Tides and Waves

Topics: Tidal power, Tide, Moon Pages: 6 (2006 words) Published: April 10, 2013
1.0 What Causes the Tides
Tides are periodic rises and falls of large bodies of water. Tides are caused by the gravitational interaction between the earth and the moon. Tides are the cyclic rising and falling of earth's ocean surface caused by the tidal forces of the moon and the sun acting on the earth . Tides cause changes in the depth of the sea and produce oscillating currents known as tidal streams, making prediction of tides important for coastal navigation. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone , is an important ecological product of ocean tides. The relative distance of the Moon from the Earth also affects tide heights. When the moon is at perigee the range is increased and when it is at apogee the range is reduced. The moon's gravity differential field at the surface of the earth is known as the Tide Generating Force . This is the primary mechanism that drives tidal action and explains two bulges, accounting for two high tides per day. Other forces, such as the Sun's gravity, also add to tidal action. The moon exerts its gravitational pull differently on different parts of the earth. The farther away the Moon, the weaker its pull.

Figure 1.0: Imagine a shell of the outer Earth , this diagram shows the Moon's gravity differential over the thickness of the shell. 1.1 Spring Tides and Neap Tides
Spring tides are especially strong tides. They occur when the earth, the sun, and the moon are in a line. The gravitational forces of the moon and the sun both contribute to the tides. Spring tides occur during the full moon and the new moon. The eccentricity of the orbit of the moon in this illustration is greatly exaggerated. The Proxigean Spring Tide is a rare, unusually high tide. This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee ) and in the New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide occurs at most once every 1.5 years. Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the earth). Neap tides occur during quarter moons.

idal Range
The tidal range is the vertical difference between the highest high tide and the lowest low tide . In other words, it is the difference in height between high and low tides. The most extreme tidal range will occur around the time of the full or new moons , when gravity of both the sun and moon are pulling the same way ( new moon ), or exact opposite way ( full ). The typical tidal range in the open ocean is about 0.6 meters (2 feet). As you get closer to the coast, however, this range gets much greater. Coastal tidal ranges vary globally and can differ anywhere from 1.8 meters to 3 meters (6–10 feet).

1.3 Tidal Power
Tidal Energy sometimes called tidal power is the power achieved by capturing the energy contained in moving water currents tides and open ocean currents . There are two types of energy systems that can be used to extract energy, kinetic energy and potential energy. Kinetic energy happens when the moving water of rivers tides and open ocean currents and the rise and fall of the tides that uses the height difference between ebbing and surging tides and potential energy from the difference in height (or head ) between high and low tides. The former method, which was generating energy from tidal currents, is considered much more feasible today then building ocean-based dams or barrages that flood eco systems and are expensive to build. Tidal power is classified as a renewable energy source, because tides are caused by the orbital mechanics of the solar system and to a lesser extent the surface effect of winds and are considered inexhaustible within a human timeframe. The root source of the energy comes from the slow...
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