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Buoyancy

An object in a fluid feels an upward buoyant force equal to the weight of the fluid it displaces, regardless of the object's own density. If the object's density is lower than the fluid's, it floats; if higher, it sinks.

F_B = \rho_{fluid}Vg

buoyant force, V is the submerged volume

Symbols

$F_B$	buoyant force	N
$\rho_{fluid}$	density of the fluid	kg/m³
$V$	submerged volume	m³

Example

A rock with $V = 0.002$ m³ is fully submerged in water ( $\rho = 1000$ kg/m³). The buoyant force is $F_B = 1000\cdot 0.002\cdot 9.81 \approx 19.6$ N.

Always use the density of the fluid, not of the object, in the buoyancy formula.

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Part of Foundations of Physics: Pressure, density and heat.