- #1

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This website and many others define the potential energy of a double pendulum as:

[tex]V=-(m_1+m_2) g l_1 cos\theta_1-m_2 g l_2 cos\theta_2[/tex]

However, I came up with the following equation:

[tex]V= (m_1+m_2) g l_1 (1-cos\theta_1)+m_2 g l_2 (1-cos\theta_2)[/tex]

I started from the position of what looks like equilibrium (when the pendulum is fully stretched and hanging freely). They seem to start at the point where the pendulum is "pinned."

Which equation should I use? Am I missing something here?

Thanks in advance.