# Two body problem - effective particle

1. May 12, 2008

### maria clara

as for the center of mass, the position vector is Rcm=$$\frac{m1r1+m2r2}{m1+m2}$$
and Vcm is determined in a similar way (it is simply the time derivative of Rcm).

But what is the radius vector of the effective particle (with the reduced mass)?
is it simply the vectoric sum of the two radius vectors?

thanks

2. May 12, 2008

### maria clara

sorry, I didn't mean the sum, but the difference, r1-r2.