NAP-Section 3. Physical Laws At the beginning of this course, we promised to show you why ships stay afloat? The reason why huge, heavy metal built ships do not sink when let in water is rather simple actually these big vessels displace more water than their own volume. The explanation for this is a physical law, first discovered by a Greek scientist Archimedes. According to his principle of physics, an object in water displaces a certain volume of the liquid. The liquid in its turn acts with a buoyant force on the object a force directed upwards and equal in magnitude to the weight of the water displaced by that same object. But keep this in mind as well, the buoyant force acting on an object that floats (or is said to be at rest, not moving up or down) is equal to the weight force of the object and acts in the opposite direction (pushing it up with the same force that gravity pulls it down with). Now it is easier to picture one of those enormous ships being submerged in waterÉ it sinks to the point at which the water it displaces equals out its own weight.