Added mass fluid quasi-momentum. Unsteady forces due to a change of the relative velocity of a body submerged in a fluid can be divided into two parts: the virtual mass effect and the Basset force. The origin of the force is that the fluid will gain kinetic energy at the expense of the work done by an accelerating submerged body. It can be shown that the virtual mass force, for a spherical particle submerged in an inviscid, incompressible fluid is where bold symbols denote vectors, formula_2 is the fluid flow velocity, formula_3 is the spherical particle velocity, formula_4 is the mass density
Mode of a linear field usually the energy of the solution "assuming that there is no other field in S". From the norm are defined the orthogonality and the scalar product of solutions. The orthogonality of solutions extends to the corresponding modes. Mode of a linear field In physics, a vector field is linear if it is a solution of a set of linear equations "E". For instance, in physics, the electromagnetic field in vacuum, defined in the usual (3 + 1)-dimensional space "S", obeys Maxwell's equations. A linear combination of electromagnetic fields, with constant, real coefficients, is a new field which obeys Maxwell's equations.