530 



MACHINES, WORK, AND ENERGY 



weight, or more correctly stated, the difference in density of 

 the cream and the skim milk is utilized to cause the separation. 

 It is much as if we were to fill a peck measure with a 

 mixture of buck shot and peas and were then to shake the 

 measure. The lead shot being heavier than the peas they 

 would settle to the bottom of the measure and the peas would 

 be forced to the top. 



If, however, we were to fasten the measure securely to a 

 rapidly rotating platform, the contents of the measure would 

 fly out against the sides of the measure. The shot being 

 heavier, or more dense, than the peas, they would be forced 

 more strongly against the outside of the measure. The shot 

 would therefore be found to gather against the outside of the 

 measure while the peas would form a sort of lining on the 

 inside of the shot. The force which holds the shot and peas 

 away from the center of the measure is called CENTRIFUGAL 



FORCE (centri, center andfugal, to fly from). 

 ROPE The shallow setting, the deep setting, and 



the water dilution methods of separating cream 

 all depend upon the force of gravity to cause 

 the separation are therefore called GRAVITY 

 METHODS. With the cream separator, how- 

 ever, centrifugal force is employed to cause 

 the cream and skim milk to separate. 



Exercise 102. To Illustrate and Study 

 Centrifugal Force 



FIG. 330. X- 



rayview. Centri- ., , , 

 fugal force holds P al1 or bucket, 

 water against side 

 of pail. 



1. Suspend from the ceiling by means of a braided 

 cord (such as a small window-sash cord) a 12-qt. 

 Place about 2 qt. of water in the 

 pail. Seizing the bail of the pail, cause it to rotate 

 rapidly (Fig. 330). Watch the effect upon the sur- 

 face of the water. When the motion dies down, 

 give it another whirl in the same direction. Continue thus to 

 whirl the pail till the braided cord has acquired considerable twist. 

 Now, by placing the hand in the water, bring it to rest, at the same 

 time preventing the cord from untwisting till the water is quiet. 

 Now, let the cord untwist; it will cause the pail to rotate rapidly. 



