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© 2011 Pearson Education, Inc. CHAPTER 9 Tides

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© 2011 Pearson Education, Inc. What are Tides? Tides – periodic raising and lowering of ocean sea level Occurs daily Caused by combination of gravity and motion between Earth, Moon, and Sun Isaac Newton’s gravitational laws explain relationship

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Tidal Range = Intertidal Zone

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© 2011 Pearson Education, Inc. Gravitational Forces Every particle attracts every other particle Gravitational force proportional to product of masses –Increase mass, increase force Inversely proportional to square of separation distance

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© 2011 Pearson Education, Inc. Gravitational Forces Greatest force at zenith – closest to moon Least force at nadir – furthest from moon and opposite zenith

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© 2011 Pearson Education, Inc. Tide-Generating Forces Resultant force has significant horizontal component Pushes water into two simultaneous bulges –One toward Moon –One away from Moon

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© 2011 Pearson Education, Inc. Tidal Bulges – Moon’s Effect Small horizontal forces push seawater into two bulges. Opposite sides of Earth

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The gravitational pull of the Sun is almost 200 times greater than the Moon, but since the Moon is almost 400 times closer to the Earth than the Sun, the Moon’s gravitational pull is more than twice that of the Sun.

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It takes 24 hours for the earth to completely revolve around the sun. If there are 2 high tides AND 2 low tides each day– then how much time is there between each tide?

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© 2011 Pearson Education, Inc. Tidal Phenomena Tidal period – time between high tides Lunar day –Time between two successive overhead moons –24 hours, 50 minutes Moon orbits Earth High tides are 12 hours and 25 minutes apart

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Tides for Northport, Northport Bay starting with October 20, 2008 Day Tide Time Feet 20 High 3:59 AM 7.1 20 Low 10:17 AM 0.6 20 High 4:20 PM 7.8 20 Low 11:08 PM 0.4

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© 2011 Pearson Education, Inc. Earth’s Rotation and Tides Flood tide – water moves toward shore Ebb tide – water moves away from shore Tidal bulges are fixed relative to the Sun’s and Moon’s positions –Earth’s rotation moves different geographic locations into bulges In between Flood and Ebb tide?

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© 2011 Pearson Education, Inc. Monthly Tidal Cycle Spring tides –New or full moons –Tidal range greatest Neap tides –Quarter moons –Tidal range least

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© 2011 Pearson Education, Inc. Earth, Moon, and Sun Positions Relative to Spring and Neap Tides

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TIDES

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© 2011 Pearson Education, Inc. Complicating Factors Elliptical orbits Earth around Sun: –Tidal range greatest at (January) –Tidal range greatest at perihelion (January) –Tidal range least at aphelion (July) Moon around Earth:Moon around Earth: –Tidal range greatest at perigee (Moon closest to Earth) –Tidal range least at apogee (Moon furthest from Earth) –Perigee–apogee cycle is 27.5 days

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© 2011 Pearson Education, Inc. Effects of Elliptical Orbits

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© 2011 Pearson Education, Inc. Idealized Tide Prediction Two high tides/two low tides per lunar day Six lunar hours between high and low tides

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© 2011 Pearson Education, Inc. Tidal Patterns Diurnal –One high tide/one low tide per day Semidiurnal –Two high tides/two low tides per day –Tidal range about same Mixed –Two high tides/two low tides per day –Tidal range different

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© 2011 Pearson Education, Inc. Tidal Patterns

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Semidiurnal Tide

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© 2011 Pearson Education, Inc. Bay of Fundy – World’s Largest Tidal Range

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Bay of Fundy 115 billion tonnes of water flow in and out of the bay With measurements of a 56 feet tidal range

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© 2011 Pearson Education, Inc. Tides and Marine Life Tide pools and life Grunion spawning

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© 2011 Pearson Education, Inc. Tide-Generated Power Does not produce power on demand Possible harmful environmental effects Renewable resource First Asian power plant in 2006 United Kingdom proposed building world’s largest tidal power plant

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© 2011 Pearson Education, Inc. Power Plant at La Rance, France Successfully producing tidal power since 1967

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