CENTRIFUGAL FORCE. 



131 



fore, necessary to employ a very heavy pendulum which 

 continues its vibrations for several hours. 



16. Centrifugal Force. When a moderately heavy 

 stone, about 200 to 500^, is fastened to one end of 

 a string, and whirled round by the hand so as to 

 describe a circle, we shall find that the string is 

 stretched, and that the strain increases as the velo- 

 city of rotation becomes greater. If the string is 

 not sufficiently strong, the strain will break it. All 



L I B li A R Y 



UNA VK UNITY 01 



FIG. 94. 



bodies which are moving in a circle are, like our stone, 

 acted upon by a force which tends to draw the body 

 away from the centre of the circle. This force is called 

 Centrifugal Force. A moving body must, by its inertia 

 alone, always move in the same direction; but if it is 

 compelled to move in a circle, it changes its direction 

 at every instant, and the centrifugal force is nothing 

 lse but the resistance of the body to this continual 

 change in the direction of its motion. Let A, in fig. 94 

 epresent a body, fastened to the string A C, and 

 noving in a circle in the direction of the arrow a. At 



K 2 



