Submarine

A submarine is a ship able to navigate under water.  

The principle of operation is based on finding a balance between the weight of the ship which tends to sink and buoyancy which makes the ship float.

• An object floats if the buoyant force is greater than the weight of the ship (positive buoyancy).
• An object sinks if the buoyant force is less than the weight of the ship (negative buoyancy).

The intensity of the buoyant force is proportional to the mass of water displaced by the immersed parts of the object.

• An object floats if the mass of the body of water it displaces is greater than its own mass.
• An object sinks if the mass of water it displaces is less than its own mass.

see the animation "float or sink".