Named after its American creator, Robert Jemison Van de Graaff (1901-1967), the Van de Graaff generator has been the highlight of many electric demonstrations in both physics classrooms and museums around the world. The device, created in 1931, consists of a hollow metal sphere that stands on an insulated plastic tube. Inside the tube is a rubber belt that moves vertically from the base of the generator to the metal sphere. A metal comb attached to the base almost touches the belt. The rubber belt carries negative charges from the comb up the tube and into the metal sphere. There, a second metal comb captures the charges. They repel each other and spread over the exterior surface of the metal sphere. As more and more charge is carried upward, it takes more and more energy from the motor to move them up because of the repulsive force of the charges already there. The energy of the charges can reach up to a million joules per coulomb of charge. That is, up to one million volts.