They include things like the speed of light, the gravitational constant, and Planck’s constant, and they’re “fundamental” in the sense that we can't derive them theoretically, we can only measure them. One of the most basic of these numbers is the electric constant, k. It's a value that lets us calculate the forces between electric charges. That’s a big deal when you consider that all matter is made of just three things—electrons, neutrons, and protons, two of which have an electric charge. But how do we know the value of the electric constant? Coulomb’s Law and ConstantWhen we say something has an electric charge, we mean it has a different number of protons and electrons.