Re: Sodaplay: Tacoma Narrows resonator

[Leigh Palmer <palmer@SFU.CA>]

> 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.