How Does FGF sin26.6 Generate Moment About Point D in Truss Analysis?

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Discussion Overview

The discussion revolves around the calculation of moments in truss analysis, specifically how the force component FGF sin26.6 generates a moment about point D. Participants explore the implications of selecting different points of application for the force components in their calculations.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant questions how FGF sin26.6, located above point D, generates a moment about D.
  • Another participant explains that when calculating moments by breaking the force into components, the choice of the point of application affects the moment generated about point D, suggesting points G, F, or O as options.
  • It is noted that using point G results in both clockwise and anticlockwise moments, while using point F only accounts for the horizontal component, and point O only considers the vertical component.
  • A participant expresses confusion about how to choose the point of application of the force, indicating that the problem does not specify this and that different choices could lead to different answers.
  • In response, another participant asserts that as long as the points are along the line of action of the force, they will yield the same moment result.

Areas of Agreement / Disagreement

Participants express differing views on the implications of selecting different points of application for the force components, with some asserting that it will yield different answers and others claiming that it will not, leading to an unresolved debate on this aspect.

Contextual Notes

The discussion highlights the dependence on the definitions of points of application and the assumptions made regarding the line of action of forces, which remain unresolved.

fonseh
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Homework Statement


For moment about D , how could the FGF sin26.6 generate moment about D ?

Homework Equations

The Attempt at a Solution


FGF sin26.6 is located above point D , right ? How could FGF sin26.6 generate moment about D ?
 

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If calculating moments by first breaking the force into components then you have to select a point of application of the force. Anywhere in the line of action will do. In this case you can use G, F or O.
If you use G there will be a clockwise moment about D from the horizontal component and an anticlockwise moment from the vertical component.
If you select F, only the horizontal component will have a moment about D, but it will be less than that of the horizontal component at G.
If you select O, as the author has done, only the vertical component has moment about D.
 
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haruspex said:
If calculating moments by first breaking the force into components then you have to select a point of application of the force. Anywhere in the line of action will do. In this case you can use G, F or O.
If you use G there will be a clockwise moment about D from the horizontal component and an anticlockwise moment from the vertical component.
If you select F, only the horizontal component will have a moment about D, but it will be less than that of the horizontal component at G.
If you select O, as the author has done, only the vertical component has moment about D.
S
haruspex said:
If calculating moments by first breaking the force into components then you have to select a point of application of the force. Anywhere in the line of action will do. In this case you can use G, F or O.
If you use G there will be a clockwise moment about D from the horizontal component and an anticlockwise moment from the vertical component.
If you select F, only the horizontal component will have a moment about D, but it will be less than that of the horizontal component at G.
If you select O, as the author has done, only the vertical component has moment about D.
Ok , i can understand what you have explained . But for this type of question ,
how do we choose the point of application of force ? It's not stated in the question . Choosing different point of application of forces will yield different answer
 
fonseh said:
Choosing different point of application of forces will yield different answer
No, as long as the points are along the line of action they will all yield the same answer.
 
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