58 



FALLING BODIES. 



or will fall with the same velocity. This resistance may 

 be avoided by trying the experi- 

 ment in a glass tube from which 

 the air has been removed. The re~ 

 sistance may be nearly equalized by 

 making the two falling bodies of 

 the same size and shape but of dif- 

 ferent weights. Take an iron and 

 a wooden ball of the same size, drop 

 them at the same time from an 

 upper window, and notice that they 

 will strike the ground at sensibly 

 the same time. 



12O. Reason of this Equal- 

 ity. The cent is heavier than the 

 feather and is therefore acted upon 

 by a greater force. The iron ball 

 has the greater weight, which shows 

 that it is acted upon by a greater 

 force than the wooden ball. But 

 this greater force has to move a 

 greater mass, has to do more work 

 than the lesser force. For the greater force to do the 

 greater ivork requires as much time as for the 

 lesser force to do the lesser work. The working force 

 and the work to be done increase in the same ratio. A 

 regiment will march a mile in no less time than a single 

 soldier would do it ; a thousand molecules can fall no fur- 

 ther in a second than a single molecule can. 



121. Galileo's Device. To avoid the necessity 

 for great heights, and the interference of rapid motion 

 with accurate observations, Galileo used an inclined 



FIG. 26. 



