Gravitational tides

Tidal Power. Tidal power is caused by the gravitational pull of the sun and especially the moon, as they pull at the earth. Reacting to this pull, the ocean s waters rise, causing a high tide where the moon is closest. The difference between low and high tide can range from a few cm to several meters. Harnessing tidal power for electricity production by the use of dams requires a tidal difference of at least 4.5 m, a requirement met at few locations in the United States. Thus, the principal demonstration sites of tidal power are in Canada, China, and France. 

The moons gravitational pull on our planet is uneven. The side of Earth closest to the moon experiences the greatest pull, and the side farthest away experiences the weakest pull. The result of this uneven pull is a subtle, planetwide elongation of our oceans. As the Earth spins underneath this elongation, Earthbound observers notice a perpetual rise and fell of sea level. These are our ocean tides, and they can be harnessed for energy. 

Vertical transport and gravitational circulation in estuaries are influenced by both stratification and turbulent mixing, which result from the destabilizing forces of tides and/or wind processes. Under highly stratified conditions, two-layered flow is largely determined by the interaction of baroclinic and barotropic forcing. 

The distribution of chemical components within the ocean is determined by both transportation and transformation processes. A brief outline of oceanic circulation is necessary to ascertain the relative influences. Two main flow systems must be considered. Surface circulation is established by tides and the prevailing wind patterns and deep circulation is determined by gravitational forces. Both are modified by Coriolis force, the acceleration due to the earth s rotation. It acts to deflect moving fluids i.e., both air and water) to the right in the northern hemisphere and to the left in the southern hemisphere. The magnitude of the effect is a function of latitude, being nil at the equator and increasing poleward. 

Fig. 1.4 Every two weeks, the Sun and Moon are aligned with Earth so that the gravitational forces of both heavenly bodies create very high tides called spring tides. When the Moon and Sun are at right angles to Earth, lower, or neap, tides result.

Tides are caused by the difference in gravitational forces resulting from the change of the position vector of a point on the earth surface relative to the position of the center of mass of... 

Migrating tides are those waves which propagate westward with the apparent motion of the Sun. They have significant diurnal and semi-diurnal components. Non-migrating tidal components are also harmonics of the solar day, but they may be stationary, or propagate either eastward or westward. Their dominant source is provided by latent heat release in the troposphere, and thus related to meteorological processes in the lower atmosphere. A small semi-diurnal tide is also forced by the gravitational attraction of the Moon. 

Clairaut s formula for the attraction of gravitation, g, at different latitudes, L, on the earth s surface, and at different altitudes, H, above mean tide level, is... 

Have you ever played on the beach and built a sand castle Soon the waves rush the shore and knock it all down. Waves are caused by wind and changes in the tide—the rise and fall of the ocean s surface caused by the gravitational pull of the moon and the sun upon the earth as they move faster or slower toward one another. Low tide happens when the water is pulled away from the shore. High tide happens when the water moves up farther onto the shore. 

It is the gravitational attraction of the Earth that gives weight to objects with mass and causes them to fall to the ground when dropped. Gravitation is responsible for the existence of the objects in our solar system. Without it, the celestial bodies would not be held together. It keeps the Earth and all the other planets in orbit around the sun, keeps the moon in orbit around the Earth, and causes the formation of the tides. 

The ocean tides are caused by the gravitational forces between the Earth, the Sun, and the Moon, along with the centrifugal force imposed by the Earth s rotation. As the Earth rotates, and as the three bodies move relative to one another, the gradual and recurring shifts in the balance of gravitational forces cause the water in the oceans to tend to move toward one coast or the other. 

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