"Donal" wrote in message
...
It doesn't "know" anything. Because the Earth and Moon are an "orbiting
pair," as you
say, they are falling towards each other. Because the gravitational field
varies, the
near side falls faster than the middle; and the far side falls slower.

Very neat! However, your view seems to be a little bit simplistic.

It is simple. That's because there really isn't that much going on (at this level).
Just the pull of gravity, which varies with distance. Everything else is red herring.



Why should a solid fall more slowly than a fluid in a gravitational field?

Why is there any difference? They both feel the same force. And, the land surfaces
are distorted by the tides, roughly a meter, IIRC. To be honest, I could never figure
out if the water is distorted more for some reason (its lighter?), or is in simply
free to move, and thus get involved in the local shoreline effects. (That is, is the
tide in the middle of the ocean the same as in the middle of a continent?)

If your theory was correct, then there wouldn't be any tide at all.

No, the force distorts both the land and the water. These distortions are the two
bulges. In fact, because there is a difference in force, there must be some
distortion - how much is a detail for the engineers!


You seem to be ignoring momentum.

Nope. If you use the "free fall" approach, momentum isn't really a factor in
computing the force, though I suppose it gets involved when you calculate the actual
motion. You sort of consider momentum with the centrifugal force approach, but you
don't calculate it because the CF gets cancelled out.

Consider an astronaut space walking outside a space station. They both float
together, feeling no force, although they are both in freefall in their orbit. If the
astronaut moves to a lower orbit, he will feel a stronger pull and be drawn in, unless
he speeds up to compensate. If the astronaut moves to a higher orbit, the force is
reduced. As I said, the force can be calculated without consideration of momentum.

A purist might say momentum is considered because the mass and velocity of the every
object in the system is folded together. And, the pure way force is defined is by how
it changes momentum. But I don't think this is what you're talking about.