Buoyancy

Buoyancy is the upward force that a fluid exerts on any object immersed in it. In a static fluid, pressure increases with depth, causing a net upward force on the submerged object. This buoyant force equals the weight of the fluid displaced by the object, an idea encapsulated in Archimedes' principle. The magnitude of the buoyant force can be expressed as F_b = ρ_fluid g V_displaced, where ρ_fluid is the fluid density, g is gravitational acceleration, and V_displaced is the submerged volume.

The relationship between the densities of the fluid and the object determines whether the object sinks or floats. If the object's density is less than the fluid's density, it will float with only part of its volume submerged. If the object's density is greater, it will sink. When densities are equal, the object is neutrally buoyant and remains at a constant depth. Submarines and other craft adjust effective density with ballast to achieve desired buoyancy.

Applications of buoyancy are widespread. Ships displace water to support their weight and float; submarines change their buoyancy to dive or surface. In air, hot air and gas balloons rise because the less-dense gas inside provides buoyancy. Buoyancy concepts are also used in measuring fluid density, in oceanography with floats and drifters, and in various engineering designs where steady vertical position is important.

Limitations and factors include that buoyancy concerns hydrostatic pressure in static fluids. When objects move through fluids, dynamic effects such as drag and added mass can influence behavior. Temperature, salinity, and compressibility alter fluid density and thus buoyancy, especially in aquatic and atmospheric contexts.