Moving Force. 195 
will strictly apply; only the diagram would 
be a little more complicated. 
Let us now suppose the first part of the 
operation in the collision of A against B, to 
be the same as already described im the case 
of a soft body, and supposing them to be in 
the situation as represented at No. 2, let us 
observe what must follow.—When A has ar- 
rived opposite to F, as represented at No. 3, 
e will have returned to its original place with 
respect to A, and B will have arrived oppo- 
site to G (FG being = EF), A will be at 
rest, and B will have acquired the full velo- 
city v.—Now it is obvious, that if A had not 
moved on from its position No. 2, ¢ would in 
this last part of the operation, have acted upon 
B only till it arrived opposite to L (FL being 
=+4EF), and its final velocity would have 
been only V2v7%. But A having moved on 
to its place No. 3, ¢ will have acted on B till 
it has arrived opposite to G; and the force 
which has been lost by A in its passage 
through the space = HF, as well as the force 
of ¢ through a space = HK, has been com- 
municated to B. In other words,—the force 
which, in the first part of the operation, had 
been expended in producing the change of 
figure, has, in the last part of the operation, 
' been reproduced by the expansion of the 
Bb2 
