Feb27_09_Tides

# Feb27_09_Tides - Tides Low tide in Bay of Fundy High tide...

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Tides

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Low tide in Bay of Fundy
High tide in Bay of Fundy

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A simple mechanical tide gauge
Gravitational attraction between Earth and the moon

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Gravitational Attraction 2 2 1 r m m G F Where F=the gravitational attraction G=the universal gravitational constant m 1 and m 2 are the masses of the two bodies r=the distance between the two bodies
In a rotating reference frame (rotation between Earth and the moon) the fictitious centrifugal force is needed

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Centrifugal Force Because of the centrifugal force, water does not spill!
Centrifugal Force r v m F 2 Where F=the centrifugal force m=the mass of the body v=the speed r=the radius

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If the gravitational force = the centrifugal force the Earth Moon system is stable
The moon does not rotate around the center of Earth. Earth and moon together the Earth moon system rotate around a common center of mass about 1,650 kilometers (1,023 miles) beneath Earth’s surface.

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The moon’s gravitational force attracts the ocean toward it. The motion of Earth around the center of mass of the Earth moon system throws up a bulge on the side of Earth opposite the moon. The combination of the two effects results in the bulge of water on both sides of Earth.
The action of gravity and centrifugal force on particles at five different locations on Earth. At points (1) and (2), the gravitations attraction of the moon slightly exceeds the outward-moving tendency of centrifugal force; the imbalance of forces causes water to move along Earth’s surface, converging at a point toward the moon. At points (3) and (4), centrifugal force exceeds gravitational force, so water moves along Earth’s surface to converge at a point opposite the moon. Forces are balanced only at the center of Earth (point CE).

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lunar tide generating force is due to the Moon's gravitational attraction on the earth's surface and the centrifugal force associated with the rotation of the earth- moon system. (Similarly, for the solar tide)
Gravity and inertia cause the ocean surface to bulge. Tides occur as Earth rotates beneath the bulges. (a) How Earth’s rotation beneath the tidal bulges produces high and low tides. Notice that the tidal cycle is 24 hrs 50 minutes long because the moon rises 50 minutes later each day. (b) A graph of the tides at the island in (a).

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The moon rotates around Earth every 27.3 days. This results in 24 hr 50 min between high tides. (Lunar diurnal tide)

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Each month, the moon moves from 28.5 o north of the equator to 28.5 o south of the equator. At intervals of about 18.5 years the plane of the moon’s orbit is inclined 28.5 o relative to the plane of Earth’s equator.
How the changing position of the moon relative to Earth’s equator produces higher and lower high tides. Sometimes the moon is below the equator, and sometimes it is above.

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Tides measured at three latitudes when the moon at the equator Equilibrium theory of tides assumes the ocean conforms instantly to the forces.
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Feb27_09_Tides - Tides Low tide in Bay of Fundy High tide...

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