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Airtight tank vs. explosion

  1. Aug 20, 2007 #1
    Hi everyone! Here's something that has been bothering me for quite some time now:
    If you detonate an explosive device outside a completely airtight tank, what happens to the air pressure inside? Does the shockwave traveling through the wall of the tank have a notable effect on the pressure inside?
     
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  3. Aug 20, 2007 #2

    DaveC426913

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    Depends on how strong the tank is. And how elastic.

    The pressure might flucuate a little due to vibration while the tank is being subjected to the insult, but unless the tank is actually deformed by the detonation, it will return to normal in a fraction of a second.
     
  4. Aug 20, 2007 #3
    So if I sat inside the tank (which would not deform, only vibrate), I wouldn't end up with my eyes and ears bleeding?
     
  5. Aug 20, 2007 #4

    russ_watters

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    In your question you said completely airtight, implying completely impervious to the explosion. You'd notice nothing.

    If the tank were slighly less than completely impervious, you'd get a shock wave traveling through the tank like being inside a big bass drum. Powerful enough and yes, it could rupture your eardrums.....and maybe everything else inside your body.

    If the tank were not so impervious, it would be crushed, of course.
     
  6. Aug 20, 2007 #5

    mgb_phys

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    If it can't deform there wouldn't be any change in pressure so your ears would be ok.
    Of course if the bang was big enough to throw the tank 100feet up in the air you might feel it!
     
  7. Aug 20, 2007 #6

    Danger

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    Airtight does not imply great structural integrity. The others have all touched upon what would be my main concern. Even if the container seal remains intact, the whole thing thing could be crushed to the extent that the internal pressure would rise significantly. Think of it as being similar to the pressure spike inside a football at the instance that it's kicked.
     
  8. Aug 20, 2007 #7

    DaveC426913

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    How does this follow? What does airtight have to do with impervious?
     
  9. Aug 20, 2007 #8

    DaveC426913

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    The air pressure rising is not of any concern. For a deformation large enough to change the air pressure, the deformation itself will injure or kill you. What is of concern is the shock wave.
     
  10. Aug 20, 2007 #9

    Danger

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    I might be missing something here, but I disagree. If you're not in contact with the deforming material, it shouldn't affect you at all; there wouldn't be any mechanical transfer of energy to your body. As a 'for instance', what about if you're suspended in a hammock or elastic net? If the pressure increase is rapid enough, though, it could still cause damage even it isn't a lot above atmospheric.
     
  11. Aug 20, 2007 #10
    I think if the tank is rigid enough and air tight that the shock wave won't do much. However I think the sound waves from the blast may still penetrate the walls of the tank where they could do what they will. Might lose your hearing after all.
     
  12. Aug 20, 2007 #11

    mgb_phys

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    If the walls don't deform, ie are infiniely rigid, then no sound can penetrate.
     
  13. Aug 20, 2007 #12

    Danger

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    The original question didn't mention anything about the walls being even semi-rigid, let alone 'infinitely' rigid.
     
  14. Aug 21, 2007 #13
    ...,
     
  15. Aug 21, 2007 #14
    First of all, a wall doesn't have to be 'infinitely rigid' to resist deformation.

    Secondly, it doesn't take the compression of a shock wave to destroy a person's hearing so where the air might not compress in the tank very much, the noise could still be dangerously loud, especially inside a tank where it will reverberate.

    Thirdly, I seriously hope we're not contributing to a dangerous experiment here.

    lol​
     
  16. Aug 21, 2007 #15

    mgb_phys

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    On his second post he said - if the walls can't deform - I was pointing out that if there is no deformation there can be no sound transferred.
    To experience no deformation with a finite applied force they have to be infinitely rigid, of course a real wall might suffer not permament plastic deformation from a sound but have some elastic deformation to allow any energy to be transferred.
     
  17. Aug 21, 2007 #16

    Danger

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    That one slipped past me. Now that I've read it, though, it's self-contradictory. He says that the walls can't deform, only vibrate. Vibration is deformation.
     
  18. Aug 21, 2007 #17

    DaveC426913

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    I think we've been treating deformation as meaning inelastic.
     
  19. Aug 21, 2007 #18

    Danger

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    :confused: I thought that any deformation was inelastic. Or does that mean something different here than in a collision?
     
  20. Aug 21, 2007 #19

    mgb_phys

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    Permanent deformation is inelastic. Elastic would still deform the surface and then it would spring back - like a drum skin
     
  21. Aug 21, 2007 #20

    DaveC426913

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    i.e.
    elastic = springy deformation = vibration
    inelastic = permanent deformation = dent
     
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