Euler-Lagrange equation for the compound pendulum (brief)

Рет қаралды 10,703

11 жыл бұрын

Putting the Lagrangian for the compound pendulum into the Euler-Lagrange equation to get the differential equations of motion. This version skims over some math. If you want the details, go here: • Euler-Lagrange equatio... .
Please leave a comment about the pace of this video. Too slow? Too fast? Do I spend too much time explaining the math? Let me know what you think.

Пікірлер: 6

@PhysicsHelps 10 жыл бұрын

Sorry for the late response. In the step before, the term you're talking about is multiplied by -theta2. This accounts for the negative sign and the square. I can see how it might have seemed like I crossed out the whole term (theta1-theta2) in the previous step, but only the theta1 should go away, leaving the -theta2. Sorry if that was unclear. Thanks for watching!

@johnnybatafljeska6368 7 жыл бұрын

@0:05 last row, I think its suposed to be -l2cos(theta2).. because we originally had y2 = -l1cos(theta1)-l2cos(theta2) .. and when you derive them.. minuses turn into pluses.. and you have U2 (in general equation) = -mg(l1cos(theta1) + l2cos(theta2))... that is potential ener. for 2nd mass.. and in general eq it is - U2.. so we remove minus sign

@johnnybatafljeska6368 7 жыл бұрын

aaaand of course I had to stop the video and couldnt see that you made a correction 3 seconds after haha

@marouanely3742 11 жыл бұрын

Thanks for great video. But how you come up to term (+ theta2 '^2sin(thita1-thita2) in the last line.I expect to get( -theta2'sin(thita1-thita2). So I don't understand why thita2 prime is squared and why its sign changed from negative to positive. Am I messing somehing??