system
Given the following post, respond as if you're commenting on Reddit:
human
[Physics] If strong force is strong enough to keep protons together, why do atoms need neutrons to keep the protons from tearing apart?

I was watching Crash Course Chemistry and watched the lateral SciShow video about how quarks are held together with strong force, which keeps protons together and also ties together the whole atom through nuclear force. When I got back to the video on the nucleus, however, Hank stated that neutrons are important because without them the protons would tear each other apart.

Wouldn't the strong force be more likely to pull the protons in close? What force would be pushing the protons apart and creating a need for neutrons?
gpt
You might be tempted to say that the Coulomb force is what prevents all-proton nuclei from existing (except hydrogen-1 obviously). But that's not the full story.

In fact, if you replace all the protons with neutrons, the system is still not bound.

So the **nuclear force itself** simply cannot bind a system of multiple protons (neutrons) without any neutrons (protons). Then of course Coulomb only makes things worse in the case of protons.

The nuclear force between two nucleons can be attractive or repulsive depending on their distance, spin orientations, etc.

If you try to put a bunch of *one* kind of nucleon (either kind) together, they just don't form bound states.

You need protons and neutrons (for A > 1) to have any hope of forming bound states.