Question

Why does an iron nail sink in water , whereas a ship made of iron floats?

Answer 1

As the density of an iron nail is more than that of water, the nail sinks in water. This is understandable. But a huge ship made of iron floats. This is because of its shape. A ship is hollow in the middle. When the ship is in water the entire volume of the ship, including the hollow portion, displaces water to make space for itself. The volume of water displaced is much greater than the volume of the iron ship. Hence, according to Archimedes' principle, the upthrust is more than the weight of the ship. That is why the iron ship floats in water.

In short, we can say that the shape of the ship makes its overall density less than that of water and hence the ship floats.