Essay on Gravity and the Earth’s Tides

Gravity is the key to the Earth’s rising and falling tides. The combined gravitational effects of the Sun and the Moon constantly pull the world’s oceans in different directions and create tidal effects. But there are several other factors that complicate this basic process. Friction, the Earth’s rotation, the tilt of its axis and the gravitational pull given off by the Sun and Moon that affects Earth’s atmosphere. These forces together conspire to make our planet’s oceans into a battleground. These forces tug the oceans this way and that way around the globe, thus creating high tides and low tides.

Help with Essay on Gravity and the Earth's Tides
Help with Essay on Gravity and the Earth’s Tides

The Moon’s gravity stretches the earth into an oval. The effect is so tiny that the solid parts of the planet are distorted by little more than eight inches. But because of of water’s fluidity, the effect on the oceans is more noticeable. At the point on the Earth directly beneath the Moon, the ocean is tugged into a bulge of high water. At the same time, a second tidal bulge forms on the opposite side of the planet. This is partly a result of the centrifugal force created by the Moon and Earth’s combined rotation around their common center of mass, a theoretical point called the barycenter.

Because the Earth spins on its axis once every 24 hours, the two bulges sweep around the planet in waves, creating two high tides per day at every point on the globe. But the twice daily cycle is complicated by he fact that the Earth is tilted, which puts the Moon alternately to the north and south of the equator. This creates slight differences between the two tide each day and adds a daily set of local variations to this natural rhythm.

A further complication is added by the Sun, whose gavational pull on the earth also affects the tides. The tidal force of the Sun and Moon together is almost a third more than that of the Moon alone, with the Sun imposing a solar rhythm. At the new and full moons, when the two bodies are in line, they combine to create extra high spring tides. When the Moon is in its first and last quarters, the Sun is at right angles to it, and their gravitational pulls work against each other to create extra low neap tides.

The story continues as the tidal waves are weakened by friction between the ocean and the seabed to the point where the twice daily tidal waves get slightly left behind the orbiting Moon. At the same time, the Earth spinning on its axis causes the tidal waves to oscillate around the world’s ocean basins like water in a bath. This means that high tides do not necessarily occur when the Moon is overhead, but when the oscillations accumulate to their greatest height. each ocean basin is a different shape and so has its own pattern of oscillations. In the North Atlantic the sweep in a counterclockwise direction. Until recently, the sheer complexity of the tidal forces acting on the earth meant that the only way to predict tides was by years of patient observation. now, computer programs do the job- a development for which oceanographers are extremely grateful.

During the 1850s, French astronomer Edouard Roche tried to work out what would happen if the Moon were nearer the Earth. According to his calculations if the Moon were just one third of its present distance, the force would be 27 times greater. This implies that ocean tides would be so enormous that they would regularly swamp many of the world’s lowland regions at every high tide. The tidal force would also be strong enough to cause parts of the earth’s crust to flex up and down with the tides resulting in catastrophic earthquakes.

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