Buoyancy and Archimedes' Principle
An object in a fluid experiences an upward buoyant force equal to the weight of displaced fluid. This explains floating, sinking, and apparent weight loss.
Archimedes' principle
The buoyant force equals ρfluid × Vdisplaced × g. If buoyancy exceeds the object's weight, it floats; otherwise it sinks.
Floating vs sinking
Average density determines fate: objects less dense than the fluid float with part of their volume submerged until displaced fluid matches their weight.
Explore buoyancy interactively
Place objects in a fluid zone, press Play, and read buoyant force and displacement live as density and volume change.
Archimedes' Principle
When an object sits in a fluid, it pushes some fluid out of the way — this is called displacement. The fluid pushes back with an upward force equal to the weight of the fluid that got displaced. If that upward push can equal the object's own weight, it floats; if the object is too heavy for the fluid it displaces, it sinks.
F_b = ρ · V · g
- ρ — fluid density (kg/m³): the fluid's mass per unit volume
- V — displaced volume (m³): the volume of fluid the object pushes out of the way
- g — gravitational acceleration (m/s²): the gravitational acceleration pulling everything down
A block pushes 0.002 cubic meters of water out of the way. Water has a density of 1000 kilograms per cubic meter. What buoyant force does the water push back with?
- ρ = 1000 kg/m³
- V = 0.002 m³
- g = 9.8 m/s²
- F_b = ρ · V · g
- F_b = 1000 kg/m³ · 0.002 m³ · 9.8 m/s²
F_b = 19.6 N