The strong and weak forces are only seen inside the nucleus of an atom. They only work over very tiny distances: distances that are about as far as a proton is wide. The electromagnetic force and gravity work over any distance, but the strength of these forces goes down as the affected objects get farther apart. The force goes down with the square of the distance between the affected objects: for example, if two objects become twice as far away from each other, the force of gravity between them goes down to a quarter (2=4).