Why do boats float but coins sink?
Show answer & explanation
Answer: Shape determines buoyancy
Water pushes boats up more — Wrong. Water does push up (buoyancy), but the amount depends on volume displaced—shape matters more than object mass.
Shape determines buoyancy ✓ — Correct! Archimedes' Principle: buoyant force equals weight of displaced water. Boat's hull shape displaces large water volume (heavy), creating upward force exceeding boat's weight—floats! Coin is dense—small volume displaces little water, insufficient buoyancy—sinks. Steel ships float because hull spreads mass over huge volume. Crush aluminum can—it sinks (same mass, less displaced water). Shape, not just density!
Coins are too small to float — Wrong. Size doesn't determine floating—leaves float, boulders sink. Buoyancy depends on displaced water volume versus object weight (shape matters).