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Questions about explosions

  1. Sep 28, 2013 #1
    Quick question:

    My friend and I are having problems on how explosions work.

    According to him, in a explosion smaller objects don't receive the full force of the blast since they only encompass a small fraction of the blast radius.

    So basically lets say if I'm in the path of a grenade blast or something, I'm not actually receiving the full force of the blast but the portion that comes contact with my body?

    Another thing is their like a scale in which when smaller objects are hit by a larger explosive blast, the damaged is amplified?
  2. jcsd
  3. Sep 28, 2013 #2

    Simon Bridge

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    That would be correct - after all, how would your body be affected by the part of the explosion that does not come into contact with it?

    To be clear - most explosions have three main parts: the debris, the fireball, and the shockwave. In some explosions, the light-pulse is strong enough to be a problem too. But each part is like being in a room sprayed by bullets ... you are only affected by the bullets that hit you.

    Note: the "full force" of the explosion on a body is the total force experienced by the body. It is the pressure difference multiplied by the area. Strictly speaking you should say that a body does not intercept the full energy of the explosion - except in special situations, like when you fire a bullet, when the explosion is contained in some way.

    I don't understand that question - can you provide an example?
  4. Sep 28, 2013 #3
    Some sloppy terminology here but your friend is basically correct. The explosion is essentially a radial pressure wave, and the force you feel derives from a gradient in that pressure wave (high pressure from the compressed air will push you backwards). Force = pressure times area, so if you present a larger area to the source, you have a proportionally larger force.

    "Damage" is a slippery term and depends a lot on the particular material. But I'd definitely recommend trying to minimise your area as seen by the source of the explosion. You'd certainly not want to do a star jump as the pressure wave comes towards you.
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