Presentation on theme: "Lecture 38: Examples of Friction Analysis"— Presentation transcript:
1Lecture 38: Examples of Friction Analysis ENGI 1313 Mechanics ILecture 38: Examples of Friction Analysis
2Lecture 38 Objectiveto illustrate the equilibrium analysis of rigid bodies subjected to dry friction force by example
3Miscellaneous Notes Lecture 37 Notes Have Been Reposted Minor correctionsQuiz and Mid-Term Marks Posted
4Example 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.
5Example 38-01 (cont.) Three Analysis Cases Impending motion at A Impending motion at BImpending motion at A & B
13Example 38-01 (cont.) Assumption What is Calculated Check Assumption Slip impending at AyxFAFBNAW = 800lbNB
14Example 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.
15Example 38-02 Impending Motion? A/B Interface B/Floor Interface Man/Floor InterfacePotential impending motion at all three interfaces (rare)Crates tip
16Example 38-02 (cont.) Assume Impending Motion for Crate A FBD Crate A AnalysisFAW = 100lbNA
17Example 38-02 (cont.) Assume Impending Motion for Crate B FBD Crate B AnalysisFBW = 200lbNB
18Example 38-02 (cont.) Assume Tipping Minimum P FBD Crate A & B AnalysisMinimum PFBW = 200lbNB
19Example 38-02 (cont.) Force Exerted by Man? FBD Analysis WPminFMNM Impending motion