Sound barrier in a liquid.

Discussion in 'Physics' started by JMW, Nov 27, 2012.

  1. JMW

    Thread Starter Member

    Nov 21, 2011
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    What would happen if you could "break" the sound barrier in water?
     
  2. MvGulik

    Member

    Nov 3, 2011
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    Mmm. ... That made me wounder a bit about this to. So looked around, and found this:
    source: www.sciforums.com (post: #8/8)
     
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  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Nobody watches the science channels? They have been working on supersonic underwater missiles for some time using rocket engines and some type of nose cavitation device that generates some gas pocket effect at the nose and back over the skin of the underwater missile.
     
  4. Blofeld

    Active Member

    Feb 21, 2010
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    This is an incredible clever trick, but it is "only" aimed at reducing the friction drag and thus achieving very high speeds by means of supercavitation (basically the effect you described). The body does not reach supersonic speeds (which would be around 1500 m/s in water).

    http://en.wikipedia.org/wiki/Supercavitation

    By the way, it is even possible to reach a speed in water that is higher than the speed of light in water. The only catch: You have to be an electron or some similar little critter.

    http://en.wikipedia.org/wiki/Cherenkov_radiation
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    OK, it's not "supersonic" as such, but it does overcome the issues of travelling at high speeds underwater. To make it supersonic just requires a higher powered rocket engine, just like in air... ;)
     
  6. DenzilPenberthy

    New Member

    May 28, 2012
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    Also, bow waves from boats are caused by travelling faster than the speed of surface waves.
     
  7. killivolt

    Active Member

    Jan 10, 2010
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    I've thought about this a couple times in my life. If you could charge the water around the object or missile with "Ultra High Voltage, High Frequency" at the very tip, creating like charges around the skin of the missile.

    Like the skin effect on high voltage wire, the water would be repelled creating your pocket and therefor being viscous the "Super Charged air or water around the object it might act as a Magnetic / hydraulic pressure adding to stability and speed.

    Sometimes I shouldn't be allowed to type, after drinking the night before:)
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    My mostly uninformed hypothesis is that it would be impossible. It is possible in air because air is compressible. You can push through it faster than it can push through itself. But water is incompressible, so you could not possibly move the molecules out of the way faster than they can could naturally displace themselves, as in a sound wave.

    Unless you were a subatomic particle which could actually travel in the space between the water molecules.

    Thoughts?
     
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  9. killivolt

    Active Member

    Jan 10, 2010
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    That makes sense, I just found that if I hold the HV cathode above water I can dimple the surface tension, so I thought maybe it was feasible to Electrically defuse the Molecules making it permeable or stretchy.
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The effect would be none, voltage with reference to what? Adding a charge to the entire body of water is a choice, but impossible in the open ocean.

    Something like coating a boat in a hydrophobic substance, which actively "repels" water, like Teflon, doesn't give much of a boost, especially when the inevitable crud build up starts.

    Image of Dew Drop on hydrophobic leaf from wiki
     
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  11. killivolt

    Active Member

    Jan 10, 2010
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    The only way to do it (Put Moses) on the nose cone of the rocket:p
     
  12. Brownout

    Well-Known Member

    Jan 10, 2012
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    That's not true. To achieve supersonic speeds, the entire aircraft has to be redesigned. Just using a higher powered engine alone wouldn't do it.
     
  13. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The "it" I was referring to was the research model underwater missile which already had the necessary features (ie nose cavitation design) which allowed the missile to travel in a cavitation pocket in the water. I believe *given enough engine power* it would be supersonic.

    I was not saying you could just stick a huge engine on *anything* and make it travel supersonic underwater. ;)
     
  14. Brownout

    Well-Known Member

    Jan 10, 2012
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    My post had a typo that changed the meaning. I was trying to say that "in air" the aircraft required a complete redesign to break the sound barrier. They tried using more power on existing designs, but couldn't break the barrier. Only a complete redesign of the airframe made the efforts successful.
     
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