The measurement that describes how close and heavy the particles in an object are is density.

Here's why:

* Closeness: Density is calculated by dividing the mass of an object by its volume. Volume is a measure of space, so a higher density means the particles are packed more closely together.

* Heaviness: Density also takes into account the mass of the particles. Heavier particles will contribute more to the overall density of the object.

In summary, density is a measure of how much mass is packed into a given volume. It's a way to quantify both the closeness and heaviness of the particles within a substance.