PopSci's Adam "Easy Joke" Weiner has worked out the physics of a super crazy Japanese water jetpack. Science is cool and all, but I just like watching this guy get tossed across a lake.
Essentially, this poor bastard left the launching pad at over 320kph due to the pressure of the water built up in the pack. It looks like he's using 25 two-litre bottles that tossed him about 25-30 metres. Unfortunately, he didn't calculate the rate of crap entering his pants during his flight, but maybe that's a job for a physicist with less scruples. [PopSci]