Phet

Phet is a combination of interactive simulations that try to make it easier to learn and understand the different laws of physics and chemistry.

Developed in Java, the simulations are organized by category and will run from any web browser, even if you don't have an Internet connection.

Momentum, work/energy/power, magnetism/electricity/circuits, and light/radiation are just some of the materials covered in Phet's simulations.

These simulations were created in English, but are currently available in a host of other languages.