Machines 



247 



applied. The forearm is the weight. A short contraction of the 

 muscle of the upper arm causes the forearm to move quickly 

 through a considerable distance, though with far less force than 

 the effort applied. Speed and distance of movement make up 

 for the loss in mechanical advantage. 



The Pulley. The principle of the lever is employed in the 

 pulley. The pulley, like the lever, is used for applying force to 

 do work, such as lifting some 

 heavy object from a lower to 

 a higher level. A pulley, in its 

 simplest form, consists of a 

 grooved wheel so arranged as 

 to turn within a frame or block 

 by means of a cord or rope 

 passing over the wheel. 



BLOCK AND TACKLE 



A little force will lift 



a heavy weight. 



Why? 



A FIXED AND A MOVABLE 

 PULLEY 



Which pulley gives mechanical advantage? 



The single fixed pulley is fastened to a standard of some 

 kind, and never gives a mechanical advantage of more than 1. 



