Gizmo of the Week: Pith Ball Lab

The Pith Ball Lab Gizmo is a great example of applying mathematical skills (mainly vectors and trigonometry) to science. The Gizmo presents two charged balls hanging from strings. The charge and mass of the balls can be adjusted, as well as the length of the strings and the force of gravity. The balls move together or apart until the electrostatic force between the balls is balanced by the gravitational force and the tension on the strings. Knowing these forces, students use trigonometry to find the angle of the strings.

After completing the Gizmo, some students may be wondering, what in the world is a pith ball? A pith ball is a small ball made of spongy wood, or pith, that can be positively or negatively charged. In the 18th century, some of the earliest electroscopes consisted of a pith ball suspended by a silk thread.