Unit Dynamics Module Newton s Three Laws page 1 of 1 Introduction to Newton s Second Law Acceleration is proportional to force a F Newton s second law F ma explains why objects accelerate Acceleration is inversely proportional to mass a The mks unit of force is the Newton N 1 kgim s2 1 m In order to understand force you must develop a method for quantifying it Scales can act as force meters If you hang one weight from a scale the needle moves a certain distance If you hang two weights from the scale the needle moves twice as far In this manner you can calibrate the scale for use as a force meter and you can use it to measure other forces A cart on an air track experiences very little friction If a weight on a string is placed over a low friction pully and attached to the cart The cart will accelerate along the track If you measure the acceleration you will find that it is constant You can double the amount of weight hanging from the string and you will find that the acceleration of the cart is still constant but that its magnitude doubles You can conclude that acceleration is proportional to force a F If you add mass to the cart on the air track but apply the same force you will find that the acceleration of the cart decreases Doing careful experiments with mass and acceleration result in the conclusion that acceleration is inversely 1 proportional to mass a m Newton s second law synthesizes the relationship between force mass and acceleration F ma Newton s second law explains why objects move kgim The mks unit of force is the Newton N 1 2 s www thinkwell com info thinkwell com Copyright 2001 Thinkwell Corp All Rights Reserved 1786 doc rev 03 29 2001
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