Some of the best science demos reveal something to the viewer -- making the previously unseen become visible.
In this case, a Ruben's tube is used to visualize how sound (mechanical waves) influences air pressure in a tube. Standing waves are the easiest to visualize, but the musical dynamics and complexity are interesting too.
Plus it uses fire and rick & roll, which always makes such projects more exciting!
By the way, after the Dave Brubeck jazz, did you see the flame gap with the rock music? I wonder if that has anything to do with how it is equalized when mastered...
Mechanical waves can create energy patterns in solids as well. This is a clever use of salt on a vibrating table to show more complex harmonics. The shape and composition of the table are also important here -- this table is "clean" enough to get distinct constructive and destructive effects that result in salt "mounds" and clear spaces: