HI, So say you have a small ball hanging vertically below a positively charged plate. When the ball is released from rest with the string at a small angle to the vertical, it swings in periodic pendulum motion. If the ball is now positively charged, does the period increase, decrease or stay the same? And why? - Well at first, when it's neutral, there would be a slight attraction between the ball and the charged plate. But when the ball becomes positive as well, there would be now a slight repulsion. So would it stay the same?