why do we have tides in the ocean

Tides may seem simple on the surface, but the ins and outs of tides confounded great scientific thinkers for centuries they even led Galileo astray into a bunk theory. Today people know that the gravitational pulls between the earth, moon and sun dictate the tides. The moon, however, influences tides the most. The moon's gravitational pull on the earth is strong enough to tug the oceans into bulge. If no other forces were at play, shores would experience one high tide a day as the earth rotated on its axis and coasts ran into the oceans' bulge facing. However, inertia -- the tendency of a moving object to keep moving -- affects the earth's oceans too. As the moon circles the earth, the earth moves in a very slight circle too, and this movement is enough to cause a centrifugal force on the oceans. (It's centrifugal force that holds water in a bucket when you swing the bucket in an overhead arc. )
This inertia, or centrifugal force, causes to bulge on the opposite side facing the moon. While the moon's gravitational pull is strong enough to attract oceans into a bulge on the side of the earth facing the moon, it is not strong enough to overcome the inertia on the opposite side of the earth. As a result, the world's oceans bulge twice once when they are on the side of Earth closest to, and once when they are on the side farthest from the moon, according to the Wood's Hole Oceanographic Institution in Wood's Hole, Mass. Geography complicates the tides, but many places on Earth experience just two high and two low tides every 24 hours and 50 minutes. (The extra 50 minutes is caused by the distance the moon moves each day as it orbits Earth).

The sun and the tides "Solar tides" are caused by the sun's gravitational pull and are weaker than lunar tides. is 27 million times more massive than the moon, but it is also 390 times farther away. As a result, the sun has 46 percent of the tide-generating forces (TGFs) that the moon has, according to the National Oceanic and Atmospheric Administration (NOAA). Solar tides are therefore often considered just variations on lunar tides. Local geography can vary tide strength as well. Just north of the coast of Maine in Canada, the Bay of Fundy has a unique funnel shape at just the right position to creates the largest tides in the world. Water in the bay can rise more than 49 feet (15 meters) or about as high as a 4-story house. FORCE, the Fundy Ocean Research Center for Energy, estimates the Bay of Fundy pushes110 billion tons (100 billion metric tons) of water with every tide. Recently, local leaders have moved to take advantage of the tides. In July, Maine's Governor John Baldacci and Nova Scotia's Premier Darrell Dexter signed a Memorandum of Understanding to share research and ideas in tidal and offshore wind sources of renewable energy, according to Business Weekly. Understanding tides: then and now When Galileo Galilei attempted to explain tides in 1595, he left the moon out of this theory and focused on the inertia of the oceans and his correct idea that the earth orbited the sun, according to a NOVA documentary.

It wasn't until 1687, that Sir Isaac Newton explained that ocean tides result from the gravitational attraction, according to NOAA. This article was provided by Life's Little Mysteries, a sister site to OurAmazingPlanet. Why are there are no tides in rivers, lakes and other water bodies except oceans? The gravitational pull of the moon acts even on these water bodies! There are. But most bodies of water are too small for the effect to be great. On the other hand, check out the Great Lakes' tide tables. Firstly, tides are not simply caused by the gravitational pull of the moon as such. The moon doesn't revolve around the Earth precisely. They both revolve around their mutual centre of gravity, but because the Earth is so much heavier this means that the moon travels in large circles while the Earth travels in very small circles. It is this movement which causes the Earth's oceans, which are all interconnected, to "slosh" around, hence tides. Lakes would be very slightly affected but they are extremely small in comparison with the world's oceans, and not interconnected so they can't slosh around so noticeably. Theoretically lakes must experience tides but the tides would be so small that even in the largest lakes the effect is masked by river inflows and wind and so on, all of which cause greater differences in water height than tides presumably must, so the latter are unmeasurable. The sloshing around is also caused by the bulge of water attracted by the pull of the sun and moon. As the earth rotates daily, the coast is dragged through the bulge, and so the water level rises and falls each day.

It is always high tide somewhere. The bulge in a lake is tiny, and enclosed, compared to the bulge in an ocean, because lakes are tiny (usually) compared to oceans, so there is no noticeable rise and fall. This is the reason the Mediterranean has less noticeable tides: it is a small ocean, and more enclosed, than others. Indeed, tides exist in all bodies of water, even one's bathtub, but is so infinitesmally small, as to be unmeasurable. Even on Lake Superior, the largest of the Great Lakes of North America, the tiny effect of a tide is overcome by the effect of barometric pressure and the phenomenon known as a seiche. There are no Tide Tables of the Great Lakes and seiche warnings are rarely broadcast, as most cause a variance of less than 50 cm. The effects of a seiche may be felt strongest in the Straits of Mackinac between Lakes Huron and Michigan. As Newton states in his expression for acceleration due to gravity that,- the force of Gravitational attraction is directly proportional to the product of the masses of two interacting bodies and inversely proportional to the square of the distance between them (ruling out the gravity constant) F=G x m1. m2 / r(squared) considering that they are at an equal distance from the moon ( thus ruling out r-squared), the mass of the Ocean is massive compared that to a lake or a bathtub or a bucket of water. Since it's mass being less, there is lesser gravitational attraction. So,it's 'size' that matters.

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