Here's why:

* Ideal Gas: An ideal gas is a theoretical concept that describes the behavior of gases under simplified conditions. In an ideal gas, particles are assumed to:

* Have negligible volume compared to the volume of the container they occupy.

* Not interact with each other (no attractive or repulsive forces).

* Move randomly and constantly in straight lines until they collide with each other or the container walls.

* Real Gases: Real gases, while they exhibit similar behaviors, deviate from the ideal gas model. This is because real gas particles do have volume, and they do interact with each other through intermolecular forces.

Therefore, while the term "freely moving particles" is often used to describe gas behavior, it's important to remember that this refers to the ideal gas model. Real gases do experience some limitations to their free movement due to intermolecular forces and particle volume.