The center of rotation is the point about which an object rotates. The center of mass is where the mass of an object can be concentrated for calculation purposes.
The center of rotation is the point about which a body rotates. The center of mass is where the mass can be considered concentrated (i. e. a 12" ruler's 6" mark).
Centre of rotation is the point from which a body can rotate freely from that point. Centre of mass is the point where entire mass of the body is located.
