Here's why:
* Solids have a fixed shape and volume. The particles in a solid are tightly packed together and vibrate around fixed positions. This restricted movement is what gives solids their rigidity.
* Liquids have a fixed volume but not a fixed shape. Their particles can move around each other more freely than solids, allowing liquids to flow and take the shape of their container.
* Gases have neither a fixed volume nor a fixed shape. Their particles are far apart and move freely, easily expanding to fill any container.
Therefore, the vibration of particles in place is a key characteristic of the solid state of matter.
