A sphere is rolling inclined wall (θ radian). and the momentum of that sphere is L = 1/2 mv^2 + 1/5 mv^2 + mgx sin(θ) = 7/10 m v^2 + mgx sin(θ) ∂L/∂v = p 7/5 m v = p but I cant understand why the factor of mv is 7/5. p is the linear momentum of sphere. which means the factor of mv must be always 1 (my thought) p = mv ↑that was an unchanging truth of my physical world. why rolling effect to the momentum? angular momentum of the sphere has no relation with p direction!!