Charge the rod by rubbing it with the wool exciter. Now bring it near one end of the two-by-four that is balanced on a watch glass, to one side, parallel to its long axis. The two-by-four slowly rotates toward the rod.

This demonstration illustrates the phenomenon of polarization by induction, with concomitant electrostatic attraction (see demonstrations 56.03 – Attract paper bits with charged rod, 56.09 – Charge pith balls, 56.18 – Induced charging of metal spheres, and demonstrations 56.03 – Attract paper bits with charged rod, and 56.06 – Electrostatically charged rods). When you rub the plastic rod with the red wool exciter, the rod charges negative. If you now bring it close to one end of the two-by-four, setting it parallel to the board’s long axis, to one side of the board, the negative charge on the rod repels the negative charges in the two-by-four, leaving it with a net positive charge at the surface. This is called polarization by induction. This positive charge is attracted to the negatively charged rod. The two-by-four, which is balanced on a watch glass and can pivot on it, slowly rotates toward the rod. As you slowly move the rod away from the board, the board follows it.