Why Does A Submarine Float And Then Sink?

Basically it has several compartments full of air that help it float...but when it needs to dive it fills these compartments full of water and the sub begins to dive (or sink)

A submarine floats on the surface due to the fact it displaces more water weight than what it weighs when its ballast tanks are filled with air. Once the ballast tanks are filled with water then the submarine weighs more than the water it is displacing causing it to sink. Much of the vertical movement of a submarine can also be attributed to the action of the bow planes which act like wings in the water to provide the submarine manuverability while it is underway.

Subs have ballast tanks. When they want to submerge, water is pumped into the tanks. When they want to surface, air is pumped into the tanks, expelling the water and making them buoyant.

Here is a great example:

www.autoblog.com

This boat emptied its balast tanks to get rid of organisms living in the water and it all went wrong.

A submarine floats and sinks because it has special air function that causes the pressure to way it down to sink and keep it up with less pressure.

Tell me know how a submarine sink ok get it