Physics_100_chapt_5 - Work and Energy Physics 100 Chapt 5...

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Work and Energy Physics 100 Chapt 5
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Physicist’s definition of “work” dist Work = F x dist A s calar (not a vector) dist
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Atlas holds up the Earth But he doesn’t move, dist = 0 Work= F x dist = 0 He doesn’t do any wor
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Garcon does work when he picks up the tray but not while he carries it around the room dist is not zero, but dist is 0
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Why this definition? Newton’s 2 nd law: F=m a Definition of work + a little calculus Work= change in ½mv 2 A s calar equation A vector equat ion This scalar quantity is given a special name: kinetic energy
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Work = change in KE This is called: the Work-Energy Theorem
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Units again… Kinetic Energy = ½mv 2 k g m 2 s 2 work = F x dist N m =k g m s 2 m =1Joule same!
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Work done by gravity start en d dist dist W=mg Work = F x dist = - mg x change in height = - change in mg h change in vertical height
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Gravitational Potential Energy Work grav = -change in mgh This is called: “Gravitational Potential Energy” (or PE grav ) Work grav = -change in PE grav change in PE grav = -Work grav
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If gravity is the only force doing work….
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