1. 
   center of mass
   centre of mass noun point representing the mean position of the matter in a body
   Found op http://wordnetweb.princeton.edu/perl/webwn?s=center%20of%20mass
   
   
2. 
   center of mass
   The point at which a system of masses would balance if placed on a pivot. If m1 and m2 are the masses of two particles placed at the points A1 and A2, and if the line A1A2
   Found op http://www.daviddarling.info/encyclopedia/C/center_of_mass.html
   
   
3. 
   center of mass
   center of mass, the point at which all the mass of a body may be considered to be concentrated in analyzing its motion. The center of mass of a sphere of uniform density coincides with the center of the sphere. The center of mass of a body need not be within the body itself; the center of mass of a ...
   Found op http://www.infoplease.com/ce6/sci/A0811086.html
   
   

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