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tide


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1 The periodic rise and fall of the Earth's oceans, caused by the relative gravitational attraction of the Sun, Moon, and Earth. The effect of the Moon is about twice that of the Sun, giving rise to the spring–neap cycle of tides. Variation in tides is caused by: (a) changes in the relative positions of the Sun, Moon, and Earth; (b) uneven distribution of water on the Earth's surface; and (c) variation in the sea-bed topography. Semi-diurnal tides are those with two high and two low waters (period 12 hours and 25 minutes) during a tidal day (24 hours and 50 minutes). Diurnal tides have one high and one low water during a tidal day.

(a) changes in the relative positions of the Sun, Moon, and Earth; (b) uneven distribution of water on the Earth's surface; and (c) variation in the sea-bed topography.

2 See earth tides.

Tide

Subjects: Earth Sciences and Geography.


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