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I certainly have heard a lot about the conservation of energy (of all forms) however when it comes to sound in particular, I just can't figure out how it could possibly be recycled into another energy form. When sound (rings of energy vibrating air molecules) is sent, how could that energy get turned into something else? Sure a tiny bit could hit something and turn into a tiny amount of kinetic energy, but doesn't the vast majority of it just fly off into oblivion?

One hypothesis I came up with was perhaps the sound/energy waves get turned into heat as they bump each molecule, but I wasn't too positive where that energy would go so... ?

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    $\begingroup$ The sound waves dissipate their energy into the medium's particles as random kinetic energy (i.e., heat). $\endgroup$ – honeste_vivere Oct 29 '16 at 14:11
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    $\begingroup$ yes. ultimately this thing we call 'heat' , the agitation of molecules $\endgroup$ – docscience Oct 29 '16 at 15:03
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Imagine your cellphone rings. It's tiny speaker is vibrating in and out, producing sound waves that have this form:

enter image description here

Image Source : Tutorvista.com

Because the speaker is just repeating the same tone, unless you have it set to a song, the pattern of sound waves will be a longitudinal wave that has areas where the sound is strongest (compressions), and then areas where the sound is weakest (rarefactions).

It's pretty much the same effect when you answer the phone, but now you are making a more complicated set of compressions and rarefactions because you are talking with far more random sound effects than the speaker produces.

As the sound waves travel through the air, they heat it up very slightly, and that's where the energy that started in your lungs and pushed air through your vocal cords ends up, heating the air around you.

I certainly have heard a lot about the conservation of energy (of all forms) however when it comes to sound in particular, I just can't figure out how it could possibly be recycled into another energy form. When sound (rings of energy vibrating air molecules) is sent, how could that energy get turned into something else? Sure a tiny bit could hit something and turn into a tiny amount of kinetic energy, but doesn't the vast majority of it just fly off into oblivion?

Depending on how dense the air is, the vibrating air coming out of your mouth as you speak will be carried to other molecules, with the further molecules vibrating less as the energy is diluted as heat.

It does fly off into oblivion, which is lucky when its a voice you particularly don't want to hear, all sounds around you get mixed together from different sources and fade away.

So energy is conserved, but what was a concentrated burst of energy when you spoke ends ups as shaking up a large bulk of air molecules, all by a tiny, tiny amount.

My point is that energy is not lost, but rather spread out further and further until it can do no useful work.

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  • $\begingroup$ Useful work by having say a recorder detect the sound waves and transform them to changes in the magnetic tape, or the phone converting your sound to electrical signals. Of course, conversion of sound vibrations in your ear into neural excitations that your brain interprets as sound. The cool thing is we can detect such weak energies, and detection is transforming it to something else $\endgroup$ – Bob Bee Oct 30 '16 at 2:17
  • $\begingroup$ @BobBee hi Bob the first time I heard (sorry) about the ability of the ear to have the range it does I was amazed. I am sure you know all this ....... I can't remember exactly but I think it's 20 hz to 20k Hz, or of that order, a huge range. Off topic, and again you know.... but funny thing about bats, they must shut their ears, scream their heads off and open ears for detection. Get it slightly wrong and they deafen themselves. $\endgroup$ – user108787 Oct 30 '16 at 2:33
  • $\begingroup$ Hi @CountTo10, thanks for that pointer, it is amazing how they see with it. Do you know if they can form acoustically images (i.e., synthetic aperture) or is it just directional and intensity? BTW, my ear has been hearing less than that, I think more internal noise than sensitivity. What does screaming their heads off do, how does that not interfere with the received sound? In RF radar and comms any simulataneous transmission that is not adaptively cancelled at the receiver blinds you, Co-site interference $\endgroup$ – Bob Bee Oct 30 '16 at 3:06
  • $\begingroup$ @BobBee. It was a Dawkins book I read years ago, the blind watchmaker I think. He spent a chapter on it. It's an arm's race between the insects,who grow fur as stealth absorption against the bats, the bats then shift frequencies, and the bats have had doppler inbuilt going way back....then bugs fly really low to get ground reflection to confuse the bats...the bats need to know their mates calls .....the parallels between evolution and the last century of aircraft and radar are uncanny. I have forgotten most of it, but he plots the escalation of strategic modifications very well. $\endgroup$ – user108787 Oct 30 '16 at 3:28
  • $\begingroup$ but if it did get absorbed by the atmosphere, doesnt that mean after a very long time, there would be no more useful energy just a very hot world? $\endgroup$ – John Hon Oct 30 '16 at 6:02

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