Re: The Moon will continue to move slowly away from the Earth

In article <1178994827.860238.132000@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
effacers@xxxxxxxxxxx wrote:

The moon is not getting lighter. Most changes in the moon's mass
would not affect its orbit.

He actually has a subtle point here.

Nothing subtle about it. Apparently, you're grasp of physics is the
only thing subtle.

Quite a few people here grasp physics (and math) better than you do.

Specificly, if the Earth-Moon
system were to loose mass, then the gravitational force between the
Earth and Moon would decrease.
The resulting decrease in acceleration
would in fact expand the orbital semi-major axis of the mutual orbit.

Whew!

Did you notice the second word in that snippet? "If"?

You can come at this from Newtonian mechanics (which, to be honest, is
a real pain), or you can come at it from the standpoint of orbital
energy (which is significantly easier).

The problem with this as a solution is first it's very difficult to
find any believable mechanism to remove mass from either the Earth or
the Moon at any significant rate. Second, you can calculate what mass
loss rate is required to sustain a 4 cm/year expanssion in the orbit
(it's rather easy; I expect my 200-level physics students could do it,
and no, it's not calc-based). It works out to 7e+12 kg/yr, not
insignificant. If that was the explaination (and if this rate had been
uniform; it's not been, as is both predicted and observed), it would
imply the moon has lost close to 3e+22 kg over the last 4 billion
years*, implying a much more massive Moon. Among other problem, this
is enough mass removed from the Moon to resurface it many times over -
in short, there should be no ancient cratered surface on the moon if
mass loss was going on at even a tiny fraction of this rate.

Wow some actuall figures!! Refreshing. Unfortunately all the energy
you've expelled here was a complete waste since NO ONE can confirm
that this CURRENT orbital expansion will continue at, near or
accelerate faster than the current rate forever. It's amazing how
people here cannot grasp that fact.

Actually, someone already has. The prediction was that tital friction
will eventually slow the Earth's rotation to match the moon's orbit. One
side of Earth will always face the moon. Then the Earth will have no
more rotational energy to transfer to the moon, and the expansion of the
moon's orbit about the Earth will cease.

If that's what you wanted to know, you could have asked.

Conclusion: the Moon is not, nor has it ever, been loosing enough
material to produce the observed orbital expanssion.

Conclusion your conclusion is baseless since again the moon's orbital
distance is almost guaranteed to be multi cyclical.

Guaranteed by what?

40 years of
distance data don't quite cut the mustard.

There's more than 40 years of distance data.

So my unanswered question still stands tall as ever, what is your
proof the moon is shedding pounds if any. If it's not "evaporating" as
some say, then it certainly is gaining weight instead as it's gravity
collects space debris.

Whose proof? No one who knows what he's talking about tis claiming that
the moon is losing mass. As for the moon's gain of mass, that's
insignificant to orbital motions. As I described earlier, since impacts
come from all directions, they have no net effect on the moon's orbit.

--
Timberwoof <me at timberwoof dot com> http://www.timberwoof.com
.

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