Designers at your local science museum are perfecting an exhibit on electrostatic discharge. The exhibit involves two long “bifilar” pendula. Each pendulum has a conducting ping-pong ball of known mass hanging from a pair of long non-conducting threads. They want visitors to “charge” the balls using a Teflon rod stroked with fur and see what happens.

The designers plan to have a local sign made while the set up is being perfected. As a student intern at the science museum, you have been asked to help one of the designers estimate how long it will take for the charges to drain off the balls before they touch. In addition, the sign makers have been asked to report on approximately how much charge is on each ball after a visitor charges the balls and touches them together.


In this activity, you will

  • Use the laws of mechanics and Coulomb’s Law to find the information the sign maker needs.