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Homework Help: Easy Physics Concept but I cannot understand

  1. Apr 22, 2012 #1
    1. The problem statement, all variables and given/known data

    Fluid is flowing from left to right through a pipe (see the drawing). Points A and B are at the same elevation, but the cross-sectional areas of the pipe are different. Points B and C are at different elevations, but the cross-sectional areas are the same. Rank the pressures at the three points, highest to lowest.

    I could not attach the image but it looks like this: [ A ]---B--- , where A is thicker than B, and C is way above these two. The answer is A,B,C.

    2. Relevant equations

    P = F/A
    Bernoulli's Equation maybe?

    3. The attempt at a solution

    I understand that Point C has the lowest pressure because it is elevated. To decipher between A and B, I am using the equation P = F/A. However, this tells me that pressure and area are inversely proportional which would suggest that Point A has a lower pressure than Point B. Where is my logic wrong?
  2. jcsd
  3. Apr 22, 2012 #2
    When you say A is thicker, what do you mean? Larger in internal diameter?
  4. Apr 22, 2012 #3
    yes A is larger in diameter than B.
  5. Apr 22, 2012 #4
    So what can you say about the velocities at A and B?
  6. Apr 22, 2012 #5
    The velocity at Point B will be greater than the velocity at Point A because area and velocity are inversely proportional according to A1v1 = A2v2.
  7. Apr 22, 2012 #6
    Now looking at Bernoulli's equation, what does that tell you about pressures at A and B?
  8. Apr 22, 2012 #7
    I see it now!!! Thank you so much!!!!!!!
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