Electric Forces

Charge Shuttle


A pith ball is hung from a nylon string so that it falls in-between two metal cans A and B.

Can A is charged positive by contact with a positively charged rod.

The charged can attracts the pith ball; the pith ball makes contact with the can then swings back toward can B.  The ball makes contact with can B and then begins to oscillate back and forth, between the two cans.

Q1: Sketch how the charged can attracts the pith ball in the first place. 

Q2: Sketch what happens when the charge can and the pith ball contact one and other. 

Q3: Why the ball begins to oscillate between the two cans.  Recall conventional current as well as the displacement of negative charges.

Advanced Question: Will the oscillating stop?  Explain why the pith ball will or will not stop.


Arons, A. (1996), Teaching Introductory Physics, Wiley: NY, p. 73.

Seat Activities