CHAPTER III 

 MOTION AND FORCE 



SECTION I 

 NEWTON'S THREE LAWS OF MOTION 



55. Newton's Laws. Three Laws of Motion are 

 named from Sir Isaac Newton, an English philosopher 

 who was the first to state them. At first thought they 

 may seem strange ; and for this reason, as well as their 

 great importance, they should be studied carefully and 

 committed to memory. 



First Law : A body at rest will stay at rest, and a body 

 in motion will keep moving in a straight line with the same 

 speed, unless acted upon by some force. 



Second Law: A change of motion follows the direction 

 of the force which causes it, and is proportional to the amount 

 of force used and the time during which it acts. 



Third Law : To every action there is an equal reaction 

 in the opposite direction. 



56. The First Law No doubt we can at once call 



to mind several cases which seem to prove this law 

 untrue but think a moment. Do any bodies really 

 begin to move from a state of rest without the action 

 of some force upon them ? Can any moving body 

 actually stop of itself? 



You may say that a body will fall to the ground all 

 of itself ; but would it fall if the force of gravity did 



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