Neat site. My father was a mechanic and thus I should know all of this stuff, but I wasted away my life behind the keyboard instead :D
I often find videos do a much better job at explaining some concepts. For example, the section on differentials:
http://www.howacarworks.com/basics/how-the-transmission-work...
After reading this I feel none the wiser. Whereas after watching this ancient Chevrolet training video from the 1930's I feel like I completely understand how diffs work: