42 



APPLIED SCIENCE 



equal to the quotient obtained by dividing the length of 

 the plane by the height. To illustrate: If a barrel weighing 

 300 Ibs. is to be rolled onto a wagon 4 ft. from the ground 

 and a plank 12 ft. long is used, a strength or force of 100 

 Ibs. would balance the barrel, because the inclined plane is 

 three times the perpendicular height. A slight force over 

 the 100 Ibs. would move the barrel. 



Roads constructed to the tops of hills are either wound 

 round and round, or made so broad that a person or driver 

 of a vehicle can wind from side to side in climbing the hill. 

 In building houses, an inclined plane in the form of a plank 

 walk is used to facilitate the transit of wheelbarrows in and 

 out of the building. The stairs of a house form a steep 

 inclined plane on which the steps enable one to secure a 

 firm footing. 



42. An Example of the Inclined Plane. Figure 26 repre- 

 sents an inclined plane supporting a ball A which is free to roll 



on an axle through its center. 

 A cord attached to the yoke 

 of the axle passes over a 

 guide pulley B to a counter- 

 weight W. The weight W 

 is then pulling against the 

 ball in a direction parallel 

 to the face of the plane and 

 is preventing the ball from 

 rolling down. 



Now it is easy to see that the weight W does not need to be 

 so heavy as the ball to keep the ball from rolling, since part of 

 the weight of the ball is supported by the plane. In other words, 

 the ball naturally tends to fall straight down in the direction of the 

 dotted line XY, just as though it were dropped from the hand 

 and fell to the floor. 



By a diagram of similar triangles, it can be proved that the 



B 



BALL A 



\ 



FIG. 26. Inclined Plane. 



