Shawn Kenny, Ph.D., P.Eng. Assistant Professor Faculty of Engineering and Applied Science Memorial University of Newfoundland ENGI 1313 Mechanics I Lecture 16:Moment of Force Examples

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 2 Lecture 16 Objective to further illustrate the concepts of moment of force by example

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 3 Example Determine the direction  (0     180  ) of the force F so that it produces (a) the maximum moment about point A and (b) the minimum moment about point A. Compute the moment in each case.

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 4 Example (cont) Maximum Moment Magnitude  Force line of action perpendicular to a line from the moment point A through the point of force application  Force can act in either direction

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 5 Example (cont) Minimum Moment Magnitude  Force line of action parallel to a line from the moment point A through the point of force application  Force can act in either direction

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 6 Example The flat-belt tensioner is manufactured by the Daton Co. and is used with V-belt drives on poultry and livestock fans. If the tension in the belt is F, when the pulley is not turning, determine the moment of each of these forces about the pin at A.

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 7 Example (cont.) Determine Projection Angles 11 11 90  11 90  -  1 F F cos  1 c cos  1

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 8 Example The pole supports a traffic light of weight W. Using Cartesian vectors, determine the moment of the weight of the traffic light about the base of the pole at A.

ENGI 1313 Statics I – Lecture 16© 2007 S. Kenny, Ph.D., P.Eng. 9 References Hibbeler (2007) mech_1