牛顿当时叙述是：“运动的变化成正比于施加的动力，并且（方向）依照力施加的直线方向”。（原文见内）

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

英文翻译：The mutation of motion is proportional to the motive force impressed; and to be done according to the straight line in which the force is impressed.