Objective:

     To explain tides and their relationship with the Earth, Sun, and Moon

Tides:

• The rhythmic rise and fall of ocean water twice a day is called a tide.
• It is high tide when the water covers much of the shore by rising to its highest level.
• It is low tide when the water falls to its lowest level and recedes from the shore.
• The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides.

Tides based on the Sun, Moon, and the Earth positions:

• The height of rising water (high tide) varies appreciably depending upon the position of the sun and moon on the earth.
• Spring tides and neap tides fall under this category.

Spring tides:

• The position of both the sun and the moon with respect to the earth has a direct bearing on tide height.
• When the sun, the moon, and the earth are in a straight line, the height of the tide will be higher.
• These are called spring tides, and they occur twice a month, one during the full moon period and another during the new moon period. See Figure 1.

                                                                                       Figure 1: Spring tide

Neap tide:

• Normally, there is a seven-day interval between the spring tides and neap tides.
• At this time, the sun and moon are at right angles to each other, and the forces of the sun and moon tend to counteract one another.
• The moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull.
• Like spring tides, these tides also occur twice a month. See Figure 2.

                                                                                         Figure 2: Neap tide

How do tides work ?

• The mechanism of tides could be understood by understanding the gravitational forces of the sun and moon.
• These bodies experience the gravitational pull over each other depending upon their mass and the distance between them. since the sun is far away from the earth as compared to the moon.
• Hence, the Sun’s gravitational pull is less over the Earth than that of the moon. Thus, the moon determines the magnitude of the tide.
• It is supposed that only the water bodies are pulled by the gravitational pull; however, that is not the fact. It is both the land and water bodies that get pulled by gravitation.
• Since the relative pull of the land is less in comparison to that of water, the effect of gravitation on the water bodies is greater.
• It should be noted that the magnitude of a tide is determined by the relative positions of the moon, the sun, and the earth.

Why are tides important ?

• Tides are used to generate electricity (tidal electricity).
• Tides are very important in controlling the depth and flow of water to help ships navigate easily near the shores.
• Using the advantage of the water level and current of water during high tides, the ships can reach the harbour conveniently.
• Commercial fishermen learn how to make use of high tides to catch fish and take advantage of the higher gathering of fish that comes near the shore.