Re: Sodaplay: Tacoma Narrows resonator

[William Beaty <billb@ESKIMO.COM>]

On Thu, 7 Dec 2000, Chuck Britton wrote:

> But let's not think that the vortex shedding was a sympathetic
> driving force for the oscillations, because THAT would break down
> this VERY tenuous distinction  ;-)

That's exactly the problem!  The bridge clearly is oscillating at a,
um... "natural frequency."

Do we agree that the flapping of a flag does *not* involve vorticies being
shed at a natural frequency of the system?  The Tacoma Narrows
phenomenon appears to me to involve a combination of "flag flapping"
and "swinging pendulum."   If it was purely "flag flapping", then we could
correctly eliminate the term "resonance" from the explanation, regardless
of whether resonance refers to driven coupled oscillators, or to the
"natural frequency" of a single oscillator.


> I just want to know how 'Sympathetic Vibrations' relate to these resonances.


People here are clearly using "resonance" with two distinct definitions.

If I set a pendulum swinging, then is its continued swinging an example of
a "resonance?"

Or must a "resonance" always involve two separate oscillators, such as the
typical coupled-pendulums lecture demonstration?


I'm beginning to suspect that "resonance" at one time referred only to
coupled oscillator effects, but it has been misused for so many centuries
that today it also means "natural frequency of a single system."


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