5A40.30: 2 x 4



Description: This demonstration shows how induced charge creates a force, causing the 2×4 to pivot.


  • 2×4 with foil
  • Watch Glass
  • Rods and Fur

Demonstration Procedure:

  1. Put the watch glass is on a level surface.
  2. Balance the 2×4 on the dish so that it does not touch the surface (glass dish is used as an insulated pivot).
  3. Show that placing a neutral rod near the neutral board does nothing.
  4. Put a charge on the rod with the fur and bring it near the aluminum foil.
  5. The board will slowly start to rotate toward the rod due to induction.

Note: As with most electricity demos, this works best under 50% humidity.