# Center of mass and distance ratio

1. Apr 20, 2007

### kthouz

how to show that the ratio of the distance between two particles from their centers of mass is the inverse of their masses? I tried but i found a way which can be possible if only we assume that they are constituted by a same number of small particles.

2. Apr 20, 2007

### lpfr

$$x_{cm}={m_1\ell_1+ m_2\ell_2 \over m_1+m_2}$$