Two masses rotating around each other can be simplied using the rigid rotator notation. This is making a onebody problem from a twobody problem using the reduced mass, M = $132;- Explain Vvhy for a hydrogen atom, the reduced mass is approximated by the mass of the electron, ,u 2 me. m1931+m2932 Where is the center of mass for the system? Recall: XCOM = m1+m2