Why does ice float?

You ask: Why ice float?

Caveman drop ice in water cup — ice sit on top, not sink. Most things get heavier-packed when hard: melt rock sink in melt rock. But water weird. When water cold and freeze, the tiny water bits grab hands and lock into open, roomy pattern — like tribe holding arms wide in circle, more gap between them than when they mill loose. So same water take more room as ice than as liquid. More room, same weight, means ice lighter for its size — lighter stuff float on heavier stuff. Ice take up near one-tenth more room than water, so on a lake only the top tenth peek up while nine parts hide below. That gap-pattern come from the bent shape of each water bit. Lucky too: ice float on top of lake, cap it, keep fish warm below through cold season. Cave wisdom: ice float because freezing spread water bits apart, so ice puff up lighter than water.