Inertial mass is a measure of a body's resistance to being accelerated: you have to push harder on a high-mass body than on a low-mass body to get it to accelerate by a given amount. For example, if t...Inertial mass is a measure of a body's resistance to being accelerated: you have to push harder on a high-mass body than on a low-mass body to get it to accelerate by a given amount. For example, if two identical bodies each have a gravitational mass m_{g} and are separated by a distance r, then the gravitational force between them is given by Newton's law of gravity: F=G m_{g}^{2} / r^{2}.