Coulomb's experiment (coulomb's law)

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SUMMARY

Coulomb's law applies specifically to stationary charges, which presents a challenge when measuring the force between charged objects. In his experiments, Charles-Augustin de Coulomb utilized a torsion balance to counteract the motion induced by the electrostatic force, ensuring that the charges remained effectively stationary. The measurement of force occurs once the torsion balance reaches equilibrium, allowing for accurate readings of force and distance without interference from movement. This method effectively resolves the issue of determining whether the force measured is at the initial separation or at a final equilibrium point.

PREREQUISITES
  • Understanding of Coulomb's law and its implications for stationary charges
  • Familiarity with the operation of a torsion balance
  • Basic knowledge of electrostatics and electric force
  • Concept of equilibrium in physical systems
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  • Research the principles of electrostatics and their applications in physics
  • Study the design and functionality of torsion balances in experimental physics
  • Explore advanced topics in electric force measurement techniques
  • Investigate the historical context and significance of Coulomb's experiments
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Students of physics, educators teaching electrostatics, and researchers interested in experimental methods for measuring electric forces will benefit from this discussion.

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Hello,

I'm trying to imagine how Coulomb would've measured the force between electrically charged objects, but there are a few things I can't figure out.

Is it true that Coulomb's law holds only for stationary charges? If it's true, then that very stipulation of the law would be violated the moment two charges come into the electrical influence of one another, for the coulomb force would produce motion in both of them. How would we then measure the "static force" between them?

I know that Coulomb used a torsion balance so the charges probably weren't free to move. Their motion must've been counteracted by the tension in the strings they were attached to, but then I fall into another confusion: After putting a charge a known distance away from another, the force would cause the other charge (assuming that the first charge is "fixed") to displace a certain amount away or toward the first charge so the final distance between the two charges would be different than what it originally was, and likewise the force between the two at that "final" location would also be different. I can't figure out if we're measuring the force that the two would've experienced at their initial separation, or is it the force that they are experiencing at their "final" equilibrium point?

Thank you for your time!
 
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The torsion balance takes care of the movement problem, and you measure the force and distance after the torsion balance has reached equilibrium so the charge is not moving and the distance is not changing.
 
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