MOVING FORCE. 
291 
of its moving fore# is expended in bruising the pile, and the rases of diffi- 
progress of the pile into the earth is very small. The heavier 
the ram is in proportion to the pile, the greater is the progress moving force. 
of the pile, by the application of the same quantity of moving 
force.— On the other hand, if the object be to produce a change 
of figure in the substance which is struck, in hammering iron 
for example, if theanvilbe light in proportion to the hammer, 
the intended effect is not'produced in the same degree as when 
the anvil, or the mass which is struck, is heavy in proportion to 
the hammer which strikes it*. 
If a non-elastic body strike a non-elastic machine moving 
with a uniform velocity (such as the float of an undershot 
water-wheel) the maximum effect of moving force will be 
communicated to the wheel when the part of it which is struck 
moves with half the velocity of the body which strikes it. 
Let A (fig. 17) be a non-elastic soft mass, uniformly 
penetrable by the cylinder c, and moving in the direction /VB 
with such a velocity v that it would be brought to rest by driv- 
ing the cylinder up to F against an immoveable obstacle — If 
instead of an immoveable obstacle, we suppose B to be the 
float of a water-wheel moving with an uniform velocity v, 
and to be struck by c at F j in that case when B has moved 
through a space FH = ^ EF, A will have arrived at G, EG 
being = fEF, and will have lost half its velocity. In this 
operation ^ of the moving force of A has been expended in 
changing the figure of A, ^ remains with it when moving on 
with the same velocity as B, and the remaining i has been 
expended in pressing B through the space FH, and it is easily 
demonstrable that if the velocity of B be either greater or less 
than I V, it will be pressed by c through a space less than FH. 
And whether A be uniformly penetrable by c or not, the same 
relative velocity of A and B is required in order that the greatest 
possible quantity of the moving force of A shall be transferred 
• Examples of moving force similar to these are referred to by Mr. 
Leslie, in his excellent work on heat, p. iSS. He explains them, 
however, on different principles. 
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