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Re: [Phys-L] Resonance with tuning forks vs small speakers

Anthony,

I wouldn't say that the sound "spreads" out quickly. There's an
interference from the opposite side of each tine making it effective at
canceling its own noise.

Perhaps the more precise way of stating this is that the tuning fork is bad
at radiating sound energy. Like the coupling between to springs with
different characteristics, there may be dramatic motion near the
connection, but if there is an impedance mismatch nearly all of the energy
if the spring motion will be reflected back.

Also... Spin the tuning fork around the axis of the handle with it held
close to your ear to observe that the direction of sound radiation varies
quite a lot.

Paul

On Fri, Oct 28, 2022 at 4:42 PM Anthony Lapinski via Phys-l <
phys-l@mail.phys-l.org> wrote:

Yes, the tuning forks are very loud. Strike one and bring close to your ear
- can be very painful sometimes. Very concentrated, then it spreads out and
becomes softer. The smartphone has good speakers and fills the room with
loud sound.

On Fri, Oct 28, 2022 at 4:26 PM Zeke Kossover via Phys-l <
phys-l@mail.phys-l.org> wrote:

Maybe tuning forks are actually quite loud but hard to perceive because
of
diffraction? Though the tines are relatively big and they have fairly
large
amplitudes, the backsides of each tine make an expansion when the front
makes a compression and vice versa.

So, if we could get rid of the vibrations from the backside then, like in
the video of the small speaker, the sound would be louder.

I cut a rectangular hole in a piece of cardboard in the shape of a tine
and
held it close but not touching the vibrating tine, and the volume went
way
up!

Thank you for the help!
-Zeke K.

On Fri, Oct 28, 2022 at 12:42 PM Paul Nord <Paul.Nord@valpo.edu> wrote:

Zeke,

For starters, the tuning fork is really bad at radiating sound energy.
They make almost no noise at a distance. The tube acts much like the
body
of a stringed instrument in helping the motion of the string couple to
the
air. Phones, on the other hand, would need to work hard to design a
speaker that transmits anything to the air.

Take a look at the 39 minute mark of this video:
https://www.youtube.com/watch?v=ADgihdzVSRY

As for the human perception of "amplitude increase" it may be related
to
the logarithmic nature of human hearing. Ten times more energy in the
sound wave doesn't sound 10 times louder.

Paul


On Fri, Oct 28, 2022 at 2:03 PM Zeke Kossover via Phys-l <
phys-l@mail.phys-l.org> wrote:

Howdy Physicists!

As a resonance activity, I bring a vibrating tuning fork towards a
tube
that is open at one end and closed at the other. When tuned
correctly,
the
air in the tube loudly resonates.

Since tuning forks are expensive and every student has a phone with a
speaker, I've tried running the activity with a frequency generated
by
their phone. To my ears, the sound generated by their phones is way
louder
than the tuning fork, but when I put the phone next to the tube, the
amplitude increase is way less.

I wonder why they are so different. Do any of y'all have ideas?
--
*Marc "Zeke" Kossover | Educator, Teacher Institute*
zkossover@exploratorium.edu
Museum: Pier 15, San Francisco, CA 94111
Mailing: 17 Pier, Suite 100, San Francisco, CA 94111
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Forum for Physics Educators
Phys-l@mail.phys-l.org
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_______________________________________________
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--
*Marc "Zeke" Kossover | Educator, Teacher Institute*
zkossover@exploratorium.edu
Museum: Pier 15, San Francisco, CA 94111
Mailing: 17 Pier, Suite 100, San Francisco, CA 94111

<https://www.exploratorium.edu/tinker>
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://www.phys-l.org/mailman/listinfo/phys-l


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