Electrostatic Force - Moving Lumber
To demonstrate polarization of water molecules
Eight foot long wooden 2x4 on low-friction pivot, charging materials.
An eight-foot long pine 2x4 is balanced on a relatively friction-free support, so that it can rotate about the balance point. A rod charged by "friction" (either positive or negative) is held alongside either end of the 2x4. A force is exerted on the 2x4 and it rotates toward the rod, so that you can pull the 2x4 around with the rod. Changing to the other polarity rod creates the same force, and again the 2x4 can be pulled around by the rod. The non-uniform field of the rod lines up the polar water molecules in the wood and exerts an attractive force on them.