Lightweight pith balls help to show electrostatic attraction and repulsion.


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Possible Incorporate Topics:

  • Positive and Negative Charge
  • Electrons and Electrostatics
  • Attraction and Repulsion



'pith\ n 1a: a usu. continuous central strand of spongy tissue in the stems of most vascular plants that prob. functions cheifly in storage.


A pith ball is a very small, lightweight object that picks up electric charge quite well. A charged pith ball works well to show the Coulomb force between two charged objects. If a glass rod is rubbed with silk, the silk rubs some electrons off the rod. The rod thus becomes positively charged.


Figure 1: Charging a glass rod
Touching the positively-charged rod to two pith ball gives the balls each a small positive charge. Since like charges repel, the pith balls repel one another
Figure 2: Charging the pith balls
If an ebonite rod is rubbed with fur, the rod rubs some electrons off the fur. The rod thus becomes negatively charged and attracts the positively-charged pith balls.

Figure 3: Charging a ebonite rod





  • Two pith balls hung by string
  • A glass rod
  • An ebonite rod
  • A piece of fur and a piece of silk cloth




  • Charge up the glass rod with the silk rod first. Then touch both pith balls with the rod. The two balls should now repel one another.
  • Next, charge the ebonite rod with the fur. Bring the rod close to the balls. You will see the positively-charged balls are attracted to the rod.