Why Implosion after Explosion?

[GrandMasterK]

http://www.metacafe.com/watch/877471/bunker_buster/

 

why does the blast get sucked back in like that?

[insane_alien]

because a whole lot of air was pushed out of that area. this results in a lower than atmospheric pressure zone which promptly gets filled again.

[YT2095]

Air is elestic, it also has Mass, so if you Throw out a lot of air it`s mass keeps it moving out due to inertia, but in doing so leaves a low pressure vacated area that must be refilled, so it all gets pushed back in again and so on.

 

in fact Explosions actually Oscillate for a time until an equilibrium is reached again.

[Mr Skeptic]

It's very similar to an incredibly loud sound source -- a compression followed by a rarefaction.

[Norman Albers]

Mass density and thus inertia mean that the relative vacuum at the center exists until the wave process reverses. This is a large transient impulse problem. Believe it or else you can view it like a hammer striking a piano string! The actual impulse of the hammer blow travels to both ends of the string, one of which moves the soundboard in response. The exact negative image would be reflected if the endpoints were rigid but they are not, so a wonderful selection called "piano tone" is experienced. Spherically, the reference is far-field pressure, and if you send stuff flying out, there will be a vacuum to be filled at the characteristic rates.

[GrandMasterK]

Nice replies!

 

Will this same event occur if a bomb explodes in a vacuum such as outer space?

 

 

It's very similar to an incredibly loud sound source -- a compression followed by a rarefaction.

 

I'm interested in what your talking about as far as sound but I don't know what you mean. Can you give an example?

[YT2095]

assuming there`s no nearby surface for the shockwave to bounce back off, in space the explosion would just carry onwards and outwards until it ran out of kinetic energy.

there`s no outside air pressure to refill the void with, so there`s no elastic effect.

 

in air the vacuum created doesn`t Suck stuff back in to refill it, the surrounding air Pushes stuff back in.

 

 

this can`t happen in space.

[Norman Albers]

Most excellent! You two stole my Q&A. Mathematically we can look at the steady state sound field, say, given a microphone at the center of circular propagation. Additionally, here we have an initial condition, a transient of a whomping pressure pulse from all the gas so quickly produced by the explosive. . . . . . . EDIT: You'll get superior results with a loudspeaker.

[YT2095]

well you Know where the Reputation button is