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 A scalar is a physical quantity that has magnitude but no direction. Symbols for physical quantities are usually chosen to be a single letter of the Latin or Greek alphabet, and are printed in italic type. Vectors are physical quantities that possess both magnitude and direction. Symbols for physical quantities that are vectors are in bold type, underlined or with an arrow above. If, e.g., "u" is the speed of a particle, then the straightforward notation for its velocity is u, u, or formula_6. Numerical quantities, even those denoted by letters, are usually printed in roman (upright) type, though sometimes