Physics of Sound http://www.physicsofsound.com/
Rigorous derivation of sound wave equations from a molecular model of an ideal diatomic gas. General solution of the wave equations. Point source radiating in a moving medium.
Simulations with Java http://www.myphysicslab.com
Provides several interactive physics simulations such as springs and masses, pendulums, molecules. Objects, mass, gravity, spring stiffness can be modified.