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Re: Speed of the shock wave?



On Tue, 19 Nov 2002 18:50:25 -0500 Tony Wayne <wayne@PEN.K12.VA.US>
writes:
This past weekend I was watching a show on TLC, (The Learning
Channel) called "The World's Biggest Explosions." In one of the
segments a
hiker takes a video of a rocket fuel storage depot exploding. The hiker
is
looking down at the depot from a mountain top. I'm guessing he was
recording
the event from a mile away. Here is the part I'm trying to make sense
of
-and I'm sure someone out there will have an answer. ASSUMING TLC DID
NOT
DOCTOR THE VIDEO, 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. The BOOM is following by a low volume
rumbling. At
the moment of the flash you also see the shock sweep across a valley
below the hiker doing the filming. After about 5 seconds you hear the
sound of
an incoming rocket (like in a cartoon) followed by the tremendously
louder boom of the shock wave as it hits the camera's location.

QUESTIONS:
To accomplish this, is the initial BOOM traveling through the ground
to the camera that fast to almost be instantaneous from a mile away?

*** Yes.... But remember that at a distance of only a mile, the B OOM
from the explosion only takes about 0.2 second to reach the hiker.

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


*** Yes. They are both being transmitted via ground and air
with only a fraction of a second delaw to the hiker.

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


*** My first guess would be YES. Howeverthere is a great deal about short

distance shock waves that can be very complicated. I defer to others on
this
list who can give a better answer.

Herb



==========================================================
Tony Wayne Those that can, do.
wayne@pen.k12.va.us Those that understand, teach.

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



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