- Slides: 16
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.