At atmospheric pressure, water in an evacuated tube travels 10.3 meters. Let's say I don't have 10.3 meters worth of water but I only have enough for 1 meter, like in the image. enter image description here

The atmosphere still pushes the fluid up the tube (hence any height at all) but we have less weight pushing the fluid down, so it should continue up the tube to 10.3 meters, But we all have experienced that the fluid establishes a fixed position, and based on personal experience I know it is less than 10.3 meters. How does this situation not violate some equilibrium condition?

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    $\begingroup$ "we all have experienced..." no we have not. If the water rises less than 10.3 m, then there must be air trapped in the tube above the water, that is, it does not have vacuum above the water. $\endgroup$ – mwengler Mar 2 '15 at 22:36

Typically, some vapor will form in the space above the liquid. The vapor pressure will be a function of temperature, and it will result in an equilibrium where there is some (small) space above the incomplete liquid column. As more liquid evaporates, the space above will fill more. It is also possible (depending on the surface tension and diameter of the tube) that air bubbles will leak past the column of water, in which case you will have a finite amount of atmospheric gas in the space above the water - again resulting in the water column not rising all the way to the top.


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