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Coulomb's experiment (coulomb's law)

  1. Sep 12, 2013 #1

    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!
  2. jcsd
  3. Sep 12, 2013 #2


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    Staff: Mentor

    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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