Exploring the Moment Generated by 0.8NB at Point A

In summary, the question is asking why there is a moment generated by the forces of 0.8NB (circled part) for the moment about A. The answer is that the d value is not directly measured from point A, but rather from a red circled part. This is because for NBx, the measurement is taken from a point that is 10 feet from A. The author includes this calculation because the line of action of NBx is at a perpendicular distance of 4 feet from A, and a force acting along a line of action can always be moved without changing anything.
  • #1
fonseh
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Homework Statement


for the moment about A , why there 's moment generated by the forces of 0.8NB (circled part) ?

Homework Equations

The Attempt at a Solution


I think it's not necessary to include the moment 0.8NB(4) because the d = 0.4m is not measured directly from point A ...it's measured from the red circled part ...
 

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  • #2
1. It's not 0.4 m but 4 feet and it's the vertical distance between B and A
and that is multiplied with the horizontal component of NB
2. the 10 feet is the horizontal distance etc.
 
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  • #3
btw, this is not a truss, but a frame. Trusses are designed only under tensile and compression forces, no bending moments
 
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  • #4
sakonpure6 said:
btw, this is not a truss, but a frame. Trusses are designed only under tensile and compression forces, no bending moments
In the diagram attached below , we can see that the d (prepedicular distance) for NBy is measured directly from A , but for the NBx ( blue part) , it's measured directly from a point which is 10 m from A . So , for the moment 4NBx , it's not moment about A , am i right ? Why the author consider it in the calculation ?
 

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  • #5
fonseh said:
So , for the moment 4NBx , it's not moment about A , am i right
No. The line of action of NBxis at a perpendicular distance of 4 feet from A
 
  • #6
BvU said:
No. The line of action of NBxis at a perpendicular distance of 4 feet from A
why ?
 
  • #7
upload_2017-1-12_11-19-59.png


A force acts along a line of action. You can always move it along that line without changing anything.
Only when you move a force perpendicular to its line of action you have to add a torque.

To reassure yourself: calculate the perpendicular distance of the line of action of NB itself to the point A and compare with the total torque from x and y components.
 
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Related to Exploring the Moment Generated by 0.8NB at Point A

1. What is the significance of the "0.8NB" in this scenario?

The "0.8NB" refers to the magnitude of the force applied at point A. It is a unit of force and indicates that the force applied is 0.8 times the normal force (NB).

2. How is the moment generated at point A calculated?

The moment is calculated by multiplying the force applied (0.8NB) by the perpendicular distance from the point of rotation (point A) to the line of action of the force. This distance is known as the lever arm.

3. What is the direction of the moment generated at point A?

The direction of the moment is determined by the direction of the force applied. In this case, since the force is applied at point A, the direction of the moment will be perpendicular to the plane of rotation at point A.

4. How does the moment generated at point A affect the object?

The moment generated at point A can cause the object to rotate or remain in equilibrium, depending on the position and direction of the applied force. If the moment is greater than the opposing moments, the object will rotate in the direction of the applied force. If the opposing moments are equal, the object will remain in equilibrium.

5. How does the distance from point A affect the moment generated?

The moment generated at point A is directly proportional to the distance from point A to the line of action of the force. The farther the distance, the greater the moment. This is because a longer lever arm creates a greater turning effect on the object.

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