A bit of a misnomer, the balls are actually graphite-coated ping-pong balls. Suspended on threads, with a system for adjusting their separation. Charge the balls using the rods/fur and show that the balls separate due to the repulsion of like charges.

The balls are also used for other demos, like the Faraday Cage.

This demo can be found in cabinet E on shelf 3 of the UCSD PUL Demo Room (WLH 2015).