> > A non-electric analog method:
> >
> > Find a string and a weight, something pointy is >

> Hello Alice,
>
> Your answer is correct, if considering the planet a perfect spherical shape.
> Are the Earth planet a good spherical shape? The planet (as almost others
> around) is a little bit "fatty" at the Equator, so, what happens at 19
> degrees south or north? the pointy weight will be pointing to the
> gravitational field center, but the vertical line will not be exactly at 90
> degrees relative to the horizontal surface... a little bit off, right?  The
> buildings will not fall down, but the grounds would seems to be descending
> when walking toward the poles, isn't it?

Well, it's actually even worse than you describe.  Any tall mass will deflect the plumb bob.  The Brits in the 18th century had a heck of a time measuring the height of Mt Everest, because its mass deflected the plumb bob of the surveyor, and the vertical angle to the peak was always off.  That, and the mountain has a big 'root' beneath it, that adds even more mass off at an angle.

In fact, that's the way they proved that most mountains Have roots by measuring local deflections in the gravitational field.

I suppose we even need to take the thickness of the sring into account, and use monofilament instead of hairy old twine for more accuracy.

welcome back

alice
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