5A20.20 Pith Ball
Electric charge, Coulomb's law, induced charge
A pith ball is charged using a previously charged PVC or glass rod to show attraction of opposite charges and repulsion of like charges.
-  Pith ball attached to a string
-  Plastic bag
-  Glass rod
-  Rabbit fur
-  PVC rod
-  Lab stand
-  90-degree clamp
-  Metal rod
-  Bulldog clip
- Attach the metal rod to the lab stand using the 90-degree clamp.
- Hang the pith ball using the bulldog clip.
- If you hear a crackling noise during charging, the rod is charging well.
- As with most electrostatic demonstrations, this works best under 50% humidity.
- Rub the fur on the PVC rod to charge the rod negatively.
- Bring the PVC rod close to the pith ball. It should attract the neutral pith ball due to induced charge.
- Touch the pith ball with the PVC rod. This makes the pith ball negatively-charged.
- Hold the PVC rod near the pith ball and show that like charges repel.
- Rub the plastic bag on the glass rod. The bag rubs some electrons off the rod, making the glass rod positive.
- Hold the glass rod near the pith ball and show that opposite charges attract.
- PIRA 5A20.20
- Don't attempt this at home!
If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.