Strong force
Also called Strong nuclear force
The strong force is the attraction that acts between nucleons at nuclear distances and holds a nucleus together against the electrical repulsion of its protons. AP Physics 2 treats it qualitatively and gives it no equation.
One sentence of the AP Physics 2 framework covers this, and it is worth quoting rather than paraphrasing. Essential knowledge 15.7.A.1: the strong force is exerted at nuclear scales and dominates the interactions of nucleons (protons or neutrons). That is the entire required treatment. The other three current CEDs do not mention it at all.
Both halves of the sentence do work.
- At nuclear scales. The force has a range, unlike the electric and gravitational forces, whose laws run on forever. That is why no strong-force expression appears in any equation group on any of the four sheets: there is no formula to apply and no numerical question to set.
- Dominates the interactions of nucleons. Inside that range it beats the Coulomb repulsion between protons, which is why a nucleus holds together at all. Outside it, the repulsion is all that is left, and two nuclei approaching each other feel only the push.
That last point is what makes nuclear fusion hard: the nuclei must arrive with enough kinetic energy to get inside the range where the strong force can take over.
Do not extend the topic beyond that sentence. Quarks, gluons, colour charge and the residual nature of the nuclear force are not in the framework. Neither is the weak force, which the Topic 15.8 boundary statement rules out by name, saying an explanation or application of it is not within the scope of this course. If a question mentions the strong force, it wants the qualitative argument above.