Transcript ENGI 1313 Mechanics I - Memorial University of Newfoundland

ENGI 1313 Mechanics I
Lecture 16:
Moment of Force Examples
Shawn Kenny, Ph.D., P.Eng.
Assistant Professor
Faculty of Engineering and Applied Science
Memorial University of Newfoundland
[email protected]
Lecture 16 Objective

2
to further illustrate the concepts of moment
of force by example
© 2007 S. Kenny, Ph.D., P.Eng.
ENGI 1313 Statics I – Lecture 16
Example 16-01

3
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.
© 2007 S. Kenny, Ph.D., P.Eng.
ENGI 1313 Statics I – Lecture 16
Example 16-01 (cont)

Maximum Moment
Magnitude


4
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
© 2007 S. Kenny, Ph.D., P.Eng.
ENGI 1313 Statics I – Lecture 16
Example 16-01 (cont)

Minimum Moment
Magnitude


5
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
© 2007 S. Kenny, Ph.D., P.Eng.
ENGI 1313 Statics I – Lecture 16
Example 16-02

6
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.
© 2007 S. Kenny, Ph.D., P.Eng.
ENGI 1313 Statics I – Lecture 16
Example 16-02 (cont.)

7
Determine
Projection
Angles
© 2007 S. Kenny, Ph.D., P.Eng.
F cos1
1
90
90- 1
c cos1 1
ENGI 1313 Statics I – Lecture 16
1
F
Example 16-03

8
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.
© 2007 S. Kenny, Ph.D., P.Eng.
ENGI 1313 Statics I – Lecture 16
References
Hibbeler (2007)
 http://wps.prenhall.com/esm_hibbeler_eng
mech_1

9
© 2007 S. Kenny, Ph.D., P.Eng.
ENGI 1313 Statics I – Lecture 16