What would happen if I bend a capillary tube and use it as shown in figure?

1.Will the water(or any other adhesive liquid) level remain same as before bending?

2.or it will come up till end?

3.Or will it fall and form perpetual motion?

Third option is impossible because of adhesion, but will the level remain same or come to edge?

enter image description here

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    $\begingroup$ I would think that the capillary effect is independent of the gravity. It can defy gravity. If you bend the tube downwards again, more of the tube will be filled as the gravity helps. The water will probably not drop out on the bottom as the surface tension will keep it there. Perpetual motion is probably forbidden by thermodynamics. $\endgroup$ Apr 30, 2016 at 12:18

1 Answer 1


Even though capillary forces may be the dominant force in this situation, hydrostatic (gravitational body) forces are still there. And that results in the equilibrium seen in the left most figure as you start this experiment. So as you bend the tube over, the head (force due to height of the fluid) is reduced and that would allow the surface tension of the interface to pull the column farther through the tube; perhaps spilling some water.

But after perhaps spilling fluid, the column will pull back. The fluid level after bending will just reach a new equilibrium position due to balance between the meniscus surface tension and the hydrostatic force at the new height. A siphon; continuous fluid motion is not possible in situations where surface tension balances hydrostatic force. The column will again remain static.


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