A proton holds two up quarks, and each carries a charge of +2/3. Like charges repel, so the proton's own parts repel one another all day, every day. Yet no proton has ever burst apart.
Something inside the proton beats that repulsion. This lesson profiles it: the strongest force in nature.
You've already seen that protons and neutrons are made of quarks, and that like charges repel. The first line of the profile says what the force acts on: the strong nuclear force acts on quarks, and through them on the protons and neutrons the quarks make up. It does not act on leptons. An electron never feels it.
The second line gives the range, and this line is new: the strong nuclear force acts only over distances about the size of an atomic nucleus or smaller.
Read that range line in both directions. Distances up to about a nucleus's size sit inside the strong force's reach, so the strong force reaches right across a single nucleus. But it reaches no farther. Gravity and the electromagnetic force reach across the universe; the strong nuclear force cannot reach even from one atom's nucleus to the next.
The third line gives the strength: the strong nuclear force is the strongest of the four fundamental forces. Inside a proton, it binds the three quarks together, overpowering the electrical repulsion between the two up quarks.
Physicists usually shorten the name: the strong nuclear force is called the strong force for short. Both names mean the same force, and this topic uses both.
A proton's two up quarks each carry a charge of +2/3, so they repel each other. What holds the proton together?
The strong force acts on quarks.
Inside the proton, the quarks sit far closer together than the size of a nucleus, so the strong force acts between them.
The strong force is the strongest of the four fundamental forces, stronger than the quarks' electrical repulsion.
The strong force binds the three quarks together, overpowering the repulsion.
Two protons sit at opposite ends of a long molecule, millions of times farther apart than a nucleus is wide. Does the strong force act between them?
The strong force acts only over distances about the size of an atomic nucleus or smaller.
These protons sit far outside that range.
No. At that separation the strong force does not act between them.
The strong nuclear force acts directly on…
Does the strong force reach right across a single atomic nucleus?
Of the four fundamental forces, the strong nuclear force is…
Inside a neutron, which particles does the strong force bind directly together?
A quark sits inside one atom; another quark sits inside a neighboring atom. Why is there no strong force between the two quarks?
Inside a neutron, quarks with like charges repel each other electrically. Yet the neutron holds together. What does this show about the strong force between its quarks?