Re: Moon's synchronism

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Tue, 17 Mar 1998, Jim Green wrote:

> > BTW, it's interesting to consider this phenomenon from a driven 
> > oscillator point of view.  The tidal force effectively drives the 
> > moon at a frequency of about 1 cycle per month.  But since that 
> > frequency is *way* above the resonant frequency, the moon's 
> > rotational inertia dominates.
>
> John, what is your evidence for this???  What tidal force?  Are you talking
> about water, crust, or magma -- Moon or Earth?  I would be grateful for
> citations.  We are now dangerously close to our annual discussion of tidal
> bulges.  Do you really want to go there? (:-)

I confess that my "evidence" was, at the time I wrote this, only the fact
that the rotational inertia of the moon *does* dominate.  That is, since
the moon's rotational velocity effectively "plows right through" the
monthly changes in the relative direction of the tidal driving torque, the
inertia manifestly dominates and, therefore, we *must* be on the high side
of resonance.  Now my back of the envelope calculation pleasingly confirms
this result.  As it turns out, however, we don't have to be very *much*
above resonance since the system undoubtedly has a high Q as David Bowman
has mentioned.

John
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