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Object with constant speed does not lose kinetic energy when faced with resistance

  1. Nov 8, 2009 #1
    Hello,

    "Potential Energy (PE) + Kinetic Energy (KE) = Total Energy

    When air travels through an airway at a CONSTANT FLOW RATE, the total energy of the fluid (PE + KE) decreases because friction converts some of this energy into heat. Since the fluid is moving at a constant flow rate, the loss is in potential energy (decrease in hydrostatic pressure)."

    I don't understand this. Shouldn't the moving object lose K.E. Shouldn't resistance decrease speed.
     
  2. jcsd
  3. Nov 8, 2009 #2

    tiny-tim

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    Hello sameeralord! :smile:
    Nope …

    conservation of mass! :wink:
     
  4. Nov 8, 2009 #3
    Re: Object with constant speed does not lose kinetic energy when faced with resistanc

    Thanks for the help but I still don't get it. I think the reason for that is I don't understand what is hydrostatic pressure, I researched but I don't get it.

    "As we move down the airway, the tubes begin to narrow. When a tube narrows, fluid velocity increases causing an increase in KE at the expense of PE (ie. a compensatory decrease in hydrostatic pressure). This is referred to as the BERNOULLI EFFECT."

    How does the fluid velocity increase when the resistance also increases when the tube narrows. Is the pressure inside this tube, exerted by moving molecules (KE) or hydrostatic pressure. I don't get it.
     
  5. Nov 8, 2009 #4

    tiny-tim

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    Hi sameeralord! :wink:

    Forget pressure …

    most fluids are incompressible, meaning that their density is constant.

    So the amount of fluid going into a particular volume equals the amount going out …

    if the exit is narrower than the entrance, then the fluid must be going faster!

    That's all it is! :smile:
     
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