Reduced mass
In physics, the reduced mass is the "effective" inertial mass appearing in the two-body problem of Newtonian mechanics. It is a quantity which allows the two-body problem to be solved as if it were a one-body problem. Note, however, that the mass determining the gravitational force is not reduced. In the computation one mass can be replaced by the reduced mass, if this is compensated by replacing the other mass by the sum of both masses. The reduced mass is frequently denoted by (Greek lower case mu), although the standard gravitational parameter is also denoted by (and so are a number of other physical quantities as well). It has the dimensions of mass, and SI unit kg.
Equation
Given two bodies, one with mass m1 and the other with mass m2, the equivalent one-body problem, with the position of one body with respect to the other as the unknown, is that of a single body of mass
where the force on this mass is given by the force between the two bodies.
Properties
The reduced mass is always less than or equal to the mass of each body: