- #1
Jillds
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I have a course next semester on Classical Mechanics (mostly Lagrangian problems), for a second time. I'm ok for the theoretical preparation, but I'm trying to work ahead on problems and exercises, which was badly explained and without much of any resources. So, one of the sources to exercise on my own is Goldstein's book, and am just working through the examples of the first chapter.
However, for the second example I stumble across a derivation I'm confused how the author got to that one.
Example: motion of one particle in polar coordinates, page 27 (3rd ed), for the theta equation.
For the derivative of $$(mr² \dot \Theta)$$ he finds: $$mr² \ddot \Theta + 2 mr \dot r \dot \Theta$$.
While I expect it to be: $$mr² \ddot \Theta + 2 mr \dot \Theta$$
Where does Goldstein get the $$\dot r$$ from?
Edited: rewrote the question in LaTex notation
However, for the second example I stumble across a derivation I'm confused how the author got to that one.
Example: motion of one particle in polar coordinates, page 27 (3rd ed), for the theta equation.
For the derivative of $$(mr² \dot \Theta)$$ he finds: $$mr² \ddot \Theta + 2 mr \dot r \dot \Theta$$.
While I expect it to be: $$mr² \ddot \Theta + 2 mr \dot \Theta$$
Where does Goldstein get the $$\dot r$$ from?
Edited: rewrote the question in LaTex notation
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