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Unformatted text preview: Geology 21 THE MOON Lecture - Wednesday, April 8, 2008 TIDES AND GRAVITY Earth's moon is the largest satellite (moon) relative to the size of the planet. Center of gravity Both rotate around center of mass; earth sort of "wobbles" with the moon it is the earth-moon system that rotates the sun Tides: the alternating rise and fall in sea level with respect to the land, produced by the gravitational attraction of the moon and the sun. (source: http://home.hiwaay.net/~krcool/Astro/moon/moontides/) Tides and gravity force of gravity depends on mass and distance: MASS / DISTANCE 2 The earth and the moon pull on each other but the only thing that can move is large bodies of water Interaction of the earth and the moon First, we start with the simplest explanation. The diagram at right represents the earth-moon system. The shaded area around the earth represents the earth's oceans (we assume for now a uniform ocean with no continents). Point A is at the surface of the ocean nearest the moon. Point C is at the surface of the ocean farthest from the moon. Point B is the center of the earth. The arrows in the top diagram pointing toward the moon represent the force of the moon's gravity at these three points. Since the force of gravity depends on distance, point A is attracted to the moon most strongly, point C least strongly, and point B at intermediate strength . The lines leading downward from each point show how each point would move under the influence of the moon's gravity. Point A moves farthest toward the moon, B, not as far, and C Page 1 of 8 Geology 21 THE MOON Lecture - Wednesday, April 8, 2008 least of all. The result is as if the ocean were bulging out toward and away from the moon. Thus, as the earth rotates under this bulge, any point on earth has two high tides and two low tides each day....
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- Spring '08