Why Are There Tides? The tides are caused by the gravitational pull of the moon and sun and by the rotations of the earth, moon, and sun. The Earth and moon both rotate around a common point This rotation produces centrifugal force

Why Are There Tides? Centrifugal force and the moon’s gravity are not in perfect balance. On the side of the earth nearest the moon, the moon’s gravity is strongest and pulls the water towards the moon On the other side away from the moon, centrifugal force predominates, pushing the water away from the moon.

Why Are There Tides? In addition to the rotation of the earth and moon the earth is spinning on its axis. High tide occurs when the point is under a bulge Since the earth takes 24 hours to complete a rotation, the point will have 2 high tides and 2 low tides every day. The moon advances in its orbit too. It takes the point on earth an extra 50 minutes to catch up and be under the moon

High tide – low tide

Cont. A full tidal cycle takes 24 hours and 50 minutes The sun produces tidal bulges too. Although the sun is larger than the moon, it is 400 times further away therefore, the pull is about half as much. When the sun and moon are in line, which happens at full and new moons, their effects add together.

Spring Tides At full and new moons, when the moon and sun are in line, the difference in eater level between successive high and low tides is large. Spring tides occur throughout the year about once every two weeks

Neap Tides When the sun and moon are at right angles their effects partially cancel each other. During these neap tides the tidal range is small Neap tides occur when the moon is in first and third quarter

Tides In The Real World Tides vary from place to place depending on the location and on the shape and depth of the basin As predicted, most places do have two high tides and two low tides a day : Semidiurnal tides Some places have mixed semidiurnal tides, with successive high tides of different height (western US, Canada)

Cont. Diurnal tides occur when there is only one high tide and one low tide every day Diurnal tides are uncommon. They occur in the Gulf of Mexico, on the coast of Antarctica, and in parts of the Caribbean and Pacific.

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