Here's why:

* Density is a measure of how much mass is packed into a given volume.

* Mass is the amount of matter in an object.

* Weight is the force of gravity acting on an object's mass.

So, a substance with high density means it has a lot of mass packed into a small volume. This means that even a small amount of the substance will have a lot of mass, and therefore, a high weight.

Example: A small piece of lead (high density) will be heavier than a large piece of Styrofoam (low density) even though the Styrofoam has a larger volume.