6 thoughts on “5.9”

  1. Paul,

    After working and viewing your solutions for Problems 9 and 10, I am confused about the substitution made for theta in the step before the small angle assumption is used (2 steps before the boxed answer).

    In problem 9, (theta - pi) was plugged in, but in problem 10, (phi + pi/2) was used. Why is this?

    1. Oh, that is an error. In this problem I should have plugged in \theta = \phi + \pi, I accidentally plugged \phi in as \theta. The line you are referencing should read:

      I_O \ddot \phi - 4 m g l \sin(\phi + \pi) = 0

      The lines after that are correct.

    1. Yes, if you look at the image of the worked out problem below the video you will see the correction has already been made!

      I found some of these sorts of errors in the middle of editing the videos immediately before posting them. I intent to go back and re-record the problems where errors exist, but it is hard (and unpaid) work so I haven't done it yet.

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