If you're running at the speed of sound would you be able to hear your iPod playing?

[D.B. Cooper]

My brother asked me this the other day and it really got me scratching my head. Sound travels into your ears at, well, the speed of sound. But if you're travelling at the same speed then it would never really reach your ears, much like two runners running at the same speed would never draw level with each other.

But I seriously doubt it's that simple.

[Serious Spamurai]

The headphones would form a closed cavity in your ear, so you would still be able to hear sound. However, If you were running away at the speed of sound from some massive speakers, as long as you were ahead of the sound waves, you wouldn't be able to hear it.

[green tea]

If you accelerated your Porsche to light-speed, would it make sense to use your headlamps?

[Wolfcp11]

If you accelerated your Porsche to light-speed, would it make sense to use your headlamps?

Highschool Physics mate...

[chris_uk_83]

Yes, because you couldn't actually reach light speed. Besides, from your point of view the light emitted from your headlights would be travelling away from you at the speed of light. Get your head round that one!

[Simetrical]

It's as Spamurai says. If you ran away from your headphones at the speed of sound, you wouldn't hear anything. But they're moving right along with you; your relative speed to them is zero, so you'd hear your iPod totally uninterrupted. (Except for your flesh possibly being torn from your face by 600 MPH winds.)

[Scorch]

(Except for your flesh possibly being torn from your face by 600 MPH winds.)

Bah! A mere technicality!

[Sphere]

Simetrical is quite wrong. It is not the relative speed between you and your IPod that matters, it is the relative speed of the fluid (gas or liquid) and the observer that matters. Here are four examples that might explain:

(1) If you were standing in front of a speaker and a fluid was moving away from you and towards the speaker at the speed of sound, you would hear nothing. (Both you and the speaker are in a wind tunnel)

(2) Also, if the fluid wasn't moving but you moved away from the speaker at the speed of sound you would hear nothing. (you are in a supersonic jet speeding away)

(3) However, if the fluid wasn't moving and the speaker moved away from you at the speed of sound, you would still hear it as both you and the fluid are stationary and the relative speed is zero. ( Similar to hearing a supersonic jet moving away from you)

(4) Finally, if both you and the fluid were moving away from the speaker at the speed of sound in the same direction, you could still hear the speaker as the relative speed between the fluid and you is still zero. (This is the toughest one to get as the relative speed between you and the speaker is the speed of sound, but not between you and the fluid.)

The fluid in between your ear and your headphones is not moving at the speed of sound so it doesn't have any effect.

[Simetrical]

Simetrical is quite wrong. It is not the relative speed between you and your IPod that matters, it is the relative speed of the fluid (gas or liquid) and the observer that matters.

You're correct, of course, sorry. I didn't think it through carefully. (Someone give me some more mathematics questions, none of this wussy physics . . .)

[Richard]

(Except for your flesh possibly being torn from your face by 600 MPH winds.)

At what speed does that actually occur?

[Cluny the Scourge]

My brother asked me this the other day and it really got me scratching my head. Sound travels into your ears at, well, the speed of sound. But if you're travelling at the same speed then it would never really reach your ears, much like two runners running at the same speed would never draw level with each other.

But I seriously doubt it's that simple.

Yes, you would be able to hear it. The sound waves being emitted from the earphone would be travelling faster than the speed of sound on the same attitude with YOU - as the iPod itself would also be travelling at the speed of sound with you - but at the speed of sound itself as the waves travelled relative to you.

You realise that YOU, right now, and EVERY SOUND WAVE YOU EVER HEAR is ALREADY travelling at faster than the speed of sound as the Earth soars around the Sun? So why are the sound waves being "whipped away" so you can't hear anything? It's the relative rate of speed that matters.

If you think about it you must realise how absurd the idea is. Do you think that when fighter pilots hit Mach 1 that they are suddenly no longer able to hear each other on their headsets? Do you think when you're on a Concorde, when it hits Mach 1 suddenly all the passengers start speaking soundlessly and it feels as though you're in a silent-era movie?

[christof139]

Sure you would hear it, especailly if it is very close to you and especially if you are wearing earphones/speakers in your ear.

Chris

[chris_uk_83]

On that note, if you were to carry around a boombox, and travelled at the speed of sound, then you wouldn't hear it, since the air would be moving backwards past both you and the boombox at the speed of sound.

[Rush Limbaugh]

This has to be the silliest thing ive ever heard, Do pilots hear things in their cockpits when going over the Mach 1 ? I sure hope so.

[chris_uk_83]

Well yes, of course they do, because the air in their cockpits is moving at the same speed as them and the plane they're sitting in.

If any noise is made that can be transmitted through the air in the cockpit, i.e. pilots talking, engine sound etc. then the pilots can hear it. However, if they towed a big speaker behind the plane on a string that vibrations can't pass along (impossible, but bear with me) then they'd cease to hear that when they reached mach 1.

[Rush Limbaugh]

But not if it were in front of them.

[chris_uk_83]

No, quite true.

[Rush Limbaugh]

Explain and besides if your listening to your I Pod I would imagine your using your earbuds.

[Simetrical]

However, if they towed a big speaker behind the plane on a string that vibrations can't pass along (impossible, but bear with me)

They could just have another plane tail them at the same speed.

[chris_uk_83]

Explain and besides if your listening to your I Pod I would imagine your using your earbuds.

Sound travels as vibrations through air. If air is moving away from you at the speed of sound, then any sound made behind you (in relation to the direction of the movement of air, such as in our jet plane scenario) will never reach your ears because the moving air will effectively carry it away faster than it can get to you.

If the noise was made in front of you then the sound would approach you at twice the speed of sound (the speed of the vibrations moving through the air + the speed of the air moving towards you). So you could hear something in front of you but not something behind you.

In the case of the ipod with earbuds there is no movement of air; the air is stationary inside your ears and that is the only place the sound has to travel. Therefore you'd hear it normally.

Sufficiently explained?