# "Speed" and "velocity" technical equivalents in French

In physics we would in English use the terms speed and velocity differently:

• Speed is a number (magnitude).
• Velocity is a vector (magnitude and direction).

In English this is traditional from more than a hundred years ago.

This is the case in several languages as well, such as the Nordic ones (fart and hastighed/t) as well as Spanish (rapidez and velocidad). It turns out to not be the case in German (they have only one: Geschwindigkeit) nor in Russian (they have only one: скорость).

In French I heard from a friend about both vitesse and vélocité. Do they represent the same technical distinction?

Can anyone confirm this?

I am writing about the origin of these technical terms, and am doing this research to have a proper understanding on their use across languages/cultures.

(No native speaker. I teach in a French University). As far as I know there is the noun vélocité but I don't encounter it very often (if at all). Instead one would use vecteur vitesse if a distinction should be made between the norm (i.e. speed) and the vector (i.e. velocity).

One can verify it here

https://fr.wikipedia.org/wiki/Vecteur_vitesse

Le vecteur vitesse, nommé parfois par son anglicisme vélocité (...)

There is also the noun rapidité corresponding to the English fastness.

En résumé : 'vitesse' (ou 'vecteur vitesse' en cas d’ambiguïté à la rigueur). (Merci @Mathieu Bouville)

Nota bene

Vélocité qualifie ce qui est véloce, c'est-à-dire qui se meut avec rapidité et agilité à la fois.

vélocité \ve.lɔ.si.te\ féminin

Vitesse, rapidité. (...)

(Physique) (Anglicisme) Vecteur vitesse. Vecteur représentant la vitesse et la direction d’un mouvement, par opposition à la vitesse, qui ne comprend pas la direction.

Vélocité is considered an anglicism when one use it to mean the vectorial quantity of kinematics (i.e. the English velocity). It is the same thing with the derivative of the acceleration. One would say jerk (USA) or jolt (Britain) whereas in French it is vecteur à-coup.

• En résumé : 'vitesse' (ou 'vecteur vitesse' en cas d’ambiguïté à la rigueur). Sep 23, 2019 at 19:08
• @Dimitris Thank you for the reply. May I ask if you teach in a technical field? In English the two terms are also fairly ambiguous in daily conversation, but in technical discussions such as in the studies of physics or engineering their different meanings have become very clear. Could this be the case for these words in French as well? Sep 24, 2019 at 7:20
• @Steeven Hi. Thanks for the comment. I teach Physics, Mechanics and Engineering Mathematics. I never say vélocité. I use vitesse and vecteur vitesse. Vélocité is considered an anglicism when one use it to mean the vectorial quantity of cinematics (i.e. the English velocity). It is the same thing with the derivative of the acceleration. We say jerk (USA) or jolt (Britain) whereas in French it is vecteur à-coup. Sep 24, 2019 at 10:34
• Sep 24, 2019 at 10:34
• @Dimitris Thank you for that clarification, and thank you for the answer. Sep 24, 2019 at 10:54

In French, you would translate both "speed" and "velocity", by "vitesse". If you want to convey that velocity is a vector, you would say "vecteur-vitesse". Now, if you want to use the word "vélocité", as it is noted above, you speak about something different: "la vélocité de ce garçon de café est impressionnante" is a sentence that can be pronounced after a long wait for the ... waiter.