Presentation on theme: "Lecture 38: Examples of Friction Analysis"— Presentation transcript:
1 Lecture 38: Examples of Friction Analysis ENGI 1313 Mechanics ILecture 38: Examples of Friction Analysis
2 Lecture 38 Objectiveto illustrate the equilibrium analysis of rigid bodies subjected to dry friction force by example
3 Miscellaneous Notes Lecture 37 Notes Have Been Reposted Minor correctionsQuiz and Mid-Term Marks Posted
4 Example 38-01The 800-lb concrete pipe is being lowered from the truck bed when it is in the position shown. If the coefficient of static friction at the points of support A and B is μs = 0.4, determine where it begins to slip first: at A or B, or both at A and B.
5 Example 38-01 (cont.) Three Analysis Cases Impending motion at A Impending motion at BImpending motion at A & B
13 Example 38-01 (cont.) Assumption What is Calculated Check Assumption Slip impending at AyxFAFBNAW = 800lbNB
14 Example 38-02The man having a weight of 150 lb pushes horizontally on the bottom of crate A, which is stacked on top of crate B. Each crate has a weight of 100 lb. If the coefficient of static friction between each crate is μs1 = 0.8 and between the bottom crate, his shoes, and the floor is μs2 = 0.3, determine if he can cause impending motion.
15 Example 38-02 Impending Motion? A/B Interface B/Floor Interface Man/Floor InterfacePotential impending motion at all three interfaces (rare)Crates tip
16 Example 38-02 (cont.) Assume Impending Motion for Crate A FBD Crate A AnalysisFAW = 100lbNA
17 Example 38-02 (cont.) Assume Impending Motion for Crate B FBD Crate B AnalysisFBW = 200lbNB
18 Example 38-02 (cont.) Assume Tipping Minimum P FBD Crate A & B AnalysisMinimum PFBW = 200lbNB
19 Example 38-02 (cont.) Force Exerted by Man? FBD Analysis WPminFMNM Impending motion