Moving Force. 187 | 
the depth of the penetration of c into A. Now | 
if A be a nonelastic soft mass, of ‘clay for 
example, we know that it cannot be pene- » 
trated without foree; nor have we any reason 
to suppose that the force which hasbeen ex- 
pended in producing the penetration, can ever 
be restored. We therefore cannot expect to 
find in the motion of A and B after collision, 
the same quantity of force which they had 
before collision: If, however, the pressure 
into the space through which it acts, be taken. 
as the measure of the force, we’ shall find, 
that a compound effect, has been produced by 
A in its passage through the space = EH, 
that only 4 of the force which A has lost has 
been communicated to B, and that the other 3 of 
that force has been spent in producing a change 
of figure in A. These proportions are obvious 
from the mere inspection of the diagram. We 
may suppose A to be a much harder substance 
than clay, so that the space represented by 
EF may be very small; but the pressure being 
proportionally greater, the product of the 
pressure into the space will still be the same, 
however small the penetration may be. 
Any explanation, however, which takes 
into consideration the force which is expended 
in producing a change of figure, is strongly 
Aa2 
