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 system may be on a macroscopic scale, such as that of the Earth-Moon, or on a microscopic scale, as for example a diatomic gas molecule. Each of the two bodies in the system has its own unique centre of mass (see gravity, centre of), but mutual gravitational attraction between them creates a balanced inertial system with a third centre of mass located somewhere between the two centres of mass of the orbiting bodies. This common centre of mass is the reduced mass and it is measured as a hypothetical value. Always smaller than the value of the less massive body, the reduced mass is equal to the product of the two masses divided by their sum.