I will have to measure very small EM forces (on the order of 10^-6...10^-5 Newtons) acting on a small copper sphere or plate (of about 0.05 kg).

I could hang the copper object with a long thread and use a micro-Newton sensor but I can't find any vendor that gives prices without contact so i guess these are very expensive equipment for me.

Then I thought maybe I could tie a lightweight rod in the center to the thread with 2 identical copper objects on the ends with balance.

It would be very similar to the Coulomb's Torsion Balance set up.

But I'm confused about what to do with this setup.

For example, there could be 10^-6 Newtons from 0.5 meters distance (half the rods length) to center. Would such a small moment produce any measurable angle of twist in a common silk thread? Even if it did, I wouldn't be able to calibrate the scale and know how much force there is.

Or should I try to add a second but much shorter rod and try to measure the "amplified" force with less sensitive force sensor?

Or is there a more common method I'm not aware of?