19. Tides_OutlineChapter 9 - Tides1. Key Questions:What causes tides?What is the difference between a lunar and solar day?What does this mean for tidal periods?How do the positions of Sun and Moon affect tidal range?How do real-life tides differ from idealized predictions?2. Overview of TidesRhythmic rise and fall of ____ ____Very long and regular shallow-water ____Caused by gravitational attraction of Sun, Moon, and Earth3. Newton’s Law of GravitationEvery particle with mass attracts every other particleGravitational force = G m1m2/r2G=Gravitational constantG = 6.67 × 10-11m3kg-1s-2Gravitational constant4. Which has the bigger effect on tides—Sun or Moon? Fig. 9.10Sun has more ________But…Moon is much ________Sun’s force is only 46% of Moon’s force creating tidesMoon is more important! – ~2x tidal force of Sun5. Equilibrium Theory of TidesASSUMPTIONSThe ocean has uniform depth on a spherical Earth.This ocean responds instantly to the gravitational forces of the sun and moonObviously these are crude approximations…7. Gravitational forces on water particles Fig. 9.3Every particle attracts every other particleGravitational force proportional to product of massesInversely proportional to square of separation distance8. Centripetal force Fig. 9.4Gravity (“string”) holds earth and moon togetherOrbiting bodies are held togetherPulls toward center of orbit, parallel to plane of orbitForce is the same at all points on the sphere9. Centripetal force Fig. 9.5Same magnitude and direction everywhere on earthTethers Earth and Moon to each other10. Tide-producing forces Fig. 9.6________forces = differences between centripetal and gravitational forcesTide-generating forces are ________components of resultant forceshttps://goo.gl/eBCMYZ10.1 Tidal forces (lunar) Fig. 9.7Small horizontal forces pull seawater into two bulges on opposite sides of Earth29. Tides_Outline11. Tidal bulges (lunar) Fig. 9.8Model used in equilibrium tide theory2 equal bulges - Moon side and opposite side of EarthOcean covers entire earth (no continents) at uniform depthAssume no friction with the seabed12. Tidal bulges (lunar)Moon closer to Earth so lunar tide-producing force greater(~2x) than that of SunFlood tide, seawater moves on shore toward High TideEbb tide tide, seawater moves offshore toward Low TideIs there a tide in the atmosphere? Lithosphere?What if the earth had no moon? What would the tides look like?13. Lunar Day Fig. 9.9https://goo.gl/bbYGx0Moon orbits Earth24 hours 50 minutes for observer to again see moon directly overheadHigh tides are 12 hours and 25 minutes apart14. Tidal bulges (solar)Similar to lunar bulges but half the ________Moon closer to EarthNew/full moon – tidal range greatest – spring tideQuarter moons – tidal range least – neap tideTime between spring tides about two ________Tidal range –Spring tide – high high tides and low low tides – high tidal rangeNeap tide – small high tides and small low tides – low tidal range15. Earth-Moon-Sun positions and spring and neap tides – animation Fig. 9.11https://goo.gl/DmuidPUp to now we have been assuming…Moon’s orbit is centered on the ________Orbits are circularEarth’s axis is vertical relative to its orbitNow for real life…The orbital plane of the moon is not aligned with Earth’s equatorOrbits are slightly ellipticalEarth’s axis is tilted 23.5° relative to orbit around sunMoon’s orbit around earth is tilted 5°Complicating factors of Earth/Moon/Sun orientation5 degree tilt of moon’s orbit, 23.5 degree tilt of Earth’s axis = 28.5 degree tilt of16. Complicating factors: declination Fig. 9.13Angular distance Moon or Sun above or below Earth’s equatorSun to Earth: 23.5oN or S of equator39. Tides_OutlineMoon to Earth: 28.5oN or S of equatorShifts lunar and solar bulges from equatorUnequal tides17. Declination and tides Fig. 9.16Unequal tides (unequal tidal ranges)19. Idealized tide predictionTwo high tides/two low tides per lunar daySix lunar hours between high and low tides20. Real tidesEarth not covered completely by ________Continents and ________with seafloor modify tidal bulgesTides are shallow water waves with speed determined by depth of water21. Tidal patterns Fig. 9.18Diurnal tidal pattern – one high tide, one low tide per lunar daySemidiurnal tidal pattern - two high tides, two low tides per lunar dayMixed tidal pattern – 2 highs, 2 lows of different heightshttp://goo.gl/J2nDvaFig. 9.19Monthly recordsTidal patterns remain the same at one locationEven through spring/neap transitions22. Tides in coastal watersAmplification of tidal rangeExample, Bay of Fundy maximum tidal range 17 m (56 ft)Between Nova Scotia and New Brunswick, Canada Fig. 9.2023. Pictures of Bay of Fundy - boats, harbor 3 slides24. Tides in coastal waters Fig. 9AA tidal bore moving up a river25. Tidal bores moving up an estuary/river 4 slides26. Coastal tidal currents Fig. 9.21Reversing currentFlood current – sea risesEarth moves into bulgeEbb current - sea dropsEarth moves out of bulgeHigh speed flow in restricted channelsCoastal tidal currentsAs tide level drops_____ currentsSea level drops – water ‘moving’ off shoreMaximum velocity 1/2 way between high and low tideAt low tide49. Tides_OutlineVelocity = 0 (low slack water)As tide level increases_______currents‘Moving’ toward shoreAt peak high tideVelocity = 0 (high slack water)27. Tide-generated power________resourceDoes not produce power on demandPossible harmful environmental effects28. Potential Tidal power sites29. Fig 9.24 La Rance tidal power plant at Saint-Malo, FranceThanks for picking up your trash as you leave!Review - Key Questions:What causes tides?Gravitational attraction between the Earth and moon, Earth and sunTide generating forceDepends on mass and distanceSun has more mass, but is much farther away from Earthmoon is strongest force on tidesTidal bulges formedEarth and Moon orbit around the barycenter (center of mass)gravitational attractionCentripetal forceTwo bulges createdMoon side, Gravitational attraction is greater than centripetal forceOpposite side, Centripetal force is greater than gravitational forceWhat is the difference between a lunar and solar day?Time elapsed from when Moon or Sun is overheadLunar day 50 minutes longerMoon has moved in orbit around Earth during 24 hoursWhat does this mean for tidal periods?Time for one full tidal cycle = 24 hrs 50 minutesHow do the positions of Sun and Moon affect tidal