Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Water in a u-shaped tube

  1. Jan 22, 2008 #1
    1. The problem statement, all variables and given/known data
    This question starts by stating.. "a U-shaped tube filled with water is closed on one end. Tube is about 1m tall. When water is removed from the open end, the water level in the closed end doesnt change.."
    Then a series of questions..

    My question is, why doesnt the water levels equal each other on each end, after you remove the amount of water?
    I know its a matter of atms acting on the water, but cant understand how that works.
    any help is really appreciated.
    Thanks you!

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jan 22, 2008 #2


    User Avatar
    Gold Member

    How much atmo is pressing down on the water at the open end?
    How much atmo is pressing down on the water at the closed end?
  4. Jan 24, 2008 #3
    ok so the open end is exposed to atmospheric pressing down on it, but the closed end is not.
    That is why open end will have lower water level than closed end right?
    please tell me if this is correct understanding of this?

  5. Jan 24, 2008 #4


    User Avatar
    Gold Member

    Well, you've got the right answer, I can't say whether or not you understand it.

    Do you?
  6. Jan 24, 2008 #5
    thanks for the response. yes i think i understand it.
    what about this: at a point at the bottem of both tubes (its u-shaped, so the bottem of it is shared) is the pressure greater, same, or less than pressure if both tubes at same level?

    i know that pressure depends on depth, but im confused because which depth do we consider (left and right tubes are different depths?
  7. Jan 24, 2008 #6
    i actually mean left and right tubes have different levels. (so= different depths)
  8. Jan 25, 2008 #7


    User Avatar
    Gold Member

    If the pressure on each side were uneven, what do you think would happen?

    Think about the open end. If the (pressure at the bottom) were greater than (the water in the open end weighed), what would happen to it? If the (pressure at the bottom) were less than (the water in the open end weighed) what would it do?

    Pressure depends on the depth of the whole column, including any air above the water's surface (about 60 miles of it , which happens to exert a pressure of 1 atmosphere).
    Last edited: Jan 25, 2008
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook