192 THE PHENOMENA OF MOTION 



whole effect produced, we must multiply the mass into 

 the velocity. This product is called the amount of 

 motion. 



The amount of motion in a given body must in all 

 cases correspond exactly to the momentum of force. 



These two, the amount of motion and the momentum 

 of force, are also called simply force; because we sup- 

 pose that a less pressure acting, for example, during 10 

 seconds, is equal to a pressure ten times greater, acting 

 only during one second. 



The momentum of motion, in mechanics, signifies the 

 effect of a moving force, without reference to the time 

 (velocity) in which it was manifested. If one man, for 

 example, raises 30 Ibs. to a height of 100 feet, and a 

 second one 30 Ibs. to a height of 200 feet, then the lat- 

 ter has expended twice as much force as the former. 

 A third who raises 60 Ibs. to a height of 50 feet, ex- 

 pends no more force than the first did in raising 30 Ibs. 

 to the height of 100 feet. The momentum of motion 

 of the first (30X100) is equal to that of the third 

 (60X50), while that of the second (30X200) is twice 

 as great. 



Momentum of force and momentum of motion, in 

 mechanics, are therefore expressions or measures for 

 effects of force, having reference to the velocity attained 

 in a given time, or to a given space ; and in this sense 

 they may be applied to the effects of all other causes of 

 motion, or of change in form and structure, howevei 

 great or however small may be the space or the time in 

 which their effects are displayed to the senses. 



