If you haven't seen the video of the FlyBoard, please have a look: http://www.youtube.com/watch?v=Cd6C1vIyQ3w&feature=youtube_gdata_player
Yes, it's amazing, but do the physics make sense or is this another "doctored" video?
Specifically, I'm wondering how Newton's 3rd law comes into play here. I'm not an expert in jetskis or physics, but I understand that a jetski sucks in water (not sure from which direction) and expels it out of a rear exhaust. Surely that should create an opposite force on the jetski itself and pushes it forward (regardless of the host that is now attached)? However, in the videos, the jetskis are relatively stationary.
Also, as we know from our garden hoses, when it's full of pressure, it tends to want to "straighten", but these hoses seem to be totally content at being full of pressure but constantly "curved".
Lastly, I think you'll need unparalleled balance to actually bring this off, almost like trying to balance a marble on top of a balloon. But I could be wrong on this.
Your inputs please?