The mass of an object is a unique number, but has two different conceptual bases.

The gravitational mass is the mass that gives rise to gravitation forces via the equation

\[F=\frac{Gm_1m_2}{r^2}\]

.The inertial mass is the mass a body has because of its resistance to force and acceleration.=br /> All the calculations imply that gravitational and inertial mass have the same value, and this is an assumption of the general theory of relativity. It is important to realise that there is no theoretical basis for the gravitational mass and inertial mass being the same, but so much of theoretical physics depends on it, and there is no evidence to contradict it.