Since, it is known that in solids strong intermolecular forces of attraction exists because of which particles are much closer to each other. Hence, they have definite shape and volume.
Particles of a solid are unable to move from their initial position unless an external force is applied to them. So, when no external force is applied then particles of a solid tend to vibrate at their fixed points.
Hence, we can conclude that particles tend to move in solids as they vibrate about fixed points.
