Why do the forces not net out to zero in a system in static equilibrium?

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SUMMARY

In a system in static equilibrium, while the sum of torques must equal zero, the forces can still be unbalanced due to external support forces. For instance, in the example of a wooden plank pivoted at the center with differing masses on either end, the pivot exerts an upward force to maintain equilibrium. This upward force counteracts the downward forces from the masses, ensuring the system remains stationary despite the forces not netting to zero. Understanding this distinction is crucial for grasping the principles of static equilibrium in physics.

PREREQUISITES
  • Understanding of static equilibrium principles
  • Knowledge of torque and force concepts
  • Familiarity with Newton's laws of motion
  • Basic physics of levers and pivots
NEXT STEPS
  • Study the concept of net forces in static systems
  • Explore the role of support forces in equilibrium
  • Learn about torque calculations in various scenarios
  • Investigate real-world applications of static equilibrium in engineering
USEFUL FOR

Students of physics, educators teaching mechanics, and engineers involved in structural design will benefit from this discussion on static equilibrium and force analysis.

Gabe805
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I understand that for a system to be in static equilibrium the sum of the forces and torques must equal zero. I understand why the torques must net out to zero but not the forces. For example, if you picture a wooden plank pivoted at the center with a small mass on the far left end and a very large mass near the pivot such that the torques net out to zero, the system is not moving yet the forces do not net out to zero. if somebody can please explain, I would be very appreciative.
 
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Don't forget that the pivot itself exerts an upward force to support the plank and the two masses.
 
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Doc Al said:
Don't forget that the pivot itself exerts an upward force to support the plank and the two masses.

oh my gosh! How could I forget that! Thank you very much.. its been bugging me for three days now.
 

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