Firstly you must understand that buoyancy is the very thing that allows anything to float. Buoyancy is defined as the force applied to an object by the fluid it is in, the force is quivalent to the...
Density (mass x volume) of the object. If the object is less dense (helium in air, or foam in water) than the fluid in which it is placed, it will float. Likewise, if the object is more dense (lead...
A submarine has buoyancy tanks along its length. To dive or sink these are filled with water, which enters through valves, so the vessel becomes heavier. Its speed of descent can be controlled by the...