Masses are to Newton's Gravitational Law as charges are to what?

Masses are to Newton’s Gravitational Law as charges are to Coulomb’s Law. The comparison works because both laws describe an inverse-square force: the interaction becomes weaker as the distance between two objects increases.

Newton’s law of universal gravitation says that every mass attracts every other mass. The force depends on the product of the two masses and decreases with the square of the distance between their centers. Coulomb’s law has a closely parallel form for electric charges, with the force depending on the product of the charges and the inverse square of their separation.

The analogy has an important limitation. Gravity is always attractive because ordinary mass has no confirmed positive-and-negative counterpart, while electric forces can attract or repel. Like charges repel, and opposite charges attract. The constants and physical strengths also differ dramatically: electromagnetic forces are vastly stronger than gravity between individual particles. Newton’s and Coulomb’s formulas are classical approximations that work well in many everyday situations, while relativity and quantum theory provide deeper descriptions.