If a mobile is moved by an external impeller which, from an indivisible moment, repeats blows always equally strong, i.e. equally quick, this generates an accelerated movement. This movement is not uniformly increasing but the increments keep diminishing until finally the acceleration comes to an end which leads to the uniformity of the movement.

Let a mobile A with the same persisting motive force and the same impetus CF gradually impel a body B during all the time DE (Table 16.​1, Fig. 63). At first, during a time DG starting from an indivisible moment, it impresses into the body a degree of velocity GL equal to the impetus FI. Consequently, afterwards the body A cannot impel the body B with all its velocity CF since the body B escapes the blow at a velocity GL. Consequently, after the time DG the body A can impel B only by the velocity CI by which it exceeds the impetus of the escaping body B. Thus, in the following time GH, equal to DG, the smaller relative impetus CI of A produces a weaker effect and adds only an impetus OM equal to IK. Since the previous impressed impetus LG persists, at the end of the time GH the whole impetus impressed into the body B will be HO equal to the sum of LG and OM. In the following time HE equal to DG, the body A can impel B only by its relative impetus CK, i.e. by the excess of the velocity CF of the pursuing body over the impetus MH of the escaping body. Therefore, the diminished impetus CK produces a smaller effect than before, i.e. NP equal to CK. But the preceding impetus MH equal to PE persists. Consequently, at the end of the time DE, all the impressed degree of velocity NE is equal to the total velocity of the impeller CF. Therefore, afterwards no other degree of velocity is again impressed by the impeller A since the body B escapes at the same velocity at which it is pursued by the impeller. Thus, after the time DE has elapsed, the movement of the body B will be uniform. But, during the preceding time DE, the velocity impressed from an indivisible impetus always increased, however not by equal increments since MO is smaller than LG, and NP is smaller than MO. Therefore, the triangular surface of the impetus DNE will not be rectilinear but will comprise the straight line ED and the curved line DN. Therefore also, the ratio of the surface of the impetus DLG to the surface of the impetus DMH or the ratio of the space travelled in the time G to the space travelled in the time DH is smaller than the ratio of the squares of the times GD and DH.