The causes of high and low tides

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What are Tides?

The ocean’s waters rise and fall on a definite schedule. These are called Tides. There are Low Tides and High Tides. Tides act on all bodies of water and are due to the gravitational forces of the sun and the moon. We notice tides the most at places where oceans and continents meet – high tide is when the ocean’s water comes very near the coast, while the low tide is when the ocean’s water moves far away from the coast.

Knowledge of tides is important for fishermen, for ships that need to dock or to sail away from land, for swimmers and clam collectors. What causes them?

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Causes of Tides

Tides follow the moon as it moves around the earth. The gravitational force of the moon tugs at earth. This force of gravity “pulls” the water nearest the moon slightly away from earth. At the same time, on the opposite side of the earth, it also “pulls” the earth away from the water. Therefore, two “bulges” are formed in the ocean – on the side of earth nearest the moon and on the opposite side of the earth. These bulges are the positions of high tide.

Now, as the earth rotates on its axis along with its waters, these “bulges” remain where they are due to the gravitational effect of the moon. High tide is formed when these bulges come in contact with land due to the rotating earth. At the same time, the other two sides of the earth which are not directly under the influence of the moon’s gravity, experience low tides.

The bulge in the water directly below the moon is called Sublunar while the bulge on the opposite side of the earth is called Antipodal.

So, a conjunction of the moon’s force of gravity and the force of the spin of the earth, together contribute to the high and low tides around the earth.

Tides change approximately every six hours, thereby causing four tides in a full calendar day, two high tides and two low. The periodic flow of water towards and away from the coast creates a Tidal Current – when it moves towards land, it is a Flood Current and when it moves away from land it is an Ebb Current.

Causes of Tides

Tides follow the moon as it moves around the earth. The gravitational force of the moon tugs at earth. This force of gravity “pulls” the water nearest the moon slightly away from earth. At the same time, on the opposite side of the earth, it also “pulls” the earth away from the water. Therefore, two “bulges” are formed in the ocean – on the side of earth nearest the moon and on the opposite side of the earth. These bulges are the positions of high tide.

Now, as the earth rotates on its axis along with its waters, these “bulges” remain where they are due to the gravitational effect of the moon. High tide is formed when these bulges come in contact with land due to the rotating earth. At the same time, the other two sides of the earth which are not directly under the influence of the moon’s gravity, experience low tides.

The bulge in the water directly below the moon is called Sublunar while the bulge on the opposite side of the earth is called Antipodal.

So, a conjunction of the moon’s force of gravity and the force of the spin of the earth, together contribute to the high and low tides around the earth.

Tides change approximately every six hours, thereby causing four tides in a full calendar day, two high tides and two low. The periodic flow of water towards and away from the coast creates a Tidal Current – when it moves towards land, it is a Flood Current and when it moves away from land it is an Ebb Current.

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Check Point

  1. When the ocean’s water comes very near the coast it is called ______.
  2. When the ocean’s waters move far away from the coast it is called ______.
  3. The flow of water towards and away from land are termed _____ current and _____ current respectively.
  4. The rotation of earth combined with the moon’s gravitational force is responsible for creating tides (True/False).
  5. The total number of tides in a day is ________.

Answer Key

  1. High tide
  2. Low tide
  3. Flood, Ebb
  4. True
  5. Four

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