In some Greek experiments, objects attracted each other after rubbing. Other experiments produced objects that pushed away, or repelled, each other. The evidence showed that electric force made matter either attract or repel other matter. Electric force is caused by electric charge. Electric charge is a property of the bits of matter within atoms. Electric force can cause matter to attract or repel because there are two kinds of charge – positive and negative charge. The effects of electric force can be summarized as the law of electric charge: Pieces of matter with the same kind of charge repel each other. Pieces of matter with the same kind of charge attr