Friday, August 18, 2017

forces - How does the 'water jet pack' work?


So I was cruising around at YouTube and saw this sweet video, and as I was watching started to wonder: "How is this possible?".


For a little bit of background, in case you decide to not watch the video, what is happening is an individual can hook out a 'pack' that sucks up water and then shoots the water downward:


enter image description here


This water Jet Levitation (JetLev) causes the rider to be able to fly upward into the air and move about forward, backward, side-to-side and even underwater (you have to watch the video for that). So my question is: How exactly is this possible?




Answer



Well I ought to be studying for a physics exam, but I'll consider answering this to be my studying.


Newton's third law states that for every action, there is an equal an opposite reaction. In this case, the jetpack is ejecting water at high velocity toward the ground. This is generating a significant force downward. The resulting opposite force pushes upward, elevating the rider.


The actual pump for the unit is located on a floating watercraft attached to but not elevated with the jetpack. This is how there is enough force for the unit to fly - otherwise, the mass of the pump would be so great that it would be difficult to maintain enough pressure to keep both the pump and rider aloft.


I don't know the specifics of how it orients itself, though I imagine that by making small variations in the water pressure and orientation of each nozzle, one can cause an imbalance in the forces acting on the rider, casing them to move one way or the other.


force diagram


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