Ron and all,
Have you some sort of reasoned refutation of the points I offered in the post
you so vigourously dismissed out of hand. You say the energy transfer model I
referred to is in essence meaningless then immediately say, however, it is not so -
should the impact be that of an airplane instead of a mosquito. It requires no
great powers of observation to conclude that the impacting plane will greatly
affect the ship - much more so than a mosquito. This entire description was
preperatory to pertinent observations about the string/bridge/soundboard
interaction, as I pointed out. .
I find myself in this debate reluctantly taking issue with you and others
whose lucid, informed opinions I generally agree with and always find interesting
but I do so for factual, intellectual reasons in the interest of presenting
another, and what I think is, a substantially better and more accurate point of
view. Is it? Beats me! but I think so. In the dialogue generated thereby we
should all arrive at a better understanding and be the better for it. This is the
utility of this list. As far as I can see the only way this can be achieved is by
point and counterpoint, argument and counterargument. Categorical rejections of
reasoned but opposing arguments are evidently useless. We should proceed
accordingly.
If the implications of the use of the fork analogy and its behavior in driving
the board are not convincing then try a little experiment which I have already done
myself. Tape and weight a piece of copper wire to the sound board, cut it off a
few feet away and then bring it in contact with a tuning fork. Even when
completely slack the sound of the fork, albeit it rather weak, will be heard coming
from the soundboard. This is because periodic strain energy is transmitted to
the board through the wire and the board then develops flexing areas as described
in the earlier post. In anticipation of the objection that I am applying this
test directly to the soundboard I would say that this the same whether the point of
application is the bridge or soundboard. I used the board because the forks I have
are weak sounding. A stronger source would work as well when the point of
application is at the bridge. Surely no one would argue that the wire in its
slackened condition is physically shaking the board in the manner you suggest is
done to the bridge by the string, and this, when the point of attachment is
substantially less stiff had the point of attachment been at the bridge.
Admittedly, if the wire is put under tension it will transmit the strain energy
from the fork to the board more effectively but in neither case is there any
shaking of the board.
If one were to consider molecular motion to be the same as visible, organized
motion of a material, which is a major, major stretch, then one could say that
some shaking is taking place. This, however, will be invisible, imperceptible,
and is, in fact, what I come back to - stress disturbance.
A similar effect can be achieved, I am told, when using a violin, and at a
greater distance.
In the example given earlier of the fork placed in contact with the plate
surely you are not going to argue that the plate is now experiencing ripples
passing across its surface as in a pond as a result of this shaking? Yet it
radiates sound in essentially the same fashion as the soundboard or any structure.
Where it differs from a soundboard in this regard is that the standing waves or
modes, generated in it have less amplitude, of course, than those in a soundboard
due, at least partially, to the difference in materials. Similarly, would one
suppose that the stiff, hard rim of a good piano is actually shaking when the fork
is brought into contact with it and a perceptible increase in sound is heard?
Regards, Robin Hufford
Ron Nossaman wrote:
> > The point that I am trying to make is that it is the
> >ratio of the mass of the objects and the duration of contact that determines
> >whether the energy transferred will in fact cause translation, rotation or a
> >stress disturbance in the oject tself.
> > For example, a mosquito hitting head on an aircraft carrier travelling
> >in a direction opposite to it when both are travelling at thirty miles an
> hour
> >will not in any way affect the velocity of the carrier even though their
> >closing speed is 60 miles an hour, notwithstanding vector addition, because
> >the energy of the mosquito on a molecular and atomic level is not sufficient
> >to propagate a stress disturbance through the carrier that is adequate to
> >reorganize the individual vectors of the particules which comprise the
> >carrier. However, the particle velocity of some of the particles on the
> >carrier will be changed, they in turn transmit a change to others and
> thereby a
> >stress disturbance of limited duration passes through a part of the ship which
> >has gained a little bit of energy, essentially in the form of heat. The
> >mosquito however, will suffer profound change both in structure, that is as
> >deformation, and velocity as the vectors of the individual particles, so to
> >speak, overcome by those of the ship and acceleration occurs.
>
> The velocity of the aircraft carrier will be influenced because the
> mosquito has mass. That's pretty inescapable. The disturbance of the
> structure of the carrier will be localized as it is pretty quickly lost in
> molecular "background noise" and dispersed as heat, but the disturbance
> does take place. It's a matter of scale, as you said. The rough equivalent
> of the same event would be something considerably smaller than a grain of
> salt being dropped on a soundboard. In either case, the event has so little
> resemblance to a string driven soundboard as to be meaningless. I propose a
> more accurate analogy of your Mosquito being a British aircraft, which
> would much more closely approximate the initial energy transfer between a
> string and soundboard assembly. In this case, I suspect the collision of
> the Mosquito with the aircraft carrier will not only be clearly heard, but
> felt by the malingerers hiding out in the head. I suspect a transverse wave
> could be fairly easily detected in the hull as well.
>
> Ron N
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