Tides
Bay of Fundy ► Boats can only travel at higher tides ► Some of the highest tides in the world
High Tide
Low Tide
What causes tides? ► Tides are created by the imbalance between two forces: 1.Gravitational force of the Moon and Sun on Earth ► If mass increases ( ), then gravitational force increases ( ) ► If distance increases ( ), then gravitational force greatly decreases ( ) 2.Centripetal (center-seeking) force required to keep bodies in nearly circular orbits
Gravitational forces on Earth due to the Moon ► Force decreases with increasing distance. ► Watch: JZFURg JZFURg JZFURg
Centripetal forces on Earth due to the Moon
Resultant forces ► Resultant forces are: The difference between gravitational (G) and centripetal (C) forces
Tide-generating forces ► Tide-generating forces are the horizontal component of the resultant force. Maximized along a “latitude” of 45º relative to the “equator”.
Tidal bulges Tide-generating forces produce 2 bulges: 1.Away from Moon on side of Earth opposite Moon 2.Toward Moon on side of Earth facing Moon Earth rotates in and out of tidal bulges, creating high and low tides. Watch: tch?v=5ohDG7RqQ9I tch?v=5ohDG7RqQ9I tch?v=5ohDG7RqQ9I
Relative sizes and distances on Earth, Moon, and Sun ► The Sun is much more massive than the Moon but much further away. Solar bulges are 46% the size of lunar bulges
The Moons Relation to Ocean Tides ► The height of the tides depends on the distance between the earth and the moon on a given day. ► Since the moon and the earth are not always the same distance apart, the tidal range changes daily. ► When the moon is farthest from the earth the lunar gravity is somewhat weaker.
► Since the moon and the earth are not always the same distance apart, the tidal range changes daily. ► When the moon is farthest from the earth the lunar gravity is somewhat weaker.
The Monthly Tidal Cycle ► About every 7 days, Earth alternates between: Spring tides (2)[Super Tides] ► Lunar and solar bulges add together ► Large tidal range ► Earth-Moon-Sun system at 180 0
Neap tides (2)[No Tides ?] ► Earth-Moon-Sun system at right angles ► Lunar and solar bulges destructively interfere
Sun and Moon Influence Tides Together
Earth-Moon-Sun positions and the monthly tidal cycle
Tidal Patterns ► Diurnal One high and one low tide each (lunar) day ► Semidiurnal Two high and two low tides of about the same height daily ► Mixed Characteristics of both diurnal and semidiurnal Not This!
Tidal patterns in the N.A
Tides in the ocean ► Shape and locations of coastlines creates irregular tides on our earth.
Tidal Patterns Vary with Ocean Basin Shape and Size The numbers indicate the hourly positions of tide crests as a cycle progresses. Dashed lines show the tide heights when the tide crest is passing.
Monthly tidal curves
The Bay of Fundy: Site of the world’s largest tidal range ► Super tides creates by shape and shallowness of Bay of Fundy (17meters )
Tidal bore = a true tidal wave ► Wall of water that moves upriver ► Caused by an incoming high tide ► Occurs in some low-lying rivers
Grunion and the tides ► Spawning cycles are timed precisely with the tides
Hurricanes and Tides
Hurricanes produce extra high tides called storm surges
Tides have high potential for tidal power generation
Power Plant at La Rance, France