Hydrostatic Pressure

Three quarters of the planet Earth is covered by water. A majority of the planet's solid surface is abyssal plain, at depths between 4,000 and 5,500 metres (13,100 and 18,000 ft) below the surface of the oceans.

Underwater refers to the region below the surface of water where the water exists in a natural feature (called a body of water) such as an ocean, sea, lake, pond, or river.


Any object immersed in water is provided with a buoyant force that counters the force of gravity, appearing to make the object less heavy. If the overall density of the object exceeds the density of water, the object sinks. If the overall density is less than the density of water, the object rises until it floats on the surface.


At sea level, the air that surrounds us presses down on our bodies at 14.5 pounds per square inch. You don't feel it because the fluids in your body are pushing outward with the same force. Dive down into the ocean even a few feet, though, and a noticeable change occurs. You can feel an increase of pressure on your eardrums. This is due to an increase in hydrostatic pressure, the force per unit area exerted by a liquid on an object.


The density of water causes pressure that increases dramatically with depth. The atmospheric pressure at the surface is 14.7 pounds per square inch or around 100 kPa. A comparable water pressure occurs at a depth of only 10 m (33 ft) (9.8 m (32 ft) for sea water). Thus, at about 10 m below the surface, the water exerts twice the pressure (2 atmospheres or 200 kPa) as air at surface level.


For every 33 feet (10.06 meters) you go down, the pressure increases by 14.5 psi. In the deepest ocean, the pressure is equivalent to the weight of an elephant balanced on a postage stamp, or the equivalent of one person trying to support 50 jumbo jets!


However, pressure differential is greatest in shallow water because the rate of pressure change is greatest at the surface of the water. For example, the pressure increase between the surface and 10 m (33 ft) is 100% (100 kPa to 200 kPa), but the pressure increase from 30 m (100 ft) to 40 m (130 ft) is only 25% (400 kPa to 500 kPa).


That pressure is available in every lake, sea, and ocean to generate energy.  For that matter, its available anywhere on the planet.  All you need do is dig a hole deep enough and retain the level of water inside of it.  Not hard to figure out, think well, deep subject, now think man made "well".  For further elucidation, look up the definition of a water hammer and a water engine.

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