John,
With all due respect to them, it is apparently true, astonishing as it is to
me, that some contributors to this list misconstrue just exactly what an
accelerometer is and can do. If it is the inference solely of bodily motion from
an accelerometer that I think leads to the tenacious misconception, at least as we
think it, of supposed motion at the bridge, and now, both at the agraffes, the
plate flanges, the capo d'astro, and who knows where else, then, surely, there
must be a sensible limit to this. Are we to think now that the piano itself has
'physical, acceleration and motion" and is now, indeed, jumping up and down on the
floor, giving it "physical acceleration and motion", which in turn is now
rendering in motion the 30 story apartment building in which it is contained, and
finally, last but not least, disrupting the orbit of the earth? All because of an
apparently physically accelerative, motile and vibrating A-440? Please! It is
too much!
In point of fact an accelerometer may, depending upon its design, register
vibration; such accelerometers are sometimes called vibrometers. It is possible
to misconstrue the energy of vibration, I guess, for the energy of translation or
rotation, although it would seem hard to me for myself to mistake the two.
Simply placing an accelerometer in contact with an object and confirming then to
oneself such a bodily motion without proper distinction of the two is indeed
fantastic, to use a term bandied about of late. It is also greatly unfortunate
as it has led to a tremendous confusion as to the differentiation of bodily
motion, that is translation or rotation or their combinations, and molecular
motion. As I have said earlier, motion may partake of any of these singly or in
combination, a salient fact apparently misunderstood by many.
I have been given credit by both sides for the first introduction of the very
apt term fantastic in the context of bridge motion, a point of distinction I would
most happily claim, but to give credit where credit is due, as I have pointed
out, it was Richard Brekne and not myself who first used it and that in regard to
the notion of motion at the bridge. Its use in this context is, I respectfully
submit, most apt. I did, perhaps, exceed the bounds of good taste when, in
public, I labeled those of the contrary view, "Ripple Theorists" and was chided
for having done so by him. Conceding to Richard's reprimand I will now content
myself merely with the term "Rock and Rollers".
The coherence or incoherence of motion is, really, central to this issue. On
one hand, the chaotic, random motion of the molecules and atoms of a substance is
at an extreme; that of incoherence. Of course, this is heat; vector analysis is
useless. On the other perfect translatory motion or fixed axis rotary motion of
a body is at the other exteme; that of coherence. In this case the molecules or
atoms are moving in parallel paths. In translation the vectors of all the
particles of a body have equal direction and magnitude; all the particles of the
body have the same acceleration. The motion of the body can be represented by
the center of mass. I attempted to suggest the importance of the distinctions of
motion a month ago, but the contrary camp has paid no attention to these details.
Rotation about a fixed axis is somewhat more complicated but, nevertheless, the
particles of the object move in parallel paths and the motion is highly coherent.
Where motion is incoherent vectors are not employed to measure the extent and
magnitude of this motion. The quantity of energy possessed by the body is used
instead. In the case of heat, as we all know, this is of course, indicated by
temperature and density.
Where motion is coherent, that is the motion of translation or rotation, or
combinations of the two, vector methods are useful, as we all know.
Those of the contrary view, disregard, in my opinion, the importance and
nature of wave motion and elastic action and confuse mightily the nature of
vibration which may occur both as recurrent translation or flexion if you will,
and wave motion. For example, coherent motion in the evidently moving tines of a
the vibrating tuning fork, to return to the chronically misunderstood analysis of
the last month, exists in one and the same body, that is the tuning fork, with
the demonstrably different motion of wave propagation in the base of the tines
and the stem. Even though such motions are evaluated on the particle level in
terms of force, mass and acceleration, on a larger scale they are best judged by
the energy they possess, as should be judged the transfer relations of the
string. With a kind of perplexity I must note that it seems the contrary
proponents have a peculiar characteristic of their view: Where they see motion
they claim it doesn't exist, where they don't see it they claim it does.
John Delacour wrote:
> At 10:51 PM -0800 1/13/02, Delwin D Fandrich wrote:
>
> From: "Phillip L Ford" <fordpiano@lycos.com>
> >>... - make the agraffe and plate system very stiff here so that
> >>they move as little as possible so that string energy is dissipated
> >>as little as possible at this point. This would certainly be easy
> >>enough to prove or disprove. Simply put an accelerometer on an
> >>agraffe and strike the string. If you are correct then the
> >>accelerometer would register zero. In my opinion, if this were to
> >>happen,it would be in your words 'fantastic'.
> >
> >Phil, this is precisely what does happen and, yes, it is proven by the
> >accelerometer tests you've described. The agraffe does move in response to
> >the motion of the string. As does the capo tastro bar. Hence the various
> >schemes to couple the capo tastro bar to the pinblock flange.
>
> >Plate flanges also move in response to the vibrating energy in the strings.
> >It also is proven by the various accelerometer tests that have been
> >conducted over the years. This motion is the basis for the Steinway bell and
> >coupling bolt along with the various nosebolt schemes that have been
> >developed over the years.
>
> At 12:59 PM -0800 12/17/01, Delwin D Fandrich wrote:
> >The accelerometer doesn't care at all about the molecules inside the bridge,
> >the bridge pin or the glue line. It measures only the physical acceleration
> >and motion of the object it is fastened to.
>
> At 9:31 AM -0800 12/19/01, Delwin D Fandrich wrote:
> >Yes. And they are not 'some kind of ripples,' they are the standard wave
> >motions of a vibrating edge-supported diaphragm.
>
> At 1:47 AM -0800 12/19/01, Robin Hufford wrote:
> >In the interests of amicable discussion I would have to say however that
> >as the members of this list are at least able to operate computers and are,
> >evidently, literate, it is not likely they misconstrue what an
> >accelerometer is
> >or what it can do although in point of fact the motion itself is not what is
> >measured but rather the time rate of change of velocity...
>
> I'm afraid, Robin, that likelihood is very real indeed! It really
> does appear that they think it is measuring bodily movement,
> fantastic though you and I find that.
>
> JD
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