Moving Force. 119 
cated ;* that is, if a given force be applied, 
or quantity of motion communicated at G, a 
progressive motion of the mass, without any 
rotatory motion, will be the result; but if the 
same force be applied at any other point D,we 
shall have the same progressive motion, and 
a rotatory motion besides. 
Is that rotatory motion produced without 
force? 
Examples of Motion destroyed, and of 
. Motion transferred from one Body to 
another. 
* 
G6. If the weight of the ball, A, (fig. 6.) be 
to that of B, as 2 to 1, and if they move in op- 
posite directions with velocities reciprocally as 
their weights, and strike at the same instant 
the ends of the spring, S. If the strength of 
the spring be such, that the balls shall be at 
rest when its ends. are brought to meet; they 
will meet at E, DE being equal to 2CE. 
Here the effect produced is the compression of 
the spring. But though the quantity of motion 
of A is equal to that of B, the portion of the 
effect, produced by A, is less than that which is 
produced by B. 
If we substitute.for B a ball equal in weight 
* Philosophical Transactions, vol. 70. p, 551, 
1 
