Algodoo

simulates electrons as a gas. potential is created through different densities and velocities in different containers.

Current = flow of electrons, indicated by flow of blue particles
Wire = grey tubes
Switch = light blue boxes blocking the tubes, click to "close" the switch
Voltage = pressure difference, indicated by grey circle with red wing (right example, layer 1)
Load = yellow wheel with black wings, place into stream, vary resistance via hinge brake.

(Make use of (de)activating the different layers to save processing power.)