I had this discussion with my dad about a question he had asked. Basically he said:

If a plane flies faster than the speed of sound, will he be able to overtake his own sound and hear itself?

(let's leave behind the fact that he can run out of fuel or that the sound finishes before he hears it)

I disagreed because it seemed illogical to me, but we never actually found hard evidence to determine if the statement is true or false.

Can a plane actually do this?

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    $\begingroup$ If the plane is already flying faster than sound, then the sound is never "ahead" of the plane to be overtaken - it is behind you as soon as it is generated. You would still hear sound as transmitted through the airframe though. If you start below the speed of sound and accelerate through it, you do indeed "catch up" with the sound you've already generated, resulting in a sonic boom. $\endgroup$ – IanF1 Apr 16 '15 at 7:00
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    $\begingroup$ Physics.SE might be a better place for this question. $\endgroup$ – kevin Apr 16 '15 at 9:35
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    $\begingroup$ While I agree that this question may be a decent fit for Physics, I disagree that it is off-topic here. VtLO $\endgroup$ – CGCampbell Apr 16 '15 at 11:17
  • $\begingroup$ @CGCampbell I'd say it's a better fit for Physics as this can be applied to any object going faster than the speed of sound (granted that only really happens in aviation) $\endgroup$ – Cole Johnson Apr 16 '15 at 14:59
  • $\begingroup$ As you've probably gathered from the accepted answer, your dad has it backwards. When not moving the plane always hears itself ("hear" means the same as you can hear yourself talking). When it's faster than the speed of sound it can no longer hear itself because it left the sound behind it (minus whatever sound transmitted via the airframe). $\endgroup$ – slebetman Apr 17 '15 at 17:09

I think you are missing some physics knowledge, so let's start from here:

If a plane flies faster than the speed of sound

Sound is a compression wave that travels through air. Given a certain air temperature, the sound will travel at different speeds through the air.

If a plane flies faster than the speed of sound means that the compression waves it is generating will remain behind the aircraft:

enter image description here

image from here

will he be able to overtake his own sound and hear itself?

As you can see on the right picture, if the aircraft is travelling faster that the speed of sound, the compression waves it generated in the past will remain behind. If it would stop/slow down, the waves would then catch up with the plane and a person on board would be theoretically capable of hearing them.

  • $\begingroup$ does this also means that the dictance between plane and his sound will become greater over time? $\endgroup$ – BRHSM Apr 16 '15 at 7:05
  • $\begingroup$ @CoderGuy depends on the velocity, if it is not Mach 1, yes. $\endgroup$ – Federico Apr 16 '15 at 7:07
  • $\begingroup$ @Frederico mach 1 is the speed of sound right? $\endgroup$ – BRHSM Apr 16 '15 at 7:20
  • $\begingroup$ @CoderGuy yes, but labeled so that you do not have to know the temperature. (and it is FEderico, no extra r) $\endgroup$ – Federico Apr 16 '15 at 7:22
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    $\begingroup$ @corsiKa I find it difficult to board a non-stopped plane. $\endgroup$ – Federico Apr 16 '15 at 15:08

Sound does not travel in a straight line. It radiates evenly in all directions. Therefore, even if your moving super fast, and I mean fast, you would not be able to catch it. I know you're trying to think if you made a really quick lap around the planet could you catch it, you would simply blow through the place it was made. But there are echoes that you could hit if you moved fast enough but even then it would not be the sound itself but a vibration left on the surrounding matter.

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    $\begingroup$ Welcome to aviation.SE! Is "a lap around the plant" meant to be "around the plane"? And what does a "vibration left on the surrounding matter" mean? $\endgroup$ – Pondlife Jan 22 '17 at 19:56
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    $\begingroup$ @Pondlife Most likely, a lap around the planet. $\endgroup$ – David Richerby Jan 22 '17 at 23:36
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    $\begingroup$ @DavidRicherby You're right, that makes a lot more sense! $\endgroup$ – Pondlife Jan 22 '17 at 23:46
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    $\begingroup$ Isn't all sound "vibration of the surrounding matter?" Isn't that basically the definition of sound? It's merely a mechanical vibration, no? $\endgroup$ – reirab Jan 23 '17 at 2:49

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