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Ocean101-Ch10 - TIDES"I derive from the celestial phenomena...

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1 TIDES TIDES “I derive from the celestial phenomena the forces of gravity with which bodies tend to the sun and several planets. Then from these forces, by other propositions which are also mathematical, I deduce the motions of the planets, the comets, the moon, and the sea.” –Sir Isaac Newton, 1686 Tides Written observations by Herodotus (~450 BCE, remember him?) Took Isaac Newton (“Mr. Gravity”) to explain History of efforts to harness tidal energy date back to at least Middle Ages (Europe) Lift water to greater height (“potential energy”) ! It runs downhill (“kinetic energy”) Can be used to turn wheel, generate electricity, etc. Tides do this naturally, regularly (though storage, ecological effects, etc.) Tides http://www.mobilegeographics.com:81/locations/5706.html Bellevue Seattle tide station Puget Sound Lake Washington At Seattle, tide dropped 4 feet (from +2 ft to -2 ft) during one 2-hour class period! http://www.dairiki.org/ tides/daily.php Tides at Seattle Seattle vs vs Tacoma Tacoma vs vs Port Townsend Port Townsend
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2 http://tidesonline.nos.noaa. gov/geographic.html Water levels: Observed vs predicted Wind speeds & directions Air pressure Air temperature & water temperature Tides Tides Tide Tide = Periodic rise and fall of sea surface (avg sea level) at a given location - Occurs throughout world Measured most often along coast, where shoreline provides fixed frame of reference Periodic measurement Periodic measurement = Measured at fixed time intervals (e.g., hourly). Usually a measuring stick embedded in bottom. Continuous measurement Continuous measurement = With float and electronic recording device How Long Is a How Long Is a “ Day Day”? Earth spins on its own axis once per solar day One complete spin per solar day = 24 hr Moon revolves around Earth once per lunar day One complete revolution per lunar day = 24 hr 50 min (Earth revolves around Sun once per year) (One complete revolution per year = 365.25 days) Solar day Solar day = 24 hr, Tidal day Tidal day = Lunar day Lunar day = 24 hr 50 min Moon revolves around Earth in same direction as Earth spins on its axis, though not quite perfectly matched timing (Moon takes a little longer)
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3 How Long Is a How Long Is a “ Day Day”? Solar day Solar day = 24 hr Tidal day = Lunar day Tidal day = Lunar day = 24 hr 50 min Solar Day Lunar Day So each day, tides arrive ~50 minutes later (And moon rises later & later) See Fig. 10.8, p. 232 How Are Tides Classified?
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