AN EXPLOSIVE QUERY

Discussion in 'Physics' started by b.shahvir, Mar 6, 2009.

  1. b.shahvir

    Thread Starter Active Member

    Jan 6, 2009
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    Hi Guys,

    My query points to the physics of explosive forces in vacuum, let me clarify;

    When an high powered explosive (simply put…..a bomb) detonates on earth (God forbid!), high intensity shock waves in the range of about 5000 lb/sq.inch are created in the surrounding air. A massive pressure wave is created followed by an equally destructive suction wave. A very loud bang is heard followed by heavy destruction! :eek:

    But the high intensity pressure waves exist due to the presence of air in our atmosphere. If the same bomb goes off in vacuum (say in space), there is no air and shock waves would be absent (I guess).

    :confused: So, what will be the nature or behavior of the explosion if the bomb detonates in an atmosphere free of gases or air (ideally vacuum)? Will one hear a loud bang……. or no sound would be heard since there is no air to create the massive mechanical forces of pressure and suction? If mechanical forces are present, what kind of energies will they emit?
    Valuable comments/inputs will be appreciated.

    Thanks & Regards,
    Shahvir
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Sound doesn't travel in a vacuum. I had a small explosion once in a high vacuum system made of glass. I saw the flash, heard the glass breaking, and felt the shards.

    John
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    There was the experimental nuclear detonation out of atmosphere over hawaii. No Bang, but most to the power grid went down.
     
  4. b.shahvir

    Thread Starter Active Member

    Jan 6, 2009
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    :confused: But will there be emission of heat or flames? What about mechanical forces like shockwaves........ if glass breaks due to explosion in vacuum, then there has to be mechanical forces involved! But how can pressure or suction waves be present in the absence of air?
     
  5. davebee

    Well-Known Member

    Oct 22, 2008
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    Well, I would say that the molecules of the explosive materials would undergo their reaction, generating heat just as on Earth. The heat would gassify all the molecular products of the reaction, which would then expand outwards because of the imbalance of pressure on the molecules. There'd be an initial pulse of electromagnetic radiation that would expand in an ever-enlarging sphere. Behind that, the heated molecules would also expand in a sphere of ever-increasing size.

    I imagine that if you were in a spacesuit nearby, then you'd feel the impact of the expanding gas. If you were close enough, you probably would hear it as a sound, since your spacesuit could be slapped with a powerful force.

    Without atmosphere to slow the molecules, they would continue to travel at a initially high velocity, slowing only by the gravitational attraction between the particles, but as they expand in the 3-dimensional volume of space, the pressure per area would decrease with distance from the explosion, so if far enough away, the overall force of the particles striking you would decrease to the point that at a great enough distance, nothing would be heard or felt.
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Sure there was a shock that broke the glass, even though it was initially under vacuum. The reaction was between sodium/potassium amalgam, which renders those alkali metals liquid at room temperature, a chlorinated hydrocarbon, and some other hydrocarbons. The resulting free-radical reaction caused plenty of gas to be released quickly.

    But back to your question, shock waves are pressure waves, which cannot travel through a true vacuum. However, shock waves are evident in stellar nebulae, so it doesn't take much pressure to allow propagation.

    John
     
  7. b.shahvir

    Thread Starter Active Member

    Jan 6, 2009
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    :) Thanx guys…… but could ya'll elaborate some more on the electromagnetic pulses and its effects? I think they are also used in the development sophisticated weapons for defense purposes.

    Also, considering an environment free of planetary gravitational forces, please re-elaborate on the mechanism of the explosion in an ideal vacuum environment.

    Kind Regards,
    Shahvir
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Nowdays EMP is being used without the explosions by the military, for burning out electronics of hostile forces. Kinda neat, as long as it's not near my house.
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
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    Particle density in a nebula is a thousand times (or more) as dense as in open space. Open space has about one particle per cubic centimeter.

    I have no clue what the "threshold" for a pressure wave might be.
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Just for context, I remember being impressed with how many molecules were still present in the highest vacuum we could easily achieve in the 1960's (about 10^-7 mm Hg). Look up "Mean Free Path" in Wikipedia for a good table.

    In brief, an ultra-high vacuum of about 10^-7 mm Hg still has about 10^9 particles per cm^3.

    John
     
  11. b.shahvir

    Thread Starter Active Member

    Jan 6, 2009
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    Thanx very much guys for such an overwhelming and informative response! any additional inputs are welcome.
     
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