Center of Mass is the point in a system which behaves as though the entire mass of system is concentrated there and its motion is same if the resultant of all forces acting on the system were applied directly to it.

Mathematically:

Where is total mass

 

You can read more about it at http://www.goiit.com/chapters/tutorial/physics/center_mass.htm

 

Will request soem expert to throw seom light too.. cheers

 

~forum administrator