 Another significant difference between the EM force and the strong force is that the coupling constant for the strong force is 137 times stronger. And most importantly, where the EM force decreases with distance, the strong force increases with distance. As the distance between quarks grows to the diameter of a proton, the strength of the force approaches 18 tons. And 18 tons focused on such a tiny spot. This makes it virtually impossible to separate quarks. In fact, with a force that strong, the energy it takes to separate two quarks in a hadron is greater than the energy it takes to create two new quarks. So before we reach separation energies, new quarks are created instead. These new quarks immediately combine to create new hadrons.