Buoyancy forces in magnetic fluids

Abstract

The ponderomotive force on a macroscopic body in a magnetic fluid is calculated by a hydrodynamic approach. The resulting equations are generally valid, neither small susceptibilities nor stationarity are assumed. The simple and widely-used formulaV(M-M ^bg)∇H is recoverd in linear order of χ; magnetostrictive effects are shown to contribute in the order χ³. The expressions derived here are definite and unambiguous, they do not depend on whether one starts from a theory in terms ofH, or in terms ofB: the correct evaluation of the contribution ∫dV[-∇p] resolves the apparent contradiction between the force density expressions μ₀ M∇H, orM∇B.