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What the destructive force of the shock wave depends on?

  1. Mar 2, 2014 #1
    When the powerful (nuclear) bomb explodes it generates the shock wave that destroys everything around it. I want to know, does the force of this shock wave depend on the air pressure and density? Imagine that we have got powerful (nuclear) bomb and the object (rocket in this case) that is subjected to this explosion. In all three cases the distance between the bomb and object/rocket is the same-100 km. But there is one difference:

    1) In first case both bomb and rocket are placed on the Earth’s surface, so the atmosphere’s (where the shock wave propagates) density and pressure is constant:
    NPUmp3T.png

    2) In the second case the bomb is on the Earth’s surface and rocket is on the 100 km altitude. So, bomb’s shock wave will be spread in relatively dense medium and then in rarified one.
    30fq2d4.png

    3) In the third case the bomb is on the 100 km altitude and rocket is on the Earth’s surface. So, bomb’s shock wave will be spread in relatively rarified medium and then in dense one.
    LByL8zh.png
    So, my question is: in which case the bomb’s destructive force will be more powerful? Or there will be no difference? :rolleyes:
     
  2. jcsd
  3. Mar 2, 2014 #2
    100 km is a very large distance for today's typical nuclear weapons, none of them would produce any significant effect at that distance, no matter whether the separation is horizontal or vertical.
     
  4. Mar 2, 2014 #3

    UltrafastPED

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    A blast wave can exist in air, water, ground, or rock ... but not in space.

    See http://en.wikipedia.org/wiki/Blast_wave

    So in space you only have the debris from the explosive device (usually quite small) plus any radiation. The question of damage depends upon the target and it's protective shielding.
     
  5. Mar 2, 2014 #4

    Drakkith

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    To answer your question, yes, the blast is going to act significantly different depending on the medium it's in. Note that greater density doesn't automatically mean that the blast wave will propagate further.
     
  6. Mar 2, 2014 #5
    Not at an arbitrarily large distance, like 100 km.
     
  7. Mar 2, 2014 #6

    Drakkith

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    Sure, but I don't think the OP is asking only about that distance.
     
  8. Mar 2, 2014 #7

    boneh3ad

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    Not to mention that such a distance isn't too out of the question. Given, no one makes the Tsar Bomba anymore, but it leveled all structures within somewhere over a hundred kilometer radius and broke windows in Scandinavia all the way from Novaya Zemlya.
     
  9. Mar 3, 2014 #8
    Looking at your avatar, I have to concede that one could pack arbitrarily many stages in a thermonuclear device for an arbitrarily humongous bang. Still, the Tsar Bomba was one of the kind and it is probably not a truly weaponised design to begin with.

    I think it is an overstatement. I see that the Wikipedia article says something vaguely similar to this, but it does not reference its sources. That same page also has a picture of the "zone of total destruction of the Tsar Bomba", 35 km radius. Are you aware of a more reliable source?
     
  10. Mar 3, 2014 #9

    boneh3ad

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    Eh, not really. I've seen a couple other sites that seem to imply the same but they either cite Wikipedia (Gizmodo) or else I just don't know their veracity (TsarBomba.org). I concede that 100 km is definitely a gigantic distance, but I also know it isn't necessarily too extreme considering how extreme some of the Cold War weapons test were and what we can build. That said, I also concede that no one builds anything these days that is likely to cause damage at these distances. I merely cited it pointing out it was in the realm of possibility, not the realm of plausibility.

    All that said, regarding the original question, if we are sticking with 100 km, I would bet that both being on the ground would be the most destructive case. The shock wave would seemingly diminish the least at that distance without having to travel through a stratified atmosphere. The case of the bomb being detonated above the target would be the most destructive if the distance was something more reasonable, say, 2 km, since the shock reflects off of the ground and passes over structures twice, giving substantially higher overpressures and wind.

    EDIT: This appears to be a more reliable source on the actual Tsar Bomba test and mentions the same things while also citing sources. I didn't sift through the sources, however, so I can't say for sure. http://nuclearweaponarchive.org/Russia/TsarBomba.html
     
  11. Mar 3, 2014 #10
    Definitely depends on air pressure and density. It's a pressure wave so it needs a physical medium to propagate through.

    It would however be very interesting to somehow detonate a nuclear device in space and observe/examine the results.
     
  12. Mar 3, 2014 #11
    Guys, the 100 km distance/altitude was taken conditionally, it could be 10 km or 5 km :smile:

    boneh3ad
    sa1988
    So, tell me briefly, in which case (first, second or third) the bomb’s destructive force will be more powerful?
    Yes of course, it needs. But what is more important-dense medium and then rarified or opposite situation? :rolleyes:
     
  13. Mar 3, 2014 #12
    The first image, where the object is at the same level as the blast and is in the densest air, will be the most effective.

    In the other two examples the blast travels through a less dense medium, which will cause a higher amount of 'damping' of the wave.

    Think of it this way:

    The most extreme case would be the 100% super dense medium of a solid that is SO solid it can't be destroyed by anything at all and has no 'sponginess' whatsoever. So even if the solid where 10'000km long, an explosion at one end would cause the whole thing to move, and an object at the other end would feel the impact. That is analogous to a 'denser' medium.

    The less dense medium - for example, the parts in your images that are closer to space - have fewer particles, with more empty space between them. The energy of the blast will still be the same, however it will propagate much more broadly because of the more random motion of the particles since they're further apart.

    Another analogy:

    Imagine punching a brick. It goes in the direction of your punch.
    Imagine punching a load of dandelion seeds as they float through the air. Hardly any effect at all.

    The denser medium is the brick.
    The less dense medium is the dandelion seeds.

    So to answer, I could have missed some major factor somewhere in my explanation, but I'm fairly sure the most effective choice of your examples is the one where the object and the blast are both in the denser air at ground level.
     
  14. Mar 3, 2014 #13
    I do not think it is correct to say that the denser the environment is, the greater the damage.

    The following factors are in play.

    1. Immediately after explosion, most of the energy is in radiation - X-ray radiation. If the medium is very "thin", most of it will just escape without attributing its energy to the shock wave. So denser medium converts more energy into the shock wave. Very high altitude nuclear explosions are known to be very different from surface or low altitude explosions, their primary effects are production of ionization and electromagnetic pulses.

    2. When the shock wave propagates, it deposits part of its energy in the medium. The denser the medium is, the more energy it absorbs. The intensity of the shock wave is thus inversely proportional to the cube of the distance - if the medium is homogeneous.

    3. If the explosion is close to the ground, the shock wave is reflected from the ground and it combines with the primary shock wave, causing more damage. If I remember correctly, for every yield there is a sweet-spot burst height that maximizes the "total destruction" radius.
     
  15. Mar 3, 2014 #14
    Ah right ok.

    Point number 1 is true for sure, however I was ignoring the radiation and just sticking to the pressure wave, as that's what the OP seemed to be asking about. I think the mention of it being 'nuclear' was just a way of saying, "The explosion is very big."

    So if we're just talking of the force of a general explosion, or any radially propagating pressure wave:

    Point number 2 seems to be the same as my brick vs dandelion seeds analogy, I think?

    Point number 3 is quite interesting though. It makes sense, really cool :thumbs:
     
  16. Mar 3, 2014 #15
    sa1988
    Of course :smile:
    I understand this, but I wanted to know what the difference between second and third cases is :rolleyes:


    voko
    So, the second case will generate more powerful damage from shock wave, right?
    Wov, this is absolutely opposite to what you have just written:
    These two effects contradict to each other, which one will prevail? :rolleyes:
     
  17. Mar 3, 2014 #16
    In theory, yes. In practice, though, the distance must be very large (100 km and more) to have a significant difference in the character of the explosion. The shock wave from a typical blast won't reach that far.

    As usual in such cases, the curve for the "radius of total destruction" goes up and then down as the density changes. Where exactly the maximum is, I am not qualified to say. If I were, I would probably not be permitted to, anyway :)
     
  18. Mar 3, 2014 #17
    Heh, actually you simply asked if case 1, 2 or 3 had a more destructive shockwave.

    The question of the difference between the second and third cases is quite interesting.

    And, come to think of it, I'd like to argue that the first case is still the most effective, when considering the three given scenarios.

    I know that Voko made the point that there is a certain altitude for a detonation that allows the wave to reflect off the ground and cause maximum destruction. But that won't be so high up that the air density is any different to that of the air at ground level.

    So when considering the three extremes presented in those image, where the density of the air above the ground is much less (since this is what was original question asked about), I would still say that case 1 is the most effective, because the detonation slightly above ground where the wave reflects, is still under conditions best represented by case 1.

    (Remember we're thinking about shock/pressure waves here - not the EM radiation - a shock wave from a v.high less dense altitude is simply not going to propagate quite as well, because it has less of a medium to propagate through)

    Just my thoughts...
     
  19. Mar 4, 2014 #18
    voko
    sa1988
    Thanks guys :smile:
     
  20. Mar 4, 2014 #19
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