rapidity

== English == === Etymology === From rapid +‎ -ity, from French rapidité, from Latin rapiditas. === Pronunciation === IPA(key): /ɹəˈpɪd.ɪ.ti/ === Noun === rapidity (countable and uncountable, plural rapidities) speed, swiftness; the condition of being rapid (relativity) A measure of velocity relative to the speed of light; defined as artanh(v), where artanh is the hyperbolic arctangent, and v = speed (with c = speed of light = 1). (physics) A measure of the velocity of a particle in a beam relative to the beam's axis ==== Derived terms ==== midrapidity pseudorapidity ==== Translations ====