EXPLAIN THE MECHANISM BY WHICH A SUBMARINE CAN DIVE IN THE WATER
Answers
Explanation:
The worst thing that could ever happen to you on a ship in the middle of the ocean would be for water to flood in and make you sink. But if you're on-board a submarine, sinking is exactly what you want! Unlike ships, which pitch and roll as they struggle across the waves, submarines slip swiftly and silently through the calmer waters beneath. They are lean, mean, military machines and they can stay submerged for weeks or even months at a time.
Submarine ahoy! When we see photos of submarines floating on the surface, it's hard to imagine how big they really are: like icebergs, virtually all of a floating sub is underwater. In this very unusual picture of a submarine in dry dock for maintenance, you can clearly see how big a submarine really is—and that it really is almost a perfect cylinder. Photo of USS City of Corpus Christi at Pearl Harbor Naval Shipyard by Dustan Longhini courtesy of US Navy.
Oceans are most turbulent where wind meets water: on their surface. The waves that race across the sea are a sign of energy, originally transmitted by the Sun and whipped up into winds, racing from one side of the planet to the other. Ships battle and lurch across tough seas where no fish—worth its salt—would ever swim. Sailing ships make good use of winds, harnessing the gusts of air to make a very effective form of propulsion. Diesel-powered ships stay on the surface for a different reason: their engines need a steady supply of oxygen to burn fuel. In theory, it should be much easier for ships to swim under the waves where the water is calmer and puts up less resistance; in practice, that creates a different set of problems.
If you've ever gone snorkeling or scuba diving, you'll know that life underwater is very different from life on the surface. It's dark and difficult to see, there's no air to breathe, and intense water pressure makes everything feel uncomfortable and claustrophobic. Submarines are ingenious bits of engineering designed to carry people safely through this very harsh environment. Although they were originally invented as military machines, and most large subs are still built for the world's navies, a few smaller subs do work as scientific research vessels. Most of these are submersibles (generally small, unpowered, one- or two-person submarines tethered to scientific research ships as they operate).
Parts of a submarine
Pressure hull
The pressure of water pushing inward is the biggest problem for anyone who wants to go deep beneath the ocean surface. Even with scuba tanks, we can dive only so far because the immense pressure soon makes it impossible to breath. At a depth of 600m (2000ft), the maximum depth subs ever dive to, the water pressure is over 60 times greater than it is at the surface!
How do subs survive where people can't? The hull of a standard ship is the metal outside that keeps the water out. Most submarines have two hulls, one inside the other, to help them survive. The outer hull is waterproof, while the inner one (called the pressure hull) is much stronger and resistant to immense water pressure. The strongest submarines have hulls made from tough steel or titanium.
Planes

Photo: The diving planes on either side of a submarine's tower generate lift as it moves forward, just like the wings on a plane. Photo of USS Emory S. Land by Jared Aldape courtesy of US Navy.
Just as sharks have fins on their bodies to help them swim and dive, so submarines have fins called diving planes or hydroplanes. They work a bit like the wings and control surfaces (swiveling flaps) on an airplane, creating an upward force called lift. Buoyancy is the tendency of something to sink, rise, or float at a certain depth. While it's underwater, a submarine is negatively buoyant, which means it tends to sink, left to its own devices, if it's not moving. But as the submarine's propellers push it forward, water rushes over the planes, creating an upward force called lift that helps it remain at a certain depth, creating a state of neutral buoyancy (floating). The planes can be tilted to change the lift force, so making the submarine climb or dive through the sea, as necessary. The planes provide most of the submarine's control of its depth, most of the time.