The “Nitten-Needle” Video for the Space Station. As the force between charged particles obeys Coulomb’s Law, which is an inverse-square law, these charged water droplets orbit the oppositely charged needle just as a spherical mass would orbit a cylindrical planet due to gravity. F is proportional to 1/r^2 in both cases.

Electrostatics Practice Problems Solutions

(Last Year’s): Ultimate Electrostatics Review Problems and Answer Key