5.67 Lagrange by Paul is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

# 5.67 Lagrange

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5.67 Lagrange by Paul is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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L = T-V ; I think you did this subtraction twice for thetai = theta1. You have dL/dtheta1 = -(......) and then you flipped the sign to positive in the next step like you were subtracting the negative.

Never mind, I see my mistake now.

Why is that you do not account for the translational kinetic energy (1/2*m*v^2) in the kinetic energy equation?

The translational kinetic energy is included in the rotational kinetic energy expressions implicitly because I'm summing moments about the fixed point. See the video on Mass moments of inertia for a deeper explanation.