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Lecture 35 sect 8.3

# Lecture 35 sect 8.3 - N f W α s = tan max = ƒ max N •...

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ME221 Lecture 35 1 ME 221 Statics Lecture #35 Sections 8.1 – 8.3

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ME221 Lecture 35 2 Homework #12 Chapter 8 problems: 1, 2, 4, 8 & 15 Due Monday, December 1
ME221 Lecture 35 3 No Class Wednesday, November 26

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ME221 Lecture 35 4 Quiz #8 Monday, December 1 Friction problem
ME221 Lecture 35 5 Final Exam Section 1 (3:00pm) Monday, 12/8, 3:00 – 5:00pm Section 2 (12:40pm) Wednesday, 12/10, 12:45 – 2:45pm See University policy for multiple exams

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ME221 Lecture 35 6 Chapter 8 - Friction Overview Coulomb friction (dry friction) Static and kinematic Fluid friction Wedges Types
ME221 Lecture 35 7 Friction Angle A body on an incline, acted upon by gravity alone, will slip at an angle related to the coefficient of friction N f W α From the FBD: N – W cos α = 0 & ƒ – W sin α = 0 Such that: ƒ = N tan α

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ME221 Lecture 35 8 Friction Angle • The Coefficient of Static Friction ( μ s ) is defined as the tangent of the maximum angle a body may be inclined before slip occurs

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Unformatted text preview: N f W α s = tan max = ƒ max / N • The angle max is called the friction angle ME221 Lecture 35 9 Coulomb Friction (dry friction) • Friction force (ƒ) is proportional to the normal force ( N ) and opposes motion • Coefficient of friction, μ , is the proportionality constant – Static coefficient, s – Kinematic coefficient, k k N s N P f P N f W f=P ME221 Lecture 35 10 Common Static Friction Coefficients Steel on steel 0.75 Rubber on concrete 0.5-0.9 Rubber on ice 0.05-0.30 Metal on wood 0.2-0.6 Teflon on Teflon 0.04 Tires on gravel 0.5 ME221 Lecture 35 11 Friction: Wedges • Wedges are a simple means for lifting • Again, friction force opposes the motion • Disassembled FBDs are essential for solving wedge problems – Apply equilibrium equations to disassembled FBDs ME221 Lecture 35 12 Example Problems...
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