# Refraction of sound atomic level

how the refraction of sound and the change in the angle of propagation can be explained at the atomic level, why the direction of propagation of molecules changes in different media?

• Sound isn't an atomic level phenomenon. Commented Oct 18, 2023 at 18:02
• To follow up on the previous comment, sound waves (by, essentially, definition) are long-wavelength waves, long-wavelength defined as "much larger than the interatomic spacing". That said, if you go from one medium to another, the molecules and their interatomic forces change, and so the "spring constant" of the "springs" connecting the molecules and the mass of the molecules change, and so the speed of sound (given schematically as $\sqrt{k/m}$, with modifications due to lots of springs and atoms) changes. A changing speed of waves causes refraction. Commented Oct 18, 2023 at 18:04
• Also, the direction of sound propagation had nothing to do with "direction of propagation of molecules". There is no such thing in a sound wave.
– nasu
Commented Oct 18, 2023 at 19:23
• I'm don't get this yet. I'm thinking i'm little confused . When a sound wave pass for example to air for water the angle of propagation changes . Why this happens . Maybe there will be a change in momentum . Like some parts are interfered destructively and other parts constructively . If there is happening how can explained with classic mechanics ? . When i refer momentum it's because i'm think in colision beteween molecules , and maybe some these colisions soffer interference, and for this the angle of propagation changes Commented Oct 18, 2023 at 19:48
• Could you describe a sound wave when the medium comprises, let’s say, 5 molecules? If you could do that, you would be one step closer to solving your problem. The hard part here is that sound is described as the “behaviour” of a bunch of molecules and not just 10 or 20. Good luck with describing the molecule movement for 5 molecules reaching a wave equation-like solution. It won’t happen due to thermal/Brownian “noise”, on the contrary, when you consider a large number of molecules this averages out. This is what others defined in their comments about sound not being an atomic phenomenon. Commented Oct 19, 2023 at 10:39