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Understanding Tides: Gravitational Pull and Centripetal Force

Learn about tidal cycles, high and low tides, spring and neap tides, and the factors that influence tidal patterns. Explore the largest tidal range in the Bay of Fundy and the phenomenon of tidal bores.

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Understanding Tides: Gravitational Pull and Centripetal Force

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  1. Tides

  2. Tides are generated by: • Gravitational pull of the moon and sun • Centripetal force of the rotating Earth

  3. Tides are generated by: • the gravitational pull of the moon and sun • - moon has 2x greater gravitational pull than the • sun • - sun is 10 million x more massive than the • moon and is 390 times farther away

  4. Centripetal force

  5. GRAVITATIONAL FORCE CENTRIPETAL GRAVITATIONAL & CENTRIPETAL

  6. Tidal Cycles • Diurnal Tide: 24 hr 50 min cycle • Semi DiurnalTide: 12 hr 25 min cycle • Mixed Tide: 12 hr 25 min cycle

  7. Description of tides • High water: a water level maximum ("high tide") • Low water: a water level minimum ("low tide") • Tidal range: the difference between high and low tide • Spring Tide: full moon and new moon (14.77 days) • Neap Tide: 1st quarter and 3rd quarter (14.77 days) Intertidal zone High tide Low tide

  8. The monthly tidal cycle(29½ days) • About every 7 days, Earth alternates between: • Spring tide • Alignment of Earth-Moon-Sun system (syzygy) • Lunar and solar bulges constructively interfere • Large tidal range • Neap tide • Earth-Moon-Sun system at right angles (quadrature) • Lunar and solar bulges destructively interfere • Small tidal range

  9. Earth-Moon-Sun positions and the monthly tidal cycle Spring Tide Highest high tide and lowest low tide Neap Tide Moderate tidal range

  10. Tidal Patterns Semidiurnal tides- two high and two low per day; Cape Cod, MA (high latitudes) Diurnal tides- one high and one low per day; Mobile, AL (low latitudes) Mixed pattern tides- Two high and two low tides per day BUT with successive high tide levels that are VERY DIFFERENT from each other; Hawaii (mid latitudes) • Type of tide depends on: • Position on the globe • Water depth • Contour- shape of ocean basins

  11. Tidal Range 56 ft 6 ft

  12. The Bay of Fundy: Site of the world’s largest tidal range • Tidal energy is focused by shape and shallowness of bay • Maximum spring tidal range in Minas Basin = 17 meters (56 feet)

  13. Alma at High Tide Alma at Low Tide

  14. La Rance tidal power plant at St. Malo, France.

  15. Tidal bore = a true tidal wave • Wall of water that moves upriver • Caused by an incoming high tide • Occurs in some low-lying rivers • Can be large enough to surf or raft

  16. Corals exposed to air at extreme low tide

  17. Tidal Information http://life.bio.sunysb.edu/marinebio/mbweb.html HAWAIIAN ISLANDS Mean Spring Mean Tide Station Latitude Longitude Range Range Level Predictions SAND ISLAND, MIDWAY ISLANDS 28° 12.7' 177° 21.6' 0.8 1.2 0.6 Predictions Laysan Island 25° 46' 171° 45' 0.7 1.0 0.4 Predictions East Island, French Frigate Shoals 23° 47' 166° 13' 0.9 1.4 0.6 Predictions Nonopapa, Niihau Island 21° 52' 160° 14' 1.0 1.6 0.7 Predictions Kauai Island Waimea Bay 21° 57' 159° 40' 1.0 1.6 0.7 Predictions Port Allen, Hanapepe Bay 21° 54' 159° 35' 1.1 1.7 0.7 Predictions NAWILIWILI 21° 57.4' 159° 21.6' Predictions Hanamaulu Bay 22° 00' 159° 20' 0.0 1.2 1.8 Predictions Hanalei Bay 22° 13' 159° 30' 1.3 1.8 0.8 Predictions Oahu Island Haleiwa, Waialua Bay 21° 36' 158° 07' - - 1.6 0.7 Predictions Waianae 21° 27' 158° 12' 1.2 1.8 0.8 Predictions HONOLULU 21° 18' 157° 52' 1.3 2.0 0.8 Predictions Hanauma Bay 21° 17' 157° 42' 1.3 1.9 0.8 Predictions Waimanalo 21° 20' 157° 42' 1.1 1.8 0.8 Predictions MOKUOLOE 21° 26.2' 157° 47.6' 1.2 2.0 1.0 Predictions Waikane, Kaneohe Bay 21° 30' 157° 51' 1.4 2.2 1.1 Predictions

  18. Inquiry • Which has the greatest tidal effect– sun or moon? • Where is the greatest tidal range located? • Which lunar phase produces moderate tides? • How is a tidal bore created?

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