A place for my students to get some help in Earth Science
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| Earth Science A place for my students to get some help in Earth Science |
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Thursday, December 07, 2006 Astromy website http://csep10.phys.utk.edu/astr161/lect/index.html Tide website http://csep10.phys.utk.edu/astr161/lect/time/tides.html Some of the main points are that relationship of earth, moon, and to a lesser extent sun is the cause of tides. The tides at a given place in the Earth's oceans occur about an hour later each day. Since the Moon passes overhead about an hour later each day, it was long suspected that the Moon was associated with tides. Newton's Law of Gravitation provided a quantitative understanding of that association. Differential ForcesConsider a water molecule in the ocean. It is attracted gravitationally by the Earth, but it also experiences a much smaller gravitational attraction from the Moon (much smaller because the Moon is much further away and much less massive than the Earth). But this gravitational attraction of the Moon is not limited to the water molecules; in fact, the Moon exerts a gravitational force on every object on and in the Earth. Tides occur because the Earth is a body of finite extent and these forces are not uniform: some parts of the Earth are closer to the Moon than other parts, and since the gravitational force drops off as the inverse square distance, those parts experience a larger gravitational tug from the Moon than parts that are further away. The fluid in the Earth's oceans is much more easily deformed and this leads to significant tidal effects. The gravitational attraction of the Moon produces two tidal bulges on opposite sides of the Earth. A given point on the surface will experience two high and two low tides for each rotation of the planet. For example, particularly large tides are experienced in the Earth's oceans when the Sun and the Moon are lined up with the Earth at new and full phases of the Moon. These are called spring tides (the name is not associated with the season of Spring). The amount of enhancement in Earth's tides is about the same whether the Sun and Moon are lined up on opposite sides of the Earth (full Lunar phase) or on the same side (new Lunar phase). Conversely, when the Moon is at first quarter or last quarter phase (meaning that it is located at right angles to the Earth-Sun line), the Sun and Moon interfere with each other in producing tidal bulges and tides are generally weaker; these are called neap tides. The figure shown above illustrates spring and neap tides. posted by James | 10:13 AM Tuesday, December 05, 2006 Eclipse Lesson Date: 12/5/2006 To: 1, 7, and 8, Earth Science, Tutoring Tues and Friday room 246 Cc: From: JGS Some of the main points of lesson were the relationship of the penumbra and the umbra with partial and total eclipses Also, the distance of the object that casts the shadow. Generally the closer the more total. The effect of apogee and perigee on eclipses. See above for that relationship. JGS posted by James | 10:18 AM |
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