38 APPLIED SCIENCE 



5. How far would the three lower pulleys and frame be raised 

 if the rope at P is pulled down 6 ft.? 



6. How does the force of the arrangement shown in Fig. 19 

 differ from the force obtained from a block and tackle having 

 three pulleys in each block (neglecting friction)? 



FIG. 22. Use of a Single Pulley. Double-platform material 

 elevator for lifting materials to a building. One elevator 

 goes up while the other comes down, so that only force 

 enough to lift the actual load is required. 



39. Wheel and Axle. The study of pulleys and tackles 

 leads naturally to that of the wheel and axle, which consists 

 of a wheel or crank attached to an axle. The weight is 

 lifted or moved by means of a rope, belt, or chain running 

 over the axle. The force is applied to the rim of the wheel. 

 In previous problems the pulleys have all been of equal 

 diameters, and operated by cords or ropes, but the wheel 

 and axle may be considered as fixed pulleys of different 

 diameters fastened on a shaft, the larger pulley being the 

 wheel, and the smaller pulley the axle. 



