SOLIDS DEFYING GRAVITY. 



M 



In a subsequent section we shall have occa- 

 sion to refer to centrifugal force, which is really 

 the result of the tendency of motion to resist 

 interference. It is a general law of nature, to 

 which we have hitherto found no exception, 

 that a moving body tends to keep moving 

 straight on at the same speed, 

 and resists any interference. 

 The force with which it can 

 so resist depends on its weight 

 and its speed. In a spinning 

 mass every particle of the 

 circumference is at any given 

 moment moving at right 

 angles to the radius, and tends 

 to go on in that direction. If 

 suddenly set free, the particles 

 will go on in that direction, 

 which is called mathematically 

 a tangent to the circle. We 

 see this in the stone of a 

 sling, which, after being 

 whirled round the head, and 

 then suddenly released, does 

 not continue its whirling motion, but con- 

 tinues that part of the whirl in which it 

 was moving at the moment of its liberation 

 namely, the tangent to the circle of 

 whirling. So, also, with muddy wheels 

 which are rapidly revolving. The drops of 

 mud fly off at a tangent to the circumference, 



2Q 



H 



FiQ. 8.-GYROSCOPE 

 RESISTING A TWIST. 



