Buoyant Force

Buoyant force F = ρgV, submerged volume, fluid density, and whether an object floats or sinks.

What to find:

g = 9.8 N/kg (problems often use 10 N/kg). Water 1000 kg/m³, seawater 1030 kg/m³, kerosene 800 kg/m³, ice 900 kg/m³.

The buoyant force calculator finds the buoyant force, the submerged volume and the fluid density, and tells whether an object sinks or floats and what part of it stays under water.

Archimedes' principle

A body immersed in a liquid or gas is pushed up by a force equal to the weight of the displaced fluid:

F_b = ρ_f · g · V_sub

Example. A 2 dm³ block fully under water: F_b = 1000 · 9.8 · 0.002 = 19.6 N.

When objects float

Densities	What happens
ρ_o > ρ_f	the object sinks
ρ_o = ρ_f	neutral buoyancy
ρ_o < ρ_f	the object floats on the surface

A floating object is submerged by the fraction ρ_o / ρ_f of its volume. Ice (900 kg/m³) in seawater (1030 kg/m³) is about 87% submerged — only the tip of the iceberg shows.