574 Mr. vince’s Invejligation of the 
p to ftrike Qjn the direction fa, a body equal to Px^~ 
were to ftrike Q_at the fame point and in the fame di- 
rection (which direction is fuppofed to pafs through the 
center of gravity of that body) the effeCt on would be 
the fame; hence, if in the quantity Q - gQc^p'^-oo * which 
from the laft Prop, exprefles the velocity of the point d 
after the ftroke, on fuppofition that the bodies are non- 
elaftic, we fubftitute for p a body equal to p x we 
flia11 have (^xGCxro + PxfoxDC for the velocity of the 
point d from the aCtion of p ; and confequently 
= the velocity of the center of gra- 
vity g of the body q_, after the ftroke, if the bodies be 
perfectly elaftic. To determine now the velocity of the 
ftriking body, let of, perpendicular to og, be the fpace 
defcribed by the point o in the firft inftant of time af- 
ter the ftroke, which, as that point is not difturbed by 
the a&ion of the bodies on each other, may reprefent 
the velocity of p before the ftroke, and let vb repre- 
fent the velocity of the point f after the ftroke ; join ft, 
and draw gd perpendicular to og, and then will gd re- 
prefent the velocity of the center of gravity g of the 
ftriking body after the ftroke. Draw fc perpendicular 
to fa, and produce gd to meet fc in e ; now the velocity 
loft 
