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In Fluid Mechanics what is the difference between yc and hc?

  1. Jan 4, 2017 #1
    When solving for the hydrostatic force on a surface we use the height to the centroid(hc), then when using the point of application we use the y coordinate of the centroid(yc), however shouldn't they be the same since they both start from the top surface and reach down to the object surface on the same axis?
     
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  3. Jan 4, 2017 #2

    boneh3ad

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    It depends on how you've defined your axes. If your y-axis is taken to be downward normal to the liquid surface, then they are the same. If your y-axis is angled to make the math more convenient then ##y## and ##h## will be different (but related through ##\theta##).
     
  4. Jan 4, 2017 #3
    Hi Beembo,
    A problem well described is half the battle.

    While I would tend to think that you are asking about the location of the resultant force on a submerged surface, that does not come quite clear in your post.
    Some questions come to mind about the axis orientation, surface shape, surface orientation for example.
     
  5. Jan 4, 2017 #4

    boneh3ad

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    That was reasonably clear to me, though it involved a few assumptions, such as that the surface is planar.
     
  6. Jan 4, 2017 #5
    Right. The basic submerged plate problem.
    Two different centroids are involved to find the location and magnitude of the resultant.
    He, himself, thinking about how to describe a problem clearly could give the OP a better insight as to why that is so.
     
  7. Jan 4, 2017 #6

    boneh3ad

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    It sounds like this is just a classic case of someone who learned a regurgitated equation without learning what it actually means or where it comes from, so you may be onto something.
     
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