A collection of exercises that had been designed for the use of students will give an idea of what was commonly understood by force at the time of the De motu Below is an example taken almost at random from one of these collections—it leaves the author’s identity to be guessed

*Problem 7*Being given the forces [*viribus*] of several agents, to determine the time in which they will together produce a given effect d

Let us suppose that the forces of the agents A, B, C are such that they produce respectively the effects*a*,*b*,*c*, in the