Here it is:
I recommend that anyone working on their game engine read the EULA on the code from books they buy, for example, I don't remember which one of these, but probably both:
3D Game Engine Architecture : Engineering Real-Time Applications with Wild Magic (The Morgan Kaufmann Series in Interactive 3d Technology)
Game Physics (Interactive 3d Technology Series)
the EULA states that you can use the software, for commercial or noncommercial purposes, provided that each memeber of your team owns a copy of the book, and as long as you dont redistribute the source.
Which is great, for the price of the book, you get a really complete physics library, that you just need to plug into your engine and use, no need to write your own.
That's what I'm doing =)