desperate!!!?

Question

Submarines can dive from the surface of the water to depths of up to 1,200 feet, then can rise to the surface again, but why can they do this over and over again? When they put water in the compartments to sink the sub, where does the air go? When they pump out the compartments to rise to shallower depths, where does the air come from? After all, they are under water. So, how is a submarine able to do all of this?

Also, can anyone help me find a diagram from a website that explains all of this?

the answer has something to do with air pressure. also could you give me the reference site you used?

Answer 1

All surface ships, as well as surfaced submarines, are in a positively buoyant condition, weighing less than the volume of water they displace. To submerge hydrostatically, a ship must gain negative buoyancy, either increasing its own weight or decreasing displacement of the water. To control their weight, submarines are equipped with ballast tanks, which can be filled with either outside water or pressurized air.

For general submersion or surfacing, submarines use the forward and aft tanks, called Main Ballast Tanks or MBTs, which are opened and completely filled with water to submerge, or filled by pressurized air to surface. Under submerged conditions, MBTs generally always stay flooded, which simplifies their design, so on many submarines these tanks are simply a section of interhull space. For more precise and quick control of depth, submarines use smaller Depth Control Tanks or DCTs, also called hard tanks due to their ability to withstand higher pressure. The amount of water in depth control tanks can be controlled either to reflect changes in outside conditions or change submersion depth. Depth control tanks can be located either near the submarine's center of gravity, or separated along the submarine body to prevent affecting trim.

http://en.wikipedia.org/wiki/Submarine#Submersion_and_navigation