1. The problem statement, all variables and given/known data Ok, so in this system, there are two point particles of mass M connected by massless levers of length L. The pair of masses pivots about the upper point and rotates about the axis at an angular frequency ω. The lower mass is constrained to slide on the vertical axis. The system is illustrated below: Find the Lagrangian in terms of Θ. 2. Relevant equations I know that the Lagrangian is represented by the difference in kinetic and potential energies, L = T - U T = ½Mv^2, and U should be derived from the gravitational force only, U = Mgh, where h is the vertical distance from the origin. 3. The attempt at a solution I have a fundamental lack of understanding regarding finding the kinetic energy of this system. It has been suggested that I view this in cylindrical coordinates, where x=LsinΘ y=LcosΘ z= z. I intuit that the origin of my cylindrical coordinate system should reside at the pivot point above the two masses. Could someone please illuminate the subtleties in finding T? I understand conceptually the Lagrangian and the parts of the problem to follow.