Static electricity, a power source and the electric circuit

When two bodies are rubbed together, tiny negative particles – electrons – pass from one to the other and the bodies become electrified (charged). The body with extra electrons is negative, the one that lost some is positive. So there are two kinds of charge: positive (+) and negative (–). Usually a glass rod rubbed with silk becomes positive and an ebonite rod rubbed with fur becomes negative. Charges of the same sign repel each other and charges of different signs attract. A charged body also attracts light uncharged things (a scrap of paper, very fine pepper): hair clinging to a comb or a balloon sticking to a wall are examples. In dry air the effect is stronger. When big charges build up in clouds and a spark (discharge) forms, lightning flashes and thunder booms. Lightning is dangerous: in a thunderstorm go inside a building and do not stand under trees, in open fields, in water or beside tall objects. Thunder comes later than the flash: the speed of sound is about 340 m/s, so multiplying the seconds between flash and thunder by 340 gives the distance to the lightning in metres.