Calculating the charge on a pith ball
The Figure below shows the vector diagram for the three forces acting on each ball in equilibrium. They are; the tension T in the nylon string, the weight Fw of the pith balls and the Coulomb force Fc between the pith balls. The mass m on the pith balls is given above. L is the length of the nylon string.
Two charged Pith Balls
From the geometry of Figure 3 if each pith ball has a mass m and the two hang from strings of length L separated by distance r because of their charge, show that the charge q on each ball is given by;
q = ((2πε₀mgr³)/(√(L² - (r²/4))))¹⁄²