Hal:
> Is there a term other than Q that is used to describe the rate of energy loss
> for things that aren't oscillators?
Jim:
> cooling (as in hot things)
> discharge (as in capacitors and batteries)
> leakage (as in pressure vessels)
> loss
Scott:
> An irreversible process would be a better description versus energy loss.
> Like joule heating (resistance, friction).
Notice that these are all energy losses over time; gradual processes with
perhaps an exponential time constant, but without cycles or periods. We know
not to apply Q in these scenarios.
But when you have an oscillator, or a resonator, or (as I suggest) a "rotator",
it seems to make sense to use Q to describe the normalized rate of decay. So
three keys to Q: you need energy; you need energy loss; you need cycles over
which that loss repeatedly occurs.
We use units of time (for example, SI seconds) when we describe a rate. But
here's why Q is unitless -- you normalize the energy (using E / dE) *and* you
also normalize the time (by cycle). No Joules. No seconds. So having period is
fundamental to Q. It's this unitless character of Q (in both energy and time)
that makes it portable from one branch of science to another. And if you
measure in radians you can even get rid of the 2*pi factor ;-)
Without controversy, lots of articles define Q as 2*pi times {total energy} /
{energy lost per cycle}. To me, a slowly decaying spinning Earth meets the
three criteria. It appears to follow both the letter and the spirit of Q.
Bob:
> ummm…. Q is the general term of rate of energy loss and we just happen to
> apply
> it to oscillators in a very elegant fashion….
Oh, no. Now we have both quality factor and elegance factor!
/tvb
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