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Re: C-SAT



Thanks, Leigh, that is the picture I needed. It is one thing to know
intellectually/accademoically, quite another to have a helpful picture.
Your lakes did the trick. We senile old men need help.

(For example I do "know" about retrograde motion, but I can't picture it at
all. The list has tried, but I still can't picture it. (:-) )

Jim


At 01:09 PM 10/15/96 -0700, you wrote:
But why, I wonder, is it a "hump"? If the local gravitational constant
there is greater, why isn't there a "depression"?

Because the extra gravity there attracts more than its normal share of the
available fluid water.

Ah, but why is this so?? Another hand-waving argument might be that there
is a grreater gravitational force "down" therefore there will be a depresion
there. An appeal to potentials just adds another layer to the question.

If ocean water runs "up hill", why don't rivers?

A better way to look at this question (and one which has a less ambiguous
answer) is this: Consider an experiment done near, but not direcetly over
the center of, a mass concentration in the crust, like a mountain. Hang a
plumb bob at that position. You will find it deviates from the direction
it would take without the mountain by being pulled toward the mountain.
The surface of a lake at the same point would be perpendicular to the
plumb line, and hence it would slope "uphill" in the direction of the
mountain everywhere around the mountain. Now connect all the lakes
together and you have an ocean which slopes uphill around the mountain
and reaches its peak above the mountaintop.

The surface of the ocean, apart from tides, is an equipotential*. It is
higher over the mountaintops because the gravitational potential at equal
radius is lower above a mountaintop than it is above a deeper part of the
ocean.

Leigh

*One would ordinarily say a gravitational equipotential in the rotating
frame of reference of Earth's surface, but some people get uncomfortable
when confronted by the centrifugal potential which is subsumed into the
gravitational potential in this case.