We can estimate the size of the strong nuclear force by working out the force of repulsion of the protons in the nucleus using Coulombs Law. Given that the diameter of a nucleus has been measured from electron diffraction experiments, it follows that nucleons are evenly spaced at about 1fm apart and the strong nuclear force acts only between adjacent nucleons.The energy needed to remove a nucleon from the nucleus with a strong nuclear force of about 200N acting over a distance of 3 to 4 fm is about 4MeV.The strong nuclear force must be repulsive at separations of 0.5fm or less since nucleons would otherwise pull each other close and the nucleus would be much smaller than it is.