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Lecture04_Pushkar

Lecture04_Pushkar - PHYSICS 220 Lecture 04 Forces and...

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Lecture 4 Purdue University, Physics 220 1 Lecture 04 Forces and Motion in 1 D Textbook Sections 3.2-3.6 PHYSICS 220
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Lecture 4 Purdue University, Physics 220 2 Mass and Weight Mass: quantifies the amount of inertia that an object possesses – an intrinsic property of the object Weight (Gravitational force exerted by the Earth) W = mg (g-acceleration due to gravity) g = GM earth /(r earth ) 2 = 9.8 m/s 2 (G – universal gravitational constant, more in Chapter 5)
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Lecture 4 Purdue University, Physics 220 3 Contact Forces Normal force: a contact force acting at an interface perpendicular to the surface of contact Frictional force: another contact force acting at an interface parallel to the surface of contact resist motion of the two surfaces sliding past each other always act opposite the direction of motion mg N F F f
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Lecture 4 Purdue University, Physics 220 4 Friction Magnitude of frictional force is proportional to the normal force. f kinetic = μ k N μ k coefficient of kinetic friction f static μ s N μ s coefficient of static friction Be Careful! Static friction , can be any value up to μ s N Direction always opposes motion
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Friction and Walking The person “pushes” off during each step The bottoms of his shoes exert a force on the ground If the shoes do not slip, the force is due to static friction The shoes do not move relative to the ground
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Lecture 4 Purdue University, Physics 220 6 Book Pushed Across Table Book sliding across table Isolate the object of interest (book) Identify all forces acting on the object
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