When Friction Isn’t Enough

If you try to build a pyramid of dry glass beads, you’ll have a hard time of it. The frictional forces simply aren’t enough to hold the beads together against the force of gravity. If you add a little water, though, the story is different. The intermolecular forces inside water give it a lot of cohesion, which helps it fill the narrow gaps between beads. That added capillary force gives just enough additional sticking power to hold a pyramid of beads together. (Image and video credit: amàco et al.)

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