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reduced mass
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Italian-born physicist Dr. Enrico Fermi draws a diagram at a blackboard with mathematical equations. circa 1950.
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reduced mass

physics
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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.

This article was most recently revised and updated by William L. Hosch.