It is necessary the existence of a force that surpasses the force of electric repulsion between the nuclei of the two atoms.
Explanation:
Nuclear fusion is the union of the protons and neutrons of two atoms to form a single atomic nucleus, of greater weight than those that gave rise to it.
In this process, an amount of energy equivalent to the difference between the binding energy of the new atom and the sum of the energies of the initial atoms is released.
For the fusion process to occur, it is necessary to overcome the electric repulsion force between the two nuclei, which grows in the direct ratio of the distance between them. This is only possible with extremely high temperatures, these reactions are also called thermonuclear reactions.
Studying atoms helps people by providing research to common problems found in our environment, universe, and ourselves. Such as cleaning up oil spills, identification of atoms in our universe, etc.