One day I took a splendid stroll through inner city Rochester. I wondered, how come I can hear all the traffic around here? One answer, sound, and here comes another blog post.
Sound is caused by the vibrations of atoms. The law of conservation of momentum and energy has a lot to do with this. Because the vibrations travel from atom to atom, there is a conservation of momentum that travels from atom to atom. Also, some times you just can't hear someone because they are too far away, this is because the momentum has been channeled into something else, such as the ground or any other obstacles in the way.