[time-nuts] Q/noise of Earth as an oscillator
Jim Palfreyman
jim77742 at gmail.com
Sun Jul 31 22:34:22 EDT 2016
Hi Tom,
You said: "you need energy; you need energy loss; you need cycles over
which that loss repeatedly occurs."
With regard to the earth, where is the first one? Sure it was there at the
start when the solar system formed, but where is it now?
Jim
On 1 August 2016 at 12:16, Tom Van Baak <tvb at leapsecond.com> wrote:
> 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:
> > ummmâ€¦. Q is the general term of rate of energy loss and we just happen
> to apply
> > it to oscillators in a very elegant fashionâ€¦.
>
> Oh, no. Now we have both quality factor and elegance factor!
>
> /tvb
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