MECHANICS 63 



CENTRIFUGAL FORCE 



If a ball is fastened to a string and is whirled so as to give 

 it a circular motion, there will be a pull of greater or less amount 

 on the string, according as the speed of the ball increases or 

 decreases. If the string is cut while the ball is in motion, 

 the ball will fly off, away from the center of the circle in which 

 it is whirling. The force that acts to draw a body away from 

 the center around which it revolves is termed the centrifugal 

 force of the body. It may be found by the formula 



F = . 00034 WRN*, 

 in which F = centrifugal force, in pounds; 



IT' = weight of revolving body, in pounds; 



R = radius, in feet, of circle in which the center of 



gravity of the revolving body moves; 

 2V = revolutions per minute of revolving body. 



MACHINE ELEMENTS 



LEVERS 



A lever is a bar that may be turned about a pivot, or point, 

 as shown in Figs. 1, 2, and 3. In each case, the object W to 



FIG. 1 FIG. 2 FIG. 3 



be lifted is called the load , or weight; the force that accomplishes 

 the lifting is represented by F; and the fulcrum, or pivot, is 

 indicated by C. The distance / from the weight to the fulcrum 

 is termed the -weight arm and the distance L from the force 

 to the fulcrum is termed the force arm. The distance between 

 the force and the weight is denoted by a. Whenever the force 

 f is just great enough to balance the load lifted, it will be 

 found that the force times the length of the force arm is equal 



