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How can a non-flowing fluid have kinetic energy?

  1. Oct 17, 2011 #1
    So a non-flowing fluid has energy that consists of internal energy, potential energy, and kinetic energy. If it is "non-flowing," how is this possible?

    A flowing fluid has energy that consists of internal energy, potential energy, kinetic energy, and flow energy Pv. My other question is, shouldn't the flow energy be a part of its kinetic energy as well? Why are they different?
  2. jcsd
  3. Oct 18, 2011 #2
    Is this a homework question?
  4. Oct 18, 2011 #3


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    Homework Helper

    Note that in this case, potential energy is gravitational potential energy.

    Bernoulli equation with gravitational term, for an ideal fluid with no external forces other than gravity:

    pressure + 1/2 ρ v2 + ρ g h = total_energy / unit_volume

    If you multiply this by some amount of volume you get energies:

    (pressure x volume) + 1/2 m v2 + m g h = total_energy

    pressure_energy + kinetic_energy + gravitational_potential_energy = total_energy

    I'm not sure where you got the additional term from.
  5. Oct 18, 2011 #4
    Make sure you understand that Internal Energy is not some kind of energy; instead it is a concept that includes kinetic and potential energy internal to the body, substance.

    Also, make sure you understand the difference between Internal Kinetic Energy and Kinetic Energy in its more common sense.

    Internal kinetic energy refers to the motion of the particles in the object, substance.

    Regular kinetic energy, the more common concept as understood by most everybody, refers to the kinetic energy of the body as a whole due to its motion, translation.
  6. Oct 18, 2011 #5
    The molecules of the fluid are moving, but the fluid doesnt necessarily have to flow.
  7. Oct 19, 2011 #6
    Put the liquid in a sealed container wait for it to stop moving from your lifting it and drop it from a height.
  8. Oct 20, 2011 #7
    You mean the internal energy term? Here's the equation from my textbook: http://imageshack.us/photo/my-images/850/unledkzh.png/
    I can kinda see where everyone's coming from with the internal kinetic energy. But I would guess that would be a part of its total internal energy, which is already a part of the equation.
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