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What Are Tides?Tides are the daily rise and fall of Earth’s waters on its coastlines
As the tide comes in, the level of water on the beach rises, and as the tide goes out, the level of water on the beach goes down
Tides occur in all bodies of waterBut most noticeable along the shore of large lakes and the ocean
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High TidesHigh tides are when the water reaches its highest point.
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Low TidesLow tides are when the water reaches its lowest point
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• Tidal range: the difference between high and low tide
Intertidal zoneHigh tide
Low tide
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Alma at High Tide
Alma at Low Tide
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1. Gravitational pull of the moon and sun
2. Centripetal force of the rotating Earth
Tides are generated by:
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The Cause of TidesGravitational and centripetal forces pull ocean water
into a huge wave with a wavelength the size of an ocean basin.
In principle, the sun and moon create two bulges on opposite sides of the Earth.
The relative positions of the sun and moon change slowly, so the bulge changes position
Tidal bulges follow Moon as it rotates around Earth The earth is also rotating, so as a coastline rotates into
the bulge, the tide rises. As it rotates out, the tide falls.
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Centripetal force vs Centrifugal force
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Why the Moon is Stronger than the SunWhich has a bigger effect on the earth and its
tides?
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Neap Tides
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The Sun, Moon, and Types of Tides
When the moon is in a quarter phase, the lines from it and the sun to the Earth form a right angle. The sun’s gravitation pulls to the side of the
moon’s tidal bulge. This tends to raise the low tide and lower the
high tide.These weaker tides are called neap tides.
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Spring Tides
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Spring tidesWhen there’s a new moon (no moon visible),
both the sun and the moon are aligned on the same side of Earth, and during a full moon, the sun and moon are aligned on opposite sides of Earth.
When the sun, the moon, and the Earth are aligned on a 180° plane, their gravity works together, raising the height of the tidal water bulges
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CENTRIPETAL
GRAVITATIONAL FORCE
GRAVITATIONAL & CENTRIPETAL
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The Cause of TidesIsaac Newton proposed a
simplistic explanation of tides equilibrium theory, which
assumes that the Earth is perfectly uniform
His Universal Gravitation theory helped to explain how the gravity of the moon (and the sun) were related to tides
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Universal Gravitation Law
Newton’s law states that all particles of mass have a gravitational attraction for all other particles
Gravitational force is: proportional to the sum of the two masses inversely proportional to the square of the
distance between their centers of mass
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The moon’s gravitational pull on liquids is much more noticeable than on solids.
Because liquids move more easily than solids
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The Cause of TidesPierre-Simon Laplace modified Newton’s model
to account for tidal variationsHis model is called dynamic theory of tides
lunar and solar gravityimperfect sphere of the Earththe season time of the monthshape of the ocean basinObstacles, reefs, islandsCoriolis effect all influence the tides
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Tides rotate around more than a dozen amphidromic pointswhere the water doesn’t rise and fall with
the tides tides occur in a pinwheel-shaped,
standing-wave patternThere is no vertical tidal movement at an
amphidromic point, but away from that point there may be magnified tidal motion as the tides change throughout the day
Amphidromic points
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Tidal flow around an amphidromic point.tidal magnitude is shown on the dotted lines and the pinwheel represents the progression of the tide around the basin.
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Tidal Patternsdiurnal tide - a single high and low tide dailyThe Gulf of Mexico has diurnal tides.semidiurnal tides - two roughly equal high and low
tides daily, as predicted by Newton’s model.The east coast of US has semidiurnal tides, Cape Codmixed tides – two unequal high and low tides dailyHawaii, Pacific coast of the US have mixed tidesLunar day has 24.8 hr or 24 hr 50 minLunar day is 50 minutes longer than a solar day
because the Moon is moving in its orbit around Earth
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TIDAL CURRENTS: The rise and fall of the tide is accompanied by the horizontal flow of water called a tidal current. The usual terms used to describe the direction of this horizontal movement are ebb and flood.Ebb currents occur when tidal currents are moving away from the coast - seaward.Flood currents move toward the coast - landward. Under certain conditions, tidal currents can move more than 10 knots.
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The Bay of Fundy: Site of the world’s largest tidal range
Tidal energy is focused by shape and shallowness of bay or ocean basin
Maximum spring tidal range in Minas Basin = 17 meters (56 feet)
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http://www.youtube.com/watch?v=u3LtEF9WPt430 sec bay of fundy time lapse tides good
http://www.youtube.com/watch?v=dmcMQU5AAg4best 2 min
http://www.youtube.com/watch?v=LWumonz87rA1.5 min nova scotia fast but wind noise
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Highest TidesOne of the world's largest tides occurs in
Turnagain Arm south of Anchorage Alaska – 42 feet
http://margymuses.blogspot.com/2010/03/tidal-flats-anchorage.html mud flats near anchorage in cook inlet
Tides in Lake Superior are measured in inches
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Tidal Patterns and Currentsdaily tides create a current that flows into and out of bays,
rivers, harbors, and other restricted spacesThe inflow is called a flood current the outflow is called a slack currentThe midpoint between high and low tides creates slack
tide, when there is little water movingLarge ships may only be able to enter or exit a harbor
during high tide to ensure sufficient water depth for travel
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Tidal boreThe incoming high tide produces a wave that
flows into a river, bay, or other relatively narrow area
is a true tidal wave and can be several meters high
On the Amazon River in South America and the Severn River in England,surfers can take long rideson the tidal bore
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Tidal borehttp://www.youtube.com/watch?
v=xiKoWAiqufE quintang river 1 min news report 90 ft
http://www.youtube.com/watch?v=J8Q1ecIr-NM3 min in Chinese good
http://www.youtube.com/watch?v=SNjVlUBmtGo50 http://www.youtube.com/watch?v=4DlqVuNMydk national geographic 1 min
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Grunion are the only fish that come completely out of the water to spawn
Spawning cycles are timed precisely with the tides
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Palolo wormThe Pacific palolo worm (Eunice viridis) and its West Indian relative
(E. fucata) incredible reproductive behavior linked to the lunar cycle the rear half of each worm transforms dramatically, developing fast-
growing reproductive organs. The worm itself reverses its position within its tube, so that it is now pointing head-down,
the posterior body half breaks off from the rest of the worm and swims up toward the sea's surface - it has developed a pair of eyes to assist it
At the surface, the bag bursts, releasing its contents – millions of palolo worms have all undergone this radical metamorphosis at precisely the same time, the sea is soon awash with a mass of sperm and eggs,
It occurs twice a year on the neap tides of the last quarter moon in October and November for the Pacific species, and the third quarter moon in June and July for the West Indian species of palolo worm
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Palolo worm spawning
http://seapics.com/feature-subject/marine-invertebrates/palolo-worm-pictures.html
palolo_smitsonian2_lge
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Atmospheric TidesLunar gravitational affects earth’s
atmosphereCause slight periodic fluctuations in weather
patterns
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