How this calculator works
Reduced mass replaces the relative motion of two interacting bodies with an equivalent one-body problem. It is smaller than either positive component mass and approaches the lighter mass when the other is much heavier. The calculation uses a rearranged ratio to avoid multiplying very large masses unnecessarily. Both masses must describe the same physical unit system.
Formula
1/mu = 1/m1 + 1/m2; mu = m1 m2/(m1 + m2); m2 = mu m1/(m1 - mu).
Worked example
Masses of 3 kg and 6 kg have reduced mass 2 kg. If the first mass is 4 kg and reduced mass is 3 kg, the second mass is 12 kg.
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Frequently asked questions
What if the masses are equal?
For two equal masses m, reduced mass is m/2.
Is reduced mass the total mass?
No. Total mass describes centre-of-mass translation; reduced mass describes relative separation motion.
Can I infer a component when reduced mass equals the other mass?
No finite positive component produces equality. Equality occurs only as a limiting approximation with an infinitely heavy partner.