76 MECHANICAL WORK. 



velocity acquired in moving through this space is pre- 

 cisely the same as that acquired through the space ef. 

 This is shown by the fact that the bullet rises again to 

 g on the left side. Precisely the same happens if the 

 tack is placed at c or d, and the bullet constrained to move 

 through the arcs ^y, or &/; it will always rise on the 

 left side to g. Conversely, if the bullet be brought by 

 the hand to g, and allowed to fall, it will move to e, if 

 the moveable pin is removed; but if the latter is 

 placed at >, the thread will be arrested by it when the 

 bullet arrives at/, and the bullet moves to h. If the 

 tack is at c or c?, the bullet describes similarly the arcs 



The law here observed with reference to circular arcs 

 of various forms holds generally with reference to 

 all kinds of spaces traversed./ The velocity acquired by 

 a body ivhich moves under the influence of gravity is 

 independent of the form of the path traversed. It is 

 solely dependent upon the vertical height of the space 

 through which the body has passed. J What is said here of 

 the velocity is also applicable to me accumulated work. 

 A body of 6 kgr which has fallen from a height of 10 m con- 

 tains 6 x 10 = 60 kilograrnmetres of work; for the 

 velocity acquired is precisely sufficient to raise the body, 

 that is a weight of 6 kgr , again through a space of 10 m . 

 Hence the work accumulated in a body which has been 

 set in motion by gravity is found by multiplying the 

 attractive force which draws it downwards into the 

 perpendicular height through which it has fallen. The 

 attractive force is in most cases nothing but the weight 

 of the body. It is always the weight, if the whole body 

 moves under the action of gravity. The case is, how- 



