MECHANICAL PARADOXES. 



in the direction B F, at C, C G, and at D, D H. 

 And these are the directions in which loose 

 particles do fly off, as may be seen in the sparks 

 from an emery wheel. But if the body went 

 from A along A E, it would be going further 

 from the centre of revolution. Consequently, 

 it requires a constant pull towards the centre 

 to tie it down to the circular path. This ten- 

 dency of revolving bodies to go further from 

 the centre is commonly called centrifugal force ; 

 and, for a given speed of the revolving body, 

 the force is greater as the circle is smaller. 



The strength of this force may be seen in 

 the tendency of rapidly revolving grindstones 

 and emery wheels to burst, so that they have 

 to be specially bound in order to prevent 

 accidents. 



It may be illustrated also by taking a can 

 or small bucket, half filled with water, and 

 swinging it higher and higher until it goes 

 right overhead and completes the circle. This 

 can be done without a drop being spilled, be- 

 cause the centrifugal force throws the water 

 upwards away from the centre against the 

 top nominally the bottom of the bucket. 

 The experiment is made easier by taking a 

 very small can and swinging it by a piece of 

 string. 



But, instead of the string, other means 

 may be taken of holding the object at the 

 same distance from the centre while it revolves. 



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