I don't understand why 4 ∏ is in so many physics formulas. For instance, Heisenberg's uncertainty uses h / 4∏. Or Coulomb's law for the electric force Or the formula for the Magnetic permeability of free space: Many formulas use 4 ∏ or 8 ∏. I just don't understand why the relationship between a circle's diameter and its circumference comes into play so much. I am sure there is a simple explanation I am just not seeing.