Here's why:
* Density is a measure of how much mass is packed into a given volume.
* Buoyancy is the upward force exerted by a fluid on an object immersed in it.
* Archimedes' Principle states that the buoyant force on an object is equal to the weight of the fluid displaced by the object.
If the object is denser than the fluid, it displaces an amount of fluid that weighs less than the object itself. This means the buoyant force is less than the object's weight, and the object sinks.
Example:
* A rock is denser than water, so it sinks.
* A piece of wood is less dense than water, so it floats.
