20 MECIIAXICS. 



ing manner: If a ball, placed at the point a (fig. 7), be 

 struck by two dilTerent forces at the same moment, in the 

 direction shown by the two ar- 

 rows, and if one force be just suf- 

 ficient to carry it from a to c, 

 and the other to carry it from a 

 to Z>, then it will move inter- 

 mediate between the two, in the 

 direction of the diagonal of the 

 parallelogram a J, and to a dis- 

 tance just equal to tlic length of this diagonal or cross- 

 diameter. 



When the forces act very nearly togetlier, tlie parallelo- 

 gram of the forces will bo very narrow aud quite long, 

 with a long diagonal Fip. 8. 



(fig. 8) ; but if they act _ _ 



on nearly opposite sides ^^ """^^^-^-^^^-^^^^^^^ ~ 



of the ball, they will 



very nearly neutralize each other, and the diagonal or re- 

 sult Avill be very short, showing that the motion given to 

 the ball will be very small (fig. 9). 



These examples show the importance of having teams 

 attached to a plow or to a wagon very nearly in a straight 

 line with the draught, or else a part of the force will be 

 Fig. 9. lost ; and also the impor- 



^^"^^^^^ -*r-^ tance, when several animals 



are drawing together, of 

 their working as nearly as 

 possible in the same straight line. For, the more such 

 forces deviate from a right line, the more they will tend 

 to destroy or neutralize each other. 



A familiar example of the result of two oblique forces 

 is furnished when a boat is rowed across a river. If the 

 river has no current, the boat will pass directly from bank 

 to bank perpendicularly ; but if there is a current, its track 

 will form a diagonal, and it will strike the opposite bank 



