Physics Engines for Dummies
Here's an A+ reference/tutorial for anyone looking for a  "not for dummies" version of rigid body dynamics:<p><a href="http://www.digitalrune.com/Portals/0/Documents/A%20Unified%20Framework%20for%20Rigid%20Body%20Dynamics.pdf" rel="nofollow">http://www.digitalrune.com/Portals/0/Documents/A%20Unified%2...</a><p>(Had to google for a fresh link; unfortunately this doesn't seem to be nearly as widely mirrored as I believe it deserves.)<p>Things I liked about it:<p>- The author continually explains, compares, & contrasts alternative approaches throughout.<p>- It builds up a full actual system, including a lot of discussion of what other references may dismiss as mere software engineering.<p>- The author starts with the fundamentals and goes from there, usually fairly thoroughly.