Re: Sodaplay: Tacoma Narrows resonator

[Tom Ford <tomford@THESCIENCESOURCE.COM>]

As this thread is getting to be a bobbin's full, it might be well to
reference the TPT article (442 TPT Vol 38, Oct. 2000) *A Simulation of the
Tacoma Narrows Bridge Oscillations* which offers explanations and cites
references relating to the current discussion. I had occasion very recently
to duplicate the activity described for a follow-on session for
participants in the (local) Kieve Summer Science Camp for Girls. The
general title was something like: "Strange Vibrations," and offered some
half-dozen demonstations (including the spiked pickle jar from this list).

A slightly simpler suspension was fashioned from the long rubber bands
often used with dynamics carts, and the apparatus was hand-held in front of
the large box fan. The box-beam section was a cardboard box of appropriate
aspect. Following a viewing of the AAPT version of the collapse, I
demonstrated the simulation. Several of the girls tried it individually
with equal quick success. I had this additional chance to play out my
favorite instructional strategy: "I'll throw your body in first and bring
your mind in later." Each participant then had a box and set of rubber
bands as part of the take-home component of the session.

I have several more sets of box/bands which I would be happy to send to
those interested in the simulation described and documented in TPT, who
will respond, off-list, with a mailing address.

Tom Ford



At 02:23 PM 12/8/00 -0800, Leigh wrote:
> > It was my understanding of the Tacoma Narrows film that the wind happened
> > to be moving at just the right speed so that the vortex-shedding frequency
> > hit a natural oscillation frequency of the bridge, and so the amplitude
> > grew enormous.  It's "flag flapping" which drives a swinging pendulum.
> > For months before the disaster, the wind was at the wrong speed.  Am I
> > mistaken?
>
> It was my understanding that the wind on the day of failure was stronger
> and/or longer lasting than it had been at earlier times. Certainly the
> wind did not remain so steady that the shedding frequency remained at
> exactly the characteristic frequency of the bridge. The curious fact that
> the bridge oscillated in at least its two lowest torsional modes* should
> be sufficient indication that this was not a resonance.
>
> Leigh
>
> *This was quite evident to me on first seeing this film. It may not be
> obvious in some edited versions.
The Science Source
Manufacturer of Science Educational
and Design Technology Equipment
P. O. Box 727
299 Atlantic Highway
Waldoboro, ME  04572-0727
(207) 832-6344
1-800-299-5469
FAX (207) 832-7281
e-mail: tomford@thesciencesource.com
http://www.thesciencesource.com