Here's why:

* Solids have a fixed shape and volume. This means their particles are tightly packed together and vibrate in place.

* The vibrations are small and rapid. Think of them as jiggling around a fixed point.

* The stronger the bonds between the particles, the less they vibrate. This is why some solids feel harder than others.

Let me know if you'd like to know more about the movement of particles in liquids or gases!