220 likes | 580 Views
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
E N D
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 • 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
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
Lecture 18 Objective • to provide scalar and vector methods for determining the moment of a force about a specified axis
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
Moment About a Specified Axis (cont.) • What is the Moment About Point O?
Moment About a Specified Axis (cont.) • What is the Moment About the X-Axis? • Tending to bend the pipe about O Mx
Moment About a Specified Axis (cont.) • What is the Moment About the Y-Axis? • Tending to unscrew the pipe about O My
L Moment About a Specified Axis (cont.)
Moment About a Specified Axis (cont.) • Moment Vector About Point O • Use cross product
Moment About a Specified Axis (cont.) • Moment Vector About Point O
Moment About a Specified Axis (cont.) • Moment Component Projected on Y-axis • Recall dot product
Triple Scalar Product • Generalized Statement • Determine the component moment magnitude (|Ma|) on a specified axis due to the moment (Mo)
Triple Scalar Product (cont.) • Determine the component moment magnitude (|Ma|) on a specified axis due to the moment (Mo)
Moment Vector on Specified Axis • Determine the moment vector (Ma) on a specified axis due to the moment (Mo) r r
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
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
References • Hibbeler (2007) • http://wps.prenhall.com/esm_hibbeler_engmech_1