Dipping a tube into a container filled with water will make the water rise in the tube. This phenomenon is called liquid capillarity. It is responsible for many natural and technical processes, for example the water absorption of trees, ink rising in a fountain pen, and sponges absorbing dishwater. But what happens if the tube is dipped into a container filled not with water but with sand? The answer is – nothing. However, if the tube is shaken up and down, the sand will also begin to rise. Scientists have now discovered the mechanism behind this effect, the so-called granular capillary effect.
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