A Van de Graaff Generator is used to charge a half-sphere conductor. Two styrofoam balls coated with electrically conductive paint are placed near the half-sphere. One is on the outside and the other is on the inside. Due to spherical symmetry, the ball on the inside does not feel any net electrical force, whereas the ball on the outside is first attracted (because it is neutral) and then polarized, which causes it to be repelled. 

See it in action here: https://www.youtube.com/watch?v=R1SW3uyFg8c...