MEE1002 ENGINEERING MECHANICS-SUM-II- L7

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Information about MEE1002 ENGINEERING MECHANICS-SUM-II- L7

Published on June 12, 2019

Author: Devaprakasam

Source: slideshare.net

1. DEVAPRAKASAM DEIVASAGAYAM Professor of Mechanical Engineering Room:11, LW, 2nd Floor School of Mechanical and Building Sciences Email: devaprakasam.d@vit.ac.in, dr.devaprakasam@gmail.com MEE1002: Engineering Mechanics (2:1:0:0:3) Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933

2. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Wedges are simple machines used to raise large stone blocks and other heavy loads. These loads can be raised by applying to the wedge a force usually considerably smaller than the weight of the load. In addition, because of the friction between the surfaces in contact, a properly shaped wedge will remain in place after being forced under the load. Wedges can thus be used advantageously to make small adjustments in the position of heavy pieces of machinery.

3. Static or Dynamic? • Static Friction • Kinetic Friction tanφs= Fm/N=µs N/N tanφk=Fk/N=µk N/N P N Ff W Ff P Motion Fm Fk

4. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction

5. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction

6. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction

7. Static or Dynamic? P N Ff W W θ θ N W sinθ W cosθ N cosθ N sinθ Case 1: Ff>P, (µsN>P) No Motion Case 2: Fm=P, (µsN=P) Impending Motion Case3: Fk<P, (µkN<P) Motion Case 1: Ff>P, (µs N Sinθ>P) , No Motion Case 2: Fm=P, (µs N Sinθ=P), Impending Motion Case3: Fk<P, (µk N Sinθ<P) Motion, θ

8. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933

9. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction

10. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction

11. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction

12. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction θ θ y x F N Maximum Friction Force

13. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction x Maximum Friction Force

14. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction

15. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction y θ θ x F N Maximum Friction Force Actual Friction Force

16. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Dry Friction y Maximum Friction Force Actual Friction Force

17. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 It is convenient to replace the normal force N and the friction force F by their resultant R. Applied force P has a horizontal component Px which tends to move the block, the force R will have a horizontal component F and, thus, will form an angle φ with the normal to the surface If Px is increased until motion becomes impending, the angle between R and the vertical grows and reaches a maximum value.This value is called the angle of static friction and is denoted by φs .

18. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 If motion actually takes place, the magnitude of the friction force drops to Fk; similarly, the angle f between R and N drops to a lower value φk, called the angle of kinetic friction

19. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933

20. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933

21. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933

22. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Two 8° wedges of negligible weight are used to move and position the 800-kg block. Knowing that the coefficient of static friction is 0.30 at all surfaces of contact, determine the smallest force P that should be applied as shown to one of the wedges.

23. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 WEDGES

24. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 WEDGES W 8° 8° 16.7° R1 R2 16.7° 16.7° R2 R1 16.7° 24.7° α 7848N

25. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 WEDGES R3 R1 90°-16.7° β P 90°-24.7° R3 R1 P 16.7° 24.7°

26. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 WEDGES

27. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 WEDGES W 16.7° R1 R2 16.7° 16.7° R2 R1 16.7° 16.7° α 7848N `

28. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 WEDGES R3 R1 90°-24.7° β P 90°-16.7° R3 R1 P 16.7° 24.7° 16.7°8°

29. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Ladder

30. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Ladder NC FC NA FA NB FB NB FB 40lb 40lb

31. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Ladder ; ; ; ; ; ; ; ; ; =0; 6 ; ; ; 17.143; ; =0; ; ;

32. Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933 Ladder

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