| a quantity obtained when one particle is moving about another, larger particle that is also moving, equivalent to the mass of the smaller particle, were the larger particle not moving, and equal to the quotient of the product of the two masses divided by their sum. |
reduced mass
in physics and astronomy, value of a hypothetical mass introduced to simplify the mathematical description of motion in a vibrating or rotating two-body system. The equations of motion of two mutually interacting bodies can be reduced to a single equation describing the motion of one body in a reference frame centred in the other body. The moving body then behaves as if its mass were the product of the two masses divided by their sum. That quantity is called the reduced mass.
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