No, you never said it wasn't needed, but you did minimize its importance, claiming
that it can't be used alone to predict the tides. You said:

"Even worse, the site then goes on to use the _differential_ expression
to calculate the ratio of forces between the moon and sun!"

You even produced a bogus formula to support your claim that centrifugal force varies
across the Earth. This would predict a tidal force 65 times stronger than
differential gravity. If that isn't minimalizing differential gravity, I don't know
what is.

You demonstrated a further lack of understanding with:

If the moon stopped its rotation around the earth and the earth and
the moon was "falling" toward each other, there would still be two
bulges.

"YES but how big would they be (Hint: Smaller than the tides?)"

Actually, the tides would be the same.

One fundamental difference that we have is that you insist that taking centrifugal
force into account is the *only* way to look at the problem. As I've said a number of
times, centrifugal force is a "fictional force" that is only needed if you wish to
work in the accelerating Earth-centric reference frame. In fact, it is required that
there must be an alternate approach that does not use "fictional" forces.

It is quite easy to explain the tides without Centrifugal force - I mentioned the
approach in one of my first posts. There is a gravitational force pulling the Earth
and Moon together. This creates an acceleration such that the Earth is in free fall,
and no net force is felt at the Earth's center. However, there is a larger force on
the Moon side, and a smaller force on the far side. Since the average force has been
accounted for it must be subtracted from these two forces, and the smaller force ends
up being the same magnitude as the larger, but in the opposite direction. Hence, two
tidal bulges, both caused solely by gravity.

Another fundamental difference we have is that I agree with the traditional value for
the tidal force. Ignoring minor effects, the result predicted by Differential Gravity
(whether or not you use centrifugal force as part of the explanation) that is about 2
feet for both the near and far side bulges. (The Sun's contribution is about half of
the Moon's.) The land masses and shallow water tends to "pile up" the water to create
tides that are somewhat higher.

You, however, have claimed that the variation of the centrifugal force from the near
side to the far creates a force that dominates the tides. Your formula predicts a
force 65 times greater than the differential formula, which would seem to create tides
100 feet or more. Your explanation that land masses dampen these tides runs counter
to common experience. And, your formula predicts the Sun's contribution is only 1% of
the Moon's, which is clearly not the case.

As to your claim that the rotation around the barycenter "powers" the tides, well,
that's not true. In fact, even if the Earth and Moon were not rotating around the
barycenter, the tides would be the same, at least, until the Earth and Moon collided.
Frankly, it clear that you still do not accept the fact that CF is constant, exactly
equals the average gravitational force, and thus has no interesting contribution to
the tides.






"Nav" wrote in message ...
Now why try to distort the truth Jeff? I never ever said differential
gravity was not needed. I always said that it's the difference between
gravity and centrifugal forces. You do understand the connotations of
the DIFFERENCE between forces don't you? It does not mean that either
component is zero and actually implies that both are important. Shesh!
Still it's nice to see that you now agree that centrifugal forces should
not be ignored (as they are in the gravity only model). As I've said so
many times, the key to understanding is that the system rotates about
the barycenter and it is not just a gravity field problem. The rotation
actually provides the energy needed to power the daily tides -think
about it OK?

Cheers

Jeff Morris wrote:

"Nav" wrote in message
...

Jeff Morris wrote:

"Nav" wrote in message

...

F= mr omega^2. The distance from the barycenter to all points on earth
is NOT the same.

As the site expalins in the next paragraph, only the center of the Earth rotates
around the barycenter. Other points rotate around neighboring points.


Anyway, the site clearly shows in Fig. 2 that it is the
_DIFFERENCE_ between gravity and centrifugal force that makes the tides,
not gravity alone.

We never disagreed on this point.

HOLY BACKPEDAL!!!!!!


I'm not sure you really want to go back over this thread - your record is rather
shaky. Mine, however, has been quite consistent. Remember, I started by posting
sites with differing approaches to show that this problem can be looked at in
different ways. I then made my first comment about Centrifugal force with:

"Remember that Centrifugal Force may be a handy explanation, but it is a
"fictional force" that only appears real to an observer in an accelerating frame
of reference. Therefore, whenever it is used to explain something, there must
be another explanation that works in a non-accelerating frame."

but then you started claiming that differential gravity wasn't needed, I responded
with:

"Before I thought you were just arguing philosophically how much we should credit
centrifugal force, but now it appears you haven't really looked at the math at
all. The reason why "differential gravity" is invoked is because it represents
the differing pull of the Moon on differing parts of the Earth. Although this
force is all obviously towards the Moon, when you subtract off the centrifugal
force this is what is left. It is this differing pull that causes the two
tides."



a few posts later:
"Given that, your argument falls apart. The centrifugal force is exactly the
same on all points of the Earth, and (not by coincidence) is exactly opposite
the net gravitational force. What is left over is the differential gravity."

The bottom line here is that the tides are properly described by the differential
gravity equation. Centrifugal force can be used to explain how an outward force
can
be generated, but it is not needed, and it does not yield the equation that
describes
the tides.

Frankly, your the one who started this by claiming that the traditional
explanation of
tides is fundamentally flawed, and that the differential force normally cited is
not
what causes the tides. You really haven't produced any coherent evidence to
support
this claim.