Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: MitjaHD on 14/06/2017 17:13:38
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Probably a strange question. Our planet is a sphere and we can't see the curvature of the Earth from ground or even from a plane. If we pour water in somewhere the top will be flat (bottles, pools...). Thanks for answering.
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Probably a strange question. Our planet is a sphere and we can't see the curvature of the Earth from ground or even from a plane. If we pour water in somewhere the top will be flat (bottles, pools...). Thanks for answering.
The water in a pool or bottle will not be perfectly flat, it is just any curvature will be too slight to notice.
Take an Olympic sized swimming pool. Due to the Earth's spherical shape. If you were to lay a perfect straight edge from end to end, the middle of the pool would deviate from that straight line by less than 50 micrometers. Not something you are going to be able to "eyeball".
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If the measurements are small enough any curved surface can be shown to be locally flat. Within reason of course.
This brings us conveniently to line elements and metric tensors.
https://en.m.wikipedia.org/wiki/Line_element
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For those wishing to explore further the following PDF may be of interest.
https://web2.ph.utexas.edu/~jcfeng/notes/Tensors_Poor_Man.pdf
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So when one looks at an ocean and can only see so far, curvature of the earth is one solution, what is yours?
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It has been known for centuries that when a ship sailed out to sea, first the hull disappeared, and later the sails disappeared from view. This is due to the curvature of the ocean. This is why the ship's lookout is in the "crow's nest", at the top of the mast.
I heard that there was a terrestrial example; the story went like this: A long tunnel was bored through a mountain, in a straight line. You could see from one end of the tunnel to the other. But when water leaked into the tunnel, it pooled in the center, and had to be pumped out. This is because the center of the tunnel was closer to the center of the Earth than the ends of the tunnel. (Or was it a classroom myth?)