290 
MOVING FORCE. 
Cases of diffi- motion.— In the estimati n of deflecting forces, the duration 
cully in the , . , ...... i 
doctrines of becomes an important element. — In investigating the pheno- 
moving force, mena of liquefaction and evaporation, temperature becomes an 
e.ssential consideration. Yet there appears to be no more 
reason for taking duration as the general measure of moving 
force, than for taking temperature as the general measure of 
heat. 
It has been shown (page 18/) that if a given non-elastic 
body, moving with a given velocity, strike an equal non-elastic 
body at rest in free space, half the moving force of the striking 
body is expended in producing change of figure ; and in the 
same manner it has been shown (page 197) that, when the 
mass of the striking body is half that of the body which is 
struck, two thirds of the moving force of the striking body is 
expended in producing change of figure.- 
Upon the same principles, the following general theorem is 
easily made out. — If any non-elastic mass A strike another 
non-elastic mass B at rest in free space, (the direction of the 
stroke passing through the centres of gravity of A and B,) the 
original moving force of A will be to that part of it which is 
expended in producing change of figure, as A-fB : B, and to 
the remaining moving force of A and B after collision, as 
A + B: A* 
The practical application of this principle is exemplified in a 
variety of instances.— In driving piles — if the weight of the 
ram be very small in proportion to that of the pile, a great part 
• The following is a demonstration of this. Let the velocity of 
V 
A before collision : then 
' A-fB 
jion. The moving force before collision will beAo®, and that after 
/ Av \* A’ 
Ia-hb; 
A-fB 
=r the velocity of A and B after colli- 
n will be A 0 ®, and that after 
v'^. But these two quantities are as 
collision A-fB 
1 : -- > bence it appears that the fractional part of the moving force 
A *7“ 13 
found in the motion of the bodies after collision is — ^ - g , consequently 
B 
tjie part which is spent in producing change of figure is ~ — ' 
A-fB 
of 
