The third of the great physics principles introduced in our introductory mechanics courses is the conservation of angular momentum, or the Angular Momentum Principle in the language of the Matter and Interactions curriculum we use. This tends to be one of the hardest topics to introduce, in no small part because it's the last thing introduced and we're usually really short on time, but also because it's really weird. Angular momentum is very different than linear momentum, and involves all sorts of vector products and things going off at right angles.
Over at Tor.com, Kate has begun a chapter-by-chapter re-read of The Hobbit, and has some thoughts on Chapter 1. It's full of interesting commentary about characters and literary technique, but let's get right to the important bit: Physics!