1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Why is there a sonic boom at Mach 1.5?

  1. Jul 1, 2017 #1
    It's my understanding that a sonic boom is the doppler effect taken to the extreme, with a sound emitting object travelling at the speed of sound, your building the ultimate constructive wave.

    I want to know, if you were travelling at Mach 1.5, why doesn't the sound you're generating cancel itself out? (in layman's terms)

    More precisely, if you understood how the frequency of the sound generated by your aircraft varied at different speeds as it's travelling, why can't you:
    a) choose to travel at a speed that would destroy the sound wave produced?
    b) deliberately place the elements of your design that cause drag (and hence, noise) offset by half the wavelength?

    Or at least I assume you can't because it still takes 8 hours to fly to America from the UK, 50 years after Concorde was invented =P.

    Cheers,
    J
     
  2. jcsd
  3. Jul 2, 2017 #2

    Drakkith

    User Avatar

    Staff: Mentor

    Once you hit Mach 1, you're no longer generating sound waves in the traditional sense. Further increases in velocity do not create sound waves with different frequencies. What's happening is that you're pushing the air out of the way faster than it can form a wave in the first place. This creates a cone-shaped region of high-pressure air which expands outwards after the plane passes, which is where the sound comes from. Increasing the plane's velocity just elongates this cone.
     
  4. Jul 2, 2017 #3
    Interesting, are there any topics you can recommend I read up on to improve my understanding of this phenomenon?
    "sonic boom" only seems to bring up high level synopsis.
     
  5. Jul 2, 2017 #4

    Drakkith

    User Avatar

    Staff: Mentor

    Other than wikipedia, I'm afraid I can't. :cry:
     
  6. Jul 2, 2017 #5

    FactChecker

    User Avatar
    Science Advisor
    Gold Member

    The sonic boom is simply a moving shock wave. Shock waves form in many places on the wing and in the jet exhaust. In fact, in the jet engine exhaust, there is a nested set of shock waves, one inside the other. There is a great deal of information in books on aerodynamics. You can go to Amazon and find many books by searching "aerodynamics shock wave". I have never studied it, so I can not recommend any particular book.
     
  7. Jul 2, 2017 #6

    Nidum

    User Avatar
    Science Advisor
    Gold Member

    Search on ' formation of shock waves on aircraft ' and ' NASA supersonic aircraft '
     
  8. Jul 7, 2017 #7

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    At a distance from the high speed object, the air will have slowed to below sonic speed. (i.e. When the object has passed) the impulse will have spread out and the particle speeds will no longer be sonic. What you hear is not a 'shock wave' but the remnants of it, spread out in time on the journey to the ground into a single pulse of long duration. Boom not crack.
    You get more than one boom when there are multiple initial shock waves.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Why is there a sonic boom at Mach 1.5?
  1. Sonic boom? (Replies: 1)

  2. Sonic boom (Replies: 6)

Loading...