Faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings in a single bound...
If Superman did exist, how would his powers function and what kind of personal power source would he need to run them? National Geographic News does a pretty good job of deconstructing them. I especially like the discussion of "X-ray vision", which in reality could not have anything to do with X-rays. It would have to be sonar or something along those lines.
Enjoy!