So when you put a thumb over a garden hose you reduce the size of the opening and to keep the same flow rate the water goes out faster, right? So why can’t you (or can you) achieve arbitrary speed with that method (something like water jet cutting)? If you move your thumb to let less and less space for water to pass, shouldn’t that increase the speed of the water even more since the flow rate needs to get higher and higher? But that obviously doesn’t happen. So what determines the max speed of water? I assume the water pressure would have to be involved somehow.
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You can’t make energy out of nothing.
When you constrict a nozzle you essentially force the pressure energy in the fluid to be turned into kinetic energy, but you only have so much pressure energy that you can convert, how much depends on your pump, and once you’re out of pressure energy that’s it, if you further constrict the flow you’ll just chocke the pump, i.e. the pump will simply start pumping LESS wate to compensate for the blockage.
And even with an arbitrarily powerful pump, you are still limited to the speed of sound, since a contracting nozzle can neverr accelerate a fluid past it’s speed of sound, you need converging – diverging nozzle for that
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