Conversation so far:
what is meant by force at a distance
Forces can be divided into those that act by direct contact, and those that that act at a distance, where there is no apparent physical contact between the objects.
what is an example of force at a distance
Magnetism, and electrical charge, and gravitation are examples of forces that act at a distance.
what is another type of force besides magnetism, electrical charge, and gravitation
Nuclear force is a force that acts between the protons and neutrons of atoms.

Question: how was the force discovered
Self-contained rewrite: how was nuclear force discovered