Theory: Like charges repel; unlike charges attract.

Description: The clear acrylic rods will be positively charged when rubbed with the black silk. You should be able to hear the snap, crackle, and pop as the charge builds up. The black plastic rods will be negatively charged when rubbed with the red wool, the fur, or the small blue cloth. In humid conditions, the blue cloth gives the best results.

Mounting a positive rod on one rotating stand and a negative rod on another is a good way to illustrate Coulomb's law. Bringing another positive rod near the positive one shows repulsion; bringing it near the negative rod shows attraction.

Setup time: 5 minutes