Electrostatic Roller Ball

Back to 5B - Electric fields and potentials
PIRA index: 5B30.00

Description

A ping-pong ball trapped between two disks will start to rotate when the disks are connected to a running Van de Graaff generator. The ping-pong ball first accumulate charges on its top surface from the the top disk. As the ball in insulator, the charges have to move the ball to reach the bottom plate. When the field is applied, the ball at rest is in an unstable equilibrium but any little nudge will allow the charges to start rolling the ball and give it momentum. Once it starts moving, the ball quickly start rotating along the edge of the disks at a steady speed.

Equipment

• Racing ball setup from Winsco
• Van de Graaff generator
• Cables with banana plugs and alligator clips.
• (Optional) Rubber stopper

Instructions

• Connect the top plate to the generators top and the bottom plate to the ground. Place a rubber stopper between the cable and the top disk for better insulation.
• Start the generator.
• Wait for the ball to start rolling. Carefully give it a nudge with an insulated stick (ruler) to start it if it takes to much time

Images & Movies

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