Questions about explosions

  • Thread starter jones111
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  • #1
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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?
 

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  • #2
Simon Bridge
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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?
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.

Another thing is their like a scale in which when smaller objects are hit by a larger explosive blast, the damaged is amplified?
I don't understand that question - can you provide an example?
 
  • #3
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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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