Spin (physics) discrete angular momenta despite having no orbital angular momentum. In some ways, spin is like a vector quantity; it has a definite magnitude, and it has a "direction" (but quantization makes this "direction" different from the direction of an ordinary vector). All elementary particles of a given kind have the same magnitude of spin angular momentum, which is indicated by assigning the particle a spin quantum number. The SI unit of spin is the (N·m·s) or (kg·m·s), just as with classical angular momentum. In practice, spin is given as a dimensionless spin quantum number by dividing the spin angular momentum
Physical quantity Physical quantity A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement. A physical quantity can be expressed as the combination of a magnitude expressed by a number – usually a real number – and a unit: formula_1 where formula_2 is the magnitude and formula_3 is the unit. For example, (the mass of the neutron), or (the speed of light). The same physical quantity formula_4 can be represented equivalently in many unit systems, "i.e." formula_5. Symbols for quantities should be chosen according to the international recommendations of ISO/IEC 80000, the IUPAP