I am going through my professor's notes and I am having a difficult time with his notes on sound waves. class notes: First off, I felt like I understood what simple harmonic motion is, but I don't know what the "simple harmonic oscillator moving through air" is referring to. Second, I do not understand where the equation s = s_max cos(kx-wt) comes from, or what in the world the s is supposed to be referring to. The next part: I'm again struggling to understand what the s is, so basically anytime an s is mentioned here I have no clue what is going on. Can somebody go through this and explain to me conceptually what is happening?