Re:A Water-Powered Jetpack
by paulgb on Thursday July 30, 2009 @06:03PM
(#733187)
I'm not a physicist, but this paragraph struck me as incorrect (or at least misleading):
Li, however, figured that if he attached a hose to his pack, and put the engine and water pump in a separate vessel that dragged behind him, he could seriously reduce his weight, and therefore the amount of thrust needed to stay aloft.
If the engine and pump were part of the jet pack, even if the engine and water pump were weightless, wouldn't it be impossible to get enough thrust to provide lift? The propellant is being thrown back in the direction it came, so doesn't the momentum cancel out?
Li, however, figured that if he attached a hose to his pack, and put the engine and water pump in a separate vessel that dragged behind him, he could seriously reduce his weight, and therefore the amount of thrust needed to stay aloft.
If the engine and pump were part of the jet pack, even if the engine and water pump were weightless, wouldn't it be impossible to get enough thrust to provide lift? The propellant is being thrown back in the direction it came, so doesn't the momentum cancel out?