The point in a system of bodies or an extended body at which the mass of the system may be considered to be concentrated and at which external forces may be considered to be applied.
The point in a body or system of bodies at which the entire mass may be assumed to be concentrated.
A point in space determined by a distribution of mass (such as a solid object, a collection of objects, or a gas), such that a uniform force acting on the whole distribution acts as if the distribution were located at just that point. For example, the gravitational force on Earth attracts small objects as if it were pulling them from their center of mass (in this case, the center of mass is also called the center of gravity ). Two stars in orbit around each other revolve around their collective center of mass.