1. The problem statement, all variables and given/known data I had a question in my physics class today that was relatively easy but what I was confused about was a misplaced negative sign. "An electron is rotating around a proton at a distance R. The mass of the electron is me and the charge is -e. Find the period." 2. Relevant equations Fc=mev2/R FE=kq1q2/R2 T=2pi*r/v 3. The attempt at a solution The solution was calculated equating the two equations given above. The problem arises when I plug in -e and +e for the charges. This leaves one side of the equation negative, which results in a negative period. How does the negative sign go away? Do I not include the sign for charges?