## buoyancy

- That property of an object that enables it to float on the surface of a liquid, or ascend through and remain freely suspended in a compressible fluid such as the atmosphere.

Quantitatively, it may be expressed as the ratio of the specific weight of the fluid to the specific weight of the object; or, in another manner, by the weight of the fluid displaced minus the weight of the object.

- (
*Or*buoyant force, buoyancy force;*also called*Archimedean buoyant force.) The upward force exerted upon a parcel of fluid (or an object within the fluid) in a gravitational field by virtue of the density difference between the parcel (or object) and that of the surrounding fluid.

The magnitude of the buoyancy force F per unit mass may be determined by Archimedes's principle aswhere*g*is the acceleration of gravity, ρ the density of the buoyed fluid parcel or object, and ρ_{0}the density of the surrounding fluid. In the atmosphere, a buoyant force on an air parcel may be attributed directly to a local increase of temperature and may be writtenwhere*T*and*T*_{0}are the temperatures of the heated air and that of the environment, respectively. The coefficient (*T*/*T*_{0}- 1) is sometimes called the buoyancy factor. The force*F*is sometimes called the reduced gravity.*See*free convection.