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Tides Fig. 10-6 Fig. 10-7

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What are tides???? Tide- the periodic, rhythmic rise and fall of the sea surface - they are essentially huge standing waves (two waves moving in opposite directions)

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**Example: Poughkeepsie, New York**

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**Tide-producing forces**

1. Gravity and motions among Earth, Moon, and Sun (causes the bulge toward the moon)

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**2. Centripetal force “tethers” Moon to Earth**

- Inertia- objects at rest will stay at rest or object in motion will say in motion unless acted upon by an external force - (causes the bulge away from the moon)

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**Resultant tidal forces**

Gravitational force and centripetal force Resultant force moves ocean water horizontally Fig. 10-6 Fig. 10-7

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**Tidal bulges Two equal and opposite tidal bulges**

Earth rotates beneath tidal bulges Two high tides and two low tides per day Fig. 10-8

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**In the video clip ; Dr. Hoffman, from Old Dominion University, explains the tides.**

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**Lunar day-24 hours and 50 minutes**

Earth has to “catch up” with Moon to reach same position Moon revolves around Earth every days ( days between full moons) Fig. 10-9

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**Time between successive high tides shifts day after day**

Moon rises later each successive night

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**Solar tidal bulges Tide-producing force of Sun is smaller**

Sun much farther away

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**Month tidal cycle Spring tides New Moon, Full Moon**

Higher than usual high tides Fig

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**Neap tide First Quarter, Last Quarter Lower than usual high tide**

Fig

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**Declination of Sun and Moon**

Orientation of Sun and Moon is never directly over the equator Sun 23.5o N and S, yearly cycle Moon 28.5o N and S, monthly cycle Unequal tides Successive tides different tidal range

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Unequal tidal range Fig

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**Elliptical orbits Perigee Earth and Moon are closer**

Lunar tidal force greater= Higher high tides Apogee Earth and Moon are futher away Lunar tidal force lesser= Lower high tides Fig

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**Tidal patterns Diurnal Semidiurnal**

One high, one low tide per lunar day Period of tidal cycle 24 hours 50 minutes Semidiurnal Two high, two low tides per lunar day Period 12 hours 25 minutes Equal range

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**Mixed Most tides are mixed Two high, two low tides per lunar day**

Unequal range Most tides are mixed

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**Standing waves Forced standing wave caused by tides**

Free-standing waves caused by strong winds or seismic disturbances Fig

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**Bay of Fundy Largest tidal range (spring tide max 17 m) Shape of basin**

Oscillation period close to tidal period Shoals and narrows to north Basin oriented toward right (Coriolis moves water toward right) Fig

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**The video clip shows tides in the Cape Cod Estuary, Massachusetts**

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**The video clip shows tides on Cape Cod Beach, Massachusetts.**

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Tidal Calendars

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