4 ANSWERS TO PRACTICAL QUESTIONS 



16. What causes the mud to fly from the ivheels of a 

 carriage in rapid motion ? 



The centrifugal force (the momentum of the mud). 



1 7. Wtiat proof have ^ve that the earth was once a soft 

 tn ass ? 



It is flattened at the poles. This effect is produced upon a 

 ball of soft clay by simply revolving it on a wire axis. 



18. On a curve in a railroad , ivhy is one track always 

 higher than the other ? 



The outer track is raised in order that centrifugal force and 

 gravity, acting together, may combine to keep the average 

 pressure perpendicular to the track. 



19. What is the principle of the sling ? 



The sling is whirled until a strong centrifugal force is gen- 

 erated ; the string, the centripetal force, is then released, when 

 the stone flies off at a tangent. 



20. The mouth of the Mississippi Miver is about 2\ miles 

 farther from the center of the earth than its source. What 

 causes its water to thus " run up hill " ? 



The centrifugal force produced by the rotation 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. 



21. Is it action or reaction that breaJcs an egg ivheti 1 

 striJte it against the table ? 



The reaction of the table. 



22. Was the tnan philosophical who said " it tvas not 

 the falling so far but the stopping so quick that hurt 

 him"? 



He was. 



23. If one person rims against another, which receives 

 the greater bloiv ? 



Action is equal to reaction ; hence the momentum given up 

 by the one is equal to that received by the other. 



