ay45c4-page37 - Notice that we never assumed that M1=M2 was...

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Unformatted text preview: Notice that we never assumed that M1=M2 was either  1 or  1, so our formulas apply both for the Sun and for the Moon. It is a numerical coincidence that the tides they raise are of the same order (though some have speculated that the resulting more-variable tides produced could have been somehow necessary to mix the oceans in a way that furthered the evolution of life | or its emergence from the sea). 4.3.2 Tidal drag and the lengthening of the day Real tides are not exactly the size we have calculated, primarily because the Earth is rotating. Thus the continents are \dragged through" the oceanic tidal bulges, causing water to pile up on the continental shelves, ow into and out of bays, etc. There can also be resonance e ects in some cases like the famous Bay of Fundy. This kind of \friction" between the rotating Earth and the tidal bulges produces two e ects. 1. The tidal bulge is, on average, dragged ahead of where it would be if it \pointed at" the Moon. 13 /day ϕ 36 0 /d ay 2. The drag slows down the rotation of the Earth. Since angular momentum must be conserved, as the Earth loses angular momentum, it must be gained by the Moon's orbital motion! How does this 96 ...
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