Engineering 36. Chp 4: Intro to Moments. Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected] Moment (Torque) Described. In Physics and Engineering a MOMENT is a measure of TWISTING Power
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Engineering 36
Chp4: Intro toMoments
Bruce Mayer, PE
Licensed Electrical & Mechanical [email protected]
distance from the Pivot to Force Loa
Moment Center (MC)or Pivot Point
Often the Most Convenient Position Vector is that which runs From the Pivot to the Point of Application
r runs from the Pivot to the Point
distance yields Shortest r
As Noted Previously the Magnitude of a Moment is related to the product of
The Position Vector, r
The Force, F
TWO-DIMENSIONAL STRUCTURES Have Length And Breadth But Negligible Depth And Are Subjected To Forces Contained In The PLANE Of The Structure
HINT:
Put r & FTail-to-Tail
F
r
A 100-lb Vertical Force Is Applied To The End Of A Lever Which Is Attached To a Shaft At O. DETERMINE
Moment About O
Horizontal Force At Pt-A Which Creates The SAME Moment
Smallest Force At Pt-A Which Produces The SAME Moment
Location For a 240-lb Vertical Force To Produce The SAME Moment
Whether Any Of The Forces From b, c, and d is EQUIVALENT To The ORIGINAL Force
Moment About O Is Equal To The Product Of The Force And The PERPENDICULAR DISTANCE Between The Line Of Action Of The Force And O
The Force Tends To Rotate The Lever CLOCKWISE, Thus The Moment Vector points INTO The Plane Of The Paper
The Moment Vector Qty is thus NEGATIVE
Horizontal Force at A That Produces The Same Moment
The Smallest Force at A To Produce The Same Moment Occurs When The Perpendicular Distance is a Maximum
i.e., When F Is Perpendicular To OA
To Determine The Point Of Application Of A 240 lb Vertical Force To Produce The Same Moment
Although Each Of The Forces In Parts b), c), and d) Produces The Same Moment As The 100 lb Force, NONE Are of The Same MAGNITUDE And SENSE (Line of Action) as the original pull
Let’s WorkProblem4.21
In order to pull out the nail at B, the force Fexerted on the handle of the hammer must produce a clockwise moment of 500 in∙lb. about point A. Determine the required magnitude of force F.