I know this is picky, and I am showing off the fact that I listened hard, but at 14:57 when evaluating dL by dTheta, he actually says "dL by d theta dot", but otherwise, it was a great and clear explanation that has helped me understand why the Lagrangian is T-U and not T+U. I wonder if it just to do with the orientation of the vectors? Even Feynman in his great lectures, does a bit of arm waving about the reason.
Hello! I don't like the fact that the bob has some negative potential energy, -mgL, when it's at its equilibrium position (I understand it's arbitrary, but it's not very intuitive to lift the bob to the x-axis and declare it has zero potential energy! Not to mention, lifting it directly vertical and declaring it has but mgL potential energy when it is 2L away from the equilibrium position is also awkward). I would rather we write the potential as U = mgL(1-cos(θ)), where h = L-Lcos(θ). This gives us zero potential energy at equilibrium, mgL potential at the x-axis, and mg2L when vertical.
I know this is picky, and I am showing off the fact that I listened hard, but at 14:57 when evaluating dL by dTheta, he actually says "dL by d theta dot", but otherwise, it was a great and clear explanation that has helped me understand why the Lagrangian is T-U and not T+U. I wonder if it just to do with the orientation of the vectors?
Even Feynman in his great lectures, does a bit of arm waving about the reason.
Hello! I don't like the fact that the bob has some negative potential energy, -mgL, when it's at its equilibrium position (I understand it's arbitrary, but it's not very intuitive to lift the bob to the x-axis and declare it has zero potential energy! Not to mention, lifting it directly vertical and declaring it has but mgL potential energy when it is 2L away from the equilibrium position is also awkward). I would rather we write the potential as U = mgL(1-cos(θ)), where h = L-Lcos(θ). This gives us zero potential energy at equilibrium, mgL potential at the x-axis, and mg2L when vertical.
Sir why v=theta dot*l ?
He explained how to do it two difffrent ways...