Explosions and Damage: How Does Size Affect Impact?

[jones111]

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 let's 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?

 

[Simon Bridge]

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 let's 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?

 

[mikeph]

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.