"Nav" wrote in message
...


Jeff Morris wrote:

You might make a case that the centrifugal explanation is easier for some
people
to understand, but claiming that gravity doesn't cause the tides is just
plain
bogus!

What are you talking about? I never said that gravity was not a part of
the equation.


Let me repost:
"The gravitational force acts only toward the center of mass of the
system. This cannot by itself produce two bulges."

Note the "by itself".

That's exactly the point - gravity is the only force at work here. Gravity does
cause the bulges. The centrifugal forces are a "fiction" caused by the
accelerating reference frame. Why is it accelerating? Because of gravity!



I'll repeat myself, the key is to understanding the _two tides_ problem
is that the system is rotating and "centrifugal" forces are balanced
only at the centers of the masses by gravity.


That is a simplified way to look at it. If it helps your understanding, fine.
Your problem, however, is that you're insisting that this is the *only* way to
understand the problem. The are numerous correct ways to look at this. You
don't have to use centrifugal force to explain the far bulge.

Frankly, for me, it doesn't help at all, because the centrifugal force is
constant throughout the Earth. If it produces the bulge on the far side, how
can it also produce a bulge in the opposite direction on the near side? The
answer, of course, is that you have to add the centrifugal force to
gravitational force. which is different throughout the Earth. The resulting
force is exactly the same as the differential gravity from the other model. Why
is this? Because the centrifugal force is a "fiction" - it is simply the
opposite of the net gravitational force that causes the Earth to rotate around
the Earth-Moon system. In the differential model you subtract this out, in the
centrifugal model you add it.

So I have trouble thinking of centrifugal force as pushing out the far bulge;
for me the bulge is caused because the far side receives less pull from the Moon
than the rest of the Earth. However, arguing that one model is more correct
than the other is like arguing whether A+B=C or A=C-B.