46 STATICS. [82. 



producing the resultant acceleration is called the resultant of the 

 forces F v F% ; these, or any other two or more forces having 

 the same resultant F t are called the components of F. 



82. In many investigations we are not so much concerned 

 with the actual accelerations produced as with the effects that 

 miglit be produced by any particular force or system of forces if 

 the particle or body were perfectly free to move, i.e. not subject 

 to other forces or restraints. 



We proceed to study the composition and resolution of forces 

 from this point of view, i.e. without reference to the accelera- 

 tions produced, but with particular attention to the conditions 

 under which the given system of forces is in equilibrium. This 

 study forms the subject of Statics. 



83. The geometrical characteristics of a force are (a) its line 

 of action, (b) its magnitude or intensity, (c) its sense. Properly 

 speaking, two forces should be called equal only when they 

 agree in these three characteristics. But it is customary to call 

 two forces equal even when they have only equal magnitude ; 

 we shall call them geometrically equal, when they agree in all 

 three characteristics. 



84. A force acting on a particle P is said to have its point 

 of application at P, and the line representing it is usually 

 drawn from P as origin. But the point of application is not an 



Fig. 14. 



essential characteristic of the force ; it may be taken at any 

 point of its line if this line be regarded as rigid. Thus the 

 force F acting on the particle P (Fig. 14) can be transferred, 

 without changing its effect, to any point P' of its line ; and two 

 equal and opposite forces in the same line, such as /<\at P and 



