Archimedes' Principle
Definition
The buoyant force on a submerged object equals the weight of the fluid it displaces — why ships float.
Unit: N
Technical definition
F_buoyant = ρ_fluid·V_displaced·g, directed upward. An object floats when its average density is less than the fluid's; it sinks when denser. Legend says Archimedes discovered it in his bathtub, shouting ‘Eureka!’
Example
A 100,000-tonne ship floats because its hull displaces 100,000 tonnes of water — the buoyant force exactly balances its weight.
Common confusion
Buoyancy depends on displaced fluid weight, not the object's weight. A tiny pebble sinks while a huge ship floats — what matters is average density versus the fluid, not size or mass.