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UNIT 6LESSON 6 TIDES AND TIDAL COMPUTATIONS OVERVIEW Recognize the effect of the Sun and the Moon on tides. Identify the four volumes of Tide Tables, and recognize how tides are computed. Identify terms relating to tidal currents. OUTLINE Factors affecting tides Tide tables Tidal currents TIDES AND TIDAL COMPUTATIONS The tides are of primary importance to ship captains when preparing to get underway or enter port. Although Navy Quartermasters do the majority of tidal computations, many oceano-graphy offices are tasked with computing and publishing tidal data for their local area.Learning Objective: Recognize the effect of the Moon and the Sun on tides. FACTORS AFFECTING TIDES Gravitational attraction exists between Earth and the Moon and Earth and the Sun. It is an invisible force that acts to pull two bodies together. The strength, or magnitude, of the attraction is dependent on the mass of the two bodies and the distance between them.Sir Isaac Newton deduced that gravitational attraction is (1) directly proportional to the product of the masses of two bodies and (2) in-versely proportional to the square of the distance between them. In other words, the force of gravity increases if the product of the mass of the two bodies increases or if the distance between the two bodies decreases. Even though the Earth-Sun mass is much greater than the Earth-Moon mass, the gravitational attraction between Earth and the Moon is approximately 2 1/2 times greater than the Earth-Sun attraction. The reason for this is that the Moon is nearer Earth. |
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