Question

when and why did the sound stop

Answer 1

Sound waves, as all mechanical waves, are the transfer of energy through the disturbance of some medium.

Travelling through a medium and not a vacuum implies working against a resistance force; friction. The frictional force, as in every other case, bothtransmits and dissipates the energy of a wave.

Sound waves are a propagation ofchanging pressure. This means that for example, in air, they push the layer of gas they have in front, which expands pushing the next one, and so forth: traveling by causing the layers of gas to oscillate, just like this: