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Homework Help: Fluid Mechanics - Highest Possible Water Can go in a Straw

  1. Mar 7, 2006 #1
    I need to figure out the highest possible height that water can be sucked up into a straw on Earth. You have unlimited water.

    So far I've figured out that when you suck, you create a vacuum that allows the water to rise up due to the atmospheric pressure and the force is creates pushing down on the rest of the water, which forces to water up the tube. I also figure that the highest height will be when the force the air pressure creates = weight of the water.

    I have been unable to figure out the equations to solve this problem to acutally get the height.

    Thanks a lot for your help!
  2. jcsd
  3. Mar 7, 2006 #2


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    the pressure causes a Force = P times Area (cross-section A of tube)
    the Volume of water in the tube = Area times height.

    How do you get a weight from a Volume?

    This is NOT advanced Physics ...
    you should post questions like these in the INTRODUCTORY physics Area.
  4. Mar 7, 2006 #3
    I believe its something like 32 feet.
  5. Mar 8, 2006 #4
    Can this be another form of the same question ?
    a mercury barometer is under free fall . what would be the height of mercury column in the barometer ?
  6. Mar 8, 2006 #5

    Your method would work if I knew the cross-sectional area. We arent given the cross-sectional area. All we are given is how high can the straw be. We have no other information.
  7. Mar 8, 2006 #6

    Meir Achuz

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    Gold Member

    All you need is \rho g H=P_{atmospheric}.
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