An Etymological Dictionary of Astronomy and Astrophysics
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The "effective" → inertial mass appearing in the → two-body problem of → Newtonian mechanics. The reduced mass is a quantity which allows the two-body problem to be solved as if it were a one-body problem. For the masses m₁ and m₂, it is given by the ratio μ = m₁m₂ / (m₁ + m₂). The value of μ is generally smaller than m₁ and m₂. The larger the difference between the two masses, the closer μ will be to the smaller mass. If the particles are of equal mass, μ is half the mass of either.

→ reduce; → mass.