1. ME221Lecture 341 ME 221 Statics Lecture #34 Sections 8.1 – 8.2

2. ME221Lecture 342 Homework #11 Chapter 6 problems: –2, 3, 6 & 7 – Method of Joints –32, 36, 47 & 53 – Method of Sections –68 & 75 Due Today

3. ME221Lecture 343 Homework #12 Chapter 8 problems: –1, 2, 4, 8 & 15 Due Monday, December 1

4. ME221Lecture 344 Quiz #7 Today Analysis of Structures Method of Joints or Method of Sections

5. ME221Lecture 345 No Class Wednesday, November 26

6. ME221Lecture 346 No Class Friday, December 5 Mechanical Engineering Design Conference MSU Union 9am to noon Demonstrations 1pm to 2pm Awards in Ballroom ME371 Mechanical Design I ME412 Heat Transfer Lab ME456 Mechatronics Systems Lab ME471 Mechanical Design II ME481 Mech Engineering Design Projects

7. ME221Lecture 347 Chapter 8 - Friction Overview Coulomb friction (dry friction) –Static and kinematic Fluid friction –Wedges –Types

8. ME221Lecture 348 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  From the FBD: N – W cos α = 0 & ƒ – W sin α = 0 Such that: ƒ = N tan α (friction force)

9. ME221Lecture 349 Friction Angle The Coefficient of Static Friction (  s ) is defined as the tangent of the maximum angle a body may be inclined before slip occurs N f W   s = tan  max = ƒ max / N The angle  max is called the friction angle

10. ME221Lecture 3410 Coulomb Friction (dry friction) Friction force (ƒ) is proportional to the normal force (N) and opposes motion Coefficient of friction, , is the proportionality constant –Static coefficient,  s –Kinematic coefficient,  k kNkN sNsN P f P N f W f=P

11. ME221Lecture 3411 Common Static Friction Coefficients Steel on steel0.75 Rubber on concrete0.5-0.9 Rubber on ice0.05-0.30 Metal on wood0.2-0.6 Teflon on Teflon0.04 Tires on gravel0.5

12. ME221Lecture 3412 Example Problem

13. ME221Lecture 3413 Quiz #7

14. ME221Lecture 3414 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 Examples: 8.71, 8.72, 8.80, 8.45