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Q & A: sonic booms

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Most recent answer: 02/01/2012
Q:
Hi. My question relates to the sonic boom that an aircraft makes when it reaches the speed of sound. I understand how it happens and why. What id like to know is. If a plane, after the first sonic boom, continues at precisly the same speed/flight path, [about 750mph i think],then why does the sonic boom not immediately repeat as the pressure wave must instantly reform itself on the nose of the plane giving rise to more sonic booms. Ive always imagined that a plane should give off a sound like a machine gun effect BOOM BOOM BOOOM BOOM. Ive been curious about this since i was about 20 years old and would much appreciate any comment/info. Thanks for any trouble taken to reply. Regards. KEN.
- Ken Rushforth (age 62)
England
A:
The constant reforming of the pressure wave at the front of the plane is in fact the source of the sonic boom itself. Because the plane is traveling faster than sound, at some point as it approaches you, the time that the wave reaches you isn't changing as a function of the time it leaves the plane. That's because the shorter transmission time for the later wave to reach you just cancels the delay time before it was sent. That's why the waves add up so much making a boom. After the boom there will be a long tail of weaker waves reaching you, but not boom-like.

Mike W.

A few times when I have heard sonic booms there seems to be a second crack a very short time after the first.  I have never heard a triple one though.    This might be explained by the fact that a secondary wave is coming from the tail end of the craft.    LeeH


(published on 02/01/2012)

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