Tides

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Tides

  1. 1. Chapter 10: TidesFig. 10-7Fig. 10-6
  2. 2. Tide-producing forces Gravity andmotions amongEarth, Moon,and SunFig. 10-2
  3. 3.  Centripetal force“tethers” Moonto Earth Directed awayfrom barycenter Click for ‘Kiddie’version of tidesFig. 10-4 a,b
  4. 4. Resultant tidal forces Gravitationalforce, Earth andMoon Centripetal force,Earth and Moon Resultant forcemoves oceanwater horizontallyFig. 10-7Fig. 10-6
  5. 5. Tidal bulges Two equal andopposite tidalbulges Earth rotatesbeneath tidalbulges Two high tides Two low tides Per day Click on picture Fig. 10-8
  6. 6. Complications to simplestequilibrium theory Oceans do not cover entire Earth Oceans do not have uniform depth Friction between ocean and seafloor Continents Moon not always in same place withrespect to Earth Lunar day longer than solar day
  7. 7. Lunar day Moon revolves around Earth Earth has to “catch up” with Moon toreach same positionFig. 10-9
  8. 8.  Time between successive hightides shifts day after day Moon rises later eachsuccessive night
  9. 9. Solar tidal bulges Tide-producing force of Sunless than half of Moon’s Sun much farther away
  10. 10. Month tidal cycle Spring tides New Moon, FullMoon Earth, Moon,Sun syzygy Higher thanusual high tidesFig. 10-12
  11. 11.  Neap tide First Quarter,Last Quarter Earth, Moon, Sunquadrature Lower than usualhigh tideFig. 10-12
  12. 12. Declination of Sun and Moon Orientation of Sun, Moon to Earth’sequator Sun 23.5oN and S, yearly cycle Moon 28.5oN and S, monthly cycle Unequal tides Successive tides different tidal range
  13. 13. Unequal tidal rangeFig. 10-15
  14. 14. Elliptical orbits Click picture forMoon phases Perigee Lunar tidal forcegreater Higher high tides Apogee Lunar tidal forcelesser Lower high tidesFig. 10-16
  15. 15. Dynamic theory of tides Tide shallow-water wave Speed varies with depth Lags behind Earth’s rotation Rotary flow in open ocean basins Amphidromic point Cotidal lines
  16. 16. Rotary flow Crest (high tide) rotates Counterclockwise in NorthernHemisphere Clockwise in SouthernHemisphere
  17. 17. Tidal patterns Diurnal 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
  18. 18.  Mixed Two high, two low tides per lunarday Unequal range Most tides are mixed
  19. 19. Standing waves Forced standingwave caused bytides Free-standingwaves caused bystrong winds orseismicdisturbancesFig. 10-22
  20. 20.  Node maximumhorizontal flow Antinodemaximumvertical flowFig. 10-23
  21. 21. Bay of Fundy Largest tidal range(spring tide max 17m) Shape of basin Oscillation periodclose to tidal period Shoals and narrowsto north Basin oriented towardright (Coriolis moveswater toward right) Click picture to seeFig. 10-24
  22. 22. Tidal bores Wave created bytide rushesupstream Large tidal range Low-lying coastalriver Max 8 m high Click picture to seea tidal bore.Fig. 10A
  23. 23. End of Chapter 10: TidesFig. 10-7Fig. 10-6

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