How did Coulomb study the repulsion and attraction forces of charged particles?

Coulomb came up with the following straightforward method: if we touch a small metallic sphere with a similar uncharged sphere and it has a charge of q, the symmetry causes the charges on each sphere to redistribute to q/2. Continuing with this method, Coulomb obtained charges of q/4, q/8, and so on.

He finally arrived at the law that is known as Coulomb's law by first varying the distance between a fixed pair of charges and measuring the force. Next, he varied the charges in pairs and maintained them at fixed separations.

It's amazing that he took all of this action without being aware of the exact nature of the charge.

Oh, yes, I forgot to mention that he measured force with a torsion balance.

Coulomb studied the repulsion and attraction forces of charged particles by conducting experiments with a torsion balance. He measured the force between two charged objects and found that it followed an inverse-square law, similar to Newton's law of gravitation. This led to Coulomb's law, which states that the force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.