[time-nuts] Q/noise of Earth as an oscillator
jimlux
jimlux at earthlink.net
Wed Jul 27 09:00:51 EDT 2016
On 7/27/16 5:43 AM, Michael Wouters wrote:
> On Wed, Jul 27, 2016 at 8:08 AM, Attila Kinali <attila at kinali.ch> wrote:
>
> "I am not sure you can apply this definition of Q onto earth."
>
> It doesn't make sense to me either.
>
> If you mark a point on the surface of a sphere then you can observe
> that point as the sphere
> rotates and count rotations to make a clock. If you think of just a
> circle, then a point on it viewed in a rectilinear coordinate system
> executes simple harmonic motion so the motion of that point looks like
> an oscillator, so that much is OK.
>
> But unlike the LCR circuit, the pendulum and quartz crystal, the
> sphere's rotational motion does not have a
> resonant frequency. Another way of characterizing the Q of an
> oscillator, the relative width of the resonance, makes
> no sense in this context.
>
There's also the thing that "things that resonate" typically have energy
transferring back and forth between modes or components: E field and H
field for an antenna; kinetic vs potential energy for pendulums and
weight/spring; charge and current (C & L, really E field/H field again).
Spinning earth is more of an "rotational inertia and loss" thing, with
zero frequency, just the exponential decay term.
If you think of a single measurand in any of these scenarios you have at
the core some sort of exp(-kt)*cos(omega*t+phi) and we're relating Q to
the coefficient k.
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