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Rate of flow, or velocity of fluid?

  1. Sep 13, 2013 #1
    I was looking at a site which described the classic demonstration to illustrate how water pressure increases with depth (shown by punching three holes, one above the other separated by a few centimeters, in a container of water): "The smaller the holes, the greater the rate of flow from the holes."

    Is this right? Does not the author mean, "The smaller the holes, the greater the velocity of the water"? (I think of "rate of flow" as being total volume passing a point per unit time, which must remain constant. And presumably these relationships only hold when the flow is laminar and frictional forces are neglected?)
  2. jcsd
  3. Sep 13, 2013 #2


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    Homework Helper

    I believe you are correct, the author meant velocity. Otherwise the continuity equation would be violated.

    cross sectional area x velocity = constant
  4. Sep 13, 2013 #3


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    It depends on what the author said. If he/she just said "flow rate" or "rate of flow", those are ambiguous terms and so they may have simply meant velocity rather than volumetric flow rate or mass flow rate. In other words, they may have been right or wrong but you can't really tell because the terminology as you describe it is ambiguous.
  5. Sep 14, 2013 #4
    If the holes are equal in size, then different flow velocity necessarily means different mass/volumetric flow, for liquids.
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