1. The problem statement, all variables and given/known data In our unit on centripetal force, a large portion of the unit has been focusing on gravity and how the orbit is related to centripetal force. Our teacher told us to prove t^2/r^3 using F=(mv^2)/r and F=G(mM/r^2) as a small side part of our homework 2. Relevant equations t^2/r^3 F=(mv^2)/r F=G(mM/r^2) where G = 6.67*10^-11 M and m are the objects' masses 3. The attempt at a solution (mv^2)/r = G(mM/r^2) mv^2 = G(mM/r) v^2 = GM/r giving 4(pi^2)(r^2)/t^2 = GM/r and GM = v^2 / r = 4(pi^2)r GM/r = (4pi^2)r / r = 4pi^2 4(pi^2)(r^2)/t^2 = (4pi^2) leaving the ratio r^2 / t^2 When it should be r^2 / t^3. What did I do wrong? Was there something I forgot?