CENTRIFUGAL FORCE. 



43 



less, and at the pole more. Thus it was discovered that, as the movements 

 of the pendulum are dependent upon the force of gravity, and as this force 

 decreases the farther we get from the centre of the earth, the equator must 

 be farther from the earth's centre than the poles, and therefore the poles 

 must be depressed. The decline of the pendulum at the equator is also, in a 

 measure, due to Centrifugal Force. 



Centrifugal Force, which means " flying from the centre," is the force 

 which causes an object to describe a circle with uniform velocity, and fly 

 away from the centre ; the force that counteracts it is called the centripetal 

 force. A very simple experiment will illustrate it. 



l-'ig. 37. Another illustration oi cenmmgal iu.c. 



To represent its action, we shall have recourse to an ordinary glass 

 tumbler placed on a round piece of cardboard, held- firmly in place by cords. 

 Some water is poured in the glass, and we then show that it can be swung 

 to and fro and round without the water being spilt, even when the glass is 

 upside down (fig. 36). 



Another experiment on the same subject is as shown in the above illus- 

 tration, by which a napkin ring can be kept in revolution around the fore- 

 finger, and by a continued force the ring may be even held suspended at 

 the tip of the finger, apparently in the air, without support (fig. 37). 



