When a solid is heated, its particles gain energy and start vibrating more rapidly. Here's a simple explanation:

Increased Particle Vibration:

In a solid, particles (atoms, molecules, or ions) are closely packed and have a fixed position due to strong attractive forces.

When heat is added, the particles absorb this energy and start vibrating more vigorously.

Breaking Bonds:

The increased vibration weakens the forces holding the particles in a fixed position.

In a solid, particles are connected by bonds (like in a crystal lattice). As they gain energy, these bonds may start to break.

Phase Transition to Liquid:

If enough heat is applied and the particles gain sufficient energy, the solid undergoes a phase transition to become a liquid.

The particles are now free to move past each other, and the substance has turned from a rigid structure (solid) to a more fluid one (liquid).

In summary, heating a solid increases the kinetic energy of its particles, causing them to vibrate more and potentially break the bonds holding them in a fixed structure. This leads to the phase transition from a solid to a liquid.