# When a plane flies faster than the speed of sound, does the distance between plane and sound increase?

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?

• 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. Apr 16, 2015 at 7:00
• 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). Apr 17, 2015 at 17:09
• @slebetman thanks for clearing that up but what do you mean with the ariframe? Apr 18, 2015 at 9:10
• Airframe = body, wing, tail etc. Basically the physical structure of the airplane. Of course the airplane is more than just the airframe. An airplane = airframe + control surfaces + electronics + engine etc. Apr 18, 2015 at 9:12
• @slebetman ahh i understand, it's the frame on which the aircraft's housing is build and the part that keeps the plane together Apr 18, 2015 at 9:17

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:

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.

• does this also means that the dictance between plane and his sound will become greater over time? Apr 16, 2015 at 7:05
• @CoderGuy depends on the velocity, if it is not Mach 1, yes. Apr 16, 2015 at 7:07
• @Frederico mach 1 is the speed of sound right? Apr 16, 2015 at 7:20
• I don't know much about planes, but I know the "stopped" phase is really bad for planes. :o Apr 16, 2015 at 15:07
• @corsiKa I find it difficult to board a non-stopped plane. Apr 16, 2015 at 15:08

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

Of course he can!

He can catch up because he is faster. But that does not fully answer this brilliant question. We want to know what would practically happen:

But what does it sound like?

We want to catch up with our own sound, so it needs to get away from us first. That means we fly slower than sound in the beginning. For example, your father shouts

Can you hear me?

in the direction of travel.

Now, we accelerate our aircraft to be faster than sound. With that, we create a shockwave in front of the plane, which can be heard as the sonic boom. Practically, the whole situation is really loud

We hear no difference.

It does get louder, but not noticeable.
But in theory, we can think about what we would hear when it would be quiet, and we could use the air molecules in front of our shockwave as a microphone.

But if we could hear it anyway?

Then, we would actually hear "Can you hear me?", but in very deep voice, so deep that it is to deep to be heard by a human. The words were spoken in some seconds, but we reach the sound waves only slowly over some minutes.

We would hear a very deep voice...

And as we creep up to our sentence from behind, we catch the last syllable first, because that is what we said at the latest time, so it had less time to go away. The direction of the time in the sound is flipped.

Speaking the words backwards!

It's a very deep

# ¿em raeh uoy naC

• @VolkerSiegel actually what you would hear is ¿em raeh uoy naC Feb 3, 2020 at 16:49
• @Jpe61 Oh yes, absolutely! I had thought about the direction for a second or so, and dismissed it. Too early, obviously. Thanks! Feb 3, 2020 at 17:07

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.

• 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? Jan 22, 2017 at 19:56
• @Pondlife Most likely, a lap around the planet. Jan 22, 2017 at 23:36
• @DavidRicherby You're right, that makes a lot more sense! Jan 22, 2017 at 23:46
• Isn't all sound "vibration of the surrounding matter?" Isn't that basically the definition of sound? It's merely a mechanical vibration, no? Jan 23, 2017 at 2:49
• downvotes are because of "even if your moving super fast, and I mean fast, you would not be able to catch it" which is very incorrect. Feb 4, 2020 at 15:34