254 Introduction to the Study of Science 



in the far western states certain tribes of Indians making use 

 of these primitive vehicles pulled by ponies. 



106. The vehicle as a machine. This simple machine, for 

 a vehicle is a machine, involves an important principle which 

 is applied to-day in the most varied and intricate ways. By 

 its use a limited force may be so directed as to overcome a 

 large resistance. The principle is fundamental, but it can be 

 presented here only in the simplest form. 



In order to understand the advantage of such a vehicle or 

 machine, let us consider the following example. Suppose a 

 plank ten feet long represents the vehicle. As it lies on the 

 ground, a load of 200 pounds is placed so that its center of 

 weight is one foot from one end. If the weight of the plank is 

 neglected, it will be found by trial that the force required to 

 lift the other end of the plank will be twenty pounds. By 

 shifting the load nearer to the end which is to remain on the 

 ground, the force required to lift the other end is decreased. 

 By shifting the load toward the end to be lifted, the lifting 

 force must be increased. Suppose that the load of 200 pounds 

 is located five feet from the end that is to rest on the ground, 

 the lifting force at the other end must be just one half the 

 weight of the load, or 100 pounds. That is, the product of 

 the weight and its distance from the place or edge where the 

 plank rests on the ground is found to be equal to the product 

 of the lifting force and its distance from the end that remains 

 on the ground. Or in this case, 200 X 5 = Force (100 pounds) 

 X 10. 



The advantage of such a machine as a vehicle is evident. It 

 requires much less force to lift and drag a load over the ground 

 with such a machine than it does to carry it, if it can be carried. 

 Give examples which verify this. 



The lever. The crude vehicle embodies an idea which has 

 had remarkable development and varied application in different 

 machines. To-day we call such a machine a lever. Its chief 

 features are the point whereon the lever rests, called the ful- 



