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Spin of Subatomic Particles

Spin In Quantum Mechanics, Spin As A Classification MethodSpin of the electron, Isospin

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.



"Building Blocks of Matter." Nature 372 (November 1994): 20. Hellemans, Alexander. "Searching for the Spin of the Proton." Science 267 (March 1995): 1767.

Martin, A. D. "The Nucleon in a Spin." Nature 363 (May 1993): 116.

Lesley Smith


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Fundamental force

—A basic force, which has its own elementary mediator particle(s). There are four fundamental forces: the strong force, the electromagnetic force, the weak force, and gravity.

Mega electron volt (MeV)

—A unit of energy. One MeV is one million Electron Volts. An Electron Volt is the amount of energy an electron gains as it passes through one Volt of potential difference.


—Believed to be the most fundamental units of protons and neutrons.

Additional topics

Science EncyclopediaScience & Philosophy: Spectroscopy to Stoma (pl. stomata)