238 MOVING FORCE. 
Cases of diffi- is strongly objected to by all those who hold that the product 
docirines of velocity is the proper measure of the force 
moving force, of a body in motion. They contend that “ all the experiments 
which are usu.illy brought to determine the impressions made 
upon soft bodies, as snow, clay, &c. are absolutely un6t for the 
purpose.” That “ the circumstances which take place in the 
production of these effects, are such as we can never discover.*’ 
And that “ the directions in which the particles recede, the 
velocities they acquire, their mutual actions upon one another, 
^ and lastly, the time in which these effects are performed, are 
all beyond the reach of computation*." 
To this it may be replied, that if only the pressure and the 
space through which it has acted be determined, it would be 
quite superfluous to enter into any farther computation of the 
circumstances above enumerated, in older to estimate the 
quantity of mechanical force expended in producing the im- 
pression. For, whatever may have been the relative directions, 
velocities, or mutual actions of the particles during the time 
that the impression was making, no internal motion remains 
after the impre.ssion is completed ; and the force can have been 
spent in no other way than in compressing the particles toge- 
ther, or in overcoming their tenacity. To take a familiar ex- 
ample.-— If a quantity of corn is to be ground, a considerable 
quantity of motion must, no doubt, be produced before that can 
be effected ; but after if is ground, there is no mo e motion in 
the flour than there w'as in the corn before it was ground, and 
the whole force employed must have been expended iii over- 
coming the tenacity or cohesion of the particles of the corn. 
In answer to the very common objection, that the quantity of 
force expended in producing an effect of this kind, cannot be 
precisely ascertained, it may be observed, that in real practice, 
3uch quantities of force are estimated with quite as much pre- 
cision as the force necessary to generate a given velocity in a 
given mafs, in projecting a cannonball, for example. The 
application and measurement of mechanical force producing 
• Dr. Pdilner. PluhTrans, 1770, p. 353. 
changes 
