"sean" wrote in message
om...
"George Dishman" wrote in message
...
"sean" wrote in message
om...
"George Dishman" wrote in message
...


Right, now this is a pattern produced by flexing of the plate or
by interference of sound travelling through the plate and being
reflected from the boundary. Clearly the medium is essential, no
plate, no resonance.

Hi George
I think whole system is elastic and on very short time scales, parts
of the `medium` resonate before parts of the container do.
In a violin it is the string then the `air and violin case` . The
string also vibrates the air as well as the frame and it almost could
be said that the air first begins to vibrate within the frame and it
then sets off sympathetic vibrations within the wooden frame which

You could say that but you would be wrong. The string does not
couple to the air directly because it is thin and cuts through
the air instead of moving it. Try bowing an electric guitar with
no amp. The string moves the bridge and the soundpost and bass
bar transmit the motion to the bulk of the panels. It is the
large surface area of the panels that moves the air like a piston.

Hi George
THats not true George.

True, I should have said it couples very poorly rather than
"does not couple", sorry. The point is that by far most of
the sound is produced by the method I outlined, not direct
coupling from string to air.

If you were right then a rubber band stretched
between your fingers and plucked would be inaudible but both of us
know that it is indeed audible . The only way to hear the band is by
the air vibrating the air about your ear. So in fact the string
resonates the case AND the air and in turn to lesser or greater
degrees each sympathetically induces further vibrations in the other.

They are coupled and all have a slight effect. If you pluck
the string once, the oscillation will die away slowly over
a large number of cycles. The energy lost per cycle is small
so the other effects can have only a small influence on the
motion of the string.

If you stopped reading books and watching the world around you you
would understand physics better

Go get yourself an empty bottle ;-)

http://www.phys.unsw.edu.au/~jw/violintro.html#bridge


then feeds back into the air and string but mostly the energy from all
3 dissapates to the concert hall and in turn to the structure , which
then disappates some back to the air and some to the outside or
foundations etc...

In different situations I think diofferent parts of the system
resonate firstbut remember this started out as my response to davids
claim that a medium could not exhibit resonance! The sad thing is that
even if you agree with me that he is wrong on that point

I don't.

There you go George you say just for the sake of it that you dont
agree with me yet later on you admit that a medium like air IS part of
a resonating system and I supply you with your own quotes to back this
up. So you contradict yourself when you say that you Do agree with
him that a medium cannot resonate within a system. Make up your mind,
can a medium within a system be said to exhibit resonance?

The system can exhibit resonance, the medium can be part of the
system, but I wouldn't say the medium was exhibiting the resonance.

Have you got that empty bottle yet? Good, now blow over the
top and see if you can get a note. The note is determined
by the shape of the bottle. Now try it without the bottle.
The air is still there but do you get a nice clean note?

Bexcause if
you say that NO a medium in a system cannot be said to exhibit
resonace then you immediately contradict yourself with the quotes
later reproduced in this post . One being that if one removes the air
or medium from a resonating system then the remaining part of the
system experiences an increase in amplituide or stored energy or Q or
whatever particular term you wish to call it . And the Q could only
increase in the remaining part of the system if it had only been
present in the air/medium before it had been removed.

One classic resonant system is a mass, spring and damper.
The mass bounces on the spring and the oscillation dies
away exponentially as energy is turned into heat in the
damper. Take away the damper and the spring bounces for
longer. I believe the letter "Q" is used because it is
a "Quality Factor", so reduce the damping and you increase
the Q. Removing the air means that sound is no longer
produced so energy is not lost that way. There are still
losses in the string and wood but Q will increase due to
the reduced loss.


I think actually George it is you who must learn what resonance is as
you seem to constantly offer opposing views of what it is.

I am trying to show examples that highlight the essential
features of resonance. With the bottle example, if you
remove either the bottle or the air you won't get the
resonance. Fill the bottle with helium and the frequency
will change. Clearly the medium plays a part but without
the bottle there is no resonance.

he will still
continue to post that a medium cannot resonate. He doesnt seem to
listen and learn.

I have said I don't agree with you several times. I have also given
you several examples of resonance in systems without waves. If you
listen and think about those, you may learn what the word "resonance"
means.

How about we stick to this short definition: Resonance is `when a
vibrating system responds in amplitude with an alternate driving force
where the two frequencies are similar. `

Fine. The key phrase there is "vibrating system". First you have
a system that vibrates, then you drive it at its natural frequency.

So for instance, if two vibrating sources in an open water tank

What is the natural frequency of water in an open tank? Put in
just a single source running at that frequency and you would have
resonance. However, the resonant frequency in a tank of water is
determined by the dimensions, typically when the wavelength on
the water is comparable to the size of the tank. Put a vibration
source in the middle of the Atlantic and you just get ripples
moving away from it and dying out before they can hit a continent.
You get travelling waves, not resonance.

as I
described earlier set up nodes of maxima patterns. (which are what you
call interfernce yet still can be said to be stationary maxima or ` a
vibrating system` or stored energy)If a third vibrating source is
added to create a triangle of 3 sources then the maxima pattern
changes and one would get a different pattern of nodes instead of
bands and the central part of the vibrating medium now or central
maxima has increased amplitude. Now that is a definition of resonance
according to the textbook definition. I have a vibrating system,the
water in between the two sources that has staionary maxima between the
two sources .And then I add a new driving force of similar wavelength
and the maxima, still stationary, now have their amplitude increased.
That is all within the textbook definition.
I think you are being dogmatic by saying a medium cannot` resonate `.
Yet there is no restriction I have read in textbook definitions of
resonance that say only solid objects like wood or metal can resonate.

Absolutely. Let me give you another example that you might find
'contradictory'. The Sun is just a ball of gas, pure medium, yet
it exhibits resonance! The subject of helio-siesmology is greatly
concerned with resonance. I talk below of "containment" and in
this case it is the boundary between regions of different density
that provides the container.

The only prerequisite is that the system has to be vibrating, and the
word system does not exclude a medium like air or water
You are being dogmatic in saying that only a vibrating string
contained at either end that has additional energy input and has its
amplitude increased can be said to resonate and yet, When water in a
vibrating container has the vibrations increased in amplitude those
maxima within the water increase. That is to me a vibrating system
that responds with an increased amplitude to additional driving force.

Of course, I agree, but there you have a container. All I am
saying is that the thing you are considering has to have a
natural vibration. Air in a container does, air without the
container doesn't.

The only difference I can see is that the strings `resonance` has a
longer sustain then the water in the tank. For instance if I vibrate
the tank the nodes appear and when I stop the vibrations they will
disappear very rapidly probably within a second

They dissapear progressively as the end of the ripples from the
source moves over the surface at the speed of the waves in the
medium.

whereas the string
will sustain for a few seconds although it must be said that the water
when the outside vibration source stops probably still has a sustain
of those nodes its just that they become too small to see with our
eyes.
And if you consider a string that is vibrating and then continuously
plucked that string continues exhibiting resonance. But surely when a
container of water is continuosuly vibrated , each shake is
essentially the same as each pluck of the string in that it is a
series of additional driving forces and the result is a continously
vibrating container of water . That water is exhibiting resonance
becuase the waves contained within the system have their amplitudes
continuosly added to by additional driving forces of similar
wavelength which in turn sustains the amplitude of the stationary
nodes. And if a different frequency of vibrations was introduced those
particular nodes would disapeear as they did not have the defining
"additional driving force of similar wavelength "

That's right, but again you are talking of "a container of water"
and "the waves contained within the system". The containment is
an esential part of the system. We talked about this befo

.... My argument would be that in an infinite
universe as long as the density is homogenous in all parts of this
infinite universe the density at any one point is constant or average.

OK. In fact any change in homogeneity could act as a boundary.

The changes in density in the Sun are an example of what I meant.

Therefore one important prerequisite for a resonating infinite medium
is met.
Secondly I thought about it and actually a medium can resonateand
standing nodes of maxima CAN occur in our observable world in water or
etc in open uncontained systems . This can be done simply by having 2
identical energy sources creating waves and at the point or in the
region between the two sources there are standing waves produced
| | |

A | | | B

| | |

Above A and B are vibrating sources in an open uncontained medium and
the vertical lines denote maxima where overlapping waves create
standing waves .

This is _interference_, not _resonance_!

For resonance you must be able to store the energy _after_ the
driving force has gone. Please try to understand what the word
means. The interference pattern exists only as long as the sources
remain active.

That is such a load of nonsense George. That is physically impossible
for those maxima to instantly disapear and if you believe that then
you believe in magic. Those maxima or nodes will disapear but within a
short time frame as the energy disapates to the surrounding air,

They disappear at the speed of the waves in the medium.

just
as a string stops vibrating over a slightly longer but still short
time frame of maybe a second or two . I bet if one took high speed
photography of my above illustration one could actually see the water
maxima decay over a few hundreths of a second maybe even a tenth of a
second. Do you really seriuosly believe that the maxima disapear
instantaneously with no decay?

No, nor did I suggest they would. Remember my diagram:


Take a very long taut wire and send two bursts of a wave
of the same frequency travelling in opposite directions
from the ends towards the cent

--\/\/\/\/\/\/\----------------------/\/\/\/\/\/\/\/---
--- ---

When they meet in the middle, they will create a standing
wave pattern of while they overlap (it's twice the height
but I can't show that) and pass through each other

-----------------\/\/\/\/\/\/\------------------------

after that they just separate though

--\/\/\/\/\/\/\----------------------/\/\/\/\/\/\/\/---
--- ---

The interference pattern in the middle is a wave phenomenon
but it is not resonance.

You have to imagine the two bursts moving in the direction
of the arrows. When they meet there is a small region of
interference (shown with '|') that grows and then shrinks.

-----------\/\/\/\/\/\/\----/\/\/\/\/\/\/\/------------
------------\/\/\/\/\/\/\--/\/\/\/\/\/\/\/-------------
-------------\/\/\/\/\/\/\/\/\/\/\/\/\/\/--------------
--------------\/\/\/\/\/\||/\/\/\/\/\/\/---------------
---------------\/\/\/\/\||||/\/\/\/\/\/----------------
----------------\/\/\/\||||||/\/\/\/\/-----------------
-----------------\/\/\||||||||/\/\/\/------------------
------------------\/\||||||||||/\/\/-------------------
-------------------\||||||||||||/\/--------------------
-------------------/|||||||||||||/---------------------
------------------/\/||||||||||||\---------------------
-----------------/\/\/||||||||||\/\--------------------
----------------/\/\/\/||||||||\/\/\-------------------
---------------/\/\/\/\/||||||\/\/\/\------------------
--------------/\/\/\/\/\/||||\/\/\/\/\-----------------
-------------/\/\/\/\/\/\/||\/\/\/\/\/\----------------
------------/\/\/\/\/\/\/\|\/\/\/\/\/\/\---------------
-----------/\/\/\/\/\/\/\/--\/\/\/\/\/\/\--------------
----------/\/\/\/\/\/\/\/----\/\/\/\/\/\/\-------------
---------/\/\/\/\/\/\/\/------\/\/\/\/\/\/\------------


Show me the experimental proof that a
system as I propose defies conservation of energy and actually some
energy according to you `disapears instantaneously` from our universe.
This is seen in water tanks etc experiments and shows how classical
waves can resonate in an open system and create maxima (in this case
bands rather than nodes)
So theoretically in a open infinite universe the aethger medium could
resonate and nodes of maxima would be possible.

Nodes and antinodes occur due to interference.

Yes,Nodes and antinodes are seen in interference patterns . But if
you read a textbook definition they are also said to occur in standing
waves. And is not a string vibrating in essence a standing wave? A
vibrating string is where the wave energy travelling down the string
is reflected back at the boundary, the guitar bridge, and is
superimposed on the incident wave creating a staionary node in the
midle of the string with the standing wave as having the same length
as the length of the confined string.

Exactly, and the point I am trying to get across is that something
to reflect the energy and keep it contained is the key to turning
travelling waves into a resonant system.

And finally how to account for the sources A and B in a infinite
classical universe? If the universe is infinite and of homogenous
density aether, wave energy of all wavelengths travels across any
point from all directions at any time . So at any point in this
universe a situation that duplicates the above illustration can occur
where the overlapping wavefronts cancel out as in a closed system and
create maxima. As the similar wavefronts come from all directions and
not just the two as in the above illustration instead of bands of
maxima one gets nodes. In otther words this is how a wave only atom
can be explained in a infinite universe using examples of resonating
open systems of mediums already observed in our world.
The medium in which
these nodes appear is not one object but can consist of air, gas,
water sand etc.
It isnt then the cavity that resonates but the medium within the
cavity that resonates

No, it is the combination. That's why I emphasise it is a system
not just the medium. For example your plate would not resonate if
^^^^^^^^^^^^^^^^^^^
it were infinite in size, it is the boundaries that create the
resonance.

Here you do admit that a medium can resonate

I suggest you read it more carefully again, I said exactly the
opposite.
You speak in riddles and contradictions. What is the opposite of me
saying a medium can resonate? Answer: You say It CANT resonate... I
assume thats what you mean by "the opposite".

I didn't use the words "the opposite".

Then you suggest that a
medium CAN resonate, within a system, by saying "no its a
combination". Ah,! a contradiction .

No, not a contradiction, that is the whole point of my saying it
that way! You have to ask yourself what is the difference between
"the combination can resonate" and "the medium on its own does not
resonate". How can both be true?

You just said a medium cant
resonate and then you suggest it can . Maybe what you mean to say is
that a medium can resonate within a contained system? Is that what you
mean by " no its the combination" ?

What I mean is that the medium can be part of a system that resonates.
It is "the system" that is resonating, not just the medium.

You can drive to work in a car but you can't drive to work on a piston
even though pistons are an essential part of the car. You get resonance
from a bottle of air but you don't get resonance from the air on its
own even though the air is an essential part of the bottle/air system.


Yes but hopefullly I have shown that in an infinite open system there
is always wave energy arriving and that in an open system resonance
can occur with maxima.

Resonance does not mean maxima and you have not deemonstrated how
energy can be stored on a small fixed region using only an
infinite and homogenous medium.

Where did I ever say that Resonance is just maxima?

You said "I have shown ... that in an open system resonance can
occur with maxima." when in fact all you had shown was that
maxima could occur. You phrasing suggests you were using "with
maxima" to imply they were the means by which you had demonstrated
resonance rather than "with" meaning "in addition to".

That doesnt even
make sense. Its kind of like me describing an orange and you saying
"NO ,you are wromg an orange isnt just orange"..
Resonance does not just mean maxima but maxima can be seen in a
resonating system.

Absolutely correct, that is what I said, but you had only shown
you could get maxima (by interference) and then claimed you had
shown resonance.

The central point of a vibrating string is a maxima
where the displacement of string mass is greatest.
And in a pendulum the maximum displacement and therefore stored
energy is in the end weight of the pendulum. Is that not a node or
maxima in both central point of a guitar string and end weight of a
pendulum?
Regarding whether or not a infinite medium can store energy in a
fixed point like a node how about this: Two vibrating sources of

Try showing it with one source.

energy A and B are infinitely far apart and have been vibrating at the
same frequency for infinity and their two wavefronts approach and
overlap as follows


A | | | | | | | | | | |

| | | | | | | | | | | B

This duplicates the earlier diagram where the two sources are a finite
distance apart and as long as the two sources have been vibrating
infinitely then when they do reach and overlap a series of standing
waves or maxima nodes occur exactly as in the finite example. And
these nodes will remain in the same spot and retain the same amplitude
as long as A and B have not moved. And finally viewed up close at one
maxima the maxima can be said to be duplicating in all respects the
same conditions and appearances as a similar maxima within a finite
container where the additinal driving force on that container is
exerted continuosly and is said to be a resonating system.

"Resonance does not just mean maxima"

In a `violin in air` situation the air within the frame also resonates
and this amplifies and feeds back into the whole system so it is
technically the string ,bridge, frame and air within the cavity that
resonate.

No, technically there are several independent resonators that are
coupled mechanically.

How petty. Thats just another way of phrasing my description.

You said "technically" and if you want to get into the
technical details we need to extend this to include
coupling coefficients and stuff. It gets a lot harder
and I don't want to get into that.

Thats
like me saying..."putting a plug into the drain will prevent the
bath from emptying".... and then you saying.." No, technically a
stopcap is coupled manually with the outflow port of a water system to
prevent leakage"

Suspend two pendulums of slightly different length on a common
mounting. Start one swinging and after a while the other will
swing. Eventually the first will stop and then the whole thing
reverses. Each swings at its own frequency.

Glue the two weights together and the combination swings at an
intermediate rate. There is a significant (technical) difference
between saying the string vibrates and excites other resonances
and saying they all resonate as a single system.

Yes the string I am sure would still vibrate in a vacuum. And if the
body were also removed yes the string itself would also vibrate . So
the conclusion is that a system of one or many parts can resonate .

Right, but remove the bridge and it wont. The string must be held
in tension, it must be fairly free to move over most of its length
but has to be clamped at the ends to reflect the wave. All those are
required for it to contain the energy of the vibration.

Of course this is true. What I was suggesting that if the string were
clamped or held rigid but the body were removed so as to remove
vibrations from a closed or semi closed wooden frame from the system.
Sort of like stretching a rubber band between your fingers.Effectively
your fingers are not part of the resonating system except that they
contain the rubber band.

But that is exactly what makes them a part of the resonating system.

The fact is, remove the clamps the string
would flop down to the floor of the room or whatever and it would be
impossible to input a energy to the string in the first place and I
never suggested that a medium or object could resonate without any
input energy.

No, but you are suggesting the rubber band will resonate without
the fingers when you say an _open_ medium can resonate.

A medium /object will also only resonate (or vibrate and
give stationary nodes) if there is energy input and the medium/object
density remains the same . For instance a bell will resonate even if
is floating in air by being thrown as long as the bells density
remains the same and if it were possible to continually strike it with
the same input driving force while mid air its resonance would not
decay.

Absolutely, and it would also resonate in a vacuum if excited by
a pure sine wave from a nearby electromagnet. By adjusting the
source frequency for maximum amplitude, you can find the resonant
frequency of the bell.

In an infinite universe the density can remain the same and the
energy input can remain constant as I have explained earlier and
therefore a uncontained medium like aether could exhibit resonance as
nodes of energy

Nope, to get nodes you _must_ have something to reflect the
waves back so they interfere with themselves.

You have shown you can get interference in an unbounded medium
which was never in dispute. You still seem not to be listening
to what the word "resonance" means. All the arguments you have
oferred are applicable to interference, not resonance. Forget
about waves for a moment and consider how a mass and spring
system or a pendulum can be resonant.

I have already answered this but I will again but if you dont mind I
will stick to my one textbook definition of resonance as yours seems
to change depending on the point you are arguing...
`Resonance is where the amplitude of a vibrating system responds to an
additional driving force of similar frequency.`

Hence... a medium in this case is constrained

That's the point Sean (or is it Jay BTW?), to make a "vibrating
system" you have to _constrain_ the medium.

and vibrating and
contains energy stored as maxima minima where the reflected waves of
the enrgy in the medium overlap and superimpose.
Or.. a string constrained is vibrating and the energy is stored as
maxima and minima in the string where the reflected waves of the
energy in the string overlap and superimpose.


Next,...
An additional driving force of similar frequency is exerted on the
medium and the amplitude/energy of the maxima and minima is increased
or sustained

Or,...An additional driving force of similar frequency is exerted on
the string and the amplitude/energy of the maxima and minima is
increased or sustained

In experiment each continued shake of the container sustains the
resonance of the system of the container and the medium and in the
case of the string each additional pluck of the string sustains the
resonance of system being the string and the clamped frame that holds
it
Your
second point doesnt make sense in grammatical terms. What do you mean
by "..but nothing else.." in the sentence above?

I meant with nothing to refect the waves back so they can be
contained in one area thus storing energy.

George

That means You said. quote ...."If you said you can get resonance
with waves in a medium but nothing else then you are also
wrong."..unquote.

That is correct, you need something to constrain the medium. Even
a change of density can be enough.

In response to me saying..."In other words David is completely wrong
in saying that a single particle or object vibrating is the only
manifestation of resonance."...

That is correct. A spring/mass system is resonant but a mass
on its own isn't, and nor would a massless spring be.

Note that my line you responded to (obliquely and with intent to
obfuscate) actually wasnt saying that a medium uncontained could
resonate but that David was wrong to assume that a medium vibrating in
a container was not exhibiting resonance.

If that's what you meant then I would not have responded but it
is not what the post I saw said, and you have continued over the
last several posts to argue that open, unconstrained medium can
resonate.

Yet you knew that if you
responded directly to my point you couldnt say that David was right in
saying that a medium in a system wasnt resonating because even above
you admit that a system with a medium and a container can be said to
resonate. So to avoid the embarrasment of having to admit David is
wrong to think a medium in a system cannot resonate you instead
fabricate the untruth that I was always insisting that only a medium
without a container could resonate . Thats absolutely untrue as
initially my point to David was quite clearly that a medium in a
container could be said to resonate.
And I know what your response will be to this will be . You will say
something contradictory that implicitly agrees with me yet tries to
make it seem you dont agree as in one of your below quotes
previously..

No, I'll just let you say it for me .....

GD.. "No, it is the combination. That's why I emphasise it is a system
not just the medium. "...



(Sean..goodness that sounds like you admit a medium constrained can
resonate)


GD..""If you said you can get resonance with waves in a medium but
nothing else then you are also wrong."...


(Sean ..there you go again, the implication in that statement is that
with nothing else, ie no container , there can be no resonace which
implies that with a container the medium and the system can resonate)

I think all of the above are very clear in the distinction
they are drawing.

GD.."Of course no air, no resonance in this case, but for the string,
bridge and fret resonance, putting the violin in a vacuum chamber
would actually increase the Q of the resonance since a large part of
the power lost from the string goes into moving the air via the
mechanical linkages to make the sound we hear."...


( Sean.. there you go again suggesting that in a vacuum without the
air to `absorb` or hold some of the resonant energy the energy
amplitude has to increase in the remaining parts of the system.
Implicit in your statement is then the assumption that with air in the
system the energy stored is less in the other parts of the system and
therefore the only conclusion is that if the air stores some of the
energy and it is part of the resonating system then a medium can be
part of a resonating system which according to David is not possible)

The energy is mainly stored in the string and some is transferred
to the flexions of the body. There is only energy stored in the air
in the form of the Helmholz resonance (as in blowing over the bottle)
but the more important aspect is that the air acts principally like
the damper in the mass/spring system. It removes energy from the
'vibrating system' of your definition and converts it as the sound
we hear.

George