# Formula Reduced mass of a two-body system

## Reduced mass

Unit
Effective mass is used to reduce a two-body problem (e.g., the motion of the Earth around the Sun about the common center of mass) to a one-body problem.

If $$m_1 ~\gg~ m_2$$ holds, then the formula for the reduced mass can be approximated by the mass of the lighter body: $$\mu ~\approx~ m_2$$.

## Mass

Unit
This can be for example the mass of the earth moving around a center of mass C.M. of the earth and sun.

## Mass

Unit
This can be, for example, the mass of the Sun rotating around a center of mass of the Earth-Sun system.