Sorry If the thread name confuse you. I want to know if I want to find the Torque from deriving Kinetic Energy and the system has Object the Rotate and the rotating cause linear motion(v). Let's say it a Rolling Disc on the non-slope plane which has angular velocity ω and that ω cause it to move forward at velocity v. Should I consider Linear Kinetic Energy? which I think will result, τ=d(½Mv2+½Iω2)/dθ τ=(I+Mr2)α or shouldn't I? τ=Iα. Sorry if my question wasn't clear or my English was confusing. Anyways, Thanks in advance.