ME221Lecture 361 ME 221 Statics Lecture #37 Sections 8.1 – 8.3

ME221Lecture 362 Homework #12 Chapter 8 problems: –1, 2, 4, 8 & 15 Due Today

ME221Lecture 363 No Class Friday, December 5

ME221Lecture 364 Quiz #8 Today Friction problem

ME221Lecture 365 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

ME221Lecture 366 Chapter 8 - Friction Last Lecture Coefficients – static & kinematic –Friction angle –Coulomb Friction Today –Wedges

ME221Lecture 367 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

ME221Lecture 368 Friction: Wedges Wedges are a simple means for lifting Again, friction force opposes the motion FBDs are essential for solving problems –Apply equilibrium equations to FBDs

ME221Lecture 369 Friction: Wedges Wedges may exert large normal forces Used to lift heavy objects Also used for splitting –Friction holds wedge in place May be used in pairs

ME221Lecture 3610 Wedges The angle θ is called the wedge angle, and it determines the amount of force P required to raise the weight W, as well as the change in height of the weight as the wedge is driven into place. N f W  P In equilibrium (P = 0): ƒ cos θ – N sin θ = 0 μ s = tan θ

ME221Lecture 3611 Example Problem