Air and Space

[TimbaLanD]

Can we class the space between air particles as “vacuum”?

[insane_alien]

yes. there is nothing in it so i don't see why not.

[gcol]

yes. there is nothing in it so i don't see why not.

 

But sound, people insist, can not travel through a vacuum, so when is a vacuum not a vacuum?

[YT2095]

well technicaly, it`s just a relative area of a given pressure, conpared to say Liquid air this that we breathe is indeed a "vacuum" or sorts by comparison.

the inter subatomic areas are a vacuum for sure if we exclude nuclear forces (I think we can).

as for going UP the scale to a moleclar level, when yes, it also is "vacuum" or at least fee space, but then there are such things as van de walls forces at play there too and electo-statics, but ignoring them again, and yes, a Vacuum it is

[5614]

You might want to look into things called virtual particles... if you want to get technical

[gcol]

O.K. then, step two:

 

What must be the separation in any units you like, between molecules of any gas you like, before sound can not be propagated?

[insane_alien]

gcol, it can propagate at any pressure where the gas still acts as a fluid and not a few widely spaced bouncy balls

[gcol]

Is it the general opinion that the answer to the OP is an unequivocal "yes", or is it a "well it all depends"?

 

There is ongoing debate about the definition of Vacuum, and a previous thread asking can sound travel through a vacuum was left as "well, it all depends on vapour density, and what is a vacuum", (as I remember it).

 

Perhaps the answer is that the the minimum vapour density of gasses which will still allow sound propagation is not quantifiable. Throw in the uncertainty as to the nature of true vacuum, and can there be a definitive answer?

[5614]

According to quantum mechanics (QM) there is no such thing as a vacuum (ie. an area containing absolutely nothing)...

 

Although QM is definately not the "general opinion"... I'd agree with gcol saying that the answer really should be "yes, between particles there is a vacuum".

 

TimbaLanD: the virtual particle thing (what I was referring to when I said QM) is not something you should really worry unless you want to - and you probably don't!

[padren]

But sound, people insist, can not travel through a vacuum, so when is a vacuum not a vacuum?

 

For sound to move through a space, particles have to bump into each other. Even in a dense gas, there would be no sound in the vacuum between the particles, and the only way for sound to be audiable in the gaps is for particles to move in and carry it there, which means its no longer a vacuum.

 

 

I forget how it works exactly...I think its that particles are always bumping around into each other and net effect is expansion unless pressure is applied to keep them condensed.

As you get into thinner areas of gas, like the upper atmo, where gravity isn't pushing air particles down onto the lower altitude air particles keeping it compressed, you have fewer and fewer particles bumping into each other, until eventually it is not a medium by which sound can transfer as they just aren't bumping into each other enough.

 

 

I think its worth making a distinction between "between the air" vacuum and space vacuum in that if you teleported in a single air particle into the gap between two particles of air at sea level, the other air particles would react to it by bumping into it, and having an overall tiny increase in air pressure.

 

But in space, if you did that in nearly outer space, the gaps between the particles are large enough that its hard to call it a single volume, but a collection of particles that now and then happen to bump each other.

 

Those are my off-the-top-of-my-head thoughts, I have no idea if they reflective of what goes on though - its been too long since I was in school.

[TimbaLanD]

So, why is air better at carrying sound than solids? This is making me think even more about sound!! I am just thinking how different solids when bumped into each other make different sounds. What makes this sound so unique? I am confused now!!!

[YT2095]

sound travels Faster in liquids and solids than in air.

[sabbath]

So, why is air better at carrying sound than solids? This is making me think even more about sound!! I am just thinking how different solids when bumped into each other make different sounds. What makes this sound so unique? I am confused now!!!

 

As yt says sound travels faster more in solids and liquids. and the last thing i heard from school is that sound travels fastest in the solid medium. sound is transmitted through the transferrence of energy (vibrations) unlike light which is the energy itself, hence it cannot travel through a vacuum.

 

However, I think we hear best through the medium of gas/air because air particles can enter our ears where the specific vibrations of the particles can be sent as impulses to the brain, and interpreted in the auditory area. It is possible because gases are fluid or have movement.

 

Though if you try placing your ear against a metal chair for example and cover your other ear, if there is movement anywhere in the room, the sound would have been amplified. I often do this when I get bored in class, and feign sleep.

 

Ever saw oater movies or an indiana jones film? don't they put their ears to the ground and listen for the sound of the galloping of their enemies' horses coming? this usually happens in cowboy movies...except for Brokeback Mountain of course.

[sabbath]

unlike light which is the energy itself:D

 

that is an erroneous statement. light and sound are forms of enery, as all of matter are. but light is in the form of photons which exhibits wave-like and particle-like properties. so light is the particle itself, whereas sound is only the energy/vibration transferred elastically from one particle to another such as gas molecules.

[gcol]

whereas sound is only the energy/vibration transferred elastically from one particle to another such as gas molecules.

 

O.K., but which part, for want of a better word, of the molecule, and do you mean physically touching, or a field effect? If a field effect, then the question of range needs to be considered.

[sabbath]

I would say physically touching.

[gcol]

That seems to me to be the only intuitive answer if sound energy is a physical transfer. I suppose that the extreme limit of sound propagation should be be where electrons in the outermost electron shells of two atoms, however briefly, actually coincide? This should mean that the "vapour density" necessary for sound propagation should be least for atoms having the largest electron orbit?

[Klaynos]

OP: true vacume = anywhere where there is no particles. So yes the area between molecules in air is vacume, but only when viewed on a short time span and on a small scale (as air molecules will move into the area). There are virtual particles in this area. QM tells us there is no true vacume.

 

The sound question, read, and also read up on what all the constants in this equation mean. If the speed tends to 0 then effectively there is no sound transphere...

http://en.wikipedia.org/wiki/Sound_speed#Speed_in_ideal_gases_and_in_air

 

Also note, electrons NEVER physically "touch", this is not required for a sound wave to propergate.