164. Explain what is represented Figs. 144, 145, and 146.
165. Explain Fig. 147. How is curved motion produced? Give the illustration of the ball and string. What are centrifugal and centripetal forces?
166. What are these two forces in the revolution of the earth around the sun? Give various illustrations of the operation of centrifugal force.
167. What is said of the formation of bends in rivers?
168. Show how eddies and whirlpools are formed. How is the centrifugal force used in the art of pottery. How in making window-glass?
169. Describe and explain the operation of the steam-governor.
170. What is said of the agency of the centrifugal force in shaping the earth?
171. Explain the operation of the apparatus represented in Fig. 154. What are the forces which act on a projectile? What is said of balls thrown horizontally from cannon with different velocities?
172. Show by Fig. 155 why a ball dropped from the mouth of a cannon will fall to the ground in the same time that one fired from it will. By What two forces is a falling body acted upon?
173. Explain Fig. 156. What is the course of a ball dropped from a railway car or from a mast-head? Give the comparison between the cannon-ball and the moon.