Imagine that an uncharged pith ball is brought into the electrostatic field of a charged rod. The side of the pith ball closest to the negatively charged end of the rod will be given a negative charge produced by the movement of electrons from the rod.

"However" is one clue word or phrase in the passage that indicates a contrast: Both are vital sources of energy for the modern world and both were formed by geologic processes over millions of years. However, petroleum was mainly formed from the remains of ocean-dwelling microorganisms.