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Re: RE:Pressure and Flow

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  • dhl@chelseamsl.com
    Hi, JG. Just think of bricks. If you are the bottomest brick, you have all the bricks above you pressing down on you, so the pressure on you is greatest. But
    Message 1 of 3 , Jun 30 8:00 PM
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      Hi, JG.

      Just think of bricks. If you are the bottomest brick, you have all
      the bricks above you pressing down on you, so the pressure on you is
      greatest. But you can't move sideways, because your neighbour bricks
      have the same pressure on them, and the brick above you has a brick
      above it, and on up to the top. Now if you were a molecule of water,
      you'd have all the molecules stacked above you and your pressure would
      be greater. You can still move a little (which is why ink will spread
      around in water even if nobody stirs it; there is molecular motion
      which would be like brick motion, but LOTS smaller :) Anyway, no
      particular molecule has any pressure to move around very much, just
      kind of randomly wandering.

      And anywhere you meauser a pressure in a static vessel, the pressure
      will be proportional to the depth of the fluid at the depth where
      you are measuring. When the stuff starts to move, then the pressure
      differentials start to show up, even at equal depths.

      Does that help?
      Donald.

      --- In hobbicast@y..., "geoff" <cyrano@a...> wrote:
      > Hi, the recent thread has me wandering. If you measure the pressure
      in a
      > glass of water, the pressure increases as the tip of the manometer
      goes
      > further in the water, but there is no motion of the water [ i don't
      think
      > convection currents are the answer ] and yet the pressure
      differential
      > remains. i don't understand the pressure's not causing currents in
      the
      > water. Also i don't understand most of the recent posts. Just
      geoff
    • catboat15@aol.com
      In a message dated 6/29/01 7:06:40 PM Pacific Daylight Time, ... That is what us inginears call static head . It is just the weight(or mass if you are ISO
      Message 2 of 3 , Jul 1, 2001
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        In a message dated 6/29/01 7:06:40 PM Pacific Daylight Time,
        cyrano@... writes:


        > . If you measure the pressure in a
        > glass of water, the pressure increases as the tip of the manometer goes
        >

        That is what us inginears call "static head". It is just the weight(or mass
        if you are ISO inclined) of the fluid above the manometer end. When the
        fluids (water or gas) start moving is when the fun begins. Look at what may
        be called a "cellar drainer" or a gadget boaters use to bail out water it is
        a venturi that uses water flow to create a low pressure to "suck" water out
        of a low place. For home shop users I think it would be enough to remember
        that as fluids flow through an expanding section pressure rises, velocity
        drops. A constriction is the other way around, velocity rises, pressure
        drops. Just keep you change of sections gradual.

        John Meacham
        High Desert of California, Palmdale, Littlerock.


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