Every schoolboy knows that a principal reason that nobody or no thing can go faster than the speed of light is that we gain mass at relativistic speeds approaching c. However, I have yet to find an explanation as to how that mass gain manifests itself in the accelerating body. Say we have a mass of 1000 gold atoms approaching c. How is this mass gain manifested to slow down its acceleration or to increase its intertia? Does the 1000 atoms all of a sudden build to 1500 atoms (or so)? Does the mass-energy of each atom increase? If so, how? Stronger vibrations between the subatomic particles? Or is it between the particles? More violent modes of oscillation between the gold atoms as we approach c? Or is it something else?