The upward force that a → fluid exerts on an immersed body which is less dense than the fluid. It is equal to the → weight of the fluid displaced. Thus a body weighs less when weighed in water, the apparent loss in weight being equal to the weight of the water displaced. Buoyancy allows a boat to float on water and provides lift for balloons. See also → buoyant force; → Archimedes' principle.
From buoy, → buoyant + -ancy a suffix used to form nouns denoting state or quality, from L. -antia, from -ant + -ia.
Bâlârâni literally "pushing up," from bâlâ "up, above, high, elevated, height" (variants boland "high, tall, elevated, sublime," borz "height, magnitude" (it occurs also in the name of the mountain chain Alborz), Laki dialect berg "hill, mountain;" Mid.Pers. buland "high;" O.Pers. baršan- "height;" Av. barəz- "high, mount," barezan- "height;" cf. Skt. bhrant- "high;" L. fortis "strong" (Fr. and E. force); O.E. burg, burh "castle, fortified place," from P.Gmc. *burgs "fortress;" Ger. Burg "castle," Goth. baurgs "city," E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- "high") + râni verbal noun of rândan "to push, drive, cause to go," causative of raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").
Fr.: fréquence de flottabilité
Same as the → Brunt-Vaisala frequency.
Fr.: flottabilité magnétique
The phenomenon whereby the presence of a → magnetic field can make a portion of → compressible fluid less dense than its surroundings, so that it floats upward under the influence of gravity. This magnetic buoyancy is thought, in fact, to be the mechanism by which magnetic flux tubes rise through the Sun's → convection zone and break at the surface in the form of → sunspots. The Sun's rotation would have a major effect on the rate at which these magnetic flux tubes rise. The rotation substantially lengthen the time taken for the flux tubes to reach the surface (D. J. Acheson, 1979, Nature 277, 41).