1. The problem statement, all variables and given/known data A mouse of mass m runs around the inner circumference of a vertical wheel which is free to rotate about the centre. The wheel has mass M and moment of inertia I. Let θ be the angle that the radius vector makes to the mouse from the downward vertical at time t. Write down the lagrangian for the motion. 2. Relevant equations L = T - V 3. The attempt at a solution So I can write down the kinetic energy of the mouse quite easily, in polar coordinates it's at constant ρ so T_mouse = 1/2*m*a^2*θ^2 Also the potential energy is V=mgacosθ. The bit i'm confused about is the rotational energy of the wheel Thanks!