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Unformatted text preview: Chapter 8 Potential Energy and Conservation of Energy Potential Energy U • The potential energy U is the energy associated with a system of objects . • Potential energy can be thought of as stored energy that can either do work or be converted to kinetic energy . • If the arrangement of the system changes, then the potential energy of the system changes. • The potential energy concept can be used only when dealing with a special class of forces called conservative forces . • When only conservative forces act within an isolated system , the balancing between the kinetic and potential energies is well known as the principal of conservation of mechanical energy . Chapter 8 Potential Energy and Conservation of Energy Gravitational Potential Energy U g y mg U g ⋅ ≡ g y x mg m W- +-- = ⋅ = j d g [ ) ( a scalar quantity f i i f i f i f mgy mgy y y mg y y x x mg- =- ⋅- =- +- ⋅- = j j j] i j ) ( ) ( ) ( ) [( ) ( g i f f i g U U U U U W Δ- =-- =- = ) ( Work & potential energy As the tomato rises c What is the force in charge? c Gravitational force c Does the force do any work to the tomato? Yes. The kinetic energy of the tomato decreases, c Yes. The kinetic energy of the tomato decreases, so the force is doing a negative work. c What is the energy flow? c The kinetic energy is transferred by the gravitational force to the gravitational potential energy of the tomato–Earth system....
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This note was uploaded on 12/27/2011 for the course LSCI 103 taught by Professor K.y.liao during the Fall '11 term at National Cheng Kung University.
- Fall '11