# How are sound waves produced?

I have been utterly confused as to what exactly happens in a sound wave and how it is produced.I understand the mathematical description of it quite well, what I don't get is its qualitative description.

So suppose I have a long air tube and I create a sound wave travelling right by sinusoidally moving the piston right and left. Now here are my questions:

1. Doesn't pushing the piston change the volume of the tube and as a result the pressure through out the tube changes? Then how come the pressure vary sinusoidally?
2. I read a bunch of books but no one book seems to explicitly explain how the sound wave is produced. I have read that pushing the piston compresses the layers of air next it causing the pressure and density to increase there. Then does this region of increased pressure cause the adjacent layers to compress or is the air molecules in this high pressure region push the layers adjacent to them causing them to compress?
3. If the above description is correct then how come the displacement and pressure equations are out of phase by π/2? I.e how come when the pressure variation at a place is zero then the displacement of air molecules is maximum there?
4. Can someone provide a qualitative description of how a sound wave is produced by sinusoidally moving the piston in the air tube?
• Doesn't pushing the piston change the volume of the tube and as a result the pressure through out the tube changes? Then how come the pressure vary sinusoidally? The pressure disturbance is the sound wave, so moving the piston doesn't instantaneously change the pressure in the tube from one constant value to another constant value. The change in pressure propagates through the tube at the speed of sound in the tube. Mar 27, 2019 at 16:40
• I understand that.. Mar 27, 2019 at 17:04
• Re, "...as a result the pressure through out the tube changes?..." When the piston starts to move, the only air molecules that can "know" that it has started to move are the ones that actually are bumping right up against it. Then their neighbors get the message, then their neighbors, etc. It takes time for the information to travel down the length of the tube, and the speed at which it travels is the speed of sound. Mar 27, 2019 at 18:25
• Can someone help me with the other questions as well? Mar 27, 2019 at 19:12