Have you ever come across a physics phenomenon that you just couldn't wrap your head around? Physics can be tough, but the University of Colorado at Boulder Physics Department has provided a slew of interactive simulations that can help make some of the most difficult concepts a little more understandable.
Originally known as the Physics Education Technology project (PhET), the project now encompasses areas as diverse as chemistry, math and biology. On their web page, you can find simulations and games for a number of physics phenomena including quantum tunneling, orbits, the photoelectric effect and quantum wave interference. The site has over 100 simulations to choose from with difficulty ranging from elementary school up to undergraduate level.
Below is a small sample of the simulations available. Just click on the images, and the simulation should launch in your browser. Some of the simulations run on Flash, while others require that you have Java installed. If you have any difficulties, please check PhET's faq page.