Why do some iron objects such as ships float when placed in water while other iron objects such as nails sink? 1. iron ships have large air pockets inside them, making them less dense than water and thus able to float. 2. the same reason that makes planes fly in the sky?

Iron ships have large air pockets inside them making them less dense than water and thus able to float. Iron objects does not have any air pockets to make them light . If you ever heard that ships sink its because  the ship must  have  a hole in the air pocket and (air pockets are at the bottom layer of ships) water fills through the air pocket and adds weight making it sink.

Hope this helps :)