The author points out two historical – methodological aspects of Newton’s scientific work which have not been analysed yet.

First, the author proves that the systematization of the concept of acceleration begins with I. Newton’s works “Gravia in Trochoide Descendentia” (ca. 1670) and PRINCIPIA but not, as the historians of mechanics have traditionally claimed, with lectures in physical mechanics by J. V. Poncelet in the years 1838–1848.

Famous LEX II in I. Newton’s PRINCIPIA can only be regarded as a true proposition if the Newtonian term “vis motrix impressa” means not force itself, but rather the impulse of the force. If the above-named term is interpreted as the habitual physical force, LEX II is false as a physical proposition.

Article in Lithuanian