The apparatus used in the tutorial. The T-shaped board is made of
foam-core material of uniform thickness. ~a! In the first part of the tutorial
the board is supported on a smooth nail that passes through a hole to the left
of its center of mass. ~The students observe that the bar can rotate with
essentially no friction.! ~b! Later the students are directed to use a piece of
clay to balance the board ~again suspended from the hole to the left of its
center of mass! horizontally