THE PULLEY. 



103 



ECTfON HI. 



THE PULLEY AND THE INCLINED PLANE. 



192. What is a Pulley?--^ pulley consists of 

 a wheel turning upon an axis and having a cord 

 passing over its grooved circumference. The frame 

 supporting the axis of the wheel is called the block. 



193. A Fixed Pulley. The advantages arising 

 from the use of a pulley depend upon the uniform tension 

 of the cord. If a cord be passed over a 



pulley fixed to the ceiling, a weight being 

 at one end and the hand applied at the 

 other, the tension of the cord will be uni- 

 form, and the hand will have to exert a 

 forca equal to the weight of the load. If 

 the weight be moved, the hand and weight 

 will move equal distances. It is evident, 

 ihen, that the fixed pulley affords no 

 increase of power, but only change 

 of direction. 



194. A Movable Pulley. If one 



end of the cord be fastened to the ceil- 

 ing, the load suspended from the pulley, 

 and the other end of the cord drawn up 

 by the hand, it will be evident, from the 

 equal tension of the cord, that the fixed 

 support carries half the load and the hand 

 the other half. It is also evident that to 

 raise the weight one foot the hand must 

 pull up two feet of the cord; that is to FIG. 52. 



FIG. 51. 



