Well, I know a little more now than I did when the thread started.... but I don't understand a whole heckuvalot more than I did.

If the bow shoots a quick arrow and feels pretty soft in the hand, then it's obviously got a low virtual mass. If it shoots a slow arrow and causes a couple of teeth to swap holes from the recoil, then it's got high virtual mass. That about sum it up from a practical, non-engineering standpoint?