84 
MOVING FORCE. 
II. 
On the Measure of Moving Force. By Mr. Peter Ewart*. 
(Continued from p. 66.) 
cuU>*in die'*' two elastic balls equal balls E and F, (fig. 10.) mo- 
doctrines of ving with the respecti-ve velocities A C and A B, at right angles 
moving loJ'ce. jQ gggjj strike at the same instant a third elastic ball A, 
equal to E or F ; E and F will be brought to rest, and A will 
move off with the velocity and in the direction A D, In this 
case, the whole amount of the forces of E and F must have been 
communicated to A; but the velocity acquired by A is less than 
the sumof the velocities of E and F. 
1 1. If the directions of E and F be not at right angles, and 
if A C=A B (as in fig. 11.) the result will be as follows: 
produce A B, and draw the perpendicular D G after the stroke, 
the velocity of A in the direction A B, will be ^ ^ 
^ A B + A G 
and E and F will each continue to move in their first directions 
. ... , . A B X B G* 
A B 4- A G. 
In this case, as in all others, the velocity and the direction 
of the centre of gravity of the system is, no doubt, the same 
before and after collision. But that is only one feature of the 
case. If we examine all the results after collision, we shall find 
that the motion of A is not the same as it would have been if 
it had been struck by a mass equal to E + F, having the same 
velocity as the common centre of gravity of E and F before 
collision. If, however, we reckon the forces as the masses 
into the squares of their absolute velocities, we shall (if they 
be perfectly elastic) always find that whatever force is lost by 
the striking balls, is gained by that which is struck. 
12. Let four equal balls A, B, D, E, (fig. 12.) revolve 
about their common centre of gravity, C. Let A and B be 
• If BAC be an obtuse angle, the same solution applies, only E and 
F rebound instead of proceeding forward. 
connected 
