Video narration
How can water rise above a coin's rim without spilling? Water molecules pull toward one another, and at the surface that pull points inward. It tightens the surface, resisting stretch. But it isn't a solid skin; molecules are still moving. It's a moving boundary that stays small and tight, helping droplets become round and letting the coin hold a dome. Add one drop too many, and gravity wins. Surface tension pulls inward, holding the dome together-until gravity spills it.