We've already used the idea of center of mass in rotating systems. 

How do we find the center of mass for an object or system?
 
 

Consider a system consisting of two particles, one with three times the mass of the other.  If the distance between the particles is 1.0 m, the system's center of mass is what distance from the lighter object?

A. = 1.0m (uh... there's no HTML character for approximately equal to...)
B. 0.75m
C. 0.66m
D. 0.33m
E. 0.25m
F. other