Re: Sonic Boom

From:         grichard@midway.uchicago.edu (Rich Benzinger)
Organization: University of Chicago
Date:         13 Oct 93 11:50:54 PDT
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>krzystek@carson.u.washington.edu asks:
>
>  P.S. Can somebody please elaborate on the original question:
>does the sonic boom arise only on passing through the sound barrier,
>or during the whole supersonic flight?

	I've encountered what I think to be a fairly convincing (and possibly
even marginally accurate) pop science analogy to sonic booms:

	Consider the spreading of waves in water.  Specifically, consider
a boat moving though the water.  If the boat moves at a very low speed,
waves will radiate from it in all directions, including directly ahead of it.
As the boat speeds up, the waves in front become progressively compressed.
As the boat exceeds the velocity of the spreading ripples, it will overtake
them, leaving smooth water in front and a single large wave spreading
triangularly behind the boat.  (This is about the point where I usually
fall off my water skis, but that's another story...)

	By analogy, the smooth surface of the water in front of the speeding
boat implies that one does not hear a supersonic aircraft approaching.
Further, the boat's triangular wake is the counterpart to the conic shock
wave behind an aircraft at mach > 1.  Thus the "boom" occurs as the wave
passes over the rowboat, plate glass window, eardrum...

	Of course, I'm willing to be shot down by more learned authorities...

	Hope this helps.

					Rich Benzinger
					grichard@quads.uchicago.edu