78 SIMPLE MACHINES. 



The work accumulated in a moving body is found l>y 

 multiplying its weight into the square of its velocity, and 

 dividing the product by twice the acceleration of gravity. 



For instance, the work accumulated in a body which 



5 x 12 x 12 



weighs 5 kgr , and has a velocity of 12 m , is 



iy *u 



= 36*73 kilogrammetres. In order to test the agree- 

 ment of this rule with the previous example we must 

 consider, 1st. That the velocity acquired by the falling 

 weight in the first experiment is the same as that 

 acquired in the experiments of Article 10; for in the 

 first experiment the moving mass is one -third of that 

 in the experiments made on falling bodies; but the 

 moving force (the extra weight) is in the first ex- 

 periment one -third of the moving force in the latter 

 experiment ; the acceleration is therefore the same in 

 both. 2ndly. That the wheel must be considered as 

 a weight of 50^, and that hence the whole moving 

 mass amounts to 50 + 72 + 74 = 196** = O kgr '196. 

 The velocity obtained after passing over a space of 

 gdecim ^ | n fa Q rg experiment, as well as in those oi 

 Article 10, 2 decimetres or O m> 2 ; the accumulated 



work is, therefore, ' 196 * ^ * ' 2 = 0-0004 kilo- 



JL / O 



grammetres. 



13. Simple Machines. "Work applied in any form 

 may be converted into another form in various ways. It 

 requires a definite though small amount of work to push 

 a needle through a piece of cloth. We know that the 

 work required is equal to the product of the expended 

 force, that is, the pressure upon the needle, into the 

 space through which the needle has moved. To drive 



