Jeff Morris wrote:

"Nav" wrote in message
...

[deleted stuff where we unfortunately seem to agree]


Good points. Well A=C-B ;-)

But, lets open this can of worms a bit further. I take and largely agree
with most of your view, but it is the kinetic energy in the system that
is powering the tides. If you locked the moon to the earth with a big
pole you would not have two tides would you? The mass is the same and so
is it's center... Gravity still works... but, just one tidal bulge.



I don't think its fair to do this - you can mathematically eliminate effects by
shifting the reference frame, but "locking" objects together is changing the
problem at a more fundamental level.

I don't see it that way, the explanation for the two tides based on
differential gravity alone does not care whether the earth is "moon
locked" at (say) an L point -and that why it is not the correct
explanation in my opinion. Of course it all comes down to gravity and
the energy of the system but the simplest close answer should consider
the rotation as well.

In this case, how to you "lock" the Earth?
In fact, the crux of this problem is that different parts of the Earth are
actually acting somewhat independently.

However, this brings up an interesting point. At some point in the distant
future the tides will be eliminated.

(Well not really, unless you ignore the Sun). But I think this point
reinforces what I've been trying to get across, without considering the
rotation(s) about the center of mass you don't get a two tide situation.
Any description that does not explicitly consider the relative motion
will not generate two tides -do you agree?

How will this happen? Because the tides
lag the Moon the high tide is not directly under the Moon, but offset. This
creates soon torque that is transferring energy from the Earth to the Moon. The
result is that the Earth is slowing down, and the Moon's orbit is increasing.
This will continue (some say) until the Earth's rotation slows down to match the
Moon, and the bulge stays under the Moon. The Earth and Moon will at that point
be locked together. Because the Moon is smaller, it has already assumed this
orientation WRT the Earth.

If we work this backwards we find the in the distant past the Moon's orbit was
much closer to the Earth, and the Earth's day much shorter. Exactly how much
depends on what other theory you're trying to support or disprove. However, we
do know the effect is real - the measurement using equipment left behind by the
astronauts shows the distance increasing about 4 cm a year, and the Earth's day
lengthening by 1.5 milliseconds a century.


I never looked it up but would have guessed the rate of slow down would
be larger than that. From that number you can calculate the energy cost
of the tidal forces... Here's a thought, at current rate of energy
consumption growth how long before even this energy source would be
insufficient for our needs?

Cheers