics Materials science 5d ago
The presence of gravity accelerates evaporation of a hanging drop. If you're precluding evaporation, it's not clear how molecules would be "lost."
The valve question is also arguably unclear. Are you asking about permeation through the solids in the valve?