Question

Which of the four forces holds the nucleus together, and which tends to push it apart?

Answer 1

The strong force holds the nucleus together and the electromagnetic force tries to push it apart.

Explanation:

An atomic nucleus contains protons and neutrons. The protons are positively charged and repel each other. The electromagnetic is responsible for the interaction between charged particles. As the electromagnetic force is long ranged, each proton in a nucleus repels every other proton in the nucleus. This is trying to make the nucleus fly apart.

The strong nuclear force is short tanged and binds adjacent protons and neutrons together. This is effectively what holds the nucleus together.

For a nucleus to be stable the strong and electromagnetic forces need to be in balance. Hence only certain number combinations of protons and neutrons can be bound into a stable nucleus.