Why do large ships float?
The basic idea is called Archimedes’ Principle. An item floats when it displaces more than its own weight of the liquid that it’s immersed in. The surrounding fluid pushes back with a force equal to that of the amount displaced, so when the two are equal the object floats.
The lower the density (weight per unit of volume) of the object being immersed, the more readily it will float because it more easily displaces its own weight. So, even though a ship can weigh thousands of tonnes its hull encloses a lot of air, meaning its density is relatively low. If some giant were to come along and crumple the ship into a solid ball of metal, it would occupy much less space and thus wouldn’t displace as much water, so it would sink quite quickly. Think Titanic, for example:
When the titanic hit the ice Berg the water got in which made the boat sink.
