34 OUTLINES OF NATURAL PHILOSOPHY. 



As we have already derived from the first law of mo- 

 tion, the proposition usually reckoned the Third, 

 viz. that the motion communicated, is always in 

 the direction of the force "impressed, 62. ; the 

 laws of motion, according to this arrangement, are 

 reduced to two, 



72. If two bodies meet with velocities which are 

 inversely as their masses, and are directly opposed 

 to one another, they will remain at rest. 



If the bodies are equal, and have equal velocities, the 

 proposition is evident. 



If A be double of B, but have only half the velocity 

 of B ; then A may be divided into two equal parts 

 to B, each of which will have half the velocity of 

 B. One of these striking against B, would destroy 

 half its velocity ; and the other striking against it, 

 would destroy the other hah . 



The same is true whatever multiple the one body be 

 of the other, and therefore also whatever ratio the 

 one bear to the other. Vid. D^ALEMBEET, Dyna- 

 mique, 46. p. 51. 



Hence bodies that have equal quantities of motion,, 

 have equal forces, or equal powers to produce mo- 

 tion. 



73. The quantity of motion in a system of 

 bodies estimated in any given direction, is not 



2 changed 



