34* 



OUR PHYSICAL WORLD 



be approximately twice the power applied. The power now will 

 move two times as far as the weight. 



The third simple machine found in many common appliances, 

 either by itself or in combination with one of the foregoing, is the 

 inclined plane. When the truck man wants to load a heavy 

 barrel into his wagon, he often lays a plank from the rear end 

 of the wagon to the ground and rolls the barrel up this plank 

 instead of trying to lift it, because he can roll it up the plank so 

 much more easily (Fig. 190). Suppose that the bed of the wagon 

 is 3 feet above the ground and the plank 1 2 feet long. Suppose 



FIG. 190. Loading a barrel on to a wagon with the inclined plane 



that it is a barrel of flour weighing 196 pounds that is to be loaded. 

 This is to be raised 3 feet from the ground, but to do this the 

 truckman applies force to it as it rolls a distance of 12 feet. 

 Remembering now that the weight multiplied by the distance it 

 is raised equals the power applied multiplied by the distance 

 through which it acts, it is evident that a push of 49 pounds is 

 sufficient to roll the barrel: 



196X3=49X12. 



The truckman, then, by applying power of 49 pounds plus 

 what is needed to overcome friction, can get the barrel weighing 

 196 pounds into his wagon. 



