If you break up "mv^2" into its constituent dimensions you get m(d/t)^2 = m(d^2)(t^-2). Now the so-called kinetic energy of the object only "manifests itself" w

If you break up "mv^2" into its constituent dimensions you get m(d/t)^2 = m(d^2)(t^-2). Now the so-called kinetic energy of the object only "manifests itself" whenever there is a change in velocity of the object in question. Well, the derivative of velocity is an acceleration, so the object in acceleration would be represented as mdt^-2, aka "a force". Hence the energy of the system is simply that force acting over some distance d. As to the internal/intrinsic energy of a given object, think of it as "hidden potential energy". It is essentially the energy that was required to turn photons into the matter that you, and I, and everything else are made of! The equation itself is mc^2 simply because that is what you get when you rearrange and simplify the experimentally-verified equations which it was drawn from. Likewise, for c is nothing more than the measured value of the speed of light in vacuum for any observer. Of course the choice of units is completely arbitrary. Whether you state it in miles per hour, kilometers per second, or whatever, the ratio remains constant.