The applets will only work if a Java runtime environment (version 1.4.2 or better) is installed on your computer.
Download is possible from Sun Microsystems at http://www.java.com/en/.

One of my favourite resources; Includes:

• Mechanics; Oscillations and Waves; Electrodynamics; Optics; Thermodynamics; Theory of Relativity; Physics of Atoms; Nuclear Physics;