Anything he hits... including air molecules [http://what-if.xkcd.com/1/].sharp_as_a_cork said:Excellent article, Russ.
and considering Newton's second (?) law of motion, anything he hits that fast will probably splat him (see bird meets plane).Girlysprite said:what is super speed good for?
Considering the strength of impact scales along with speed, it gets you pretty far