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Unformatted text preview: • The concept of energy (and the conservation of energy – chapter 8) is one of the most important topics in physics. • Work • Kinetic energy • Energy approach (“system model”) is often simpler than Newton’s second law (“particle model”). • Scalar product (dot product); work is scalar product of force and displacement. • Hooke’s law, springs • Power Chapter 7: Work; Energy of a System Reading assignment: Chapter 7 Homework : CQ1, CQ5, QQ1, QQ2, AE2, 1, 9, 11, 12, 14, 15, 17, 25, 27, 31, 33, 42, 43 Due dates: Tu/Th, and MWF section : Monday, Feb. 28 Remember HW 6 due Monday, Feb. 21 Work (as defined by a physicist) Definition: The work done on an object by an external force is: the product of the component of the force in the direction of the displacement and the magnitude of the displacement. θ cos ⋅ ⋅ = d F W How much work is done when just holding up an object? = ⋅ ⋅ = W d F W θ cos How much work is done when the displacement is perpendicular to the force? = ⋅ ⋅ = W d F W θ cos What is the work done when lifting? (at constant speed) By the applied force? By the gravitational force? = ⋅ ⋅ = W d F W θ cos Sign convention: W positive: If F and d are parallel . If energy is transferred into the system. W negative: If F and d are antiparallel . If energy is transferred out of the system....
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This document was uploaded on 02/29/2012.
 Spring '09
 Energy, Work

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