5A20.20 • Coulomb’s Law: Pith Balls

Location: Cabinet 1

Photo of Demonstration Used at the University of Texas at Austin.

Instructions / Notes:

• Two small pith balls are suspended from a support with nylon filaments.
• This demonstration uses a PVC rod with fur - or - glass rod with silk to charge the pith balls.
• Note: This demo uses static surface charges - which require very dry air conditions in order to work effectively.
  • If the air in the classroom is humid - then the surface charges will bleed away rather quickly.
• Once charged - the pith ball will be repelled by the provided PVC rod. (See the image below)
• It is also possible to show the forces between like charges by bringing two similarly charged pith balls near each other.
• To show opposite charges:
  • On a day with very low humidity - one pith ball can be charged with the PVC rod rubbed with a piece of fur
  • Then charge the second pith ball charged with a glass rod rubbed with a piece of silk cloth.
  • This only works - if it is very dry day.

The 2 minute video below is intended for staff use.

Last updated on June 5, 2026