Links for 2009-09-01

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In algebraic topology, one of the most basic ideas is *the fundamental group* of a point in the space. The fundamental group tells you a lot about the basic structure or shape of the group in a reasonably simple way.
A while ago, we had a ton of lightning. As a bonus, it always happened in the middle of the night. I love sleeping where it sounds like I am on the front line in WWI - no, I don't. But, while lying awake waiting for the next BOOM I thought of something.
I learned something new today, and something surprising.
One of the points I make repeatedly in teaching introductory mechanics (as I'm doing this term) is that absolutely every problem students encounter can, in principle, be solved using just Newton's Laws or, in the terminology used by Matter and Interactions, the Momentum Principle.