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69 Cards in this Set
- Front
- Back
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What are the two kinds of tidal currents called?
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flood and ebb
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What is Newton's law of gravitation?
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F=GM_1M_2/D^2
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What is the ratio of the mass of the Earth to that of the moon?
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81 to 1
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Where is the barycenter of the Earth-moon system?
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4700 km from Earth's center, 1640 km below Earth's surface
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Why is the centripetal force the same for all points on the Earth?
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The radius of rotation about the barycenter is the same for all points.
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What is the ratio of the gravitational acceleration provided by the moon on points on either side of the Earth?
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1 to 1.034
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Why do the tides arise, in general?
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The centripetal force required is constant everywhere, but the gravitational force supplied is unequally distributed.
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What is the result of an imbalance in the centripetal and gravitational forces?
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a pressure gradient, which generates tides in fluids but not solids
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How much more do humans weigh when the moon is overhead than when it is on the horizon?
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.1 mg
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Where are the largest tidal forces?
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under the moon and on the other side
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What must happen for the tidal forces to do anything?
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The force must be directed horizontally.
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Where is the horizontal tidal force the greatest?
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when the moon is 45 degrees above the horizon
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For a two-body system, what is the tide-generating force proportional to?
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directly to the mass of the second body and inversely to the cube of the distance between the bodies
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What percentage of the moon's tide-generating force does the sun provide?
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46%
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What is a tidal curve?
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a graph of water level against time
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What are the three types of tides?
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diurnal, semidiurnal, and mixed
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What is the period of a lunar diurnal tide?
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24:49
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What is the period of a lunar semidiurnal tide?
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12:24:30
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What is the difference between semidiurnal and mixed tides?
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The high tides are equal for semidiurnal tides and unequal for mixed tides.
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What are the four extremes of mixed tides called?
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higher high water, lower high water, higher low water and lower low water
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What tides are found on the US coast?
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mixed in the Pacific, semidiurnal in the Atlantic, and diurnal in a part of the Gulf of Mexico
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Where are diurnal tides found around the world?
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the Gulf of Mexico, New Guinea, and parts of Antarctica
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Where are semidiurnal tides found around the world?
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most of Europe and Africa, the Atlantic coast of the Americas, the Bay of Bengal, Greenland, northern Australia and New Zealand
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Where are mixed tides found around the world?
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the Pacific Ocean, Caribbean Sea, Indian Ocean, and Siberia
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How much time passes between consecutive spring tides?
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14.8 days, half a lunar month
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What does equilibrium tide theory assume?
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Earth is covered in deep oceans with no friction between them and the seafloor.
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How can the equilibrium tide theory explain the three types of tides?
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If the moon is at near-maximum declination, the bulges at a particular latitude are unequal, producing diurnal tides at high latitude, mixed tides at mid-latitude, and semidiurnal tides at low latitude.
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When in the lunar cycle do spring tides result?
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at new and full moon
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When in the lunar cycle do neap tides result?
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at first and third quarter, or quadrature
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What is the period of a solar diurnal tide?
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24:00
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What is the period of a solar semidiurnal tide?
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12:00
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What are the components of the overall tide called?
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partial tides
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What are the major semidiurnal partial tides?
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principal lunar, principal solar, larger lunar ecliptic, and lunisolar semidiurnal
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What are the major diurnal partial tides?
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lunisolar diurnal, principal lunar diurnal, and principal solar diurnal
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What are the partial tides with periods longer than a day?
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lunar fortnightly, lunar monthly, solar semiannual, and anomalistic year
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What can cause each partial tide?
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Earth's rotation, changes in declination, and variation in orbital distance
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What four factors make Earth's tides differ from the equilibrium model?
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landmasses, ocean depth, differences in orbital velocity, and the Coriolis effect
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What kinds of wave is a tide wave?
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shallow-water, forced wave
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How fast can tide waves go?
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limited by depth, just 700 kph
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Why must the tide wave lag behind the moon or sun?
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It can only go 700 kph, whereas the moon and sun move at around 1620 kph at the equator.
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How does seafloor topography affect the tide wave?
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It refracts it the same way waves are refracted on beaches.
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How do differences in orbital velocity affect the tide wave?
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At high latitudes, the orbital velocity is not larger than the velocity of the tide wave, whereas at low latitudes, it must lag.
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How does the amphidromic system result from tidal theory?
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As waves in horizontally elliptical orbits, water in the tide wave is subject to the Coriolis effect, and it rotates to form a standing wave.
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Which direction does a wave crest travel in the Northern Hemisphere amphidromic systems?
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counterclockwise
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What lies at the center of an amphidromic system?
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a node, the amphidromic point, where the tidal range is zero
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How do partial tides affect dynamic tide theory?
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Each component sets up its own set of amphidromic systems.
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Which way does equilibrium tide theory predict the tide wave should go?
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east to west, like the sun and moon
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Where does the equilibrium theory of tides best predict the tide wave?
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the Southern Ocean, where continents stay out of the way and orbital velocities are low enough
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Which way does the tide wave go in the Atlantic Ocean?
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south to north, fed by the Southern Ocean wave and deflected both right and left with the Coriolis effect
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Why do semidiurnal tides dominate the North Atlantic?
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The amphidromic system is well-tuned to the semidiurnal oscillation.
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Why do diurnal tides dominate the Gulf of Mexico?
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The Gulf of Mexico is better tuned to the diurnal standing waves than the semidiurnal.
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Why do mixed tides dominate the Pacific Ocean?
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The Pacific is wider than the Atlantic and has a stronger east-west tide wave, allowing both diurnal and semidiurnal waves to become well tuned.
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How do tides generate currents?
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The orbital velocities of their waves are horizontal currents.
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How are tidal waves represented in the open ocean?
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They are slow, circling currents of water.
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Why do maximum tidal currents rarely coincide with high or low tide?
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They are combinations of many components, progressive and standing waves, and the waves are reflected and refracted.
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When are tidal currents at a maximum for progressive waves?
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at high and low tide
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When are tidal currents at a maximum for standing waves?
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halfway between high and low tide
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What information do tide tables give us on tidal currents?
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Nothing can be gathered from high tide and low tide times, but the tidal range gives an indication as to the magnitude.
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How are river tides different?
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Because the high tide wave can move more easily, a larger time gap exists after high tide than low tide.
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When do tidal bores occur?
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when the flood current of a tide goes faster than shallow water waves in a channel or bay
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What are the trademarks of a progressive wave in a bay?
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moving locations of slack water and currents in opposite directions in different parts of the bay
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What are examples of bays with progressive and standing wave tides?
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Chesapeake Bay has a progressive wave tide, and Long Island Sound has a standing wave tide.
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How is tidal prediction done?
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by looking at records and using harmonic analysis
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What is harmonic analysis?
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a way of determining the individual components of a wave, and their parameters
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In general, how do tides affect organisms?
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Organisms in the intertidal zone must deal with partial exposure to the air. Some organisms use the tides to time reproductive cycles.
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What are examples of organisms that use high tide to spawn?
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corals, horseshoe crabs, sea turtles, grunions, and surf smelts
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What advantages does tidal energy offer?
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It's renewable, clean, and supplies a lot of energy.
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Where would tidal energy be most productive?
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bays or estuaries with tidal ranges above 5 meters, where a dam can be built
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What problems does tidal energy have?
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Tides cannot operate continuously, and building a dam significantly alters the ecology of the area.
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