APPLICATION OF GRAPHIC METHODS 339 



and acts along the line of the rod towards B. The third component, 



eW 



9 d*'- 



and acts at right angles to the rod through the centre of the per- 



A-- 

 cussion H, which is at a distance from B. 



*o 



These three forces may be most conveniently compounded by shifting 

 F 3 to G, and introducing a couple whose moment is F 3 - H G, or 



where I is the moment of inertia of the rod about G. 



Forces equal and opposite to those components form the several 

 parts of the whole resistance to acceleration, and when these are 

 combined with the weight, the resultant is the whole load on the 

 element. (See Part I., 27.) This composition is effected graphi- 

 cally, and a single force is obtained acting through G, which has 

 then to be shifted parallel to itself to such a distance as to give rise 



to the moment ,. This process gives a single force of determi- 



i/ 



nate magnitude and position, as the load on the element in each 

 position of the engine. 



The following tables show the component parts of the accelera- 

 tion and force in the eases which have been actually examined. In 

 Table II. the connecting rod is 41" long, and its mass is 34 Ibs. ; / is 



20". and *~ is 34'08 inches. In Table III. the connecting rod is 28'' 

 <o 



k 2 

 long, and its mass is 28 Ibs. ; Z is 14", and is 25-32 inches. In 



*o 



both cases the crank radius is 8", the mass of the piston and piston 

 rod 46 Ibs.. and the speed is 1 revolution per second, whence 



da 

 *f-*" 



The positions of the crank in column 1 are numbered thus : Posi- 

 tions and 24 are the same, and correspond to a = 0. Position 12 

 corresponds to a = 180. The movement in Fig. 56 is contrary to 

 that of the hands of a watch, and the interval between two succes- 

 sive positions is 15. Looked at from the other side, as in earlier 

 figures of the engine, the movement would be in the direction of the 

 hands of a watch. 



z 2 



