Physics – 1.4 Density | e-Consult

Ships are designed with a large volume, even though they are made of dense steel. This large volume results in a low average density for the ship (ρ_ship). While the steel block has a high density (ρ_steel), its volume is small. Therefore, the mass of the steel block (m_block = ρ_steel * V_block) is much greater than the buoyant force exerted by the water on the block.

A ship, however, displaces a volume of water equal to its own volume. The buoyant force on the ship is equal to the weight of the water displaced. Because the ship's volume is large, the buoyant force is large enough to support the ship's weight, even though the ship is made of a dense material. The average density of the ship is less than the density of water, allowing it to float. The steel block, with its small volume, displaces a much smaller volume of water, resulting in a buoyant force that is insufficient to support its weight, causing it to sink.