 The physical intuition behind the Newtonian concept of inertial mass is basic if we can avail ourselves of the notion of a Newtonian force. Given two bodies \(B_1\) and \(B_2\) in suitably idealized conditions, if it takes twice the force for \(B_2\) to attain the same final velocity as \(B_1\), \(B_2\) has twice the mass of \(B_1\), i.e., \(B_2\) has twice the inertia of \(B_1\). In Newtonian physics, the inertial mass of an object, and even its gravitational mass, can only change by either physically removing a part of the object or attaching a part to the object to make a bigger whole. 