32 



NATURAL PHILOSOPHY. 



[Lesson XIV. 



178. r. Does the centrifugal fon-t- \ .u y 

 with the distance from the earth's axis ? 



P. Yes ; all the different points of the 

 earth are not equidistant from the axis of 

 rotation, and this force is greatest at the 

 equator, and diminishes as it approaches 

 the poles, acting against gravity, and 

 lessening its intensity. This apparatus 

 (Fig. 22) will explain how it is that 



Fig 22. 



the earth is flattened at the poles. You 

 observe there are two discs, which re- 

 volve horizontally. When the handle 

 m Is turned it conveys the motion of the 

 larger disc by means of the string d to the 

 lesser disc, which has the vertical axis c 

 fixed in its centre. A spring a b, is fas- 

 tened by its lower end to the axis, and the 

 upper part can be moved up and down, 

 and when the machine is at rest it forms a 

 spherical figure, but assumes an elliptical 

 figure when the axis revolves rapidly, owing 

 to the centrifugal force acting upon those 

 points most remote from the axis. 



179. T. Can you give me any other 

 examples of centrifugal force overcoming 

 the force of gravity ? 



P. A horseman at a circus, when stand- 

 ing upon the horse which is running round 

 the ring, inclines his body inwards, and 

 when the horse is going round at full speed, 

 any one may see both rider and horse 

 influenced by this force. 



180. T. Why does the horseman incline 

 his body inwards ? 



P. To counteract the centrifugal force. 



181. T. If this force impels bodies out- 

 wards, how do you account for bodies 

 inclining towards the centre when going 

 round a circle? 



P. Because there is another force acting, 

 called the centripetal, or centre-seeking force, 

 which draws them towards the centre, so 

 that all bodies moving in circles are acted 

 upon by both forces. 



182. T. What is the axis of a body ? 

 P. The real or imaginary line round 



which a body rotates. 



183. T. The other matters in connec- 

 tion with Natural Philosophy must be left 

 for another occasion. 



GENERAL QUESTIONS ON LESSON XIV. 



1. What is centrifugal force 1 



2. How does it act ? 



3. Prove its existence. 



4. What is centripetal force ? 



5. What does a body rotate upon ? 



W. EGL1NUTO.S-, 



:.r.T, LONDON, 



