Proper velocity Proper velocity In relativity, proper velocity, also known as celerity, is an alternative to velocity for measuring motion. Whereas velocity relative to an observer is distance per unit time where both distance and time are measured by the observer, proper velocity relative to an observer divides observer-measured distance by the time elapsed on the clocks of the traveling object. Proper velocity equals velocity at low speeds. Proper velocity at high speeds, moreover, retains many of the properties that velocity loses in relativity compared with Newtonian theory. For example, proper velocity equals momentum per unit mass at any speed, and therefore
Distribution function (physics) Distribution function (physics) In molecular kinetic theory in physics, a particle's distribution function is a function of seven variables, formula_1, which gives the number of particles per unit volume in single-particle phase space. It is the number of particles per unit volume having approximately the velocity formula_2 near the position formula_3 and time formula_4. The usual normalization of the distribution function is where, "N" is the total number of particles, and "n" is the number density of particles – the number of particles per unit volume, or the density divided by the mass of individual particles. A distribution function may