360 Introduction to the Study of Science 



tion. Such a statement is the following, though it should be 

 considered as merely suggestive and you should try to express 

 in your own terms the essential facts. 



Any force may be resolved into two or more forces. When 

 the effects of a single force act in a direction different from that 

 of the original force, the effects may be determined by taking 

 the line representing the direction and amount of the given 

 force as the diagonal of a parallelogram, whose sides are drawn 

 from the point of application of the force in the directions 

 which the resolved forces must follow. If, moreover, the 

 diagonal is drawn to a convenient scale, the numerical values 

 of the resolved forces may be found by measuring the sides 

 and multiplying their lengths by the scale number. 



This general statement of the facts is known in physical 

 science as the resolution of forces. 



Parallelogram of forces. The resolution of forces is but a 

 half truth ; for two or more forces may combine at a common 

 point to produce a single effect, just as readily as a single force 

 may be resolved into several effects. That is, the resolution of 

 forces must be supplemented by the composition of forces. 

 The chief difference involved is that in composition the forces 

 uniting at a common point are described as the component 

 forces and their effect as the resultant. The method of deter- 

 mining the magnitude and direction of a resultant of component 

 forces is similar to that of determining the magnitudes and 

 directions of the effects of a resolved force. The resolution 

 and the composition of forces are included in a single general 

 principle known as the parallelogram of forces. 



Exercise : On the parallelogram of forces. Because of the impor- 

 tance of the principle, it will be helpful, if time allows, to demonstrate 

 experimentally by such an arrangement of spring balances as in Fig. 

 123, the following : 



1. The direction of the resultant of two components is always more 

 nearly in alignment with the direction of the greater force. 



2. The magnitude of the resultant decreases as the angle formed 

 by the components increases ; or 



