In what state of aggregation of the body do the molecules vibrate around the equilibrium position?

In solids with a crystal lattice, the molecules vibrate around their equilibrium position.

While the body is in such an aggregate state, its molecules are not capable of movement, the molecular bonds of the crystal lattice are strong and do not release them “into free floating”. Therefore, solid bodies retain their shape.

When a solid is heated, the vibrations of its molecules about their equilibrium position in the lattice nodes increase, neighboring nodes also begin to increase vibrations – this is how thermal energy is transferred inside the solid.

When the body is heated to the melting temperature, the destruction of the crystal lattice occurs, which is no longer able to hold the “raging” molecules in their places. The body begins to melt, pass into a liquid state of aggregation, and the molecules gain freedom of movement.