Re: Sodaplay: Tacoma Narrows resonator

[William Beaty <billb@ESKIMO.COM>]

On Thu, 7 Dec 2000, Bob Sciamanda wrote:

> There is a semantic question here which may be worth elaborating.  The
> (small)motion of a complex system (eg. a stretched string) may be
> mathematically analyzed into a compounding of "normal mode" oscillations
> at its "natural" frequencies.

Perhaps one typical use of the word "resonant" is a corruption.  It is
widespread though.  For example, an RLC circuit has a single "resonant
frequency".  In electronics nobody calls it a "natural frequency".  If I
strike a bell or pulse an RLC circuit, it "resounds."   An RLC circuit is
frequently called a "resonator."  Does this refer to its ability to
respond in sympathy to incoming AC signals?  Or to its ability to
"resound" when exited with a single pulse?

> "Resonance" is a relation between such a system and an excitation
> mechanism which itself oscillates in time at one of the system's natural
> frequencies (or, more generally, when its frequency spectrum contains a
> large component at such a frequency).
>
> I would not apply this term ("resonance") to the natural oscillations
> which result from an "amorphous" excitation - eg, a plucked or bowed
> string.

Many others would apply it that way:  when you pluck a string, it
oscillates at several "resonant frequencies."   The system has several
"resonant modes."

On the other hand, maybe a struck bell should be described as "sounding"
rather than "resounding."  A bell has many "sonance modes" rather than
resonance modes.  An RLC circuit is an EM "sonator" rather than an EM
resonator.

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