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1.4Unit 3: The Solar System and energy

Tides

5 min read 7 parts Lesson 4 of 8 1 quiz

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Lesson summary

1.4 Tides — CHECKPOINT EARTH AND SPACE 0893 notes: Describe tides, explain their cause by the gravity of the Moon and Sun and describe their effects.Tide = the regular change in depth of the ocean in a place during the dayDepth — the distance from the water surface to the ocean b…

  • Tidal range
  • Largest range
  • Smallest ranges
  • Earth tide
  • High tides
  • High to low

Part 1 of 7What tides are

  • Tide the regular change in depth of the ocean in a place during the day
  • Depththe distance from the water surface to the ocean bottom
  • Tidal range the difference in depth of water between high and low tides
  • Largest range16.3 m in the Bay of Fundy, Canada
  • Smallest rangesthe Caribbean and Mediterranean seas have very small tidal ranges
  • Earth tidethe land also rises and falls by about 30 cm each day

Part 2 of 7Timing of tides

  • High tidesthey are about 12 hours apart
  • Low tidesthey are also about 12 hours apart
  • High to lowthe time from a high tide to the next low tide is six hours
  • Two a daya place has two high tides and two low tides every day

Part 3 of 7Tidal force from the Moon

  • Moon's gravitythe Moon is held in orbit by the Earth's gravity but its own gravity pulls on the Earth
  • Tidal force the pull of the Moon's gravity that causes tides
  • Water and landthe pull moves the water of the oceans more easily than the land
  • Near sidethe side of the Earth closer to the Moon has a high tide
  • Far sidethe side furthest from the Moon also has a high tide

Part 4 of 7Why high tides are 12 hours apart

  1. The Earth spins once on its axis in 24 hours.
  2. A place facing the Moon has a high tide.
  3. After 12 hours the same place is on the opposite side of the Earth.
  4. The bulge of water on the far side gives it a second high tide.
  5. So a place has high tides 12 hours apart.

Part 5 of 7The Sun and the tidal range

  • Sun's tidal forcethe Sun also produces a tidal force but weaker because it is further away than the Moon
  • Alignmentwhen the Sun, Moon and Earth are in line the tidal forces add together
  • Greatest rangethis happens at full Moon and new Moon
  • Frequencyit happens twice each lunar month

Part 6 of 7Effects of tides

  • Harbourssome can be used only at certain times because boats need enough depth
  • Floodingcoastal areas are more likely to flood at high tide in strong winds
  • Small boatsthe flow of water in and out of some coasts can be dangerous
  • Food chainsat low tide birds eat shellfish that are uncovered, and some fish move with the tides
  • Earth tidesthey have been linked with volcano eruptions and earthquakes
  • Energymoving tidal water can be used to generate electricity

Part 7 of 7How the cause of tides was found

  • Observationin 330 BCE a Greek sailor noticed the depth changed twice a day and linked it to the Moon
  • Early ideaaround 1600 a German scientist suggested a magnetic attraction between the Moon and water, which is now known to be wrong
  • SolutionNewton calculated tidal forces from gravity in 1687
  • Acceptancehis calculations were accurate enough to show gravity from the Moon and Sun causes tides

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