Hello. I have some problems with making Lagrangian. I need your advice. 1. The problem statement, all variables and given/known data I have this situation: Consider the circular path is intangible and without friction. I have to find Lagrangian for coordinates x and θ. 2. Relevant equations L = U - V 3. The attempt at a solution I know the result from a book: The origin of the coordinate system is at the center of the initial position of the circular trajectory. I understand that the fist part is kinetic energy of big cube of mass M in coordinate x.The second part is kinetic energy of bead of mass m in a circle in coordinate x. I don't understand to third part. I think that the m (mass of bead) is missing there. If I will consider that m is there, it is kinetic energy of bead in coordinate θ. What is the poind of fourth part? I don't see it. The last part is potentional energy of bead, I understand. I wrote it there: So, could you tell me, if this Lagrangian right? And if it is not, how it has to look? Thank you.