COMPOUND MOTION, 



83 



What effect 

 does the action 

 of Contrifugal 

 Force have up- 

 on the figure of 

 »body? 



Fia. 56. 



of tho -wheel is much larger than that described by the inner part, and as 

 both move round the center in the same time, the outer part must move with 

 a greater velocity. 



170. If the particles of a rotating body have 

 freedom of motion among themselves, a change 

 in the figure of the body may be occasioned by 

 the difference of the Centrifugal Force in the 

 different parts. 



A ball of soft clay, with a wire for an axis, forced through its center, if macia 

 to turn quickly, soon ceases to be a perfect ball It bulges out in the middle, 

 where the Centrifugal Force is, and becomes flattened toward the ends, or 

 whsre the wire issues. 



This change in the form of 

 revolving bodies may be illus- 

 trated by an apparatus repre- 

 sented in Fig. 56. This con- 

 sists of an elastic circle, or hoop, 

 &stened at the lower side on a 

 vertical shaft, v.hile the upper 

 side is free to move. On turn- 

 ing the wheels, so arranged aa 

 to impart a very rapid motion 

 to the shaft and hoop, the hoop 

 win be observed to bulge out 

 in the middle (owing to the 

 Centrifugal Force acting with 

 greater intensity upon those parts furthest removed from the axis) and to be- 

 come flattened at the ends. 



.„^ . . 171. The earth itself is an example of the operation of this 



what 18 the „ ^ ,. , ■ , ^ ^ ^ • -, 



cause of the force. Its diameter at the equator is about twenty-six miJes 



of «f "earth''^ greater than its polar diameter. The earth is supposed to 

 have assumed this form at the commencement of its revolu- 

 tion, through the action of the Centrifugal Force, while its particles were in a 



semi-fluid, or plastic state. In Fig. 57 we 

 have a representation of the general figure of 

 the earth, in which N S is the jxjlar diameter, 

 6nd also the axis of rotation, and E W the 

 equatorial diameter. 



172. At the equator the 

 amount of Ccif- Centrifugal Force of a part icle 

 tripptal Force ^f matter is l-290ths of its 

 At the equator T . ,. . . , 



gravity. This diminishes as 



•we approach tl.e poles, where it becomes 6. 

 If the earth revolved 17 times faster than 

 it now docs, or in 8-i minutes instead of 24 



Fig. 57. 



