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Shawn Kenny, Ph.D., P.Eng. Assistant Professor Faculty of Engineering and Applied Science Memorial University of Newfoundland spkenny@engr.mun.ca ENGI 1313 Mechanics I Lecture 38:Examples of Friction Analysis

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 2 Lecture 38 Objective to illustrate the equilibrium analysis of rigid bodies subjected to dry friction force by example

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 3 Miscellaneous Notes Lecture 37 Notes Have Been Reposted Minor corrections Quiz and Mid-Term Marks Posted

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 4 Example 38-01 The 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 μ s = 0.4, determine where it begins to slip first: at A or B, or both at A and B.

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 5 Example 38-01 (cont.) Three Analysis Cases Impending motion at A Impending motion at B Impending motion at A & B

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 6 Example 38-01 (cont.) Draw FBD FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 7 Example 38-01 (cont.) Assume Impending Motion at A & B Analysis FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 8 Example 38-01 (cont.) Analysis FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 9 Example 38-01 (cont.) Assumption What is Calculated Check Assumption not correct FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 10 Example 38-01 (cont.) Assume Impending Motion at A FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 11 Example 38-01 (cont.) Analysis FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 12 Example 38-01 (cont.) Analysis FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 13 Example 38-01 (cont.) Assumption What is Calculated Check Assumption Slip impending at A FAFA NANA FBFB NBNB x y W = 800lb

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 14 Example 38-02 The 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 μ s1 = 0.8 and between the bottom crate, his shoes, and the floor is μ s2 = 0.3, determine if he can cause impending motion.

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 15 Example 38-02 Impending Motion? A/B Interface B/Floor Interface Man/Floor Interface Potential impending motion at all three interfaces (rare) Crates tip

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 16 Example 38-02 (cont.) Assume Impending Motion for Crate A FBD Crate A Analysis W = 100lb FAFA NANA

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 17 Example 38-02 (cont.) Assume Impending Motion for Crate B FBD Crate B Analysis W = 200lb FBFB NBNB

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 18 Example 38-02 (cont.) Assume Tipping FBD Crate A & B Analysis Minimum P W = 200lb FBFB NBNB

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 19 Example 38-02 (cont.) Force Exerted by Man? FBD Analysis P min W FMFM NMNM Impending motion

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ENGI 1313 Statics I – Lecture 38© 2007 S. Kenny, Ph.D., P.Eng. 20 References Hibbeler (2007) http://wps.prenhall.com/esm_hibbeler_eng mech_1

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