🚀 go-pugleaf

In article <scottj-221292163050@iamac-1.dml.georgetown.edu> scottj@magic.dml.georgetown.edu (John L. Scott) writes:
>In article <1h50c7INNees@news.aero.org>, shag@aero.org (Robert M.
>Unverzagt) wrote:
>> 
>> In article <scottj-211292091243@iamac-1.dml.georgetown.edu> scottj@magic.dml.georgetown.edu (John L. Scott) writes:
>>> The high tide facing the moon is, of course, explained by the gravitational
>>> pull of the moon.  However, there have been at least two explanations for
>>> the high tide on the opposite side of the earth:
>>> 
>>>    A.  The moon stretches the earth
>>>    B.  Centrifugal pseudo-force
>>> 
>>> So... which is it, A, B, both, or neither?
>>> 
>> [ explanation deleted ]
>>
>Thanks for the reply.  I got "stretches the earth" from somebody else's
>post.  I took it to mean that the earth's shape was actually deformed to
>the point that it had a noticeable effect of the oceans.  I was skeptical
>of that idea.
>
>So, are you saying that the moon pulls the earth away from the water on the
>far side?  That certainly sounds reasonable to me.
>
>--John L. Scott

Maybe I can add something to this discussion. This explanation, while 
technically correct, applies mostly to solid bodies. For example, a solid
satellite comig close to a massive planet will be disrupted by the differential
force between the center and the close and far sides of the satellite.

However, this effect is small and can't explain the tides by itself. 
The principal effect is, strangely, the force perpendicular to the axis
between the two bodies. If you compute the effective (vectorial) force
on the surface of the ocean (i.e. the gravitational pull from the moon
minus the force that keeps the Earth-Moon system together), you will notice 
that this force is oriented outward when you are along E-M axis, inward
when you are perpendicular to it, and parallel to the surface of the earth 
when at 45 degrees.

This last force is directed toward E-M axis and can easily move the water
since it is not opposed to the Earth's gravity. This effect is supposed
to be the main cause of the observed tidal bulge.

(for a simple mathematical derivation, see Zeilik and Smith, 
"an introduction to astronomy and astrophysics")

-----
Jean-Remi Duquet
Physics dept.
Universite Laval
Quebec