I'm not sure if this is the right place to post my question, but I'll give it a try and let me know if I'm mistaken.
In chapter 3.1, the links to the animations of "longitudinal and transverse waves, single particles being disturbed by a transverse wave or by a longitudinal wave, and particles being disturbed by transverse and longitudinal waves", seem to be broken, at least in my tablet..
Is it me or is it me in a hurry, since you're in the beginning of the project?