Description
Suspend two small, similarly charged pith balls and observe that they repel each other.
Pith balls are covered with a conducting material. (Aluminum foil or graphite spray paint)
1. Hang pith balls side by side, touching.
2. Rub down rubber rod with fur, rod will acquire a negative charge.
3. Carefully slide charged rod over one of the pith balls to transfer over as much negative charge as possible.
4. Since pith ball surfaces are conducting and in contact with each other, negative charge will spread out uniformly over both surfaces, and in turn repel each other.

NOTE: If irregularities are observed in the interactions of the charged objects, it is recommended that all synthetic, "static-loving", materials involved (including the demo cart itself) be rinsed off with water or wiped down with a wet cloth.
ALTERNATES:
- Use glass rods rubbed down with a piece of silk. (Glass rods will lose electrons in the process.) When gently sliding glass rod over  the pith ball, electrons from the pith ball will transferred to the positively charged glass rod and pith ball will gain a net positive charge.
- Use two balloons, one hanging and the other handheld. Charge (negatively) with fur. Balloons will be statically charged and will not transfer charge from one to the other by contact.

Web simulation:

Equipment
Two hanging graphite coated Styrofoam balls
Optional: Two hanging balloons