Sounds At The Edge Of The Atmosphere ?

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Offline neilep

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Sounds At The Edge Of The Atmosphere ?
« on: 14/07/2009 10:03:22 »
Dearest Soundologists,

As a sheepy I of course luff sound. I am an authority on having ewe's make sound !

See Arthur Carbuthnot Simpkins-Clusternuts here ?

Arthur Inventing Sound Yesterday

He's a fine fellow, a chap of real good sorts.
Arthur has just invented sound ! That's chipper !..we can now take advantage of sound and do all sorts of things.

But, only within the atmosphere. Ewe see, Arthur has yet to invent a way to make sound travel through a vacuum !

look, here's the proof !


Sound Being Heard & Not Heard Earlier Today

Is there a fine line that cuts off sound immediately when it leaves the atmosphere ?..or does it gradually decrease as the atmosphere thins ?

If so, does this mean that sound on top of Mount Everest is slightly quieter than at ground level ?

If one was to be just a gnats todgers width outside the atmosphere and the loudest sound ever happenned just the other side would nothing at all be heard ?

whajafink ?

hugs & shmishes

mwah mwah mwah !

Of Sound Mind ?

Men are the same as women, just inside out !


Offline daveshorts

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Sounds At The Edge Of The Atmosphere ?
« Reply #1 on: 14/07/2009 11:17:45 »
Sound is a vibration which travels. If it is travelling through a gas it travels as a compression wave.

For a compression wave to exist you need enough air molecules to collide with the object that is vibrating and then to collide with one another many times before they reach your microphone/ear.

This can be the case at a very very low pressure probably lower than the pressure around the international space station, however the lower the gas pressure the smaller the forces the gas can apply to any sensor, so the weaker the signal it will pick up. 

For example with the bell in a vacuum jar experiment that you probably saw at school, there was still enough air in the jar to support sound waves, but those sound waves were so weak that they couldn't make the jar vibrate enough for you to hear.

So essentially as you get higher and higher your microphone/ear will pick up a smaller and smaller signal until the forces are essentially zero and you can say that there is no sound.
« Last Edit: 14/07/2009 12:50:34 by daveshorts »



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Sounds At The Edge Of The Atmosphere ?
« Reply #2 on: 14/07/2009 11:29:11 »
Written during Daveshorts post but I'll post it anyway.
There is more than one issue here (as usual).
The sound doesn't just 'stop' somewhere. The waves are transmitted by molecules bumping into each other and the speed depends on the temperature of the gases. Colder means slower. The pressure doesn't make any difference to the speed but sounds will get 'quieter and quieter' because it is difficult to couple the energy from the source (say a loudspeaker) into the gas or into the receiver (your ears).  The density reduces so the 'wave impedance' gets less and less. You would need bigger and bigger earholes / horns to couple enough energy to hear it. It's all a matter of what is called Impedance Matching.
As far as I remember, the pressure halves every 5km as you go up. If there were enough air to keep you alive, then you could hear sounds.