THE INCLINED PLANE. 105 



her of movable pulleys used ; that whan the fixed end of 

 the cord is attached to the movable block the number of 

 parts of the cord is one more than twice the number of 

 movable pulleys used. 



198. What is an Inclined Plane? The in- 



dined plane is a smooth, hard, inflexible surface 

 inclined so as to make an oblique angle ivith the 

 direction of the force to be overcome. In most cases it 

 is a plane surface inclined to the horizon at an acute angle, 

 and is used to aid in the performance of work against the 

 force of gravity. 



199. Resolution of the Force of Gravity. 



When a weight is placed upon an inclined plane, the force 

 of gravity tends to draw it vertically downward. This 

 force may be resolved into two forces ( 91), one acting per- 

 pendicularly to the plane, producing pressure completely 

 resisted by the plane, the other component acting opposite 

 to the direction of the power which it is to counterbalance. 

 The first component shows how much pressure is exerted 

 upon the plane ; the other shows what force must be 

 exerted to maintain equilibrium. The value of the second 

 component will, plainly, vary with the direction of the 

 power. 



200. Three Cases. In the use of an inclined plane, three 

 cases may arise : 



(1.) Where the power acts in a direction parallel to the length of 

 the plane. ' 



(2.) Where the power acts in a direction parallel to the base of the 

 plane (generally horizontal). 



(3.) Where the power acts in a direction parallel to neither the 

 length nor the base of the plane. 



20 1. The First Case. In the accompanying figure, let 



