Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 01/04/2012 09:34:01
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Peter Conway asked the Naked Scientists:
Question - Tides
A question for you, a little while ago you explained how the tides work but concentrated on the high tide created by the Moon's gravity on the Moon side of the Earth but didn't seem to explain the second daily high tide, so...
What causes the high tide on the side of the Earth facing away from the Moon giving us our second high tide each day, and is it as high as the tide on the Moon side of the Earth?
Many thanks
Peter Conway
What do you think?
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The tide nearest to the Moon occurs because the Moon's gravity pulls the water towards it.
The tide on the other side of the Moon (that furtherest away occurs because the water on that side is pulled less that all the other regions on the Earth; so, it rises, but not as much as the one nearest the Moon.
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I think of the tide on the opposite side of the Earth in two ways.
- The moon shifts the center of gravity of the Earth/Moon complex slightly away from the center of the Earth, towards the moon. Thus, for any water molecule on the far side of the earth, the distance to the center of gravity of the planet is slightly further, and thus the gravity is lower... thus allowing a bulge to form.
- The rotation of the Earth/Moon complex around its center of gravity would also create a wobble in Earth's movement, and a slight centrifugal force (less centripetal force) on the far side of the Earth.