AGE OF MACHINERY 



495 



With the screw, as with other machines, the distance the weight 

 moves multiplied by the weight is equal to the distance the force 

 moves multiplied by the force. The pitch of a screw is the distance 

 a screw will sink into a board or nut, or raise an object on a jack- 

 screw, by turning the screw once around. 



TKe Wirxdlass 



->Force 



orce 



Force Arm 



Ice Oea.m 

 Freezer 



Mill 



Door Krvob 



Fulcrum 



(Radius of 



Wheel and Axle 

 FIG. 375. 



In the case of the jackscrew, as shown in the illustration, the 

 distance from the screw to the hand is the radius of a circle. When 

 the screw is turned around once the distance traveled by the power 

 is equal to the circumference of the circle, and the distance traveled 

 by the weight is equal to the pitch of the screw. 



What force would be required to raise a thousand-pound weight 

 on a jack screw which has a bar 24 inches long, the pitch of the 

 screw being f inch? 



