60 UNIFORM MOTION. ACCELERATED MOTION. 



the same law as would determine its motion if it 

 were falling freely. 



The law which has been derived from the first, fifth, 

 and sixth experiments, was that different masses move 

 with the same velocity, if the forces which act upon 

 them are proportional to the masses. Now all bodies 

 fall with equal velocity, if unresisted by the air. It 

 follows from this that the force with which gravity acts 

 upon different masses must be proportional to these 

 masses. A mass, for instance, which is six times as 

 great as another mass, is attracted by the earth with 

 six times the force which acts upon the smaller mass. 

 A body once in motion maintains, by its inertia, the 

 acquired velocity unaltered, if not acted upon by any 

 force, and if it has not to overcome any resistance ; it 

 passes over equal spaces in equal consecutive times ; it 

 has a uniform motion. But if constantly acted upon by 

 a force which impels the body more and more, its 

 velocity will continually increase ; such a body has an 

 accelerated motion. If a force, as is the case with the 

 force of gravity, has constantly the same effect upon a 

 body, its velocity will continually increase by the same 

 quantity, and the motion is in that case uniformly 

 accelerated. When we have on the left side of the 

 machine 70 + 98 + 98 = 266 gr , on the right, 

 70 + 98 + 98 + 4 + 1 + 1 = 272 gr , or, with the wheel, 

 altogether 588^, moved by a force of 6 gr , the velocity 

 increases in every second by one decimetre ; for at the 

 commencement it is zero, and after 1 s it will be l decim , 

 after 2 s it will be 2 decim , etc. But the space traversed 

 in the first second is not l^ cim ^ nor is it in the second 

 2 decim , etc., for the weight has not a velocity of l decim 



