Production Of Sound

[hazelm]

Suddenly an old fun question (the unpopulated forest and falling tree question) has become very serious to me.  I have a feeling this was taught in third grade and I missed it - probably one of my poison ivy days.  Anyway, please tell me.

 

I just Googled the question "how do sound waves make sound?" and got this answer:  "Sound is produced when something vibrates".  That is the ear drum.  Yes?  So, serious answer is there is no sound in the wave.  it has to echo back from a hearing ear drum.  I was confused.

Edited October 6, 2017 by hazelm

[exchemist]

Suddenly an old fun question (the unpopulated forest and falling tree question) has become very serious to me.  I have a feeling this was taught in third grade and I missed it - probably one of my poison ivy days.  Anyway, please tell me.

 

I just Googled the question "how do sound waves make sound?" and got this answer:  "Sound is produced when something vibrates".  That is the ear drum.  Yes?  So, serious answer is there is no sound in the wave.  it has to echo back from a hearing ear drum.  I was confused.

No. Sound is the wave. The wave is produced when something (a source) vibrates in a medium that can transmit sound. Air is the commonest example but water would do equally well. Anything vibrating in a medium makes the bit of the medium next to it move back and forth, setting up waves of alternate compression and rarefaction, which then travel outward through the medium - at the speed of sound. 

 

The eardrum ( a detector) vibrates in sympathy when sounds waves arrive at it.   

Edited October 6, 2017 by exchemist

[hazelm]

No. Sound is the wave. The wave is produced when something (a source) vibrates in a medium that can transmit sound. Air is the commonest example but water would do equally well. Anything vibrating in a medium makes the bit of the medium next to it move back and forth, setting up waves of alternate compression and rarefaction, which then travel outward through the medium - at the speed of sound. 

 

The eardrum ( a detector) vibrates in sympathy when sounds waves arrive at it.   

I'll take your word for it since you know more about it than I.  Doesn't sound right but must be. So the answer to the  old question of the falling tree is yes, there is sound even if there is no one there to hear it.  Strange.  Thanks.

[exchemist]

I'll take your word for it since you know more about it than I.  Doesn't sound right but must be. So the answer to the  old question of the falling tree is yes, there is sound even if there is no one there to hear it.  Strange.  Thanks.

Just like light. Do we really think the stars stop shining when we are not looking? 

[hazelm]

Just like light. Do we really think the stars stop shining when we are not looking? 

Good point.  Only, in the case of the stars, someone is seeing them.  Supposedly there is no one in that forest.  Of course, I always wanted to ask "not even a small field mouse? Or a Katydid?

[exchemist]

Good point.  Only, in the case of the stars, someone is seeing them.  Supposedly there is no one in that forest.  Of course, I always wanted to ask "not even a small field mouse? Or a Katydid?

Well I would invoke Ockham's Razor. This simplest explanation consistent with the observations is that both sound and light continue, regardless of whether or not they are observed.

 

Furthermore, thinking abut it, the light we observe today from stars was emitted millions of years before sentient life on earth existed. So nobody was around to observe it at the time of emission. So how would that work?  

 

You'd go nuts trying to make such an idea work, and even if you succeeded, the result would indistinguishable from the assumption that light is emitted regardless of observation. So what would be the point, apart from a job creation scheme for men in white coats?    

[hazelm]

Well I would invoke Ockham's Razor. This simplest explanation consistent with the observations is that both sound and light continue, regardless of whether or not they are observed.

 

Furthermore, thinking abut it, the light we observe today from stars was emitted millions of years before sentient life on earth existed. So nobody was around to observe it at the time of emission. So how would that work?  

 

You'd go nuts trying to make such an idea work, and even if you succeeded, the result would indistinguishable from the assumption that light is emitted regardless of observation. So what would be the point, apart from a job creation scheme for men in white coats?    

I know.  I always saw waves as just waves traveling somewhere.  They would have been silent.  So the presence of sentient life would not have entered into the question, would it?   You have posed a quandary that I must ponder on.  I'll just add it to my long list of scientific quandaries.  Thanks - I think.  :-)

[exchemist]

I know.  I always saw waves as just waves traveling somewhere.  They would have been silent.  So the presence of sentient life would not have entered into the question, would it?   You have posed a quandary that I must ponder on.  I'll just add it to my long list of scientific quandaries.  Thanks - I think.  :-)

Of course, you could choose to define "light" and "sound" as the sensations we perceive through our eyes and ears, rather than the physical phenomena giving rise to the sensations. But then you would need to invent new terms for these physical phenomena. So you'd be back to square one. 

 

To say a sound wave is silent until it is heard different. That is an arguable proposition. Just as light does not illuminate anything until there is something in its path for it to illuminate. But the sound or light waves, i.e. the physical phenomena, have to be assumed to be still there in order for the relevant physics to work.  Or so it seems to me.

[Maine farmer]

Of course, you could choose to define "light" and "sound" as the sensations we perceive through our eyes and ears, rather than the physical phenomena giving rise to the sensations. But then you would need to invent new terms for these physical phenomena. So you'd be back to square one. 

 

To say a sound wave is silent until it is heard different. That is an arguable proposition. Just as light does not illuminate anything until there is something in its path for it to illuminate. But the sound or light waves, i.e. the physical phenomena, have to be assumed to be still there in order for the relevant physics to work.  Or so it seems to me.

Our eyes and ears are receivers that collect light and sound, and it is up to the brain to process and translate the information, so you could ask if sound and light  exist without sentient life forms.    It's like asking if the universe can exist without sentient life.  If it can, then who would be around to care?

[hazelm]

I am not into physics.  I am doing exactly what Exchemist said and he does make sense.  All I know so far is that waves contain (or are caused by) moving electrons.  Then there are  two definitions I found.  Electromagnetic waves (wherever they fit in) are "transverse" and sound waves are "longitudinal".  Yet the picture of moving sound waves seems to show them going the same direction as electromagnetic waves. 

 

Be back later.  Thanks.

[pzkpfw]

Take a look at a speaker sometime (of a home stereo, "HiFi", or similar). Watch the speaker cone jiggle.

 

A combination of an electromagnet and permanent magnet (there are other types of speaker, but this'd be most common) make the speaker cone move in and out. It's physically moving the air. Making pressure waves - vibrations - in the molecules of air.

 

All I know so far is that waves contain (or are caused by) moving electrons.

Technically, there are electrons in the atoms in the molecules of air (O₂ etc), but at the level of sound vibrations, we're not talking at the scale of electrons.

 

Those vibrations travel through the air (or as above, it could be water or something else, maybe even the string of a tin-can kids "telephone") to your ear.

 

Your eardrum is vibrated by the jiggling air, and through a series of very small bones jiggles a little tube full of water. In that water are little hairs, these are connected to nerves that run into your brain - and that's how you perceive the sound.

 

 

If your stereo is turned on and playing your favourite music, the speakers are vibrating the air, whether you are in the room listening to it or not.

 

 

Yet the picture of moving sound waves seems to show them going the same direction as electromagnetic waves.

That's just because they are illustrating the pressure waves, high and low pressure; the vibrations that constitute the sound. They are not literal illustrations of the actual movement of the molecules that make up the medium (air, water, whatever).

Edited October 7, 2017 by pzkpfw