16 - Non-Conservative Forces

16 - Non-Conservative Forces - Power For next time: Re-read...

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Power For next time: Re-read Chapters 7 & 8 Homework: Chapter 7 : 36, 40, 54
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Conservative forces We saw examples where the work was only dependent on the initial and the final position of the object. By definition we call a force conservative , if the work done by the force depends only on the initial and final positions and not on the path taken. We call such forces also internal forces.
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Conservative forces • Work is independent of path • Work around closed path is zero • Gravitational force: 12 2 G mm FG r = • Spring force: S F kx = −∆
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Potential energy Potential energy is the negative of the work done by the conservative force () 2 1 Gravitational potential energy y fi y PE PE PE mg dy ∆= − = −− f i x x x PE PE PE F dx [ ] 2 1 21 y y PE m gy m y = PE mgh = PE mgh =
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Spring potential energy 0 x f i x fi x x PE PE PE F dx ∆= − = () 0 0 Spring potential energy x PE PE PE kx dx −− 2 0 1 2 PE kx Potential energy is the negative of the work done by the conservative force 2 0 1 2 PE kx =
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16 - Non-Conservative Forces - Power For next time: Re-read...

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