Sound is a mechanical wave and depends on the medium to propagate. Some of the characteristics from the medium like density or elasticity determine the speed of propagation.
Explanation:
In the air, the speed of propagation in 331 m/s, and in a solid like the iron is 5190 m/s. This is caused because at structural level, each molecule in the material structure needs to crash and transfer the energy to another. In “crowed spaces” that propagation will be faster, kind of similar o a domino effect.
