1. Tides An ocean tide refers to the cyclic rise and fall of seawater.

2. High & Low Tides Bay of Fundy Nova Scotia One boat went to sea before the tide went out!

3. Six Hours makes a big Difference

4. Tides Tides are a form of ocean wave that results from: –the gravitational attraction between the earth and the moon and sun –The centrifugal force resulting from the spin of the earth

5. The moon's gravitational pull is the primary force responsible for the tides on the Earth. Photo taken by the Galileo spacecraft from a distance of about 6.2 million kilometers from Earth, on December 16, 1992. (Source: NASA). NASA

6. THEORY

7. Gravitational Forces

8. Tides & Inertia Why is there a bulge on the side of the earth opposite the moon? The earth spins. The centrifugal force from the spin causes water to bulge outward. –Like clothes sticking to the sides of a washing machine after the spin cycle

9. Some Facts Related to Tides Water on earth is attracted by the moon Water on earth is attracted by the sun The earth rotates on its axis once every 24 hours Moon rotates around the earth once every 28 days Earth rotates around sun once every 365.25 days Orbits of moon and earth are elliptical (not circular)

10. Effect of Earth’s Rotation

11. Why Time of High & Low Tides Changes Daily Time for H & L tides advances by 50 minutes every day because the moon is rotating around the earth in the same direction as the earth is turning on its axis 28 X 50 minutes = 24 hours and the cycle repeats

12. Why Patterns Change During the Year

13. Highest tidal range occurs in early January when perihelion (earth closest position to sun) and lunar perigee (earth’s closest position to moon) occur together

14. Spring and Neap Tides When the sun and moon are in line, the tidal range is highest (Highest highs & lowest lows) –This is a spring tide (not related to the season) When the sun and moon are at 90 o, the tidal range is lowest –This is a neap tide

15. Spring Tide: highest tides of the year

16. Neap Tide: lowest tides of the year

17. Types of Tidal Patterns Tidal Patterns vary because the shapes of ocean basins are so different Continents get in the way and “mess up” the smooth motion of tides. Tides would be much more predictable if there were no continents.

18. 1. diurnal tides. In parts of the northern Gulf of Mexico and Southeast Asia, tides have one high and one low water per tidal day.

19. 2. Semi-diurnal tides: have two high and two low waters per tidal day. They are common on the Atlantic coasts of the United States and Europe.

20. 3. mixed tides: successive high-water and low-water stands differ appreciably. In these tides, we have a higher high water and lower high water as well as higher low water and lower low water. The tides around west coast of Canada and the United States are of this type.

21. Tides Around the World

22. Links: http://oceanlink.island.net/oinfo/tides/tides.html http://topex-www.jpl.nasa.gov/aviso/graphics/general/discover/results/tides.htm