Solve Forces & Couples at Point G - Moment & Resultant Calculations

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Discussion Overview

The discussion revolves around the interpretation of a problem involving forces and couples at a point G, specifically addressing the implications of a rivet's inability to withstand a couple. Participants explore the concepts of resultant moments and forces, the nature of couples, and the mechanical behavior of rivets in relation to rotational and translational motion.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express confusion about the problem's statement regarding the rivet's inability to withstand a couple, questioning whether this means it cannot withstand rotation.
  • Others clarify that a couple consists of anti-parallel forces that produce rotation without translation, suggesting that the rivet prevents translational motion but not rotational motion.
  • There are inquiries about how to apply the scientific method to decipher the problem and test various possibilities regarding the rivet's behavior.
  • Some participants propose that the resultant force must act on the rivet to prevent motion, leading to further questions about the nature of rotation in relation to the rivet.
  • A later reply discusses the effectiveness of a single rivet compared to a line of rivets in resisting rotation, indicating that friction may play a role in this context.

Areas of Agreement / Disagreement

Participants generally agree on the definition of a couple and its effects on motion, but there remains uncertainty about the implications of the rivet's inability to withstand a couple and how this affects the problem's solution. Multiple viewpoints exist regarding the interpretation of the rivet's mechanical behavior.

Contextual Notes

Limitations include potential misunderstandings of the problem statement, the need for clarification on the mechanical properties of rivets, and unresolved questions about the application of the scientific method to the scenario presented.

ual8658
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I know how to calculate the resultant moments and forces but in the solution, it says to turn into a force couple system at point G, and then solve for where the resultant should be on the line FG, and then GH.
upload_2016-10-21_21-19-12.png

My question is, what is the question even saying in the first place when it states that the rivet cannot withstand a couple. Isn't a couple a pair of parallel forces that produces motion? And as a result I don't understand what the solution means.
 
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Simon Bridge said:
A couple is a pair of anti-parallel forces producing a rotation, but not translation.
https://en.wikipedia.org/wiki/Couple_(mechanics)#Forces_and_couples

It means it prevents translation but not rotation.

I get that but when the problem says the rivet can't stand a couple, what does that mean? Does it mean that it can't stand rotation?
 
I just told you - and you said "I get that"... how about applying scientific method to decipher the problem?
What are the possibilies? How could you test them?
 
Perhaps think about how rivets work (I mean one on its own).
 
Simon Bridge said:
I just told you - and you said "I get that"... how about applying scientific method to decipher the problem?
What are the possibilies? How could you test them?

Ok so the rivet will prevent translational motion but not rotational. But does this mean any rotation at all whether the rotational axis is on the rivet or not? And thus after obtaining the force couple system at g, you move the resultant in such a way that it cancels out the moment at g?
 
ual8658 said:
Ok so the rivet will prevent translational motion but not rotational. But does this mean any rotation at all whether the rotational axis is on the rivet or not? And thus after obtaining the force couple system at g, you move the resultant in such a way that it cancels out the moment at g?
Have you ever seen a rivet before?
Do you know how they work?
 
Simon Bridge said:
Have you ever seen a rivet before?
Do you know how they work?

Honestly no. This problem has confused me a lot. What I've interpreted so far is the resultant force must act on the rivet because it will be the only thing preventing motion? And since it can't withstand a couple, it basically cannot withstand rotation?
 
Correct.

_One_ rivet will act like a single bolt. It can clamp two plates together so there could be some friction resisting rotation but a line of rivets would be much more effective in resisting rotation. If there was a line of rivets all but one would have to shear for there to be rotation.
 
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CWatters said:
Correct.

_One_ rivet will act like a single bolt. It can clamp two plates together so there could be some friction resisting rotation but a line of rivets would be much more effective in resisting rotation. If there was a line of rivets all but one would have to shear for there to be rotation.

Thank you!
 

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