# Why do translators translate Newton's 2nd law as though it referred to "force" when it does not mention force?

Here's Newton's 2nd law.

Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur.

The term esse vi motrici is often translated as motor force, but we actually have related words: essive meaning being alive and motrix meaning a cause of something.

In addition, Leonardo da Vinci uses the word forza ,
which (I think) can be compared to sforzàre meaning to strain, to overexert.

Here is Leonardo da Vinci’s definition:

Force as cause and effect

La forza è causa del moto, el moto è causa della forza

The force is the cause of the motion; the motion is the cause of force.

Tbh, my latin is almost non-existent, so if anyone answers this, please explain step by step.

• My comments on this Quora post relate to this: quora.com/What-is-the-proof-of-f-dp-dt Sep 19, 2022 at 0:20
• The Latin word vis means force and vi is the ablative form of vis. Sep 19, 2022 at 2:36
• essive meaning being alive” ← in what language? Certainly not Latin … Sep 19, 2022 at 19:41
• The "vi" can also mean "vigor" as with the well known phrase "vim and vigor", and "esse" means "to be". Motrici is often said to be related to "motrix" which is the female case of "an instigator" (eg. "flexion": "bending") - a mover is an instigator and "-i" indicates a plural, so it's "movers". Also, "mutationem" could mean "muta" ("mute") + "-tion"= "mute action" which to me implies a decay of motion, i.e "damping", so maybe it's really: Damping of motion is proportional to the vigor of movers impressed. Oct 9, 2022 at 9:15
• "vi" might be from a root word "ve-" ("out of-") wordsense.eu/vemens/#Latin wordsense.eu/vehemens wordsense.eu/vehement Oct 9, 2022 at 9:38

As you mention, the phrase corresponding to "force" here is vī mōtrici, the ablative of vīs mōtrix. Vīs is a fairly standard word for "power" or "strength", while mōtrix is a feminine form of mōtor ("that which moves [something]"), which comes from mōveō "to move". The pair is usually translated into English as "motive force": literally, "the power that moves something".

Forza isn't a Latin word; Leonardo is writing in Italian, not Latin. Forza goes back to Latin fortis "strong", a separate word.

• Related. (And a good reminder to fix that post.)
– cmw
Sep 19, 2022 at 2:16
• It should be noted that the word motrix was used before by Newtown - for example by Kepler. Specifically, it was not vi motrix but anima motrix a "soul" that resides in the plants or even vacant point. It was necessary to have an anima motrix in the absent of the solid orbs. Kepler later also used specifically the term vis motrix, brilliantly realizing that it must originate from the Sun (fons virtutis motricis ex jam demonstratis in Solem competet). Having said that, I don't make the claim that Newton's vis motrix comes directly (or even indirectly) from Kepler's vis motrix.
– d_e
Sep 19, 2022 at 8:15
• @d_e Very interesting, I didn't know vis motrix existed prior to Newton! Even if the usage is different that's cool to know. Removed the sentence attributing it only to Newton.
– Draconis
Sep 19, 2022 at 16:50
• Also related (as the OP seems to have been confused by esse). Sep 19, 2022 at 19:38