MOVING FORCE. 
85 
connected by a rod of no sensible inertia, and D and E by a Cases of diffi- 
liniilar rod, but unconnected with A and B. Let the distance 
doctriHes oi 
of the centres of gyration of A and £ be twice that of D and moving force. 
E, and let D and E make two revolutions while A and B make 
one. If the balls and rods be elastic, and the velocity of each 
ball 10, and if the rod connecting A and B be struck by the 
balls D and E at their c-entre of gyration, the velocity of A 
and B after the stroke will be 14, and that of D and E will ’ 
be 2. If the balls and rods be non-elastic, the velocity of A 
and B after the stroke will be 12 and that of D and E, 0. 
In the first case, the sum of the products of the masses 
into the squares of their respective velocities, is the same 
before and after collision ; but in the second case, that sum is 
less after than before collision ; and it must, I presume, be 
admitted, that the rotatory force in that case is diminished by 
the collision. 
13. If an iron prism A B, (fig. 13 ) moveable on a fixt 
centre at A, be let fall on a piece of soft day C, the greatest 
mpression might be expected to be made when the clay is 
placed under P, (he centre of percussion of the prism. But 
:tf the experiment be made, the impression will be found to be 
he same, whether the clay be placed at C, D, or E, or at any 
other distance from the centre of motion. 
14. Let two equal elastic bails A and R, (fig. 14.) be con- 
aected by an elastic rod, and be at rest in free space, and let 
ijr be their common centre of gravity. If another elastic ball 
whase mass is equal to the joint masses of A, B, and the 
od, moving with the velocity v in the direction C G at right 
ngles to the rod, strike it at G ; C will be brought to rest, * 
nd G will move otf with the velocity v, in the direction C G. 
jut if we repeat the experiment, applying the (jjirce of D 
rstead of C, the mass of D being equal to that of A or B 
nd half the rod ; and its velocity equal 2y, striking A at its 
entre of gyration round the point G, the result will be as 
>llows : D will be brought to rest, G will move off as before 
•ith the velocity v, and A and B will have a rotatory motion 
aout g, with the velocity v at their centres of gyration. In 
both 
