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Why is the pressure of two different liquids in a manometer the same?

  1. Oct 26, 2008 #1
    I just finished a question in which a u-shaped tube (manometer) is filled with water to a certain height. Another substance, in this instance, oil, is added to one side of the manometer. I was asked to find the height of the new substance. I used the formula P(water) = P(oil), or
    (ϱwater)gh = (ϱoil)gh. So, I know how to solve it, but I don't really understand it. Why is the pressure of both substances the same? Thanks for your replies.
  2. jcsd
  3. Oct 26, 2008 #2


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    Staff: Mentor

    Think about what happens at the bottom of the U-tube. What happens if the pressure on one side is greater than the pressure on the other at the bottom?
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