fun developing the Coulomb lab

I had a fun morning developing different ways to explore Coulomb's law, trying to find a way where students could get reasonable data on the 1/r^2 dependence. We eventually settled on the repulsion between the end of a charegd rod and a pithball on a thread. By suspending the ball just above graph paper you can get reasonable measurements of both the separation between the charged objects and the how far the pithball is deflected from the vertical.




For each separation the static equilibrium condition of no net torque gives you a measure of how the repiulsion depends on separation, the results were pretty close to 1/r^2 ! It was definiately fun futzing with alternative ways to create setups.