strong force, electromagnetism, weak force, gravity.
“•The strong interaction is very strong, but very short-ranged. It acts only over ranges of order ##10^-13## centimeters and is responsible for holding the nuclei of atoms together. It is basically attractive, but can be effectively repulsive in some circumstances.
• The electromagnetic force causes electric and magnetic effects such as the repulsion between like electrical charges or the interaction of bar magnets. It is long-ranged, but much weaker than the strong force. It can be attractive or repulsive, and acts only between pieces of matter carrying electrical charge.
• The weak force is responsible for radioactive decay and neutrino interactions. It has a very short range and, as its name indicates, it is very weak.
• The gravitational force is weak, but very long ranged. Furthermore, it is always attractive, and acts between any two pieces of matter in the Universe since mass is its source. “