Question about System of Forces

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SUMMARY

The discussion centers on the concept of forces and couples in physics, specifically addressing the condition where the sum of moments (∑ri x Fi) is not equal to zero. It clarifies that while a force can theoretically act through any point, the resulting couple will differ based on the chosen point. The conversation emphasizes that a couple can be represented by two equal and opposite forces in the same plane, allowing for flexibility in their magnitudes and directions, provided the distance between them is adjusted accordingly.

PREREQUISITES
  • Understanding of vector mechanics
  • Familiarity with the concept of moments in physics
  • Knowledge of forces and couples
  • Basic principles of equilibrium in statics
NEXT STEPS
  • Study the principles of vector addition in mechanics
  • Learn about the conditions for static equilibrium
  • Explore the concept of couples and their applications in engineering
  • Investigate the effects of non-coplanar forces on rigid bodies
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This discussion is beneficial for physics students, mechanical engineers, and anyone interested in the principles of force systems and their applications in real-world scenarios.

Trickster_00
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Hi Trickster_00! :smile:
Trickster_00 said:
We have ∑ri x Fi ≠ 0, so why does the force act through the origin?

it can act through anywhere

you could write it as a force acting through (97,6,300000) if you wanted to, but the accompanying couple would be different :wink:

(btw, if the force and the couple were co-planar, you could choose to make the couple vanish)
 
oh, I see you've asked about that in another thread …
Trickster_00 said:
Untitled.png

it's because we can always replace a couple by two equal and opposite forces in the same plane as the couple …

so we can make the two forces any magnitude we like, and in any direction in that plane that we like, so long as we adjust the distance between the two forces …

so make one of the two forces (in the couple) equal and opposite to the given force …

then they cancel, leaving only the other force in the couple :wink:​
 

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