Leigh says that Mark's stakes exert forces. Certainly. Mark and I looked at
this because this is what we thought Don was proposing to make tides without
considering the fact that the earth and moon orbit the center of mass.
If they aren't orbiting something has to hold them apart! I claimed the
water would run to one side because the stake couldn't hold it and I know
that the "solid" earth has not had time to become an equipotential surface.
Therefore, the water would have to make the adjustment. Mark & I also tried
to explain that we were measuring everything relative to stakes fixed in the
stars. Again, this is what we thought Don was doing. John measured everything
relative to a center which moves relative to the stars as he adds or removes
the moon or rotation.
Honestly, I think are differences are more a question of language and
explaination than they are of Physics. I haven't seem any physics posted
that I think is actually wrong. Just people doing different problems and
explaining them with a different emphasis.
I do think Don is going a little too far. How can you claim to make tides
without considering the orbiting of the earth and moon when without the
orbiting they will crash into each other! The two are not independent.
What you can claim is that the gravitational gradient makes a shape that
sticks out on both ends like a football. However, as John and Ian? point
out this is not the same shape that results when orbiting effects are added.
Finally, I do agree that Leigh has a good model for the real earth, but it
is not what Mark and I thought Don was suggesting.
One final thought and them I'm off this aspect of tides for the duration.
If we have this much trouble understanding each other, is it any wonder
students have problems. Maybe it is because we aren't drawing pictures!
At school I would never try to explain anything without drawing a picture.