When a glass rod is rubbed with silk, the rod develops a static charge and will attract small pieces of paper, according to HowStuffWorks. The charge develops because glass is positively charge, while silk is negatively charged.
Static electricity is created when a naturally positively charged item comes in contact with a naturally negatively charged object, and the two objects form a chemical bond. When the items are separated, the static electricity phenomenon is observed. The greater the difference between the items on the positive and negative charge scale, the greater the effect will be. The triboelectric series shows the range between the charges of various items.