[sdiy] The Origins of Q

[nN AAt e e]

short for Quality Factor.

quality factor (symbol Q)
A measure of the sharpness of resonance or frequency selectivity of a
resonant vibratory system having a single degree of freedom, either
mechanical or electrical. See vibration.
In a mechanical system, this quantity is very nearly equal to one-half the
reciprocal of the damping ratio. When used with reference to a lightly
damped system, it is also approximately equal to the following: (1)
transmissibility at resonance; (2) ?/? where ? is the logarithmic decrement;
(3) 2?W/?W where W is the stored energy and ?W the energy dissipation per
cycle; and (4) fr/?f where fr is the resonance frequency and ?f is the
bandwidth between the half-power points. Historically the letter Q was an
arbitrarily chosen symbol to designate the ratio of reactance to resistance
of a circuit element. The name quality factor was introduced later

http://roland.lerc.nasa.gov/~dglover/dictionary/q.html

- nate [googled: resonance first use of q, which the keywords aren't even on
the page :P ]