202 ANSWERS TO PRACTICAL QUESTIONS 



40. Why are ships becalmed at sea of ten floated by strong 

 currents into dangerous localities without the knowkdge of 

 the crew ? 



As there are no fixed objects with which to compare 

 their motion, the officers are not sensible of any move- 

 ment, and so are often drifted far out of their course. 



41. A man in a wagon holds a $o-lb. weight in his hand. 

 Suddenly the wagon falls over a precipice. Will he, while 

 dropping, bear the strain of the weight ? 



No. While on solid ground, his hand resisted the 

 tendency of the weight to fall toward the earth's centre 

 of gravity ; but all are now descending freely under the 

 influence of gravity, and he no longer feels the pressure. 



42. Why are we not sensible of the rapid motion of the 

 earth ? 



Because all the objects around us are moving in the 

 same direction with the earth, and there is nothing at 

 hand with which to compare. 



43. A feather is dropped from a balloon which is im- 

 mersed in and swept along by a swift current of air. Will 

 the feather be blown away, or will it appear to a person in 

 the balloon to drop directly down ? 



It will seem to drop directly downward, as if in a dead 

 calm. Its fall is vertical, however, only as regards the 

 balloon, and not as regards the earth. 



(See Stewart's Physics, p. 18.) 



44. Suppose a bomb-shell, flying through the air at the 

 rate of 500 feet per second, explodes into two parts of equal 

 weight, driving one-half forward in the same direction as 



