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ENGI 1313 Mechanics I

ENGI 1313 Mechanics I . Lecture 18: Moment of a Force About a Specified Axis. Mid-Term. For This Class Date: October 18 Time: 830am-945am Location: to be determined Material: Up to and including problem set #4 Alternate Exam

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ENGI 1313 Mechanics I

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  1. ENGI 1313 Mechanics I Lecture 18: Moment of a Force About a Specified Axis

  2. Mid-Term • For This Class • Date: October 18 • Time: 830am-945am • Location: to be determined • Material: Up to and including problem set #4 • Alternate Exam • Only if there is a compelling reason to miss October 18thand I must be informed by October 15th with reason provided • Date: October 22 • Time: 700pm-815pm • Location: EN 2007 • Material: Up to and including problem set #4

  3. Mid-Term (cont.) • General Comments • All students will be required to take the examination • Resources • Tutorial problem sets • Quiz problems • Student societies • http://www.engr.mun.ca/~societya/ • http://www.socb.ca/sample_finals.html

  4. Lecture 18 Objective • to provide scalar and vector methods for determining the moment of a force about a specified axis

  5. Moment About a Specified Axis • The axis of the moment (Mo) about point O is perpendicular to force (F) and position vector (r) plane • What is the component moment about the x-, y- or z-axes? • Why is this information important? Mz My Mx

  6. Moment About a Specified Axis (cont.) • What is the Moment About Point O?

  7. Moment About a Specified Axis (cont.) • What is the Moment About the X-Axis? • Tending to bend the pipe about O Mx

  8. Moment About a Specified Axis (cont.) • What is the Moment About the Y-Axis? • Tending to unscrew the pipe about O My

  9. L Moment About a Specified Axis (cont.)

  10. Moment About a Specified Axis (cont.) • Moment Vector About Point O • Use cross product

  11. Moment About a Specified Axis (cont.) • Moment Vector About Point O

  12. Moment About a Specified Axis (cont.) • Moment Component Projected on Y-axis • Recall dot product

  13. Triple Scalar Product • Generalized Statement • Determine the component moment magnitude (|Ma|) on a specified axis due to the moment (Mo)

  14. Triple Scalar Product (cont.) • Determine the component moment magnitude (|Ma|) on a specified axis due to the moment (Mo)

  15. Triple Scalar Product (cont.)

  16. Triple Scalar Product (cont.)

  17. Triple Scalar Product (cont.)

  18. Triple Scalar Product (cont.)

  19. Moment Vector on Specified Axis • Determine the moment vector (Ma) on a specified axis due to the moment (Mo) r r

  20. Comprehension Quiz 18-01 • The force F is acting along DC. Using the triple product to determine the moment of F about the bar BA, you could use any of the following position vectors except ______. • A) rBC • A) rAD • C) rAC • D) rDB • A) rBD • Answer: D Force Line of Action Moment Axis

  21. Comprehension Quiz 18-02 • For finding the moment of the force F about the x-axis, the position vector (r) in the triple scalar product should be ___ . • A) rAC • A) rBA • C) rAB • D) rBC • Answer: C

  22. References • Hibbeler (2007) • http://wps.prenhall.com/esm_hibbeler_engmech_1

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