1. The problem statement, all variables and given/known data The problem is a Lagrangian problem that solves for a differential equation. I need to write a program to solve the Lagrangian numerically. My professor said you do not need mass for the program, but I'm not sure how. The problem is a vertical cone with a bead rolling around the cone. I drew it: http://puu.sh/d4sN4/37c910ca4f.png [Broken] In the diagram, θ is the angle displacement of the bead. Here is a vertical view to show θ. http://puu.sh/d4t13/e7de35cb2e.png [Broken] the variables are r and θ. x_0, dx/dt, dy/dt are all given. α=45 degrees. Assume θ_0 =0, implying y_0=0 2. Relevant equations Solving for the Lagrangian gives: d^2r/dt^2 =(L^2*sin^2α)/(m^2*r^3)-gsinα*cosα d/dt(mr^2*dθ/dt)=0 showing angular momentum is conserved. 3. The attempt at a solution Is it as simple as plugging L=mr^2*dθ/dt into the differential equation for r''? This would cancel out the masses in that equation, but I feel like that is too simple and I am missing something.