z_Ch8_lecture_notes

z_Ch8_lecture_notes - Ch 8: Moron Energy When a...

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1 Ch 8: Moron Energy When a conservative force does work on an object w/in a system, that force transfers Energy between the Kinetic Energy of the object and the Potential Energy of the system. Ex: Consider a system of objects: { Ball + ___?___ } Drop the ball from point A and let it fall to point B. W = ∆K And recall for a conservative force; W = – ∆U , so equate W = W to get
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2 ∆K = – ∆U or ∆K + ∆U = 0 (K f K o ) + (U f U o ) = 0 (K f + U f ) – ( K o + U o ) = 0 E f - E o = 0 , where “E” is the Total Mechanic Energy; E = K + U so ∆E = 0 or E o = E f This is the Law of Conservation of Mechanical Energy. As the ball falls to Earth, the work done by gravity is converted into kinetic energy (at the expense of reducing the ball’s potential energy).
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So the total mechanic energy E of the ball (really the ball-Earth system) remains unchanged. K while U . Law of Conservation of Mechanical Energy * it holds only when conservatives force act ( no fingers, strings, wind,…) * conservati ve forces ( gravity, spring…) lead to conservati on principles. Here’s another way of looking at the falling ball
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z_Ch8_lecture_notes - Ch 8: Moron Energy When a...

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