Rigid Body Dynamics Resources
Chris Hecker wrote a series of articles as well as a number of reference web pages and made them available to anyone for free. The first three articles he has written take you through linear and angular physics with collisions in two dimensions. The fourth article teaches you how to integrate these equations into a three dimensional situation. He does admits that you cannot only use his articles to base your physics engine, so he lists various references and examples to guide you towards a rigid body physics system.
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