The density of an object is a major factor that decides if an object floats (like a basketball) or sinks (like a stone). All itema that have an average density less lhan water will float. Since the stone is thicker and denser than the air-filled basketball, the stone will sink. The basketball being less dense means that it will float. Boats, whether they are a tiny sailboat or even a bery large oil tanker, all have hollow hulls. A hull is the bottom section of the boat or ship's frame. The hollow hulls are filled with air. This makes them less dense than water. Hence, the effect of having and air-filled bottom section to a ship means that it will float.