Say we have 2 bodies of m1 , m2 . The distance between them is a) r1 Ma=m1+m2 b) r2>r1 Mb=m1 +m2 In each case the mass was measured by an inertial observer . Is it true that Ma<Mb I saw this kind of thinking in measuring the energy neccesar to separate a nucleon from a nucelous . It said that a nucleus mass is less than the mass of the component nucleons added . I only read special relativity . Is this a general relativity case ?