Spin of Subatomic Particles

Spin, s, is the rotation of a particle on its axis, as the earth spins on its axis. The spin of a particle is also called intrinsic angular momentum. Angular momentum is momentum (mass times velocity) times the perpendicular lever arm (distance between point of rotation and application of force). An intrinsic property is one that depends on the essential nature of an object. The total angular momentum of a particle is the spin combined with the angular momentum from the moving particle.

The idea of spin has been around for a long time. In 1925 G. E. Uhlenbeck and S. Goudsmit proposed that the electron has a spin, and the spin of the electron has been proven experimentally. The spin of the electron combined with its electric charge gives the electron magnetic qualities because of the electromagnetic force.

Spin should not be confused with a quantum mechanical idea called isospin, isotopic spin, or isobaric spin. Isospin is the theoretical quality assigned to quarks and their combinations, which enables physicists to study the strong force that acts independently of electric charge.