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Thread: Dissipation of potential energy in a waterfall

  1. #1 Dissipation of potential energy in a waterfall 
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    I have recently visited the Iguazu Falls, and had a discussion about how much of the potential energy in water at the top of the fall was converted into kinetik energy, and how much was converted into sound, temperature increase, vaporisation, and other effects. I think that sound is an important part (in a waterfall as loud as Iguazu), but have no real numbers to back this up. The same goes for the other effects.

    Does any of you have an estimate on how the potential energy could be distributed into sound energy, temperature increase, etc?


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    Forum Ph.D. william's Avatar
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    Try to imagine one molecule of water throughout its journey. It starts at the top with lots of potential energy. As it falls, the potential energy is transformed into kinetic energy. Just as the molecule is about to hit bottom, almost all this energy is kinetic. But just as the molecule hits, almost all the kinetic energy is transformed into other forms of energy. So I think to answer your question, almost all the kinetic energy (which was once potential energy) is converted into other forms including temperature and sound.

    Anyway, that's my 2.


    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  4. #3 Re: Dissipation of potential energy in a waterfall 
    Reptile Dysfunction drowsy turtle's Avatar
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    Quote Originally Posted by gonvaled
    Does any of you have an estimate on how the potential energy could be distributed into sound energy, temperature increase, etc?
    The simple answer is that all the potential lost must be accounted for by other forms of energy. We know this because energy cannot be created or destroyed, and so where a system loses energy the energy must go somewhere else.

    By the way, we're not talking about a huge amount of energy here:
    The water drops, at most, 82m. Approximating g=9.81, we are talking about a loss of roughly 804J/kg. If all of the energy were subsequently used to heat the water, the resulting temperature increase would be roughly 0.19 k.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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