Statics Question / Understanding Direction

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SUMMARY

The discussion focuses on determining the sign of a couple in statics, specifically a 30 lb couple acting on the zy-plane. The negative value for the couple's moment is confirmed to be due to the clockwise rotation it induces, which aligns with the Right Hand Rule (RHR). To apply the RHR correctly, one must orient their thumb perpendicular to the zy-plane, ensuring the moment's sign remains consistent with the established conventions in statics.

PREREQUISITES
  • Understanding of static equilibrium principles
  • Familiarity with the Right Hand Rule (RHR)
  • Knowledge of moment calculations using M = Fd
  • Basic concepts of forces and couples in physics
NEXT STEPS
  • Study the application of the Right Hand Rule in various coordinate planes
  • Explore examples of calculating moments for different types of couples
  • Review static equilibrium problems involving multiple forces and moments
  • Learn about the implications of clockwise and counterclockwise moments in engineering
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Students in engineering or physics courses, particularly those studying statics, as well as educators looking for clear explanations of couple moments and the Right Hand Rule.

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Homework Statement



I'm trying to understand how to determine the sign (+/-) of a given couple. In the sample problem below it shows the 30 lb couple (on the zy-plane) having a negative value for it's force. Is this found by using the RHR? And if so, in which direction do I orient my hand? In the positive direction of the axis it's parallel to?

C3kmH.jpg


Homework Equations



[itex]M = Fd[/itex]

Right Hand Rule

The Attempt at a Solution



I tried to depict the two orientations inside of the picture above.

Thank you for any help / feedback is appreciated.
 
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I think you meant to say that it has a negative value for its moment? If you look at the couple you'll see that it causes a clockwise moment in the z-y plane which means it causes a negative moment in the z-y plane. This means that your thumb should be perpendicular to the z-y plane in order for the RHR to be obeyed and keep the same sign of the moment created.
 

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