Coulomb's Invisible Arm

Coulomb's Law is the equation that governs how charges push and pull each other. Two positive charges? They repel. Positive and negative? They attract. The force depends on two things: how much charge each object has and how far apart they are.

The force drops off with the square of the distance — double the gap and the force falls to one-quarter. This is why static cling works only at contact distance, while lightning can leap across kilometers when the charge buildup is enormous.