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# Tides

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• 1. CHAPTER 9Tides © 2011 Pearson Education, Inc.
• 2. Chapter OverviewTides are the rhythmic rise and fall of sea level.Tides are very long and regular shallow-water wavesTides are caused by gravitational attraction of the Sun, Moon, and Earth © 2011 Pearson Education, Inc.
• 3. 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 © 2011 Pearson Education, Inc.
• 4. Tide-Generating ForcesBarycenter between Moon and Earth Common center of mass or balance point Beneath Earth’s surface because of Earth’s greater mass © 2011 Pearson Education, Inc.
• 5. Gravitational ForcesEvery particle attracts every other particleGravitational force proportional to product of masses Increase mass, increase force © 2011 Pearson Education, Inc.
• 6. Centripetal ForceCenter-seeking forceTethers Earth and Moon to each other © 2011 Pearson Education, Inc.
• 7. Resultant ForcesMathematical difference between gravitational and centripetal forcesRelatively small © 2011 Pearson Education, Inc.
• 8. Tide-Generating ForcesResultant force has significant horizontal componentPushes water into two simultaneous bulges One toward Moon One away from Moon © 2011 Pearson Education, Inc.
• 9. 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 © 2011 Pearson Education, Inc.
• 10. Tidal Bulges – Sun’s EffectSimilar to lunar bulges but much smallerMoon closer to Earth © 2011 Pearson Education, Inc.
• 11. Earth’s Rotation and TidesFlood tide – water moves toward shoreEbb tide – water moves away from shore Earth’s rotation moves different geographic locations into bulges © 2011 Pearson Education, Inc.
• 12. Monthly Tidal CycleSpring tides New or full moons Tidal range greatestNeap tides Quarter moons Tidal range least © 2011 Pearson Education, Inc.
• 13. Earth, Moon, and Sun Positions Relative toSpring and Neap Tides © 2011 Pearson Education, Inc.
• 14. Idealized Tide PredictionTwo high tides/two low tides per lunar daySix lunar hours between high and low tides © 2011 Pearson Education, Inc.
• 15. Real TidesContinents and friction with seafloor modify tidal bulgesTides are shallow-water waves with speed determined by depth of water © 2011 Pearson Education, Inc.
• 16. 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 (1 higher than the other)/two low tides (1 lower than the other) per day Tidal range different Most common © 2011 Pearson Education, Inc.
• 17. Tidal Patterns © 2011 Pearson Education, Inc.
• 18. Monthly Tidal Curves © 2011 Pearson Education, Inc.
• 19. Tides in Coastal WatersStanding Waves Tide waves reflected by coast Amplification of tidal range Example: Bay of Fundy maximum tidal range 17 meters (56 feet) © 2011 Pearson Education, Inc.
• 20. Bay of Fundy – World’s Largest Tidal Range © 2011 Pearson Education, Inc.
• 21. Tides in Coastal WatersTidal Bores Wall of water Moves up certain rivers Tide-generated © 2011 Pearson Education, Inc.
• 22. Coastal Tidal CurrentsWhirlpool Rapidly spinning seawater Restricted channel connecting two basins with different tidal cycles © 2011 Pearson Education, Inc.
• 23. Moon and Tides