1. The problem statement, all variables and given/known data I did a lab involving Van de Graaff generator. Basically, below the charged sphere, I put a neutral sphere on a scale and measure the difference in mass which then I can calculate the force acting on the neutral sphere. I repeated the experiment with different distance. What is the proportionality between the force and the distance? One of the tutor said the force is proportional to 1/r^5 but he didn't explain much about it. 2. Relevant equations - 3. The attempt at a solution I know that from coulomb law that the force is proportional to 1/r^2. However I can only use this equation to calculate the force between two charged objects, while my experiment is about the force between a charged and a neutral object.