NOTE: This video will appear in a playlist on Smarter Every Day hence the references to Veritasium. Destin does lots of cool science stuff - check out his channel if you haven't already http://www.youtube.com/destinws2
We have been collaborating on rotational motion, which is timely for some of the videos I've been doing lately. In this video I talk about gyroscopic precession - the "wobbling" of a spinning top around its axis.
This is caused by the torque due to the object's weight. The big idea is that the torque vector increases angular momentum in the direction of torque. So if there is no angular momentum initially, it will cause the system to swing in such a direction that it is rotating with new angular momentum in the direction of the torque. However, if there was angular momentum to begin with, the torque will change the direction of that angular momentum by causing precession.