Wednesday, January 25, 2012
WHAT IS A TIDE?
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth.
Most places in the ocean usually experience two high tides and two low tides each day (semi-diurnal tide), but some locations experience only one high and one low tide each day (diurnal tide). The times and amplitude of the tides at the coast are influenced by the alignment of the sun and moon, by the pattern of tides in the deep ocean and by the shape of the coastline and near-shore bathymetry
Tides vary on timescales ranging from hours to years due to numerous influences. To make accurate records, tide gauges at fixed stations measure the water level over time. Gauges ignore variations caused by waves with periods shorter than minutes. These data are compared to the reference (or datum) level usually called mean sea level.
While tides are usually the largest source of short-term sea-level fluctuations, sea levels are also subject to forces such as wind and barometric pressure changes, resulting in storm surges, especially in shallow seas and near coasts.
Tidal phenomena are not limited to the oceans, but can occur in other systems whenever a gravitational field that varies in time and space is present. For example, the solid part of the Earth is affected by tides, though this is not as easily seen as
the water tidal movements.
From ancient times, tidal observation and discussion has increased in sophistication, first marking the daily recurrence, then tides' relationship to the sun and moon. Pytheas travelled to the British Isles about 325 BC and seems to be the first to have related spring tides to the phase of the moon.
In the 2nd century BC, the Babylonian astronomer, Seleucus of Seleucia, correctly described the phenomenon of tides in order to support his heliocentric theory. He correctly theorized that tides were caused by the moon, although he believed that the interaction was mediated by the pneuma. He noted that tides varied in time and strength in different parts of the world. According to Strabo (1.1.9), Seleucus was the first to link tides to the lunar attraction, and that the height of the tides depends on the moon's position relative to the sun.
In China, Wang Chong (27–100 AD) correlated tide to the moon's movement in the book entitled Lunheng. He noted that "tide's rise and fall follow the moon and vary in magnitude."
WHAT CAUSES A TIDE?Tides are caused by the gravitational interaction between the Earth and the Moon. The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side).
- Spring tide: Spring tide is the type of tide that has the greatest range between high and low waters. This happens during the full and new moon phases.
- Neap tide: Neap tide is the type of tide with the least difference between low and hig tides. This happens duuring the first and third quarter moons.
- The highest tides in the world are at the Bay of Fundy in Nova Scotia, Canada.
- Because the earth rotates on its axis the moon completes one orbit in our sky every 25 hours (Not to be confused with moon's 27 day orbit around the earth), we get two tidal peaks as well as two tidal troughs. These events are separated by about 12 hours.
- The sun's gravitational force on the earth is only 46 percent that of the moon. Making the moon the single most important factor for the creation of tides.
- The gravitational force of the moon is one ten-millionth that of earth, but when you combine other forces such as the earth’s centrifugal force created by its spin, you get tides.
- Since the moon moves around the Earth, it is not always in the same place at the same time each day. So, each day, the times for high and low tides change by 50 minutes.
- Offshore, in the deep ocean, the difference in tides is usually less than 1.6 feet
Tractive Force is the force created by the moon used to pull and push the tides. This force is basically the force in pounds, tons...etc.
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MANY THANKS TO:
- "thebayoffundy" user on YouTube
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- "minutephysics" user on YouTube
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