Number of known elementary particles: 61
The particles that are in an atom: protons, neutrons and electrons
The particles that are in protons and neutrons: quarks
The four fundamental forces: gravity, electromagnetism, the strong force and the weak force
Particle physics describes the universe at the smallest scale. This includes subatomic particles, like protons and neutrons, as well as elementary particles, like quarks and electrons, which make up subatomic particles. It also includes the forces that govern how particles interact, including electromagnetism and the strong and weak forces holding atoms together. Weirdly, there are even particles that carry forces, such as photons (which transport energy from the electromagnetic force, or light particles).
