3 ms·

To rephrase the question, how much of the lift is generated by high-pressure air below the screwdriver, and how much is generated by low-pressure air above?

• userbinator 11y ago
  Pressure is relative, and it is this pressure difference that causes the lifting force. So what is "high pressure" relative to the top of the screwdriver is "low pressure" relative to the bottom of it (and the atmosphere.)
  • raldi 11y ago
    Relative to 1 atm.
    • userbinator 11y ago
      Then there is no high pressure at the bottom, only low pressure at the top.
      • raldi 11y ago
        The air coming out of the nozzle is high pressure, is it not?
        • userbinator 11y ago
          It depends what type of pressure you mean; the stream of air has a high dynamic pressure, but its static pressure is the same as atmospheric.[1] In any case, the air is not directed at the bottom of the screwdriver but at its side. It follows the surface (Coandă effect[2]) and then creates a region of low (static) pressure near the tip when it separates. This is lower than the atmospheric pressure at the bottom; thus there is lift. [1] http://www-stud.rbi.informatik.uni-frankfurt.de/~plass/MIS/mis6.html http://www-stud.rbi.informatik.uni-frankfurt.de/~plass/MIS/m... [2] https://en.wikipedia.org/wiki/Coand%C4%83_effect https://en.wikipedia.org/wiki/Coand%C4%83_effect
          • raldi 11y ago
            Okay so how much of the lift is generated by high-dynamic-pressure air at the side of the screwdriver? None?
          • idlewords 11y ago
            The air at the nozzle mouth is at 100 psi, and there is a high pressure region around the nozzle. It is not correct to say that the static pressure is the same as atmospheric.
            • arcseco 11y ago
              It is correct to say that the static pressure is atmospheric pressure. Inside the nozzle the pressure was 100psi when stationary, the static pressure was traded for dynamic pressure when it exited the confinement of the pressure vessel.