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Underwater barrier

  1. Jun 30, 2003 #1
    [SOLVED] Underwater barrier

    [?] Since i've been lookin a the concept and knowledge to what happens when the sound barrier gets broken and how it happens, it got me thinking about if the same thing can happen in water.
    i.e. If an object was to move faster than the water molecues could move what would happen????
    An if anything at all would it be physically possible.

  2. jcsd
  3. Jun 30, 2003 #2


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    You would get a water shock wave forming at the bow of the object. Sonar wouldn't work (the sound would be going slower than the object).
    You'd also get huge cavitation: localized drop in pressure would cause air to bubble out of the water (I don't know the technical term for the phenomena).

    Do a search for 'supercavitating torpedos' for a real life example of this. Cool Stuff.
  4. Jun 30, 2003 #3


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    A couple of points: moving "faster than sound" means moving faster than a sound wave. It has nothing to do with "moving faster than water molecules".

    The speed of sound increases as density of the medium increases so the speed of sound is greater in water than it is in air. At the same time, it is harder for a physical object to move through a denser medium. No boat or torpedo goes anywhere near the speed of sound. Propellors spinning rapidly can: that's where you get "super cavitation".
  5. Jun 30, 2003 #4


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    Actually, the supercavitating "torpedos" do move faster than sound in water, afaik.

    They are shaped in such a way that a bubble of air cavitates around it, and it effectively turns into an underwater missile.

    EDIT: You're right though, Ivy. Those "torpedos" (which are still in development) don't actually go faster than sound in water. They form a bubble of *not water* which they are going fast in.
    Last edited: Jun 30, 2003
  6. Jul 7, 2003 #5
    [?] thanx for that and to the person above the post above.
    I saw that definition of speed of sound. an i thought that the sound barrier is when an object moves faster than air particles can move. I was just asking if a similar effect happened in water i wasnt saying they were related!
    Thanks both
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