# lec03 - Physics I Class 03 Newton's Laws of Motion Rev...

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03-1 Physics I Class 03 Newton’s Laws of Motion Rev. 05-Jan-05 GB

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03-2 Important Notice Activity 4 (for next time) has some individual preparation that you should do before class. Go to the Activities page of the website and check out the Activity Document. You will save a lot of time by having your activity #4 write-up started before class with the first 5 steps completed. It would also be a good idea to start thinking about the exercise in activity #4 before you come to class.
03-3 Newton’s Laws of Motion Isaac Newton, 1642-1727 Philosophiae Naturalis Principia Mathematica (“Mathematical Principles of Physics”) 1687 There are three laws of motion. They explain the motion of any object resulting from its initial state of motion and the forces acting on it.

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03-4 What is a Force? Target Source Force A force is an interaction between two objects. A force always requires two objects: 1. The target (acted upon). 2. The source (due to). Gravity is a familiar force. What are the target and source objects for the force of gravity pulling you down at this moment?
03-5 Forces Are Vectors - Adding Force Vectors + = 0 N +3 N +3 N +6 N = + +3 N -3 N To add forces, first write the individual force vectors in component form. In one dimension, there is only one component and the + or – sign tells you the direction. Add components for each dimension (X,Y,Z). Examples (1D):

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03-6 Newton’s First Law Consider a body on which zero net* force acts. If the body is at rest, it will remain at rest. If the body is in motion with constant velocity, it will continue to do so. How does this law relate to our common experiences with real objects in motion on the earth? In what ways do our experiences confirm this law? In what ways do our experiences seem to contradict this law? *“net” means the same thing as “total”
03-7 Newton’s Second Law “F = ma” The correct expression for Newton’s Second Law: a m F F net = or m F a net =

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