MOVEMENT 



51 



laws of motion." In order to make it more easy 

 to take measurements from this photograph, the 

 original plate is enlarged, and the different positions 

 of the falling body are obtained on a convenient scale. 

 Let us draw a horizontal tangent to the ball in each 

 of its positions. The distances fallen during the various 

 periods since the 

 commencement of 

 the fall will then 

 be seen in series, 

 and it will be ob- 

 served that these 

 distances increase 

 as the square of the 

 time. For instance, 

 the distance tra-» 

 versed during the 

 second period of 

 fall, that is to say, 

 after the second 

 exposure, is four 

 times as much as 

 that which was tra- 

 versed in the first 

 period. 



If one wishes to 

 construct a time- 

 curve of the dis- 

 tance traversed, the sheet of paper should be divided 

 by vertical lines at equal distances. At the inter- 

 sections of each of these lines with the horizontal 

 tangents a mark is made (a dot in the centre of a 

 circle). The curve E, which joins all of these marks, 

 is a parabola, and represents the time-curve of a body 

 moving at an uniformly accelerated rate. 



The curve of velocity can be constructed by marking 



Fig. 34.— Photography of the movement of a falling 

 body. 



