This site from Georgia State University Physics Department defines and explains the concept of potential energy. Using equations and graphics to illustrate the idea, it discusses the many types of potential energy (gravitational,...

Explains the Law of Conservation of Mass, or Law of Conservation of Matter, and gives two examples for it.

Official site with information and resources relating to all aspects of environmental conservation: data, maps and laws. Specific environmental information by zip code provides immediate relevance to your world.