Tides

The alternate rise and fall of the ocean waters twice in 24 hours are known as tides. Along coasts, the water slowly rises up over the shore and then slowly falls back again.

High Tide

The moon's gravitational pull is strongest on the side of Earth that faces it, and weakest on the side facing away. This difference in force causes the ocean to form two bulges simultaneously. One bulge appears where the moon pulls the ocean towards it. The other bulge forms on the opposite side, where the ocean extends away from the moon because the moon is pulling the Earth itself more than the ocean there.

Also Check: Force

These ocean bulges lead to high tides. The tide on the side facing the moon is known as the higher high tide, while the tide on the opposite side is called the lower high tide. In deep waters, the ocean stretches towards the moon, but near the coast, it rises and flows onto the shore.

Low Tide

One side of Earth always faces the moon, causing high tide there, while the opposite side also experiences high tide. Between these high tides, the sea level drops, creating low tides. The movement of water from high tide to low tide is known as ebb tide.

Tides generally occur twice a day, known as semidiurnal tides. When a part of the ocean faces the moon, the moon's gravitational pull causes a significant rise in sea level, or high tide. As Earth rotates away from the moon, the tide lowers, leading to low tide. This cycle repeats every 24 hours.

The height difference between high and low tide is called the tidal range, which varies monthly due to the sun's gravitational influence on Earth. Despite being much farther than the moon, the sun's significant mass still impacts the tides.

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Tides vary globally due to Earth's uneven surface and ocean floor shapes. For instance, a smooth, broad beach may see a small tidal range, whereas a narrow bay might experience a much larger one. The smallest tides occur in enclosed seas like the Mediterranean, rising about 30 centimeters, while the largest, about 17 meters high, happen in Canada's Bay of Fundy.

Tides are especially high or low when the moon aligns with the sun and Earth during new and full moons, respectively. These heightened tides are called spring tides, unrelated to the season but named after the German word "springen," meaning "to jump."

In contrast, when the moon is at a right angle to the sun relative to Earth, the gravitational pull is weaker, resulting in lower-than-usual tides called neap tides.

How Tides are formed

Tides are caused by the gravitational pull of the sun and the moon, on the earth’s surface.

1. The moon exerts gravitational pull on the earth as it orbits around it. This has little effect on land which is solid and inflexible but it has a great effect on the ocean waters because water is liquid and can freely move about.
2. The water of the earth nearest the moon is pulled by the moon’s gravitational force. This makes the water on the earth bulge on the side facing the moon causing a high tide.
3. A similar bulge occurs on the opposite side of the earth. This is caused due to the rotation of the earth.
4. Between these areas of high tides are areas of lower water levels. These are areas of low tides.

Also Check: Waves

Importance of Tides

The tides are very important in estuaries and harbors. The water, when rising is called the “flood tide” and when receding is called the “ebb tide”.

1. The increased depth of water at high tide enables larger ships to enter the harbor.
2. Many ships use the retreating waters of the low tide to leave harbors.
3. Tides constantly sweep the coasts, carrying away the silt brought down by rivers. Thus, it helps in keeping the river channels and many harbors free from sediment.
4. The tidal energy can be harnessed to produce electricity.
5. In cold countries tides prevent ports from becoming ice-bound in winter by bringing in salt water and by keeping the sea in constant motion.
6. During high tides low lying areas along sea coasts are flooded and this water is trapped for manufacturing salt.Salt is produced in this manner along the west coast of India.
7. Strong tidal currents help rivers in building their flood plains.
8. Fishermen depend on the regular rhythm of high and low tide for their livelihood. They sail out into the sea and return with the tide.

Also Check: Frictional Force

Two high tides and two low tides usually take place each day along most of the earth’s coastal areas. A high tide is followed by a low tide six hours later, then a high tide again after another six hours.