Archimedes' principle is the explanation for why a steel ship with an 8 inch thick hull floats. This ship floats because it is buoyant. Buoyancy is the ability of a fluid to exert an upward force on an object immersed in it. Archimedes Principle states that the amount of buoyancy force on an object in a fluid must equal the amount of weight of displaced fluid. If you place a block of wood in a completely full tub of water, the water that spills out must weigh as much as the block of wood itself. If an object is placed in a full tub of water and it only displaces water equal to 1/2 of the mass of the block, then the object will sink. This is where shape comes into play. If a 1500 gram block of steel is placed in water, it will sink, yet if that shape block of steel is shaped in the form of a cup, the steel will float because it will push or displace more water. Surface area in contact with the water, and density of the object impact the buoyancy of an object.