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Hmm, wondering

  1. Sep 21, 2005 #1
    Say you were strapped to a plane, which flies at twice the speed of sound, and you decide to scream....would you be able to hear yourself and would other people be able to hear you?
     
    Last edited: Sep 22, 2005
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  3. Sep 21, 2005 #2

    DaveC426913

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    "...which flies at twice the speed of sound..."

    Not anymore it doesn't...
     
  4. Sep 21, 2005 #3

    FredGarvin

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    It all depends on the relative position of the observer. Who makes the noise and who is supposed to hear it? If the observer and the source are inside the aircraft then it would be the same as both were on the ground not moving at all.
     
  5. Sep 21, 2005 #4
    yes, but without echo
     
  6. Sep 21, 2005 #5

    Galileo

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    You would travel faster then the sound wave you produce, so they will not reach your eardrum. However, you will still hear yourself (if we neglect the enormous wind gushing in your ear). That's because when you speak, your vocal chords vibrate and this vibration is also carried internally to your ears. You might notice how weird you sound when you listen to a tape of your own voice. That's your voice as others hear them. You think it sounds different because when you speak, vibrations from your glottis also travel to your ears, making it sound differently. You still have this effect if you go faster than sound.

    Actually, you don't have to be strapped to a concorde (thank heavens). If you stand on a vast plain with no obstacles (so you hear no echo. Assume the ground doesn't reflect the sound). You won't hear your voice from sound waves in air, since they leave your vocal chords and don't return. You'll still hear yourself for the same reason given above.
     
  7. Sep 24, 2005 #6

    DaveC426913

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    I am extremely dubious about this.

    If I undestand you correctly, you are suggesting that we only hear our own voices from two sources: through our skull, and from an echo.

    Are you suggesting that if I stood in the middle of a gymnasium that is 100 feet to the nearest wall, that I will not hear my voice - except through my skull - until I hear the echo after a 0.2 second delay?


    I've used high efficiency industrial earplugs, the ones that block virtually all external sound. I can hear my own voice, because it is transmitted through my skull, but I don't hear anything else external, including my own voice. And it sounds NOTHING like what you're suggesting.
     
  8. Sep 24, 2005 #7

    russ_watters

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    Since sound waves are pressure waves, they don't just propagate linearly. Otherwise, someone standing behind you wouldn't be able to hear you!
     
  9. Sep 24, 2005 #8
    I think if you were strapped to the out side of a plane travailing twice the speed of sound you would be in a rather terrible position regardless considering the sheer force of the air hitting your ear drums would render you deaf.
     
  10. Sep 24, 2005 #9
    a much simpler solution would be to find someone whose ever flown on the concord and ask them "could you hear anything up there other than the rush of air"

    on the inside of an aircraft the things you say are going at mach 1, and its coming from you and your traveling at mach 2 relative to the ground, so to someone inside the aircraft what your saying is reaching them at normal mach 1 and not mach 3 or something if you are facing them and they are behind you. same thing applies to someone in front of you
     
  11. Sep 24, 2005 #10
    you would also have to take into account localized and delocalized factors aka inertia of the sound waves and of corse the doppler effect
     
  12. Sep 24, 2005 #11
    Hello, this question bothers me as well as I am not quite sure how talking works. I imagine that the vibration of the larynx provides energy to the air, creating a vibration in the air molecues which is the propogated in a wavelike manner outwards? More or less? Well my question, essentially is, will it not seem to the still observer that a large amount of energy was expended by the talker, relative to them with their measuring that the sound itself is super sonic? Will the sound itself create a sonic boom?

    For a much simpler example to see where I am coming from consider the speed of sound of people talking in a Concorde with respect to a ground observer with awesome equipment.
     
  13. Sep 24, 2005 #12

    Galileo

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    Granted. You may hear something, since pressure waves don't spread out as nicely as e.g. light waves and ofcourse some vibrations from your throat will reach your ear. What I`m saying is that, if we ignore that (for the sake of argument), you would still hear yourself. You don't need sound waves for that.

    I didn't describe anywhere how you'd hear yourself with earplugs in.
     
  14. Sep 24, 2005 #13
    In response to my own question with an uncertain answer (almost itself a question), I am guessing that the motion of the air right in front of you will be so slow that the propogating sound waves collide with the slower moving air molecules resuting in the air just heating up? The sound dissapates rapidly as its ordered state is lost quite quickly.
     
  15. Sep 25, 2005 #14
    I guess this question is somewhat related-how is a sonic boom produced?

    Would a fellow on the ground hear 2 sonic booms-one of the plane and other of the screamer? Assume that the walls of the plane offer no hindrance to sound.
     
  16. Sep 25, 2005 #15

    russ_watters

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    Just because a sound wave is supersonic doesn't mean there is a lot of energy associated with it. Sound is a pressure wave in air (or another object). Air is very light, so making a pressure wave propagate in it requires very little energy (humans are capable of producing a few watts at most).
    That doesn't really make sense. A sonic boom is a sound wave, just a higher than average energy one.
    Forget about people talking. For some reason that's confusing people. Consider this: When the Concorde flies over you, can you hear it? Of course!
     
  17. Sep 25, 2005 #16
    Thank you for taking the time to answer my questions but it seems you misunderstood me. I am also wishing to take into account the principle of galilean relativity. That is why I need an observer on the ground and the people talking. Surely he would measure a higher kinetic energy than those in the plane? Or does relativity not apply here?

    I asked about the sonic boom because I made the stupid mistake of forgetting that there is no forward motion of particles (i had looked at it as a bunch of fast moving molecules who were outrunning their own pressure wave, weird mistake...), which is in fact wrong. There is no sonic boom, thank you for helping me clarifying that.

    The remainder though I am not so confident in on their accuracy: Should it not be that since the sound is a traverling pressure wave then the relative slower motion of the particles should be of no consequence and respond due to the seeming higher energy from their frame. The compression wave simply moves a lot faster and I assume that only a fast moving person would not hear a loud whirring sound or something similar?
     
    Last edited: Sep 25, 2005
  18. Sep 25, 2005 #17

    russ_watters

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    The total amount of energy expended by the person talking will match what someone recording the sound measures, but doppler shift will make the power vary.

    Again, sound is a pressure wave and it moves at a constant speed relative to the still air. It isn't as if the person on the plane is throwing a baseball to the person on the ground. In that case, the person on the ground would, indeed, measure a different energy for the baseball than the person on the plane.

    Your last paragraph doesn't make any sense to me.
     
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