DYNAMICS. 37 



mains the same, and also in the direction BD, we 

 have the equations, 



A . AC 4- B . DC = (A + B) FC ; and 



Hence CG may be found. 



77. When the bodies between which the collision 

 takes place are elastic, or such, that after suffering 

 an alteration in their figure by collision, they re- 

 sume that figure with a force which causes them to 

 separate from one another, the result is considerably 

 different from any of the preceding, A Jpody is ac- 

 counted perfectly elastic, when, in restoring its fi- 

 gure, as much motion is produced, as was destroyed 

 in altering it. 



78. If A and B are two perfectly elastic bodies, 

 moving with the velocities a and b in the same di- 

 rection, so that A overtakes B, the velocity of A 



Aa Ba-f 2B& 



after the stroke is - . . ' - ; and that 



J\. -j- > 



P-D 2 A a 



A+B A + 



The investigation turns on this ; that the body which 

 overtakes the other must lose twice as much velo- 

 city as if it were hard; and the other gain twice 

 as much. 



If 



