# Why are 'speed' and 'velocity' not given the same name?

• Position is a vector. Distance/length is a name of its magnitude.
• Velocity is a vector. Speed is a name of its magnitude.
• Acceleration is a name of a vector and its magnitude.
• Force is a name of a vector and its magnitude.
• Momentum is a name of a vector and its magnitude.
• ...

Of all the vastly many types of vector quantities we traditionally have defined in physics (and other technical sciences), two leap out at us as oddly different, regarding their terminology: Position and velocity.

These two vectors have scalar magnitudes that are named differently than themselves. For all other vectors, the naming convention is to use the same term for both the vector itself as well as for its scalar magnitude. If we are talking about the vector or the scalar then depends on context - at least we don't have to memorise two terms for each defined vector quantity.

I am aware of the use in the English language. These many different words exist in English, sure, such as distance, length, displacement in relation to position, and such as speed in relation to velocity. But just because many words exist in the shared language, this doesn't have to require scientists to include all those words into accurate definitions in physics.

Are there any historical reasons for why only these two vector quantities have differently named scalar magnitudes, a practice which breaks the otherwise consistent terminology pattern, and a practice that confuses and complicates the introductory teaching of physics (these two quantites are after all the very first ones you learn about in your high-school and/or university science class).

• This separation is not even universally followed, and in some languages (like Russian) non-existent. But it makes sense to emphasize the difference to beginners with different names, so later they are less likely to confuse vectors with their magnitudes (which they still do). And because they are the simplest (and the oldest), with the most colloquial uses and connotations, different names were more readily available for the task. Sep 12, 2019 at 12:14
• Both speed and velocity are скорость in Russian. Also, distance or length are not the magnitude of the position vector even in English (it does not really have any physical meaning since depends on the choice of the origin). The reason is pedagogical rather than historical (unless you mean history of textbooks), it is also reflected in elementary texts boldfacing vector letters, or putting little arrows over them. They'd probably use a universal suffix construction for magnitude if there was one, instead of having to write "magnitude of..." to disambiguate, e.g. velocitude, forcitude, etc. Sep 12, 2019 at 19:40
• The Russians are not alone... Germans use 'Geschwindigkeit' only. The French employ 'vitesse', and the Spanish 'velocidad'... Sep 15, 2019 at 9:23
• I first learned position, velocity, acceleration in 1D linear motion. They were called “signed magnitudes,” not “vectors,” and were treated as real numbers, like distance and speed. Speed helped distinguish negative acceleration and the common notion of deceleration. Years later in physics vectors were introduced, and in higher physics the term “speed” seemed to drop out in favor of “velocity.“ Distance which corresponds to change in position has its own value in, say, distance traveled (arc length) which does not correspond to a vector. The parallelism being suggested is perhaps not absolute. Sep 15, 2019 at 16:06
• @Steeven You'll find 'rapidez' only in those physics books in Spanish that are translations of books written in English. The translator has resorted to the very artificial and unusual (in physics...) 'rapidez' in order to have two words and thus cope with 'speed' and 'velocity'... Sep 24, 2019 at 11:51