Electromagnetic and strong force

[johann1301]

I have heard that the strong nuclear force is stronger then the electromagnetic force at short ranges, "Up to two and a half times the proton diameter". Ok, so i have an approximation of the length it dominates over the electromagnetic force, but i don't know where the force starts from; is it at the center of the proton, or is it from the edge? And why does my source say "up to" and not exactly? Why is this length only an approximation??


source: look at 0:50
http://www.youtube.com/watch?v=yTkojROg-t8&feature=related

 

[lugita15]

Protons and neutrons are made of quarks, which are point particles. The strong force is a force between quarks.

 

[jtbell]

The "strong force" between nucleons (protons and neutrons) is a sort of "residual effect" from the interactions among the quarks that they're composed of. It's analogous to the van der Waals force between atoms and molecules, which is a residual effect of the electromagnetic forces among the nuciel and electrons that they're composed of.

 

[johann1301]

What does residual mean?