High Quality Content by WIKIPEDIA articles! Proper-velocity, the distance traveled per unit time elapsed on the clocks of a traveling object, equals coordinate velocity at low speeds. Proper velocity at high speeds, moreover, retains many of the properties that coordinate-velocity loses. For example proper-velocity equals momentum per unit mass at any speed, and therefore has no upper limit. At high speeds, as shown in the figure at right, it is proportional to an object's energy as well.