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I have seen a bucket full of water, and sand in it so that the sand just creates a pile just above the water level, and the sand that is above the water level is first dry.

As time passes, the water starts to soak the pile of sand, and water climbs up higher then the water level in the bucket.

I thought that water cannot come higher then the overall water level in the bucket, and I thought that water cannot climb up in sand, and I do not understand how water can climb against gravity.

Question:

  1. How can water climb up in the sand against gravity, and soak up the sandpile above the water level?

enter image description here

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  • $\begingroup$ I don't think the Quanum Mechanics tag is needed here. $\endgroup$ – Aaron Stevens Oct 1 '18 at 3:42
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This effect is an artifact of surface tension, which generally allows water to stick to other objects.

Water is a polar molecule. And polar molecules have tendencies to mix and "stick" to other polar substances. This is generally why water will stick to most things. This "sticking" stems from inter-molecular electromagnetic forces resulting from the specific configuration of atoms in the water molecules. Since the water "sticks" to adjacent pieces of sand, it naturally gets pulled through the small crevasses within the sand. This general process is called capillary action and is also the mechanism behind how plants deliver water from its root into the rest of the plant.

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  • $\begingroup$ +1 To add, sand behaves like a porous medium. $\endgroup$ – Deep Oct 1 '18 at 4:58

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