Why does a submarine float on water?

A submarine floats on water due to the principle of buoyancy, which states that an object will float if it displaces a volume of water equal to its weight. When a submarine is submerged, it adjusts its buoyancy by taking in or expelling water from its ballast tanks, allowing it to control its depth. When the tanks are filled with water, it becomes denser and sinks; when air is pumped in to replace the water, it becomes less dense and rises. This ability to manage buoyancy enables submarines to float, dive, and navigate underwater.