I have been reviewing some of the recent tides posts and see that I have
misspoken in a place or two. I do NOT intend that this present post
inflame this well worn thread, however, on the off chance that some
impressionable teacher is actually paying attention to this diatribe, let
me please offer a summary and some errata:
1) In as much as when the word "tide" is used, most of the galaxy thinks of
water, we should probably use distinctive language for oceanic tides and
for .... well I don't know what to call them: "Earth tides" doesn't
distinguish between water and dirt nor between Earth and other orbs;
"crustal tides" isn't inclusive enough and doesn't even apply to the likes
of the Moon; "dirt" doesn't include the magma if any; "solid" is not
correct at all; I don't know if "plastic" or "elastic" is helpful; so I
don't know what to use. BUT "tide" alone should mean water! IMVHO
2) This thread began with the question of why the Moon's "face" is always
toward the Earth. The simple answer is that the Moon isn't spherical and
that the Earth applies a torque on the Moon to keep it aligned.
3) I said that the Moon is _loosing_ energy in the process and that the
Earth _gains_ energy -- this is backward! Yes the Moon does work on the
Earth and the Earth on the Moon, but the work on the Moon _increases_ its
energy (and the angular momentum is increased as well) while the work done
on the Earth decreases the Earth's energy (NB energy doesn't flow!!!) BUT
that portion of the work that the Moon does on the Earth's _oceans_ is
positive -- such that the water _gains_ energy through frictional sloshing.
[and causes things like global warming and El Nino (:-)]
4) The torque on the Moon is often ASSUMED to be due to the Earth's so
called "tidal bulges" -- and calculations are made as to how much those
bulges must lead or lag the Earth/Moon line. It is more likely that this
torque is due to the Earth's _dirt tidal bulges_, which _do_ exist.
5) Before next year's tides discussion, I will look into the following:
a) What evidence is there that there really _are_ tidal bulges on the
Earth. Even some sort of "average" or "underlying" bulges of some sort,
which torque the Moon? I really doubt this, but I am going to give this a
fair chance.
b) Has the Topex team produced a better co-tidal map of the Earth -- ie one
that is derived from real-time altitude measurements (rather than the
"surmised" or calculated data on the co-tidal map on my web page)?
c) What velocity can one expect from a _driven_ water wave.
d) If there is anything else important for my attention, please advise me
privately.