1 8 ANSWERS TO PRACTICAL QUESTIONS 



The outer track is raised that gravity may balance the cen- 

 trifugal force. 



22. What is the principle of the sling f 



The sling is whirled until a strong centrifugal force is 

 generated ; the string, the centripetal force, is then released, 

 when the stone flies off at a tangent. 



23. The mouth of the Mississippi river is about T.\ miles 

 further from the centre of the earth than its source. What 

 causes its water to thus "run up hill?" 



The centrifugal force produced by the revolution of the earth 

 on its axis tends to drive the water from the poles toward the 

 equator. Were the earth to stand still in its daily rotation, the 

 Gulf of Mexico would empty its waters back through the Mis- 

 sissippi to the northern regions. 



24. Is it action or reaction that breaks an egg when I strike 

 it against the table f 



The reaction of the table. 



25. Was the man philosophical who said ll it was not thr 

 falling so far but the stopping so quick that hurt him f" 



He was. 



26. If one person runs against another, which receives the 

 greater blow f 



Action is equal to reaction : hence the blows must be equal. 



27. Would it vary the effect if the two persons were running 

 in opposite directions ? 



The blow would then be the sum of both their momenta. 



If they were running in the same direction ? 



The blow would be equal to the difference of their momenta. 



28. Why can you not fire a rifle-ball around a hill? 

 Because a single force always produces motion in a straight 



line. 



29. Why does a heavy gun " kicK" less than a light one? 

 See problem 15. 



30. A man on the deck of a large steamer draws a small 



