GSU's Hyperphysics down for the moment. Many people here reference articles on the Hyperphysics website (Georgia State University). It has been down for a couple of days. It is an excellent reference for physics. It was developed by faculty in the Department of Physics and Astronomy (http://www.phy-astr.gsu.edu/new_web/newmain.html [Broken]) as a reference for both undergraduate and graduate students. Lot of cools stuff they do! I emailed Rod Nave (Hyperphysics admin) to find out what's up. I'll post a status once I get a response.