Occasionally, it’s usual to notice an oncoming track courtesy of the sound it produces. It’s important we understand how the sound travels to your ears without passing through any medium.
In reality, the track is vibrating and knocking off a layers of atoms in the air. The atom in turn knocks against their neighbouring atoms. It is easy to understand this concept if you picture motorcyclist racing in a sequence. Then imagine the top cyclist toppling off and causing accident to the rest of the cyclists. That is how atoms knock each other successively until they reach your ears.
Such pressure wave is called sound. The atoms yank their neighbouring atoms upon springing back and forth.
Try blowing air forcefully through a narrow hole. What follows is a high pitched sound. This happens because the air atoms are knocking against each other forcing their way out.
Alternatively, try bumping one end of a metal rod against a hard surface. You will create a region of high pressure on one end of the bar. The pressure will in turn travel through the other end of the bar. This, when done properly, will make your hand feel as though it were vibrating. An evidence that indeed the pressure wave has traveled the other end of the rod.