FORCE AND MOTION. 41 



9O. Parallelepiped of Forces. The component 

 forces may not all act in the 

 same plane, but the method of 

 composition is still the same. 

 In the particular case of three 

 such forces it will be readily 

 seen that the resultant of the 

 FlG forces AB, AC, and AD is rep- 



resented by AR, the diagonal 

 of the parallelepiped constructed upon the lines represent- 

 ing these forces. 



91. Resolution of Forces. ^e operation of 

 finding the components to which a given force is 

 equivalent is called the resolution of forces. 



It is the converse of the composition of forces. Repre- 

 sent the given force by a line. On this line as a diagonal 

 construct a parallelogram. An infinite number of such 

 parallelograms may be constructed with a given diagonal. 

 When the problem is to resolve or decompose the given 

 force into two or more components having given direction^ 

 it is definite only one construction being possible. The 

 sides that meet at the point of application will represent 

 the component forces. 



92. Example of Resolution of Forces. As 



we. proceed we shall find more than one example of the 

 resolution of forces. A single one will answer in this 

 place. It is a familiar fact that a sail-boat may move in a 

 direction widely different from that of the propelling wind, 

 and that, under such circumstances, the velocity of the 

 boat is less than it would be if it were sailing in the direc- 

 tion of the wind. The force due to the pressure of the 



OF THE 



