When I put a finger on a straw with water in it, it wouldn't fall out of this straw. But is there maximum size (length and diameter) of this straw/pipe to get this effect and what causes this limit?
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Given a height of the liquid column, the limit is caused by the fact that the weight of the liquid (pulling the liquid down) grows, roughly, as a square of the straw diameter, while the adhesion forces between the liquid and the inner walls of the straw (keeping the liquid from falling down) grow, roughly, linearly with the diameter.
The linear and square relationships are not exact because (among other factors), as the diameter increases, the shape of the surface of the liquid (meniskus) changes as well.
Of course, a specific breaking point depends on the properties of the liquid and the straw.
V.F.
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