Date: Wed Aug 5 11:21:13 2009

Author: Dick Heckathorn

Subject: Re: Stroking an Aluminum Rod with Rosin

Post:

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Greetings,

=20

Are you referring to the article from T=E2=80=9DPT?=20

=20

What I posted after are longitudinal waves in the rod. It just shows =
that the second overtone is louder than the lowest or what I call the =
fundamental. At the beginning and I have to dampen out the overtone.

=20

Dick

=20

From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On =
Behalf Of Paul Nord
Sent: Wednesday, August 05, 2009 10:47 AM
To: tap-l@lists.ncsu.edu
Cc: Paul Nord
Subject: Re: [tap-l] Stroking an Aluminum Rod with Rosin

=20

Dick,

=20

My first guess would be that you found both transverse and compression =
vibration modes of the rod.

=20

I'd think that the compression mode would be higher in pitch since the =
wave would essentially travel at the speed of sound through the bulk =
solid.

=20

The transverse wave would be more like the vibration of a string. To =
hear an audible tone you probably found some harmonic of that vibration =
mode. The fundamental for a rod of that size would be a few Hz at most.

=20

A torsional vibration mode is also possible. But that probably would =
not couple well to the air.

=20

Ok... now that I've flapped my gums about this I should probably go find =
our rod and actually try this! ;-)

=20

Paul

=20

=20

On Aug 5, 2009, at 9:31 AM, Dick Heckathorn wrote:





Greetings,

=20

There is a short article from the Chicago group on page 56 and 57 of The =
Physics Teacher Jan 1986 which follows (OCR software sure is nice.)

=20

TWO=E2=80=91TONE ROD

=20

Scott Welty stood before us, holding an aluminum rod (about 1 cm diam. =
and a meter long) at its midpoint. Putting rosin on his fingers, he =
stroked the rod and set it ringing. The sound was loud, clear, and =
persistent. With the rod still ringing, Scott made it rotate in the =
horizontal plane (somewhat like a baton twirler), and we heard a Doppler =
shift quite clearly. Nice!

=20

Next, Scott held the rod at a position1/4 of its length from its upper =
end (the =E2=80=9C1/4 position"), and stroked it again. This time the =
pitch of the sound was higher as most of us had expected, though some =
asked for an explanation from nearby friends. So far, so good. Nothing =
unexplained.

=20

But then, again holding the rod at its midpoint, Scott stroked it much =
harder and more rapidly, putting more and more energy into it. Suddenly =
the sound dropped to an obviously lower pitch =E2=80=91 the usual pitch =
was not heard at all (Fig. 4)! "What is going on here?"! we wondered.

=20

In order to convince ourselves that he was not playing some kind of =
trick, we asked Scott to repeat this several more times. He did, and we =
became satisfied that we were observing a phenomenon new to us.

=20

Could we produce a similar effect, but starting with the higher pitch =
obtained by holding the rod at the 1/4 position? Scott tried this, but =
it failed to work.

=20

Could the failure be related to lack of a symmetry =E2=80=91 imposed =
boundary condition? With Ed McNeil holding the rod at the 1/4 position =
from the lower end, Scott again held it at the 'A position from its =
upper end and stroked vigorously. To our disappointment, the rod still =
did not break into a hoped =E2=80=91 for, lower pitch resonance.

=20

Still other experiments, conducted by holding the rod at various =
intervals along its length, produced sounds of other pitches, but none =
of them matched the lower pitch produced by the energetic stroking with =
the rod held at its midpoint.

=20

We found no explanation, so this obviously needs more investigation. If =
you can get your aluminum rod to behave in a similar fashion, would your =
group be interested? Do you suppose you could find out what is =
happening? If you do, won't you let us know? Have fun! =20

=20

TPT January 1986 p 56 and 57

=20

A aluminum rod I now have and used many years when held at the center =
with just one finger and thumb will resonate at a certain frequency when =
rubbed with finger and thumb covered rosin. Next if I grab the rod with =
2 or 3 fingers and thumb, it will resonate at frequency 1/3 the original =
or what I call the original frequency.

=20

Happy Rod Strumming

=20

Dick

=20

=20

From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On =
Behalf Of Thomas Senior
Sent: Monday, April 27, 2009 12:23 PM
To: tap-l
Subject: [tap-l] 2007 PIRA Business Minutes

=20

Hello Tappers,

I have just posted the minutes on the PIRA Forum at =
www.pira-online.org for your reading =
pleasure.=20

If you need a copy emailed to you, drop me a line at =
.

=20

Have Phun,

=20

Tom

=20

=20


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Greetings,



Are you referring to the article from T=E2=80=9DPT? =



What I posted after are longitudinal waves in the rod. It = just
shows that the second overtone is louder than the lowest or what I
call = the fundamental. At the beginning and I have to dampen out
the = overtone.



Dick



*From:= * tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.edu] *On = Behalf Of *Paul Nord
*Sent:* Wednesday, August 05, 2009 10:47 AM
*To:* tap-l@lists.ncsu.edu
*Cc:* Paul Nord
*Subject:* Re: [tap-l] Stroking an Aluminum Rod with = Rosin



Dick,



My first guess would be that you found both = transverse and
compression vibration modes of the rod.



I'd think that the compression mode would be higher = in pitch since
the wave would essentially travel at the speed of sound through =
the bulk solid.



The transverse wave would be more like the = vibration of a string.
To hear an audible tone you probably found some harmonic = of that
vibration mode. The fundamental for a rod of that size would be a =
few Hz at most.



A torsional vibration mode is also possible. = But that probably
would not couple well to the air.



Ok... now that I've flapped my gums about this I = should probably
go find our rod and actually try this! ;-)



Paul





On Aug 5, 2009, at 9:31 AM, Dick Heckathorn = wrote:



Greetings,



There is a short article from the Chicago group on page = 56 and 57
of The Physics Teacher Jan 1986 which follows (OCR software sure is
= nice.)



TWO=E2=80=91TONE = ROD



Scott Welty stood before us, holding an aluminum rod (about 1 cm
diam. and a = meter long) at its midpoint. Putting rosin on his
fingers, he stroked the rod = and set it ringing. The sound was
loud, clear, and persistent. With the rod = still ringing, Scott
made it rotate in the horizontal plane (somewhat like a = baton
twirler), and we heard a Doppler shift quite clearly. = Nice!



Next, Scott held the rod at a position1/4 of its length from its
upper end = (the =E2=80=9C1/4 position"), and stroked it again. This
time the pitch of the sound = was higher as most of us had expected,
though some asked for an explanation = from nearby friends. So far,
so good. Nothing = unexplained.



But then, again holding the rod at its midpoint, Scott stroked it
much = harder and more rapidly, putting more and more energy into
it. Suddenly the sound = dropped to an obviously lower pitch
=E2=80=91 the usual pitch was not heard at = all (Fig. 4)! "What is
going on here?"! we wondered.



In order to convince ourselves that he was not playing some kind of
trick, = we asked Scott to repeat this several more times. He did,
and we became = satisfied that we were observing a phenomenon new to us.



Could we produce a similar effect, but starting with the higher
pitch obtained = by holding the rod at the 1/4 position? Scott tried
this, but it failed to work.



Could the failure be related to lack of a symmetry =E2=80=91 imposed
boundary = condition? With Ed McNeil holding the rod at
the 1/4 position from the lower end, Scott again held it at the 'A
position from its = upper end and stroked vigorously. To our
disappointment, the rod still did not = break into a hoped =E2=80=91
for, lower pitch resonance.



Still other experiments, conducted by holding the rod at various
intervals = along its length, produced sounds of other pitches, but
none of them matched the = lower pitch produced by the energetic
stroking with the rod held at its = midpoint.



We found no explanation, so this obviously needs more investigation.
If you = can get your aluminum rod to behave in a similar fashion,
would your group = be interested? Do you suppose you could find out
what is happening? If you = do, won't you let us know? Have = fun!



TPT January 1986 p 56 and 57



A aluminum rod I now have and used many years when held = at the
center with just one finger and thumb will resonate at a certain =
frequency when rubbed with finger and thumb covered rosin. Next if I
grab the rod with = 2 or 3 fingers and thumb, it will resonate at
frequency 1/3 the original or = what I call the original frequency.



Happy Rod Strumming



Dick





*From:*= = tap-l-owner@lists.ncsu.edu
<3D"mailto:tap-l-owner@lists.ncsu.edu">=
[mailto:tap-l-owner@lists.ncsu.= edu
<3D"mailto:tap-l-owner@lists.ncsu.edu">] *On Behalf Of *Thomas Senior
*Sent:* Monday, = April 27, 2009 12:23 PM
*To:* tap-l
*Subject:* [tap-l] = 2007 PIRA Business Minutes



Hello = Tappers,

I have just posted the minutes on the PIRA Forum at
www.pira-online.org <3D"http://www.pira-online.org/"> for your =
reading pleasure.

If you need a copy emailed to you, drop me a line at =
= >.



Have Phun,



Tom







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