EM interactions involve the exchange of photons. Within an atomic nucleus, the strong force dominates. It is stronger than any of the other forces, without the strong force the protons within a nucleus would fly apart. When neither the strong or electromagnetic forces apply, the weak force becomes important. Weak interactions always involve neutrinos, the only particle that responds to neither the strong nor EM force.
Weak interactions involve the exchange of particles known as vector bosons.
Weak interactions occur in some forms of radioactive decay and contribute to energy production in some stars. When physicists attempted to describe the strong interaction, they found some problems. It is possible to map particle interactions using special diagrams called Feynman diagrams. A single diagram describes up to four different particle interactions with the same mathematical formula. These descriptions frequently involved infinite quantities since quantum mechanics allows so-called virtual particles to be created and destroyed anywhere and accounting for virtual particles is not easy.