lecture21 - Potential Energy Work and potential energy...

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Potential Energy Serway and Jewett 8.1 – 8.3 Work and potential energy Conservative and non-conservative forces Gravitational and elastic potential energy Conservation of Mechanical Energy
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Gravitational Work s 2 y s 1 m g When the block is lowered, gravity does work: W g1 = m g . s 1 = mgy or, taking a different route: W g2 = m g . s 2 = mgy y m g F P = m g To lift the block to a height y requires work (by F P :) W P = F P y = mgy
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Work done (against gravity) to lift the box is “stored” as gravitational potential energy U g : U g =(weight) x (height) = mgy ( uniform g ) When the block moves, (work by gravity) = P.E. lost W g = - U g The position where U g = 0 is arbitrary. U g is a function of position only . (It depends only on the relative positions of the earth and the block.) The work W g depends only on the initial and final heights, NOT on the path.
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Conservative Forces A force is called “conservative” if the work done (in going from some point A to B) is
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lecture21 - Potential Energy Work and potential energy...

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