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Tides Fig. 10-6 Fig. 10-7.

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Presentation on theme: "Tides Fig. 10-6 Fig. 10-7."— Presentation transcript:

1 Tides Fig. 10-6 Fig. 10-7

2 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)

3 Example: Poughkeepsie, New York

4 Tide-producing forces
1. Gravity and motions among Earth, Moon, and Sun (causes the bulge toward the moon)

5 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)

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

7 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

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

9 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

10 Time between successive high tides shifts day after day
Moon rises later each successive night

11 Solar tidal bulges Tide-producing force of Sun is smaller
Sun much farther away

12 Month tidal cycle Spring tides New Moon, Full Moon
Higher than usual high tides Fig


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

15 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

16 Unequal tidal range Fig

17 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

18 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

19 Mixed Most tides are mixed Two high, two low tides per lunar day
Unequal range Most tides are mixed

20 Standing waves Forced standing wave caused by tides
Free-standing waves caused by strong winds or seismic disturbances Fig

21 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

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

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

24 Tidal Calendars

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