Corrected entry: The premise of the story is that a watch speeds up the molecular structure of the wearer to the point where the rest of the world appears to be at a standstil, a state called 'hypertime'. In that state, the wearer moves through the world so fast that he appears to be invisible to other people. I would estimate that the speed at which someone would have to move to appear 'invisible' would be about the speed of a bullet. I suspect that someone moving through the air at such a speed would experience friction much like a meteor does when entering the earth's atmosphere and thus burn up, or at least they would create massive turbulence such as a supersonic jet creates.
Phixius
10th Apr 2002
Correction: If we can suspend disbelief to allow a watch that speeds a person's molecules up in this manner, it's not too much more of a stretch to assume that the science involved also protects that person from the friction of moving through seemingly stationary air molecules.
Phixius ★