HyperPhysics is uniquely organized: Its navigation process is set up in the form of a mind map, so the topics (mechanics, heat, sound, electricity, etc.) are linked to and arranged in a circle around the central subject. If high schoolers know what topic they're looking for, the mind map system is helpful; navigating between topics, however, is more difficult, especially since HyperPhysics doesn't have a search engine. A bonus: The site's examples allow you to input various numbers and see how your changes affect the answer, which is very helpful. This site was also able to address all of our test science questions, although not as completely as Physics Classroom.