Final answer:
The four basic classes of forces in nature are gravitational, electromagnetic, weak nuclear, and strong nuclear forces, fundamental to all interactions, from subatomic to cosmic scales.
Step-by-step explanation:
The four basic classes of forces encountered by humans in nature are the gravitational force, the electromagnetic force, the weak nuclear force, and the strong nuclear force. These are the only forces responsible for all the interactions that are observed in nature. The gravitational force is responsible for the weight of a body and the movement of galaxies. The electromagnetic force includes static electricity and magnetism and is responsible for the attraction among atoms in bulk matter. The weak nuclear force and the strong nuclear force, however, act over an extremely short range, limited to the size of a nucleus or less, and are essential to the structure of matter, even though we do not experience them directly.