Unit Dynamics Module Newton s Three Laws page 1 of 1 The Vector Nature of Force and Newton s Second Law Newton s second law F net m a is the fundamental law of dynamics Objects do not require forces to maintain uniform motion The only way to change the velocity of an object is by applying an external force to it Newton s second law F net m a is one of the most fundamental law of physics and we use it to understand and explain motion if you apply a force on an object it will accelerate Consider for example the Voyager in outer space What is keeping the Voyager going at such high speed The answer is in Newton s second law an object does not require any force to maintain its motion as long as it is not accelerating Independent of the magnitude of v if the velocity does not change the acceleration is zero Objects do not require forces to maintain uniform motion Consider two players hitting a hockey puck What is the acceleration of the puck Remember that force is a vector and there are two ways to add vectors graphically and by components To add the vectors graphically slide them so they are tip to tail The vector that begins at the tail of one and ends at the tip of the other is the vector sum Because the vectors form a right angle use the Pythagorean theorem to calculate the magnitude of the net force F net 1 N 2 1 N 2 1 4 N For graphical vector addition slide the vectors tip to tail The acceleration of the puck is F 1 4 kg m s2 m a net 14 2 0 1 kg m s To add the vectors using components first write F net in its component form F net 1 N j 1 N i The ratio of the force vector and the mass is the acceleration vector 1N 1N m m i j 10 2 i 10 2 j Use the a 0 1 kg 0 1 kg s s Pythagorean theorem to calculate the magnitude of the acceleration vector m a 10 m s2 2 10 m s2 2 14 2 s www thinkwell com info thinkwell com Copyright 2001 Thinkwell Corp All Rights Reserved 1784 doc rev 03 29 2001
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