- #36

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The repulsive force is ##F_\mathrm e =k\frac {q_0 Q_0}{r^2}## in this case, but I must be able to calculate ##Q## of the straw dependent on time, see post #12. I can do so by measuring the distance ##r##, and then by using geometry, I can determine ##F_\mathrm e## thanks to the deflected nut/washer. Then I calculate ##Q## as ##Q=2r\sqrt{\pi \epsilon F_\mathrm e}##.Why do you need to be able to say that?

If the initial charges are q_{0}and Q_{0}, what is the repulsive force at distance r, time t?

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