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

A needle sinks in water because the weight of water displaced by it is less than the weight of needle .AND an iron ship is shaped that it can displace a large volume of water.The weight of the water displaced by the immersed portion of the ship is equal to the weight of the ship hence it can float. According to the law of floatation a body floats in a liquid when the weight of the whole body is equal to the weight of the liquid displaced by the immersed portion of the body.



As the density of an iron nail is more than that of water, the nail sinks in water. 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.