Listening to some music, I observe that most of the drumbeat sounds 
appear to be in the region below 200 Hz.

Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a 
wavelength of about 170 cm.

Question: Since the doorway to be bedroom is less than 170 cm wide, does 
that mean those waves can't leave the room? Or does the fact that it's 
more than 170 cm tall negate that?

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Orchid XP v8 <voi### [at] devnull> wrote:
> Listening to some music, I observe that most of the drumbeat sounds 
> appear to be in the region below 200 Hz.

> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a 
> wavelength of about 170 cm.

> Question: Since the doorway to be bedroom is less than 170 cm wide, does 
> that mean those waves can't leave the room? Or does the fact that it's 
> more than 170 cm tall negate that?

  I think you have a misconception of what wavelength means. The misconception
probably comes from those 2D drawings of wave functions.

  A sound wave (nor an electromagnetic wave for that matter) is not some
kind of sine wave which goes through the air. The sine wave function you
see drawn on a picture is just the representation of the function which
tells which direction the wave is "pushing" at certain point (and how
"strongly" it's "pusing"). The sine wave drawing is just a graph which maps
time to amplitude ("strength" of the sound wave), it's in no way meant to
represent the *physical* appearance of a sound wave.

  A sound wave is simply a phenomenon of air molecules pushing (and pulling)
adjacent air molecules. The phenomenon traverses through air. The maximum
strength at which this "pushing" happens is the amplitude of the wave, and
the rate of change between "pushing" and "pulling" is the frequency. The
distance between two "pushing" peaks is the wavelength.

-- 
                                                          - Warp

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Orchid XP v8 <voi### [at] devnull> wrote:
> Listening to some music, I observe that most of the drumbeat sounds
> appear to be in the region below 200 Hz.
>
> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a
> wavelength of about 170 cm.
>
> Question: Since the doorway to be bedroom is less than 170 cm wide, does
> that mean those waves can't leave the room? Or does the fact that it's
> more than 170 cm tall negate that?

Neither. It just means that the sound will spread very uniformly in the bedroom:

http://en.wikipedia.org/wiki/Diffraction#Single-slit_diffraction

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"Orchid XP v8" <voi### [at] devnull> wrote in message
news:4a74431c$1@news.povray.org...

> Question: Since the doorway to be bedroom is less than 170 cm wide, does
> that mean those waves can't leave the room? Or does the fact that it's
> more than 170 cm tall negate that?

Sound (pressure) waves are longitudunal. You are thinking electromagnetic
waves, which are transverse.

Post a reply to this message

somebody <x### [at] ycom> wrote:
> You are thinking electromagnetic waves, which are transverse.

  A photon will travel rectilinearly, not in a sine wave pattern.

-- 
                                                          - Warp

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"Warp" <war### [at] tagpovrayorg> wrote in message
news:4a747a87@news.povray.org...
> somebody <x### [at] ycom> wrote:
> > You are thinking electromagnetic waves, which are transverse.
>
>   A photon will travel rectilinearly, not in a sine wave pattern.

Transverse waves doesn't mean that the particle (or force carrier) travels
sinusoidally. In EM waves, field disturbances (E and B) are perpendicular
(mutually and) to the direction of motion. This is all the way back from
classical EM. Photons come in play with QFT with wave/particle duality, but
that still doesn't make EM waves longitudunal. Further, you cannot pinpoint
a photon's trajectory if you precisely know its wavelength (HUP), which of
course doesn't mean photons follow a sinusoidal path, but it makes the
transition from classical to quantum somewhat more intuitive, I think. A
wave packet (short duration in relation to wavelength) with high enough
energy will look just like a classical particle zipping by, but such
characterizations are scale dependent. With everyday EM signals, we are
mostly dealing in the wave realm.

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Orchid XP v8 wrote:
> Question: Since the doorway to be bedroom is less than 170 cm wide, does 
> that mean those waves can't leave the room? 

Sound waves are longitudinal.
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l1b.html
Hence, they'll fit thru any hole big enough to not diffract the wave as it 
goes through the hole.

Light is (essentially) a traverse wave[1], which is why your microwave oven 
has little holes in the screen so you can see in without getting fried. It's 
working like you think - the light has a frequency high enough that it fits 
thru the holes, while the microwaves are bigger and bounce off.

On the other hand, radio waves are *so* big they go thru lots of inter-atom 
holes at once (like a wave going past a row of pylons holding up a pier) and 
hence will go thru walls where visible light won't.

[1] Of course, it's not a wave, but the math makes it have many of the same 
properties as a wave, and this is one of them. That's why polarizers work 
such as in sun-glasses. You can't polarize a longitudinal wave.

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> On the other hand, radio waves are *so* big they go thru lots of inter-atom 
> holes at once (like a wave going past a row of pylons holding up a pier) and 
> hence will go thru walls where visible light won't.

  I don't think it's as simple as the wavelength determining how well
electromagnetic radiation can traverse through matter. For example, x-rays
have a shorter wavelength than visible light, yet x-rays have more penetration
through matter.

-- 
                                                          - Warp

Post a reply to this message

Warp wrote:
> somebody <x### [at] ycom> wrote:
>> You are thinking electromagnetic waves, which are transverse.
> 
>   A photon will travel rectilinearly, not in a sine wave pattern.

But the math that describes the photon's interaction with nearby photons and 
electrons is based on multiplication (and addition) of complex vectors, 
which means it behaves as if there are conic-section waves involved, 
sometimes. Bascially, any given photon goes straight (until it interacts 
with something, at least), but a collection of photons will statistically 
have some properties in common with waves because of complex 
probabilities[1] involved in the interactions, which is why you get 
diffraction and such.


[1] As in, probabilities in which the probability of an event happening is a 
complex number (more specifically, a complex vector whose length is <= 1), 
and the probability of two events happening is the product of the complex 
numbers, etc.  I found it interesting that someone proved that only 
1-dimensional and 2-dimensional probabilities are consistent, and you can't 
build the same sort of system with (say) 3D vectors.

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

Post a reply to this message

Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> On the other hand, radio waves are *so* big they go thru lots of inter-atom 
>> holes at once (like a wave going past a row of pylons holding up a pier) and 
>> hence will go thru walls where visible light won't.
> 
>   I don't think it's as simple as the wavelength determining how well
> electromagnetic radiation can traverse through matter. For example, x-rays
> have a shorter wavelength than visible light, yet x-rays have more penetration
> through matter.

I think the way it works is this:

X-rays actually are small enough to go between the atoms (altho they'll 
still interact with the electrons, which is why metal still stops them, 
having a "sea" of electrons on the surface).

Visible light hits (most) atoms and gets absorbed, reflected, etc.

Radio waves are physically bigger than the atoms (and the whole house, for 
that matter) so they basically are ghosting along like a car through air.

If you have a stiff screen with water waves going thru, waves much smaller 
than the holes will go thru, and waves much bigger than the holes will go 
thru all the holes at once and reform on the other side. Waves bigger than 
the holes but smaller than two holes will mostly bounce.

The higher the frequency, the "smaller" the photon is physically (as in, the 
more precisely you can know its position).

At least, that's the naive layman understanding I use to sound like I know 
what I'm talking about in newsgroups. ;-)

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> At least, that's the naive layman understanding I use to sound like I know 
> what I'm talking about in newsgroups. ;-)

  Of course it gets more complicated when you consider that some materials
let visible light through (such as glass) while other materials don't, even
though their density might be the same.

-- 
                                                          - Warp

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On Sat, 01 Aug 2009 14:29:00 +0100, Orchid XP v8 <voi### [at] devnull> wrote:

>Listening to some music, I observe that most of the drumbeat sounds 
>appear to be in the region below 200 Hz.
>
>Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a 
>wavelength of about 170 cm.
>
>Question: Since the doorway to be bedroom is less than 170 cm wide, does 
>that mean those waves can't leave the room? Or does the fact that it's 
>more than 170 cm tall negate that?

Sound waves are compressional (is that a word?) and rely on a medium to travel
in. 
So tell your mother that she can't possibly be hearing them. ;)
-- 

Regards
     Stephen

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On 2-8-2009 11:22, Stephen wrote:
> On Sat, 01 Aug 2009 14:29:00 +0100, Orchid XP v8 <voi### [at] devnull> wrote:
> 
>> Listening to some music, I observe that most of the drumbeat sounds 
>> appear to be in the region below 200 Hz.
>>
>> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a 
>> wavelength of about 170 cm.
>>
>> Question: Since the doorway to be bedroom is less than 170 cm wide, does 
>> that mean those waves can't leave the room? Or does the fact that it's 
>> more than 170 cm tall negate that?
> 
> Sound waves are compressional (is that a word?) and rely on a medium to travel
> in. 
> So tell your mother that she can't possibly be hearing them. ;)

Because Andy's mum is not a medium?

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On Sun, 02 Aug 2009 15:40:29 +0200, andrel <a_l### [at] hotmailcom> wrote:

>On 2-8-2009 11:22, Stephen wrote:
>> 
>> Sound waves are compressional (is that a word?) and rely on a medium to travel
>> in. 
>> So tell your mother that she can't possibly be hearing them. ;)
>
>Because Andy's mum is not a medium?

If she were then Andrew could give her a drink then punch her. Which would be
striking a happy medium. :P
-- 

Regards
     Stephen

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On 08/01/09 13:54, Darren New wrote:
> I think the way it works is this:
>
> X-rays actually are small enough to go between the atoms (altho they'll
> still interact with the electrons, which is why metal still stops them,
> having a "sea" of electrons on the surface).

	Here I'd rather view them as photons, to whom I do not want to attach a 
size. Perhaps the wavelength can be used to "fake" a size of the photon, 
though.

	Keep in mind that everything I say is a bit of guessing and not 
actually studied (well, not all of it at least).

> Visible light hits (most) atoms and gets absorbed, reflected, etc.

	Essentially, an electron in an atom will usually absorb a photon only 
if the photon has an energy such that there is an available energy level 
for the electron to go to. For insulators, that means it will (usually) 
have to cross the band gap. For metals, there is no (initial) band gap 
and so electrons of low frequency are readily absorbed. Perhaps that's 
why metals can easily get in the way of radio waves?

	However, I think there are higher bandgaps in metals, and so photons of 
a certain energy range will pass through.

	(Insulators also have higher bandgaps).

	There's no "true" reflection. Quoting Wikipedia:

"Light waves incident on a material induce small oscillations of 
polarisation in the individual atoms, causing each atom to radiate a 
weak secondary wave (in all directions like a dipole antenna). All of 
these waves add up to specular reflection..."

	For stuff like refraction, essentially, the material will get polarized 
by the fields of the photons trying to pass through it. This will result 
in internal electric fields that interact with that of the photon, and 
result in a reduced speed, change in direction, etc. Essentially, the 
relative permittivity that we used in physics courses is simply a model 
of the effect of polarization on the external waves.

	I find it disturbing that Wikipedia's article on refraction has no 
actual physical explanation, but I suspect I'm close. 	

> Radio waves are physically bigger than the atoms (and the whole house,
> for that matter) so they basically are ghosting along like a car through
> air.

	For me, I'd prefer to view it more in terms of photons interacting 
electrically with the solid (and/or taking into account the band 
structure) rather than size. Although as I said, perhaps one could 
produce an "effective" size which matches both what you say and the 
actual theory - although there may be materials that fail the "size" 
theory.

	When I studied solid state physics, we didn't cover interactions with 
light. And I never thought to see if there was a pattern between lattice 
constants (the spacing between atoms in the crystal), and their band 
energies. I actually expect that the relationship between the band 
energies/gaps and lattice constant is poor/nonexistent - which may 
weaken your approach of using size for intermediate frequencies.


-- 
Kotter: "Have you ever considered becoming a vet?"
Epstein: "Uh...Uh no. My brother Sanchez was in the army. Didn't like it 
a bit."

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Neeum Zawan <m.n### [at] ieeeorg> wrote:
>         I find it disturbing that Wikipedia's article on refraction has no 
> actual physical explanation

  Does science even fully agree on the physics of refraction?

-- 
                                                          - Warp

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On 08/02/09 10:01, Warp wrote:
> Neeum Zawan<m.n### [at] ieeeorg>  wrote:
>>          I find it disturbing that Wikipedia's article on refraction has no
>> actual physical explanation
>
>    Does science even fully agree on the physics of refraction?

	Don't really know. However, I think it does agree on the physics behind 
refractive index. It's just a function of the permittivity, which 
electromagnetics precisely describes (in terms of waves). I don't know 
if there's a "particle" explanation.

-- 
Kotter: "Have you ever considered becoming a vet?"
Epstein: "Uh...Uh no. My brother Sanchez was in the army. Didn't like it 
a bit."

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Neeum Zawan wrote:
>     Don't really know. However, I think it does agree on the physics 
> behind refractive index. It's just a function of the permittivity, which 
> electromagnetics precisely describes (in terms of waves). I don't know 
> if there's a "particle" explanation.

IIRC, it's accurate enough that predictions of refraction based on 
permittivity yield correct results, even for fringe cases like negative 
or really high indices of refraction.

-- 
Chambers

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"Warp" <war### [at] tagpovrayorg> wrote in message
news:4a75aa3e@news.povray.org...
> Neeum Zawan <m.n### [at] ieeeorg> wrote:

> >         I find it disturbing that Wikipedia's article on refraction has
no
> > actual physical explanation

>   Does science even fully agree on the physics of refraction?

Yes, AFAIK, but the "problem" is that there are many levels of
understanding. Our everyday experiences can be a hindrance when trying to
understand things at a more "fundamental" level. Refraction (reflection,
dispersion, ...etc) are all emergent and not fundamental processes in QFT,
for instance. There, all you have are 1) emission of a photon  2) absorption
of a photon and the boring case of 3) unhindered transmission of a photon.
There's practically no common ground as far as the fundamental processes go
with classical wave mechanics. But it turns out, that within applicable
domains, their conclusions/predictions agree, and where they don't, we
realize we are out of the respective applicable domains.

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> Light is (essentially) a traverse wave[1], which is why your microwave oven
> has little holes in the screen so you can see in without getting fried. It's
> working like you think - the light has a frequency high enough that it fits
> thru the holes, while the microwaves are bigger and bounce off.

Even this is only the case because the screen is conductive.

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> I think the way it works is this:
>
> X-rays actually are small enough to go between the atoms (altho they'll
> still interact with the electrons, which is why metal still stops them,
> having a "sea" of electrons on the surface).
>
> Visible light hits (most) atoms and gets absorbed, reflected, etc.
>
> Radio waves are physically bigger than the atoms (and the whole house, for
> that matter) so they basically are ghosting along like a car through air.

There's another thing that takes effect in these scenario, and that's quantum
effects: Electromagnetic waves transmit energy in "standardized" packets, with
the energy of a single packet being dependent on the wavelength. Similarly, the
energy levels in whatever it interacts with are quantized, and in order to
interact, the EM packet's energy dose must be fitting to bring the "target's"
energy to a higher "valid" level.

Radio waves are too weak to interact with atomic particles presently bound to an
individual atom, and therefore can only interact with free electrons - which is
why they zip straight through insulating materials without effect, but readily
interact with conductors.

Visible light waves are strong enough to "kick" around electrons within an
individual atom, but they're too weak to kick it "loose" and impart any excess
energy to it as kinetic energy, so they are particularly picky what materials
they will interact with.

X-Rays are strong enough to kick eletrons loose from atoms, and any excess
energy will simply be converted to kinetic energy of the electron, so they will
interact with everything, just depending on the material density.


> If you have a stiff screen with water waves going thru, waves much smaller
> than the holes will go thru, and waves much bigger than the holes will go
> thru all the holes at once and reform on the other side. Waves bigger than
> the holes but smaller than two holes will mostly bounce.

Try, and you'll see it's not true. In water, the ratio of pass-through vs.
bounce is primarily a matter of size of holes vs. size of non-holes.

Post a reply to this message

clipka wrote:
> There's another thing that takes effect in these scenario, and that's quantum
> effects: 

Thank you for that excellent clarification. :-)  Or, rather, correction.

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

Post a reply to this message

> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a wavelength 
> of about 170 cm.
>
> Question: Since the doorway to be bedroom is less than 170 cm wide, does 
> that mean those waves can't leave the room?

No.  Anyway sound goes through solid things as well as air so even if it 
couldn't go through the gap it would go through the wall itself.

Try producing a tone that has the exact wavelength of the distance between 
your speakers and the doorway :-)

Post a reply to this message

scott wrote:
>> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a 
>> wavelength of about 170 cm.
>>
>> Question: Since the doorway to be bedroom is less than 170 cm wide, 
>> does that mean those waves can't leave the room?
> 
> No.  Anyway sound goes through solid things as well as air so even if it 
> couldn't go through the gap it would go through the wall itself.

OK... but presumably the velocity of sound inside a brick wall is 
different to free air, so there would be some kind of diffraction effect?

Post a reply to this message

>> Question: Since the doorway to be bedroom is less than 170 cm wide, does 
>> that mean those waves can't leave the room? Or does the fact that it's 
>> more than 170 cm tall negate that?
> 
>   I think you have a misconception of what wavelength means. The misconception
> probably comes from those 2D drawings of wave functions.
> 
>   A sound wave (nor an electromagnetic wave for that matter) is not some
> kind of sine wave which goes through the air. The sine wave function you
> see drawn on a picture is just the representation of the function which
> tells which direction the wave is "pushing" at certain point (and how
> "strongly" it's "pusing"). The sine wave drawing is just a graph which maps
> time to amplitude ("strength" of the sound wave), it's in no way meant to
> represent the *physical* appearance of a sound wave.
> 
>   A sound wave is simply a phenomenon of air molecules pushing (and pulling)
> adjacent air molecules. The phenomenon traverses through air. The maximum
> strength at which this "pushing" happens is the amplitude of the wave, and
> the rate of change between "pushing" and "pulling" is the frequency. The
> distance between two "pushing" peaks is the wavelength.

...all of which is true. However, a simple experiment with a wavetank 
quickly demonstrates that, for some reason that I don't comprehend, 
large waves won't go through small gaps, and yet small waves will. This 
is the precise opposite of what you would expect, but the results are clear.

(This also explains why animals that use echo-location use such 
high-frequency sounds; they give better spatial resolution. I might even 
go as far as to say that's why electron microscopes give better 
resolution than light microscopes...)

Post a reply to this message

>> No.  Anyway sound goes through solid things as well as air so even if it 
>> couldn't go through the gap it would go through the wall itself.
>
> OK... but presumably the velocity of sound inside a brick wall is 
> different to free air, so there would be some kind of diffraction effect?

Probably, along with all the echo paths and different attenuation amounts of 
different materials at different frequencies it probably explains why music 
sounds horrible from the next room :-)

Post a reply to this message

scott wrote:
>>> No.  Anyway sound goes through solid things as well as air so even if 
>>> it couldn't go through the gap it would go through the wall itself.
>>
>> OK... but presumably the velocity of sound inside a brick wall is 
>> different to free air, so there would be some kind of diffraction effect?
> 
> Probably, along with all the echo paths and different attenuation 
> amounts of different materials at different frequencies it probably 
> explains why music sounds horrible from the next room :-)

It doesn't sound *that* bad. But there is a quite pronounced decrease in 
bass as I walk through the doorway. You listen to the music and you 
think the neighbors will be banking on the wall any minute now, and then 
you step just outside the door and it suddenly seems radpically less 
loud. I don't know if it's because you're out of line-of-sight with the 
speakers or the width of the doorway or what...

Post a reply to this message

On Mon, 10 Aug 2009 10:57:59 +0100, Invisible <voi### [at] devnull> wrote:

>It doesn't sound *that* bad. But there is a quite pronounced decrease in 
>bass as I walk through the doorway. You listen to the music and you 
>think the neighbors will be banking on the wall any minute now, and then 
>you step just outside the door and it suddenly seems radpically less 
>loud. I don't know if it's because you're out of line-of-sight with the 
>speakers or the width of the doorway or what...

Probably due to reasonable sound insulation of the walls and floor. I've lived
in flats where you would think that your neighbours were sitting in the same
room. 
-- 

Regards
     Stephen

Post a reply to this message

In article <4a744518@news.povray.org>,
Warp wrote:

[...]

>   A sound wave (nor an electromagnetic wave for that matter) is not some
> kind of sine wave which goes through the air. The sine wave function you
> see drawn on a picture is just the representation of the function which
> tells which direction the wave is "pushing" at certain point (and how
> "strongly" it's "pusing"). The sine wave drawing is just a graph which maps
> time to amplitude ("strength" of the sound wave), it's in no way meant to
> represent the *physical* appearance of a sound wave.
>
>   A sound wave is simply a phenomenon of air molecules pushing (and pulling)
> adjacent air molecules. The phenomenon traverses through air. The maximum
> strength at which this "pushing" happens is the amplitude of the wave, and
> the rate of change between "pushing" and "pulling" is the frequency. The
> distance between two "pushing" peaks is the wavelength.

Did you read one or more books that explain this and possibly more
with this level of clarity and language (more or less)? Could you cite
their names? 

How come molecules "push" and "pull"? How come the strength varies?
I'd first think that it always gets weaker.

Post a reply to this message

> How come molecules "push" and "pull"? How come the strength varies?

The "push" and "pull" Warp is referring to (I guess) are the forces caused 
by a pressure difference.  This causes the next "bit" of air to be moved, 
thus creating another pressure difference, and the next bit moved, etc, this 
is how the wave propagates - it's the same as a longitudinal wave in a 
slinky spring.

Of course at a molecular level "pressure" is caused by colliding molecules 
etc, but I don't think you need to work at this level of detail to model how 
sound waves propagate, you can just assume that each bit of air has a 
pressure, and pressure differences will generate forces.

Post a reply to this message

In article <4a80139b@news.povray.org>,
scott wrote:

>> How come molecules "push" and "pull"? How come the strength varies?
>
> The "push" and "pull" Warp is referring to (I guess) are the forces caused 
> by a pressure difference.  This causes the next "bit" of air to be moved, 
> thus creating another pressure difference, and the next bit moved, etc, this 
> is how the wave propagates - it's the same as a longitudinal wave in a 
> slinky spring.
>
> Of course at a molecular level "pressure" is caused by colliding molecules 
> etc, but I don't think you need to work at this level of detail to model how 
> sound waves propagate, you can just assume that each bit of air has a 
> pressure, and pressure differences will generate forces.

Alright. But I guess my question is how do I distinguish, for example,
a push from a pull. Should it all be just forces pushing one another? 

But I guess when we talk about pressure, then a context in lower
pressure can be seen as pulling a context in higher pressure. Is that
the sort of pull that we're talking about?

Post a reply to this message

On 10-8-2009 12:19, Stephen wrote:
> 
> Probably due to reasonable sound insulation of the walls and floor. I've lived
> in flats where you would think that your neighbours were sitting in the same
> room. 
The sitting would not be the real problem I guess.

Post a reply to this message

Daniel Bastos schrieb:
> Alright. But I guess my question is how do I distinguish, for example,
> a push from a pull. Should it all be just forces pushing one another? 

Strictly speaking, with pressure there's only "push", with "pull" being 
actually a push in the opposite direction:

(1) Pressure differential exerts a "pushing" force from high-pressure to 
low-pressure region

(2) Pushing force accelerates medium in the gradient zone, speeding it 
up until the pressure differential is compensated

(3) Inertia of the accelerated medium causes "overcompensation" of the 
pressure differential

(4) Pressure differential is now reversed -> back to (1), now with 
opposite direction


This is all that happens locally; at a larger scale, this will cause the 
pressure differential to propagate through the medium as a wave.

Post a reply to this message

On Mon, 10 Aug 2009 17:50:35 +0200, andrel <a_l### [at] hotmailcom> wrote:

>On 10-8-2009 12:19, Stephen wrote:
>> 
>> Probably due to reasonable sound insulation of the walls and floor. I've lived
>> in flats where you would think that your neighbours were sitting in the same
>> room. 
>The sitting would not be the real problem I guess.

Indeed not! Thanks to the walls and the lack of a blunt instrument, I'm still at
liberty :)
-- 

Regards
     Stephen

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:
> Strictly speaking, with pressure there's only "push", with "pull" being 
> actually a push in the opposite direction:

  The "push" and the "pull" are differentiated by the direction in which
the effect propagates. Also a "push" is a higher pressure wave which moves
towards some directin, while a "pull" is a lower pressure wave which moves
in that same direction.

  This can be visualized by imagining a long string of small spheres, each
sphere being connected to the next with a spring. If you push the first
sphere, it will push the next sphere (through their connecting spring),
which will push the next one, and so on. Overall this causes an advancing
phenomenon which traverses through the entire string.

  If you *pull* the first sphere, it will pull the next one, which will
pull the next one, and so on. Again, the overall effect advances in the
same direction and the pushing did.

  If you think what a loudspeaker does, it's exact that: By using air
pressure it "pushes" and "pulls" air alternatively. When it does so in
fast succession, our ears perceive these differential waves as sound.

-- 
                                                          - Warp

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Invisible wrote:
> It doesn't sound *that* bad. But there is a quite pronounced decrease in 
> bass as I walk through the doorway. You listen to the music and you 
> think the neighbors will be banking on the wall any minute now, and then 
> you step just outside the door and it suddenly seems radpically less 
> loud. I don't know if it's because you're out of line-of-sight with the 
> speakers or the width of the doorway or what...

It's because you're out of line-of-sight of the speakers.  They can't be 
bothered to sing to you if they can't *see* you.  They're even less 
intelligent than the Bugblatter Beast of Traal, so closing your eyes 
where they can see you doesn't work as a noise-silencer.

--
Tim Cook
http://empyrean.freesitespace.net

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Invisible schrieb:
> ...all of which is true. However, a simple experiment with a wavetank 
> quickly demonstrates that, for some reason that I don't comprehend, 
> large waves won't go through small gaps, and yet small waves will. This 
> is the precise opposite of what you would expect, but the results are 
> clear.

Hum... I hate to admit this, but it seems you're right: I just hacked 
together a POV-Ray script to simulate a wavetank-kind-of-apparatus (very 
idealized, but still...), initially to disprove your statement - only to 
find that indeed small gaps will not let low-frequency waves pass. 
Changes in gradient will pass through - but not oscillations.

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Warp schrieb:
>   This can be visualized by imagining a long string of small spheres, each
> sphere being connected to the next with a spring. If you push the first
> sphere, it will push the next sphere (through their connecting spring),
> which will push the next one, and so on. Overall this causes an advancing
> phenomenon which traverses through the entire string.
> 
>   If you *pull* the first sphere, it will pull the next one, which will
> pull the next one, and so on. Again, the overall effect advances in the
> same direction and the pushing did. 

Speaking of pressure, this visualization attempt is flawed. I repeat: 
Strictly speaking, there's no such thing as a "pulling" force in air.

A proper way of visualizing it would be an arrangement of *loaded* 
springs: If you displace the first sphere towards you, it will still 
"push" the next one - but less so than the opposing push from the third 
sphere, so the second sphere will give way towards you. Similarly, the 
third sphere will then be pushed towards you by the fourth one, and so on.

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clipka wrote:
> Strictly speaking, there's no such thing as a "pulling" force in air.

Sure there is.  Ever heard the phrase "nature abhors a vacuum"?  That's 
a pulling force.  Any decrease in pressure in an atmosphere will cause 
molecules to be drawn to the source of the pressure difference.

--
Tim Cook
http://empyrean.freesitespace.net

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>> ...all of which is true. However, a simple experiment with a wavetank 
>> quickly demonstrates that, for some reason that I don't comprehend, 
>> large waves won't go through small gaps, and yet small waves will. 
>> This is the precise opposite of what you would expect, but the results 
>> are clear.
> 
> Hum... I hate to admit this, but it seems you're right: I just hacked 
> together a POV-Ray script to simulate a wavetank-kind-of-apparatus (very 
> idealized, but still...), initially to disprove your statement - only to 
> find that indeed small gaps will not let low-frequency waves pass. 
> Changes in gradient will pass through - but not oscillations.

Weird, isn't it?

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Tim Cook schrieb:
> clipka wrote:
>> Strictly speaking, there's no such thing as a "pulling" force in air.
> 
> Sure there is.  Ever heard the phrase "nature abhors a vacuum"?  That's 
> a pulling force.  Any decrease in pressure in an atmosphere will cause 
> molecules to be drawn to the source of the pressure difference.

"Natura abhoret vacui" is a very old misconception. At 0 degrees Kelvin, 
nature has no problems with vacuum.

What is commonly percieved as a pulling force of the vaccum is in 
reality a stronger pushing force (due to collisions of molecules) from 
the high-pressure region than from the low-pressure region. As a matter 
of fact, *both* exert a pushing force.

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On 08/11/09 03:51, Tim Cook wrote:
> clipka wrote:
>> Strictly speaking, there's no such thing as a "pulling" force in air.
>
> Sure there is. Ever heard the phrase "nature abhors a vacuum"? That's a
> pulling force. Any decrease in pressure in an atmosphere will cause
> molecules to be drawn to the source of the pressure difference.

	That's a push, not a pull.

	If you dip a straw into a glass of water, and "suck", all you're doing 
is forcing your diaphragm to go down a bit, causing your lungs to 
expand. This creates a region of low pressure in your lungs, and the 
atmospheric pressure *outside* is what will actually push the water into 
your mouth - it's a push by the atmosphere, not a pull by you.

-- 
Whose cruel idea was it for the word "Lisp" to have a "S" in it?

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Neeum Zawan wrote:
>     That's a push, not a pull.
>     If you dip a straw into a glass of water, and "suck", all you're 
> doing is forcing your diaphragm to go down a bit, causing your lungs to 
> expand. This creates a region of low pressure in your lungs, and the 
> atmospheric pressure *outside* is what will actually push the water into 
> your mouth - it's a push by the atmosphere, not a pull by you.

*thinks about it*  Seems to me like six of one, half-dozen of another, 
but then again, centrifugal force is a nonexistent force conjured up to 
describe motion in a particular frame of reference, too...from an 
outside point of view, the math is easier/makes more sense when you 
reduce everything to a single set of common elements with no overlap.

But having a word for 'suck' is handy for us lay-people--lets us 
describe life in a shorter phrase than "region of low density of 
pleasantness at self causes misfortune to be pushed onto me", as "life 
sucks".

;)

--
Tim Cook
http://empyrean.freesitespace.net

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On Tue, 11 Aug 2009 21:39:33 -0400, Tim Cook <z99### [at] gmailcom> wrote:

>"life sucks".

No! Death pushes ;)
-- 

Regards
     Stephen

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On 08/11/09 20:39, Tim Cook wrote:
> *thinks about it* Seems to me like six of one, half-dozen of another,
> but then again, centrifugal force is a nonexistent force conjured up to
> describe motion in a particular frame of reference, too...from an
> outside point of view, the math is easier/makes more sense when you
> reduce everything to a single set of common elements with no overlap.

	Oh sure. If your goal was just to have simple models, then your 
interpretation is fine (and even more accurate than centrifugal force).

	Note that I didn't say there _isn't_ a force on your part. Pulling down 
that diaphragm requires force - about the same amount of force that the 
atmospheric pressure applies to push the air in.

	Same as a vacuum cleaner. The mechanism requires a force/energy to 
*push* air out from the back. This causes a vacuum and atmospheric 
pressure then pushes the air into the tube from the other end - taking 
the mess along with it.

> But having a word for 'suck' is handy for us lay-people--lets us

	Well, I didn't imply you don't suck (no pun intended).

	Just think of the process of moving that diaphragm down as sucking 
(which it is).


-- 
If Wile E. Coyote had enough money to buy all those Acme goods, why 
didn't he just buy dinner?

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On 08/12/09 06:59, Stephen wrote:
> On Tue, 11 Aug 2009 21:39:33 -0400, Tim Cook<z99### [at] gmailcom>  wrote:
>
>> "life sucks".
>
> No! Death pushes ;)

Obligatory:

http://www.theatrecrafts.com/humour_darksuckers.html

-- 
If Wile E. Coyote had enough money to buy all those Acme goods, why 
didn't he just buy dinner?

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On Wed, 12 Aug 2009 09:38:55 -0500, Neeum Zawan <m.n### [at] ieeeorg> wrote:

>On 08/12/09 06:59, Stephen wrote:
>> On Tue, 11 Aug 2009 21:39:33 -0400, Tim Cook<z99### [at] gmailcom>  wrote:
>>
>>> "life sucks".
>>
>> No! Death pushes ;)
>
>Obligatory:
>
>http://www.theatrecrafts.com/humour_darksuckers.html

LOL
-- 

Regards
     Stephen

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A sound wave can be diffracted, this helps it to travel.

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clipka wrote:
> At 0 degrees Kelvin, 
> nature has no problems with vacuum.

Actually, it does. It like big vacuums better than small vacuums, tho.

http://en.wikipedia.org/wiki/Casimir_effect

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

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