Suppose there is a slanted capillary tube and a fluid rises in it. Why does the fluid rise to the same vertical height as when the tube is perfectly vertical?
If I'm right surface tension force balances the weight of the lifted fluid. But in the case of a slanted tube, more fluid will be lifted and thus weight also increases. So why will fluid rise to same height?
Best Answer
The stretching of the air-liquid meniscus matches the pressure exerted by the liquid, not the mass of liquid in the tube.
In a closed tube of water the pressure at the top of the tube is $P = P_0 - \rho g h$ where $h$ is the vertical distance (P_0 is atmospheric pressure), so in the diagram above $P_1 = P_2$. So if we replace the closed end of the tubes by the air-water meniscus the curvature of the meniscus will be the same. It doesn't matter that there is a greater weight of water in the slanted tube. That's why the vertical height of the capillary rise is the same.