To deal with the variable accelerations predicted by these laws, Newton invented the differential and integral calculus. This investion was also made (apparently independently) by Leibniz (1646-1716), and Newton acknowledges getting the idea from a method of Fermat for finding tangents to curves. Newton's Principia, containing a systematic account of the inventions and discoveries just alluded to, was published in 1687, half a century after the books of Descartes and Galileo.
所以牛顿也是从切线的几何图像得到启发但是他用动体停止一刻的瞬时速度的存在使得这概念在时间上活起来。至于动体停止那是相对的，如伽利略已经反复指出。 所以其他未停的时刻也行。