Tides

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Tides

  1. 1. TidesTidesWhat are they?What are they?What are they caused by?What are they caused by?Are there different kinds of tides?Are there different kinds of tides?
  2. 2. • Those of you who have spent some time onThose of you who have spent some time onthe beach have probably noticed that the waterthe beach have probably noticed that the waterlevel of the ocean does not stay the same alllevel of the ocean does not stay the same allday long. Although waves continually wash theday long. Although waves continually wash theshore, the actual water level changes as theshore, the actual water level changes as theday passes.day passes.
  3. 3. • It rises for a period ofIt rises for a period ofhours until it reaches itshours until it reaches itshighest level, and thenhighest level, and thenit begins to fall, orit begins to fall, orrecede, to its lowestrecede, to its lowestlevel. This rise and falllevel. This rise and fallof the ocean is knownof the ocean is knownas theas the tidetide. Its highest. Its highestand lowest levels are,and lowest levels are,of course called highof course called highand low tides.and low tides.
  4. 4. High TideHigh Tide Low TideLow Tide
  5. 5. Tides – What are they?Tides – What are they?• Tides are daily changes in the level ofTides are daily changes in the level ofocean water.ocean water.• They are the periodic rise and fall of theThey are the periodic rise and fall of thewater level in the oceans and other largewater level in the oceans and other largebodies of water.bodies of water.• I wonder how often this periodic rise andI wonder how often this periodic rise andfall happens each day?fall happens each day?
  6. 6. What causes tides?What causes tides?What moves ocean water?What moves ocean water?• WindWind• EarthquakesEarthquakes• Plate tectonicsPlate tectonics• The dominant force that moves oceanThe dominant force that moves oceanwater is the gravitational forces from bothwater is the gravitational forces from boththethe sunsun and theand the moonmoon..
  7. 7. Early thoughts about whatEarly thoughts about whatcaused the tides.caused the tides.• Some believed the earth was aSome believed the earth was aliving animal and the tides a resultliving animal and the tides a resultof its breathing.of its breathing.• Others, who thought the ocean’sOthers, who thought the ocean’swaters were the earth’s blood,waters were the earth’s blood,decided the tides were its pulse,decided the tides were its pulse,caused by the beating of its greatcaused by the beating of its greatheart.heart.
  8. 8. Early thoughts about whatEarly thoughts about whatcaused the tides.caused the tides.• Early followers of the religious prophetEarly followers of the religious prophetMuhammad believed that the rise and fallMuhammad believed that the rise and fallof the waters were caused when theof the waters were caused when the“Angel of the Sea” placed his foot in and“Angel of the Sea” placed his foot in andout of the ocean.out of the ocean.• Primitive natives thought the tides werePrimitive natives thought the tides werea sign of a sea god’s anger and madea sign of a sea god’s anger and madehuman sacrifices to please him.human sacrifices to please him.
  9. 9. The Lure of the MoonThe Lure of the Moon• The relationship between the phases ofThe relationship between the phases ofthe moon and the tides was discoveredthe moon and the tides was discoveredmore than 2,000 years ago!more than 2,000 years ago!• People of the time knew the moon hadPeople of the time knew the moon hadsomething to do with the tides, but theysomething to do with the tides, but theycouldn’t explain why.couldn’t explain why.
  10. 10. Sir Isaac Newton to the Rescue!Sir Isaac Newton to the Rescue!• Newton’sNewton’s UniversalUniversalGravitationGravitation theorytheoryhelped to explainhelped to explainhow the gravity ofhow the gravity ofthe moon (and thethe moon (and thesun) were relatedsun) were relatedto tides.to tides.
  11. 11. What causes tides?What causes tides?• The gravity of the moon pulls onThe gravity of the moon pulls oneverything on the Earth.everything on the Earth.• The moon’s gravitational pull on liquids isThe moon’s gravitational pull on liquids ismuch more noticeable than on solids.much more noticeable than on solids.• Why? Because liquids move more easilyWhy? Because liquids move more easilythan solids.than solids.
  12. 12. What causes tides?What causes tides?• How often tides occur and the differenceHow often tides occur and the differencein tidal levels depend on the position of thein tidal levels depend on the position of themoon as it revolves around the Earth.moon as it revolves around the Earth.• The moon’s pull is strongest on the part ofThe moon’s pull is strongest on the part ofthe Earth directly facing the moon.the Earth directly facing the moon.
  13. 13. High TideHigh Tide• The part of the ocean directly facing theThe part of the ocean directly facing themoon, bulges towards the moon.moon, bulges towards the moon.• There is a corresponding bulge on theThere is a corresponding bulge on theopposite side of the Earth.opposite side of the Earth.• These bulges are calledThese bulges are called high tide.high tide.
  14. 14. Low TideLow Tide• When high tides occur, water is drawnWhen high tides occur, water is drawnaway from the area between the highaway from the area between the hightides, which causestides, which causes low tideslow tides to occur.to occur.
  15. 15. How often is there a change in tides?How often is there a change in tides?Try to figure it out . . .Try to figure it out . . .• High tides happen on opposite sides ofHigh tides happen on opposite sides ofthe Earth.the Earth.• The Earth rotates once on its axis everyThe Earth rotates once on its axis every24 hours.24 hours.• How many high tides would any one placeHow many high tides would any one placein the ocean experience each day?in the ocean experience each day?
  16. 16. AnswerAnswer• The periodic rise andThe periodic rise andfall of the water levelfall of the water levelin the oceans andin the oceans andother large bodies ofother large bodies ofwater happens . . .water happens . . .• Twice each day!Twice each day!
  17. 17. What effect does the sunWhat effect does the sunhave on tides?have on tides?• The sun is much larger than the moon.The sun is much larger than the moon.• The sun is farther away from the EarthThe sun is farther away from the Earththan the moon.than the moon.Q: Which one (the sun or the moon) do youQ: Which one (the sun or the moon) do youthink has a bigger effect on tides?think has a bigger effect on tides?A: The moon, just because it is closer.A: The moon, just because it is closer.
  18. 18. Tidal VariationsTidal Variations• Tidal RangeTidal Range = the difference in levels of= the difference in levels ofocean water at high tide and low tide.ocean water at high tide and low tide.• Tidal ranges vary greatly due to theTidal ranges vary greatly due to thecombined forces of the sun and the mooncombined forces of the sun and the moonon the Earthon the Earth• It all depends on the position of the Earth,It all depends on the position of the Earth,moon, and the sun in space.moon, and the sun in space.
  19. 19. Spring TideSpring Tide• A tide with a largeA tide with a largetidal range that occurstidal range that occurstwo times a monthtwo times a month(new moon and full(new moon and fullmoon)moon)• Sun, Earth, and theSun, Earth, and themoon are alignedmoon are aligned
  20. 20. Neap TidesNeap Tides• A tide of minimumA tide of minimumrange that occursrange that occursduring the first andduring the first andthird quarters of thethird quarters of themoonmoon• The sun, Earth, andThe sun, Earth, andmoon form a 90moon form a 90degree angledegree angle
  21. 21. Weird Science!Weird Science!• The moon also creates tides in ourThe moon also creates tides in ouratmosphereatmosphere• They are calledThey are called lunar windslunar winds• They can be detected by studying slightThey can be detected by studying slightperiodic fluctuations in weather pattersperiodic fluctuations in weather patters• Very strange, indeed!Very strange, indeed!
  22. 22. ReviewReviewQ:Q: What are tides?What are tides?• TideTide = the periodic rise and fall of the water level= the periodic rise and fall of the water levelin the oceans and other large bodies of water.in the oceans and other large bodies of water.Q:Q: What is the dominant force that moves oceanWhat is the dominant force that moves oceanwater?water?• The gravitational forces from both theThe gravitational forces from both the sunsun andandthethe moonmoon..
  23. 23. Review (cont’d)Review (cont’d)Q:Q: Where is the moon’s pull is strongest onWhere is the moon’s pull is strongest onthe Earth?the Earth?• The moon’s pull is strongest on the part ofThe moon’s pull is strongest on the part ofthe Earth directly facing the moon.the Earth directly facing the moon.
  24. 24. Review (cont’d)Review (cont’d)Q:Q: Which one (the sun or the moon) has aWhich one (the sun or the moon) has abigger effect on tides?bigger effect on tides?• The moonThe moon
  25. 25. Review (cont’d)Review (cont’d)Q:Q: What is the difference in levels of oceanWhat is the difference in levels of oceanwater at high tide and low tide called?water at high tide and low tide called?• Tidal RangeTidal RangeQ:Q: Tidal ranges vary greatly due to theTidal ranges vary greatly due to thecombined forces of the _________ and thecombined forces of the _________ and the________ on the Earth________ on the Earth• Sun, moonSun, moon
  26. 26. Review (cont’d)Review (cont’d)Q:Q: How are the sun,How are the sun,Earth, and moonEarth, and moonsituated in space sosituated in space sothat we experience athat we experience aspring tide?spring tide?• Sun, Earth, and theSun, Earth, and themoon are alignedmoon are aligned
  27. 27. Review (cont’d)Review (cont’d)Q:Q: How are the sun,How are the sun,Earth, and moonEarth, and moonsituated in space sosituated in space sothat we experience athat we experience aneap tide?neap tide?• The sun, Earth, andThe sun, Earth, andmoon form a 90moon form a 90degree angledegree angle

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