OUTLINES OF NATURAL PHILOSOPHY. 



ty of the water and the wheel is so small, that the 

 force of the water is no greater than is sufficient 

 to balance the resistance. The case is nearly the 

 same whatever be the moving power, provided its 

 action diminish with the velocity it communi- 

 cates. 



191. In all machines, the work done is to be 

 estimated not merely from the quantity of resist- 

 ance overcome, but from the quantity overcome 

 in a given time, or which is the same, from the 

 quantity of the resistance multiplied into the ve- 

 locity communicated. 



The resistance is supposed here to be expressed by 

 weight, and the effect by that weight multiplied 

 into the velocity with which it is raised. 



As this is also the expression for the momentum of 

 the resistance, and as that momentum is equal, 

 when the motion is uniform, to the momentum of 

 the power, this last, or the product of the moving 

 force into its velocity, is also the measure of the 

 effect. 



192. In all machines, that work with a uniform 

 motion, there is a certain velocity, and a certain 

 load, which yield the greatest effect, and are there- 

 fore more advantageous than any other. 



If the machine is loaded heavily, though the resist- 

 ance overcome may be great, it may be overcome 

 so slowly, that the total effect shall be but small. 



And, 



