http://en.wikipedia.org/wiki/Walter_Lewin
Really brilliant professor, and very into demonstrations.
http://youtube.com/watch?v=P4XZ-hMHNuc
(Sometimes I hate camera framerates.)
http://youtube.com/watch?v=oY1eyLEo8_A
http://youtube.com/watch?v=X8ZHQQUusGo
Type?