Buoyant force is the upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. It is directly proportional to the density of the fluid and the volume of the object displaced by the fluid.

Mathematically, the buoyant force (Fb) acting on an object can be calculated using the following formula:

Fb = ρf * Vd * g

where:

ρf is the density of the fluid in kilograms per cubic meter (kg/m³).

Vd is the volume of the fluid displaced by the object in cubic meters (m³).

g is the acceleration due to gravity (approximately 9.8 m/s² on Earth).

In simpler terms, the buoyant force is equal to the weight of the fluid displaced by the object. This principle is known as Archimedes' principle and explains why objects float or sink in fluids. If the buoyant force is greater than the weight of the object, it will float, and if it is less, it will sink.