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What Causes Tides

Omkar Phatak Mar 3, 2019
Tides are a rhythmic dance of the oceans. Sitting on the seashore, if you have always been curious about why tides occur, this write-up has some answers for you.
I gotta keep breathing. Because tomorrow the sun will rise. Who knows what the tide could bring? - Chuck Noland (From the movie, Castaway)
Tides are so much a part of human culture that we even have a proverb about it - 'Time and tide wait for no man.'. Those of you, who have lived near seashores or visited one often, must have noticed the rising and falling of the seawater level every day. This phenomenon is called tidal motion. The advancing and receding volumes of water are called tides.
Sitting on the seashore, especially in the evening, we are either too captivated by the splendid view or too involved in our own thoughts to notice the advancing and receding of the tides.

About Tides

Tides are a periodic phenomenon. A high tide is the maximum advancement of seawater towards the shore, covering the 'intertidal' zone. This zone is the region of the seashore that has no water, except during a tide.
Subsequently, a low tide occurs, when the water recedes back into the sea, exposing the intertidal zone. Every coast around the world experiences two high and two low tides every day, separated by a period of approximately twelve and a half hours.
Once in a while, a record-breaking high tide occurs, known as a spring tide, that is the highest of all the high tides. Generally, they occur during a Full Moon and a New Moon. Sometimes, the high tides go very low and are called 'Neap Tides'. They occur on a half Moon.
The sea tides have a very deep connection with the rhythm of life in the sea. Life originated in the oceans and perhaps the ancestors of the first land dwelling organisms were washed up on the shores by tides.
Let us look at the facts that may help us in understanding how tides form and the forces that create these phenomena. One peculiar feature is their periodicity. They definitely have something to do with the Moon as their maxima and minima are connected with its phases. Without further investigating observational evidence, let us see the mystery unraveled.

What Causes Tides to Occur?

Gravity can never be switched off and it's Moon's gravitational pull, along with the Sun's, that causes tides to occur. Another factor that causes tidal formations in our oceans is Earth's rotation, which creates a centrifugal force.
Sir Isaac Newton discovered the law of gravitation and one of the first explanations of the phenomena influenced by gravity, provided by him, was the formation of tides.
The Sun and the Moon exert gravitational influence on Earth and a by-product of that influence, along with Earth's rotation, are sea tides.
When the Moon is right overhead a region on Earth, the water in the sea below gets pulled up by its gravitational tug. This creates a high tide in that region.
When this is happening on one side of the globe, on the exact opposite side too, there is a high tide. That is because, though the water on the other side does not rise, Earth itself is slightly pulled by the Moon's gravity, effectively raising the level of water, relative to Earth.
Since, the total volume of sea water on Earth remains constant, when two points on the Earth's surface have a 'High Tide', regions separated by 90 degrees on both sides of a high tide, naturally experience a low tide.
As the Earth rotates around itself, every twenty four hours, these high and low tides, separated from each other by a 90 degree phase, travel around the planet. Rotation of the Earth makes tides change with time, across the oceans of the globe.
On a New Moon or Full Moon, the Sun and the Moon get aligned in a straight line and their combined gravitational influence causes the highest tides ever, which are spring tides.
Whereas, during a Half Moon phase, the Moon and the Sun are at right angles and they nullify each other's gravitational pull, giving rise to the lowest high tide, which is the 'Neap Tide'.
Every tide is thus influenced by the gravitational pull of the Sun and the Moon. In fact, the Moon also has an influence on the Earth's crust, which is a floating landmass over a sea of magma. 'Earth tides' are a result of this gravitational influence.
To summarize, tides are caused due to the eternal, periodically waxing and waning forces of gravity, exerted by the Sun and the Moon, along with Earth's rotation.