A hand-driven Van de Graaff generator. This machine is used in experiments with static electricity. Turning the handle causes the rubber band in the column to run over pulleys at either end. At the base, the band runs past fine points which generate an electrical charge. The band carries the charge up to the dome, where a metal 'brush' transfers the charge to the dome itself. After a short time, the dome accumulates a substantial charge of static electricity. Bringing an earthed object close (such as the sphere at right) enables the dome to discharge across a large air gap. Potential differences of tens of thousands of volts may be generated.