Re: Speed of the shock wave?

["John S. Denker" <jsd@MONMOUTH.COM>]

Tony Wayne wrote:

> "The World's Biggest Explosions." ....
> rocket fuel storage depot .... ASSUMING TLC DID NOT DOCTOR
> THE VIDEO,

Why would anybody assume that????

>  when the fuel depot explodes (a mile away) you can hear a BOOM
> ALMOST at the instant the flash is seen. The BOOM sounds like it
> contains no high frequencies.

> Does the shock wave caused by the explosion travel through the air at the
> speed of sound for air ?

A shock, by definition, is supersonic.

> is the initial BOOM traveling through the ground to the
> camera that fast to almost be instantaneous from a mile away?

Not very likely.

The speed of sound in, say, granite is very fast,
almost 6000 m/sec.  This _exceeds_ the detonation
velocity of ordinary mining-grade high explosives.
The most brisant military explosives have a slightly
higher detonation velocity, but not much.

And rocket fuel, by construction, is not supposed
to detonate at all.  Sure, it will make a whale
of a boom, but a shock in the rock?  I very much
doubt it.

A shock wave does not sound like a boom and
certainly not like a rumble.  It sounds like a SNAP!
It's unforgettable and unmistakable.

> Is the rumbling between the flash of the explosion and the shock wave
> caused by sound being carried through the ground to the camera?

To repeat:

I find the timing hard to believe.
I also find it hard to believe that a rocket-fuel
depot would go up all at once.

Plausible scenarios include:
 -- probably it took several seconds for the reaction to
take place, with much burbling and rumbling.
 -- maybe the first few seconds were hidden from view.
 -- maybe the soundtrack was doctored.
 -- a subsonic wave that starts out with a sharp
wavefront will lose its sharpness as it propagates
outward, due to dispersion and due to preferential
absorption of the high frequencies.

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.